Internet DRAFT - draft-templin-intarea-omni
draft-templin-intarea-omni
Network Working Group F. L. Templin, Ed.
Internet-Draft The Boeing Company
Updates: 4291 (if approved) 16 February 2024
Intended status: Standards Track
Expires: 19 August 2024
Transmission of IP Packets over Overlay Multilink Network (OMNI)
Interfaces
draft-templin-intarea-omni-67
Abstract
Air/land/sea/space mobile nodes (e.g., aircraft of various
configurations, terrestrial vehicles, seagoing vessels, space
systems, enterprise wireless devices, pedestrians with cell phones,
etc.) communicate with networked correspondents over wireless and/or
wired-line data links and configure mobile routers to connect end
user networks. This document presents a multilink virtual interface
specification that enables mobile nodes to coordinate with a network-
based mobility service, fixed node correspondents and/or other mobile
node peers. The virtual interface provides an adaptation layer
service suited for both mobile and more static deployments such as
enterprise and home networks. This document specifies the
transmission of IP packets over Overlay Multilink Network (OMNI)
Interfaces.
Status of This Memo
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This Internet-Draft will expire on 19 August 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 18
4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 19
5. OMNI Interface Maximum Transmission Unit (MTU) . . . . . . . 25
5.1. IP Parcels . . . . . . . . . . . . . . . . . . . . . . . 27
5.2. Advanced Jumbos (AJs) . . . . . . . . . . . . . . . . . . 28
5.3. Control/Data Plane Considerations . . . . . . . . . . . . 29
6. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 29
6.1. OAL Source Encapsulation and Fragmentation . . . . . . . 30
6.2. OAL L2 Encapsulation and Re-Encapsulation . . . . . . . . 34
6.2.1. OMNI Extension Headers and Fragmentation . . . . . . 37
6.2.2. Carrier Fragment Size (CFS) Determination . . . . . . 40
6.3. Reassembly and Decapsulation . . . . . . . . . . . . . . 41
6.4. OMNI Extension Headers . . . . . . . . . . . . . . . . . 43
6.5. OMNI Full and Compressed Headers (OFH/OCH) . . . . . . . 46
6.6. OAL and L2 Encapsulation Avoidance . . . . . . . . . . . 50
6.7. OAL Identification Window Maintenance . . . . . . . . . . 51
6.8. OAL Fragmentation Reports and Retransmissions . . . . . . 55
6.9. OMNI Interface MTU Feedback Messaging . . . . . . . . . . 56
6.10. OAL Super-Packets . . . . . . . . . . . . . . . . . . . . 59
6.11. OAL Bubbles . . . . . . . . . . . . . . . . . . . . . . . 60
6.12. OMNI Hosts . . . . . . . . . . . . . . . . . . . . . . . 61
6.13. IP Parcels . . . . . . . . . . . . . . . . . . . . . . . 63
6.14. OAL Requirements . . . . . . . . . . . . . . . . . . . . 66
6.15. OAL Fragmentation Security Implications . . . . . . . . . 67
7. Ethernet-Compatible Link Layer Frame Format . . . . . . . . . 69
8. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 70
9. Unique-Local Addresses (ULAs) . . . . . . . . . . . . . . . . 71
10. Global Unicast Addresses (GUAs) . . . . . . . . . . . . . . . 74
11. Node Identification . . . . . . . . . . . . . . . . . . . . . 75
12. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 76
12.1. The OMNI Option . . . . . . . . . . . . . . . . . . . . 77
12.2. OMNI Sub-Options . . . . . . . . . . . . . . . . . . . . 78
12.2.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 80
12.2.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 81
12.2.3. Node Identification . . . . . . . . . . . . . . . . 81
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12.2.4. Authentication . . . . . . . . . . . . . . . . . . . 83
12.2.5. Window Synchronization . . . . . . . . . . . . . . . 84
12.2.6. Neighbor Control . . . . . . . . . . . . . . . . . . 85
12.2.7. Interface Attributes . . . . . . . . . . . . . . . . 87
12.2.8. Traffic Selector . . . . . . . . . . . . . . . . . . 91
12.2.9. AERO Forwarding Parameters . . . . . . . . . . . . . 93
12.2.10. Geo Coordinates . . . . . . . . . . . . . . . . . . 98
12.2.11. Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
Message . . . . . . . . . . . . . . . . . . . . . . . 98
12.2.12. PIM-SM Message . . . . . . . . . . . . . . . . . . . 99
12.2.13. Host Identity Protocol (HIP) Message . . . . . . . . 100
12.2.14. QUIC-TLS Message . . . . . . . . . . . . . . . . . . 102
12.2.15. Fragmentation Report (FRAGREP) . . . . . . . . . . . 102
12.2.16. ICMPv6 Error . . . . . . . . . . . . . . . . . . . . 104
12.2.17. Proxy/Server Departure . . . . . . . . . . . . . . . 104
12.2.18. Sub-Type Extension . . . . . . . . . . . . . . . . . 105
13. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 108
14. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 109
14.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 109
14.2. Client-Proxy/Server Loop Prevention . . . . . . . . . . 110
15. Router Discovery and Prefix Registration . . . . . . . . . . 110
15.1. Window Synchronization . . . . . . . . . . . . . . . . . 120
15.2. Router Discovery in IP Multihop and IPv4-Only
Networks . . . . . . . . . . . . . . . . . . . . . . . . 121
15.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 124
15.4. OMNI Link Extension . . . . . . . . . . . . . . . . . . 125
16. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 126
17. Proxy/Server Resilience . . . . . . . . . . . . . . . . . . . 127
18. Detecting and Responding to Proxy/Server Failures . . . . . . 127
19. Transition Considerations . . . . . . . . . . . . . . . . . . 128
20. OMNI Interfaces on Open Internetworks . . . . . . . . . . . . 128
21. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 131
22. (H)HITs and Temporary ULA (TLA)s . . . . . . . . . . . . . . 131
23. Address Selection . . . . . . . . . . . . . . . . . . . . . . 132
24. Error Messages . . . . . . . . . . . . . . . . . . . . . . . 133
25. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 133
25.1. Protocol Numbers Registry . . . . . . . . . . . . . . . 133
25.2. IEEE 802 Numbers Registry . . . . . . . . . . . . . . . 133
25.3. IPv4 Special-Purpose Address Registry . . . . . . . . . 134
25.4. IPv6 Neighbor Discovery Option Formats Registry . . . . 134
25.5. Ethernet Numbers Registry . . . . . . . . . . . . . . . 134
25.6. ICMPv6 Code Fields . . . . . . . . . . . . . . . . . . . 134
25.7. ICMPv4 PTB Messages . . . . . . . . . . . . . . . . . . 135
25.8. OMNI Option Sub-Types (New Registry) . . . . . . . . . . 135
25.9. OMNI Node Identification ID-Types (New Registry) . . . . 136
25.10. OMNI Geo Coordinates Types (New Registry) . . . . . . . 137
25.11. OMNI Option Sub-Type Extensions (New Registry) . . . . . 137
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25.12. OMNI RFC4380 UDP/IP Header Option Types (New
Registry) . . . . . . . . . . . . . . . . . . . . . . . 137
25.13. OMNI RFC6081 UDP/IP Trailer Option Types (New
Registry) . . . . . . . . . . . . . . . . . . . . . . . 138
25.14. Additional Considerations . . . . . . . . . . . . . . . 138
26. Security Considerations . . . . . . . . . . . . . . . . . . . 139
27. Implementation Status . . . . . . . . . . . . . . . . . . . . 140
28. Document Updates . . . . . . . . . . . . . . . . . . . . . . 140
29. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 141
30. References . . . . . . . . . . . . . . . . . . . . . . . . . 142
30.1. Normative References . . . . . . . . . . . . . . . . . . 142
30.2. Informative References . . . . . . . . . . . . . . . . . 145
Appendix A. IPv4 Fragmentation Checksum Algorithm . . . . . . . 155
Appendix B. IPv6 Compatible Addresses . . . . . . . . . . . . . 155
Appendix C. IPv6 ND Message Authentication and Integrity . . . . 156
Appendix D. VDL Mode 2 Considerations . . . . . . . . . . . . . 157
Appendix E. Client-Proxy/Server Isolation Through Link-Layer
Address Mapping . . . . . . . . . . . . . . . . . . . . . 158
Appendix F. Change Log . . . . . . . . . . . . . . . . . . . . . 158
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 158
1. Introduction
Air/land/sea/space mobile nodes (e.g., aircraft of various
configurations, terrestrial vehicles, seagoing vessels, space
systems, enterprise wireless devices, pedestrians with cellphones,
etc.) configure mobile routers with multiple interface connections to
wireless and/or wired-line data links. These data links may have
diverse performance, cost and availability properties that can change
dynamically according to mobility patterns, flight phases, proximity
to infrastructure, etc. The mobile router acts as a Client of a
network-based Mobility Service (MS) by configuring a virtual
interface over its underlay interface data link connections.
Each Client configures a virtual interface (termed the "Overlay
Multilink Network Interface (OMNI)") as a thin layer over its
underlay network interfaces (which may themselves connect to virtual
or physical links). The OMNI interface is therefore the only
interface abstraction exposed to the IP layer and behaves according
to the Non-Broadcast, Multiple Access (NBMA) interface principle,
while underlay interfaces appear as link layer communication channels
in the architecture. The OMNI interface internally employs the "OMNI
Adaptation Layer (OAL)" to ensure that original IP packets or parcels
[I-D.templin-6man-parcels2][I-D.templin-intarea-parcels2] are adapted
to diverse underlay interfaces with heterogeneous properties.
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The OMNI interface connects to a virtual overlay known as the "OMNI
link". The OMNI link spans one or more Internetworks that may
include private-use infrastructures (e.g., enterprise networks,
operator networks, etc.) and/or the global public Internet itself.
Together, OMNI and the OAL provide the foundational elements required
to support the "6 M's of Modern Internetworking", including:
1. Multilink - a Client's ability to coordinate multiple diverse
underlay interfaces as a single logical unit (i.e., the OMNI
interface) to achieve the required communications performance and
reliability objectives.
2. Multinet - the ability to span the OMNI link over a segment
routing topology with multiple diverse administrative domain
network segments while maintaining seamless end-to-end
communications between mobile Clients and correspondents such as
air traffic controllers, fleet administrators, etc.
3. Mobility - a Client's ability to change network points of
attachment (e.g., moving between wireless base stations) which
may result in an underlay interface address change, but without
disruptions to ongoing communication sessions with peers over the
OMNI link.
4. Multicast - the ability to send a single network transmission
that reaches multiple Clients belonging to the same interest
group, but without disturbing other Clients not subscribed to the
interest group.
5. Multihop - a mobile Client vehicle-to-vehicle relaying capability
useful when multiple forwarding hops between vehicles may be
necessary to "reach back" to an infrastructure access point
connection to the OMNI link.
6. (Performance) Maximization - the ability to exchange large
packets/parcels between peers without loss due to a link size
restriction, and to adaptively adjust packet/parcel sizes to
maintain the best performance profile for each independent
traffic flow.
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Client OMNI interfaces interact with the MS and/or other OMNI nodes
through IPv6 Neighbor Discovery (ND) control message exchanges
[RFC4861]. The MS consists of a distributed set of service nodes
(including Proxy/Servers and other infrastructure elements) that also
configure OMNI interfaces. Automatic Extended Route Optimization
(AERO) in particular provides a companion MS compatible with the OMNI
architecture [I-D.templin-intarea-aero]. AERO discusses details of
ND message based multilink forwarding, route optimization, mobility
management, and multinet traversal while the fundamental aspects of
OMNI link operation are discussed in this document.
Each OMNI interface provides a multilink nexus for exchanging inbound
and outbound traffic via selected underlay interfaces. The IP layer
sees the OMNI interface as a point of connection to the OMNI link.
Each OMNI link has one or more associated Mobility Service Prefixes
(MSPs), which are typically IP Global Unicast Address (GUA) prefixes
assigned to the link and from which Mobile Network Prefixes (MNPs)
are delegated to Client end systems. If there are multiple OMNI
links, the IP layer will see multiple OMNI interfaces.
Each Client receives an MNP delegation through IPv6 ND control
message exchanges with Proxy/Servers over Access Networks (ANETs)
and/or open Internetworks (INETs). The Client sub-delegates the MNP
to downstream-attached End-user Networks (ENETs) independently of the
underlay interfaces selected for data transport. The Client acts as
a fixed or mobile router on behalf of ENET peers, and uses OMNI
interface control messaging to coordinate with Hosts, Proxy/Servers
and/or other Clients. The Client iterates its control messaging over
each of the OMNI interface's ANET/INET underlay interfaces in order
to register each interface with the MS (see Section 15). The Client
can also provide Proxy/Server-like services for a recursively nested
chain of other Clients and Hosts connected via downstream-attached
ENETs.
Clients may connect to multiple distinct OMNI links within the same
OMNI domain by configuring multiple OMNI interfaces, e.g., omni0,
omni1, omni2, etc. Each OMNI interface is configured over a distinct
set of underlay interfaces and provides a nexus for Safety-Based
Multilink (SBM) operation. The IP layer applies SBM routing to
select a specific OMNI interface, then the selected OMNI interface
applies Performance-Based Multilink (PBM) internally to select
appropriate underlay interfaces. Applications select SBM topologies
based on IP layer Segment Routing [RFC8402], while each OMNI
interface orchestrates PBM internally based on OAL Multinet
traversal.
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OMNI provides a link model suitable for a wide range of use cases.
For example, the International Civil Aviation Organization (ICAO)
Working Group-I Mobility Subgroup is developing a future Aeronautical
Telecommunications Network with Internet Protocol Services (ATN/IPS)
and has issued a liaison statement requesting IETF adoption [ATN] in
support of ICAO Document 9896 [ATN-IPS]. The IETF IP Wireless Access
in Vehicular Environments (ipwave) working group has further included
problem statement and use case analysis for OMNI in
[I-D.ietf-ipwave-vehicular-networking]. Still other communities of
interest include AEEC, RTCA Special Committee 228 (SC-228) and NASA
programs that examine commercial aviation, Urban Air Mobility (UAM)
and Unmanned Air Systems (UAS). Pedestrians with handheld mobile
devices represent another large class of potential OMNI users.
This document specifies the transmission of original IP packets/
parcels and control messages over OMNI interfaces. The operation of
both IP protocol versions (i.e., IPv4 [RFC0791] and IPv6 [RFC8200])
is specified as the network layer data plane, while OMNI interfaces
use IPv6 ND messaging in the control plane independently of the data
plane protocol(s). OMNI interfaces also provide an adaptation layer
based on encapsulation and fragmentation over heterogeneous underlay
interfaces as an OAL sublayer between L3 and L2. OMNI and the OAL
are specified in detail throughout the remainder of this document.
2. Terminology
The terminology in the normative references applies; especially, the
terms "link" and "interface" are the same as defined in the IPv6
[RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications.
This document assumes the following IPv6 ND control plane message
types: Router Solicitation (RS), Router Advertisement (RA), Neighbor
Solicitation (NS), Neighbor Advertisement (NA), unsolicited NA (uNA)
and Redirect.
OMNI interfaces normally limit the size of their IPv6 ND control
plane messages to the minimum IPv6 link MTU, but some messages may
exceed this size if there are sufficient OMNI parameters and/or IP
packet/parcel attachments. These larger messages can still travel
over secured underlying network control plane paths that include
IPsec tunnels [RFC4301] and/or secured direct point-to-point links
without loss due to a size restriction by engaging OMNI IPv6
encapsulation/fragmentation as necessary up to a maximum size of
65535 octets.
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Host, Client and Proxy/Server OMNI interfaces that employ IPv6 ND
control plane messaging maintain per-neighbor state in Neighbor Cache
Entries (NCEs). Each NCE is indexed by the neighbor's network layer
address(es) while the neighbor's OAL encapsulation address provides
context for Identification verification.
The Protocol Constants defined in Section 10 of [RFC4861] are used in
their same format and meaning in this document. The terms "All-
Routers multicast", "All-Nodes multicast" and "Subnet-Router anycast"
are the same as defined in [RFC4291] (with Link-Local scope assumed).
Also, IPv6 ND state names, variables and constants including
REACHABLE, ReachableTime and REACHABLE_TIME are the same as defined
in [RFC4861].
The term "IP" is used to refer collectively to either Internet
Protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) when a
specification at the layer in question applies equally to either
version.
The terms Host, Client and Proxy/Server are intentionally capitalized
to denote an instance of that particular node type that also
configures an OMNI interface and engages the OMNI Adaptation Layer.
The terms "application layer (L5 and higher)", "transport layer
(L4)", "network layer (L3)", "(data) link layer (L2)" and "physical
layer (L1)" are used consistently with common Internetworking
terminology, with the understanding that reliable delivery protocol
users of UDP are considered as transport layer elements. The OMNI
specification further defines an "adaptation layer" positioned below
the network layer but above the link layer, which may include
physical links and Internet- or higher-layer tunnels. A (network)
interface is a node's attachment to a link (via L2), and an OMNI
interface is therefore a node's attachment to an OMNI link (via the
adaptation layer).
The L3, adaptation and (virtual) L2 layers each include distinct
packet Identification numbering spaces although L3 and L2 packet
headers often omit the Identification for unfragmented packets. The
adaptation layer employs an 8-octet Identification numbering space
that is distinct from L3/L2 spaces, with an Identification value
appearing in an IPv6 Extended Fragment Header
[I-D.templin-6man-ipid-ext] or an OMNI Compressed Header (OCH) (see:
Section 6.5) in each adaptation layer encapsulation.
The terms "IP jumbogram", "advanced jumbo (AJ)" and "IP parcel" refer
to special packet formats that enable a new link model for the
Internet as discussed in [I-D.templin-6man-parcels2]
[I-D.templin-intarea-parcels2].
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The following terms are defined within the scope of this document:
L3
The Network layer in the OSI network model. Also known as "layer
3", "IP layer", etc.
L2
The Data Link layer in the OSI network model. Also known as
"layer 2", "link layer", "sub-IP layer", etc.
Adaptation layer
An encapsulation mid-layer that adapts L3 to a diverse collection
of L2 underlay interfaces and their encapsulations. (No layer
number is assigned, since numbering was an artifact of the legacy
reference model that need not carry forward in the modern
architecture.) The adaptation layer sees the network layer as
"L3" and sees all link layer encapsulations as "L2
encapsulations", which may include UDP, IP and true link layer
(e.g., Ethernet, etc.) headers.
Access Network (ANET)
a connected network region (e.g., an aviation radio access
network, corporate enterprise network, satellite service provider
network, cellular operator network, residential WiFi network,
etc.) that connects Clients to the Mobility Service. Physical
and/or data link level security is assumed (sometimes referred to
as "protected spectrum" for wireless domains). ANETs such as
private enterprise networks and ground domain aviation service
networks often provide multiple secured IP hops between the
Client's physical point of connection and the nearest Proxy/
Server.
Internetwork (INET)
a connected network region with a coherent IP addressing plan that
provides transit forwarding services between ANETs and/or OMNI
nodes that coordinate with the Mobility Service over unprotected
media. Since physical and/or data link level security cannot
always be assumed, security must be applied by the network and/or
higher layers if necessary. The global public Internet itself is
an example.
End-user Network (ENET)
a simple or complex "downstream" network tethered to a Client as a
single logical unit that travels together. The ENET could be as
simple as a single link connecting a single Host, or as complex as
a large network with many links, routers, bridges and end user
devices. The ENET provides an "upstream" link for arbitrarily
many low-, medium- or high-end devices dependent on the Client for
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their upstream connectivity, i.e., as Internet of Things (IoT)
entities. The ENET can also support a recursively-descending
chain of additional Clients such that the ENET of an upstream
Client is seen as the ANET of a downstream Client.
ANET/INET/ENET interface
a Client's attachment to a link in an ANET/INET/ENET.
*NET
a "wildcard" term used when a given specification applies equally
to both ANET/INET cases. From the Client's perspective, *NET
interfaces are "upstream" interfaces that connect the Client to
the Mobility Service, while ENET interfaces are "downstream"
interfaces that the Client uses to connect downstream ENETs, Hosts
and/or other Clients.
underlay interface
an ANET/INET/ENET interface over which an OMNI interface is
configured. The OMNI interface is seen as an L3 interface by the
network layer, and each underlay interface is seen as an L2
interface by the OMNI interface. The underlay interface either
connects directly to the physical communications media or
coordinates with another node where the physical media is hosted.
Mobile Ad-hoc NETwork (MANET)
a connected network region that shares the same properties as an
ANET except that links often have undetermined connectivity
properties, physical and/or link layer security cannot always be
assumed and multihop forwarding between Clients acting as MANET
routers may be necessary. Proxy/Servers that connect the MANET to
outside networks act as Clients on their MANET interfaces and act
as ordinary Proxy/Servers on their ANET/INET interfaces, while
Clients configure MANET interfaces and provide multihop forwarding
services for other Clients as necessary.
MANET Interface
a node's underlay interface connection to a local network with
indeterminant neighborhood properties over which multihop relaying
may be necessary. All MANET interfaces used by AERO/OMNI are IPv6
interfaces and therefore must configure a Maximum Transmission
Unit (MTU) at least as large as the IPv6 minimum MTU (1280 octets)
even if lower-layer fragmentation is needed.
OMNI link
a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured
over one or more INETs and their connected ANETs/ENETs. An OMNI
link may comprise multiple distinct "segments" joined by L2
forwarding devices the same as for any link; the addressing plans
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in each segment may be mutually exclusive and managed by different
administrative entities. Proxy/Servers and other infrastructure
elements extend the link to support communications between Clients
as single-hop neighbors.
OMNI interface
a node's attachment to an OMNI link, and configured over one or
more underlay interfaces. If there are multiple OMNI links in an
OMNI domain, a separate OMNI interface is configured for each
link. The OMNI interface configures a Maximum Transmission Unit
(MTU) and an Effective MTU to Receive (EMTU_R) the same as any
interface.
OMNI Adaptation Layer (OAL)
an OMNI interface sublayer service that encapsulates original IP
packets/parcels admitted into the interface in an IPv6 header and/
or subjects them to fragmentation and reassembly. The OAL is also
responsible for generating MTU-related control messages as
necessary, and for providing addressing context for OMNI link SRT
traversal. The OAL presents a new layer in the Internet
architecture known simply as the "adaptation layer". The OMNI
link is an example of a limited domain [RFC8799] at the adaptation
layer although its segments may be joined over open Internetworks
at L2.
(OMNI) Host
an end user device that extends the OMNI link over an ENET
interface serviced by a Client. (As an implementation matter, the
Host either assigns the same IP address from the ENET (underlay)
interface to an (overlay) OMNI interface, or configures an OMNI-
like function as a virtual sublayer of the ENET interface itself.)
The IP addresses assigned to each Host ENET interface remain
stable even if the Client's upstream *NET interface connections
change.
(OMNI) Client
a network platform/device mobile router that configures one or
more OMNI interfaces over distinct sets of underlay interfaces
grouped as logical OMNI link units. The Client coordinates with
the Mobility Service via upstream networks over *NET interfaces,
and provides Proxy/Server services for Hosts and other Clients on
ENET interface downstream networks. The Client's *NET interface
addresses and performance characteristics may change over time
(e.g., due to node mobility, link quality, etc.) while downstream-
attached Hosts and other Clients see the ENET as a stable ANET.
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(OMNI) Proxy/Server
a segment routing topology edge node that configures an OMNI
interface and connects Clients to the Mobility Service. As a
server, the Proxy/Server responds directly to some Client IPv6 ND
messages. As a proxy, the Proxy/Server forwards other Client IPv6
ND messages to other Proxy/Servers and Clients. As a router, the
Proxy/Server provides a forwarding service for ordinary data
messages that may be essential in some environments and a last
resort in others. Proxy/Servers at ANET boundaries configure both
an ANET downstream interface and *NET upstream interface, while
INET-based Proxy/Servers configure only an INET interface.
First-Hop Segment (FHS) Proxy/Server
a Proxy/Server connected to the source Client's *NET that forwards
OAL packets sent by the source into the segment routing topology.
FHS Proxy/Servers also act as intermediate forwarding systems to
facilitate RS/RA exchanges between Clients and Hub Proxy/Servers.
Last-Hop Segment (LHS) Proxy/Server
a Proxy/Server connected to the target Client's *NET that forwards
OAL packets received from the segment routing topology to the
target.
Hub Proxy/Server
a single Proxy/Server selected by the Client that provides a
designated router service for all of the Client's*NET underlay
networks. Since all Proxy/Servers provide equivalent services,
Clients normally select the first FHS Proxy/Server they coordinate
with to serve as the Hub. However, the Hub can instead be any
available Proxy/Server for the OMNI link, i.e., and not
necessarily one of the Client's FHS Proxy/Servers.
Segment Routing Topology (SRT)
a multinet forwarding region configured over one or more INETs
between the FHS Proxy/Server and LHS Proxy/Server. The SRT spans
the OMNI link on behalf of source/target Client pairs using
segment routing in a manner outside the scope of this document
(see: [I-D.templin-intarea-aero]).
Mobility Service (MS)
a mobile routing service that tracks Client movements and ensures
that Clients remain continuously reachable even across mobility
events. The MS consists of the set of all Proxy/Servers plus any
other OMNI link supporting infrastructure nodes. Specific MS
details are out of scope for this document, with an example found
in [I-D.templin-intarea-aero].
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Mobility Service Prefix (MSP)
an aggregated IP Global Unicast Address (GUA) prefix (e.g.,
2001:db8::/32, 192.0.2.0/24, etc.) assigned to the OMNI link and
from which more-specific Mobile Network Prefixes (MNPs) are
delegated. OMNI link administrators typically obtain MSPs from an
Internet address registry, however private-use prefixes can also
be used subject to certain limitations (see: Section 10). OMNI
links that connect to the global Internet advertise their MSPs to
their interdomain routing peers.
Mobile Network Prefix (MNP)
a longer IP prefix delegated from an MSP (e.g.,
2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a
Client. Clients receive MNPs from Proxy/Servers and sub-delegate
them to routers, Hosts and other Clients located in ENETs.
original IP packet/parcel
a whole IP packet/parcel or fragment admitted into the OMNI
interface by the network layer prior to OAL encapsulation/
fragmentation, or an IP packet/parcel delivered to the network
layer by the OMNI interface following OAL reassembly/
decapsulation.
OAL packet
an original IP packet/parcel encapsulated in an OAL IPv6 header
with an IPv6 Extended Fragment Header extension that includes an
8-octet (64-bit) OAL Identification value. Each OAL packet is
then subject to OAL fragmentation and reassembly.
OAL fragment
a portion of an OAL packet following fragmentation but prior to L2
encapsulation/fragmentation, or following L2 reassembly/
decapsulation but prior to OAL reassembly.
(OAL) atomic fragment
an OAL packet that can be forwarded without fragmentation, but
still includes an IPv6 Extended Fragment Header with an 8-octet
(64-bit) OAL Identification value and with Fragment Offset and
More Fragments both set to 0.
(L2) carrier packet
an encapsulated OAL fragment following L2 encapsulation or prior
to L2 decapsulation. OAL sources and destinations exchange
carrier packets over underlay interfaces, and may be separated by
one or more OAL intermediate systems. OAL intermediate systems
may perform re-encapsulation on carrier packets by removing the L2
headers of the first hop network and replacing them with new L2
headers for the next hop network. Carrier packets may themselves
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be subject to fragmentation and reassembly in L2 underlay networks
at a layer below the OAL. Carrier packets sent over unsecured
paths use OMNI protocol L2 encapsulations, while those sent over
secured paths use L2 security encapsulations such as IPsec
[RFC4301], etc. (The term "carrier" honors agents of the service
postulated by [RFC1149] and [RFC6214].)
OAL source
an OMNI interface acts as an OAL source when it encapsulates
original IP packets/parcels to form OAL packets, then performs OAL
fragmentation and encapsulation to create carrier packets which
may themselves be subject to fragmentation at their layer. Every
OAL source is also an OMNI link ingress.
OAL destination
an OMNI interface acts as an OAL destination when it decapsulates
carrier packets (while reassembling first, if necessary), then
performs OAL reassembly/decapsulation to derive the original IP
packet/parcel. Every OAL destination is also an OMNI link egress.
OAL intermediate system
an OMNI interface acts as an OAL intermediate system when it
reassembles/decapsulates carrier packets received from a first
segment to obtain the original OAL packet/fragment, then re-
encapsulates in new L2 headers appropriate for the next segment
and sends these new carrier packets into the next segment (while
re-fragmenting first, if necessary). OAL intermediate systems
decrement the Hop Limit in OAL packets/fragments during
forwarding, and discard the OAL packet/fragment if the Hop Limit
reaches 0. OAL intermediate systems do not decrement the TTL/Hop
Limit of the original IP packet/parcel, which can only be updated
by the network and higher layers.
OMNI Option
an IPv6 Neighbor Discovery option providing multilink parameters
for the OMNI interface as specified in Section 12.
Interface Identifier (IID)
the least significant 64 bits of an IPv6 address, as specified in
the IPv6 addressing architecture [RFC4291].
(OMNI) Link Local Address (LLA)
an IPv6 address beginning with fe80::/64 per the IPv6 addressing
architecture [RFC4291] and with either a 64-bit MNP (LLA-MNP) or a
56-bit random value (LLA-RND) encoded in the IID as specified in
Section 8.
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(OMNI) Unique Local Address (ULA)
an IPv6 address beginning with fd00::/8 followed by a 40-bit
Global ID followed by a 16-bit Subnet ID per [RFC4193] and with
either a 64-bit MNP (ULA-MNP) or a 56-bit random value (ULA-RND)
encoded in the IID as specified in Section 9. (Note that
[RFC4193] specifies a second form of ULAs based on the prefix
fc00::/8, which are referred to as "ULA-C" throughout this
document to distinguish them from the ULAs defined here.)
(OMNI) Temporary Local Address (TLA)
a ULA beginning with fd00::/16 followed by a 48-bit randomly-
initialized value followed by an MNP-based (TLA-MNP) or random
(TLA-RND) IID as specified in Section 9. Clients use TLAs to
bootstrap autoconfiguration in the presence of OMNI link
infrastructure or for sustained communications in the absence of
infrastructure. (Note that in some environments Clients can
instead use a (Hierarchical) Host Identity Tag ((H)HIT) instead of
a TLA - see: Section 22.)
(OMNI) eXtended Local Address (XLA)
a TLA beginning with fd00::/64 followed by an MNP-based (XLA-MNP)
or random (XLA-RND) IID as specified in Section 9. An XLA is
simply a TLA with an all-0 48-bit value following fd00::/16, and
can be used to supply a "wildcard match" for IPv6 ND cache
entries, a routing table entry for the OMNI link routing system,
etc. (Note that XLAs can also be statelessly formed from LLAs
(and vice-versa) simply by inverting prefix bits 7 and 8.)
Multilink
a Client OMNI interface's manner of managing multiple diverse *NET
underlay interfaces as a single logical unit. The OMNI interface
provides a single unified interface to the network layer, while
underlay interface selections are performed on a per-flow basis
considering traffic selectors such as DSCP, flow label,
application policy, signal quality, cost, etc. Multilink
selections are coordinated in both the outbound and inbound
directions based on source/target underlay interface pairs.
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Multinet
an intermediate system's manner of spanning multiple diverse IP
Internetwork and/or private enterprise network "segments" through
OAL encapsulation. Through intermediate system concatenation of
SRT network segments, multiple diverse Internetworks (such as the
global public IPv4 and IPv6 Internets) can serve as transit
segments in an end-to-end OAL forwarding path. This OAL
concatenation capability provides benefits such as supporting
IPv4/IPv6 transition and coexistence, joining multiple diverse
operator networks into a cooperative single service network, etc.
See: [I-D.templin-intarea-aero] for further information.
Multihop
an iterative relaying of carrier packets between Client's over an
OMNI underlay interface technology (such as omnidirectional
wireless) without support of fixed infrastructure. Multihop
services entail Client-to-Client relaying within a Mobile/
Vehicular Ad-hoc Network (MANET/VANET) for Vehicle-to-Vehicle
(V2V) communications and/or for Vehicle-to-Infrastructure (V2I)
"range extension" where Clients within range of communications
infrastructure elements provide forwarding services for other
Clients.
Mobility
any action that results in a change to a Client underlay interface
address. The change could be due to, e.g., a handover to a new
wireless base station, loss of link due to signal fading, an
actual physical node movement, etc.
Safety-Based Multilink (SBM)
A means for ensuring fault tolerance through redundancy by
connecting multiple OMNI interfaces within the same domain to
independent routing topologies (i.e., multiple independent OMNI
links).
Performance Based Multilink (PBM)
A means for selecting one or more underlay interface(s) for
carrier packet transmission and reception within a single OMNI
interface.
OMNI Domain
The set of all SBM/PBM OMNI links that collectively provides
services for a common set of MSPs. All OMNI links within the same
domain configure, advertise and respond to the same OMNI IPv6
Anycast address(es).
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AERO Forwarding Information Base (AFIB)
A multilink forwarding table on each OAL source, destination and
intermediate system that includes AERO Forwarding Vectors (AFV)
with both next hop forwarding instructions and context for
reconstructing compressed headers for specific underlay interface
pairs used to communicate with peers. See:
[I-D.templin-intarea-aero] for further discussion.
AERO Forwarding Vector (AFV)
An AFIB entry that includes soft state for each underlay interface
pairwise communication session between peer neighbors. AFVs are
identified by both a next-hop and previous-hop AFV Index (AFVI),
with the next-hop established based on an IPv6 ND solicitation and
the previous hop established based on the solicited IPv6 ND
advertisement response. The AFV also caches underlay interface
pairwise Identification sequence number parameters to support
carrier packet filtering. See: [I-D.templin-intarea-aero] for
further discussion.
AERO Forwarding Vector Index (AFVI)
A locally-unique 2-octet or 4-octet value automatically generated
by an OAL node when it creates an AFV. OAL intermediate systems
assign two distinct 4-octet AFVIs (called "A" and "B") to each
AFV, with "A" representing the forward path and "B" representing
the reverse path. Meanwhile, the OAL source assigns a single "B"
AFVI, and the OAL destination assigns a single "A" AFVI. Each OAL
node advertises its "A" AFVI to previous hop nodes on the reverse
path toward the source and advertises its "B" AFVI to next hop
nodes on the forward path toward the destination. Clients in
MANETs also assign distinct 2-octet AFVIs (called "C" and "D") to
support local multihop forwarding. The same as for the A/B AFVIs,
the "C" AFVI represents the forward path and the "D" AFVI
represents the reverse path. For unidirectional MANET paths, only
the forward path ("C") AFVI is used. See:
[I-D.templin-intarea-aero] for further discussion.
(OMNI) L2 encapsulation
the OMNI protocol encapsulation of OAL packets/fragments in an
outer header or headers to form carrier packets that can be routed
within the scope of the local ANET/INET/ENET underlay network
partition. The OAL node that performs encapsulation is known as
the "L2 source" while the OAL node that performs decapsulation is
known as the "L2 destination"; both OAL end and intermediate
systems can also act as an L2 source or destination. Common L2
encapsulation combinations include UDP, IP and/or Ethernet using a
port/protocol/type number for OMNI.
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L2 address (L2ADDR)
an address that appears in the OMNI protocol L2 encapsulation for
an underlay interface and also in IPv6 ND message OMNI options.
L2ADDR can be either an IP address for IP encapsulations or an
IEEE EUI address [EUI] for direct data link encapsulation. (When
UDP/IP encapsulation is used, the UDP port number is considered an
ancillary extension of the IP L2ADDR.)
OAL Fragment Size (OFS)
the current size for OAL source fragmentation which must be no
smaller than 1024 octets and no larger than 65279 octets (allowing
for up to 256 octets of L2 encapsulations for each OAL fragment).
Each OAL source maintains an OFS in AERO Forwarding Vectors (AFVs)
for each OAL destination. The source discovers the "maximum OFS"
through IPv6 Minimum Path MTU options [RFC9268] and maintains an
equal or smaller value "effective OFS" according to dynamic
network control message feedback. The OAL source should
adaptively seek to use the largest possible effective OFS under
current network conditions to provide better performance for upper
layers. OAL fragments prepared by the source must not be further
fragmented by OAL intermediate systems on the path to the OAL
destination.
Carrier Fragment Size (CFS)
the current size for L2 carrier packet fragments including the
headers, trailers and OAL fragment body. The OAL L2 source
applies source fragmentation if necessary to each L2-encapsulated
OAL fragment under the default CFS of 1280 octets (i.e., the IPv6
minimum MTU) until it can either engage IPv4 network fragmentation
or determine whether a larger CFS is possible through
Packetization Layer Path MTU Discovery for Datagram Transports
[RFC8899]. The L2 source should adaptively seek to maximize CFS
to provide better performance for upper layers.
3. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
An implementation is not required to internally use the architectural
constructs described here so long as its external behavior is
consistent with that described in this document.
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4. Overlay Multilink Network (OMNI) Interface Model
An OMNI interface is a virtual interface configured over one or more
underlay interfaces, which may be physical (e.g., an aeronautical
radio link, a cellular wireless link, etc.) or virtual (e.g., an
internet-layer or higher-layer "tunnel"). The OMNI interface
architectural layering model is the same as in [RFC5558][RFC7847],
and augmented as shown in Figure 1. The network layer therefore sees
the OMNI interface as a single L3 interface nexus for multiple
underlay interfaces that appear as L2 communication channels in the
architecture.
