Network Working Group F. L. Templin, Ed.
Internet-Draft The Boeing Company
Intended status: Standards Track 10 April 2025
Expires: 12 October 2025
Transmission of IP Packets over Overlay Multilink Network (OMNI)
Interfaces
draft-templin-6man-omni3-53
Abstract
Air/land/sea/space mobile nodes (e.g., aircraft of various
configurations, terrestrial vehicles, seagoing vessels, space
systems, enterprise wireless devices, pedestrians with cell phones,
etc.) communicate with networked correspondents over wireless and/or
wired-line data links and configure mobile routers to connect end
user networks. This document presents a multilink virtual interface
specification that enables mobile nodes to coordinate with a network-
based mobility service, fixed node correspondents and/or other mobile
node peers. The virtual interface provides an adaptation layer
service suited for both mobile and more static environments such as
enterprise and home networks. Both Provider-Aggregated (PA) and
Provider-Independent (PI) addressing services are supported. 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 12 October 2025.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 18
4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 19
5. OMNI Interface Maximum Transmission Unit (MTU) . . . . . . . 25
6. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 26
6.1. OAL Source Encapsulation and Fragmentation . . . . . . . 27
6.2. OAL L2 Encapsulation and Re-Encapsulation . . . . . . . . 31
6.3. Reassembly and Decapsulation . . . . . . . . . . . . . . 34
6.4. OMNI-Encoded IPv6 Extension Headers . . . . . . . . . . . 36
6.5. OMNI Full and Compressed Headers (OFH/OCH) . . . . . . . 39
6.6. L2 UDP/IP Encapsulation Avoidance . . . . . . . . . . . . 44
6.7. OAL Identification Window Maintenance . . . . . . . . . . 45
6.8. OAL Fragmentation Reports and Retransmissions . . . . . . 50
6.9. OMNI Interface MTU Feedback Messaging . . . . . . . . . . 51
6.10. OAL Composite Packets . . . . . . . . . . . . . . . . . . 53
6.11. OAL Bubbles . . . . . . . . . . . . . . . . . . . . . . . 55
6.12. OAL Requirements . . . . . . . . . . . . . . . . . . . . 55
6.13. OAL Fragmentation Security Implications . . . . . . . . . 56
6.14. Control/Data Plane Considerations . . . . . . . . . . . . 57
7. Ethernet-Compatible Link Layer Frame Format . . . . . . . . . 58
8. OMNI Addressing . . . . . . . . . . . . . . . . . . . . . . . 59
9. Node Identification . . . . . . . . . . . . . . . . . . . . . 63
10. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 63
10.1. The OMNI Option . . . . . . . . . . . . . . . . . . . . 65
10.2. OMNI Sub-Options . . . . . . . . . . . . . . . . . . . . 68
10.2.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 69
10.2.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 70
10.2.3. Node Identification . . . . . . . . . . . . . . . . 70
10.2.4. CGA . . . . . . . . . . . . . . . . . . . . . . . . 72
10.2.5. RSA Signature . . . . . . . . . . . . . . . . . . . 73
10.2.6. Timestamp . . . . . . . . . . . . . . . . . . . . . 74
10.2.7. Nonce . . . . . . . . . . . . . . . . . . . . . . . 75
10.2.8. Trust Anchor . . . . . . . . . . . . . . . . . . . . 75
10.2.9. Certificate . . . . . . . . . . . . . . . . . . . . 76
10.2.10. Hashed Message Authentication Code (HMAC) . . . . . 76
10.2.11. Neighbor Synchronization . . . . . . . . . . . . . . 77
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10.2.12. Interface Attributes . . . . . . . . . . . . . . . . 79
10.2.13. Traffic Selector . . . . . . . . . . . . . . . . . . 83
10.2.14. Geo Coordinates . . . . . . . . . . . . . . . . . . 85
10.2.15. Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
Message . . . . . . . . . . . . . . . . . . . . . . . 86
10.2.16. PIM-SM Message . . . . . . . . . . . . . . . . . . . 86
10.2.17. Fragmentation Report (FRAGREP) . . . . . . . . . . . 87
10.2.18. ICMPv6 Error . . . . . . . . . . . . . . . . . . . . 89
10.2.19. Proxy/Server Departure . . . . . . . . . . . . . . . 89
11. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 90
12. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 91
12.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 91
12.2. Client-Proxy/Server Loop Prevention . . . . . . . . . . 92
13. Router Discovery and Address/Prefix Delegation . . . . . . . 93
13.1. Client-Proxy/Server Window Synchronization . . . . . . . 104
13.2. Router Discovery in IP Multihop and IPv4-Only
Networks . . . . . . . . . . . . . . . . . . . . . . . . 106
13.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 110
14. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 111
15. Proxy/Server Resilience . . . . . . . . . . . . . . . . . . . 111
16. Detecting and Responding to Proxy/Server Failures . . . . . . 112
17. Transition Considerations . . . . . . . . . . . . . . . . . . 112
18. OMNI Interfaces on Open Internetworks . . . . . . . . . . . . 113
19. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 115
20. Error Messages . . . . . . . . . . . . . . . . . . . . . . . 115
21. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 115
21.1. Protocol Numbers . . . . . . . . . . . . . . . . . . . . 116
21.2. IEEE 802 Numbers . . . . . . . . . . . . . . . . . . . . 116
21.3. ICMP Parameters . . . . . . . . . . . . . . . . . . . . 116
21.4. ICMPv6 Parameters . . . . . . . . . . . . . . . . . . . 117
21.5. IPv4 Special-Purpose Address . . . . . . . . . . . . . . 117
21.6. IANA OUI Ethernet Numbers . . . . . . . . . . . . . . . 117
21.7. Overlay Multilink Network Interface (OMNI) Registry
Group . . . . . . . . . . . . . . . . . . . . . . . . . 118
21.7.1. OMNI Option Sub-Types (New Registry) . . . . . . . . 118
21.7.2. OMNI Node Identification ID-Types (New Registry) . . 118
21.7.3. OMNI Geo Coordinates Types (New Registry) . . . . . 119
21.8. Additional Considerations . . . . . . . . . . . . . . . 119
22. Security Considerations . . . . . . . . . . . . . . . . . . . 120
23. Implementation Status . . . . . . . . . . . . . . . . . . . . 121
24. Document Updates . . . . . . . . . . . . . . . . . . . . . . 121
25. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 122
26. References . . . . . . . . . . . . . . . . . . . . . . . . . 123
26.1. Normative References . . . . . . . . . . . . . . . . . . 123
26.2. Informative References . . . . . . . . . . . . . . . . . 126
Appendix A. IPv6 Compatible Addresses . . . . . . . . . . . . . 136
Appendix B. IPv6 ND Message Authentication and Integrity . . . . 137
Appendix C. VDL Mode 2 Considerations . . . . . . . . . . . . . 138
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Appendix D. Client-Proxy/Server Isolation Through Link-Layer
Address Mapping . . . . . . . . . . . . . . . . . . . . . 139
Appendix E. IPv6 ND Virtual Interface Model . . . . . . . . . . 139
Appendix F. Change Log . . . . . . . . . . . . . . . . . . . . . 140
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 141
1. Introduction
Air/land/sea/space mobile nodes (e.g., aircraft of various
configurations, terrestrial vehicles, seagoing vessels, space
systems, enterprise wireless devices, pedestrians with cellphones,
etc.) configure mobile routers with multiple interface connections to
wireless and/or wired-line data links. These data links often 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 network interface (termed the
"Overlay Multilink Network Interface (OMNI)") as a thin layer over
its underlay 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 each
underlay interface appears as a link layer communication channel in
the architecture. The OMNI interface appears as a "virtual Ethernet
(veth)" interface to the IP layer and internally employs the "OMNI
Adaptation Layer (OAL)" to ensure that original IP packets 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,
operator networks, etc.) and/or the global public Internet itself.
Together, OMNI and the OAL provide the foundational elements required
to support the "6 M's of Modern Internetworking", including:
1. Multilink - a Client's ability to coordinate multiple diverse
underlay interfaces as a single logical unit (i.e., the OMNI
interface) to achieve the required communications performance and
reliability objectives.
2. Multinet - the ability to span the OMNI link over a segment
routing topology with multiple diverse administrative domain
network segments while maintaining seamless end-to-end
communications between mobile Clients and correspondents such as
air traffic controllers, fleet administrators, etc.
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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 peer-to-peer relaying capability
useful when multiple forwarding hops between peers may be
necessary to reach a target peer or an infrastructure access
point connection to the OMNI link.
6. (Performance) Maximization - the ability to exchange large
packets between peers without loss due to a link size
restriction, and to adaptively adjust packet sizes to maintain
the best performance profile for each independent traffic flow.
Client OMNI interfaces coordinate with the MS and/or OMNI peer nodes
through secure 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-aero3]. AERO discusses details of ND
message based multilink forwarding, route optimization, mobility
management, and multinet traversal while the fundamental aspects of
OMNI link operation are discussed in this document.
Each OMNI interface provides a multilink nexus for exchanging inbound
and outbound traffic flows via selected underlay interfaces. The IP
layer sees the OMNI interface as a point of connection to the OMNI
link. Each OMNI link assigns one or more associated Mobility Service
Prefixes (MSPs), which are typically IP Global Unicast Address (GUA)
prefixes. The MS then delegates Mobile Network Prefixes (MNPs) taken
from an MSP to Client end systems as PI address blocks. Clients in
local domains also obtain PA addresses from internal/external Stable
Network Prefixes (SNPs) assigned to Proxy/Servers that connect the
local domain to the global topology per [RFC6296]. If there are
multiple OMNI links, the IP layer will see multiple OMNI interfaces.
Clients receive SNP addresses and optionally also MNP prefix
delegations through IPv6 ND control message exchanges with Proxy/
Servers over MANETs, Access Networks (ANETs) and/or open
Internetworks (INETs). Clients sub-delegate MNPs to downstream-
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attached End-user Networks (ENETs) independently of the underlay
interfaces selected for upstream data transport. Each Client acts as
a fixed or mobile router on behalf of ENET peers, and uses OMNI
interface control messaging to coordinate with Proxy/Servers and/or
other Clients. The Client iterates its control messaging over each
of the OMNI interface's (M)ANET/INET underlay interfaces in order to
register each interface with the MS (see Section 13). The Client can
also provide (proxyed) multihop forwarding services for a recursively
extended chain of other Clients and end systems connected via
downstream-attached *NETs.
Each Proxy/Server on the link delegates SNP GUA addresses from its
unique IPv6 prefix to Clients via the Dynamic Host Configuration
Protocol for IPv6 (DHCPv6) service. DHCPv6 messaging is carried as
IPv6 ND message extensions since each Proxy/Server provides the
combined services of a DHCPv6 Server and IPv6 router. Since the
DHCPv6 service running on each Proxy/Server provides assurance
against address duplication within its own prefix, Clients need not
test the IPv6 SNP GUA addresses they receive for uniqueness. Clients
instead regard each Proxy/Server as the address delegation authority
and designated router for a distinct OMNI link segment.
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 [RFC9365]. Still
other communities of interest include AEEC, RTCA Special Committee
228 (SC-228) and NASA programs that examine commercial aviation,
Urban Air Mobility (UAM) and Unmanned Air Systems (UAS). Pedestrians
with handheld mobile devices using 5G/6G wireless services, home and
small office networks, enterprise networks and many others represent
additional large classes of potential OMNI users.
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This document specifies the transmission of original IP packets and
control messages over OMNI interfaces. The operation of both IP
protocol versions (i.e., IPv4 [RFC0791] and IPv6 [RFC8200]) is
specified as the network layer data plane, while OMNI interfaces use
IPv6 ND messaging in the control plane independently of the data
plane protocol(s). OMNI interfaces also provide an adaptation layer
based on encapsulation and fragmentation over heterogeneous underlay
interfaces as an OAL sublayer between L3 and L2. OMNI and the OAL
are specified in detail throughout the remainder of this document.
2. Terminology
The terminology in the normative references applies; especially, the
terms "link" and "interface" are the same as defined in the IPv6
[RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications.
This document assumes the following IPv6 ND control plane message
types: Router Solicitation (RS), Router Advertisement (RA), Neighbor
Solicitation (NS), Neighbor Advertisement (NA), unsolicited NA (uNA)
and Redirect. AERO further introduces new IPv6 ND pseudo-message
types Multilink Initiate (MI), Multilink Respond (MR) and Multilink
Control (MC) with formats identical to the standard uNA message but
with different Code values. These messages are used to control
adaptation layer functions only and are not exposed to the network
layer. See [I-D.templin-6man-aero3] for a full specification of
MI/MR/MC.
The terms "All-Routers multicast", "All-Nodes multicast" and "Subnet-
Router anycast" are the same as defined in [RFC4291]. Also, IPv6 ND
state names, variables and constants including REACHABLE,
ReachableTime and REACHABLE_TIME are the same as defined in
[RFC4861].
The term "IP" is used to refer collectively to either Internet
Protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) when a
specification at the layer in question applies equally to either
version.
The terms (Proxy/)Client and Proxy/Server are intentionally
capitalized to denote an instance of a particular node type that also
configures an OMNI interface and engages the OMNI Adaptation Layer.
The terms "application layer (L5 and higher)", "transport layer
(L4)", "network layer (L3)", "(data) link layer (L2)" and "physical
layer (L1)" are used consistently with common Internetworking
terminology, with the understanding that reliable delivery protocol
users of UDP are considered as transport layer elements. The OMNI
specification further defines an "adaptation layer" positioned below
the network layer but above the link layer, which may include
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physical links and Internet- or higher-layer tunnels. A (network)
interface is a node's attachment to a link (via L2), and an OMNI
interface is therefore a node's attachment to an OMNI link (via the
adaptation layer).
The terms "IP jumbogram", "advanced jumbo (AJ)" and "IP parcel" refer
to alternative packet formats discussed in
[I-D.templin-6man-parcels2] and [I-D.templin-intarea-parcels2].
The following terms are defined within the scope of this document:
GUA, ULA, LLA, MLA
A Globally-Unique (GUA), Unique-Local (ULA) or Link-Local (LLA)
Address per the IPv6 addressing architecture [RFC4193] [RFC4291],
or a Multilink-Local Address (MLA) per [I-D.templin-6man-mla].
IPv4 prefixes other than those reserved for special purposes
[RFC6890] are also considered as GUA prefixes.
L3
The Network layer in the OSI network model. Also known as "layer
3", "IP layer", etc.
L2
The Data Link layer in the OSI network model. Also known as
"layer 2", "link layer", "sub-IP layer", etc.
Adaptation layer
An encapsulation mid-layer that adapts L3 to a diverse collection
of L2 underlay interfaces and their encapsulations. (No layer
number is assigned, since numbering was an artifact of the legacy
reference model that need not carry forward in the modern
architecture.) The adaptation layer sees the network layer as
"L3" and sees all link layer encapsulations as "L2
encapsulations", which may include UDP, IP and true link layer
(e.g., Ethernet, etc.) headers.
Access Network (ANET)
a connected network region (e.g., an aviation radio access
network, corporate enterprise network, satellite service provider
network, cellular operator network, residential WiFi network,
etc.) that connects Clients to the rest of the OMNI link.
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.
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Mobile Ad-hoc NETwork (MANET)
a connected ANET region for which links often have undetermined
connectivity properties, lower layer security services cannot
always be assumed and multihop forwarding between Clients acting
as MANET routers may be necessary. Clients nested deeply within a
MANET often require adaptation layer proxy services from
"upstream" peer Proxy/Clients located progressively nearer the
MANET border.
Internetwork (INET)
a connected network region with a coherent IP addressing plan that
provides transit forwarding services between ANETs and/or OMNI
nodes that coordinate with the Mobility Service over unprotected
media. Since physical and/or data link level security cannot
always be assumed, security must be applied by the network and/or
higher layers if necessary. The global public Internet itself is
an example.
End-user Network (ENET)
a simple or complex "downstream" network tethered to a Client as a
single logical unit that travels together. The ENET could be as
simple as a single link connecting a single host, or as complex as
a large network with many links, routers, bridges and end user
devices. The ENET provides an "upstream" link for arbitrarily
many low-, medium- or high-end devices dependent on the Client for
their upstream connectivity, i.e., as Internet of Things (IoT)
entities. The ENET can also support a recursively-descending
chain of additional Clients such that the ENET of an upstream
Client is seen as the ANET of a downstream Client.
*NET
a "wildcard" term used when a given specification applies equally
to all MANET/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 and/or
other Clients. Local communications between correspondents within
the same *NET can often be conducted based on IPv6 ULAs [RFC4193]
or MLAs [I-D.templin-6man-mla].
underlay interface
a *NET or ENET interface over which an OMNI interface is
configured. The OMNI interface is seen as an L3 interface by the
network layer, and each underlay interface is seen as an L2
interface by the OMNI interface. The underlay interface either
connects directly to the physical communications media or
coordinates with another node where the physical media is hosted.
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MANET Interface
a node's underlay interface to a local network with indeterminant
neighborhood properties over which multihop relaying may be
necessary. All MANET interfaces used by AERO/OMNI are IPv6
interfaces and therefore must configure a Maximum Transmission
Unit (MTU) no smaller than the IPv6 minimum MTU (1280 octets) even
if lower-layer fragmentation is needed.
OMNI link
a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured
over one or more INETs and their connected (M)ANETs/ENETs. An
OMNI link may comprise multiple distinct "segments" joined by
"bridges" 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 link segment
a Proxy/Server and all of its constituent Clients within any
attached *NETs is considered as a leaf OMNI link segment, with
each leaf interconnected via links and "bridge" nodes in
intermediate OMNI link segments. When the *NETs of multiple leaf
segments overlap (e.g., due to network mobility), they can combine
to form larger *NETs with no changes to Client-to-Proxy/Server
relationships. The OMNI link consists of the concatenation of all
OMNI link leaf and intermediate segments as a loop-free spanning
tree.
OMNI interface
a node's virtual Ethernet (veth) interface to an OMNI link, and
configured over one or more underlay interfaces. If there are
multiple OMNI links in an OMNI domain, a separate OMNI interface
is configured for each link. The OMNI interface configures a
Maximum Transmission Unit (MTU) and an Effective MTU to Receive
(EMTU_R) the same as any interface. The OMNI interface assigns an
LLA the same as for any IPv6 interface and assigns an MLA for
adaptation layer addressing over its underlay networks. The OMNI
interface further assigns any unicast or anycast ULA/GUA addresses
acquired through address autoconfiguration. Since OMNI interface
addresses are managed for uniqueness, OMNI interfaces do not
require Duplicate Address Detection (DAD) and therefore set the
administrative variable 'DupAddrDetectTransmits' to zero
[RFC4862].
OMNI Adaptation Layer (OAL)
an OMNI interface sublayer service that encapsulates original IP
packets admitted into the interface in an IPv6 header and/or
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subjects them to fragmentation and reassembly. The OAL is also
responsible for generating MTU-related control messages as
necessary, and for providing addressing context for OMNI link SRT
traversal. The OAL presents a new layer in the Internet
architecture known simply as the "adaptation layer". The OMNI
link is an example of a limited domain [RFC8799] at the adaptation
layer although its segments may be joined over open Internetworks
at L2.
OMNI Option
a pseudo IPv6 ND option providing multilink parameters for the
OMNI interface as specified in Section 10. The OMNI option is
appended to the end of an IPv6 ND message during OAL encapsulation
such that it appears immediately following the final message
option.
(OMNI) Client
a network platform/device mobile router or end system 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 may also serve as a Proxy for other
Clients on downstream *NETs. The Client's upstream network
interface addresses and performance characteristics may change
over time (e.g., due to node mobility, link quality, etc.) while
other Clients on downstream networks can engage the (upstream)
Client as a Proxy.
(OMNI) Proxy/Server
a segment routing topology edge node that configures an OMNI
interface and connects Clients to the Mobility Service. As a
server, the Proxy/Server responds directly to some Client IPv6 ND
messages. As a proxy, the Proxy/Server forwards other Client IPv6
ND messages to other Proxy/Servers and Clients. As a router, the
Proxy/Server provides a forwarding service for ordinary data
messages that may be essential in some environments and a last
resort in others. Proxy/Servers at (M)ANET boundaries configure
both an (M)ANET downstream interface and *NET upstream interface,
while INET-based Proxy/Servers configure only an INET interface.
All Proxy/Servers configure a Stable Network Prefix (SNP) and
manage 1x1 mappings of internal ULAs and external GUAs according
to [RFC6296].
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 allocate Provider-Aggregated (Proxy/Server-
Aggregated) addresses to Clients within their local networks. FHS
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Proxy/Servers also act as intermediate forwarding systems to
facilitate RS/RA-based Provider-Independent Prefix Delegation
exchanges between Clients and Mobility Anchor Point (MAP) 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.
Mobility Anchor Point (MAP) Proxy/Server
a Proxy/Server selected by the Client that provides a designated
router service for any *NET underlay networks that register the
Client's Mobile Network Prefix (MNP). Since all Proxy/Servers
provide equivalent services, Clients normally select the first FHS
Proxy/Server they coordinate with to serve as the MAP. However,
the MAP can instead be any available Proxy/Server for the OMNI
link, i.e., and not necessarily one of the Client's FHS Proxy/
Servers. This flexible arrangement supports a fully distributed
mobility management service.
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 communicating peer nodes using segment
routing in a manner outside the scope of this document (see:
[I-D.templin-6man-aero3]).
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 all
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-aero3].
Mobility Service Prefix (MSP)
an aggregated IP GUA prefix (e.g., 2001:db8::/32,
2002:192.0.2.0::/40, etc.) assigned to the OMNI link and from
which more-specific Mobile and Stable Network Prefixes (MNPs/SNPs)
are delegated, where IPv4 MSPs are represented as "6to4 prefixes"
per [RFC3056]. 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 8).
OMNI links that connect to the global Internet advertise their
MSPs to their interdomain routing peers.
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Mobile Network Prefix (MNP)
a longer IP prefix delegated from an MSP (e.g.,
2001:db8:1000:2000::/56, 2002:192.0.2.8::/46, etc.) and assigned
to a Client. Clients receive MNPs from MAP Proxy/Servers and sub-
delegate them to routers in downstream ENETs.
Stable Network Prefix (SNP)
a ULA/GUA IP prefix pair assigned to one or more Proxy/Servers
that connect local *NET Client groups to the rest of the OMNI
link. Clients request address delegations from the SNP that can
be used to support global and local-scoped communications.
Clients communicate internally within *NET groups using IPv6 ULAs
assigned in 1x1 correspondence to SNP GUAs made visible to
external peers through IP network address/prefix translation
[RFC6145][RFC6146][RFC6147][RFC6296].
Foreign Network Prefix (FNP)
a global IP prefix not covered by a MSP and assigned to a link or
network outside of the OMNI domain.
Subnet Router Anycast (SRA) Address
An IPv6 address taken from an FNP/MNP/SNP in which the remainder
of the address beyond the prefix is set to the value "all-zeros".
For example, the SRA for 2001:db8:1::/48 is simply 2001:db8:1::
(i.e., with the 80 least significant bits set to 0). For IPv4,
the IPv6 SRA corresponding to the IPv4 prefix 192.0.2.0/24 is
2002:192.0.2.0::/40 per [RFC3056].
Provider-Aggregated (PA) Address
a ULA/GUA address pair delegated to a Client from an FHS Proxy/
Server SNP is considered Provider-Aggregated (PA) or "Proxy/
Server-Aggregated". The Client either assigns the GUA PA address
to its own OMNI interface or allows the FHS Proxy/Server to supply
the address via Network Prefix Translation for IPv6 (NPTv6)
[RFC6296].
Provider-Independent (PI) Address
a GUA allocated from an MNP delegated to a Client via a MAP Proxy/
Server is considered Provider-Independent (PI) or "Proxy/Server-
Independent". The Client assigns PI addresses to (downstream)
ENET interfaces and can also sub-delegate the MNP to downstream
ENET nodes.
original IP packet
a whole IP packet or fragment admitted into the OMNI interface by
the network layer prior to OAL encapsulation/fragmentation, or an
IP packet delivered to the network layer by the OMNI interface
following OAL reassembly/decapsulation.
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OAL packet
an original IP packet encapsulated in an OAL IPv6 header with an
IPv6 Extended Fragment Header extension that includes an 8-octet
(64-bit) OAL Identification value. Each OAL packet is then
subject to fragmentation by the source and reassembly by the
destination.
OAL fragment
a portion of an OAL packet following fragmentation but prior to L2
encapsulation, or following L2 decapsulation but prior to OAL
reassembly.
(OAL) atomic fragment
an OAL packet that can be forwarded without fragmentation, but
still includes an IPv6 Extended Fragment Header with an 8-octet
(64-bit) OAL Identification value and with Index and More
Fragments both set to 0.
(L2) carrier packet
an encapsulated OAL fragment following L2 encapsulation or prior
to L2 decapsulation. OAL sources and destinations exchange
carrier packets over underlay interfaces, and may be separated by
one or more OAL intermediate systems. OAL intermediate systems
may perform re-encapsulation on carrier packets by removing the L2
headers of the first hop network and replacing them with new L2
headers for the next hop network. Carrier packets may themselves
be subject to fragmentation and reassembly in L2 underlay networks
at a layer below the OAL. Carrier packets sent over unsecured
paths use OMNI protocol L2 encapsulations, while those sent over
secured paths use L2 security encapsulations such as IPsec
[RFC4301]. (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 to form OAL packets, then performs OAL
fragmentation and encapsulation to create carrier packets which
may themselves be subject to fragmentation at lower layers. Every
OAL source is also an OMNI link ingress.
OAL destination
an OMNI interface acts as an OAL destination when it decapsulates
carrier packets (while reassembling first, if necessary), then
performs OAL reassembly/decapsulation to derive the original IP
packet. Every OAL destination is also an OMNI link egress.
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OAL intermediate system
an OMNI interface acts as an OAL intermediate system when it
decapsulates carrier packets received from a first segment to
obtain the original OAL packet/fragment, then re-encapsulates in
new L2 headers and sends these new carrier packets into the next
segment. OAL intermediate systems decrement the Hop Limit in OAL
packets/fragments during forwarding, and discard the OAL packet/
fragment if the Hop Limit reaches 0. OAL intermediate systems do
not decrement the TTL/Hop Limit of the original IP packet, which
can only be updated by the network and higher layers. OAL
intermediate systems along the path explicitly addressed by the
OAL IPv6 Destination (e.g., Proxys, etc.) are regarded as
"endpoint" intermediate systems while those not explicitly
addressed (e.g., MANET routers, AERO Gateways, etc.) are regarded
as "transit" intermediate systems.
Multilink
a Client OMNI interface's manner of managing multiple diverse *NET
underlay interfaces as a single logical unit. The OMNI interface
provides a single unified interface to the network layer, while
underlay interface selections are performed on a per-flow basis
considering traffic selectors such as Traffic Class, 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 system's manner of spanning multiple diverse IP
Internetwork and/or private enterprise network "segments" through
OAL encapsulation. Multiple diverse Internetworks (such as the
global public IPv4 and IPv6 Internets) can serve as transit
segments in an end-to-end OAL forwarding path through intermediate
system concatenation of SRT network segments. 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-aero3] for further information.
Multihop
an iterative relaying of carrier packets between Clients 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.
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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 SRA address(es)
corresponding to the MSP(s) assigned to the domain.
AERO Forwarding Information Base (AFIB)
A multilink forwarding table on each OAL source, destination and
intermediate system that includes AERO Forwarding Vectors (AFV)
with both next hop forwarding instructions and context for
reconstructing compressed headers for specific underlay interface
pairs used to communicate with peers. See:
[I-D.templin-6man-aero3] for further discussion.
AERO Forwarding Vector (AFV)
An AFIB entry that includes soft state for each underlay interface
pairwise communication session between peer neighbors. AFVs are
identified by an AFV Index (AFVI) paired with the previous hop L2
address, with the pair established based on an IPv6 ND
solicitation and 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-aero3] for further discussion.
AERO Forwarding Vector Index (AFVI)
A 2-octet or 4-octet integer value supplied by a previous hop OAL
node when it requests a next hop OAL node to create an AFV. (The
AFVI is always processed as a 4-octet value, but compressed
headers may omit the 2 most significant octets when they encode
the value 0.) The next hop OAL node caches the AFVI and L2
address supplied by the previous hop as header compression/
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decompression state for future OAL packets with compressed
headers. The previous hop OAL node must ensure that the AFVI
values it assigns to the next hop via a specific underlay
interface are distinct and reused only after their useful
lifetimes expire. The special value 0 means that no AFVI is
asserted.
flow
a sequence of packets sent from a particular source to a
particular unicast, anycast, or multicast destination that a node
desires to label as a flow. The 3-tuple of the Flow Label, Source
Address and Destination Address fields enable efficient IPv6 flow
classification. The IPv6 Flow Label Specification is observed per
[RFC6437] [RFC6438].
(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 *NET underlay network partition.
The OAL node that performs encapsulation is known as the "L2
source" while the OAL node that performs decapsulation is known as
the "L2 destination"; both OAL end and intermediate systems can
also act as an L2 source or destination. Common L2 encapsulation
combinations include UDP, IP and/or Ethernet using a
port/protocol/type number for OMNI.
