Network Working Group F. Templin, Ed.
Internet-Draft The Boeing Company
Intended status: Standards Track A. Whyman
Expires: April 28, 2022 MWA Ltd c/o Inmarsat Global Ltd
October 25, 2021
Transmission of IP Packets over Overlay Multilink Network (OMNI)
Interfaces
draft-templin-6man-omni-49
Abstract
Mobile network platforms and devices (e.g., aircraft of various
configurations, terrestrial vehicles, seagoing vessels, enterprise
wireless devices, pedestrians with cell phones, etc.) communicate
with networked correspondents over multiple access network data links
and configure mobile routers to connect end user networks. A
multilink interface specification is presented that enables mobile
nodes to coordinate with a network-based mobility service and/or with
other mobile node peers. 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 April 28, 2022.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 13
4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 13
5. OMNI Interface Maximum Transmission Unit (MTU) . . . . . . . 19
6. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 20
6.1. OAL Source Encapsulation and Fragmentation . . . . . . . 21
6.2. OAL *NET Encapsulation and Re-Encapsulation . . . . . . . 25
6.3. OAL *NET Decapsulation and Reassembly . . . . . . . . . . 28
6.4. OAL Header Compression . . . . . . . . . . . . . . . . . 28
6.5. OAL-in-OAL Encapsulation . . . . . . . . . . . . . . . . 31
6.6. OAL Identification Window Maintenance . . . . . . . . . . 33
6.7. OAL Fragment Retransmission . . . . . . . . . . . . . . . 38
6.8. OAL MTU Feedback Messaging . . . . . . . . . . . . . . . 39
6.9. OAL Requirements . . . . . . . . . . . . . . . . . . . . 41
6.10. OAL Fragmentation Security Implications . . . . . . . . . 42
6.11. OAL Super-Packets . . . . . . . . . . . . . . . . . . . . 44
6.12. OAL Bubbles . . . . . . . . . . . . . . . . . . . . . . . 46
7. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 46
8. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 46
9. Unique-Local Addresses (ULAs) . . . . . . . . . . . . . . . . 48
10. Global Unicast Addresses (GUAs) . . . . . . . . . . . . . . . 50
11. Node Identification . . . . . . . . . . . . . . . . . . . . . 51
12. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 52
12.1. The OMNI Option . . . . . . . . . . . . . . . . . . . . 53
12.2. OMNI Sub-Options . . . . . . . . . . . . . . . . . . . . 53
12.2.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 56
12.2.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 56
12.2.3. Interface Attributes . . . . . . . . . . . . . . . . 57
12.2.4. Multilink Forwarding Parameters . . . . . . . . . . 60
12.2.5. Traffic Selector . . . . . . . . . . . . . . . . . . 64
12.2.6. Geo Coordinates . . . . . . . . . . . . . . . . . . 66
12.2.7. Dynamic Host Configuration Protocol for IPv6
(DHCPv6) Message . . . . . . . . . . . . . . . . . . 66
12.2.8. Host Identity Protocol (HIP) Message . . . . . . . . 67
12.2.9. PIM-SM Message . . . . . . . . . . . . . . . . . . . 70
12.2.10. Reassembly Limit . . . . . . . . . . . . . . . . . . 71
12.2.11. Fragmentation Report . . . . . . . . . . . . . . . . 72
12.2.12. Node Identification . . . . . . . . . . . . . . . . 73
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12.2.13. ICMPv6 Error . . . . . . . . . . . . . . . . . . . . 75
12.2.14. QUIC-TLS Message . . . . . . . . . . . . . . . . . . 75
12.2.15. Proxy/Server Departure . . . . . . . . . . . . . . . 76
12.2.16. OMNI Header Extension . . . . . . . . . . . . . . . 77
12.2.17. Sub-Type Extension . . . . . . . . . . . . . . . . . 78
13. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 82
14. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 82
14.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 83
14.2. Client-Proxy/Server Loop Prevention . . . . . . . . . . 83
15. Router Discovery and Prefix Registration . . . . . . . . . . 84
15.1. Window Synchronization . . . . . . . . . . . . . . . . . 91
15.2. Router Discovery in IP Multihop and IPv4-Only Networks . 92
15.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 94
16. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 95
17. Proxy/Server Resilience . . . . . . . . . . . . . . . . . . . 96
18. Detecting and Responding to Proxy/Server Failures . . . . . . 96
19. Transition Considerations . . . . . . . . . . . . . . . . . . 97
20. OMNI Interfaces on Open Internetworks . . . . . . . . . . . . 97
21. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 100
22. (H)HITs and Temporary ULAs . . . . . . . . . . . . . . . . . 100
23. Address Selection . . . . . . . . . . . . . . . . . . . . . . 101
24. Error Messages . . . . . . . . . . . . . . . . . . . . . . . 102
25. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 102
25.1. "Protocol Numbers" Registry . . . . . . . . . . . . . . 102
25.2. "IEEE 802 Numbers" Registry . . . . . . . . . . . . . . 102
25.3. "IPv4 Special-Purpose Address" Registry . . . . . . . . 103
25.4. "IPv6 Neighbor Discovery Option Formats" Registry . . . 103
25.5. "Ethernet Numbers" Registry . . . . . . . . . . . . . . 103
25.6. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry . 103
25.7. "OMNI Option Sub-Type Values" (New Registry) . . . . . . 104
25.8. "OMNI Geo Coordinates Type Values" (New Registry) . . . 104
25.9. "OMNI Node Identification ID-Type Values" (New Registry) 105
25.10. "OMNI Option Sub-Type Extension Values" (New Registry) . 105
25.11. "OMNI RFC4380 UDP/IP Header Option" (New Registry) . . . 106
25.12. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry) . . 106
25.13. Additional Considerations . . . . . . . . . . . . . . . 107
26. Security Considerations . . . . . . . . . . . . . . . . . . . 107
27. Implementation Status . . . . . . . . . . . . . . . . . . . . 109
28. Document Updates . . . . . . . . . . . . . . . . . . . . . . 109
29. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 109
30. References . . . . . . . . . . . . . . . . . . . . . . . . . 111
30.1. Normative References . . . . . . . . . . . . . . . . . . 111
30.2. Informative References . . . . . . . . . . . . . . . . . 113
Appendix A. OAL Checksum Algorithm . . . . . . . . . . . . . . . 121
Appendix B. IPv6 ND Message Authentication and Integrity . . . . 122
Appendix C. VDL Mode 2 Considerations . . . . . . . . . . . . . 123
Appendix D. Client-Proxy/Server Isolation Through L2 Address
Mapping . . . . . . . . . . . . . . . . . . . . . . 124
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Appendix E. Change Log . . . . . . . . . . . . . . . . . . . . . 124
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 124
1. Introduction
Mobile network platforms and devices (e.g., aircraft of various
configurations, terrestrial vehicles, seagoing vessels, enterprise
wireless devices, pedestrians with cellphones, etc.) configure mobile
routers with multiple interface connections to wireless and/or wired-
line data links. These data links may have diverse performance, cost
and availability properties that can change dynamically according to
mobility patterns, flight phases, proximity to infrastructure, etc.
The mobile router acts as a Client of a network-based Mobility
Service (MS) by configuring a virtual interface over its underlying
interface data link connections to support the "6M's of modern
Internetworking" (see below).
Each Client configures a virtual interface (termed the "Overlay
Multilink Network Interface (OMNI)") as a thin layer over its
underlying interfaces. 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 underlying interfaces appear as link layer communication
channels in the architecture. The OMNI interface internally employs
the "OMNI Adaptation Layer (OAL)" to ensure that original IP packets
are delivered without loss due to size restrictions. The OMNI
interface connects to a virtual overlay service known as the "OMNI
link". The OMNI link spans one or more Internetworks that may
include private-use infrastructures and/or the global public Internet
itself.
The Client's OMNI interface interacts with the MS and/or other
Clients through IPv6 Neighbor Discovery (ND) control message
exchanges [RFC4861]. The MS consists of a distributed set of service
nodes known as Proxy/Servers (and other infrastructure elements) that
also configure OMNI interfaces. An example MS termed "Automatic
Extended Route Optimization (AERO)" appears in
[I-D.templin-6man-aero]. In terms of precedence, the AERO
specification may provide first-principle insights into a
representative mobility service architecture as useful context for
this specification.
Each OMNI interface provides a multilink nexus for exchanging inbound
and outbound traffic via selected underlying interface(s). The IP
layer sees the OMNI interface as a point of connection to the OMNI
link. Each OMNI link has one or more associated Mobility Service
Prefixes (MSPs), which are typically IP Global Unicast Address (GUA)
prefixes assigned to the link and from which Mobile Network Prefixes
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(MNPs) are derived. If there are multiple OMNI links, the IP layer
will see multiple OMNI interfaces.
Each Client receives an MNP through IPv6 ND control message exchanges
with Proxy/Servers. The Client uses the MNP for numbering
downstream-attached End User Networks (EUNs) independently of the
access network data links selected for data transport. The Client
acts as a mobile router on behalf of its EUNs, 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 underlying interfaces in order to register
each interface with the MS (see Section 15).
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 set of
underlying interfaces and provides a nexus for Safety-Based Multilink
(SBM) operation. Each OMNI interface within the same OMNI domain
configures a common ULA prefix [ULA]::/48, and configures a unique
16-bit Subnet ID '*' to construct the sub-prefix [ULA*]::/64 (see:
Section 9). 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 underlying
interfaces. Applications select SBM topologies based on IP layer
Segment Routing [RFC8402], while each OMNI interface orchestrates PBM
internally based on OMNI layer Segment Routing.
OMNI provides a link model suitable for a wide range of use cases.
In particular, the International Civil Aviation Organization (ICAO)
Working Group-I Mobility Subgroup is developing a future Aeronautical
Telecommunications Network with Internet Protocol Services (ATN/IPS)
and has issued a liaison statement requesting IETF adoption [ATN] in
support of ICAO Document 9896 [ATN-IPS]. The IETF IP Wireless Access
in Vehicular Environments (ipwave) working group has further included
problem statement and use case analysis for OMNI in a document now in
AD evaluation for RFC publication
[I-D.ietf-ipwave-vehicular-networking]. Still other communities of
interest include AEEC, RTCA Special Committee 228 (SC-228) and NASA
programs that examine commercial aviation, Urban Air Mobility (UAM)
and Unmanned Air Systems (UAS). Pedestrians with handheld devices
represent another large class of potential OMNI users.
OMNI supports the "6M's of modern Internetworking" including:
1. Multilink - a Client's ability to coordinate multiple diverse
underlying data links as a single logical unit (i.e., the OMNI
interface) to achieve the required communications performance and
reliability objectives.
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2. Multinet - the ability to span the OMNI link over a segment
routing topology with multiple diverse administrative domain
network segments while maintaining seamless end-to-end
communications between mobile Clients and correspondents such as
air traffic controllers, fleet administrators, etc.
3. Mobility - a Client's ability to change network points of
attachment (e.g., moving between wireless base stations) which
may result in an underlying interface address change, but without
disruptions to ongoing communication sessions with peers over the
OMNI link.
4. Multicast - the ability to send a single network transmission
that reaches multiple Clients belonging to the same interest
group, but without disturbing other Clients not subscribed to the
interest group.
5. Multihop - a mobile Client vehicle-to-vehicle relaying capability
useful when multiple forwarding hops between vehicles may be
necessary to "reach back" to an infrastructure access point
connection to the OMNI link.
6. MTU assurance - the ability to deliver packets of various robust
sizes between peers without loss due to a link size restriction,
and to dynamically adjust packets sizes to achieve the optimal
performance for each independent traffic flow.
This document specifies the transmission of IP packets and control
messages over OMNI interfaces. The OMNI interface supports either IP
protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) as the
network layer data plane, while using IPv6 ND messaging as the
control plane independently of the data plane IP protocol(s). The
OAL operates as a sublayer between L3 and L2 based on IPv6
encapsulation [RFC2473] as discussed in the following sections.
2. Terminology
The terminology in the normative references applies; especially, the
terms "link" and "interface" are the same as defined in the IPv6
[RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications.
Additionally, this document assumes the following IPv6 ND message
types: Router Solicitation (RS), Router Advertisement (RA), Neighbor
Solicitation (NS), Neighbor Advertisement (NA) and Redirect. Clients
and Proxy/Servers that implement IPv6 ND maintain per-neighbor state
in Neighbor Cache Entries (NCEs). Each NCE is indexed by the
neighbor's Link-Local Address (LLA), while the Unique-Local Address
(ULA) used for encapsulation provides context for Identification
verification.
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The Protocol Constants defined in Section 10 of [RFC4861] are used in
their same format and meaning in this document. The terms "All-
Routers multicast", "All-Nodes multicast" and "Subnet-Router anycast"
are the same as defined in [RFC4291] (with Link-Local scope assumed).
The term "IP" is used to refer collectively to either Internet
Protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) when a
specification at the layer in question applies equally to either
version.
The following terms are defined within the scope of this document:
Client
a network platform/device mobile router that has one or more
distinct upstream data link connections grouped together into one
or more logical units. The Client's data link connection
parameters can change over time due to, e.g., node mobility, link
quality, etc. The Client further connects downstream-attached End
User Networks (EUNs).
End User Network (EUN)
a simple or complex downstream-attached mobile network that
travels with the Client as a single logical unit. The IP
addresses assigned to EUN devices remain stable even if the
Client's upstream data link connections change.
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 (and any
other supporting infrastructure nodes) for the OMNI link.
Specific MS details are out of scope for this document, with an
example found in [I-D.templin-6man-aero].
Proxy/Server
a segment routing topology edge node that provides Clients with a
multi-purpose interface to the MS. 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 packets that may be
essential in some environments and a last resort in others.
First-Hop Segment (FHS) Proxy/Server
a Proxy/Server reached via an underlying interface of the source
Client that forwards packets sent by the source Client over that
interface into the segment routing topology. FHS Proxy/Servers
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act as intermediate forwarding nodes to facilitate RS/RA exchanges
between a Client and its Hub Proxy/Server.
Last-Hop Segment (LHS) Proxy/Server
a Proxy/Server for an underlying interface of the target Client
that forwards packets received from the segment routing topology
to the target Client over that interface.
Hub Proxy/Server
a single Proxy/Server selected by the Client that provides a
designated router service for all of the Client's underlying
interfaces. Clients normally select the first FHS Proxy/Server
they coordinate with to serve in the Hub role (as all FHS Proxy/
Servers are equally capable candidates to serve in that capacity),
however the Hub can also be any available Proxy/Server for the
OMNI link (as there is no requirement that the Hub must also be
one of the Client's FHS Proxy/Servers).
Segment Routing Topology (SRT)
a multinet forwarding region between the FHS Proxy/Server and LHS
Proxy/Server. FHS/LHS Proxy/Servers and the SRT span the OMNI
link on behalf of source/target Client pairs using segment routing
in a manner outside the scope of this document (see:
[I-D.templin-6man-aero]).
Mobility Service Prefix (MSP)
an aggregated IP Global Unicast Address (GUA) prefix (e.g.,
2001:db8::/32, 192.0.2.0/24, etc.) assigned to the OMNI link and
from which more-specific Mobile Network Prefixes (MNPs) are
delegated. OMNI link administrators typically obtain MSPs from an
Internet address registry, however private-use prefixes can
alternatively be used subject to certain limitations (see:
Section 10). OMNI links that connect to the global Internet
advertise their MSPs to their interdomain routing peers.
Mobile Network Prefix (MNP)
a longer IP prefix delegated from an MSP (e.g.,
2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a
Client. Clients sub-delegate the MNP to devices located in EUNs.
Note that OMNI link Relay nodes may also service non-MNP routes
(i.e., GUA prefixes not covered by an MSP) but that these
correspond to fixed correspondent nodes and not Clients. Other
than this distinction, MNP and non-MNP routes are treated exactly
the same by the OMNI routing system.
Access Network (ANET)
a data link service network (e.g., an aviation radio access
network, satellite service provider network, cellular operator
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network, WiFi network, etc.) that connects Clients. Physical and/
or data link level security is assumed, and sometimes referred to
as "protected spectrum". Private enterprise networks and ground
domain aviation service networks may provide multiple secured IP
hops between the Client's point of connection and the nearest
Proxy/Server.
ANET interface
a Client's attachment to a link in an ANET.
Internetwork (INET)
a connected network region with a coherent IP addressing plan that
provides transit forwarding services between ANETs and nodes that
connect directly to the open INET via unprotected media. No
physical and/or data link level security is assumed, therefore
security must be applied by upper layers. The global public
Internet itself is an example.
INET interface
a node's attachment to a link in an INET.
*NET
a "wildcard" term used when a given specification applies equally
to both ANET and INET cases.
INADDR
the IP address (and also the UDP port number when UDP is used)
that appear in *NET header address fields. The terms "*NET
address" and "INADDR" are used interchangeably.
OMNI link
a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured
over one or more INETs and their connected ANETs. 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 MS infrastructure elements
extend the link to support communications between Clients as
single-hop neighbors.
OMNI interface
a node's attachment to an OMNI link, and configured over one or
more underlying *NET interfaces. If there are multiple OMNI links
in an OMNI domain, a separate OMNI interface is configured for
each link.
OMNI Adaptation Layer (OAL)
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an OMNI interface sublayer service whereby original IP packets
admitted into the interface are wrapped in an IPv6 header and
subject 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.
original IP packet
a whole IP packet or fragment admitted into the OMNI interface by
the network layer prior to OAL encapsulation and fragmentation, or
an IP packet delivered to the network layer by the OMNI interface
following OAL decapsulation and reassembly.
OAL packet
an original IP packet encapsulated in OAL headers and trailers,
which is then submitted for OAL fragmentation and reassembly.
OAL fragment
a portion of an OAL packet following fragmentation but prior to
*NET encapsulation, or following *NET encapsulation but prior to
OAL reassembly.
(OAL) atomic fragment
an OAL packet that does not require fragmentation is always
encapsulated as an "atomic fragment" with a Fragment Header with
Fragment Offset and More Fragments both set to 0, but with a valid
Identification value.
(OAL) carrier packet
an encapsulated OAL fragment following *NET encapsulation or prior
to *NET decapsulation. OAL sources and destinations exchange
carrier packets over underlying interfaces, and may be separated
by one or more OAL intermediate nodes. OAL intermediate nodes may
perform re-encapsulation on carrier packets by removing the *NET
headers of the first hop network and replacing them with new *NET
headers for the next hop network.
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 *NET encapsulation to create carrier packets.
OAL destination
an OMNI interface acts as an OAL destination when it decapsulates
carrier packets, then performs OAL reassembly and decapsulation to
derive the original IP packet.
OAL intermediate node
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an OMNI interface acts as an OAL intermediate node when it removes
the *NET headers of carrier packets received on a first segment,
then re-encapsulates the carrier packets in new *NET headers and
forwards them into the next segment.
OMNI Option
an IPv6 Neighbor Discovery option providing multilink parameters
for the OMNI interface as specified in Section 12.
Mobile Network Prefix Link Local Address (MNP-LLA)
an IPv6 Link Local Address that embeds the most significant 64
bits of an MNP in the lower 64 bits of fe80::/64, as specified in
Section 8.
Mobile Network Prefix Unique Local Address (MNP-ULA)
an IPv6 Unique-Local Address derived from an MNP-LLA.
Administrative Link Local Address (ADM-LLA)
an IPv6 Link Local Address that embeds a 32-bit administratively-
assigned identification value in the lower 32 bits of fe80::/96,
as specified in Section 8.
Administrative Unique Local Address (ADM-ULA)
an IPv6 Unique-Local Address derived from an ADM-LLA.
Multilink
an OMNI interface's manner of managing diverse underlying
interface connections to data links as a single logical unit. The
OMNI interface provides a single unified interface to upper
layers, while underlying interface selections are performed on a
per-packet basis considering traffic selectors such as DSCP, flow
label, application policy, signal quality, cost, etc. Multilink
selections are coordinated in both the outbound and inbound
directions based on source/target underlying interface pairs.
Multinet
an OAL intermediate node's manner of spanning multiple diverse IP
Internetwork and/or private enterprise network "segments" at the
OAL layer below IP. Through intermediate node concatenation of
SRT bridged network segments, multiple diverse Internetworks (such
as the global public IPv4 and IPv6 Internets) can serve as transit
segments in a bridged path for forwarding IP packets end-to-end.
This bridging capability provide benefits such as supporting IPv4/
IPv6 transition and coexistence, joining multiple diverse operator
networks into a cooperative single service network, etc.
Multihop
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an iterative relaying of IP packets between Client's over an OMNI
underlying 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.
L2
The second layer in the OSI network model. Also known as "layer-
2", "link-layer", "sub-IP layer", "data link layer", etc.
L3
The third layer in the OSI network model. Also known as "layer-
3", "network-layer", "IP layer", etc.
underlying interface
a *NET interface over which an OMNI interface is configured. The
OMNI interface is seen as a L3 interface by the IP layer, and each
underlying interface is seen as a L2 interface by the OMNI
interface. The underlying interface either connects directly to
the physical communications media or coordinates with another node
where the physical media is hosted.
Mobility Service Identification (MSID)
All MS elements (including Proxy/Servers and other MS nodes)
assign a unique 32-bit Identification (MSID) (see: Section 8)
according to MS-specific guidelines (e.g., see:
[I-D.templin-6man-aero]).
Safety-Based Multilink (SBM)
A means for ensuring fault tolerance through redundancy by
connecting multiple affiliated OMNI interfaces to independent
routing topologies (i.e., multiple independent OMNI links).
Performance Based Multilink (PBM)
A means for selecting one or more underlying interface(s) for
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. Each OMNI domain consists of a
set of affiliated OMNI links that all configure the same ::/48 ULA
prefix with a unique 16-bit Subnet ID as discussed in Section 9.
Multilink Forwarding Information Base (MFIB)
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A forwarding table on each OMNI source, destination and
intermediate node that includes Multilink Forwarding Vectors (MFV)
with both next hop forwarding instructions and context for
reconstructing compressed headers for specific underlying
interface pairs used to communicate with peers. See:
[I-D.templin-6man-aero] for further discussion.
Multilink Forwarding Vector (MFV)
An MFIB entry that includes soft state for each underlying
interface pairwise communication session between peers. MFVs are
identified by both a next-hop and previous-hop MFV Index (MFVI),
with the next-hop established based on an IPv6 ND solicitation and
the previous hop established based on the solicited IPv6 ND
advertisement response. See: [I-D.templin-6man-aero] for further
discussion.
Multilink Forwarding Vector Index (MVFI)
A 4 octet value selected by an OMNI node when it creates an MFV,
then advertised to either a next-hop or previous-hop. OMNI
intermediate nodes assign two distinct MFVIs for each MFV and
advertise one to the next-hop and the other to the previous-hop.
OMNI end systems assign and advertise a single MFVI. See:
[I-D.templin-6man-aero] for further discussion.
3. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
An implementation is not required to internally use the architectural
constructs described here so long as its external behavior is
consistent with that described in this document.
4. Overlay Multilink Network (OMNI) Interface Model
An OMNI interface is a virtual interface configured over one or more
underlying interfaces, which may be physical (e.g., an aeronautical
radio link, etc.) or virtual (e.g., an Internet or higher-layer
"tunnel"). The OMNI interface architectural layering model is the
same as in [RFC5558][RFC7847], and augmented as shown in Figure 1.
The IP layer therefore sees the OMNI interface as a single L3
interface nexus for multiple underlying interfaces that appear as L2
communication channels in the architecture.
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+----------------------------+
| Upper Layer Protocol |
Session-to-IP +---->| |
Address Binding | +----------------------------+
+---->| IP (L3) |
IP Address +---->| |
Binding | +----------------------------+
+---->| OMNI Interface |
Logical-to- +---->| (OMNI Adaptation Layer) |
Physical | +----------------------------+
Interface +---->| L2 | L2 | | L2 |
Binding |(IF#1)|(IF#2)| ..... |(IF#n)|
+------+------+ +------+
| L1 | L1 | | L1 |
| | | | |
+------+------+ +------+
Figure 1: OMNI Interface Architectural Layering Model
Each underlying interface provides an L2/L1 abstraction according to
one of the following models:
o INET interfaces connect to an INET either natively or through one
or several IPv4 Network Address Translators (NATs). Native INET
interfaces have global IP addresses that are reachable from any
INET correspondent. NATed INET interfaces typically have private
IP addresses and connect to a private network behind one or more
NATs with the outermost NAT providing INET access.
o ANET interfaces connect to a protected and secured ANET that is
separated from the open INET by Proxy/Servers. The ANET interface
may be either on the same L2 link segment as a Proxy/Server, or
separated from a Proxy/Server by multiple IP hops. (Note that
NATs may appear internally within an ANET and may require NAT
traversal on the path to the Proxy/Server the same as for the INET
case.)
o VPNed interfaces use security encapsulation over a *NET to a
Proxy/Server acting as a Virtual Private Network (VPN) gateway.
Other than the link-layer encapsulation format, VPNed interfaces
behave the same as for Direct interfaces.
o Direct (aka "point-to-point") interfaces connect directly to a
peer (i.e., a Proxy/Server or another Client) without crossing any
*NET paths. An example is a line-of-sight link between a remote
pilot and an unmanned aircraft.
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The OMNI interface forwards original IP packets from the network
layer (L3) using the OMNI Adaptation Layer (OAL) (see: Section 5) as
an encapsulation and fragmentation sublayer service. This "OAL
source" then further encapsulates the resulting OAL packets/fragments
in *NET headers to create "carrier packets" for transmission over
underlying interfaces (L2/L1). The target OMNI interface receives
the carrier packets from underlying interfaces (L1/L2) and discards
the *NET headers. If the resulting OAL packets/fragments are
addressed to itself, the OMNI interface acts as an "OAL destination"
and performs reassembly if necessary, discards the OAL encapsulation,
and delivers the original IP packet to the network layer (L3). If
the OAL fragments are addressed to another node, the OMNI interface
instead acts as an "OAL intermediate node" by re-encapsulating in new
*NET headers and forwarding the new carrier packets over an
underlying interface without reassembling or discarding the OAL
encapsulation. The OAL source and OAL destination are seen as
"neighbors" on the OMNI link, while OAL intermediate nodes provide a
virtual bridging service that joins the segments of a (multinet)
Segment Routing Topology (SRT).
The OMNI interface can send/receive original IP packets to/from
underlying interfaces while including/omitting various encapsulations
including OAL, UDP, IP and L2. The network layer can also access the
underlying interfaces directly while bypassing the OMNI interface
entirely when necessary. This architectural flexibility may be
beneficial for underlying interfaces (e.g., some aviation data links)
for which encapsulation overhead may be a primary consideration.
OMNI interfaces that send original IP packets directly over
underlying 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
forwards the packets into the SRT spanning tree, which transports
them to a Last-Hop Segment (LHS) Proxy/Server for the target Client.
Original IP packets sent directly over underlying interfaces are
subject to the same path MTU related issues as for any
Internetworking path, and do not include per-packet identifications
that can be used for data origin verification and/or link-layer
retransmissions. Original IP packets presented directly to an
underlying interface that exceed the underlying network path MTU are
dropped with an ordinary ICMPv6 Packet Too Big (PTB) message
returned. These PTB messages are subject to loss [RFC2923] the same
as for any non-OMNI IP interface.
The OMNI interface encapsulation/decapsulation layering possibilities
are shown in Figure 2 below. Imaginary vertical lines drawn between
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the Network Layer and Underlying interfaces in the figure denote the
encapsulation/decapsulation layering combinations possible. Common
combinations include NULL (i.e., direct access to underlying
interfaces with or without using the OMNI interface), IP/IP, IP/UDP/
IP, IP/UDP/IP/L2, IP/OAL/UDP/IP, IP/OAL/UDP/L2, etc.
