Internet DRAFT - draft-templin-6man-omni
draft-templin-6man-omni
Network Working Group F. L. Templin, Ed.
Internet-Draft The Boeing Company
Intended status: Informational 12 October 2022
Expires: 15 April 2023
Transmission of IP Packets over Overlay Multilink Network (OMNI)
Interfaces
draft-templin-6man-omni-74
Abstract
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. A
multilink virtual interface specification is presented 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 that also
applies for 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 15 April 2023.
Copyright Notice
Copyright (c) 2022 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 . . . . . . . . . . . . . . . . . . . . . . . . 16
4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 16
5. OMNI Interface Maximum Transmission Unit (MTU) . . . . . . . 23
5.1. Jumbograms . . . . . . . . . . . . . . . . . . . . . . . 24
5.2. IP Parcels . . . . . . . . . . . . . . . . . . . . . . . 25
6. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 25
6.1. OAL Source Encapsulation and Fragmentation . . . . . . . 26
6.2. OAL L2 Encapsulation and Re-Encapsulation . . . . . . . . 32
6.3. OAL L2 Decapsulation and Reassembly . . . . . . . . . . . 35
6.4. OAL Header Compression . . . . . . . . . . . . . . . . . 36
6.5. OAL Identification Window Maintenance . . . . . . . . . . 40
6.6. OAL Fragment Retransmission . . . . . . . . . . . . . . . 45
6.7. OAL MTU Feedback Messaging . . . . . . . . . . . . . . . 46
6.8. OAL Super-Packets . . . . . . . . . . . . . . . . . . . . 49
6.9. OAL Bubbles . . . . . . . . . . . . . . . . . . . . . . . 50
6.10. OMNI Hosts . . . . . . . . . . . . . . . . . . . . . . . 51
6.11. IP Parcels . . . . . . . . . . . . . . . . . . . . . . . 53
6.12. OAL Requirements . . . . . . . . . . . . . . . . . . . . 55
6.13. OAL Fragmentation Security Implications . . . . . . . . . 56
7. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 58
8. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 59
9. Unique-Local Addresses (ULAs) . . . . . . . . . . . . . . . . 60
10. Global Unicast Addresses (GUAs) . . . . . . . . . . . . . . . 63
11. Node Identification . . . . . . . . . . . . . . . . . . . . . 64
12. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 65
12.1. The OMNI Option . . . . . . . . . . . . . . . . . . . . 66
12.2. OMNI Sub-Options . . . . . . . . . . . . . . . . . . . . 67
12.2.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 70
12.2.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 70
12.2.3. Node Identification . . . . . . . . . . . . . . . . 71
12.2.4. Authentication . . . . . . . . . . . . . . . . . . . 73
12.2.5. Window Synchronization . . . . . . . . . . . . . . . 73
12.2.6. Prefix Length . . . . . . . . . . . . . . . . . . . 74
12.2.7. Interface Attributes . . . . . . . . . . . . . . . . 75
12.2.8. Traffic Selector . . . . . . . . . . . . . . . . . . 80
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12.2.9. AERO Forwarding Parameters . . . . . . . . . . . . . 81
12.2.10. Geo Coordinates . . . . . . . . . . . . . . . . . . 85
12.2.11. Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
Message . . . . . . . . . . . . . . . . . . . . . . . 86
12.2.12. PIM-SM Message . . . . . . . . . . . . . . . . . . . 87
12.2.13. Host Identity Protocol (HIP) Message . . . . . . . . 88
12.2.14. QUIC-TLS Message . . . . . . . . . . . . . . . . . . 90
12.2.15. Fragmentation Report (FRAGREP) . . . . . . . . . . . 91
12.2.16. ICMPv6 Error . . . . . . . . . . . . . . . . . . . . 92
12.2.17. Proxy/Server Departure . . . . . . . . . . . . . . . 93
12.2.18. Sub-Type Extension . . . . . . . . . . . . . . . . . 93
13. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 96
14. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 97
14.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 98
14.2. Client-Proxy/Server Loop Prevention . . . . . . . . . . 98
15. Router Discovery and Prefix Registration . . . . . . . . . . 99
15.1. Window Synchronization . . . . . . . . . . . . . . . . . 108
15.2. Router Discovery in IP Multihop and IPv4-Only
Networks . . . . . . . . . . . . . . . . . . . . . . . . 109
15.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 112
15.4. OMNI Link Extension . . . . . . . . . . . . . . . . . . 113
16. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 114
17. Proxy/Server Resilience . . . . . . . . . . . . . . . . . . . 114
18. Detecting and Responding to Proxy/Server Failures . . . . . . 115
19. Transition Considerations . . . . . . . . . . . . . . . . . . 115
20. OMNI Interfaces on Open Internetworks . . . . . . . . . . . . 116
21. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 118
22. (H)HITs and Temporary ULA (TLA)s . . . . . . . . . . . . . . 119
23. Address Selection . . . . . . . . . . . . . . . . . . . . . . 120
24. Error Messages . . . . . . . . . . . . . . . . . . . . . . . 120
25. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 120
25.1. "Protocol Numbers" Registry . . . . . . . . . . . . . . 121
25.2. "IEEE 802 Numbers" Registry . . . . . . . . . . . . . . 121
25.3. "IPv4 Special-Purpose Address" Registry . . . . . . . . 121
25.4. "IPv6 Neighbor Discovery Option Formats" Registry . . . 121
25.5. "Ethernet Numbers" Registry . . . . . . . . . . . . . . 121
25.6. "ICMPv6 Code Fields: Type 2 - Packet Too Big"
Registry . . . . . . . . . . . . . . . . . . . . . . . 122
25.7. "OMNI Option Sub-Type Values" (New Registry) . . . . . . 122
25.8. "OMNI Node Identification ID-Type Values" (New
Registry) . . . . . . . . . . . . . . . . . . . . . . . 123
25.9. "OMNI Geo Coordinates Type Values" (New Registry) . . . 124
25.10. "OMNI Option Sub-Type Extension Values" (New
Registry) . . . . . . . . . . . . . . . . . . . . . . . 124
25.11. "OMNI RFC4380 UDP/IP Header Option" (New Registry) . . . 124
25.12. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry) . . 125
25.13. Additional Considerations . . . . . . . . . . . . . . . 125
26. Security Considerations . . . . . . . . . . . . . . . . . . . 126
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27. Implementation Status . . . . . . . . . . . . . . . . . . . . 127
28. Document Updates . . . . . . . . . . . . . . . . . . . . . . 127
29. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 128
30. References . . . . . . . . . . . . . . . . . . . . . . . . . 129
30.1. Normative References . . . . . . . . . . . . . . . . . . 129
30.2. Informative References . . . . . . . . . . . . . . . . . 131
Appendix A. OAL Checksum Algorithm . . . . . . . . . . . . . . . 141
Appendix B. IPv6 ND Message Authentication and Integrity . . . . 141
Appendix C. VDL Mode 2 Considerations . . . . . . . . . . . . . 142
Appendix D. Client-Proxy/Server Isolation Through Link-Layer
Address Mapping . . . . . . . . . . . . . . . . . . . . . 143
Appendix E. Change Log . . . . . . . . . . . . . . . . . . . . . 143
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 144
1. Introduction
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-intarea-parcels] are adapted to diverse underlay
interfaces with heterogeneous properties.
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) 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:
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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. MTU assurance - the ability to deliver packets/parcels of various
robust sizes between peers without loss due to a link size
restriction, and to dynamically adjust packet/parcels sizes to
achieve the optimal performance for each independent traffic
flow.
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-6man-aero]. AERO discusses details of ND
message based 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 interface(s). 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
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Prefixes (MSPs), which are typically IP Global Unicast Address (GUA)
prefixes assigned to the link and from which Mobile Network Prefixes
(MNPs) are derived. If there are multiple OMNI links, the IP layer
will see multiple OMNI interfaces.
Each Client receives an MNP 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 located in 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.
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 a document now in
AD evaluation for RFC publication
[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 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])
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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 OAL based on
encapsulation and fragmentation over heterogeneous underlay
interfaces as an adaptation sublayer between L3 and L2. Both 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.
Additionally, this document assumes the following IPv6 ND message
types: Router Solicitation (RS), Router Advertisement (RA), Neighbor
Solicitation (NS), Neighbor Advertisement (NA) and Redirect. Hosts,
Clients and Proxy/Servers that implement IPv6 ND 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).
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 a node of that particular node type that also configures an
OMNI interface and engages the OMNI Adaptation Layer.
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.
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Adaptation layer
A 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 upper layer as "L3" and sees all
lower 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 upper layers if
necessary. The global public Internet itself is an example.
End-user Network (ENET)
a simple or complex "downstream" network that travels with the
Client as a single logical unit. 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 Hosts. The ENET
could also provide an "upstream" link in a recursively-descending
chain of additional Clients and ENETs. In this way, an ENET of an
upstream Client is seen as the ANET of a downstream Client.
{A,I,E}NET interface
a Client's attachment to a link in an {A,I,E}NET.
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*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
IP 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.
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
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 a Maximum Reassembly Unit (MRU) 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".
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-
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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.
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.
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 nodes 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.
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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-6man-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-6man-aero].
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 and
fragmentation, or an IP packet/parcel delivered to the network
layer by the OMNI interface following OAL decapsulation and
reassembly.
OAL packet
an original IP packet/parcel encapsulated in an OAL IPv6 header
before OAL fragmentation, or following OAL reassembly.
OAL fragment
a portion of an OAL packet following fragmentation but prior to L2
encapsulation, or following L2 decapsulation but prior to OAL
reassembly.
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(OAL) atomic fragment
an OAL packet that does not require fragmentation is always
encapsulated as an "atomic fragment" with a Fragment Header with
Fragment Offset and More Fragments both set to 0, but with a valid
Identification value.
(OAL) 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 nodes. OAL intermediate nodes 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. (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.
OAL destination
an OMNI interface acts as an OAL destination when it decapsulates
carrier packets, then performs OAL reassembly and decapsulation to
derive the original IP packet/parcel.
OAL intermediate node
an OMNI interface acts as an OAL intermediate node when it removes
the L2 encapsulation headers of 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. OAL
intermediate nodes decrement the Hop Limit in OAL packets/
fragments during forwarding, and discard the OAL packet/fragment
if the Hop Limit reaches 0. OAL intermediate nodes do not
decrement the TTL/Hop Limit of the original IP packet/parcel,
which can only be examined by upper 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].
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(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.
(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 upper layers, 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.
Multinet
an intermediate node's manner of spanning multiple diverse IP
Internetwork and/or private enterprise network "segments" at the
OAL layer below IP. Through intermediate node concatenation of
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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 L2 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-6man-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 node 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-6man-aero] for further discussion.
AERO Forwarding Vector (AFV)
An AFIB entry that includes soft state for each underlay interface
pairwise communication session between peers. 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-6man-aero] for
further discussion.
AERO Forwarding Vector Index (AVFI)
A locally-unique 4 octet value that an OAL node generates when it
creates an AFV, then advertises to either next-hop or previous-hop
nodes. OAL intermediate nodes assign two distinct AFVIs for each
AFV and advertise one to next-hops and the other to previous-hops.
