Network Working Group F. Templin, Ed.
Internet-Draft The Boeing Company
Updates: rfc1191, rfc4443, rfc8201 (if A. Whyman
approved) MWA Ltd c/o Inmarsat Global Ltd
Intended status: Standards Track December 10, 2020
Expires: June 13, 2021
Transmission of IP Packets over Overlay Multilink Network (OMNI)
Interfaces
draft-templin-6man-omni-interface-56
Abstract
Mobile nodes (e.g., aircraft of various configurations, terrestrial
vehicles, seagoing vessels, enterprise wireless devices, 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 therefore needed
for coordination with the network-based mobility service. This
document specifies the transmission of IP packets over Overlay
Multilink Network (OMNI) Interfaces.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 13, 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 8
5. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 13
5.1. Fragmentation Security Implications . . . . . . . . . . . 17
6. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 18
7. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 18
8. Domain-Local Addresses (DLAs) . . . . . . . . . . . . . . . . 20
9. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 21
9.1. Sub-Options . . . . . . . . . . . . . . . . . . . . . . . 23
9.1.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 24
9.1.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 24
9.1.3. Interface Attributes . . . . . . . . . . . . . . . . 24
9.1.4. Traffic Selector . . . . . . . . . . . . . . . . . . 28
9.1.5. MS-Register . . . . . . . . . . . . . . . . . . . . . 29
9.1.6. MS-Release . . . . . . . . . . . . . . . . . . . . . 29
9.1.7. Network Access Identifier (NAI) . . . . . . . . . . . 30
9.1.8. Geo Coordinates . . . . . . . . . . . . . . . . . . . 31
9.1.9. DHCP Unique Identifier (DUID) . . . . . . . . . . . . 31
9.1.10. DHCPv6 Message . . . . . . . . . . . . . . . . . . . 32
10. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 32
11. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 33
11.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 33
11.2. MN<->AR Traffic Loop Prevention . . . . . . . . . . . . 34
12. Router Discovery and Prefix Registration . . . . . . . . . . 34
12.1. Router Discovery in IP Multihop and IPv4-Only Access
Networks . . . . . . . . . . . . . . . . . . . . . . . . 38
12.2. MS-Register and MS-Release List Processing . . . . . . . 40
12.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 41
13. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 42
14. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 43
15. Detecting and Responding to MSE Failures . . . . . . . . . . 43
16. Transition Considerations . . . . . . . . . . . . . . . . . . 44
17. OMNI Interfaces on the Open Internet . . . . . . . . . . . . 44
18. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 45
19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46
20. Security Considerations . . . . . . . . . . . . . . . . . . . 47
21. Implementation Status . . . . . . . . . . . . . . . . . . . . 47
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22. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 48
23. References . . . . . . . . . . . . . . . . . . . . . . . . . 48
23.1. Normative References . . . . . . . . . . . . . . . . . . 48
23.2. Informative References . . . . . . . . . . . . . . . . . 50
Appendix A. Interface Attribute Preferences Bitmap Encoding . . 55
Appendix B. VDL Mode 2 Considerations . . . . . . . . . . . . . 57
Appendix C. MN / AR Isolation Through L2 Address Mapping . . . . 58
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 59
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 61
1. Introduction
Mobile Nodes (MNs) (e.g., aircraft of various configurations,
terrestrial vehicles, seagoing vessels, enterprise wireless devices,
etc.) often have multiple data links for communicating with networked
correspondents. 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.
MNs coordinate their data links in a discipline known as "multilink",
in which a single virtual interface is configured over the underlying
data links.
The MN configures a virtual interface (termed the "Overlay Multilink
Network (OMNI) interface") as a thin layer over the underlying Access
Network (ANET) 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 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.
Each MN receives a Mobile Network Prefix (MNP) for numbering
downstream-attached End User Networks (EUNs) independently of the
access network data links selected for data transport. The MN
performs router discovery over the OMNI interface (i.e., similar to
IPv6 customer edge routers [RFC7084]) and acts as a mobile router on
behalf of its EUNs. The router discovery process is iterated over
each of the OMNI interface's underlying interfaces in order to
register per-link parameters (see Section 12).
The OMNI interface provides a multilink nexus for exchanging inbound
and outbound traffic via the correct 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) from which OMNI link MNPs are derived. If there are
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multiple OMNI links, the IPv6 layer will see multiple OMNI
interfaces.
MNs may connect to multiple distinct OMNI links 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. The IP
layer selects an OMNI interface based on SBM routing considerations,
then the selected interface applies Performance-Based Multilink (PBM)
to select the correct underlying interface. Applications can apply
Segment Routing [RFC8402] to select independent SBM topologies for
fault tolerance.
The OMNI interface interacts with a network-based Mobility Service
(MS) through IPv6 Neighbor Discovery (ND) control message exchanges
[RFC4861]. The MS provides Mobility Service Endpoints (MSEs) that
track MN movements and represent their MNPs in a global routing or
mapping system.
Many OMNI use cases are currently under active consideration. 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.
This document specifies the transmission of IP packets and MN/MS
control messages over OMNI interfaces. The OMNI interface supports
either IP protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200])
as the network layer in the data plane, while using IPv6 ND messaging
as the control plane independently of the data plane IP protocol(s).
The OMNI Adaptation Layer (OAL) which operates as a mid-layer between
L3 and L2 is based on IP-in-IPv6 encapsulation per [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.
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Additionally, this document assumes the following IPv6 ND message
types: Router Solicitation (RS), Router Advertisement (RA), Neighbor
Solicitation (NS), Neighbor Advertisement (NA) and Redirect.
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:
Mobile Node (MN)
an end system with a mobile router having multiple distinct
upstream data link connections that are grouped together in one or
more logical units. The MN's data link connection parameters can
change over time due to, e.g., node mobility, link quality, etc.
The MN further connects a downstream-attached End User Network
(EUN). The term MN used here is distinct from uses in other
documents, and does not imply a particular mobility protocol.
End User Network (EUN)
a simple or complex downstream-attached mobile network that
travels with the MN as a single logical unit. The IP addresses
assigned to EUN devices remain stable even if the MN's upstream
data link connections change.
Mobility Service (MS)
a mobile routing service that tracks MN movements and ensures that
MNs remain continuously reachable even across mobility events.
Specific MS details are out of scope for this document.
Mobility Service Endpoint (MSE)
an entity in the MS (either singular or aggregate) that
coordinates the mobility events of one or more MN.
Mobility Service Prefix (MSP)
an aggregated IP prefix (e.g., 2001:db8::/32, 192.0.2.0/24, etc.)
advertised to the rest of the Internetwork by the MS, and from
which more-specific Mobile Network Prefixes (MNPs) are derived.
Mobile Network Prefix (MNP)
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a longer IP prefix taken from an MSP (e.g.,
2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a MN.
MNs sub-delegate the MNP to devices located in EUNs.
Access Network (ANET)
a data link service network (e.g., an aviation radio access
network, satellite service provider network, cellular operator
network, wifi network, etc.) that connects MNs. Physical and/or
data link level security between the MN and ANET are assumed.
Access Router (AR)
a first-hop router in the ANET for connecting MNs to
correspondents in outside Internetworks.
ANET interface
a MN'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 for ANET MNs and INET
correspondents. Examples include private enterprise networks,
ground domain aviation service networks and the global public
Internet itself.
INET interface
a node's attachment to a link in an INET.
OMNI link
a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured
over one or more INETs and their connected ANETs. An OMNI link
can comprise multiple INET 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.
OMNI domain
a set of affiliated OMNI links that collectively provide services
under a common (set of) Mobility Service Prefixes (MSPs).
OMNI interface
a node's attachment to an OMNI link, and configured over one or
more underlying ANET/INET interfaces. If there are multiple OMNI
links in an OMNI domain, a separate OMNI interface is configured
for each link.
OMNI Adaptation Layer (OAL)
an OMNI interface process whereby packets admitted into the
interface are wrapped in a mid-layer IPv6 header and fragmented/
reassembled if necessary to support the OMNI link Maximum
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Transmission Unit (MTU). The OAL is also responsible for
generating MTU-related control messages as necessary, and for
providing addressing context for spanning multiple segments of a
bridged OMNI link.
OMNI Link-Local Address (LLA)
a link local IPv6 address per [RFC4291] constructed as specified
in Section 7.
OMNI Domain-Local Address (DLA)
an IPv6 address from the prefix [DLA]::/48 constructed as
specified in Section 8. OMNI DLAs are statelessly derived from
OMNI LLAs, and vice-versa.
OMNI Option
an IPv6 Neighbor Discovery option providing multilink parameters
for the OMNI interface as specified in Section 9.
Multilink
an OMNI interface's manner of managing diverse underlying data
link interfaces as a single logical unit. The OMNI interface
provides a single unified interface to upper layers, while
underlying data link selections are performed on a per-packet
basis considering factors such as DSCP, flow label, application
policy, signal quality, cost, etc. Multilinking decisions are
coordinated in both the outbound (i.e. MN to correspondent) and
inbound (i.e., correspondent to MN) directions.
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
an ANET/INET 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.
Mobility Service Identification (MSID)
Each MSE and AR is assigned a unique 32-bit Identification (MSID)
as specified in Section 7.
Safety-Based Multilink (SBM)
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A means for ensuring fault tolerance through redundancy by
connecting multiple independent OMNI interfaces to independent
routing topologies (i.e., multiple independent OMNI links).
Performance Based Multilink (PBM)
A means for selecting underlying interface(s) for packet
transmission and reception within a single OMNI interface.
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.
OMNI links maintain a constant value "MAX_MSID" selected to provide
MNs with an acceptable level of MSE redundancy while minimizing
control message amplification. It is RECOMMENDED that MAX_MSID be
set to the default value 5; if a different value is chosen, it should
be set uniformly by all nodes on the OMNI link.
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 MN virtual interface configured over one or
more underlying interfaces, which may be physical (e.g., an
aeronautical radio link) or virtual (e.g., an Internet or higher-
layer "tunnel"). The MN receives a MNP from the MS, and coordinates
with the MS through IPv6 ND message exchanges. The MN uses the MNP
to construct a unique OMNI LLA through the algorithmic derivation
specified in Section 7 and assigns the LLA to the OMNI interface.