L2 address (L2ADDR)
an address that appears in the OMNI protocol L2 encapsulation for
an underlay interface and also in IPv6 ND message OMNI options.
L2ADDR can be either an IP address for IP encapsulations or an
IEEE EUI address [EUI] for direct data link encapsulation. (When
UDP/IP encapsulation is used, the UDP port number is considered an
ancillary extension of the IP L2ADDR.)
OAL Fragment Size (OFS)
the current OAL source fragmentation size for a given flow which
must be no smaller than 1024 octets and should be no larger than
65279 octets to allow sufficient space for OAL and L2
encapsulations. Each OAL source maintains an OFS in an AERO
Forwarding Vector (AFV) for each independent flow. The OAL source
discovers OFS through dynamic probing the same as defined for
Maximum Packet Size (MPS) probing per Section 4.4 of [RFC8899] and
should adaptively seek to maintain the largest possible OFS for
each flow according to current network conditions.
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3. Requirements
OMNI interfaces maintain the same Conceptual Data Structures as for
any IPv6 interface, including the Neighbor Cache, Destination Cache,
Prefix List and Default Router List [RFC4861]. The same as for any
IPv6 interface, different routers on the link may advertise different
prefixes. The OMNI interface must therefore ensure that any
addresses configured from the prefixes and assigned to the interface
are associated with the correct default routers.
OMNI interfaces should limit the size of their IPv6 ND control plane
messages (plus any original IP packet attachments) to the adaptation
layer path MTU which may be as small as the minimum IPv6 link MTU
minus encapsulation overhead. If there are sufficient OMNI
parameters and/or IP packet attachments that would exceed this size,
the OMNI interface should forward the information as multiple smaller
IPv6 ND messages and the recipient accepts the union of all
information received. This allows the messages to travel without
loss due to a size restriction over secured control plane paths that
include IPsec tunnels [RFC4301], secured direct point-to-point links
and/or unsecured paths that require an authentication signature.
Client and Proxy/Server OMNI interfaces maintain per-destination
state in Destination Cache Entries (DCEs) as a level of indirection
into per-neighbor state in Neighbor Cache Entries (NCEs). The
function of these caches and the IPv6 ND Protocol Constants defined
in Section 10 of [RFC4861] apply for this document.
The L3, adaptation and (virtual) L2 layers each include distinct
packet Identification numbering spaces. The adaptation layer employs
an 8-octet Identification numbering space that is distinct from L3/L2
spaces, with an Identification value appearing in an IPv6 Extended
Fragment Header [I-D.templin-6man-ipid-ext2] or an OMNI Compressed
Header (OCH) (see: Section 6.5) in each adaptation layer
encapsulation.
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.
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4. Overlay Multilink Network (OMNI) Interface Model
The IP layer sees the OMNI interface as a virtual Ethernet (veth)
interface configured over one or more underlay interfaces, which may
be physical (e.g., an aeronautical radio link, a cellular wireless
link, etc.) or virtual (e.g., an internet-layer or higher-layer
"tunnel"). The OMNI interface architectural layering model is the
same as in [RFC5558][RFC7847], and augmented as shown in Figure 1.
The network layer therefore sees the OMNI interface as a single L3
interface nexus for multiple underlay interfaces that appear as L2
communication channels in the architecture.
+----------------------------+
| Upper Layer Protocol |
Session-to-IP +---->| |
Address Binding | +----------------------------+
+---->| IP (L3) |
IP Address +---->| |
Binding | +----------------------------+
+---->| OMNI Interface |
Logical-to- +---->| (OMNI Adaptation Layer) |
Physical | +----------------------------+
Interface +---->| L2 | L2 | | L2 |
Binding |(IF#1)|(IF#2)| ..... |(IF#n)|
+------+------+ +------+
| L1 | L1 | | L1 |
| | | | |
+------+------+ +------+
Figure 1: OMNI Interface Architectural Layering Model
Each underlay interface provides an L2/L1 abstraction according to
one of the following models:
* (M)ANET interfaces connect to a (M)ANET that is separated from the
open INET by Proxy/Servers. The (M)ANET interface may be either
on the same link segment as a Proxy/Server, or separated from a
Proxy/Server by multiple adaptation layer and/or L2 hops. (Note
that NATs may appear internally within a (M)ANET or on the Proxy/
Server itself and may require NAT traversal the same as for the
INET case.)
* INET interfaces connect to an INET either natively or through IP
Network Address Translators (NATs). Native INET interfaces have
global IP addresses that are reachable from any INET
correspondent. NATed INET interfaces typically configure private
IP addresses and connect to a private network behind one or more
NATs with the outermost NAT providing INET access.
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* ENET interfaces connect a Client's downstream-attached networks,
where the Client provides forwarding services for ENET end system
communications to remote peers. An ENET may be as simple as a
small IoT sub-network that travels with a mobile Client to as
complex as a large private enterprise network that the Client
connects to a larger *NET. Downstream-attached Clients engage the
ENET as a *NET and engage the (upstream) Client as a Proxy.
* VPN interfaces use security encapsulations (e.g. IPsec tunnels)
over underlay networks to connect Client, Proxy/Server or other
critical infrastructure nodes. VPN interfaces provide security
services at lower layers of the architecture (L2/L1), with
securing properties similar to Direct point-to-point interfaces.
* Direct point-to-point interfaces securely connect Clients, Proxy/
Servers and/or other critical infrastructure nodes over physical
or virtual media that does not transit any open Internetwork
paths. Examples include a line-of-sight link between a remote
pilot and an unmanned aircraft, a fiberoptic link between
gateways, etc.
The OMNI interface forwards original IP packets from the network
layer using the OMNI Adaptation Layer (OAL) (see: Section 5) as an
encapsulation and fragmentation sublayer service. This "OAL source"
then further encapsulates the resulting OAL packets/fragments in
underlay network headers (e.g., UDP/IP, IP-only, Ethernet-only, etc.)
to create L2 encapsulated "carrier packets" for fragmentation and
transmission over underlay interfaces. The target OMNI interface
then receives the carrier packets from underlay interfaces and
performs L2 decapsulation.
If the resulting OAL packets/fragments are addressed to itself, the
OMNI interface performs reassembly/decapsulation as an "OAL
destination" and delivers the original IP packet to the network
layer. If the OAL packets/fragments are addressed to another node,
the OMNI interface instead re-encapsulates them in new underlay
network L2 headers as an "OAL intermediate system" then forwards the
resulting carrier packets over an underlay interface. The OAL source
and OAL destination are seen as "neighbors" on the OMNI link, while
OAL intermediate systems provide a virtual bridging service that
joins the segments of a (multinet) Segment Routing Topology (SRT).
The OMNI interface transports carrier packets over either secured or
unsecured underlay interfaces to access the secured/unsecured OMNI
link spanning trees as discussed further throughout the document.
Carrier packets that carry control plane messages over secured
underlay interfaces use secured L2/L1 services such as IPsec, direct
encapsulation over secured point-to-point links, etc. Carrier
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packets that carry data plane messages over unsecured underlay
interfaces instead use L2 encapsulations appropriate for public or
private Internetworks and are subject for the following sections.
The OMNI interface and its OAL can forward original IP packets over
underlay interfaces while including/omitting various lower layer
encapsulations including OAL, UDP, IP and (ETH)ernet or other link
layer header. The network layer can also engage underlay interfaces
directly while bypassing the OMNI interface entirely when necessary.
This architectural flexibility may be beneficial for underlay
interfaces (e.g., some aviation data links) for which encapsulation
overhead is a primary consideration. OMNI interfaces that send
original IP packets directly over underlay interfaces without
invoking the OAL can only reach peers located on the same OMNI link
segment. Source Clients can instead use the OAL to coordinate with
target Clients in the same or different OMNI link segments by sending
initial carrier packets to a First-Hop Segment (FHS) Proxy/Server.
The FHS Proxy/Sever then sends the carrier packets into the SRT
spanning tree, which transports them to a Last-Hop Segment (LHS)
Proxy/Server for the target Client.
The OMNI interface encapsulation/decapsulation layering possibilities
are shown in Figure 2 below. An imaginary vertical lines drawn
between the Network Layer at the top of the figure and Underlay
Interfaces at the bottom of the figure then allowed to slide
horizontally either to the right or left illustrates the various
encapsulation/decapsulation layering combination possibilities.
Common combinations include IP-only (i.e., direct access to underlay
interfaces with or without using the OMNI interface), IP/IP, IP/UDP/
IP, IP/UDP/IP/ETH, IP/OAL/UDP/IP, IP/OAL/UDP/ETH, etc.
+------------------------------------------------------------+ ^
| Network Layer (Original IP packets) | |
+--+---------------------------------------------------------+ L3
| OMNI Interface (virtual sublayer nexus) | |
+--------------------------+------------------------------+ -
| OAL Encaps/Decaps | ^
+------------------------------+ OAL
| OAL Frag/Reass | v
+------------+---------------+--------------+ -
| 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 |
+------------------------------------------------------------+
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Figure 2: OMNI Interface Layering
The OMNI/OAL model gives rise to a number of opportunities:
* Clients coordinate with the MS and receive both SNP addresses and
MNP delegations through IPv6 ND control plane message exchanges
with Proxy/Servers. Since GUA and ULA addresses are managed for
uniqueness, no Duplicate Address Detection (DAD) or Multicast
Listener Discovery (MLD) messaging is necessary over the OMNI
interface.
* underlay interfaces on the same L2 link segment as a Proxy/Server
do not require any L3 addresses (i.e., not even link-local) in
environments where communications are coordinated entirely over
the OMNI interface.
* as underlay interface properties change (e.g., link quality, cost,
availability, etc.), any active interface can be used to update
the profiles of multiple additional interfaces in a single
message. This allows for timely adaptation and service continuity
under dynamically changing conditions.
* coordinating underlay interfaces in this way allows them to be
represented in a unified MS profile with provisions to support the
"6 M's of Modern Internetworking".
* header compression and path MTU determination is conducted on a
per-flow basis, with each flow adapting to the best performance
profiles and path selections.
* exposing a single virtual interface abstraction to the network
layer allows for multilink operation (including QoS based link
selection, carrier packet replication, load balancing, etc.) at L2
while still permitting L3 traffic shaping based on, e.g., Traffic
Class, Flow Label, etc.
* the OMNI interface supports multinet traversal over the SRT when
communications across different administrative domain network
segments are necessary. This mode of operation would not be
possible via direct communications over the underlay interfaces
themselves.
* the OAL supports lossless and adaptive path MTU mitigations not
available for communications directly over the underlay interfaces
themselves. The OAL supports "packing" of multiple original IP
payload packets within a single OAL "composite packet" and also
supports transmission of IP packets of all sizes up to and
including (advanced) jumbograms.
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* the OAL assigns per-packet Identification values that allow for
adaptation/link layer reliability and data origin authentication.
* L3 sees the OMNI interface as a point of connection to the OMNI
link; if there are multiple OMNI links, L3 will see multiple OMNI
interfaces.
* Multiple independent OMNI interfaces can be used for increased
fault tolerance through Safety-Based Multilink (SBM), with
Performance-Based Multilink (PBM) applied within each interface.
* Multiple independent OMNI links can be joined together into a
single link without requiring renumbering of infrastructure
elements, since the GUAs/ULAs assigned by Proxy/Servers of the
different links will be mutually exclusive.
* OMNI provides robust support for both Provider-Aggregated (PA) and
Provider-Independent (PI) addressing resulting in a versatile
service for all Client use cases.
* The concept of OMNI endpoint intermediate systems allows for
logical partitioning within MANETs without requiring address
aggregation. Instead, MANET routing within each partition is
based on MLA "host routes" that are not redistributed into other
partitions. Each partition connects via multiple interface Proxy/
Clients in a hierarchy of partitions on the path to an FHS Proxy/
Server.
Figure 3 depicts the architectural model for a source Client with an
attached ENET connecting to the OMNI link via multiple independent
*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 shared NBMA 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 forward the carrier packets via FHS Proxy/Servers for
the correct underlay *NETs. The FHS Proxy/Server then re-
encapsulates the carrier packets and forwards them over the SRT which
delivers them to an LHS Proxy/Server, and the LHS Proxy/Server in
turn re-encapsulates and forwards 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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Mobile Clients select a MAP Proxy/Server (not shown in the figure),
which will often be one of their FHS Proxy/Servers but may also be
any Proxy/Server on the OMNI link. Clients then register all of
their *NET underlay interfaces with the MAP Proxy/Server via per
interface FHS Proxy/Servers in a pure proxy role. The MAP Proxy/
Server then provides a designated router that advertises the Client's
MNPs into the OMNI link routing system, and the Client can quickly
migrate to a new MAP Proxy/Server if the former becomes unresponsive.
Clients therefore use Proxy/Servers as bridges into the SRT to reach
OMNI link correspondents via a spanning tree established in a manner
outside the scope of this document. Proxy/Servers forward critical
MS control messages via the secured spanning tree and forward other
messages via the unsecured spanning tree (see Security
Considerations). When AERO route optimization is applied, Clients
can instead forward directly to correspondents in the same SRT
segment to reduce Proxy/Server and/or Gateway load.
Note: Original IP packets sent into an OMNI interface will receive
consistent consideration according to their size as discussed in the
following sections, while those sent directly over underlay
interfaces that exceed the underlay network path MTU are dropped with
an ordinary ICMP Packet Too Big (PTB) message returned. These PTB
messages are subject to loss the same as for any non-OMNI IP
interface [RFC2923].
5. OMNI Interface Maximum Transmission Unit (MTU)
The OMNI interface observes the link nature of tunnels, including the
Maximum Transmission Unit (MTU), Effective MTU to Send (EMTU_S),
Effective MTU to Receive (EMTU_R) and the role of fragmentation and
reassembly [I-D.ietf-intarea-tunnels]. The OMNI interface is
configured over one or more underlay interfaces as discussed in
Section 4, where underlay links and network paths may have diverse
MTUs. OMNI interface considerations for accommodating original IP
packets 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 EMTU_R of 1500 octets [RFC8200].
Therefore, the minimum IPv6 path MTU is 1280 octets since routers on
the path are not permitted to perform network fragmentation even
though the destination is required to reassemble more. The network
therefore MUST forward original IP packets as large as 1280 octets
without generating an IPv6 Path MTU Discovery (PMTUD) Packet Too Big
(PTB) message [RFC8201].
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IPv4 underlay interfaces are REQUIRED to configure a minimum MTU of
68 octets [RFC0791] and a minimum EMTU_R of 576 octets
[RFC0791][RFC1122]. However, links that configure small MTUs are
likely to have low-end performance and occur only at the extreme
network edges while higher-performance interior network links should
configure MTUs no smaller than 1280 octets and EMTU_Rs no smaller
than 1500 octets [RFC3819].
The OMNI interface itself sets an "unlimited" MTU of (2**32 - 1)
octets. The network layer therefore unconditionally admits all
original IP packets into the OMNI interface, where the adaptation
layer accommodates them if possible according to their size. The OAL
source then invokes adaptation layer encapsulation/fragmentation
services to transform all original IP packets no larger than 65535
octets into OAL packets/fragments. The OAL source then applies L2
encapsulation to form carrier packets and finally forwards the
carrier packets via underlay interfaces.
When the OAL source performs IPv6 encapsulation and fragmentation
(see: Section 6), the Payload Length field limits the maximum-sized
original IP packet that the OAL can accommodate while applying IPv6
fragmentation to (2**16 - 1) = 65535 octets (i.e., not including the
OAL encapsulation header lengths). The OAL source is also permitted
to forward packets larger than this size as a best-effort delivery
service if the L2 path can accommodate them through "jumbo-in-jumbo"
encapsulation (see: [I-D.templin-6man-parcels2]); otherwise, the OAL
source discards the packet and arranges to return a PTB "hard error"
to the original source (see: Section 6.9).
Each OMNI interface therefore sets a minimum EMTU_R of 65535 octets
(plus the length of the OAL encapsulation headers), and each OAL
destination must consistently either accept or reject still larger
whole packets that arrive over any of its underlay interfaces
according to their size. If an underlay interface presents a whole
packet larger than the OAL destination is prepared to accept (e.g.,
due to a buffer size restriction), the OAL destination discards the
packet and arranges to return a PTB "hard error" to the OAL source
which in turn forwards the PTB to the original source (see:
Section 6.9).
6. The OMNI Adaptation Layer (OAL)
The OMNI interface forwards original IP packets from the network
layer for transmission over one or more underlay interfaces. The
OMNI Adaptation Layer (OAL) acting as the OAL source then replaces
the virtual Ethernet header with an IPv6 encapsulation header to form
OAL packets. OAL source fragmentation then breaks the packets into
IPv6 fragments suitable for L2 encapsulation and transmission as
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carrier packets.
The carrier packets then traverse one or more underlay networks
spanned by OAL intermediate systems in the SRT. Each successive OAL
intermediate system then re-encapsulates by removing the L2 headers
of the first underlay network and appending L2 headers appropriate
for the next underlay network. (This process supports the multinet
concatenation capability needed for joining multiple diverse
networks.) Following any forwarding by OAL intermediate systems, the
carrier packets eventually arrive at the OAL destination.
When the OAL destination receives the carrier packets, it discards
the L2 headers and reassembles the resulting OAL fragments into an
OAL packet as described in Section 6.3. The OAL destination next
replaces the OAL packet IPv6 encapsulation header with a virtual
Ethernet header to obtain the original IP packet for delivery to the
network layer via the OMNI interface. 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 per [I-D.templin-6man-aero3]) may also
serve as OAL intermediate systems.
The OAL presents an OMNI sublayer abstraction similar to ATM
Adaptation Layer 5 (AAL5). Unlike AAL5 which performs segmentation
and reassembly with fixed-length 53-octet cells over ATM networks,
however, the OAL uses IPv6 encapsulation, fragmentation and
reassembly with larger variable-length cells over heterogeneous
networks. Detailed operations of the OAL are specified in the
following sections.
6.1. OAL Source Encapsulation and Fragmentation
When the network layer forwards an original IP packet into the OMNI
interface, it either sets the TTL/Hop Limit for locally-generated
packets or decrements the TTL/Hop Limit according to standard IP
forwarding rules. The OAL source next creates an "OAL packet" by
replacing the virtual Ethernet header with an IPv6 encapsulation
header per [RFC2473]. The OAL source sets the IPv6 encapsulation
header Version to "OMNI-OFH" (see: Section 6.2) and Next Header to
TBD1 (see: IANA Considerations).
When the OAL source performs IPv6 encapsulation, it sets the IPv6
header "Flow Label" as specified in [RFC6438]. The OAL source next
copies the "Type of Service/Traffic Class Differentiated Service Code
Point (DSCP)" [RFC2474][RFC2983] and "Explicit Congestion
Notification (ECN)" [RFC3168] values in the original packet's IP
header into the corresponding fields of the OAL IPv6 header.
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For original IP packets with DSCP '111111' (including ordinary
network control/data plane messages), the OAL source resets the OAL
IPv6 encapsulation header DSCP to '110111'. The OAL source instead
sets the IPv6 encapsulation header DSCP to '111111' for adaptation
layer control plane messages that must be processed by all OAL
intermediate systems on the path including both endpoints and
transits. These DSCP values belong to the "Pool 2 Experimental and
Local Use (EXP/LU)" range reserved in [RFC2474] and correspond to
Network/Internetwork Control precedence in [RFC0791].
The OAL source next sets the IPv6 header Payload Length to the length
of the original IP packet and sets Hop Limit to a value that is
sufficiently large to support loop-free forwarding over multiple
concatenated OAL intermediate hops. The OAL source next selects OAL
IPv6 Source and Destination Addresses associated with its own OMNI
interface and the OMNI interface of the target. (These are MLA
addresses that correspond to the virtual Ethernet source and
destination MAC addresses as maintained in a per neighbor address
mapping cache for the interface - see: Section 8.)
The OAL source next inserts any necessary extension headers following
the IPv6 header as specified in Section 6.4. For OAL data plane
packets, the source first inserts any per-fragment extension headers
(e.g., Hop-by-Hop, Routing, etc.) then inserts an IPv6 Extended
Fragment Header (see: [I-D.templin-6man-ipid-ext2]) with an 8-octet
(64-bit) OAL packet Identification. Note that the extension header
insertions could cause the IPv6 Payload Length to exceed 65535 octets
by a small amount when the original IP packet is (nearly) the maximum
length.
The OAL source then source-fragments the OAL packet if necessary
according to an OAL Fragment Size (OFS) maintained in AERO Forwarding
Vectors (AVFs) for each independent flow. (The OAL source
encapsulates payloads that are no larger than the OFS and original IP
packets larger than 65535 octets as "atomic fragments".) OAL
fragments prepared by the source must not be fragmented further by
OAL intermediate systems on the path to the OAL destination.
OAL packets that contain original IP packets no larger than 65535
octets are subject to OAL source fragmentation using the IPv6
Extended Fragment Header (EFH) fragmentation specification
[I-D.templin-6man-ipid-ext2] with the exception that the IPv6 Payload
Length may exceed 65535 by at most the length of the extension
headers. For each independent flow, the OAL source MUST set OFS to a
size no smaller than 1024 octets and thereafter adjust OFS according
to dynamic network control message feedback. The OAL source SHOULD
limit OFS to a size no larger than 65279 octets unless it has
assurance that the path can accommodate a larger size. (Note: the
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minimum size ensures that OAL fragments can be accommodated over any
potential combination of IPv4/IPv6 underlay network paths where
transit for smaller sizes is assured without probing, while the
maximum size observes the 65535 octet limitation for conventional IP
packets.)
When the OAL source performs fragmentation, it SHOULD produce the
minimum number of fragments under current OFS constraints. The
fragments produced MUST be non-overlapping and the portion of each
non-final fragment following the IPv6 Extended Fragment Header MUST
be equal in length while that of the final fragment MAY be smaller
and MUST NOT be larger.
For each consecutive OAL fragment beginning with the first, the OAL
source then writes a monotonically-increasing "ordinal" value between
0 and 63 in the Extended Fragment Header Index field. Specifically,
the OAL source writes the ordinal value '0' for the first fragment,
'1' for the first non-first fragment, '2' for the next, '3' for the
next, etc. up to the final fragment. The final fragment may assign
an ordinal as large as '63' such that at most 64 fragments are
possible. During a network path change, an OAL intermediate system
may apply further OAL fragmentation to produce minimum-length
(sub-)fragments. The OAL destination will then reassemble these
(sub-)fragments then combine each reassembled fragment with all other
fragments of the same OAL packet and return rate-limited indications
to inform the OAL source that the path has changed.
The OAL source finally encapsulates the fragments in L2 headers to
form carrier packets for transmission over underlay interfaces, while
retaining the fragments and their ordinal numbers (i.e., #0, #1, #2,
etc.) for a brief period to support adaptation layer retransmissions
(see: Section 6.8). OAL fragment and carrier packet formats are
shown in Figure 4.
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+----------+-------------------------+---------------+
|OAL Header| Original Packet Headers | Frag #0 |
+----------+-------------------------+---------------+
+----------+----------------+
|OAL Header| Frag #1 |
+----------+----------------+
+----------+----------------+
|OAL Header| Frag #2 |
+----------+----------------+
....
+----------+----------------+
|OAL Header| Frag #(N-1) |
+----------+----------------+
a) OAL fragmentation
+----------+-----------------------------+
|OAL Header| Original IP packet |
+----------+-----------------------------+
b) An OAL atomic fragment
+--------+----------+----------------+
|L2 Hdrs |OAL Header| Frag #i |
+--------+----------+----------------+
c) OAL carrier packet after L2 encapsulation
Figure 4: OAL Fragments and Carrier Packets
After establishing AFV state in the forward path for a given flow,
the OAL source dynamically manages the per-flow OFS by continually
probing the forward path to the OAL destination beginning with a size
no smaller than 1024 octets and increasing to progressively larger
sizes per [RFC8899]. In this process, the OAL source acts as a
datagram packetization layer for the flow when it applies OAL
encapsulation, fragmentation and header compression.
The OAL source creates a probe by setting the P flag in the Type 1
OMNI Compressed Header (OCH1) (see: Section 6.5) of a probe packet
for the flow. For probes that advance the OFS to a larger size, the
probe packet can include discard data (e.g., an IP packet with Next
Header/Protocol set to 59 ("No Next Header"), a UDP packet with
service port number set to 9 ("discard"), etc.) or live protocol data
with null padding. For probes that confirm the current OFS, the
probe packet can instead entirely include live protocol data. The
OAL source then admits the probe for L2 encapsulation and
transmission.
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When the OAL destination receives the probe, it returns an OAL-
encapsulated secured control message to the OAL source with an OMNI
option that includes an ICMPv6 Error sub-option. The OAL destination
sets the ICMPv6 message Type to 2 ("Packet Too Big") and Code to "MTU
Probe Reply" (see: IANA Considerations), then sets MTU to the size of
the probe message minus the difference in size between the OAL/IP
full headers and the OCH1 header. The OAL destination then copies
the leading 512 octets of the probe beginning with the full OAL and
IP headers (i.e., replacing the OCH1 header) into the ICMPv6 message
body. The OAL destination then returns the secured control message
to the OAL source without marking it for examination by OAL
intermediate systems.
When the OAL source receives the secured control message, it can
determine that the message did not originate from an attacker. The
OAL source can then tentatively advance OFS for this flow to the
larger size reported in the ICMPv6 MTU option (minus OAL
encapsulation overhead) but should maintain an ongoing stream of
additional probes for the flow to confirm the current OFS and/or to
advance to still larger OFS values. The OAL source may additionally
receive MTU soft error feedback from an OMNI destination or
intermediate system and should compensate accordingly as discussed in
Section 6.9.
6.2. OAL L2 Encapsulation and Re-Encapsulation
The OAL source or intermediate system next encapsulates each OAL
fragment (with either full or compressed headers) in L2 encapsulation
headers to create a carrier packet. The OAL source or intermediate
system (i.e., the L2 source) includes a UDP header as the innermost
sublayer if NATs and/or filtering middleboxes might occur on the
path. Otherwise, the L2 source includes a full/compressed IP header
and/or an actual link layer header (e.g., such as for Ethernet-
compatible links) as the innermost sublayer. The L2 source also
appends any additional encapsulation sublayer headers necessary
(e.g., IPsec AH/ESP, jumbo-in-jumbo encapsulation, etc.).
The L2 source encapsulates the OAL information immediately following
the innermost L2 sublayer header. The L2 source next interprets the
first 4 bits following the L2 headers as a Type field that determines
the type of OAL header that follows. The OAL source sets Type to
(OMNI-OFH) for an uncompressed IPv6 OMNI Full Header (OFH) or (OMNI-
OCH1/2) for an OMNI Compressed Header, Type 1 (OCH1) or 2 (OCH2) as
specified in Section 6.5. For IP packets that do not include an OAL
IPv6 encapsulation header, the L2 source instead interprets the first
4 bits as a Version field that encodes '4' (OMNI-IP4) for an ordinary
IPv4 packet or '6' (OMNI-IP6) for an ordinary IPv6 packet. Other
Type values may also appear as specified in Section 6.5.
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The OAL node prepares the L2 encapsulation headers for OAL packets/
fragments as follows:
* For UDP/IP encapsulation, the L2 source sets the UDP source port
to 8060 (i.e., the port number reserved for AERO/OMNI). When the
L2 destination is a Proxy/Server or Gateway, the L2 source sets
the UDP Destination Port to 8060; otherwise, the L2 source sets
the UDP Destination Port to its cached port number value for the
peer. The L2 source next sets the UDP Length the same as
specified in [I-D.ietf-tsvwg-udp-options].
* The L2 source then sets the IP {Protocol, Next Header} to '17'
(the UDP protocol number) and sets the {Total, Payload} Length the
same as specified in the base IP protocol specifications for
ordinary IP packets (see: [RFC0791], [RFC8200] and
[I-D.ietf-tsvwg-udp-options]). The L2 source then continues to
set the remaining IP header fields as discussed below.
* For raw IP 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]. The L2 source then continues to set the remaining IP
header fields as discussed below.
* For IPsec AH/ESP encapsulation, the L2 source sets the appropriate
IP or UDP header to indicate AH/ESP then sets the AH/ESP Next
Header field to TBD1 the same as for raw IP encapsulation.
* For direct encapsulations over Ethernet-compatible links, the L2
source prepares an Ethernet Header with EtherType set to TBD2
(see: Section 21.2) (see: Section 7).
* For OAL packet/fragment encapsulations over secured underlay
interface connections to the secured spanning tree, the L2 source
applies any L2 security encapsulations according to the protocol
(e.g., IPsec). These secured carrier packets are then subject to
lower layer security services.
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When an L2 source includes a UDP header, it SHOULD calculate and
include a UDP checksum in carrier packets with full OAL headers to
prevent mis-delivery and/or detect IPv4 reassembly corruption; the L2
source MAY set UDP checksum to 0 (disabled) in carrier packets with
compressed OAL headers (see: Section 6.5) or when reassembly
corruption is not a concern. If the L2 source discovers that a path
is dropping carrier packets with UDP checksums disabled, it should
supply UDP checksums in future carrier packets sent to the same L2
destination. If the L2 source discovers that a path is dropping
carrier packets that do not include a UDP header, it should include a
UDP header in future carrier packets.
