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 February 9, 2021
Expires: August 13, 2021
Transmission of IP Packets over Overlay Multilink Network (OMNI)
Interfaces
draft-templin-6man-omni-interface-80
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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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 13, 2021.
Copyright Notice
Copyright (c) 2021 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 . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 9
5. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 14
5.1. Fragmentation Security Implications . . . . . . . . . . . 19
5.2. OAL "Super-Packet" Packing . . . . . . . . . . . . . . . 20
6. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 22
7. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 22
8. Unique-Local Addresses (ULAs) . . . . . . . . . . . . . . . . 23
9. Global Unicast Addresses (GUAs) . . . . . . . . . . . . . . . 25
10. Node Identification . . . . . . . . . . . . . . . . . . . . . 26
11. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 26
11.1. Sub-Options . . . . . . . . . . . . . . . . . . . . . . 28
11.1.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 30
11.1.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 30
11.1.3. Interface Attributes (Type 1) . . . . . . . . . . . 31
11.1.4. Interface Attributes (Type 2) . . . . . . . . . . . 32
11.1.5. Traffic Selector . . . . . . . . . . . . . . . . . . 36
11.1.6. MS-Register . . . . . . . . . . . . . . . . . . . . 37
11.1.7. MS-Release . . . . . . . . . . . . . . . . . . . . . 38
11.1.8. Geo Coordinates . . . . . . . . . . . . . . . . . . 38
11.1.9. Dynamic Host Configuration Protocol for IPv6
(DHCPv6) Message . . . . . . . . . . . . . . . . . . 39
11.1.10. Host Identity Protocol (HIP) Message . . . . . . . . 40
11.1.11. Node Identification . . . . . . . . . . . . . . . . 41
11.1.12. Sub-Type Extension . . . . . . . . . . . . . . . . . 42
12. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 45
13. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 46
13.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 46
13.2. MN<->AR Traffic Loop Prevention . . . . . . . . . . . . 47
14. Router Discovery and Prefix Registration . . . . . . . . . . 47
14.1. Router Discovery in IP Multihop and IPv4-Only Networks . 52
14.2. MS-Register and MS-Release List Processing . . . . . . . 53
14.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 55
15. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 57
16. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 57
17. Detecting and Responding to MSE Failures . . . . . . . . . . 57
18. Transition Considerations . . . . . . . . . . . . . . . . . . 58
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19. OMNI Interfaces on Open Internetworks . . . . . . . . . . . . 58
20. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 60
21. (H)HITs and Temporary ULAs . . . . . . . . . . . . . . . . . 61
22. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 62
22.1. "IPv6 Neighbor Discovery Option Formats" Registry . . . 62
22.2. "Ethernet Numbers" Registry . . . . . . . . . . . . . . 62
22.3. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry . 62
22.4. "OMNI Option Sub-Type Values" (New Registry) . . . . . . 62
22.5. "OMNI Node Identification ID-Type Values" (New Registry) 63
22.6. "OMNI Option Sub-Type Extension Values" (New Registry) . 63
22.7. "OMNI RFC4380 UDP/IP Header Option" (New Registry) . . . 64
22.8. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry) . . 64
22.9. Additional Considerations . . . . . . . . . . . . . . . 65
23. Security Considerations . . . . . . . . . . . . . . . . . . . 65
24. Implementation Status . . . . . . . . . . . . . . . . . . . . 66
25. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 66
26. References . . . . . . . . . . . . . . . . . . . . . . . . . 67
26.1. Normative References . . . . . . . . . . . . . . . . . . 67
26.2. Informative References . . . . . . . . . . . . . . . . . 69
Appendix A. Interface Attribute Preferences Bitmap Encoding . . 75
Appendix B. VDL Mode 2 Considerations . . . . . . . . . . . . . 77
Appendix C. MN / AR Isolation Through L2 Address Mapping . . . . 78
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 79
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 81
1. Introduction
Mobile Nodes (MNs) (e.g., aircraft of various configurations,
terrestrial vehicles, seagoing vessels, enterprise wireless devices,
pedestrians with cellphones, etc.) often have multiple interface
connections to wireless and/or wired-link data links used 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 node's underlying interface
connections to the data links.
The MN configures a virtual interface (termed the "Overlay Multilink
Network (OMNI) interface") as a thin layer over the underlying
interfaces. The OMNI interface is therefore the only interface
abstraction exposed to the IP layer and behaves according to the Non-
Broadcast, Multiple Access (NBMA) interface principle, while
underlying interfaces appear as link layer communication channels in
the architecture. The OMNI interface connects to a virtual overlay
service known as the "OMNI link". The OMNI link spans one or more
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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 14).
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), which are typically IP Global Unicast Address (GUA)
prefixes from which OMNI link MNPs are derived. If there are
multiple OMNI links, the IPv6 layer will see multiple OMNI
interfaces.
MNs may connect to multiple distinct OMNI links within the same OMNI
domain by configuring multiple OMNI interfaces, e.g., omni0, omni1,
omni2, etc. Each OMNI interface is configured over a set of
underlying interfaces and provides a nexus for Safety-Based Multilink
(SBM) operation. Each OMNI interface within the same OMNI domain
configures a common ULA prefix [ULA]::/48, and configures a unique
16-bit Subnet ID '*' to construct the sub-prefix [ULA*]::/64 (see:
Section 8). The IP layer applies SBM routing to select an OMNI
interface, which then 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 have been proposed. 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
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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. OMNI interfaces enable
multilink, mobility, multihop and multicast services, with provisions
for both Vehicle-to-Infrastructure (V2I) communications and Vehicle-
to-Vehicle (V2V) communications outside the context of
infrastructure.
2. Terminology
The terminology in the normative references applies; especially, the
terms "link" and "interface" are the same as defined in the IPv6
[RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications.
Additionally, this document assumes the following IPv6 ND message
types: Router Solicitation (RS), Router Advertisement (RA), Neighbor
Solicitation (NS), Neighbor Advertisement (NA) and Redirect.
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
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(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 Global Unicast Address (GUA) prefix (e.g.,
2001:db8::/32, 192.0.2.0/24, etc.) assigned to the OMNI link and
from which more-specific Mobile Network Prefixes (MNPs) are
delegated. OMNI link administrators typically obtain MSPs from an
Internet address registry, however private-use prefixes can
alternatively be used subject to certain limitations (see:
Section 9). OMNI links that connect to the global Internet
advertise their MSPs to their interdomain routing peers.
Mobile Network Prefix (MNP)
a longer IP prefix delegated from an MSP (e.g.,
2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a 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 is assumed, and sometimes referred to as
"protected spectrum". Private enterprise networks and ground
domain aviation service networks may provide multiple secured IP
hops between the MN's point of connection and the nearest Access
Router.
Access Router (AR)
a router in the ANET for connecting MNs to correspondents in
outside Internetworks. The AR may be located on the same physical
link as the MN, or may be located multiple IP hops away. In the
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latter case, the MN uses encapsulation to communicate with the AR
as though it were on the same physical link.
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 between ANETs and nodes that
connect directly to the open INET via unprotected media. No
physical and/or data link level security is assumed, therefore
security must be applied by upper layers. The global public
Internet itself is an example.
INET interface
a node's attachment to a link in an INET.
*NET
a "wildcard" term used when a given specification applies equally
to both ANET and INET cases.
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 interface
a node's attachment to an OMNI link, and configured over one or
more underlying *NET interfaces. If there are multiple OMNI links
in an OMNI domain, a separate OMNI interface is configured for
each link.
OMNI Adaptation Layer (OAL)
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
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 Option
an IPv6 Neighbor Discovery option providing multilink parameters
for the OMNI interface as specified in Section 11.
Mobile Network Prefix Link Local Address (MNP-LLA)
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an IPv6 Link Local Address that embeds the most significant 64
bits of an MNP in the lower 64 bits of fe80::/64, as specified in
Section 7.
Mobile Network Prefix Unique Local Address (MNP-ULA)
an IPv6 Unique-Local Address derived from an MNP-LLA.
Administrative Link Local Address (ADM-LLA)
an IPv6 Link Local Address that embeds a 32-bit administratively-
assigned identification value in the lower 32 bits of fe80::/96,
as specified in Section 7.
Administrative Unique Local Address (ADM-ULA)
an IPv6 Unique-Local Address derived from an ADM-LLA.
Multilink
an OMNI interface's manner of managing diverse underlying
interface connections to data links as a single logical unit. The
OMNI interface provides a single unified interface to upper
layers, while underlying interface selections are performed on a
per-packet basis considering 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.