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 with
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 LLA) |
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 that provide INET access.
o ANET interfaces connect to a protected ANET that is separated from
the open INET by an AR acting as a proxy. The ANET interface may
be either on the same L2 link segment as the AR, or separated from
the AR by multiple IP hops.
o VPNed interfaces use security encapsulation over an INET/ANET to 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 without crossing any ANET/INET paths. An example is a line-
of-sight link between a remote pilot and an unmanned aircraft.
The OMNI virtual interface model gives rise to a number of
opportunities:
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o since MN OMNI LLAs are uniquely derived from an MNP, no Duplicate
Address Detection (DAD) or Multicast Listener Discovery (MLD)
messaging is necessary.
o since Temporary OMNI LLAs are statistically unique, they can be
used without DAD for short-term purposes, e.g. until an MN OMNI
LLA is obtained.
o ANET interfaces on the same L2 link segment as an AR do not
require any L3 addresses (i.e., not even link-local) in
environments where communications are coordinated entirely over
the OMNI interface. (An alternative would be to also assign the
same OMNI LLA to all ANET interfaces.)
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
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 inter-INET traversal when nodes located
in different INETs need to communicate with one another. This
mode of operation would not be possible via direct communications
over the underlying interfaces themselves.
o the OMNI Adaptation Layer (OAL) within the OMNI interface supports
lossless and adaptive path MTU mitigations not available for
communications directly over the underlying interfaces themselves.
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.
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Other opportunities are discussed in [RFC7847]. 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.
However, the opportunities discussed above are not available when the
architectural layering is bypassed in this way.
Figure 2 depicts the architectural model for a MN with an attached
EUN connecting to the MS via multiple independent ANETs. When an
underlying interface becomes active, the MN's OMNI interface sends
IPv6 ND messages without encapsulation if the first-hop Access Router
(AR) is on the same underlying link; otherwise, the interface uses
IP-in-IP encapsulation. The IPv6 ND messages traverse the ground
domain ANETs until they reach an AR (AR#1, AR#2, ..., AR#n), which
then coordinates with a Mobility Service Endpoint (MSE#1, MSE#2, ...,
MSE#m) in the INET and returns an IPv6 ND message response to the MN.
The Hop Limit in IPv6 ND messages is not decremented due to
encapsulation; hence, the OMNI interface appears to be attached to an
ordinary link.
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+--------------+ (:::)-.
| MN |<-->.-(::EUN:::)
+--------------+ `-(::::)-'
|OMNI interface|
+----+----+----+
+--------|IF#1|IF#2|IF#n|------ +
/ +----+----+----+ \
/ | \
/ | \
v v v
(:::)-. (:::)-. (:::)-.
.-(::ANET:::) .-(::ANET:::) .-(::ANET:::)
`-(::::)-' `-(::::)-' `-(::::)-'
+----+ +----+ +----+
... |AR#1| .......... |AR#2| ......... |AR#n| ...
. +-|--+ +-|--+ +-|--+ .
. | | |
. v v v .
. <----- INET Encapsulation -----> .
. .
. +-----+ (:::)-. .
. |MSE#2| .-(::::::::) +-----+ .
. +-----+ .-(::: INET :::)-. |MSE#m| .
. (::::: Routing ::::) +-----+ .
. `-(::: System :::)-' .
. +-----+ `-(:::::::-' .
. |MSE#1| +-----+ +-----+ .
. +-----+ |MSE#3| |MSE#4| .
. +-----+ +-----+ .
. .
. .
. <----- Worldwide Connected Internetwork ----> .
...........................................................
Figure 2: MN/MS Coordination via Multiple ANETs
After the initial IPv6 ND message exchange, the MN (and/or any nodes
on its attached EUNs) can send and receive IP data packets over the
OMNI interface. OMNI interface multilink services will forward the
packets via ARs in the correct underlying ANETs. The AR encapsulates
the packets according to the capabilities provided by the MS and
forwards them to the next hop within the worldwide connected
Internetwork via optimal routes.
OMNI links span one or more underlying Internetwork via the OMNI
Adaptation Layer (OAL) which is based on a mid-layer overlay
encapsulation using [RFC2473]. Each OMNI link corresponds to a
different overlay (differentiated by an address codepoint) which may
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be carried over a completely separate underlying topology. Each MN
can facilitate SBM by connecting to multiple OMNI links using a
distinct OMNI interface for each link.
5. The OMNI Adaptation Layer (OAL)
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 that may have diverse MTUs. OMNI interfaces accommodate
MTU diversity through the use of the OMNI Adaptation Layer (OAL) as
discussed in this section.
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 packets of at least 1280 bytes without generating an
IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) message
[RFC8201]. (Note: the source can apply "source fragmentation" for
locally-generated IPv6 packets up to 1500 bytes and larger still if
it if has a way to determine that the destination configures a larger
MRU, but 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 DF bit in the IPv4 encapsulation
headers of packets sent over IPv4 underlying interfaces therefore
MUST be set to 0. (Note: even if the encapsulation source has a way
to determine that the encapsulation destination configures an MRU
larger than 576 bytes, it should not assume a larger minimum IPv4
path MTU without careful consideration of the issues discussed in
Section 5.1.)
The OMNI interface configures both an MTU and MRU of 9180 bytes
[RFC2492]; the size is therefore not a reflection of the underlying
interface MTUs, but rather determines the largest packet the OMNI
interface can forward or reassemble. The OMNI interface uses the
OMNI Adaptation Layer (OAL) to admit packets from the network layer
that are no larger than the OMNI interface MTU while generating
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
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as "PTBs", and introduces a distinction between PTB "hard" and "soft"
errors as discussed below.
For IPv4 packets with DF=0, the network layer performs IPv4
fragmentation if necessary then admits the packets/fragments into the
OMNI interface; these fragments will be reassembled by the final
destination. For IPv4 packets with DF=1 and IPv6 packets, the
network layer admits the packet if it is no larger than the OMNI
interface MTU; otherwise, it drops the packet and returns a PTB hard
error message to the source.
For each admitted IP packet/fragment, the OMNI interface internally
employs the OAL when necessary by inserting a mid-layer IPv6 header
between the inner IP packet/fragment and any outer IP encapsulation
headers per [RFC2473]. (The OAL does not decrement the inner IP Hop
Limit/TTL during enapsulation since the insertion occurs at a layer
below IP forwarding.) The OAL then calculates the 32-bit CRC over
the entire mid-layer packet and writes the value in a trailing
4-octet field at the end of the packet. Next, the OAL fragments this
mid-layer IPv6 packet, forwards the fragments (using outer IP
encapsulation if necessary), and returns an internally-generated PTB
soft error message (subject to rate limiting) if it deems the 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 OAL operates with respect to both the minimum IPv6 and IPv4 path
MTUs as follows:
o When an OMNI interface sends a packet toward a final destination
via an ANET peer, it sends without OAL encapsulation if the packet
(including any outer-layer ANET encapsulations) is no larger than
the underlying interface MTU for on-link ANET peers or the minimum
ANET path MTU for peers separated by multiple IP hops. Otherwise,
the OAL inserts an IPv6 header per [RFC2473] with source address
set to the node's own OMNI Domain-Local Address (DLA) (see:
Section 8) and destination set to the OMNI DLA of the ANET peer.
The OAL then calculates and appends the trailing 32-bit CRC, then
uses IPv6 fragmentation to break the packet into a minimum number
of non-overlapping fragments where the largest fragment size
(including both the OMNI and any outer-layer ANET encapsulations)
is determined by the underlying interface MTU for on-link ANET
peers or the minimum ANET path MTU for peers separated by multiple
IP hops. The OAL then encapsulates the fragments in any ANET
headers and sends them to the ANET peer, which reassembles before
forwarding toward the final destination.
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o When an OMNI interface sends a packet toward a final destination
via an INET interface, it sends packets (including any outer-layer
INET encapsulations) no larger than the minimum INET path MTU
without OAL encapsulation if the destination is reached via an
INET address within the same OMNI link segment. Otherwise, the
OAL inserts an IPv6 header per [RFC2473] with source address set
to the node's OMNI DLA, destination set to the DLA of the next hop
OMNI node toward the final destination and (if necessary) with a
Segment Routing Header with the remaining Segment IDs on the path
to the final destination. The OAL then calculates and appends the
trailing 32-bit CRC, then uses IPv6 fragmentation to break the
packet into a minimum number of non-overlapping fragments where
the largest fragment size (including both the OMNI and outer-layer
INET encapsulations) is the minimum INET path MTU, and the
smallest fragment size is no smaller than 256 bytes (i.e.,
slightly less than half the minimum IPv4 path MTU). The OAL then
encapsulates the fragments in any INET headers and sends them to
the OMNI link neighbor, which reassembles before forwarding toward
the final destination.
The OAL unconditionally drops all OAL fragments received from an INET
peer that are smaller than 256 bytes (note that no minimum fragment
size is specified for ANET peers since the underlying ANET is secured
against tiny fragment attacks). In order to set the correct context
for reassembly, the OAL of the OMNI interface that inserts the IPv6
header MUST also be the one that inserts the IPv6 Fragment Header
Identification value. While not strictly required, sending all
fragments of the same fragmented OAL packet consecutively over the
same underlying interface with minimal inter-fragment delay may
increase the likelihood of successful reassembly.
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. However, the
OAL can also forward large packets via encapsulation and
fragmentation while at the same time returning PTB soft error
messages (subject to rate limiting) indicating that a forwarded
packet was uncomfortably large. The OMNI interface can therefore
continuously forward large packets without loss while returning PTB
soft error messages recommending a smaller size. 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.
The OAL sets the ICMPv4 header "unused" field or ICMPv6 header Code
field to the value 1 in PTB soft error messages. The OAL sets the
PTB destination address to the source address of the original packet,
and sets the source address to the MNP Subnet Router Anycast address
of the MN (i.e., whether the MN was the source or target of the
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original packet). When the original source receives the PTB, it
reduces its path MTU estimate the same as for hard errors but does
not regard the message as a loss indication. (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.) This document therefore updates
[RFC1191][RFC4443] and [RFC8201]. Furthermore, implementations of
[RFC4821] must be aware that PTB hard or soft errors may arrive at
any time even if after a successful MTU probe (this is the same
consideration as for an ordinary path fluctuation following a
successful probe).
In summary, the OAL 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 loss,
original sources that receive soft errors can quickly scan for path
MTU increases without waiting for the minimum 10 minutes specified
for loss-oriented PTB hard errors [RFC1191][RFC8201]. The OAL
therefore provides a lossless and adaptive service that accommodates
MTU diversity especially well-suited for dynamic multilink
environments.