+------------------------------------------------------------+
| Network Layer (Original IP packets) |
+--+---------------------------------------------------------+
| OMNI Interface (virtual sublayer nexus) |
+--------------------------+------------------------------+
| OAL Encaps/Decaps |
+------------------------------+
| OAL Frag/Reass |
+------------+---------------+--------------+
| UDP Encaps/Decaps/Compress |
+----+---+------------+--------+--+ +--------+
| IP E/D | | IP E/D | | IP E/D |
+---+------+-+----+ +--+---+----+ +----+---+--+
|L2 E/D| |L2 E/D| |L2 E/D| |L2 E/D|
+-------+------+---+------+----+------+---------------+------+
| Underlying Interfaces |
+------------------------------------------------------------+
Figure 2: OMNI Interface Layering
The OMNI/OAL model gives rise to a number of opportunities:
o Clients receive MNPs from the MS, and coordinate with the MS
through IPv6 ND message exchanges with Proxy/Servers. Clients use
the MNP to construct a unique Link-Local Address (MNP-LLA) through
the algorithmic derivation specified in Section 8 and assign the
LLA to the OMNI interface. Since MNP-LLAs are uniquely derived
from an MNP, no Duplicate Address Detection (DAD) or Multicast
Listener Discovery (MLD) messaging is necessary.
o since Temporary ULAs are statistically unique, they can be used
without DAD until an MNP-LLA is obtained.
o underlying 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.
o as underlying 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
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message. This allows for timely adaptation and service continuity
under dynamically changing conditions.
o coordinating underlying interfaces in this way allows them to be
represented in a unified MS profile with provisions for mobility
and multilink operations.
o exposing a single virtual interface abstraction to the IPv6 layer
allows for multilink operation (including QoS based link
selection, packet replication, load balancing, etc.) at L2 while
still permitting L3 traffic shaping based on, e.g., DSCP, flow
label, etc.
o the OMNI interface allows multinet traversal over the SRT when
communications across different administrative domain network
segments are necessary. This mode of operation would not be
possible via direct communications over the underlying interfaces
themselves.
o the OAL supports lossless and adaptive path MTU mitigations not
available for communications directly over the underlying
interfaces themselves. The OAL supports "packing" of multiple IP
payload packets within a single OAL "super-packet".
o the OAL applies per-packet identification values that allow for
link-layer reliability and data origin authentication.
o L3 sees the OMNI interface as a point of connection to the OMNI
link; if there are multiple OMNI links (i.e., multiple MS's), L3
will see multiple OMNI interfaces.
o 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.
Note that even when the OMNI virtual interface is present,
applications can still access underlying interfaces either through
the network protocol stack using an Internet socket or directly using
a raw socket. This allows for intra-network (or point-to-point)
communications without invoking the OMNI interface and/or OAL. For
example, when an IPv6 OMNI interface is configured over an underlying
IPv4 interface, applications can still invoke IPv4 intra-network
communications as long as the communicating endpoints are not subject
to mobility dynamics.
Figure 3 depicts the architectural model for a source Client with an
attached EUN connecting to the OMNI link via multiple independent
*NETs. The Client's OMNI interface sends IPv6 ND messages over
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available underlying interfaces to FHS Proxy/Servers using any
necessary *NET 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 message response and/or forwards a
proxyed version of the message over the SRT to an LHS Proxy/Server
near the target Client (LHS#1, LHS#2, ..., LHS#m). The Hop Limit in
IPv6 ND messages is not decremented due to encapsulation; hence, the
source and target Client OMNI interfaces appear to be attached to a
common link.
+--------------+ (:::)-.
|Source Client |<-->.-(::EUN:::)
+--------------+ `-(::::)-'
|OMNI interface|
+----+----+----+
+--------|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
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After the initial IPv6 ND message exchange, the source Client (and/or
any nodes on its attached EUNs) can send packets to the target Client
over the OMNI interface. OMNI interface multilink services will
forward the packets via FHS Proxy/Servers for the correct underlying
*NETs. The FHS Proxy/Server then forwards them over the SRT which
delivers them to an LHS Proxy/Server, and the LHS Proxy/Server in
turn forwards the packets to the target Client. (Note that when the
source and target Client are on the same SRT segment, the FHS and LHS
Proxy/Servers may be one and the same.)
Clients select a Hub Proxy/Server (not shown in the figure), which
will often be one of their FHS Proxy/Servers but could also be any
Proxy/Server on the OMNI link. Clients then register all of their
underlying interfaces with the Hub Proxy/Server via the FHS Proxy/
Server in a pure proxy role. The Hub Proxy/Server then provides a
designated router service for the Client, and the Client can quickly
migrate to a new Hub Proxy/Server if the first becomes unresponsive.
Clients therefore use Proxy/Servers as gateways into the SRT to reach
OMNI link correspondents via a spanning tree established in a manner
outside the scope of this document. Proxy/Servers forward critical
MS control messages via the secured spanning tree and forward other
messages via the unsecured spanning tree (see Security
Considerations). When route optimization is applied as discussed in
[I-D.templin-6man-aero], Clients can instead forward directly to an
SRT intermediate node themselves (or directly to correspondents in
the same SRT segment) to reduce Proxy/Server load.
5. OMNI Interface Maximum Transmission Unit (MTU)
The OMNI interface observes the link nature of tunnels, including the
Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and
the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels].
The OMNI interface is configured over one or more underlying
interfaces as discussed in Section 4, where the interfaces (and their
associated *NET paths) may have diverse MTUs. OMNI interface
considerations for accommodating original IP packets of various sizes
are discussed in the following sections.
IPv6 underlying interfaces are REQUIRED to configure a minimum MTU of
1280 bytes and a minimum MRU of 1500 bytes [RFC8200]. Therefore, the
minimum IPv6 path MTU is 1280 bytes 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 of at least 1280 bytes without
generating an IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB)
message [RFC8201]. (While the source can apply "source
fragmentation" for locally-generated IPv6 packets up to 1500 bytes
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and larger still if it knows the destination configures a larger MRU,
this does not affect the minimum IPv6 path MTU.)
IPv4 underlying interfaces are REQUIRED to configure a minimum MTU of
68 bytes [RFC0791] and a minimum MRU of 576 bytes [RFC0791][RFC1122].
Therefore, when the Don't Fragment (DF) bit in the IPv4 header is set
to 0 the minimum IPv4 path MTU is 576 bytes since routers on the path
support network fragmentation and the destination is required to
reassemble at least that much. The OMNI interface therefore MUST set
DF to 0 in the IPv4 encapsulation headers of carrier packets that are
no larger than 576 bytes, and SHOULD set DF to 1 in larger carrier
packets unless it has a way to determine the encapsulation
destination MRU and has carefully considered the issues discussed in
Section 6.10.
The OMNI interface configures an MTU and MRU of 9180 bytes [RFC2492];
the size is therefore not a reflection of the underlying interface or
*NET path MTUs, but rather determines the largest original IP packet
the OAL (and/or underlying interface) can forward or reassemble. For
each OAL destination (i.e., for each OMNI link neighbor), the OAL
source may discover "hard" or "soft" Reassembly Limit values smaller
than the MRU based on receipt of IPv6 ND messages with OMNI
Reassembly Limit sub-options (see: Section 12.2.10). The OMNI
interface employs the OAL as an encapsulation sublayer service to
transform original IP packets into OAL packets/fragments, and the OAL
in turn uses *NET encapsulation to forward carrier packets over the
underlying interfaces (see: Section 6).
6. The OMNI Adaptation Layer (OAL)
When an OMNI interface forwards an original IP packet from the
network layer for transmission over one or more underlying
interfaces, the OMNI Adaptation Layer (OAL) acting as the OAL source
drops the packet and returns a PTB message if the packet exceeds the
MRU and/or the hard Reassembly Limit for the intended OAL
destination. Otherwise, the OAL source applies encapsulation to form
OAL packets subject to fragmentation producing OAL fragments suitable
for *NET encapsulation and transmission as carrier packets over
underlying interfaces as described in Section 6.1.
These carrier packets travel over one or more underlying networks
spanned by OAL intermediate nodes in the SRT, which re-encapsulate by
removing the *NET headers of the first underlying network and
appending *NET headers appropriate for the next underlying network in
succession. (This process supports the multinet concatenation
capability needed for joining multiple diverse networks.) After re-
encapsulation by zero or more OAL intermediate nodes, the carrier
packets arrive at the OAL destination.
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When the OAL destination receives the carrier packets, it discards
the *NET headers and reassembles the resulting OAL fragments into an
OAL packet as described in Section 6.3. The OAL destination then
decapsulates the OAL packet to obtain the original IP packet, which
it then delivers to the network layer. The OAL source may be either
the source Client or its FHS Proxy/Server, while the OAL destination
may be either the LHS Proxy/Server or the target Client. Proxy/
Servers (and other SRT infrastructure node types such as those
discussed in [I-D.templin-6man-aero]) may also serve as OAL
intermediate nodes.
The OAL presents an OMNI sublayer abstraction similar to ATM
Adaptation Layer 5 (AAL5). Unlike AAL5 which performs segmentation
and reassembly with fixed-length 53 octet cells over ATM networks,
however, the OAL uses IPv6 encapsulation, fragmentation and
reassembly with larger variable-length cells over heterogeneous
underlying 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, the OAL source inserts an OAL header consisting of an IPv6
encapsulation header followed by an IPv6 Fragment Header (see
[RFC2473] and below) but does not decrement the Hop Limit/TTL of the
original IP packet since encapsulation occurs at a layer below IP
forwarding. The OAL source copies the "Type of Service/Traffic
Class" [RFC2983] and "Congestion Experienced" [RFC3168] values in the
original packet's IP header into the corresponding fields in the OAL
header, then sets the OAL header "Flow Label" as specified in
[RFC6438]. The OAL source finally sets the OAL header IPv6 Hop Limit
to a conservative value sufficient to enable loop-free forwarding
over multiple concatenated OMNI link segments and sets the Payload
Length to the length of the original IP packet.
The OAL next selects source and destination addresses for the IPv6
header of the resulting OAL packet. Client OMNI interfaces set the
OAL header source address to a Unique Local Address (ULA) based on
the Mobile Network Prefix (MNP-ULA), while Proxy/Server OMNI
interfaces set the source address to an Administrative ULA (ADM-ULA)
(see: Section 9). When a Client OMNI interface does not (yet) have
an MNP-ULA, it can use a Temporary ULA and/or Host Identity Tag (HIT)
instead (see: Section 22) as OAL addresses. (In addition to ADM-
ULAs, Proxy/Servers also process packets with anycast and/or
multicast OAL addresses.)
Following OAL encapsulation and address selection, the OAL source
next appends a 2 octet trailing Checksum field (initialized to 0) at
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the end of the original IP packet while incrementing the OAL header
IPv6 Payload Length field to reflect the addition of the trailer.
The format of the resulting OAL packet following encapsulation is
shown in Figure 4:
+----------+-----+-----+-----+-----+-----+-----+----+
|OAL Header| Original IP packet |Csum|
+----------+-----+-----+-----+-----+-----+-----+----+
Figure 4: OAL Packet Before Fragmentation
The OAL source next selects a 32-bit Identification value for the
packet to place in the Fragment Header as specified in Section 6.6
then calculates an OAL checksum using the algorithm specified in
Appendix A. The OAL source calculates the checksum over the OAL
packet beginning with a pseudo-header of the OAL header similar to
that found in Section 8.1 of [RFC8200], followed by the Original IP
packet and extending to the end of the (0-initialized) Checksum
trailer. The OAL pseudo-header is formed as shown in Figure 5:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ OAL Source Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ OAL Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL Payload Length | zero | Next Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: OAL Pseudo-Header
After calculating the checksum, the OAL source next fragments the OAL
packet if necessary while assuming the IPv4 minimum path MTU (i.e.,
576 bytes) as the worst case for OAL fragmentation regardless of the
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underlying interface IP protocol version since IPv6/IPv4 protocol
translation and/or IPv6-in-IPv4 encapsulation may occur in any *NET
path. By always assuming the IPv4 minimum even for IPv6 underlying
interfaces, the OAL source may produce smaller fragments with
additional encapsulation overhead but will always interoperate and
never run the risk of loss due to an MTU restriction or due to
presenting an underlying interface with a carrier packet that exceeds
its MRU. Additionally, the OAL path could traverse multiple SRT
segments with intermediate OAL forwarding nodes performing re-
encapsulation where the *NET encapsulation of the previous segment is
replaced by the *NET encapsulation of the next segment which may be
based on a different IP protocol version and/or encapsulation sizes.
The OAL source therefore assumes a default minimum path MTU of 576
bytes at each SRT segment for the purpose of generating OAL fragments
for *NET encapsulation and transmission as carrier packets. Each
successive SRT intermediate node may include either a 20 byte IPv4 or
40 byte IPv6 header, an 8 byte UDP header and in some cases an IP
security encapsulation (40 bytes maximum assumed) during re-
encapsulation. Intermediate nodes at any SRT segment may also insert
a Routing Header (40 bytes maximum assumed) as an extension to the
existing 40 byte OAL IPv6 header plus 8 byte Fragment Header.
Therefore, assuming a worst case of (40 + 40 + 8) = 88 bytes for *NET
encapsulation plus (40 + 40 + 8) = 88 bytes for OAL encapsulation
leaves no less than (576 - 88 - 88) = 400 bytes remaining to
accommodate a portion of the original IP packet/fragment. The OAL
source therefore sets a minimum Maximum Payload Size (MPS) of 400
bytes as the basis for the minimum-sized OAL fragment that can be
assured of traversing all SRT segments without loss due to an MTU/MRU
restriction. The Maximum Fragment Size (MFS) for OAL fragmentation
is therefore determined by the MPS plus the size of the OAL
encapsulation headers. (Note that the OAL source includes the 2
octet trailer as part of the payload during fragmentation, and the
OAL destination regards it as ordinary payload until reassembly and
checksum verification are complete.)
The OAL source SHOULD maintain "path MPS" values for individual OAL
destinations initialized to the minimum MPS and increased to larger
values (up to the OMNI interface MTU) if better information is known
or discovered. For example, when *NET peers share a common
underlying link or a fixed path with a known larger MTU, the OAL
source can set path MPS to this larger size (i.e., greater than 576
bytes) as long as the *NET peer reassembles before re-encapsulating
and forwarding (while re-fragmenting if necessary). Also, if the OAL
source has a way of knowing the maximum *NET encapsulation size for
all SRT segments along the path it may be able to increase path MPS
to reserve additional room for payload data. Even when OAL header
compression is used, the OAL source must include the uncompressed OAL
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header size in its path MPS calculation since it may need to include
a full header at any time.
The OAL source can also optimistically set a larger path MPS and/or
actively probe individual OAL destinations to discover larger sizes
using packetization layer probes in a similar fashion as
[RFC4821][RFC8899], but care must be taken to avoid setting static
values for dynamically changing paths leading to black holes. The
probe involves sending an OAL packet larger than the current path MPS
and receiving a small acknowledgement response (with the possible
receipt of link-layer error message when a probe is lost). For this
purpose, the OAL source can send an NS message with one or more OMNI
options with large PadN sub-options (see: Section 12) in order to
receive a small NA response from the OAL destination. While
observing the minimum MPS will always result in robust and secure
behavior, the OAL source should optimize path MPS values when more
efficient utilization may result in better performance (e.g. for
wireless aviation data links). The OAL source should maintain
separate path MPS values for each (source, target) underlying
interface pair for the same OAL destination, since different
underlying interface pairs may support differing path MPS values.
When the OAL source performs fragmentation, it SHOULD produce the
minimum number of non-overlapping fragments under current MPS
constraints, where each non-final fragment MUST be at least as large
as the minimum MPS, while the final fragment MAY be smaller. The OAL
source also converts all original IP packets no larger than the
current MPS into "atomic fragments" by including a Fragment Header
with Fragment Offset and More Fragments both set to 0.
For each fragment produced, the OAL source writes an ordinal number
for the fragment into the Reserved field in the IPv6 Fragment Header.
Specifically, the OAL source writes the ordinal number '0' for the
first fragment, '1' for the second fragment, '2' for the third
fragment, etc. up to and including the final fragment. Since the
minMPS is 400 and the MTU is 9180, the OAL source will produce at
most 23 fragments for each OAL packet; the OAL destination therefore
unconditionally discards any fragments with an ordinal number larger
than 22.
The OAL source finally encapsulates the fragments in *NET headers to
form carrier packets and forwards them over an underlying interface,
while retaining the fragments and their ordinal numbers (i.e., #0,
#1, #2, etc.) for a brief period to support link-layer
retransmissions (see: Section 6.7). OAL fragment and carrier packet
formats are shown in Figure 6.
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+----------+----------------+
|OAL Header| Frag #0 |
+----------+----------------+
+----------+----------------+
|OAL Header| Frag #1 |
+----------+----------------+
+----------+----------------+
|OAL Header| Frag #2 |
+----------+----------------+
....
+----------+----------------+----+
|OAL Header| Frag #(N-1) |Csum|
+----------+----------------+----+
a) OAL fragmentation (Csum in final fragment)
+----------+-----+-----+-----+-----+-----+----+
|OAL Header| Original IP packet |Csum|
+----------+-----+-----+-----+-----+-----+----+
b) An OAL atomic fragment
+--------+----------+----------------+
|*NET Hdr|OAL Header| Frag #i |
+--------+----------+----------------+
c) OAL carrier packet after *NET encapsulation
Figure 6: OAL Fragments and Carrier Packets
6.2. OAL *NET Encapsulation and Re-Encapsulation
The OAL source or intermediate node encapsulates each OAL fragment
(with either full or compressed headers) in *NET encapsulation
headers to create a carrier packet. The OAL source or intermediate
node (i.e., the *NET source) includes a UDP header as the innermost
sublayer if NAT traversal and/or packet filtering middlebox traversal
are required; otherwise, the *NET source includes either a full or
compressed IP header or a true L2 header (e.g., such as for Ethernet-
compatible links). The *NET source then appends any additional
encapsulation sublayer headers necessary and presents the resulting
carrier packet to an underlying interface, where the underlying
network conveys it to a next-hop OAL intermediate node or destination
(i.e., the *NET destination).
The *NET source encapsulates the OAL information immediately
following the *NET innermost sublayer header. If the first four bits
of the encapsulated OAL information following the innermost sublayer
header encode the value '6', the information must include an
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uncompressed IPv6 header followed by any IPv6 extension headers
followed by upper layer protocol headers and data. Otherwise, the
first four bits include a "Type" value, and the OAL information
appears in an alternate format as specified in Section 6.4).
Alternate formats for Types '0' and '1' are currently specified,
while Type value '4' is permanently reserved and all other values are
reserved for future use. Carrier packets that contain an unsupported
Type value are unconditionally dropped.
The OAL node prepares the innermost *NET encapsulation header for OAL
packets as follows:
o For UDP, the *NET source sets the UDP source port to 8060 (i.e.,
the port number reserved for AERO/OMNI). When the *NET
destination is a Proxy/Server or Bridge, the *NET source sets the
UDP destination port to 8060; otherwise, the *NET source sets the
UDP destination port to its cached port number value for the peer.
The *NET source finally sets the UDP Length the same as specified
in [RFC0768].
o For IP encapsulation, the IP protocol number or Next Header is set
to TBD1 as the Internet Protocol number for OMNI (see: IANA
Considerations). For IPv4, the *NET source sets the Total Length
the same as specified in [RFC0791]; for IPv6, the *NET source sets
the Payload Length the same as specified in [RFC8200].
o For encapsulations over Ethernet-compatible L2s, the EtherType is
set to TBD2 as the EtherType number for OMNI (see: IANA
Considerations). Since the Ethernet header does not include a
length field, for the OMNI EtherType the Ethernet header is
followed by a two-octet length field followed immediately by the
encapsulated OAL information. The length field encodes the length
in octets (in network byte order) of the information following the
Ethernet header including the length field, but excluding the
Ethernet trailer.
When a *NET source includes a UDP header, it SHOULD calculate and
include a UDP checksum in carrier packets with full OAL headers to
prevent mis-delivery, and MAY disable UDP checksums in carrier
packets with compressed OAL headers (see: Section 6.4). If the *NET
source discovers that a path is dropping carrier packets with UDP
checksums disabled, it should enable UDP checksums in future carrier
packets sent to the same *NET destination. If the *NET 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.
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When a *NET source sends carrier packets with compressed OAL headers
and with UDP checksums disabled, mis-delivery due to corruption of
the 4-octet Multilink Forwarding Vector Index (MFVI) is possible but
unlikely since the corrupted index would somehow have to match valid
state in the (sparsely-populated) Multilink Forwarding Information
Based (MFIB). In the unlikely event that a match occurs, an OAL
destination may receive a mis-delivered carrier packet but can
immediately reject packet with an incorrect Identification. If the
Identification value is somehow accepted, the OAL destination may
submit the mis-delivered carrier packet to the reassembly cache where
it will most likely be rejected due to incorrect reassembly
parameters. If a reassembly that includes the mis-delivered carrier
packets somehow succeeds (or, for atomic fragments) the OAL
destination will verify the OAL checksum to detect corruption.
Finally, any spurious data that somehow eludes all prior checks will
be detected and rejected by end-to-end upper layer security. See:
[RFC6935][RFC6936] for further discussion.
For *NET encapsulations over IP, when the *NET source is also the OAL
source it next copies the "Type of Service/Traffic Class" [RFC2983]
and "Congestion Experienced" [RFC3168] values in the OAL header into
the corresponding fields in the *NET IP header, then (for IPv6) set
the *NET IPv6 header "Flow Label" as specified in [RFC6438]. The
*NET source then sets the *NET IP TTL/Hop Limit the same as for any
host (i.e., it does not copy the Hop Limit value from the OAL header)
and finally sets the source and destination IP addresses to direct
the carrier packet to the next hop. For carrier packets undergoing
re-encapsulation, the OAL intermediate node *NET source decrements
the OAL header Hop Limit and discards the carrier packet if the value
reaches 0. The *NET source then copies the "Type of Service/Traffic
Class" and "Congestion Experienced" values from the previous hop *NET
encapsulation header into the OAL header, then finally sets the
source and destination IP addresses the same as above.
Following *NET encapsulation/re-encapsulation, the *NET source sends
the resulting carrier packets over one or more underlying interfaces.
The underlying interfaces often connect directly to physical media on
the local platform (e.g., 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 underlying interface) to the node hosting the physical media.
The OMNI interface may also apply encapsulation at the underlying
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 underlying interface must monitor the node hosting the physical
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media (e.g., through periodic keepalives) so that it can convey
up/down/status information to the OMNI interface.
6.3. OAL *NET Decapsulation and Reassembly
When an OMNI interface receives a carrier packet from an underlying
interface, it discards the *NET encapsulation headers and examines
the OAL header of the enclosed OAL fragment. If the OAL fragment is
addressed to a different node, the OMNI interface (acting as an OAL
intermediate node) re-encapsulates and forwards as discussed in
Section 6.2. If the OAL fragment is addressed to itself, the OMNI
interface (acting as an OAL destination) accepts or drops the
fragment based on the (Source, Destination, Identification)-tuple
and/or integrity checks.
The OAL destination next drops all non-final OAL fragments smaller
than the minimum MPS and all fragments that would overlap or leave
"holes" smaller than the minimum MPS with respect to other fragments
already received. The OAL destination updates a checklist of the
ordinal numbers of each accepted fragment of the same OAL packet
(i.e., as Frag #0, Frag #1, Frag #2, etc.), then admits the fragments
into the reassembly cache. When reassembly is complete, the OAL
destination next verifies the OAL packet checksum and discards the
packet if the checksum is incorrect. If the OAL packet was accepted,
the OAL destination then removes the OAL header/trailer and delivers
the original IP packet to the network layer.
Carrier packets often travel over paths where all links in the path
include CRC-32 integrity checks for effective hop-by-hop error
detection for payload sizes up to the OMNI interface MTU [CRC], but
other paths may traverse links (such as tunnels over IPv4) that do
not include integrity checks. The OAL checksum therefore allows OAL
destinations to detect reassembly misassociation splicing errors and/
or carrier packet corruption caused by unprotected links [CKSUM].
The OAL checksum also provides algorithmic diversity with respect to
both lower layer CRCs and upper layer Internet checksums as part of a
complimentary multi-layer integrity assurance architecture. Any
corruption not detected by lower layer integrity checks is therefore
very likely to be detected by upper layer integrity checks that use
diverse algorithms.
6.4. OAL Header Compression
OAL sources that send carrier packets with full OAL headers include a
CRH-32 extension for segment-by-segment forwarding based on a
Multilink Forwarding Information Base (MFIB) in each OAL intermediate
node. OAL source, intermediate and destination nodes can instead
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establish header compression state through IPv6 ND NS/NA message
exchanges. After an initial NS/NA exchange, OAL nodes can apply OAL
Header Compression to significantly reduce encapsulation overhead.
Each OAL node establishes MFIB soft state entries known as Multilink
Forwarding Vectors (MVFs) which support both carrier packet
forwarding and OAL header compression/decompression. For OAL
sources, each MFV is referenced by a single MFV Index (MFVI) that
provides compression/decompression and forwarding context for the
next hop. For OAL destinations, the MFV is referenced by a single
MFVI that provides context for the previous hop. For OAL
intermediate nodes, the MFV is referenced by two MFVIs - one for the
previous hop and one for the next hop.
When an OAL node forwards carrier packets to a next hop, it can
include a full OAL header with a CRH-32 extension containing one or
more MVFIs. The OAL node can instead omit significant portions of
the OAL header (including the CRH-32) while applying OAL header
compression. The full or compressed OAL header follows immediately
after the innermost *NET encapsulation (i.e., UDP, IP or L2) as
discussed in Section 6.2. Two OAL compressed header types (Type '0'
and Type '1') are currently specified below.
For OAL first-fragments (including atomic fragments), the OAL node
uses OMNI Compressed Header - Type 0 (OCH-0) as shown in Figure 7:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type=0 | Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hop Limit |I|M| Identification (0-1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification (2-3) | MFVI (0-1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MFVI (2-3) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: OMNI Compressed Header - Type 0 (OCH-0)
The format begins with a 4-bit Type field set to 0, and is followed
by the uncompressed Traffic Class and Flow Label copied from the OAL
header, followed by a Next Header field set to the protocol number
for the header immediately following the IPv6 Fragment Header. The
Next Header field is then followed by a 6-bit compressed Hop Limit
field set to the minimum of 63 and the uncompressed OAL IPv6 Hop
Limit value. The Hop Limit is then followed by an (I)ndex bit and a
compressed Fragment Header that includes only the (M)ore Fragments
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bit and the 4-octet Identification and with all other fields omitted.
When the I bit is set, the compressed Fragment Header is then
followed by a 4-octet Multilink Forwarding Vector Index (MFVI);
otherwise, the MFVI is omitted.
The OAL fragment body is then included immediately following the
OCH-0 header, and the *NET header length field is reduced by the
difference in length between the compressed headers and full-length
IPv6 and Fragment headers. The OCH-0 format applies for first
fragments only, which are always regarded as ordinal fragment 0 even
though no explicit Ordinal field is included.
For OAL non-first fragments (i.e., those with non-zero Fragment
Offsets), the OAL uses OMNI Compressed Header - Type 1 (OCH-1) as
shown in Figure 8:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type=1 | Ordinal |I|M| Fragment Offset | Id(0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification (1-3) | MFVI(0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MFVI (1-3) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: OMNI Compressed Header - Type 1 (OCH-1)
The format begins with a Type field set to 1 and the IPv6 header is
omitted entirely. The Type field is then followed by a compressed
IPv6 Fragment Header with a 5-bit Ordinal number field, an (I)ndex
bit, and with ((M)ore Fragments/Fragment Offset/Identification)
copied from the uncompressed fragment header. When the I bit is set,
the compressed Fragment Header is followed by a 4-octet MFVI;
otherwise the MFVI is omitted (i.e., the same as for OCH-0).