+----------------------------+
| Upper Layer Protocol |
Session-to-IP +---->| |
Address Binding | +----------------------------+
+---->| IP (L3) |
IP Address +---->| |
Binding | +----------------------------+
+---->| OMNI Interface |
Logical-to- +---->| (OMNI Adaptation Layer) |
Physical | +----------------------------+
Interface +---->| L2 | L2 | | L2 |
Binding |(IF#1)|(IF#2)| ..... |(IF#n)|
+------+------+ +------+
| L1 | L1 | | L1 |
| | | | |
+------+------+ +------+
Figure 1: OMNI Interface Architectural Layering Model
Each underlay interface provides an L2/L1 abstraction according to
one of the following models:
* ANET interfaces connect to a protected and secured ANET that is
separated from the open INET by Proxy/Servers. The ANET interface
may be either on the same L2 link segment as a Proxy/Server, or
separated from a Proxy/Server by multiple L2 hops. (Note that
NATs may appear internally within an ANET or on the Proxy/Server
itself and may require NAT traversal the same as for the INET
case.)
* INET interfaces connect to an INET either natively or through IP
Network Address Translators (NATs). Native INET interfaces have
global IP addresses that are reachable from any INET
correspondent. NATed INET interfaces typically configure private
IP addresses and connect to a private network behind one or more
NATs with the outermost NAT providing INET access.
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* ENET interfaces connect a Client's downstream-attached networks,
where the Client provides forwarding services for ENET Host and
Client communications to remote peers. An ENET may be as simple
as a small IoT sub-network that travels with a mobile Client to as
complex as a large private enterprise network that the Client
connects to a larger ANET or INET. Downstream-attached Hosts and
Clients see the ENET as an ANET and see the (upstream) Client as a
Proxy/Server.
* VPN interfaces use security encapsulations (e.g. IPsec tunnels)
over underlay networks to connect Client, Proxy/Server or other
critical infrastructure nodes. VPN interfaces provide security
services at lower layers of the architecture (L2/L1), with
securing properties similar to Direct point-to-point interfaces.
* Direct point-to-point interfaces securely connect Clients, Proxy/
Servers and/or other critical infrastructure nodes over physical
or virtual media that does not transit any open Internetwork
paths. Examples include a line-of-sight link between a remote
pilot and an unmanned aircraft, a fiberoptic link between
gateways, etc.
The OMNI interface forwards original IP packets/parcels from the
network layer using the OMNI Adaptation Layer (OAL) (see: Section 5)
as an encapsulation and fragmentation sublayer service. This "OAL
source" then further encapsulates the resulting OAL packets/fragments
in underlay network headers (e.g., UDP/IP, IP-only, Ethernet-only,
etc.) to create L2 encapsulated "carrier packets" for fragmentation
and transmission over underlay interfaces. The target OMNI interface
then receives the carrier packets from underlay interfaces and
performs L2 reassembly/decapsulation.
If the resulting OAL packets/fragments are addressed to itself, the
OMNI interface performs reassembly/decapsulation as an "OAL
destination" and delivers the original IP packet/parcel to the
network layer. If the OAL packets/fragments are addressed to another
node, the OMNI interface instead re-encapsulates them in new underlay
network L2 headers as an "OAL intermediate system" then performs L2
fragmentation and forwards the resulting carrier packets over an
underlay interface. The OAL source and OAL destination are seen as
"neighbors" on the OMNI link, while OAL intermediate systems provide
a virtual bridging service that joins the segments of a (multinet)
Segment Routing Topology (SRT).
The OMNI interface transports carrier packets over either secured or
unsecured underlay interfaces to access the secured/unsecured OMNI
link spanning trees as discussed further throughout the document.
Carrier packets that carry control plane messages over secured
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underlay interfaces use secured L2/L1 services such as IPsec, direct
encapsulation over secured point-to-point links, etc. Carrier
packets that carry data plane messages over unsecured underlay
interfaces instead use L2 encapsulations appropriate for public or
private Internetworks and are subject for the following sections.
The OMNI interface and its OAL can forward original IP packets/
parcels over underlay interfaces while including/omitting various
lower layer encapsulations including OAL, UDP, IP and (ETH)ernet or
other link layer header. The network layer can also engage underlay
interfaces directly while bypassing the OMNI interface entirely when
necessary. This architectural flexibility may be beneficial for
underlay interfaces (e.g., some aviation data links) for which
encapsulation overhead is a primary consideration. OMNI interfaces
that send original IP packets/parcels directly over underlay
interfaces without invoking the OAL can only reach peers located on
the same OMNI link segment. Source Clients can instead use the OAL
to coordinate with target Clients in the same or different OMNI link
segments by sending initial carrier packets to a First-Hop Segment
(FHS) Proxy/Server. The FHS Proxy/Sever then sends the carrier
packets into the SRT spanning tree, which transports them to a Last-
Hop Segment (LHS) Proxy/Server for the target Client.
The OMNI interface encapsulation/decapsulation layering possibilities
are shown in Figure 2 below. Imaginary vertical lines drawn between
the Network Layer at the top of the figure and Underlay Interfaces at
the bottom of the figure denote the various encapsulation/
decapsulation layering combination possibilities. Common
combinations include IP-only (i.e., direct access to underlay
interfaces with or without using the OMNI interface, IP/IP, IP/UDP/
IP, IP/UDP/IP/ETH, IP/OAL/UDP/IP, IP/OAL/UDP/ETH, etc.).
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+------------------------------------------------------------+ ^
| Network Layer (Original IP packets/parcels) | |
+--+---------------------------------------------------------+ L3
| OMNI Interface (virtual sublayer nexus) | |
+--------------------------+------------------------------+ -
| OAL Encaps/Decaps | |
+------------------------------+ OAL
| OAL Frag/Reass | |
+------------+---------------+--------------+ -
| UDP Encaps/Decaps/Compress | |
+----+---+------------+--------+--+ +--------+ |
| IP E/D | | IP E/D | | IP E/D | L2
+----+-----+--+----+ +--+----+---+ +---+----+--+ |
|ETH E/D| |ETH E/D| |ETH E/D| |ETH E/D| |
+------+-------+--+-------+----+-------+-------------+-------+ v
| Underlay Interfaces |
+------------------------------------------------------------+
Figure 2: OMNI Interface Layering
The OMNI/OAL model gives rise to a number of opportunities:
* Clients coordinate with the MS and receive MNP delegations through
IPv6 ND control plane message exchanges with Proxy/Servers.
Clients use the MNP to construct Link-Local and Unique-Local
Addresses (LLA-MNP / ULA-MNP) through the algorithmic derivation
specified in Section 8 and assign the addresses to the OMNI
interface. Since the LLA and ULA are derived from a unique MNP,
no Duplicate Address Detection (DAD) or Multicast Listener
Discovery (MLD) messaging is necessary.
* since Temporary ULAs with random IIDs (TLA-RNDs) are statistically
unique, they can be used without DAD until an MNP is obtained.
* underlay interfaces on the same L2 link segment as a Proxy/Server
do not require any L3 addresses (i.e., not even link-local) in
environments where communications are coordinated entirely over
the OMNI interface.
* as underlay interface properties change (e.g., link quality, cost,
availability, etc.), any active interface can be used to update
the profiles of multiple additional interfaces in a single
message. This allows for timely adaptation and service continuity
under dynamically changing conditions.
* coordinating underlay interfaces in this way allows them to be
represented in a unified MS profile with provisions to support the
"6 M's of Modern Internetworking".
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* exposing a single virtual interface abstraction to the network
layer allows for multilink operation (including QoS based link
selection, carrier packet replication, load balancing, etc.) at L2
while still permitting L3 traffic shaping based on, e.g., DSCP,
flow label, etc.
* the OMNI interface supports multinet traversal over the SRT when
communications across different administrative domain network
segments are necessary. This mode of operation would not be
possible via direct communications over the underlay interfaces
themselves.
* the OAL supports lossless and adaptive path MTU mitigations not
available for communications directly over the underlay interfaces
themselves. The OAL supports "packing" of multiple original IP
payload packets/parcels within a single OAL "super-packet" and
also supports transmission of IP packets/parcels of all sizes up
to and including (advanced) jumbograms.
* the OAL assigns per-packet Identification values that allow for
adaptation/link layer reliability and data origin authentication.
* L3 sees the OMNI interface as a point of connection to the OMNI
link; if there are multiple OMNI links, L3 will see multiple OMNI
interfaces.
* Multiple independent OMNI interfaces can be used for increased
fault tolerance through Safety-Based Multilink (SBM), with
Performance-Based Multilink (PBM) applied within each interface.
* Multiple independent OMNI links can be joined together into a
single link without requiring renumbering of infrastructure
elements, since the ULAs assigned to the different links will be
mutually exclusive.
* the OMNI/OAL model supports transmission of a new form of IP
packets known as "IP parcels" that improve performance and
efficiency for both transport layer protocols and networked paths.
Figure 3 depicts the architectural model for a source Client with an
attached ENET connecting to the OMNI link via multiple independent
ANETs/INETs (i.e., *NETs). The Client's OMNI interface forwards
adaptation layer IPv6 ND solicitation messages over available *NET
underlay interfaces using any necessary L2 encapsulations. The IPv6
ND messages traverse the *NETs until they reach an FHS Proxy/Server
(FHS#1, FHS#2, ..., FHS#n), which returns an IPv6 ND advertisement
message and/or forwards a proxyed version of the message over the SRT
to an LHS Proxy/Server near the target Client (LHS#1, LHS#2, ...,
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LHS#m). The Hop Limit in IPv6 ND messages is not decremented due to
encapsulation; hence, the source and target Client OMNI interfaces
appear to be attached to a common link.
+--------------+
|Source Client |
+--------------+ (:::)-.
|OMNI interface|<-->.-(::ENET::)
+----+----+----+ `-(::::)-'
+--------|IF#1|IF#2|IF#n|------ +
/ +----+----+----+ \
/ | \
/ | \
v v v
(:::)-. (:::)-. (:::)-.
.-(::*NET:::) .-(::*NET:::) .-(::*NET:::)
`-(::::)-' `-(::::)-' `-(::::)-'
+-----+ +-----+ +-----+
... |FHS#1| ......... |FHS#2| ......... |FHS#n| ...
. +--|--+ +--|--+ +--|--+ .
. | | |
. \ v / .
. \ / .
. v (:::)-. v .
. .-(::::::::) .
. .-(::: Segment :::)-. .
. (::::: Routing ::::) .
. `-(:: Topology ::)-' .
. `-(:::::::-' .
. / | \ .
. / | \ .
. v v v
. +-----+ +-----+ +-----+ .
... |LHS#1| ......... |LHS#2| ......... |LHS#m| ...
+--|--+ +--|--+ +--|--+
\ | /
v v v
<-- Target Clients -->
Figure 3: Source/Target Client Coordination over the OMNI Link
After the initial IPv6 ND message exchange, the source Client (as
well as any nodes on its attached ENETs) can send carrier packets to
the target Client via the OMNI interface. OMNI interface multilink
services will send the carrier packets via FHS Proxy/Servers for the
correct underlay *NETs. The FHS Proxy/Server then re-encapsulates
the carrier packets and sends them over the SRT which delivers them
to an LHS Proxy/Server, and the LHS Proxy/Server in turn re-
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encapsulates and sends them to the target Client. (Note that when
the source and target Client are on the same SRT segment, the FHS and
LHS Proxy/Servers may be one and the same.)
Clients select a Hub Proxy/Server (not shown in the figure), which
will often be one of their FHS Proxy/Servers but could also be any
Proxy/Server on the OMNI link. Clients then register all of their
*NET underlay interfaces with the Hub Proxy/Server via the FHS Proxy/
Server in a pure proxy role. The Hub Proxy/Server then provides a
designated router service for the Client, and the Client can quickly
migrate to a new Hub Proxy/Server if the first becomes unresponsive.
Clients therefore use Proxy/Servers as gateways into the SRT to reach
OMNI link correspondents via a spanning tree established in a manner
outside the scope of this document. Proxy/Servers forward critical
MS control messages via the secured spanning tree and forward other
messages via the unsecured spanning tree (see Security
Considerations). When AERO route optimization is applied, Clients
can instead forward directly to SRT intermediate systems (or directly
to correspondents in the same SRT segment) to reduce Proxy/Server
load.
Note: while not shown in the figure, a Client's ENET may connect many
additional Hosts and even other Clients in a recursive extension of
the OMNI link. This OMNI virtual link extension will be discussed
more fully throughout the document.
Note: Original IP packets/parcels sent into an OMNI interface will
receive consistent consideration according to their size as discussed
in the following sections, while those sent directly over underlay
interfaces that exceed the underlay network path MTU are dropped with
an ordinary ICMP Packet Too Big (PTB) message returned. These PTB
messages are subject to loss the same as for any non-OMNI IP
interface [RFC2923].
5. OMNI Interface Maximum Transmission Unit (MTU)
The OMNI interface observes the link nature of tunnels, including the
Maximum Transmission Unit (MTU), Effective MTU to Send (EMTU_S),
Effective MTU to Receive (EMTU_R) and the role of fragmentation and
reassembly [I-D.ietf-intarea-tunnels]. The OMNI interface is
configured over one or more underlay interfaces as discussed in
Section 4, where underlay links and network paths may have diverse
MTUs. OMNI interface considerations for accommodating original IP
packets/parcels of various sizes are discussed in the following
sections.
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IPv6 underlay interfaces are REQUIRED to configure a minimum MTU of
1280 octets and a minimum EMTU_R of 1500 octets [RFC8200].
Therefore, the minimum IPv6 path MTU is 1280 octets since routers on
the path are not permitted to perform network fragmentation even
though the destination is required to reassemble more. The network
therefore MUST forward original IP packets/parcels as large as 1280
octets without generating an IPv6 Path MTU Discovery (PMTUD) Packet
Too Big (PTB) message [RFC8201]. Since each OAL intermediate system
must configure an EMTU_R of at least 65535 octets (see: Section 6.3),
the source can apply "source fragmentation" for carrier packets as
large as that size but this does not affect the minimum IPv6 path
MTU.)
IPv4 underlay interfaces are REQUIRED to configure a minimum MTU of
68 octets [RFC0791] and a minimum EMTU_R of 576 octets
[RFC0791][RFC1122]. Therefore, when the Don't Fragment (DF) bit in
the IPv4 header is set to 0 the minimum IPv4 path MTU is 576 octets
since routers on the path support network fragmentation and the
destination is required to reassemble at least that much. The OMNI
interface therefore SHOULD set DF to 0 in the IPv4 encapsulation
headers of carrier packets no larger than 576 octets, and SHOULD set
DF to 1 in larger carrier packets unless it has a way to determine
the EMTU_R of the next OAL hop as discussed in Section 6.15. This
limitation is therefore relaxed by the requirement that each OAL
intermediate system must configure a minimum EMTU_R of 65535 octets
(see: Section 6.3) allowing for IPv4 fragmentation and reassembly for
larger carrier packets.
The OMNI interface itself sets an "unlimited" MTU of (2**32 - 1)
octets. The network layer therefore unconditionally admits all
original IP packets/parcels into the OMNI interface, where the
adaptation layer accommodates them if possible according to their
size. For each parcel that it accommodates, the OAL source within
the OMNI interface first performs "parcellation" if necessary to
break large parcels into smaller sub-parcels that can transit the OAL
path (see: Section 5.1). The OAL source then invokes adaptation
layer encapsulation/fragmentation services to transform all original
IP packets and (sub-)parcels no larger that 65535 octets into OAL
packets/fragments. The OAL source then applies L2 encapsulation and
fragmentation if necessary to form carrier packets and finally
forwards the carrier packets via underlay interfaces.
When the OAL source performs IPv6 encapsulation and fragmentation
(see: Section 6), the Fragment Offset field limits the maximum-sized
original IP packet/parcel that the OAL can accommodate while applying
IPv6 fragmentation to (2**16 - 1) = 65535 octets (plus the length of
the OAL encapsulation extension headers). The OAL source is also
permitted to forward packets/parcels larger than this size as a best-
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effort delivery service if the L2 path can accommodate them through
"jumbo-in-jumbo" encapsulation (see: Section 5.2); otherwise, the OAL
source discards the packet and arranges to return a PTB "hard error"
to the original source (see: Section 6.9).
Each OMNI interface therefore sets a minimum EMTU_R of 65535 octets
(plus the length of the OAL encapsulation headers), and each OAL
destination must consistently either accept or reject still larger
whole packets that arrive over any of its underlay interfaces
according to their size. If an underlay interface presents a whole
packet larger than the OAL destination is prepared to accept (e.g.,
due to a buffer size restriction), the OAL destination discards the
packet and arranges to return a PTB "hard error" to the OAL source
which in turn forwards the PTB to the original source (see:
Section 6.9).
5.1. IP Parcels
As specified in [I-D.templin-6man-parcels2]
[I-D.templin-intarea-parcels2], an IP parcel is an IP jumbogram
variant for which the IP {Total, Payload} Length field encodes a
value between 256 and 65535 octets denoting the non-final transport
layer protocol segment length while the parcel body includes as many
as 64 individual transport layer protocol segments. The Jumbo
Payload length field is modified to include a Parcel Index field plus
flags followed by a 22-bit Parcel Payload Length field which together
determine the size and number of transport layer segments included in
the parcel.
IP parcel "parcellation" and "reunification" procedures for OMNI
interfaces are specified in [I-D.templin-6man-parcels2]
[I-D.templin-intarea-parcels2], while OAL encapsulation and
fragmentation procedures are specified in Section 6.13 of this
document. The maximum-sized IP parcel that can be conveyed over an
OMNI interface using OAL parcellation and IPv6 fragmentation-based
assured delivery is one with 64 segments of 65535 (minus headers)
octets in length. (The OAL source can instead forward large parcels
as a best-effort service using jumbo-in-jumbo encapsulation if the
OAL/L2 path can accommodate them.)
IP parcels follow the same link models described for Advanced Jumbos
below. IP parcels that accumulate link errors on the path are
subject to error detection and correction at the final destination.
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ENET end systems that implement either the full OMNI interface (i.e.,
Clients) or enough of the OAL to process parcels (i.e., Hosts) are
permitted to exchange parcels with consenting peers. This
accommodates nodes that connect to the OMNI link but do not assign
OAL addresses.
5.2. Advanced Jumbos (AJs)
While the maximum-sized original IP packet/parcel that the OAL can
accommodate using IPv6 fragmentation-based assured delivery is 65535
octets, OMNI interfaces can forward much larger singleton parcels
termed "Advanced Jumbos (AJs)" via jumbo-in-jumbo encapsulation as
specified in
[I-D.templin-6man-parcels2][I-D.templin-intarea-parcels2]. For
jumbo-in-jumbo encapsulation of large AJs, the OAL source appends an
OAL IPv6 header plus extensions then appends any L2 headers to
identify this as an AJ. Since the Jumbo Payload Length is 32 bits,
the largest possible AJ is limited to (2**32 - 1) octets minus the
lengths of any extension/encapsulation headers, or smaller still for
transmission over underlay interfaces that include additional
extensions/encapsulations.
Basic IPv6 jumbograms per [RFC2675] use the Jumbo Payload option and
set the IPv6 Payload Length field to 0. IP parcels and AJs instead
use the IPv6 Minimum Path MTU option per [RFC9268] and set the IP
{Total, Payload} Length to other values. The OAL/L2 source forwards
basic jumbograms and AJs as giant carrier packets via jumbo-in-jumbo
encapsulation, noting that traditional 32-bit link CRCs do not
provide adequate integrity protection for such large sizes [CRC]. If
a basic jumbogram is dropped along the path to the OAL destination,
the OAL source arranges to return an ICMP PTB "hard error" to the
original source. If an AJ is dropped, the OAL source instead
arranges to return ICMP PTB "soft errors" (see: Section 6.9).
AJs range in size from the largest possible unit as discussed above
to the smallest unit that includes only the headers and a small or
possibly even null payload. Intermediate hops forward AJs that
follow a new DTN link model for the Internet (instead of dropping)
even if link errors were incurred along the path. The AJ will then
arrive at the destination along with any cumulative link errors
collected on the path, then the final destination applies end-to-end
integrity checks and/or error correction while requesting
retransmission only as a last resort. This link model may be more
appropriate for delay/disruption-tolerant environments such as
anticipated for air/land/sea/space mobile Internetworking.
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Advanced jumbo services for both IPv6 and IPv4 (including jumbo path
probing and jumbo-in-jumbo encapsulation) are specified in
[I-D.templin-6man-parcels2][I-D.templin-intarea-parcels2].
5.3. Control/Data Plane Considerations
The above sections primarily concern data plane aspects of the OMNI
interface MTU and describe the data plane service model offered to
the network layer. OMNI interfaces also internally employ a control
plane service based on IPv6 Neighbor Discovery (ND) messaging. These
control plane messages must be sent over secured underlay interfaces
(e.g., IPsec tunnels, secured direct point-to-point links, etc.)
where the IPv6 minimum MTU of 1280 octets must be assumed.
OMNI interfaces therefore offer an unlimited data plane MTU to the
network layer but set a more conservative MTU for the internal
control plane operation. OMNI interfaces assume a fixed control
plane path MTU of 1280 octets for transmission of IPv6 ND messages
over underlay interface connections to the secured spanning tree.
OMNI interface control plane messages must therefore engage IPv6
encapsulation followed by fragmentation if necessary for any larger
control plane messages up to a maximum of 65535 octets. Recognizing
that larger control plane messages are sometimes unavoidable, OMNI
interfaces should send multiple smaller IPv6 ND messages instead of
singleton larger messages whenever possible to minimize
fragmentation.
6. The OMNI Adaptation Layer (OAL)
When an OMNI interface forwards an original IP packet/parcel from the
network layer for transmission over one or more underlay interfaces,
the OMNI Adaptation Layer (OAL) acting as the OAL source applies IPv6
encapsulation to form OAL packets subject to OAL fragmentation
producing fragments suitable for L2 encapsulation and transmission as
carrier packets. These carrier packets may in turn be subject to IP
fragmentation over underlay interface paths as described in
Section 6.1. The carrier packets/fragments then travel over one or
more underlay networks spanned by OAL intermediate systems in the
SRT, which first reassemble (if necessary) then re-encapsulate by
removing the L2 headers of the first underlay network and appending
L2 headers appropriate for the next underlay network in succession
while re-fragmenting if necessary. (This process supports the
multinet concatenation capability needed for joining multiple diverse
networks.) Following any forwarding by OAL intermediate systems, the
carrier packets arrive at the OAL destination.
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When the OAL destination receives the carrier packets, it reassembles
(if necessary) then discards the L2 headers and reassembles the
resulting OAL fragments (if necessary) into an OAL packet as
described in Section 6.3. The OAL destination next decapsulates the
OAL packet to obtain the original IP packet/parcel which it then
delivers to the network layer. The OAL source may be either the
source Client or its FHS Proxy/Server, while the OAL destination may
be either the LHS Proxy/Server or the target Client. Proxy/Servers
(and SRT Gateways as discussed in [I-D.templin-intarea-aero]) may
also serve as OAL intermediate systems.
The OAL presents an OMNI sublayer abstraction similar to ATM
Adaptation Layer 5 (AAL5). Unlike AAL5 which performs segmentation
and reassembly with fixed-length 53-octet cells over ATM networks,
however, the OAL uses IPv6 encapsulation, fragmentation and
reassembly with larger variable-length cells over heterogeneous
networks. Detailed operations of the OAL are specified in the
following sections.
6.1. OAL Source Encapsulation and Fragmentation
When the network layer forwards an original IP packet/parcel into the
OMNI interface, it sets the TTL/Hop Limit for locally-generated
packets or decrements it according to standard IP forwarding rules
for forwarded packets. The OAL source next creates an "OAL packet"
by prepending an IPv6 OAL encapsulation header in the spirit of
[RFC2473] but with Next Header set to TBD1 (see: IANA Considerations)
and with the IPv6 OAL header followed by an IPv4 or IPv6 original
packet. The OAL source copies the "Type of Service/Traffic Class"
[RFC2983] and "Explicit Congestion Notification (ECN)" [RFC3168]
values in the original packet/parcel's IP header into the
corresponding fields in the OAL header, then sets the OAL header
"Flow Label" as specified in [RFC6438]. The OAL source next sets the
OAL header IPv6 Payload Length to the length of the original IP
packet/parcel and sets Hop Limit to a value that MUST NOT be larger
than 63 yet is still sufficiently large to support loop-free
forwarding over multiple concatenated OAL intermediate hops.
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The OAL source next selects OAL packet source and destination
addresses. Client OMNI interfaces set the OAL source address to a
Unique Local Address (ULA) based on the Mobile Network Prefix (ULA-
MNP). When a Client OMNI interface does not (yet) have a ULA prefix
and/or an MNP suffix, it can instead use a Temporary ULA (TLA) (or a
(Hierarchical) Host Identity Tag ((H)HIT - see: Section 22) as an OAL
address. Finally, when the Client needs to express its MNP outside
the context of a specific ULA prefix, it can use an eXtended ULA
(XLA). Proxy/Server OMNI interfaces instead set the source address
to a Random ULA (ULA-RND) (see: Section 9), but also process carrier
packets with anycast and/or multicast OAL addresses that they are
configured to recognize.)
The OAL source next inserts any necessary extension headers following
the OAL IPv6 header but before the payload packet as specified in
Section 6.2.1. The source first inserts any per-fragment extension
headers (e.g., Hop-by-Hop, Routing, etc.) then inserts an IPv6
Extended Fragment Header (see: [I-D.templin-6man-ipid-ext]) with an
8-octet (64-bit) OAL packet Identification. Note that the extension
header insertions could cause the IPv6 Payload Length to exceed 65535
octets when the original IPv6 packet is (nearly) the maximum length.
The OAL source then fragments the OAL packet if necessary according
to an OAL Fragment Size (OFS) maintained in AERO Forwarding Vectors
(AVFs) for each OAL destination. (OAL packets that are no larger
than the OFS and original IP packets/parcels larger than 65535 octets
are instead processed as "atomic fragments".) OAL fragments prepared
by the source must not be fragmented further by OAL intermediate
systems on the path to the OAL destination.
OAL packets that contain original IP parcels no larger than
(64*65535) octets may be first subject to OMNI interface
parcellation, after which the (sub-)parcels (as well as OAL packets
that contain original IP packets no larger than 65535 octets) are
subject to OAL fragmentation-based assured delivery. Advanced Jumbos
(AJs) larger than 65535 octets (see: [I-D.templin-6man-parcels2]
[I-D.templin-intarea-parcels2]) are not eligible for OAL
fragmentation but instead engage a best effort jumbo-in-jumbo
encapsulation service as discussed in Section 5.2. (Note: the
original source can optionally elect this best-effort jumbo-in-jumbo
delivery service for any parcel/AJ regardless of its size.)
OAL fragmentation is conducted as specified in Section 6.2.1, which
is the same as for standard IPv6 fragmentation (see: [RFC8200]) with
the exception that the IPv6 Payload Length may exceed 65535 by at
most the length of the extension headers. The OAL source MUST set a
"maximum OFS" to a size no smaller than 1024 octets and no larger
than 65279 octets and thereafter reduce or increase the "effective
OFS" according to dynamic network control message feedback. (Note
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that these sizes allow for up to 256 octets of L2 encapsulation
relative to the IPv6 minimum MTU of 1280 octets and the maximum-sized
reassembled packet of 65535 octets.) Specifically, if an OAL
intermediate system or the OAL destination advertises a reduced size,
the OAL source SHOULD reduce the effective OFS accordingly (to a size
no smaller than 1024 octets) and can later increase the effective OFS
(to a size no larger than the maximum OFS) as network conditions
improve. When the OAL source performs fragmentation, it SHOULD
produce the minimum number of fragments under the effective OFS
constraints, where the fragments MUST be non-overlapping and the
portion of each non-final fragment following the IPv6 Extended
Fragment Header MUST be equal in length while that of the final
fragment may be a different length.
The OAL source discovers the maximum OFS by including an IPv6 Minimum
Path MTU Hop-by-Hop option [RFC9268] in the OAL encapsulation header
of its Neighbor Solicitation (NS) / Neighbor Advertisement (NA)
exchanges over the secured spanning tree used to establish multilink
forwarding state (see: [I-D.templin-intarea-aero]). Each OAL
intermediate system on the path sets the minimum path MTU in the NS
message OAL extension header to the maximum OFS capable of traversing
the next segment. (Note that segments traversed by L2 encapsulations
such as IPsec tunnels can normally regard the MTU for their unsecured
overlay network segments as 65535 octets while those traversed by
direct point-to-point links must regard the link MTU as a restricting
size; therefore, each OAL intermediate system MUST correctly
recognize and honor the IPv6 Minimum Path MTU Hop-by-Hop option.
Note also that OAL intermediate systems forward the NS/NA messages in
the control plane, but the returned MTU reflects the maximum OFS for
the data plane.) When the OAL destination returns an NA message with
an OAL header containing an IPv6 Minimum Path MTU Hop-by-Hop option,
the OAL source can then set the maximum OFS for this AFV by deducting
256 from the returned MTU. The OAL source can later adaptively
increase or decrease the effective OFS if it receives dynamic path
MTU feedback from an OAL intermediate node or destination.
During fragmentation, the OAL source replaces the IPv6 Extended
Fragment Header 1-octet "Reserved" field with OMNI-specific encodings
as shown in Figure 4:
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Parcel ID |P|S| | Ordinal |Res|
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
a) First fragment a) Non-first fragment
Figure 4: IPv6 Extended Fragment Header Reserved Field Coding
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For the first fragment (i.e., the one with Fragment Offset set to 0),
the OAL source sets "Parcel ID", "(P)arcel" and "More (S)egments" as
specified in Section 6.13. For each non-first fragment, the OAL
source instead writes a monotonically-increasing "Ordinal" value
between 1 and 63. Specifically, the OAL source writes the Ordinal
value '1' for the first non-first fragment, '2' for the second, '3'
for the third, etc. up to the final fragment. The first fragment is
logically considered Ordinal number '0' while the final fragment may
assign an Ordinal as large as '63'; therefore at most 64 fragments
are possible. For this reason, OAL fragments produced by OAL source
fragmentation must not be subjected to further adaptation layer
fragmentation by an OAL intermediate system or IPv6 router on the
path.
The OAL source finally encapsulates the fragments in L2 headers to
form carrier packets for transmission over underlay interfaces, while
retaining the fragments and their ordinal numbers (i.e., #0, #1, #2,
etc.) for a brief period to support adaptation layer retransmissions
(see: Section 6.8). OAL fragment and carrier packet formats are
shown in Figure 5 (note that IPv4 carrier packets include a trailing
checksum if necessary as discussed in Section 6.2).
+----------+-------------------------+---------------+
|OAL Header| Original Packet Headers | Frag #0 |
+----------+-------------------------+---------------+
+----------+----------------+
|OAL Header| Frag #1 |
+----------+----------------+
+----------+----------------+
|OAL Header| Frag #2 |
+----------+----------------+
....
+----------+----------------+
|OAL Header| Frag #(N-1) |
+----------+----------------+
a) OAL fragmentation
+----------+-----------------------------+
|OAL Header| Original IP packet/parcel |
+----------+-----------------------------+
b) An OAL atomic fragment
+--------+----------+----------------+------+
|L2 Hdrs |OAL Header| Frag #i | Csum |
+--------+----------+----------------+------+
c) OAL carrier packet after L2 encapsulation
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Figure 5: OAL Fragments and Carrier Packets
6.2. OAL L2 Encapsulation and Re-Encapsulation
The OAL source or intermediate system next encapsulates each OAL
fragment (with either full or compressed headers) in L2 encapsulation
headers to create a carrier packet. The OAL source or intermediate
system (i.e., the L2 source) includes a UDP header as the innermost
sublayer if NATs and/or filtering middleboxes might occur on the
path. Otherwise, the L2 source includes a full/compressed IP header
and/or an actual link layer header (e.g., such as for Ethernet-
compatible links) as the innermost sublayer. The L2 source also
appends any additional encapsulation sublayer headers necessary
(e.g., security encapsulations, jumbo-in-jumbo encapsulation, etc.).
The L2 source encapsulates the OAL information immediately following
the innermost L2 sublayer header. The L2 source next interprets the
first four bits following the L2 headers as a Type field that
determines the type of OAL header that follows. The L2 source sets
Type to "OMNI-OFH" for an uncompressed IPv6 OMNI Full Header (OFH) or
"OMNI-OCH" for an OMNI Compressed Header (OCH) as specified in
Section 6.5. For raw IP packets/parcels (i.e., those that do not
include an OAL header), the L2 source instead interprets the first
four bits as a Version field that encodes '4' for an ordinary IPv4
packet/parcel or '6' for an ordinary IPv6 packet/parcel. Other Type
values (including a Type for a Hop-by-Hop options header that
includes an Advanced Jumbo option) may also appear as specified in
Section 6.5.
The OAL node prepares the L2 encapsulation headers for OAL packets/
fragments as follows:
* For UDP/IP encapsulation, the L2 source sets the UDP source port
to 8060 (i.e., the port number reserved for AERO/OMNI). When the
L2 destination is a Proxy/Server or Gateway, the L2 source sets
the UDP destination port to 8060; otherwise, the L2 source sets
the UDP destination port to its cached port number value for the
peer. The L2 source next sets the UDP Length the same as
specified in [I-D.ietf-tsvwg-udp-options]. (If the OAL packet is
submitted for jumbo-in-jumbo encapsulation, the L2 source instead
includes a Hop-by-Hop Options header with Advanced Jumbo option
following the L2 UDP/IP header with the length of the L2 UDP
header included in the Jumbo Payload Length.) The L2 source then
sets the IP {Protocol, Next Header} to '17' (the UDP protocol
number) and sets the {Total, Payload} Length the same as specified
in the base IP protocol specifications for IP parcels and Advanced
Jumbos [I-D.templin-6man-parcels2][I-D.templin-intarea-parcels2]
or for ordinary IP packets
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[RFC0791][RFC8200][I-D.ietf-tsvwg-udp-options]. The L2 source
then continues to set the remaining IP header fields as discussed
below.
* For IP-only encapsulation, the L2 source sets the IP {Protocol,
Next Header} to TBD1 (see: IANA Considerations) and sets the
{Total, Payload} Length the same as specified in [RFC0791] or
[RFC8200]. (If the OAL header includes an Advanced Jumbo option,
the L2 source includes an Advanced Jumbo option in the L2 IP
header.) The L2 source then continues to set the remaining IP
header fields as discussed below.
* For direct encapsulations over Ethernet-compatible links, the L2
source prepares an Ethernet Header with EtherType set to TBD2
(see: Section 25.2) (see: Section 7).
* For OAL packet/fragment encapsulations over secured underlay
interface connections to the secured spanning tree, the L2 source
applies any L2 security encapsulations according to the protocol
(e.g., IPsec). These secured carrier packets are then subject to
lower layer security services including fragmentation and
reassembly.
When an L2 source includes a UDP header, it SHOULD calculate and
include a UDP checksum in carrier packets with full OAL headers to
prevent mis-delivery and/or detect IPv4 reassembly corruption; the L2
source MAY set UDP checksum to 0 (disabled) in carrier packets with
compressed OAL headers (see: Section 6.5) or when reassembly
corruption is not a concern. If the L2 source discovers that a path
is dropping carrier packets with UDP checksums disabled, it should
supply UDP checksums in future carrier packets sent to the same L2
destination. If the L2 source discovers that a path is dropping
carrier packets that do not include a UDP header, it should include a
UDP header in future carrier packets.
When an L2 source sends carrier packets with compressed OAL headers
and with UDP checksums disabled, mis-delivery due to corruption of
the AERO Forwarding Vector Index (AFVI) is possible but unlikely
since the corrupted index would somehow have to match valid state in
the (sparsely-populated) AERO Forwarding Information Base (AFIB). In
the unlikely event that a match occurs, an OAL destination may
receive carrier packets that contain a mis-delivered OAL fragment but
can immediately reject any with incorrect Identifications. If the
Identification value is somehow accepted, the OAL destination may
submit the mis-delivered OAL fragment to the reassembly cache where
it will most likely be rejected due to incorrect reassembly
parameters. If a reassembly that includes the mis-delivered OAL
fragment somehow succeeds (or, for atomic fragments) the OAL
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destination will verify any included checksums to detect corruption.
Finally, any spurious data that somehow eludes all prior checks will
be detected and rejected by end-to-end upper layer integrity checks.
See: [RFC6935] [RFC6936] for further discussion.
For UDP/IP or IP-only L2 encapsulations, when the L2 source is also
the OAL source it next copies the "Type of Service/Traffic Class"
[RFC2983] and "Explicit Congestion Notification (ECN)" [RFC3168]
values in the OAL header into the corresponding fields in the L2 IP
header, then (for IPv6) set the L2 IPv6 header "Flow Label" as
specified in [RFC6438]. The L2 source then sets the L2 IP TTL/Hop
Limit the same as for any host (i.e., it does not copy the Hop Limit
value from the OAL header) and finally sets the source and
destination IP addresses to direct the carrier packet to the next OAL
hop. For carrier packets subject to re-encapsulation, the OAL
intermediate system as the L2 source reassembles if necessary then
removes the L2 header(s). The L2 source then decrements the OAL
header Hop Limit and discards the OAL packet/fragment if the value
reaches 0. The L2 source then copies the Type of Service/Traffic
Class and ECN values from the previous segment L2 encapsulation
header into the next segment L2 encapsulation header while setting
the next segment L2 source and destination IP addresses the same as
above. (The L2 source also writes the ECN value into the OAL full/
compressed header.)