Multihop
an iterative relaying of IP packets between MNs over an OMNI
underlying interface technology (such as omnidirectional wireless)
without support of fixed infrastructure. Multihop services entail
node-to-node relaying within a Mobile/Vehicular Ad-hoc Network
(MANET/VANET) for MN-to-MN communications and/or for "range
extension" where MNs within range of communications infrastructure
elements provide forwarding services for other MNs.
L2
The second layer in the OSI network model. Also known as "layer-
2", "link-layer", "sub-IP layer", "data link layer", etc.
L3
The third layer in the OSI network model. Also known as "layer-
3", "network-layer", "IP layer", etc.
underlying interface
a *NET interface over which an OMNI interface is configured. The
OMNI interface is seen as a L3 interface by the IP layer, and each
underlying interface is seen as a L2 interface by the OMNI
interface. The underlying interface either connects directly to
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the physical communications media or coordinates with another node
where the physical media is hosted.
Mobility Service Identification (MSID)
Each MSE and AR is assigned a unique 32-bit Identification (MSID)
(see: Section 7). IDs are assigned according to MS-specific
guidelines (e.g., see: [I-D.templin-intarea-6706bis]).
Safety-Based Multilink (SBM)
A means for ensuring fault tolerance through redundancy by
connecting multiple affiliated OMNI interfaces to independent
routing topologies (i.e., multiple independent OMNI links).
Performance Based Multilink (PBM)
A means for selecting underlying interface(s) for packet
transmission and reception within a single OMNI interface.
OMNI Domain
The set of all SBM/PBM OMNI links that collectively provides
services for a common set of MSPs. Each OMNI domain consists of a
set of affiliated OMNI links that all configure the same ::/48 ULA
prefix with a unique 16-bit Subnet ID as discussed in Section 8.
3. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
An implementation is not required to internally use the architectural
constructs described here so long as its external behavior is
consistent with that described in this document.
4. Overlay Multilink Network (OMNI) Interface Model
An OMNI interface is a 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 Link-Local Address (MNP-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
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therefore sees the OMNI interface as a single L3 interface with
multiple underlying interfaces that appear as L2 communication
channels in the architecture.
+----------------------------+
| Upper Layer Protocol |
Session-to-IP +---->| |
Address Binding | +----------------------------+
+---->| IP (L3) |
IP Address +---->| |
Binding | +----------------------------+
+---->| OMNI Interface |
Logical-to- +---->| (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 a *NET 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 *NET paths. An example is a line-of-
sight link between a remote pilot and an unmanned aircraft.
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The OMNI virtual interface model gives rise to a number of
opportunities:
o since MNP-LLAs are uniquely derived from an MNP, no Duplicate
Address Detection (DAD) or Multicast Listener Discovery (MLD)
messaging is necessary.
o since Temporary ULAs are statistically unique, they can be used
without DAD, e.g. for MN-to-MN communications until an MNP-LLA is
obtained.
o *NET 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 LLA to all *NET 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.
The OAL supports "packing" of multiple IP payload packets within a
single OAL packet.
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.
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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.
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 *NETs. 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 *NETs until they reach an AR (AR#1, AR#2, ..., AR#n), which
then coordinates with an INET Mobility Service Endpoint (MSE#1,
MSE#2, ..., MSE#m) 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
(:::)-. (:::)-. (:::)-.
.-(::*NET:::) .-(::*NET:::) .-(::*NET:::)
`-(::::)-' `-(::::)-' `-(::::)-'
+----+ +----+ +----+
... |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 *NETs
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 *NETs. 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.
Note: OMNI interface underlying interfaces often connect directly to
physical media on the local platform (e.g., a laptop computer with
WiFi, etc.), but in some configurations the physical media may be
hosted on a separate Local Area Network (LAN) node. In that case,
the OMNI interface can establish a Layer-2 VLAN or a point-to-point
tunnel (at a layer below the underlying interface) to the node
hosting the physical media. The OMNI interface may also apply
encapsulation at a layer above the underlying interface such that
packets would appear "double-encapsulated" on the LAN; the node
hosting the physical media in turn removes the LAN encapsulation
prior to transmission or inserts it following reception. Finally,
the underlying interface must monitor the node hosting the physical
media (e.g., through periodic keepalives) so that it can convey
up/down/status information to the OMNI interface.
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 "Don't Fragment" (DF) bit in the
IPv4 encapsulation headers of packets sent over IPv4 underlying
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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.)
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. By always assuming
the IPv4 minimum path MTU even for IPv6 underlying interfaces, the
OAL may produce smaller fragments and additional header overhead but
will always interoperate and never run the risk of presenting a
destination interface with a packet that exceeds its MRU.
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
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 encapsulating the inner IP packet/
fragment in a mid-layer IPv6 header per [RFC2473] before adding any
outer IP encapsulations. (The OAL does not decrement the inner IP
Hop Limit/TTL during encapsulation since the insertion occurs at a
layer below IP forwarding.) If the OAL packet will itself require
fragmentation, the OMNI interface then calculates the 32-bit CRC over
the entire mid-layer packet and writes the value in a trailing field
at the end of the packet. Next, the OAL fragments this mid-layer
IPv6 packet, forwards the fragments (using *NET 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,
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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 Unique-Local Address (ULA) (see: Section 8)
and destination set to either the Administrative ULA (ADM-ULA) of
the ANET peer or the Mobile Network Prefix ULA (MNP-ULA)
corresponding to the final destination (see below). 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 size of each non-final fragment
(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 either reassembles
before forwarding if the OAL destination is its own ADM-ULA or
forwards the fragments toward the final destination without first
reassembling otherwise.
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 ULA, destination set to the ULA of the next hop OMNI
node toward the final destination and (if necessary) with an OMNI
Routing Header (ORH) (see: [I-D.templin-intarea-6706bis]) with
final segment addressing information. The OAL next 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 size of each non-final fragment (including
both the OMNI and outer-layer INET encapsulations) is determined
by the minimum INET 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.
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In light of the above considerations, the OAL SHOULD assume a minimum
path MTU of 576 bytes for the purpose of generating OAL fragments.
Each OAL fragment will undergo *NET encapsulation including either a
20 byte IPv4 or 40 byte IPv6 header (plus an 8 byte UDP header for
INETs), leaving a minimum of 528 bytes for each fragment. Each OAL
fragment must reserve 40 bytes for the OAL IPv6 header plus 8 bytes
for the fragment header (while reserving 40 additional bytes in case
a maximum-length ORH is inserted during re-encapsulation), leaving
440 bytes to accommodate the actual inner IP packet fragment. OAL
fragmentation algorithms therefore MUST produce non-final fragments
with the OAL IPv6 header Payload Length set to no less than 448 bytes
(8 bytes for the fragment header plus 440 bytes for the inner packet
fragment), while the Payload Length of the final fragment may be
smaller. OAL reassembly algorithms MUST drop any non-final fragments
with Payload Length less than 448 bytes.
Note that OAL fragmentation algorithms MAY produce larger non-final
OAL fragments if better path MTU information is available. For
example, for ANETs in which no UDP encapsulation header is needed the
algorithm can increase the minimum non-final fragment length by 8
bytes. In a second example, for ANETs in which no IPv6 hops will be
traversed over the path the algorithm can increase the minimum length
by 20 bytes. In a third example, if there is assurance that no ORH
will be inserted in the path the algorithm can increase the minimum
length by 40 bytes. In a final example, when two ANET peers share a
common physical or virtual link with a larger MTU (e.g., 1280 bytes
or larger), the OAL can base the minimum non-final fragment length on
this larger MTU size as long as the receiving ANET peer reassembles
(and possibly also refragments) before forwarding. (Other examples
are possible, and dependent on actual ANET/INET deployment
scenarios.)
In all of the above examples, optimizing the minimum OAL fragment
size may be important for accommodating links where performance is
dependent on maximum use of the available link MTU, e.g. for wireless
aviation data links. Additionally, the OMNI interface that inserts
the OAL header MUST also be the one that inserts the IPv6 fragment
header Identification value in order to set the correct context for
reassembly. 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
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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. The OAL then sets the MTU field to a value no smaller
than 576 for ICMPv4 or 1280 for ICMPv6, and returns the PTB soft
error to the original source.
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: 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 refrain from
sending PTB soft errors and simply regard the loss as an ordinary
unreported congestion event for which the original source will
eventually compensate.