Note: In network paths where IPv6/IPv4 protocol translation or IPv6-
in-IPv4 encapsulation may be prevalent, it may be prudent for the OAL
to always assume the IPv4 minimum path MTU (i.e., 576 bytes)
regardless of the underlying interface IP protocol version. Always
assuming the IPv4 minimum path MTU even for IPv6 underlying
interfaces may produce more fragments and additional header overhead,
but will always interoperate and never run the risk of presenting an
IPv4 interface with a packet that exceeds its MRU.
Note: An OMNI interface that reassembles OAL fragments may experience
congestion-oriented loss in its reassembly cache and can optionally
send PTB soft errors to the original source and/or ICMP "Time
Exceeded" messages to the source of the OAL fragments. In
environments where the messages may contribute to unacceptable
additional congestion, however, the OMNI interface can simply regard
the loss as an ordinary unreported congestion event for which the
original source will eventually compensate.
Note: When the network layer forwards an IPv4 packet/fragment with
DF=0 into the OMNI interface, the interface can optionally perform
(further) IPv4 fragmentation before invoking the OAL so that the
fragments will be reassembled by the final destination. When the
network layer performs IPv6 fragmentation for locally-generated IPv6
packets, the OMNI interface typically invokes the OAL without first
applying (further) IPv6 fragmentation; the network layer should
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therefore fragment to the minimum IPv6 path MTU (or smaller still) to
push the reassembly burden to the final destination and avoid
receiving PTB soft errors from the OMNI interface. Aside from these
non-normative guidelines, the manner in which any IP fragmentation is
invoked prior to OAL encapsulation/fragmentation is an implementation
matter.
Note: Inclusion of the 32-bit CRC prior to fragmentation assumes that
the receiving OAL will discard any packets with incorrect CRC values
following reassembly. The 32-bit CRC is sufficient to detect
reassembly misassociations for packet sizes up to the OMNI interface
MTU 9180 but may not be sufficient to detect errors for larger sizes
[CRC].
Note: Some underlying interface types (e.g., VPNs) may already
provide their own robust fragmentation and reassembly services even
without OAL encapsulation. In those cases, the OAL can invoke the
inherent underlying interface schemes instead while employing PTB
soft errors in the same fashion as described above. Other underlying
interface properties such as header/message compression can also be
harnessed in a similar fashion.
Note: Applications can dynamically tune the size of the 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.
5.1. 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
underlying interface such that congestion experienced over a
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first underlying interface does not cause discard of incomplete
reassemblies for uncongested underlying interfaces.
3. Attacks based on predictable fragment identification values -
this threat is mitigated by selecting a suitably random ID value
per [RFC7739].
4. Evasion of Network Intrusion Detection Systems (NIDS) - this
threat is mitigated by disallowing "tiny fragments" per the OAL
fragmentation procedures specified above.
Additionally, IPv4 fragmentation 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 packets while the fragments of
old packets using the same ID are still alive in the network
[RFC4963]. However, since the largest OAL fragment that will be sent
via an IPv4 INET path is 576 bytes any IPv4 fragmentation would occur
only on links with an IPv4 MTU smaller than this size, and [RFC3819]
recommendations suggest that such links will have low data rates.
Since IPv6 provides a 32-bit Identification value, IP ID wraparound
at high data rates is not a concern for IPv6 fragmentation.
6. Frame Format
The OMNI interface transmits IPv6 packets according to the native
frame format of each 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 tunnels over IPv6 the frame format is specified in
[RFC2473], etc.
7. Link-Local Addresses (LLAs)
OMNI nodes are assigned OMNI interface IPv6 Link-Local Addresses
(i.e., "OMNI LLAs") through pre-service administrative actions. MN
OMNI LLAs embed the MNP assigned to the mobile node, while MS OMNI
LLAs include an administratively-unique ID that is guaranteed to be
unique on the link. OMNI LLAs are configured as follows:
o IPv6 MN OMNI LLAs encode the most-significant 64 bits of a 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 MN OMNI LLA is fe80::2001:db8:1000:2000/120.
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o IPv4-compatible MN OMNI 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-Compatible MN OMNI LLA for
192.0.2.0/24 is fe80::ffff:192.0.2.0/120 (also written as
fe80::ffff:c000:0200/120).
o MS OMNI LLAs are assigned to ARs and MSEs and MUST be managed for
uniqueness. The lower 32 bits of the LLA includes a unique
integer "MSID" value between 0x00000001 and 0xfeffffff, e.g., as
in fe80::1, fe80::2, fe80::3, etc., fe80::feff:ffff. The MS OMNI
LLA prefix length is determined by adding 96 to the MSID prefix
length. For example, if the MSID '0x10002000' prefix length is 16
then the MS OMNI LLA prefix length is set to 112 and the LLA is
written as fe80::1000:2000/112. The MSID 0x00000000 is the
"Anycast" MSID and corresponds to the link-local Subnet-Router
anycast address (fe80::) [RFC4291]; the MSID range 0xff000000
through 0xffffffff is reserved for future use.
o Temporary OMNI LLAs are constructed per [I-D.ietf-6man-rfc4941bis]
and used by MNs for the short-term purpose of procuring an actual
MN OMNI LLA upon startup or (re)connecting to the network. MNs
may use Temporary OMNI LLAs as the IPv6 source address of an RS
message in order to request a MN OMNI LLA from the MS.
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 various OMNI LLA constructs
discussed above.
Since MN OMNI LLAs are based on the distribution of administratively
assured unique MNPs, and since MS OMNI LLAs are guaranteed unique
through administrative assignment, OMNI interfaces set the
autoconfiguration variable DupAddrDetectTransmits to 0 [RFC4862].
Temporary OMNI LLAs employ optimistic DAD principles [RFC4429] since
they are probabilistically unique and their use is short-duration in
nature.
Note: If future extensions of the IPv6 protocol permit extension of
the /64 boundary, the additional prefix bits of IPv6 MN OMNI LLAs
would be encoded in bits 16 through 63 of the LLA. (The most-
significant 64 bits would therefore still be in LLA bits 64-127, and
the remaining bits would be in bits 16 through 48 of the LLA. This
would permit encoding of IPv6 prefix lengths up to /112.)
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8. Domain-Local Addresses (DLAs)
OMNI links use IPv6 Domain-Local Addresses (i.e., "OMNI DLAs") as the
source and destination addresses in OAL IPv6 encapsulation headers.
This document assumes availability of a prefix [DLA]::/48 for mapping
OMNI LLAs to routable OMNI DLAs. Since DLAs are only routable within
the scope of an OMNI domain, they are normally derived from the IPv6
Unique Local Address (ULA) 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 [DLA]::/48, which is then followed by a 16-bit
Subnet ID then finally followed by a 64 bit Interface ID exactly as
described in Section 3 of [RFC4193]. ULA prefixes with the L bit set
to 0 a(i.e., as fc00::/8) and IPv6 Globally Unique Address (GUA)
prefixes represent other DLA candidates, but their use within an OMNI
domain must not conflict with any other uses inside or outside the
domain.
Each OMNI link instance is identified by a value between 0x0000 and
0xfeff in bits 48-63 of [DLA]::/48 (the values 0xff00 through 0xfffe
are reserved for future use and the value 0xffff denotes a Temporary
OMNI DLA). For example, OMNI DLAs associated with instance 0 are
configured from the prefix [DLA]:0000::/64, instance 1 from
[DLA]:0001::/64, instance 2 from [DLA]:0002::/64, etc. OMNI DLAs and
their associated prefix lengths are configured in correspondence with
OMNI LLAs through stateless prefix translation. For example, for
OMNI link instance [DLA]:1010::/64:
o the OMNI DLA corresponding to the MN OMNI 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 DLA as
[DLA]:1010:2001:db8:1:2/120 (where, the DLA prefix length becomes
64 plus the IPv6 MNP length).
o the OMNI DLA 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 [DLA]:1010:0:ffff:192.0.2.0/124 (where, the
DLA prefix length is 64 plus 32 plus the IPv4 MNP length).
o the OMNI DLA corresponding to fe80::1000/112 is simply
[DLA]:1010::1000/112.
o the OMNI DLA corresponding to fe80::/128 is simply
[DLA]:1010::/128.
o the OMNI DLA corresponding to a Temporary OMNI LLA is simply
[DLA]:ffff:[64-bit Temporary Interface ID]/128.
o etc.
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Each OMNI interface assigns the Anycast OMNI DLA specific to the OMNI
link instance. For example, the OMNI interface connected to instance
3 assigns the Anycast OMNI DLA [DLA]:0003::/128. Routers that
configure OMNI interfaces advertise the OMNI service prefix (e.g.,
[DLA]:0003::/64) into the local routing system so that applications
can direct traffic according to SBM requirements.
The OMNI DLA presents an IPv6 address format that is routable within
the OMNI domain 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 ARs and MSEs. All MNs are also
considered to be connected to the OMNI link, however OAL
encapsulation is omitted over ANET links when possible to conserve
bandwidth (see: Section 11).
Each OMNI link can be subdivided into "segments" that often
correspond to different administrative domains or physical
partitions. OMNI nodes can use IPv6 Segment Routing [RFC8402] when
necessary to support efficient packet forwarding to destinations
located in other OMNI link segments. A full discussion of Segment
Routing over the OMNI link appears in [I-D.templin-intarea-6706bis].
9. Address Mapping - Unicast
OMNI interfaces maintain a neighbor cache for tracking per-neighbor
state and use the link-local address format specified in Section 7.
OMNI interface IPv6 Neighbor Discovery (ND) [RFC4861] messages sent
over physical underlying 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]). OMNI interface IPv6 ND messages sent over underlying
interfaces via encapsulation do not include S/TLLAOs which were
intended for encoding physical L2 media address formats and not
encapsulation IP addresses. Furthermore, S/TLLAOs are not intended
for encoding additional interface attributes needed for multilink
coordination. 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.