During L2 (re-)encapsulation for (UDP/)IPv6 carrier packets and
(UDP/)IPv4 carrier packets that set DF to 1, the L2 source includes
an IPv6 Extended Fragment Header per [I-D.templin-6man-ipid-ext]
without including a trailing checksum. For UDP/IPv4
(re-)encapsulation of carrier packets that set DF to 0, the L2 source
instead calculates the UDP checksum and also includes a trailing
2-octet IPv4 fragmentation checksum as specified in Appendix A. The
L2 source calculates the checksums simultaneously in a single pass
over the packet, then writes the UDP result in the UDP header and the
IPv4 fragmentation result as the final 2 octets of the packet while
incrementing the IPv4 length by 2. For IPv4-only carrier packet
(re-)encapsulation with DF set to 0, the source instead includes a
trailing 4-octet CRC-32 calculated as specified for the Alternate
Payload Checksum (APC) in [I-D.ietf-tsvwg-udp-options] while
incrementing the IPv4 length by 4. (In both cases, the trailing
checksum lengths will not cause the carrier packet to exceed 65535
octets since each OAL fragment reserves space for up to 256 L2
encapsulation octets.)
The L2 source then applies source fragmentation if necessary to
produce carrier packet fragments no larger than the current Carrier
Fragment Size (CFS). For IPv6, the L2 source should prepare carrier
packet fragments no larger than 1280 octets (i.e., the IPv6 minimum
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MTU) until it can determine whether a larger CFS is possible, e.g.,
through dynamic path probing to the L2 destination. For IPv4, until
a true CFS is confirmed (e.g., through probing) the L2 source must
set DF to 0 and include a trailing fragmentation checksum as
discussed above. In that case, the L2 source can optionally send
IPv4 carrier packet fragments that exceed the currently known CFS if
there is reason to believe the network will deliver them to the L2
destination; these IPv4 carrier packet fragments may be (further)
fragmented by an intermediate system in the L2 network path.
The L2 source then sends the resulting carrier packet fragments over
one or more underlay interfaces. Underlay interfaces often connect
directly to physical media on the local platform (e.g., an aircraft
with a radio frequency link, a laptop computer with WiFi, etc.), but
in some configurations the physical media may be hosted on a separate
Local Area Network (LAN) node. In that case, the OMNI interface can
establish a Layer-2 VLAN or a point-to-point tunnel (at a layer below
the underlay interface) to the node hosting the physical media. The
OMNI interface may also apply encapsulation at the underlay interface
layer (e.g., as for a tunnel virtual interface) such that carrier
packets would appear "double-encapsulated" on the LAN; the node
hosting the physical media in turn removes the LAN encapsulation
prior to transmission or inserts it following reception. Finally,
the underlay interface must monitor the node hosting the physical
media (e.g., through periodic keepalives) so that it can convey up-
to-date Interface Attribute information to the OMNI interface.
6.2.1. OMNI Extension Headers and Fragmentation
Ordinary IP fragments may be dropped along the paths to some OAL or
L2 destinations by a NAT, firewall or other middlebox. Middleboxes
may also unconditionally drop IP packets that contain IPv6 extension
headers of any kind. OMNI therefore provides an alternate
encapsulation method that encodes IPv6 extension headers (including
an (extended) fragment header) following the innermost OAL/L2 header
instead of before according to Section 6.4). This format is shown in
Figure 6:
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+----------------------------+
| L2 Ethernet Header |
+----------------------------+
| L2 IP Header |
+----------------------------+
| L2 UDP Header (port 8060) |
+----------------------------+
~ L2 IPv6 Extension Headers ~
+----------------------------+
| OAL IPv6 Encapsulation |
+----------------------------+
~ OAL IPv6 Extension Headers ~
+----------------------------+
| |
~ ~
~ Original IP Packet ~
~ ~
| |
+----------------------------+
Figure 6: OMNI Extension Header Encapsulation
The OMNI interface first encapsulates each original IP packet in an
OAL IPv6 encapsulation header plus any extensions to form an OAL
packet. When the OAL packet requires OAL and/or L2 fragmentation,
the OMNI interface then performs the following operations:
* Perform OAL IPv6 encapsulation of the original packet with any
necessary OAL IPv6 extension headers, then perform normal
extension header processing including fragmentation per [RFC8200].
Each resulting OAL fragment will include an IPv6 Extended Fragment
Header with the correct fragmentation parameters.
* Encapsulate each OAL packet/fragment in any L2 IP or Ethernet
headers. If the innermost L2 header is IPv4 or Ethernet, convert
it to an IPv6 header while converting the IPv4/EUI source and
destination addresses to IPv6 compatible addresses as discussed in
Appendix B.
* Encapsulate the OAL packet/fragment following this L2 IPv6 header
with any necessary L2 IPv6 extension headers, then perform normal
extension header processing including fragmentation per [RFC8200].
For ordinary packets, each resulting L2 fragment will include an
IPv6 (Extended) Fragment Header with the correct fragmentation
parameters. (For jumbo-in-jumbo encapsulation, no L2 fragment
header is included and the L2 Identification (if present) appears
in the L2 Advanced Jumbo option.)
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* For each L2 fragment, insert a UDP header between the L2 IPv6
header and extension headers, then change the Next Header field of
the first L2 IPv6 extension header as specified in Figure 6.
* If the original L2 header was IPv4 or Ethernet, re-convert the
IPv6 header back to IPv4/Ethernet.
* Change the L2 IP header {Protocol, Next Header} to '17' (UDP), set
the remaining UDP/IP header fields to the correct values for each
L2 fragment, then transmit each fragment to the L2 destination.
If the OAL IPv6 header (plus extensions) is also subject to
compression the OAL source next applies OAL header compression so
that the compressed header immediately follows the L2 extension
headers. The L2 source then sets the UDP port number to either 8060
(the port number reserved for AERO/OMNI) or the cached number for
this L2 destination and finally calculates and sets the UDP checksum
as specified in [RFC0768].
The L2 source then sends the carrier packet fragments to the L2
destination. If the L2 IPv6 extension headers change en route to the
next OAL hop, each L2 forwarding node that modifies the extension
headers must re-calculate and re-set the UDP checksum. (Note that
the L2 source can instead set the L2 UDP checksum to 0, but some L2
paths may drop such packets - see Section 6.2 for further details.)
For L2 (re-)encapsulations that do not include a UDP header (e.g.,
IP-only), these fragments will include the IPv6 extension headers
immediately after the L2 IP header. The L2 IP header must then set
its IP {Protocol, Next Header} to TBD1.
For L2 (re-)encapsulations that do not include UDP/IP headers (e.g.,
Ethernet-only), these fragments will include the L2 IPv6 extension
headers immediately after the true L2 header. The L2 header must
then set its L2 type to TBD2.
For L2 (re-)encapsulations over secured underlay interfaces, the
native L2 security encapsulations (e.g., IPsec) are used instead of
the OMNI protocol L2 encapsulations depicted in Figure 6. This
presents a limiting factor for L2 fragmentation and reassembly;
therefore, sources should limit the size of the OAL packets/fragments
they send over the secured spanning tree to 1280 octets. (Note that
OMNI protocol L2 encapsulations could be used above the L2 security
services, but this could result in excessive encapsulation in some
instances.)
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Note: under this format, both OAL fragments and carrier packet
fragments will appear as ordinary whole packets to network
middleboxes that inspect headers. This allows network middleboxes to
make consistent forwarding decisions on each fragment of the same
original OAL packet and without first attempting virtual fragment
reassembly since each fragment appears as a whole packet.
6.2.2. Carrier Fragment Size (CFS) Determination
For paths that cannot rely on IPv4 network fragmentation to deliver
carrier packets that exceed the path MTU, the L2 source should
actively probe the path to determine the largest possible Carrier
Fragment Size (CFS) for the L2 destination under current path
conditions. The L2 source conducts probing in the spirit of
"Packetization Layer Path MTU Discovery for Datagram Transports"
[RFC8899] using a probe packet such as an NS message that includes
Nonce and Timestamp options [RFC3971] plus a discard trailing packet
attachment as specified in Section 6.10. The L2 source then
encapsulates the message in L2 headers as a whole carrier packet and
sends the message over the unsecured underlay interface (for IPv4,
the L2 source also sets the probe packet DF flag to 1.)
Prior to any probing, the L2 source assumes a nominal CFS of 1280
octets (the IPv6 minimum MTU) for both IPv6 and IPv4. Since this
size is greater than the IPv4 minimum MTU, the L2 source must set the
DF bit to 0 in each carrier packet to increase the likelihood that it
will reach the L2 destination. When the L2 source sets DF to 0, it
must include an IPv4 fragmentation checksum as discussed above.
When the L2 source engages probing, it will receive NA responses from
the L2 destination to confirm delivery of its OAL and L2 encapsulated
padded NS messages. When the L2 source receives an NA with a
matching Nonce, it can then advance CFS to the size of the NS probe.
The L2 source must then continuously probe to confirm the current CFS
or advance to even larger CFS values using the probing strategies
specified in [RFC8899].
After the L2 source confirms a CFS through probing, it can send
carrier packet fragments up to CFS octets in length and with DF set
to 1 for IPv4. If the path changes, the L2 source may receive a PTB
message from a router on the path and should then reduce and/or re-
probe the CFS accordingly.
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6.3. Reassembly and Decapsulation
All OAL intermediate systems and destinations MUST configure an L2
EMTU_R of 65535 octets on all unsecured underlay interfaces to enable
successful reassembly of fragmented carrier packets no larger than
that size (conversely, secured underlay interfaces use an EMTU_R
specific to the L2 security service such as IPsec). OAL nodes are
permitted to accept still larger unfragmented parcels/AJs as a best-
effort service. OAL nodes must further recognize and honor the
extended Identification specified in [I-D.templin-6man-ipid-ext].
When an OAL node reassembles an IPv4 or IPv6 carrier packet with an
extended Identification, it accepts the reassembled packet following
UDP checksum verification if necessary. When an OAL node reassembles
an IPv4 carrier packet with DF set to 0, it must verify both the UDP
checksum (if present) and the trailing IPv4 fragmentation checksum.
The OAL node then accepts the reassembled packet only if the included
checksums are correct, then trims the trailing fragmentation checksum
(if present) by decrementing the IPv4 length before processing the
packet further. When an OAL node detects a checksum error or failed
reassembly for either IPv4 or IPv6 carrier packets, and the IP first
fragment includes enough of the OAL packet header, the OAL node
returns a uNA message with an OMNI Fragmentation Report (FRAGREP)
option to the OAL source as specified in Section 6.8. The FRAGREP
provides immediate feedback allowing the OAL source to very quickly
retransmit the corrupted OAL fragment(s).
If the carrier packet encodes OMNI L2 extension headers per
Section 6.4, the OAL node instead removes the UDP header if necessary
and submits the packet for IPv6 extension header processing per
[RFC8200] (while converting IPv4/Ethernet headers to IPv6 and
converting IPv4/EUI addresses to IPv6 compatible addresses if
necessary as specified above). The OAL node first sets the IPv6 Next
Header field to the 8 bit protocol value for the first extension.
When an (Extended) Fragment Header is included, reassembly then
restores the (fragmented) L2 packet included by the previous hop.
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When an OMNI interface processes a (reassembled) carrier packet from
an underlay interface, it copies the ECN value from the L2
encapsulation headers into the OAL header if the carrier packet
contains an OAL first-fragment. The OMNI interface next discards the
L2 encapsulation headers and examines the OAL header of the enclosed
OAL fragment according to the value in the Type field as discussed in
Section 6.2. If the OAL fragment is addressed to a different node,
the OMNI interface (acting as an OAL intermediate system) performs L2
encapsulation and fragmentation if necessary then forwards while
decrementing the OAL Hop Limit as discussed in Section 6.2. If the
OAL fragment is addressed to itself, the OMNI interface (acting as an
OAL destination) accepts or drops the fragment based on the (Source,
Destination, Identification)-tuple.
The OAL destination next drops all ordinal OAL non-first fragments
that would overlap or leave "holes" with respect to other ordinal
fragments already received. The OAL destination updates a checklist
of accepted ordinal fragments of the same OAL packet but admits all
accepted fragments into the reassembly cache.
During reassembly at the OAL destination, the reassembled OAL packet
may exceed 65535 by a small amount equal to the size of the OAL
encapsulation extension headers. The OAL destination does not write
this (too-large) value into the OAL header Payload Length field, but
rather remembers the value during reassembly. When reassembly is
complete, the OAL destination finally removes the OAL headers and
delivers the original IP packet/parcel to the network layer. The
original IP packet/parcel may therefore be as large as 65535 octets,
or larger still for large parcels/AJs delivered through jumbo-in-
jumbo encapsulation without invoking fragmentation.
When an OAL path traverses an IPv6 network with routers that perform
adaptation layer forwarding based on full IPv6 headers with OAL
addresses, the OAL intermediate system at the head of the IPv6 path
forwards the OAL packet/fragment the same as an ordinary IPv6 packet
without decapsulating and delivering to the network layer. Once
within the IPv6 network, these OAL packets/fragments may traverse
arbitrarily-many IPv6 hops before arriving at an OAL intermediate
system which may again encapsulate the OAL packets/fragments as
carrier packets for transmission over underlay interfaces.
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Note: carrier packets often traverse paths with underlying links that
use integrity checks such as CRC-32 which provide adequate hop-by-hop
integrity assurance for payloads up to ~9K octets [CRC]. However,
other paths may traverse links (such as fragmenting tunnels over IPv4
- see: [RFC4963]) that do not include adequate checks. The end-to-
end integrity checks in IP parcels and AJs therefore allow the final
destination to detect any link errors that may have accumulated along
the path even if the links themselves do not provide adequate error
checking.
6.4. OMNI Extension Headers
The IPv6 specification [RFC8200] defines extension headers that
follow the base IPv6 header, while Upper Layer Protocols (ULPs) are
specified in other documents. Each extension header present is
identified by a "Next Header" octet in the previous (extension)
header and encodes a "Next Header" field in the first octet that
identifies the next extension header or ULP instance. The OMNI
specification supports encoding of IPv6 extension header chains
immediately following the OMNI L2 UDP, IP or Ethernet header even if
the L2 IP protocol version is IPv4. In all cases, the length of the
IPv6 extension header chain is limited by [I-D.ietf-6man-eh-limits].
The OAL source prepares an OMNI extension header chain by setting the
first 4 bits of the first IPv6 extension header in the chain to a
Type value for the extension header itself immediately following the
OMNI L2 protocol header. The source then sets the next 4 bits to a
Next value that identifies either a terminating ULP or the next
extension header in the chain. The source then sets the first 8 bits
of each subsequent IPv6 extension header in the chain to the standard
Next Header encoding as shown in Figure 7:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ OMNI L2 UDP, IP or Ethernet Header ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Next | Extension Header #1 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Extension Header #2 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Extension Header #3 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Extension Header #N ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ OMNI Full/Compressed, IPv6/IPv4, TCP/UDP, ICMPv6, ESP, etc. ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: OMNI Extension Header Chains
The following Type/Next values are currently defined:
0 (OMNI-RES) - Reserved for experimentation.
1 (OMNI-OFH) - OMNI Full Header, per Section 6.5.
2 (OMNI-OCH) - OMNI Compressed Header, per Section 6.5.
3 (OMNI-HBH) - Hop-by-Hop Options per Section 4.3 of [RFC8200].
4 (OMNI-IP4) - IPv4 header per [RFC0791].
5 (OMNI-RH) - Routing Header per Section 4.4 of [RFC8200].
6 (OMNI-IP6) - IPv6 header per [RFC8200].
7 (OMNI-FH) - Fragment Header per Section 4.5 of [RFC8200].
8 (OMNI-DO) - Destination Options per Section 4.6 of [RFC8200].
9 (OMNI-AH) - Authentication Header per [RFC4302].
10 (OMNI-ESP) - Encapsulating Security Payload per [RFC4303].
11 (OMNI-NNH) - No Next Header per Section 4.7 of [RFC8200].
12 (OMNI-TCP) - TCP Header per [RFC9293].
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13 (OMNI-UDP) - UDP Header per [RFC0768].
14 (OMNI-ICMP) - ICMPv6 Header per [RFC4443].
15 (OMNI-ULP) - Upper Layer Protocol shim (see below).
Entries OMNI-OFH through OMNI-AH in the above list follow the
convention that the OMNI Type/Version appears in the first 4 bits of
the extension header (or IP header) itself. Conversely, entries
OMNI-ESP through OMNI-ICMP represent commonly-used ULPs which do not
encode a Type/Version in the first 4 bits.
Entries OMNI-HBH, OMNI-RH, OMNI-FH, OMNI-DO and OMNI-AH represent
true IPv6 extension headers encoded for OMNI, which may be chained.
Source and destination processing of OMNI extension headers follows
exactly per their definitions in the normative references, with the
exception of the special (Type, Next) coding in the first 8 bits of
the first extension header.
When a ULP not found in the above table immediately follows the OMNI
L2 UDP, IP or Ethernet header, the source includes a 2-octet "Type 1
ULP Shim" before the ULP where both the first 4 bit (Type) and next 4
bit (Next) fields encode the special value 15 (OMNI-ULP). The source
then includes a Next Header field that encodes the IP protocol number
of the ULP. The source then includes the ULP data immediately after
the shim as shown in Figure 8.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type=15|Next=15| Next Header | Upper Layer Protocol ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: OMNI Upper Layer Protocol (ULP) Shim (Type 1)
When a ULP "OMNI-(N)" found in the above table immediately follows
the OMNI L2 UDP, IP or Ethernet header, the source includes a 1-octet
"Type 2 ULP Shim" before the ULP where the first 4 bits encode the
special Type value 15 (OMNI-ULP) and the next 4 bits encode the Next
ULP type "N" taken from the table above. The source then includes
the ULP data immediately after the shim as shown in Figure 9.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type=15| Next=N| Upper Layer Protocol ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: OMNI Upper Layer Protocol (ULP) Shim (Type 2)
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When a ULP not found in the above table follows a first OMNI
extension header, the source sets the extension header Next field to
OMNI-ULP (15) and includes a 1-octet "Type 3 ULP Shim" that encodes
the IP protocol number for the Next Header of the ULP data that
follows as shown in Figure 10.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Upper Layer Protocol ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: OMNI Upper Layer Protocol (ULP) Shim (Type 3)
When a ULP "OMNI-(N)" found in the above table follows a first OMNI
extension header, the source sets the extension header Next field to
the ULP Type "N" and does not include a shim. The ULP then begins
immediately after the first OMNI extension header.
When a ULP of any kind follows a non-first OMNI extension header, the
source sets the extension header Next Header field to the IP protocol
number for the ULP and does not include a shim. The ULP then begins
immediately after the non-first OMNI extension header.
Note: The L2 UDP header (when present) is logically considered as the
first L2 extension header in the chain. If an Advanced Jumbo
extension header is also present, its Jumbo Payload length includes
the length of the L2 UDP header.
Note: After a node parses the extension header chain, it changes the
"Type/Next" field in the first extension header back to the correct
"Next Header" value before processing the first extension header.
6.5. OMNI Full and Compressed Headers (OFH/OCH)
OAL sources that send carrier packets with OMNI Full Headers (OFH)
include a full IPv6 header with Compressed Routing Header
[I-D.ietf-6man-comp-rtg-hdr] and IPv6 Extended Fragment Header
extensions for segment-by-segment forwarding based on an AERO
Forwarding Information Base (AFIB) in each OAL intermediate system.
OAL sources, intermediate systems and destinations can also establish
header compression state through IPv6 ND NS/NA message exchanges.
After an initial NS/NA exchange, OAL nodes can apply OMNI Header
Compression to significantly reduce OAL encapsulation overhead.
Each OAL node establishes AFIB soft state entries known as AERO
Forwarding Vectors (AFVs) which support both OAL packet/fragment
forwarding and OAL header compression/decompression. For FHS OAL
sources, each AFV is referenced by a single AERO Forwarding Vector
Index (AFVI) that provides compression/decompression and forwarding
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context for the next hop. For LHS OAL destinations, the AFV is
referenced by a single AFVI that provides context for the previous
hop. For OAL intermediate systems, the AFV is referenced by two
AFVIs - one for the previous hop and one for the next hop.
When an OAL node sends carrier packets that contain OAL packets/
fragments to a next hop, it can include an OFH with Compressed
Routing Header containing AFVI forwarding information. In that case,
the first four bits following the L2 headers must encode the Type
OMNI-OFH to signify that an uncompressed OFH (plus extensions) is
present. The Type OMNI-OFH differentiates OFHs from ordinary L3 IP
headers which are identified by the (Version) value 4 for IPv4 or 6
for IPv6.
When an OAL intermediate system forwards an OAL packet with Type
OMNI-OFH to an IPv6 router for the SRT, it discards the L2
encapsulation headers and resets the Type field value to 6. When an
OAL intermediate system forwards an OAL packet received from an SRT
IPv6 router, it resets the Type field value to OMNI-OFH and includes
new L2 encapsulation headers.
Whenever possible, the OAL source should omit significant portions of
the OAL header (plus extensions) while applying OMNI header
compression when sufficient AFV state is available. For OAL first
fragments (including atomic fragments), the OAL node uses OMNI
Compressed Header (OCH) Format (a) as shown in Figure 11:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Hop Limit | Parcel ID | Next Header |P|S|ECN|R|X|F|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Identification (8 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ AFVI (2 or 4 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: OMNI Compressed Header (OCH) Format (a)
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The format begins with a 4-bit Type, a 6-bit Hop Limit, a 6-bit
Parcel ID octet, and an 8-bit Next Header followed by P/S flags, a
2-bit Explicit Congestion Notification (ECN) field and finally
followed by R/X/F/M flags. The format concludes with an 8-octet
Identification field followed by a 2- or 4-octet AFVI field. The OAL
node sets Type to OMNI-OCH, sets Hop Limit to the minimum of the
uncompressed OAL header Hop Limit and 63 and sets ECN the same as for
an uncompressed OAL header. The OAL node next sets e(X)tended to 0/1
according to whether the AFVI field is 2/4 octets in length and sets
(F)irst to 1 as a first fragment. The OAL node finally sets (M)ore
Fragments, Parcel ID, ((P)arcel, and More (S)egments the same as for
an uncompressed fragment header.
The OAL first fragment (beginning with the original IP header) is
then included immediately following the OCH header, and the L2 header
length field is reduced by the difference in length between the
compressed headers and full-length OFH headers. The OAL destination
can therefore determine the Payload Length by examining the L2 header
length field and/or the length field(s) in the original IP header.
Note that first fragments are logically considered Ordinal fragment
0.
For OAL non-first fragments (i.e., those with non-zero Fragment
Offsets), the OAL uses OMNI Compressed Header (OCH) Format (b) as
shown in Figure 12:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Hop Limit | Ordinal | Fragment Offset |X|F|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Identification (8 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ AFVI (2 or 4 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-~~~-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: OMNI Compressed Header (OCH) Format (b)
The format begins with a 4-bit Type, a 6-bit Hop Limit, a 6-bit
Ordinal, a 13-bit Fragment Offset, an X (AFVI extension) flag a
F(irst) flag and a M(ore Fragments) flag. The format concludes with
an 8-octet Identification field followed by a 2/4-octet AFVI field.
The OAL node sets Type to OMNI-OCH, sets Hop Limit to the minimum of
the uncompressed OAL header Hop Limit and 63, and sets (Ordinal,
Fragment Offset, (M)ore Fragments, Identification) the same as for an
uncompressed fragment header. The OAL node finally sets X to 0/1
according to whether the AFVI field is 2/4-octets in length and sets
F to 0 as a non-first fragment.
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The OAL non-first fragment body is then included immediately
following the OCH header, and the L2 header length field is reduced
by the difference in length between the compressed headers and full-
length OFH plus extensions. The OAL destination will then be able to
determine the Payload Length by examining the L2 header length field.
The OCH (b) format applies for non-first fragments only; therefore,
the OAL source sets Ordinal to a monotonically increasing value
beginning with 1 for the first non-first fragment, 2 for the second
non-first fragment, 3 for the third non-first fragment, etc., up to
at most 63 for the final fragment.
When an OAL destination or intermediate system receives a carrier
packet, it determines the length of the encapsulated OAL information
by examining the length field of the innermost L2 header, verifies
that the innermost next header field indicates OMNI (see:
Section 6.2), then processes any included OMNI L2 extension headers
as specified in Section 6.4. The OAL destination then examines the
Next Header field of the final L2 extension header. If the Next
Header field contains the value TBD1, and the 4-bit Type that follows
encodes a value OMNI-OFH or OMNI-OCH the OAL node processes the
remainder of the OAL header as a full (OFH) or compressed (OCH)
header as specified above.
The OAL node then uses the AFVI to locate the cached AFV which
determines the next hop. During forwarding, the OAL node changes the
AFVI to the cached value for the AFV next hop. If the OAL node is
the destination, it instead reconstructs the OFH then adds the
resulting OAL fragment to the reassembly cache if the Identification
is acceptable. (Note that for carrier packets that contain OAL first
fragments with an OCH with both the F and M flags set to 0, the OAL
node can instead locate forwarding state by examining the original IP
packet/parcel header information that appears immediately after the
OCH header.)
For all OCH types, the source node sets all Reserved fields and bits
to 0 on transmission and the destination node ignores the values on
reception.
Note: The OCH format does not include the Traffic Class and Flow
Label information that appears in uncompressed OAL IPv6 headers.
Therefore, when OAL header compression state is initialized the
Traffic Class and Flow Label are considered fixed for as long as the
flow uses OCH headers. If the flow requires frequent changes to
Traffic Class and/or Flow Label information, it can include OFH
headers as necessary to update header compression state.
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6.6. OAL and L2 Encapsulation Avoidance
When the OAL source and OAL destination are on the same OMNI link
segment as determined by neighbor discovery, the OMNI interface
forwards packets directly to the specific underlay interface without
applying OAL encapsulation. In that case, the OAL source treats the
IPv6 header of the original packet the same as if it had applied an
OAL encapsulation header. The Next Header field will therefore
encode a value specific to the transport layer protocol (e.g., '6'
for TCP, '17' for UDP, etc.) since the OAL does not insert an IPv6
encapsulation header. The OAL source then applies fragmentation,
header compression and L2 encapsulation the same as described above
even though a single IPv6 header (and not an additional OAL
encapsulation header) is present.
The OAL source can also apply these same encapsulation avoidance
procedures for IPv4 by first translating the IPv4 header of the
original packet into an IPv6 header and translating the IPv4
addresses into IPv4-compatible IPv6 addresses as discussed in
Appendix B. These translated headers can then be manipulated the
same as for IPv6 headers as described above, including fragmentation,
header compression, etc.
When an OAL node and its next OAL hop are known to be connected to
the same underlay link, or when the node's underlay interface
connects to a Mobile Ad-Hoc Network (MANET) where MANET-local IPv6
routing protocols are applied, the node does not include full UDP/IP
headers as part of the carrier packet L2 encapsulation and instead
uses link layer encapsulation using EtherType TBD2 for Ethernet-
compatible data links. The MANET-local IPv6 routing protocols will
then direct the packets to the correct destination which may be one
or more MANET routing hops away from the source.
When the OAL node is unable to determine whether the next OAL hop is
connected to the same underlay link, it should perform carrier packet
L2 encapsulation for initial packets sent via the next hop over a
specific underlay interface by including full UDP/IP headers and with
the UDP port numbers set as discussed in Section 6.2. The node can
thereafter attempt to send an NS to the next OAL hop in carrier
packet(s) that omit the UDP header and set the IP protocol number to
TBD1. If the OAL node receives an NA reply, it can omit the UDP
header in subsequent packets. The node can further attempt to send
an NS in carrier packet(s) that omit both the UDP and IP headers and
set EtherType to TBD2. If the source receives an NA reply, it can
begin omitting both the UDP and IP headers in subsequent packets.
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Note: in the above, "next OAL hop" refers to the first OAL node
encountered on the optimized path to the destination over a specific
underlay interface as determined through route optimization (e.g.,
see: [I-D.templin-intarea-aero]). The next OAL hop could be a Proxy/
Server, Gateway or the OAL destination itself.
6.7. OAL Identification Window Maintenance
The OAL encapsulates each original IP packet/parcel as an OAL packet
then performs fragmentation to produce one or more carrier packets
with the same 8-octet Identification value. In environments where
spoofing is not considered a threat, OMNI interfaces send OAL packets
with Identifications beginning with an unpredictable Initial Send
Sequence (ISS) value [RFC7739] monotonically incremented (modulo
2**64) for each successive OAL packet sent to either a specific
neighbor or to any neighbor. (The OMNI interface may later change to
a new unpredictable ISS value as long as the Identifications are
assured unique within a timeframe that would prevent the fragments of
a first OAL packet from becoming associated with the reassembly of a
second OAL packet.) In other environments, OMNI interfaces should
maintain explicit per-interface-pair send and receive windows to
detect and exclude spurious carrier packets that might clutter the
reassembly cache as discussed below.
OMNI interface neighbors use a window synchronization service similar
to TCP [RFC9293] to maintain unpredictable ISS values incremented
(modulo 2**64) for each successive OAL packet and re-negotiate
windows often enough to maintain an unpredictable profile. OMNI
interface neighbors exchange IPv6 ND messages that include OMNI
Window Synchronization sub-options (see: Section 12.2.5) with TCP-
like information fields and flags to manage streams of OAL packets
instead of streams of octets. As a link layer service, the OAL
provides low-persistence best-effort retransmission with no
mitigations for duplication, reordering or deterministic delivery.
Since the service model is best-effort and only control message
sequence numbers are acknowledged, OAL nodes can select unpredictable
new initial sequence numbers outside of the current window without
delaying for the Maximum Segment Lifetime (MSL).
OMNI interface neighbors maintain current and previous per-interface-
pair window state in IPv6 ND NCEs and/or AFVs to support dynamic
rollover to a new window while still sending OAL packets and
accepting carrier packets from the previous windows. OMNI interface
neighbors synchronize windows through asymmetric and/or symmetric
IPv6 ND message exchanges. When a node receives an IPv6 ND message
with new interface pair-based window information, it resets the
previous window state based on the current window then resets the
current window based on new and/or pending information.
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The IPv6 ND message OMNI option header extension sub-option includes
TCP-like information fields including Sequence Number,
Acknowledgement Number, Window and flags (see: Section 12). OMNI
interface neighbors maintain the following TCP-like state variables
on a per-interface-pair basis (i.e., through a combination of NCE and
AFV state):
Send Sequence Variables (current, previous and pending)
SND.NXT - send next
SND.WND - send window
ISS - initial send sequence number
Receive Sequence Variables (current and previous)
RCV.NXT - receive next
RCV.WND - receive window
IRS - initial receive sequence number
OMNI interface neighbors "OAL A" and "OAL B" exchange IPv6 ND
messages per [RFC4861] with OMNI options that include TCP-like
information fields as well as interface pair parameters such as
Interface Attributes or AERO Forwarding Parameters. When OAL A
synchronizes with OAL B, it maintains both a current and previous
SND.WND beginning with a new unpredictable ISS and monotonically
increments SND.NXT for each successive OAL packet transmission. OAL
A initiates synchronization by including the new ISS in the Sequence
Number of an authentic IPv6 ND message with the SYN flag set and with
Window set to M (up to 2**24) as a tentative receive window size
while creating a NCE in the INCOMPLETE state if necessary. OAL A
caches the new ISS as pending, uses the new ISS as the Identification
for OAL encapsulation, then sends the resulting OAL packet to OAL B
and waits up to RetransTimer milliseconds to receive an IPv6 ND
message response with the ACK flag set (retransmitting up to
MAX_UNICAST_SOLICIT times if necessary).
When OAL B receives the SYN, it creates a NCE in the STALE state and
also an AFV if necessary, resets its RCV variables, caches the
tentative (send) window size M, and selects a (receive) window size N
(up to 2**24) to indicate the number of OAL packets it is willing to
accept under the current RCV.WND. (The RCV.WND should be large
enough to minimize control message overhead yet small enough to
provide an effective filter for spurious carrier packets.) OAL B
then prepares an IPv6 ND message with the ACK flag set, with the
Acknowledgement Number set to OAL A's next sequence number, and with
Window set to N. Since OAL B does not assert an ISS of its own, it
uses the IRS it has cached for OAL A as the Identification for OAL
encapsulation then sends the ACK to OAL A.
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When OAL A receives the ACK, it notes that the Identification in the
OAL header matches its pending ISS. OAL A then sets the NCE state to
REACHABLE and resets its SND variables based on the Window size and
Acknowledgement Number (which must include the sequence number
following the pending ISS). OAL A can then begin sending OAL packets
to OAL B with Identification values within the (new) current SND.WND
for this interface pair for up to ReachableTime milliseconds or until
the NCE is updated by a new IPv6 ND message exchange. This implies
that OAL A must send a new SYN before sending more than N OAL packets
within the current SND.WND, i.e., even if ReachableTime is not
nearing expiration. After OAL B returns the ACK, it accepts carrier
packets received from OAL A via this interface pair within either the
current or previous RCV.WND as well as any new authentic NS/RS SYN
messages received from OAL A even if outside the windows.
OMNI interface neighbors can employ asymmetric window synchronization
as described above using two independent (SYN -> ACK) exchanges
(i.e., a four-message exchange), or they can employ symmetric window
synchronization using a modified version of the TCP three-way
handshake as follows:
* OAL A prepares a SYN with an unpredictable ISS not within the
current SND.WND and with Window set to M as a tentative receive
window size. OAL A caches the new ISS and Window size as pending
information, uses the pending ISS as the Identification for OAL
encapsulation, then sends the resulting OAL packet to OAL B and
waits up to RetransTimer milliseconds to receive an ACK response
(retransmitting up to MAX_UNICAST_SOLICIT times if necessary).
* OAL B receives the SYN, then resets its RCV variables based on the
Sequence Number while caching OAL A's tentative receive Window
size M and a new unpredictable ISS outside of its current window
as pending information. OAL B then prepares a response with
Sequence Number set to the pending ISS and Acknowledgement Number
set to OAL A's next sequence number. OAL B then sets both the SYN
and ACK flags, sets Window to N and sets the OPT flag according to
whether an explicit concluding ACK is optional or mandatory. OAL
B then uses the pending ISS as the Identification for OAL
encapsulation, sends the resulting OAL packet to OAL A and waits
up to RetransTimer milliseconds to receive an acknowledgement
(retransmitting up to MAX_UNICAST_SOLICIT times if necessary).
* OAL A receives the SYN/ACK, then resets its SND variables based on
the Acknowledgement Number (which must include the sequence number
following the pending ISS) and OAL B's advertised Window N. OAL A
then resets its RCV variables based on the Sequence Number and
marks the NCE as REACHABLE. If the OPT flag is clear, OAL A next
prepares an immediate unsolicited NA message with the ACK flag
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set, the Acknowledgement Number set to OAL B's next sequence
number, with Window set a value that may be the same as or
different than M, and with the OAL encapsulation Identification to
SND.NXT, then sends the resulting OAL packet to OAL B. If the OPT
flag is set and OAL A has OAL packets queued to send to OAL B, it
can optionally begin sending their carrier packets under the (new)
current SND.WND as implicit acknowledgements instead of returning
an explicit ACK. In that case, the tentative Window size M
becomes the current receive window size.
* OAL B receives the implicit/explicit acknowledgement(s) then
resets its SND state based on the pending/advertised values and
marks the NCE as REACHABLE. If OAL B receives an explicit
acknowledgement, it uses the advertised Window size and abandons
the tentative size. (Note that OAL B sets the OPT flag in the
SYN/ACK to assert that it will interpret timely receipt of carrier
packets within the (new) current window as an implicit
acknowledgement. Potential benefits include reduced delays and
control message overhead, but use case analysis is outside the
scope of this specification.)
Following synchronization, OAL A and OAL B hold updated NCEs and
AFVs, and can exchange OAL packets with Identifications set to
SND.NXT for each interface pair while the state remains REACHABLE and
there is available window capacity. Either neighbor may at any time
send a new SYN to assert a new ISS. For example, if OAL A's current
SND.WND for OAL B is nearing exhaustion and/or ReachableTime is
nearing expiration, OAL A continues to send OAL packets under the
current SND.WND while also sending a SYN with a new unpredictable
ISS. When OAL B receives the SYN, it resets its RCV variables and
may optionally return either an asymmetric ACK or a symmetric SYN/ACK
to also assert a new ISS. While sending SYNs, both neighbors
continue to send OAL packets with Identifications set to the current
SND.NXT for each interface pair then reset the SND variables after an
acknowledgement is received.
While the optimal symmetric exchange is efficient, anomalous
conditions such as receipt of old duplicate SYNs can cause confusion
for the algorithm as discussed in Section 3.5 of [RFC9293]. For this
reason, the OMNI Window Synchronization sub-option includes an RST
flag which OAL nodes set in solicited NA responses to ACKs received
with incorrect acknowledgement numbers. The RST procedures (and
subsequent synchronization recovery) are conducted exactly as
specified in [RFC9293].
OMNI interfaces that employ the window synchronization procedures
described above observe the following requirements:
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* OMNI interfaces MUST select new unpredictable ISS values that are
at least a full window outside of the current SND.WND.
* OMNI interfaces MUST set the initial SYN message Window field to a
tentative value to be used only if no concluding NA ACK is sent.
* OMNI interfaces MUST send IPv6 ND messages used for window
synchronization securely while using unpredictable initial
Identification values until synchronization is complete.
Note: Although OMNI interfaces employ TCP-like window synchronization
and support uNA ACK responses to SYNs, all other aspects of the IPv6
ND protocol (e.g., control message exchanges, NCE state management,
timers, retransmission limits, etc.) are honored exactly per
[RFC4861]. OMNI interfaces further manage per-interface-pair window
synchronization parameters in one or more AFVs for each neighbor
pair.
Note: Recipients of OAL-encapsulated IPv6 ND messages index the NCE
based on the message source address, which also determines the
carrier packet Identification window. However, IPv6 ND messages may
contain a message source address that does not match the OMNI
encapsulation source address when the recipient acts as a proxy.