OAL end systems assign and advertise a single AFVI. See:
[I-D.templin-6man-aero] for further discussion.
IP Jumbogram
an IPv4 or IPv6 packet with a Jumbo Payload option that includes a
32-bit length field to be used instead of the 16-bit {Total,
Payload} Length field (see: Section 5.1). For IPv4, the Total
Length field must be set to the length of the IPv4 header only.
For IPv6, the Payload Length must be set to 0. Original IP
packets, OAL packets and carrier packets may all appear as IP
Jumbograms.
IP Parcel
a special form of an IP Jumbogram with a segment length value
included in the {Total, Payload} Length field and also with a
Jumbo Payload option that encodes an 8-bit "Nsegs" field followed
by a 24-bit length field (see: Section 5.2). Only original IP
packets may appear as IP Parcels.
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(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 {A,I,E}NET underlay network
partition. Common L2 encapsulation combinations include UDP/IP/
Ethernet, etc. using a port/protocol/type number for OMNI.
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.)
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.
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, etc.) or virtual (e.g., an Internet 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 IP 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.
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+----------------------------+
| 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 one
or several IPv4 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.
* 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 stub network that travels with a mobile Client (e.g.,
an Internet-of-Things) 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.
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* VPNed interfaces use security encapsulation over an underlay
network to a Client or Proxy/Server acting as a Virtual Private
Network (VPN) gateway. Other than the link-layer encapsulation
format, VPNed interfaces behave the same as for Direct interfaces.
* Direct (aka "point-to-point") interfaces connect directly to a
Client or Proxy/Server without crossing any networked paths. An
example is a line-of-sight link between a remote pilot and an
unmanned aircraft.
The OMNI interface forwards original IP packets/parcels from the
network layer (L3) 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
transmission over underlay interfaces. The target OMNI interface
receives the carrier packets from underlay interfaces and discards
the L2 encapsulation headers. If the resulting OAL packets/fragments
are addressed to itself, the OMNI interface acts as an "OAL
destination" and performs reassembly if necessary, discards the OAL
encapsulation, and delivers the original IP packet/parcel to the
network layer. If the OAL fragments are addressed to another node,
the OMNI interface instead acts as an "OAL intermediate node" by re-
encapsulating the carrier packets in new underlay network L2 headers
and forwarding them over an underlay interface without reassembling
or discarding the OAL encapsulation. The OAL source and OAL
destination are seen as "neighbors" on the OMNI link, while OAL
intermediate nodes provide a virtual bridging service that joins the
segments of a (multinet) Segment Routing Topology (SRT).
The OMNI interface can forward original IP packets/parcels over
underlay interfaces while including/omitting various lower layer
encapsulations including OAL, UDP, IP and Ethernet (ETH) or other
link-layer header. The network layer can also engage the 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 may be 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.
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Original IP packets/parcels sent directly over underlay interfaces
are subject to the same path MTU related issues as for any
Internetworking path, and do not include per-packet identifications
that can be used for data origin verification and/or link-layer
retransmissions. Original IP packets/parcels presented directly to
an underlay interface that exceed the underlay network path MTU are
dropped with an ordinary ICMPv6 Packet Too Big (PTB) message
returned. These PTB messages are subject to loss [RFC2923] the same
as for any non-OMNI IP interface.
The OMNI interface encapsulation/decapsulation layering possibilities
are shown in Figure 2 below. Imaginary vertical lines drawn between
the Network Layer and Underlay interfaces in the figure denote the
encapsulation/decapsulation layering combinations possible. 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(ERNET), IP/OAL/UDP/IP, IP/OAL/UDP/ETH, etc.
+------------------------------------------------------------+ ^
| 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 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.
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* 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 for "6 M"
operations.
* exposing a single virtual interface abstraction to the IPv6 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 allows 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 Jumbograms.
* the OAL applies per-packet identification values that allow for
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.
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* 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 upper layer protocols and networked paths.
Note that even when the OMNI virtual interface is present,
applications can still access underlay interfaces either through the
network protocol stack using an Internet socket or directly using a
raw socket. This allows for intra-network (or point-to-point)
communications without invoking the OMNI interface and/or OAL. For
example, when an OMNI interface is configured over an underlay IP
interface, applications can still invoke intra-network IP
communications directly over the underlay interface as long as the
communicating endpoints are not subject to mobility dynamics.
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, ...,
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.
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+--------------+
|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-
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.)
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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 route optimization is applied as discussed in
[I-D.templin-6man-aero], Clients can instead forward directly to SRT
intermediate nodes (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.
5. OMNI Interface Maximum Transmission Unit (MTU)
The OMNI interface observes the link nature of tunnels, including the
Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) 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 the interfaces (and their associated
underlay network paths) may have diverse MTUs. OMNI interface
considerations for accommodating original IP packets/parcels of
various sizes are discussed in the following sections.
IPv6 underlay interfaces are REQUIRED to configure a minimum MTU of
1280 octets and a minimum MRU 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 of at least 1280 octets
without generating an IPv6 Path MTU Discovery (PMTUD) Packet Too Big
(PTB) message [RFC8201]. (While the source can apply "source
fragmentation" for locally-generated original IPv6 packets/parcels up
to 1500 octets and larger still if it knows the destination
configures a larger MRU, this does not affect the minimum IPv6 path
MTU.)
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IPv4 underlay interfaces are REQUIRED to configure a minimum MTU of
68 octets [RFC0791] and a minimum MRU 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 that are no larger than 576 octets, and
SHOULD set DF to 1 in larger carrier packets unless it has a way to
determine the encapsulation destination MRU and has carefully
considered the issues discussed in Section 6.13.
When the network layer admits an original IP packet/parcel into the
OMNI interface the OAL prepends an IPv6 encapsulation header (see:
Section 6) where the 16-bit Payload Length field limits the maximum-
sized original IP packet/parcel to (2**16 -1) = 65535 octets; this is
also the maximum size that the OAL can accommodate with IPv6
fragmentation. The OMNI interface therefore sets an MTU and MRU of
65535 octets to support assured delivery of original IP packets/
parcels no larger than this size even if OAL fragmentation is
required. (The OMNI interface MAY instead set a larger MTU to
support best-effort delivery for IP Jumbograms and/or assured
delivery of IP parcels; see below.) The OMNI interface then employs
the OAL as an encapsulation sublayer service to transform original IP
packets/parcels into OAL packets/fragments, and the OAL in turn uses
underlay network L2 encapsulation to send carrier packets over
underlay interfaces (see: Section 6).
5.1. Jumbograms
While the maximum-sized original IP packet/parcel that the OAL can
accommodate using IPv6 fragmentation is 65535 octets, OMNI interfaces
can forward still larger packets through the application of IP
Jumbograms [RFC2675]. For such larger IPv6 packets, the OMNI
interface performs OAL encapsulation by appending an IPv6 header
followed by a Hop-by-Hop header with a Jumbo Payload option followed
by a Routing Header (if necessary) followed by a Fragment Header but
without applying fragmentation.
Since the Jumbo Payload option includes a 32-bit length field, OMNI
interfaces can therefore configure a larger IP MTU up to a maximum of
((2**32 - 1) - 8 - 40 - 8) = 4294967239 octets. In that case, the
OAL will still provide original IP packets/parcels no larger than
65535 with an IPv6 fragmentation-based assured delivery service while
IP Jumbograms will receive a best-effort delivery service made
possible since the OAL destination is permitted to accept atomic
fragments that exceed the OMNI interface MRU.
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The OAL source forwards IP Jumbograms as "atomic fragments" under the
assumption that upper and lower layers will employ sufficient
integrity assurance, noting that commonly-used 32-bit CRCs may be
inadequate for such large sizes [CRC]. If the original IP packet/
parcel is dropped along the path to the OAL destination, the OAL
source must arrange to return a PTB "hard error" to the original
source Section 6.7.
This document notes that a Jumbogram service for IPv4 is also
specified in [I-D.templin-intarea-parcels], where all OMNI link
aspects of the service are conducted in a similar fashion as for IPv6
above.
5.2. IP Parcels
As specified in [I-D.templin-intarea-parcels], an IP Parcel is a
variation of the IP Jumbogram construction where the IP header
{Total, Payload} Length field encodes the length of the first upper
layer protocol segment, while the Jumbo Payload Length field is
modified to encode both the number of segments ("Nsegs") and the
length of the entire parcel. Together, these fields determine the
size and number of upper layer protocol segments within the parcel.
Upper layer protocol IP Parcel format and transmission/reception
procedures for OMNI interfaces are specified in
[I-D.templin-intarea-parcels], while lower layer OMNI encapsulation
and fragmentation procedures are specified in Section 6.11 of this
document. The maximum-sized IP Parcel that can be conveyed over an
OMNI interface using fragmentation is one with 64 segments of 64KB
(minus headers) octets in length; therefore, OMNI interfaces can set
an MTU of slightly less than 4MB to provide assured delivery of IP
Parcels up to that size.
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.
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
encapsulation to form OAL packets subject to fragmentation producing
OAL fragments suitable for L2 encapsulation and transmission as
carrier packets over underlay interfaces as described in Section 6.1.
These carrier packets travel over one or more underlay networks
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spanned by OAL intermediate nodes in the SRT, which re-encapsulate by
removing the L2 headers of the first underlay network and appending
L2 headers appropriate for the next underlay network in succession.
(This process supports the multinet concatenation capability needed
for joining multiple diverse networks.) After re-encapsulation by
zero or more OAL intermediate nodes, the carrier packets arrive at
the OAL destination.
When the OAL destination receives the carrier packets, it 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-6man-aero]) may also serve as OAL intermediate nodes.
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, the TTL/Hop Limit is maintained or decremented
according to standard IP forwarding rules the same as for any
interface. The OAL source next creates an "OAL packet" by prepending
an IPv6 OAL encapsulation header per [RFC2473] with Next Header set
to '4' for IPv4 or '41' for IPv6 original packets. 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 enable loop-free forwarding over multiple
concatenated OAL intermediate hops. The OAL source then includes
IPv6 extension headers following the OAL IPv6 header but before the
original IP packet/parcel (if necessary) as discussed further
throughout this document.
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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.)
If the original IP packet/parcel includes a Jumbo Payload option
(see: [I-D.templin-intarea-parcels]) the OAL source includes the
necessary jumbo extension headers as discussed in Section 5.1. Note
that original IP packets/parcels no larger than 65535 octets do not
require an OAL Jumbo Payload encapsulation and may be subject to
fragmentation the same as for any OAL packet. Conversely, true IP
Jumbograms and IP parcels larger than 65535 octets require an OAL
Jumbo Payload encapsulation for transmission as ordinary jumbograms
according to best-effort delivery (i.e., and without applying
fragmentation).