When an L2 source sends carrier packets with compressed OAL headers
and with UDP checksums disabled, mis-delivery due to corruption of
the AFVI is possible but unlikely since the corrupted index would
somehow have to match valid state in the (sparsely-populated) AERO
Forwarding Information Base (AFIB). In the unlikely event that a
match occurs, an OAL destination may receive carrier packets that
contain a mis-delivered OAL fragment but can immediately reject any
with incorrect Identifications. If the Identification value is
somehow accepted, the OAL destination may submit the mis-delivered
OAL fragment to the reassembly cache where it will most likely be
rejected due to incorrect reassembly parameters. If a reassembly
that includes the mis-delivered OAL fragment somehow succeeds (or,
for atomic fragments) the OAL destination will verify any included
checksums to detect corruption. Finally, any spurious data that
somehow eludes all prior checks will be detected and rejected by end-
to-end upper layer integrity checks. See: [RFC6935] [RFC6936] for
further discussion.
For UDP/IP or IP-only L2 encapsulations, when the L2 source is also
the OAL source it next copies the DSCP, ECN and Flow Label values
from the OAL header into the L2 header. 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 IP
Source and Destination Addresses to direct the carrier packet to the
next OAL hop. For carrier packets subject to re-encapsulation, the
OAL intermediate system removes the L2 header(s) then prepares to act
as the L2 source for the next hop.
The L2 source first decrements the OAL header Hop Limit and discards
the OAL packet/fragment if the value reaches 0. Otherwise, the L2
source copies the DSCP value from OAL IPv6 header into the next
segment L2 encapsulation header while setting the next segment L2 IP
Source and Destination Addresses the same as above. The L2 source
then copies the ECN value from the previous segment L2 encapsulation
header into both the OAL full/compressed header and the next segment
L2 encapsulation header.
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The L2 source then prepares to forward the carrier packets to the
next OAL intermediate system or destination. For L2 encapsulations
over IPv4, if the carrier packet is no larger than 1280 octets the L2
source sets the IPv4 Don't Fragment (DF) bit to 0 and includes a
suitable IPv4 Identification value; otherwise, the OAL source sets DF
to 1. This ensures that all IPv4 carrier packets no larger than 1280
octets will be delivered to the L2 destination even if a small amount
of fragmentation occurs in the path (see: [RFC3819] for IPv4 link MTU
expectations according to their performance characteristics).
For IPv4 carrier packets that set DF to 1 and for all IPv6 carrier
packets, delivery is best-effort according to the available path MTU
in the spirit of [RFC2473] and [RFC4213]. Since carrier packet
transmissions are not within the scope of an explicit tunnel required
to pass the IPv6 minimum MTU, however, there is no need for the L2
source to apply L2 source fragmentation since the 1024 octet minimum
OFS is operationally assured over all IPv4 and IPv6 paths. The L2
source should therefore ignore any ICMPv6 Packet Too Big or IPv4
Fragmentation Needed messages returned from the network in response
to any of its large carrier packet transmissions since the OAL source
engages in active probing per [RFC8899].
The L2 source then sends the resulting carrier packets over one or
more underlay interfaces. Underlay interfaces often connect directly
to physical media on the local platform (e.g., an aircraft with a
radio frequency link, a laptop computer with WiFi, etc.), but in some
configurations the physical media may be hosted on a separate Local
Area Network (LAN) node. In that case, the OMNI interface can
establish a Layer-2 VLAN or a point-to-point tunnel (at a layer below
the underlay interface) to the node hosting the physical media. The
OMNI interface may also apply encapsulation at the underlay interface
layer (e.g., as for a tunnel virtual interface) such that carrier
packets would appear "double-encapsulated" on the LAN; the node
hosting the physical media in turn removes the LAN encapsulation
prior to transmission or inserts it following reception. Finally,
the underlay interface must monitor the node hosting the physical
media (e.g., through periodic keepalives) so that it can convey up-
to-date Interface Attribute information to the OMNI interface.
6.3. Reassembly and Decapsulation
For both IPv4 and IPv6, OAL intermediate systems and destinations
MUST configure an L2 minimum EMTU_R of 1500 octets on all unsecured
underlay interfaces. (Secured underlay interfaces instead use an
EMTU_R specific to the L2 security service such as IPsec.) OAL
intermediate systems and destinations are permitted to configure a
larger L2 EMTU_R in order to pass larger unfragmented carrier
packets, but need not reassemble more than 1500.
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OAL destinations MUST configure an adaptation layer EMTU_R of 65535
octets to support reassembly of fragmented OAL packets of all sizes.
OAL nodes must further recognize and honor the extended
Identifications included in the IPv6 Extended Fragment Header
[I-D.templin-6man-ipid-ext2].
When an OMNI interface processes a carrier packet received on an
underlay interface, it copies the ECN value from the L2 encapsulation
headers into the OAL header but does not copy the DSCP value from the
L2 encapsulation headers into the OAL header according to the
differentiated services pipe model for tunnels [RFC2983]. The OMNI
interface next discards the L2 encapsulation headers and examines the
OAL header of the enclosed OAL packet/fragment according to the value
in the Type field as discussed in Section 6.2
If the OAL packet/fragment is addressed to a different node, the OMNI
interface (acting as an OAL intermediate system) decrements the OAL
Hop Limit as discussed in Section 6.2 then performs L2 encapsulation
and forwards the resulting carrier packet. If the OAL packet/
fragment is addressed to itself, the OMNI interface (acting as an OAL
destination) accepts or drops based on the (Source, Destination,
Identification)-tuple.
The OAL destination next drops all ordinal OAL non-first fragments
that would overlap or leave "holes" with respect to other ordinal
fragments already received. The OAL destination updates a checklist
of accepted ordinal fragments of the same OAL packet but admits all
accepted fragments into the reassembly cache.
During reassembly at the OAL destination, the reassembled OAL packet
may exceed 65535 by a small amount equal to the size of the OAL
encapsulation extension headers. The OAL destination does not write
this (too-large) value into the OAL header Payload Length field, but
instead remembers the value during reassembly. When reassembly is
complete, the OAL destination finally replaces the OAL IPv6
encapsulation header with a virtual Ethernet header. The OAL
destination's OMNI interface then delivers the original IP packet to
the network layer. The original IP packet may therefore be as large
as 65535 octets.
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When an OAL path traverses an IPv6 network with routers that perform
adaptation layer forwarding based on full IPv6 headers with OAL
addresses, the OAL intermediate system at the head of the IPv6 path
forwards the OAL packet/fragment the same as an ordinary IPv6 packet
without decapsulating and delivering to the network layer. Once
within the IPv6 network, these OAL packets/fragments may traverse
arbitrarily-many IPv6 hops before arriving at an OAL intermediate
system which may again encapsulate the OAL packets/fragments as
carrier packets for transmission over underlay interfaces.
Note: carrier packets often traverse paths with underlying links that
use integrity checks such as CRC-32 which provide adequate hop-by-hop
integrity assurance for payloads up to ~9K octets [CRC]. However,
other paths may traverse links (such as fragmenting tunnels over IPv4
- see: [RFC4963]) that do not include adequate checks.
6.4. OMNI-Encoded IPv6 Extension Headers
The IPv6 specification [RFC8200] defines extension headers that
follow the base IPv6 header, while Upper Layer Protocols (ULPs) are
specified in other documents. Each extension header present is
identified by a "Next Header" octet in the previous (extension)
header and encodes a "Next Header" field in the first octet that
identifies the next extension header or ULP instance. The OMNI
specification supports encoding of IPv6 extension header chains
immediately following the OMNI L2 UDP, IP or Ethernet header even if
the L2 IP protocol version is IPv4. In all cases, the length of the
IPv6 extension header chain is limited by [I-D.ietf-6man-eh-limits].
The OAL source prepares an OMNI extension header chain by setting the
first 4 bits of the first IPv6 extension header in the chain to a
Type value for the extension header itself immediately following the
OMNI L2 protocol header. The source then sets the next 4 bits to a
Next value that identifies either a terminating ULP or the next
extension header in the chain. The source then sets the first 8 bits
of each subsequent IPv6 extension header in the chain to the standard
Next Header encoding as shown in Figure 5:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ OMNI L2 UDP, IP or Ethernet Header ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Next | Extension Header #1 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Extension Header #2 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Extension Header #3 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Extension Header #N ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ OMNI Full/Compressed, IPv6/IPv4, TCP/UDP, ICMPv6, ESP, etc. ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: OMNI Extension Header Chains
The following Type/Next values are currently defined:
0 (OMNI-RES) - Reserved for experimentation.
1 (OMNI-OCH1) - OMNI Compressed Header, Type 1 per Section 6.5.
2 (OMNI-OCH2) - OMNI Compressed Header, Type 2 per Section 6.5.
3 (OMNI-OFH) - OMNI Full Header, per Section 6.5.
4 (OMNI-IP4) - IPv4 header per [RFC0791].
5 (OMNI-HBH) - Hop-by-Hop Options per Section 4.3 of [RFC8200].
6 (OMNI-IP6) - IPv6 header per [RFC8200].
7 (OMNI-RH) - Routing Header per Section 4.4 of [RFC8200].
8 (OMNI-FH) - Fragment Header per Section 4.5 of [RFC8200].
9 (OMNI-DO) - Destination Options per Section 4.6 of [RFC8200].
10 (OMNI-AH) - Authentication Header per [RFC4302].
11 (OMNI-ESP) - Encapsulating Security Payload per [RFC4303].
12 (OMNI-NNH) - No Next Header per Section 4.7 of [RFC8200].
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13 (OMNI-TCP) - TCP Header per [RFC9293].
14 (OMNI-UDP) - UDP Header per [RFC0768].
15 (OMNI-ULP) - Upper Layer Protocol shim (see below).
Entries OMNI-OCH1 through OMNI-AH in the above list follow the
convention that the OMNI Type/Version appears in the first 4 bits of
the extension header (or IP header) itself. Conversely, entries
OMNI-ESP through OMNI-UDP represent commonly-used ULPs which do not
encode a Type/Version in the first 4 bits.
Entries OMNI-HBH, OMNI-RH, OMNI-FH, OMNI-DO and OMNI-AH represent
true IPv6 extension headers encoded for OMNI, which may be chained.
Source and destination processing of OMNI extension headers follows
exactly per their definitions in the normative references, with the
exception of the special (Type, Next) coding in the first 8 bits of
the first extension header.
When a ULP not found in the above table immediately follows the OMNI
L2 UDP, IP or Ethernet header, the source includes a 2-octet "Type 1
ULP Shim" before the ULP where both the first 4 bit (Type) and next 4
bit (Next) fields encode the special value 15 (OMNI-ULP). The source
then includes a Next Header field that encodes the IP protocol number
of the ULP. The source then includes the ULP data immediately after
the shim as shown in Figure 6.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type=15|Next=15| Next Header | Upper Layer Protocol ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: OMNI Upper Layer Protocol (ULP) Shim (Type 1)
When a ULP "OMNI-(N)" found in the above table immediately follows
the OMNI L2 UDP, IP or Ethernet header, the source includes a 1-octet
"Type 2 ULP Shim" before the ULP where the first 4 bits encode the
special Type value 15 (OMNI-ULP) and the next 4 bits encode the Next
ULP type "N" taken from the table above. The source then includes
the ULP data immediately after the shim as shown in Figure 7.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type=15| Next=N| Upper Layer Protocol ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: OMNI Upper Layer Protocol (ULP) Shim (Type 2)
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When a ULP not found in the above table follows a first OMNI
extension header, the source sets the extension header Next field to
OMNI-ULP (15) and includes a 1-octet "Type 3 ULP Shim" that encodes
the IP protocol number for the Next Header of the ULP data that
follows as shown in Figure 8.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Upper Layer Protocol ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: OMNI Upper Layer Protocol (ULP) Shim (Type 3)
When a ULP "OMNI-(N)" found in the above table follows a first OMNI
extension header, the source sets the extension header Next field to
the ULP Type "N" and does not include a shim. The ULP then begins
immediately after the first OMNI extension header.
When a ULP of any kind follows a non-first OMNI extension header, the
source sets the extension header Next Header field to the IP protocol
number for the ULP and does not include a shim. The ULP then begins
immediately after the non-first OMNI extension header.
Note: The L2 UDP header (when present) is logically considered as the
first L2 extension header in the chain. If an Advanced Jumbo
extension header is also present, its Jumbo Payload length includes
the length of the L2 UDP header.
Note: After a node parses the extension header chain, it changes the
"Type/Next" field in the first extension header back to the correct
"Next Header" value before processing the first extension header.
6.5. OMNI Full and Compressed Headers (OFH/OCH)
OAL sources that send OAL packets with OMNI Full Headers (OFH)
include a Segment Routing Header (SRH) as an OFH extension per
[RFC8754]. The Segment List elements include the MLAs of the OAL end
systems themselves, the MLAs of any edge network partition border OAL
intermediate systems and the SNP SRA GUAs of OAL intermediate systems
in the global Internetwork. Client end systems discover the Segment
List elements in their RS/RA exchanges with Internetworking Proxy/
Servers, where each partition border OAL intermediate system in the
RS message forward path records its MLA before forwarding to the next
partition border OAL intermediate system.
The SRH is followed by an IPv6 Extended Fragment Header to support
segment-by-segment forwarding based on an AERO Forwarding Information
Base (AFIB) in each OAL intermediate system. OAL sources,
intermediate systems and destinations establish header compression
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state in the AFIB through IPv6 ND control message exchanges. After
an initial control message exchange, OAL nodes can apply OMNI Header
Compression to significantly reduce header overhead.
OAL nodes apply header compression in order to avoid transmission of
redundant data found in the original IP packet and OAL encapsulation
headers; the resulting compressed headers are often significantly
smaller than the original IP packet header itself even when OAL
encapsulation is applied. Header compression is limited to the OAL
IPv6 encapsulation header plus extensions along with the base
original IP packet header; it does not extend to include any
extension headers of the original IP packet which appear as upper
layer payload immediately following the compressed headers.
Each OAL node establishes AFIB soft state entries known as AERO
Forwarding Vectors (AFVs) which support both OAL packet/fragment
forwarding and OAL/IPv6 header compression/decompression. The FHS
OAL sources references each AFV by an AERO Forwarding Vector Index
(AFVI) which in conjunction with the previous hop L2ADDR provides
compression/decompression and next hop forwarding context.
When an OAL node sends carrier packets that contain OAL packets/
fragments to a next hop, it includes an OFH with an SRH containing
segment addressing information followed by an Extended Fragment
Header. If the OAL source applied OAL encapsulation, the first 4
bits following the L2 headers must encode the Type OMNI-OFH to
signify that an uncompressed OFH (plus extensions) is present;
otherwise, the first 4 bits must encode the value OMNI-IP6 as a Type/
Version value for IPv6.
When AFV state is available, the OAL source should omit significant
portions of the OAL header (plus extensions) and the entire original
IP packet header by applying OMNI header compression. For OAL first
fragments (including atomic fragments), the OAL source uses OMNI
Compressed Header, Type 1 (OCH1) Format (a) as shown in Figure 9:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |A|F|M|P| Reserved | Traffic Class | OAL Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL Identification (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFVI (2 or 4 octets) / Payload Len (0 or 2 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L3 Next Header| L3 Hop Limit |Header Checksum (0 or 2 octets)|
+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+
Figure 9: OMNI Compressed Header (OCH1) Format (a)
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The format begins with a 4-bit Type followed by 4 flag bits followed
by an 8-bit Reserved field followed by the 8-bit Traffic Class
(copied into the OAL header from the original IP packet header)
followed by an 8-bit (OAL) Hop Limit. The header next includes the 4
least significant octets of the OAL Identification followed by a
2/4-octet AFVI according to whether the (A) flag is set to 0/1,
respectively. The format then includes a 2-octet Payload Length only
if the L2 header does not include a length field. The format finally
includes the Next Header and Hop Limit values from the original (L3)
IP packet header, plus a 2-octet Header Checksum only for IPv4
original packets. (Note that these values represent compression of
the original IP packet header plus the OFH header along with its SRH
and Extended Fragment Header in a unified concatenation.)
The OAL node sets Type to OMNI-OCH1, sets Hop Limit to the
uncompressed OAL header Hop Limit and sets the ECN bits in the
Traffic Class field the same as for an uncompressed IP header. The
OAL node next sets (F)ormat to 0 then sets (M)ore Fragments the same
as for an uncompressed Extended Fragment Header while also setting
Reserved to 0 (note that when the Reserved field is non-zero it is
interpreted according to [I-D.templin-6man-parcels2]). The OAL node
finally sets the L3 Next Header and Hop Limit fields to the values
that would appear in the uncompressed original IP header; the OAL
node also includes a 2-octet Header Checksum for IPv4 original
packets, or omits the Header Checksum for IPv6 original packets.
The payload of the OAL first fragment (i.e., beginning after the
original IP header) is then included immediately following the OCH1
header, and the L2 header length field (if present) is reduced by the
difference in length between the compressed and full-length headers.
If the L2 header includes a length field, the OAL destination can
determine the payload length by examining the L2 header; otherwise,
the OCH1 header itself includes a 2-octet Payload Length field that
encodes the length of the packet payload that follows the OCH1. Note
that OAL first fragments (and atomic packets) are logically
considered ordinal fragment 0 even though no ordinal value is
transmitted.
When the OAL source needs to probe the OAL Fragment Size (OFS) for a
given flow, it sets the (P)robe flag and includes a probe message of
the desired size following the OCH1 header. Upon receipt, the OAL
destination returns a control message to the OAL source. When the
OAL source receives the control message, it can either maintain its
current OFS for this flow or advanced to a larger OFS according to
the probe size.
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For OAL non-first fragments (i.e., those with non-zero Index), the
OAL uses OMNI Compressed Header, Type 1 (OCH1) Format (b) as shown in
Figure 10:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |A|F|M|R|Res| Index | Traffic Class | OAL Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFVI (2 or 4 octets) / Payload Len (0 or 2 octets) |
+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+
Figure 10: OMNI Compressed Header (OCH1) Format (b)
The format begins with a 4-bit Type followed by 4 flags followed by a
2-bit Reserved field (set to 0) followed by a 6-bit ordinal fragment
Index. All other fields up to and including the Payload Length (if
present) are included the same as for an OCH1 first fragment.
The OAL node sets Type to OMNI-OCH1, sets Hop Limit to the
uncompressed OAL header Hop Limit value, sets (Index, (A)FVI, (M)ore
Fragments, Identification) to their appropriate values as a non-first
fragment and sets (F)ormat to 1. In the process, the OAL Node sets
Index to a monotonically increasing ordinal value beginning with 1
for the first non-first fragment, 2 for the second non-first
fragment, 3 for the third non-first fragment, etc., up to at most 63
for the final fragment.
The OAL non-first fragment body is then included immediately
following the OCH1 header, and the L2 header length field (if
present) is reduced by the difference in length between the
compressed headers and full-length original IP header with OFH plus
extensions. The OAL destination will then be able to determine the
Payload Length by examining the L2 header length field if present;
otherwise by examining the 2-octet OCH1 Payload Length the same as
for first fragments.
The OCH1 Format (a) is used for all original IPv6 packets that do not
include a Fragment Header as well as for original IPv4 packets that
set IHL to 5, DF to 1 and (MF; Fragment Offset) to 0 (the OCH1 Format
(b) is used for all non-first fragments regardless of the original IP
version).
For other "non-atomic" original IP packets and first fragments, the
OAL uses the "Type 2" OMNI Compressed Header (OCH2) formats shown in
Figure 11 and Figure 12:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |A|F|M|R| Reserved | Traffic Class | OAL Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL Identification (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFVI (2 or 4 octets) / Payload Len (0 or 2 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L3 Next Header| L3 Hop Limit | Fragment Offset |Res|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: OMNI Compressed Header, Type 2 (OCH2) Format (a)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |A|F|M|R| Reserved |Type of Service| OAL Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL Identification (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFVI (2 or 4 octets) / Payload Len (0 or 2 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL | IPv4 Identification |Flags|Offset(1)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Offset(2) | Time to Live | Protocol | Checksum (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum (2) | Options | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: OMNI Compressed Header, Type 2 (OCH2) Format (b)
In both of the above OCH2 formats, the leading octets up to and
including the Payload Len (when present) include the same information
that would appear in a corresponding OCH1 format (a) header with the
exception that the (P) flag is unused and replaced with a (R)eserved
flag. The (F) flag is set to 0 for OCH2 format (a) or 1 for OCH2
format (b), while all other flags are processed the same as for OCH1
format (a). The 8-bit Reserved field is set to 0 in both formats.
The remainder of the OCH2 format (a) includes fields that would
appear in an uncompressed IPv6 header plus Fragment Header extension
per [RFC8200], while the remainder of format (b) includes fields that
would appear in an uncompressed IPv4 header per [RFC0791] with the
Options and Padding lengths calculated based on IHL. In both cases,
the Source and Destination Addresses are not transmitted.
When an OAL destination or intermediate system receives a carrier
packet, it determines the length of the encapsulated OAL information
and verifies that the innermost L2 next header field indicates OMNI
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(see: Section 6.2), then processes any included OMNI L2 extension
headers as specified in Section 6.4. The OAL destination then
examines the Next Header field of the final L2 extension header. If
the Next Header field contains the value TBD1, and the 4-bit Type
that follows encodes a value OMNI-IP6, OMNI-OFH, OMNI-OCH1 or OMNI-
OCH2 the OAL node processes the remainder of the OAL header as a full
or compressed header as specified above.
When an OAL node forwards an OAL packet, it determines the AFVI for
the next OAL hop by using the AFVI included in the OCH to search for
a matching AFV. The OAL intermediate system then writes the next hop
AFVI into the OCH and forwards the OAL packet to the next hop. This
same AFVI re-writing progression begins with the OAL source then
continues over all OAL intermediate nodes and finally ends at the OAL
destination.
If the OAL node is the destination, it instead reconstructs the OFH
and original IP headers based on the information cached in the AFV
combined with the received information in the OCH1/2. For non-atomic
fragments, the OAL node then adds the resulting OAL fragment to the
reassembly cache if the Identification is acceptable. Following OAL
reassembly if necessary, the OAL node delivers the original IP packet
to the network layer.
For all OCH1/2 types, the source node sets all Reserved fields and
bits to 0 on transmission and the destination node ignores the values
on reception. For both OCH1/2, ECN information is compiled for first
fragments, and not for non-first fragments.
Finally, if an IPv6 Hop-by-Hop (HBH) and/or Routing Header extension
header is required to appear as per-fragment extensions with each OAL
fragment that uses OCH1 format (b) or OCH2 compression the OAL node
inserts an OMNI-HBH and/or OMNI-RH header as the first extension(s)
following the L2 header and before the OMNI-OCH1/2 as discussed in
Section 6.4.
6.6. L2 UDP/IP Encapsulation Avoidance
When the OAL node is unable to determine whether the next OAL hop is
connected to the same underlay link, it should perform carrier packet
L2 encapsulation for initial packets sent via the next hop over a
specific underlay interface by including full UDP/IP headers and with
the UDP port numbers set as discussed in Section 6.2. The node can
thereafter attempt to send an IPv6 ND solicitation message to the
next OAL hop in carrier packet(s) that omit the UDP header and set
the IP protocol number to TBD1. If the OAL node receives an IPv6 ND
reply, it can omit the UDP header in subsequent packets. The node
can further attempt to send an IPv6 ND solicitation in carrier
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packet(s) that omit both the UDP and IP headers and set EtherType to
TBD2. If the source receives an IPv6 ND reply, it can begin omitting
both the UDP and IP headers in subsequent packets.
Note: in the above, "next OAL hop" refers to the first OAL node
encountered on the optimized path to the destination over a specific
underlay interface as determined through route optimization (e.g.,
see: [I-D.templin-6man-aero3]). The next OAL hop could be a Proxy/
Server, Gateway or the OAL destination itself.
6.7. OAL Identification Window Maintenance
The OAL encapsulates each original IP packet as an OAL packet then
performs fragmentation to produce one or more carrier packets with
the same 8-octet Identification value. In environments where
spoofing is not considered a threat, OMNI interfaces send OAL packets
with Identifications beginning with an unpredictable Initial Send
Sequence (ISS) value [RFC7739] monotonically incremented (modulo
2**64) for each successive OAL packet sent to either a specific
neighbor or to any neighbor. (The OMNI interface may later change to
a new unpredictable ISS value as long as the Identifications are
assured unique within a timeframe that would prevent the fragments of
a first OAL packet from becoming associated with the reassembly of a
second OAL packet.) In other environments, OMNI interfaces should
maintain explicit per-flow send and receive windows to detect and
exclude spurious carrier packets that might clutter the reassembly
cache as discussed below.
OMNI interface neighbors use a window synchronization service similar
to TCP [RFC9293] to maintain unpredictable ISS values incremented
(modulo 2**64) for each successive OAL packet and re-negotiate
windows often enough to maintain an unpredictable profile. OMNI
interface neighbors exchange IPv6 ND messages that include OMNI
Neighbor Synchronization sub-options that include TCP-like
information fields and flags to manage streams of OAL packets instead
of streams of octets. As a link layer service, the OAL provides low-
persistence best-effort retransmission with no mitigations for
duplication, reordering or deterministic delivery. Since the service
model is best-effort and only control message sequence numbers are
acknowledged, OAL nodes can select unpredictable new initial sequence
numbers outside of the current window without delaying for the
Maximum Segment Lifetime (MSL).
OMNI interface end neighbors and intermediate systems maintain
current and previous per-flow 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/
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or symmetric IPv6 ND message exchanges. When OMNI end and
intermediate systems receive an IPv6 ND message with new per-flow
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 Neighbor Synchronization sub-option
includes TCP-like information fields including Sequence Number,
Acknowledgement Number, Window and flags (see: Section 10). OMNI
interface neighbors and intermediate systems maintain the following
TCP-like state variables on a per-interface-pair basis (i.e., through
a combination of NCE and/or 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 in a Neighbor Synchronization. When OAL A
synchronizes with OAL B, it maintains both a current and previous
SND.WND beginning with a new unpredictable ISS and monotonically
increments SND.NXT for each successive OAL packet transmission. OAL
A initiates synchronization by including the new ISS in the Sequence
Number of an authentic IPv6 ND message with the SYN flag set and with
Window set to M (up to 2**24) as its advertised send 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).
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When OAL B receives the SYN, it creates a NCE in the STALE state and
also an AFV if necessary, resets its RCV variables and caches the
source's send window size M as its receive window size. 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 M. 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 IPv6 ND
messages with the SYN flag set received from OAL A even if outside
the windows.
OMNI interface neighbors can employ asymmetric window synchronization
as described above using 2 independent (SYN -> ACK) exchanges (i.e.,
a 4-message exchange), or they can employ symmetric window
synchronization using a modified version of the TCP "3-way handshake"
as follows:
* OAL A prepares a SYN with an unpredictable ISS not within the
current SND.WND and with Window set to M as its advertised send
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 send window size M as its
receive window size. OAL B then selects a new unpredictable ISS
outside of its current window, 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 a chosen send window size 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
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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). OAL A then resets its RCV variables
based on the Sequence Number and OAL B's advertised send Window N
and marks the NCE as REACHABLE. If the OPT flag is clear, OAL A
next prepares an immediate unsolicited IPv6 ND control message
with the ACK flag set, the Acknowledgement Number set to OAL B's
next sequence number, with Window set to N, 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 current SND.WND as implicit
acknowledgements instead of returning an explicit ACK.
* 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. Note that OAL B sets the OPT flag in
the SYN/ACK to assert that it will interpret timely receipt of
carrier packets within the (new) current window as an implicit
acknowledgement. Potential benefits include reduced delays and
control message overhead, but use case analysis is outside the
scope of this specification.)
Following synchronization, OAL A and OAL B hold updated NCEs and
AFVs, and can exchange OAL packets with Identifications set to
SND.NXT for each flow while the state remains REACHABLE and there is
available window capacity. (Intermediate systems that establish AFVs
for the per-flow window synchronization exchanges can also use the
Identification window for source validation.) 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 can continue sending OAL packets under
the current SND.WND while also sending a SYN with a new unpredictable
ISS. When OAL B receives the SYN, it resets its RCV variables and
may optionally return either an asymmetric ACK or a symmetric SYN/ACK
to also assert a new ISS. While sending SYNs, both neighbors
continue to send OAL packets with Identifications set to the current
SND.NXT for each interface pair then reset the SND variables after an
acknowledgement is received.
While the optimal symmetric exchange is efficient, anomalous
conditions such as receipt of old duplicate SYNs can cause confusion
for the algorithm as discussed in Section 3.5 of [RFC9293]. For this
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reason, the OMNI Neighbor Synchronization sub-option includes an RST
flag which OAL nodes set in solicited IPv6 ND message responses to
ACKs received with incorrect acknowledgement numbers. The RST
procedures (and subsequent synchronization recovery) are conducted
exactly as specified in [RFC9293].