Note: OMNI interface neighbors apply separate send and receive
windows for all of their (multilink) underlay interface pairs that
exchange carrier packets. Each interface pair represents a distinct
underlay network path, and the set of paths traversed may be highly
diverse when multiple interface pairs are used. OMNI intermediate
systems therefore become aware of each distinct set of interface pair
window synchronization parameters based on periodic IPv6 ND message
updates to their respective AFVs.
6.8. OAL Fragmentation Reports and Retransmissions
The OAL source should maintain a short-term cache of the OAL
fragments it sends to OAL destinations in case timely best-effort
selective retransmission is requested. The OAL destination in turn
maintains a checklist for (Source, Destination, Identification)-
tuples of recently received OAL fragments and notes the ordinal
numbers of OAL fragments already received (i.e., as ordinals #0, #1,
#2, #3, etc.). The timeframe for maintaining the OAL source and
destination caches determines the link persistence (see: [RFC3366]).
If the OAL destination notices some fragments missing after most
other fragments within the same link persistence timeframe have
already arrived, it may issue an Automatic Repeat Request (ARQ) with
Selective Repeat (SR) by sending a uNA message to the OAL source.
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The OAL destination creates a uNA message with an OMNI option with
one or more Fragmentation Report (FRAGREP) sub-options that include
(Identification, Bitmap)-tuples for fragments received and missing
from this OAL source (see: Section 12). The OAL destination includes
an authentication signature if necessary, performs OAL encapsulation
(with the its own address as the OAL source and the source address of
the message that prompted the uNA as the OAL destination) and sends
the message to the OAL source.
If an OAL intermediate system or OAL destination processes an OAL
fragment for which corruption is detected, it may similarly issue an
immediate ARQ/SR the same as described above. The FRAGREP provides
an immediate (rather than time-bounded) indication to the OAL source
that a retransmission is required.
When the OAL source receives the uNA message, it authenticates the
message then examines any enclosed FRAGREPs. For each (Source,
Destination, Identification)-tuple, the OAL source determines whether
it still holds the corresponding OAL fragments in its cache and
retransmits any for which the Bitmap indicates a loss event. For
example, if the Bitmap indicates that ordinal fragments #3, #7, #10
and #13 from the OAL packet with Identification 0x0123456789abcdef
are missing the OAL source only retransmits those fragments. When
the OAL destination receives the retransmitted OAL fragments, it
admits them into the reassembly cache and updates its checklist. If
some fragments are still missing, the OAL destination may send a
small number of additional uNA ARQ/SRs within the link persistence
timeframe.
The OAL therefore provides a link layer low-to-medium persistence
ARQ/SR service consistent with [RFC3366] and Section 8.1 of
[RFC3819]. The service provides the benefit of timely best-effort
link layer retransmissions which may reduce OAL fragment loss and
avoid some unnecessary end-to-end delays. This best-effort network-
based service therefore compliments transport and higher layer end-
to-end protocols responsible for true reliability.
6.9. OMNI Interface MTU Feedback Messaging
When the OMNI interface forwards original IP packets/parcels from the
network layer, it invokes the OAL and returns internally-generated
Path MTU Discovery (PMTUD) ICMPv4 "Fragmentation Needed and Don't
Fragment Set" [RFC1191] or ICMPv6 "Packet Too Big (PTB)" [RFC8201]
messages as necessary. This document refers to both message types as
"PTBs" and introduces a distinction between PTB "hard" and "soft"
errors as discussed below.
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Ordinary PTB messages are hard errors that always indicate loss due
to a real MTU restriction has occurred. However, the OMNI interface
can also forward original IP packets/packets via OAL encapsulation
and fragmentation while at the same time returning PTB soft error
messages (subject to rate limiting) to the original source to suggest
smaller sizes due to factors such as link performance
characteristics, number of fragments needed, reassembly congestion,
etc.
This ensures that the path MTU is adaptive and reflects the current
path used for a given data flow. The OMNI interface can therefore
continuously forward original IP packets/parcels without loss while
returning PTB soft error messages recommending a smaller size if
necessary. Original sources that receive the soft errors in turn
reduce the size of the original IP packets/parcels they send, i.e.,
the same as for hard errors but not necessarily due to a loss event.
The original source can then resume sending larger packets/parcels
without delay if the soft errors subside.
OAL destinations and intermediate systems may experience reassembly
cache congestion, and can return uNA messages to the OAL source that
include OMNI encapsulated PTB messages with a PTB soft error Code to
OAL sources that originate the fragments (subject to rate limiting).
The OAL node creates a uNA message with an authentication signature
and an OMNI option containing an ICMPv6 Error sub-option. The OAL
node encodes a PTB message in the sub-option with MTU set to a
reduced value and with the leading portion an OAL first fragment
containing the header of an original IP packet/parcel for which the
source must be notified (see: Section 12).
The OAL node that sends the uNA encapsulates the leading portion of
the OAL first fragment (beginning with the OAL header) in the PTB
"packet in error" field, signs the message if an authentication
signature is included, performs OAL encapsulation (with the its own
address as the OAL source and the source address of the message that
prompted the uNA as the OAL destination) and sends the message to the
OAL source.
When the OAL source receives a uNA message from an OAL intermediate
system, it can reduce its OFS estimate and begin sending smaller OAL
fragments and/or reduce its CFS estimate and begin sending smaller
carrier packet fragments. When the OAL source receives a uNA message
from the OAL destination, it sends a corresponding network layer PTB
soft error to the original source to recommend a smaller size.
The OAL source prepares the PTB soft error by first setting the Type
field to 2 for IPv6 [RFC4443] or TBD6 for IPv4 (see: IANA
considerations). The OAL source then sets the Code field to "PTB
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Soft Error (no loss)" if the OAL destination forwarded the original
IP packet/parcel successfully or "PTB Soft Error (loss)" if it was
dropped (see: IANA considerations). The OAL source next sets the PTB
destination address to the original IP packet/parcel source, and sets
the source address to one of its OMNI interface addresses that is
reachable from the perspective of the original source.
The OAL source then sets the MTU field to a value smaller than the
original IP packet/parcel size but no smaller than 1280, writes as
much of the original IP packet/parcel first fragment as possible into
the "packet in error" field such that the entire PTB including the IP
header is no larger than 1280 octets for IPv6 or 576 octets for IPv4.
The OAL source then calculates and sets the ICMP Checksum and returns
the PTB to the original source.
An original sources that receives these PTB soft errors first
verifies that the ICMP Checksum is correct and the packet-in-error
contains the leading portion of one of its recent packet/parcel
transmissions. The original source can then adaptively tune the size
of the original IP packets/parcels it sends to produce the best
possible throughput and latency, with the understanding that these
parameters may fluctuate over time due to factors such as congestion,
mobility, network path changes, etc. Original sources should
therefore consider receipt or absence of soft errors as hints of when
decreasing or increasing packet/parcel sizes may provide better
performance.
The OMNI interface supports continuous transmission and reception of
packets/parcels of various sizes in the face of dynamically changing
network conditions. Moreover, since PTB soft errors do not indicate
a hard limit, original sources that receive soft errors can resume
sending larger packets/parcels without waiting for the recommended 10
minutes specified for PTB hard errors [RFC1191][RFC8201]. The OMNI
interface therefore provides an adaptive service that accommodates
MTU diversity especially well-suited for dynamic multilink networks.
The OMNI interface may also return PTB messages with Parcel Report
and/or Jumbo Report Codes in response to parcels and/or AJs delivered
by the network layer and forwarded through jumbo-in-jumbo
encapsulation. These Parcel/Jumbo Report messages are prepared the
same as for PTB soft errors discussed above. IP parcels and AJs are
discussed in
[I-D.templin-6man-parcels2][I-D.templin-intarea-parcels2].
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6.10. OAL Super-Packets
The OAL source ordinarily includes a 40-octet IPv6 encapsulation
header for each original IP packet/parcel during OAL encapsulation.
The OAL source then performs fragmentation such that a copy of the
40-octet IPv6 header plus a 16-octet IPv6 Extended Fragment Header is
included in each OAL fragment (when a Routing Header is added, the
OAL encapsulation headers become larger still). However, these
encapsulations may represent excessive overhead in some environments.
OAL header compression can dramatically reduce the amount of
encapsulation overhead, however a complimentary technique known as
"packing" (see: [I-D.ietf-intarea-tunnels]) supports encapsulation of
multiple original IP packets/parcels and/or control messages within a
single OAL "super-packet". (The super-packet normally includes a
control message as the first message of the packet, with one or more
original IP packets/parcels included as trailing attachments.)
When the OAL source has multiple original IP packets/parcels to send
to the same OAL destination with total length no larger than the OAL
destination EMTU_R, it can concatenate them into a super-packet
encapsulated in a single OAL header. Within the OAL super-packet,
the IP header of the first original IP packet/parcel (iHa) followed
by its data (iDa) is concatenated immediately following the OAL
header, then the IP header of the next original packet/parcel (iHb)
followed by its data (iDb) is concatenated immediately following the
first, etc. The OAL super-packet format is transposed from
[I-D.ietf-intarea-tunnels] and shown in Figure 13:
<------- Original IP packets ------->
+-----+-----+
| iHa | iDa |
+-----+-----+
|
| +-----+-----+
| | iHb | iDb |
| +-----+-----+
| |
| | +-----+-----+
| | | iHc | iDc |
| | +-----+-----+
| | |
v v v
+----------+-----+-----+-----+-----+-----+-----+
| OAL Hdr | iHa | iDa | iHb | iDb | iHc | iDc |
+----------+-----+-----+-----+-----+-----+-----+
<--- OAL "Super-Packet" with single OAL Hdr --->
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Figure 13: OAL Super-Packet Format
When the OAL source prepares a super-packet, it applies OAL
fragmentation then applies L2 encapsulation/fragmentation and sends
the resulting carrier packets to the OAL destination. When the OAL
destination receives the super-packet it first reassembles if
necessary. The OAL destination then selectively extracts each
original IP packet/parcel (e.g., by setting pointers into the super-
packet buffer and maintaining a reference count, by copying each
packet into a separate buffer, etc.) and forwards each one to the
network layer. During extraction, the OAL determines the IP protocol
version of each successive original IP packet/parcel 'j' by examining
the four most-significant bits of iH(j), and determines the length of
each one by examining the rest of iH(j) according to the IP protocol
version.
When an OAL source prepares a super-packet that includes an IPv6 ND
message with an authentication signature as the first original IP
packet/parcel (i.e., iHa/iDa), it calculates the authentication
signature over the remainder of super-packet. Security and integrity
for forwarding initial data messages in conjunction with IPv6 ND
messages used to establish NCE state are therefore supported. (A
second common use case entails a path MTU probe beginning with an
unsigned IPv6 ND message followed by a suitably large NULL packet
(e.g., an IP packet with padding octets added beyond the IP header
and with {Protocol, Next Header} set to 59 ("No Next Header"), a UDP/
IP packet with port number set to '9' ("discard") [RFC0863], etc.)
The OAL header of a super packet may also include an Advanced Jumbo
option if the total length of all payload packets/parcels exceeds
65535 octets. In that case, the super-packet must be forwarded as an
atomic fragment over OAL paths that support such large sizes.
6.11. OAL Bubbles
OAL sources may send NULL OAL packets known as "bubbles" for the
purpose of establishing Network Address Translator (NAT) state on the
path to the OAL destination. The OAL source prepares a bubble by
crafting an OAL header with appropriate IPv6 source and destination
ULAs, with the IPv6 Next Header field set to the value 59 ("No Next
Header" - see [RFC8200]) and with 0 or more octets of NULL protocol
data immediately following the IPv6 header.
The OAL source includes a random Identification value then
encapsulates the OAL packet in L2 headers destined to either the
mapped address of the OAL destination's first-hop ingress NAT or the
L2 address of the OAL destination itself. When the OAL source sends
the resulting carrier packet, any egress NATs in the path toward the
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L2 destination will establish state based on the activity but the
bubble will be harmlessly discarded by either an ingress NAT on the
path to the OAL destination or by the OAL destination itself.
The bubble concept for establishing NAT state originated in [RFC4380]
and was later updated by [RFC6081]. OAL bubbles may be employed by
mobility services such as AERO.
6.12. OMNI Hosts
OMNI Hosts are end systems that connect to the OMNI link over ENET
underlay interfaces (i.e., either via an OMNI interface or as a
sublayer of the ENET interface itself). Each ENET connects to the
rest of the OMNI link via a Client that receives an MNP delegation.
Clients delegate MNP addresses and/or sub-prefixes to ENET nodes
(i.e., Hosts, other Clients, routers and non-OMNI hosts) using
standard mechanisms such as DHCP [RFC8415][RFC2131] and IPv6
Stateless Address AutoConfiguration (SLAAC) [RFC4862]. Clients
forward original IP packets/parcels between their ENET Hosts and
peers on external networks acting as routers and/or OAL intermediate
systems.
OMNI Hosts coordinate with Clients and/or other Hosts connected to
the same ENET using OMNI L2 encapsulation of OMNI IPv6 ND messages.
The L2 encapsulation headers and ND messages both use the MNP-based
addresses assigned to ENET underlay interfaces as source and
destination addresses (i.e., instead of ULAs). For IPv4 MNPs, the ND
messages use IPv4-Compatible IPv6 addresses [RFC4291] in place of the
IPv4 addresses.
Hosts discover Clients by sending encapsulated RS messages using an
OMNI link IP anycast address (or the unicast address of the Client)
as the RS L2 encapsulation destination as specified in Section 15.
The Client configures the IPv4 and/or IPv6 anycast addresses for the
OMNI link on its ENET interface and advertises the address(es) into
the ENET routing system. The Client then responds to the
encapsulated RS messages by sending an encapsulated RA message that
uses its ENET unicast address as the source. (To differentiate
itself from an INET border Proxy/Server, the Client sets the RA
message OMNI Interface Attributes sub-option LHS field to 0 for the
Host's interface index. When the RS message includes an L2 anycast
destination address, the Client also includes an Interface Attributes
sub-option for interface index 0 to inform the Host of its L2 unicast
address - see: Section 15 for full details on the RS and RA message
contents.)
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Hosts coordinate with peer Hosts on the same ENET by sending
encapsulated NS messages to receive an NA reply. (Hosts determine
whether a peer is on the same ENET by matching the peer's IP address
with the MNP (sub)-prefix for the ENET advertised in the Client's RA
message [RFC8028].) Each ENET peer then creates a NCE and
synchronizes Identification windows the same as for OMNI link
neighbors, and the Host can then engage in OMNI link transactions
with the Client and/or other ENET Hosts. The Host therefore regards
the Client as if it were an ANET Proxy/Server, and the Client
provides the same services that a Proxy/Server would provide. By
coordinating with other Hosts, the peers can exchange large IP
packets/parcels over the ENET using encapsulation and fragmentation
if necessary.
When a Host prepares an original IP packet/parcel, it uses the IP
address of its OMNI interface (which is the same as the IP address of
the underlying native ENET interface) as the source and the IP
address of the (remote) peer as the destination. The Host next
performs parcellation if necessary (see: Section 6.13) then
encapsulates the packet(s)/(sub-)parcel(s) in OMNI L2 headers while
setting the L2 source to the L3 source address and L2 destination to
either the L3 destination address if the peer is on the local ENET,
or to the IP address of the Client otherwise. The Host can then
proceed to exchange packets/parcels with the destination, either
directly or via the Client as an intermediate system.
The encapsulation procedures are coordinated per Section 6.1, except
that the OMNI L2 encapsulation header is followed by an IPv6 Extended
Fragment Header. When the L2 encapsulation is based on an EUI or
IPv4 address, the Host next translates the encapsulation header into
an IPv6 header with IPv6 compatible addresses per Appendix B. Next,
for IPv4 ENETs the Host sets the {IPv6 Traffic Class, Payload Length,
Next Header, Hop Limit} fields according to the IPv4 {Type of
Service, Total Length, Protocol, TTL} fields, respectively and also
sets Flow Label as specified in [RFC6438]. The Host then applies
IPv6 fragmentation to produce IPv6 fragments no smaller than the
effective OFS described in Section 6.1. The Host next translates the
IPv6 encapsulation headers back to OMNI L2 headers for the native
ENET address format and with Type set to indicate the presence of the
L2 IPv6 Extended Fragment Header. The Host finally sends the
resultant carrier packets to the ENET peer.
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When the ENET peer receives the carrier packets, it first translates
the OMNI L2 headers back to IPv6 headers with compatible addresses.
The peer then reassembles and verifies the OAL checksum. If the
checksum is correct, the peer next removes the encapsulation headers
and applies parcel reunification if necessary. The peer then either
delivers the original IP packet/parcel to the transport layers if it
is also the final destination or forwards the packet/parcel via the
next hop if it is a Client acting as an intermediate system.
Hosts and Clients that initiate OMNI-based original IP packet/parcel
transactions should first test the path toward the final destination
using the parcel path qualification procedure specified in
[I-D.templin-6man-parcels2][I-D.templin-intarea-parcels2]. An OMNI
Host that sends and receives parcels need not implement the full OMNI
interface abstraction but MUST implement enough of the OAL to be
capable of fragmenting and reassembling maximum-length encapsulated
IP packets/parcels and sub-parcels as discussed above and in the
following section.
Note: Hosts and their peer Clients/Hosts on the same ANET/ENET can
improve efficiency by forwarding original IP packets/parcels that do
not require fragmentation as direct encapsulations within the OMNI L2
header and without including a L2 IPv6 Extended Fragment Header. In
that case, the first four bits immediately following the OMNI L2
encapsulation header encode the value '4' for IPv4 or '6' for IPv6.
Note that this savings comes at the expense of omitting a well-
behaved Identification, but this may be an acceptable tradeoff in
many secured ANET/ENET instances.
6.13. IP Parcels
IP parcels are formed by an OMNI Host or Client transport layer
protocol entity identified by the "5-tuple" (source address,
destination address, source port, destination port, protocol number)
when it produces a {TCP,UDP} protocol data unit containing the
concatenation of multiple transport layer protocol segments. The
transport layer protocol entity then presents the buffer and non-
final segment size to the network layer which appends a single
{TCP,UDP}/IP header (plus any extension headers) before presenting
the parcel to the OMNI Interface. Transport and network protocol
formatting and processing rules as well as parcellation and
reunification procedures for IP parcels are specified in
[I-D.templin-6man-parcels2][I-D.templin-intarea-parcels2], while
detailed OAL encapsulation and fragmentation procedures are specified
here.
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When the network layer forwards a parcel, the OMNI interface invokes
the OAL which forwards it to either an intermediate system or the
final destination itself. The OAL source first invokes parcellation
by subdividing the parcel into sub-parcels if necessary with each
sub-parcel no larger than 65535 (minus headers). The OAL source also
maintains a Parcel ID for each sub-parcel of the same original parcel
that along with the Identification value for this OAL packet supports
reassembly; the OAL source increments Parcel ID (modulo 64) for each
successive parcel.
The OAL source next performs encapsulation on each sub-parcel with
destination set to the next hop address. If the next hop is reached
via an ANET/INET interface, the OAL source inserts an OAL header the
same as discussed in Section 6.1 and sets the destination to the ULA-
MNP of the target Client. If the next hop is reached via an ENET
interface, the OAL source instead inserts an IP header of the
appropriate protocol version for the underlay ENET (i.e., even if the
encapsulation header is IPv4) and sets the destination to the ENET IP
address of the next hop. The OAL source inserts the encapsulation
header even if no actual fragmentation is needed and/or even if the
Parcel/Jumbo Payload option is present.
The OAL source next assigns an appropriate Identification number that
is monotonically-incremented for each consecutive sub-parcel, then
performs IPv6 fragmentation over the sub-parcel if necessary to
create fragments small enough to traverse the path to the next hop.
(If the encapsulation header is IPv4, the OAL source first translates
the encapsulation header into an IPv6 header with IPv4-Compatible
IPv6 addresses during fragmentation/reassembly while inserting the
IPv6 Extended Fragment Header.) The OAL source then writes the
"Parcel ID" and sets/clears the "(P)arcel" and "More (S)egments" bits
in the Reserved field of the IPv6 Extended Fragment Header of the
first fragment (see: Figure 4). (The OAL source sets P to 1 for a
parcel or to 0 for a non-parcel. When P is 1, the OAL next sets S to
1 for non-final sub-parcels or to 0 if the sub-parcel contains the
final segment.) The OAL source then sends each resulting carrier
packet to the next hop, i.e., after first translating the IPv6
encapsulation header back to IPv4 if necessary.
When the OAL destination receives the carrier packets, it reassembles
if necessary (i.e., after first translating the IPv4 encapsulation
header to IPv6 if necessary). If the P flag in the first fragment is
0, the OAL destination then processes the reassembled entity as an
ordinary IP packet; otherwise it continues processing as a sub-
parcel. If the OAL destination is not the final destination, it can
optionally retain the sub-parcels along with their Parcel ID and
Identification values for a brief time for opportunistic
reunification with peer sub-parcels of the same original parcel
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identified by the 4-tuple consisting of the adaptation layer (OAL
source, OAL destination, Parcel ID, Identification). (Note that the
OAL destination must not consult the parcel's network layer "5-tuple"
at the adaptation layer, since it is possible that multiple sub-
parcels of the same parcel may be forwarded over different network
paths).
The OAL destination performs adaptation layer reunification by
concatenating the segments included in sub-parcels with the same
Parcel ID and Identification values within 64 of one another to
create a larger sub-parcel possibly even as large as the entire
original (sub)parcel. Order of concatenation is determined by
increasing Identification values, noting that a sub-parcel that sets
any TCP control flags must occur as a first concatenation, and the
final sub-parcel (i.e., the one with S set to 0) must occur as a
final concatenation and not as an intermediate. The OAL destination
then appends common {TCP,UDP}/IP headers plus extensions to each
reunified sub-parcel as specified in
[I-D.templin-6man-parcels2][I-D.templin-intarea-parcels2].
When the OAL destination is not the final destination, it next
forwards the reunified (sub-)parcel(s) to the next hop toward the
final destination while ensuring that the S flag remains set to 0 in
the sub-parcel that contains the final segment. When the parcel or
sub-parcels arrive at the final destination, it performs network
layer reunification to form the largest possible (sub)-parcels (while
honoring the S flag) then delivers them to the transport layer entity
which acts on the enclosed 5-tuple information supplied by the
original source.
Note: IP parcels may also originate from a non-OMNI original source
and travel over multiple parcel-capable IP links before reaching an
OMNI link ingress node (i.e., either a Client or Proxy/Server acting
as a "relay"). The ingress node then forwards the parcel into the
OMNI link according to the rules established above for locally-
generated parcels, with the exception that the parcel IP TTL/Hop
Limit is decremented. Similarly, when the IP parcel arrives at the
OMNI link egress node (i.e., either a Client or Proxy/Server acting
as a "relay"), the parcel may travel over multiple parcel-capable IP
links before reaching the final destination.
Note: The OAL destination process of reunifying parcels at the
adaptation layer is optional, and should be avoided in cases where
performance could be negatively impacted. It is always acceptable
(albeit sometimes sub-optimal) for the OAL destination to forward
sub-parcels on toward the final destination without performing
adaptation layer reunification, since each sub-parcel will contain a
well-formed header and an integral number of transport layer protocol
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segments and with the Parcel ID field and P, S flag set
appropriately. The final destination can then optionally perform
network layer reunification independently of any adaptation layer
reunification that may have been applied by the OAL.
Note: The "Parcel ID" that appears in OFH and OCH headers is an
adaptation layer value that encodes the same value for all sub-
parcels of the original parcel at the adaptation layer. This is
different than the "(Parcel) Index" that appears in the Parcel
Payload option header as well as L2/L3 IPv6 Extended Fragment
Headers, which is a network layer value that encodes a transport
layer segment index.
Note: Parcel Path Qualification procedures require two additional
ICMP PTB message Code values to identify a Parcel Report and Jumbo
Report. These Code values are specified in
[I-D.templin-6man-parcels2] for IPv6 and
[I-D.templin-intarea-parcels2] for IPv4.
6.14. OAL Requirements
In light of the above, OAL sources, destinations and intermediate
systems observe the following normative requirements:
* OAL sources MUST forward original IP packets/parcels either larger
than the OMNI interface minimum EMTU_R or smaller than the minimum
OFS as atomic fragments (i.e., and not as multiple fragments).
* OAL sources MUST produce non-final fragments with payloads no
smaller than the minimum OFS during fragmentation.
* OAL intermediate systems SHOULD and OAL destinations MUST
unconditionally drop any non-final OAL fragments with payloads
smaller than the minimum OFS.
* OAL destinations MUST drop any new OAL fragments with offset and
length that would overlap with other fragments and/or leave holes
smaller than the minimum OFS between fragments that have already
been received.
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Note: Under the minimum OFS, an ordinary 1500-octet original IP
packet/parcel would require at most 2 OAL fragments, with the first
fragment containing 1024 payload octets and the final fragment
containing the remainder. For all packet/parcel sizes, the
likelihood of successful reassembly may improve when the OMNI
interface sends all fragments of the same fragmented OAL packet
consecutively over the same underlay interface pair instead of spread
across multiple underlay interface pairs. Finally, an assured
minimum OFS allows continuous operation over all paths including
those that traverse bridged L2 media with dissimilar MTUs.
Note: Certain legacy network hardware of the past millennium was
unable to accept IP fragment "bursts" resulting from a fragmentation
event - even to the point that the hardware would reset itself when
presented with a burst. This does not seem to be a common problem in
the modern era, where fragmentation and reassembly can be readily
demonstrated at line rate (e.g., using tools such as 'iperf3') even
over fast links on ordinary hardware platforms. Even so, while the
OAL destination is reporting reassembly congestion (see: Section 6.9)
the OAL source could impose "pacing" by inserting an inter-fragment
delay and increasing or decreasing the delay according to congestion
indications.
6.15. OAL Fragmentation Security Implications
As discussed in Section 3.7 of [RFC8900], there are four basic
threats concerning IPv6 fragmentation; each of which is addressed by
effective mitigations as follows:
1. Overlapping fragment attacks - reassembly of overlapping
fragments is forbidden by [RFC8200]; therefore, this threat does
not apply to the OAL.
2. Resource exhaustion attacks - this threat is mitigated by
providing a sufficiently large OAL reassembly cache and
instituting "fast discard" of incomplete reassemblies that may be
part of a buffer exhaustion attack. The reassembly cache should
be sufficiently large so that a sustained attack does not cause
excessive loss of good reassemblies but not so large that (timer-
based) data structure management becomes computationally
expensive. The cache should also be indexed based on the arrival
underlay interface such that congestion experienced over a first
underlay interface does not cause discard of incomplete
reassemblies for uncongested underlay interfaces.
3. Attacks based on predictable fragment Identification values - in
environments where spoofing is possible, this threat is mitigated
through the use of Identification windows beginning with
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unpredictable values per Section 6.7. By maintaining windows of
acceptable Identifications, OAL neighbors can quickly discard
spurious carrier packets that might otherwise clutter the
reassembly cache. The OAL additionally provides an integrity
check to detect corruption that may be caused by spurious
fragments received with in-window Identification values.
4. Evasion of Network Intrusion Detection Systems (NIDS) - since the
OAL source employs a robust OFS, network-based firewalls can
inspect and drop OAL fragments containing malicious data thereby
disabling reassembly by the OAL destination. However, since OAL
fragments may take different paths through the network (some of
which may not employ a firewall) each OAL destination must also
employ a firewall.
IPv4 includes a 2-octet (16-bit) Identification (IP ID) field with
only 65535 unique values such that even at moderate data rates the
field could wrap and apply to new carrier packets while the fragments
of old carrier packets using the same IP ID are still alive in the
network [RFC4963]. Carrier packets sent via an IPv4 path with DF set
to 0 and with an IPv4 fragmentation checksum therefore ensure
sufficient integrity to detect and discard reassembly errors. Since
IPv6 provides a 4-octet (32-bit) Identification value, IP ID
wraparound for IPv6 fragmentation may only be a concern at extreme
data rates (e.g., 1Tbps or more). Note that these limitations are
fully addressed through still longer Identification formats supported
by "Identification Extensions for the Internet Protocol"
[I-D.templin-6man-ipid-ext].
Fragmentation security concerns for large IPv6 ND messages are
documented in [RFC6980]. These concerns are addressed when the OMNI
interface employs the OAL instead of directly fragmenting the IPv6 ND
message itself. For this reason, OMNI interfaces MUST employ OAL
encapsulation and fragmentation for IPv6 ND messages larger than the
effective OFS for this OAL destination.
Unless the path is secured at the network layer or below (i.e., in
environments where spoofing is possible), OMNI interfaces MUST NOT
send OAL packets/fragments with Identification values outside the
current window and MUST secure IPv6 ND messages used for address
resolution or window state synchronization. OAL destinations SHOULD
therefore discard without reassembling any out-of-window OAL
fragments received over an unsecured path.
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7. Ethernet-Compatible Link Layer Frame Format
When the OMNI interface forwards original IP packets/parcels from the
network layer it first invokes OAL encapsulation and fragmentation,
then wraps each resulting OAL packet/fragment in any necessary L2
headers to produce carrier packets according to the native frame
format of the underlay interface. For example, for Ethernet-
compatible interfaces the frame format is specified in [RFC2464], for
aeronautical radio interfaces the frame format is specified in
standards such as ICAO Doc 9776 (VDL Mode 2 Technical Manual), for
various forms of tunnels the frame format is found in the appropriate
tunneling specification, etc.
When the OMNI interface encapsulates an OAL packet/fragment directly
over an Ethernet-compatible link layer, the over-the-wire
transmission format is shown in Figure 14:
+--- ~~~ ---+-------~~~------+---------~~~---------+--- ~~~ ---+
| eth-hdr | OMNI Ext. Hdrs | OAL Packet/Fragment | eth-trail |
+-- ~~~ ---+-------~~~------+---------~~~---------+--- ~~~ ---+
|<------- Ethernet Payload -------->|
Figure 14: OMNI Ethernet Frame Format
The format includes a standard Ethernet Header ("eth-hdr") with
EtherType TBD2 (see: Section 25.2) followed by an Ethernet Payload
that includes zero or more OMNI Extension Headers followed by an OAL
(or native IPv6/IPv4) Packet/Fragment. The Ethernet Payload is then
followed by a standard Ethernet Trailer ("eth-trail").
The first OMNI extension header and the OAL Packet/Fragment both
begin with a 4-bit "Type/Version" as discussed in Section 6.2. When
"Type/Version" encodes an OMNI extension header type, the length of
the extension headers is limited by [I-D.ietf-6man-eh-limits] and the
length of the OAL Packet/Fragment is determined by the IP header
fields that follow the extension headers.
When "Type/Version" encodes '0', '4' or '6', the OAL Packet/Fragment
includes an uncompressed OAL IPv6, native IPv4, or native IPv6 header
(respectively). In that case, the IP header {Total, Payload} and/or
Parcel/Jumbo Payload Length fields determine the packet/fragment
length. When "Type/Version" encodes '1' the OAL Packet/Fragment
instead includes an OCH, and the length fields found in the
uncompressed IP packet/fragment that follows determine the length.
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See Figure 2 for a map of the various L2 layering combinations
possible. For any layering combination, the final layer (e.g., UDP,
IP, Ethernet, etc.) must have an assigned number and frame format
representation that is compatible with the selected underlay
interface.
8. Link-Local Addresses (LLAs)
[RFC4861] requires that nodes assign Link-Local Addresses (LLAs) to
all interfaces, and that routers use their LLAs as the source address
for RA and Redirect messages. OMNI interfaces honor the first
requirement, but do not honor the second since the OMNI link could
consist of the concatenation of multiple links with diverse ULA
prefixes (see Section 9) but for which multiple nodes might configure
identical interface identifiers (IIDs). OMNI interface LLAs are
therefore considered only as context for IID formation as discussed
below and have no other operational role.
OMNI interfaces assign IPv6 LLAs through pre-service administrative
actions. Clients assign "LLA-MNPs" with IIDs that embed the Client's
unique MNP, while Proxy/Servers assign "LLA-RNDs" that include a
randomly-generated IIDs generated as specified in [RFC7217]. LLAs
are configured as follows:
* IPv6 LLA-MNPs encode the most-significant 64 bits of an MNP within
the least-significant 64 bits of the IPv6 link-local prefix
fe80::/64, i.e., in the IID portion of the LLA. The LLA prefix
length is determined by adding 64 to the MNP prefix length. e.g.,
for the MNP 2001:db8:1000:2000::/56 the corresponding LLA-MNP
prefix is fe80::2001:db8:1000:2000/120. (The base LLA-MNP for
each "/N" prefix sets the final 128-N bits to 0, but all LLA-MNPs
that match the prefix are also accepted.) Non-MNP IPv6 prefix-
based LLAs are also represented the same as for LLA-MNPs, but
include a GUA prefix that is not properly covered by the MSP.
* IPv4-Compatible LLA-MNPs are constructed as fe80::{IPv4-Prefix},
i.e., the IID consists of 32 '0' bits followed by a 32 bit IPv4
address/prefix, which may be either public or private in
correspondence with the network layer addressing plan. The
IPv4-Compatible LLA-MNP prefix length is determined by adding 96
to the IPv4 prefix length. For example, the IPv4-Compatible LLA-
MNP for 192.0.2.0/24 is fe80::192.0.2.0/120, also written as
fe80::c000:0200/120. (The base LLA-MNP for each "/N" prefix sets
the final 128-N bits to 0, but all LLA-MNPs that match the prefix
are also accepted.) Non-MNP IPv4 prefix-based LLAs are also
represented the same as for LLA-MNPs, but include a GUA prefix
that is not properly covered by the MSP.
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* LLA-RNDs are randomly-generated and assigned to Proxy/Servers and
other SRT infrastructure elements. They may also be assigned by
Clients to support the MNP delegation process. The upper 72 bits
of the LLA-RND encode the prefix fe80::/72, and the lower 56 bits
include a randomly-generated candidate pseudo-random value
configured as specified in [RFC7217][RFC8981]; if the most
significant 24 bits of the 56 bit candidate encodes the value '0',
the node generates a new candidate to obtain one with a different
most significant 24 bits to avoid overlap with IPv4-Compatible
LLAs.
* The address fe80::/128 (i.e., the LLA /64 prefix followed by an
all-zero IID) is considered the LLA Subnet Router Anycast address
Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no
MNPs can be allocated from that block ensuring that there is no
possibility for overlap between the different MNP and RND LLA
constructs discussed above.
Since LLA-MNPs are based on the distribution of administratively
assured unique MNPs, and since LLA-RNDs are assumed unique through
pseudo-random assignment, OMNI interfaces set the autoconfiguration
variable DupAddrDetectTransmits to 0 [RFC4862].
Note: If future protocol extensions relax the 64-bit boundary in IPv6
addressing, the additional prefix bits of an MNP could be encoded in
bits 16 through 63 of the LLA-MNP. (The most-significant 64 bits
would therefore still be in bits 64-127, and the remaining bits would
appear in bits 16 through 48.) However, this would interfere with
the relationship between OMNI LLAs and ULAs (see: Section 9) and
therefore deprecate many OMNI functions. The analysis provided in
[RFC7421] furthermore suggests that the 64-bit boundary will remain
in the IPv6 architecture for the foreseeable future.
9. Unique-Local Addresses (ULAs)
OMNI links use IPv6 Unique-Local Addresses (ULAs) as the source and
destination addresses in both IPv6 ND messages and OAL packet IPv6
encapsulation headers. ULAs are routable only within the scope of an
OMNI link, and are derived from the IPv6 Unique Local Address prefix
fd00::/8 (i.e., the prefix fc00::/7 followed by the L bit set to 1).
When the first 16 bits of the ULA encode the value fd00::/16, the
address is considered as either a Temporary ULA (TLA) or an eXtended
ULA (XLA) - see below. For all other ULAs, the 56 bits following
fd00::/8 encode a 40-bit Global ID followed by a 16-bit Subnet ID as
specified in Section 3 of [RFC4193]. All OMNI link ULA types finally
include a 64-bit value in the IID portion of the address ULA::/64 as
specified below.
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When a node configures a ULA for OMNI, it selects a 40-bit Global ID
for the OMNI link initialized to a candidate pseudo-random value as
specified in Section 3 of [RFC4193]; if the most significant 8 bits
of the candidate encodes the value '0', the node selects a new
candidate until it obtains one with a different most significant 8
bits. All nodes on the same OMNI link use the same Global ID, and
statistical uniqueness of the pseudo-random Global ID provides a
unique OMNI link identifier allowing different links to be joined
together in the future without requiring renumbering.
Next, for each logical segment of the same OMNI link the node selects
a 16-bit Subnet ID value between 0x0000 and 0xffff. Nodes on the
same logical segment configure the same Subnet ID, but nodes on
different segments of the same OMNI link can still exchange IPv6 ND
messages as single-hop neighbors even if they configure different
Subnet IDs. When a node moves to a different OMNI link segment, it
resets the Global ID and Subnet ID value according to the new segment
but need not change the IID.
ULAs and their associated prefix lengths are configured in
correspondence with LLAs through stateless prefix translation where
"ULA-MNPs" simply copy the IIDs of their corresponding LLA-MNPs and
"ULA-RNDs" simply copy the IIDs of their corresponding LLA-RNDs. For
example, for the OMNI link ULA prefix fd{Global}:{Subnet}::/64:
* the ULA-MNP corresponding to the LLA-MNP fe80::2001:db8:1:2 with a
56-bit MNP length is simply fd{Global}:{Subnet}:2001:db8:1:2/120
(where, the ULA prefix length becomes 64 plus the IPv6 MNP
length).
* the ULA-MNP corresponding to fe80::192.0.2.0 with a 28-bit MNP
length is simply fd{Global}:{Subnet}::192.0.2.0/124 (where, the
ULA prefix length becomes 96 plus the IPv4 MNP length).