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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
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: The source OAL includes a trailing 32-bit CRC only for OAL
packets that require fragmentation, and the destination OAL discards
any OAL packets with incorrect CRC values following reassembly. (The
source OAL calculates the CRC over the entire packet, then appends
the CRC to the end of the packet and adds the CRC length to the OAL
Payload Length prior to fragmentation. The destination OAL subtracts
the CRC length from the OAL Payload Length and verifies the CRC
following reassembly.) A 32-bit CRC is sufficient for detecting
reassembly misassociations for packet sizes no larger than the OMNI
interface MTU 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 facilities 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:
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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
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 *NET 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.
Finally, [RFC6980] documents fragmentation security concerns for
large IPv6 ND messages. These concerns are addressed when the OMNI
interface employs the OAL instead of directly fragmenting the IPv6 ND
message itself. For this reason, OMNI interfaces MUST NOT admit IPv6
ND messages larger than the OMNI interface MTU, and MUST employ the
OAL for IPv6 ND messages admitted into the OMNI interface the same as
discussed above.
5.2. OAL "Super-Packet" Packing
By default, the source OAL includes a 40-byte IPv6 encapsulation
header for each inner IP payload packet during OAL encapsulation.
When fragmentation is needed, the source OAL also calculates and
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includes a 32-bit trailing CRC for the entire packet then performs
fragmentation such that a copy of the 40-byte IPv6 header plus an
8-byte IPv6 Fragment Header is included in each fragment. However,
these encapsulations may represent excessive overhead in some
environments. A technique known as "packing" discussed in
[I-D.ietf-intarea-tunnels] is therefore supported so that multiple
inner IP payload packets can be included within a single OAL packet
known as a "super-packet".
When the source OAL has multiple inner IP payload packets with total
length no larger than the OMNI interface MTU to send to the same
destination, it can optionally concatenate them into a super-packet
encapsulated in a single OAL header. Within the super-packet, the IP
header of the first inner packet (iHa) followed by its data (iDa) is
concatenated immediately following the OAL header, then the inner IP
header of the next packet (iHb) followed by its data (iDb) is
concatenated immediately following the first packet, etc. The super-
packet format is transposed from [I-D.ietf-intarea-tunnels] and shown
in Figure 3:
<-- Multiple inner IP payload packets to be "packed" -->
+-----+-----+
| iHa | iDa |
+-----+-----+
|
| +-----+-----+
| | iHb | iDb |
| +-----+-----+
| |
| | +-----+-----+
| | | iHc | iDc |
| | +-----+-----+
| | |
v v v
+----------+-----+-----+-----+-----+-----+-----+
| OAL Hdr | iHa | iDa | iHb | iDb | iHc | iDc |
+----------+-----+-----+-----+-----+-----+-----+
<-- OMNI "Super-Packet" with single OAL Hdr -->
Figure 3: OAL Super-Packet Format
When the source OAL sends a super-packet, it calculates a CRC and
applies OAL fragmentation if necessary then sends the packet or
fragments to the destination OAL. When the destination OAL receives
the super-packet as a whole packet or as fragments, it reassembles
and verifies the CRC if necessary then regards the OAL header Payload
Length (after subtracting the CRC length) as the sum of the lengths
of all payload packets. The destination OAL then selectively
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extracts each individual payload packet (e.g., by setting pointers
into the buffer containing the super-packet and maintaining a
reference count, by copying each payload packet into its own buffer,
etc.) and forwards each payload packet or processes it locally as
appropriate. During extraction, the OAL determines the IP protocol
version of each successive inner payload packet 'j' by examining the
first four bits of iH(j), and determines the length of the inner
packet by examining the rest of iH(j) according to the IP protocol
version.
Note: OMNI interfaces must take care to avoid processing super-packet
payload elements that would subvert security. Specifically, if a
super-packet contains a mix of data and control payload packets
(which could include critical security codes), the node MUST NOT
process the data packets before processing the control packets.
6. Frame Format
The OMNI interface transmits IP 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
(LLAs) through pre-service administrative actions. "MNP-LLAs" embed
the MNP assigned to the mobile node, while "ADM-LLAs" include an
administratively-unique ID that is guaranteed to be unique on the
link. LLAs are configured as follows:
o IPv6 MNP-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 MNP-LLA is fe80::2001:db8:1000:2000/120.
o IPv4-compatible MNP-LLAs are constructed as fe80::ffff:[IPv4],
i.e., the interface identifier consists of 16 '0' bits, followed
by 16 '1' bits, followed by a 32bit IPv4 address/prefix. The
prefix length for the LLA is determined by adding 96 to the MNP
prefix length. For example, the IPv4-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).
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o ADM-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::feffffff. The ADM-LLA
prefix length is determined by adding 96 to the MSID prefix
length. For example, if the prefix length for MSID 0x10012001 is
16 then the ADM-LLA prefix length is set to 112 and the LLA is
written as fe80::1001:2001/112. The "zero" address for each ADM-
LLA prefix is the Subnet-Router anycast address for that prefix
[RFC4291]; for example, the Subnet-Router anycast address for
fe80::1001:2001/112 is simply fe80::1001:2000. The MSID range
0xff000000 through 0xffffffff is reserved for future use.
Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no
MNPs can be allocated from that block ensuring that there is no
possibility for overlap between the different MNP- and ADM-LLA
constructs discussed above.
Since MNP-LLAs are based on the distribution of administratively
assured unique MNPs, and since ADM-LLAs are guaranteed unique through
administrative assignment, OMNI interfaces set the autoconfiguration
variable DupAddrDetectTransmits to 0 [RFC4862].
Note: If future protocol extensions relax the 64-bit boundary in IPv6
addressing, the additional prefix bits of an MNP could be encoded in
bits 16 through 63 of the MNP-LLA. (The most-significant 64 bits
would therefore still be in bits 64-127, and the remaining bits would
appear in bits 16 through 48.) However, the analysis provided in
[RFC7421] suggests that the 64-bit boundary will remain in the IPv6
architecture for the foreseeable future.
Note: Even though this document honors the 64-bit boundary in IPv6
addressing, it specifies prefix lengths longer than /64 for routing
purposes. This effectively extends IPv6 routing determination into
the interface identifier portion of the IPv6 address, but it does not
redefine the 64-bit boundary. Modern routing protocol
implementations honor IPv6 prefixes of all lengths, up to and
including /128.
8. Unique-Local Addresses (ULAs)
OMNI domains use IPv6 Unique-Local Addresses (ULAs) as the source and
destination addresses in OAL IPv6 encapsulation headers. ULAs are
only routable within the scope of a an OMNI domain, and are derived
from the IPv6 Unique Local Address prefix fc00::/7 followed by the L
bit set to 1 (i.e., as fd00::/8) followed by a 40-bit pseudo-random
Global ID to produce the prefix [ULA]::/48, which is then followed by
a 16-bit Subnet ID then finally followed by a 64 bit Interface ID as
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specified in Section 3 of [RFC4193]. All nodes in the same OMNI
domain configure the same 40-bit Global ID as the OMNI domain
identifier. The statistic uniqueness of the 40-bit pseudo-random
Global ID allows different OMNI domains to be joined together in the
future without requiring renumbering.
Each OMNI link instance is identified by a value between 0x0000 and
0xfeff in bits 48-63 of [ULA]::/48; the values 0xff00 through 0xfffe
are reserved for future use, and the value 0xffff denotes the
presence of a Temporary ULA (see below). For example, OMNI ULAs
associated with instance 0 are configured from the prefix
[ULA]:0000::/64, instance 1 from [ULA]:0001::/64, instance 2 from
[ULA]:0002::/64, etc. ULAs and their associated prefix lengths are
configured in correspondence with LLAs through stateless prefix
translation where "MNP-ULAs" are assigned in correspondence to MNP-
LLAs and "ADM-ULAs" are assigned in correspondence to ADM-LLAs. For
example, for OMNI link instance [ULA]:1010::/64:
o the MNP-ULA corresponding to the MNP-LLA fe80::2001:db8:1:2 with a
56-bit MNP length is derived by copying the lower 64 bits of the
LLA into the lower 64 bits of the ULA as
[ULA]:1010:2001:db8:1:2/120 (where, the ULA prefix length becomes
64 plus the IPv6 MNP length).
o the MNP-ULA corresponding to fe80::ffff:192.0.2.0 with a 28-bit
MNP length is derived by simply writing the LLA interface ID into
the lower 64 bits as [ULA]:1010:0:ffff:192.0.2.0/124 (where, the
ULA prefix length is 64 plus 32 plus the IPv4 MNP length).
o the ADM-ULA corresponding to fe80::1000/112 is simply
[ULA]:1010::1000/112.
o the ADM-ULA corresponding to fe80::/128 is simply
[ULA]:1010::/128.
o etc.