The OAL fragment body is then included immediately following the
OCH-1 header, and the *NET header length field is reduced by the
difference in length between the compressed headers and full-length
IPv6 and Fragment headers. The OCH-1 format applies for non-first
fragments only; therefore, Ordinal is set to a monotonically
increasing value beginning with 1 for the first non-first fragment, 2
for the second non-first fragment, etc., up to and including the
final fragment (with maximum value 22 since there are at most 23
fragments).
When an OAL destination or intermediate node receives a carrier
packet, it determines the length of the encapsulated OAL information
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by examining the length field of the innermost *NET header, verifies
that the appropriate *NET header next header field indicates OMNI
(see: Section 6.2), then examines the first four bits immediately
following the *NET header. If the bits contain the value 6, the OAL
node processes the remainder as an uncompressed OAL header. If the
bits contain the value 0 or 1, the OAL node instead processes the
remainder of the header as an OCH-0 or OCH-1, respectively.
For carrier packets with OCH-0/1 or full OAL headers addressed to
itself and with CRH-32 extensions, the OAL node then uses the MFVI to
locate the cached MFV which determines the next hop. During
forwarding, the OAL node changes the MFVI to the cached value for the
MVF next hop. If the OAL node is the destination, it instead
reconstructs the full OAL headers then adds the resulting OAL
fragment to the reassembly cache if the Identification is acceptable.
For carrier packets with OCH-1 headers that do not include Traffic
Class, Flow Label, Next Header or Hop Limit information, the OAL node
writes the value 0 into those fields when it reconstructs the full
OAL headers. The values will be correctly populated during
reassembly after an OAL first fragment with an OCH-0 or uncompressed
OAL header arrives.
Note: OAL header compression does not interfere with checksum
calculation and verification, which must be applied according to the
full OAL pseudo-header per Section 6.1 even when compression is used.
Note: when OAL-in-OAL encapsulation is used, any outer OCH-0/1
headers or full OAL headers with CRH-32 extensions include an MVFI,
while the innermost OCH-0/1 header or full OAL header must not
include an MFVI.
6.5. OAL-in-OAL Encapsulation
When an OAL source is unable to forward carrier packets directly to
an OAL destination without "tunneling" through a pair of OAL
intermediate nodes, the OAL source must regard the intermediate nodes
as ingress and egress tunnel endpoints. This will result in nested
OAL-in-OAL encapsulation in which the OAL source performs
fragmentation on the inner OAL packet then forwards the fragments to
the ingress tunnel endpoint which encapsulates each resulting OAL
fragment in an additional OAL header/trailer before performing
fragmentation following encapsulation.
For example, if the OAL source has an NCE for the OAL destination
with MFVI 0x2376a7b5 and Identification 0x12345678 and the OAL
ingress tunnel endpoint has an NCE for the OAL egress tunnel endpoint
with MFVI 0xacdebf12 and Identification 0x98765432, the OAL source
prepares the carrier packets using compressed/uncompressed OAL
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headers that include the MFVI and Identification corresponding to the
OAL destination and with *NET header information addressed to the
next hop toward the ingress tunnel endpoint. When the ingress tunnel
endpoint receives the carrier packet, it recognizes the current MFVI
included by the OAL source and determines the correct next hop MFVI.
The ingress tunnel endpoint then discards the *NET headers from the
previous hop and encapsulates the original compressed/uncompressed
OAL header within a second compressed/uncompressed OAL header/trailer
while including the next-hop MVFI in the outer OAL encapsulation
header and omitting the MFVI in the inner header. The ingress tunnel
endpoint then includes *NET encapsulation headers with destinations
appropriate for the next hop on the path to the egress tunnel
endpoint. The encapsulation appears as shown in Figure 9:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| *NET headers (previous hop) | | *NET headers (next hop) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Original OAL/OCH Hdr | | Encapsulation OAL/OCH Hdr |
| Id=0x12345678 | | Id=0x98765432 |
| MFVI=0x2376a7b5 | | MFVI=0xacdebf12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | Original OAL/OCH Hdr |
| | | Id=0x12345678 |
| Carrier packet data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Carrier packet data |
| Original OAL Checksum | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
Original Carrier packet +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
from OAL source | Original OAL Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encapsulation OAL Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Carrier packet following OAL ingress
(re)encapsulation before fragmentation
Figure 9: Carrier Packet in Carrier Packet Encapsulation
Note that only a single OAL-in-OAL encapsulation layer is supported,
and that MFVIs appear only in the outer OAL header (i.e., either
within a CRH-32 routing header when a full OAL header is used or
within an OCH-0/1 header). The inner OAL/OCH header should omit the
CRH-32 header or set I to 0, respectively.
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Note that OAL/OCH encapsulation may cause the payloads of OAL packets
produced by the ingress tunnel endpoint to exceed the minimum MPS by
a small amount. If the ingress has assurance that the path to the
egress will include only links capable of transiting the resulting
(slightly larger) carrier packets it should forward without further
fragmentation. Otherwise, the ingress must perform fragmentation
following encapsulation to produce two fragments such that the size
of the first fragment matches the size of the original OAL packet,
and with the remainder in a second fragment. The egress tunnel
endpoint must then reassemble then decapsulate to arrive at the
original OAL packet which is then subject to further forwarding.
6.6. 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 32-bit Identification value. In environments where spoofing
is not considered a threat, OMNI interfaces send OAL packets with
Identifications beginning with an unpredictable Initial Send Sequence
(ISS) value [RFC7739] monotonically incremented (modulo 2**32) for
each successive OAL packet sent to either a specific neighbor or to
any neighbor. (The OMNI interface may later change to a new
unpredictable ISS value as long as the Identifications are assured
unique within a timeframe that would prevent the fragments of a first
OAL packet from becoming associated with the reassembly of a second
OAL packet.) In other environments, OMNI interfaces should maintain
explicit per-neighbor send and receive windows to detect and exclude
spurious carrier packets that might clutter the reassembly cache as
discussed below.
OMNI interface neighbors use TCP-like synchronization to maintain
windows with unpredictable ISS values incremented (modulo 2**32) for
each successive OAL packet and re-negotiate windows often enough to
maintain an unpredictable profile. OMNI interface neighbors exchange
IPv6 ND messages with OMNI options that include TCP-like information
fields to manage streams of OAL packets instead of streams of octets.
As a link-layer service, the OAL provides low-persistence best-effort
retransmission with no mitigations for duplication, reordering or
deterministic delivery. Since the service model is best-effort and
only control message sequence numbers are acknowledged, OAL nodes can
select unpredictable new initial sequence numbers outside of the
current window without delaying for the Maximum Segment Lifetime
(MSL).
OMNI interface neighbors maintain current and previous window state
in IPv6 ND neighbor cache entries (NCEs) to support dynamic rollover
to a new window while still sending OAL packets and accepting carrier
packets from the previous windows. Each NCE is indexed by the
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neighbor's LLA, which must also match the ULA used for OAL
encapsulation. OMNI interface neighbors synchronize windows through
asymmetric and/or symmetric IPv6 ND message exchanges. When a node
receives an IPv6 ND message with new window information, it resets
the previous window state based on the current window then resets the
current window based on new and/or pending information.
The IPv6 ND message OMNI option header extension sub-option includes
TCP-like information fields including Sequence Number,
Acknowledgement Number, Window and flags (see: Section 12). OMNI
interface neighbors maintain the following TCP-like state variables
in the NCE:
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. When OAL A synchronizes with OAL B, it maintains
both a current and previous SND.WND beginning with a new
unpredictable ISS and monotonically increments SND.NXT for each
successive OAL packet transmission. OAL A initiates synchronization
by including the new ISS in the Sequence Number of an authentic IPv6
ND message with the SYN flag set and with Window set to M (up to
2**24) as a tentative receive window size while creating a NCE in the
INCOMPLETE state if necessary. OAL A caches the new ISS as pending,
uses the new ISS as the Identification for OAL encapsulation, then
sends the resulting OAL packet to OAL B and waits up to RetransTimer
milliseconds to receive an IPv6 ND message response with the ACK flag
set (retransmitting up to MAX_UNICAST_SOLICIT times if necessary).
When OAL B receives the SYN, it creates a NCE in the STALE state if
necessary, resets its RCV variables, caches the tentative (send)
window size M, and selects a (receive) window size N (up to 2**24) to
indicate the number of OAL packets it is willing to accept under the
current RCV.WND. (The RCV.WND should be large enough to minimize
control message overhead yet small enough to provide an effective
filter for spurious carrier packets.) OAL B then prepares an IPv6 ND
message with the ACK flag set, with the Acknowledgement Number set to
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OAL A's next sequence number, and with Window set to N. Since OAL B
does not assert an ISS of its own, it uses the IRS it has cached for
OAL A as the Identification for OAL encapsulation then sends the ACK
to OAL A.
When OAL A receives the ACK, it notes that the Identification in the
OAL header matches its pending ISS. OAL A then sets the NCE state to
REACHABLE and resets its SND variables based on the Window size and
Acknowledgement Number (which must include the sequence number
following the pending ISS). OAL A can then begin sending OAL packets
to OAL B with Identification values within the (new) current SND.WND
for 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 within either the current or previous RCV.WND as well as any
new authentic NS/RS SYN messages received from OAL A even if outside
the windows.
OMNI interface neighbors can employ asymmetric window synchronization
as described above using two independent (SYN -> ACK) exchanges
(i.e., a four-message exchange), or they can employ symmetric window
synchronization using a modified version of the TCP three-way
handshake as follows:
o OAL A prepares a SYN with an unpredictable ISS not within the
current SND.WND and with Window set to M as a tentative receive
window size. OAL A caches the new ISS and Window size as pending
information, uses the pending ISS as the Identification for OAL
encapsulation, then sends the resulting OAL packet to OAL B and
waits up to RetransTimer milliseconds to receive an ACK response
(retransmitting up to MAX_UNICAST_SOLICIT times if necessary).
o OAL B receives the SYN, then resets its RCV variables based on the
Sequence Number while caching OAL A's tentative receive Window
size M and a new unpredictable ISS outside of its current window
as pending information. OAL B then prepares a response with
Sequence Number set to the pending ISS and Acknowledgement Number
set to OAL A's next sequence number. OAL B then sets both the SYN
and ACK flags, sets Window to N and sets the OPT flag according to
whether an explicit concluding ACK is optional or mandatory. OAL
B then uses the pending ISS as the Identification for OAL
encapsulation, sends the resulting OAL packet to OAL A and waits
up to RetransTimer milliseconds to receive an acknowledgement
(retransmitting up to MAX_UNICAST_SOLICIT times if necessary).
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o OAL A receives the SYN/ACK, then resets its SND variables based on
the Acknowledgement Number (which must include the sequence number
following the pending ISS) and OAL B's advertised Window N. OAL A
then resets its RCV variables based on the Sequence Number and
marks the NCE as REACHABLE. If the OPT flag is clear, OAL A next
prepares an immediate solicited NA message with the ACK flag set,
the Acknowledgement Number set to OAL B's next sequence number,
with Window set a value that may be the same as or different than
M, and with the OAL encapsulation Identification to SND.NXT, then
sends the resulting OAL packet to OAL B. If the OPT flag is set
and OAL A has OAL packets queued to send to OAL B, it can
optionally begin sending their carrier packets under the (new)
current SND.WND as implicit acknowledgements instead of returning
an explicit ACK. In that case, the tentative Window size M
becomes the current receive window size.
o OAL B receives the implicit/explicit acknowledgement(s) then
resets its SND state based on the pending/advertised values and
marks the NCE as REACHABLE. If OAL B receives an explicit
acknowledgement, it uses the advertised Window size and abandons
the tentative size. (Note that OAL B sets the OPT flag in the
SYN/ACK to assert that it will interpret timely receipt of carrier
packets within the (new) current window as an implicit
acknowledgement. Potential benefits include reduced delays and
control message overhead, but use case analysis is outside the
scope of this specification.)
Following synchronization, OAL A and OAL B hold updated NCEs and can
exchange OAL packets with Identifications set to SND.NXT while the
state remains REACHABLE and there is available window capacity.
Either neighbor may at any time send a new SYN to assert a new ISS.
For example, if OAL A's current SND.WND for OAL B is nearing
exhaustion and/or ReachableTime is nearing expiration, OAL A
continues to send OAL packets under the current SND.WND while also
sending a SYN with a new unpredictable ISS. When OAL B receives the
SYN, it resets its RCV variables and may optionally return either an
asymmetric ACK or a symmetric SYN/ACK to also assert a new ISS.
While sending SYNs, both neighbors continue to send OAL packets with
Identifications set to the current SND.NXT then reset the SND
variables after an acknowledgement is received.
While the optimal symmetric exchange is efficient, anomalous
conditions such as receipt of old duplicate SYNs can cause confusion
for the algorithm as discussed in Section 3.4 of [RFC0793]. For this
reason, the OMNI option header includes an RST flag which OAL nodes
set in solicited NA responses to ACKs received with incorrect
acknowledgement numbers. The RST procedures (and subsequent
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synchronization recovery) are conducted exactly as specified in
[RFC0793].
OMNI interfaces may set the PNG ("ping") flag when a reachability
confirmation outside the context of the IPv6 ND protocol is needed
(OMNI interfaces therefore most often set the PNG flag in
advertisement messages and ignore it in solicitation messages). When
an OMNI interface receives a PNG, it returns an unsolicited NA (uNA)
ACK with the PNG message Identification in the Acknowledgment, but
without updating RCV state variables. OMNI interfaces return unicast
uNA ACKs even for multicast PNG destination addresses, since OMNI
link multicast is based on unicast emulation.
OMNI interfaces that employ the window synchronization procedures
described above observe the following requirements:
o OMNI interfaces MUST select new unpredictable ISS values that are
at least a full window outside of the current SND.WND.
o OMNI interfaces MUST set the initial SYN message Window field to a
tentative value to be used only if no concluding NA ACK is sent.
o OMNI interfaces that receive advertisements with the PNG and/or
SYN flag set MUST NOT set the PNG and/or SYN flag in uNA
responses.
o OMNI interfaces that send advertisements with the PNG and/or SYN
flag set MUST ignore uNA responses with the PNG and/or SYN flag
set.
o OMNI interfaces MUST send IPv6 ND messages used for window
synchronization securely while using unpredictable initial
Identification values until synchronization is complete.
Note: Although OMNI interfaces employ TCP-like window synchronization
and support uNA ACK responses to SYNs and PNGs, all other aspects of
the IPv6 ND protocol (e.g., control message exchanges, NCE state
management, timers, retransmission limits, etc.) are honored exactly
per [RFC4861].
Note: Recipients of OAL-encapsulated IPv6 ND messages index the NCE
based on the ULA source address, which also determines the carrier
packet Identification window. However, IPv6 ND messages may contain
an LLA source address that does not match the ULA source address when
the recipient acts as a proxy.
Note: OMNI interface neighbors apply the same send and receive
windows for all of their (multilink) underlying interface pairs that
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exchange carrier packets. Each interface pair represents a distinct
underlying network path, and the set of paths traversed may be highly
diverse when multiple interface pairs are used. OMNI intermediate
nodes therefore SHOULD NOT cache window synchronization parameters in
IPv6 ND messages they forward since there is no way to ensure
network-wide middlebox state consistency.
6.7. OAL Fragment Retransmission
When the OAL source sends carrier packets to an OAL destination, it
should cache recently sent packets in case timely best-effort
selective retransmission is requested. The OAL destination in turn
maintains a checklist for the (Source, Destination, Identification)-
tuple of recently received carrier packets and notes the ordinal
numbers of OAL packet fragments already received (i.e., as Frag #0,
Frag #1, Frag #2, etc.). The timeframe for maintaining the OAL
source and destination caches determines the link persistence (see:
[RFC3366]).
If the OAL destination notices some fragments missing after most
other fragments within the same link persistence timeframe have
already arrived, it may issue an Automatic Repeat Request (ARQ) with
Selective Repeat (SR) by sending a uNA message to the OAL source.
The OAL destination creates a uNA message with an OMNI option with
one or more Fragmentation Report sub-options that include a list of
(Identification, Bitmap)-tuples for fragments received and missing
from this OAL source (see: Section 12). The OAL destination includes
an authentication signature if necessary, performs OAL encapsulation
(with the its own address as the OAL source and the source address of
the message that prompted the uNA as the OAL destination) and sends
the message to the OAL source.
When the OAL source receives the uNA message, it authenticates the
message then examines the Fragmentation Report. For each (Source,
Destination, Identification)-tuple, the OAL source determines whether
it still holds the corresponding carrier packets in its cache and
retransmits any for which the Bitmap indicates a loss event. For
example, if the Bitmap indicates that ordinal fragments #3, #7, #10
and #13 from the OAL packet with Identification 0x12345678 are
missing the OAL source only retransmits carrier packets containing
those fragments. When the OAL destination receives the retransmitted
carrier packets, it admits the enclosed fragments into the reassembly
cache and updates its checklist. If some fragments are still
missing, the OAL destination may send a small number of additional
uNA ARQ/SRs within the link persistence timeframe.
The OAL therefore provides a link-layer low persistence ARQ/SR
service consistent with [RFC3366] and Section 8.1 of [RFC3819]. The
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service provides the benefit of timely best-effort link-layer
retransmissions which may reduce packet loss and avoid some
unnecessary end-to-end delays. This best-effort network-based
service therefore compliments higher layer end-to-end protocols
responsible for true reliability.
6.8. OAL MTU Feedback Messaging
When the OMNI interface forwards original IP packets from the network
layer, it invokes the OAL and returns internally-generated ICMPv4
Fragmentation Needed [RFC1191] or ICMPv6 Path MTU Discovery (PMTUD)
Packet Too Big (PTB) [RFC8201] messages as necessary. This document
refers to both of these ICMPv4/ICMPv6 message types simply as "PTBs",
and introduces a distinction between PTB "hard" and "soft" errors as
discussed below.
Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6
header Code field value 0 are hard errors that always indicate that a
packet has been dropped due to a real MTU restriction. In
particular, the OAL source drops the packet and returns a PTB hard
error if the packet exceeds the OAL destination MRU. However, the
OMNI interface can also forward large original IP packets via OAL
encapsulation and fragmentation while at the same time returning PTB
soft error messages (subject to rate limiting) if it deems the
original IP packet too large according to factors such as link
performance characteristics, 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 packets without loss while returning PTB soft
error messages recommending a smaller size if necessary. Original
sources that receive the soft errors in turn reduce the size of the
packets they send (i.e., the same as for hard errors), but can soon
resume sending larger packets if the soft errors subside.
An OAL source sends PTB soft error messages by setting the ICMPv4
header "unused" field or ICMPv6 header Code field to the value 1 if a
original IP packet was deemed lost (e.g., due to reassembly timeout)
or to the value 2 otherwise. The OAL source sets the PTB destination
address to the original IP packet source, and sets the source address
to one of its OMNI interface addresses that is routable from the
perspective of the original source. The OAL source then sets the MTU
field to a value smaller than the original packet size but no smaller
than 576 for ICMPv4 or 1280 for ICMPv6, writes the leading portion of
the original IP packet into the "packet in error" field, and returns
the PTB soft error to the original source. When the original source
receives the PTB soft error, it temporarily reduces the size of the
packets it sends the same as for hard errors but may seek to increase
future packet sizes dynamically while no further soft errors are
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arriving. (If the original source does not recognize the soft error
code, it regards the PTB the same as a hard error but should heed the
retransmission advice given in [RFC8201] suggesting retransmission
based on normal packetization layer retransmission timers.)
An OAL destination may experience reassembly cache congestion, and
can return uNA messages to the OAL source that originated the
fragments (subject to rate limiting) to advertise reduced hard/soft
Reassembly Limits and/or to report individual reassembly failures.
The OAL destination creates a uNA message with an OMNI option
containing an authentication message sub-option if necessary followed
optionally by at most one hard and one soft Reassembly Limit sub-
options with reduced hard/soft values, and with one of them
optionally including the leading portion an OAL first fragment
containing the header of an original IP packet whose source must be
notified (see: Section 12). The OAL destination encapsulates the
leading portion of the OAL first fragment (beginning with the OAL
header) in the "OAL First Fragment" field of sub-option, signs the
message if an authentication sub-option is included, performs OAL
encapsulation (with the its own address as the OAL source and the
source address of the message that prompted the uNA as the OAL
destination) and sends the message to the OAL source.
When the OAL source receives the uNA message, it records the new
hard/soft Reassembly Limit values for this OAL destination if the
OMNI option includes Reassembly Limit sub-options. If a hard or soft
Reassembly Limit sub-option includes an OAL First Fragment, the OAL
source next sends a corresponding network layer PTB hard or soft
error to the original source to recommend a smaller size. For hard
errors, the OAL source sets the PTB Code field to 0. For soft
errors, the OAL source sets the PTB Code field to 1 if the L flag in
the Reassembly Limit sub-option is 1; otherwise, the OAL source sets
the Code field to 2. The OAL source crafts the PTB by extracting the
leading portion of the original IP packet from the OAL First Fragment
field (i.e., not including the OAL header) and writes it in the
"packet in error" field of a PTB with destination set to the original
IP packet source and source set to one of its OMNI interface
addresses that is routable from the perspective of the original
source. For future transmissions, if the original IP packet is
larger than the hard Reassembly Limit for this OAL destination the
OAL source drops the packet and returns a PTB hard error with MTU set
to the hard Reassembly Limit. If the packet is no larger than the
current hard Reassembly Limit but larger than the current soft limit,
the OAL source can also return a PTB soft error (subject to rate
limiting) with Code set to 2 and MTU set to the current soft limit
while still forwarding the packet to the OMNI destination.
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Original sources that receive PTB soft errors can dynamically tune
the size of the original IP packets they to send to produce the best
possible throughput and latency, with the understanding that these
parameters may change over time due to factors such as congestion,
mobility, network path changes, etc. The receipt or absence of soft
errors should be seen as hints of when increasing or decreasing
packet sizes may be beneficial. 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 begin sending 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 dynamic multilink environments.
6.9. OAL Requirements
In light of the above, OAL sources, destinations and intermediate
nodes observe the following normative requirements:
o OAL sources MUST NOT use the OAL to forward original IP packets
larger than the OMNI interface MTU or the OAL destination hard
Reassembly Limit (i.e., whether as atomic fragments or multiple
fragments).
o OAL sources MUST forward original IP packets smaller than the
minimum MPS minus the trailer size as atomic fragments (i.e., and
not as multiple fragments).
o OAL sources MUST produce non-final fragments with payloads no
smaller than the minimum MPS during fragmentation.
o OAL sources MUST NOT produce fragments that include any extension
headers other than a single Fragment Header.
o OAL intermediate nodes SHOULD and OAL destinations MUST
unconditionally drop any OAL fragments with offset and length that
would cause the reassembled packet to exceed the OMNI interface
MRU and/or OAL destination hard Reassembly Limit.
o OAL intermediate nodes SHOULD and OAL destinations MUST
unconditionally drop any non-final OAL fragments with payloads
smaller than the minimum MPS.
o OAL intermediate nodes SHOULD and OAL destinations MUST
unconditionally drop OAL fragments that include any extension
headers other than a single Fragment Header.
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o OAL destinations MUST drop any new OAL fragments with Offset and
Payload length that would overlap with other fragments and/or
leave holes smaller than the minimum MPS between fragments that
have already been received.
Note: Under the minimum MPS, ordinary 1500 byte original IP packets
would require at most 4 OAL fragments, with each non-final fragment
containing 400 payload bytes and the final fragment containing 302
payload bytes (i.e., the final 300 bytes of the original IP packet
plus the 2 octet trailer). Likewise, maximum-length 9180 byte
original IP packets would require at most 23 fragments. For all
packet sizes, the likelihood of successful reassembly may improve
when the OMNI interface sends all fragments of the same fragmented
OAL packet consecutively over the same underlying interface pair
instead of spread across multiple underlying interface pairs.
Finally, an assured minimum/path MPS allows continuous operation over
all paths including those that traverse bridged L2 media with
dissimilar MTUs.
Note: Certain legacy network hardware of the past millennium was
unable to accept packet "bursts" resulting from an IP 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, the OAL
source could impose an inter-fragment delay while the OAL destination
is reporting reassembly congestion (see: Section 6.8) and decrease
the delay when reassembly congestion subsides.
6.10. OAL Fragmentation Security Implications
As discussed in Section 3.7 of [RFC8900], there are four basic
threats concerning IPv6 fragmentation; each of which is addressed by
effective mitigations as follows:
1. Overlapping fragment attacks - reassembly of overlapping
fragments is forbidden by [RFC8200]; therefore, this threat does
not apply to the OAL.
2. Resource exhaustion attacks - this threat is mitigated by
providing a sufficiently large OAL reassembly cache and
instituting "fast discard" of incomplete reassemblies that may be
part of a buffer exhaustion attack. The reassembly cache should
be sufficiently large so that a sustained attack does not cause
excessive loss of good reassemblies but not so large that (timer-
based) data structure management becomes computationally
expensive. The cache should also be indexed based on the arrival
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underlying interface such that congestion experienced over a
first underlying interface does not cause discard of incomplete
reassemblies for uncongested underlying interfaces.
3. Attacks based on predictable fragment identification values - in
environments where spoofing is possible, this threat is mitigated
through the use of Identification windows beginning with
unpredictable values per Section 6.6. By maintaining windows of
acceptable Identifications, OAL neighbors can quickly discard
spurious carrier packets that might otherwise clutter the
reassembly cache. The OAL additionally provides an integrity
check to detect corruption that may be caused by spurious
fragments received with in-window Identification values.
4. Evasion of Network Intrusion Detection Systems (NIDS) - since the
OAL source employs a robust MPS, network-based firewalls can
inspect and drop OAL fragments containing malicious data thereby
disabling reassembly by the OAL destination. However, since OAL
fragments may take different paths through the network (some of
which may not employ a firewall) each OAL destination must also
employ a firewall.
IPv4 includes a 16-bit Identification (IP ID) field with only 65535
unique values such that at high data rates the field could wrap and
apply to new carrier packets while the fragments of old packets using
the same IP ID are still alive in the network [RFC4963]. Since
carrier packets sent via an IPv4 path with DF=0 are normally no
larger than 576 bytes, IPv4 fragmentation is possible only at small-
MTU links in the path which should support data rates low enough for
safe reassembly [RFC3819]. (IPv4 carrier packets larger than 576
bytes with DF=0 may incur high data rate reassembly errors in the
path, but the OAL checksum provides OAL destination integrity
assurance.) Since IPv6 provides a 32-bit Identification value, IP ID
wraparound at high data rates is not a concern for IPv6
fragmentation.
Fragmentation security concerns for large IPv6 ND messages are
documented in [RFC6980]. These concerns are addressed when the OMNI
interface employs the OAL instead of directly fragmenting the IPv6 ND
message itself. For this reason, OMNI interfaces MUST NOT send IPv6
ND messages larger than the OMNI interface MTU, and MUST employ OAL
encapsulation and fragmentation for IPv6 ND messages larger than the
minimum/path MPS for this OAL destination.
Unless the path is secured at the network-layer or below (i.e., in
environments where spoofing is possible), OMNI interfaces MUST NOT
send ordinary carrier packets with Identification values outside the
current window and MUST secure IPv6 ND messages used for address
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resolution or window state synchronization. OAL destinations SHOULD
therefore discard without reassembling any out-of-window OAL
fragments received over an unsecured path.
6.11. OAL Super-Packets
By default, the OAL source includes a 40-byte IPv6 encapsulation
header for each original IP packet during OAL encapsulation. The OAL
source also calculates and appends a 2 octet trailing Checksum field
then performs fragmentation such that a copy of the 40-byte IPv6
header plus an 8-byte IPv6 Fragment Header is included in each OAL
fragment (when a Routing Header is added, the OAL encapsulation
headers become larger still). However, these encapsulations may
represent excessive overhead in some environments. OAL header
compression can dramatically reduce the amount of encapsulation
overhead, however a complimentary technique known as "packing" (see:
[I-D.ietf-intarea-tunnels]) supports encapsulation of multiple
original IP packets and/or control messages within a single OAL
"super-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 MRU, it can concatenate them into a super-packet
encapsulated in a single OAL header and trailing Checksum field.