The OAL source next calculates a 16-bit OAL checksum using the
algorithm specified in Appendix A beginning with a pseudo-header of
the full OAL IPv6 header the same as specified in Section 8.1 of
[RFC8200]. The OAL source sets the pseudo-header "Upper-Layer Packet
Length" to the entire length of the original IP packet/parcel and
"Next Header" to the value '4' for IPv4 or '41' for IPv6 original
packets. The OAL source then continues the checksum calculation over
the full length of the original IP packet/parcel which immediately
follows the OAL IPv6 header plus extensions.
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After calculating the checksum, the OAL source next selects a 32-bit
OAL packet Identification value as specified in Section 6.5 then
fragments the OAL packet if necessary. The OAL source assumes the
IPv4 minimum path MTU (i.e., 576 octets) as the worst case for OAL
fragmentation regardless of the underlay interface IP protocol
version since IPv6/IPv4 protocol translation and/or IPv6-in-IPv4
encapsulation may occur in any underlay network path. By initially
assuming the IPv4 minimum even for IPv6 underlay interfaces, the OAL
source may produce smaller fragments with additional encapsulation
overhead but avoids loss due to presenting an underlay interface with
a carrier packet that exceeds its MRU. Additionally, the OAL path
could traverse multiple SRT segments with intermediate OAL forwarding
nodes performing re-encapsulation where the L2 encapsulation of the
previous segment is replaced by the L2 encapsulation of the next
segment which may be based on a different IP protocol version and/or
encapsulation sizes.
The OAL source therefore assumes a default minimum path MTU of 576
octets at each SRT segment for the purpose of generating OAL
fragments for L2 encapsulation and transmission as carrier packets.
Each successive SRT intermediate node may include either a 20 octet
IPv4 or 40 octet IPv6 header, an 8 octet UDP header and in some cases
an IP security encapsulation (40 octets maximum assumed) during re-
encapsulation. Intermediate nodes at any SRT segment may also insert
or modify the Routing Header (40 octets maximum) following the 40
octet OAL IPv6 header and preceding the 8 octet Fragment Header.
Therefore, assuming a worst case of (40 + 40 + 8) = 88 octets for L2
encapsulations plus (40 + 40 + 8) = 88 octets for OAL encapsulation
leaves no less than (576 - 88 - 88) = 400 octets remaining to
accommodate a portion of the original IP packet/parcel. The OAL
source therefore sets a minimum Maximum Payload Size (MPS) of 400
octets as the basis for the minimum-sized OAL fragment that can be
assured of traversing all SRT segments without loss due to an MTU/MRU
restriction. The Maximum Fragment Size (MFS) for OAL fragmentation
is therefore determined by the MPS plus the size of the OAL
encapsulation headers.
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The OAL source SHOULD maintain "path MPS" values for individual OAL
destinations initialized to the minimum MPS and increased to larger
values if better information is known or discovered. For example,
when peers share a common underlay network link or a fixed path with
a known larger MTU, the OAL source can set path MPS to a larger size
(i.e., greater than 400 octets) as long as the peer reassembles
before re-encapsulating and forwarding (while re-fragmenting if
necessary). Also, if the OAL source has a way of knowing the maximum
L2 encapsulation size for all SRT segments along the path it may be
able to increase path MPS to reserve additional room for payload
data. Even when OAL header compression is used, the OAL source must
include the uncompressed OAL header size in its path MPS calculation
since it may need to include a full header at any time.
The OAL source can also optimistically set a larger path MPS and/or
actively probe individual OAL destinations to discover larger sizes
using packetization layer probes in a similar fashion as
[RFC4821][RFC8899], but care must be taken to avoid setting static
values for dynamically changing paths leading to black holes. The
probe involves sending an OAL packet larger than the current path MPS
and receiving a small acknowledgement response (with the possible
receipt of link-layer error message when a probe is lost). For this
purpose, the OAL source can send an NS message with one or more OMNI
options with large PadN sub-options (see: Section 12) and/or with a
trailing large NULL packet in a super-packet (see: Section 6.8) in
order to receive a small NA response from the OAL destination. While
observing the minimum MPS will always result in robust and secure
behavior, the OAL source should optimize path MPS values when more
efficient utilization may result in better performance (e.g. for
wireless aviation data links). The OAL source should maintain
separate path MPS values for each (source, target) underlay interface
pair for the same OAL destination, since different underlay interface
pairs may support differing path MPS values.
When the OAL source performs fragmentation, it SHOULD produce the
minimum number of non-overlapping fragments under current MPS
constraints, where each non-final fragment MUST be at least as large
as the minimum MPS, while the final fragment MAY be smaller. The OAL
source also converts all original IP packets/parcels no larger than
the current MPS (or larger than 65535 octets) into atomic fragments
by including a Fragment Header with Fragment Offset and More
Fragments both set to 0. The OAL source then inserts a Routing
Header (if necessary) following the IPv6 encapsulation header and
before the Fragment Header. If the original IP packet/parcel is
larger than 65535, the OAL source also inserts a Hop-By-Hop header
with Jumbo Payload option immediately following the IPv6
encapsulation header and before the Routing Header (if necessary),
then includes an (atomic) Fragment Header. The header extension
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order for each fragment therefore appears as the OAL IPv6 header
followed by Hop-By-Hop header followed by Routing Header followed by
Fragment Header.
The OAL source next appends the OAL checksum as the final two octets
of the final fragment while increasing its (Jumbo) Payload Length by
2. If appending the checksum would cause the final fragment to
exceed the current MPS, the OAL source instead reduces this "former"
final fragment's Payload Length (PL) by (N*8 + (PL mod 8)) octets,
where N is an integer that would result in a non-zero reduction but
without causing the former final fragment to become smaller than the
minimum MPS. The OAL source then creates a "new" final fragment by
copying the OAL IPv6 header and extension headers from the former
final fragment, then copying the (N*8 + (PL mod 8)) octets from the
end of the former final fragment immediately following the new final
fragment extension headers. The OAL source then sets the former
final fragment's More Fragments flag to 1, increments the new final
fragment's fragment offset by the former final fragment's new (PL /
8) and finally appends the checksum the same as discussed above.
Next, the OAL source replaces the IPv6 Fragment Header 1-octet
"Reserved" field (and for first fragments also the 2-bit "Reserved
Flags" field) with OMNI-specific encodings as shown in:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Parcel ID |A| Fragment Offset |P|S|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
a) First fragment
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Ordinal |A| Fragment Offset |Res|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
a) Non-first fragment
Figure 4: IPv6 Fragment Header Reserved Fields Redefined
For the first fragment (i.e., the one with Fragment Offset set to 0),
the OAL source sets the "(A)RQ" flag then sets "Parcel ID",
"(P)arcel" and "(S)ub-Parcels" as specified in Section 6.11. For
each non-first fragment, the OAL source instead sets the "(A)RQ" flag
and writes a monotonically-increasing "Ordinal" value between 1 and
127. Specifically, the OAL source writes the Ordinal value '1' for
the first non-first fragment, '2' for the second, '3' for the third,
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etc. up to the final fragment or the Ordinal value '127', whichever
comes first. (For any additional non-first fragments beyond true
ordinal '127', the OAL source also sets the Ordinal value '127' but
OAL packets with such a large number of fragments should rarely
occur.) The first fragment is always considered ordinal number '0'
even though the header does not include an explicit Ordinal field;
non-first fragments that contain the Ordinal value '0' must be
unconditionally dropped.
The OAL source finally encapsulates the fragments in L2 headers to
form carrier packets and sends them over an underlay interface, while
retaining the fragments and their ordinal numbers (i.e., #0, #1, #2,
etc.) for a brief period to support link-layer retransmissions (see:
Section 6.6). OAL fragment and carrier packet formats are shown in
Figure 5.
+----------+----------------+
|OAL Header| Frag #0 |
+----------+----------------+
+----------+----------------+
|OAL Header| Frag #1 |
+----------+----------------+
+----------+----------------+
|OAL Header| Frag #2 |
+----------+----------------+
....
+----------+----------------+----+
|OAL Header| Frag #(N-1) |Csum|
+----------+----------------+----+
a) OAL fragmentation (Csum in final fragment)
+----------+-----------------------------+----+
|OAL Header| Original IP packet/parcel |Csum|
+----------+-----------------------------+----+
b) An OAL atomic fragment
+--------+----------+----------------+
|L2 Hdrs |OAL Header| Frag #i |
+--------+----------+----------------+
c) OAL carrier packet after L2 encapsulation
Figure 5: OAL Fragments and Carrier Packets
Note: the minimum MPS assumes that any middleboxes (e.g. IPv4 NATs)
that connect private networks with path MTUs smaller than 576 octets
must reassemble any fragmented (outbound) IPv4 carrier packets sent
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by OAL sources before forwarding them to external Internetworks since
middleboxes that connect OAL destinations often unconditionally drop
(inbound) IPv4 fragments. However, when the path MTU in the
destination private network is small, the OAL destination itself will
be able to reassemble any IPv4 fragmentation that occurs in the
inbound path.
Note: appending the 2-octet checksum to the final fragment after
fragmentation instead of to the end of the original IP packet/parcel
before fragmentation ensures consistent support for all packet sizes.
Otherwise, 65534 and 65535 octet packets would be unable to append
the checksum without inserting a jumbo payload option which would
inhibit transmission over legacy links.
6.2. OAL L2 Encapsulation and Re-Encapsulation
The OAL source or intermediate node 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
node (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). The L2 source then appends any additional
encapsulation sublayer headers necessary and presents the resulting
carrier packet to an underlay interface, where the underlay network
conveys it to a next-hop OAL intermediate node or destination (i.e.,
the L2 destination).
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 '0' for an uncompressed OAL IPv6 header or '1', '2', '3' for
an OMNI Compressed Header as specified in Section 6.4. 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. (Type values '0' through '3' and
Version values '4' and '6' are currently specified, while all other
values are reserved for future use. Carrier packets that contain an
unrecognized Type/Version value are unconditionally dropped.)
The OAL node prepares the L2 encapsulation headers for OAL packets as
follows:
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* 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 finally sets the UDP Length the same as
specified in [RFC0768]. (If the OAL header includes a Jumbo
Payload option, the L2 source instead sets the UDP length to 0 and
includes a Jumbo Payload option in the L2 IP header.) 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 [RFC0791] or [RFC8200]. The L2 source then sets 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 a Jumbo Payload option,
the L2 source includes a Jumbo Payload option in the L2 IP
header.) The L2 source then sets 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) and sets the Ethernet Payload to a 2-octet OAL
Length followed by the actual OAL packet/fragment (see:
Section 7).
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 MAY disable UDP checksums in carrier
packets with compressed OAL headers (see: Section 6.4). If the L2
source discovers that a path is dropping carrier packets with UDP
checksums disabled, it should enable 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 4-octet 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 a mis-delivered carrier packet but can
immediately reject carrier packets with an incorrect Identification.
If the Identification value is somehow accepted, the OAL destination
may submit the mis-delivered carrier packet to the reassembly cache
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where it will most likely be rejected due to incorrect reassembly
parameters. If a reassembly that includes the mis-delivered carrier
packets somehow succeeds (or, for atomic fragments) the OAL
destination will verify the OAL checksum 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
hop. For carrier packets undergoing re-encapsulation, the OAL
intermediate node L2 source 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. (Note: the L2
source also writes the ECN value into the OAL full/compressed
header.)