Each OMNI interface assigns the Anycast ADM-ULA specific to the OMNI
link instance. For example, the OMNI interface connected to instance
3 assigns the Anycast address [ULA]:0003::/128. Routers that
configure OMNI interfaces advertise the OMNI service prefix (e.g.,
[ULA]:0003::/64) into the local routing system so that applications
can direct traffic according to SBM requirements.
The ULA presents an IPv6 address format that is routable within the
OMNI routing system and can be used to convey link-scoped IPv6 ND
messages across multiple hops using IPv6 encapsulation [RFC2473].
The OMNI link extends across one or more underling Internetworks to
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include all ARs and MSEs. All MNs are also considered to be
connected to the OMNI link, however OAL encapsulation is omitted
whenever possible to conserve bandwidth (see: Section 13).
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].
Temporary ULAs are constructed per [I-D.ietf-6man-rfc4941bis] based
on the prefix [ULA]:ffff::/64 and used by MNs when they have no other
addresses. Temporary ULAs can be used for MN-to-MN communications
outside the context of any supporting OMNI link infrastructure, and
can also be used as an initial address while the MN is in the process
of procuring an MNP. Temporary ULAs are not routable within the OMNI
routing system, and are therefore useful only for OMNI link "edge"
communications. Temporary ULAs employ optimistic DAD principles
[RFC4429] since they are probabilistically unique.
Note: IPv6 ULAs taken from the prefix fc00::/7 followed by the L bit
set to 0 (i.e., as fc00::/8) are never used for OMNI OAL addressing,
however the range could be used for MSP and MNP addressing under
certain limiting conditions (see: Section 9).
9. Global Unicast Addresses (GUAs)
OMNI domains use IP Global Unicast Address (GUA) prefixes [RFC4291]
as Mobility Service Prefixes (MSPs) from which Mobile Network
Prefixes (MNP) are delegated to Mobile Nodes (MNs).
For IPv6, GUA prefixes are assigned by IANA [IPV6-GUA] and/or an
associated regional assigned numbers authority such that the OMNI
domain can be interconnected to the global IPv6 Internet without
causing inconsistencies in the routing system. An OMNI domain could
instead use ULAs with the 'L' bit set to 0 (i.e., from the prefix
fc00::/8)[RFC4193], however this would require IPv6 NAT if the domain
were ever connected to the global IPv6 Internet.
For IPv4, GUA prefixes are assigned by IANA [IPV4-GUA] and/or an
associated regional assigned numbers authority such that the OMNI
domain can be interconnected to the global IPv4 Internet without
causing routing inconsistencies. An OMNI domain could instead use
private IPv4 prefixes (e.g., 10.0.0.0/8, etc.) [RFC3330], however
this would require IPv4 NAT if the domain were ever connected to the
global IPv4 Internet.
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10. Node Identification
OMNI MNs and MSEs that connect over open Internetworks generate a
Host Identity Tag (HIT) as specified in [RFC7401] and use the value
as a robust general-purpose node identification value. Hierarchical
HITs (HHITs) [I-D.ietf-drip-rid] may provide a useful alternative in
certain domains such as the Unmanned (Air) Traffic Management (UTM)
service for Unmanned Air Systems (UAS). MNs and MSEs can then use
their (H)HITs in IPv6 ND control message exchanges.
When a MN is truly outside the context of any infrastructure, it may
have no MNP information at all. In that case, the MN can use its
(H)HIT as an IPv6 source/destination address for sustained
communications in Vehicle-to-Vehicle (V2V) and (multihop) Vehicle-to-
Infrastructure (V2I) scenarios. The MN can also propagate the (H)HIT
into the multihop routing tables of (collective) Mobile/Vehicular Ad-
hoc Networks (MANETs/VANETs) using only the vehicles themselves as
communications relays.
When a MN connects to ARs over (non-multihop) protected-spectrum
ANETs, an alternate form of node identification (e.g., MAC address,
serial number, airframe identification value, VIN, etc.) may be
sufficient. In that case, the MN should still generate a (H)HIT and
maintain it in conjunction with any other node identifiers. The MN
can then include OMNI "Node Identification" sub-options (see:
Section 11.1.11) in IPv6 ND messages should the need to transmit
identification information over the network arise.
11. 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.
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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 4:
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 | Preflen | S/T-omIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Sub-Options ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: OMNI Option Format
In this format:
o Type is set to TBD1.
o Length is set to the number of 8 octet blocks in the option. The
value 0 is invalid, while the values 1 through 255 (i.e., 8
through 2040 octets, respectively) indicate the total length of
the OMNI option.
o Preflen is an 8 bit field that determines the length of prefix
associated with an LLA. Values 0 through 128 specify a valid
prefix length (all other values are invalid). For IPv6 ND
messages sent from a MN to the MS, Preflen applies to the IPv6
source LLA and provides the length that the MN is requesting or
asserting to the MS. For IPv6 ND messages sent from the MS to the
MN, Preflen applies to the IPv6 destination LLA and indicates the
length that the MS is granting to the MN. For IPv6 ND messages
sent between MS endpoints, Preflen provides the length associated
with the source/target MN that is subject of the ND message.
o S/T-omIndex is an 8 bit field corresponds to the omIndex value for
source or target underlying interface used to convey this IPv6 ND
message. OMNI interfaces MUST number each distinct underlying
interface with an omIndex value between '1' and '255' that
represents a MN-specific 8-bit mapping for the actual ifIndex
value assigned by network management [RFC2863] (the omIndex value
'0' is reserved for use by the MS). For RS and NS messages, S/
T-omIndex corresponds to the source underlying interface the
message originated from. For RA and NA messages, S/T-omIndex
corresponds to the target underlying interface that the message is
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destined to. (For NS messages used for Neighbor Unreachability
Detection (NUD), S/T-omIndex instead identifies the neighbor's
underlying interface to be used as the target interface to return
the NA.)
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 11.1.
The OMNI option may appear in any IPv6 ND message type; it is
processed by interfaces that recognize the option and ignored by all
other interfaces. If multiple OMNI option instances appear in the
same IPv6 ND message, the interface processes the Preflen and S/
T-omIndex fields in the first instance and ignores those fields in
all other instances. The interface processes the Sub-Options of all
OMNI option instances in the same IPv6 ND message in the consecutive
order in which they occur.
The OMNI option(s) in each IPv6 ND message may include full or
partial information for the neighbor. The union of the information
in the most recently received OMNI options is therefore retained, and
the information is aged/removed in conjunction with the corresponding
neighbor cache entry.
11.1. Sub-Options
Each 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 5: Sub-Option Format
o Sub-Type is a 5-bit field that encodes the Sub-Option type. Sub-
Options defined in this document are:
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Sub-Option Name Sub-Type
Pad1 0
PadN 1
Interface Attributes (Type 1) 2
Interface Attributes (Type 2) 3
Traffic Selector 4
MS-Register 5
MS-Release 6
Geo Coordinates 7
DHCPv6 Message 8
HIP Message 9
Node Identification 10
Sub-Type Extension 30
Figure 6
Sub-Types 11-29 are available for future assignment for major
protocol functions. Sub-Type 31 is reserved by IANA.
o Sub-Length is an 11-bit field that encodes the length of the Sub-
Option Data ranging from 0 to 2034 octets.
o Sub-Option Data is a block of data with format determined by Sub-
Type and length determined by Sub-Length.
During transmission, the OMNI interface codes Sub-Type and Sub-Length
together in network byte order in 2 consecutive octets, where Sub-
Option Data may be up to 2034 octets in length. This allows ample
space for coding large objects (e.g., ascii character strings,
protocol messages, security codes, etc.), while a single OMNI option
is limited to 2040 octets the same as for any IPv6 ND option. If the
Sub-Options to be coded would cause an OMNI option to exceed 2040
octets, the OMNI interface codes any remaining Sub-Options in
additional OMNI option instances in the intended order of processing
in the same IPv6 ND message. Implementations must therefore observe
size limitations, and must refrain from sending IPv6 ND messages
larger than the OMNI interface MTU.
During reception, the OMNI interface processes each OMNI option Sub-
Option while skipping over and ignoring any unrecognized Sub-Options.
The OMNI interface processes the Sub-Options of all OMNI option
instances in the consecutive order in which they appear in the IPv6
ND message, beginning with the first instance and continuing through
any additional instances to the end of the message. If a Sub-Option
length would cause the running total for that OMNI option to exceed
the length coded in the option header, the interface accepts any Sub-
Options already processed and ignores the remainder of that OMNI
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option. The interface then processes any remaining OMNI options in
the same fashion to the end of the IPv6 ND message.