MNs such as aircraft typically have many 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 use
an IPv6 ND option called the OMNI option formatted as shown in
Figure 3:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |T| Preflen | S/T-ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Sub-Options ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: OMNI Option Format
In this format:
o Type is set to TBD. If multiple OMNI option instances appear in
the same IPv6 ND message, the first instance is processed and all
other instances are ignored.
o Length is set to the number of 8 octet blocks in the option.
o T is a 1-bit flag set to 1 for Temporary OMNI LLAs (otherwise, set
to 0) and Preflen is a 7 bit field that determines the length of
prefix associated with an MN OMNI LLA. Values 1 through 127
specify a prefix length, while the value 0 indicates
"unspecified". For IPv6 ND messages sent from a MN to the MS, T
and Preflen apply to the IPv6 source LLA and provide the length
that the MN is requesting or asserting to the MS. For IPv6 ND
messages sent from the MS to the MN, T and Preflen apply to the
IPv6 destination LLA and indicate the length that the MS is
granting to the MN. For IPv6 ND messages sent between MS
endpoints, T is set to 0 and Preflen provides the length
associated with the source/target MN that is subject of the ND
message.
o S/T-ifIndex corresponds to the ifIndex value for source or target
underlying interface used to convey this IPv6 ND message. OMNI
interfaces MUST number each distinct underlying interface with an
ifIndex value between '1' and '255' that represents a MN-specific
8-bit mapping for the actual ifIndex value assigned by network
management [RFC2863] (the ifIndex value '0' is reserved for use by
the MS). For RS and NS messages, S/T-ifIndex corresponds to the
source underlying interface the message originated from. For RA
and NA messages, S/T-ifIndex corresponds to the target underlying
interface that the message is destined to.
o Sub-Options is a Variable-length field, of length such that the
complete OMNI Option is an integer multiple of 8 octets long.
Contains one or more Sub-Options, as described in Section 9.1.
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9.1. Sub-Options
The OMNI option includes zero or more Sub-Options. Each consecutive
Sub-Option is concatenated immediately after its predecessor. All
Sub-Options except Pad1 (see below) are in type-length-value (TLV)
encoded in the following format:
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 4: Sub-Option Format
o Sub-Type is a 1-octet field that encodes the Sub-Option type.
Sub-Options defined in this document are:
Option Name Sub-Type
Pad1 0
PadN 1
Interface Attributes 2
Traffic Selector 3
MS-Register 4
MS-Release 5
Network Access Identifier 6
Geo Coordinates 7
DHCP Unique Identifier (DUID) 8
DHCPv6 Message 9
Figure 5
Sub-Types 253 and 254 are reserved for experimentation, as
recommended in [RFC3692].
o Sub-Length is a 1-octet field that encodes the length of the Sub-
Option Data (i.e., ranging from 0 to 255 octets).
o Sub-Option Data is a block of data with format determined by Sub-
Type.
During processing, unrecognized Sub-Options are ignored and the next
Sub-Option processed until the end of the OMNI option is reached.
The following Sub-Option types and formats are defined in this
document:
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9.1.1. Pad1
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Sub-Type=0 |
+-+-+-+-+-+-+-+-+
Figure 6: Pad1
o Sub-Type is set to 0. If multiple instances appear in the same
OMNI option all are processed.
o No Sub-Length or Sub-Option Data follows (i.e., the "Sub-Option"
consists of a single zero octet).
9.1.2. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Sub-Type=1 | Sub-length=N | N padding octets ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 7: PadN
o Sub-Type is set to 1. If multiple instances appear in the same
OMNI option all are processed.
o Sub-Length is set to N (from 0 to 255) being the number of padding
octets that follow.
o Sub-Option Data consists of N zero-valued octets.
9.1.3. Interface Attributes
The Interface Attributes sub-option provides L2 forwarding
information for the multilink conceptual sending algorithm discussed
in Section 11. The L2 information is used for selecting among
potentially multiple candidate underlying interfaces that can be used
to forward packets to the neighbor based on factors such as DSCP
preferences and link quality. Interface Attributes further include
link-layer address information to be used for either OAL
encapsulation or direct UDP/IP encapsulation (when OAL encapsulation
can be avoided). The Interface Attributes format and contents are
given in Figure 8 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=2 | Sub-length=N | ifIndex | ifType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Provider ID | Link |R| API | SRT | FMT | LHS (0 - 7) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LHS (bits 8 - 31) | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ ~
~ Link Layer Address (L2ADDR) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bitmap(0)=0xff|P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P28|P29|P30|P31| Bitmap(1)=0xff|P32|P33|P34|P35|P36| ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 8: Interface Attributes
o Sub-Type is set to 2. If multiple instances with different
ifIndex values appear in the same OMNI option all are processed;
if multiple instances with the same ifIndex value appear, the
first is processed and all others are ignored.
o Sub-Length is set to N (from 4 to 255) that encodes the number of
Sub-Option Data octets that follow.
o Sub-Option Data contains an "Interface Attribute" option encoded
as follows (note that the first four octets must be present):
* ifIndex is set to an 8-bit integer value corresponding to a
specific underlying interface the same as specified above for
the OMNI option header S/T-ifIndex. An OMNI option may include
multiple Interface Attributes Sub-Options, with each distinct
ifIndex value pertaining to a different underlying interface.
The OMNI option will often include an Interface Attributes Sub-
Option with the same ifIndex value that appears in the S/
T-ifIndex. In that case, the actual encapsulation address of
the received IPv6 ND message should be compared with the L2ADDR
encoded in the Sub-Option (see below); if the addresses are
different (or, if L2ADDR absent) the presence of a Network
Address Translator (NAT) is indicated.
* ifType is set to an 8-bit integer value corresponding to the
underlying interface identified by ifIndex. The value
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represents an OMNI interface-specific 8-bit mapping for the
actual IANA ifType value registered in the 'IANAifType-MIB'
registry [http://www.iana.org].
* Provider ID is set to an OMNI interface-specific 8-bit ID value
for the network service provider associated with this ifIndex.
* 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").
* R is reserved for future use.
* API - a 3-bit "Address/Preferences/Indexed" code that
determines the contents of the remainder of the sub-option as
follows:
+ When the most significant bit (i.e., "Address") is set to 1,
the SRT, FMT, LHS and L2ADDR fields are included immediately
following the API code; else, they are omitted.
+ When the next most significant bit (i.e., "Preferences") is
set to 1, a preferences block is included next; else, it is
omitted. (Note that if "Address" is set the preferences
block immediately follows L2ADDR; else, it immediately
follows the API code.)
+ When a preferences block is present and the least
significant bit (i.e., "Indexed") is set to 0, the block is
encoded in "Simplex" form as shown in Figure 8; else it is
encoded in "Indexed" form as discussed below.
* When API indicates that an "Address" is included, the following
fields appear in consecutive order (else, they are omitted):
+ SRT - a 5-bit Segment Routing Topology prefix length value
that (when added to 96) determines the prefix length to
apply to the DLA formed from concatenating fe*::/96 with the
32 bit LHS MSID value that follows. For example, the value
16 corresponds to the prefix length 112.
+ FMT - a 3-bit "Framework/Mode/Type" code corresponding to
the included Link Layer Address as follows:
- When the most significant bit (i.e., "Framework") is set
to 0, L2ADDR is the INET encapsulation address of a
Proxy/Server; otherwise, it is the address for the
Source/Target itself
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- When the next most significant bit (i.e., "Mode") is set
to 0, the Source/Target L2ADDR is on the open INET;
otherwise, it is (likely) located behind a Network
Address Translator (NAT).
- When the least significant bit (i.e., "Type") is set to
0, L2ADDR includes a UDP Port Number followed by an IPv4
address; else, a UDP Port Number followed by an IPv6
address.
+ LHS - the 32 bit MSID of the Last Hop Server/Proxy on the
path to the target. When SRT and LHS are both set to 0, the
LHS is considered unspecified in this IPv6 ND message. When
SRT is set to 0 and LHS is non-zero, the prefix length is
set to 128. SRT and LHS provide guidance to the OMNI
interface forwarding algorithm. Specifically, if SRT/LHS is
located in the local OMNI link segment then the OMNI
interface can encapsulate according to FMT/L2ADDR; else, it
must forward according to the OMNI link spanning tree. See
[I-D.templin-intarea-6706bis] for further discussion.
+ Link Layer Address (L2ADDR) - Formatted according to FMT,
and identifies the link-layer address (i.e., the
encapsulation address) of the source/target. The UDP Port
Number appears in the first two octets and the IP address
appears in the next 4 octets for IPv4 or 16 octets for IPv6.
The Port Number and IP address are recorded in ones-
compliment "obfuscated" form per [RFC4380]. The OMNI
interface forwarding algorithm uses FMT/L2ADDR to determine
the encapsulation address for forwarding when SRT/LHS is
located in the local OMNI link segment.
* When API indicates that "Preferences" are included, a
preferences block appears as the remainder of the Sub-Option as
a series of Bitmaps and P[*] values. In "Simplex" form, the
index for each singleton Bitmap octet is inferred from its
sequential position (i.e., 0, 1, 2, ...) as shown in Figure 8.
In "Indexed" form, each Bitmap is preceded by an Index octet
that encodes a value "i" = (0 - 255) as the index for its
companion Bitmap as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Index=i | Bitmap(i) |P[*] values ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 9
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* The preferences consist of a first (simplex/indexed) Bitmap
(i.e., "Bitmap(i)") followed by 0-8 single-octet blocks of
2-bit P[*] values, followed by a second Bitmap (i), followed by
0-8 blocks of P[*] values, etc. Reading from bit 0 to bit 7,
the bits of each Bitmap(i) that are set to '1'' indicate the
P[*] blocks from the range P[(i*32)] through P[(i*32) + 31]
that follow; if any Bitmap(i) bits are '0', then the
corresponding P[*] block is instead omitted. For example, if
Bitmap(0) contains 0xff then the block with P[00]-P[03],
followed by the block with P[04]-P[07], etc., and ending with
the block with P[28]-P[31] are included (as shown in Figure 8).
The next Bitmap(i) is then consulted with its bits indicating
which P[*] blocks follow, etc. out to the end of the Sub-
Option.
* Each 2-bit P[*] field is set to the value '0' ("disabled"), '1'
("low"), '2' ("medium") or '3' ("high") to indicate a QoS
preference for underlying interface selection purposes. Not
all P[*] values need to be included in the OMNI option of each
IPv6 ND message received. Any P[*] values represented in an
earlier OMNI option but omitted in the current OMNI option
remain unchanged. Any P[*] values not yet represented in any
OMNI option default to "medium".
* The first 16 P[*] blocks correspond to the 64 Differentiated
Service Code Point (DSCP) values P[00] - P[63] [RFC2474]. Any
additional P[*] blocks that follow correspond to "pseudo-DSCP"
traffic classifier values P[64], P[65], P[66], etc. See
Appendix A for further discussion and examples.