Within the OAL super-packet, the IP header of the first original IP
packet (iHa) followed by its data (iDa) is concatenated immediately
following the OAL header, then the IP header of the next original
packet (iHb) followed by its data (iDb) is concatenated immediately
following the first original packet, etc. with the trailing Checksum
field included last. The OAL super-packet format is transposed from
[I-D.ietf-intarea-tunnels] and shown in Figure 10:
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<------- Original IP packets ------->
+-----+-----+
| iHa | iDa |
+-----+-----+
|
| +-----+-----+
| | iHb | iDb |
| +-----+-----+
| |
| | +-----+-----+
| | | iHc | iDc |
| | +-----+-----+
| | |
v v v
+----------+-----+-----+-----+-----+-----+-----+----+
| OAL Hdr | iHa | iDa | iHb | iDb | iHc | iDc |Csum|
+----------+-----+-----+-----+-----+-----+-----+----+
<--- OAL "Super-Packet" with single OAL Hdr/Csum --->
Figure 10: OAL Super-Packet Format
When the OAL source prepares a super-packet, it applies OAL
fragmentation and *NET encapsulation then sends the resulting carrier
packets to the OAL destination. When the OAL destination receives
the super-packet it reassembles if necessary, verifies the checksum,
removes the trailing Checksum field, then regards the remaining OAL
header Payload Length as the sum of the lengths of all payload
packets. The OAL destination then selectively extracts each original
IP packet (e.g., by setting pointers into the super-packet buffer and
maintaining a reference count, by copying each packet into a separate
buffer, etc.) and forwards each packet to the network layer. During
extraction, the OAL determines the IP protocol version of each
successive original IP packet 'j' by examining the four most-
significant bits of iH(j), and determines the length of the packet by
examining the rest of iH(j) according to the IP protocol version.
When an OAL source prepares a super-packet that includes an IPv6 ND
message with an authentication signature or checksum as the first
original IP packet (i.e., iHa/iDa), it calculates the authentication
signature or checksum over the remainder of super-packet up to but
not including the trailing OAL Checksum field. Security and
integrity for forwarding initial protocol data packets in conjunction
with IPv6 ND messages used to establish NCE state are therefore
supported.
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6.12. OAL Bubbles
OAL sources may send NULL OAL packets known as "bubbles" for the
purpose of establishing Network Address Translator (NAT) state on the
path to the OAL destination. The OAL source prepares a bubble by
crafting an OAL header with appropriate IPv6 source and destination
ULAs, with the IPv6 Next Header field set to the value 59 ("No Next
Header" - see [RFC8200]) and with only the trailing OAL Checksum
field (i.e., and no protocol data) immediately following the IPv6
header.
The OAL source includes a random Identification value then
encapsulates the OAL packet in *NET headers destined to either the
mapped address of the OAL destination's first-hop ingress NAT or the
INADDR of the OAL destination itself. When the OAL source sends the
resulting carrier packet, any egress NATs in the path toward the *NET
destination will establish state based on the activity but the bubble
will be harmlessly discarded by either an ingress NAT on the path to
the OAL destination or by the OAL destination itself.
The bubble concept for establishing NAT state originated in [RFC4380]
and was later updated by [RFC6081]. OAL bubbles may be employed by
mobility services such as [I-D.templin-6man-aero].
7. Frame Format
When the OMNI interface forwards original IP packets from the network
layer it first invokes the OAL to create OAL packets/fragments if
necessary, then includes any *NET encapsulations and finally engages
the native frame format of the underlying 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.
See Figure 2 for a map of the various *NET 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 underlying
interface.
8. Link-Local Addresses (LLAs)
OMNI interfaces assign IPv6 Link-Local Addresses (LLAs) through pre-
service administrative actions. Clients assign "MNP-LLAs" with
interface identifiers that embed the Client's unique MNP, while
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Proxy/Servers assign "ADM-LLAs" that include an administrative ID
guaranteed to be unique on the link. LLAs are configured as follows:
o IPv6 MNP-LLAs encode the most-significant 64 bits of an MNP within
the least-significant 64 bits of the IPv6 link-local prefix
fe80::/64, i.e., in the LLA "interface identifier" portion. The
prefix length for the LLA is determined by adding 64 to the MNP
prefix length. For example, for the MNP 2001:db8:1000:2000::/56
the corresponding MNP-LLA prefix is fe80::2001:db8:1000:2000/120.
(The base MNP-LLA for each "/N" prefix sets the final 128-N bits
to 0, but all MNP-LLAs that match the prefix are also accepted.)
Non-MNP routes are also represented the same as for MNP-LLAs, but
include a GUA prefix that is not properly covered by the MSP.
o IPv4-mapped MNP-LLAs are constructed as fe80::ffff:[IPv4], i.e.,
the interface identifier consists of 16 '0' bits, followed by 16
'1' bits, followed by a 32bit IPv4 address/prefix. The prefix
length for the LLA is determined by adding 96 to the MNP prefix
length. For example, the IPv4-mapped MNP-LLA for 192.0.2.0/24 is
fe80::ffff:192.0.2.0/120, also written as
fe80::ffff:c000:0200/120. (The base MNP-LLA for each "/N" prefix
sets the final 128-N bits to 0, but all MNP-LLAs that match the
prefix are also accepted.)
o ADM-LLAs are assigned to Proxy/Servers (and possibly other SRT
infrastructure elements) and MUST be managed for uniqueness. The
upper 96 bits of the LLA encode the prefix fe80::/96, and the
lower 32 bits include a unique integer "MSID" value between
0x00000001 and 0xfeffffff, e.g., as in fe80::1, fe80::2, fe80::3,
etc., fe80::feffffff. The ADM-LLA prefix length is determined by
adding 96 to the MSID prefix length. For example, if the prefix
length for MSID 0x10012001 is 16 then the ADM-LLA prefix length is
set to 112 and the LLA is written as fe80::1001:2001/112. The
"zero" address for each ADM-LLA prefix is the Subnet-Router
anycast address for that prefix [RFC4291]; for example, the
Subnet-Router anycast address for fe80::1001:2001/112 is simply
fe80::1001:2000. The MSID range 0xff000000 through 0xffffffff is
reserved for future use.
Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no
MNPs can be allocated from that block ensuring that there is no
possibility for overlap between the different MNP- and ADM-LLA
constructs discussed above.
Since MNP-LLAs are based on the distribution of administratively
assured unique MNPs, and since ADM-LLAs are guaranteed unique through
administrative assignment, OMNI interfaces set the autoconfiguration
variable DupAddrDetectTransmits to 0 [RFC4862].
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Note: If future protocol extensions relax the 64-bit boundary in IPv6
addressing, the additional prefix bits of an MNP could be encoded in
bits 16 through 63 of the MNP-LLA. (The most-significant 64 bits
would therefore still be in bits 64-127, and the remaining bits would
appear in bits 16 through 48.) However, the analysis provided in
[RFC7421] suggests that the 64-bit boundary will remain in the IPv6
architecture for the foreseeable future.
Note: Even though this document honors the 64-bit boundary in IPv6
addressing, it specifies prefix lengths longer than /64 for routing
purposes. This effectively extends IPv6 routing determination into
the interface identifier portion of the IPv6 address, but it does not
redefine the 64-bit boundary. Modern routing protocol
implementations honor IPv6 prefixes of all lengths, up to and
including /128.
9. Unique-Local Addresses (ULAs)
OMNI domains use IPv6 Unique-Local Addresses (ULAs) as the source and
destination addresses in OAL packet IPv6 encapsulation headers. ULAs
are only routable within the scope of a an OMNI domain, and are
derived from the IPv6 Unique Local Address prefix fc00::/7 followed
by the L bit set to 1 (i.e., as fd00::/8) followed by a 40-bit
pseudo-random Global ID to produce the prefix [ULA]::/48, which is
then followed by a 16-bit Subnet ID then finally followed by a 64 bit
Interface ID as specified in Section 3 of [RFC4193]. All nodes in
the same OMNI domain configure the same 40-bit Global ID as the OMNI
domain identifier. The statistic uniqueness of the 40-bit pseudo-
random Global ID allows different OMNI domains to be joined together
in the future without requiring renumbering.
Each OMNI link instance is identified by a 16-bit Subnet ID value
between 0x0000 and 0xfeff in bits 48-63 of [ULA]::/48. The Subnet ID
values 0xff00 through 0xfffe are reserved for future use, while
0xffff denotes the presence of a Temporary ULA (see below). For
example, OMNI ULAs associated with instance 0 are configured from the
prefix [ULA]:0000::/64, instance 1 from [ULA]:0001::/64, instance 2
from [ULA]:0002::/64, etc. ULAs and their associated prefix lengths
are configured in correspondence with LLAs through stateless prefix
translation where "MNP-ULAs" are assigned in correspondence to MNP-
LLAs and "ADM-ULAs" are assigned in correspondence to ADM-LLAs. For
example, for OMNI link instance [ULA]:1010::/64:
o the MNP-ULA corresponding to the MNP-LLA fe80::2001:db8:1:2 with a
56-bit MNP length is derived by copying the lower 64 bits of the
LLA into the lower 64 bits of the ULA as
[ULA]:1010:2001:db8:1:2/120 (where, the ULA prefix length becomes
64 plus the IPv6 MNP length).
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o the MNP-ULA corresponding to fe80::ffff:192.0.2.0 with a 28-bit
MNP length is derived by simply writing the LLA interface ID into
the lower 64 bits as [ULA]:1010:0:ffff:192.0.2.0/124 (where, the
ULA prefix length is 64 plus 32 plus the IPv4 MNP length).
o the ADM-ULA corresponding to fe80::1000/112 is simply
[ULA]:1010::1000/112.
o the ADM-ULA corresponding to fe80::/128 is simply
[ULA]:1010::/128.
o etc.
The ULA presents an IPv6 address format that is routable within the
OMNI routing system and can be used to convey link-scoped IPv6 ND
messages across multiple hops using IPv6 encapsulation [RFC2473].
The OMNI link extends across one or more underling Internetworks to
include all Proxy/Servers. All Clients are also considered to be
connected to the OMNI link, however unnecessary encapsulations are
omitted whenever possible to conserve bandwidth (see: Section 14).
Temporary ULAs are constructed per [RFC8981] based on the prefix
[ULA]:ffff::/64 and used by Clients when they have no other
addresses. Temporary ULAs can be used for Client-to-Client
communications outside the context of any supporting OMNI link
infrastructure, and can also be used as an initial address while the
Client is in the process of procuring an MNP. Temporary ULAs are not
routable within the OMNI routing system, and are therefore useful
only for OMNI link "edge" communications. Temporary ULAs employ
optimistic DAD principles [RFC4429] since they are probabilistically
unique.
Each OMNI link may be subdivided into SRT segments that often
correspond to different administrative domains or physical
partitions. OMNI nodes can use Segment Routing [RFC8402] to support
efficient forwarding to destinations located in other OMNI link
segments. A full discussion of Segment Routing over the OMNI link
appears in [I-D.templin-6man-aero].
Note: IPv6 ULAs taken from the prefix fc00::/7 followed by the L bit
set to 0 (i.e., as fc00::/8) are never used for OMNI OAL addressing,
however the range could be used for MSP/MNP addressing under certain
limiting conditions (see: Section 10).
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10. Global Unicast Addresses (GUAs)
OMNI domains use IP Global Unicast Address (GUA) prefixes [RFC4291]
as Mobility Service Prefixes (MSPs) from which Mobile Network
Prefixes (MNP) are delegated to Clients. Fixed correspondent node
networks reachable from the OMNI domain are represented by non-MNP
GUA prefixes that are not derived from the MSP, but are treated in
all other ways the same as for MNPs.
For IPv6, GUA MSPs are assigned by IANA [IPV6-GUA] and/or an
associated regional assigned numbers authority such that the OMNI
domain can be interconnected to the global IPv6 Internet without
causing inconsistencies in the routing system. An OMNI domain could
instead use ULAs with the 'L' bit set to 0 (i.e., from the prefix
fc00::/8)[RFC4193], however this would require IPv6 NAT if the domain
were ever connected to the global IPv6 Internet.
For IPv4, GUA MSPs are assigned by IANA [IPV4-GUA] and/or an
associated regional assigned numbers authority such that the OMNI
domain can be interconnected to the global IPv4 Internet without
causing routing inconsistencies. An OMNI domain could instead use
private IPv4 prefixes (e.g., 10.0.0.0/8, etc.) [RFC3330], however
this would require IPv4 NAT if the domain were ever connected to the
global IPv4 Internet. OMNI interfaces advertise IPv4 MSPs into IPv6
routing systems as IPv4-mapped IPv6 prefixes [RFC4291] (e.g., the
IPv6 prefix for the IPv4 MSP 192.0.2.0/24 is ::ffff:192.0.2.0/120).
OMNI interfaces assign the IPv4 anycast address TBD3, and IPv4
routers that configure OMNI interfaces advertise the prefix TBD3/N
into the routing system of other networks (see: IANA Considerations).
OMNI interfaces also configure global IPv6 anycast addresses formed
according to [RFC3056] as:
2002:TBD3[32]:MNP[64]:Link_ID[16]
where TBD3[32] is the 32 bit IPv4 anycast address, MNP[64] encodes an
MSP zero-padded to 64 bits (if necessary) and Link_ID[16] encodes a
16 bit value between 0 and 0xfffe that identifies a specific OMNI
link within an OMNI domain (the Link_ID value 0xffff is an OMNI link
"anycast" value configured by all OMNI interfaces within the same
domain). For example, the OMNI IPv6 anycast address for MSP
2001:db8::/32 is 2002:TBD3[32]:2001:db8:0:0:Link_ID[16], the OMNI
IPv6 anycast address for MSP 192.0.2.0/24 is
2002:TBD3[32]:0000:ffff:c000:0200:Link_ID[16], etc.).
OMNI interfaces assign OMNI IPv6 anycast addresses, and IPv6 routers
that configure OMNI interfaces advertise the corresponding prefixes
into the routing system of other networks. An OMNI IPv6 anycast
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prefix is formed the same as for any IPv6 prefix; for example, the
prefix 2002:TBD3[32]:2001:db8::/80 matches all OMNI IPv6 anycast
addresses covered by the prefix. By advertising OMNI IPv6 anycast
prefixes in this way, OMNI Clients can locate and associate with the
OMNI domain and/or a specific link within the OMNI domain that
services the MSP of interest.
OMNI interfaces use OMNI IPv6 and IPv4 anycast addresses to support
Service Discovery in the spirit of [RFC7094], i.e., the addresses are
not intended for use in long-term transport protocol sessions.
Specific applications for OMNI IPv6 and IPv4 anycast addresses are
discussed throughout the document as well as in
[I-D.templin-6man-aero].
11. Node Identification
OMNI Clients and Proxy/Servers that connect over open Internetworks
include a unique node identification value for themselves in the OMNI
options of their IPv6 ND messages (see: Section 12.2.12). An example
identification value alternative is the Host Identity Tag (HIT) as
specified in [RFC7401], while Hierarchical HITs (HHITs)
[I-D.ietf-drip-rid] may be more appropriate for certain domains such
as the Unmanned (Air) Traffic Management (UTM) service for Unmanned
Air Systems (UAS). Another example is the Universally Unique
IDentifier (UUID) [RFC4122] which can be self-generated by a node
without supporting infrastructure with very low probability of
collision.
When a Client is truly outside the context of any infrastructure, it
may have no MNP information at all. In that case, the Client can use
an IPv6 temporary ULA or (H)HIT as an IPv6 source/destination address
for sustained communications in Vehicle-to-Vehicle (V2V) and
(multihop) Vehicle-to-Infrastructure (V2I) scenarios. The Client can
also propagate the ULA/(H)HIT into the multihop routing tables of
(collective) Mobile/Vehicular Ad-hoc Networks (MANETs/VANETs) using
only the vehicles themselves as communications relays.
When a Client connects via a protected-spectrum ANET, an alternate
form of node identification (e.g., MAC address, serial number,
airframe identification value, VIN, etc.) embedded in an LLA/ULA may
be sufficient. The Client can then include OMNI "Node
Identification" sub-options (see: Section 12.2.12) in IPv6 ND
messages should the need to transmit identification information over
the network arise.
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12. Address Mapping - Unicast
OMNI interfaces maintain a neighbor cache for tracking per-neighbor
state and use the link-local address format specified in Section 8.
IPv6 Neighbor Discovery (ND) [RFC4861] messages sent over OMNI
interfaces without encapsulation observe the native underlying
interface Source/Target Link-Layer Address Option (S/TLLAO) format
(e.g., for Ethernet the S/TLLAO is specified in [RFC2464]). IPv6 ND
messages sent over OMNI interfaces using encapsulation do not include
S/TLLAOs, but instead include a new option type that encodes
encapsulation addresses, interface attributes and other OMNI link
information. Hence, this document does not define an S/TLLAO format
but instead defines a new option type termed the "OMNI option"
designed for these purposes. (Note that OMNI interface IPv6 ND
messages sent without encapsulation may include both OMNI options and
S/TLLAOs, but the information conveyed in each is mutually
exclusive.)
OMNI interfaces prepare IPv6 ND messages that include one or more
OMNI options (and any other IPv6 ND options) then completely populate
all option information. If the OMNI interface includes an
authentication signature, it sets the IPv6 ND message Checksum field
to 0 and calculates the authentication signature over the length of
the entire OAL packet or super-packet (beginning with a pseudo-header
of the IPv6 ND message IPv6 header up to but not including the
trailing OAL Checksum field) but does not calculate/include the IPv6
ND message checksum itself. Otherwise, the OMNI interface calculates
the standard IPv6 ND message checksum over the entire OAL packet or
super-packet and writes the value in the Checksum field noting that
optimized implementations can verify both the OAL and IPv6 ND message
checksums in a single pass over the message data. OMNI interfaces
verify authentication and/or integrity of each IPv6 ND message
received according to the specific check(s) included, and process the
message further only following verification.
OMNI interface Clients such as aircraft typically have multiple
wireless data link types (e.g. satellite-based, cellular,
terrestrial, air-to-air directional, etc.) with diverse performance,
cost and availability properties. The OMNI interface would therefore
appear to have multiple L2 connections, and may include information
for multiple underlying 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.
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12.1. The OMNI Option
OMNI options appear in IPv6 ND messages formatted as shown in
Figure 11:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-Options ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: OMNI Option Format
In this format:
o Type is set to TBD4 (see: IANA Considerations).
o Length is set to the number of 8 octet blocks in the option. The
value 0 is invalid, while the values 1 through 255 (i.e., 8
through 2040 octets, respectively) indicate the total length of
the OMNI option. If multiple OMNI option instances appear in the
same IPv6 ND message, the union of the contents of all OMNI
options is accepted unless otherwise qualified for specific sub-
options below.
o Sub-Options is a Variable-length field padded if necessary such
that the complete OMNI Option is an integer multiple of 8 octets
long. Sub-Options contains zero or more sub-options as specified
in Section 12.2.
The OMNI option is included in all OMNI interface IPv6 ND messages;
the option is processed by receiving interfaces that recognize it and
otherwise ignored. The OMNI interface processes all OMNI option
instances received in the same IPv6 ND message in the consecutive
order in which they appear. The OMNI option(s) included in each IPv6
ND message may include full or partial information for the neighbor.
The OMNI interface therefore retains the union of the information in
the most recently received OMNI options in the corresponding NCE.
12.2. OMNI Sub-Options
Each OMNI option includes a Sub-Options block containing zero or more
individual sub-options. Each consecutive sub-option is concatenated
immediately following its predecessor. All sub-options except Pad1
(see below) are in an OMNI-specific type-length-value (TLV) format
encoded as follows:
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0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Sub-Type| Sub-Length | Sub-Option Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 12: Sub-Option Format
o Sub-Type is a 5-bit field that encodes the sub-option type. Sub-
option types defined in this document are:
Sub-Option Name Sub-Type
Pad1 0
PadN 1
Interface Attributes 2
Multilink Fwding Parameters 3
Traffic Selector 4
Geo Coordinates 5
DHCPv6 Message 6
HIP Message 7
PIM-SM Message 8
Reassembly Limit 9
Fragmentation Report 10
Node Identification 11
ICMPv6 Error 12
QUIC-TLS Message 13
Proxy/Server Departure 14
OMNI Header Extension 15
Sub-Type Extension 30
Figure 13
Sub-Types 16-29 are available for future assignment for major
protocol functions. Sub-Type 31 is reserved by IANA.
o Sub-Length is an 11-bit field that encodes the length of the Sub-
Option Data in octets.
o Sub-Option Data is a block of data with format determined by Sub-
Type and length determined by Sub-Length. Note that each
individual sub-option may end on an arbitrary octet boundary,
whereas the OMNI option itself must include padding if necessary
for 8-octet alignment.
The OMNI interface codes each sub-option with a 2 octet header that
includes Sub-Type in the most significant 5 bits followed by Sub-
Length in the next most significant 11 bits. Each sub-option encodes
a maximum Sub-Length value of 2038 octets minus the lengths of the
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OMNI option header and any preceding sub-options. This allows ample
Sub-Option Data space for coding large objects (e.g., ASCII strings,
domain names, protocol messages, security codes, etc.), while a
single OMNI option is limited to 2040 octets the same as for any IPv6
ND option.
The OMNI interface codes initial sub-options in a first OMNI option
instance and subsequent sub-options in additional instances in the
same IPv6 ND message in the intended order of processing. The OMNI
interface can then code any remaining sub-options in additional IPv6
ND messages if necessary. Implementations must observe these size
limits and refrain from sending IPv6 ND messages larger than the OMNI
interface MTU.
The OMNI interface processes all OMNI option Sub-Options received in
an IPv6 ND message while skipping over and ignoring any unrecognized
sub-options. The OMNI interface processes the Sub-Options of all
OMNI option instances in the consecutive order in which they appear
in the IPv6 ND message, beginning with the first instance and
continuing through any additional instances to the end of the
message. If an individual sub-option length would cause processing
to exceed the OMNI option instance and/or IPv6 ND message lengths,
the OMNI interface accepts any sub-options already processed and
ignores the remainder of that instance. The interface then processes
any remaining OMNI option instances in the same fashion to the end of
the IPv6 ND message.
When an OMNI interface includes an authentication sub-option (e.g.,
see: Section 12.2.8), it MUST appear as the first sub-option of the
first OMNI option which must appear immediately following the IPv6 ND
message header. If the IPv6 ND message includes additional
authentication sub-options, only the first sub-option is processed
and all others are ignored. If the IPv6 ND message is the first
packet in a combined OAL super-packet, the OMNI interface calculates
the authentication signature over the entire length of the super-
packet, i.e., and not just to the end of the IPv6 ND message itself.
(When no authentication sub-option is included, the OMNI interface
instead calculates the IPv6 ND message checksum over the entire
length of the packet/super-packet.)
When a Client OMNI interface prepares a secured unicast RS message,
it includes an Interface Attributes sub-option specific to the
underlying interface that will transmit the RS (see: Section 12.2.3)
immediately following the authentication and header extension sub-
options if present; otherwise as the first sub-option of the first
OMNI option which must appear immediately following the IPv6 ND
message header. When a Client OMNI interface prepares a secured
unicast NS message, it instead includes a Multilink Forwarding
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Parameters sub-option specific to the underlying interface that will
transmit the NS (see: Section 12.2.4).
Note: large objects that exceed the maximum Sub-Option Data length
are not supported under the current specification; if this proves to
be limiting in practice, future specifications may define support for
fragmenting large sub-options across multiple OMNI options within the
same IPv6 ND message (or even across multiple IPv6 ND messages, if
necessary).
The following sub-option types and formats are defined in this
document:
12.2.1. Pad1
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| S-Type=0|x|x|x|
+-+-+-+-+-+-+-+-+
Figure 14: Pad1
o Sub-Type is set to 0. If multiple instances appear in OMNI
options of the same message all are processed.
o Sub-Type is followed by 3 'x' bits, set to any value on
transmission (typically all-zeros) and ignored on reception. Pad1
therefore consists of 1 octet with the most significant 5 bits set
to 0, and with no Sub-Length or Sub-Option Data fields following.
If more than one octet of padding is required, the PadN option,
described next, should be used, rather than multiple Pad1 options.
12.2.2. PadN
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| S-Type=1| Sub-length=N | N padding octets ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 15: PadN
o Sub-Type is set to 1. If multiple instances appear in OMNI
options of the same message all are processed.
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o Sub-Length is set to N that encodes the number of padding octets
that follow.
o Sub-Option Data consists of N octets, set to any value on
transmission (typically all-zeros) and ignored on receipt.
When a proxy forwards an IPv6 ND message with OMNI options, it can
employ PadN to cancel any sub-options (other than Pad1) that should
not be processed by the next hop by simply writing the value '1' over
the Sub-Type. When the proxy alters the IPv6 ND message contents in
this way, any included authentication and integrity checks are
invalidated. See: Appendix B for a discussion of IPv6 ND message
authentication and integrity.
12.2.3. Interface Attributes
The Interface Attributes sub-option provides neighbors with
forwarding information for the multilink conceptual sending algorithm
discussed in Section 14. Neighbors use the forwarding information to
selecting among potentially multiple candidate underlying interfaces
that can be used to forward carrier packets to the neighbor based on
factors such as traffic selectors and link quality. Interface
Attributes further include link-layer address information to be used
for either direct INET encapsulation for targets in the local SRT
segment or spanning tree forwarding for targets in remote SRT
segments.
OMNI nodes include Interface Attributes for some/all of a target
Client's underlying interfaces in NS/NA and uNA messages used to
publish Client information (see: [I-D.templin-6man-aero]). At most
one Interface Attributes sub-option for each distinct omIndex may be
included; if an NS/NA message includes multiple Interface Attributes
sub-options for the same omIndex, the first is processed and all
others are ignored. OMNI nodes that receive NS/NA messages can use
all of the included Interface Attributes and/or Traffic Selectors to
formulate a map of the prospective target node as well as to seed the
information to be populated in a Multilink Forwarding Parameters sub-
option (see: Section 12.2.4).
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 omIndex
corresponding to the Client's underlying 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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OMNI Client RS and Proxy/Server RA messages MUST include the
Interface Attributes sub-option for the Client underlying interface
in the first OMNI option immediately following an authentication
message sub-option if present; otherwise, immediately following the
OMNI header. When an FHS Proxy/Server receives an RS message
destined to an anycast *NET address, it MUST include an Interface
Attributes sub-option with omIndex '0' that encodes a unicast *NET
INADDR immediately after the Interface Attributes sub-option for the
Client's underlying interface in the solicited RA response. Any
additional Interface Attributes sub-options that appear in RS/RA
messages are ignored.
The Interface Attributes sub-options are formatted as shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=2| Sub-length=N | omIndex | omType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Provider ID | Link | Resvd | FMT | SRT | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ LHS Proxy/Server MSID/INADDR ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: Interface Attributes
o Sub-Type is set to 2.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
o Sub-Option Data contains an "Interface Attributes" option encoded
as follows:
* omIndex is a 1-octet value corresponding to a specific
underlying interface. Client OMNI interfaces MUST number each
distinct underlying interface with an omIndex value between '1'
and '255' that represents a Client-specific 8-bit mapping for
the actual ifIndex value assigned by network management
[RFC2863], then set omIndex to either a specific omIndex value
or '0' to denote "unspecified".
* omType is set to an 8-bit integer value corresponding to the
underlying interface identified by omIndex. The value
represents an OMNI interface-specific 8-bit mapping for the
actual IANA ifType value registered in the 'IANAifType-MIB'
registry [http://www.iana.org].