OMNI interfaces that employ the window synchronization procedures
described above observe the following requirements:
* 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 Window field in SYN messages as a
non-negotiable advertised send window size.
* OMNI interfaces MUST send IPv6 ND messages used for window
synchronization securely while using unpredictable initial
Identification values until synchronization is complete.
It is essential to understand that the above window synchronization
operations between nodes OAL(A) and OAL(B) are conducted in IPv6 ND
message exchanges over multihop paths with potentially many OAL(i)
intermediate hops in the forward and reverse paths (which may be
disjoint). Each such forward path OAL(i) caches the sequence number
and window size advertised from OAL(A) to OAL(B) in its AFV entry
indexed by the previous hop L2ADDR and AFVI, while each such reverse
path OAL(i) caches the sequence number, window size and AFVI
advertised from OAL(B) to OAL(A). (The forward/reverse path OAL(i)
nodes then select new unique next-hop AFVIs before forwarding.)
Note: Although OMNI interfaces employ TCP-like window synchronization
and support ACK responses to SYNs, all other aspects of the IPv6 ND
protocol (e.g., control message exchanges, NCE state management,
timers, retransmission limits, etc.) are honored exactly per
[RFC4861]. OMNI interfaces further manage per-interface-pair window
synchronization parameters in one or more AFVs for each neighbor
pair.
Note: Recipients of OAL-encapsulated IPv6 ND messages index the NCE
based on the message Source Address, which also determines the
carrier packet Identification window. However, IPv6 ND messages may
contain a message Source Address that does not match the OMNI
encapsulation Source Address when the recipient acts as a proxy.
Note: OMNI interface neighbors apply separate send and receive
windows for all of their (multilink) underlay interface pairs that
exchange carrier packets. Each interface pair represents a distinct
underlay network path, and the set of paths traversed may be highly
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diverse when multiple interface pairs are used. OMNI intermediate
systems therefore become aware of each distinct set of interface pair
window synchronization parameters based on periodic IPv6 ND message
updates to their respective AFVs.
6.8. OAL Fragmentation Reports and Retransmissions
When the round-trip delay from the original source to the final
destination is long while the route-trip time from the OAL source the
OAL destination is significantly shorter, the OAL source can maintain
a short-term cache of the OAL fragments it sends to OAL destinations
in case timely best-effort selective retransmission is requested.
The OAL destination in turn maintains a checklist for (Source,
Destination, Identification)-tuples of recently received OAL
fragments and notes the ordinal numbers of OAL fragments already
received (i.e., as ordinals #0, #1, #2, #3, etc.). The timeframe for
maintaining the OAL source and destination caches determines the link
persistence (see: [RFC3366]).
If the OAL destination notices some fragments missing after most
other fragments within the same link persistence timeframe have
already arrived, it may issue an Automatic Repeat Request (ARQ) with
Selective Repeat (SR) by sending an unsolicited IPv6 ND neighbor
control message to the OAL source. The OAL destination creates a
message with an OMNI option with one or more Fragmentation Report
(FRAGREP) sub-options that include (Identification, Bitmap)-tuples
for fragments received and missing from this OAL source (see:
Section 10). The OAL destination includes an authentication
signature if necessary, performs OAL encapsulation (with its own
address as the OAL Source Address and the Source Address of the
message that prompted the unsolicited IPv6 ND as the OAL Destination
Address) and sends the message to the OAL source.
If an OAL intermediate system or OAL destination processes an OAL
fragment for which corruption is detected, it may similarly issue an
immediate ARQ/SR the same as described above. The FRAGREP provides
an immediate (rather than time-bounded) indication to the OAL source
that a fragment has been lost.
When the OAL source receives the IPv6 ND message, it authenticates
the message then examines any enclosed FRAGREPs. For each (Source,
Destination, Identification)-tuple, the OAL source determines whether
it still holds the corresponding OAL fragments in its cache and
retransmits any for which the Bitmap indicates a loss event. For
example, if the Bitmap indicates that ordinal fragments #3, #7, #10
and #13 from the OAL packet with Identification 0x0123456789abcdef
are missing the OAL source only retransmits those fragments. When
the OAL destination receives the retransmitted OAL fragments, it
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admits them into the reassembly cache and updates its checklist. If
some fragments are still missing, the OAL destination may send a
small number of additional IPv6 ND ARQ/SRs within the link
persistence timeframe.
The OAL therefore provides a link layer low-to-medium persistence
ARQ/SR service consistent with [RFC3366] and Section 8.1 of
[RFC3819]. The service provides the benefit of timely best-effort
link layer retransmissions which may reduce OAL fragment loss and
avoid some unnecessary end-to-end delays. This best-effort network-
based service therefore complements transport and higher layer end-
to-end protocols responsible for true reliability.
6.9. OMNI Interface MTU Feedback Messaging
When the OMNI interface forwards original IP packets from the network
layer, it invokes the OAL and returns internally-generated Path MTU
Discovery (PMTUD) ICMPv4 "Fragmentation Needed and Don't Fragment
Set" [RFC1191] or ICMPv6 "Packet Too Big (PTB)" [RFC8201] messages as
necessary. This document refers to both message types as "PTBs" and
introduces a distinction between PTB "hard" and "soft" errors as
discussed below.
Ordinary PTB messages are hard errors that always indicate loss due
to a real MTU restriction has occurred. However, the OMNI interface
can also forward original IP packets via OAL encapsulation and
fragmentation while at the same time returning PTB soft error
messages (subject to rate limiting) to the original source to suggest
smaller sizes due to factors such as link performance
characteristics, excessive 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 without loss while returning
PTB soft error messages that recommend smaller sizes. Original
sources that receive the soft errors in turn reduce the size of the
original IP packets they send the same as for hard errors, but not
necessarily due to a loss event. The original source can then resume
sending larger packets if the soft errors subside.
OAL intermediate systems that experience fragment loss and OAL end
systems that experience reassembly cache congestion can return
unsolicited IPv6 ND control messages that include OMNI encapsulated
PTB soft error messages to OAL sources that originate fragments
(subject to rate limiting). The OAL node creates a secured control
message with an OMNI option containing an ICMPv6 Error sub-option.
The OAL node encodes a PTB message in the sub-option with MTU set to
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a reduced value and with the leading portion an OAL first fragment
containing the header of an original IP packet for which the source
must be notified (see: Section 10).
The OAL node that sends the IPv6 ND message encapsulates the leading
portion of the OAL first fragment (beginning with the OAL header) in
the PTB "packet in error" field and signs the message if an
authentication signature is included. The OAL node then performs OAL
encapsulation (with its own address as the Source Address and the
Source Address of the message that prompted the IPv6 ND response as
the Destination Address) and sends the message to the OAL source.
(Note that OAL intermediate systems forward IPv6 ND control messages
via the secured spanning tree while OAL source and destination end
systems include an authentication signature when necessary.)
The OAL source prepares the PTB soft error by first setting the Type
field to 2 for IPv6 [RFC4443] or TBD3 for IPv4 (see: IANA
considerations). The OAL source then sets the Code field to "PTB
Soft Error (no loss)" if the OAL destination forwarded the original
IP packet successfully or "PTB Soft Error (loss)" if it was dropped
(see: IANA considerations). The OAL source next sets the PTB
Destination Address to the original IP packet Source Address, and
sets the PTB Source Address to one of its OMNI interface addresses
that is reachable from the perspective of the original source.
The OAL source then sets the MTU field to a value smaller than the
original IP packet size but no smaller than 1280, writes as much of
the original IP packet first fragment as possible into the "packet in
error" field such that the entire PTB including the IP header is no
larger than 1280 octets for IPv6 or 576 octets for IPv4. The OAL
source then calculates and sets the ICMP Checksum and returns the PTB
to the original source.
An original sources that receives these PTB soft errors first
verifies that the ICMP Checksum is correct and the packet-in-error
contains the leading portion of one of its recent packet
transmissions. The original source can then adaptively tune the size
of the original IP packets it sends to produce the best possible
throughput and latency, with the understanding that these parameters
may fluctuate over time due to factors such as congestion, mobility,
network path changes, etc. Original sources should therefore
consider receipt or absence of soft errors as hints of when
decreasing or increasing packet sizes may provide better performance.
The OMNI interface supports continuous transmission and reception of
packets 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
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larger packets 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 air/land/sea/space mobile
Internetworking.
Note: when the OAL source receives persistent Fragmentation Reports
for a given flow (see: Section 6.8), it should return PTB soft errors
to the original source (subject to rate limiting) the same as if it
had received PTB soft errors from the OAL destination. When the
original source is likely to retransmit an entire original IP packet
on its own behalf in case of loss, the OAL destination can elect to
return only PTB soft errors and refrain from returning Fragmentation
Reports.
Note: the OAL source may receive control messages that include both a
PTB soft error and Fragmentation Report(s). If so, the OAL source
both returns PTB soft errors to the original source (subject to rate
limiting) and retransmits any missing fragments if it is configured
to do so.
6.10. OAL Composite Packets
The OAL source ordinarily includes a 40-octet IPv6 encapsulation
header for each original IP packet during OAL encapsulation. The OAL
source then performs fragmentation such that a copy of the 40-octet
IPv6 header plus a 16-octet IPv6 Extended Fragment Header is included
in each OAL fragment (when a Routing Header is added, the OAL
encapsulation headers become larger still). However, these
encapsulations may represent excessive overhead in some environments.
OAL header compression as discussed in Section 6.5 can dramatically
reduce encapsulation overhead, however a complementary technique
known as "packing" (see: [I-D.ietf-intarea-tunnels]) supports
encapsulation of multiple original IP packets and/or control messages
within a single OAL "composite packet".
When the OAL source has multiple original IP packets to send to the
same OAL destination with total length no larger than the OAL
destination EMTU_R, it can concatenate them into a composite packet
encapsulated in a single OAL header. Within the OAL composite
packet, the IP header of the first original IP packet (iHa) followed
by its data (iDa) is concatenated immediately following the OAL
header. The IP header of the next original packet (iHb) followed by
its data (iDb) is then concatenated immediately following the first,
with each remaining original IP packet concatenated in succession.
The OAL composite packet format is transposed from
[I-D.ietf-intarea-tunnels] and shown in Figure 13:
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<------- Original IP packets ------->
+-----+-----+
| iHa | iDa |
+-----+-----+
|
| +-----+-----+
| | iHb | iDb |
| +-----+-----+
| |
| | +-----+-----+
| | | iHc | iDc |
| | +-----+-----+
| | |
v v v
+----------+-----+-----+-----+-----+-----+-----+
| OAL Hdr | iHa | iDa | iHb | iDb | iHc | iDc |
+----------+-----+-----+-----+-----+-----+-----+
<-- OAL composite packet with single OAL Hdr -->
Figure 13: OAL Composite Packet Format
When the OAL source prepares a composite packet, it applies OAL
fragmentation then applies L2 encapsulation and sends the resulting
carrier packets to the OAL destination. When the OAL destination
receives the composite packet it first reassembles if necessary. The
OAL destination then selectively extracts each original IP packet
(e.g., by setting pointers into the composite 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 'j' by examining the 4 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 composite packet that includes an IPv6
ND message as the first original IP packet (i.e., iHa/iDa) it
includes any additional original IP packets in concatenated
succession then includes a trailing OMNI option. If the OMNI option
contains an authentication sub-option, the OAL source calculates the
authentication signature over the entire length of the composite
packet. (A second common use case entails a path MTU probe beginning
with an unsigned IPv6 ND message followed by a suitably large NULL
packet (e.g., an IP packet with padding octets added beyond the IP
header and with {Protocol, Next Header} set to 59 ("No Next Header"),
a UDP/IP packet with port number set to 9 ("discard") [RFC0863],
etc.)
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The OAL source can also apply this composite packet packing technique
at the same time it performs OCH1 header compression as discussed in
Section 6.5. Note that this technique can only be applied for
original IP packets of a single flow, such as for a stream of packets
for the flow that are queued for transmission service at roughly the
same time.
6.11. OAL Bubbles
OAL sources may send NULL OAL packets known as "bubbles" for the
purpose of establishing Network Address Translator (NAT) state on the
path to the OAL destination. The OAL source prepares a bubble by
crafting an OAL header with appropriate IPv6 Source and Destination
ULAs, with the IPv6 Next Header field set to the value 59 ("No Next
Header" - see [RFC8200]) and with 0 or more octets of NULL protocol
data immediately following the IPv6 header.
The OAL source includes a random Identification value then
encapsulates the OAL packet in L2 headers destined to either the
mapped address of the OAL destination's first-hop ingress NAT or the
L2 address of the OAL destination itself. When the OAL source sends
the resulting carrier packet, any egress NATs in the path toward the
L2 destination will establish state based on the activity. At the
same time, the bubble themselves will be harmlessly discarded by
either an ingress NAT on the path to the OAL destination or by the
OAL destination itself.
The bubble concept for establishing NAT state originated in [RFC4380]
and was later updated by [RFC6081]. OAL bubbles may be employed by
mobility services such as AERO.
6.12. OAL Requirements
In light of the above, OAL sources, destinations and intermediate
systems observe the following normative requirements:
* OAL sources MUST forward original IP packets either larger than
the OMNI interface minimum EMTU_R or smaller than the minimum OFS
as atomic fragments (i.e., and not as multiple fragments).
* OAL sources MUST perform OAL fragmentation such that all non-final
fragments are equal in length while the final fragment may be a
different length.
* OAL sources MUST produce non-final fragments with payloads no
smaller than the minimum OFS during fragmentation.
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* OAL intermediate systems SHOULD and OAL destinations MUST
unconditionally drop any non-final OAL fragments with payloads
smaller than the minimum OFS.
* OAL destinations MUST drop any new OAL fragments that would
overlap with other fragments and/or leave holes smaller than the
minimum OFS between fragments that have already been received.
Note: Certain legacy network hardware of the past millennium was
unable to accept IP fragment "bursts" resulting from a fragmentation
event - even to the point that the hardware would reset itself when
presented with a burst. This does not seem to be a common problem in
the modern era, where fragmentation and reassembly can be readily
demonstrated at line rate (e.g., using tools such as 'iperf3') even
over fast links on ordinary hardware platforms. Even so, while the
OAL destination is reporting reassembly congestion (see: Section 6.9)
the OAL source could impose "pacing" by inserting an inter-fragment
delay and increasing or decreasing the delay according to congestion
indications.
6.13. OAL Fragmentation Security Implications
As discussed in Section 3.7 of [RFC8900], there are 4 basic threats
concerning IPv6 fragmentation; each of which is addressed by
effective mitigations as follows:
1. Overlapping fragment attacks - reassembly of overlapping
fragments is forbidden by [RFC8200]; therefore, this threat does
not apply to the OAL.
2. Resource exhaustion attacks - this threat is mitigated by
providing a sufficiently large OAL reassembly cache and
instituting "fast discard" of incomplete reassemblies that may be
part of a buffer exhaustion attack. The reassembly cache should
be sufficiently large so that a sustained attack does not cause
excessive loss of good reassemblies but not so large that (timer-
based) data structure management becomes computationally
expensive. The cache should also be indexed based on the arrival
underlay interface such that congestion experienced over a first
underlay interface does not cause discard of incomplete
reassemblies for uncongested underlay interfaces.
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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 6.7. By maintaining windows of
acceptable Identifications, OAL neighbors can quickly discard
spurious carrier packets that might otherwise clutter the
reassembly cache.
4. Evasion of Network Intrusion Detection Systems (NIDS) - since the
OAL source employs a robust OFS, network-based firewalls can
inspect and drop OAL fragments containing malicious data thereby
disabling reassembly by the OAL destination. However, each OAL
destination should also employ a (host-based) firewall.
IPv4 includes a 2-octet (16-bit) Identification (IP ID) field with
only 65535 unique values such that even at moderate data rates the
field could wrap and apply to new carrier packets while the fragments
of old carrier packets using the same IP ID are still alive in the
network [RFC4963]. However, IPv4 links that configure a small MTU
are likely to occur only at extreme network edges where low data rate
links occur [RFC3819]. Since IPv6 provides a 4-octet (32-bit)
Identification value, IP ID wraparound for IPv6 fragmentation may
only be a concern at extreme data rates (e.g., 1Tbps or more). These
limitations are fully addressed through the 8-octet (64-bit) Extended
Identification format supported by [I-D.templin-6man-ipid-ext2].
Unless the path is secured at the network layer or below (i.e., in
environments where spoofing is possible), OMNI interfaces MUST NOT
send OAL packets/fragments with Identification values outside the
current window and MUST secure IPv6 ND messages used for address
resolution or window state synchronization. OAL destinations SHOULD
therefore discard without reassembling any out-of-window OAL
fragments received over an unsecured path.
6.14. Control/Data Plane Considerations
The above sections primarily concern data plane aspects of the OMNI
interface service and describe the data plane service model offered
to the network layer. OMNI interfaces also internally employ a
control plane service based on IPv6 ND messaging. These control
plane messages are first subject to OAL encapsulation then forwarded
over secured underlay interfaces (e.g., IPsec tunnels, secured direct
point-to-point links, etc.) or over unsecured underlay interfaces and
with an authentication signature included.
OMNI interfaces must send all control plane messages as "atomic OAL
packets". This means that these messages must not be subjected to
OAL fragmentation and reassembly, although they may be subjected to
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L2 fragmentation and reassembly along some paths. Fragmentation
security concerns for large IPv6 ND messages are documented in
[RFC6980].
7. Ethernet-Compatible Link Layer Frame Format
When the OMNI interface forwards original IP packets from the network
layer it first invokes OAL encapsulation and fragmentation, then
wraps each resulting OAL packet/fragment in any necessary L2 headers
to produce carrier packets according to the native frame format of
the underlay interface. For example, for Ethernet-compatible
interfaces the frame format is specified in [RFC2464], for
aeronautical radio interfaces the frame format is specified in
standards such as ICAO Doc 9776 (VDL Mode 2 Technical Manual), for
various forms of tunnels the frame format is found in the appropriate
tunneling specification, etc.
When the OMNI interface encapsulates an OAL packet/fragment directly
over an Ethernet-compatible link layer, the over-the-wire
transmission format is shown in Figure 14:
+--- ~~~ ---+-------~~~------+---------~~~---------+--- ~~~ ---+
| eth-hdr | OMNI Ext. Hdrs | OAL Packet/Fragment | eth-trail |
+-- ~~~ ---+-------~~~------+---------~~~---------+--- ~~~ ---+
|<------- Ethernet Payload -------->|
Figure 14: OMNI Ethernet Frame Format
The format includes a standard Ethernet Header ("eth-hdr") with
EtherType TBD2 (see: Section 21.2) followed by an Ethernet Payload
that includes zero or more OMNI Extension Headers followed by an OAL
(or native IPv6/IPv4) Packet/Fragment. The Ethernet Payload is then
followed by a standard Ethernet Trailer ("eth-trail").
The first OMNI extension header and the OAL Packet/Fragment both
begin with a 4-bit "Type/Version" as discussed in Section 6.2. When
"Type/Version" encodes an OMNI extension header type, the length of
the extension headers is limited by [I-D.ietf-6man-eh-limits] and the
length of the OAL Packet/Fragment is determined by the IP header
fields that follow the extension headers.
When "Type/Version" encodes OMNI-OFH, OMNI-OCH1/2, OMNI-IP4 or OMNI-
IP6 the length of the OAL Packet/Fragment is determined by the
{Total, Payload} Length field found in the full/compressed header
according to the specific protocol rules.
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See Figure 2 for a map of the various L2 layering combinations
possible. For any layering combination, the final layer (e.g., UDP,
IP, Ethernet, etc.) must have an assigned number and frame format
representation that is compatible with the selected underlay
interface.
8. OMNI Addressing
OMNI addressing observes the IPv6 addressing architecture [RFC4291]
requirement that: "IPv6 addresses of all types are assigned to
interfaces, not nodes. An IPv6 unicast address refers to a single
interface. Since each interface belongs to a single node, any of
that node's interfaces' unicast addresses may be used as an
identifier for the node." OMNI addressing further follows the IPv6
address selection policies specified in [RFC6724] as updated by
[I-D.ietf-6man-rfc6724-update].
Each OMNI interface is configured over a set of underlay interfaces
as a virtual data link layer for the OAL. OMNI nodes assign IP
addresses to their underlay interfaces according to the native *NET
autoconfiguration service(s) or through manual configuration. OMNI
nodes assign IPv6 addresses to their OMNI interfaces as specified in
this section.
[RFC4861] requires that hosts and routers assign Link-Local Addresses
(LLAs) to all interfaces including the OMNI interface, and that
routers use their LLAs as the Source Address for RA and Redirect
messages. The OMNI interface satisfies this property by maintaining
an internal mapping cache to present the network layer with an LLA-
based view of all neighbors while the adaptation layer within the
OMNI interface maps IPv6 message Source and Destination LLAs to
Multilink Local Addresses (MLAs). (If the node assigns multiple LLAs
to the OMNI interface, e.g., as suggested by [I-D.link-6man-gulla] it
must also assign multiple MLAs in 1x1 correspondence. In that case,
the node would appear as multiple separate nodes on the OMNI link.)
[I-D.templin-6man-mla] specifies MLA types that OMNI nodes can assign
to the OMNI interface given sufficient uniqueness and authentication
assurances. Candidate MLA types include the Host Identity Tag (HIT)
[RFC7343], Hierarchical HIT (HHIT) [RFC9374], and Segment Routing
over IPv6 (SRv6) Segment Identifiers [RFC9602] but could also include
future special-purpose IPv6 address types identified by the IPv6
prefix. The node assigns an MLA to an OMNI interface configured over
its set of underlay interfaces per the IPv6 scoped addressing
architecture "site" abstraction [RFC4007]. MLAs are considered as
adaptation layer addresses in the architecture.
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When the data link layer presents an OAL-encapsulated IPv6 packet
with MLA Source/Destination Addresses to the OMNI interface, the
adaptation layer decapsulates the IPv6 packet if the MLA Destination
Address matches its own address then rewrites the Destination Address
with its own LLA while forwarding the packet to the network layer.
For IPv6 ND messages that install the neighbor's LLA in the neighbor
cache, the adaptation layer first generates a new local LLA for the
neighbor with a randomized Modified EUI-64 format interface
identifier per [RFC4291] that is unique among all current neighbor
LLAs. For all IPv6 ND messages that include a Source/Target Link
Layer Address Option (S/TLLAO) the adaptation layer then rewrites the
S/TLLAO based on the EUI-64 format interface identifier from the
local LLA. For all IPv6 packets with MLA Source Addresses, the
adaptation layer then rewrites the Source Address with the local LLA
before presenting the IPv6 packet to the network layer.
When the network layer presents an IP packet with LLA Source/
Destination Addresses to an OMNI interface, the adaptation layer
rewrites the LLA Source Address with its own MLA and rewrites the LLA
Destination Address to the MLA of the peer or to a site-scoped
multicast or anycast address. The OMNI interface then encapsulates
the packet in an OAL header with MLA Source/Destination Addresses and
presents it to the data link layer. The adaptation layer mapping
table therefore must ensure that the network layer sees a unique
local representation of the LLA for each active neighbor while
mapping its local S/TLLAO view to the neighbor's view and while
including only MLAs (and not LLAs) in actual message exchanges with
neighbors.
OMNI interfaces assign IPv6 Unique Local Addresses (ULAs) and use
them as the Source and Destination Addresses in IPv6 packets
forwarded over the OMNI interface within the local OMNI link segment.
OMNI interfaces also assign corresponding IPv6 Globally Unique
Addresses (GUAs) and use them as Source and Destination Addresses for
IPv6 packets exchanged with peers in external networks. ULAs are
routable only within the scope of an OMNI link segment, and are
derived from the IPv6 prefix fd00::/8 (i.e., the ULA prefix fc00::/7
followed by the L bit set to 1). The 56 bits following fd00::/8
encode a 40-bit Global ID followed by a 16-bit Subnet ID followed by
a 64-bit Interface Identifier as specified in Section 3 of [RFC4193].
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When a Proxy/Server configures a ULA prefix for OMNI, it selects a
40-bit Global ID for the OMNI link segment initialized to a candidate
pseudo-random value as specified in Section 3 of [RFC4193]. All
nodes on the same OMNI link segment use the same Global ID, and
statistical uniqueness of the pseudo-random Global ID provides a
unique OMNI link segment identifier. This property allows different
link segments to join together in the future without requiring
renumbering even if the segments come in contact with one another and
overlap, e.g., as a result of a mobility event.
Proxy/Servers for each OMNI link segment use the DHCPv6 service to
delegate 1x1 mapped ULA/GUA SNP addresses for each Client that
requests an address delegation. (A suitable method for SNP GUA
address delegation appears in [I-D.gont-dhcwg-dhcpv6-iids], while the
corresponding ULA is formed by appending the 64-bit GUA interface
identifier to the 64-bit ULA prefix.) Clients in turn assign the
ULA/GUA delegations to their OMNI interfaces which ensures that the
addresses are available for use and that no duplicates will be
assigned within each OMNI link segment. IPv6 address selection at
the network layer above the OMNI interface then determines the
underlay interface used for service at the data link layer below the
OMNI interface. Further considerations for 1x1 ULA/GUA address
mapping are discussed in [I-D.ietf-v6ops-ula-usage-considerations]
and [RFC6296].
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 12). An OMNI domain consists of one or more OMNI links
joined together to provide service for a common set of MSPs.
OMNI domains include one or more OMNI links that together coordinate
a common set of MSPs delegated from the IP GUA prefix space [RFC4291]
from which the MS delegates MNPs to support Client PI addressing.
OMNI Proxy Servers also configure an SNP paired with a ULA prefix
configured as above to delegate PA internal (ULA) and external (GUA)
addresses to Clients within their local *NETs.
For IPv6, MSPs are assigned to an OMNI domain by IANA and/or an
associated Regional Internet Registry [IPV6] such that the link(s)
can be connected to the global IPv6 Internet without causing routing
inconsistencies. Instead of GUAs, an OMNI link could 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.
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For IPv4, MSPs are assigned to an OMNI domain by IANA and/or an
associated RIR [IPV4] such that the link(s) can be connected to the
global IPv4 Internet without causing routing inconsistencies. An
OMNI *NET could instead use private IPv4 prefixes (e.g., 10.0.0.0/8,
etc.) [RFC6890], however this would require IPv4 NAT at the *NET
boundary. OMNI interfaces advertise IPv4 MSPs into IPv6 routing
systems as "6to4 prefixes" [RFC3056] (e.g., the IPv6 prefix for the
IPv4 MSP "V4ADDR/24" is 2002:V4ADDR::/40).
IPv4 routers that configure OMNI interfaces advertise the prefix
TBD4/N (see: IANA Considerations) into the routing systems of their
connected *NETs and assign the IPv4 OMNI anycast address TBD4.1 to
their *NET interfaces. IPv6 routers that configure OMNI interfaces
advertise the prefix 2002:TBD4::/(N+16) into the routing systems of
their connected *NETs and assign the IPv6 OMNI anycast address
2002:TBD4:: to their *NET interfaces.
Proxy/Server OMNI interfaces configure ULA/GUA IPv6 SNP SRA addresses
per [RFC4291] and accept packets addressed to the SRA the same as for
any IPv6 router. Proxy/Servers also configure the global IPv6 SRA
address for each MSP managed by this OMNI link and accept packets
addressed to the SRA address on their internal interfaces to support
Client OMNI link discovery. Client OMNI interfaces configure the
IPv6 SRA address corresponding to their MNP delegations.
OMNI interfaces use their OMNI IPv6 and IPv4 anycast addresses to
support control plane Service Discovery in the spirit of [RFC7094],
i.e., the addresses are not intended for use in supporting longer
term data plane flows. Specific applications for OMNI IPv6 and IPv4
anycast addresses are discussed throughout the document as well as in
[I-D.templin-6man-aero3].
OMNI Clients and Proxy/Servers use their MLAs as OAL Source and
Destination Addresses within the FHS *NET. FHS Proxy/Servers rewrite
OAL Source and Destination MLAs as SNP GUAs before forwarding packets
over intervening Internetworks on the paths to LHS Proxy/Servers.
LHS Proxy servers in turn rewrite OAL Source and Destination SNP GUAs
as MLAs for forwarding within the LHS *NET. (Proxy/Servers rewrite
the OAL Source Address in the same manner as for NATs and rewrite the
OAL Destination Address based on information found in an included
SRH.)
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9. Node Identification
OMNI Clients and Proxy/Servers that connect over open Internetworks
include a unique node identification value for themselves in the IPv6
Source Address and/or in an OMNI option of their IPv6 ND messages
(see: Section 10.2.3). Each node configures and includes an MLA as a
node identification as discussed in Section 8. (The Universally
Unique IDentifier (UUID) [RFC9562] is another example of a node
identifier 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 addressing information at all. In that case, the Client
can use an MLA as an IPv6 Source/Destination Address for sustained
communications in Vehicle-to-Vehicle (V2V) and (multihop) Vehicle-to-
Infrastructure (V2I) scenarios. The Client can also propagate the
MLA into the multihop routing tables of (collective) Mobile/Vehicular
Ad-hoc Networks (MANETs/VANETs) using only the vehicles themselves as
communications relays. MLAs provide an especially useful node
identification construct since they appear as properly-formed IPv6
addresses.