9.1.4. Traffic Selector
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=3 | Sub-length=N | ifIndex | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ ~
~ RFC 6088 Format Traffic Selector ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Traffic Selector
o Sub-Type is set to 3. If multiple instances appear in the same
OMNI option all are processed, i.e., even if the same ifIndex
value appears multiple times.
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o Sub-Length is set to N (the number of Sub-Option Data octets that
follow).
o Sub-Option Data contains a 1-octet ifIndex encoded exactly as
specified in Section 9.1.3, followed by an N-1 octet traffic
selector formatted per [RFC6088] beginning with the "TS Format"
field. The largest traffic selector for a given ifIndex is
therefore 254 octets.
9.1.5. MS-Register
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=4 | Sub-length=4n | MSID[1] (bits 0 - 15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... ... ... ... ... ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSID [n] (bits 16 - 32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: MS-Register Sub-option
o Sub-Type is set to 4. If multiple instances appear in the same
OMNI option all are processed. Only the first MAX_MSID values
processed (whether in a single instance or multiple) are retained
and all other MSIDs are ignored.
o Sub-Length is set to 4n.
o A list of n 4-octet MSIDs is included in the following 4n octets.
The Anycast MSID value '0' in an RS message MS-Register sub-option
requests the recipient to return the MSID of a nearby MSE in a
corresponding RA response.
9.1.6. MS-Release
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=5 | Sub-length=4n | MSID[1] (bits 0 - 15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... ... ... ... ... ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSID [n] (bits 16 - 32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: MS-Release Sub-option
o Sub-Type is set to 5. If multiple instances appear in the same
IPv6 OMNI option all are processed. Only the first MAX_MSID
values processed (whether in a single instance or multiple) are
retained and all other MSIDs are ignored.
o Sub-Length is set to 4n.
o A list of n 4 octet MSIDs is included in the following 4n octets.
The Anycast MSID value '0' is ignored in MS-Release sub-options,
i.e., only non-zero values are processed.
9.1.7. Network Access Identifier (NAI)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=6 | Sub-length=N |Network Access Identifier (NAI)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 13: Network Access Identifier (NAI) Sub-option
o Sub-Type is set to 6. If multiple instances appear in the same
OMNI option the first is processed and all others are ignored.
o Sub-Length is set to N.
o A Network Access Identifier (NAI) up to 255 octets in length is
coded per [RFC7542].
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9.1.8. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=7 | Sub-length=N | Geo Coordinates
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 14: Geo Coordinates Sub-option
o Sub-Type is set to 7. If multiple instances appear in the same
OMNI option the first is processed and all others are ignored.
o Sub-Length is set to N.
o A set of Geo Coordinates up to 255 octets in length (format TBD).
Includes Latitude/Longitude at a minimum; may also include
additional attributes such as altitude, heading, speed, etc.).
9.1.9. DHCP Unique Identifier (DUID)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=8 | Sub-length=N | DUID-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. type-specific DUID body (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: DHCP Unique Identifier (DUID) Sub-option
o Sub-Type is set to 8. If multiple instances appear in the same
OMNI option the first is processed and all others are ignored.
o Sub-Length is set to N (i.e., the length of the option beginning
with the DUID-Type and continuing to the end of the type-specific
body).
o DUID-Type is a two-octet field coded in network byte order that
determines the format and contents of the type-specific body
according to Section 11 of [RFC8415]. DUID-Type 4 in particular
corresponds to the Universally Unique Identifier (UUID) [RFC6355]
which will occur in common operational practice.
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o A type-specific DUID body up to 253 octets in length follows,
formatted according to DUID-type. For example, for type 4 the
body consists of a 128-bit UUID selected according to [RFC6355].
9.1.10. DHCPv6 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=9 | Sub-length=N | msg-type | id (octet 0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| transaction-id (octets 1-2) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
. DHCPv6 options .
. (variable number and length) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: DHCPv6 Message Sub-option
o Sub-Type is set to 9. If multiple instances appear in the same
OMNI option the first is processed and all others are ignored.
o Sub-Length is set to N (i.e., the length of the DHCPv6 message
beginning with 'msg-type' and continuing to the end of the DHCPv6
options). The length of the entire DHCPv6 message is therefore
restricted to 255 octets.
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.
10. Address Mapping - Multicast
The multicast address mapping of the native underlying interface
applies. The mobile router on board the MN also serves as an IGMP/
MLD Proxy for its EUNs and/or hosted applications per [RFC4605] while
using the L2 address of the AR as the L2 address for all multicast
packets.
The MN uses Multicast Listener Discovery (MLDv2) [RFC3810] to
coordinate with the AR, and ANET L2 elements use MLD snooping
[RFC4541].
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11. Multilink Conceptual Sending Algorithm
The MN's IPv6 layer selects the outbound OMNI interface according to
SBM considerations when forwarding data packets from local or EUN
applications to external correspondents. Each OMNI interface
maintains a neighbor cache the same as for any IPv6 interface, but
with additional state for multilink coordination. Each OMNI
interface maintains default routes via ARs discovered as discussed in
Section 12, and may configure more-specific routes discovered through
means outside the scope of this specification.
After a packet enters the OMNI interface, one or more outbound
underlying interfaces are selected based on PBM traffic attributes,
and one or more neighbor underlying interfaces are selected based on
the receipt of Interface Attributes sub-options in IPv6 ND messages
(see: Figure 8). Underlying interface selection for the nodes own
local interfaces are based on attributes such as DSCP, application
port number, cost, performance, message size, etc. OMNI interface
multilink selections could also be configured to perform replication
across multiple underlying interfaces for increased reliability at
the expense of packet duplication. The set of all Interface
Attributes received in IPv6 ND messages determine the multilink
forwarding profile for selecting the neighbor's underlying
interfaces.
When the OMNI interface sends a packet over a selected outbound
underlying interface, the OAL includes or omits a mid-layer
encapsulation header as necessary as discussed in Section 5 and as
determined by the L2 address information received in Interface
Attributes. The OAL also performs encapsulation when the nearest AR
is located multiple hops away as discussed in Section 12.1.
OMNI interface multilink service designers MUST observe the BCP
guidance in Section 15 [RFC3819] in terms of implications for
reordering when packets from the same flow may be spread across
multiple underlying interfaces having diverse properties.
11.1. Multiple OMNI Interfaces
MNs may connect to multiple independent OMNI links concurrently in
support of SBM. Each OMNI interface is distinguished by its Anycast
OMNI DLA (e.g., [DLA]:0002::, [DLA]:1000::, [DLA]:7345::, etc.). The
MN configures a separate OMNI interface for each link so that
multiple interfaces (e.g., omni0, omni1, omni2, etc.) are exposed to
the IPv6 layer. A different Anycast OMNI DLA is assigned to each
interface, and the MN injects the service prefixes for the OMNI link
instances into the EUN routing system.
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Applications in EUNs can use Segment Routing to select the desired
OMNI interface based on SBM considerations. The Anycast OMNI DLA is
written into the IPv6 destination address, and the actual destination
(along with any additional intermediate hops) is written into the
Segment Routing Header. Standard IP routing directs the packets to
the MN's mobile router entity, and the Anycast OMNI DLA identifies
the OMNI interface to be used for transmission to the next hop. When
the MN receives the message, it replaces the IPv6 destination address
with the next hop found in the routing header and transmits the
message over the OMNI interface identified by the Anycast OMNI DLA.
Multiple distinct OMNI links can therefore be used to support fault
tolerance, load balancing, reliability, etc. The architectural model
is similar to Layer 2 Virtual Local Area Networks (VLANs).
11.2. MN<->AR Traffic Loop Prevention
After an AR has registered an MNP for a MN (see: Section 12), the AR
will forward packets destined to an address within the MNP to the MN.
The MN will under normal circumstances then forward the packet to the
correct destination within its internal networks.
If at some later time the MN loses state (e.g., after a reboot), it
may begin returning packets destined to an MNP address to the AR as
its default router. The AR therefore must drop any packets
originating from the MN and destined to an address within the MN's
registered MNP. To do so, the AR institutes the following check:
o if the IP destination address belongs to a neighbor on the same
OMNI interface, and if the link-layer source address is the same
as one of the neighbor's link-layer addresses, drop the packet.
12. Router Discovery and Prefix Registration
MNs interface with the MS by sending RS messages with OMNI options
under the assumption that one or more AR on the ANET will process the
message and respond. The MN then configures default routes for the
OMNI interface via the discovered ARs as the next hop. The manner in
which the ANET ensures AR coordination is link-specific and outside
the scope of this document (however, considerations for ANETs that do
not provide ARs that recognize the OMNI option are discussed in
Section 17).
For each underlying interface, the MN sends an RS message with an
OMNI option to coordinate with MSEs identified by MSID values.
Example MSID discovery methods are given in [RFC5214] and include
data link login parameters, name service lookups, static
configuration, a static "hosts" file, etc. The MN can also send an
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RS with an MS-Register suboption that includes the Anycast MSID value
'0', i.e., instead of or in addition to any non-zero MSIDs. When the
AR receives an RS with a MSID '0', it selects a nearby MSE (which may
be itself) and returns an RA with the selected MSID in an MS-Register
suboption. The AR selects only a single wildcard MSE (i.e., even if
the RS MS-Register suboption included multiple '0' MSIDs) while also
soliciting the MSEs corresponding to any non-zero MSIDs.
MNs configure OMNI interfaces that observe the properties discussed
in the previous section. 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.
When an OMNI interface transitions to UP, the MN sends RS messages to
register its MNP and an initial set of underlying interfaces that are
also UP. The MN sends additional RS messages to refresh lifetimes
and to register/deregister underlying interfaces as they transition
to UP or DOWN. The MN sends initial RS messages over an UP
underlying interface with its MN OMNI LLA as the source and with
destination set to All-Routers multicast (ff02::2) [RFC4291]. The RS
messages include an OMNI option per Section 9 with a Preflen
assertion, Interface Attributes appropriate for underlying
interfaces, MS-Register/Release sub-options containing MSID values,
and with any other necessary OMNI sub-options (e.g., a DUID suboption
as an identity for the MN). The S/T-ifIndex field is set to the
index of the underlying interface over which the RS message is sent.