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* Provider ID is set to an OMNI interface-specific 8-bit ID value
for the network service provider associated with this omIndex.
* Link encodes a 4-bit link metric. The value '0' means the link
is DOWN, and the remaining values mean the link is UP with
metric ranging from '1' ("lowest") to '15' ("highest").
* Resvd is a 4-bit Reserved field set to 0 on transmission and
ignored on reception.
* FMT - a 3-bit "Forward/Mode/Type" code interpreted as follows:
+ The most significant two bits (i.e., "FMT-Forward" and "FMT-
Mode") are interpreted in conjunction with one another.
When FMT-Forward is clear, the LHS Proxy/Server performs OAL
reassembly and decapsulation to obtain the original IP
packet before forwarding. If the FMT-Mode bit is clear, the
LHS Proxy/Server then forwards the original IP packet at
layer 3; otherwise, it invokes the OAL to re-encapsulate,
re-fragment and forwards the resulting carrier packets to
the Client via the selected underlying interface. When FMT-
Forward is set, the LHS Proxy/Server forwards unsecured OAL
fragments to the Client without reassembling, while
reassembling secured OAL fragments before re-fragmenting and
forwarding to the Client. If FMT-Mode is clear, all carrier
packets destined to the Client must always be forwarded
through 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.
+ The least significant bit (i.e., "FMT-Type") determines the
length of the LHS Proxy/Server INADDR field for NS/NA
messages; if FMT-Type is clear, INADDR includes a 4-octet
IPv4 address (otherwise a 16-octet IPv6 address). For RS/RA
messages, the LHS Proxy/Server INADDR field is always
exactly 16 octets. If FMT-type is clear, INADDR encodes an
IPv4-mapped IPv6 address; otherwise an ordinary IPv6
address.
* SRT - a 5-bit Segment Routing Topology prefix length value that
(when added to 96) determines the prefix length to apply to the
ULA formed from concatenating [ULA*]::/96 with the 32 bit LHS
MSID value that follows. For example, the value 16 corresponds
to the prefix length 112.
* LHS Proxy/Server MSID/INADDR - the first 32 bits includes the
MSID of the LHS Proxy/Server on the path from a source neighbor
to the target Client's underlying interface. When SRT and MSID
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are both set to 0, the LHS Proxy/Server is considered
unspecified in this IPv6 ND message. FMT, SRT and LHS together
provide guidance for the OMNI interface forwarding algorithm.
Specifically, if SRT/LHS is located in the local OMNI link
segment, then the source can reach the target Client either
through its dependent Proxy/Server or through direct
encapsulation following NAT traversal according to FMT.
Otherwise, the target Client is located on a different SRT
segment and the path from the source must employ a combination
of route optimization and spanning tree hop traversals. INADDR
identifies the LHS Proxy/Server's INET-facing interface not
located behind NATs, therefore no UDP port number is included
since port number 8060 is used when the *NET encapsulation
includes a UDP header. Instead, INADDR includes only a 4-octet
IPv4 or 16-octet IPv6 address with type and length determined
by FMT-Type. The IP address is recorded in network byte order
in ones-compliment "obfuscated" form per [RFC4380].
12.2.4. Multilink Forwarding Parameters
OMNI nodes include the Multilink Forwarding Parameters sub-option in
NS/NA messages used to coordinate with multilink route optimization
targets. If an NS message includes the sub-option, the solicited NA
response must also include the sub-option. The OMNI node MUST
include the sub-option in the first OMNI option immediately following
an authentication message sub-option. Otherwise, the OMNI node MUST
include the sub-option immediately following the OMNI header. Each
NS/NA message may contain at most one Multilink Forwarding Parameters
sub-option; if an NS/NA message contains additional Multlink
Forwarding Parameters sub-options, the first is processed and all
others are ignored.
When an NS/NA message includes the sub-option, the FHS Client omIndex
MUST correspond to the underlying interface used to transmit the
message. When the NS/NA message also includes Interface Attributes
sub-options any that include the same FHS/LHS Client omIndex are
ignored while all others are processed.
The Multilink Forwarding Parameters sub-option includes the necessary
state for establishing Multilink Forwarding Vectors (MFVs) in the
Multilink Forwarding Information Bases (MFIBs) of the OAL source,
destination and intermediate nodes in the path. The sub-option also
records addressing information for FHS/LHS nodes on the path,
including "INADDRs" which MUST be unicast IP encapsulation addresses
(i.e., and not anycast/multicast). The manner for populating
multilink forwarding information is specified in detail in
[I-D.templin-6man-aero].
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The Multilink Forwarding Parameters sub-option is formatted as shown
in Figure 17:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=3| Sub-length=N |Job| A | B | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ Multilink Forwarding Vector Index (MFVI) List ~
~ (5 consecutive 4-octet MFVIs) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Tunnel Window Synchronization Parameters ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|FHS Cli omIndex| omType | Provider ID | Link | Resvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FMT | SRT | ~
+-+-+-+-+-+-+-+-+ ~
~ FHS Proxy/Server MSID/INADDR ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ FHS Bridge MSID/INADDR ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|LHS Cli omIndex| omType | Provider ID | Link | Resvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FMT | SRT | ~
+-+-+-+-+-+-+-+-+ ~
~ LHS Proxy/Server MSID/INADDR ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ LHS Bridge MSID/INADDR ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: Multilink Forwarding Parameters
o Sub-Type is set to 3. If multiple instances appear in the same
message (i.e., whether in a single OMNI option or multiple) the
first instance is processed and all others are ignored.
o Sub-Length encodes the number of Sub-Option Data octets that
follow. The length includes all fields up to and including the
Tunnel Window Synchronization Parameters for all Job codes, while
including the remaining fields only for Job codes "00" and "01"
(see below).
o Sub-Option Data contains Multilink Forwarding Parameters as
follows:
* Job/A/B is a 1-octet field that determines per-hop processing
of the MFVI List, where A is a 3-bit count of the number of "A"
MVFI List entries and B is a 3-bit count of the number of "B"
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MVFI List entries (valid A/B values are 0-5). Job is a 2-bit
code interpreted as follows:
+ 00 - "Initialize; Build B" - the FHS source sets this code
in an NS used to initialize MFV state (any other messages
that include this code MUST be dropped). The FHS source
first sets A/B to 0, and the FHS source and each
intermediate node along the path to the LHS destination that
processes the message creates a new MFV. Each node that
processes the message then assigns a unique 4-octet "B" MFVI
to the MVF and also writes the value into list entry B, then
increments B. When the message arrives at the LHS
destination, B will contain the number of MFVI List "B"
entries, with the FHS source entry first, followed by
entries for each consecutive intermediate node and ending
with an entry for the final intermediate node (i.e., the
list is populated in the forward direction).
+ 01 - "Follow B; Build A" - the LHS source sets this code in
a solicited NA response to a solicitation with code "00"
(any other messages that include this code MUST be dropped).
The LHS source first copies the MFVI List and B value from
the code "00" solicitation into these fields and sets A to
0. The LHS source and each intermediate node along the path
to the FHS destination that processes the message then uses
MFVI List entry B to locate the corresponding MFV. Each
node that processes the message then assigns a unique
4-octet "A" MFVI to the MVF and also writes the value into
list entry B, then increments A and decrements B. When the
message arrives at the FHS destination, A will contain the
number of MFVI List "A" entries, with the LHS source entry
last, preceded by entries for each consecutive intermediate
node and beginning with an entry for the final intermediate
node (i.e., the list is populated in the reverse direction).
+ 10 - "Follow A; Record B" - the FHS node that sent the
original code "00" solicitation and received the
corresponding code "01" advertisement sets this code in any
subsequent NS/NA messages sent to the same LHS destination.
The FHS source copies the MVFI List and A value from the
code "01" advertisement into these fields and sets B to 0.
The FHS source and each intermediate node along the path to
the LHS destination that processes the message then uses the
"A" MFVI found at list entry B to locate the corresponding
MFV. Each node that processes the message then writes the
MVF's "B" MFVI into list entry B, then decrements A and
increments B. When the message arrives at the LHS
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destination, B will contain the number of MFVI List "B"
entries populated in the forward direction.
+ 11 - "Follow B; Record A" - the LHS node that received the
original code "00" solicitation and sent the corresponding
code "01" advertisement sets this code in any subsequent NS/
NA messages sent to the same FHS destination. The LHS
source copies the MVFI List and B values from the code "00"
solicitation into these fields and sets A to 0. The LHS
source and each intermediate node along the path to the FHS
destination that processes the message then uses the "B"
MFVI List entry found at list entry B to locate the
corresponding MFV. Each node that processes the message
then writes the MFV's "A" MFVI into list entry B, then
increments A and decrements B. When the message arrives at
the FHS destination, A will contain the number of MFVI List
"A" entries populated in the reverse direction.
Job/A/B together determine the per-hop behavior at each FHS/LHS
source, intermediate node and destination that processes an
IPv6 ND message. When a Job code specifies "Initialize", each
FHS/LHS node that processes the message creates a new MVF.
When a Job code specifies "Build", each node that processes the
message assigns a new MFVI. When a Job code specifies
"Follow", each node that processes the message uses an A/B MFVI
List entry to locate an MFV (if the MFV cannot be located, the
node returns a parameter problem and drops the message). Using
this algorithm, FHS sources that send code "00" solicitations
and receive code "01 advertisements discover only "A"
information, while LHS sources that receive code "00"
solicitations and return code "01" advertisements discover only
"B" information. FHS/LHS intermediate nodes can instead
examine A, B and the MFVI List to determine the number of
previous hops, the number of remaining hops, and the A/B MFVIs
associated with the previous/remaining hops. However, no
intermediate nodes will discover inappropriate A/B MFVIs for
their location in the multihop forwarding chain. See:
[I-D.templin-6man-aero] for further discussion on A/B MFVI
processing.
* Multilink Forwarding Vector Index (MFVI) List is a 20-octet
block that contains 5 consecutive 4-octet MFVI entries. The
FHS/LHS source and each intermediate node on the path to the
destination processes the list according to the Job/A/B codes
(see above).
* Tunnel Window Synchronization Parameters is a 12-octet block
that consists of a 4-octet Sequence Number followed by a
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4-octet Acknowledgement Number followed by a 1-octet Flags
field followed by a 3-octet Window field (i.e., the same as for
the OMNI header parameters). Tunnel endpoints use these
parameters for simultaneous middlebox window synchronization in
a single solicitation/advertisement message exchange.
* For Job codes "00" and "01" only, two trailing state variable
blocks are included for First-Hop Segment (FHS) followed by
Last-Hop Segment (LHS) network elements. When present, each
block encodes the following information:
+ Client omIndex, omType, Provider ID and Resvd/Link are
1-octet fields (at offset 0 from the beginning of the Sub-
Option Data) that include link parameters for the Client
underlying interface. These fields are populated based on
information discovered in Interface Attributes sub-options
included in earlier RS/RA and/or NS/NA exchanges.
+ FMT/SRT is a 1-octet field with a 5-bit SRT prefix length
that applies to all elements in the segment. The FMT-
Forward/Mode bits determine the characteristics of the
Proxy/Server relationship for this specific Client
underlying interface (i.e., the same as described in
Section 12.2.3), and the FMT-Type bits determine the IP
address version for all INADDR fields relative to this SRT
segment. Unlike the case for Interface Attributes, all
INADDR fields are always 16 bits in length regardless of the
IP protocol version (for IPv4, INADDR is encoded as an
IPv4-mapped IPv6 address [RFC4291]). The IP address is
recoded in network byte order, and in ones-compliment
"obfuscated" form the same as described in Section 12.2.3.
+ Proxy/Server MSID/INADDR includes a 4-octet Proxy/Server
MSID followed by a 16 octet INADDR. INADDR identifies an
open INET interface not located behind NATs, therefore no
UDP port number is included since port number 8060 is used
when the *NET encapsulation includes a UDP header.
+ Bridge MSID/INADDR encodes a 4 octet MSID followed by a
16-octet INADDR exactly as for the Proxy/Server MSID/INADDR.
12.2.5. Traffic Selector
When used in conjunction with Interface Attributes and/or Multilink
Forwarding Parameters information, the Traffic Selector sub-option
provides forwarding information for the multilink conceptual sending
algorithm discussed in Section 14.
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IPv6 ND messages include Traffic Selectors for some or all of the
source/target Client's underlying interfaces. Traffic Selectors for
some or all of a target Client's underlying interfaces are also
included in uNA messages used to publish Client information changes.
See: [I-D.templin-6man-aero] for more information.
Traffic Selectors must be honored by all implementations in the
format shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=4| Sub-length=N | omIndex | TS Format |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ RFC 6088 Format Traffic Selector ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: Traffic Selector
o Sub-Type is set to 4. Each IPv6 ND message may contain zero or
more Traffic Selectors for each omIndex; when multiple Traffic
Selectors for the same omIndex appear, all are processed and the
cumulative information from all is accepted.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
o Sub-Option Data contains a "Traffic Selector" encoded as follows:
* omIndex is a 1-octet value corresponding to a specific
underlying interface the same as specified above for Interface
Attributes and Multilink Forwarding Parameters above. The OMNI
options of a single message may include multiple Traffic
Selector sub-options; each with the same or different omIndex
values.
* TS Format is a 1-octet field that encodes a Traffic Selector
version per [RFC6088]. If TS Format encodes the value 1 or 2,
the Traffic Selector includes IPv4 or IPv6 information,
respectively. If TS Format encodes any other value, the sub-
option is ignored.
* The remainder of the sub-option includes a traffic selector
formatted per [RFC6088] beginning with the "Flags (A-N)" field,
and with the Traffic Selector IP protocol version coded in the
TS Format field. If a single interface identified by omIndex
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requires Traffic Selectors for multiple IP protocol versions,
or if a Traffic Selector block would exceed the available
space, the remaining information is coded in additional Traffic
Selector sub-options that all encode the same omIndex.
12.2.6. Geo Coordinates
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=5| Sub-length=N | Geo Type |Geo Coordinates
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 19: Geo Coordinates Sub-option
o Sub-Type is set to 5. If multiple instances appear in OMNI
options of the same message all are processed.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
o 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.
o A set of Geo Coordinates of length up to the remaining available
space for this OMNI option. New formats to be specified in future
documents and may include attributes such as latitude/longitude,
altitude, heading, speed, etc.
12.2.7. Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Message
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) sub-option
may be included in the OMNI options of Client RS messages and Proxy/
Server RA messages. FHS Proxy/Servers that forward RS/RA messages
between a Client and an LHS Proxy/Server also forward DHCPv6 Sub-
Options unchanged. Note that DHCPv6 messages do not include a
Checksum field since integrity is protected by the IPv6 ND message
checksum, authentication signature and/or lower-layer authentication
and integrity checks.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=6| Sub-length=N | msg-type | id (octet 0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| transaction-id (octets 1-2) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
. DHCPv6 options .
. (variable number and length) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: DHCPv6 Message Sub-option
o Sub-Type is set to 6. If multiple instances appear in OMNI
options of the same message the first is processed and all others
are ignored.
o 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.
o 'msg-type' and 'transaction-id' are coded according to Section 8
of [RFC8415].
o A set of DHCPv6 options coded according to Section 21 of [RFC8415]
follows.
12.2.8. Host Identity Protocol (HIP) Message
The Host Identity Protocol (HIP) Message sub-option (when present)
provides authentication for IPv6 ND messages exchanged between
Clients and FHS Proxy/Servers over an open Internetwork. FHS Proxy/
Servers authenticate the HIP authentication signatures in source
Client IPv6 ND messages before securely forwarding them to other OMNI
nodes. LHS Proxy/Servers that receive secured IPv6 ND messages from
other OMNI nodes that do not already include a security sub-option
insert HIP authentication signatures before forwarding them to the
target Client.
OMNI interfaces MUST include the HIP message (when present) as the
first sub-option of the first OMNI option, which MUST appear
immediately following the IPv6 ND message header. OMNI interfaces
can therefore easily locate the HIP message and verify the
authentication signature without applying deep inspection. OMNI
interfaces that receive IPv6 ND messages without a HIP (or other
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authentication) sub-option instead verify the IPv6 ND message
checksum.
OMNI interfaces include the HIP message sub-option when they forward
IPv6 ND messages that require security over INET underlying
interfaces, i.e., where authentication and integrity is not already
assured by lower layers. The OMNI interface calculates the
authentication signature over the entire length of the OAL packet (or
super-packet) beginning with a pseudo-header of the IPv6 ND message
header and extending over the remainder of the OAL packet up to but
not including the trailing OAL Checksum field. OMNI interfaces that
process OAL packets that contain secured IPv6 ND messages verify the
signature then either process the rest of the message locally or
forward a proxyed copy to the next hop.
When a FHS Client inserts a HIP message sub-option in an NS/NA
message destined to a target in a remote spanning tree segment, it
must ensure that the insertion does not cause the message to exceed
the OMNI interface MTU. When the remote segment LHS Proxy/Server
forwards the NS/NA message from the spanning tree to the target
Client, it inserts a new HIP message sub-option if necessary while
overwriting or cancelling the (now defunct) HIP message sub-option
supplied by the FHS Client.
If the defunct HIP sub-option size was smaller than the space needed
for the LHS Client HIP message (or, if no defunct HIP sub-option is
present), the LHS Proxy/Server adjusts the space immediately
following the OMNI header by copying the preceding portion of the
IPv6 ND message into buffer headroom free space or copying the
remainder of the IPv6 ND message into buffer tailroom free space.
The LHS Proxy/Server then insets the new HIP sub-option immediately
after the OMNI header and immediately before the next sub-option
while properly overwriting the defunct sub-option if present.
If the defunct HIP sub-option size was larger than the space needed
for the LHS Client HIP message, the LHS Proxy/Server instead
overwrites the existing sub-option and writes a single Pad1 or PadN
sub-option over the next 1-2 octets to cancel the remainder of the
defunct sub-option. If the LHS Proxy/Server cannot create sufficient
space through any means without causing the OMNI option to exceed
2040 bytes or causing the IPv6 ND message to exceed the OMNI
interface MTU, it returns a suitable error (see: Section 12.2.13) and
drops the message.
The HIP message sub-option is formatted as shown below:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=7| Sub-length=N |0| Packet Type |Version| RES.|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Controls |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ HIP Parameters /
/ /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: HIP Message Sub-option
o Sub-Type is set to 7. If multiple instances appear in OMNI
options of the same message the first is processed and all others
are ignored.
o Sub-Length is set to N, i.e., the length of the option in octets
beginning immediately following the Sub-Length field and extending
to the end of the HIP parameters. The length of the entire HIP
message is therefore limited by the remaining available space for
this OMNI option.
o The HIP message is coded per Section 5 of [RFC7401], except that
the OMNI "Sub-Type" and "Sub-Length" fields replace the first 2
octets of the HIP message header (i.e., the Next Header and Header
Length fields). Also, since the IPv6 ND message is already
protected by the authentication signature and/or lower-layer
authentication and integrity checks, the HIP message Checksum
field is replaced by a Reserved field set to 0 on transmission and
ignored on reception.
Note: In some environments, maintenance of a Host Identity Tag (HIT)
namespace may be unnecessary for securely associating an OMNI node
with an IPv6 address-based identity. In that case, other types of
IPv6 addresses (e.g., a Client's MNP-LLA, a Proxy/Server's ADM-LLA,
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etc.) can be used instead of HITs in the authentication signature as
long as the address can be uniquely associated with the Sender/
Receiver.
12.2.9. PIM-SM Message
The Protocol Independent Multicast - Sparse Mode (PIM-SM) Message
sub-option may be included in the OMNI options of IPv6 ND messages.
PIM-SM messages are formatted as specified in Section 4.9 of
[RFC7761], with the exception that the Checksum field is replaced by
a Reserved field (set to 0) since the IPv6 ND message is already
protected by the IPv6 ND message checksum, authentication signature
and/or lower-layer authentication and integrity checks. The PIM-SM
message sub-option format is shown in Figure 22:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=8| Sub-length=N |PIM Ver| Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ PIM-SM Message /
/ /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: PIM-SM Message Option Format
o Sub-Type is set to 8. If multiple instances appear in OMNI
options of the same message all are processed.
o 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.
o The PIM-SM message is coded exactly as specified in Section 4.9 of
[RFC7761], except that the Checksum field is replaced by a
Reserved field set to 0 on transmission and ignored on reception.
The "PIM Ver" field MUST encode the value 2, and the "Type" field
encodes the PIM message type. (See Section 4.9 of [RFC7761] for a
list of PIM-SM message types and formats.)
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12.2.10. Reassembly Limit
The Reassembly Limit sub-option may be included in the OMNI options
of IPv6 ND messages. The message consists of a 15-bit Reassembly
Limit value, followed by a flag bit (H) optionally followed by an (N-
2)-octet leading portion of an OAL First Fragment that triggered the
message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=9| Sub-length=N | Reassembly Limit |H|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL First Fragment (As much of invoking packet |
+ as possible without causing the IPv6 ND message +
| to exceed the minimum IPv6 MTU) |
+ +
Figure 23: Reassembly Limit
o Sub-Type is set to 9. If multiple instances appear in OMNI
options of the same message the first occurring "hard" and "soft"
Reassembly Limit values are accepted, and any additional
Reassembly Limit values are ignored.
o Sub-Length is set to 2 if no OAL First Fragment is included, or to
a value N greater than 2 if an OAL First Fragment is included.
o A 15-bit Reassembly Limit follows, and includes a value between
1500 and 9180. If any other value is included, the sub-option is
ignored. The value indicates the hard or soft limit for original
IP packets that the source of the message is currently willing to
reassemble; the source may increase or decrease the hard or soft
limit at any time through the transmission of new IPv6 ND
messages. Until the first IPv6 ND message with a Reassembly Limit
sub-option arrives, OMNI nodes assume initial default hard/soft
limits of 9180 (I.e., the OMNI interface MRU). After IPv6 ND
messages with Reassembly Limit sub-options arrive, the OMNI node
retains the most recent hard/soft limit values until new IPv6 ND
messages with different values arrive.
o The 'H' flag is set to 1 if the Reassembly Limit is a "Hard"
limit, and set to 0 if the Reassembly Limit is a "Soft" limit.
o If N is greater than 2, the remainder of the Reassembly Limit sub-
option encodes the leading portion of an OAL First Fragment that
prompted this IPv6 ND message. The first fragment is included
beginning with the OAL header, and continuing with as much of the
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fragment payload as possible without causing the IPv6 ND message
to exceed the minimum IPv6 MTU.
12.2.11. Fragmentation Report
The Fragmentation Report may be included in the OMNI options of uNA
messages sent from an OAL destination to an OAL source. The message
consists of (N / 8)-many (Identification, Bitmap)-tuples which
include the Identification values of OAL fragments received plus a
Bitmap marking the ordinal positions of individual fragments received
and fragments missing.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=10| Sub-Length = N | Identification #1 (bits 0 -15)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification #1 (bits 15-31)| Bitmap #1 (bits 0 - 15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bitmap #1 (bits 16-31) | Identification #2 (bits 0 -15)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification #2 (bits 15-31)| Bitmap #2 (bits 0 - 15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bitmap #2 (bits 16-31) | Identification #3 (bits 0 -15)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification #3 (bits 15-31)| Bitmap #3 (bits 0 - 15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bitmap #3 (bits 16-31) | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +
| ... |
+ ... +
Figure 24: Fragmentation Report
o Sub-Type is set to 10. If multiple instances appear in OMNI
options of the same message all are processed.
o Sub-Length is set to N, i.e., the length of the option in octets
beginning immediately following the Sub-Length field and extending
to the end of the sub-option. If N is not an integral multiple of
8 octets, the sub-option is ignored. The length of the entire
sub-option should not cause the entire IPv6 ND message to exceed
the minimum IPv6 MTU.
o Identification (i) includes the IPv6 Identification value found in
the Fragment Header of a received OAL fragment. (Only those
Identification values included represent fragments for which loss
was unambiguously observed; any Identification values not included
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correspond to fragments that were either received in their
entirety or may still be in transit.)
o Bitmap (i) includes an ordinal checklist of fragments, with each
bit set to 1 for a fragment received or 0 for a fragment missing.
(Each OAL packet may consist of at most 23 fragments, therefore
Bitmap (i) bits 0-22 are consulted while bits 23-31 are reserved
for future use and ignored.) For example, for a 20-fragment OAL
packet with ordinal fragments #3, #10, #13 and #17 missing and all
other fragments received, Bitmap (i) encodes the following:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|1|1|1|0|1|1|1|1|1|1|0|1|1|0|1|1|1|0|1|1|0|0|0|...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 25
(Note that loss of an OAL atomic fragment is indicated by a
Bitmap(i) with all bits set to 0.)
12.2.12. Node Identification
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=11| Sub-length=N | ID-Type | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ Node Identification Value (N-1 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 26: Node Identification
o Sub-Type is set to 11. If multiple instances appear in OMNI
options of the same IPv6 ND message the first instance of a
specific ID-Type is processed and all other instances of the same
ID-Type are ignored. (It is therefore possible for a single IPv6
ND message to convey multiple distinct Node Identifications - each
with a different ID-Type.)
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The ID-Type field is always present; hence,
the maximum Node Identification Value length is limited by the
remaining available space in this OMNI option.
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o ID-Type is a 1 octet field that encodes the type of the Node
Identification Value. The following ID-Type values are currently
defined:
* 0 - Universally Unique IDentifier (UUID) [RFC4122]. Indicates
that Node Identification Value contains a 16 octet UUID.
* 1 - Host Identity Tag (HIT) [RFC7401]. Indicates that Node
Identification Value contains a 16 octet HIT.
* 2 - Hierarchical HIT (HHIT) [I-D.ietf-drip-rid]. Indicates
that Node Identification Value contains a 16 octet HHIT.
* 3 - Network Access Identifier (NAI) [RFC7542]. Indicates that
Node Identification Value contains an N-1 octet NAI.
* 4 - Fully-Qualified Domain Name (FQDN) [RFC1035]. Indicates
that Node Identification Value contains an N-1 octet FQDN.
* 5 - IPv6 Address. Indicates that Node Identification contains
a 16-octet IPv6 address that is not a (H)HIT. The IPv6 address
type is determined according to the IPv6 addressing
architecture [RFC4291].
* 6 - 252 - Unassigned.
* 253-254 - Reserved for experimentation, as recommended in
[RFC3692].
* 255 - reserved by IANA.
o Node Identification Value is an (N - 1) octet field encoded
according to the appropriate the "ID-Type" reference above.
OMNI interfaces code Node Identification Values used for DHCPv6
messaging purposes as a DHCP Unique IDentifier (DUID) using the
"DUID-EN for OMNI" format with enterprise number 45282 (see:
Section 25) as shown in Figure 27:
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DUID-Type (2) | EN (high bits == 0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EN (low bits = 45282) | ID-Type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. Node Identification Value .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 27: DUID-EN for OMNI Format
In this format, the OMNI interface codes the ID-Type and Node
Identification Value fields from the OMNI sub-option following a 6
octet DUID-EN header, then includes the entire "DUID-EN for OMNI" in
a DHCPv6 message per [RFC8415].
12.2.13. ICMPv6 Error
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=12| Sub-length=N | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ~
~ RFC4443 Error Message Body ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 28: ICMPv6 Error
o Sub-Type is set to 12. If multiple instances appear in OMNI
options of the same IPv6 ND message all are processed.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
o RFC4443 Error Message Body is an N-octet field encoding the body
of an ICMPv6 Error Message per Section 2.1 of [RFC4443] (ICMPv6
informational messages must not be included and must be ignored if
received). OMNI interfaces include as much of the ICMPv6 error
message body in the sub-option as possible without causing the
IPv6 ND message to exceed the minimum IPv6 MTU.