When a Client already includes its MLA in the IPv6 Source Address of
an original IP packet or IPv6 ND message, it need not also include
the MLA in an OMNI Node Identification sub-option.
10. Address Mapping - Unicast
OMNI interfaces maintain network layer conceptual Neighbor and
Destination Caches per [RFC1256][RFC4861] the same as for any IP
interface. The network layer maintains state through static and/or
dynamic Neighbor/Destination Cache Entry (NCE/DCE) configurations.
Each OMNI interface also maintains an internal adaptation layer view
of the neighbor cache that supplements the network layer NCEs for
each of its active neighbors. For each peer NCE, neighbors also
maintain AERO Forwarding Vectors (AFVs) in the OAL which map per-
interface-pair parameters. Throughout this document, the terms
"neighbor cache", "NCE" and "AFV" refer to this OAL neighbor cache
view unless otherwise specified.
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When a Client's network layer sends or receives IPv6 Neighbor
Discovery (ND) messages over an OMNI interface, it follows the
procedures in [RFC4861] using the Source/Target Link-Layer Address
Option (S/TLLAO) format defined for Ethernet [RFC2464]. On
transmission, the OMNI interface OAL leaves the S/TLLAO unchanged.
On reception, the OAL uses the IPv6 Source Address to translate the
S/TLLAO Ethernet address into a unique locally-generated value for
this neighbor.
When a Client's network layer sends or receives an ordinary IP packet
over an OMNI interface, the OAL consults the Ethernet to OAL IPv6
address mappings established by earlier IPv6 ND message exchanges.
On transmission, the OAL uses the Ethernet destination address to
determine the Destination Address for an OAL encapsulation header
while including an SRH extension if necessary. On reception, the OAL
uses the IPv6 encapsulation header Source Address to determine the
source address for the virtual Ethernet header.
The OMNI interface must therefore maintain internal per neighbor NCEs
that map local Ethernet addresses to remote Ethernet addresses and
GUAs/MLAs while exposing only the local representation of the
addresses to the IP layer. When the OMNI interface discovers a new
neighbor (e.g., when it creates a new NCE based on receipt of an IPv6
ND message), it maps the remote Ethernet address and GUA/MLA to a
randomly-chosen 6 octet local Ethernet address that must be unique
for this interface then installs the mapping in the cache. When the
OMNI interface discards an existing neighbor (e.g., when it deletes
an expired NCE), it removes the internal address mappings from the
cache.
When the OAL forwards IPv6 ND messages from the network layer to the
link layer, it performs encapsulation by adding an adaptation layer
IPv6 header (plus any necessary routing headers) and a new pseudo
IPv6 ND option trailer that encodes OMNI link-specific information.
When the OAL forwards IPv6 ND messages from the link layer to the
network layer, it performs decapsulation by removing the adaptation
layer IPv6 header while also parsing and removing the trailer.
Hence, this document defines a new pseudo IPv6 ND option type termed
the "OMNI option" designed for these purposes. Since the pseudo-
option is inserted and removed by the adaptation layer and never
examined by the network layer, it does not require a formal IPv6 ND
option number assignment.
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
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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.
10.1. The OMNI Option
During OAL IPv6 encapsulation of each IPv6 ND message, the OAL source
appends a single OMNI (pseudo-)option as a contiguous block of data
immediately following the end of the (composite) packet and includes
the length of the option in the OAL IPv6 header Payload Length.
During decapsulation of each IPv6 ND message, the OAL destination
processes the OMNI option contents then removes the option before
delivering the original IPv6 ND message (plus any additional original
IP packets from the composite packet) to the network layer.
The OMNI option therefore appears if and only if the (composite)
packet begins with an IPv6 ND message. The OMNI option format is
shown in Figure 15.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ OMNI Sub-Options (0 or more octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OMNI Len | Reserved | Checksum1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AERO Forwarding Vector Index (AFVI) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Segment List (zero or more 128-bit IPv6 Addresses) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Optional Type Length Value objects (variable) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Len | NSegs | Checksum2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: OMNI Option Format
In this format:
* OMNI Sub-Options is a variable-length concatenation of 0 or more
sub-option entries formatted as specified in Section 10.2 such
that the total length of all Sub-Options is an integer multiple of
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8 octets long, i.e., even if padding octets are necessary. The
final sub-option is followed by a variable-length trailer
containing the fields described below.
* Option Length is an 8-bit unsigned integer that encodes the
combined integer length of all Sub-Options in 8-octet units. If
there are no OMNI sub-options, Option Length encodes the value 0.
* Reserved is a 1-octet reserved field, set to 0 on transmission and
ignored on reception.
* Checksum1 is a 2-octet Internet checksum calculated over the
length of the OMNI option beginning with the first Sub-Options
octet and extending to include the OMNI Length and Reserved
fields. The OAL source calculates the Internet checksum and
writes the resulting value into the Checksum1 field. The OAL
destination verifies the checksum upon receipt and processes the
OMNI option further only if the checksum is correct. OAL
intermediate systems do not verify the OMNI option checksum and
simply pass the option contents up to and including the Checksum1
field unchanged.
* AERO Forwarding Vector Index (AFVI) is a 4-octet field initialized
by the IPv6 ND message source for each independent flow and
rewritten by each transit and endpoint OAL intermediate system on
the path ending at the IPv6 ND message destination (the special
value 0 denotes "AFVI unspecified"). The OAL source can then
begin sending OAL packets with OCH headers that include the AFVI
which each forwarding OAL intermediate system in the path can use
to determine the next OAL hop.
* Segment List records the MLAs of endpoint OAL intermediate systems
on the path from the original source Client to its FHS Proxy/
Server. For RS messages only, each successive endpoint
intermediate system "Proxy/Client" appends its MLA as the final
IPv6 address in the Segment List then increments the OAL IPv6
Payload Length by 16 and increments NSegs by 1 (see below).
* Optional Type Length Value (TLV) objects are included the same as
specified in [RFC8754] and may include a Hashed Message
Authentication Code (HMAC) [RFC2104] which covers the AFVI and
Segment List only. When included, the HMAC is checked then reset
by each successive OAL intermediate system in a hop-by-hop
fashion. If resetting the HMAC causes its length to change, the
OAL intermediate system must also reset both TLV Len and the OAL
IPv6 Payload Length accordingly.
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* TLV Len is the length in octets of the TLV objects field, and
provides an offset to the beginning of the TLV objects (or the
value 0 if the TLV objects field is null).
* NSegs includes the number of IPv6 addresses in the Segment List,
initialized to 0 by the OAL source for all IPv6 ND message types.
For RS messages only, each successive endpoint intermediate system
updates the Segment List and OAL IPv6 Payload Length (see above)
then increments NSegs by 1.
* Checksum2 is the Internet checksum calculated beginning with the
OAL IPv6 pseudo-header per Section 8.1 of [RFC8200] then
continuing over the AFVI, Segment List, TLV objects then finally
the TLV Len and NSegs fields. The OAL source calculates the
Internet checksum and writes the resulting value into the
Checksum2 field. Each OAL intermediate system up to and including
the OAL destination verifies the checksum upon receipt and
processes the OMNI option further only if the checksum is correct.
The intermediate system then adjusts the OAL header and trailer
fields as necessary and resets Checksum2 before forwarding to the
next hop.
OMNI encapsulated IPv6 ND messages exchanged over unsecured *NETs
between peer Clients or Clients and their Proxy/Servers use either
SEND per [RFC3971] or HMAC per [RFC8754][RFC2104] as an adaptation
layer authentication service. Since the adaptation layer already
applies authentication from within the OMNI interface, the network
layer need not also apply IPv6 ND message authentication over the
OMNI interface unless there is some reason to propagate a digital
signature to the final destination. The OMNI option therefore
provides sub-options to support either SEND or HMAC as adaptation
layer authentication services.
Although originally specified to operate with Cryptographically
Generated Addresses (CGAs) per [RFC3972], SEND notes that: "This
specification also allows a node to use non-CGAs with certificates
that authorize their use. However, the details of such use are
beyond the scope of this specification and are left for future work."
Since CGAs do not support verification through an address
registration and certification service, OMNI specifically requires
alternative MLA types that can satisfy these properties.
The OMNI Sub-Options may include full or partial information for the
neighbor. The OMNI interface therefore retains the union of the most
recently received information in the corresponding NCE.
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10.2. OMNI Sub-Options
The OMNI option includes a Sub-Options block containing zero or more
individual sub-options in standard Type-Length-Value (TLV) format.
Each successive sub-option is concatenated immediately following its
predecessor. All sub-options are encoded as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Sub-Type | Sub-Length | Sub-Option Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 16: Sub-Option Format
* Sub-Type is a 8-bit field that encodes the sub-option type. Sub-
option types defined in this document include:
Sub-Option Name Sub-Type
Pad1 0
PadN 1
Node Identification 2
CGA 3
RSA Signature 4
Timestamp 5
Nonce 6
Trust Anchor 7
Certificate 8
HMAC 9
Neighbor Synchronization 10
Interface Attributes 11
Traffic Selector 12
Geo Coordinates 13
DHCPv6 Message 14
PIM-SM Message 15
Fragmentation Report 16
ICMPv6 Error 17
Proxy/Server Departure 18
Figure 17
Unassigned Sub-Types are available for future assignment, except
that Sub-Types 253 and 254 are reserved for experimentation while
Sub-Type 255 is reserved by IANA.
* Sub-Length is an 8-bit field that encodes the length of the Sub-
Option Data in octets (i.e., not including the Sub-Type and Sub-
Length fields themselves).
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* Sub-Option Data is a block of data with format determined by Sub-
Type and length determined by Sub-Length. Note that each sub-
option is concatenated immediately following the previous and may
therefore begin and/or end on an arbitrary octet boundary.
The OMNI interface codes all sub-options in a single OMNI option in
the same IPv6 ND message in the intended order of processing. If the
size of the sub-options would cause the IPv6 ND message to exceed the
path MTU, the OMNI interface includes as many sub-options as possible
and codes any remaining sub-options in additional IPv6 ND messages.
The OMNI interface processes the OMNI option received in an IPv6 ND
message while skipping over and ignoring any unrecognized sub-
options. 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.
IPv6 ND messages that require OMNI authentication services include an
RSA Signature or HMAC sub-option as the first sub-option. A single
IPv6 ND message includes a single effective OMNI authentication
service sub-option; if multiple are included, the first sub-option is
processed and all others are ignored.
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 IPv6 ND messages, if
necessary.
The following sub-option types and formats are defined in this
document:
10.2.1. Pad1
+-+-+-+-+-+-+-+-+
| Sub-Type=0 |
+-+-+-+-+-+-+-+-+
Figure 18: Pad1
* Sub-Type is set to 0. If multiple contiguous instances of Pad1
appear in the OMNI option of the same message the message should
be dropped. (If more than a single octet of padding is necessary,
the PadN option is used.)
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* Sub-Type is followed by 3 'x' bits, set to any value on
transmission (typically all-zeros) and ignored on reception. Pad1
therefore consists of a single octet with the most significant 5
bits set to 0, and with no Sub-Length or Sub-Option Data fields
following.
10.2.2. PadN
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Sub-Type=1 | Sub-Length=N | N padding octets ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 19: PadN
* Sub-Type is set to 1.
* 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 reception.
10.2.3. Node Identification
Nodes may include the Node Identification sub-option as supplementary
identification information in addition to the IPv6 ND message Source
Address. If multiple instances appear in the same OMNI option, the
first instance of a specific ID-Type is processed and all other
instances of the same ID-Type are ignored. (A single IPv6 ND message
can therefore convey multiple distinct Node Identifications - each
with a different ID-Type.)
The format and contents of the sub-option are shown in Figure 20:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=2 | Sub-length=N | ID-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Node Identification Value (N-2 octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: Node Identification
* Sub-Type is set to 2. Multiple instances are processed as
discussed above.
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* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The ID-Type field is always present, and the
maximum Node Identification Value length is limited by the
remaining available space in this OMNI option.
* ID-Type is a 2-octet field that encodes the type of the Node
Identification Value. The following ID-Type values are currently
defined:
- 0 - Multilink Local Address (MLA). A special-purpose IPv6
address assigned to an OMNI interface for adaptation layer
addressing as discussed in Section 8. Indicates that Node
Identification Value contains a 16-octet MLA.
- 1 - Universally Unique IDentifier (UUID) [RFC9562]. Indicates
that Node Identification Value contains a 16-octet UUID.
- 2 - Network Access Identifier (NAI) [RFC7542]. Indicates that
Node Identification Value contains an (N-1)-octet NAI.
- 3 - Fully-Qualified Domain Name (FQDN) [RFC1035]. Indicates
that Node Identification Value contains an (N-1)-octet FQDN.
- 4 - IPv4 Address. Indicates that Node Identification contains
a 4-octet IPv4 address. The IPv4 address type is determined
with reference to the IANA IPv4 Address Space Registry [IPV4].
- 5 - Unassigned.
- 6 - IPv6 Address. Indicates that Node Identification contains
a general-purpose 16-octet IPv6 address that is not an MLA.
The IPv6 address type is determined according to the IPv6
addressing architecture [RFC4291] with reference to the IANA
IPv6 Global Unicast Address Assignments Registry [IPV6].
- 7 - 65532 - Unassigned.
- 65533 - 65534 - reserved for experimentation, as recommended in
[RFC3692].
- 65535 - reserved by IANA.
* Node Identification Value is an (N-2)-octet field encoded
according to the appropriate the "ID-Type" reference above.
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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 21) as shown in Figure 21:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DUID-Type (2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Enterprise Number (45282) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID-Type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
| ~
~ Node Identification Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: DUID-EN for OMNI Format
In this format, the OMNI interface codes the ID-Type and Node
Identification Value fields from the OMNI sub-option following a
6-octet DUID-EN header, then includes the entire "DUID-EN for OMNI"
in a DHCPv6 message per [I-D.ietf-dhc-rfc8415bis].
10.2.4. CGA
OMNI nodes include an OMNI Cryptographically Generated Address (CGA)
sub-option for IPv6 ND messages the same as per Section 5.1 of
[RFC3971] with the exception that the CGA body field itself need not
be an integral number of 8-octet words. The OMNI CGA sub-option has
the following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=3 | Sub-length=N | Pad Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ CGA Parameters (N-2 octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: CGA
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10.2.5. RSA Signature
The OMNI RSA Signature sub-option includes a public key-based
signature extending over the length of the OMNI-encapsulated IPv6 ND
message followed by any composite packet extensions then finally over
the OMNI option itself up to but not including this sub-option. When
present, the RSA Signature sub-option MUST appear as the first OMNI
sub-option.
Each OMNI encapsulated IPv6 ND message should include at most one RSA
Signature or HMAC sub-option. If an IPv6 ND message includes
multiple RSA Signature and/or HMAC sub-options, the first one is
processed and all others ignored.
The IPv6 ND message source calculates the IPv6 ND message checksum
over the length of just the ND message itself and writes the value
into the ICMPv6 Checksum field as a first step. The OAL source can
then calculate a digital signature to include in an OMNI RSA
Signature sub-option as discussed below. The OAL source finally
calculates the OMNI option checksum and writes its value into the
OMNI trailing Checksum1 field, then includes any trailing information
and calculates/writes the Checksum2 field.
The RSA Signature sub-option is formatted as shown in Figure 23:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=4 | Sub-length=N | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Key Hash ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Digital Signature ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Padding ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23: RSA Signature
* Sub-Type is set to 4. The RSA Signature sub-option should appear
at most once in any OMNI option; if multiple instances appear in
the same OMNI option the final one 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 Padding. The Key Hash is always 128 bits in
length per [RFC3971] while the length of the Digital Signature is
constrained by the remaining available space for this sub-option.
* Key Hash, Digital Signature and Padding are included as specified
in Section 5.2 of [RFC3971].
The sender constructs the Digital Signature in the same manner as
Section 5.2 of [RFC3971] except over the following data:
1. For CGAs, the 128-bit CGA Message Type tag [RFC3972] value for
SEND, 0x086F CA5E 10B2 00C9 9C8C E001 6427 7C08 [RFC3971]. For
MLA types that include cryptographically generated elements, the
128-bit Context ID found in the "CGA Extension Type Tags"
registry [IANA-CGA].
2. The entire IPv6 ND message beginning with the IPv6 header, then
extending over the ND message header and all ND message options.
3. All composite IP packet extensions up to the beginning of the
OMNI option.
4. All OMNI sub-options preceding this RSA Signature sub-option.
Note: the same as for ordinary IPv6 ND SEND operations, the CGA/MLA
subject to authentication appears in the IPv6 ND message IPv6 Source
Address. Note also that the OAL IPv6 Source and Destination Address
as well as Payload Length are not included in the Digital Signature
since these values may be rewritten by proxies on the path (i.e.,
both Proxy/Servers in different OMNI link segments and Proxy/Clients
within the same OMNI link segment).
10.2.6. Timestamp
OMNI nodes include an OMNI Timestamp sub-option in IPv6 ND messages
to ensure that unsolicited advertisements and redirects have not been
replayed. The Timestamp sub-option is processed exactly the same as
in Section 5.3.1 of [RFC3971]. The OMNI Timestamp sub-option has the
following format:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=5 | Sub-length=8 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Reserved (6 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Timestamp (8 octets) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 24: Timestamp
10.2.7. Nonce
OMNI nodes include an OMNI Nonce sub-option in IPv6 ND messages to
ensure that an advertisement is a fresh response to a solicitation
sent earlier by the node. The Nonce sub-option is processed exactly
the same as in Section 5.3.2 of [RFC3971] with the exception that the
Nonce field itself need not be an integral number of 8-octet words.
The OMNI Nonce sub-option has the following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=6 | Sub-length=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Nonce (N octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 25: Nonce
10.2.8. Trust Anchor
OMNI nodes include an OMNI Trust Anchor sub-option the same as
described in Section 6.4.3 of [RFC3971] with the exception that the
sub-option does not require 8-octet alignment and need not contain an
integral number of 8 octet units. The Trust Anchor sub-option has
the following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=7 | Sub-length=N | Name Type | Pad Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Trust Anchor Body (N-2 octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 26: Trust Anchor
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10.2.9. Certificate
OMNI nodes include an OMNI Certificate sub-option in IPv6 ND messages
the same as described in Section 6.4.4 of [RFC3971] with the
exception that the sub-option does not require 8-octet alignment and
need not contain an integral number of 8 octet units. The
Certificate sub-option has the following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=8 | Sub-length=N | Cert Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Certificate Body (N-2 octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 27: Certificate
10.2.10. Hashed Message Authentication Code (HMAC)
OMNI nodes may include a Hashed Message Authentication Code (HMAC)
sub-option. When present, the HMAC sub-option must appear as the
first sub-option the same as specified for RSA Signature above.
Each OMNI encapsulated IPv6 ND message should include at most one RSA
Signature or HMAC sub-option. If an IPv6 ND message includes
multiple RSA Signature and/or HMAC sub-options, the first one is
processed and all others ignored.
The format of the HMAC option is taken directly from Section 2.1.2 of
[RFC8754] as shown in Figure 28:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=9 | Sub-length=N |D| RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HMAC Key ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ HMAC (variable) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 28: Hashed Message Authentication Code (HMAC)
The HMAC sub-option is encoded and processed the same as specified in
[RFC2104] and Section 2.1.2 of [RFC8754] except that the HMAC is
applied over the following text:
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1. For CGAs, the 128-bit CGA Message Type tag [RFC3972] value for
SEND, 0x086F CA5E 10B2 00C9 9C8C E001 6427 7C08 [RFC3971]. For
MLA types that include different cryptographically generated
elements, the 128-bit Context ID found in the "CGA Extension Type
Tags" registry [IANA-CGA].
2. The entire IPv6 ND message beginning with the IPv6 header, then
extending over the ND message header and all ND message options.
3. All composite IP packet extensions up to the beginning of the
OMNI option.
4. All OMNI sub-options following this HMAC sub-option.
Note: the same as for ordinary IPv6 ND SEND operations, the CGA/MLA
subject to authentication appears in the IPv6 ND message IPv6 Source
Address. Note also that the OAL IPv6 Source and Destination Address
as well as Payload Length are not included in the Digital Signature
since these values may be rewritten by proxies on the path (i.e.,
both Proxy/Servers in different OMNI link segments and Proxy/Clients
within the same OMNI link segment).
10.2.11. Neighbor Synchronization
IPv6 ND messages that establish or update neighbor state between
Clients and their Proxy/Servers or peer Clients include a Neighbor
Synchronization OMNI sub-option. Each IPv6 ND message includes at
most one Neighbor Synchronization sub-option which must be specific
to the underlying interface pair over which ND messages are
exchanged.
The Neighbor Synchronization sub-option is formatted as follows:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=10 |Sub-length=28+N|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FHS (initiator) ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LHS (responder) ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Sequence Number ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Acknowledgment Number ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N|A|R|A|O|R|S|P| |
|U|R|P|C|P|S|Y|C| Window |
|D|R|T|K|T|T|N|H| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved ...
+-+-+-+-+-+-+-+-+-+-
Figure 29: Neighbor Synchronization
* Sub-Type is set to 10. If multiple instances appear in the same
OMNI option, the first is processed and all others are ignored.
* Sub-Length is set to (28 + N), where N is the length in octets of
the trailing Reserved field if present; otherwise, 0.
* the first 8 octets include the 4-octet ifIndex of the FHS
(initiator) node followed by the 4-octet ifIndex of the LHS
(responder) node.
* the next 20 octets of Sub-Option Data follows from the
Transmission Control Protocol (TCP) header specified in
Section 3.1 of [RFC9293]. The field is formatted as an 8-octet
Sequence Number, followed by an 8-octet Acknowledgement Number,
followed by a 1-octet flags field followed by a 3-octet Window
size. The TCP (ACK, RST, SYN) flags are used for TCP-like window
synchronization as discussed in Section 6.7, while the TCP (CWR,
ECE, URG, PSH, FIN) flags are unused and replaced by the OMNI-
specific flags (NUD, ARR, RPT, OPT, PCH).
* Clients set the Neighbor Unreachability Detection (NUD), Address
Resolution Responder (ARR) and Report (RPT) flags in RS messages
to control the operation of their Proxy/Server neighbors as
discussed in Section 13.
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* Neighbors set the OPT flag as discussed in Section 6.7 during a
(SYN, SYN/ACK) synchronization exchange that does not require a
concluding ACK.
* OAL intermediate systems set the Path Change (PCH) flag in IPv6 ND
control messages used to report a change in a path established by
multilink forwarding.
* An N-octet trailing Reserved field is available for expansion to
include additional flags as necessary for future applications.
Currently, no additional flags are defined and N should be set to
0.
10.2.12. Interface Attributes
The Interface Attributes sub-option provides neighbors with
forwarding information for the multilink conceptual sending algorithm
discussed in Section 12. Neighbors use the forwarding information to
select among candidate underlay interfaces that can be used to
forward carrier packets to the neighbor based on factors such as
traffic selectors and link metrics. Interface Attributes further
include link layer address information to be used for either direct
INET encapsulation for targets in the local SRT segment or spanning
tree forwarding for targets in remote SRT segments.
OMNI nodes include Interface Attributes for some/all of a source or
target Client's underlay interfaces in IPv6 ND solicitation and
response messages that exchange peer-to-peer Client information (see:
[I-D.templin-6man-aero3]). 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 IPv6 ND 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 populated in future neighbor exchanges.
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.
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When an FHS Proxy/Server receives an RS message destined to an
anycast L2 address, it MUST include an additional Interface
Attributes sub-option with ifIndex '0' that encodes its own unicast
L2 address relative to the Client's underlay interface in the
solicited RA response. Any additional Interface Attributes sub-
options that appear in RS/RA messages (i.e., besides those for the
Client's own ifIndex and ifIndex '0') are ignored.
The Interface Attributes sub-option is formatted as shown below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=11 | Sub-length=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifProvider |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifMetric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifGroup |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRT | FMT | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
| ~
~ LHS L3ADDR/L2ADDR ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Segment List (zero or more 128-bit IPv6 Addresses) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 30: Interface Attributes
* Sub-Type is set to 11. 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:
- ifIndex is a 4-octet index value corresponding to a specific
underlay interface. Client OMNI interfaces MUST number each
distinct underlay interface with a unique non-zero ifIndex
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value assigned by network management per [RFC2863] and include
the value in this field. The ifIndex value '0' denotes
"unspecified".
- ifType is a 4-octet type value corresponding to this underlay
interface. The value is coded per the 'IANAifType-MIB'
registry [http://www.iana.org].
- ifProvider is a 4-octet provider identifier corresponding to
this underlay interface. This document defines the single
provider identifier value '0' (undefined). Future documents
may define other values.
- ifMetric encodes a 4-octet interface metric. Lower values
indicate higher priorities, and the highest value indicates an
interface that should not be selected. The ifMetric setting
provides an instantaneous indication of the interface
bandwidth, link quality, signal strength, cost, etc.; hence,
its value may change in successive IPv6 ND messages.
- ifGroup is a 4-octet identifier for a Link Aggregation Group
(LAG) [IEEE802.1AX] corresponding to the underlay interface
identified by ifIndex. Interface attributes for ifIndex
members of the same group will encode the same value in
ifGroup. This document defines the single ifGroup value '0'
meaning "no group assigned". Future documents will specify the
setting of other values.
- SRT is a 1-octet Segment Routing Topology prefix length that
determines the length associated with this sub-tree of a larger
Internetworking topology that may include the concatenation of
multiple connected segments. Correspondent nodes apply the SRT
prefix length to LHS L3ADDR (see below) to discover a
topological orientation for this interface.
- FMT - a 1-octet "Forward/Mode/Type" code interpreted as
follows:
o The most significant 2 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 before forwarding. If the FMT-Mode bit is clear, the
LHS Proxy/Server then forwards the original IP packet at L3;
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 unmodified OAL fragments to
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the Client without reassembling. 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 least significant 6 bits ("FMT-Type") determines the
type of L2 encapsulation needed to reach the target Client
interface within its local *NET. When the most significant
bit (msb) of FMT-Type is set, the interface has been
determined to reside behind a Network Address Translator
(NAT) as discovered during Client exchanges with their
Proxy/Servers. The least significant 5 bits of FMT-Type
encode an L2 encapsulation type value as follows:
+ 0 - L2 encapsulation type is unspecified. No L2ADDR is
included and the msb is ignored.
+ 1 - Client interface is within a MANET where multihop
forwarding occurs as an adaptation layer service. No
L2ADDR is included and the msb is ignored.
+ 2 - L2 encapsulation type is EUI-48 only. L2ADDR is 6
octets in length and encodes an EUI-48 address [EUI].
+ 3 - L2 encapsulation type is EUI-64 only. L2ADDR is 8
octets in length and encodes an EUI-64 address [EUI].
+ 4 - L2 encapsulation type is IPv4 only. L2ADDR is 4
octets in length and encodes an IPv4 address.
+ 6 - L2 encapsulation type is IPv6 only. L2ADDR is 16
octets in length and encodes an IPv6 address.
+ 7 - L2 encapsulation type is UDP/IPv4. L2ADDR is 6
octets in length and encodes a 2-octet UDP port number
followed by a 4-octet IPv4 address.
+ 8 - L2 encapsulation type is UDP/IPv6. L2ADDR is 18
octets in length and encodes a 2-octet UDP port number
followed by a 16-octet IPv6 address.
+ 5, [9 - 31] - Reserved for future use.
- LHS L3ADDR/L2ADDR - encodes the 16 octet SNP IPv6 GUA L3ADDR of
the LHS Client delegated by the Proxy/Server for this interface
optionally followed by an L2ADDR field as above. When present,
L2ADDR identifies the LHS Client's *NET interface which may be
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on an open INET or behind one or more NATs. The LHS Client may
also be serving as an outermost Proxy for other Clients nested
within a MANET multihop forwarding region. When L2ADDR
includes an IPv4 or IPv6 address, it appears in network byte
order in ones-complement "obfuscated" form per [RFC4380]. The
LHS information therefore satisfies per-interface address
resolution and FMT/SRT/LHS together provide guidance for the
OMNI interface forwarding algorithm. Specifically, if
LHS::/SRT is located in the FHS OMNI link segment, then the
source can address the target Client either through its
dependent Proxy/Server or through direct L2 encapsulation
(while engaging NAT traversal if necessary) 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.
- Segment List echoes the MLAs recorded in the source Client's RS
message transmission to the FHS Proxy/Server in subsequent IPv6
ND messages. The ordered list includes the MLAs of all
endpoint Proxy/Client on the path with the first entry
representing the Proxy/Client nearest the source Client and the
final entry representing the Proxy/Client nearest the FHS
Proxy/Server. The length of the Segment List is determined by
subtracting the lengths of all prior fields from the sub-option
length. The Segment List provides context for filling the SRH
header in subsequent IPv6 ND message exchanges.