ARs process IPv6 ND messages with OMNI options and act as an MSE
themselves and/or as a proxy for other MSEs. ARs receive RS messages
and create a neighbor cache entry for the MN, then coordinate with
any MSEs named in the Register/Release lists in a manner outside the
scope of this document. When an MSE processes the OMNI information,
it first validates the prefix registration information then injects/
withdraws the MNP in the routing/mapping system and caches/discards
the new Preflen, MNP and Interface Attributes. The MSE then informs
the AR of registration success/failure, and the AR returns an RA
message to the MN with an OMNI option per Section 9.
The AR returns the RA message via the same underlying interface of
the MN over which the RS was received, and with destination address
set to the MN OMNI LLA (i.e., unicast), with source address set to
its own OMNI LLA, and with an OMNI option with S/T-ifIndex set to the
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value included in the RS. The OMNI option also includes a Preflen
confirmation, Interface Attributes, MS-Register/Release and any other
necessary OMNI sub-options (e.g., a DUID suboption as an identity for
the AR). The RA also includes any information for the link,
including RA Cur Hop Limit, M and O flags, Router Lifetime, Reachable
Time and Retrans Timer values, and includes any necessary options
such as:
o PIOs with (A; L=0) that include MSPs for the link [RFC8028].
o RIOs [RFC4191] with more-specific routes.
o an MTU option that specifies the maximum acceptable packet size
for this ANET interface.
The AR MAY also send periodic and/or event-driven unsolicited RA
messages per [RFC4861]. In that case, the S/T-ifIndex field in the
OMNI header of the unsolicited RA message identifies the target
underlying interface of the destination MN.
The AR can combine the information from multiple MSEs into one or
more "aggregate" RAs sent to the MN in order conserve ANET bandwidth.
Each aggregate RA includes an OMNI option with MS-Register/Release
sub-options with the MSEs represented by the aggregate. If an
aggregate is sent, the RA message contents must consistently
represent the combined information advertised by all represented
MSEs. Note that since the AR uses its own OMNI LLA as the RA source
address, the MN determines the addresses of the represented MSEs by
examining the MS-Register/Release OMNI sub-options.
When the MN receives the RA message, it creates an OMNI interface
neighbor cache entry for each MSID that has confirmed MNP
registration via the L2 address of this AR. If the MN connects to
multiple ANETs, it records the additional L2 AR addresses in each
MSID neighbor cache entry (i.e., as multilink neighbors). The MN
then configures a default route via the MSE that returned the RA
message, and assigns the Subnet Router Anycast address corresponding
to the MNP (e.g., 2001:db8:1:2::) to the OMNI interface. The MN then
manages its underlying interfaces according to their states as
follows:
o When an underlying interface transitions to UP, the MN sends an RS
over the underlying interface with an OMNI option. The OMNI
option contains at least one Interface Attribute sub-option with
values specific to this underlying interface, and may contain
additional Interface Attributes specific to other underlying
interfaces. The option also includes any MS-Register/Release sub-
options.
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o When an underlying interface transitions to DOWN, the MN sends an
RS or unsolicited NA message over any UP underlying interface with
an OMNI option containing an Interface Attribute sub-option for
the DOWN underlying interface with Link set to '0'. The MN sends
an RS when an acknowledgement is required, or an unsolicited NA
when reliability is not thought to be a concern (e.g., if
redundant transmissions are sent on multiple underlying
interfaces).
o When the Router Lifetime for a specific AR nears expiration, the
MN sends an RS over the underlying interface to receive a fresh
RA. If no RA is received, the MN can send RS messages to an
alternate MSID in case the current MSID has failed. If no RS
messages are received even after trying to contact alternate
MSIDs, the MN marks the underlying interface as DOWN.
o When a MN wishes to release from one or more current MSIDs, it
sends an RS or unsolicited NA message over any UP underlying
interfaces with an OMNI option with a Release MSID. Each MSID
then withdraws the MNP from the routing/mapping system and informs
the AR that the release was successful.
o When all of a MNs underlying interfaces have transitioned to DOWN
(or if the prefix registration lifetime expires), any associated
MSEs withdraw the MNP the same as if they had received a message
with a release indication.
The MN 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 MSEs), the MN declares this underlying interface as DOWN.
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 that is consistent with the
information received from the RAs generated by the MS. Whether the
OMNI interface IPv6 ND messaging process is initiated from the
receipt of an RS message from the IPv6 layer is an implementation
matter. Some implementations may elect to defer the IPv6 ND
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 the ordinary RS/RA
messaging used by the IPv6 layer over the OMNI interface, since they
are not required to drive the internal RS/RA processing. (Note that
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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 MN 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). ARs are
therefore responsible for keeping MS state alive on a shorter
timescale than the MN is required to do on its own behalf.
Note: On multicast-capable underlying interfaces, MNs should send
periodic unsolicited multicast NA messages and ARs 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 an AR acting as a proxy forwards a MN's RS message to
another node acting as an MSE using UDP/IP encapsulation, it must use
a distinct UDP source port number for each MN. This allows the MSE
to distinguish different MNs behind the same AR at the link-layer,
whereas the link-layer addresses would otherwise be
indistinguishable.
12.1. Router Discovery in IP Multihop and IPv4-Only Access Networks
On some ANET types a MN may be located multiple IP hops away from the
nearest AR. Forwarding through IP multihop ANETs is conducted
through the application of a routing protocol (e.g., a Mobile Ad-hoc
Network (MANET) routing protocol over omni-directional wireless
interfaces, an inter-domain routing protocol in an enterprise
network, etc.). These ANETs could be either IPv6-enabled or
IPv4-only, while IPv4-only ANETs could be either multicast-capable or
unicast-only (note that for IPv4-only ANETs the following procedures
apply for both single-hop and multihop cases).
A MN located potentially multiple ANET hops away from the nearest AR
prepares an RS message with source address set to either its MN OMNI
LLA or a Temporary OMNI LLA, and with destination set to link-scoped
All-Routers multicast the same as discussed above. For IPv6-enabled
ANETs, the MN then encapsulates the message in an IPv6 header with
source address set to the DLA corresponding to the LLA source address
and with destination set to either a unicast or anycast DLA. For
IPv4-only ANETs, the MN instead encapsulates the RS message in an
IPv4 header with source address set to the node's own IPv4 address
and with destination address set to either the unicast IPv4 address
of an AR [RFC5214] or an IPv4 anycast address reserved for OMNI. The
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MN then sends the encapsulated RS message via the ANET interface,
where it will be forwarded by zero or more intermediate ANET hops.
When an intermediate ANET 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 MN). This process
repeats iteratively until the RS message is received by a penultimate
ANET hop within single-hop communications range of an AR, which
forwards the message to the AR.
When the AR receives the message, it decapsulates the RS and
coordinates with the MS the same as for an ordinary link-local RS,
since the inner Hop Limit will not have been decremented by the
multihop forwarding process. The AR then prepares an RA message with
source address set to its own LLA and destination address set to the
LLA of the original MN, then encapsulates the message in an IPv4/IPv6
header with source address set to its own IPv4/DLA address and with
destination set to the encapsulation source of the RS.
The AR then forwards the message to an ANET node within
communications range, which forwards the message according to its
routing tables to an intermediate node. The multihop forwarding
process within the ANET continues repetitively until the message is
delivered to the original MN, which decapsulates the message and
performs autoconfiguration the same as if it had received the RA
directly from the AR as an on-link neighbor.
Note: An alternate approach to multihop forwarding via IPv6
encapsulation would be to statelessly translate the IPv6 LLAs into
DLAs and forward the 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 advocates
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].
Note: An alternate approach to multihop forwarding via IPv4
encapsulation would be to employ IPv6/IPv4 protocol translation.
However, for IPv6 ND messages the OMNI LLA addresses 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.
Note: An IPv4 anycast address for OMNI in IPv4 networks could be part
of a new IPv4 /24 prefix allocation, but this may be difficult to
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obtain given IPv4 address exhaustion. An alternative would be to re-
purpose the prefix 192.88.99.0 which has been set aside from its
former use by [RFC7526].
12.2. MS-Register and MS-Release List Processing
When a MN sends an RS message with an OMNI option via an underlying
interface to an AR, the MN must convey its knowledge of its
currently-associated MSEs. Initially, the MN will have no associated
MSEs and should therefore include an MS-Register sub-option with the
single MSID value 0 which requests the AR to select and assign an
MSE. The AR will then return an RA message with source address set
to the OMNI LLA containing the MSE of the selected MSE.
As the MN activates additional underlying interfaces, it can
optionally include an MS-Register sub-option with MSID value 0, or
with non-zero MSIDs for MSEs discovered from previous RS/RA
exchanges. The MN will thus eventually begin to learn and manage its
currently active set of MSEs, and can register with new MSEs or
release from former MSEs with each successive RS/RA exchange. As the
MN's MSE constituency grows, it alone is responsible for including or
omitting MSIDs in the MS-Register/Release lists it sends in RS
messages. The inclusion or omission of MSIDs determines the MN's
interface to the MS and defines the manner in which MSEs will
respond. The only limiting factor is that the MN should include no
more than MAX_MSID values in each list per each IPv6 ND message, and
should avoid duplication of entries in each list unless it wants to
increase likelihood of control message delivery.
When an AR receives an RS message sent by a MN with an OMNI option,
the option will contain zero or more MS-Register and MS-Release sub-
options containing MSIDs. After processing the OMNI option, the AR
will have a list of zero or more MS-Register MSIDs and a list of zero
or more of MS-Release MSIDs. The AR then processes the lists as
follows:
o For each list, retain the first MAX_MSID values in the list and
discard any additional MSIDs (i.e., even if there are duplicates
within a list).
o Next, for each MSID in the MS-Register list, remove all matching
MSIDs from the MS-Release list.
o Next, proceed according to whether the AR's own MSID or the value
0 appears in the MS-Register list as follows:
* If yes, send an RA message directly back to the MN and send a
proxy copy of the RS message to each additional MSID in the MS-
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Register list with the MS-Register/Release lists omitted.
Then, send a uNA message to each MSID in the MS-Release list
with the MS-Register/Release lists omitted and with an OMNI
header with S/T-ifIndex set to 0.
* If no, send a proxy copy of the RS message to each additional
MSID in the MS-Register list with the MS-Register list omitted.
For the first MSID, include the original MS-Release list; for
all other MSIDs, omit the MS-Release list.