Note: large objects that exceed the Sub-Option Data limit of 2034
octets are not supported under the current specification; if this
proves to be limiting in practice, future specifications may define
support for fragmenting large objects across multiple OMNI options
within the same IPv6 ND message.
The following Sub-Option types and formats are defined in this
document:
11.1.1. Pad1
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| S-Type=0|x|x|x|
+-+-+-+-+-+-+-+-+
Figure 7: Pad1
o Sub-Type is set to 0. If multiple instances appear in OMNI
options of the same message all are processed.
o Sub-Type is followed by three 'x' bits, set randomly on
transmission and ignored on receipt. Pad1 therefore consists of a
1 octet with the most significant 5 bits set to 0, and with no
Sub-Length or Sub-Option Data fields following.
11.1.2. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| S-Type=1| Sub-length=N | N padding octets ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 8: PadN
o Sub-Type is set to 1. If multiple instances appear in OMNI
options of the same message all are processed.
o Sub-Length is set to N (from 0 to 2034) that encodes the number of
padding octets that follow.
o Sub-Option Data consists of N zero-valued octets.
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11.1.3. Interface Attributes (Type 1)
The Interface Attributes (Type 1) sub-option provides a basic set of
attributes for underlying interfaces. Interface Attributes (Type 1)
is deprecated throughout the rest of this specification, and
Interface Attributes (Type 2) (see: Section 11.1.4) are indicated
wherever the term "Interface Attributes" appears without an
associated Type designation.
Nodes SHOULD NOT include Interface Attributes (Type 1) sub-options in
IPv6 ND messages they send, and MUST ignore any in IPv6 ND messages
they receive. If an Interface Attributes (Type 1) is included, it
must have the following format:
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 | omIndex | omType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Provider ID | Link | Resvd |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|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|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Interface Attributes (Type 1)
o Sub-Type is set to 2. If multiple instances with different
omIndex values appear in OMNI option of the same message all are
processed; if multiple instances with the same omIndex value
appear, the first is processed and all others are ignored
o Sub-Length is set to N (from 4 to 2034) that encodes the number of
Sub-Option Data octets that follow.
o omIndex is a 1-octet field containing a value from 0 to 255
identifying the underlying interface for which the attributes
apply.
o omType is a 1-octet field containing a value from 0 to 255
corresponding to the underlying interface identified by omIndex.
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o Provider ID is a 1-octet field containing a value from 0 to 255
corresponding to the underlying interface identified by omIndex.
o 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").
o Resvd is reserved for future use. Set to 0 on transmission and
ignored on reception.
o A 16-octet ""Preferences" field immediately follows 'Resvd', with
values P[00] through P[63] corresponding to the 64 Differentiated
Service Code Point (DSCP) values [RFC2474]. 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.
11.1.4. Interface Attributes (Type 2)
The Interface Attributes (Type 2) sub-option provides L2 forwarding
information for the multilink conceptual sending algorithm discussed
in Section 13. 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 (Type 2) further
includes link-layer address information to be used for either OAL
encapsulation or direct UDP/IP encapsulation (when OAL encapsulation
can be avoided).
Interface Attributes (Type 2) are the sole Interface Attributes
format in this specification that all OMNI nodes must honor.
Wherever the term "Interface Attributes" occurs throughout this
specification without a "Type" designation, the format given below is
indicated:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=3| Sub-length=N | omIndex | omType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 10: Interface Attributes (Type 2)
o Sub-Type is set to 3. If multiple instances with different
omIndex values appear in OMNI options of the same message all are
processed; if multiple instances with the same omIndex value
appear, the first is processed and all others are ignored.
o Sub-Length is set to N (from 4 to 2034) that encodes the number of
Sub-Option Data octets that follow. The 'omIndex', 'omType',
'Provider ID', 'Link', 'R' and 'API' fields are always present;
hence, the remainder of the Sub-Option Data is limited to 2030
octets.
o Sub-Option Data contains an "Interface Attributes (Type 2)" option
encoded as follows:
* omIndex is set to an 8-bit integer value corresponding to a
specific underlying interface the same as specified above for
the OMNI option S/T-omIndex field. The OMNI options of a same
message may include multiple Interface Attributes Sub-Options,
with each distinct omIndex value pertaining to a different
underlying interface. The OMNI option will often include an
Interface Attributes Sub-Option with the same omIndex value
that appears in the S/T-omIndex. 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 is absent) the
presence of a NAT is assumed.
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* omType is set to an 8-bit integer value corresponding to the
underlying interface identified by omIndex. The value
represents an OMNI interface-specific 8-bit mapping for the
actual IANA ifType value registered in the 'IANAifType-MIB'
registry [http://www.iana.org].
* Provider ID is set to an OMNI interface-specific 8-bit ID value
for the network service provider associated with this omIndex.
* Link encodes a 4-bit link metric. The value '0' means the link
is DOWN, and the remaining values mean the link is UP with
metric ranging from '1' ("lowest") to '15' ("highest").
* 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 9; 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 ULA formed from concatenating [ULA*]::/96 with
the 32 bit LHS MSID value that follows. For example, the
value 16 corresponds to the prefix length 112.
+ 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 1, L2ADDR is the INET encapsulation address for the
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Source/Target Client itself; otherwise L2ADDR is the
address of the Server/Proxy named in the LHS.
- When the next most significant bit (i.e., "Mode") is set
to 1, the Framework node is (likely) located behind an
INET Network Address Translator (NAT); otherwise, it is
on the open INET.
- When the least significant bit (i.e., "Type") is set to
0, L2ADDR includes a UDP Port Number followed by an IPv4
address; otherwise, it includes 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 together 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 (following
any necessary NAT traversal messaging); 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 2 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 network byte
order, and 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. Note that if the target is behind a NAT, L2ADDR
will contain the mapped INET address stored in the NAT;
otherwise, L2ADDR will contain the native INET information
of the target itself.
* 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 10.
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:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Index=i | Bitmap(i) |P[*] values ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 11
* 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 9).
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.
11.1.5. Traffic Selector
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=4| Sub-length=N | omIndex | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ ~
~ RFC 6088 Format Traffic Selector ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Traffic Selector
o Sub-Type is set to 4. If multiple instances appear in OMNI
options of the same message all are processed, i.e., even if the
same omIndex value appears multiple times.
o Sub-Length is set to N (from 1 to 2034) that encodes the number of
Sub-Option Data octets that follow.
o Sub-Option Data contains a 1 octet omIndex encoded exactly as
specified in Section 11.1.3, followed by an N-1 octet traffic
selector formatted per [RFC6088] beginning with the "TS Format"
field. The largest traffic selector for a given omIndex is
therefore 2033 octets.
11.1.6. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-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 13: MS-Register Sub-option
o Sub-Type is set to 5. If multiple instances appear in OMNI
options of the same message 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.
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o Sub-Length is set to 4n, with 508 as the maximum value for n. The
length of the Sub-Option Data section is therefore limited to 2032
octets.
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.
11.1.7. MS-Release
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=6| Sub-length=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 14: MS-Release Sub-option
o Sub-Type is set to 6. If multiple instances appear in OMNI
options of the same message 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, with 508 as the maximum value for n. The
length of the Sub-Option Data section is therefore limited to 2032
octets.
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.
11.1.8. Geo Coordinates
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=7| Sub-length=N | Geo Coordinates
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 15: Geo Coordinates Sub-option
o Sub-Type is set to 7. If multiple instances appear in OMNI
options of the same message the first is processed and all others
are ignored.
o Sub-Length is set to N (from 0 to 2034) that encodes the number of
Sub-Option Data octets that follow.
o A set of Geo Coordinates of maximum length 2034 octets. Format(s)
to be specified in future documents; should include Latitude/
Longitude, plus any additional attributes such as altitude,
heading, speed, etc.
11.1.9. Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Message
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) sub-option
may be included in the OMNI options of RS messages sent by MNs and RA
messages returned by MSEs. ARs that act as proxys to forward RS/RA
messages between MNs and MSEs also forward DHCPv6 sub-options
unchanged and do not process DHCPv6 sub-options themselves.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=8| Sub-length=N | 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 8. If multiple instances appear in OMNI
options of the same message the first is processed and all others
are ignored.