12.2.14. QUIC-TLS Message
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=13| Sub-length=N | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ~
~ QUIC-TLS Message ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 29: QUIC-TLS Message
o Sub-Type is set to 13. If multiple instances appear in OMNI
options of the same IPv6 ND message, the first is processed and
all others are ignored.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
o The QUIC-TLS message [RFC9000][RFC9001][RFC9002] encodes the QUIC
and TLS message parameters necessary to support QUIC connection
establishment.
When present, the QUIC-TLS Message sub-option MUST appear immediately
after the header of the first OMNI option in the IPv6 ND message; if
the sub-option appears in any other location it MUST be ignored.
IPv6 ND solicitation and advertisement messages serve as couriers to
transport the QUIC and TLS parameters necessary to establish a
secured QUIC connection.
12.2.15. Proxy/Server Departure
OMNI Clients include a Proxy/Server Departure sub-option in RS
messages when they associate with a new FHS and/or Hub Proxy/Server
and need to send a departure indication to an old FHS and/or Hub
Proxy/Server. The Proxy/Server Departure sub-option is formatted as
shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=14| Sub-length=8 |Old FHS Proxy/Server MSID (0-1)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Old FHS Proxy/Server MSID (2-3)|Old Hub Proxy/Server MSID (0-1)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Old Hub Proxy/Server MSID (2-3)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 30: Proxy/Server Departure
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o Sub-Type is set to 14.
o Sub-Length is set to 8.
o Sub-Option Data contains the 4-octet MSID for the "Old FHS Proxy/
Server" followed by a 4-octet MSID for an "Old Hub Proxy/Server.
(If the Old FHS/Hub is unspecified, the corresponding MSID instead
includes the value 0.)
12.2.16. OMNI Header Extension
IPv6 ND messages used for Prefix Length assertion, service
coordination and/or Window Synchronization include an OMNI Header
Extension sub-option. If an OMNI Header Extension sub-option is
included, it must appear immediately after the authentication sub-
option if present; otherwise, as the first (non-padding) sub-option
of the first OMNI option. If multiple OMNI Header Extension sub-
options are included (whether in a single OMNI option or multiple),
only the first is processed and all others are ignored.
The OMNI Header Extension sub-option is formatted as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=15| Sub-length=14 | Preflen |N|A|U| Reservd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Acknowledgment Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|A|R|O|P| | |
|Y|C|S|P|N|Res| Window |
|N|K|T|T|G| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 31: OMNI Header Extension
o Sub-Type is set to 15.
o Sub-Length is set to 14.
o The first two octets of Sub-Option Data contains a 1-octet Prefix
Length followed by a 1-octet flags field interpreted as follows:
* Preflen is an 8 bit field that determines the length of prefix
associated with an LLA. Values 0 through 128 specify a valid
prefix length (if any other value appears the OMNI option must
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be ignored). For IPv6 ND messages sent from a Client to the
MS, Preflen applies to the IPv6 source LLA and provides the
length that the Client is requesting from or asserting to the
MS. For IPv6 ND messages sent from the MS to the Client,
Preflen applies to the IPv6 destination LLA and indicates the
length that the MS is granting to the Client. For IPv6 ND
messages sent between MS endpoints, Preflen provides the length
associated with the source/target Client MNP that is subject of
the ND message. When an IPv6 ND RS/RA message sets Preflen to
0, the recipient regards the message as a prefix release
indication.
* The N/A/U flags are set or cleared in Client RS messages as
directives to FHS and Hub Proxy/Servers and ignored in all
other IPv6 ND messages. When an FHS Proxy/Server forwards or
processes an RS with the N flag set, it responds directly to NS
Neighbor Unreachability Detection (NUD) messages by returning
NA(NUD) replies; otherwise, it forwards NS(NUD) messages to the
Client. When the Hub Proxy/Server receives an RS with the A
flag set, it responds directly to NS Address Resolution (AR)
messages by returning NA(AR) replies; otherwise, it forwards
NS(AR) messages to the Client. When the Hub Proxy/Server
receives an RS with the U flag set, it maintains a Report List
of recent NS(AR) message sources for this Client and sends uNA
messages to all list members if any aspects of the Client's
underlying interfaces change. Proxy/Servers function according
to the N/A/U flag settings received in the most recent RS
message to support dynamic Client updates. In all IPv6 ND
messages, the remaining 5 flag bits are set to 0 on
transmission and ignored on reception.
o The remainder of Sub-Option Data contains a 4-octet Sequence
Number, followed by a 4-octet Acknowledgement Number, followed by
a 1-octet flags field followed by a 3-octet Window size modeled
from the Transmission Control Protocol (TCP) header specified in
Section 3.1 of [RFC0793]. The (SYN, ACK, RST) flags are used for
TCP-like window synchronization, while the TCP (URG, PSH, FIN)
flags are not used and therefore omitted. The (OPT, PNG) flags
are OMNI-specific, and the remaining flags are Reserved.
Together, these fields support the asymmetric and symmetric OAL
window synchronization services specified in Section 6.6.
12.2.17. Sub-Type Extension
Since the Sub-Type field is only 5 bits in length, future
specifications of major protocol functions may exhaust the remaining
Sub-Type values available for assignment. This document therefore
defines Sub-Type 30 as an "extension", meaning that the actual Sub-
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Option type is determined by examining a 1 octet "Extension-Type"
field immediately following the Sub-Length field. The Sub-Type
Extension is formatted as shown in Figure 32:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Extension-Type| ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ ~
~ Extension-Type Body ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 32: Sub-Type Extension
o Sub-Type is set to 30. If multiple instances appear in OMNI
options of the same message all are processed, where each
individual extension defines its own policy for processing
multiple of that type.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The Extension-Type field is always present,
and the maximum Extension-Type Body length is limited by the
remaining available space in this OMNI option.
o Extension-Type contains a 1 octet Sub-Type Extension value between
0 and 255.
o Extension-Type Body contains an N-1 octet block with format
defined by the given extension specification.
Extension-Type values 0 and 1 are defined in the following
subsections, while Extension-Type values 2 through 252 are available
for assignment by future specifications which must also define the
format of the Extension-Type Body and its processing rules.
Extension-Type values 253 and 254 are reserved for experimentation,
as recommended in [RFC3692], and value 255 is reserved by IANA.
12.2.17.1. RFC4380 Header Extension Option
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Ext-Type=0 | Header Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Header Option Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 33: RFC4380 Header Extension Option (Extension-Type 0)
o Sub-Type is set to 30.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The Extension-Type and Header Type fields are
always present, and the Header Option Value is limited by the
remaining available space in this OMNI option.
o Extension-Type is set to 0. Each instance encodes exactly one
header option per Section 5.1.1 of [RFC4380], with Ext-Type and
Header Type representing the first two octets of the option. If
multiple instances of the same Header Type appear in OMNI options
of the same message the first instance is processed and all others
are ignored. If Header Type indicates an Authentication
Encapsulation (see below), the entire sub-option MUST appear as
the first sub-option of the first OMNI option, which MUST appear
immediately following the IPv6 ND message header.
o Header Type and Header Option Value are coded exactly as specified
in Section 5.1.1 of [RFC4380]; the following types are currently
defined:
* 0 - Origin Indication (IPv4) - value coded as a UDP port number
followed by a 4-octet IPv4 address both in "obfuscated" form
per Section 5.1.1 of [RFC4380].
* 1 - Authentication Encapsulation - value coded per
Section 5.1.1 of [RFC4380].
* 2 - Origin Indication (IPv6) - value coded per Section 5.1.1 of
[RFC4380], except that the address is a 16-octet IPv6 address
instead of a 4-octet IPv4 address.
o Header Type values 3 through 252 are available for assignment by
future specifications, which must also define the format of the
Header Option Value and its processing rules. Header Type values
253 and 254 are reserved for experimentation, as recommended in
[RFC3692], and value 255 is Reserved by IANA.
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12.2.17.2. RFC6081 Trailer Extension Option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Ext-Type=1 | Trailer Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Trailer Option Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 34: RFC6081 Trailer Extension Option (Extension-Type 1)
o Sub-Type is set to 30.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The Extension-Type and Trailer Type fields
are always present, and the maximum-length Trailer Option Value is
limited by the remaining available space in this OMNI option.
o Extension-Type is set to 1. Each instance encodes exactly one
trailer option per Section 4 of [RFC6081]. If multiple instances
of the same Trailer Type appear in OMNI options of the same
message the first instance is processed and all others ignored.
o Trailer Type and Trailer Option Value are coded exactly as
specified in Section 4 of [RFC6081]; the following Trailer Types
are currently defined:
* 0 - Unassigned
* 1 - Nonce Trailer - value coded per Section 4.2 of [RFC6081].
* 2 - Unassigned
* 3 - Alternate Address Trailer (IPv4) - value coded per
Section 4.3 of [RFC6081].
* 4 - Neighbor Discovery Option Trailer - value coded per
Section 4.4 of [RFC6081].
* 5 - Random Port Trailer - value coded per Section 4.5 of
[RFC6081].
* 6 - Alternate Address Trailer (IPv6) - value coded per
Section 4.3 of [RFC6081], except that each address is a
16-octet IPv6 address instead of a 4-octet IPv4 address.
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o Trailer Type values 7 through 252 are available for assignment by
future specifications, which must also define the format of the
Trailer Option Value and its processing rules. Trailer Type
values 253 and 254 are reserved for experimentation, as
recommended in [RFC3692], and value 255 is Reserved by IANA.
13. Address Mapping - Multicast
The multicast address mapping of the native underlying interface
applies. The Client mobile router also serves as an IGMP/MLD Proxy
for its EUNs and/or hosted applications per [RFC4605].
The Client uses Multicast Listener Discovery (MLDv2) [RFC3810] to
coordinate with Proxy/Servers, and *NET L2 elements use MLD snooping
[RFC4541]. The Client can also employ multicast routing protocols to
coordinate with network-based multicast sources as specified in
[I-D.templin-6man-aero].
Since the OMNI link model is NBMA, OMNI links support link-scoped
multicast through iterative unicast transmissions to individual
multicast group members (i.e., unicast/multicast emulation).
14. Multilink Conceptual Sending Algorithm
The Client's IPv6 layer selects the outbound OMNI interface according
to SBM considerations when forwarding original IP packets from local
or EUN applications to external correspondents. Each OMNI interface
maintains a neighbor cache the same as for any IPv6 interface, but
includes additional state for multilink coordination. Each Client
OMNI interface maintains default routes via Proxy/Servers discovered
as discussed in Section 15, and may configure more-specific routes
discovered through means outside the scope of this specification.
For each original IP packet it forwards, the OMNI interface selects
one or more source underlying interfaces based on PBM factors (e.g.,
traffic attributes, cost, performance, message size, etc.) and one or
more target underlying interfaces for the neighbor based on Interface
Attributes received in IPv6 ND messages (see: Section 12.2.3).
Multilink forwarding may also direct packet replication across
multiple underlying 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 underlying
interfaces.
When the OMNI interface sends an original IP packet over a selected
source underlying interface, it first employs OAL encapsulation and
fragmentation as discussed in Section 5, then performs *NET
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encapsulation as directed by the appropriate MFV. The OMNI interface
also performs *NET encapsulation (following OAL encapsulation) when
the nearest Proxy/Server is located multiple hops away as discussed
in Section 15.2.
OMNI interface multilink service designers MUST observe the BCP
guidance in Section 15 [RFC3819] in terms of implications for
reordering when original IP packets from the same flow may be spread
across multiple underlying interfaces having diverse properties.
14.1. Multiple OMNI Interfaces
Clients may connect to multiple independent OMNI links within the
same or different OMNI domains to support SBM. The Client configures
a separate OMNI interface for each link so that multiple interfaces
(e.g., omni0, omni1, omni2, etc.) are exposed to the IP layer. Each
OMNI interface configures one or more OMNI anycast addresses (see:
Section 10), and the Client injects the corresponding anycast
prefixes into the EUN routing system. Multiple distinct OMNI links
can therefore be used to support fault tolerance, load balancing,
reliability, etc.
Applications in EUNs can use Segment Routing to select the desired
OMNI interface based on SBM considerations. The application writes
an OMNI anycast address into the original IP packet'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 anycast 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 hop found in the
Segment Routing Header and forwards the message via the OMNI
interface identified by the anycast address.
14.2. Client-Proxy/Server Loop Prevention
After a Proxy/Server has registered an MNP for a Client (see:
Section 15), the Proxy/Server will forward all packets destined to an
address within the MNP to the Client. The Client will under normal
circumstances then forward the packet to the correct destination
within its internal networks.
If at some later time the Client loses state (e.g., after a reboot),
it may begin returning 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 LLA, ULA or GUA), and drops any carrier packets with both
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source and destination address corresponding to the same Client's MNP
regardless of their origin.
15. Router Discovery and Prefix Registration
Clients engage the MS by sending RS messages with OMNI options under
the assumption that one or more Proxy/Server will process the message
and respond. The RS message is received by a FHS Proxy/Server, which
may in turn forward a proxyed copy of the RS to a Hub Proxy/Server
located on the same or different SRT segment. The Hub Proxy/Server
then returns an RA message either directly to the Client or via an
FHS Proxy/Server acting as a proxy.
Clients and FHS Proxy/Servers include an authentication signature in
their RS/RA exchanges when necessary; otherwise, they calculate and
include a valid IPv6 ND message checksum (see: Section 12 and
Appendix B). FHS and Hub Proxy/Server RS/RA message exchanges over
the SRT secured spanning tree instead always include the checksum and
omit the authentication signature. Clients and Proxy/Servers use the
information included in RS/RA messages to establish NCE state and
OMNI link autoconfiguration information as discussed in this section.
For each underlying interface, the Client sends RS messages with OMNI
options to coordinate with a (potentially different) FHS Proxy/Server
for each interface and a single Hub Proxy/Server. All Proxy/Servers
are identified by their MSIDs and accept carrier packets addressed to
their anycast/unicast *NET INADDRs; the Hub Proxy/Server may be
chosen among any of the Client's FHS Proxy/Servers or may be any
other Proxy/Server for the OMNI link. Example MSID/INADDR discovery
methods are given in [RFC5214] and include data link login
parameters, name service lookups, static configuration, a static
"hosts" file, etc. In the absence of other information, the Client
can resolve the DNS Fully-Qualified Domain Name (FQDN)
"linkupnetworks.[domainname]" where "linkupnetworks" is a constant
text string and "[domainname]" is a DNS suffix for the OMNI link
(e.g., "example.com").
Clients configure OMNI interfaces that observe the properties
discussed in previous sections. The OMNI interface and its
underlying interfaces are said to be in either the "UP" or "DOWN"
state according to administrative actions in conjunction with the
interface connectivity status. An OMNI interface transitions to UP
or DOWN through administrative action and/or through state
transitions of the underlying interfaces. When a first underlying
interface transitions to UP, the OMNI interface also transitions to
UP. When all underlying interfaces transition to DOWN, the OMNI
interface also transitions to DOWN.
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When a Client OMNI interface transitions to UP, it sends RS messages
to register its MNP and an initial set of underlying interfaces that
are also UP. The Client sends additional RS messages to refresh
lifetimes and to register/deregister underlying interfaces as they
transition to UP or DOWN. The Client's OMNI interface sends initial
RS messages over an UP underlying interface with its MNP-LLA as the
source (or with the unspecified address (::) as the source if it does
not yet have an MNP-LLA) and with destination set to link-scoped All-
Routers multicast or the ADM-LLA of a specific Proxy/Server. The
OMNI interface includes an OMNI option per Section 12 with an OMNI
header extension with Preflen assertion, N/A/U flags, an Interface
Attributes sub-option for the underlying interface and with any other
necessary OMNI sub-options such as authentication, Proxy/Server
Departure, Reassembly Limits, etc.
The Client then calculates the authentication signature or checksum
and prepares to forward the RS over the underlying interface using
OAL encapsulation and fragmentation if necessary. If the Client uses
OAL encapsulation for RS messages sent to an unsynchronized FHS
Proxy/Server over an INET interface, the entire RS message must fit
within a single carrier packet (i.e., an atomic fragment) so that the
FHS Proxy/Server can verify the authentication signature without
having to reassemble. The OMNI interface selects an Identification
value (see: Section 6.6), sets the OAL source address to the ULA
corresponding to the RS source (or a Temporary ULA or (H)HIT if the
RS source is the unspecified address (::)), sets the OAL destination
to an OMNI IPv6 anycast or ADM-ULA unicast address then performs
fragmentation if necessary. When *NET encapsulation is used, the
Client includes the discovered FHS Proxy/Server INADDR or an anycast
address as the *NET destination then forwards the resulting carrier
packet(s) into the *NET.
When an FHS Proxy/Server receives the carrier packets containing an
RS it sets aside the *NET headers, verifies the Identifications and
reassembles if necessary, sets aside the OAL header, then verifies
the RS authentication signature or checksum. The FHS Proxy/Server
then caches the OMNI Window Synchronization parameters, Interface
Attributes and any Traffic Selector sub-options in a NCE for the
Client while also caching the *NET (UDP/IP) and OAL (ULA) source and
destination address information. The FHS Proxy/Server next caches
the OMNI option N flag to determine its role in processing NS(NUD)
messages (see: Section 12.1) then examines the RS destination
address. If the destination matches its own ADM-LLA, the FHS Proxy/
Server assumes the Hub role and acts as the sole entry point for
injecting the Client's MNP into the MS routing system (i.e., after
performing any necessary MNP prefix delegation operations) according
to the RS source address and OMNI option Prefix Length. The FHS/Hub
Proxy/Server then caches the OMNI option A/U flags to determine its
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role in processing NS(AR) messages and generating uNA messages (see:
Section 12.1).
The FHS/Hub Proxy/Server then prepares to return an RA message
directly to the Client by first populating the Cur Hop Limit, Flags,
Router Lifetime, Reachable Time and Retrans Timer fields with values
appropriate for the OMNI link. The FHS/Hub Proxy/Server next
includes as the first RA message option an OMNI option with Window
Synchronization information, an authentication sub-option if
necessary and a (proxyed) copy of the Client's original Interface
Attributes sub-option with its INET-facing interface information
written in the FMT/SRT and LHS Proxy/Server MSID/INADDR fields. If
the RS *NET destination IP address was anycast, the FHS/Hub Proxy/
Server next includes a second Interface Attributes sub-option with
omIndex set to '0' and with a unicast *NET IP address for its Client-
facing interface in the INADDR field.
The FHS/Hub Proxy/Server next includes an Origin Indication sub-
option that includes the RS *NET source INADDR information (see:
Section 12.2.17.1), then includes any other necessary OMNI sub-
options (either within the same OMNI option or in additional OMNI
options). Following the OMNI option(s), the FHS/Hub Proxy/Server
next includes any other necessary RA options such as PIOs with (A;
L=0) that include the OMNI link MSPs [RFC8028], RIOs [RFC4191] with
more-specific routes, Nonce and Timestamp options, etc. The FHS/Hub
Proxy/Server then sets the RA source address to its own ADM-LLA and
destination address to the Client's MNP-LLA, then calculates the
authentication signature or checksum. The FHS/Hub Proxy/Server
finally performs OAL encapsulation with source set to its own ADM-ULA
and destination set to the OAL source that appeared in the RS, then
fragments if necessary, encapsulates each fragment in appropriate
*NET headers with source and destination address information reversed
from the RS *NET information and returns the resulting carrier
packets to the Client over the same underlying interface the RS
arrived on.
When an FHS Proxy/Server receives an RS with a valid authentication
signature or checksum and with destination set to link-scoped All-
Routers multicast, it can either assume the Hub role the same as
above or act as a proxy and select the ADM-LLA of another Proxy/
Server to serve as the Hub. When an FHS Proxy/Server assumes the
proxy role or receives an RS with destination set to the ADM-LLA of
another Proxy/Server, it proxys the message. The FHS Proxy/Server
caches the Client's Window Synchronization, N flag, Interface
Attributes and *NET/OAL address information as above then writes its
own INET-facing FMT/SRT and LHS Proxy/Server MSID/INADDR information
into the appropriate Interface Attributes sub-option fields. The FHS
Proxy/Server then calculates and includes the checksum, performs OAL
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encapsulation with source set to its own ADM-ULA and destination set
to the ADM-ULA of the Hub Proxy/Server, fragments if necessary,
encapsulates each fragment in appropriate *NET headers and sends the
resulting carrier packets into the SRT secured spanning tree.
When the Hub Proxy/Server receives the carrier packets, it discards
the *NET headers, reassembles if necessary to obtain the proxyed RS
(i.e., one with an ADM-ULA source address) then caches any state
(including the A/U flags, OAL addresses, Interface Attributes
information and Traffic Selectors) in a NCE for the Client and
performs any necessary prefix delegation and routing protocol
injection. The Hub Proxy/Server then returns an RA that echoes the
Client's (proxyed) Interface Attributes sub-option and with any RA
parameters the same as specified above. The Hub Proxy/Server then
sets the RA source address to its own ADM-LLA and destination address
to the Client's MNP-LLA, calculates the checksum then encapsulates
the RA as an OAL packet with source set to its own ADM-ULA and
destination set to the ADM-ULA of the FHS Proxy/Server that sent the
RS. The Hub Proxy/Server finally fragments if necessary,
encapsulates each fragment in appropriate *NET headers and sends the
resulting carrier packets into the secured spanning tree.
When the FHS Proxy/Server receives the carrier packets it discards
the *NET headers, reassembles to obtain the RA message, verifies the
checksum then updates the OMNI interface NCEs for both the Hub and
Client. The FHS Proxy/Server then proxies the RA by changing the OAL
source to its own ADM-ULA and the OAL destination to the MNP-ULA or
temporary ULA of the Client, then sets the P flag in the RA flags
field [RFC4389]. The FHS Proxy/Server next includes Window
Synchronization parameters responsive to those in the Client's RS, an
Interface Attributes sub-option with omIndex '0' and with its unicast
*NET IP address if necessary (see above), an Origin Indication sub-
option with the Client's cached INADDR and an authentication sub-
option if necessary. The FHS Proxy/Server finally selects an
Identification value per Section 6.6, calculates the authentication
signature or checksum, fragments if necessary, encapsulates each
fragment in *NET headers with addresses taken from the Client's NCE
and returns the resulting carrier packets via the same underlying
interface over which the RS was received.
When the Client receives the carrier packets, it discards the *NET
headers, reassembles and removes the OAL header/trailer to obtain the
RA message, verifies the authentication signature or checksum, then
updates the OMNI interface NCEs for both the Hub and FHS Proxy/
Server. If the Client has multiple underlying interfaces, it creates
additional FHS Proxy/Server NCEs as necessary when it receives RAs
over those interfaces (noting that multiple of the Client's
underlying interfaces may be serviced by the same FHS Proxy/Server).
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For each underlying interface, the Client caches the (filled-out)
Interface Attributes for its own omIndex and Origin Indication
information that it received in an RA message over that interface so
that it can include them in future NS/NA messages to provide
neighbors with accurate FMT/SRT/LHS information. (If the message
includes an Interface Attributes sub-option with omIndex '0', the
Client also caches the INADDR as the *NET-local unicast address of
the FHS Proxy//Server via that underlying interface.) The Client
then compares the Origin Indication INADDR information with its own
underlying interface addresses to determine whether there may be NATs
on the path to the FHS Proxy/Server; if the INADDR information
differs, the Client is behind a NAT and must supply the Origin
information in IPv6 ND message exchanges with prospective neighbors
on the same SRT segment. The Client finally configures default
routes and assigns the OMNI Subnet Router Anycast address
corresponding to the MNP (e.g., 2001:db8:1:2::) to the OMNI
interface.
Following the initial exchange, the FHS Proxy/Server MAY later send
additional periodic and/or event-driven unsolicited RA messages per
[RFC4861]. (The unsolicited RAs may be initiated either by the FHS
Proxy/Server itself or by the Hub via the FHS as a proxy.) The
Client then continuously manages its underlying interfaces according
to their states as follows:
o When an underlying interface transitions to UP, the Client sends
an RS over the underlying interface with an OMNI option with sub-
options as specified above.
o When an underlying interface transitions to DOWN, the Client sends
unsolicited NA messages over any UP underlying interface with an
OMNI option containing Interface Attributes sub-options for the
DOWN underlying interface with Link set to '0'. The Client sends
isolated unsolicited NAs when reliability is not thought to be a
concern (e.g., if redundant transmissions are sent on multiple
underlying interfaces), or may instead set the PNG flag in the
OMNI header to trigger a uNA reply.
o When the Router Lifetime for the Hub Proxy/Server nears
expiration, the Client sends an RS over any underlying interface
to receive a fresh RA from the Hub. If no RA messages are received
over a first underlying interface (i.e., after retrying), the
Client marks the underlying interface as DOWN and should attempt
to contact the Hub Proxy/Server via a different underlying
interface. If the Hub Proxy/Server is unresponsive over
additional underlying interface, the Client selects a different
FHS Proxy/Server and sends an RS message with destination set to
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the ADM-LLA of the FHS Proxy/Server which will then assume the Hub
role.
o When all of a Client's underlying interfaces have transitioned to
DOWN (or if the prefix registration lifetime expires), the Hub
Proxy/Server withdraws the MNP the same as if it had received a
message with a release indication.
The Client is responsible for retrying each RS exchange up to
MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL
seconds until an RA is received. If no RA is received over an UP
underlying interface (i.e., even after attempting to contact
alternate Proxy/Servers), the Client declares this underlying
interface as DOWN. When changing to a new FHS or Hub Proxy/Server,
the Client also includes a Proxy/Server Departure OMNI sub-option in
new RS messages; the (new) FHS Proxy/Server will in turn send uNA
messages to the old FHS and/or Hub Proxy/Server to announce the
Client's departure as discussed in [I-D.templin-6man-aero].
The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface.
Therefore, when the IPv6 layer sends an RS message the OMNI interface
returns an internally-generated RA message as though the message
originated from an IPv6 router. The internally-generated RA message
contains configuration information consistent with the information
received from the RAs generated by the Hub Proxy/Server. Whether the
OMNI interface IPv6 ND messaging process is initiated from the
receipt of an RS message from the IPv6 layer or independently of the
IPv6 layer is an implementation matter. Some implementations may
elect to defer the OMNI interface internal RS/RA messaging process
until an RS is received from the IPv6 layer, while others may elect
to initiate the process proactively. Still other deployments may
elect to administratively disable IPv6 layer RS/RA messaging over the
OMNI interface, since the messages are not required to drive the OMNI
interface internal RS/RA process. (Note that this same logic applies
to IPv4 implementations that employ ICMP-based Router Discovery per
[RFC1256].)
Note: The Router Lifetime value in RA messages indicates the time
before which the Client must send another RS message over this
underlying interface (e.g., 600 seconds), however that timescale may
be significantly longer than the lifetime the MS has committed to
retain the prefix registration (e.g., REACHABLETIME seconds). Proxy/
Servers are therefore responsible for keeping MS state alive on a
shorter timescale than the Client may be required to do on its own
behalf.
Note: On certain multicast-capable underlying interfaces, Clients
should send periodic unsolicited multicast NA messages and Proxy/
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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 a unicast exchange to test reachability.
Note: If a single FHS Proxy/Server services multiple of a Client's
underlying interfaces, Window Synchronization will initially be
repeated for the RS/RA exchange over each underlying interface, i.e.,
until the Client discovers the many-to-one relationship.
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/MSID/INADDR as last-hop segment (LHS) information. This
allows both the Client and Hub Proxy/Server to supply the information
to neighbors that will perceive it as LHS information on the return
path to the Client.
Note: The Hub Proxy/Server injects Client MNP-ULAs into the routing
system by simply creating a route-to-interface forwarding table entry
for the MNP-ULA via the OMNI interface. The dynamic routing protocol
will notice the new entry and advertise the MNP-ULA to its peers. If
the Hub receives additional RS messages, it need not re-create the
MNP-ULA forwarding table entry (nor disturb the dynamic routing
protocol) if an entry is already present.