10.2.13. Traffic Selector
The Traffic Selector sub-option provides forwarding information for
the multilink conceptual sending algorithm discussed in Section 12.
The sub-option includes an augmented traffic selector per [RFC6088]
as ancillary information for an Interface Attributes sub-option with
the same ifIndex value, or as discrete information for the included
ifIndex when no Interface Attributes sub-option is present. (Note
that the OMNI augmented traffic selector includes additional fields
'O' and 'P' that do not appear in [RFC6088].)
IPv6 ND messages may include multiple Traffic Selectors for some or
all of the source/target Client's underlay interfaces (see:
[I-D.templin-6man-aero3] for further discussion). Traffic Selectors
must be honored by all implementations in the format shown below:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=12 | Sub-length=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TS Length | TS Format |A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (A)Start Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (B)End Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (C)Start Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (D)End Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (E)Start IPsec SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (F)End IPsec SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (G)Start Source port | (H)End Source port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (I)Start Destination port | (J)End Destination port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (K)Start DS | (L)End DS |(M)Start Prot. | (N) End Prot. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (O)Start Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (P)End Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Additional Traffic Selector Blocks ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
Figure 31: Traffic Selector
* Sub-Type is set to 12. Multiple instances with the same or
different ifIndex values may appear in the same OMNI option. When
multiple instances appear, all are processed and the cumulative
information from all is accepted.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
* Sub-Option data begins with a 4-octet ifIndex value corresponding
to a specific underlay interface.
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* The remainder of Sub-Option Data contains one or more "Traffic
Selector" blocks for this ifIndex that each begin with 1-octet "TS
Length" and "TS Format" fields. TS length encodes the combined
lengths of the TS* fields plus the Traffic Selector body that
follows (i.e. a value between 2-255 octets). When TS Format
encodes the value 1 or 2, the Traffic Selector body encodes an
IPv4 or IPv6 traffic selector per [RFC6088] beginning with 16 flag
bits ("A-P"); when TS Format encodes any other value the Traffic
Selector block is skipped and processing resumes beginning with
the next Traffic Selector block (note that future specifications
may define new TS Formats).
* The Traffic Selector block elements then appear immediately after
the flags (with no 16-bit Reserved field included) and encode the
information corresponding to any set flag bit(s) in order the same
as specified in [RFC6088]. Each included Traffic Selector block
is processed consecutively, with its length subtracted from the
remaining sub-option length until all blocks are processed. If
the length of any Traffic Selector block would exceed the
remaining length for the entire sub-option, the remainder of the
sub-option is ignored.
10.2.14. Geo Coordinates
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=13 | Sub-length=N | Geo Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Geo Coordinates ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 32: Geo Coordinates
* Sub-Type is set to 13. If multiple instances appear in the same
OMNI option all are processed.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
* Geo Type is a 1-octet field that encodes a type designator that
determines the format and contents of the Geo Coordinates field
that follows. The following types are currently defined:
- 0 - NULL, i.e., the Geo Coordinates field is zero-length.
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* 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.
10.2.15. 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. The DHCPv6 sub-option is formatted per Section 8
of [I-D.ietf-dhc-rfc8415bis] as shown in Figure 33:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=14 | Sub-length=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | transaction-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ DHCPv6 options ~
~ (variable number and length) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 33: DHCPv6 Message
* Sub-Type is set to 14. At most 2 instances may appear in a single
OMNI option. If more instances appear, the first 2 are 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 [I-D.ietf-dhc-rfc8415bis].
* A set of DHCPv6 options coded according to Section 21 of
[I-D.ietf-dhc-rfc8415bis] follows.
10.2.16. 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.
The PIM-SM message sub-option is formatted per Section 4.9 of
[RFC7761] and as shown in Figure 34:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=15 | Sub-length=N |PIM Ver| Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ PIM-SM Message ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 34: PIM-SM Message Option Format
* Sub-Type is set to 15. If multiple instances appear in a single
OMNI option all are processed.
* Sub-Length is set to N, i.e., the length of the option in octets
beginning immediately following the Sub-Length field and extending
to the end of the PIM-SM message. The length of the entire PIM-SM
message is therefore limited by the remaining available space for
this OMNI option.
* The PIM-SM message is coded exactly as specified in Section 4.9 of
[RFC7761], except that the Checksum field is omitted since message
integrity is already assured by the OMNI option checksum. The
Reserved field is set to 0 on transmission and ignored on
reception. The "PIM Ver" field encodes the value 2, and the
"Type" field encodes the PIM message type. (See Section 4.9 of
[RFC7761] for a list of PIM-SM message types and formats.)
10.2.17. Fragmentation Report (FRAGREP)
Fragmentation Report (FRAGREP) sub-options may be included in the
OMNI options of unsolicited IPv6 ND control messages sent from an OAL
destination to an OAL source. The message consists of (N/16)-many
(Identification, Bitmap)-tuples which include the Identification
values of OAL fragments received plus a Bitmap marking the ordinal
positions of individual fragments received and missing.
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=16 | Sub-Length=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification (0) (64 bits) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Bitmap (0) (64 bits) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification (1) (64 bits) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Bitmap (1) (64 bits) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
Figure 35: Fragmentation Report (FRAGREP)
* Sub-Type is set to 16. If multiple instances appear in the same
OMNI option all are processed.
* Sub-Length is set to N which must be a multiple of 16, i.e., the
combined lengths of each (Identification, Bitmap) pair beginning
immediately following the Sub-Length field and extending to the
end of the sub-option.
* Identification(i) includes the 8-octet Identification value found
in a received OAL fragment.
* Bitmap(i) includes a 64-bit checklist of up to 64 ordinal
fragments for this Identification, with each bit set to 1 for a
fragment received or 0 for a fragment corrupted, lost or still in
transit. For example, for a 20-fragment OAL packet with ordinal
fragments #3, #10, #13 and #17 missing or corrupted and all other
fragments received or still in transit, Bitmap(i) encodes the
following:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|1|1|1|0|1|1|1|1|1|1|0|1|1|0|1|1|1|0|1|1|0|0|0|...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 36
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10.2.18. ICMPv6 Error
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=17 | Sub-length=N | Type | Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ICMPv6 Error Message Body ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 37: ICMPv6 Error
* Sub-Type is set to 17. If multiple instances appear in the same
OMNI option all are processed.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
* Sub-Option Data includes an N-octet ICMPv6 Error Message body
encoded per Section 2.1 of [RFC4443], but with the IPv6 header and
Checksum fields omitted. OMNI interfaces include as much of the
"packet in error" in the ICMPv6 error message body as possible
without causing the IPv6 ND message to exceed the IPv6 minimum
MTU. While all ICMPv6 error message types are supported, OAL
destinations often include ICMPv6 PTB messages in unsolicited IPv6
ND control messages to provide MTU feedback information via the
OAL source (see: Section 6.9). Note: ICMPv6 informational
messages must not be included on transmission and must be ignored
if received.
10.2.19. Proxy/Server Departure
OMNI Clients include a Proxy/Server Departure sub-option in RS
messages when they associate with a new FHS and/or MAP Proxy/Server
and need to send a departure indication to an old FHS and/or MAP
Proxy/Server. The Proxy/Server Departure sub-option is formatted as
shown below:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=18 | Sub-length=32 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Old FHS Proxy/Server L3ADDR (16 octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Old MAP Proxy/Server L3ADDR (16 octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 38: Proxy/Server Departure
* Sub-Type is set to 18. If multiple instances appear in the same
OMNI option, the first is processed and all others are ignored.
* Sub-Length is set to 32.
* Sub-Option Data contains the 16-octet L3ADDR for the "Old FHS
Proxy/Server" followed by a 16-octet L3ADDR for an "Old MAP Proxy/
Server. If the Old FHS/MAP is a different node, the corresponding
L3ADDR includes the address of the (foreign) Proxy/Server. If the
Old FHS/MAP is the local node, the corresponding L3ADDR includes
the node's own address. If the FHS/MAP is unspecified, the
corresponding L3ADDR instead includes the value "::/128".
11. Address Mapping - Multicast
The multicast address mapping of the native underlay interface
applies. The Client mobile router also serves as an IGMP/MLD Proxy
for its ENETs and/or hosted applications per [RFC4605].
The Client uses Multicast Listener Discovery (MLDv2) [RFC3810] to
coordinate with Proxy/Servers, and underlay network elements use MLD
snooping [RFC4541]. The Client can also employ multicast routing
protocols to coordinate with network-based multicast sources as
specified in [I-D.templin-6man-aero3].
Since the OMNI link model is NBMA, OMNI links support link-scoped
multicast through iterative unicast transmissions to individual
multicast group members (i.e., unicast/multicast emulation).
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12. Multilink Conceptual Sending Algorithm
The Client's network layer selects the outbound OMNI interface
according to SBM considerations when forwarding original IP packets
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 13, and may configure more-specific routes discovered through
means outside the scope of this specification.
For each original IP packet 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 10.2.11).
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 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 13.2.
OMNI interface multilink service designers MUST observe the BCP
guidance in Section 15 [RFC3819] in terms of implications for
reordering when original IP packets from the same flow may be spread
across multiple underlay interfaces having diverse properties.
12.1. Multiple OMNI Interfaces
Clients may connect to multiple independent OMNI links within the
same or different OMNI domains to support SBM. The Client configures
a separate OMNI interface for each link so that multiple interfaces
(e.g., omni0, omni1, omni2, etc.) are exposed to the network layer.
Each OMNI interface is configured over a separate set of underlying
interfaces and configures one or more OMNI link SRA addresses (see:
Section 8); the Client injects the corresponding SRA prefixes into
the ENET routing system. Multiple distinct OMNI links can therefore
be used to support fault tolerance, load balancing, reliability, etc.
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Applications in ENETs can use Segment Routing to select the desired
OMNI interface based on SBM considerations. The application writes
an OMNI link SRA address into the original IP packet'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 to the Client's mobile router entity,
where the OMNI link SRA address identifies the correct OMNI interface
for next hop forwarding. When the Client receives the packet, it
replaces the IP Destination Address with the next Address found in
the Segment Routing Header and forwards the message via the OMNI
interface identified by the SRA 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.
12.2. Client-Proxy/Server Loop Prevention
After a Proxy/Server has registered an MNP for a Client (see:
Section 13), the Proxy/Server will forward all original IP packets
(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 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 (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 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.
Proxy/Servers support "hairpinning" for packets with SNP Source and
Destination Addresses that would convey useful data from a source SNP
Client to a target SNP Client both located in the same OMNI link
segment. Proxy/Servers support this hairpinning according to
[RFC6296], however ULA-to-ULA addressing between peer nodes within
the same OMNI link segment is preferred whenever possible.
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13. Router Discovery and Address/Prefix Delegation
Clients engage their FHS Proxy/Servers and the MS by sending OAL
encapsulated 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 an FHS Proxy/Server, which may in turn
forward a proxyed copy to a MAP Proxy/Server located in a local or
remote SRT segment if the Client requires MNP service. The MAP
Proxy/Server then returns an OAL encapsulated RA message either
directly to the Client or via the original FHS Proxy/Server acting as
a proxy.
Clients send RS messages under the conditions specified in
Section 6.3.7 of [RFC4861] which includes not only interface/link
initialization conditions but also mobility factors. In particular,
Clients may send RS messages when the OMNI interface or an underlay
interface changes state, or when the Client moves to a new link and
needs to discover addressing parameters for its new topological
orientation. The Client's RS/RA exchanges therefore maintain the
most current OMNI link state information even across frequent
mobility events.
To initiate Router Discovery and Address/Prefix Delegation, the
Client uses its OMNI interface LLA as the IPv6 Source Address for RS
messages it sends to candidate FHS Proxy/Servers. The OMNI interface
adaptation layer in turn translates the LLA into its MLA while also
including OMNI authentication, Interface Attributes and any other
sub-options. The FHS Proxy/Server first consults an address
registration service to determine whether the Client is authorized to
use its claimed MLA and discards the RS message if authorization
fails. Otherwise, the FHS Proxy/Server provides Router Discovery and
Address/Prefix Delegation services for the Client per the remainder
of this section.
To support Client to service coordination, the OMNI option provides
flag bits in the OMNI Neighbor Synchronization sub-option as
discussed in Section 10.2.11. Clients set or clear Neighbor
Synchronization flags in RS messages as directives to the Mobility
Service FHS/MAP Proxy/Servers. Proxy/Servers interpret the flags as
follows:
* When an FHS Proxy/Server forwards or processes an RS with the NUD
flag set, it responds directly to future NS Neighbor
Unreachability Detection (NUD) messages with the Client as the
target by returning NA(NUD) replies; otherwise, it forwards
NS(NUD) messages to the Client.
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* When the MAP Proxy/Server receives an RS with the ARR flag set, it
responds directly to future NS Address Resolution (AR) messages
with the Client as the target by returning NA(AR) replies;
otherwise, it forwards NS(AR) messages to the Client.
* When the MAP Proxy/Server receives an RS with the RPT flag set, it
maintains a Report List of recent NS(AR) message sources for the
source or target Client and sends unsolicited IPv6 ND control
messages to all list members if any aspects of the Client's
underlay interfaces change.
Mobility Service Proxy/Servers function according to the NUD, ARR and
RPT flag settings received in the most recent RS message to support
dynamic Client updates.
Clients and FHS Proxy/Servers include an authentication signature as
an OMNI sub-option in their RS/RA exchanges when necessary but always
include valid IPv6 ND message and OMNI option checksums. 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 (normally) only with one MAP Proxy/Server at a
given time. All Proxy/Servers accept original IP packets addressed
to their LLAs or link-scoped multicast, OAL packets addressed to
their anycast/unicast MLA/ULA/GUAs and carrier packets addressed to
their anycast/unicast L2ADDRs. The Client typically selects one MAP
Proxy/Server among any of its FHS Proxy/Servers, but may instead
select any other Proxy/Server on the OMNI link.
Example L2ADDR discovery methods appear in [RFC5214] and include data
link login parameters, name service lookups, static configuration, a
DHCP option, a static "hosts" file, etc. In the absence of other
information, the Client can resolve the DNS Fully-Qualified Domain
Name (FQDN) "linkupnetworks.[domainname]" where "linkupnetworks" is a
constant text string and "[domainname]" is a DNS suffix for the OMNI
link (e.g., "example.com"). The name resolution will return a set of
DNS resource records to populate a Potential Router List (PRL) that
contains addresses of Proxy/Servers for the local OMNI link segment.
When the underlay *NET does not support standard unicast server-based
name resolution [RFC1035] the Client can engage a multicast service
such as mDNS [RFC6762] within the local OMNI link segment.
Each FHS Proxy/Server configures an MLA and SNP ULA/GUA prefix pairs
for the local OMNI link segment then advertises its L2ADDR(s) for
discovery as above. Each Client can then manage its own SNP ULA/GUA
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addresses through DHCPv6 address autoconfiguration exchanges with FHS
Proxy/Servers. The FHS Proxy/Servers discovered over multiple of the
Client's underlay interfaces may configure the same or different SNP
ULA/GUA prefix pairs, and the Client's ULA/GUA for each underlay
interface will fall within the ULA/GUA for the OMNI link segment
relative to each FHS Proxy/Server.
Clients configure OMNI interfaces that observe the properties
discussed in previous sections. The OMNI interface and its underlay
interfaces are said to be in either the "UP" or "DOWN" state
according to administrative actions in conjunction with the interface
connectivity status. An OMNI interface transitions to UP/DOWN
through administrative action and/or through underlay interface state
transitions. When a first underlay interface transitions to UP, the
OMNI interface also transitions to UP. When all underlay interfaces
transition to DOWN, the OMNI interface also transitions to DOWN.
When a Client OMNI interface transitions to UP, the IP layer sends an
initial series of RS messages. The OMNI interface then appends a
single OMNI option at the end of each RS message while sending an
interface-specific copy of the message over each underlay interface.
These OMNI RS messages will register an initial set of underlay
interfaces that are also UP and optionally also request an MNP
delegation. The Client sends additional RS messages to refresh
lifetimes and to register/deregister underlay interfaces as they
transition to UP or DOWN. Guidelines for sending additional RS
messages to generate corresponding RAs are found in Section 8.3.4 of
[RFC5214], and are further extended to include proactive responses to
mobility events.
The Client's OMNI interface sends initial RS messages over an UP
underlay interface with source set to its LLA (otherwise with source
set to the unspecified address ("::/128") per [RFC4861]). The OMNI
interface further sets the Destination Address to the LLA of a
specific (MAP) Proxy/Server (otherwise to the link-scoped All-Routers
multicast address ff02::2 [RFC4291]). The Client includes an OMNI
option per Section 10 with a Neighbor Synchronization sub-option with
the RS NUD, ARR and RPT flags set or cleared as necessary.
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Clients also include an OMNI Neighbor Synchronization sub-option with
FHS ifIndex set to the ifIndex of its own underlay interface and with
LHS ifIndex set to 0 (i.e., the default ifIndex configured by all
Proxy/Servers). The Client also sets Sequence Number to a randomly-
chosen 8-octet value, sets AFVI to a randomly-chosen initial value
and sets the Flow Label in the IPv6 header to 0. (If the Client
needs to coordinate with a MAP Proxy/Server other than this FHS
Proxy/Server, it also includes an SRH with the SNP SRA GUA for the
MAP.) The resulting exchange will establish symmetric Identification
windows for the Client and FHS Proxy/Server.
The Client next includes an Interface Attributes sub-option for the
underlay interface with LHS L3ADDR initially set to unspecified
("::/128") and a NULL Segment List plus a DHCPv6 Solicit sub-option
with IA_PD options. The Client then includes any other necessary
OMNI sub-options such as Traffic Selectors, RSA Signature / HMAC,
Timestamp, Nonce, etc. The OMNI interface finally sets or clears the
Interface Attributes FMT-Forward and FMT-Mode bits according to its
desired FHS Proxy/Server service model as described in
Section 10.2.11.
The Client next prepares to forward the RS over the underlay
interface using OAL encapsulation. The Client's OMNI interface first
changes the RS LLA Source Address to its own MLA and (if the RS
Destination Address is an LLA unicast address) changes the RS
Destination Address to the MLA of the FHS Proxy/Server. The OMNI
interface then includes a certificate and authentication signature if
necessary followed by the OMNI option trailing fields including the
AFVI, Checksum1/2 and Null Segment List. The OMNI interface next
optionally includes an SRH extension as specified above, sets the OAL
Source Address to its own MLA and sets the OAL Destination Address to
site-scoped All-Routers multicast (ff05::2) [RFC4291], the known FHS
Proxy/Server MLA or an anycast address. When L2 encapsulation is
used, the Client next includes the discovered FHS Proxy/Server L2ADDR
or an anycast address as the L2 destination then fragments if
necessary and forwards the resulting carrier packet(s) into the
underlay network. Note that the Client does not yet create a NCE,
but instead caches its RS message transmissions in the OAL to match
against any received RA messages.
When an FHS Proxy/Server receives a carrier packet containing an RS
it sets aside the L2 and OAL headers then verifies the checksums/
authentication signature while also consulting an MLA registration
service based on the Client's claimed certificate. If the RS message
authenticity/integrity is verified, the FHS Proxy/Server then
creates/updates a NCE indexed by the Client's MLA. The FHS Proxy/
Server then caches the OMNI Interface Attributes and any Traffic
Selector sub-options while also caching the AFVI plus L2 (UDP/IP) and
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OAL Source/Destination Address information. The FHS Proxy/Server
next examines the Interface Attributes L3ADDR then coordinates with
the local DHCPv6 server to either allocate a new SNP GUA (i.e., if
L3ADDR is "::/128") or extend the lease lifetime for an existing
Client SNP GUA.
The FHS Proxy/Server then generates an IPv6 address for the Client
from its GUA prefix and proposes it in an IA_NA option of the DHCPv6
message for the local DHCPv6 server that includes the Client's MLA in
a DUID option. A suitable method for address generation appears in
[I-D.gont-dhcwg-dhcpv6-iids].) If the proposed address is unique (or
already leased to this Client), the DHCPv6 Server will return
success; otherwise, the FHS Proxy/Server generates new IPv6 addresses
and repeats the DHCPv6 message exchange. The DHCPv6 address lease
lifetime must be the same as the Router Lifetime reported in RA
messages. The DHCPv6 lease lifetime must therefore be refreshed
through additional RS/RA exchanges before Router Lifetime expires.
After successful DHCPv6 Address registration, the FHS Proxy/Server
next caches the confirmed SNP ULA/GUAs in the (newly-created) NCE.
The FHS Proxy/Server next caches the RS Neighbor Synchronization NUD
flag and Neighbor Synchronization parameters if present (see:
Section 10.1). If no SRH is included but an OMNI DHCPv6 sub-option
with IA_PD options is present, the FHS Proxy/Server coordinates with
the local DHCPv6 server for prefix delegation then assumes the MAP
role as a default router entry point for injecting the Client's
MNP(s) into the OMNI link routing system. The FHS/MAP Proxy/Server
then caches the RS ARR and RPT flags to determine its role in
processing NS(AR) messages and generating unsolicited IPv6 ND control
messages (see: Section 10.1).
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The FHS/MAP 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/MAP Proxy/Server next
includes an OMNI option with a unique AFVI for this Client plus a
Neighbor Synchronization sub-option with responsive window
synchronization information. The FHS/MAP Proxy/Server also includes
an authentication sub-option if necessary and a DHCPv6 Reply sub-
option for the IA_PD option that was processed/populated by the
DHCPv6 exchange. The Proxy Server then includes a 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 L3ADDR/L2ADDR fields and also with the Segment List that was
received in the RS message trailer. The Proxy/Server sets L3ADDR to
the SNP GUA received in the DHCPv6 exchange and sets L2ADDR to the
address it observes in the RS message L2 source address. If the
Proxy/Server observes a different L2ADDR than the one supplied by the
Client, it sets the NAT indication in FMT-Type.
The FHS/MAP Proxy/Server next 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
establishes different values (see: Section 10.2.11 for further
discussion). If the FHS/MAP 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', with a unicast L2 address for its Client-facing interface in the
L2ADDR field and with its SRA ULA in the L3ADDR field.
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The FHS/MAP Proxy/Server next then includes any other necessary OMNI
sub-options such as Nonce, Timestamp, etc. The FHS/MAP Proxy/Server
also includes any other necessary RA options including 2 PIOs to
advertise the ULA/GUA SNP prefixes for the segment with (A=0; L=0)
per [RFC8028]. The FHS/MAP Proxy/Server then sets the RA Source
Address to its own LLA and sets the RA Destination Address to the RS
Source Address. The FHS/MAP Proxy/Server's OMNI interface then
changes the RA Source Address to its own MLA, calculates the
authentication signature/checksums and performs OAL encapsulation
while setting the OAL Source Address to its own MLA and Destination
Address to the OAL Source Address that appeared in the RS. If the RS
Segment List was non-null, the FHS/MAP Proxy/Server also includes an
SRH that contains the MLAs of endpoint OAL intermediate systems on
the reverse path from the Proxy/Server to the original Client (while
resetting the OAL Destination Address accordingly). The FHS/MAP
Proxy/Server then performs L2 encapsulation with L2 Source and
Destination address information reversed from the RS L2 information
and returns the resulting carrier packets to the Client over the same
underlay interface the RS arrived on.
When an FHS Proxy/Server receives an RS with Destination Address set
to link-scoped all-Routers multicast (ff02::2) or the MLA of a
different Proxy/Server, with valid checksum/authentication signature
and with an SRH supplied by the Client that contains an SNP SRA GUA,
it acts as a proxy for a different Proxy/Server to serve as the MAP.
The FHS Proxy/Server first locally processes the RS message the same
as described above except that it does not process any DHCPv6 IA_PD
options. The FHS Proxy/Server then sets the OAL Source Address to
the Client's SNP GUA and sets the OAL Destination according to the RS
message SRH provided by the Client. The FHS Proxy/Server next
creates or updates a NCE for the Client (i.e., based on the Client's
MLA) and caches the OAL Source Address, Neighbor Synchronization and
Interface Attributes information as above.
The FHS Proxy/Server then clears the Neighbor Synchronization
SYN/ACK/OPT flags and writes the Client's SNP GUA L3ADDR, RS L2ADDR
and RS Segment List into the corresponding Interface Attributes
fields. The FHS Proxy/Server next calculates and includes the
message checksums then performs L2 encapsulation and sends the
resulting carrier packets into the SRT secured spanning tree.
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When the MAP Proxy/Server receives the carrier packet, it performs L2
decapsulation and OAL decapsulation to obtain the proxyed RS,
verifies the checksums, then performs DHCPv6 IA_PD processing to
obtain or update any MNPs for the Client. The MAP Proxy/Server then
creates/updates a NCE indexed by the Client's MLA and caches any
state (including delegated MNPs, the ARR and RPT flags, IA_NA
addresses, OAL addresses, Interface Attributes information and
Traffic Selectors), then finally injects any delegated MNPs into the
OMNI link routing protocol.
The MAP Proxy/Server then returns an OMNI encapsulated RA that echoes
the Client's (proxyed) Interface Attributes sub-option and with any
RA parameters the same as specified for the FHS/MAP Proxy/Server case
above while also including a DHCPv6 Reply sub-option with the IA_PD
transaction results. The MAP Proxy/Server sets the RA Source Address
to its own MLA and sets the Destination Address to the RS Source
Address. The OMNI interface of the MAP Proxy/Server then sets the
OAL Source Address to its own SNP SRA GUA and Destination Address to
the cached value for the RS source. The MAP Proxy/Server then
calculates the message checksums and encapsulates the RA as an OAL
packet. The MAP Proxy/Server finally performs L2 encapsulation and
sends the resulting carrier packet into the secured spanning tree.
When the FHS Proxy/Server receives the carrier packet it performs L2
decapsulation followed by OAL decapsulation to obtain the RA message,
verifies checksums then updates the OMNI interface NCE for the Client
and creates/updates a NCE for the MAP. 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 MLA and changing the OAL Destination
Address to the Source Address from the Client's original RS message
while also recording the Client's SNP ULA/GUA address pair as
alternate indexes into the Client NCE. The FHS Proxy/Server then
includes 2 RA message PIOs with (A=0; L=0) with the SNP ULA/GUA
prefixes for the segment per [RFC8028].
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The FHS Proxy/Server next includes a Neighbor Synchronization sub-
option with its responses to its cached initiations from the Client.
The FHS Proxy/Server also includes an Interface Attributes sub-option
with ifIndex '0' and with its Client-facing interface unicast L2
address if necessary (see above) and includes an RSA Signature or
HMAC sub-option if necessary. The FHS Proxy/Server next includes a
unique AFVI for this Client then calculates the authentication
signature and message checksums. The FHS Proxy/Server then includes
an SRH extension to the OAL header if necessary with the MLAs of
endpoint intermediate systems on the reverse path to the Client and
with the OAL Destination Address adjusted accordingly. The FHS
Proxy/Server finally performs L2 encapsulation with L2 addresses
taken from the Client's NCE and sends the resulting carrier packet
via the same underlay interface over which the RS was received.
When the Client receives the carrier packet, it performs L2
decapsulation followed by OAL decapsulation to obtain the RA message.
The Client next verifies the authentication signature/checksums, then
matches the RA 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 the values match, the Client
then creates/updates OMNI interface NCEs for both the MAP and FHS
Proxy/Server and caches the information in the RA message. The
Client next discovers its own SNP GUA address by examining the
proxyed Interface Attributes sub-option and discovers the SNP ULA/GUA
PIO prefixes for the OMNI link segment per [RFC8028].
The Client then adds the ULA/GUA prefixes to the OMNI interface
Prefix List associated with this FHS Proxy/Server and regards the
corresponding ULA/GUA SRA addresses as the Proxy/Server addresses.
If the Client has multiple underlay interfaces, it creates additional
FHS Proxy/Server NCEs 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). If the
RA message includes a DHCPv6 Reply with the results of an IA_PD
transaction, the Client provisions the delegated prefixes on
downstream-facing links. The network layer of the Client finally
adds each FHS Proxy/Server LLA (i.e., as determined by the adaptation
layer mapping of the MLA) to the OMNI interface Default Router List.
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For each underlay interface, the Client next caches the (filled-out)
Interface Attributes for its own ifIndex including the L3ADDR/L2ADDR
and Segment List information that it received in an RA message over
that interface so that it can include them in future IPv6 ND messages
to provide neighbors with accurate FMT/SRT/LHS information. (If the
message includes an Interface Attributes sub-option with ifIndex '0',
the Client also caches the L2ADDR as the underlay network-local
unicast address of the FHS Proxy/Server via that underlay interface.)
The Client then consults the FMT-Type and L2ADDR to determine whether
there may be NATs on the path to the FHS Proxy/Server.
The Client then caches the Neighbor Synchronization responsive window
synchronization parameters for use in future IPv6 ND message
exchanges via this FHS Proxy/Server. The Client finally configures
default routes and assigns the IPv6 SRA address corresponding to the
MNP (e.g., 2001:db8:1:2::) to a downstream network interface. The
Client's OMNI interface then forwards the RA message to the IP layer
which can then update its view of the neighbor cache and default
router list.