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o Sub-Length is set to N (from 4 to 2034) that encodes the number of
Sub-Option Data octets that follow. The 'msg-type' and
'transaction-id' fields are always present; hence, the length of
the DHCPv6 options is restricted to 2030 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.
11.1.10. Host Identity Protocol (HIP) Message
The Host Identity Protocol (HIP) Message sub-option may be included
in the OMNI options of RS messages sent by MNs and RA messages
returned by ARs. ARs that act as proxys authenticate and remove HIP
messages in RS messages they forward from a MN to an MSE. ARs that
act as proxys insert and sign HIP messages in the RA messages they
forward from an MSE to a MN.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=9| Sub-length=N |0| Packet Type |Version| RES.|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum | Controls |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ HIP Parameters /
/ /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: HIP Message Sub-option
o Sub-Type is set to 9. If multiple instances appear in OMNI
options of the same message the first is processed and all others
are ignored.
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o Sub-Length is set to N, i.e., the length of the option in octets
beginning immediately following the Sub-Length field and extending
to the end of the HIP parameters. The length of the entire HIP
message is therefore restricted to 2034 octets.
o The HIP message is coded exactly as specified in Section 5 of
[RFC7401], except that the OMNI "Sub-Type" and "Sub-Length" fields
replace the first 2 octets of the HIP message header (i.e., the
Next Header and Header Length fields).
11.1.11. Node Identification
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=10| Sub-length=N | ID-Type | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ Node Identification Value (N-1 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: Node Identification
o Sub-Type is set to 10. If multiple instances appear in OMNI
options of the same IPv6 ND message the first instance of a
specific ID-Type is processed and all other instances of the same
ID-Type are ignored. (Note therefore that it is possible for a
single IPv6 ND message to convey multiple Node Identifications -
each having a different ID-Type.)
o Sub-Length is set to N (from 1 to 2034) that encodes the number of
Sub-Option Data octets that follow. The ID-Type field is always
present; hence, the maximum Node Identification Value length is
2033 octets.
o ID-Type is a 1 octet field that encodes the type of the Node
Identification Value. The following ID-Type values are currently
defined:
* 0 - Universally Unique IDentifier (UUID) [RFC4122]. Indicates
that Node Identification Value contains a 16 octet UUID.
* 1 - Host Identity Tag (HIT) [RFC7401]. Indicates that Node
Identification Value contains a 16 octet HIT.
* 2 - Hierarchical HIT (HHIT) [I-D.ietf-drip-rid]. Indicates
that Node Identification Value contains a 16 octet HHIT.
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* 3 - Network Access Identifier (NAI) [RFC7542]. Indicates that
Node Identification Value contains an N-1 octet NAI.
* 4 - Fully-Qualified Domain Name (FQDN) [RFC1035]. Indicates
that Node Identification Value contains an N-1 octet FQDN.
* 5 - 252 - Unassigned.
* 253-254 - Reserved for experimentation, as recommended in
[RFC3692].
* 255 - reserved by IANA.
o Node Identification Value is an (N - 1) octet field encoded
according to the appropriate the "ID-Type" reference above.
When a Node Identification Value is needed for DHCPv6 messaging
purposes, it is encoded as a DHCP Unique IDentifier (DUID) using the
"DUID-EN for OMNI" format with enterprise number 45282 (see:
Section 22) as shown in Figure 19:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DUID-Type (2) | EN (high bits == 0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EN (low bits = 45282) | ID-Type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. Node Identification Value .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: DUID-EN for OMNI Format
In this format, the ID-Type and Node Identification Value fields are
coded exactly as in Figure 18 following the 6 octet DUID-EN header,
and the entire "DUID-EN for OMNI" is included in a DHCPv6 message per
[RFC8415].
11.1.12. Sub-Type Extension
Since the Sub-Type field is only 5 bits in length, future
specifications of major protocol functions may exhaust the remaining
Sub-Type values available for assignment. This document therefore
defines Sub-Type 30 as an "extension", meaning that the actual sub-
option type is determined by examining a 1 octet "Extension-Type"
field immediately following the Sub-Length field. The Sub-Type
Extension is formatted as shown in Figure 20:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Extension-Type| ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ ~
~ Extension-Type Body ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: Sub-Type Extension
o Sub-Type is set to 30. If multiple instances appear in OMNI
options of the same message all are processed, where each
individual extension defines its own policy for processing
multiple of that type.
o Sub-Length is set to N (from 1 to 2034) that encodes the number of
Sub-Option Data octets that follow. The Extension-Type field is
always present; hence, the maximum Extension-Type Body length is
2033 octets.
o Extension-Type contains a 1 octet Sub-Type Extension value between
0 and 255.
o Extension-Type Body contains an N-1 octet block with format
defined by the given extension specification.
Extension-Type values 2 through 252 are available for assignment by
future specifications, which must also define the format of the
Extension-Type Body and its processing rules. Extension-Type values
253 and 254 are reserved for experimentation, as recommended in
[RFC3692], and value 255 is reserved by IANA. Extension-Type values
0 and 1 are defined in the following subsections:
11.1.12.1. RFC4380 UDP/IP Header Option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Ext-Type=0 | Header Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Header Option Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: RFC4380 UDP/IP Header Option (Extension-Type 0)
o Sub-Type is set to 30.
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o Sub-Length is set to N (from 2 to 2034) that encodes the number of
Sub-Option Data octets that follow. The Extension-Type and Header
Type fields are always present; hence, the maximum-length Header
Option Value is 2032 octets.
o Extension-Type is set to 0. Each instance encodes exactly one
header option per Section 5.1.1 of [RFC4380], with the leading '0'
octet omitted and the following octet coded as Header Type. If
multiple instances of the same Header Type appear in OMNI options
of the same message the first instance is processed and all others
are ignored.
o Header Type and Header Option Value are coded exactly as specified
in Section 5.1.1 of [RFC4380]; the following types are currently
defined:
* 0 - Origin Indication (IPv4) - value coded per Section 5.1.1 of
[RFC4380].
* 1 - Authentication Encapsulation - value coded per
Section 5.1.1 of [RFC4380].
* 2 - Origin Indication (IPv6) - value coded per Section 5.1.1 of
[RFC4380], except that the address is a 16-octet IPv6 address
instead of a 4-octet IPv4 address.
o Header Type values 3 through 252 are available for assignment by
future specifications, which must also define the format of the
Header Option Value and its processing rules. Header Type values
253 and 254 are reserved for experimentation, as recommended in
[RFC3692], and value 255 is Reserved by IANA.
11.1.12.2. RFC6081 UDP/IP Trailer Option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Ext-Type=1 | Trailer Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Trailer Option Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: RFC6081 UDP/IP Trailer Option (Extension-Type 1)
o Sub-Type is set to 30.
o Sub-Length is set to N (from 2 to 2034) that encodes the number of
Sub-Option Data octets that follow. The Extension-Type and
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Trailer Type fields are always present; hence, the maximum-length
Trailer Option Value is 2032 octets.
o Extension-Type is set to 1. Each instance encodes exactly one
trailer option per Section 4 of [RFC6081]. If multiple instances
of the same trailer type appear in OMNI options of the same
message the first instance is processed and all others ignored.
o Trailer Type and Trailer Option Value are coded exactly as
specified in Section 4 of [RFC6081]; the following Trailer Types
are currently defined:
* 0 - Unassigned
* 1 - Nonce Trailer - value coded per Section 4.2 of [RFC6081].
* 2 - Unassigned
* 3 - Alternate Address Trailer (IPv4) - value coded per
Section 4.3 of [RFC6081].
* 4 - Neighbor Discovery Option Trailer - value coded per
Section 4.4 of [RFC6081].
* 5 - Random Port Trailer - value coded per Section 4.5 of
[RFC6081].
* 6 - Alternate Address Trailer (IPv6) - value coded per
Section 4.3 of [RFC6081], except that each address is a
16-octet IPv6 address instead of a 4-octet IPv4 address.
o Trailer Type values 7 through 252 are available for assignment by
future specifications, which must also define the format of the
Trailer Option Value and its processing rules. Trailer Type
values 253 and 254 are reserved for experimentation, as
recommended in [RFC3692], and value 255 is Reserved by IANA.
12. 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 *NET L2 elements use MLD snooping
[RFC4541].
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13. 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 14, 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 9). 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 determines 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 14.1. (Note
that the OAL MAY employ packing when multiple packets are available
for forwarding to the same destination.)
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.
13.1. Multiple OMNI Interfaces
MNs may connect to multiple independent OMNI links concurrently in
support of SBM. Each OMNI interface is distinguished by its Anycast
ULA (e.g., [ULA]:0002::, [ULA]:1000::, [ULA]: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 ULA is assigned to each interface, and
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the MN injects the service prefixes for the OMNI link instances into
the EUN routing system.