* the ULA-RND corresponding to fe80::0012:3456:789a:bcde is simply
fd{Global}:{Subnet}::0012:3456:789a:bcde/128.
* the Subnet Router Anycast ULA corresponding to fe80::/128 is
simply fd{Global}:{Subnet}::/128.
The ULA presents an IPv6 address format that is routable within the
OMNI link routing system and can be used to convey link-scoped (i.e.,
single-hop) IPv6 ND messages across multiple hops through OAL IPv6
encapsulation. The OMNI link extends across one or more underlying
Internetworks to include all Proxy/Servers and other service nodes.
All Clients are also considered to be connected to the OMNI link,
however unnecessary encapsulations are omitted whenever possible to
conserve bandwidth (see: Section 14).
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Clients can configure TLAs when they have no other ULA addresses by
setting the ULA prefix to fd00::/16 followed by a 48-bit randomly-
generated number followed by a random or MNP-based IID the same as
specified in Section 8. XLAs are special-case TLAs that use the
prefix fd00::/64; XLAs can also be formed from LLAs simply by
inverting bits 7 and 8 of 'fe80' to form 'fd00'.
OMNI nodes use XLA-MNPs as "default" ULAs for representing MNPs in
the OMNI link routing system. Clients use {TLA,XLA}-MNPs when they
already know their MNP but need to express it outside the context of
a specific ULA prefix, and Proxy/Servers advertise XLA-MNPs into the
OMNI link routing system instead of advertising fully-qualified
{TLA,ULA}-MNPs and/or non-routable LLA-MNPs.
{TLAs,XLAs} provide initial "bootstrapping" addresses while the
Client is in the process of procuring an MNP and/or identifying the
ULA prefix for the OMNI link segment; TLAs are not advertised into
the OMNI link routing system but can be used for Client-to-Client
communications within a single ANET/INET/ENET when no OMNI link
infrastructure is present. Within each individual ANET/INET/ENET,
TLAs employ optimistic DAD principles [RFC4429] since they are
statistically unique.
Each OMNI link may be subdivided into SRT segments that often
correspond to different administrative domains or physical
partitions. Each SRT segment is identified by a different Subnet ID
within the same ULA ::/48 prefix. Multiple distinct OMNI links with
different ULA ::/48 prefixes can also be joined together into a
single unified OMNI link through simple interconnection without
requiring renumbering. In that case, the (larger) unified OMNI link
routing system may carry multiple distinct ULA prefixes.
OMNI nodes can use Segment Routing [RFC8402] to support efficient
forwarding to destinations located in other OMNI link segments. A
full discussion of Segment Routing over the OMNI link appears in
[I-D.templin-intarea-aero].
Note: IPv6 ULAs taken from the prefix fc00::/7 followed by the L bit
set to 0 (i.e., as fc00::/8) are never used for OMNI OAL addressing,
however the range could be used for MSP/MNP addressing under certain
limiting conditions (see: Section 10). When used within the context
of OMNI, ULAs based on the prefix fc00::/8 are referred to as "ULA-
C's".
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Note: When they appear in the OMNI link routing table, ULA-RNDs
always use prefix lengths between /48 and /64 (or, /128) while XLA-
MNPs always use prefix lengths between /65 and /128. {TLA,ULA}-MNPs
and {TLA,XLA}-RNDs should never appear in the OMNI link routing
table, but may appear in ANET/INET/ENET routing tables.
10. Global Unicast Addresses (GUAs)
OMNI domains use IP Global Unicast Address (GUA) prefixes [RFC4291]
as Mobility Service Prefixes (MSPs) from which Mobile Network
Prefixes (MNP) are delegated to Clients. Fixed correspondent node
networks reachable from the OMNI link are represented by non-MNP GUA
prefixes that are not derived from the MSP, but are treated in all
other ways the same as for MNPs.
For IPv6, GUA MSPs are assigned by IANA [IPV6-GUA] and/or an
associated Regional Internet Registry (RIR) such that the OMNI link
can be interconnected to the global IPv6 Internet without causing
inconsistencies in the routing system. An OMNI link could instead
use ULAs with the 'L' bit set to 0 (i.e., from the "ULA-C" prefix
fc00::/8)[RFC4193], however this would require IPv6 NAT if the domain
were ever connected to the global IPv6 Internet.
For IPv4, GUA MSPs are assigned by IANA [IPV4-GUA] and/or an
associated RIR such that the OMNI link can be interconnected to the
global IPv4 Internet without causing routing inconsistencies. An
OMNI ANET/ENET could instead use private IPv4 prefixes (e.g.,
10.0.0.0/8, etc.) [RFC3330], however this would require IPv4 NAT at
the INET-to-ANET/ENET boundary. OMNI interfaces advertise IPv4 MSPs
into IPv6 routing systems as IPv4-Compatible IPv6 prefixes [RFC4291]
(e.g., the IPv6 prefix for the IPv4 MSP 192.0.2.0/24 is
::192.0.2.0/120).
OMNI interfaces assign the IPv4 anycast address TBD3 (see: IANA
Considerations), and IPv4 routers that configure OMNI interfaces
advertise the prefix TBD3/N into the routing system of other networks
(see: IANA Considerations). OMNI interfaces also configure global
IPv6 anycast addresses formed according to [RFC3056] as:
2002:TBD3{32}:MSP{64}:Link-ID{16}
where TBD3{32} is the 32 bit IPv4 anycast address and MSP{64} encodes
an MSP zero-padded to 64 bits (if necessary). For example, the OMNI
IPv6 anycast address for MSP 2001:db8::/32 is
2002:TBD3{32}:2001:db8:0:0:{Link-ID}, the OMNI IPv6 anycast address
for MSP 192.0.2.0/24 is 2002:TBD3{32}::c000:0200:{Link-ID}, etc.).
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The 16-bit Link-ID in the OMNI IPv6 anycast address identifies a
specific OMNI link within the domain that services the MSP. The
special Link-ID value '0' is a wildcard that matches all links, while
all other values identify specific links. Mappings between Link-ID
values and the ULA Global IDs assigned to OMNI links are outside the
scope of this document.
OMNI interfaces assign OMNI IPv6 anycast addresses, and IPv6 routers
that configure OMNI interfaces advertise the corresponding prefixes
into the routing systems of other networks. An OMNI IPv6 anycast
prefix is formed the same as for any IPv6 prefix; for example, the
prefix 2002:TBD3{32}:2001:db8::/80 matches all OMNI IPv6 anycast
addresses covered by the prefix. When IPv6 routers advertise OMNI
IPv6 anycast prefixes in this way, Clients can locate and associate
with either a specific OMNI link or any OMNI link within the domain
that services the MSP of interest.
OMNI interfaces use OMNI IPv6 and IPv4 anycast addresses to support
Service Discovery in the spirit of [RFC7094], i.e., the addresses are
not intended for use in long-term transport protocol sessions.
Specific applications for OMNI IPv6 and IPv4 anycast addresses are
discussed throughout the document as well as in
[I-D.templin-intarea-aero].
11. Node Identification
OMNI Clients and Proxy/Servers that connect over open Internetworks
include a unique node identification value for themselves in the OMNI
options of their IPv6 ND messages (see: Section 12.2.3). An example
identification value alternative is the Host Identity Tag (HIT) as
specified in [RFC7401], while Hierarchical HITs (HHITs)
[I-D.ietf-drip-rid] may be more appropriate for certain domains such
as the Unmanned (Air) Traffic Management (UTM) service for Unmanned
Air Systems (UAS). Another example is the Universally Unique
IDentifier (UUID) [RFC4122] which can be self-generated by a node
without supporting infrastructure with very low probability of
collision.
When a Client is truly outside the context of any infrastructure, it
may have no MNP information at all. In that case, the Client can use
a TLA or (H)HIT as an IPv6 source/destination address for sustained
communications in Vehicle-to-Vehicle (V2V) and (multihop) Vehicle-to-
Infrastructure (V2I) scenarios. The Client can also propagate the
ULA/(H)HIT into the multihop routing tables of (collective) Mobile/
Vehicular Ad-hoc Networks (MANETs/VANETs) using only the vehicles
themselves as communications relays.
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When a Client connects via a protected-spectrum ANET, an alternate
form of node identification (e.g., MAC address, serial number,
airframe identification value, VIN, etc.) embedded in a ULA may be
sufficient. The Client can then include OMNI "Node Identification"
sub-options (see: Section 12.2.3) in IPv6 ND messages should the need
to transmit identification information over the network arise.
HHITs provide an especially useful construct since they appear as
properly-formed IPv6 GUAs and can therefore be assigned to
interfaces. Clients may assign an HHIT to their OMNI interface to
support peer-to-peer communications with other OMNI nodes that
configure HHITs within the same OMNI link segment without the need
for encapsulation. Clients may inject their HHIT into the local
routing system of each OMNI link segment, but Proxy/Servers must not
inject HHITs into the OMNI link global routing system.
12. Address Mapping - Unicast
OMNI interfaces maintain a network layer conceptual neighbor cache
per [RFC1256] or [RFC4861] the same as for any IP interface, and (for
IPv6) use the link-local address format specified in Section 8. The
network layer maintains state through static and/or dynamic Neighbor
Cache Entry (NCE) configurations.
Each OMNI interface also maintains a separate internal adaptation
layer conceptual neighbor cache that includes a NCE for the unique-
local address of each of its active OAL neighbors (see: Section 8).
For each peer NCE, OAL neighbors also maintain AERO Forwarding
Vectors (AFVs) which map per-interface-pair parameters. Throughout
this document, the terms "neighbor cache", "NCE" and "AFV" refer to
this OAL neighbor information unless otherwise specified.
IPv6 Neighbor Discovery (ND) [RFC4861] messages sent over OMNI
interfaces without OAL encapsulation observe the native underlay
interface Source/Target Link-Layer Address Option (S/TLLAO) format
(e.g., for Ethernet the S/TLLAO is specified in [RFC2464]). IPv6 ND
messages sent from within the OMNI interface using OAL encapsulation
do not include S/TLLAOs, but instead include a new option type that
encodes OMNI link-specific information. Hence, this document does
not define a new S/TLLAO format but instead defines a new option type
termed the "OMNI option" designed for these purposes. (Note that
OMNI interface IPv6 ND messages sent without encapsulation may
include both OMNI options and S/TLLAOs, but the information conveyed
in each is mutually exclusive.)
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For each IPv6 ND message, the OMNI interface includes one or more
OMNI options (and any other ND message options) then completely
populates all option information. OMNI options should be padded when
necessary to ensure that they end on their natural 64-bit boundaries
the same as for any IPv6 ND message option.
If the OMNI interface includes an OMNI option with an authentication
signature, it first sets the signature field to 0 then calculates the
authentication signature beginning after the IPv6 ND message header
checksum field. The OMNI interface extends the calculation over the
entire length of the ND message (as well as any concatenated
extensions in the case of a super-packet) then writes the
authentication signature value into the appropriate OMNI
authentication sub-option field.
The OMNI interface then applies any non-OMNI authentication
signatures, calculates the IPv6 ND message checksum per [RFC4443]
beginning with a pseudo-header of the IPv6 header and writes the
value into the Checksum field. OMNI interfaces verify first
integrity then authenticity of each IPv6 ND message or super-packet
received, and process the message further only following successful
verification.
OMNI interface Clients such as aircraft typically have multiple
wireless data link types (e.g. satellite-based, cellular,
terrestrial, air-to-air directional, etc.) with diverse performance,
cost and availability properties. The OMNI interface would therefore
appear to have multiple L2 connections, and may include information
for multiple underlay interfaces in a single IPv6 ND message
exchange. OMNI interfaces manage their dynamically-changing
multilink profiles by including OMNI options in IPv6 ND messages as
discussed in the following subsections.
12.1. The OMNI Option
OMNI options appear in IPv6 ND messages formatted as shown in
Figure 15:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-Options ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: OMNI Option Format
In this format:
* Type is set to TBD4 (see: IANA Considerations).
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* Length is set to the number of 8-octet blocks in the option. The
value 0 is invalid, while the values 1 through 255 (i.e., 8
through 2040 octets, respectively) indicate the total length of
the OMNI option. If multiple OMNI option instances appear in the
same IPv6 ND message, the union of the contents of all OMNI
options is accepted unless otherwise qualified for specific sub-
options below.
* Sub-Options is a Variable-length field padded with Pad1/N sub-
options if necessary (see below) such that the complete OMNI
Option is an integer multiple of 8 octets long. The Sub-Options
field contains zero or more sub-options as specified in
Section 12.2.
The OMNI option is included in OMNI interface IPv6 ND messages; the
option is processed by receiving interfaces that recognize it and
otherwise ignored. The OMNI interface processes all OMNI option
instances received in the same IPv6 ND message in the consecutive
order in which they appear. The OMNI option(s) included in each IPv6
ND message may include full or partial information for the neighbor.
The OMNI interface therefore retains the union of the information in
the most recently received OMNI options in the corresponding NCE.
12.2. OMNI Sub-Options
Each OMNI option includes a Sub-Options block containing zero or more
individual sub-options. Each consecutive sub-option is concatenated
immediately following its predecessor. All sub-options except Pad1
(see below) are in an OMNI-specific type-length-value (TLV) format
encoded as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Sub-Type| Sub-Length | Sub-Option Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 16: Sub-Option Format
* Sub-Type is a 5-bit field that encodes the sub-option type. Sub-
option types defined in this document are:
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Sub-Option Name Sub-Type
Pad1 0
PadN 1
Node Identification 2
Authentication 3
Window Synchronization 4
Neighbor Control 5
Interface Attributes 6
Traffic Selector 7
AERO Forwarding Parameters 8
Geo Coordinates 9
DHCPv6 Message 10
PIM-SM Message 11
HIP Message 12
QUIC-TLS Message 13
Fragmentation Report 14
ICMPv6 Error 15
Proxy/Server Departure 16
Sub-Type Extension 30
Figure 17
Sub-Types 17-29 are available for future assignment for major
protocol functions, while Sub-Type 30 supports scalable extension
to include other functions. Sub-Type 31 is reserved by IANA.
* Sub-Length is an 11-bit field that encodes the length of the Sub-
Option Data in octets.
* Sub-Option Data is a block of data with format determined by Sub-
Type and length determined by Sub-Length. Note that each sub-
option is concatenated consecutively with the previous and may
therefore begin and/or end on an arbitrary octet boundary.
The OMNI interface codes each sub-option with a 2-octet header that
includes Sub-Type in the most significant 5 bits followed by Sub-
Length in the next most significant 11 bits. Each sub-option encodes
a maximum Sub-Length value of 2038 octets minus the lengths of the
OMNI option header and any preceding sub-options. This allows ample
Sub-Option Data space for coding large objects (e.g., ASCII strings,
domain names, protocol messages, security codes, etc.), while a
single OMNI option is limited to 2040 octets the same as for any IPv6
ND option.
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The OMNI interface codes initial sub-options in a first OMNI option
instance and any additional sub-options in additional instances in
the same IPv6 ND message in the intended order of processing. If the
size of all OMNI options with their sub-options would cause the IPv6
ND message to exceed the OMNI interface MTU, the OMNI interface can
code any remaining sub-options in additional IPv6 ND messages.
The OMNI interface processes all OMNI options received in an IPv6 ND
message while skipping over and ignoring any unrecognized sub-
options. The OMNI interface processes the sub-options of all OMNI
option instances in the consecutive order in which they appear in the
IPv6 ND message, beginning with the first instance and continuing
through any additional instances to the end of the message. If an
individual sub-option length would cause processing to exceed the
OMNI option instance and/or IPv6 ND message lengths, the OMNI
interface accepts any sub-options already processed and ignores the
remainder of that instance. The interface then processes any
remaining OMNI option instances in the same fashion to the end of the
IPv6 ND message.
IPv6 ND messages that require OMNI authentication services MUST
include a Node Identification sub-option as the first sub-option of
the first OMNI option, and MUST include some form of authentication
(e.g., HMAC, HIP, QUIC, etc.) as the immediately next sub-option
whether in the same or different OMNI option. A single IPv6 ND
messages may include only one OMNI authentication service sub-option;
if multiple are included, the first sub-option is processed and all
others are ignored. The IPv6 ND message may also include non-OMNI
authentication options such as those specified in [RFC3971] or
[RFC8928] either instead of or in addition to an OMNI authentication
option. Nodes that receive IPv6 ND messages over unsecured
underlying networks first verify the IPv6 ND message checksum then
authenticate the message by processing any authentication options/
sub-options.
Note: large objects that exceed the maximum Sub-Option Data length
are not supported under the current specification; if this proves to
be limiting in practice, future specifications may define support for
fragmenting large sub-options across multiple OMNI options within the
same IPv6 ND message (or even across multiple IPv6 ND messages, if
necessary).
The following sub-option types and formats are defined in this
document:
12.2.1. Pad1
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+-+-+-+-+-+-+-+-+
| S-Type=0|x|x|x|
+-+-+-+-+-+-+-+-+
Figure 18: Pad1
* Sub-Type is set to 0. If multiple instances appear in OMNI
options of the same message all are processed.
* Sub-Type is followed by 3 'x' bits, set to any value on
transmission (typically all-zeros) and ignored on reception. Pad1
therefore consists of a single octet with the most significant 5
bits set to 0, and with no Sub-Length or Sub-Option Data fields
following.
If more than a single octet of padding is required, the PadN option,
described next, should be used, rather than multiple Pad1 options.
12.2.2. PadN
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| S-Type=1| Sub-length=N | N padding octets ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 19: PadN
* Sub-Type is set to 1. If multiple instances appear in OMNI
options of the same message all are processed.
* Sub-Length is set to N that encodes the number of padding octets
that follow.
* Sub-Option Data consists of N octets, set to any value on
transmission (typically all-zeros) and ignored on receipt.
When a proxy forwards an IPv6 ND message with OMNI options, it can
employ PadN to void any non-Pad1 sub-options that should not be
processed by the next hop by simply writing the value '1' over the
Sub-Type. When the proxy alters the IPv6 ND message contents in this
way, any included authentication and integrity checks are
invalidated. See: Appendix C for a discussion of IPv6 ND message
authentication and integrity.
12.2.3. Node Identification
The Node Identification sub-option includes a form of identification
for the node, and (when present) must appear as the first sub-option
of the first OMNI option in each IPv6 ND message.
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At least one instance of the sub-option must be present in messages
that also include an OMNI authentication service sub-option. If
multiple instances appear in OMNI options of the same IPv6 ND message
the first instance of a specific ID-Type is processed and all other
instances of the same ID-Type are ignored. (It is therefore possible
for a single IPv6 ND message to convey multiple distinct Node
Identifications - each with a different ID-Type.)
The format and contents of the sub-option are shown in Figure 20:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=2| Sub-length=N | ID-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Node Identification Value (N-1 octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: Node Identification
* Sub-Type is set to 2. Multiple instances are processed as
discussed above.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The ID-Type field is always present; hence,
the maximum Node Identification Value length is limited by the
remaining available space in this OMNI option.
* ID-Type is a 1-octet field that encodes the type of the Node
Identification Value. The following ID-Type values are currently
defined:
- 0 - Universally Unique IDentifier (UUID) [RFC4122]. Indicates
that Node Identification Value contains a 16-octet UUID.
- 1 - Host Identity Tag (HIT) [RFC7401]. Indicates that Node
Identification Value contains a 16-octet HIT.
- 2 - Hierarchical HIT (HHIT) [I-D.ietf-drip-rid]. Indicates
that Node Identification Value contains a 16-octet HHIT.
- 3 - Network Access Identifier (NAI) [RFC7542]. Indicates that
Node Identification Value contains an (N-1)-octet NAI.
- 4 - Fully-Qualified Domain Name (FQDN) [RFC1035]. Indicates
that Node Identification Value contains an (N-1)-octet FQDN.
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- 5 - IPv6 Address. Indicates that Node Identification contains
a 16-octet IPv6 address that is not a (H)HIT. The IPv6 address
type is determined according to the IPv6 addressing
architecture [RFC4291].
- 6 - 252 - Unassigned.
- 253 - 254 - reserved for experimentation, as recommended in
[RFC3692].
- 255 - reserved by IANA.
* Node Identification Value is an (N-1)-octet field encoded
according to the appropriate the "ID-Type" reference above.
OMNI interfaces code Node Identification Values used for DHCPv6
messaging purposes as a DHCP Unique IDentifier (DUID) using the
"DUID-EN for OMNI" format with enterprise number 45282 (see:
Section 25) as shown in Figure 21:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DUID-Type (2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Enterprise Number (45282) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID-Type | |
+-+-+-+-+-+-+-+-+ ~
~ Node Identification Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: DUID-EN for OMNI Format
In this format, the OMNI interface codes the ID-Type and Node
Identification Value fields from the OMNI sub-option following a
6-octet DUID-EN header, then includes the entire "DUID-EN for OMNI"
in a DHCPv6 message per [RFC8415].
12.2.4. Authentication
The Authentication sub-option includes a Hashed Message
Authentication Code (HMAC) computed according to [RFC2104] and
[RFC6234].
The Authentication sub-option is formatted as shown in Figure 22:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=3| Sub-length=N | Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Hashed Message Authentication Code (HMAC) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: Authentication
* Sub-Type is set to 3. The Authentication sub-option must appear
at most once in any IPv6 ND message; if multiple instances appear
in OMNI options of the same message the first is processed and all
others are ignored.
* Sub-Length is set to N, i.e., the length of the option in octets
beginning immediately following the Sub-Length field and extending
to the end of the HMAC. The length of the HMAC is therefore
limited by the remaining available space for this sub-option.
* Type encodes the authentication algorithm type found in the IANA
"ICMPv6 Parameters - Trust Anchor Option (Type 15) Name Field"
registry, and determines the length of the HMAC. For example,
when Type is 3 the authentication algorithm is SHA-1 and the HMAC
is 160 bits (20 octets) in length, when Type is 5 the algorithm is
SHA-256 and the HMAC is 256 bits (32 octets) in length, etc. A
full list of available Types is found in the registry, which cites
[RFC6495] for several well-known Types.
* HMAC includes the Hashed Message Authentication Code for this IPv6
ND message with field length determined by Type.
12.2.5. Window Synchronization
IPv6 ND messages used for window synchronization between Clients and
Proxy/Servers include a Window Synchronization sub-option.
The Window Synchronization sub-option is formatted as follows:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=4| Sub-length=12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Sequence Number ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Acknowledgment Number ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|R|O|A|R|R|S|R| |
|E|E|P|C|E|S|Y|E| Window |
|S|S|T|K|S|T|N|S| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23: Window Synchronization
* Sub-Type is set to 4. If instances appear in OMNI options of the
same message, the first is processed and all others are ignored.
* Sub-Length is set to 12.
* Sub-Option Data is modeled from the Transmission Control Protocol
(TCP) header specified in Section 3.1 of [RFC9293]. The field is
formatted as an 8-octet Sequence Number, followed by an 8-octet
Acknowledgement Number, followed by a 1-octet flags field followed
by a 3-octet Window size. The TCP (ACK, RST, SYN) flags are used
for TCP-like window synchronization, while the TCP (CWR, ECE, URG,
PSH, FIN) flags are unused. The OPT flag (discussed in
Section 6.7) is an OMNI-specific replacement for the TCP URG flag,
and the four remaining unused flags appear as reserved (RES).
Together, these fields support the OAL window synchronization
services specified in Section 6.7.
12.2.6. Neighbor Control
IPv6 ND messages that need to assert/request an MNP prefix length or
assert neighbor control flags can include a simple Neighbor Control
sub-option instead of a full DHCPv6 message and/or other large sub-
options. The Neighbor Control sub-option is formatted as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |N|A|R|S| |
| S-Type=5| Sub-length=N | Preflen |U|R|P|N| Resv1 |
| | | |D|R|T|R| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Reserved2 | Reserved3 | Reserved4 |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 24: Neighbor Control
* Sub-Type is set to 5. If multiple instances appear in OMNI
options of the same message, the first is processed and all others
are ignored.
* Sub-Length is set to a value N between 1 and 5; if any other value
appears the sub-option is ignored. The Sub-Length value
determines the number of Preflen/flag bit fields that follow.
* Preflen is an 1-octet field that determines the length of a
subject MNP. Values 1 through 64 specify a valid MNP length; any
other value that appears must be ignored. Nodes should only
accept Preflen values in authentic IPv6 ND messages received
through trusted neighbors, since untrusted neighbors may assert
Preflen values they are not authorized to use. Preflen is
interpreted according to the specific IPv6 ND message type as
follows:
- For RS messages, when the source address contains an MNP
Preflen refers to the RS source address; otherwise it
determines the MNP delegation length the Client wishes to
receive from the service.
- For RA messages, Preflen refers to the MNP found in the RA
destination address.
- For NS messages, Preflen refers to the MNP found in the NS
source address.
- For NA messages, Preflen refers to the MNP found in the Target
Address field within the NA message body.
- For Redirect messages, Preflen refers to the MNP found in the
Destination Address field within the Redirect message body.
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* For Sub-length values larger than 1, a first octet containing
neighbor control flags plus up to 3 additional octets follow.
Clients set the Neighbor Unreachability Detection (NUD), Address
Resolution Responder (ARR) and Report (RPT) flags in RS messages
to control the operation of their Proxy/Server neighbors as
discussed in Section 15. Nodes set the Synchronous (u)NA Required
(SNR) flag in non-solicitation IPv6 ND messages (i.e., solicited/
unsolicited NA/RA and Redirects) for which they require a
synchronous (but technically "unsolicited") NA reply (see:
[I-D.templin-intarea-aero]). The next 4 bits following the
neighbor control flags are (Reserved1) and up to 3 additional flag
octets (Reserved2 - Reserved4) follow. Any included Reserved
flags must be set to zero on transmission and ignored on reception
(future specifications may define new values).
Note that in the above Preflen applies only to the MNP itself. Any
ULAs/XLAs that include the MNP in the interface identifier are
represented in the forwarding and routing information as (64 +
Preflen).
12.2.7. Interface Attributes
The Interface Attributes sub-option provides neighbors with
forwarding information for the multilink conceptual sending algorithm
discussed in Section 14. Neighbors use the forwarding information to
selecting among potentially multiple candidate underlay interfaces
that can be used to forward carrier packets to the neighbor based on
factors such as traffic selectors and link metrics. Interface
Attributes further include link layer address information to be used
for either direct INET encapsulation for targets in the local SRT
segment or spanning tree forwarding for targets in remote SRT
segments.
OMNI nodes include Interface Attributes for some/all of a source or
target Client's underlay interfaces in NS/NA and uNA messages used to
publish Client information (see: [I-D.templin-intarea-aero]). At
most one Interface Attributes sub-option for each distinct ifIndex
may be included; if an IPv6 ND message includes multiple Interface
Attributes sub-options for the same ifIndex, the first is processed
and all others are ignored. OMNI nodes that receive NS/NA messages
can use all of the included Interface Attributes and/or Traffic
Selectors to formulate a map of the prospective source or target node
as well as to seed the information to be later populated in an AERO
Forwarding Parameters sub-option (see: Section 12.2.9).
OMNI Clients and Proxy/Servers also include Interface Attributes sub-
options in RS/RA messages used to initialize, discover and populate
routing and addressing information. Each RS message MUST contain
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exactly one Interface Attributes sub-option with an ifIndex
corresponding to the Client's underlay interface used to transmit the
message, and each RA message MUST echo the same Interface Attributes
sub-option with any (proxyed) information populated by the FHS Proxy/
Server to provide operational context.
When an FHS Proxy/Server receives an RS message destined to an
anycast L2 address, it MUST include an additional Interface
Attributes sub-option with ifIndex '0' that encodes its own unicast
L2 address relative to the Client's underlay interface in the
solicited RA response. Any additional Interface Attributes sub-
options that appear in RS/RA messages (i.e., besides those for the
Client's own ifIndex and ifIndex '0') are ignored.
The Interface Attributes sub-option is formatted as shown below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=6| Sub-length=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifProvider |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifMetric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifGroup |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRT | FMT | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ LHS Proxy/Server ULA/L2ADDR ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Traffic Selector Blocks ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
Figure 25: Interface Attributes
* Sub-Type is set to 6. Multiple instances are processed as
discussed above.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
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* Sub-Option Data contains an "Interface Attributes" option encoded
as follows:
- ifIndex is a 4-octet index value corresponding to a specific
underlay interface. Client OMNI interfaces MUST number each
distinct underlay interface with a non-zero ifIndex value
assigned by network management per [RFC2863] and include the
value in this field. The ifIndex value '0' denotes
"unspecified".
- ifType is a 4-octet type value corresponding to this underlay
interface. The value is coded per the 'IANAifType-MIB'
registry [http://www.iana.org].
- ifProvider is a 4-octet provider identifier corresponding to
this underlay interface. This document defines the single
provider identifier value '0' (undefined). Future documents
may define other values.
- ifMetric encodes a 4-octet interface metric. Lower values
indicate higher priorities, and the highest value indicates an
interface that should not be selected. The ifMetric setting
provides an instantaneous indication of the interface
bandwidth, link quality, signal strength, cost, etc.; hence,
its value may change in successive IPv6 ND messages.
- ifGroup is a 4-octet identifier for a Link Aggregation Group
(LAG) [IEEE802.1AX] corresponding to the underlay interface
identified by ifIndex. Interface attributes for ifIndex
members of the same group will encode the same value in
ifGroup. This document defines the single ifGroup value '0'
meaning "no group assigned". Future documents will specify the
setting of other values.
- SRT is a 1-octet Segment Routing Topology prefix length value
between 0 and 128 that determines the prefix length associated
with the LHS ULA.
- FMT - a 1-octet "Forward/Mode/Type" code interpreted as
follows:
o The most significant two bits (i.e., "FMT-Forward" and "FMT-
Mode") are interpreted in conjunction with one another.
When FMT-Forward is clear, the LHS Proxy/Server performs OAL
reassembly and decapsulation to obtain the original IP
packet/parcel before forwarding. If the FMT-Mode bit is
clear, the LHS Proxy/Server then forwards the original IP
packet/parcel at L3; otherwise, it invokes the OAL to re-
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encapsulate, re-fragment and sends the resulting carrier
packets to the Client via the selected underlay interface.
When FMT-Forward is set, the LHS Proxy/Server forwards
unsecured OAL fragments to the Client without reassembling,
while reassembling secured OAL fragments before re-
fragmenting and forwarding to the Client. If FMT-Mode is
clear, all carrier packets destined to the Client must
always be sent via the LHS Proxy/Server; otherwise the
Client is eligible for direct forwarding over the open INET
where it may be located behind one or more NATs.
o The value encoded in the least significant 6 bits (i.e.,
"FMT-Type") determines the type and length of the L2ADDR
field. The following values are currently defined:
+ 0 - L2ADDR is 4 octets in length and encodes an IPv4
address.
+ 1 - L2ADDR is 16 octets in length and encodes an IPv6
address.
+ 2 - L2ADDR is 6 octets in length and encodes an EUI-48
address [EUI].
+ 3 - L2ADDR is 8 octets in length and encodes an EUI-64
address [EUI].
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- LHS Proxy/Server ULA/L2ADDR - encodes the 15 least significant
octets of the Proxy/Server ULA followed by the L2ADDR field
formatted as above (note that the FMT code is replaced with the
value "fd" after processing to form a proper 16-octet ULA).
When SRT and ULA are both set to 0, the LHS Proxy/Server is
considered unspecified in this IPv6 ND message. FMT, SRT and
LHS together provide guidance for the OMNI interface forwarding
algorithm. Specifically, if LHS::/SRT is located in the local
OMNI link segment, then the source can address the target
Client either through its dependent Proxy/Server or through
direct encapsulation following NAT traversal according to FMT.
Otherwise, the target Client is located on a different SRT
segment and the path from the source must employ a combination
of route optimization and spanning tree hop traversals. L2ADDR
identifies the LHS Proxy/Server's INET-facing interface not
located behind NATs, therefore no UDP port number is included
since port number 8060 is used when the L2 encapsulation
includes a UDP header. Instead, L2ADDR includes only an L2
address with type and length determined by FMT-Type as
described above. When L2ADDR includes an IPv4 or IPv6 address,
it is recorded in network byte order in ones-compliment
"obfuscated" form per [RFC4380].
- Traffic Selector Blocks(s) - zero or more Traffic Selector
blocks follow, with their total length determined by the number
of octets remaining in the Interface Attributes sub-option
beyond the end of the LHS Proxy/Server information. Each
Traffic Selector block is formatted the same as specified in
Section 12.2.8 and processed consecutively, with its length
subtracted from the remaining length of the Interface
Attributes sub-option.
12.2.8. Traffic Selector
The Traffic Selector sub-option provides forwarding information for
the multilink conceptual sending algorithm discussed in Section 14.
The sub-option includes traffic selector information per [RFC6088] as
ancillary information for an Interface Attributes sub-option with the
same ifIndex value, or as discrete information for the included
ifIndex when no Interface Attributes sub-option is present.
IPv6 ND messages may include multiple Traffic Selectors for some or
all of the source/target Client's underlay interfaces (see:
[I-D.templin-intarea-aero] for further discussion). Traffic
Selectors must be honored by all implementations in the format shown
below:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=7| Sub-length=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TS Length | TS Format |A|B|C|D|E|F|G|H|I|J|K|L|M|N|RES|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (A)Start Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (B)End Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (C)Start Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (D)End Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (E)Start IPsec SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (F)End IPsec SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (G)Start Source port | (H)End Source port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (I)Start Destination port | (J)End Destination port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (K)Start DS | (L)End DS |(M)Start Prot. | (N) End Prot. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Additional Traffic Selector Blocks ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
Figure 26: Traffic Selector
* Sub-Type is set to 7. Multiple instances with the same or
different ifIndex values may appear in the same IPv6 ND message.
When multiple instances appear, all are processed and the
cumulative information from all is accepted.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
* Sub-Option data begins with a 4-octet ifIndex value corresponding
to a specific underlay interface.
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* The remainder of Sub-Option Data contains one or more "Traffic
Selector" blocks for this ifIndex that each begin with 1-octet "TS
Length" and "TS Format" fields. TS length encodes the combined
lengths of the TS* fields plus the Traffic Selector body that
follows (i.e. a value between 2-255 octets). When TS Format
encodes the value 1 or 2, the Traffic Selector body encodes an
IPv4 or IPv6 traffic selector per [RFC6088] beginning with 16 flag
bits ("A-N" plus 2 "Reserved"); when TS Format encodes any other
value the Traffic Selector block is skipped and processing resumes
beginning with the next Traffic Selector block (if any). The
Traffic Selector block elements then appear immediately after the
flags (with no 16-bit Reserved field included) and encode the
information corresponding to any set flag bit(s) in order the same
as specified in [RFC6088]. Each included Traffic Selector block
is processed consecutively, with its length subtracted from the
remaining sub-option length until all blocks are processed. If
the length of any Traffic Selector block would exceed the
remaining length for the entire sub-option, the remainder of the
sub-option is ignored.
12.2.9. AERO Forwarding Parameters
OMNI nodes include the AERO Forwarding Parameters sub-option in NS/NA
messages used to coordinate with multilink route optimization
targets. If an NS/NA message includes the sub-option in a manner
that solicits a response, the NA response must also include the sub-
option. Each NS/NA message may contain at most one AERO Forwarding
Parameters sub-option; if an NS/NA message contains additional AERO
Forwarding Parameters sub-options, the first is processed and all
others are ignored.
When an NS/NA message includes an AERO Forwarding Parameters sub-
option with Job code '00' (see below), the FHS Client Interface
Attributes MUST correspond to the underlay interface used to transmit
the solicitation message. When the NS/NA message also includes
Interface Attributes sub-options and/or Traffic Selectors, the
options must appear following the AERO Forwarding Parameters sub-
option.
The AERO Forwarding Parameters sub-option includes the necessary
state for establishing AERO Forwarding Vectors (AFVs) in the AERO
Forwarding Information Bases (AFIBs) of the OAL source, destination
and intermediate systems in the path. The sub-option also records
addressing information for FHS/LHS nodes on the path, including
"L2ADDRs" which MUST be unicast encapsulation addresses (i.e., and
not anycast/multicast). The manner for populating multilink
forwarding information is specified in detail in
[I-D.templin-intarea-aero].
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The AERO Forwarding Parameters sub-option is formatted as shown in
Figure 27:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=8| Sub-length=N | A | B |Job|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ AERO Forwarding Vector Index (AFVI) List ~
~ (5 consecutive 4-octet AFVIs) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FHS Client ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ FHS Proxy/Server FMT/ULA/L2ADDR ~
~ FHS Gateway FMT/ULA/L2ADDR ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LHS Client ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ LHS Proxy/Server FMT/ULA/L2ADDR ~
~ LHS Gateway FMT/ULA/L2ADDR ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 27: AERO Forwarding Parameters
* Sub-Type is set to 8. If multiple instances appear in OMNI
options of the same message the first instance is processed and
all others are ignored.
* Sub-Length encodes the number of Sub-Option Data octets that
follow. The length includes all fields up to and including the
AFVI List for all Job codes, while including the remaining FHS/LHS
fields only for Job codes "0" and "1" (see below).