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 MAP 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 IPv6 ND control messages over any UP underlay
interface with an OMNI option containing Interface Attributes sub-
options for the DOWN underlay interface with ifMetric set to
'ffffffff'. The Client sends isolated unsolicited IPv6 ND control
messages when reliability is not thought to be a concern (e.g., if
redundant transmissions are sent on multiple underlay interfaces),
or may instead send an IPv6 ND solicitation message to receive a
solicited reply.
* When the Router Lifetime for the MAP Proxy/Server nears
expiration, the Client sends an RS over any underlay interface to
receive a fresh RA from the MAP. 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 MAP Proxy/Server via a different underlay interface. If the
MAP Proxy/Server is unresponsive over additional underlay
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interfaces, the Client sends an RS message with Destination
Address set to the MLA of another Proxy/Server which will then
assume the MAP role.
* When all of a Client's underlay interfaces have transitioned to
DOWN (or if a prefix delegation lifetime expires), the MAP 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 can either declare this underlay interface
as DOWN or continue to use the interface to support any peer-to-peer
local communications with peers located in the same *NET. When
changing to a new FHS/MAP 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 unsolicited IPv6 ND control
messages to the old FHS and/or MAP Proxy/Server to announce the
Client's departure as discussed in [I-D.templin-6man-aero3].
The network layer engages the OMNI interface as an ordinary IPv6
interface. Therefore, when the network layer sends an RS message the
OMNI interface eventually returns corresponding RA messages from each
responding FHS Proxy/Server. Each RA message contains configuration
information consistent with the information received from the RAs
generated by the Proxy/Servers. Note that this same logic applies to
IPv4 implementations that employ "ICMP Router Discovery" per
[RFC1256]; the OAL must convert ICMPv4 RS/RA messages into IPv6 ND
RS/RA messages in a manner outside the scope of this specification
prior to OMNI encapsulation.
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., REACHABLE_TIME seconds). Proxy/
Servers are therefore responsible for updating MS state on a shorter
timescale than the Client may be required to do on its own behalf.
Note: On certain multicast-capable underlay interfaces, Clients
should send periodic unsolicited multicast NA messages and Proxy/
Servers should send periodic unsolicited multicast RA messages as
"beacons" that can be heard by other nodes on the link. If a node
fails to receive a beacon after a timeout value specific to the link,
it can initiate Neighbor Unreachability Detection (NUD) exchanges to
test reachability.
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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/L3ADDR/L2ADDR as last-hop segment (LHS) information to supply
to neighbors. This allows both the Client and MAP Proxy/Server to
supply the information to neighbors that will perceive it as LHS
information on the return path to the Client.
Note: The MAP Proxy/Server injects Client MNPs into the OMNI link
routing system by simply creating a route-to-interface forwarding
table entry for MNP::/N via the OMNI interface. The dynamic routing
protocol will notice the new entry and propagate the route to its
peers. If the MAP 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 MAP ceases to
receive RS messages from any of the Client's interfaces, it removes
the Client MNP(s) from the forwarding table (i.e., after a short
delay) which also results in their removal from the routing system.
Note: If the Client's initial RS message includes an anycast L2
Destination Address, the FHS Proxy/Server returns the solicited RA
using the same anycast address as the L2 source while including an
Interface Attributes sub-option with ifIndex '0' and its true unicast
address in the L2ADDR. When the Client sends additional RS messages,
it includes this FHS Proxy/Server unicast address as the L2
Destination Address and the FHS Proxy/Server returns the solicited RA
using the same unicast address as the L2 Source Address. 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.
Note: Clients should set the NUD, ARR and RPT flags consistently in
successive RS messages and only change those settings when an FHS/MAP
Proxy/Server service profile update is necessary.
13.1. Client-Proxy/Server Window Synchronization
The RS/RA exchanges discussed above observe the principles specified
in Section 6.7. Window synchronization is conducted between the
Client and each FHS Proxy/Server used to contact the MAP Proxy/
Server, i.e., and not between the Client and the MAP. This is due to
the fact that the MAP Proxy/Server is responsible only for forwarding
messages via the secured spanning tree to FHS Proxy/Servers, and is
not responsible for forwarding messages directly to the Client over
unsecured networks.
When a Client sends an RS to perform window synchronization via a new
FHS Proxy/Server, it includes an OMNI Neighbor Synchronization sub-
option with window synchronization parameters with FHS ifIndex set to
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its own interface index, with LHS ifIndex set to 0, with the SYN flag
set and ACK flag clear, and with an initial Sequence Number. The
Client also includes an Interface Attributes sub-option then performs
OAL encapsulation and L2 encapsulation and sends the resulting
carrier packet to the FHS Proxy/Server. When the FHS Proxy/Server
receives the carrier packet, it performs L2 decapsulation, then
extracts the RS message and caches the Neighbor Synchronization
parameters. In the process, the FHS Proxy/Server removes the
Neighbor Synchronization sub-option itself, since the path to the MAP
Proxy/Server is not included in window synchronization.
The FHS Proxy/Server then performs L2 encapsulation and sends the
resulting carrier packet via the secured spanning tree to the MAP
Proxy/Server, which updates the Client's Interface Attributes and
returns a unicast RA message. The MAP Proxy/Server performs OAL
encapsulation followed by L2 encapsulation and sends the resulting
carrier packet 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 a Neighbor Synchronization sub-option
with responsive window synchronization information. The FHS Proxy/
Server then forwards the message to the Client via OAL encapsulation
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 RS/RA exchanges between its own MLA and the MLAs of the
FHS Proxy/Servers at any time without having to disturb the MAP.
When the Client also needs to refresh MAP state, it can set the RS
Destination Address to the MAP MLA and include an SRH if necessary to
support FHS Proxy/Server RS forwarding.
This window synchronization is necessary only for MANET and INET
Clients that must include authentication signatures with their IPv6
ND messages; Clients in secured ANETs can omit window
synchronization. When Client-to-Proxy/Server window synchronization
is used, subsequent IPv6 ND messages exchanged between peers include
IPv6 Extended Fragment Headers in the OAL encapsulations with in-
window Identification values to support message authentication. No
header compression state is maintained by OAL intermediate systems,
which only maintain state for per-flow data plane windows.
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13.2. Router Discovery in IP Multihop and IPv4-Only Networks
On some *NETs, a Client may be located multiple intermediate OAL hops
away from the nearest OMNI link Proxy/Server. Clients in multihop
networks perform route discovery through the application of an
adaptation layer routing protocol (e.g., a MANET routing protocol
over omnidirectional wireless interfaces, etc.). Example routing
protocols optimized for MANET operations include OSPFv3 [RFC5340]
with MANET Designated Router (OSPF-MDR) extensions [RFC5614], OLSRv2
[RFC7181], AODVv2 [I-D.perkins-manet-aodvv2] and others. Clients
employ the routing protocol according to the link model found in
[RFC5889] and subnet model articulated in [RFC5942]. For unique
identification within the MANET, Clients use an MLA as a Router ID.
MANETs can be compartmentalized internally with some nodes configured
as simple Clients and others (typically having both "upstream" and
"downstream" underlay interfaces) configured as cluster heads that
act as Proxy/Clients. The Proxy/Clients configure and listen to the
same multicast and anycast addresses as for Proxy/Servers on their
downstream interfaces in order to act as endpoint OAL intermediate
node proxys for other downstream Clients. Clusters within clusters
based on these cluster head Proxy/Clients can then be recursively
nested to arbitrary depths as long as at least one ultimate Proxy/
Client configures an upstream interface that can directly address a
Proxy/Server with connectivity to the outside Internetwork.
A Client located potentially multiple OAL hops away from the nearest
Proxy/Server prepares an RS message, sets the Source Address to its
MLA, and sets the Destination Address to link-scoped All-Routers
multicast (ff02::2) or the MLA of a Proxy/Client or Proxy/Server as
discussed above. The OMNI interface then employs OAL encapsulation,
sets the OAL Source Address to its MLA and sets the OAL Destination
Address to the MLA of the Proxy, the site-scoped All-Routers
multicast address (ff05::2) or the OMNI IPv6 anycast address.
For IPv6-enabled *NETs where the underlay interface observes the
MANET properties discussed above, the Client injects the MLA into the
IPv6 multihop routing system and forwards the RS message without
further encapsulation. Otherwise, the Client encapsulates the
message in UDP/IPv6 L2 headers, sets the L2 Source Address to the
underlay interface IPv6 address and sets the L2 Destination Address
to the discovered unicast or anycast address of a Proxy. The Client
then forwards the message into the IPv6 multihop routing system which
conveys it to the nearest Proxy.
For IPv4-only *NETs, the Client encapsulates the RS message in UDP/
IPv4 L2 headers, sets the L2 Source Address to the underlay interface
IPv4 address and sets the L2 Destination Address to the discovered
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unicast address of a Proxy/Server or 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 advertising the
corresponding IPv4 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 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 OAL intermediate node that participates in the routing
protocol receives the encapsulated RS, it forwards the message
according to its OAL IPv6 forwarding table (note that an OAL
intermediate system could be a fixed infrastructure element such as a
roadside unit or another MANET/VANET Client). This process repeats
iteratively until the RS message is received by a penultimate OAL hop
within single-hop communications range of a Proxy/Server, which
forwards the message to the Proxy/Server final hop.
When a Proxy/Server that configures the OMNI IPv6 anycast address
receives the message, it decapsulates the RS and assumes either the
MAP or FHS role (in which case, it may forward the RS to a candidate
MAP). The MAP/FHS Proxy/Server then prepares an RA message using the
same addressing disciplines as discussed in Section 13 and forwards
the RA either to the FHS Proxy/Server or directly to the Client.
When the MAP or FHS Proxy/Server forwards the RA to the Client, it
encapsulates the message in L2 encapsulation headers if necessary.
The Proxy/Server then forwards the message to an OAL node within
communications range, which forwards the message according to the
next OAL hop by consulting its OAL IPv6 forwarding tables. The
multihop forwarding process within the *NET continues repetitively
until the message arrives at 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 can optionally inject the delegated ULA/GUA and any
MNP SRA GUAs into the IPv6 multihop routing system but this may cause
excessive routing protocol overhead in some networks.
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MANETs often include Clients that configure multiple interfaces, with
downstream interfaces internal to the MANET and upstream interfaces
connected to external *NETs. Such Clients can provide proxy services
to enable router discovery for peer Clients that connect only
internally within the MANET. These Proxy/Clients first perform
router discovery to associate with true Proxy/Servers located on
upstream *NETs. The Proxy/Clients also subscribe to the site-scoped
all-routers multicast group (i.e., ff05::2) and advertise
reachability for the OMNI IPv6 anycast address over their MANET
interfaces.
When a source Client sends an initial RS message seeking service,
MANET routing will direct the RS to one or more nearby Proxy/Clients
which in turn forward the RS to one or more upstream interface
Proxys. Each such Proxy/Client writes its MLA as the final Segment
List IPv6 address at the end of the RS OMNI option trailer. The
natural progression continues from innermost Proxy/Clients to
outermost Proxy/Clients until the RS message reaches a Proxy/Server.
By that time, the Segment List at the end of the RS OMNI option
trailer will contain an ordered list of MLAs of all Proxy/Clients in
the reverse path.
The Proxy/Server processes the RS and returns an RA while including
its own MLA in the OAL Source Address and the MLA of the outermost
Proxy/Client in the OAL Destination Address. The Proxy/Server also
includes an SRH with the ordered list of Proxy/Client MLAs received
from the RS message plus the MLA of the original source Client as the
ultimate Segment List entry. When the outermost Proxy/Client
receives the RA, it forwards the message to the MLA of the next hop
Proxy/Client in succession based on the SRH information until the
message arrives at the source Client. The source Client can then
update its SNP GUA/ULA addresses, prefix list and default router list
based on the information returned by the Proxy/Server. The Client
also retains the Interface Attributes Segment List for future peer
address resolution and multihop forwarding purposes.
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The MANET Proxy/Client model recursively extends to include
arbitrarily many layers of nested MANETs between the source Client
and external Proxy/Servers. When the source Client's first-hop
Proxy/Client forwards an RS, it updates an adaptation layer neighbor
cache entry for this Client's RS Source Address to include the OAL
address of both the previous hop downstream (Proxy/)Client and next
hop upstream (Proxy/)Client. The Proxy/Client then changes the OAL
Source Address to its own MLA and forwards the RS to the next
upstream Proxy/Client in succession which also updates state and
changes the OAL Source Address to its own MLA. The progression
continues until the RS reaches an ultimate upstream Proxy/Client that
can directly contact a Proxy/Server via L2 encapsulation over an
upstream *NET interface.
When the Proxy/Server returns an RA, each upstream Proxy/Client
forwards the RA through the recursively descending chain of
downstream Proxy/Clients on the path to the source Client. Each
Proxy/Client rewrites the OAL Destination Address according to the
SRH next hop MLA address for the next downstream Proxy/Client hop
toward the source Client and rewrites the OAL Source Address to its
own MLA while caching the OAL Source Address from the previous
upstream hop. When the RA arrives at the source Client, all upstream
Proxy/Clients in the path will have established the state necessary
for future packet forwarding.
Note that this service model applies equally for MANETs that have
only Proxy/Client access to external *NET Proxy/Servers as well as
those that have some mix of Proxy/Clients and true Proxy/Servers at
the MANET border. True Proxy/Servers at the MANET border will
service MANET Client router discovery requests the same as for any
*NET, while external Proxy/Servers will discover potentially many
MANET Clients all using the same L2ADDR belonging to a single Proxy/
Client. This arrangement ensures that MANET-internal Clients are
able to access external Internetworking services the same as for
MANET border Clients that also have direct connections to external
*NETs.
Note: When the RS message includes an anycast L2 encapsulation
Destination Address, the FHS Proxy/Server must use the same anycast
addresses as the L2 encapsulation Source Address 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 outermost (Proxy/)Client receives the RA, it
will discover the FHS Proxy/Server unicast L2 encapsulation address
and can send future carrier packets using the unicast (instead of
anycast) addresses to populate NAT state in the forward path. (If
the Client does not have immediate data to send to the FHS Proxy/
Server, it can instead send an OAL "bubble" - see Section 6.11.)
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After the Client begins using unicast L2 encapsulation addresses in
this way, the FHS Proxy/Server should also begin using the same
unicast address in the reverse direction.
Note: When an OMNI interface configures an MLA, any nodes that
forward an encapsulated RS message with the MLA as the OAL source
must not consider the message as being specific to a particular OMNI
link segment. MLAs can therefore also serve as the Source and
Destination Addresses of unencapsulated IPv6 data communications
within the local routing region; if the MLAs are injected into the
local network routing protocol their prefix length must be set to 128
per [RFC5889].
13.3. DHCPv6-based Prefix Registration
When a Client requires SNP ULA/GUA delegations via a specific Proxy/
Server (or, when the Client requires MNP delegations for the OMNI
link), it invokes the DHCPv6 service [I-D.ietf-dhc-rfc8415bis] in
conjunction with its OMNI RS/RA message exchanges.
When a Client requires the MS to delegate PA ULA/GUA pairs or PI
MNPs, it sends an RS message to an FHS Proxy/Server that includes an
Interface Attributes OMNI sub-option with L3ADDR set to either
unspecified ("::/128") or to a previously-delegated SNP GUA. If the
Client also requires one or more MNP delegations, it includes an OMNI
DHCPv6 Message sub-option for MNP delegations. Each DHCPv6 sub-
option contains a Client Identifier, an IA_PD option 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 Address to link-scoped All-Routers multicast (ff02::2)
and sends the message using OAL encapsulation as discussed above.
When the FHS/MAP Proxy/Server receives the RS message, it examines
the OMNI option contents. Next, if the OMNI option includes an
Interface Attributes sub-option the FHS/MAP Proxy/Server acts as a
"Proxy DHCPv6 Client" in a self-generated DHCPv6 IA_NA message
exchange with the locally-resident DHCPv6 server while supplying the
MLA of the Client as a DUID. When the Interface Attributes L3ADDR is
unspecified (::/128), the FHS/MAP should first generate an SNP GUA
that is likely to be unique using a suitable method such as that
proposed in [I-D.gont-dhcwg-dhcpv6-iids]. The FHS/MAP Proxy/Server
then includes the SNP GUA in an IA_NA option and sends the DHCPv6
message to the DHCPv6 Server, which verifies the SNP GUA and returns
a DHCPv6 Reply message with autoconfiguration parameters. Next, if
the Proxy/Server will act as a MAP it processes any DHCPv6 sub-
options with an IA_PD message and performs a 2-message DHCPv6 PD
exchange with the local DHCPv6 server exactly as specified in
[I-D.ietf-dhc-rfc8415bis].
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When the FHS Proxy/Server receives a DHCPv6 Reply with delegated
addresses, it records the delegated SNP GUA plus a ULA from the
companion ULA prefix that uses the same interface identifier in the
NCE for the Client, then forwards the RS message to the MAP Proxy/
Server for prefix delegation if necessary; otherwise, it returns an
immediate RA message to the Client.
When the MAP Proxy/Server receives a DHCPv6 Reply with delegated
prefixes, it creates OMNI interface MNP forwarding table entries
(i.e., to prompt the dynamic routing protocol). The MAP Proxy/Server
then sends an RA back to the FHS Proxy/Server with the Client's
filled-out Interface Attributes sub-option and the DHCPv6 Reply
message for the IA_PD delegation included in an OMNI DHCPv6 message
sub-option. The FHS Proxy/Server then returns the RA to the Client.
14. Secure Redirection
If the *NET 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 through the use of the
DHCPv6 address delegation service. When the Client sends an RS
message on a multiple access *NET, the Proxy/Server verifies that the
Client is authorized to use the address and responds with an RA (or
forwards the RS to the MAP) only if the Client is authorized.
After verifying Client authorization and returning an RA, the Proxy/
Server MAY return IPv6 ND Redirect messages in response to subsequent
data plane packet transmissions to direct Clients located on the same
*NET 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
*NETs, 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.
15. 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.
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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.
16. Detecting and Responding to Proxy/Server Failures
In environments where fast recovery from Proxy/Server failure is
essential, FHS Proxy/Servers SHOULD use proactive Neighbor
Unreachability Detection (NUD) in a manner that parallels
Bidirectional Forwarding Detection (BFD) [RFC5880] to track MAP
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 MAP Proxy/Servers for
which there are currently active Clients. If a MAP 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 Address set to the GUA of the MAP,
with Destination Address set to link-scoped 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) MAP Proxy/Server will receive the RA
messages.
17. Transition Considerations
When a Client connects to a *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/MAP 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 an ordinary 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.
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If the *NET link model is multiple access, there must be assurance
that address duplication cannot corrupt the neighbor caches of other
nodes on the link. When the Client sends an RS message on a multiple
access *NET link with an OMNI option, first hop routers that
recognize the option ensure that the Client is authorized to use the
address and return an RA with a non-zero Router Lifetime only if the
Client is authorized. First hop routers that do not recognize the
OMNI option instead return an RA that makes no statement about the
Client's authorization to use the Source Address. In that case, the
Client should perform Duplicate Address Detection to ensure that it
does not interfere with other nodes on the link.
An alternative approach for multiple access *NET links to ensure
isolation for Client-Proxy/Server communications is through link
layer address mappings as discussed in Appendix D. This arrangement
imparts a (virtual) point-to-point link model over the (physical)
multiple access link.
18. OMNI Interfaces on Open Internetworks
Client OMNI interfaces configured over IPv6-enabled underlay
interfaces on an open Internetwork without an OMNI-aware first-hop
router receive IPv6 RA messages with no OMNI options, while OMNI
interfaces configured over IPv4-only underlay interfaces receive no
IPv6 RA messages at all (but may receive IPv4 RA messages per
[RFC1256]). Client OMNI interfaces that receive RA messages with
OMNI options configure addresses, on-link prefixes, etc. on the
underlay interface that received the RA according to standard IPv6 ND
and address resolution conventions [RFC4861] [RFC4862]. Client OMNI
interfaces configured over IPv4-only underlay interfaces configure
IPv4 address information on the underlay interfaces using mechanisms
such as DHCPv4 [RFC2131].
Client OMNI interfaces configured over underlay interfaces connected
to open Internetworks can apply lower layer security services such as
VPNs (e.g., IPsec tunnels) to connect to a Proxy/Server, or can
establish a secured direct point-to-point link to the Proxy/Server
through some other means (see Section 4). In environments where
lower layer security may be impractical or undesirable, Client OMNI
interfaces can instead send IPv6 ND messages with OMNI sub-options
that include authentication parameters.
OMNI interfaces use UDP/IP as L2 encapsulation headers for
transmission over open Internetworks with UDP service port number
8060 for both IPv4 and IPv6 underlay interfaces. The OMNI interface
submits original IP packets for OAL encapsulation, then encapsulates
the resulting OAL fragments in UDP/IP L2 headers to form carrier
packets. (The first 4 bits following the UDP header determine
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whether the OAL headers are uncompressed/compressed as discussed in
Section 6.5.) The OMNI interface sets the UDP length to the
encapsulated OAL fragment length and sets the IP length to an
appropriate value at least as large as the UDP datagram.
When necessary, sources include an OMNI option with an RSA Signature
or HMAC sub-option in IPv6 ND messages. Procedures for including
OMNI authentication sub-options are discussed in Section 10.
After establishing a secured underlay link or preparing for UDP/IP
encapsulation, OMNI interfaces send RS/RA messages for Client-Proxy/
Server coordination (see: Section 13) and peer-to-peer IPv6 ND
solicitation and response messages for multilink forwarding, route
optimization, and mobility management (see:
[I-D.templin-6man-aero3]). 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.
Transport and higher layer protocol sessions over OMNI interfaces
that connect over open Internetworks without an explicit underlay
link security services should therefore employ security at their
layers to ensure authentication, integrity and/or confidentiality.
Clients should avoid using INET Proxy/Servers as general-purpose
routers for steady streams of carrier packets that do not require
authentication. Clients should therefore perform route optimization
to coordinate with other INET nodes that can provide forwarding
services (or preferably coordinate with peer Clients directly)
instead of burdening the Proxy/Server. Procedures for coordinating
with peer Clients and discovering INET nodes that can provide better
forwarding services are discussed in [I-D.templin-6man-aero3].
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-aero3]. FHS Proxy/Servers include L2ADDR
information in an Interface Attributes sub-option in RA messages to
allow Clients to detect the presence of NATs.
Note: Following the initial IPv6 ND message exchange, OMNI interfaces
configured over INET underlay interfaces maintain neighbor
relationships by transmitting periodic IPv6 ND messages with OMNI
options that include authentication signatures.
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Note: OMNI interfaces configured over INET underlay interfaces should
employ the Identification window synchronization mechanisms specified
in Section 6.7 in order to exclude spurious carrier packets that
might otherwise clutter the reassembly cache. This is especially
important in environments where carrier packet spoofing and/or
corruption is a threat.
Note: NATs may be present on the path from a Client to its FHS Proxy/
Server, but never on the path from the FHS Proxy/Server to the MAP
where only INET and/or spanning tree hops occur. Therefore, the FHS
Proxy/Server does not communicate Client origin information to the
MAP where it would serve no purpose.
19. 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 occasionally to defeat adversarial tracking.
The prefix delegation services discussed in Section 13.3 allows
Clients that desire time-varying MNPs to obtain short-lived prefixes
to send RS messages with an OMNI option with DHCPv6 IA_PD sub-
options. The Client would then be obligated to renumber its internal
networks whenever its MNPs change. 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.
20. Error Messages
An OAL destination or intermediate system may need to return
ICMPv6-like error messages (e.g., Destination Unreachable, Packet Too
Big, Time Exceeded, etc.) [RFC4443] to an OAL source. Since ICMPv6
error messages do not themselves include authentication codes, OAL
nodes can instead return error messages as an OMNI ICMPv6 Error sub-
option in a secured unsolicited IPv6 ND control message.
21. IANA Considerations
The following IANA actions are requested in accordance with
[RFC8126]. Both existing registries and new registries specific to
OMNI are affected. Existing registries should be updated according
to standard IANA practices. New registries should be created under a
new registry group for "Overlay Multilink Network Interface (OMNI)".
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21.1. Protocol Numbers
The IANA is instructed to allocate an Internet Protocol number TBD1
from the https://www.iana.org/assignments/protocol-numbers registry
for the Overlay Multilink Network Interface (OMNI) as a non IPv6
Extension Header protocol. Guidance is found in [RFC5237]
(registration procedure is IESG Approval or Standards Action).
21.2. IEEE 802 Numbers
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 Ethertypes registry of the
https://www.iana.org/assignments/ieee-802-numbers registry group for
"Overlay Multilink Network Interface (OMNI) encapsulation on Ethernet
networks". Guidance is found in [RFC7042] (registration procedure is
Expert Review).
21.3. ICMP Parameters
The IANA is instructed to assign a new Type number TBD3 in the "ICMP
Type Numbers" registry in the https://www.iana.org/assignments/icmp-
parameters registry group (registration procedures IESG Approval or
Standards Action). The entry should set "Type" to TBD3, "Name" to
"Packet Too Big (PTB)" and "Reference" to [RFCXXXX] (i.e., this
document).
The IANA is further instructed to create a new table titled: "Type
TBD3 - Packet Too Big (PTB)" in the "Code Fields" registry, with
registration procedures IESG Approval or Standards Action. The table
should have the following initial format:
Code Name Reference
--- ---- ---------
0 Reserved [RFCXXXX]
1 (suggested) PTB Soft Error (no loss) [RFCXXXX]
2 (suggested) PTB Soft Error (loss) [RFCXXXX]
Figure 39: Type TBD3 - Packet Too Big (PTB)
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21.4. ICMPv6 Parameters
The IANA is instructed to assign new Code values in the "ICMPv6 Code
Fields: Type 2 - Packet Too Big" registry in the
https://www.iana.org/assignments/icmpv6-parameters registry group
(registration procedure is Standards Action or IESG Approval). The
registry entries should appear as follows:
Code Name Reference
--- ---- ---------
0 PTB Hard Error [RFC4443]
1 (suggested) PTB Soft Error (no loss) [RFCXXXX]
2 (suggested) PTB Soft Error (loss) [RFCXXXX]
3 (suggested) MTU Probe Reply [RFCXXXX]
Figure 40: ICMPv6 Code Fields: Type 2 - Packet Too Big Values
21.5. IPv4 Special-Purpose Address
The IANA is instructed to assign TBD4/N as an "OMNI IPv4 anycast"
address/prefix in the https://www.iana.org/assignments/iana-ipv4-
special-registry registry in a similar fashion as for [RFC3068]. The
assignment also automatically provides the basis for an OMNI IPv6
subnet router anycast address configured as 2002:TBD4::. The IANA is
requested to assist the author's efforts to obtain a TBD4/N public
IPv4 prefix, whether through an RIR allocation, a delegation from the
"Current Recovered IPv4 Pool" of the
https://www.iana.org/assignments/ipv4-recovered-address-space
registry or through an unspecified third party donation.
21.6. IANA OUI Ethernet Numbers
The IANA is instructed to allocate one Ethernet unicast address TBD5
(suggested value '00-52-14') in the "IANA Unicast 48-bit MAC
Addresses" registry in the https://www.iana.org/assignments/ethernet-
numbers registry group (registration procedure is Expert Review).
The registration should appear as follows:
Addresses Usage Reference
--------- ----- ---------
00-52-14 Overlay Multilink Network (OMNI) Interface [RFCXXXX]
Figure 41: IANA Unicast 48-bit MAC Addresses
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21.7. Overlay Multilink Network Interface (OMNI) Registry Group
The IANA is instructed to create a new 'omni-interface' registry
group for "Overlay Multilink Network Interface (OMNI)". The registry
group must include the following new registries:
21.7.1. OMNI Option Sub-Types (New Registry)
The OMNI option defines a 5-bit Sub-Type field, for which IANA is
instructed to create and maintain a new registry entitled "OMNI
Option Sub-Type Values". Initial values are given below
(registration procedure is RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 Pad1 [RFCXXXX]
1 PadN [RFCXXXX]
2 Node Identification [RFCXXXX]
3 CGA [RFCXXXX]
4 RSA Signature [RFCXXXX]
5 Timestamp [RFCXXXX]
6 Nonce [RFCXXXX]
7 Trust Anchor [RFCXXXX]
8 Certificate [RFCXXXX]
9 HMAC [RFCXXXX]
10 Neighbor Synchronization [RFCXXXX]
11 Interface Attributes [RFCXXXX]
12 Traffic Selector [RFCXXXX]
13 Geo Coordinates [RFCXXXX]
14 DHCPv6 Message [RFCXXXX]
15 PIM-SM Message [RFCXXXX]
16 Fragmentation Report [RFCXXXX]
17 ICMPv6 Error [RFCXXXX]
18 Proxy/Server Departure [RFCXXXX]
19-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 42: OMNI Option Sub-Type Values
21.7.2. OMNI Node Identification ID-Types (New Registry)
The OMNI Node Identification sub-option (see: Section 10.2.3)
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):
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Value Sub-Type name Reference
----- ------------- ----------
0 MLA [RFCXXXX]
1 UUID [RFCXXXX]
2 Network Access Identifier [RFCXXXX]
3 FQDN [RFCXXXX]
4 IPv4 Address [RFCXXXX]
5 Unassigned [RFCXXXX]
6 IPv6 Address [RFCXXXX]
7-65532 Unassigned [RFCXXXX]
65533 Reserved for Experimental Use [RFCXXXX]
65534 Reserved for Experimental Use [RFCXXXX]
65535 Reserved by IANA [RFCXXXX]
Figure 43: OMNI Node Identification ID-Type Values
21.7.3. OMNI Geo Coordinates Types (New Registry)
The OMNI Geo Coordinates sub-option (see: Section 10.2.14) 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 Experimental Use [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 44: OMNI Geo Coordinates Type
21.8. Additional Considerations
IANA has assigned UDP port number "8060" for an earlier experimental
version of AERO [RFC6706]. This document reclaims UDP port number
"8060" for 'aero' as the service port for OMNI interface 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'.) 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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IANA has assigned a 4-octet Private Enterprise Number (PEN) code
"45282" in the https://www.iana.org/assignments/enterprise-numbers
registry. This document is the normative reference for using code
"45282" in DHCP Unique IDentifiers based on Enterprise Numbers
("DUID-EN for OMNI Interfaces") (see: Section 9). IANA is therefore
instructed to change the enterprise designation for PEN code "45282"
from "LinkUp Networks" to "Overlay Multilink Network Interface
(OMNI)".