Applications in EUNs can use Segment Routing to select the desired
OMNI interface based on SBM considerations. The Anycast ULA 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 ULA 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 ULA.
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).
13.2. MN<->AR Traffic Loop Prevention
After an AR has registered an MNP for a MN (see: Section 14), 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.
14. 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 *NET 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 *NET ensures AR coordination is link-specific and outside
the scope of this document (however, considerations for *NETs that do
not provide ARs that recognize the OMNI option are discussed in
Section 19).
For each underlying interface, the MN sends an RS message with an
OMNI option to coordinate with MSEs identified by MSID values.
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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
RS with an MS-Register sub-option 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 sub-option. The AR selects only a single wildcard MSE
(i.e., even if the RS MS-Register sub-option 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's OMNI interface sends initial RS messages
over an UP underlying interface with its MNP-LLA as the source and
with destination set to link-scoped All-Routers multicast (ff02::2)
[RFC4291]. The OMNI interface includes an OMNI option per Section 11
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
Node Identification sub-option as an identity for the MN). The OMNI
interface then sets the S/T-omIndex field to the index of the
underlying interface over which the RS message is sent. The OMNI
interface then sends the RS over the underlying interface, using OAL
encapsulation and fragmentation if necessary. If OAL encapsulation
is used, the OMNI interface sets the OAL source address to the ULA
corresponding to the RS source and sets the OAL destination to site-
scoped All-Routers multicast (ff05::2).
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
(while performing OAL reassembly if necessary) 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
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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 11.
The AR's OMNI interface 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 MNP-LLA (i.e., unicast), with
source address set to its own LLA, and with an OMNI option with S/
T-omIndex set to the 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 Node
Identification sub-option 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 underlying interface.
The OMNI interface then sends the RA, using OAL encapsulation and
fragmentation if necessary. If OAL encapsulation is used, the OMNI
interface sets the OAL source address to the ULA corresponding to the
RA source and sets the OAL destination to the ULA corresponding to
the RA destination. The AR MAY also send periodic and/or event-
driven unsolicited RA messages per [RFC4861]. In that case, the S/
T-omIndex field in the OMNI option 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 *NET 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 ADM-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
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multiple *NETs, 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.
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.
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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
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.
Note: when an AR acting as an MSE returns an RA to an INET Client, it
includes an OMNI option with an Interface Attributes sub-option with
omIndex set to 0 and with SRT, FMT, LHS and L2ADDR information for
its INET interface. This provides the Client with partition prefix
context regarding the local OMNI link segment.
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14.1. Router Discovery in IP Multihop and IPv4-Only Networks
On some *NETs, a MN may be located multiple IP hops away from the
nearest AR. Forwarding through IP multihop *NETs is conducted
through the application of a routing protocol (e.g., a MANET/VANET
routing protocol over omni-directional wireless interfaces, an inter-
domain routing protocol in an enterprise network, etc.). These *NETs
could be either IPv6-enabled or IPv4-only, while IPv4-only *NETs
could be either multicast-capable or unicast-only (note that for
IPv4-only *NETs the following procedures apply for both single-hop
and multihop cases).
A MN located potentially multiple *NET hops away from the nearest AR
prepares an RS message with source address set to its MNP-LLA (or to
the unspecified address (::) if it does not yet have an MNP-LLA), and
with destination set to link-scoped All-Routers multicast the same as
discussed above. If OAL encapsulation and fragmentation are
necessary, the OMNI interface sets the OAL source address to the ULA
corresponding to the RS source (or to a Temporary ULA if the RS
source was the unspecified address (::)) and sets the OAL destination
to site-scoped All-Routers multicast (ff05::2). For IPv6-enabled
*NETs, the MN then encapsulates the message in UDP/IPv6 headers with
source address set to the underlying interface address (or to the ULA
that would be used for OAL encapsulation if the underlying interface
does not yet have an address) and sets the destination to either a
unicast or anycast address of an AR. For IPv4-only *NETs, the MN
instead encapsulates the RS message in an IPv4 header with source
address set to the IPv4 address of the underlying interface and with
destination address set to either the unicast IPv4 address of an AR
[RFC5214] or an IPv4 anycast address reserved for OMNI. The MN then
sends the encapsulated RS message via the *NET interface, where it
will be forwarded by zero or more intermediate *NET hops.
When an intermediate *NET hop that participates in the routing
protocol receives the encapsulated RS, it forwards the message
according to its routing tables (note that an intermediate node could
be a fixed infrastructure element or another MN). This process
repeats iteratively until the RS message is received by a penultimate
*NET 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 (while
performing OAL reassembly, if necessary) 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
ADM-LLA and destination address set to the LLA of the original MN.
The AR then performs OAL encapsulation and fragmentation if
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necessary, with OAL source set to its own ADM-ULA and destination set
to the ULA corresponding to the RA source. The AR then encapsulates
the message in an IPv4/IPv6 header with source address set to its own
IPv4/ULA address and with destination set to the encapsulation source
of the RS.
The AR then forwards the message to an *NET node within
communications range, which forwards the message according to its
routing tables to an intermediate node. The multihop forwarding
process within the *NET continues repetitively until the message is
delivered to the original 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 for the MN and AR to statelessly translate the
IPv6 LLAs into ULAs and forward the RS/RA messages without
encapsulation. This would violate the [RFC4861] requirement that
certain IPv6 ND messages must use link-local addresses and must not
be accepted if received with Hop Limit less than 255. This document
therefore mandates encapsulation since the overhead is nominal
considering the infrequent nature and small size of IPv6 ND messages.
Future documents may consider encapsulation avoidance through
translation while updating [RFC4861].
Note: An alternate approach to multihop forwarding via IPv4
encapsulation would be to employ IPv6/IPv4 protocol translation.
However, for IPv6 ND messages the LLAs would be truncated due to
translation and the OMNI Router and Prefix Discovery services would
not be able to function. The use of IPv4 encapsulation is therefore
indicated.
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
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].
14.2. MS-Register and MS-Release List Processing
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.
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
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currently-associated MSEs. Initially, the MN will have no associated
MSEs and should therefore include an MS-Register sub-option with the
single "anycast" 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 ADM-LLA 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-
Register list with the MS-Register/Release lists omitted.
Then, send an unsolicited NA (uNA) message to each MSID in the
MS-Release list with the MS-Register/Release lists omitted and
with an OMNI option with S/T-omIndex 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.
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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 OAL
encapsulation header with the ADM-ULA of the AR as the source and the
ADM-ULA 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 with an OMNI option with S/T-omIndex set to 0. The
Register MSE then sends an RA message back to the (Proxy) AR wrapped
in an OAL encapsulation header with source and destination addresses
reversed, and with RA destination set to the MNP-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 sent by the first-hop AR or by a Register
MSE) will include an OMNI option and an OAL encapsulation header with
the ADM-ULA of the Register MSE as the source and the ADM-ULA of the
Release MSE 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.
14.3. DHCPv6-based Prefix Registration
When a MN is not pre-provisioned with an MNP-LLA (or, when the MN
requires additional MNP delegations), it requests the MSE 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 MSE select MNPs, it sends an RS message
with source set to the unspecified address (::) if it has no
MNP_LLAs. If the MN requires only a single MNP delegation, it can
then include a Node Identification sub-option in the OMNI option and
set Preflen to the length of the desired MNP. If the MN requires
multiple MNP delegations and/or more complex DHCPv6 services, it
instead includes a DHCPv6 Message sub-option containing a Client
Identifier, one or more IA_PD options and a Rapid Commit option then
sets the 'msg-type' field to "Solicit", and includes a 3 octet
'transaction-id'. The MN then sets the RS destination to All-Routers
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multicast and sends the message using OAL encapsulation and
fragmentation if necessary as discussed above.
When the MSE receives the RS message, it performs OAL reassembly if
necessary. Next, if the RS source is the unspecified address (::)
and/or the OMNI option includes a DHCPv6 message sub-option, the MSE
acts as a "Proxy DHCPv6 Client" in a message exchange with the
locally-resident DHCPv6 server. If the RS did not contain a DHCPv6
message sub-option, the MSE generates a DHCPv6 Solicit message on
behalf of the MN using an IA_PD option with the prefix length set to
the OMNI header Preflen value and with a Client Identifier formed
from the OMNI option Node Identification sub-option; otherwise, the
MSE uses the DHCPv6 Solicit message contained in the OMNI option.