Following L2 encapsulation/re-encapsulation, the L2 source sends the
resulting carrier packets over one or more underlay interfaces. The
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/down/status information to the
OMNI interface.
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6.3. OAL L2 Decapsulation and Reassembly
When an OMNI interface receives a 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 a 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 node) re-encapsulates and 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 and/or integrity checks.
The OAL destination next drops all non-final OAL fragments smaller
than the minimum MPS and all fragments that would overlap or leave
"holes" smaller than the minimum MPS with respect to other fragments
already received. The OAL destination updates a checklist of
accepted fragments of the same OAL packet that include an Ordinal
number (i.e., Ordinals 0 through 127), but admits all accepted
fragments into the reassembly cache after first removing any
extension headers except for the fragment header itself. When the
OAL destination receives the final fragment (i.e., the one with More
Fragments set to 0), it caches the trailing checksum and reduces the
Payload Length by 2. When reassembly is complete, the OAL
destination verifies the OAL packet checksum and discards the OAL
packet if the checksum is incorrect. If the OAL packet was accepted,
the OAL destination finally removes the OAL headers and delivers the
original IP packet/parcel to the network layer.
Carrier packets often travel over paths where all links in the path
include CRC-32 integrity checks for effective hop-by-hop error
detection for payload sizes up to 9180 octets [CRC], but other paths
may traverse links (such as fragmenting tunnels over IPv4) that do
not include adequate integrity protection. The OAL checksum
therefore allows OAL destinations to detect reassembly misassociation
splicing errors and/or carrier packet corruption caused by
unprotected links [CKSUM].
The OAL checksum also provides algorithmic diversity with respect to
both lower layer CRCs and upper layer Internet checksums as part of a
complimentary multi-layer integrity assurance architecture. Any
corruption not detected by lower layer integrity checks is therefore
very likely to be detected by upper layer integrity checks that
employ diverse algorithms.
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6.4. OAL Header Compression
OAL sources that send carrier packets with full OAL headers include a
CRH-32 extension for segment-by-segment forwarding based on an AERO
Forwarding Information Base (AFIB) in each OAL intermediate node.
OAL source, intermediate and destination nodes can instead establish
header compression state through IPv6 ND NS/NA message exchanges.
After an initial NS/NA exchange, OAL nodes can apply OAL Header
Compression to significantly reduce 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
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 nodes, 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 a full OAL IPv6 header with a
CRH-32 extension containing one or more AFVIs. In that case, the
first four bits following the L2 headers must encode the Type value
'0' (Type '0') to signify that an uncompressed OAL IPv6 header (plus
extensions) is present. The (Type) value '0' differentiates
uncompressed OAL IPv6 headers from ordinary IP headers which are
identified by the (Version) value '4' for IPv4 or '6' for IPv6.
When an OAL intermediate node forwards an OAL packet with '0' in the
Type/Version field to an IPv6 router for the SRT, it discards the L2
encapsulation headers and resets the Type/Version field value to '6'.
When an OAL intermediate node forwards an OAL packet received from an
SRT IPv6 router, it resets the Type/Version field value to '0' and
includes new L2 encapsulation headers.
Whenever possible, OAL nodes should omit significant portions of the
OAL header (plus extensions) while applying OAL header compression
when sufficient AFV state is available. Three OAL compressed header
types (Types '1' through '3') are currently specified.
For OAL first-fragments (including atomic fragments), the OAL node
uses OMNI Compressed Header - Type 1 (OCH-1) format as shown in
Figure 6:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Hop Limit |ECN| Parcel ID |R|X|P|S|M| Ident. (0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification (1-3) | AFVI (0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFVI (1-3) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: OMNI Compressed Header - Type 1 (OCH-1)
The format begins with a 4-bit Type, a 6-bit Hop Limit, a 2-bit
Explicit Congestion Notification (ECN) field, a 7-bit Parcel ID and 5
flag bits. The format concludes with a 4-octet Identification field
followed (optionally) by a 4-octet AFVI field. The OAL node sets
Type to the value 1, sets Hop Limit to the minimum of the
uncompressed OAL header Hop Limit and 63, sets ECN the same as for an
uncompressed OAL header, and sets (Parcel ID, (P)arcel, (S)ub-
parcels, (M)ore Fragments, Identification) the same as for an
uncompressed fragment header. The OAL node finally sets Inde(X) and
includes an AFVI if necessary; otherwise, it clears Inde(X) and omits
the AFVI. (The (R)eserved flag is set to 0 on transmission and
ignored on reception.)
The OAL first fragment (beginning with the original IP header) is
then included immediately following the OCH-1 header, and the L2
header length field is reduced by the difference in length between
the compressed headers and full-length OAL IPv6 and Fragment 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. The OCH-1 format applies for first fragments
only, which are always regarded as ordinal fragment 0 even though no
explicit Ordinal field is included. The (A)RQ flag is always
implicitly set, and therefore omitted from the OCH-1 header.
For OAL non-first fragments (i.e., those with non-zero Fragment
Offsets), the OAL uses OMNI Compressed Header - Type 2 (OCH-2) format
as shown in Figure 7:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Hop Limit | Ordinal | Fragment Offset |X|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFVI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: OMNI Compressed Header - Type 2 (OCH-2)
The format begins with a 4-bit Type, a 6-bit Hop Limit, a 7-bit
Ordinal, a 13-bit Fragment Offset and 2 flag bits. The format
concludes with a 4-octet Identification field followed (optionally)
by a 4-octet AFVI field. The OAL node sets Type to the value 2, 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. If
an AFVI is needed, the OAL node finally sets Inde(X) and includes an
AFVI; otherwise, the node clears Inde(X) and omits the AFVI.
The OAL non-first fragment body is then included immediately
following the OCH-2 header, and the L2 header length field is reduced
by the difference in length between the compressed headers and full-
length OAL IPv6 and Fragment headers. The OAL destination will then
be able to determine the Payload Length by examining the L2 header
length field. The OCH-2 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, etc., up to and including the final
fragment. If more than 127 non-first fragments appear, all fragments
beyond Ordinal 127 also set the value 127. (The Ordinal value 0 is
undefined; all OCH-2 carrier packets received with Ordinal value 0
must be unconditionally dropped.) The (A)RQ flag is always
implicitly set, and therefore omitted from the OCH-2 header.
When the entire OAL header is compressed, only the information that
would normally appear in the IPv6 Fragment Header is included and
with no information from the OAL IPv6 header. The OMNI Compressed
Header - Type 3 (OCH-3) is shown in Figure 8:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Ordinal |A| Next Header | Parcel ID |Res|P|S|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
a) First fragment
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Ordinal |A| Resvd | Fragment Offset |Res|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
a) Non-first fragment
Figure 8: OMNI Compressed Header - Type 3 (OCH-3)
The format begins with a 4-bit Type set to the value 3 followed by a
7-bit Ordinal. When Ordinal encodes the value 0, the format
continues according to the "First fragment" specification discussed
above; otherwise, the format continues according to the above "Non-
first fragment" specification. The fields for both formats include
the same information that would appear in a (modified) IPv6 Fragment
Header as specified in Figure 4 with the exception that the first
fragment does not include a Fragment Offset (since its offset is
always 0) and non-first fragments do not include a Next Header field
(since that field already appears in the first fragment).
When an OAL destination or intermediate node 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 examines the first four bits immediately following
the innermost header. If the bits contain a value 0 through 3 the
OAL node processes the remainder of the header as a full OAL header
or OCH-1/2/3 compressed header as specified above. If the bits
contain the value 4 or 6, the OAL node instead processes the
remainder as an ordinary IP header.
For carrier packets that contain OAL packets/fragments with OCH-1/2
headers (or full OAL headers with CRH-32 extensions) and addressed to
itself, 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 full OAL
headers then adds the resulting OAL fragment to the reassembly cache
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if the Identification is acceptable. (Note that for carrier packets
that contain OAL packets/fragments with an OCH-1 with both the X 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-1 header.)
Note: OAL header compression does not interfere with checksum
calculation and verification, which must be applied according to the
full OAL pseudo-header per Section 6.1 even when compression is used.
Note: The OCH-1/2 formats do 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-1/2 headers. If the flow requires frequent changes to
Traffic Class and/or Flow Label information, it can include
uncompressed OAL headers either continuously or periodically to
update header compression state.
6.5. 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 32-bit 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**32) 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.
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OMNI interface neighbors use TCP-like synchronization to maintain
windows with unpredictable ISS values incremented (modulo 2**32) for
each successive OAL packet and re-negotiate windows often enough to
maintain an unpredictable profile. OMNI interface neighbors exchange
IPv6 ND messages with OMNI options that include TCP-like information
fields 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.
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
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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.
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:
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* 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 solicited NA message with the ACK flag 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.)
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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 3.4 of [RFC0793]. For this
reason, the OMNI option header 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
[RFC0793].
OMNI interfaces may set the PNG ("ping") flag when a reachability
confirmation outside the context of the standard IPv6 ND protocol
messaging protocol is needed (OMNI interfaces therefore only set the
PNG flag in advertisement messages and ignore it in solicitation
messages). When an OMNI interface receives a PNG, it returns an
unsolicited NA (uNA) ACK with the PNG message Identification in the
Acknowledgment, but without updating RCV state variables. OMNI
interfaces return unicast uNA ACKs even for multicast PNG destination
addresses, since OMNI link multicast is based on unicast emulation.
OMNI interfaces that employ the window synchronization procedures
described above observe the following requirements:
* 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 that receive advertisements with the PNG and/or
SYN flag set MUST NOT set the PNG and/or SYN flag in uNA
responses.
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* OMNI interfaces that send advertisements with the PNG and/or SYN
flag set MUST ignore uNA responses with the PNG and/or SYN flag
set.
* 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 and PNGs, 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
nodes therefore become aware of each distinct set of interface pair
window synchronization parameters based on periodic IPv6 ND message
updates to their respective AFVs.
6.6. OAL Fragment Retransmission
When the OAL source sends carrier packets to an OAL destination, it
should cache recently sent carrier packets in case timely best-effort
selective retransmission is requested. The OAL destination in turn
maintains a checklist for the (Source, Destination, Identification)-
tuple of recently received carrier packets and notes the ordinal
numbers of OAL packet fragments already received (i.e., as Frag #0,
Frag #1, Frag #2, 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.
The OAL destination creates a uNA message with an OMNI option with
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one or more Fragmentation Report (FRAGREP) sub-options that include a
list of (Identification, Bitmap)-tuples for fragments received and
missing from this OAL source (see: Section 12 and
[I-D.templin-6man-fragrep]). 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.