Note: If the Client's initial RS message includes an anycast *NET
destination address, the FHS Proxy/Server returns the solicited RA
using the same anycast address as the *NET source while including an
Interface Attributes sub-option with omIndex '0' and its true unicast
address in the INADDR. When the Client sends additional RS messages,
it includes this FHS Proxy/Server unicast address as the *NET
destination and the FHS Proxy/Server returns the solicited RA using
the same unicast address as the *NET source. This will ensure that
RS/RA exchanges are not impeded by any NATs on the path while
avoiding long-term exposure of messages that use an anycast address
as the source.
Note: The Origin Indication sub-option is included only by the FHS
Proxy/Server and not by the Hub (unless the Hub is also serving as an
FHS).
Note: Clients should set the N/A/U flags consistently in successive
RS messages and only change those settings when an FHS/Hub Proxy/
Server service profile update is necessary.
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15.1. Window Synchronization
In environments where Identification window synchronization is
necessary, the RS/RA exchanges discussed above observe the principles
specified in Section 6.6. Window synchronization is conducted
between the Client and each FHS Proxy/Server used to contact the Hub
Proxy/Server, i.e., and not between the Client and the Hub. This is
due to the fact that the Hub Proxy/Server is responsible only for
forwarding all control and data messages via the secured spanning
tree to FHS Proxy/Servers, and is not responsible for forwarding
messages directly to the Client under a synchronized window. Also,
in the reverse direction the FHS Proxy/Servers handle all default
forwarding actions without forwarding Client-initiated data to the
Hub.
When a Client needs to perform window synchronization via a new FHS
Proxy/Server, it sets the RS source address to its own MNP-LLA and
destination address to the ADM-LLA of the Hub Proxy/Server, then sets
the SYN flag and includes an initial Sequence Number for Window
Synchronization. The Client then performs OAL encapsulation using
its own MNP-ULA as the source and the ADM-ULA of the FHS Proxy/Server
as the destination and includes an Interface Attributes sub-option
then forwards the resulting carrier packets to the FHS Proxy/Server.
The FHS Proxy/Server then extracts the RS message and caches the
Window Synchronization parameters then re-encapsulates with its own
ADM-ULA as the source and the ADM-ULA of the Hub Proxy/Server as the
target.
The FHS Proxy/Server then forwards the resulting carrier packets via
the secured spanning tree to the Hub Proxy/Server, which updates the
Client's Interface Attributes and returns a unicast RA message with
source set to its own ADM-LLA and destination set to the Client's
MNP-LLA and with the Client's Interface Attributes echoed. The Hub
Proxy/Server then performs OAL encapsulation using its own ADM-ULA as
the source and the ADM-ULA of the FHS Proxy/Server as the
destination, then forwards the carrier packets via the secured
spanning tree to the FHS Proxy/Server. The FHS Proxy/Server then re-
encapsulates the message using its own ADM-ULA as the source, the
MNP-ULA of the Client as the destination and includes responsive
Window Synchronization information. The FHS Proxy/Server then
forwards the message to the Client which updates its window
synchronization information for the FHS Proxy/Server as necessary.
Following the initial RS/RA-driven window synchronization, the Client
can re-assert new windows with specific FHS Proxy/Servers by
performing NS/NA exchanges between its own MNP-LLA and the ADM-LLAs
of the FHS Proxy/Servers without having to disturb the Hub.
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15.2. Router Discovery in IP Multihop and IPv4-Only Networks
On some *NETs, a Client may be located multiple IP hops away from the
nearest OMNI link Proxy/Server. Forwarding through IP multihop *NETs
is conducted through the application of a routing protocol (e.g., a
MANET/VANET routing protocol over omni-directional wireless
interfaces, an inter-domain routing protocol in an enterprise
network, etc.).
A Client located potentially multiple *NET hops away from the nearest
Proxy/Server prepares an RS message, sets the source address to its
MNP-LLA (or to the unspecified address (::) if it does not yet have
an MNP-LLA), and sets the destination to link-scoped All-Routers
multicast or a unicast ADM-LLA the same as discussed above. The OMNI
interface then employs OAL encapsulation, sets the OAL source address
to the ULA corresponding to the RS source (or to a Temporary ULA if
the RS source was the unspecified address (::)) and sets the OAL
destination to an OMNI IPv6 anycast address based on either a native
IPv6 or IPv4-mapped IPv6 prefix (see: Section 10).
For IPv6-enabled *NETs, if the underlying interface does not
configure an IPv6 GUA the Client forwards the message without further
encapsulation. Otherwise, the Client encapsulates the message in
UDP/IPv6 *NET headers, sets the source to the underlying interface
GUA and sets the destination to the same OMNI IPv6 anycast address.
The Client then forwards the message into the IPv6 multihop routing
system which conveys it to the nearest Proxy/Server that advertises a
matching OMNI IPv6 anycast prefix.
For IPv4-only *NETs, the Client encapsulates the RS message in UDP/
IPv4 *NET headers, sets the source to the underlying interface IPv4
address and sets the destination to the IPv4 anycast address TBD3
(see: IANA Considerations). The Client then forwards the message
into the IPv4 multihop routing system which conveys it to the nearest
Proxy/Server that advertises the corresponding IPv4 prefix. If the
nearest Proxy/Server is too busy and/or does not configure the
specified OMNI IPv6 anycast address, it should forward (without
Proxying) the OAL-encapsulated RS to another nearby Proxy/Server
connected to the same IPv4 (multihop) network that configures the
OMNI IPv6 anycast address. (In environments where reciprocal RS
forwarding cannot be supported, the first Proxy/Server should instead
return an RA based on its own MSP(s).)
When an intermediate *NET hop that participates in the routing
protocol receives the encapsulated RS, it forwards the message
according to its routing tables (note that an intermediate node could
be a fixed infrastructure element or another MANET/VANET node). This
process repeats iteratively until the RS message is received by a
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penultimate *NET hop within single-hop communications range of a
Proxy/Server, which forwards the message to the Proxy/Server.
When a Proxy/Server that configures the OMNI IPv6 anycast OAL
destination receives the message, it decapsulates the RS and assumes
either the Hub or FHS role (in which case, it forwards the RS to a
candidate Hub). The Hub Proxy/Server then prepares an RA message
with source address set to its own ADM-LLA and destination address
set to the Client MNP-LLA. The Hub Proxy/Server then performs OAL
encapsulation with the RA OAL source/destination set to the RS OAL
destination/source and forwards the RA to the FHS Proxy/Server or
directly to the Client.
When the Hub or FHS Proxy/Server forwards the RA to the Client, it
encapsulates the message in *NET encapsulation headers (if necessary)
with (src, dst) set to the (dst,src) of the RS *NET encapsulation
headers. The Proxy/Server then forwards the message to a *NET node
within communications range, which forwards the message according to
its routing tables to an intermediate node. The multihop forwarding
process within the *NET continues repetitively until the message is
delivered to the original Client, which decapsulates the message and
performs autoconfiguration the same as if it had received the RA
directly from a Proxy/Server on the same physical link.
Note: When the RS message includes anycast OAL and/or *NET
encapsulation destinations, the FHS Proxy/Server must use the same
anycast addresses as the OAL and/or *NET encapsulation sources to
support forwarding of the RA message and any initial data packets
over any NATs on the path. When the Client receives the RA, it will
discover the unicast OAL and/or IPv4 encapsulation addresses and can
forward future 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 6.12.) After the Client
begins using unicast OAL/*NET encapsulation addresses in this way,
the FHS Proxy/Server should also begin using the same unicast
addresses in the reverse direction.
Note: As an alternate approach to multihop forwarding via IPv6
encapsulation, the Client and Proxy/Server could statelessly
translate the IPv6 LLAs into ULAs and forward the RS/RA messages
without encapsulation. This would violate the [RFC4861] requirement
that certain IPv6 ND messages must use link-local addresses and must
not be accepted if received with Hop Limit less than 255. This
document therefore mandates encapsulation since the overhead is
nominal considering the infrequent nature and small size of IPv6 ND
messages. Future documents may consider encapsulation avoidance
through translation while updating [RFC4861].
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Note: An alternate approach to multihop forwarding via IPv4
encapsulation would be to employ IPv6/IPv4 protocol translation.
However, for IPv6 ND messages the LLAs would be truncated due to
translation and the OMNI Router and Prefix Discovery services would
not be able to function. The use of IPv4 encapsulation is therefore
indicated.
15.3. DHCPv6-based Prefix Registration
When a Client is not pre-provisioned with an MNP-LLA (or, when the
Client requires additional MNP delegations), it requests the MS to
select MNPs on its behalf and set up the correct routing state. The
DHCPv6 service [RFC8415] supports this requirement.
When a Client requires the MS to select MNPs, it sends an RS message
with source set to the unspecified address (::) if it has no
MNP_LLAs. If the Client requires only a single MNP delegation, it
can then include a Node Identification sub-option in the OMNI option
and set the OMNI extension header Preflen to the length of the
desired MNP. If the Client requires multiple MNP delegations and/or
more complex DHCPv6 services, it instead includes a DHCPv6 Message
sub-option containing a Client Identifier, one or more IA_PD options
and a Rapid Commit option then sets the 'msg-type' field to
"Solicit", and includes a 3 octet 'transaction-id'. The Client then
sets the RS destination to link-scoped All-Routers multicast and
sends the message using OAL encapsulation and fragmentation if
necessary as discussed above.
When the Hub Proxy/Server receives the RS message, it performs OAL
reassembly if necessary. Next, if the RS source is the unspecified
address (::) and/or the OMNI option includes a DHCPv6 message sub-
option, the Hub Proxy/Server acts as a "Proxy DHCPv6 Client" in a
message exchange with the locally-resident DHCPv6 server. If the RS
did not contain a DHCPv6 message sub-option, the Hub Proxy/Server
generates a DHCPv6 Solicit message on behalf of the Client using an
IA_PD option with the prefix length set to the OMNI extension header
Preflen value and with a Client Identifier formed from the OMNI
option Node Identification sub-option; otherwise, the Hub Proxy/
Server uses the DHCPv6 Solicit message contained in the OMNI option.
The Hub Proxy/Server then sends the DHCPv6 message to the DHCPv6
Server, which delegates MNPs and returns a DHCPv6 Reply message with
PD parameters. (If the Hub Proxy/Server wishes to defer creation of
Client state until the DHCPv6 Reply is received, it can instead act
as a Lightweight DHCPv6 Relay Agent per [RFC6221] by encapsulating
the DHCPv6 message in a Relay-forward/reply exchange with Relay
Message and Interface ID options. In the process, the Hub Proxy/
Server packs any state information needed to return an RA to the
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Client in the Relay-forward Interface ID option so that the
information will be echoed back in the Relay-reply.)
When the Hub Proxy/Server receives the DHCPv6 Reply, it create OMNI
interface MNP-ULA forwarding table entries (i.e., to prompt the
dynamic routing protocol) and creates MNP-LLAs based on the delegated
MNPs. The Hub Proxy/Server then sends an RA back to the Client with
the DHCPv6 Reply message included in an OMNI DHCPv6 message sub-
option if and only if the RS message had included an explicit DHCPv6
Solicit. If the RS message source was the unspecified address (::),
the Hub Proxy/Server includes one of the (newly-created) MNP-LLAs as
the RA destination address and sets the OMNI extension header Preflen
accordingly; otherwise, the Hub Proxy/Server includes the RS source
address as the RA destination address. The Hub Proxy/Server then
sets the RA source address to its own ADM-LLA, performs OAL
encapsulation and fragmentation, performs *NET encapsulation and
sends the RA to the Client (i.e., either directly or via an FHS
Proxy/Server as discussed above). When the Client receives the RA,
it reassembles and discards the OAL encapsulation, then creates a
default route, assigns Subnet Router Anycast addresses and uses the
RA destination address as its primary MNP-LLA. The Client will then
use this primary MNP-LLA as the source address of any IPv6 ND
messages it sends as long as it retains ownership of the MNP.
16. 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. When the Client sends an
RS message on a multiple access *NET link, the Proxy/Server verifies
that the Client is authorized to use the address and responds with an
RA (or forwards the RS to the Hub) only if the Client is authorized.
After verifying Client authorization and returning an RA, the Proxy/
Server MAY return IPv6 ND Redirect messages to direct Clients located
on the same *NET link to exchange packets directly without transiting
the Proxy/Server. In that case, the Clients can exchange packets
according to their unicast L2 addresses discovered from the Redirect
message instead of using the dogleg path through the Proxy/Server.
In some *NET links, however, such direct communications may be
undesirable and continued use of the dogleg path through the Proxy/
Server may provide better performance. In that case, the Proxy/
Server can refrain from sending Redirects, and/or Clients can ignore
them.
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17. Proxy/Server Resilience
*NETs SHOULD deploy Proxy/Servers in Virtual Router Redundancy
Protocol (VRRP) [RFC5798] configurations so that service continuity
is maintained even if one or more Proxy/Servers fail. Using VRRP,
the Client is unaware which of the (redundant) FHS Proxy/Servers is
currently providing service, and any service discontinuity will be
limited to the failover time supported by VRRP. Widely deployed
public domain implementations of VRRP are available.
Proxy/Servers SHOULD use high availability clustering services so
that multiple redundant systems can provide coordinated response to
failures. As with VRRP, widely deployed public domain
implementations of high availability clustering services are
available. Note that special-purpose and expensive dedicated
hardware is not necessary, and public domain implementations can be
used even between lightweight virtual machines in cloud deployments.
18. Detecting and Responding to Proxy/Server Failures
In environments where fast recovery from Proxy/Server failure is
required, FHS Proxy/Servers SHOULD use proactive Neighbor
Unreachability Detection (NUD) in a manner that parallels
Bidirectional Forwarding Detection (BFD) [RFC5880] to track Hub
Proxy/Server reachability. FHS Proxy/Servers can then quickly detect
and react to failures so that cached information is re-established
through alternate paths. Proactive NUD control messaging is carried
only over well-connected ground domain networks (i.e., and not low-
end *NET links such as aeronautical radios) and can therefore be
tuned for rapid response.
FHS Proxy/Servers perform proactive NUD for Hub Proxy/Servers for
which there are currently active Clients on the *NET. If a Hub
Proxy/Server fails, the FHS Proxy/Server can quickly inform Clients
of the outage by sending multicast RA messages on the *NET interface.
The FHS Proxy/Server sends RA messages to Clients via the *NET
interface with source set to the ADM-LLA of the Hub, with destination
address set to All-Nodes multicast (ff02::1) [RFC4291] and with
Router Lifetime set to 0.
The FHS Proxy/Server SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA
messages separated by small delays [RFC4861]. Any Clients on the
*NET interface that have been using the (now defunct) Hub Proxy/
Server will receive the RA messages.
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19. Transition Considerations
When a Client connects to an *NET link for the first time, it sends
an RS message with an OMNI option. If the first hop router
recognizes the option, it responds according to the appropriate FHS/
Hub Proxy/Server role resulting in an RA message with an OMNI option
returned to the Client. The Client then engages this FHS Proxy/Sever
according to the OMNI link model specified above. If the first hop
router is a legacy IPv6 router, however, it instead returns an RA
message with no OMNI option and with a non-OMNI unicast source LLA as
specified in [RFC4861]. In that case, the Client engages the *NET
according to the legacy IPv6 link model and without the OMNI
extensions specified in this document.
If the *NET link model is multiple access, there must be assurance
that address duplication cannot corrupt the neighbor caches of other
nodes on the link. When the Client sends an RS message on a multiple
access *NET link with an LLA source address and an OMNI option, first
hop routers that recognize the OMNI 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 L2
address mappings as discussed in Appendix D. This arrangement
imparts a (virtual) point-to-point link model over the (physical)
multiple access link.
20. OMNI Interfaces on Open Internetworks
Client OMNI interfaces configured over IPv6-enabled underlying
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 underlying interfaces receive no
IPv6 RA messages at all (but may receive IPv4 RA messages [RFC1256]).
Client OMNI interfaces that receive RA messages with OMNI options
configure addresses, on-link prefixes, etc. on the underlying
interface that received the RA according to standard IPv6 ND and
address resolution conventions [RFC4861] [RFC4862]. Client OMNI
interfaces configured over IPv4-only underlying interfaces configure
IPv4 address information on the underlying interfaces using
mechanisms such as DHCPv4 [RFC2131].
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Client OMNI interfaces configured over underlying interfaces
connected to open Internetworks can apply security services such as
VPNs to connect to a Proxy/Server, or can establish a direct link to
the Proxy/Server through some other means (see Section 4). In
environments where an explicit VPN or direct link may be impractical,
Client OMNI interfaces can instead send IPv6 ND messages with OMNI
options that include authentication signatures.
OMNI interfaces use UDP/IP as *NET encapsulation headers for
transmission over open Internetworks with UDP service port number
8060 (see: Section 25.13 and Section 3.6 of [I-D.templin-6man-aero])
for both IPv4 and IPv6 underlying interfaces. The OMNI interface
submits original IP packets for OAL encapsulation, then encapsulates
the resulting OAL fragments in UDP/IP *NET headers to form carrier
packets. (The first four bits following the UDP header determine
whether the OAL headers are uncompressed/compressed as discussed in
Section 6.4.) The OMNI interface sets the UDP length to the
encapsulated OAL fragment length and sets the IP length to an
appropriate value at least as large as the UDP datagram.
For Client-Proxy/Server (e.g., "Vehicle-to-Infrastructure (V2I)")
neighbor exchanges, the source must include an OMNI option with an
authentication sub-option in all IPv6 ND messages. The source can
apply HIP security services per [RFC7401] using the IPv6 ND message
OMNI option as a "shipping container" to convey an authentication
signature in a (unidirectional) HIP "Notify" message. For Client-
Client (e.g., "Vehicle-to-Vehicle (V2V)") neighbor exchanges, two
Clients can exchange HIP "Initiator/Responder" messages coded in OMNI
options of multiple IPv6 NS/NA messages for mutual authentication
according to the HIP protocol. (Note: a simple Hashed Message
Authentication Code (HMAC) such as specified in [RFC4380] or the
QUIC-TLS connection-oriented service [RFC9000] can be used as an
alternate authentication service in some environments.)
When an OMNI interface includes an authentication sub-option, it must
appear as the first sub-option of the first OMNI option in the IPv6
ND message which must appear immediately following the IPv6 ND
message header. When an OMNI interface prepares a HIP message sub-
option, it includes its own (H)HIT as the Sender's HIT and the
neighbor's (H)HIT if known as the Receiver's HIT (otherwise 0). If
(H)HITs are not available within the OMNI operational environment,
the source can instead include other IPv6 address types instead of
(H)HITs as long as the Sender and Receiver have some way to associate
information embedded in the IPv6 address with the neighbor; such
information could include a node identifier, vehicle identifier, MAC
address, etc.
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Before calculating the authentication signature, the source includes
any other necessary sub-options (such as Interface Attributes and
Origin Indication) and sets both the IPv6 ND message Checksum and
authentication signature fields to 0. The source then calculates the
authentication signature over the full length of the IPv6 ND message
beginning with a pseudo-header of the IPv6 header (i.e., the same as
specified in [RFC4443]) and extending over the length of the message.
(If the IPv6 ND message is part of an OAL super-packet, the source
instead calculates the authentication signature over the remainder of
the super-packet up to but not including the trailing OAL Checksum
field.) The source next writes the authentication signature into the
sub-option signature field and forwards the message.
After establishing a VPN or preparing for UDP/IP encapsulation, OMNI
interfaces send RS/RA messages for Client-Proxy/Server coordination
(see: Section 15) and NS/NA messages for route optimization, window
synchronization and mobility management (see:
[I-D.templin-6man-aero]). These control plane messages must be
authenticated while other control and data plane messages are
delivered the same as for ordinary best-effort traffic with source
address and/or Identification window-based data origin verification.
Upper layer protocol sessions over OMNI interfaces that connect over
open Internetworks without an explicit VPN should therefore employ
transport- or higher-layer security to ensure authentication,
integrity and/or confidentiality.
Clients should avoid using INET Proxy/Servers as general-purpose
routers for steady streams of carrier packets that do not require
authentication. Clients should instead coordinate with other INET
nodes that can provide forwarding services instead of burdening the
Proxy/Server (or preferably coordinate directly with peer Clients
directly). Procedures for coordinating with peer Clients and
discovering INET nodes that can provide better forwarding services
are discussed in [I-D.templin-6man-aero].
Clients that attempt to contact peers over INET underlying interfaces
often encounter NATs in the path. OMNI interfaces accommodate NAT
traversal using UDP/IP encapsulation and the mechanisms discussed in
[I-D.templin-6man-aero]. FHS Proxy/Servers include Origin
Indications in RA messages to allow Clients to detect the presence of
NATs.
Note: Following the initial IPv6 ND message exchange, OMNI interfaces
configured over INET underlying interfaces maintain neighbor
relationships by transmitting periodic IPv6 ND messages with OMNI
options that include HIP "Update" and/or "Notify" messages. When
HMAC authentication is used instead of HIP, the Client and Proxy/
Server exchange all IPv6 ND messages with HMAC signatures included
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based on a shared-secret. When QUIC-TLS connections are used, the
Client and Proxy/Server observe QUIC-TLS conventions
[RFC9000][RFC9001].
Note: OMNI interfaces configured over INET underlying interfaces
should employ the Identification window synchronization mechanisms
specified in Section 6.6 in order to reject spurious carrier packets
that might otherwise clutter the reassembly cache. This is
especially important in environments where carrier packet spoofing
and/or corruption is a threat.
Note: NATs may be present on the path from a Client to its FHS Proxy/
Server, but never on the path from the FHS Proxy/Server to the Hub
where only INET and/or spanning tree hops occur. Therefore, the FHS
Proxy/Server does not communicate Client origin information to the
Hub where it would serve no purpose.
21. Time-Varying MNPs
In some use cases, it is desirable, beneficial and efficient for the
Client to receive a constant MNP that travels with the Client
wherever it moves. For example, this would allow air traffic
controllers to easily track aircraft, etc. In other cases, however
(e.g., intelligent transportation systems), the Client may be willing
to sacrifice a modicum of efficiency in order to have time-varying
MNPs that can be changed every so often to defeat adversarial
tracking.
The prefix delegation services discussed in Section 15.3 allows
Clients that desire time-varying MNPs to obtain short-lived prefixes
to send RS messages with source set to the unspecified address (::)
and/or with an OMNI option with DHCPv6 Option sub-options. The
Client would then be obligated to renumber its internal networks
whenever its MNP (and therefore also its OMNI address) changes. This
should not present a challenge for Clients with automated network
renumbering services, but may disrupt persistent sessions that would
prefer to use a constant address.
22. (H)HITs and Temporary ULAs
Clients that generate (H)HITs but do not have pre-assigned MNPs can
request MNP delegations by issuing IPv6 ND messages that use the
(H)HIT instead of a Temporary ULA. In particular, when a Client
creates an RS message it can set the source to the unspecified
address (::) and destination to link-scoped All-Routers multicast.
The IPv6 ND message includes an OMNI option with a HIP message sub-
option, and need not include a Node Identification sub-option if the
Client's HIT appears in the HIP message. The Client then
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encapsulates the message in an IPv6 header with the (H)HIT as the
source address. The Client then sends the message as specified in
Section 15.2.
When a Proxy/Server receives the RS message, it notes that the source
was the unspecified address (::), then examines the OAL encapsulation
source address to determine that the source is a (H)HIT and not a
Temporary ULA. The Proxy/Server next invokes the DHCPv6 protocol to
request an MNP prefix delegation while using the HIT (in the form of
a DUID) as the Client Identifier, then prepares an RA message with
source address set to its own ADM-LLA and destination set to the MNP-
LLA corresponding to the delegated MNP. The Proxy/Server next
includes an OMNI option with a HIP message sub-option and any DHCPv6
prefix delegation parameters. The Proxy/Server finally encapsulates
the RA in an IPv6 header with source address set to its own ADM-ULA
and destination set to the (H)HIT from the RS encapsulation source
address, then returns the encapsulated RA to the Client.
Clients can also use (H)HITs and/or Temporary ULAs for direct Client-
to-Client communications outside the context of any OMNI link
supporting infrastructure. When two Clients encounter one another
they can use their (H)HITs and/or Temporary ULAs as original IPv6
packet source and destination addresses to support direct
communications. Clients can also inject their (H)HITs and/or
Temporary ULAs into a MANET/VANET routing protocol to enable multihop
communications. Clients can further exchange IPv6 ND messages (such
as NS/NA) using their (H)HITs and/or Temporary ULAs as source and
destination addresses.
Lastly, when Clients are within the coverage range of OMNI link
infrastructure a case could be made for injecting (H)HITs and/or
Temporary ULAs into the global MS routing system. For example, when
the Client sends an RS to an FHS Proxy/Server it could include a
request to inject the (H)HIT / Temporary ULA into the routing system
instead of requesting an MNP prefix delegation. This would
potentially enable OMNI link-wide communications using only (H)HITs
or Temporary ULAs, and not MNPs. This document notes the
opportunity, but makes no recommendation.
23. Address Selection
Clients use LLAs only for link-scoped communications on the OMNI
link. Typically, Clients use LLAs as source/destination IPv6
addresses of IPv6 ND messages, but may also use them for addressing
ordinary original IP packets exchanged with an OMNI link neighbor.
Clients use MNP-ULAs as source/destination IPv6 addresses in the
encapsulation headers of OAL packets. Clients use Temporary ULAs for
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OAL addressing when an MNP-ULA is not available, or as source/
destination IPv6 addresses for communications within a MANET/VANET
local area. Clients can also use (H)HITs instead of Temporary ULAs
when operation outside the context of a specific ULA domain and/or
source address attestation is necessary.
Clients use MNP-based GUAs as original IP packet source and
destination addresses for communications with Internet destinations
when they are within range of OMNI link supporting infrastructure
that can inject the MNP into the routing system.
Clients use anycast GUAs as OAL and/or *NET encapsulation destination
addresses for RS messages used to discover the nearest FHS Proxy/
Server. When the Proxy/Server returns a solicited RA, it must also
use the same anycast address as the RA OAL/*NET encapsulation source
in order to successfully traverse any NATs in the path. The Client
should then immediately transition to using the FHS Proxy/Server's
discovered unicast OAL/*NET address as the destination in order to
minimize dependence on the Proxy/Server's use of an anycast source
address.
24. Error Messages
An OAL destination or intermediate node may need to return
ICMPv6-like error messages (e.g., Destination Unreachable, Packet Too
Big, Time Exceeded, etc.) [RFC4443] to an OAL source. Since ICMPv6
error messages do not themselves include authentication codes, OAL
nodes can return error messages as an OMNI ICMPv6 Error sub-option in
a secured IPv6 ND uNA message.
25. IANA Considerations
The following IANA actions are requested in accordance with [RFC8126]
and [RFC8726]:
25.1. "Protocol Numbers" Registry
The IANA is instructed to allocate an Internet Protocol number TBD1
from the 'protocol numbers' registry for the Overlay Multilink
Network Interface (OMNI) protocol. Guidance is found in [RFC5237]
(registration procedure is IESG Approval or Standards Action).
25.2. "IEEE 802 Numbers" Registry
During final publication stages, the IESG will be requested to
procure an IEEE EtherType value TBD2 for OMNI according to the
statement found at https://www.ietf.org/about/groups/iesg/statements/
ethertypes/.
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Following this procurement, the IANA is instructed to register the
value TBD2 in the 'ieee-802-numbers' registry for Overlay Multilink
Network Interface (OMNI) encapsulation on Ethernet networks.
Guidance is found in [RFC7042] (registration procedure is Expert
Review).
25.3. "IPv4 Special-Purpose Address" Registry
The IANA is instructed to assign TBD3/N as an "OMNI IPv4 anycast"
address/prefix in the "IPv4 Special-Purpose Address" registry. This
specification recommends assigning the address 192.88.99.100/24 as
the "OMNI IPv4 anycast" address/prefix, since the former use of the
address/prefix 192.88.99.1/24 is deprecated by [RFC7526]. In the
event that conflicts with the former use are deemed irreconcilable,
the IANA is instructed to work with authors to determine an alternate
TBD3/N address/prefix.