Each proxy copy of the RS message will include an OMNI option and
encapsulation header with the DLA of the AR as the source and the DLA
of the Register MSE as the destination. When the Register MSE
receives the proxy RS message, if the message includes an MS-Release
list the MSE sends a uNA message to each additional MSID in the
Release list. The Register MSE then sends an RA message back to the
(Proxy) AR wrapped in an OMNI encapsulation header with source and
destination addresses reversed, and with RA destination set to the
LLA of the MN. When the AR receives this RA message, it sends a
proxy copy of the RA to the MN.
Each uNA message (whether send by the first-hop AR or by a Register
MSE) will include an OMNI option and an encapsulation header with the
DLA of the Register MSE as the source and the DLA of the Release ME
as the destination. The uNA informs the Release MSE that its
previous relationship with the MN has been released and that the
source of the uNA message is now registered. The Release MSE must
then note that the subject MN of the uNA message is now "departed",
and forward any subsequent packets destined to the MN to the Register
MSE.
Note that it is not an error for the MS-Register/Release lists to
include duplicate entries. If duplicates occur within a list, the AR
will generate multiple proxy RS and/or uNA messages - one for each
copy of the duplicate entries.
12.3. DHCPv6-based Prefix Registration
When a MN is not pre-provisioned with an OMNI LLA containing a MNP
(or, when multiple MNPs are needed), it will require the AR to select
MNPs on its behalf and set up the correct routing state within the
MS. The DHCPv6 service [RFC8415] supports this requirement.
When an MN needs to have the AR select MNPs, it sends an RS message
with a DHCPv6 Message suboption containing a Client Identifier, one
or more IA_PD options and a Rapid Commit option. The MN also sets
the 'msg-type' field to "Solicit", and includes a 3-octet
'transaction-id'.
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When the AR receives the RS message, it extracts the DHCPv6 message
from the OMNI option. The AR then acts as a "Proxy DHCPv6 Client" in
a message exchange with the locally-resident DHCPv6 server, which
delegates MNPs and returns a DHCPv6 Reply message with PD parameters.
(If the AR wishes to defer creation of MN 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.)
When the AR receives the DHCPv6 Reply, it adds routes to the routing
system and creates MN OMNI LLAs based on the delegated MNPs. The AR
then sends an RA back to the MN with the DHCPv6 Reply message
included in an OMNI DHCPv6 message sub-option. If the RS message
source address was a Temporary address, the AR includes one of the
(newly-created) MN OMNI LLAs as the RA destination address. The MN
then creates a default route, assigns Subnet Router Anycast addresses
and uses the RA destination address as its primary MN OMNI LLA. The
MN will then use this primary MN OMNI LLA as the source address of
any IPv6 ND messages it sends as long as it retains ownership of the
MNP.
Note: The single-octet OMNI sub-option length field restricts the
DHCPv6 Message sub-option to a maximum of 255 octets for both the RS
and RA messages. This provides sufficient room for the DHCPv6
message header, a Client/Server Identifier option, a Rapid Commit
option, at least 3 Identity Association for Prefix Delegation (IA_PD)
options and any other supporting DHCPv6 options. A MN requiring more
DHCPv6-based configuration information than this can either perform
multiple independent RS/RA exchanges (with each exchange providing a
subset of the total configuration information) or simply perform an
actual DHCPv6 message exchange in addition to any RS/RA exchanges.
Note: After a MN performs a DHCPv6-based prefix registration exchange
with a first AR, it would need to repeat the exchange with each
additional MSE it registers with. In that case, the MN supplies the
MNP delegations received from the first AR in the IA_PD fields of a
DHCPv6 message when it engages the additonal MSEs.
13. Secure Redirection
If the ANET link model is multiple access, the AR is responsible for
assuring that address duplication cannot corrupt the neighbor caches
of other nodes on the link. When the MN sends an RS message on a
multiple access ANET link, the AR verifies that the MN is authorized
to use the address and returns an RA with a non-zero Router Lifetime
only if the MN is authorized.
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After verifying MN authorization and returning an RA, the AR MAY
return IPv6 ND Redirect messages to direct MNs located on the same
ANET link to exchange packets directly without transiting the AR. In
that case, the MNs can exchange packets according to their unicast L2
addresses discovered from the Redirect message instead of using the
dogleg path through the AR. In some ANET links, however, such direct
communications may be undesirable and continued use of the dogleg
path through the AR may provide better performance. In that case,
the AR can refrain from sending Redirects, and/or MNs can ignore
them.
14. AR and MSE Resilience
ANETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP)
[RFC5798] configurations so that service continuity is maintained
even if one or more ARs fail. Using VRRP, the MN is unaware which of
the (redundant) ARs 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.
MSEs 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.
15. Detecting and Responding to MSE Failures
In environments where fast recovery from MSE failure is required, ARs
SHOULD use proactive Neighbor Unreachability Detection (NUD) in a
manner that parallels Bidirectional Forwarding Detection (BFD)
[RFC5880] to track MSE reachability. ARs 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 ANET links such as aeronautical radios) and can therefore be
tuned for rapid response.
ARs perform proactive NUD for MSEs for which there are currently
active MNs on the ANET. If an MSE fails, ARs can quickly inform MNs
of the outage by sending multicast RA messages on the ANET interface.
The AR sends RA messages to MNs via the ANET interface with an OMNI
option with a Release ID for the failed MSE, and with destination
address set to All-Nodes multicast (ff02::1) [RFC4291].
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The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated
by small delays [RFC4861]. Any MNs on the ANET interface that have
been using the (now defunct) MSE will receive the RA messages and
associate with a new MSE.
16. Transition Considerations
When a MN connects to an ANET link for the first time, it sends an RS
message with an OMNI option. If the first hop AR recognizes the
option, it returns an RA with its MS OMNI LLA as the source, the MN
OMNI LLA as the destination and with an OMNI option included. The MN
then engages the AR according to the OMNI link model specified above.
If the first hop AR 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 MN engages
the ANET according to the legacy IPv6 link model and without the OMNI
extensions specified in this document.
If the ANET 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 MN sends an RS message on a multiple
access ANET link with an OMNI LLA source address and an OMNI option,
ARs that recognize the option ensure that the MN is authorized to use
the address and return an RA with a non-zero Router Lifetime only if
the MN is authorized. ARs that do not recognize the option instead
return an RA that makes no statement about the MN's authorization to
use the source address. In that case, the MN should perform
Duplicate Address Detection to ensure that it does not interfere with
other nodes on the link.
An alternative approach for multiple access ANET links to ensure
isolation for MN / AR communications is through L2 address mappings
as discussed in Appendix C. This arrangement imparts a (virtual)
point-to-point link model over the (physical) multiple access link.
17. OMNI Interfaces on the Open Internet
OMNI interfaces configured over IPv6-enabled underlying interfaces on
the open Internet without an OMNI-aware first-hop AR receive RA
messages that do not include an OMNI option, while OMNI interfaces
configured over IPv4-only underlying interfaces do not receive any
(IPv6) RA messages at all. OMNI interfaces that receive RA messages
without an OMNI option 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]. 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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OMNI interfaces configured over underlying interfaces that connect to
the open Internet can apply security services such as VPNs to connect
to an MSE or establish a direct link to an MSE through some other
means (see Section 4). In environments where an explicit VPN or
direct link may be impractical, OMNI interfaces can instead use UDP/
IP encapsulation and HMAC-based message authentication per
[RFC6081][RFC4380].
After establishing a VPN or preparing for UDP/IP encapsulation, OMNI
interfaces send control plane messages to interface with the MS,
including Neighbor Solicitation (NS) and Neighbor Advertisement (NA)
messages used for address resolution / route optimization (see:
[I-D.templin-intarea-6706bis]). The control plane messages must be
authenticated while data plane messages are delivered the same as for
ordinary best-effort Internet traffic with basic source address-based
data origin verification. Data plane communications via OMNI
interfaces that connect over the open Internet without an explicit
VPN should therefore employ transport- or higher-layer security to
ensure integrity and/or confidentiality.
OMNI interfaces in the open Internet are often located behind Network
Address Translators (NATs). The OMNI interface accommodates NAT
traversal using UDP/IP encapsulation and the mechanisms discussed in
[RFC6081][RFC4380][I-D.templin-intarea-6706bis].
18. Time-Varying MNPs
In some use cases, it is desirable, beneficial and efficient for the
MN to receive a constant MNP that travels with the MN 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 MN 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 12.3 allows OMNI
MNs that desire time-varying MNPs to obtain short-lived prefixes to
use a Temporary OMNI LLA as the source address of an RS message with
an OMNI option with DHCPv6 Option sub-options. The MN 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 MNs with automated network renumbering services,
however presents limits for the durations of ongoing sessions that
would prefer to use a constant address.
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19. IANA Considerations
The IANA is instructed to allocate an official Type number TBD from
the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI
option. Implementations set Type to 253 as an interim value
[RFC4727].
The IANA is instructed to assign a new Code value "1" in the "ICMPv6
Code Fields: Type 2 - Packet Too Big" registry. The registry should
read as follows:
Code Name Reference
--- ---- ---------
0 Diagnostic Packet Too Big [RFC4443]
1 Advisory Packet Too Big [RFCXXXX]
Figure 17: OMNI Option Sub-Type Values
The IANA is instructed to allocate one Ethernet unicast address TBD2
(suggest 00-00-5E-00-52-14 [RFC5214]) in the registry "IANA Ethernet
Address Block - Unicast Use".
The OMNI option also defines an 8-bit Sub-Type field, for which IANA
is instructed to create and maintain a new registry entitled "OMNI
option Sub-Type values". Initial values for the OMNI option Sub-Type
values registry are given below; future assignments are to be made
through Expert Review [RFC8126].
Value Sub-Type name Reference
----- ------------- ----------
0 Pad1 [RFCXXXX]
1 PadN [RFCXXXX]
2 Interface Attributes [RFCXXXX]
3 Traffic Selector [RFCXXXX]
4 MS-Register [RFCXXXX]
5 MS-Release [RFCXXXX]
6 Network Access Identifier [RFCXXXX]
7 Geo Coordinates [RFCXXXX]
8 DHCP Unique Identifier (DUID) [RFCXXXX]
9 DHCPv6 Message [RFCXXXX]
10-252 Unassigned
253-254 Experimental [RFCXXXX]
255 Reserved [RFCXXXX]
Figure 18: OMNI Option Sub-Type Values
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20. Security Considerations
Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6
Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages
SHOULD include Nonce and Timestamp options [RFC3971] when transaction
confirmation and/or time synchronization is needed.