When the OAL source receives the uNA message, it authenticates the
message then examines the FRAGREP. For each (Source, Destination,
Identification)-tuple, the OAL source determines whether it still
holds the corresponding carrier packets 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 0x12345678 are missing the OAL source
only retransmits carrier packets containing those fragments. When
the OAL destination receives the retransmitted carrier packets, it
admits the enclosed fragments 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 carrier packet loss and
avoid some unnecessary end-to-end delays. This best-effort network-
based service therefore compliments higher layer end-to-end protocols
responsible for true reliability.
Note: If a FRAGREP for a fragmented OAL packet that includes more
than 128 fragments sets ordinal fragment bit #127, the OAL source
should retransmit all ordinal fragments beginning with the actual
#127 and continuing to the final fragment. Fragmented OAL packets
with such a large number of fragments should occur very rarely if
ever, however.
6.7. OAL MTU Feedback Messaging
When the OMNI interface forwards original IP packets/parcels from the
network layer, it invokes the OAL and returns internally-generated
ICMPv4 Fragmentation Needed [RFC1191] or ICMPv6 Path MTU Discovery
(PMTUD) Packet Too Big (PTB) [RFC8201] messages as necessary. This
document refers to both of these ICMPv4/ICMPv6 message types simply
as "PTBs", and introduces a distinction between PTB "hard" and "soft"
errors as discussed below and also in [I-D.templin-6man-fragrep].
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Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6
header Code field value 0 are hard errors that always indicate loss
due to a real MTU restriction has occurred. However, the OMNI
interface can also forward large original IP packets/packets via OAL
encapsulation and fragmentation while at the same time returning PTB
soft error messages (subject to rate limiting) if it deems the
original IP packet/parcel too large according 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
can soon resume sending larger packets/parcels if the soft errors
subside.
An OAL source sends PTB soft error messages by setting the ICMPv4
header "unused" field or ICMPv6 header Code field to the value 1 if
the original IP packet/parcel was dropped or 2 if it was forwarded
successfully (see: Section 25). The OAL source 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
routable 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 576 for ICMPv4 or 1280 for
ICMPv6, writes the leading portion of the original IP packet/parcel
first fragment into the "packet in error" field, and returns the PTB
soft error to the original source. When the original source receives
the PTB soft error, it temporarily reduces the size of the IP
packets/parcels it sends the same as for hard errors but may seek to
increase future packet/parcel sizes dynamically while no further soft
errors are arriving. (If the original source does not recognize the
soft error code, it regards the PTB the same as a hard error but
should heed the retransmission advice given in [RFC8201] suggesting
retransmission based on normal packetization layer retransmission
timers.)
An OAL destination may experience reassembly cache congestion, and
can return uNA messages to the OAL source that originated the
fragments (subject to rate limiting) that include OMNI encapsulated
PTB messages with code 1 or 2. The OAL destination creates a uNA
message with an OMNI option containing an authentication message sub-
option if necessary followed optionally by a ICMPv6 Error sub-option
that encodes a PTB message with a reduced value and with the leading
portion an OAL first fragment containing the header of an original IP
packet/parcel whose source must be notified (see: Section 12). The
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OAL destination 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 sub-option 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 the uNA message, it sends a
corresponding network layer PTB soft error to the original source to
recommend a smaller size. The OAL source crafts the PTB by
extracting the leading portion of the original IP packet/parcel from
the OMNI encapsulated PTB message (i.e., not including the OAL
header) and writes it in the "packet in error" field of a network
layer PTB with destination set to the original IP packet/parcel
source and source set to one of its OMNI interface addresses that is
routable from the perspective of the original source.
Original sources that receive PTB soft errors can dynamically tune
the size of the original IP packets/parcels they to send to produce
the best possible throughput and latency, with the understanding that
these parameters may change 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 increasing or decreasing 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 environments.
Since IP layer middleboxes often filter raw ICMP messages (even those
as important as PTBs), the OAL source SHOULD instead use only ICMPv6
PTB messages encapsulated in UDP/IP headers to return MTU feedback to
the original source. The OAL source sets the ICMPv6 source to its
own IP address and destination to the IP address of the original
source (while using IPv4-Compatible IPv6 addresses for IPv4). The
OAL source then prepares the PTB message as discussed above while
encapsulating the message in UDP/IP headers using the same IP source
and destination addresses and with the UDP port number reserved for
OMNI. Original sources therefore SHOULD implement enough of the OMNI
specification to be able to recognize and process these messages.
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6.8. 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 also calculates the OAL checksum then performs
fragmentation such that a copy of the 40-octet IPv6 header plus an
8-octet IPv6 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".
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 MRU, 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. with the trailing OAL checksum included in the final
fragment. The OAL super-packet format is transposed from
[I-D.ietf-intarea-tunnels] and shown in Figure 9:
<------- Original IP packets ------->
+-----+-----+
| iHa | iDa |
+-----+-----+
|
| +-----+-----+
| | iHb | iDb |
| +-----+-----+
| |
| | +-----+-----+
| | | iHc | iDc |
| | +-----+-----+
| | |
v v v
+----------+-----+-----+-----+-----+-----+-----+----+
| OAL Hdr | iHa | iDa | iHb | iDb | iHc | iDc |Csum|
+----------+-----+-----+-----+-----+-----+-----+----+
<--- OAL "Super-Packet" with single OAL Hdr/Csum --->
Figure 9: OAL Super-Packet Format
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When the OAL source prepares a super-packet, it applies OAL
fragmentation, includes a trailing checksum in the final fragment,
applies L2 encapsulation to each fragment then sends the resulting
carrier packets to the OAL destination. When the OAL destination
receives the super-packet it sets aside the trailing checksum,
reassembles if necessary, then verifies the checksum while regarding
the remaining OAL header Payload Length as the sum of the lengths of
all payload packets/parcels. 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
common use case entails a path MPS probe beginning with a signed IPv6
ND message followed by a NULL IPv6 packet with a suitably large
(Jumbo) Payload Length but with Next Header set to 59 for "No Next
Header".)
6.9. 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 only the trailing OAL Checksum
field (i.e., and no 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
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.
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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 [I-D.templin-6man-aero].
6.10. 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 is connected to
the rest of the OMNI link by 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
nodes.
OMNI Hosts coordinate with Clients and/or other Hosts connected to
the same ENET using OMNI L2 encapsulation of IPv6 ND messages without
including OAL encapsulation. 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.)
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
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neighbors, and the Host can then engage in OMNI link transactions
with the Client and/or other ENET Hosts. By coordinating with the
Client in this way, the Host treats 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 peer
hosts 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 parcel segmentation if necessary (see: Section 6.11) then
encapsulates the packet/parcel 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 node.
The encapsulation procedures are coordinated per Section 6.1, except
that the OMNI L2 encapsulation header is followed by a Type value of
'3' as the first four bits of an OCH-3 OMNI compressed header that
includes Fragment Header information (see: Section 6.4). When the L2
encapsulation is based on an EUI [EUI] or IPv4 address, the Host next
translates the encapsulation header into an IPv6 header with
compatible addresses that include the N octets of the EUI or IPv4
address in the N least significant bits of the IPv6 address while
setting the (16-N) most significant octets to 0. 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 to 0. The Host then calculates an OAL checksum (using a
pseudo-header based on this IPv6 header instead of an OAL header),
writes the value as the final two octets of the encapsulation then
applies IPv6 fragmentation to produce IPv6 fragments no smaller than
the MPS the same as 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 3 to indicate the
presence of an OCH-3 header. The Host finally sends the resultant
carrier packets to the ENET peer.
When the ENET peer receives the carrier packets, it first translates
the OMNI L2 headers back to IPv6 headers with compatible addresses
and translates the OCH-3 headers into IPv6 Fragment Headers the same
as above. The peer then reassembles and verifies the OAL checksum.
If the checksum is correct, the peer next removes the encapsulation
headers and applies parcel reassembly if necessary. The peer then
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either delivers the original IP packet/parcel to upper layers if the
peer is the destination or forwards the packet/parcel toward the
final destination if the peer is a Client acting as an intermediate
node.
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-intarea-parcels]. 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 an OCH-3 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.
6.11. IP Parcels
IP parcels are formed by an OMNI Host or Client upper 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 upper layer protocol segments. The upper layer protocol
then presents the buffer and non-final segment size to the IP layer
which appends a single {TCP,UDP}/IP header (plus any extension
headers) before presenting the parcel to the OMNI Interface. Upper
layer protocol formatting and processing rules for IP parcels are
specified in [I-D.templin-intarea-parcels], while detailed OAL
encapsulation and fragmentation procedures are specified here.
When the IP layer forwards a parcel, the OMNI interface invokes the
OAL which forwards it to either an intermediate node or the final
destination itself. The OAL source first assigns a monotonically-
incrementing (modulo 127) "Parcel ID" and subdivides the parcel into
sub-parcels if necessary as specified in
[I-D.templin-intarea-parcels] with each sub-parcel no larger than the
maximum of the path MTU to the next hop or 64KB (minus headers). 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
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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
Jumbo Payload option is present.
The OAL source next assigns an appropriate Identification number that
is monotonically-incremented for each consecutive sub-parcel,
calculates and appends the OAL checksum, 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 before performing the fragmentation/reassembly operation
while inserting the IPv6 Fragment Header.) The OAL source then
writes the "Parcel ID" and sets/clears the "(P)arcel" and "(More)
(S)ub-Parcels" bits in the 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 next hop receives the carrier packets, it acts as an OAL
destination and 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 re-combining with peer sub-parcels of the same
original parcel identified by the 4-tuple consisting of the IP
encapsulation source and destination, Identification and Parcel ID.
The OAL destination re-combines peers by concatenating the segments
included in sub-parcels with the same Parcel ID and with
Identification values within 64 of one another to create a larger
sub-parcel possibly even as large as the entire original parcel.
Order of concatenation need not be strictly observed, with the
exception that 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 a common {TCP,UDP}/IP header plus
extensions to each re-combined sub-parcel as specified in
[I-D.templin-intarea-parcels].
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When the current OAL destination is an intermediate node, it next
becomes an OAL source to forward the re-combined (sub-)parcel(s) to
the next hop toward the final destination using encapsulation/
translation the same as specified above. (Each such intermediate
node MUST ensure 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 OAL destination, it re-combines them into the
largest possible (sub)-parcels while honoring the S flag then
delivers them to upper layers which act on the enclosed 5-tuple
information supplied by the original source.
The Parcel Path Qualification procedures specified in
[I-D.templin-intarea-parcels] require a new Code value in the ICMPv6
PTB field to identify a Parcel Reply. These ICMPv6 PTB messages are
always encapsulated according to OMNI rules and are processed only by
nodes that implement at least enough of the OMNI specification to
recognize the messages. This document therefore defines a new ICMPv6
PTB Code value 3 for Parcel Reply messages (see: Section 25).
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 process of re-combining parcels at the OAL destination is
optional, and should be avoided in cases where performance could be
negatively impacted. It is always acceptable to forward sub-parcels
on toward the final destination without first re-combining, since
each sub-parcel will contain a well-formed header and an integral
number of upper layer protocol segments.