* Sub-Option Data contains AERO Forwarding Parameters as follows:
- A/B and Job are fields that determine per-hop processing of the
AFVI List, where A is a 3-bit count of the number of "A" AFVI
List entries and B is a 3-bit count of the number of "B" AFVI
List entries (valid A/B values are 0-5). Job is a 2-bit code
interpreted as follows:
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o '00' - "Initialize; Build B" - the FHS source sets this code
in an NS/NA used to initialize AFV state. The FHS source
first sets A/B to 0, and the FHS source and each
intermediate system along the path to the LHS destination
that processes the message creates a new AFV. Each node
that processes the message then assigns a unique 4-octet "B"
AFVI to the AFV, writes the value into list entry B, then
finally increments B. When the message arrives at the LHS
destination, B will contain the number of AFVI List "B"
entries, with the FHS source entry first, followed by
entries for each consecutive intermediate system and ending
with an entry for the final intermediate system (i.e., the
list is populated in the forward direction). An NS/NA
message containing a Job Code '00' AERO Forwarding
Parameters sub-option always solicits a responsive NA
message containing Job Code '01'.
o '01' - "Follow B; Build A" - the LHS source sets this code
in a solicited NA response to an NS/NA with Job code "0".
The LHS source first copies the AFVI List and B value from
the code '00' solicitation into these fields and sets A to
0. The LHS source and each intermediate system along the
path to the FHS destination that processes the message then
uses AFVI List entry B to locate the corresponding AFV.
Each node that processes the message then assigns a unique
4-octet "A" AFVI to the AFV, writes the value into list
entry B, then finally increments A and decrements B. When
the message arrives at the FHS destination, A will contain
the number of AFVI List "A" entries, with the LHS source
entry last, preceded by entries for each consecutive
intermediate system and beginning with an entry for the
final intermediate system (i.e., the list is populated in
the reverse direction).
o '10' - "Follow A; Record B" - the FHS node that sent the
original code '00' solicitation and received the
corresponding code '01' advertisement sets this code in any
subsequent NS/NA messages sent to the same LHS destination.
The FHS source copies the AFVI List and A value from the
code '01' advertisement into these fields and sets B to 0.
The FHS source and each intermediate system along the path
to the LHS destination that processes the message then uses
the "A" AFVI found at list entry B to locate the
corresponding AFV. Each node that processes the message
then writes the AFV's "B" AFVI into list entry B, then
decrements A and increments B. When the message arrives at
the LHS destination, B will contain the number of AFVI List
"B" entries populated in the forward direction.
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o '11' - "Follow B; Record A" - the LHS node that received the
original code '00' solicitation and sent the corresponding
code '01' advertisement sets this code in any subsequent NS/
NA messages sent to the same FHS destination. The LHS
source copies the AFVI List and B values from the code '00'
solicitation into these fields and sets A to 0. The LHS
source and each intermediate system along the path to the
FHS destination that processes the message then uses the "B"
AFVI List entry found at list entry B to locate the
corresponding AFV. Each node that processes the message
then writes the AFV's "A" AFVI into list entry B, then
increments A and decrements B. When the message arrives at
the FHS destination, A will contain the number of AFVI List
"A" entries populated in the reverse direction.
Job and A/B together determine the per-hop behavior at each
FHS/LHS source, intermediate system and destination that
processes an IPv6 ND message. When a Job code specifies
"Initialize", each FHS/LHS node that processes the message
creates a new AFV. When a Job code specifies "Build", each
node that processes the message assigns a new AFVI. When a Job
code specifies "Follow", each node that processes the message
uses an A/B AFVI List entry to locate an AFV (if the AFV cannot
be located, the node returns a parameter problem and drops the
message). Using this algorithm, FHS sources that send code
'00' solicitations and receive code '01' advertisements
discover only "A" information, while LHS sources that receive
code '00' solicitations and return code '01' advertisements
discover only "B" information. FHS/LHS intermediate systems
can instead examine A, B and the AFVI List to determine the
number of previous hops, the number of remaining hops, and the
A/B AFVIs associated with the previous/remaining hops.
However, no intermediate systems will discover inappropriate A/
B AFVIs for their location in the multihop forwarding chain.
See: [I-D.templin-intarea-aero] for further discussion on A/B
AFVI processing.
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- AERO Forwarding Vector Index (AFVI) List is a 20-octet block
that contains 5 consecutive 4-octet AFVI entries. The FHS/LHS
source and each intermediate system on the path to the
destination processes the list according to the Job and A/B
codes (see above). Note that the reason the AFVI list contains
at most 5 entries is that only the FHS (Client, Proxy/Server,
Gateway) and LHS (Client, Proxy/Server, Gateway) nodes are
eligible for OMNI link route optimization resulting in at most
5 AFVIs "hops" that must be exposed. All other OMNI link nodes
(i.e., downstream Clients that connect via an FHS/LHS Client)
must forward through their upstream-dependent OMNI link
neighbors without applying OMNI link route optimization.
- For Job codes '00' and '01' only, trailing state variable
blocks are included for First-Hop Segment (FHS) followed by
Last-Hop Segment (LHS) network elements. When present, the
FHS/LHS blocks encode the following information:
o Client ifIndex encodes the 4-octet index for this Client
interface. The source sets the FHS/LHS ifIndex values
according to its own local interface information and
neighbor information discovered from earlier NS/NA address
resolution exchanges.
o Proxy/Server FMT/ULA/L2ADDR encodes a 1-octet FMT code
immediately followed by the 15 least significant octets of
the Proxy/Server ULA, where FMT/ULA are interpreted the same
as defined for the Interface Attribute sub-option in
Section 12.2.7 but with the FMT-Forward and FMT-Mode bits
set to 0 and ignored. FMT/ULA is then followed by a
16-octet L2ADDR that identifies an open INET interface not
located behind NATs, therefore no UDP port number is
included since port number 8060 is used when the L2
encapsulation includes a UDP header. Unlike the Interface
Attribute sub-option, L2ADDR is always exactly 16 octets in
length and interpreted according to FMT-Type with IPv4/EUI
addresses encoded as specified in Appendix B; this fixed
size supports efficient hop-by-hop sub-option processing
without requiring resizing to accommodate diverse L2ADDR
types. When L2ADDR includes an IPv4 or IPv6 address, it is
encoded in network byte order in ones-compliment
"obfuscated" form per [RFC4380].
o Gateway FMT/ULA/L2ADDR encodes a 1-octet FMT code followed
by the 15 least significant ULA octets followed by a
16-octet L2ADDR exactly as for the Proxy/Server FMT/ULA/
L2ADDR above.
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12.2.10. Geo Coordinates
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=9| Sub-length=N | Geo Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Geo Coordinates ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 28: Geo Coordinates
* Sub-Type is set to 9. If multiple instances appear in OMNI
options of the same message all are processed.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
* Geo Type is a 1-octet field that encodes a type designator that
determines the format and contents of the Geo Coordinates field
that follows. The following types are currently defined:
- 0 - NULL, i.e., the Geo Coordinates field is zero-length.
* Geo Coordinates is a type-specific format field of length up to
the remaining available space for this OMNI option. New formats
to be specified in future documents and may include attributes
such as latitude/longitude, altitude, heading, speed, etc.
12.2.11. Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Message
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) sub-option
may be included in the OMNI options of Client RS messages and Proxy/
Server RA messages.
FHS Proxy/Servers that forward RS/RA messages between a Client and an
LHS Proxy/Server also forward DHCPv6 sub-options unchanged. Note
that OMNI DHCPv6 messages do not include a Checksum field since
integrity is protected by the IPv6 ND message checksum,
authentication signature and/or link or physical layer authentication
and integrity checks.
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=10| Sub-length=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | transaction-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ DHCPv6 options ~
~ (variable number and length) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 29: DHCPv6 Message
* Sub-Type is set to 10. If multiple instances appear in OMNI
options of the same message the first is processed and all others
are ignored.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The 'msg-type' and 'transaction-id' fields
are always present; hence, the length of the DHCPv6 options is
limited by the remaining available space for this OMNI option.
* 'msg-type' and 'transaction-id' are coded according to Section 8
of [RFC8415].
* A set of DHCPv6 options coded according to Section 21 of [RFC8415]
follows.
12.2.12. PIM-SM Message
The Protocol Independent Multicast - Sparse Mode (PIM-SM) Message
sub-option may be included in the OMNI options of IPv6 ND messages.
PIM-SM messages are formatted as specified in Section 4.9 of
[RFC7761], with the exception that the Checksum field is omitted
since the IPv6 ND message is already protected by the IPv6 ND message
checksum, authentication signature and/or link or physical layer
authentication and integrity checks.
The PIM-SM message sub-option format is shown in Figure 30:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=11| Sub-length=N |PIM Ver| Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ PIM-SM Message ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 30: PIM-SM Message Option Format
* Sub-Type is set to 11. If multiple instances appear in OMNI
options of the same message all are processed.
* Sub-Length is set to N, i.e., the length of the option in octets
beginning immediately following the Sub-Length field and extending
to the end of the PIM-SM message. The length of the entire PIM-SM
message is therefore limited by the remaining available space for
this OMNI option.
* The PIM-SM message is coded exactly as specified in Section 4.9 of
[RFC7761], except that the Checksum field is omitted, and the
Reserved field is set to 0 on transmission and ignored on
reception. The "PIM Ver" field encodes the value 2, and the
"Type" field encodes the PIM message type. (See Section 4.9 of
[RFC7761] for a list of PIM-SM message types and formats.)
12.2.13. Host Identity Protocol (HIP) Message
The Host Identity Protocol (HIP) Message sub-option (when present)
provides an authentication service alternative for IPv6 ND messages
exchanged between Clients and FHS Proxy/Servers (or between Clients
and their peers) over an open Internetwork. When the HIP service is
used, FHS Proxy/Servers verify the HIP authentication signatures in
source Client IPv6 ND messages then remove the HIP message sub-option
and securely forward the ND messages to other OMNI nodes. LHS Proxy/
Servers that receive secured IPv6 ND messages from other OMNI nodes
that do not already include a security sub-option can insert HIP
authentication signatures before forwarding them to the target
Client.
OMNI interfaces that use the HIP service include the HIP message sub-
option when they forward IPv6 ND messages that require security over
INET underlay interfaces, i.e., where authentication and integrity is
not already assured by link/physical layers or other OMNI layer
services. The OMNI interface calculates the authentication signature
over the entire length of the OAL packet (or super-packet) beginning
after the IPv6 ND message header and extending over the remainder of
the OAL packet or super-packet. OMNI interfaces that process OAL
packets containing secured IPv6 ND messages verify the signature then
either process the rest of the message locally or forward a proxyed
copy to the next hop.
When an FHS Client inserts a HIP message sub-option in an IPv6 ND
message destined to a target in a remote spanning tree segment, it
must ensure that the insertion does not cause the message to exceed
the OMNI interface MTU. If the LHS Proxy/Server cannot create
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sufficient space through any means without causing the OMNI option to
exceed 2040 octets or causing the IPv6 ND message to exceed the OMNI
interface MTU, it returns a suitable error (see: Section 12.2.16) and
drops the message.
The HIP message sub-option is formatted as shown below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=12| Sub-length=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Packet Type |Version| RES.|1| Controls |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Sender's Host Identity Tag (HIT) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Receiver's Host Identity Tag (HIT) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ HIP Parameters ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 31: HIP Message
* Sub-Type is set to 12. If multiple instances appear in OMNI
options of the same message the first is processed and all others
are ignored.
* Sub-Length is set to N, i.e., the length of the option in octets
beginning immediately following the Sub-Length field and extending
to the end of the HIP parameters. The length of the entire HIP
message is therefore limited by the remaining available space for
this OMNI option.
* The HIP message is coded per Section 5 of [RFC7401], except that
the OMNI "Sub-Type" and "Sub-Length" fields replace the first 2
octets of the HIP message header (i.e., the Next Header and Header
Length fields). Also, since the IPv6 ND message is already
protected by its own checksum, the 2-octet HIP message Checksum
field is omitted.
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Note: In some environments, maintenance of a Host Identity Tag (HIT)
namespace may be unnecessary for securely associating an OMNI node
with an IPv6 address-based identity. In that case, IPv6 ULAs can be
used instead of HITs in the authentication signature as long as the
address can be uniquely associated with the Sender/Receiver.
12.2.14. QUIC-TLS Message
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=13| Sub-length=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ QUIC-TLS Message ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 32: QUIC-TLS Message
* Sub-Type is set to 13. If multiple instances appear in OMNI
options of the same IPv6 ND message, the first is processed and
all others are ignored.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
* The QUIC-TLS message [RFC9000][RFC9001][RFC9002] encodes the QUIC
and TLS message parameters necessary to support QUIC connection
establishment.
IPv6 ND messages serve as couriers to transport the QUIC and TLS
parameters necessary to establish a secured QUIC connection.
12.2.15. Fragmentation Report (FRAGREP)
Fragmentation Report (FRAGREP) sub-options may be included in the
OMNI options of uNA messages sent from an OAL destination to an OAL
source. The message consists of (N/16)-many (Identification,
Bitmap)-tuples which include the Identification values of OAL
fragments received plus a Bitmap marking the ordinal positions of
individual non-first fragments received and missing.
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=14| Sub-Length=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+- Identification (0) (64 bits) -+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+- Bitmap (0) (64 bits) -+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+- Identification (1) (64 bits) -+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+- Bitmap (1) (64 bits) -+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
Figure 33: Fragmentation Report (FRAGREP)
* Sub-Type is set to 14. If multiple instances appear in OMNI
options of the same message all are processed.
* Sub-Length is set to N which must be a multiple of 16, i.e., the
combined lengths of each (Identification, Bitmap) pair beginning
immediately following the Sub-Length field and extending to the
end of the sub-option.
* Identification(i) includes the 8-octet Identification value found
in a received OAL fragment.
* Bitmap(i) includes a 64-bit checklist of up to 64 ordinal
fragments for this Identification, with each bit set to 1 for a
fragment received or 0 for a fragment corrupted, lost or still in
transit. For example, for a 20-fragment OAL packet with ordinal
fragments #3, #10, #13 and #17 missing or corrupted and all other
fragments received or still in transit, Bitmap(i) encodes the
following:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|1|1|1|0|1|1|1|1|1|1|0|1|1|0|1|1|1|0|1|1|0|0|0|...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 34
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12.2.16. ICMPv6 Error
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=15| Sub-length=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ICMPv6 Error Message Body ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 35: ICMPv6 Error
* Sub-Type is set to 15. If multiple instances appear in OMNI
options of the same IPv6 ND message all are processed.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
* Sub-Option Data includes an N-octet ICMPv6 Error Message body
encoded exactly as per Section 2.1 of [RFC4443], i.e., with the
IPv6 header omitted. OMNI interfaces include as much of the
"packet in error" in the ICMPv6 error message body as possible
without causing the IPv6 ND message that includes the OMNI option
to exceed the IPv6 minimum MTU. While all ICMPv6 error message
types are supported, OAL destinations in particular often include
ICMPv6 PTB messages in uNA messages to provide MTU feedback
information via the OAL source (see: Section 6.9). Note: ICMPv6
informational messages must not be included and must be ignored if
received.
12.2.17. Proxy/Server Departure
OMNI Clients include a Proxy/Server Departure sub-option in RS
messages when they associate with a new FHS and/or Hub Proxy/Server
and need to send a departure indication to an old FHS and/or Hub
Proxy/Server. The Proxy/Server Departure sub-option is formatted as
shown below:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=16| Sub-length=32 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Old FHS Proxy/Server ULA (16 octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Old Hub Proxy/Server ULA (16 octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 36: Proxy/Server Departure
* Sub-Type is set to 16. If multiple instances appear in OMNI
options of the same message, the first is processed and all others
are ignored.
* Sub-Length is set to 32.
* Sub-Option Data contains the 16-octet ULA for the "Old FHS Proxy/
Server" followed by a 16-octet ULA for an "Old Hub Proxy/Server.
(If the Old FHS/Hub is a different node, the corresponding ULA
includes the address of the (foreign) Proxy/Server. If the Old
FHS/Hub is the local node, the corresponding ULA includes the
node's own address. If the FHS/Hub is unspecified, the
corresponding ULA instead includes the value 0.)
12.2.18. Sub-Type Extension
Since the Sub-Type field is only 5 bits in length, future
specifications of major protocol functions may exhaust the remaining
Sub-Type values available for assignment. This document therefore
defines Sub-Type 30 as an "extension", meaning that the actual sub-
option type is determined by examining a 1-octet "Extension-Type"
field immediately following the Sub-Length field. The Sub-Type
Extension is formatted as shown in Figure 37:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Extension-Type|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Extension-Type Body ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 37: Sub-Type Extension
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* Sub-Type is set to 30. If multiple instances appear in OMNI
options of the same message all are processed, where each
individual extension defines its own policy for processing
multiple of that type.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The Extension-Type field is always present,
and the maximum Extension-Type Body length is limited by the
remaining available space in this OMNI option.
* Extension-Type contains a 1-octet Sub-Type Extension value between
0 and 255.
* Extension-Type Body contains an (N-1)-octet block with format
defined by the given extension specification.
Extension-Type values 0 and 1 are defined in the following
subsections, while Extension-Type values 2 through 252 are available
for assignment by future specifications which must also define the
format of the Extension-Type Body and its processing rules.
Extension-Type values 253 and 254 are reserved for experimentation,
as recommended in [RFC3692], and value 255 is reserved by IANA.
12.2.18.1. RFC4380 Header Extension Option
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Ext-Type=0 | Header Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Header Option Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 38: RFC4380 Header Extension Option (Extension-Type 0)
* Sub-Type is set to 30.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The Extension-Type and Header Type fields are
always present, and the Header Option Value is limited by the
remaining available space in this OMNI option.
* Extension-Type is set to 0. Each instance encodes exactly one
header option per Section 5.1.1 of [RFC4380], with Ext-Type and
Header Type representing the first 2 octets of the option. If
multiple instances of the same Header Type appear in OMNI options
of the same message the first instance is processed and all others
are ignored.
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* Header Type and Header Option Value are coded exactly as specified
in Section 5.1.1 of [RFC4380]; the following types are currently
defined:
- 0 - Origin Indication (IPv4) - value coded as a UDP port number
followed by a 4-octet IPv4 address both in "obfuscated" form
per Section 5.1.1 of [RFC4380].
- 1 - Authentication Encapsulation - value coded per
Section 5.1.1 of [RFC4380].
- 2 - Origin Indication (IPv6) - value coded as a UDP port number
followed by an IP address both in "obfuscated" form per
Section 5.1.1 of [RFC4380], except that the IP address is a
16-octet IPv6 address instead of a 4-octet IPv4 address.
* Header Type values 3 through 252 are available for assignment by
future specifications, which must also define the format of the
Header Option Value and its processing rules. Header Type values
253 and 254 are reserved for experimentation, as recommended in
[RFC3692], and value 255 is reserved by IANA.
12.2.18.2. RFC6081 Trailer Extension Option
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Ext-Type=1 | Trailer Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Trailer Option Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 39: RFC6081 Trailer Extension Option (Extension-Type 1)
* Sub-Type is set to 30.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The Extension-Type and Trailer Type fields
are always present, and the maximum-length Trailer Option Value is
limited by the remaining available space in this OMNI option.
* Extension-Type is set to 1. Each instance encodes exactly one
trailer option per Section 4 of [RFC6081]. If multiple instances
of the same Trailer Type appear in OMNI options of the same
message the first instance is processed and all others ignored.
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* Trailer Type and Trailer Option Value are coded exactly as
specified in Section 4 of [RFC6081]; the following Trailer Types
are currently defined:
- 0 - Unassigned
- 1 - Nonce Trailer - value coded per Section 4.2 of [RFC6081].
- 2 - Unassigned
- 3 - Alternate Address Trailer (IPv4) - value coded per
Section 4.3 of [RFC6081].
- 4 - Neighbor Discovery Option Trailer - value coded per
Section 4.4 of [RFC6081].
- 5 - Random Port Trailer - value coded per Section 4.5 of
[RFC6081].
- 6 - Alternate Address Trailer (IPv6) - value coded per
Section 4.3 of [RFC6081], except that each address is a
16-octet IPv6 address instead of a 4-octet IPv4 address.
* Trailer Type values 7 through 252 are available for assignment by
future specifications, which must also define the format of the
Trailer Option Value and its processing rules. Trailer Type
values 253 and 254 are reserved for experimentation, as
recommended in [RFC3692], and value 255 is reserved by IANA.
13. Address Mapping - Multicast
The multicast address mapping of the native underlay interface
applies. The Client mobile router also serves as an IGMP/MLD Proxy
for its ENETs and/or hosted applications per [RFC4605].
The Client uses Multicast Listener Discovery (MLDv2) [RFC3810] to
coordinate with Proxy/Servers, and underlay network elements use MLD
snooping [RFC4541]. The Client can also employ multicast routing
protocols to coordinate with network-based multicast sources as
specified in [I-D.templin-intarea-aero].
Since the OMNI link model is NBMA, OMNI links support link-scoped
multicast through iterative unicast transmissions to individual
multicast group members (i.e., unicast/multicast emulation).
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14. Multilink Conceptual Sending Algorithm
The Client's network layer selects the outbound OMNI interface
according to SBM considerations when forwarding original IP packets/
parcels from local or ENET applications to external correspondents.
Each OMNI interface maintains an internal OAL neighbor cache
maintained the same as discussed in [RFC4861], but also includes
additional state for multilink coordination. Each Client OMNI
interface maintains default routes via Proxy/Servers discovered as
discussed in Section 15, and may configure more-specific routes
discovered through means outside the scope of this specification.
For each original IP packet/parcel it forwards, the OMNI interface
selects one or more source underlay interfaces based on PBM factors
(e.g., traffic attributes, cost, performance, message size, etc.) and
one or more target underlay interfaces for the neighbor based on
Interface Attributes received in IPv6 ND messages (see:
Section 12.2.7). Multilink forwarding may also direct carrier packet
replication across multiple underlay interface pairs for increased
reliability at the expense of duplication. The set of all Interface
Attributes and Traffic Selectors received in IPv6 ND messages
determines the multilink forwarding profile for selecting target
underlay interfaces.
When the OMNI interface forwards an original IP packet/parcel over a
selected source underlay interface, it first employs OAL
encapsulation and fragmentation as discussed in Section 5, then
performs L2 encapsulation as directed by the appropriate AFV. The
OMNI interface also performs L2 encapsulation (following OAL
encapsulation) when the nearest Proxy/Server is located multiple hops
away as discussed in Section 15.2.
OMNI interface multilink service designers MUST observe the BCP
guidance in Section 15 [RFC3819] in terms of implications for
reordering when original IP packets/parcels from the same flow may be
spread across multiple underlay interfaces having diverse properties.
14.1. Multiple OMNI Interfaces
Clients may connect to multiple independent OMNI links within the
same or different OMNI domains to support SBM. The Client configures
a separate OMNI interface for each link so that multiple interfaces
(e.g., omni0, omni1, omni2, etc.) are exposed to the network layer.
Each OMNI interface configures one or more OMNI anycast addresses
(see: Section 10), and the Client injects the corresponding anycast
prefixes into the ENET routing system. Multiple distinct OMNI links
can therefore be used to support fault tolerance, load balancing,
reliability, etc.
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Applications in ENETs can use Segment Routing to select the desired
OMNI interface based on SBM considerations. The application writes
an OMNI anycast address into the original IP packet/parcel's
destination address, and writes the actual destination (along with
any additional intermediate hops) into the Segment Routing Header.
Standard IP routing directs the packet/parcel to the Client's mobile
router entity, where the anycast address identifies the correct OMNI
interface for next hop forwarding. When the Client receives the
packet/parcel, it replaces the IP destination address with the next
hop found in the Segment Routing Header and forwards the message via
the OMNI interface identified by the anycast address.
Note: The Client need not configure its OMNI interface indexes in
one-to-one correspondence with the global OMNI Link-IDs configured
for OMNI domain administration since the Client's indexes (i.e.,
omni0, omni1, omni2, etc.) are used only for its own local interface
management.
14.2. Client-Proxy/Server Loop Prevention
After a Proxy/Server has registered an MNP for a Client (see:
Section 15), the Proxy/Server will forward all original IP packets/
parcels (or carrier packets) destined to an address within the MNP to
the Client. The Client will under normal circumstances then forward
the resulting original IP packet/parcel to the correct destination
within its connected (downstream) ENETs.
If at some later time the Client loses state (e.g., after a reboot),
it may begin returning original IP packets/parcels (or carrier
packets) with destinations corresponding to its MNP to the Proxy/
Server as its default router. The Proxy/Server therefore drops any
original IP packets/parcels received from the Client with a
destination address that corresponds to the Client's MNP (i.e.,
whether ULA or GUA), and drops any carrier packets with both source
and destination address corresponding to the same Client's MNP
regardless of their origin.
15. Router Discovery and Prefix Registration
Clients engage the MS by sending RS messages with OMNI options under
the assumption that one or more Proxy/Server will process the message
and respond. The RS message is received by a FHS Proxy/Server, which
may in turn forward a proxyed copy of the RS to a Hub Proxy/Server
located on the same or different SRT segment. The Hub Proxy/Server
then returns an RA message either directly to the Client or via an
FHS Proxy/Server acting as a proxy.
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To support Client to service coordination, OMNI defines three flag
bits in the OMNI Neighbor Coordination sub-option discussed in
Figure 24. Clients set or clear the NUD, ARR and/or RPT flags in RS
messages as directives to the Mobility Service FHS and Hub Proxy/
Servers. Proxy/Servers interpret the flags as follows:
* When an FHS Proxy/Server forwards or processes an RS with the NUD
flag set, it responds directly to future NS Neighbor
Unreachability Detection (NUD) messages with the Client as the
target by returning NA(NUD) replies; otherwise, it forwards
NS(NUD) messages to the Client.
* When the Hub Proxy/Server receives an RS with the ARR flag set, it
responds directly to future NS Address Resolution (AR) messages
with the Client as the target by returning NA(AR) replies;
otherwise, it forwards NS(AR) messages to the Client.
* When the Hub Proxy/Server receives an RS with the RPT flag set, it
maintains a Report List of recent NS(AR) message sources for the
source or target Client and sends uNA messages to all list members
if any aspects of the Client's underlay interfaces change.
Mobility Service Proxy/Servers function according to the NUD, ARR and
RPT flag settings received in the most recent RS message to support
dynamic Client updates.
Clients and FHS Proxy/Servers include an authentication signature in
their RS/RA exchanges when necessary but always include a valid IPv6
ND message checksum. FHS and Hub Proxy/Server RS/RA message
exchanges over the SRT secured spanning tree instead always include
the checksum and omit the authentication signature. Clients and
Proxy/Servers use the information included in RS/RA messages to
establish NCE state and OMNI link autoconfiguration information as
discussed in this section.
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For each underlay interface, the Client sends RS messages with OMNI
options to coordinate with a (potentially) different FHS Proxy/Server
for each interface but with a single Hub Proxy/Server. All Proxy/
Servers are identified by their ULA-RNDs and accept carrier packets
addressed to their anycast/unicast L2ADDRs; the Hub Proxy/Server may
be chosen among any of the Client's FHS Proxy/Servers or may be any
other Proxy/Server for the OMNI link. Example ULA/L2ADDR discovery
methods are given in [RFC5214] and include data link login
parameters, name service lookups, static configuration, a static
"hosts" file, etc. In the absence of other information, the Client
can resolve the DNS Fully-Qualified Domain Name (FQDN)
"linkupnetworks.[domainname]" where "linkupnetworks" is a constant
text string and "[domainname]" is a DNS suffix for the OMNI link
(e.g., "example.com"). The name resolution will return a set of DNS
resource records with the addresses of Proxy/Servers for the domain.
Each FHS Proxy/Server configures a ULA-RND based on a /64 ULA prefix
for the link/segment with randomly-generated Global ID to assure
global uniqueness then administratively assigned to FHS Proxy/Servers
for the link to assure global consistency. The Client can then
configure ULA-MNPs derived from the 64-bit ULA prefix assigned to a
FHS Proxy/Server for each underlay interface. The FHS Proxy/Servers
discovered over multiple of the Client's underlay interfaces may
configure the same or different ULA prefixes, and the Client's ULA-
MNP for each underlay interface will fall within the ULA (multilink)
subnet relative to each FHS Proxy/Server.
Clients configure OMNI interfaces that observe the properties
discussed in previous sections. The OMNI interface and its underlay
interfaces are said to be in either the "UP" or "DOWN" state
according to administrative actions in conjunction with the interface
connectivity status. An OMNI interface transitions to UP/DOWN
through administrative action and/or through underlay interface state
transitions. When a first underlay interface transitions to UP, the
OMNI interface also transitions to UP. When all underlay interfaces
transition to DOWN, the OMNI interface also transitions to DOWN.
When a Client OMNI interface transitions to UP, it sends RS messages
to register its MNP and an initial set of underlay interfaces that
are also UP. The Client sends additional RS messages to refresh
lifetimes and to register/deregister underlay interfaces as they
transition to UP or DOWN. The Client's OMNI interface sends initial
RS messages over an UP underlay interface with its XLA-MNP as the
source (or with a HHIT or TLA-RND as the source if it does not yet
have an MNP) and with destination set to link-scoped All-Routers
multicast or the ULA of a specific (Hub) Proxy/Server. The Client
sets or clears the RS NUD, ARR and RPT flags, then includes an OMNI
option per Section 12 with an OMNI Window Coordination sub-option, a
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Neighbor Control or DHCPv6 Solicit sub-option if necessary, an
Interface Attributes sub-option for the underlay interface, and with
any other necessary OMNI sub-options such as authentication, Proxy/
Server Departure, etc. The OMNI interface finally sets or clears the
Interface Attributes FMT-Forward and FMT-Mode bits according to the
behavior it would like to receive from the FHS Proxy/Server as
described in Section 12.2.7.
The Client then calculates the authentication signature checksum and
prepares to forward the RS over the underlay interface using OAL
encapsulation. The OMNI interface selects an Identification value
(see: Section 6.7), sets the OAL source address to the ULA-MNP
corresponding to the RS source if known (otherwise to an HHIT/TLA),
sets the OAL destination to an OMNI IPv6 anycast address or a known
Proxy/Server ULA, optionally includes a Nonce and/or Timestamp, then
performs OAL fragmentation if necessary. When L2 encapsulation is
used, the Client next includes the discovered FHS Proxy/Server L2ADDR
or an anycast address as the L2 destination then fragments if
necessary and forwards the resulting carrier packet(s) into the
underlay network. Note that the Client does not yet create a NCE,
but instead caches the Identification, Nonce and/or Timestamp values
included in its RS message transmissions to match against any
received RA messages.
When an FHS Proxy/Server receives the carrier packets containing an
RS it reassembles if necessary, sets aside the L2 headers, verifies
the Identifications, performs OAL reassembly if necessary, sets aside
the OAL header, then verifies the RS authentication signature/
checksum. The FHS Proxy/Server then creates/updates a NCE indexed by
the Client's RS source address and caches the OMNI Interface
Attributes and any Traffic Selector sub-options while also caching
the L2 (UDP/IP) and OAL source and destination address information.
The FHS Proxy/Server next caches the RS NUD flag and Window
Synchronization parameters (see: Section 12.1) then examines the RS
destination address.
If the destination matches its own ULA, the FHS Proxy/Server assumes
the Hub role and acts as the sole entry point for injecting the
Client's XLA-MNP into the OMNI link routing system (i.e., after
performing any necessary prefix delegation operations) while setting
the prefix to fd00::/64 and suffix to the 64-bit MNP, then including
a prefix length set to the MNP prefix length plus 64. (For example,
if the MNP prefix length is 48, the prefix length field encodes the
value 112.) The FHS/Hub Proxy/Server then caches the RS ARR and RPT
flags to determine its role in processing NS(AR) messages and
generating uNA messages (see: Section 12.1).
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The FHS/Hub Proxy/Server then prepares to return an RA message
directly to the Client by first populating the Cur Hop Limit, Flags,
Router Lifetime, Reachable Time and Retrans Timer fields with values
appropriate for the OMNI link. The FHS/Hub Proxy/Server next
includes as the first RA message option an OMNI option with a Window
Synchronization sub-option, an authentication sub-option if necessary
and a (proxyed) copy of the Client's original Interface Attributes
sub-option with its INET-facing interface information written in the
FMT, SRT and LHS Proxy/Server ULA/L2ADDR fields. The Proxy/Server
also sets or clears the FMT-Forward and FMT-Mode flags if necessary
to convey its capabilities to the Client, noting that it should honor
the Client's stated preferences for those parameters if possible or
override otherwise. The FMT-Forward/Mode flags thereafter remain
fixed unless and until a new RS/RA exchange produces different values
(see: Section 12.2.7 for further discussion). If the FHS/Hub Proxy/
Server's Client-facing interface is different than its INET-facing
interface, the Proxy/Server next includes a second Interface
Attributes sub-option with ifIndex set to '0' and with a unicast L2
address for its Client-facing interface in the L2ADDR field.
The FHS/Hub Proxy/Server next includes an Origin Indication sub-
option that includes the RS L2 source L2ADDR information (see:
Section 12.2.18.1), then includes any other necessary OMNI sub-
options (either within the same OMNI option or in additional OMNI
options). Following the OMNI option(s), the FHS/Hub Proxy/Server
next includes any other necessary RA options such as PIOs with (A=0;
L=0) that include the OMNI link MSPs [RFC8028], RIOs [RFC4191] with
more-specific routes, Nonce and Timestamp options, etc. The FHS/Hub
Proxy/Server then sets the RA source address to its own ULA and
destination address to the Client's ULA-MNP (i.e., relative to the
ULA /64 prefix for its Client-facing underlay interface) while also
recording the corresponding XLA-MNP as an (alternate) index to the
Client NCE, then calculates the authentication signature/checksum.
The FHS/Hub Proxy/Server finally performs OAL encapsulation while
setting the source to its own ULA and destination to the OAL source
that appeared in the RS, then includes an appropriate Identification,
performs OAL fragmentation, performs L2 encapsulation/fragmentation
with L2 source and destination address information reversed from the
RS L2 information and returns the resulting carrier packets to the
Client over the same underlay interface the RS arrived on.
When an FHS Proxy/Server receives an RS with a valid authentication
signature/checksum and with destination set to link-scoped All-
Routers multicast, it can either assume the Hub role itself the same
as above or act as a proxy and select the ULA of another Proxy/Server
to serve as the Hub. When an FHS Proxy/Server assumes the proxy role
or receives an RS with destination set to the ULA of another Proxy/
Server, it forwards the message while acting as a proxy. The FHS
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Proxy/Server creates or updates a NCE for the Client (i.e., based on
the RS source address) and caches the OAL source, Window
Synchronization, NUD flag, Interface Attributes addressing
information as above then writes its own INET-facing FMT, SRT and LHS
Proxy/Server ULA/L2ADDR information into the appropriate Interface
Attributes sub-option fields (while also setting/clearing FMT-Forward
and FMT-Type as above). The FHS Proxy/Server then calculates and
includes the checksum, performs OAL encapsulation while setting the
source to its own ULA and destination to the ULA of the Hub Proxy/
Server, includes an appropriate Identification, performs OAL
fragmentation, performs L2 encapsulation/fragmentation and sends the
resulting carrier packets into the SRT secured spanning tree.
When the Hub Proxy/Server receives the carrier packets, it performs
L2 reassembly/decapsulation, performs OAL reassembly/decapsulation to
obtain the proxyed RS, verifies checksums, then performs DHCPv6
Prefix Delegation (PD) to obtain the Client's MNP if the RS source is
not already MNP-based. The Hub Proxy/Server then creates/updates a
NCE for the Client's XLA-MNP and caches any state (including the ARR
and RPT flags, OAL addresses, Interface Attributes information and
Traffic Selectors), then finally performs routing protocol injection.
The Hub Proxy/Server then returns an RA that echoes the Client's
(proxyed) Interface Attributes sub-option and with any RA parameters
the same as specified for the FHS/Hub Proxy/Server case above. The
Hub Proxy/Server then sets the RA source address to its own ULA and
destination address to the RS source address; if the RS source
address is an HHIT/TLA, the Hub Proxy/Server also includes the MNP in
a DHCPv6 PD Reply OMNI sub-option. The Hub Proxy/Server next
calculates the checksum, then encapsulates the RA as an OAL packet
with source set to its own ULA and destination set to the ULA of the
FHS Proxy/Server that forwarded the RS. The Hub Proxy/Server finally
includes an appropriate Identification, performs OAL fragmentation
followed by L2 encapsulation/fragmentation and sends the resulting
carrier packets into the secured spanning tree.
When the FHS Proxy/Server receives the carrier packets it performs L2
reassembly/decapsulation followed by OAL reassembly/decapsulation to
obtain the RA message, verifies checksums then updates the OMNI
interface NCE for the Client and creates/updates a NCE for the Hub.
The FHS Proxy/Server then sets the P flag in the RA flags field
[RFC4389] and proxys the RA by changing the OAL source to its own
ULA, changing the OAL destination to the OAL address found in the
Client's NCE, and changing the RA destination address to the ULA-MNP
of the Client relative to its own /64 ULA prefix while also recording
the corresponding XLA-MNP as an alternate index into the Client NCE.
(If the RA destination address was an HHIT/TLA, the FHS Proxy Server
determines the MNP by consulting the DHCPv6 PD Reply message sub-
option.) The FHS Proxy/Server next includes Window Synchronization
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parameters responsive to those in the Client's RS, an Interface
Attributes sub-option with ifIndex '0' and with its Client-facing
interface unicast L2 address if necessary (see above), an Origin
Indication sub-option with the Client's cached L2ADDR and an
authentication sub-option if necessary. The FHS Proxy/Server finally
includes an Identification value per Section 6.7, calculates the
authentication signature/checksum, performs OAL fragmentation,
performs L2 encapsulation/fragmentation with addresses taken from the
Client's NCE and sends the resulting carrier packets via the same
underlay interface over which the RS was received.