25.4. "IPv6 Neighbor Discovery Option Formats" Registry
The IANA is instructed to allocate an official Type number TBD4 from
the "IPv6 Neighbor Discovery Option Formats" registry for the OMNI
option (registration procedure is RFC required). Implementations set
Type to 253 as an interim value [RFC4727].
25.5. "Ethernet Numbers" Registry
The IANA is instructed to allocate one Ethernet unicast address TBD5
(suggested value '00-52-14') in the 'ethernet-numbers' registry under
"IANA Unicast 48-bit MAC Addresses" (registration procedure is Expert
Review). The registration should appear as follows:
Addresses Usage Reference
--------- ----- ---------
00-52-14 Overlay Multilink Network (OMNI) Interface [RFCXXXX]
Figure 35: IANA Unicast 48-bit MAC Addresses
25.6. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry
The IANA is instructed to assign two new Code values in the "ICMPv6
Code Fields: Type 2 - Packet Too Big" registry (registration
procedure is Standards Action or IESG Approval). The registry should
appear as follows:
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Code Name Reference
--- ---- ---------
0 PTB Hard Error [RFC4443]
1 PTB Soft Error (loss) [RFCXXXX]
2 PTB Soft Error (no loss) [RFCXXXX]
Figure 36: ICMPv6 Code Fields: Type 2 - Packet Too Big Values
(Note: this registry also to be used to define values for setting the
"unused" field of ICMPv4 "Destination Unreachable - Fragmentation
Needed" messages.)
25.7. "OMNI Option Sub-Type Values" (New Registry)
The OMNI option defines a 5-bit Sub-Type field, for which IANA is
instructed to create and maintain a new registry entitled "OMNI
Option Sub-Type Values". Initial values are given below
(registration procedure is RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 Pad1 [RFCXXXX]
1 PadN [RFCXXXX]
2 Interface Attributes [RFCXXXX]
3 Multilink Fwding Parameters [RFCXXXX]
4 Traffic Selector [RFCXXXX]
5 Geo Coordinates [RFCXXXX]
6 DHCPv6 Message [RFCXXXX]
7 HIP Message [RFCXXXX]
8 PIM-SM Message [RFCXXXX]
9 Reassembly Limit [RFCXXXX]
10 Fragmentation Report [RFCXXXX]
11 Node Identification [RFCXXXX]
12 ICMPv6 Error [RFCXXXX]
13 QUIC-TLS Message [RFCXXXX]
14 Proxy/Server Departure [RFCXXXX]
15 OMNI Header Extension [RFCXXXX]
16-29 Unassigned
30 Sub-Type Extension [RFCXXXX]
31 Reserved by IANA [RFCXXXX]
Figure 37: OMNI Option Sub-Type Values
25.8. "OMNI Geo Coordinates Type Values" (New Registry)
The OMNI Geo Coordinates sub-option (see: Section 12.2.6) contains an
8-bit Type field, for which IANA is instructed to create and maintain
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a new registry entitled "OMNI Geo Coordinates Type Values". Initial
values are given below (registration procedure is RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 NULL [RFCXXXX]
1-252 Unassigned [RFCXXXX]
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 38: OMNI Geo Coordinates Type
25.9. "OMNI Node Identification ID-Type Values" (New Registry)
The OMNI Node Identification sub-option (see: Section 12.2.12)
contains an 8-bit ID-Type field, for which IANA is instructed to
create and maintain a new registry entitled "OMNI Node Identification
ID-Type Values". Initial values are given below (registration
procedure is RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 UUID [RFCXXXX]
1 HIT [RFCXXXX]
2 HHIT [RFCXXXX]
3 Network Access Identifier [RFCXXXX]
4 FQDN [RFCXXXX]
5 IPv6 Address [RFCXXXX]
6-252 Unassigned [RFCXXXX]
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 39: OMNI Node Identification ID-Type Values
25.10. "OMNI Option Sub-Type Extension Values" (New Registry)
The OMNI option defines an 8-bit Extension-Type field for Sub-Type 30
(Sub-Type Extension), for which IANA is instructed to create and
maintain a new registry entitled "OMNI Option Sub-Type Extension
Values". Initial values are given below (registration procedure is
RFC required):
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Value Sub-Type name Reference
----- ------------- ----------
0 RFC4380 UDP/IP Header Option [RFCXXXX]
1 RFC6081 UDP/IP Trailer Option [RFCXXXX]
2-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 40: OMNI Option Sub-Type Extension Values
25.11. "OMNI RFC4380 UDP/IP Header Option" (New Registry)
The OMNI Sub-Type Extension "RFC4380 UDP/IP Header Option" defines an
8-bit Header Type field, for which IANA is instructed to create and
maintain a new registry entitled "OMNI RFC4380 UDP/IP Header Option".
Initial registry values are given below (registration procedure is
RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 Origin Indication (IPv4) [RFC4380]
1 Authentication Encapsulation [RFC4380]
2 Origin Indication (IPv6) [RFCXXXX]
3-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 41: OMNI RFC4380 UDP/IP Header Option
25.12. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry)
The OMNI Sub-Type Extension for "RFC6081 UDP/IP Trailer Option"
defines an 8-bit Trailer Type field, for which IANA is instructed to
create and maintain a new registry entitled "OMNI RFC6081 UDP/IP
Trailer Option". Initial registry values are given below
(registration procedure is RFC required):
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Value Sub-Type name Reference
----- ------------- ----------
0 Unassigned
1 Nonce [RFC6081]
2 Unassigned
3 Alternate Address (IPv4) [RFC6081]
4 Neighbor Discovery Option [RFC6081]
5 Random Port [RFC6081]
6 Alternate Address (IPv6) [RFCXXXX]
7-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 42: OMNI RFC6081 Trailer Option
25.13. Additional Considerations
The IANA has assigned the UDP port number "8060" for an earlier
experimental version of AERO [RFC6706]. This document reclaims the
UDP port number "8060" for 'aero' as the service port for UDP/IP
encapsulation. (Note that, although [RFC6706] was not widely
implemented or deployed, any messages coded to that specification can
be easily distinguished and ignored since they use an invalid ICMPv6
message type number '0'.) The IANA is therefore instructed to update
the reference for UDP port number "8060" from "RFC6706" to "RFCXXXX"
(i.e., this document) while retaining the existing name 'aero'.
The IANA has assigned a 4 octet Private Enterprise Number (PEN) code
"45282" in the "enterprise-numbers" registry. This document is the
normative reference for using this code in DHCP Unique IDentifiers
based on Enterprise Numbers ("DUID-EN for OMNI Interfaces") (see:
Section 11). The IANA is therefore instructed to change the
enterprise designation for PEN code "45282" from "LinkUp Networks" to
"Overlay Multilink Network Interface (OMNI)".
The IANA has assigned the ifType code "301 - omni - Overlay Multilink
Network Interface (OMNI)" in accordance with Section 6 of [RFC8892].
The registration appears under the IANA "Structure of Management
Information (SMI) Numbers (MIB Module Registrations) - Interface
Types (ifType)" registry.
No further IANA actions are required.
26. Security Considerations
Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6
Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages
SHOULD include Nonce and Timestamp options [RFC3971] when transaction
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confirmation and/or time synchronization is needed. (Note however
that when OAL encapsulation is used the (echoed) OAL Identification
value can provide sufficient transaction confirmation.)
Client OMNI interfaces configured over secured ANET interfaces
inherit the physical and/or link-layer security properties (i.e.,
"protected spectrum") of the connected ANETs. Client OMNI interfaces
configured over open INET interfaces can use symmetric securing
services such as VPNs or can by some other means establish a direct
link. When a VPN or direct link may be impractical, however, the
security services specified in [RFC7401] and/or [RFC4380] can be
employed. While the OMNI link protects control plane messaging,
applications must still employ end-to-end transport- or higher-layer
security services to protect the data plane.
Strong network layer security for control plane messages and
forwarding path integrity for data plane messages between Proxy/
Servers MUST be supported. In one example, the AERO service
[I-D.templin-6man-aero] constructs an SRT spanning tree with Proxy/
Serves as leaf nodes and secures the spanning tree links with network
layer security mechanisms such as IPsec [RFC4301] or WireGuard.
Secured control plane messages are then constrained to travel only
over the secured spanning tree paths and are therefore protected from
attack or eavesdropping. Other control and data plane messages can
travel over route optimized paths that do not strictly follow the
secured spanning tree, therefore end-to-end sessions should employ
transport- or higher-layer security services. Additionally, the OAL
Identification value can provide a first level of data origin
authentication to mitigate off-path spoofing in some environments.
Identity-based key verification infrastructure services such as iPSK
may be necessary for verifying the identities claimed by Clients.
This requirement should be harmonized with the manner in which
(H)HITs are attested in a given operational environment.
Security considerations for specific access network interface types
are covered under the corresponding IP-over-(foo) specification
(e.g., [RFC2464], [RFC2492], etc.).
Security considerations for IPv6 fragmentation and reassembly are
discussed in Section 6.10. 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.
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27. Implementation Status
AERO/OMNI Release-3.2 was tagged on March 30, 2021, and is undergoing
internal testing. Additional internal releases expected within the
coming months, with first public release expected end of 1H2021.
Many AERO/OMNI functions are implemented and undergoing final
integration. OAL fragmentation/reassembly buffer management code has
been cleared for public release.
28. Document Updates
This document does not itself update other RFCs, but suggests that
the following could be updated through future IETF initiatives:
o [RFC1191]
o [RFC4443]
o [RFC8201]
o [RFC7526]
Updates can be through, e.g., standards action, the errata process,
etc. as appropriate.
29. Acknowledgements
The first version of this document was prepared per the consensus
decision at the 7th Conference of the International Civil Aviation
Organization (ICAO) Working Group-I Mobility Subgroup on March 22,
2019. Consensus to take the document forward to the IETF was reached
at the 9th Conference of the Mobility Subgroup on November 22, 2019.
Attendees and contributors included: Guray Acar, Danny Bharj,
Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo,
Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu
Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg
Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane
Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman,
Fryderyk Wrobel and Dongsong Zeng.
The following individuals are acknowledged for their useful comments:
Amanda Barber, Stuart Card, Donald Eastlake, Michael Matyas, Robert
Moskowitz, Madhu Niraula, Greg Saccone, Stephane Tamalet, Eduard
Vasilenko, Eric Vyncke. Pavel Drasil, Zdenek Jaron and Michal
Skorepa are especially recognized for their many helpful ideas and
suggestions. Madhuri Madhava Badgandi, Sean Dickson, Don Dillenburg,
Joe Dudkowski, Vijayasarathy Rajagopalan, Ron Sackman and Katherine
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Tran are acknowledged for their hard work on the implementation and
technical insights that led to improvements for the spec.
Discussions on the IETF 6man and atn mailing lists during the fall of
2020 suggested additional points to consider. The authors gratefully
acknowledge the list members who contributed valuable insights
through those discussions. Eric Vyncke and Erik Kline were the
intarea ADs, while Bob Hinden and Ole Troan were the 6man WG chairs
at the time the document was developed; they are all gratefully
acknowledged for their many helpful insights. Many of the ideas in
this document have further built on IETF experiences beginning in the
1990s, with insights from colleagues including Ron Bonica, Brian
Carpenter, Ralph Droms, Christian Huitema, Thomas Narten, Dave
Thaler, Joe Touch, 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
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.
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30. References
30.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[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>.
[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>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <https://www.rfc-editor.org/info/rfc4191>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
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[RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4,
ICMPv6, UDP, and TCP Headers", RFC 4727,
DOI 10.17487/RFC4727, November 2006,
<https://www.rfc-editor.org/info/rfc4727>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont,
"Traffic Selectors for Flow Bindings", RFC 6088,
DOI 10.17487/RFC6088, January 2011,
<https://www.rfc-editor.org/info/rfc6088>.
[RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by
Hosts in a Multi-Prefix Network", RFC 8028,
DOI 10.17487/RFC8028, November 2016,
<https://www.rfc-editor.org/info/rfc8028>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
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30.2. Informative References
[ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground
Interface for Civil Aviation, IETF Liaison Statement
#1676, https://datatracker.ietf.org/liaison/1676/", March
2020.
[ATN-IPS] WG-I, ICAO., "ICAO Document 9896 (Manual on the
Aeronautical Telecommunication Network (ATN) using
Internet Protocol Suite (IPS) Standards and Protocol),
Draft Edition 3 (work-in-progress)", December 2020.
[CKSUM] Stone, J., Greenwald, M., Partridge, C., and J. Hughes,
"Performance of Checksums and CRC's Over Real Data, IEEE/
ACM Transactions on Networking, Vol. 6, No. 5", October
1998.
[CRC] Jain, R., "Error Characteristics of Fiber Distributed Data
Interface (FDDI), IEEE Transactions on Communications",
August 1990.
[I-D.ietf-drip-rid]
Moskowitz, R., Card, S. W., Wiethuechter, A., and A.
Gurtov, "DRIP Entity Tag (DET) for Unmanned Aircraft
System Remote Identification (UAS RID)", draft-ietf-drip-
rid-11 (work in progress), October 2021.
[I-D.ietf-intarea-tunnels]
Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", draft-ietf-intarea-tunnels-10 (work in
progress), September 2019.
[I-D.ietf-ipwave-vehicular-networking]
(editor), J. (. J., "IPv6 Wireless Access in Vehicular
Environments (IPWAVE): Problem Statement and Use Cases",
draft-ietf-ipwave-vehicular-networking-24 (work in
progress), October 2021.
[I-D.ietf-tsvwg-udp-options]
Touch, J., "Transport Options for UDP", draft-ietf-tsvwg-
udp-options-13 (work in progress), June 2021.
[I-D.templin-6man-aero]
Templin, F. L., "Automatic Extended Route Optimization
(AERO)", draft-templin-6man-aero-35 (work in progress),
October 2021.
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[I-D.templin-6man-lla-type]
Templin, F. L., "The IPv6 Link-Local Address Type Field",
draft-templin-6man-lla-type-02 (work in progress),
November 2020.
[I-D.templin-6man-omni-interface]
Templin, F. L. and T. Whyman, "Transmission of IP Packets
over Overlay Multilink Network (OMNI) Interfaces", draft-
templin-6man-omni-interface-99 (work in progress), March
2021.
[IPV4-GUA]
Postel, J., "IPv4 Address Space Registry,
https://www.iana.org/assignments/ipv4-address-space/ipv4-
address-space.xhtml", December 2020.
[IPV6-GUA]
Postel, J., "IPv6 Global Unicast Address Assignments,
https://www.iana.org/assignments/ipv6-unicast-address-
assignments/ipv6-unicast-address-assignments.xhtml",
December 2020.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC1146] Zweig, J. and C. Partridge, "TCP alternate checksum
options", RFC 1146, DOI 10.17487/RFC1146, March 1990,
<https://www.rfc-editor.org/info/rfc1146>.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/info/rfc1191>.
[RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages",
RFC 1256, DOI 10.17487/RFC1256, September 1991,
<https://www.rfc-editor.org/info/rfc1256>.
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[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.
[RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over
ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998,
<https://www.rfc-editor.org/info/rfc2225>.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
<https://www.rfc-editor.org/info/rfc2464>.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
December 1998, <https://www.rfc-editor.org/info/rfc2473>.
[RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM
Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999,
<https://www.rfc-editor.org/info/rfc2492>.
[RFC2526] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast
Addresses", RFC 2526, DOI 10.17487/RFC2526, March 1999,
<https://www.rfc-editor.org/info/rfc2526>.
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529,
DOI 10.17487/RFC2529, March 1999,
<https://www.rfc-editor.org/info/rfc2529>.
[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>.
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[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330,
DOI 10.17487/RFC3330, September 2002,
<https://www.rfc-editor.org/info/rfc3330>.
[RFC3366] Fairhurst, G. and L. Wood, "Advice to link designers on
link Automatic Repeat reQuest (ARQ)", BCP 62, RFC 3366,
DOI 10.17487/RFC3366, August 2002,
<https://www.rfc-editor.org/info/rfc3366>.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692,
DOI 10.17487/RFC3692, January 2004,
<https://www.rfc-editor.org/info/rfc3692>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, DOI 10.17487/RFC3819, July 2004,
<https://www.rfc-editor.org/info/rfc3819>.
[RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local
Addresses", RFC 3879, DOI 10.17487/RFC3879, September
2004, <https://www.rfc-editor.org/info/rfc3879>.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/info/rfc4122>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[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>.
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[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
DOI 10.17487/RFC4380, February 2006,
<https://www.rfc-editor.org/info/rfc4380>.
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
2006, <https://www.rfc-editor.org/info/rfc4389>.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
<https://www.rfc-editor.org/info/rfc4429>.
[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605,
August 2006, <https://www.rfc-editor.org/info/rfc4605>.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
<https://www.rfc-editor.org/info/rfc4821>.
[RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly
Errors at High Data Rates", RFC 4963,
DOI 10.17487/RFC4963, July 2007,
<https://www.rfc-editor.org/info/rfc4963>.
[RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router
Advertisement Flags Option", RFC 5175,
DOI 10.17487/RFC5175, March 2008,
<https://www.rfc-editor.org/info/rfc5175>.
[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>.
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[RFC5237] Arkko, J. and S. Bradner, "IANA Allocation Guidelines for
the Protocol Field", BCP 37, RFC 5237,
DOI 10.17487/RFC5237, February 2008,
<https://www.rfc-editor.org/info/rfc5237>.
[RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)",
RFC 5558, DOI 10.17487/RFC5558, February 2010,
<https://www.rfc-editor.org/info/rfc5558>.
[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>.
[RFC6081] Thaler, D., "Teredo Extensions", RFC 6081,
DOI 10.17487/RFC6081, January 2011,
<https://www.rfc-editor.org/info/rfc6081>.
[RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A.
Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221,
DOI 10.17487/RFC6221, May 2011,
<https://www.rfc-editor.org/info/rfc6221>.
[RFC6247] Eggert, L., "Moving the Undeployed TCP Extensions RFC
1072, RFC 1106, RFC 1110, RFC 1145, RFC 1146, RFC 1379,
RFC 1644, and RFC 1693 to Historic Status", RFC 6247,
DOI 10.17487/RFC6247, May 2011,
<https://www.rfc-editor.org/info/rfc6247>.
[RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based
DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355,
DOI 10.17487/RFC6355, August 2011,
<https://www.rfc-editor.org/info/rfc6355>.
[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>.
[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>.
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[RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization
(AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012,
<https://www.rfc-editor.org/info/rfc6706>.
[RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
UDP Checksums for Tunneled Packets", RFC 6935,
DOI 10.17487/RFC6935, April 2013,
<https://www.rfc-editor.org/info/rfc6935>.
[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, DOI 10.17487/RFC6936, April 2013,
<https://www.rfc-editor.org/info/rfc6936>.
[RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation
with IPv6 Neighbor Discovery", RFC 6980,
DOI 10.17487/RFC6980, August 2013,
<https://www.rfc-editor.org/info/rfc6980>.
[RFC7042] Eastlake 3rd, D. and J. Abley, "IANA Considerations and
IETF Protocol and Documentation Usage for IEEE 802
Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042,
October 2013, <https://www.rfc-editor.org/info/rfc7042>.
[RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
Requirements for IPv6 Customer Edge Routers", RFC 7084,
DOI 10.17487/RFC7084, November 2013,
<https://www.rfc-editor.org/info/rfc7084>.
[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>.
[RFC7323] Borman, D., Braden, B., Jacobson, V., and R.
Scheffenegger, Ed., "TCP Extensions for High Performance",
RFC 7323, DOI 10.17487/RFC7323, September 2014,
<https://www.rfc-editor.org/info/rfc7323>.
[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<https://www.rfc-editor.org/info/rfc7401>.
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[RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S.,
Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit
Boundary in IPv6 Addressing", RFC 7421,
DOI 10.17487/RFC7421, January 2015,
<https://www.rfc-editor.org/info/rfc7421>.
[RFC7526] Troan, O. and B. Carpenter, Ed., "Deprecating the Anycast
Prefix for 6to4 Relay Routers", BCP 196, RFC 7526,
DOI 10.17487/RFC7526, May 2015,
<https://www.rfc-editor.org/info/rfc7526>.
[RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542,
DOI 10.17487/RFC7542, May 2015,
<https://www.rfc-editor.org/info/rfc7542>.
[RFC7739] Gont, F., "Security Implications of Predictable Fragment
Identification Values", RFC 7739, DOI 10.17487/RFC7739,
February 2016, <https://www.rfc-editor.org/info/rfc7739>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface
Support for IP Hosts with Multi-Access Support", RFC 7847,
DOI 10.17487/RFC7847, May 2016,
<https://www.rfc-editor.org/info/rfc7847>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8726] Farrel, A., "How Requests for IANA Action Will Be Handled
on the Independent Stream", RFC 8726,
DOI 10.17487/RFC8726, November 2020,
<https://www.rfc-editor.org/info/rfc8726>.
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[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>.
[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., Tuexen, M., Ruengeler, I., and
T. Voelker, "Packetization Layer Path MTU Discovery for
Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
September 2020, <https://www.rfc-editor.org/info/rfc8899>.
[RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
and F. Gont, "IP Fragmentation Considered Fragile",
BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,
<https://www.rfc-editor.org/info/rfc8900>.
[RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves,
"Temporary Address Extensions for Stateless Address
Autoconfiguration in IPv6", RFC 8981,
DOI 10.17487/RFC8981, February 2021,
<https://www.rfc-editor.org/info/rfc8981>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[RFC9001] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
<https://www.rfc-editor.org/info/rfc9001>.
[RFC9002] Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
and Congestion Control", RFC 9002, DOI 10.17487/RFC9002,
May 2021, <https://www.rfc-editor.org/info/rfc9002>.
Appendix A. OAL Checksum Algorithm
The OAL Checksum Algorithm adopts the 8-bit Fletcher algorithm
specified in Appendix I of [RFC1146] as also analyzed in [CKSUM].
[RFC6247] declared [RFC1146] historic for the reason that the
algorithms had never seen widespread use with TCP, however this
document adopts the 8-bit Fletcher algorithm for a different purpose.
Quoting from Appendix I of [RFC1146], the OAL Checksum Algorithm
proceeds as follows:
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"The 8-bit Fletcher Checksum Algorithm is calculated over a
sequence of data octets (call them D[1] through D[N]) by
maintaining 2 unsigned 1's-complement 8-bit accumulators A and B
whose contents are initially zero, and performing the following
loop where i ranges from 1 to N:
A := A + D[i]
B := B + A
It can be shown that at the end of the loop A will contain the
8-bit 1's complement sum of all octets in the datagram, and that B
will contain (N)D[1] + (N-1)D[2] + ... + D[N]."
To calculate the OAL checksum, the above algorithm is applied over
the N-octet concatenation of the OAL pseudo-header, the encapsulated
IP packet and the two-octet trailing checksum field initialized to 0.
Specifically, the algorithm is first applied over the 40 octets of
the OAL pseudo-header as data octets D[1] through D[40], then
continues over the entire length of the original IP packet as data
octets D[41] through D[N-2] and finally concludes with the two
trailing 0 octets as data octets D[N-1] and D[N].
Appendix B. IPv6 ND Message Authentication and Integrity
OMNI interface IPv6 ND messages are subject to authentication and
integrity checks at multiple levels. When an OMNI interface sends an
IPv6 ND message over an INET interface, it includes an authentication
sub-option with a valid signature but does not include an IPv6 ND
message checksum. The OMNI interface that receives the message
verifies the OAL checksum as a first-level integrity check, then
verifies the authentication signature (while ignoring the IPv6 ND
message checksum) to ensure IPv6 ND message authentication and
integrity.
When an OMNI interface sends an IPv6 ND message over an underlying
interface connected to a secured network, it omits the authentication
sub-option but instead calculates/includes an IPv6 ND message
checksum. The OMNI interface that receives the message applies any
lower-layer authentication and integrity checks, then verifies both
the OAL checksum (if present) and the IPv6 ND message checksum.
(Note that optimized implementations can verify both the OAL and IPv6
ND message checksums in a single pass over the data.) When an OMNI
interface sends IPv6 ND messages to a synchronized neighbor, it
includes an authentication sub-option only if authentication is
necessary; otherwise, it calculates/includes the IPv6 ND message
checksum.
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When the OMNI interface calculates the authentication signature or
IPv6 ND message checksum, it performs the calculation beginning with
a pseudo-header of the IPv6 ND message header and extends over all
following OAL packet data up to but not including the trailing OAL
checksum field. In particular, for OAL super-packets any additional
original IP packets included beyond the end of the IPv6 ND message
are simply considered as extensions of the IPv6 ND message for the
purpose of the calculation.
OAL destinations discard carrier packets with unacceptable
Identifications and submit the encapsulated fragments in others for
reassembly. The reassembly algorithm rejects any fragments with
unacceptable sizes, offsets, etc. and reassembles all others.
Following reassembly, the OAL checksum algorithm provides an
integrity assurance layer that compliments any integrity checks
already applied by lower layers as well as a first-pass filter for
any checks that will be applied later by upper layers.
Appendix C. VDL Mode 2 Considerations
ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2"
(VDLM2) that specifies an essential radio frequency data link service
for aircraft and ground stations in worldwide civil aviation air
traffic management. The VDLM2 link type is "multicast capable"
[RFC4861], but with considerable differences from common multicast
links such as Ethernet and IEEE 802.11.
First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of
magnitude less than most modern wireless networking gear. Second,
due to the low available link bandwidth only VDLM2 ground stations
(i.e., and not aircraft) are permitted to send broadcasts, and even
so only as compact layer 2 "beacons". Third, aircraft employ the
services of ground stations by performing unicast RS/RA exchanges
upon receipt of beacons instead of listening for multicast RA
messages and/or sending multicast RS messages.
This beacon-oriented unicast RS/RA approach is necessary to conserve
the already-scarce available link bandwidth. Moreover, since the
numbers of beaconing ground stations operating within a given spatial
range must be kept as sparse as possible, it would not be feasible to
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
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amount of data. The IETF lpwan working group is considering possible
alternatives: [https://datatracker.ietf.org/wg/lpwan/documents].
Appendix D. Client-Proxy/Server Isolation Through L2 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 *NET. 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 *NET links, Proxy/
Servers can maintain an OMNI-specific unicast L2 address ("MSADDR").
For Ethernet-compatible *NETs, this specification reserves one
Ethernet unicast address TBD5 (see: IANA Considerations). For non-
Ethernet statically-addressed *NETs, MSADDR is reserved per the
assigned numbers authority for the *NET addressing space. For still
other *NETs, MSADDR may be dynamically discovered through other
means, e.g., L2 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 L2 address. In this way, all of the Client's
IPv6 ND messages will be received by Proxy/Servers that are
configured to accept packets destined to MSADDR. Note that multiple
Proxy/Servers on the link could be configured to accept packets
destined to MSADDR, e.g., as a basis for supporting redundancy.
Therefore, Proxy/Servers must accept and process packets destined to
MSADDR, while all other devices must not process packets destined to
MSADDR. This model has well-established operational experience in
Proxy Mobile IPv6 (PMIP) [RFC5213][RFC6543].
Appendix E. Change Log
<< RFC Editor - remove prior to publication >>
Differences from earlier versions to draft-templin-6man-omni-45:
o New baseline version with corrections and section reorganizations
to improve document flow.
Authors' Addresses
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Fred L. Templin (editor)
The Boeing Company
P.O. Box 3707
Seattle, WA 98124
USA
Email: fltemplin@acm.org
Tony Whyman
MWA Ltd c/o Inmarsat Global Ltd
99 City Road
London EC1Y 1AX
England
Email: tony.whyman@mccallumwhyman.com
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