OMNI interfaces configured over secured ANET interfaces inherit the
physical and/or link-layer security properties of the connected
ANETs. 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, an asymmetric security service such as the
authentication option specified in [RFC4380] or other protocol
control message security mechanisms may be necessary. 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.
The Mobility Service MUST provide strong network layer security for
control plane messages and forwarding path integrity for data plane
messages. In one example, the AERO service
[I-D.templin-intarea-6706bis] constructs a spanning tree between
mobility service elements and secures the links in the spanning tree
with network layer security mechanisms such as IPsec [RFC4301] or
Wireguard. Control plane messages are then constrained to travel
only over the secured spanning tree paths and are therefore protected
from attack or eavesdropping. Since data plane messages can travel
over route optimized paths that do not strictly follow the spanning
tree, however, end-to-end transport- or higher-layer security
services are still required.
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 5.1.
21. Implementation Status
Draft -29 is implemented in the recently tagged AERO/OMNI 3.0.0
internal release, and Draft -30 is now tagged as the AERO/OMNI 3.0.1.
Newer specification versions will be tagged in upcoming releases.
First public release expected before the end of 2020.
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22. 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:
Michael Matyas, Madhu Niraula, Michael Richardson, Greg Saccone,
Stephane Tamalet, Eric Vyncke. Pavel Drasil, Zdenek Jaron and Michal
Skorepa are recognized for their many helpful ideas and suggestions.
Madhuri Madhava Badgandi, Katherine Tran, and Vijayasarathy
Rajagopalan are acknowledged for their hard work on the
implementation and insights that led to improvements to 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.
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.
23. References
23.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
[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>.
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[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>.
23.2. 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.
[CRC] Jain, R., "Error Characteristics of Fiber Distributed Data
Interface (FDDI), IEEE Transactions on Communications",
August 1990.
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[I-D.ietf-6man-rfc4941bis]
Gont, F., Krishnan, S., Narten, T., and R. Draves,
"Temporary Address Extensions for Stateless Address
Autoconfiguration in IPv6", draft-ietf-6man-rfc4941bis-12
(work in progress), November 2020.
[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]
Jeong, J., "IPv6 Wireless Access in Vehicular Environments
(IPWAVE): Problem Statement and Use Cases", draft-ietf-
ipwave-vehicular-networking-19 (work in progress), July
2020.
[I-D.templin-6man-dhcpv6-ndopt]
Templin, F., "A Unified Stateful/Stateless Configuration
Service for IPv6", draft-templin-6man-dhcpv6-ndopt-10
(work in progress), June 2020.
[I-D.templin-6man-lla-type]
Templin, F., "The IPv6 Link-Local Address Type Field",
draft-templin-6man-lla-type-02 (work in progress),
November 2020.
[I-D.templin-intarea-6706bis]
Templin, F., "Asymmetric Extended Route Optimization
(AERO)", draft-templin-intarea-6706bis-74 (work in
progress), December 2020.
[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>.
[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>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.
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[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>.
[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>.
[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>.
[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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[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>.
[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>.
[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>.
[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>.
[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>.
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[RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542,
DOI 10.17487/RFC7542, May 2015,
<https://www.rfc-editor.org/info/rfc7542>.
[RFC7739] Gont, F., "Security Implications of Predictable Fragment
Identification Values", RFC 7739, DOI 10.17487/RFC7739,
February 2016, <https://www.rfc-editor.org/info/rfc7739>.
[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>.
[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>.
[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>.
Appendix A. Interface Attribute Preferences Bitmap Encoding
Adaptation of the OMNI option Interface Attributes Preferences Bitmap
encoding to specific Internetworks such as the Aeronautical
Telecommunications Network with Internet Protocol Services (ATN/IPS)
may include link selection preferences based on other traffic
classifiers (e.g., transport port numbers, etc.) in addition to the
existing DSCP-based preferences. Nodes on specific Internetworks
maintain a map of traffic classifiers to additional P[*] preference
fields beyond the first 64. For example, TCP port 22 maps to P[67],
TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc.
Implementations use Simplex or Indexed encoding formats for P[*]
encoding in order to encode a given set of traffic classifiers in the
most efficient way. Some use cases may be more efficiently coded
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using Simplex form, while others may be more efficient using Indexed.
Once a format is selected for preparation of a single Interface
Attribute the same format must be used for the entire Interface
Attribute sub-option. Different sub-options may use different
formats.
The following figures show coding examples for various Simplex and
Indexed formats:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=2 | Sub-length=N | ifIndex | ifType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Provider ID | Link |R| API | Bitmap(0)=0xff|P00|P01|P02|P03|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bitmap(2)=0xff|P64|P65|P67|P68| ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 19: Example 1: Dense Simplex Encoding
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=2 | Sub-length=N | ifIndex | ifType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Provider ID | Link |R| API | Bitmap(0)=0x00| Bitmap(1)=0x0f|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Bitmap(10)=0x00| ...
+-+-+-+-+-+-+-+-+-+-+-
Figure 20: Example 2: Sparse Simplex Encoding
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type=2 | Sub-length=N | ifIndex | ifType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Provider ID | Link |R| API | Index = 0x00 | Bitmap = 0x80 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bitmap = 0x01 |796|797|798|799| ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 21: Example 3: Indexed Encoding
Appendix B. 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.
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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
amount of data. The IETF lpwan working group is considering possible
alternatives: [https://datatracker.ietf.org/wg/lpwan/documents].
Appendix C. MN / AR 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 MN and AR only without
invoking other nodes on the ANET. This implies that MN / AR control
messaging should be isolated and not overheard by other nodes on the
link.
To support MN / AR isolation on some ANET links, ARs can maintain an
OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible
ANETs, this specification reserves one Ethernet unicast address TBD2
(see: Section 19). For non-Ethernet statically-addressed ANETs,
MSADDR is reserved per the assigned numbers authority for the ANET
addressing space. For still other ANETs, MSADDR may be dynamically
discovered through other means, e.g., L2 beacons.
MNs 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 MN's IPv6
ND messages will be received by ARs that are configured to accept
packets destined to MSADDR. Note that multiple ARs on the link could
be configured to accept packets destined to MSADDR, e.g., as a basis
for supporting redundancy.
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Therefore, ARs 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 D. Change Log
<< RFC Editor - remove prior to publication >>
Differences from draft-templin-6man-omni-interface-35 to draft-
templin-6man-omni-interface-36:
o Major clarifications on aspects such as "hard/soft" PTB error
messages
o Made generic so that either IP protocol version (IPv4 or IPv6) can
be used in the data plane.
Differences from draft-templin-6man-omni-interface-31 to draft-
templin-6man-omni-interface-32:
o MTU
o Support for multi-hop ANETS such as ISATAP.
Differences from draft-templin-6man-omni-interface-29 to draft-
templin-6man-omni-interface-30:
o Moved link-layer addressing information into the OMNI option on a
per-ifIndex basis
o Renamed "ifIndex-tuple" to "Interface Attributes"
Differences from draft-templin-6man-omni-interface-27 to draft-
templin-6man-omni-interface-28:
o Updates based on implementation expereince.
Differences from draft-templin-6man-omni-interface-25 to draft-
templin-6man-omni-interface-26:
o Further clarification on "aggregate" RA messages.
o Expanded Security Considerations to discuss expectations for
security in the Mobility Service.
Differences from draft-templin-6man-omni-interface-20 to draft-
templin-6man-omni-interface-21:
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o Safety-Based Multilink (SBM) and Performance-Based Multilink
(PBM).
Differences from draft-templin-6man-omni-interface-18 to draft-
templin-6man-omni-interface-19:
o SEND/CGA.
Differences from draft-templin-6man-omni-interface-17 to draft-
templin-6man-omni-interface-18:
o Teredo
Differences from draft-templin-6man-omni-interface-14 to draft-
templin-6man-omni-interface-15:
o Prefix length discussions removed.
Differences from draft-templin-6man-omni-interface-12 to draft-
templin-6man-omni-interface-13:
o Teredo
Differences from draft-templin-6man-omni-interface-11 to draft-
templin-6man-omni-interface-12:
o Major simplifications and clarifications on MTU and fragmentation.
o Document now updates RFC4443 and RFC8201.
Differences from draft-templin-6man-omni-interface-10 to draft-
templin-6man-omni-interface-11:
o Removed /64 assumption, resulting in new OMNI address format.
Differences from draft-templin-6man-omni-interface-07 to draft-
templin-6man-omni-interface-08:
o OMNI MNs in the open Internet
Differences from draft-templin-6man-omni-interface-06 to draft-
templin-6man-omni-interface-07:
o Brought back L2 MSADDR mapping text for MN / AR isolation based on
L2 addressing.
o Expanded "Transition Considerations".
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Differences from draft-templin-6man-omni-interface-05 to draft-
templin-6man-omni-interface-06:
o Brought back OMNI option "R" flag, and discussed its use.
Differences from draft-templin-6man-omni-interface-04 to draft-
templin-6man-omni-interface-05:
o Transition considerations, and overhaul of RS/RA addressing with
the inclusion of MSE addresses within the OMNI option instead of
as RS/RA addresses (developed under FAA SE2025 contract number
DTFAWA-15-D-00030).
Differences from draft-templin-6man-omni-interface-02 to draft-
templin-6man-omni-interface-03:
o Added "advisory PTB messages" under FAA SE2025 contract number
DTFAWA-15-D-00030.
Differences from draft-templin-6man-omni-interface-01 to draft-
templin-6man-omni-interface-02:
o Removed "Primary" flag and supporting text.
o Clarified that "Router Lifetime" applies to each ANET interface
independently, and that the union of all ANET interface Router
Lifetimes determines MSE lifetime.
Differences from draft-templin-6man-omni-interface-00 to draft-
templin-6man-omni-interface-01:
o "All-MSEs" OMNI LLA defined. Also reserved fe80::ff00:0000/104
for future use (most likely as "pseudo-multicast").
o Non-normative discussion of alternate OMNI LLA construction form
made possible if the 64-bit assumption were relaxed.
First draft version (draft-templin-atn-aero-interface-00):
o Draft based on consensus decision of ICAO Working Group I Mobility
Subgroup March 22, 2019.
Authors' Addresses
Templin & Whyman Expires June 13, 2021 [Page 61]
Internet-Draft IPv6 over OMNI Interfaces December 2020
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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