6.12. OAL Requirements
In light of the above, OAL sources, destinations and intermediate
nodes observe the following normative requirements:
* OAL sources MUST forward original IP packets/parcels either larger
than the OMNI interface MRU or smaller than the minimum MPS minus
the trailing checksum size as atomic fragments (i.e., and not as
multiple fragments).
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* OAL sources MUST produce non-final fragments with payloads no
smaller than the minimum MPS during fragmentation.
* OAL intermediate nodes SHOULD and OAL destinations MUST
unconditionally drop any non-final OAL fragments with payloads
smaller than the minimum MPS.
* 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 MPS between fragments that have already
been received.
Note: Under the minimum MPS, an ordinary 1500 octet original IP
packet/parcel would require at most 4 OAL fragments, with each non-
final fragment containing 400 payload octets and the final fragment
containing 302 payload octets (i.e., the final 300 octets of the
original IP packet/parcel plus the 2 octet trailing checksum). 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/path MPS 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 6.7)
the OAL source could impose "pacing" by inserting an inter-fragment
delay and increasing or decreasing the delay according to congestion
indications.
6.13. 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.
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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
unpredictable values per Section 6.5. 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 MPS, 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 16-bit Identification (IP ID) field with only 65535
unique values such that at high 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]. Since carrier packets sent via an IPv4 path with DF=0 are
normally no larger than 576 octets, IPv4 fragmentation is possible
only at small-MTU links in the path which should support data rates
low enough for safe reassembly [RFC3819]. (IPv4 carrier packets
larger than 576 octets with DF=0 may incur high data rate reassembly
errors in the path, but the OAL checksum provides OAL destination
integrity assurance.) Since IPv6 provides a 32-bit Identification
value, IP ID wraparound at high data rates is not a concern for IPv6
fragmentation.
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 NOT send IPv6
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ND messages larger than the OMNI interface MTU, and MUST employ OAL
encapsulation and fragmentation for IPv6 ND messages larger than the
minimum/path MPS 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 ordinary carrier packets 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.
7. 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 10:
+--- ~~~ ---+--------+--------+-------- ~~~ --------+--- ~~~ ---+
| eth-hdr | OAL Length | OAL Packet/Fragment | eth-trail |
+-- ~~~ ---+--------+--------+-------- ~~~ --------+--- ~~~ ---+
|<------- Ethernet Payload -------->|
Figure 10: 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
beginning with a 2-octet OAL Length field followed by an OAL (or
native IPv6/IPv4) Packet/Fragment. The Ethernet Payload is then
followed by a standard Ethernet Trailer ("eth-trail").
The OAL Packet/Fragment begins with a 4-bit "Type/Version" as
discussed in Section 6.2. When "Type/Version" encodes '1', '2' or
'3', the OAL Packet/Fragment includes a compressed OAL IPv6 header
and OAL Length MUST encode the value that would appear in the
uncompressed header Payload Length. When "Type/Version" encodes '0',
'4' or '6', the OAL Packet/Fragment instead includes an uncompressed
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OAL IPv6, native IPv4, or native IPv6 header (respectively). In that
case, the IP header {Total, Payload} and/or Jumbo Payload Length
fields determine the packet/fragment length and the OAL Length field
is ignored (noting that future documents MAY specify an alternate
use).
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
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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.
* 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]; 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
render many OMNI functions inoperable. 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
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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.
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.
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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 IPv6
encapsulation [RFC2473]. 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).
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 as discussed
in Section 8. XLAs are a special-case TLA that use the prefix
fd00::/64. (Note that 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 {A,I,E}NET when no OMNI link
infrastructure is present. Within each individual {A,I,E}NET, 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-6man-aero].
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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".
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 {A,I,E}NET 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}
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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.).
The16-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-6man-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-
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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.
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.
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. This
network layer neighbor cache maintains state through static and/or
dynamic configurations.
Each OMNI interface also maintains a separate internal OAL
(adaptation layer) conceptual neighbor cache that includes a Neighbor
Cache Entry (NCE) for each of its active OAL neighbors per [RFC4861].
For each NCE, OAL neighbors also maintain one or more 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.)
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. If the OMNI interface includes an
authentication signature, it first sets the OMNI authentication sub-
option 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
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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 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 11:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-Options ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: OMNI Option Format
In this format:
* Type is set to TBD4 (see: IANA Considerations).
* 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.
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* Sub-Options is a Variable-length field padded if necessary such
that the complete OMNI Option is an integer multiple of 8 octets
long. Sub-Options contains zero or more sub-options as specified
in Section 12.2.
The OMNI option is included in all 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:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Sub-Type| Sub-Length | Sub-Option Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 12: 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
Prefix Length 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 13
Sub-Types 16-29 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
individual sub-option may end on an arbitrary octet boundary,
whereas the OMNI option itself must include padding if necessary
for 8-octet alignment.
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.
The OMNI interface codes initial sub-options in a first OMNI option
instance and subsequent sub-options in additional instances in the
same IPv6 ND message in the intended order of processing. The OMNI
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interface can then code any remaining sub-options in additional IPv6
ND messages if necessary. Implementations must observe these size
limits and refrain from sending IPv6 ND messages larger than the OMNI
interface MTU.
The OMNI interface processes all OMNI option Sub-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]. Nodes that receive IPv6 ND messages over unsecured
underlying networks first verify the IPv6 ND message checksum then
authenticate the message by processing any valid authentication
options/sub-options.
When a Client OMNI interface prepares a secured unicast RS message,
it includes a single Interface Attributes sub-option specific to the
underlay interface that will transmit the RS (see: Section 12.2.7).
When a Client OMNI interface prepares a secured unicast NS message,
it can instead include an AERO Forwarding Parameters sub-option
specific to the underlay interface that will transmit the NS (see:
Section 12.2.9).
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).
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The following sub-option types and formats are defined in this
document:
12.2.1. Pad1
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| S-Type=0|x|x|x|
+-+-+-+-+-+-+-+-+
Figure 14: 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 1 octet with the most significant 5 bits set
to 0, and with no Sub-Length or Sub-Option Data fields following.
If more than one octet of padding is required, the PadN option,
described next, should be used, rather than multiple Pad1 options.
12.2.2. PadN
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| S-Type=1| Sub-length=N | N padding octets ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 15: 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.
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When a proxy forwards an IPv6 ND message with OMNI options, it can
employ PadN to void any sub-options (other than Pad1) 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 B 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.
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 16:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=2| Sub-length=N | ID-Type | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ Node Identification Value (N-1 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: 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.
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- 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.
- 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 17:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DUID-Type (2) | EN (high bits == 0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EN (low bits = 45282) | ID-Type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ Node Identification Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: 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].
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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 18:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=3| Sub-length=N | Reserved | Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Hashed Message Authentication Code (HMAC) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: 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.
* Reserved is set to 0 on transmission and ignored on reception.
* 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.
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The Window Synchronization sub-option is formatted as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=4| Sub-length=12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Acknowledgment Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|A|R|O|P| | |
|Y|C|S|P|N| Res | Window |
|N|K|T|T|G| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: 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 contains a 4-octet Sequence Number, followed by a
4-octet Acknowledgement Number, followed by a 1-octet flags field
followed by a 3-octet Window size modeled from the Transmission
Control Protocol (TCP) header specified in Section 3.1 of
[RFC0793]. The (SYN, ACK, RST) flags are used for TCP-like window
synchronization, while the TCP (URG, PSH, FIN) flags are not used
and therefore omitted. The (OPT, PNG) flags are OMNI-specific,
and the remaining flags are Reserved. Together, these fields
support the asymmetric and symmetric OAL window synchronization
services specified in Section 6.5.
12.2.6. Prefix Length
IPv6 ND messages that need to assert or receive an MNP prefix length
can include a simple Prefix Length sub-option instead of a full
DHCPv6 message. The Prefix Length sub-option therefore may appear in
RS/RA messages, Redirect messages, NS/NA messages used for address
resolution and certain uNA messages as follows:
* For RS messages, Prefix Length refers either to the MNP found in
the RS source address or to the length of the MNP delegation the
Client wishes to receive.
* For RA messages, Prefix Length refers to the RA destination
address.
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* For Redirect messages, Prefix Length refers to the MNP found in
the Destination Address field within the Redirect message body.
* For NS messages used for address resolution, Prefix Length refers
to the MNP found in the NS source address.
* For NA messages used for address resolution, and for uNA messages
originated by MS endpoints, Prefix Length refers to the MNP found
in the NA Target Address field.
* The Prefix Length option is ignored in all other messages.
The Prefix Length sub-option is formatted as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=5| Sub-length=2 | Preflen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: Prefix Length
* 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 1.
* Preflen is an 8 bit field that determines the length of a subject
MNP. Values 1 through 64 specify a valid MNP length; if any other
value appears the sub-option must be ignored.
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 quality. 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
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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-6man-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
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 Interface Attributes sub-
option with ifIndex '0' that encodes its unicast L2 address relative
to the Client's underlay interface immediately after the Client
Interface Attributes sub-option in the solicited RA response. Any
additional Interface Attributes sub-options that appear in RS/RA
messages are ignored.
The Interface Attributes sub-option is formatted as shown below:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=6| Sub-length=N | Link |TS Form| SRT |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifProvider |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FMT | ~
+-+-+-+-+-+-+-+-+ ~
~ LHS Proxy/Server ULA/L2ADDR ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ RFC 6088 Format Traffic Selector ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: 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.
* Sub-Option Data contains an "Interface Attributes" option encoded
as follows:
- Link encodes a 4-bit link metric. The value '0' means the link
is DOWN, and the remaining values mean the link is UP with
metric ranging from '1' ("lowest") to '15' ("highest").
- TS-Form is a 4-bit field that encodes the same value that would
appear in an [RFC6088] TS Format and determines the trailing
RFC 6088 Format Traffic Selector type, if present. The
following values are defined:
o 0 - no traffic selector
o 1 - IPv4 binary traffic selector
o 2 - IPv6 binary traffic selector
o 0 - 15 - reserved for future use
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- 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.
- 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.
- 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 layer 3; otherwise, it invokes the OAL to
re-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 as follows:
+ 0 - L2ADDR is 4 octets in length and encodes an IPv4
address.
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+ 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].
+ 4-63 - Reserved for future use.
- 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 as specified in [RFC4380].
- RFC 6088 Format Traffic Selector - traffic selectors formatted
according to TS Form, with length determined by the remainder
of the sup-option length following the LHS information. When
TS Form encodes the value 1 or 2, the field is processed per
[RFC6088]; when TS Form encodes any other value the field (if
present) is ignored.
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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 the same information that would appear in an
Interface Attributes sub-option; hence, it can be used as an
extension to any Interface Attributes with the same ifIndex value
present.
IPv6 ND messages may include Traffic Selectors for some or all of the
source/target Client's underlay interfaces (see:
[I-D.templin-6man-aero] for more information).
Traffic Selectors must be honored by all implementations in the
format shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=7| Sub-length=N | TS Format | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ RFC 6088 Format Traffic Selector ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: Traffic Selector
* Sub-Type is set to 7. Multiple instances with the same ifIndex
value 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 contains a "Traffic Selector" encoded as follows:
- TS Format is a 1-octet field that encodes a Traffic Selector
version per [RFC6088]. If TS Format encodes the value 1 or 2,
the Traffic Selector includes IPv4 or IPv6 information,
respectively. If TS Format encodes any other value, the sub-
option is ignored.