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
https://www.iana.org/assignments/smi-numbers registry group Interface
Types (ifType)" registry, and the IANA is instructed to change the
reference to [RFCXXXX] (i.e., this document).
No further IANA actions are required.
22. Security Considerations
Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6
Neighbor Discovery [RFC4861] apply. For end-to-end peer exchanges
not fully protected by security associations, OMNI interfaces SHOULD
use SEcure Neighbor Discovery (SEND) per [RFC3971] or a Hashed
Message Authentication Code (HMAC) per [RFC8754] as an adaptation
layer service to ensure authentic exchanges. These services provide
authentication for unsecured FHS and LHS *NETs, while intermediate
hops are protected by the secured spanning tree (see below).
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 *NET interfaces can use symmetric securing services such as
IPsec tunnels [RFC4301] or can by some other means establish a direct
point-to-point link secured at lower layers.
OMNI link mobility services MUST support strong authentication for
control plane messages and forwarding path integrity for data plane
messages. In particular, the AERO service [I-D.templin-6man-aero3]
constructs a secured spanning tree with Proxy/Servers as leaf nodes
and secures the spanning tree links with network layer security
services based on IPsec [RFC4301] with IKEv2 [RFC7296]. (Note that
direct point-to-point links secured at lower layers can also be used
instead of or in addition to network layer security.) Together,
these services provide connectionless integrity and data origin
authentication with optional protection against replays.
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Control plane messages that affect the routing system or neighbor
state either include authentication signatures or are constrained to
travel only over secured spanning tree paths; in both cases, the
messages are protected by network (and/or lower-layer) security.
Other control and data plane messages can travel over unsecured route
optimized paths that do not strictly follow the spanning tree,
therefore end-to-end sessions should employ transport or higher layer
security services (e.g., TLS/SSL [RFC8446], DTLS [RFC6347], etc.).
Additionally, the OAL Identification value can provide a first level
of data origin authentication to mitigate off-path spoofing.
Identity-based key verification infrastructure services such as iPSK
may be necessary for verifying the identities claimed by Clients.
This requirement should be harmonized with the manner in which
identifiers such as MLAs are certified 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.
23. Implementation Status
AERO/OMNI Release-3.2 was tagged on March 30, 2021, and was subject
to internal testing. The implementation is not planned for public
release.
A write-from-scratch reference implementation is under active
internal development, with release version v0.1 tagged on December 9,
2024 and version v0.2 tagged on January 22, 2025. Future versions
will be made available for public release.
24. Document Updates
This document suggests that the following could be updated through
future IETF initiatives:
* [RFC1191]
* [RFC4443]
* [RFC8200]
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* [RFC8201]
Updates can be through, e.g., standards action, the errata process,
etc. as appropriate.
25. 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:
Felipe Magno de Almeida, Amanda Baber, Scott Burleigh, Stuart Card,
Donald Eastlake, Adrian Farrel, Michael Matyas, Robert Moskowitz,
Madhu Niraula, Greg Saccone, Stephane Tamalet, Eliot Lear, Eduard
Vasilenko, Eric Vyncke. Pavel Drasil, Zdenek Jaron and Michal
Skorepa are especially recognized for their many helpful ideas and
suggestions. Akash Agarwal, Madhuri Madhava Badgandi, Sean Dickson,
Don Dillenburg, Joe Dudkowski, Vijayasarathy Rajagopalan, Ron
Sackman, Bhargava Raman Sai Prakash and Katherine Tran are
acknowledged for their hard work on the implementation and technical
insights that led to improvements for the spec.
Discussions on the IETF 6man and atn mailing lists during the fall of
2020 suggested additional points to consider. The authors gratefully
acknowledge the list members who contributed valuable insights
through those discussions. Eric Vyncke and Erik Kline were the
intarea ADs, while Bob Hinden and Ole Troan were the 6man WG chairs
at the time the document was developed; they are all gratefully
acknowledged for their many helpful insights. Many of the ideas in
this document have further built on IETF experiences beginning in the
1990s, with insights from colleagues including Ron Bonica, Brian
Carpenter, Ralph Droms, Tom Herbert, Bob Hinden, Christian Huitema,
Thomas Narten, Dave Thaler, Joe Touch, Pascal Thubert, and many
others who deserve recognition.
Early observations on IP fragmentation performance implications were
noted in the 1986 Digital Equipment Corporation (DEC) "qe reset"
investigation, where fragment bursts from NFS UDP traffic triggered
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hardware resets resulting in communication failures. Jeff Chase,
Fred Glover and Chet Juzsczak of the Ultrix Engineering Group led the
investigation, and determined that setting a smaller NFS mount block
size reduced the amount of fragmentation and suppressed the resets.
Early observations on L2 media MTU issues were noted in the 1988 DEC
FDDI investigation, where Raj Jain, KK Ramakrishnan and Kathy Wilde
represented architectural considerations for FDDI networking in
general including FDDI/Ethernet bridging. Jeff Mogul (who led the
IETF Path MTU Discovery working group) and other DEC colleagues who
supported these early investigations are also acknowledged.
Throughout the 1990's and into the 2000's, many colleagues supported
and encouraged continuation of the work. Beginning with the DEC
Project Sequoia effort at the University of California, Berkeley,
then moving to the DEC research lab offices in Palo Alto CA, then to
Sterling Software at the NASA Ames Research Center, then to SRI in
Menlo Park, CA, then to Nokia in Mountain View, CA and finally to the
Boeing Company in 2005 the work saw continuous advancement through
the encouragement of many. Those who offered their support and
encouragement are gratefully acknowledged.
This work is aligned with the NASA Safe Autonomous Systems Operation
(SASO) program under NASA contract number NNA16BD84C.
This work is aligned with the FAA as per the SE2025 contract number
DTFAWA-15-D-00030.
This work is aligned with the Boeing Information Technology (BIT)
Mobility Vision Lab (MVL) program.
This work is aligned with the Boeing/Virginia Tech Network Security
Institute (VTNSI) 5G MANET research program.
Honoring life, liberty and the pursuit of happiness.
26. References
26.1. Normative References
[I-D.ietf-dhc-rfc8415bis]
Mrugalski, T., Volz, B., Richardson, M., Jiang, S., and T.
Winters, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", Work in Progress, Internet-Draft, draft-ietf-
dhc-rfc8415bis-09, 15 March 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-dhc-
rfc8415bis-09>.
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[I-D.templin-6man-ipid-ext2]
Templin, F. and T. Herbert, "IPv6 Extended Fragment Header
(EFH)", Work in Progress, Internet-Draft, draft-templin-
6man-ipid-ext2-05, 31 December 2024,
<https://datatracker.ietf.org/doc/html/draft-templin-6man-
ipid-ext2-05>.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
December 1998, <https://www.rfc-editor.org/info/rfc2473>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<https://www.rfc-editor.org/info/rfc3972>.
[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
DOI 10.17487/RFC4007, March 2005,
<https://www.rfc-editor.org/info/rfc4007>.
[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>.
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[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>.
[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>.
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>.
[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>.
[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>.
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[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>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC9293] Eddy, W., Ed., "Transmission Control Protocol (TCP)",
STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022,
<https://www.rfc-editor.org/info/rfc9293>.
26.2. Informative References
[ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground
Interface for Civil Aviation, IETF Liaison Statement
#1676, https://datatracker.ietf.org/liaison/1676/", 3
March 2020.
[ATN-IPS] "ICAO Document 9896 (Manual on the Aeronautical
Telecommunication Network (ATN) using Internet Protocol
Suite (IPS) Standards and Protocol), Draft Edition 3
(work-in-progress)", 10 December 2020.
[CRC] Jain, R., "Error Characteristics of Fiber Distributed Data
Interface (FDDI), IEEE Transactions on Communications",
August 1990.
[EUI] "IEEE Guidelines for Use of Extended Unique Identifier
(EUI), Organizationally Unique Identifier (OUI), and
Company ID, https://standards.ieee.org/wp-
content/uploads/import/documents/tutorials/eui.pdf", 3
August 2017.
[I-D.gont-dhcwg-dhcpv6-iids]
Gont, F., "A Method for Generating Semantically Opaque
IPv6 Interface Identifiers (IIDs) with Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)", Work in
Progress, Internet-Draft, draft-gont-dhcwg-dhcpv6-iids-00,
10 February 2025, <https://datatracker.ietf.org/doc/html/
draft-gont-dhcwg-dhcpv6-iids-00>.
Templin Expires 12 October 2025 [Page 126]
Internet-Draft IPv6 over OMNI Interfaces April 2025
[I-D.herbert-ipv4-eh]
Herbert, T., "IPv4 Extension Headers and Flow Label", Work
in Progress, Internet-Draft, draft-herbert-ipv4-eh-03, 22
February 2024, <https://datatracker.ietf.org/doc/html/
draft-herbert-ipv4-eh-03>.
[I-D.ietf-6man-eh-limits]
Herbert, T., "Limits on Sending and Processing IPv6
Extension Headers", Work in Progress, Internet-Draft,
draft-ietf-6man-eh-limits-19, 27 February 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-6man-eh-
limits-19>.
[I-D.ietf-6man-rfc6724-update]
Buraglio, N., Chown, T., and J. Duncan, "Prioritizing
known-local IPv6 ULAs through address selection policy",
Work in Progress, Internet-Draft, draft-ietf-6man-rfc6724-
update-18, 16 March 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-6man-
rfc6724-update-18>.
[I-D.ietf-intarea-tunnels]
Touch, J. D. and M. Townsley, "IP Tunnels in the Internet
Architecture", Work in Progress, Internet-Draft, draft-
ietf-intarea-tunnels-14, 3 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-intarea-
tunnels-14>.
[I-D.ietf-tsvwg-udp-options]
Touch, J. D. and C. M. Heard, "Transport Options for UDP",
Work in Progress, Internet-Draft, draft-ietf-tsvwg-udp-
options-45, 16 March 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-
udp-options-45>.
[I-D.ietf-v6ops-ula-usage-considerations]
Jiang, S., Liu, B., and N. Buraglio, "Considerations For
Using Unique Local Addresses", Work in Progress, Internet-
Draft, draft-ietf-v6ops-ula-usage-considerations-05, 11
December 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-v6ops-ula-usage-considerations-05>.
[I-D.link-6man-gulla]
Linkova, J., "Using Prefix-Specific Link-Local Addresses
to Improve SLAAC Robustness", Work in Progress, Internet-
Draft, draft-link-6man-gulla-01, 3 March 2025,
<https://datatracker.ietf.org/doc/html/draft-link-6man-
gulla-01>.
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[I-D.perkins-manet-aodvv2]
Perkins, C. E., Dowdell, J., Steenbrink, L., and V.
Pritchard, "Ad Hoc On-demand Distance Vector Version 2
(AODVv2) Routing", Work in Progress, Internet-Draft,
draft-perkins-manet-aodvv2-05, 22 November 2024,
<https://datatracker.ietf.org/doc/html/draft-perkins-
manet-aodvv2-05>.
[I-D.templin-6man-aero3]
Templin, F., "Automatic Extended Route Optimization
(AERO)", Work in Progress, Internet-Draft, draft-templin-
6man-aero3-40, 31 March 2025,
<https://datatracker.ietf.org/doc/html/draft-templin-6man-
aero3-40>.
[I-D.templin-6man-mla]
Templin, F. L., "IPv6 Addresses for Ad Hoc Networks", Work
in Progress, Internet-Draft, draft-templin-6man-mla-27, 3
April 2025, <https://datatracker.ietf.org/doc/html/draft-
templin-6man-mla-27>.
[I-D.templin-6man-parcels2]
Templin, F., "IPv6 Parcels and Advanced Jumbos (AJs)",
Work in Progress, Internet-Draft, draft-templin-6man-
parcels2-21, 2 January 2025,
<https://datatracker.ietf.org/doc/html/draft-templin-6man-
parcels2-21>.
[I-D.templin-intarea-parcels2]
Templin, F., "IPv4 Parcels and Advanced Jumbos (AJs)",
Work in Progress, Internet-Draft, draft-templin-intarea-
parcels2-15, 31 December 2024,
<https://datatracker.ietf.org/doc/html/draft-templin-
intarea-parcels2-15>.
[IANA-CGA] Postel, J., "Cryptographically Generated Addresses (CGA)
Message Type Name Space, https://www.iana.org/assignments/
cga-message-types/cga-message-types.xhtml", 15 March 2023.
[IEEE802.1AX]
"Institute of Electrical and Electronics Engineers, Link
Aggregation, IEEE Standard 802.1AX-2008,
https://standards.ieee.org/ieee/802.1AX/6768/", 29 May
2020.
[IPV4] Postel, J., "IPv4 Address Space Registry,
https://www.iana.org/assignments/ipv4-address-space/ipv4-
address-space.xhtml", 14 December 2020.
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[IPV6] Postel, J., "IPv6 Global Unicast Address Assignments,
https://www.iana.org/assignments/ipv6-unicast-address-
assignments/ipv6-unicast-address-assignments.xhtml", 14
December 2020.
[RFC0863] Postel, J., "Discard Protocol", STD 21, RFC 863,
DOI 10.17487/RFC0863, May 1983,
<https://www.rfc-editor.org/info/rfc863>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC1149] Waitzman, D., "Standard for the transmission of IP
datagrams on avian carriers", RFC 1149,
DOI 10.17487/RFC1149, April 1990,
<https://www.rfc-editor.org/info/rfc1149>.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/info/rfc1191>.
[RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages",
RFC 1256, DOI 10.17487/RFC1256, September 1991,
<https://www.rfc-editor.org/info/rfc1256>.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/info/rfc2104>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
<https://www.rfc-editor.org/info/rfc2464>.
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[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM
Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999,
<https://www.rfc-editor.org/info/rfc2492>.
[RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
RFC 2675, DOI 10.17487/RFC2675, August 1999,
<https://www.rfc-editor.org/info/rfc2675>.
[RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group
MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000,
<https://www.rfc-editor.org/info/rfc2863>.
[RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery",
RFC 2923, DOI 10.17487/RFC2923, September 2000,
<https://www.rfc-editor.org/info/rfc2923>.
[RFC2983] Black, D., "Differentiated Services and Tunnels",
RFC 2983, DOI 10.17487/RFC2983, October 2000,
<https://www.rfc-editor.org/info/rfc2983>.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, DOI 10.17487/RFC3056, February
2001, <https://www.rfc-editor.org/info/rfc3056>.
[RFC3068] Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
RFC 3068, DOI 10.17487/RFC3068, June 2001,
<https://www.rfc-editor.org/info/rfc3068>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[RFC3366] Fairhurst, G. and L. Wood, "Advice to link designers on
link Automatic Repeat reQuest (ARQ)", BCP 62, RFC 3366,
DOI 10.17487/RFC3366, August 2002,
<https://www.rfc-editor.org/info/rfc3366>.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692,
DOI 10.17487/RFC3692, January 2004,
<https://www.rfc-editor.org/info/rfc3692>.
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[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, DOI 10.17487/RFC3819, July 2004,
<https://www.rfc-editor.org/info/rfc3819>.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213,
DOI 10.17487/RFC4213, October 2005,
<https://www.rfc-editor.org/info/rfc4213>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
DOI 10.17487/RFC4380, February 2006,
<https://www.rfc-editor.org/info/rfc4380>.
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
2006, <https://www.rfc-editor.org/info/rfc4389>.
[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>.
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[RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly
Errors at High Data Rates", RFC 4963,
DOI 10.17487/RFC4963, July 2007,
<https://www.rfc-editor.org/info/rfc4963>.
[RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
Chowdhury, K., and B. Patil, "Proxy Mobile IPv6",
RFC 5213, DOI 10.17487/RFC5213, August 2008,
<https://www.rfc-editor.org/info/rfc5213>.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
DOI 10.17487/RFC5214, March 2008,
<https://www.rfc-editor.org/info/rfc5214>.
[RFC5237] Arkko, J. and S. Bradner, "IANA Allocation Guidelines for
the Protocol Field", BCP 37, RFC 5237,
DOI 10.17487/RFC5237, February 2008,
<https://www.rfc-editor.org/info/rfc5237>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)",
RFC 5558, DOI 10.17487/RFC5558, February 2010,
<https://www.rfc-editor.org/info/rfc5558>.
[RFC5614] Ogier, R. and P. Spagnolo, "Mobile Ad Hoc Network (MANET)
Extension of OSPF Using Connected Dominating Set (CDS)
Flooding", RFC 5614, DOI 10.17487/RFC5614, August 2009,
<https://www.rfc-editor.org/info/rfc5614>.
[RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
Version 3 for IPv4 and IPv6", RFC 5798,
DOI 10.17487/RFC5798, March 2010,
<https://www.rfc-editor.org/info/rfc5798>.
[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>.
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[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>.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, DOI 10.17487/RFC6145, April 2011,
<https://www.rfc-editor.org/info/rfc6145>.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
DOI 10.17487/RFC6147, April 2011,
<https://www.rfc-editor.org/info/rfc6147>.
[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>.
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, DOI 10.17487/RFC6296, June 2011,
<https://www.rfc-editor.org/info/rfc6296>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[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>.
[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
<https://www.rfc-editor.org/info/rfc6724>.
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[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/info/rfc6762>.
[RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman,
"Special-Purpose IP Address Registries", BCP 153,
RFC 6890, DOI 10.17487/RFC6890, April 2013,
<https://www.rfc-editor.org/info/rfc6890>.
[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", RFC 7042, DOI 10.17487/RFC7042, October 2013,
<https://www.rfc-editor.org/info/rfc7042>.
[RFC7094] McPherson, D., Oran, D., Thaler, D., and E. Osterweil,
"Architectural Considerations of IP Anycast", RFC 7094,
DOI 10.17487/RFC7094, January 2014,
<https://www.rfc-editor.org/info/rfc7094>.
[RFC7181] Clausen, T., Dearlove, C., Jacquet, P., and U. Herberg,
"The Optimized Link State Routing Protocol Version 2",
RFC 7181, DOI 10.17487/RFC7181, April 2014,
<https://www.rfc-editor.org/info/rfc7181>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC7343] Laganier, J. and F. Dupont, "An IPv6 Prefix for Overlay
Routable Cryptographic Hash Identifiers Version 2
(ORCHIDv2)", RFC 7343, DOI 10.17487/RFC7343, September
2014, <https://www.rfc-editor.org/info/rfc7343>.
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[RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542,
DOI 10.17487/RFC7542, May 2015,
<https://www.rfc-editor.org/info/rfc7542>.
[RFC7739] Gont, F., "Security Implications of Predictable Fragment
Identification Values", RFC 7739, DOI 10.17487/RFC7739,
February 2016, <https://www.rfc-editor.org/info/rfc7739>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface
Support for IP Hosts with Multi-Access Support", RFC 7847,
DOI 10.17487/RFC7847, May 2016,
<https://www.rfc-editor.org/info/rfc7847>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet
Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
<https://www.rfc-editor.org/info/rfc8799>.
[RFC8892] Thaler, D. and D. Romascanu, "Guidelines and Registration
Procedures for Interface Types and Tunnel Types",
RFC 8892, DOI 10.17487/RFC8892, August 2020,
<https://www.rfc-editor.org/info/rfc8892>.
[RFC8899] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T.
Völker, "Packetization Layer Path MTU Discovery for
Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
September 2020, <https://www.rfc-editor.org/info/rfc8899>.
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[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>.
[RFC9365] Jeong, J., Ed., "IPv6 Wireless Access in Vehicular
Environments (IPWAVE): Problem Statement and Use Cases",
RFC 9365, DOI 10.17487/RFC9365, March 2023,
<https://www.rfc-editor.org/info/rfc9365>.
[RFC9374] Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov,
"DRIP Entity Tag (DET) for Unmanned Aircraft System Remote
ID (UAS RID)", RFC 9374, DOI 10.17487/RFC9374, March 2023,
<https://www.rfc-editor.org/info/rfc9374>.
[RFC9562] Davis, K., Peabody, B., and P. Leach, "Universally Unique
IDentifiers (UUIDs)", RFC 9562, DOI 10.17487/RFC9562, May
2024, <https://www.rfc-editor.org/info/rfc9562>.
[RFC9602] Krishnan, S., "Segment Routing over IPv6 (SRv6) Segment
Identifiers in the IPv6 Addressing Architecture",
RFC 9602, DOI 10.17487/RFC9602, October 2024,
<https://www.rfc-editor.org/info/rfc9602>.
Appendix A. IPv6 Compatible Addresses
Section 2.5.5.1 of [RFC4291] defines an "IPv4-Compatible IPv6
Address" with the following structure:
| 80 bits | 16 | 32 bits |
+--------------------------------------+----+---------------------+
|0000..............................0000|0000| IPv4 address |
+--------------------------------------+----+---------------------+
Figure 45: IPv4-Compatible IPv6 Address
Although [RFC4291] deprecates the address format from its former use
in IPv6 transition mechanisms, this document defines OMNI-specific
uses.
When an IPv4-Compatible IPv6 address appears in a packet sent over an
OMNI link, the most significant 96 bits are 0 and the least
significant 32 bits include an IPv4 address as shown above.
When the address format is used for temporary local address
conversions to IPv6, however, it can also be used to represent EUI-48
and EUI-64 addresses as shown below:
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| 80 bits | 48 bits |
+--------------------------------------+--------------------------+
|0000..............................0000| EUI-48 address |
+--------------------------------------+--------------------------+
| 64 bits | 64 bits |
+--------------------------------+--------------------------------+
|0000........................0000| EUI-64 address |
+--------------------------------+--------------------------------+
Figure 46: EUI-[48/64] Compatible IPv6 Addresses
The above EUI-48 and EUI-64 compatible IPv6 forms MAY be used for
temporary local address conversions, such as when converting EUI
addresses to IPv6 to support IPv6 fragmentation/reassembly. The
address forms MUST NOT appear in the IPv6 headers of packets sent
over the OMNI link, however they MAY appear in the body of a packet
if also accompanied by a Type designator.
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 first includes a standard
IPv6 ND message checksum, then optionally includes an RSA Signature
or HMAC sub-option with a valid signature if necessary then finally
always includes an OMNI option checksum. The OMNI interface that
receives the message verifies the OMNI option checksum followed by
the authentication signature (if present) to ensure IPv6 ND message
integrity and authenticity. (The network layer will then verify the
IPv6 ND message checksum following OAL processing.)
When an OMNI interface sends an IPv6 ND message over an underlay
interface connected to a secured network, it omits the Authentication
(sub-)option but always calculates/includes the IPv6 ND message and
OMNI option checksums. When an OMNI interface sends an IPv6 ND
message over an underlay interface connected to an unsecured network,
it first includes an OMNI RSA Signature or HMAC sub-option and
calculates the signature beginning with the IPv6 ND message header
checksum field and extending to the end of the entire (composite)
packet followed by any OMNI sub-options up to but not including the
authentication sub-option itself. The OMNI interface next writes the
signature into the appropriate field, then calculates the OMNI option
checksum as above.
The OMNI interface that receives the message applies any link layer
authentication and integrity checks, then verifies the OMNI option
checksum. If the checks are correct, the OMNI interface next
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verifies the authentication signature. The OMNI interface then
delivers the IPv6 ND message to the network layer only if the OMNI
option checksum and authentication signature were correct.
OAL destinations also discard carrier packets with unacceptable
Identifications and submit the encapsulated fragments in all others
for reassembly. The reassembly algorithm rejects any fragments with
unacceptable sizes, offsets, etc. and reassembles all others. During
reassembly, the extended Identification value provides an integrity
assurance vector that complements 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 link layer "beacons". Third, aircraft employ the
services of ground stations by performing unicast RS/RA exchanges
upon receipt of beacons instead of listening for multicast RA
messages and/or sending multicast RS messages.
This beacon-oriented unicast RS/RA approach is necessary to conserve
the already-scarce available link bandwidth. Moreover, since the
numbers of beaconing ground stations operating within a given spatial
range must be kept as sparse as possible, it would not be feasible to
have different classes of ground stations within the same region
observing different protocols. It is therefore highly desirable that
all ground stations observe a common language of RS/RA as specified
in this document.
Note that links of this nature may benefit from compression
techniques that reduce the bandwidth necessary for conveying the same
amount of data. The IETF lpwan working group is considering possible
alternatives: [https://datatracker.ietf.org/wg/lpwan/documents].
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Appendix 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. IPv6 ND Virtual Interface Model
The OMNI interface linkage between the network and adaptation layers
described in this document is based on a virtual Ethernet interface
abstraction in a point-to-multipoint configuration. The abstraction
allows the network layer and adaptation layer to exchange packets via
a virtual Ethernet as though the network layer represents a singular
host on one end of the link communicating with a multitude of host
entities at the adaptation layer on the other end. This allows the
network layer to manage the OMNI interface according to standard IPv6
ND procedures including address resolution, neighbor unreachability
detection, duplicate address detection, router discovery and
multicast listener discovery.
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In an alternative arrangement, the adaptation layer could also
emulate a singular host instead of multiple and the virtual link
appears as point-to-point. In this model, the network layer
configures a static permanent neighbor cache entry for a fictitious
hardware address that represents the adaptation layer side of the
virtual link. The network layer then forwards all IP packets to this
singular adaptation layer neighbor address, and the OMNI interface
internally assumes the role of performing all IPv6 ND coordination
with external peers without network layer intervention.
While this document is written from the perspective of the point-to-
multipoint model, implementations are free to use the point-to-point
model as an alternative. Note that it is not required for all nodes
on the OMNI link to engage the same model as long as the external
appearance of IPv6 ND messages over interconnecting networks is
consistent.
Appendix F. Change Log
<< RFC Editor - remove prior to publication >>
Differences from earlier versions:
Draft -51 to -52
* Support OFS probing based on live data (and not just discard
data).
Draft -50 to -51
* Removed instances of carrier packet source fragmentation.
* New ICMPv6 Code for "MTU Probe Reply".
Draft -49 to -50
* Dynamic per-flow OAL fragment size determination through active
probing.
* Greatly reduced dependence on network-based reassembly.
Draft -47 to -49
* Major simplification of Carrier Packet MTU handling with
fragmentation avoidance.
* Purged stale references with no citations.
Draft -46 to -47
* Specified conditions for sending additional RS messages to
generate new RAs.
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* DHCPv6 address delegation lease lifetime must be the same as
the Router Lifetime advertised in RA messages.
* Updated Checksum2 specification to include pseudo-header of OAL
IPv6 header.
Draft -45 to -46
* Re-factored compressed header formats for maximum
implementation flexibility.
* Clarified the role of the Interface Attributes sub-option for
supporting per-interface Client-to-Proxy/Server address
discovery. Accordingly adjusted DHCPv6 considerations.
Draft -43 to -45
* Changed OMNI sub-options to use 8/8 TLV format instead of the
5/11 from previous versions.
* Changed compressed header formats to avoid spanning octet
fields across multiple-octet boundaries.
* Removed Teredo sub-options.
Draft -42 to -43
* Imported SRv6 addresses per [RFC9602].
* Cleaned up sub-option figures plus supporting text.
Draft -41 to -42
* Replaced ORH with RFC8754 Segment Routing Header (SRH). Now,
MLA-addressed partition border nodes within edge networks can
be nested to an arbitrary depth. The SRH is now used to
navigate MANET clusters to arbitrary depths in both the FHS and
LHS MANETs.
* Reverted SEND sub-option specifications to match RFC3971 and
also included an HMAC sub-option for use with pre-shared keys.
Draft -40 to -41
* Discussion of the DHCPv6 service model for the OMNI link.
Author's Address
Fred L. Templin (editor)
The Boeing Company
P.O. Box 3707
Seattle, WA 98124
United States of America
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Email: fltemplin@acm.org
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