When the Client receives the carrier packets, it performs L2
reassembly/decapsulation followed by OAL reassembly/decapsulation to
obtain the RA message. The Client next verifies the authentication
signature/checksum, then matches the RA message with its previously-
sent RS by comparing the RS Sequence Number with the RA
Acknowledgement Number and also comparing the Nonce and/or Timestamp
values if present. If the values match, the Client then creates/
updates OMNI interface NCEs for both the Hub and FHS Proxy/Server and
caches the information in the RA message. In particular, the Client
caches the RA source address as the Hub Proxy/Server ULA and uses the
OAL source address to configure both an underlay interface-specific
ULA for the Hub Proxy/Server and the ULA of this FHS Proxy/Server.
The Client then uses the ULA-MNP in the RA destination address to
configure its address within the ULA (multilink) subnet prefix of the
FHS Proxy/Server. If the Client has multiple underlay interfaces, it
creates additional FHS Proxy/Server NCEs and ULA-MNPs as necessary
when it receives RAs over those interfaces (noting that multiple of
the Client's underlay interfaces may be serviced by the same or
different FHS Proxy/Servers). The Client finally adds the Hub Proxy/
Server ULA to the default router list if necessary.
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For each underlay interface, the Client next caches the (filled-out)
Interface Attributes for its own ifIndex and Origin Indication
information that it received in an RA message over that interface so
that it can include them in future NS/NA messages to provide
neighbors with accurate FMT/SRT/LHS information. (If the message
includes an Interface Attributes sub-option with ifIndex '0', the
Client also caches the L2ADDR as the underlay network-local unicast
address of the FHS Proxy//Server via that underlay interface.) The
Client then compares the Origin Indication L2ADDR information with
its own underlay interface addresses to determine whether there may
be NATs on the path to the FHS Proxy/Server; if the L2ADDR
information differs, the Client is behind one or more NATs and must
supply the Origin information in IPv6 ND message exchanges with
prospective neighbors on the same SRT segment. The Client finally
configures default routes and assigns the OMNI Subnet Router Anycast
address corresponding to the MNP (e.g., 2001:db8:1:2::) to the OMNI
interface.
Following the initial exchange, the FHS Proxy/Server MAY later send
additional periodic and/or event-driven unsolicited RA messages per
[RFC4861]. (The unsolicited RAs may be initiated either by the FHS
Proxy/Server itself or by the Hub via the FHS as a proxy.) The
Client then continuously manages its underlay interfaces according to
their states as follows:
* When an underlay interface transitions to UP, the Client sends an
RS over the underlay interface with an OMNI option with sub-
options as specified above.
* When an underlay interface transitions to DOWN, the Client sends
unsolicited NA messages over any UP underlay interface with an
OMNI option containing Interface Attributes sub-options for the
DOWN underlay interface with ifMetric set to 'ffffffff'. The
Client sends isolated unsolicited NAs when reliability is not
thought to be a concern (e.g., if redundant transmissions are sent
on multiple underlay interfaces), or may instead set the SNR flag
in an OMNI Neighbor Control sub-option to trigger an unsolicited
NA reply (see: [I-D.templin-intarea-aero]).
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* When the Router Lifetime for the Hub Proxy/Server nears
expiration, the Client sends an RS over any underlay interface to
receive a fresh RA from the Hub. If no RA messages are received
over a first underlay interface (i.e., after retrying), the Client
marks the underlay interface as DOWN and should attempt to contact
the Hub Proxy/Server via a different underlay interface. If the
Hub Proxy/Server is unresponsive over additional underlay
interfaces, the Client sends an RS message with destination set to
the ULA of another Proxy/Server which will then assume the Hub
role.
* When all of a Client's underlay interfaces have transitioned to
DOWN (or if the prefix registration lifetime expires), the Hub
Proxy/Server withdraws the MNP the same as if it had received a
message with a release indication.
The Client is responsible for retrying each RS exchange up to
MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL
seconds until an RA is received. If no RA is received over an UP
underlay interface (i.e., even after attempting to contact alternate
Proxy/Servers), the Client declares this underlay interface as DOWN.
When changing to a new FHS or Hub Proxy/Server, the Client also
includes a Proxy/Server Departure OMNI sub-option in new RS messages;
the (new) FHS Proxy/Server will in turn send uNA messages to the old
FHS and/or Hub Proxy/Server to announce the Client's departure as
discussed in [I-D.templin-intarea-aero].
The network layer sees the OMNI interface as an ordinary IPv6
interface. Therefore, when the network layer sends an RS message the
OMNI interface returns an internally-generated RA message as though
the message originated from an IPv6 router. The internally-generated
RA message contains configuration information consistent with the
information received from the RAs generated by the Hub Proxy/Server.
Whether the OMNI interface IPv6 ND messaging process is initiated
from the receipt of an RS message from the network layer or
independently of the network layer is an implementation matter. Some
implementations may elect to defer the OMNI interface internal RS/RA
messaging process until an RS is received from the network layer,
while others may elect to initiate the process proactively. Still
other deployments may elect to administratively disable network layer
RS/RA messaging over the OMNI interface, since the messages are not
required to drive the OMNI interface internal RS/RA process. (Note
that this same logic applies to IPv4 implementations that employ
"ICMP Router Discovery" [RFC1256].)
Note: The Router Lifetime value in RA messages indicates the time
before which the Client must send another RS message over this
underlay interface (e.g., 600 seconds), however that timescale may be
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significantly longer than the lifetime the MS has committed to retain
the prefix registration (e.g., REACHABLE_TIME seconds). Proxy/
Servers are therefore responsible for keeping MS state alive on a
shorter timescale than the Client may be required to do on its own
behalf.
Note: On certain multicast-capable underlay interfaces, Clients
should send periodic unsolicited multicast NA messages and Proxy/
Servers should send periodic unsolicited multicast RA messages as
"beacons" that can be heard by other nodes on the link. If a node
fails to receive a beacon after a timeout value specific to the link,
it can initiate Neighbor Unreachability Detection (NUD) exchanges to
test reachability.
Note: If a single FHS Proxy/Server services multiple of a Client's
underlay interfaces, Window Synchronization will initially be
repeated for the RS/RA exchange over each underlay interface, i.e.,
until the Client discovers the many-to-one relationship. This will
naturally result in a single window synchronization that applies over
the Client's multiple underlay interfaces for the same FHS Proxy/
Server.
Note: Although the Client's FHS Proxy/Server is a first-hop segment
node from its own perspective, the Client stores the Proxy/Server's
FMT/SRT/ULA/L2ADDR as last-hop segment (LHS) information to supply to
neighbors. This allows both the Client and Hub Proxy/Server to
supply the information to neighbors that will perceive it as LHS
information on the return path to the Client.
Note: The Hub Proxy/Server injects Client XLA-MNP into the OMNI link
routing system by simply creating a route-to-interface forwarding
table entry for fd00::{MNP}/N via the OMNI interface. The dynamic
routing protocol will notice the new entry and propagate the route to
its peers. If the Hub receives additional RS messages, it need not
re-create the forwarding table entry (nor disturb the dynamic routing
protocol) if an entry is already present. If the Hub ceases to
receive RS messages from any of the Client's interfaces, it removes
the Client XLA-MNP from the forwarding table (i.e., after a short
delay) which also results in its removal from the routing system.
Note: If the Client's initial RS message includes an anycast L2
destination address, the FHS Proxy/Server returns the solicited RA
using the same anycast address as the L2 source while including an
Interface Attributes sub-option with ifIndex '0' and its true unicast
address in the L2ADDR. When the Client sends additional RS messages,
it includes this FHS Proxy/Server unicast address as the L2
destination and the FHS Proxy/Server returns the solicited RA using
the same unicast address as the L2 source. This will ensure that RS/
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RA exchanges are not impeded by any NATs on the path while avoiding
long-term exposure of messages that use an anycast address as the
source.
Note: The Origin Indication sub-option is included only by the FHS
Proxy/Server and not by the Hub (unless the Hub is also serving as an
FHS).
Note: Clients should set the NUD, ARR and RPT flags consistently in
successive RS messages and only change those settings when an FHS/Hub
Proxy/Server service profile update is necessary.
Note: Although the Client adds the Hub Proxy/Server ULA to the
default router list, it also caches the ULAs of the FHS Proxy/Servers
on the path to the Hub over each underlying interface. When the
Client needs to send an original IP packet/parcel to a default
router, it engages OAL encapsulation/fragmentation while using a
destination ULA corresponding to the selected interface which directs
the packet to an FHS Proxy/Server for that interface. The FHS Proxy/
Server then performs L2 encapsulation/fragmentation and sends the
resulting carrier packets without disturbing the Hub.
15.1. Window Synchronization
In environments where Identification window synchronization is
necessary, the RS/RA exchanges discussed above observe the principles
specified in Section 6.7. Window synchronization is conducted
between the Client and each FHS Proxy/Server used to contact the Hub
Proxy/Server, i.e., and not between the Client and the Hub. This is
due to the fact that the Hub Proxy/Server is responsible only for
forwarding control and data messages via the secured spanning tree to
FHS Proxy/Servers, and is not responsible for forwarding messages
directly to the Client under a synchronized window. Also, in the
reverse direction the FHS Proxy/Servers handle all default forwarding
actions without forwarding Client-initiated data to the Hub.
When a Client needs to perform window synchronization via a new FHS
Proxy/Server, it sets the RS source address to its own {TLA,XLA}-MNP
(or an HHIT/TLA) and destination address to the ULA of the Hub Proxy/
Server (or to All-Routers multicast in an initial RS), then sets the
SYN flag and includes an initial Sequence Number for Window
Synchronization. The Client then performs OAL encapsulation/
fragmentation using its own ULA-MNP (or the HHIT/TLA) as the source
and the ULA of the FHS Proxy/Server as the destination and includes
an Interface Attributes sub-option then performs L2 encapsulation/
fragmentation and sends the resulting carrier packets to the FHS
Proxy/Server. The FHS Proxy/Server then performs L2 and OAL
reassembly/decapsulation to extract the RS message and caches the
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Window Synchronization parameters then re-encapsulates/fragments with
its own ULA as the source and the ULA of the Hub Proxy/Server as the
target.
The FHS Proxy/Server then performs L2 encapsulation/fragmentation and
sends the resulting carrier packets via the secured spanning tree to
the Hub Proxy/Server, which updates the Client's Interface Attributes
and returns a unicast RA message with source set to its own ULA and
destination set to the RS source address and with the Client's
Interface Attributes echoed. The Hub Proxy/Server then performs OAL
encapsulation/fragmentation using its own ULA as the source and the
ULA of the FHS Proxy/Server as the destination, then performs L2
encapsulation/fragmentation and sends the carrier packets via the
secured spanning tree to the FHS Proxy/Server. The FHS Proxy/Server
then proxys the message as discussed in the previous section and
includes responsive Window Synchronization information. The FHS
Proxy/Server then forwards the message to the Client which updates
its window synchronization information for the FHS Proxy/Server as
necessary.
Following the initial RS/RA-driven window synchronization, the Client
can re-assert new windows with specific FHS Proxy/Servers by
performing NS/NA exchanges between its own XLA-MNPs and the ULAs of
the FHS Proxy/Servers without having to disturb the Hub.
15.2. Router Discovery in IP Multihop and IPv4-Only Networks
On some *NETs, a Client may be located multiple intermediate system
hops away from the nearest OMNI link Proxy/Server. Clients in
multihop networks perform route discovery through the application of
a routing protocol (e.g., a MANET/VANET routing protocol over
omnidirectional wireless interfaces, an inter-domain routing protocol
in an enterprise network, etc.) then apply corresponding forwarding
entries to the OMNI interface. Example routing protocols optimized
for MANET/VANET operations include OSPFv3 [RFC5340] with MANET
Designated Router (OSPF-MDR) extensions [RFC5614], OLSRv2 [RFC7181],
AODVv2 [I-D.perkins-manet-aodvv2] and others. Clients employ the
routing protocol according to the link model found in [RFC5889] and
subnet model articulated in [RFC5942]. For unique identification,
Clients use an HHIT/TLA as a Router ID or set an administrative value
that is managed for uniqueness within the MANET/VANET.
A Client located potentially multiple *NET hops away from the nearest
Proxy/Server prepares an RS message, sets the source address to its
XLA-MNP (or to its HHIT/TLA if it does not yet have an MNP), and sets
the destination to link-scoped All-Routers multicast or the unicast
ULA of a Proxy/Server the same as discussed above. The OMNI
interface then employs OAL encapsulation, sets the OAL source address
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to its HHIT/TLA and sets the OAL destination to an OMNI IPv6 anycast
address based on either a native IPv6 or IPv4-Compatible IPv6 prefix
(see: Section 10).
For IPv6-enabled *NETs where the underlay interface observes the
MANET properties discussed above, the Client injects the HHIT/TLA
into the IPv6 multihop routing system and forwards the message
without further encapsulation. Otherwise, the Client encapsulates
the message in UDP/IPv6 L2 headers, sets the source to the underlay
interface IPv6 address and sets the destination to the same OMNI IPv6
anycast address. The Client then forwards the message into the IPv6
multihop routing system which conveys it to the nearest Proxy/Server
that advertises a matching OMNI IPv6 anycast prefix. If the nearest
Proxy/Server is too busy, it should forward (without Proxying) the
OAL-encapsulated RS to another nearby Proxy/Server connected to the
same IPv6 (multihop) network that also advertises the matching OMNI
IPv6 anycast prefix.
For IPv4-only *NETs, the Client encapsulates the RS message in UDP/
IPv4 L2 headers, sets the source to the underlay interface IPv4
address and sets the destination to the OMNI IPv4 anycast address.
The Client then forwards the message into the IPv4 multihop routing
system which conveys it to the nearest Proxy/Server that advertises
the corresponding IPv4 prefix. If the nearest Proxy/Server is too
busy and/or does not configure the specified OMNI IPv6 anycast
address, it should forward (without Proxying) the OAL-encapsulated RS
to another nearby Proxy/Server connected to the same IPv4 (multihop)
network that configures the OMNI IPv6 anycast address. (In
environments where reciprocal RS forwarding cannot be supported, the
first Proxy/Server should instead return an RA based on its own
MSP(s).)
When a *NET intermediate system that participates in the routing
protocol receives the encapsulated RS, it forwards the message
according to its routing tables (note that an intermediate system
could be a fixed infrastructure element such as a roadside unit or
another MANET/VANET Client). This process repeats iteratively until
the RS message is received by a penultimate *NET hop within single-
hop communications range of a Proxy/Server, which forwards the
message to the Proxy/Server.
When a Proxy/Server that configures the OMNI IPv6 anycast OAL
destination receives the message, it decapsulates the RS and assumes
either the Hub or FHS role (in which case, it forwards the RS to a
candidate Hub). The Hub Proxy/Server then prepares an RA message
with source address set to its own ULA and destination address set to
the RS source address if it is acting only as the Hub (or to the
Client ULA-MNP within its ULA subnet prefix if it is also acting as
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the FHS Proxy/Server). The Hub Proxy/Server then performs OAL
encapsulation with the RA OAL source/destination set to the RS OAL
destination/source and forwards the RA either to the FHS Proxy/Server
or directly to the Client.
When the Hub or FHS Proxy/Server forwards the RA to the Client, it
encapsulates the message in L2 encapsulation headers (if necessary)
with (src, dst) set to the (dst, src) of the RS L2 encapsulation
headers. The Proxy/Server then forwards the message to a *NET node
within communications range, which forwards the message according to
its routing tables to an intermediate system. The multihop
forwarding process within the *NET continues repetitively until the
message is delivered to the original Client, which decapsulates the
message and performs autoconfiguration the same as if it had received
the RA directly from a Proxy/Server on the same physical link. The
Client then injects the ULA-MNP into the IPv6 multihop routing system
to advertise a unique address within the FHS Proxy/Server's
"Multilink Subnet".
Note: When the RS message includes anycast OAL and/or L2
encapsulation destinations, the FHS Proxy/Server must use the same
anycast addresses as the OAL and/or L2 encapsulation sources to
support forwarding of the RA message plus any initial data messages.
The FHS Proxy/Server then sends the resulting carrier packets over
any NATs on the path. When the Client receives the RA, it will
discover its unicast ULA-MNP and/or L2 encapsulation addresses and
can send future carrier packets using the unicast (instead of
anycast) addresses to populate NAT state in the forward path. (If
the Client does not have immediate data to send to the FHS Proxy/
Server, it can instead send an OAL "bubble" - see Section 6.11.)
After the Client begins using unicast OAL/L2 encapsulation addresses
in this way, the FHS Proxy/Server should also begin using the same
unicast addresses in the reverse direction.
Note: When an OMNI interface configures a HHIT/TLA, any nodes that
forward an encapsulated RS message with the HHIT/TLA as the OAL
source must not consider the message as being specific to a
particular OMNI link. HHITs/TLAs can therefore also serve as the
source and destination addresses of unencapsulated IPv6 data
communications within the local routing region, and if the HHIT/TLAs
are injected into the local network routing protocol their prefix
length must be set to 128.
Note: Each node normally conducts the multi-hop relaying between
intermediate forwarding systems using the same underlay interface in
both the inbound and outbound directions, i.e. as opposed to
different underlay interfaces. The final forwarding node within
range of a Proxy/Server could use the same or a different underlay
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interface to exchange carrier packets with the Proxy/Server, but may
not be well positioned to perform multilink selections over multiple
underlay interfaces on behalf of multihop dependent peers.
15.3. DHCPv6-based Prefix Registration
When a Client is not pre-provisioned with an MNP (or, when the Client
requires additional MNP delegations), it requests the MS to select
MNPs on its behalf and set up the correct routing state. The DHCPv6
service [RFC8415] supports this requirement.
When a Client requires the MS to select MNPs, it sends an RS message
with source set to an HHIT/TLA-RND. If the Client requires only a
single MNP delegation, it can then include an OMNI Node
Identification sub-option plus an OMNI Neighbor Control sub-option
with Preflen set to the length of the desired MNP. If the Client
requires multiple MNP delegations and/or more complex DHCPv6
services, it instead includes a DHCPv6 Message sub-option containing
a Client Identifier, one or more IA_PD options and a Rapid Commit
option then sets the 'msg-type' field to "Solicit", and includes a
3-octet 'transaction-id'. The Client then sets the RS destination to
link-scoped All-Routers multicast and sends the message using OAL
encapsulation and fragmentation if necessary as discussed above.
When the Hub Proxy/Server receives the RS message, it performs OAL
reassembly if necessary. Next, if the RS source is an HHIT/TLA-RND
and/or the OMNI option includes a DHCPv6 message sub-option, the Hub
Proxy/Server acts as a "Proxy DHCPv6 Client" in a message exchange
with the locally-resident DHCPv6 server. If the RS did not contain a
DHCPv6 message sub-option, the Hub Proxy/Server generates a DHCPv6
Solicit message on behalf of the Client using an IA_PD option with
the prefix length set to the OMNI Neighbor Control sub-option Preflen
value and with a Client Identifier formed from the OMNI option Node
Identification sub-option; otherwise, the Hub Proxy/Server uses the
DHCPv6 Solicit message contained in the OMNI option. The Hub Proxy/
Server then sends the DHCPv6 message to the DHCPv6 Server, which
delegates MNPs and returns a DHCPv6 Reply message with PD parameters.
(If the Hub Proxy/Server wishes to defer creation of Client state
until the DHCPv6 Reply is received, it can instead act as a
Lightweight DHCPv6 Relay Agent per [RFC6221] by encapsulating the
DHCPv6 message in a Relay-forward/reply exchange with Relay Message
and Interface ID options. In the process, the Hub Proxy/Server packs
any state information needed to return an RA to the Client in the
Relay-forward Interface ID option so that the information will be
echoed back in the Relay-reply.)
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When the Hub Proxy/Server receives the DHCPv6 Reply, it creates XLA-
MNPs based on the delegated MNPs and creates OMNI interface XLA-MNP
forwarding table entries (i.e., to prompt the dynamic routing
protocol). The Hub Proxy/Server then sends an RA back to the FHS
Proxy/Server with the DHCPv6 Reply message included in an OMNI DHCPv6
message sub-option. The Hub Proxy/Server sets the RA destination
address to the RS source address, sets the RA source address to its
own ULA, performs OAL encapsulation and fragmentation, performs L2
encapsulation and sends the RA to the Client via the FHS Proxy/Server
as discussed above.
When the FHS Proxy/Server receives the RA, it changes the RA
destination address to the ULA-MNP for the Client within its own ULA
subnet prefix, includes a Neighbor Control sub-option with Preflen
set to the length of the MNP, then forwards the RA to the Client.
When the Client receives the RA, it reassembles and discards the OAL
encapsulation then creates a default route, assigns Subnet Router
Anycast addresses and uses the RA destination address or
DHCPv6-delegated MNP to automatically configure its primary ULA-MNP.
The Client will then use these primary MNP-based addresses as the
source address of any IPv6 ND messages it sends as long as it retains
ownership of the MNP.
Note: when the Hub Proxy/Server is also the FHS Proxy/Server, it
forwards the RA message directly to the Client with the destination
set to the Client's ULA-MNP (i.e., instead of forwarding via another
Proxy/Server).
15.4. OMNI Link Extension
Clients can provide an OMNI link ingress point for other nodes on
their (downstream) ENETs that also act as Clients. When Client A has
already coordinated with an (upstream) ANET/INET Proxy/Server, Client
B on an ENET serviced by Client A can send OAL-encapsulated RS
messages with addresses set the same as specified in Section 15.2.
When Client A receives the RS message, it infers from the OAL
encapsulation that Client B is seeking to establish itself as a
Client instead of just a simple ENET Host.
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Client A then returns an RA message the same as a Proxy/Server would
do as specified in Section 15.2 except that it instead uses its own
ULA-MNP as the RA and OAL source addresses and performs (recursive)
DHCPv6 Prefix Delegation. The MNP delegation in the RA message must
be a sub-MNP from the MNP delegated to Client A. For example, if
Client A receives the MNP 2001:db8:1000::/48 it can provide a sub-
delegation such as 2001:db8:1000:2000::/56 to Client B. Client B can
in turn sub-delegate 2001:db8:1000:2000::/56 to its own ENET(s),
where there may be a further prospective Client C that would in turn
request OMNI link services via Client B.
To support this Client-to-Client chaining, Clients send IPv6 ND
messages addressed to the OMNI link anycast address via their ANET/
INET (i.e., upstream) interfaces, but advertise the OMNI link anycast
address into their ENET (i.e., downstream) networks where there may
be further prospective Clients wishing to join the chain. The ENET
of the upstream Client is therefore seen as an ANET by downstream
Clients, and the upstream Client is seen as a Proxy/Server by
downstream Clients.
16. Secure Redirection
If the underlay network link model is multiple access, the FHS Proxy/
Server is responsible for assuring that address duplication cannot
corrupt the neighbor caches of other nodes on the link. When the
Client sends an RS message on a multiple access underlay network, the
Proxy/Server verifies that the Client is authorized to use the
address and responds with an RA (or forwards the RS to the Hub) only
if the Client is authorized.
After verifying Client authorization and returning an RA, the Proxy/
Server MAY return IPv6 ND Redirect messages to direct Clients located
on the same underlay network to exchange OAL packets directly without
transiting the Proxy/Server. In that case, the Clients can exchange
OAL packets according to their unicast L2 addresses discovered from
the Redirect message instead of using the dogleg path through the
Proxy/Server. In some underlay networks, however, such direct
communications may be undesirable and continued use of the dogleg
path through the Proxy/Server may provide better performance. In
that case, the Proxy/Server can refrain from sending Redirects, and/
or Clients can ignore them.
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17. Proxy/Server Resilience
*NETs SHOULD deploy Proxy/Servers in Virtual Router Redundancy
Protocol (VRRP) [RFC5798] configurations so that service continuity
is maintained even if one or more Proxy/Servers fail. Using VRRP,
the Client is unaware which of the (redundant) FHS Proxy/Servers is
currently providing service, and any service discontinuity will be
limited to the failover time supported by VRRP. Widely deployed
public domain implementations of VRRP are available.
Proxy/Servers SHOULD use high availability clustering services so
that multiple redundant systems can provide coordinated response to
failures. As with VRRP, widely deployed public domain
implementations of high availability clustering services are
available. Note that special-purpose and expensive dedicated
hardware is not necessary, and public domain implementations can be
used even between lightweight virtual machines in cloud deployments.
18. Detecting and Responding to Proxy/Server Failures
In environments where fast recovery from Proxy/Server failure is
required, FHS Proxy/Servers SHOULD use proactive Neighbor
Unreachability Detection (NUD) in a manner that parallels
Bidirectional Forwarding Detection (BFD) [RFC5880] to track Hub
Proxy/Server reachability. FHS Proxy/Servers can then quickly detect
and react to failures so that cached information is re-established
through alternate paths. Proactive NUD control messaging is carried
only over well-connected ground domain networks (i.e., and not low-
end links such as aeronautical radios) and can therefore be tuned for
rapid response.
FHS Proxy/Servers perform proactive NUD for Hub Proxy/Servers for
which there are currently active Clients. If a Hub Proxy/Server
fails, the FHS Proxy/Server can quickly inform Clients of the outage
by sending multicast RA messages. The FHS Proxy/Server sends RA
messages to Clients with source set to the ULA of the Hub, with
destination address set to All-Nodes multicast (ff02::1) [RFC4291]
and with Router Lifetime set to 0.
The FHS Proxy/Server SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA
messages separated by small delays [RFC4861]. Any Clients that have
been using the (now defunct) Hub Proxy/Server will receive the RA
messages.
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19. Transition Considerations
When a Client connects to an *NET link for the first time, it sends
an RS message with an OMNI option. If the first hop router
recognizes the option, it responds according to the appropriate FHS/
Hub Proxy/Server role resulting in an RA message with an OMNI option
returned to the Client. The Client then engages this FHS Proxy/Sever
according to the OMNI link model specified above. If the first hop
router is a legacy IPv6 router, however, it instead returns an RA
message with no OMNI option and with a non-OMNI unicast source LLA as
specified in [RFC4861]. In that case, the Client engages the *NET
according to the legacy IPv6 link model and without the OMNI
extensions specified in this document.
If the *NET link model is multiple access, there must be assurance
that address duplication cannot corrupt the neighbor caches of other
nodes on the link. When the Client sends an RS message on a multiple
access *NET link with an OMNI option, first hop routers that
recognize the option ensure that the Client is authorized to use the
address and return an RA with a non-zero Router Lifetime only if the
Client is authorized. First hop routers that do not recognize the
OMNI option instead return an RA that makes no statement about the
Client's authorization to use the source address. In that case, the
Client should perform Duplicate Address Detection to ensure that it
does not interfere with other nodes on the link.
An alternative approach for multiple access *NET links to ensure
isolation for Client-Proxy/Server communications is through link
layer address mappings as discussed in Appendix E. This arrangement
imparts a (virtual) point-to-point link model over the (physical)
multiple access link.
20. OMNI Interfaces on Open Internetworks
Client OMNI interfaces configured over IPv6-enabled underlay
interfaces on an open Internetwork without an OMNI-aware first-hop
router receive IPv6 RA messages with no OMNI options, while OMNI
interfaces configured over IPv4-only underlay interfaces receive no
IPv6 RA messages at all (but may receive IPv4 RA messages per
[RFC1256]). Client OMNI interfaces that receive RA messages with
OMNI options configure addresses, on-link prefixes, etc. on the
underlay interface that received the RA according to standard IPv6 ND
and address resolution conventions [RFC4861] [RFC4862]. Client OMNI
interfaces configured over IPv4-only underlay interfaces configure
IPv4 address information on the underlay interfaces using mechanisms
such as DHCPv4 [RFC2131].
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Client OMNI interfaces configured over underlay interfaces connected
to open Internetworks can apply lower layer security services such as
VPNs (e.g., IPsec tunnels) to connect to a Proxy/Server, or can
establish a secured direct point-to-point link to the Proxy/Server
through some other means (see Section 4). In environments where
lower layer security may be impractical or undesirable, Client OMNI
interfaces can instead send IPv6 ND messages with OMNI options that
include authentication signatures.
OMNI interfaces use UDP/IP as L2 encapsulation headers for
transmission over open Internetworks with UDP service port number
8060 for both IPv4 and IPv6 underlay interfaces. The OMNI interface
submits original IP packets/parcels for OAL encapsulation, then
encapsulates the resulting OAL fragments in UDP/IP L2 headers to form
carrier packets. (The first four bits following the UDP header
determine whether the OAL headers are uncompressed/compressed as
discussed in Section 6.5.) The OMNI interface sets the UDP length to
the encapsulated OAL fragment length and sets the IP length to an
appropriate value at least as large as the UDP datagram.
When necessary, sources include an OMNI option with an authentication
sub-option in IPv6 ND messages. The source can employ a simple
Hashed Message Authentication Code (HMAC) as specified in
[RFC2104][RFC6234] or a message-based authentication service such as
HIP [RFC7401], QUIC-TLS [RFC9000][RFC9001], etc., using the IPv6 ND
message OMNI option as a "shipping container". Before calculating
the authentication signature, the source fully populates any
necessary OMNI sub-options as well as any ordinary IPv6 ND options as
necessary.
The source then sets both the IPv6 ND message Checksum and
authentication signature fields to 0 and calculates the
authentication signature over the full length of the IPv6 ND message
beginning after the IPv6 ND message checksum field and extending over
the length of the message. (If the IPv6 ND message is part of an OAL
super-packet, the source instead continues to calculate the
authentication signature over the entire length of the super-packet.)
The source next writes the authentication signature into the
appropriate sub-option field and forwards the message.
After establishing a secured underlay link or preparing for UDP/IP
encapsulation, OMNI interfaces send RS/RA messages for Client-Proxy/
Server coordination (see: Section 15) and NS/NA messages for
multilink forwarding, route optimization, window synchronization and
mobility management (see: [I-D.templin-intarea-aero]). These control
plane messages must be authenticated while other control and data
plane messages are delivered the same as for ordinary best effort
traffic with source address and/or Identification window-based data
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origin verification. Transport and higher layer protocol sessions
over OMNI interfaces that connect over open Internetworks without an
explicit underlay link security services should therefore employ
security at their layers to ensure authentication, integrity and/or
confidentiality.
Clients should avoid using INET Proxy/Servers as general-purpose
routers for steady streams of carrier packets that do not require
authentication. Clients should therefore perform route optimization
to coordinate with other INET nodes that can provide forwarding
services (or preferably coordinate with peer Clients directly)
instead of burdening the Proxy/Server. Procedures for coordinating
with peer Clients and discovering INET nodes that can provide better
forwarding services are discussed in [I-D.templin-intarea-aero].
Clients that attempt to contact peers over INET underlay interfaces
often encounter NATs in the path. OMNI interfaces accommodate NAT
traversal using UDP/IP encapsulation and the mechanisms discussed in
[I-D.templin-intarea-aero]. FHS Proxy/Servers include Origin
Indications in RA messages to allow Clients to detect the presence of
NATs.
Note: Following the initial IPv6 ND message exchange, OMNI interfaces
configured over INET underlay interfaces maintain neighbor
relationships by transmitting periodic IPv6 ND messages with OMNI
options that include authentication signatures. Other authentication
services that use their own IPv6 ND option types such as [RFC3971]
and [RFC8928] can also be used in addition to any OMNI authentication
services.
Note: OMNI interfaces configured over INET underlay interfaces should
employ the Identification window synchronization mechanisms specified
in Section 6.7 in order to exclude spurious carrier packets that
might otherwise clutter the reassembly cache. This is especially
important in environments where carrier packet spoofing and/or
corruption is a threat.
Note: NATs may be present on the path from a Client to its FHS Proxy/
Server, but never on the path from the FHS Proxy/Server to the Hub
where only INET and/or spanning tree hops occur. Therefore, the FHS
Proxy/Server does not communicate Client origin information to the
Hub where it would serve no purpose.
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21. Time-Varying MNPs
In some use cases, it is desirable, beneficial and efficient for the
Client to receive a constant MNP that travels with the Client
wherever it moves. For example, this would allow air traffic
controllers to easily track aircraft, etc. In other cases, however
(e.g., intelligent transportation systems), the Client may be willing
to sacrifice a modicum of efficiency in order to have time-varying
MNPs that can be changed every so often to defeat adversarial
tracking.
The prefix delegation services discussed in Section 15.3 allows
Clients that desire time-varying MNPs to obtain short-lived prefixes
to send RS messages with an HHIT/TLA source address and/or with an
OMNI option with DHCPv6 Option sub-options. The Client would then be
obligated to renumber its internal networks whenever its MNP (and
therefore also its OMNI address) changes. This should not present a
challenge for Clients with automated network renumbering services,
but may disrupt persistent sessions that would prefer to use a
constant address.
22. (H)HITs and Temporary ULA (TLA)s
Clients that generate (H)HITs but do not have pre-assigned MNPs can
request MNP delegations by issuing IPv6 ND messages that use the
(H)HIT instead of a TLA. For example, when a Client creates an RS
message it can set the source to a (H)HIT and destination to link-
scoped All-Routers multicast. The IPv6 ND message includes an OMNI
option with a Node Identification sub-option, then encapsulates the
message in an IPv6 header with the (H)HIT as the source address. The
Client then sends the message as specified in Section 15.2.
When the Hub Proxy/Server receives the RS message, it notes that the
source was a (H)HIT, then invokes the DHCPv6 protocol to request an
MNP prefix delegation while using the (H)HIT (in the form of a DUID)
as the Client Identifier. The Hub Proxy/Server then prepares an RA
message with source address set to its own ULA and destination set to
the source of the RS message. The Hub Proxy/Server next includes an
OMNI option with a Node Identification sub-option and any DHCPv6
prefix delegation parameters. The Proxy/Server finally encapsulates
the RA in an OAL header with source address set to its own ULA and
destination set to the RS OAL source address, then returns the
encapsulated RA to the Client either directly or by way of the FHS
Proxy/Server as a proxy.
Clients can also use (H)HITs and/or TLAs for direct Client-to-Client
communications outside the context of any OMNI link supporting
infrastructure. When two Clients encounter one another they can use
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their (H)HITs and/or TLAs as original IPv6 packet/parcel source and
destination addresses to support direct communications. Clients can
also inject their (H)HITs and/or TLAs into an IPv6 multihop routing
protocol to enable multihop communications as discussed in
Section 15.2. Clients can further exchange other IPv6 ND messages
using their (H)HITs and/or TLAs as source and destination addresses.
Lastly, when Clients are within the coverage range of OMNI link
infrastructure a case could be made for injecting (H)HITs and/or TLAs
into the global MS routing system. For example, when the Client
sends an RS to an FHS Proxy/Server it could include a request to
inject the (H)HIT / TLA into the routing system instead of requesting
an MNP prefix delegation. This would potentially enable OMNI link-
wide communications using only (H)HITs or TLAs, and not MNPs. This
document notes the opportunity, but makes no recommendation.
23. Address Selection
Clients assign LLAs to the OMNI interface, but do not use LLAs as
IPv6 ND message source/destination addresses nor for addressing
ordinary original IP packets/parcels exchanged with OMNI link
neighbors.
Clients use ULA-MNPs as source/destination IPv6 addresses in the
encapsulation headers of OAL packets and use XLA-MNPs as the IPv6
source addresses of the IPv6 ND messages themselves. Clients use
TLAs when an MNP is not available, or as source/destination IPv6
addresses for communications within a MANET/VANET local area.
Clients can also use (H)HITs instead of TLAs for local communications
when operation outside the context of a specific ULA domain and/or
source address attestation is necessary.
Clients use MNP-based GUAs as original IP packet/parcel source and
destination addresses for communications with Internet destinations
when they are within range of OMNI link supporting infrastructure
that can inject the MNP into the routing system. Clients can also
use MNP-based GUAs within multihop routing regions that are currently
disconnected from infrastructure as long as the corresponding ULA-
MNPs have been injected into the routing system.
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Clients use anycast GUAs as OAL and/or L2 encapsulation destination
addresses for RS messages used to discover the nearest FHS Proxy/
Server. When the Proxy/Server returns a solicited RA, it must also
use the same anycast address as the RA OAL/L2 encapsulation source in
order to successfully traverse any NATs in the path. The Client
should then immediately transition to using the FHS Proxy/Server's
discovered unicast OAL/L2 address as the destination in order to
minimize dependence on the Proxy/Server's use of an anycast source
address.
24. Error Messages
An OAL destination or intermediate system may need to return
ICMPv6-like error messages (e.g., Destination Unreachable, Packet Too
Big, Time Exceeded, etc.) [RFC4443] to an OAL source. Since ICMPv6
error messages do not themselves include authentication codes, OAL
nodes can instead return error messages as an OMNI ICMPv6 Error sub-
option in a secured IPv6 ND uNA message.
25. IANA Considerations
The following IANA actions are requested in accordance with [RFC8126]
and [RFC8726]:
25.1. Protocol Numbers Registry
The IANA is instructed to allocate an Internet Protocol number TBD1
from the 'protocol numbers' registry for the Overlay Multilink
Network Interface (OMNI) protocol. Guidance is found in [RFC5237]
(registration procedure is IESG Approval or Standards Action).
25.2. IEEE 802 Numbers Registry
During final publication stages, the IESG will be requested to
procure an IEEE EtherType value TBD2 for OMNI according to the
statement found at https://www.ietf.org/about/groups/iesg/statements/
ethertypes/.
Following this procurement, the IANA is instructed to register the
value TBD2 in the 'ieee-802-numbers' registry for Overlay Multilink
Network Interface (OMNI) encapsulation on Ethernet networks.
Guidance is found in [RFC7042] (registration procedure is Expert
Review).
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25.3. IPv4 Special-Purpose Address Registry
The IANA is instructed to assign TBD3/N as an "OMNI IPv4 anycast"
address/prefix in the "IPv4 Special-Purpose Address" registry in a
similar fashion as for [RFC3068]. The IANA is requested to work with
the authors to obtain a TBD3/N public IPv4 prefix, whether through an
RIR allocation, a delegation from IANA's "IPv4 Recovered Address
Space" registry or through an unspecified third party donation.