- Reserved is a 1-octet field set to 0 on transmission and
ignored on receipt
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- ifIndex is a 4-octet value corresponding to a specific underlay
interface the same as specified above for Interface Attributes
and AERO Forwarding Parameters above. The OMNI options of a
single message may include multiple Traffic Selector sub-
options; each with the same or different ifIndex values.
- The remainder of the sub-option includes a traffic selector
formatted per [RFC6088] beginning with the "Flags (A-N)" field,
and with the Traffic Selector IP protocol version coded in the
TS Format field. If a single interface identified by ifIndex
requires Traffic Selectors for multiple IP protocol versions,
or if a Traffic Selector block would exceed the available
space, the remaining information is coded in additional Traffic
Selector sub-options that all encode the same ifIndex.
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 nodes 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-6man-aero].
The AERO Forwarding Parameters sub-option is formatted as shown in
Figure 23:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=8| Sub-length=N | Reserved | 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 23: 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
Tunnel Window Synchronization Parameters for all Job codes, while
including the remaining fields only for Job codes "0" and "1" (see
below).
* Sub-Option Data contains AERO Forwarding Parameters as follows:
- Reserved is a 1-octet reserved field set to 0 on transmission
and ignored on receipt.
- 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:
o '00' - "Initialize; Build B" - the FHS source sets this code
in an NS/NA used to initialize AFV state (any other messages
that include this code MUST be dropped). The FHS source
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first sets A/B to 0, and the FHS source and each
intermediate node 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 and also writes the value into list entry B, then
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 node and ending
with an entry for the final intermediate node (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"
(any other messages that include this code MUST be dropped).
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 node 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 and also writes the value 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, with the LHS source entry
last, preceded by entries for each consecutive intermediate
node and beginning with an entry for the final intermediate
node (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 node 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 node 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 node 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 nodes 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 nodes will discover inappropriate A/B AFVIs for
their location in the multihop forwarding chain. See:
[I-D.templin-6man-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 node 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, two trailing state variable
blocks are included for First-Hop Segment (FHS) followed by
Last-Hop Segment (LHS) network elements. When present, each
block encodes 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
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 regardless of the
actual L2 address length 'N' with the L2 address appearing
in the N least-significant octets and the (16 - N) most-
significant octets set to '0'. When L2ADDR includes an IPv4
or IPv6 address, it is recorded in network byte order in
ones-compliment "obfuscated" form as specified in [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.
12.2.10. Geo Coordinates
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=9| Sub-length=N | Reserved | Geo Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Geo Coordinates ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 24: 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.
* Reserved is a 1 octet field set to 0 on transmission and ignored
on reception.
* 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 DHCPv6 messages do not include a Checksum field since integrity
is protected by the IPv6 ND message checksum, authentication
signature and/or lower-layer authentication and integrity checks.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=10| Sub-length=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | transaction-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. DHCPv6 options .
. (variable number and length) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 25: 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 replaced by
a Reserved field (set to 0) since the IPv6 ND message is already
protected by the IPv6 ND message checksum, authentication signature
and/or lower-layer authentication and integrity checks.
The PIM-SM message sub-option format is shown in Figure 26:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=11| Sub-length=N |PIM Ver| Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ PIM-SM Message /
/ /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 26: 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 replaced by a
Reserved field set to 0 on transmission and ignored on reception.
The "PIM Ver" field MUST encode 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 authenticate 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
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 lower layers or other OMNI layer services.
The OMNI interface calculates the authentication signature over the
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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 a 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
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:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=12| Sub-length=N |0| Packet Type |Version| RES.|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Controls |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ HIP Parameters /
/ /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 27: 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.
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* 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 HIP message Checksum field is
replaced by a Reserved field set to 0 on transmission and ignored
on reception.
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
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=13| Sub-length=N | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ~
~ QUIC-TLS Message ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 28: 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.
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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 / 20)-many (Identification,
Bitmap)-tuples which include the Identification values of OAL
fragments received plus a Bitmap marking the ordinal positions of
individual fragments received and fragments missing.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=14| Sub-Length = N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Bitmap #1 ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Bitmap #2 ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ~
| ... |
+ ... +
Figure 29: 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, i.e., the length of the option in octets
beginning immediately following the Sub-Length field and extending
to the end of the sub-option. If N is not an integral multiple of
20 octets, the sub-option is ignored. The length of the entire
sub-option should not cause the entire IPv6 ND message to exceed
the minimum IPv6 MTU.
* Identification (i) includes the 32-bit IPv6 Identification value
found in the Fragment Header of a received OAL fragment. (Only
those Identification values included represent fragments for which
loss was experienced; any Identification values not included
correspond to fragments that were either received in their
entirety or may still be in transit.)
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* Bitmap (i) includes a 128-bit ordinal checklist of up to 128
fragments, with each bit set to 1 for a fragment received or 0 for
a fragment missing. For example, for a 20-fragment OAL packet
with ordinal fragments #3, #10, #13 and #17 missing and all other
fragments received, Bitmap (i) encodes the following:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|1|1|1|0|1|1|1|1|1|1|0|1|1|0|1|1|1|0|1|1|0|0|0|...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 30
(Note that loss of an OAL atomic fragment is indicated by a
Bitmap(i) with all bits set to 0.)
12.2.16. ICMPv6 Error
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=15| Sub-length=N | Type | Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Message Body +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 31: 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 a one octet Type followed by a one octet
Code followed by an (N-2)-octet Message Body encoded exactly as
per Section 2.1 of [RFC4443]. OMNI interfaces include as much of
the ICMPv6 error message body in the sub-option as possible
without causing the entire IPv6 ND message to exceed the minimum
IPv6 MTU. While all ICMPv6 error message types are supported, OAL
destinations in particular may include ICMPv6 PTB messages in uNA
messages to provide MTU feedback information via the OAL source
(see: Section 6.7). Note: ICMPv6 informational messages must not
be included and must be ignored if received.
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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:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=16| Sub-length=32 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Old FHS Proxy/Server ULA (16 octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Old Hub Proxy/Server ULA (16 octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 32: 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 33:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Extension-Type| ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ ~
~ Extension-Type Body ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 33: Sub-Type Extension
* 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
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Ext-Type=0 | Header Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Header Option Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 34: RFC4380 Header Extension Option (Extension-Type 0)
* Sub-Type is set to 30.
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* 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 two 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.
* 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 per Section 5.1.1 of
[RFC4380], except that the 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
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Ext-Type=1 | Trailer Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Trailer Option Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 35: RFC6081 Trailer Extension Option (Extension-Type 1)
* Sub-Type is set to 30.
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* 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.
* 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].
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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-6man-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).
14. Multilink Conceptual Sending Algorithm
The Client's IPv6 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.
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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 IP 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.
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.
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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.
To support Client to service coordination, OMNI defines three new
flag bits in the IPv6 ND RS message format as shown in Figure 36:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N|A|U| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 36: OMNI-Enhanced Router Solicitation Message Format
Clients set or clear the N/A/U 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 N
flag set, it responds directly to NS Neighbor Unreachability
Detection (NUD) messages by returning NA(NUD) replies; otherwise,
it forwards NS(NUD) messages to the Client.
* When the Hub Proxy/Server receives an RS with the A flag set, it
responds directly to NS Address Resolution (AR) messages by
returning NA(AR) replies; otherwise, it forwards NS(AR) messages
to the Client.
* When the Hub Proxy/Server receives an RS with the U 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.
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Mobility Service Proxy/Servers function according to the N/A/U flag
settings received in the most recent RS message to support dynamic
Client updates. In all IPv6 RS messages, the remaining flags in the
RS header Reserved field must be set to 0 on transmission and ignored
on reception.
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.
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 retain 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 or DOWN
through administrative action and/or through state transitions of the
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underlay interfaces. 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 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 the RS
N/A/U flags, then includes an OMNI option per Section 12 with an OMNI
Window Coordination sub-option, a Prefix Length 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 and fragmentation if necessary. The OMNI interface
selects an Identification value (see: Section 6.5), sets the OAL
source address to the ULA-MNP corresponding to the RS source if known
(otherwise to a TLA-RND), 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 fragmentation if necessary.
When L2 encapsulation is used, the Client includes the discovered FHS
Proxy/Server L2ADDR or an anycast address as the L2 destination then
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 sets aside the L2 headers, verifies the Identifications and
reassembles 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 N flag and Window Synchronization parameters (see:
Section 12.1) then examines the RS destination address. If the
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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 A/U flags to
determine its role in processing NS(AR) messages and generating uNA
messages (see: Section 12.1).
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;
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 with
source set to its own ULA and destination set to the OAL source that
appeared in the RS, then calculates the OAL checksum, selects an
appropriate Identification, fragments if necessary, encapsulates each
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fragment in appropriate L2 headers with 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
Proxy/Server creates/updates a NCE for the Client (i.e., based on the
RS source address) and caches the OAL source, Window Synchronization,
N 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 with source set to its own ULA
and destination set to the ULA of the Hub Proxy/Server, calculates
the OAL checksum, selects an appropriate Identification, fragments if
necessary, encapsulates each fragment in appropriate L2 headers and
sends the resulting carrier packets into the SRT secured spanning
tree.
When the Hub Proxy/Server receives the carrier packets, it discards
the L2 headers, reassembles if necessary to obtain the proxyed RS,
verifies checksums, then performs DHCPv6 Prefix Delegation (PD) to
obtain the Client's MNP if the RS source is a (TLA,XLA}-RND. The Hub
Proxy/Server then creates/updates a NCE for the Client's XLA-MNP and
caches any state (including the A/U 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 a TLA-RND, 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 calculates the OAL checksum,
selects an appropriate Identification, fragments if necessary,
encapsulates each fragment in appropriate L2 headers and sends the
resulting carrier packets into the secured spanning tree.
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When the FHS Proxy/Server receives the carrier packets it discards
the L2 headers, reassembles if necessary 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 a TLA-RND, the FHS Proxy Server determines the MNP by consulting
the DHCPv6 PD Reply message sub-option.) The FHS Proxy/Server next
includes Window Synchronization 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 selects an Identification value per Section 6.5,
calculates the authentication signature/checksum, fragments if
necessary, encapsulates each fragment in L2 headers 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 discards the L2
headers, reassembles if necessary and removes the OAL header 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.
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
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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 a NAT 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 Link set to '0'. 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 PNG flag in the OMNI
header to trigger a uNA reply.
* 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.
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* 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-6man-aero].
The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface.
Therefore, when the IPv6 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 IPv6 layer or independently of the
IPv6 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 IPv6 layer, while others may elect
to initiate the process proactively. Still other deployments may
elect to administratively disable IPv6 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
significantly longer than the lifetime the MS has committed to retain
the prefix registration (e.g., REACHABLETIME 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.
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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) resulting in its removal also 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/
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.