25.4. IPv6 Neighbor Discovery Option Formats Registry
The IANA is instructed to allocate an official Type number TBD4 from
the "IPv6 Neighbor Discovery Option Formats" registry for the OMNI
option (registration procedure is RFC required).
25.5. Ethernet Numbers Registry
The IANA is instructed to allocate one Ethernet unicast address TBD5
(suggested value '00-52-14') in the 'ethernet-numbers' registry under
"IANA Unicast 48-bit MAC Addresses" (registration procedure is Expert
Review). The registration should appear as follows:
Addresses Usage Reference
--------- ----- ---------
00-52-14 Overlay Multilink Network (OMNI) Interface [RFCXXXX]
Figure 40: IANA Unicast 48-bit MAC Addresses
25.6. ICMPv6 Code Fields
The IANA is instructed to assign new Code values in the "ICMPv6 Code
Fields: Type 2 - Packet Too Big" table in the 'icmpv6-parameters'
registry (registration procedure is Standards Action or IESG
Approval). The registry entries should appear as follows:
Code Name Reference
--- ---- ---------
0 PTB Hard Error [RFC4443]
1 (suggested) PTB Soft Error (no loss) [RFCXXXX]
2 (suggested) PTB Soft Error (loss) [RFCXXXX]
Figure 41: ICMPv6 Code Fields: Type 2 - Packet Too Big Values
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25.7. ICMPv4 PTB Messages
The IANA is instructed to assign a new Type number TBD6 in the 'icmp-
parameters' registry "ICMP Type Numbers" table (registration
procedures IESG Approval or Standards Action). The entry should set
"Type" to TBD6, "Name" to "Packet Too Big (PTB)" and "Reference" to
[RFCXXXX] (i.e., this document).
The IANA is further instructed to create a new table titled: "Type
TBD6 - Packet Too Big (PTB)" in the 'icmp-parameters' Code tables,
with registration procedures IESG Approval or Standards Action. The
table should have the following initial format:
Code Name Reference
--- ---- ---------
0 Reserved [RFCXXXX]
1 (suggested) PTB Soft Error (no loss) [RFCXXXX]
2 (suggested) PTB Soft Error (loss) [RFCXXXX]
Figure 42: Type TBD6 - Packet Too Big (PTB)
25.8. OMNI Option Sub-Types (New Registry)
The OMNI option defines a 5-bit Sub-Type field, for which IANA is
instructed to create and maintain a new registry entitled "OMNI
Option Sub-Type Values". Initial values are given below
(registration procedure is RFC required):
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Value Sub-Type name Reference
----- ------------- ----------
0 Pad1 [RFCXXXX]
1 PadN [RFCXXXX]
2 Node Identification [RFCXXXX]
3 Authentication [RFCXXXX]
4 Window Synchronization [RFCXXXX]
5 Neighbor Control [RFCXXXX]
6 Interface Attributes [RFCXXXX]
7 Traffic Selector [RFCXXXX]
8 AERO Forwarding Parameters [RFCXXXX]
9 Geo Coordinates [RFCXXXX]
10 DHCPv6 Message [RFCXXXX]
11 PIM-SM Message [RFCXXXX]
12 HIP Message [RFCXXXX]
13 QUIC-TLS Message [RFCXXXX]
14 Fragmentation Report [RFCXXXX]
15 ICMPv6 Error [RFCXXXX]
16 Proxy/Server Departure [RFCXXXX]
17-29 Unassigned
30 Sub-Type Extension [RFCXXXX]
31 Reserved by IANA [RFCXXXX]
Figure 43: OMNI Option Sub-Type Values
25.9. OMNI Node Identification ID-Types (New Registry)
The OMNI Node Identification sub-option (see: Section 12.2.3)
contains an 8-bit ID-Type field, for which IANA is instructed to
create and maintain a new registry entitled "OMNI Node Identification
ID-Type Values". Initial values are given below (registration
procedure is RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 UUID [RFCXXXX]
1 HIT [RFCXXXX]
2 HHIT [RFCXXXX]
3 Network Access Identifier [RFCXXXX]
4 FQDN [RFCXXXX]
5 IPv6 Address [RFCXXXX]
6-252 Unassigned [RFCXXXX]
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 44: OMNI Node Identification ID-Type Values
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25.10. OMNI Geo Coordinates Types (New Registry)
The OMNI Geo Coordinates sub-option (see: Section 12.2.10) contains
an 8-bit Type field, for which IANA is instructed to create and
maintain a new registry entitled "OMNI Geo Coordinates Type Values".
Initial values are given below (registration procedure is RFC
required):
Value Sub-Type name Reference
----- ------------- ----------
0 NULL [RFCXXXX]
1-252 Unassigned [RFCXXXX]
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 45: OMNI Geo Coordinates Type
25.11. OMNI Option Sub-Type Extensions (New Registry)
The OMNI option defines an 8-bit Extension-Type field for Sub-Type 30
(Sub-Type Extension), for which IANA is instructed to create and
maintain a new registry entitled "OMNI Option Sub-Type Extension
Values". Initial values are given below (registration procedure is
RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 RFC4380 UDP/IP Header Option [RFCXXXX]
1 RFC6081 UDP/IP Trailer Option [RFCXXXX]
2-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 46: OMNI Option Sub-Type Extension Values
25.12. OMNI RFC4380 UDP/IP Header Option Types (New Registry)
The OMNI Sub-Type Extension "RFC4380 UDP/IP Header Option" defines an
8-bit Header Type field, for which IANA is instructed to create and
maintain a new registry entitled "OMNI RFC4380 UDP/IP Header Option".
Initial registry values are given below (registration procedure is
RFC required):
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Value Sub-Type name Reference
----- ------------- ----------
0 Origin Indication (IPv4) [RFC4380]
1 Authentication Encapsulation [RFC4380]
2 Origin Indication (IPv6) [RFCXXXX]
3-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 47: OMNI RFC4380 UDP/IP Header Option
25.13. OMNI RFC6081 UDP/IP Trailer Option Types (New Registry)
The OMNI Sub-Type Extension for "RFC6081 UDP/IP Trailer Option"
defines an 8-bit Trailer Type field, for which IANA is instructed to
create and maintain a new registry entitled "OMNI RFC6081 UDP/IP
Trailer Option". Initial registry values are given below
(registration procedure is RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 Unassigned
1 Nonce [RFC6081]
2 Unassigned
3 Alternate Address (IPv4) [RFC6081]
4 Neighbor Discovery Option [RFC6081]
5 Random Port [RFC6081]
6 Alternate Address (IPv6) [RFCXXXX]
7-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 48: OMNI RFC6081 Trailer Option
25.14. Additional Considerations
The IANA has assigned the UDP port number "8060" for an earlier
experimental version of AERO [RFC6706]. This document reclaims the
UDP port number "8060" for 'aero' as the service port for UDP/IP
encapsulation. (Note that, although [RFC6706] is not widely
implemented or deployed, any messages coded to that specification can
be easily distinguished and ignored since they include an invalid
ICMPv6 message type number '0'.) The IANA is therefore instructed to
update the reference for UDP port number "8060" from "RFC6706" to
"RFCXXXX" (i.e., this document) while retaining the existing name
'aero'.
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The IANA has assigned a 4-octet Private Enterprise Number (PEN) code
"45282" in the "enterprise-numbers" registry. This document is the
normative reference for using this code in DHCP Unique IDentifiers
based on Enterprise Numbers ("DUID-EN for OMNI Interfaces") (see:
Section 11). The IANA is therefore instructed to change the
enterprise designation for PEN code "45282" from "LinkUp Networks" to
"Overlay Multilink Network Interface (OMNI)".
The IANA has assigned the ifType code "301 - omni - Overlay Multilink
Network Interface (OMNI)" in accordance with Section 6 of [RFC8892].
The registration appears under the IANA "Structure of Management
Information (SMI) Numbers (MIB Module Registrations) - Interface
Types (ifType)" registry.
No further IANA actions are required.
26. Security Considerations
Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6
Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages
SHOULD include Nonce and Timestamp options [RFC3971] when transaction
confirmation and/or time synchronization is needed.
OMNI interfaces configured over secured ANET/ENET interfaces inherit
the physical and/or link layer security properties (i.e., "protected
spectrum") of the connected networks. OMNI interfaces configured
over open INET interfaces can use symmetric securing services such as
IPsec tunnels [RFC4301] or can by some other means establish a direct
point-to-point link secured at lower layers. When lower layer
security may be impractical or undesirable, however, control message
integrity and authorization services such as those specified in
[RFC7401], [RFC4380], [RFC6234], [RFC9000], etc. must be employed.
OMNI link mobility services MUST support strong network layer
authentication for control plane messages and forwarding path
integrity for data plane messages. In particular, the AERO service
[I-D.templin-intarea-aero] constructs a secured spanning tree with
Proxy/Servers as leaf nodes and secures the spanning tree links with
network layer security mechanisms such as IPsec [RFC4301] with IKEv2
[RFC7296]. (Note that direct point-to-point links secured at lower
layers can also be used instead of or in addition to network layer
security.) These network (and/or lower-layer) services together
provide connectionless integrity and data origin authentication with
optional protection against replays.
Control plane messages that affect the routing system must be
constrained to travel only over secured spanning tree paths and are
therefore protected by network (and/or lower-layer) security. Other
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control and data plane messages can travel over unsecured route
optimized paths that do not strictly follow the spanning tree,
therefore end-to-end sessions should employ transport or higher layer
security services (e.g., TLS/SSL [RFC8446], DTLS [RFC6347], etc.).
Additionally, the OAL Identification value can provide a first level
of data origin authentication to mitigate off-path spoofing.
Identity-based key verification infrastructure services such as iPSK
may be necessary for verifying the identities claimed by Clients.
This requirement should be harmonized with the manner in which
identifiers such as (H)HITs are attested in a given operational
environment.
Security considerations for specific access network interface types
are covered under the corresponding IP-over-(foo) specification
(e.g., [RFC2464], [RFC2492], etc.).
Security considerations for IPv6 fragmentation and reassembly are
discussed in Section 6.15. In environments where spoofing is
considered a threat, OMNI nodes SHOULD employ Identification window
synchronization and OAL destinations SHOULD configure an (end-system-
based) firewall.
27. Implementation Status
AERO/OMNI Release-3.2 was tagged on March 30, 2021, and is undergoing
internal testing. Additional internal releases expected within the
coming months, with first public release expected end of 1H2021.
Many AERO/OMNI functions are implemented and undergoing final
integration. OAL fragmentation/reassembly buffer management code has
been cleared for public release.
Implementation of AERO/OMNI functions specified in more recent
document versions is considered work in progress.
28. Document Updates
This document suggests that the following could be updated through
future IETF initiatives:
* [RFC1191]
* [RFC2675]
* [RFC4443]
* [RFC8200]
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* [RFC8201]
Updates can be through, e.g., standards action, the errata process,
etc. as appropriate.
29. Acknowledgements
The first version of this document was prepared per the consensus
decision at the 7th Conference of the International Civil Aviation
Organization (ICAO) Working Group-I Mobility Subgroup on March 22,
2019. Consensus to take the document forward to the IETF was reached
at the 9th Conference of the Mobility Subgroup on November 22, 2019.
Attendees and contributors included: Guray Acar, Danny Bharj,
Francois D´Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo,
Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu
Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg
Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane
Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman,
Fryderyk Wrobel and Dongsong Zeng.
The following individuals are acknowledged for their useful comments:
Amanda Baber, Scott Burleigh, Stuart Card, Donald Eastlake, Adrian
Farrel, Michael Matyas, Robert Moskowitz, Madhu Niraula, Greg
Saccone, Stephane Tamalet, Eliot Lear, Eduard Vasilenko, Eric Vyncke.
Pavel Drasil, Zdenek Jaron and Michal Skorepa are especially
recognized for their many helpful ideas and suggestions. Akash
Agarwal, Madhuri Madhava Badgandi, Sean Dickson, Don Dillenburg, Joe
Dudkowski, Vijayasarathy Rajagopalan, Ron Sackman, Bhargava Raman Sai
Prakash and Katherine Tran are acknowledged for their hard work on
the implementation and technical insights that led to improvements
for the spec.
Discussions on the IETF 6man and atn mailing lists during the fall of
2020 suggested additional points to consider. The authors gratefully
acknowledge the list members who contributed valuable insights
through those discussions. Eric Vyncke and Erik Kline were the
intarea ADs, while Bob Hinden and Ole Troan were the 6man WG chairs
at the time the document was developed; they are all gratefully
acknowledged for their many helpful insights. Many of the ideas in
this document have further built on IETF experiences beginning in the
1990s, with insights from colleagues including Ron Bonica, Brian
Carpenter, Ralph Droms, Tom Herbert, Bob Hinden, Christian Huitema,
Thomas Narten, Dave Thaler, Joe Touch, Pascal Thubert, and many
others who deserve recognition.
Early observations on IP fragmentation performance implications were
noted in the 1986 Digital Equipment Corporation (DEC) "qe reset"
investigation, where fragment bursts from NFS UDP traffic triggered
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hardware resets resulting in communication failures. Jeff Chase,
Fred Glover and Chet Juzsczak of the Ultrix Engineering Group led the
investigation, and determined that setting a smaller NFS mount block
size reduced the amount of fragmentation and suppressed the resets.
Early observations on L2 media MTU issues were noted in the 1988 DEC
FDDI investigation, where Raj Jain, KK Ramakrishnan and Kathy Wilde
represented architectural considerations for FDDI networking in
general including FDDI/Ethernet bridging. Jeff Mogul (who led the
IETF Path MTU Discovery working group) and other DEC colleagues who
supported these early investigations are also acknowledged.
Throughout the 1990's and into the 2000's, many colleagues supported
and encouraged continuation of the work. Beginning with the DEC
Project Sequoia effort at the University of California, Berkeley,
then moving to the DEC research lab offices in Palo Alto CA, then to
Sterling Software at the NASA Ames Research Center, then to SRI in
Menlo Park, CA, then to Nokia in Mountain View, CA and finally to the
Boeing Company in 2005 the work saw continuous advancement through
the encouragement of many. Those who offered their support and
encouragement are gratefully acknowledged.
This work is aligned with the NASA Safe Autonomous Systems Operation
(SASO) program under NASA contract number NNA16BD84C.
This work is aligned with the FAA as per the SE2025 contract number
DTFAWA-15-D-00030.
This work is aligned with the Boeing Information Technology (BIT)
Mobility Vision Lab (MVL) program.
Honoring life, liberty and the pursuit of happiness.
30. References
30.1. Normative References
[I-D.templin-6man-ipid-ext]
Templin, F., "IPv6 Extended Fragment Header", Work in
Progress, Internet-Draft, draft-templin-6man-ipid-ext-14,
1 February 2024, <https://datatracker.ietf.org/doc/html/
draft-templin-6man-ipid-ext-14>.
[I-D.templin-6man-parcels2]
Templin, F. L., "IPv6 Parcels and Advanced Jumbos (AJs)",
Work in Progress, Internet-Draft, draft-templin-6man-
parcels2-00, 16 February 2024,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
templin-6man-parcels2/>.
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[I-D.templin-intarea-parcels2]
Templin, F., "IPv4 Parcels and Advanced Jumbos (AJs)",
Work in Progress, Internet-Draft, draft-templin-intarea-
parcels2-00, 15 February 2024,
<https://datatracker.ietf.org/doc/html/draft-templin-
intarea-parcels2-00>.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
December 1998, <https://www.rfc-editor.org/info/rfc2473>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <https://www.rfc-editor.org/info/rfc4191>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
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[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont,
"Traffic Selectors for Flow Bindings", RFC 6088,
DOI 10.17487/RFC6088, January 2011,
<https://www.rfc-editor.org/info/rfc6088>.
[RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by
Hosts in a Multi-Prefix Network", RFC 8028,
DOI 10.17487/RFC8028, November 2016,
<https://www.rfc-editor.org/info/rfc8028>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
[RFC9268] Hinden, R. and G. Fairhurst, "IPv6 Minimum Path MTU Hop-
by-Hop Option", RFC 9268, DOI 10.17487/RFC9268, August
2022, <https://www.rfc-editor.org/info/rfc9268>.
[RFC9293] Eddy, W., Ed., "Transmission Control Protocol (TCP)",
STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022,
<https://www.rfc-editor.org/info/rfc9293>.
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30.2. Informative References
[ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground
Interface for Civil Aviation, IETF Liaison Statement
#1676, https://datatracker.ietf.org/liaison/1676/", 3
March 2020.
[ATN-IPS] "ICAO Document 9896 (Manual on the Aeronautical
Telecommunication Network (ATN) using Internet Protocol
Suite (IPS) Standards and Protocol), Draft Edition 3
(work-in-progress)", 10 December 2020.
[CKSUM] Stone, J., Greenwald, M., Partridge, C., and J. Hughes,
"Performance of Checksums and CRC's Over Real Data, IEEE/
ACM Transactions on Networking, Vol. 6, No. 5", October
1998.
[CRC] Jain, R., "Error Characteristics of Fiber Distributed Data
Interface (FDDI), IEEE Transactions on Communications",
August 1990.
[EUI] "IEEE Guidelines for Use of Extended Unique Identifier
(EUI), Organizationally Unique Identifier (OUI), and
Company ID, https://standards.ieee.org/wp-
content/uploads/import/documents/tutorials/eui.pdf", 3
August 2017.
[I-D.ietf-6man-comp-rtg-hdr]
Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L.
Jalil, "The IPv6 Compact Routing Header (CRH)", Work in
Progress, Internet-Draft, draft-ietf-6man-comp-rtg-hdr-03,
18 January 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-6man-comp-rtg-hdr-03>.
[I-D.ietf-6man-eh-limits]
Herbert, T., "Limits on Sending and Processing IPv6
Extension Headers", Work in Progress, Internet-Draft,
draft-ietf-6man-eh-limits-12, 18 December 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-6man-eh-
limits-12>.
[I-D.ietf-drip-rid]
Moskowitz, R., Card, S. W., Wiethuechter, A., and A.
Gurtov, "DRIP Entity Tag (DET) for Unmanned Aircraft
System Remote ID (UAS RID)", Work in Progress, Internet-
Draft, draft-ietf-drip-rid-37, 2 December 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-drip-
rid-37>.
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[I-D.ietf-intarea-tunnels]
Touch, J. D. and M. Townsley, "IP Tunnels in the Internet
Architecture", Work in Progress, Internet-Draft, draft-
ietf-intarea-tunnels-13, 26 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-intarea-
tunnels-13>.
[I-D.ietf-ipwave-vehicular-networking]
Jeong, J. P., "IPv6 Wireless Access in Vehicular
Environments (IPWAVE): Problem Statement and Use Cases",
Work in Progress, Internet-Draft, draft-ietf-ipwave-
vehicular-networking-30, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-ipwave-
vehicular-networking-30>.
[I-D.ietf-tsvwg-udp-options]
Touch, J. D., "Transport Options for UDP", Work in
Progress, Internet-Draft, draft-ietf-tsvwg-udp-options-28,
17 November 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-tsvwg-udp-options-28>.
[I-D.perkins-manet-aodvv2]
Perkins, C. E., Ratliff, S., Dowdell, J., Steenbrink, L.,
and V. Pritchard, "Ad Hoc On-demand Distance Vector
Version 2 (AODVv2) Routing", Work in Progress, Internet-
Draft, draft-perkins-manet-aodvv2-03, 28 February 2019,
<https://datatracker.ietf.org/doc/html/draft-perkins-
manet-aodvv2-03>.
[I-D.templin-intarea-aero]
Templin, F., "Automatic Extended Route Optimization
(AERO)", Work in Progress, Internet-Draft, draft-templin-
intarea-aero-66, 12 February 2024,
<https://datatracker.ietf.org/doc/html/draft-templin-
intarea-aero-66>.
[IEEE802.1AX]
"Institute of Electrical and Electronics Engineers, Link
Aggregation, IEEE Standard 802.1AX-2008,
https://standards.ieee.org/ieee/802.1AX/6768/", 29 May
2020.
[IPV4-GUA] Postel, J., "IPv4 Address Space Registry,
https://www.iana.org/assignments/ipv4-address-space/ipv4-
address-space.xhtml", 14 December 2020.
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[IPV6-GUA] Postel, J., "IPv6 Global Unicast Address Assignments,
https://www.iana.org/assignments/ipv6-unicast-address-
assignments/ipv6-unicast-address-assignments.xhtml", 14
December 2020.
[RFC0863] Postel, J., "Discard Protocol", STD 21, RFC 863,
DOI 10.17487/RFC0863, May 1983,
<https://www.rfc-editor.org/info/rfc863>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC1146] Zweig, J. and C. Partridge, "TCP alternate checksum
options", RFC 1146, DOI 10.17487/RFC1146, March 1990,
<https://www.rfc-editor.org/info/rfc1146>.
[RFC1149] Waitzman, D., "Standard for the transmission of IP
datagrams on avian carriers", RFC 1149,
DOI 10.17487/RFC1149, April 1990,
<https://www.rfc-editor.org/info/rfc1149>.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/info/rfc1191>.
[RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages",
RFC 1256, DOI 10.17487/RFC1256, September 1991,
<https://www.rfc-editor.org/info/rfc1256>.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/info/rfc2104>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
<https://www.rfc-editor.org/info/rfc2464>.
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[RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM
Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999,
<https://www.rfc-editor.org/info/rfc2492>.
[RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
RFC 2675, DOI 10.17487/RFC2675, August 1999,
<https://www.rfc-editor.org/info/rfc2675>.
[RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group
MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000,
<https://www.rfc-editor.org/info/rfc2863>.
[RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery",
RFC 2923, DOI 10.17487/RFC2923, September 2000,
<https://www.rfc-editor.org/info/rfc2923>.
[RFC2983] Black, D., "Differentiated Services and Tunnels",
RFC 2983, DOI 10.17487/RFC2983, October 2000,
<https://www.rfc-editor.org/info/rfc2983>.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, DOI 10.17487/RFC3056, February
2001, <https://www.rfc-editor.org/info/rfc3056>.
[RFC3068] Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
RFC 3068, DOI 10.17487/RFC3068, June 2001,
<https://www.rfc-editor.org/info/rfc3068>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330,
DOI 10.17487/RFC3330, September 2002,
<https://www.rfc-editor.org/info/rfc3330>.
[RFC3366] Fairhurst, G. and L. Wood, "Advice to link designers on
link Automatic Repeat reQuest (ARQ)", BCP 62, RFC 3366,
DOI 10.17487/RFC3366, August 2002,
<https://www.rfc-editor.org/info/rfc3366>.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692,
DOI 10.17487/RFC3692, January 2004,
<https://www.rfc-editor.org/info/rfc3692>.
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[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, DOI 10.17487/RFC3819, July 2004,
<https://www.rfc-editor.org/info/rfc3819>.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/info/rfc4122>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
DOI 10.17487/RFC4380, February 2006,
<https://www.rfc-editor.org/info/rfc4380>.
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
2006, <https://www.rfc-editor.org/info/rfc4389>.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
<https://www.rfc-editor.org/info/rfc4429>.
[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>.
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[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605,
August 2006, <https://www.rfc-editor.org/info/rfc4605>.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
<https://www.rfc-editor.org/info/rfc4821>.
[RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly
Errors at High Data Rates", RFC 4963,
DOI 10.17487/RFC4963, July 2007,
<https://www.rfc-editor.org/info/rfc4963>.
[RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
Chowdhury, K., and B. Patil, "Proxy Mobile IPv6",
RFC 5213, DOI 10.17487/RFC5213, August 2008,
<https://www.rfc-editor.org/info/rfc5213>.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
DOI 10.17487/RFC5214, March 2008,
<https://www.rfc-editor.org/info/rfc5214>.
[RFC5237] Arkko, J. and S. Bradner, "IANA Allocation Guidelines for
the Protocol Field", BCP 37, RFC 5237,
DOI 10.17487/RFC5237, February 2008,
<https://www.rfc-editor.org/info/rfc5237>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)",
RFC 5558, DOI 10.17487/RFC5558, February 2010,
<https://www.rfc-editor.org/info/rfc5558>.
[RFC5614] Ogier, R. and P. Spagnolo, "Mobile Ad Hoc Network (MANET)
Extension of OSPF Using Connected Dominating Set (CDS)
Flooding", RFC 5614, DOI 10.17487/RFC5614, August 2009,
<https://www.rfc-editor.org/info/rfc5614>.
[RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
Version 3 for IPv4 and IPv6", RFC 5798,
DOI 10.17487/RFC5798, March 2010,
<https://www.rfc-editor.org/info/rfc5798>.
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[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC5889] Baccelli, E., Ed. and M. Townsley, Ed., "IP Addressing
Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889,
September 2010, <https://www.rfc-editor.org/info/rfc5889>.
[RFC5942] Singh, H., Beebee, W., and E. Nordmark, "IPv6 Subnet
Model: The Relationship between Links and Subnet
Prefixes", RFC 5942, DOI 10.17487/RFC5942, July 2010,
<https://www.rfc-editor.org/info/rfc5942>.
[RFC6081] Thaler, D., "Teredo Extensions", RFC 6081,
DOI 10.17487/RFC6081, January 2011,
<https://www.rfc-editor.org/info/rfc6081>.
[RFC6214] Carpenter, B. and R. Hinden, "Adaptation of RFC 1149 for
IPv6", RFC 6214, DOI 10.17487/RFC6214, April 2011,
<https://www.rfc-editor.org/info/rfc6214>.
[RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A.
Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221,
DOI 10.17487/RFC6221, May 2011,
<https://www.rfc-editor.org/info/rfc6221>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>.
[RFC6247] Eggert, L., "Moving the Undeployed TCP Extensions RFC
1072, RFC 1106, RFC 1110, RFC 1145, RFC 1146, RFC 1379,
RFC 1644, and RFC 1693 to Historic Status", RFC 6247,
DOI 10.17487/RFC6247, May 2011,
<https://www.rfc-editor.org/info/rfc6247>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>.
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[RFC6495] Gagliano, R., Krishnan, S., and A. Kukec, "Subject Key
Identifier (SKI) SEcure Neighbor Discovery (SEND) Name
Type Fields", RFC 6495, DOI 10.17487/RFC6495, February
2012, <https://www.rfc-editor.org/info/rfc6495>.
[RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for
Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May
2012, <https://www.rfc-editor.org/info/rfc6543>.
[RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization
(AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012,
<https://www.rfc-editor.org/info/rfc6706>.
[RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
UDP Checksums for Tunneled Packets", RFC 6935,
DOI 10.17487/RFC6935, April 2013,
<https://www.rfc-editor.org/info/rfc6935>.
[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, DOI 10.17487/RFC6936, April 2013,
<https://www.rfc-editor.org/info/rfc6936>.
[RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation
with IPv6 Neighbor Discovery", RFC 6980,
DOI 10.17487/RFC6980, August 2013,
<https://www.rfc-editor.org/info/rfc6980>.
[RFC7042] Eastlake 3rd, D. and J. Abley, "IANA Considerations and
IETF Protocol and Documentation Usage for IEEE 802
Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042,
October 2013, <https://www.rfc-editor.org/info/rfc7042>.
[RFC7094] McPherson, D., Oran, D., Thaler, D., and E. Osterweil,
"Architectural Considerations of IP Anycast", RFC 7094,
DOI 10.17487/RFC7094, January 2014,
<https://www.rfc-editor.org/info/rfc7094>.
[RFC7181] Clausen, T., Dearlove, C., Jacquet, P., and U. Herberg,
"The Optimized Link State Routing Protocol Version 2",
RFC 7181, DOI 10.17487/RFC7181, April 2014,
<https://www.rfc-editor.org/info/rfc7181>.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<https://www.rfc-editor.org/info/rfc7217>.
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[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<https://www.rfc-editor.org/info/rfc7401>.
[RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S.,
Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit
Boundary in IPv6 Addressing", RFC 7421,
DOI 10.17487/RFC7421, January 2015,
<https://www.rfc-editor.org/info/rfc7421>.
[RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542,
DOI 10.17487/RFC7542, May 2015,
<https://www.rfc-editor.org/info/rfc7542>.
[RFC7739] Gont, F., "Security Implications of Predictable Fragment
Identification Values", RFC 7739, DOI 10.17487/RFC7739,
February 2016, <https://www.rfc-editor.org/info/rfc7739>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface
Support for IP Hosts with Multi-Access Support", RFC 7847,
DOI 10.17487/RFC7847, May 2016,
<https://www.rfc-editor.org/info/rfc7847>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
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[RFC8726] Farrel, A., "How Requests for IANA Action Will Be Handled
on the Independent Stream", RFC 8726,
DOI 10.17487/RFC8726, November 2020,
<https://www.rfc-editor.org/info/rfc8726>.
[RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet
Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
<https://www.rfc-editor.org/info/rfc8799>.
[RFC8892] Thaler, D. and D. Romascanu, "Guidelines and Registration
Procedures for Interface Types and Tunnel Types",
RFC 8892, DOI 10.17487/RFC8892, August 2020,
<https://www.rfc-editor.org/info/rfc8892>.
[RFC8899] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T.
Völker, "Packetization Layer Path MTU Discovery for
Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
September 2020, <https://www.rfc-editor.org/info/rfc8899>.
[RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
and F. Gont, "IP Fragmentation Considered Fragile",
BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,
<https://www.rfc-editor.org/info/rfc8900>.
[RFC8928] Thubert, P., Ed., Sarikaya, B., Sethi, M., and R. Struik,
"Address-Protected Neighbor Discovery for Low-Power and
Lossy Networks", RFC 8928, DOI 10.17487/RFC8928, November
2020, <https://www.rfc-editor.org/info/rfc8928>.
[RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves,
"Temporary Address Extensions for Stateless Address
Autoconfiguration in IPv6", RFC 8981,
DOI 10.17487/RFC8981, February 2021,
<https://www.rfc-editor.org/info/rfc8981>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[RFC9001] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
<https://www.rfc-editor.org/info/rfc9001>.
[RFC9002] Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
and Congestion Control", RFC 9002, DOI 10.17487/RFC9002,
May 2021, <https://www.rfc-editor.org/info/rfc9002>.
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Appendix A. IPv4 Fragmentation Checksum Algorithm
The IPv4 fragmentation checksum algorithm adopts the 8-bit Fletcher
algorithm specified in Appendix I of [RFC1146] as also analyzed in
[CKSUM]. [RFC6247] declared [RFC1146] historic for the reason that
the algorithms had never seen widespread use with TCP, however this
document adopts the 8-bit Fletcher algorithm for a different purpose.
Quoting from Appendix I of [RFC1146], the IPv4 Fragmentation Checksum
Algorithm proceeds as follows:
"The 8-bit Fletcher Checksum Algorithm is calculated over a
sequence of data octets (call them D[1] through D[N]) by
maintaining 2 unsigned 1's-complement 8-bit accumulators A and B
whose contents are initially zero, and performing the following
loop where i ranges from 1 to N:
A := A + D[i]
B := B + A
It can be shown that at the end of the loop A will contain the
8-bit 1's complement sum of all octets in the datagram, and that B
will contain (N)D[1] + (N-1)D[2] + ... + D[N]."
To calculate the IPv4 fragmentation checksum, the above algorithm is
applied over the N-octets of the L2-encapsulated OAL packet/fragment
body beginning immediately after the L2 encapsulation header(s).
Appendix B. IPv6 Compatible Addresses
Section 2.5.5.1 of [RFC4291] defines an "IPv4-Compatible IPv6
Address" with the following structure:
| 80 bits | 16 | 32 bits |
+--------------------------------------+----+---------------------+
|0000..............................0000|0000| IPv4 address |
+--------------------------------------+----+---------------------+
Figure 49: IPv4-Compatible IPv6 Address
Although [RFC4291] deprecates the address format from its former use
in IPv6 transition mechanisms, this document now assigns new uses and
therefore updates [RFC4291].
When an IPv4-Compatible IPv6 address appears in a packet sent over
the wire, the most significant 96 bits are 0 and the least
significant 32 bits include an IPv4 address as shown above.
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When the address format is used for temporary local address
conversions to IPv6, however, it can also be used to represent EUI-48
and EUI-64 addresses as shown below:
| 80 bits | 48 bits |
+--------------------------------------+--------------------------+
|0000..............................0000| EUI-48 address |
+--------------------------------------+--------------------------+
| 64 bits | 64 bits |
+--------------------------------+--------------------------------+
|0000........................0000| EUI-64 address |
+--------------------------------+--------------------------------+
Figure 50: EUI-[48/64] Compatible IPv6 Addresses
The above EUI-48 and EUI-64 compatible IPv6 forms MAY be used for
temporary local address conversions, such as when converting EUI
addresses to IPv6 to support IPv6 fragmentation/reassembly. The
address forms MUST NOT appear in the IPv6 headers of packets sent
over the wire, however they MAY appear in the body of a packet if
also accompanied by a Type designator.
Appendix C. IPv6 ND Message Authentication and Integrity
OMNI interface IPv6 ND messages are subject to authentication and
integrity checks at multiple levels. When an OMNI interface sends an
IPv6 ND message over an INET interface, it includes an authentication
sub-option with a valid signature if necessary and always includes an
IPv6 ND message checksum. The OMNI interface that receives the
message verifies the IPv6 ND message checksum followed by the
authentication signature (if present) to ensure IPv6 ND message
integrity and authenticity.
When an OMNI interface sends an IPv6 ND message over an underlay
interface connected to a secured network, it omits authentication
(sub-)options but always calculates/includes an IPv6 ND message
checksum beginning with a pseudo-header of the IPv6 header and
extending to the end of the IPv6 ND message only with the Checksum
field itself set to 0. When an OMNI interface sends an IPv6 ND
message over an underlay interface connected to an unsecured network,
it first includes an authentication (sub-)option and calculates the
signature beginning with the first octet following the IPv6 ND
message header Checksum field and extending to the end of the entire
packet or super-packet with the authentication signature field set to
0. The OMNI interface next writes the signature into the signature
field, then calculates the IPv6 ND message checksum as above.
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The OMNI interface that receives the message applies any link layer
authentication and integrity checks, then verifies the IPv6 ND
message checksum. If the checks are correct, the OMNI interface next
verifies the authentication signature. The OMNI interface then
processes the packet further only if all checksums and authentication
signatures were correct.
OAL destinations also discard carrier packets with unacceptable
Identifications and submit the encapsulated fragments in all others
for reassembly. The reassembly algorithm rejects any fragments with
unacceptable sizes, offsets, etc. and reassembles all others. During
reassembly, the extended Identification value provides an integrity
assurance vector that compliments any integrity checks already
applied by lower layers as well as a first-pass filter for any checks
that will be applied later by upper layers.
Appendix D. VDL Mode 2 Considerations
ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2"
(VDLM2) that specifies an essential radio frequency data link service
for aircraft and ground stations in worldwide civil aviation air
traffic management. The VDLM2 link type is "multicast capable"
[RFC4861], but with considerable differences from common multicast
links such as Ethernet and IEEE 802.11.
First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of
magnitude less than most modern wireless networking gear. Second,
due to the low available link bandwidth only VDLM2 ground stations
(i.e., and not aircraft) are permitted to send broadcasts, and even
so only as compact link layer "beacons". Third, aircraft employ the
services of ground stations by performing unicast RS/RA exchanges
upon receipt of beacons instead of listening for multicast RA
messages and/or sending multicast RS messages.
This beacon-oriented unicast RS/RA approach is necessary to conserve
the already-scarce available link bandwidth. Moreover, since the
numbers of beaconing ground stations operating within a given spatial
range must be kept as sparse as possible, it would not be feasible to
have different classes of ground stations within the same region
observing different protocols. It is therefore highly desirable that
all ground stations observe a common language of RS/RA as specified
in this document.
Note that links of this nature may benefit from compression
techniques that reduce the bandwidth necessary for conveying the same
amount of data. The IETF lpwan working group is considering possible
alternatives: [https://datatracker.ietf.org/wg/lpwan/documents].
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Appendix E. Client-Proxy/Server Isolation Through Link-Layer Address
Mapping
Per [RFC4861], IPv6 ND messages may be sent to either a multicast or
unicast link-scoped IPv6 destination address. However, IPv6 ND
messaging should be coordinated between the Client and Proxy/Server
only without invoking other nodes on the underlay network. This
implies that Client-Proxy/Server control messaging should be isolated
and not overheard by other nodes on the link.
To support Client-Proxy/Server isolation on some links, Proxy/Servers
can maintain an OMNI-specific unicast link layer address ("MSADDR").
For Ethernet-compatible links, this specification reserves one
Ethernet unicast address TBD5 (see: IANA Considerations). For non-
Ethernet statically-addressed links MSADDR is reserved per the
assigned numbers authority for the link layer addressing space. For
still other links, MSADDR may be dynamically discovered through other
means, e.g., link layer beacons.
Clients map the L3 addresses of all IPv6 ND messages they send (i.e.,
both multicast and unicast) to MSADDR instead of to an ordinary
unicast or multicast link layer address. In this way, all of the
Client's IPv6 ND messages will be received by Proxy/Servers that are
configured to accept carrier packets destined to MSADDR. Note that
multiple Proxy/Servers on the link could be configured to accept
carrier packets destined to MSADDR, e.g., as a basis for supporting
redundancy.
Therefore, Proxy/Servers must accept and process carrier packets
destined to MSADDR, while all other devices must not process carrier
packets destined to MSADDR. This model has well-established
operational experience in Proxy Mobile IPv6 (PMIP)
[RFC5213][RFC6543].
Appendix F. Change Log
<< RFC Editor - remove prior to publication >>
Differences from earlier versions:
* Submit for review.
Author's Address
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Fred L. Templin (editor)
The Boeing Company
P.O. Box 3707
Seattle, WA 98124
United States of America
Email: fltemplin@acm.org
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