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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 N/A/U flags consistently in successive
RS messages and only change those settings when an FHS/Hub Proxy/
Server service profile update is necessary.
Note: After a Client has discovered its ULA-MNPs for a given set of
FHS Proxy/Servers, it should begin using its XLA-MNP as the IPv6 ND
message source address and ULA-MNP as the OAL source address in
future IPv6 ND messages and refrain from further use of TLAs. In any
case, the Client SHOULD NOT gratuitously configure and use large
numbers of additional TLAs, as doing so would simply result in
address change churn in NCEs with no operational advantages.
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 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 6.5. 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 a {TLA,XLA}-RND) 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 using
its own ULA-MNP (or the TLA-RND) as the source and the ULA of the FHS
Proxy/Server as the destination and includes an Interface Attributes
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sub-option then performs L2 encapsulation and sends the resulting
carrier packets to the FHS Proxy/Server. The FHS Proxy/Server then
extracts the RS message and caches the Window Synchronization
parameters then re-encapsulates 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 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 using its own ULA as the source and the ULA of the FHS
Proxy/Server as the destination, then performs L2 encapsulation 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 IP hops away from the
nearest OMNI link Proxy/Server. Forwarding through IP multihop *NETs
is conducted 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.). Example routing protocols optimized for MANET/VANET
operations include [RFC3684] and [RFC5614] which operate according to
the link model articulated in [RFC5889] and subnet model articulated
in [RFC5942].
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 a TLA-RND 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
to a 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).
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For IPv6-enabled *NETs, if the underlay interface does not configure
an IPv6 GUA the Client injects the 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 an intermediate *NET hop that participates in the routing
protocol receives the encapsulated RS, it forwards the message
according to its routing tables (note that an intermediate node could
be a fixed infrastructure element such as a roadside unit or another
MANET/VANET node). 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
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.
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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 node. 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 if
necessary, then begins using the ULA-MNP as its OAL source address
and suspends use of its TLA since it now has 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 6.9.)
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 TLA, any nodes that forward
an encapsulated RS message with the TLA as the OAL source must not
consider the message as being specific to a particular OMNI link.
TLAs can therefore also serve as the source and destination addresses
of unencapsulated IPv6 data communications within the local routing
region, and if the 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 nodes 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
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.
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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 a TLA-RND. If the Client requires only a single
MNP delegation, it can then include an OMNI Node Identification sub-
option plus an OMNI Prefix Length 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 a 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 Prefix Length 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.)
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
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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 Prefix Length 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.
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
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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.
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.
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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.
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
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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 D. 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 [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].
Client OMNI interfaces configured over underlay interfaces connected
to open Internetworks can apply security services such as VPNs to
connect to a Proxy/Server, or can establish a direct link to the
Proxy/Server through some other means (see Section 4). In
environments where an explicit VPN or direct link 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 (see: Section 25.13 and Section 3.6 of [I-D.templin-6man-aero])
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 6.4.) 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
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[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
any 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 VPN 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 route optimization, window
synchronization and mobility management (see:
[I-D.templin-6man-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 origin verification.
Upper layer protocol sessions over OMNI interfaces that connect over
open Internetworks without an explicit VPN should therefore employ
transport- or higher-layer security 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 directly 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-6man-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-6man-aero]. FHS Proxy/Servers include Origin
Indications in RA messages to allow Clients to detect the presence of
NATs.
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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 either instead of or in addition to
the OMNI authentication services specified here.
Note: OMNI interfaces configured over INET underlay interfaces should
employ the Identification window synchronization mechanisms specified
in Section 6.5 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.
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 a {TLA,XLA}-RND 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.
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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
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.
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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 ULAs 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.
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 node 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]:
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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).
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). Implementations set
Type to 253 as an interim value [RFC4727].
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 37: IANA Unicast 48-bit MAC Addresses
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25.6. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry
The IANA is instructed to assign three new Code values in the "ICMPv6
Code Fields: Type 2 - Packet Too Big" registry (registration
procedure is Standards Action or IESG Approval). The registry should
appear as follows:
Code Name Reference
--- ---- ---------
0 PTB Hard Error [RFC4443]
1 PTB Soft Error (loss) [RFCXXXX]
2 PTB Soft Error (no loss) [RFCXXXX]
3 Parcel Reply [RFCXXXX]
Figure 38: ICMPv6 Code Fields: Type 2 - Packet Too Big Values
(Note: this registry also to be used to define values for setting the
"unused" field of ICMPv4 "Destination Unreachable - Fragmentation
Needed" messages.)
25.7. "OMNI Option Sub-Type Values" (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 Prefix Length [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]
15-29 Unassigned
30 Sub-Type Extension [RFCXXXX]
31 Reserved by IANA [RFCXXXX]
Figure 39: OMNI Option Sub-Type Values
25.8. "OMNI Node Identification ID-Type Values" (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 40: OMNI Node Identification ID-Type Values
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25.9. "OMNI Geo Coordinates Type Values" (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 41: OMNI Geo Coordinates Type
25.10. "OMNI Option Sub-Type Extension Values" (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 42: OMNI Option Sub-Type Extension Values
25.11. "OMNI RFC4380 UDP/IP Header Option" (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 43: OMNI RFC4380 UDP/IP Header Option
25.12. "OMNI RFC6081 UDP/IP Trailer Option" (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 44: OMNI RFC6081 Trailer Option
25.13. 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. (Note however
that when OAL encapsulation is used the (echoed) OAL Identification
value can provide sufficient transaction confirmation.)
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
VPNs or can by some other means establish a direct link. When a VPN
or direct link may be impractical or undesirable, however, the
security services specified in [RFC7401], [RFC4380] or [RFC9000] can
be employed. While the OMNI link protects control plane messaging,
applications must still employ end-to-end transport- or higher-layer
security services to protect the data plane.
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Strong network layer security for control plane messages and
forwarding path integrity for data plane messages between Proxy/
Servers MUST be supported. In one example, the AERO service
[I-D.templin-6man-aero] constructs an SRT spanning tree with Proxy/
Serves as leaf nodes and secures the spanning tree links with network
layer security mechanisms such as IPsec [RFC4301] or WireGuard [WG].
Secured control plane messages are then constrained to travel only
over the secured spanning tree paths and are therefore protected from
attack or eavesdropping. Other control and data plane messages can
travel over route optimized paths that do not strictly follow the
secured spanning tree, therefore end-to-end sessions should employ
transport- or higher-layer security services. Additionally, the OAL
Identification value can provide a first level of data origin
authentication to mitigate off-path spoofing in some environments.
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
(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 6.13. 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.
28. Document Updates
This document does not itself update other RFCs, but suggests that
the following could be updated through future IETF initiatives:
* [RFC1191]
* [RFC2675]
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* [RFC4291]
* [RFC4443]
* [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, 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, Christian Huitema, Thomas Narten, Dave
Thaler, Joe Touch, Pascal Thubert, and many others who deserve
recognition.
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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
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.
30. References
30.1. Normative References
[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>.
[RFC0793] Postel, J., "Transmission Control Protocol", RFC 793,
DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
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[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>.
[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>.
[RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4,
ICMPv6, UDP, and TCP Headers", RFC 4727,
DOI 10.17487/RFC4727, November 2006,
<https://www.rfc-editor.org/info/rfc4727>.
[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>.
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[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>.
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] WG-I, ICAO., "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.
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[EUI] IEEE, I., "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-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-32, 3 August 2022,
<https://www.ietf.org/archive/id/draft-ietf-drip-rid-
32.txt>.
[I-D.ietf-intarea-tunnels]
Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", Work in Progress, Internet-Draft, draft-
ietf-intarea-tunnels-10, 12 September 2019,
<https://www.ietf.org/archive/id/draft-ietf-intarea-
tunnels-10.txt>.
[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-29, 19 May 2022,
<https://www.ietf.org/archive/id/draft-ietf-ipwave-
vehicular-networking-29.txt>.
[I-D.templin-6man-aero]
Templin, F., "Automatic Extended Route Optimization
(AERO)", Work in Progress, Internet-Draft, draft-templin-
6man-aero-62, 5 October 2022,
<https://www.ietf.org/archive/id/draft-templin-6man-aero-
62.txt>.
[I-D.templin-6man-fragrep]
Templin, F. L., "IPv6 Fragment Retransmission and Path MTU
Discovery Soft Errors", Work in Progress, Internet-Draft,
draft-templin-6man-fragrep-07, 29 March 2022,
<https://www.ietf.org/archive/id/draft-templin-6man-
fragrep-07.txt>.
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[I-D.templin-6man-lla-type]
Templin, F. L., "The IPv6 Link-Local Address Type Field",
Work in Progress, Internet-Draft, draft-templin-6man-lla-
type-02, 23 November 2020,
<https://www.ietf.org/archive/id/draft-templin-6man-lla-
type-02.txt>.
[I-D.templin-intarea-parcels]
Templin, F., "IP Parcels", Work in Progress, Internet-
Draft, draft-templin-intarea-parcels-16, 6 October 2022,
<https://www.ietf.org/archive/id/draft-templin-intarea-
parcels-16.txt>.
[IPV4-GUA] Postel, J., "IPv4 Address Space Registry,
https://www.iana.org/assignments/ipv4-address-space/ipv4-
address-space.xhtml", 14 December 2020.
[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.
[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>.
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[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>.
[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>.
[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>.
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[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>.
[RFC3684] Ogier, R., Templin, F., and M. Lewis, "Topology
Dissemination Based on Reverse-Path Forwarding (TBRPF)",
RFC 3684, DOI 10.17487/RFC3684, February 2004,
<https://www.rfc-editor.org/info/rfc3684>.
[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>.
[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>.
[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>.
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[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>.
[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>.
[RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)",
RFC 5558, DOI 10.17487/RFC5558, February 2010,
<https://www.rfc-editor.org/info/rfc5558>.
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[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>.
[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>.
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[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>.
[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>.
[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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[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>.
[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>.
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[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>.
[WG] WireGuard, W., "WireGuard, Fast, Modern, Secure VPN
Tunnel, https://wireguard.com/", 7 March 2022.
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Appendix A. OAL Checksum Algorithm
The OAL 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 OAL 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 OAL checksum, the above algorithm is applied over
the N-octet concatenation of the OAL pseudo-header and the
encapsulated original IP packet(s)/parcel(s). Specifically, the
algorithm is first applied over the 40 octets of the OAL pseudo-
header as data octets D[1] through D[40], then continues over the
entire length of the original IP packet(s)/parcel(s) as data octets
D[41] through D[N].
Appendix B. 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 OAL checksum as a first-level integrity check,
then 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
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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.
The OMNI interface that receives the message applies any lower-layer
authentication and integrity checks, then verifies both the OAL
checksum and the IPv6 ND message checksum. If the checksums 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.
Following reassembly, the OAL checksum algorithm provides an
integrity assurance layer 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 C. 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 layer 2 "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
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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].
Appendix D. 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 E. Change Log
<< RFC Editor - remove prior to publication >>
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Differences from earlier versions:
* Submit for RFC publication.
Author's Address
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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