The MSE then sends the DHCPv6 message to the DHCPv6 Server, which
delegates MNPs and returns a DHCPv6 Reply message with PD parameters.
(If the MSE 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.
In the process, the MSE packs any state information needed to return
an RA to the MN in the Relay-forward Interface ID option so that the
information will be echoed back in the Relay-reply.)
When the MSE receives the DHCPv6 Reply, it adds routes to the routing
system and creates MNP-LLAs based on the delegated MNPs. The MSE
then sends an RA back to the MN with the DHCPv6 Reply message
included in an OMNI DHCPv6 message sub-option if and only if the RS
message had included an explicit DHCPv6 Solicit. If the RS message
source was the unspecified address (::), the MSE includes one of the
(newly-created) MNP-LLAs as the RA destination address and sets the
OMNI option Preflen accordingly; otherwise, the MSE includes the RS
source address as the RA destination address. The MSE then sets the
RA source address to its own ADM-LLA then performs OAL encapsulation
and fragmentation if necessary and sends the RA to the MN. When the
MN receives the RA, it reassembles and discards the OAL encapsulation
if necessary, then creates a default route, assigns Subnet Router
Anycast addresses and uses the RA destination address as its primary
MNP-LLA. The MN will then use this primary MNP-LLA as the source
address of any IPv6 ND messages it sends as long as it retains
ownership of the MNP.
Note: After a MN performs a DHCPv6-based prefix registration exchange
with a first MSE, it would need to repeat the exchange with each
additional MSE it registers with. In that case, the MN supplies the
MNP delegation information received from the first MSE when it
engages the additional MSEs.
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15. Secure Redirection
If the *NET 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 *NET 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.
After verifying MN authorization and returning an RA, the AR MAY
return IPv6 ND Redirect messages to direct MNs located on the same
*NET 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 *NET 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.
16. AR and MSE Resilience
*NETs 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.
17. 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 *NET links such as aeronautical radios) and can therefore be
tuned for rapid response.
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ARs perform proactive NUD for MSEs for which there are currently
active MNs on the *NET. If an MSE fails, ARs can quickly inform MNs
of the outage by sending multicast RA messages on the *NET interface.
The AR sends RA messages to MNs via the *NET 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].
The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated
by small delays [RFC4861]. Any MNs on the *NET interface that have
been using the (now defunct) MSE will receive the RA messages and
associate with a new MSE.
18. Transition Considerations
When a MN connects to an *NET 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 ADM-LLA as the source, the MNP-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 *NET
according to the legacy IPv6 link model and without the OMNI
extensions specified in this document.
If the *NET link model is multiple access, there must be assurance
that address duplication cannot corrupt the neighbor caches of other
nodes on the link. When the MN sends an RS message on a multiple
access *NET link with an 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 *NET 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.
19. OMNI Interfaces on Open Internetworks
OMNI interfaces configured over IPv6-enabled underlying interfaces on
an open Internetwork 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
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(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].
OMNI interfaces configured over underlying interfaces that connect to
an open Internetwork can apply security services such as VPNs to
connect to an MSE, or can 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 per [RFC6081][RFC4380] and HIP-based message
authentication per [RFC7401].
OMNI interfaces that use UDP/IP encapsulation use the UDP service
port number 8060 for 'aero' (see: Section 22), but do not include
[RFC4380] header nor [RFC6081] trailer extension options (the
interface instead includes them as OMNI sub-options when needed).
OMNI interfaces therefore unconditionally drop any UDP encapsulated
messages that include any such header/trailer extension options.
Furthermore, OMNI UDP/IP encapsulation over IPv6 underlying
interfaces uses the encapsulation format specified in [RFC4380] with
the exception that IPv6 is used as the outer IP protocol instead of
IPv4.
For "Vehicle-to-Infrastructure (V2I)" coordination, the MN codes a
HIP "Initiator" message in an OMNI option of an IPv6 RS message and
the AR responds with a HIP "Responder" message coded in an OMNI
option of an IPv6 RA message. HIP security services are applied per
[RFC7401], using the RS/RA messages as simple "shipping containers"
to convey the HIP parameters. In that case, a "two-message HIP
exchange" through a single RS/RA exchange may be sufficient for
mutual authentication. For "Vehicle-to-Vehicle (V2V)" coordination,
two MNs can coordinate directly with one another with HIP "Initiator/
Responder" messages coded in OMNI options of IPv6 NS/NA messages. In
that case, a four-message HIP exchange (i.e., two back-to-back NS/NA
exchanges) may be necessary for the two MNs to attain mutual
authentication.
After establishing a VPN or preparing for UDP/IP encapsulation, OMNI
interfaces send control plane messages to interface with the MS,
including RS/RA messages used according to Section 14 and NS/NA
messages used for route optimization and mobility (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 traffic with basic source address-based data
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origin verification. Data plane communications via OMNI interfaces
that connect over open Internetworks without an explicit VPN should
therefore employ transport- or higher-layer security to ensure
integrity and/or confidentiality.
OMNI interfaces configured over open Internetworks are often located
behind NATs. The OMNI interface accommodates NAT traversal using
UDP/IP encapsulation and the mechanisms discussed in
[I-D.templin-intarea-6706bis]. To support NAT determination, ARs
include an Origin Indication sub-option in RA messages sent in
response to RS messages received from a Client via UDP/IP
encapsulation.
Note: Following the initial HIP Initiator/Responder exchange, OMNI
interfaces configured over open Internetworks maintain HIP
associations through the transmission of IPv6 ND messages that
include OMNI options with HIP "Update" and "Notify" messages. OMNI
interfaces use the HIP "Update" message when an acknowledgement is
required, and use the "Notify" message in unacknowledged isolated
IPv6 ND messages (e.g., unsolicited NAs).
Note: ARs that act as proxys on an open Internetwork authenticate and
remove HIP message OMNI sub-options from RSes they forward from a MN
to an MSE, and insert and sign HIP message and Origin Indication sub-
options in RAs they forward from an MSE to an MN. Conversely, ARs
that act as proxys forward without processing any DHCPv6 information
in RS/RA message exchanges between MNs and MSEs. The AR is therefore
responsible for MN authentication while the MSE is responsible for
registering/delegating MNPs.
20. 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 14.3 allows OMNI
MNs that desire time-varying MNPs to obtain short-lived prefixes to
send RS messages with source set to the unspecified address (::) and/
or with an OMNI option with DHCPv6 Option sub-options. The 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
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services, however presents limits for the durations of ongoing
sessions that would prefer to use a constant address.
21. (H)HITs and Temporary ULAs
MNs that generate (H)HITs but do not have pre-assigned MNPs can
request MNP delegations by issuing IPv6 ND messages that use the
(H)HIT instead of a Temporary ULA. In particular, when a MN creates
an RS message it can set the source to the unspecified address (::)
and destination to All-Routers multicast. The IPv6 ND message
includes an OMNI option with a HIP "Initiator" message sub-option,
and need not include a Node Identification sub-option since the MN's
HIT appears in the HIP message. The MN then encapsulates the message
in an IPv6 header with the (H)HIT as the source address and with
destination set to either a unicast or anycast ADM-ULA. The MN then
sends the message to the AR as specified in Section 14.1.
When the AR receives the message, it notes that the RS source was the
unspecified address (::), then examines the RS encapsulation source
address to determine that the source is a (H)HIT and not a Temporary
ULA. The AR next invokes the DHCPv6 protocol to request an MNP
prefix delegation while using the MN's HIT found in the HIP message
as the Client Identifier, then prepares an RA message with source
address set to its own ADM-LLA and destination set to the MNP-LLA
corresponding to the delegated MNP. The AR next includes an OMNI
option with a HIP "Responder" message and any DHCPv6 prefix
delegation parameters. The AR then finally encapsulates the RA in an
IPv6 header with source address set to its own ADM-ULA and
destination set to the (H)HIT from the RS encapsulation source
address, then returns the encapsulated RA to the MN.
MNs can also use (H)HITs and/or Temporary ULAs for direct MN-to-MN
communications outside the context of any OMNI link supporting
infrastructure. When two MNs encounter one another they can use
their (H)HITs and/or Temporary ULAs as IPv6 packet source and
destination addresses to support direct communications. MNs can also
inject their (H)HITs and/or Temporary ULAs into a MANET/VANET routing
protocol to enable multihop communications. MNs can further exchange
IPv6 ND messages (such as NS/NA) using their (H)HITs and/or Temporary
ULAs as source and destination addresses. Note that the HIP security
protocols for establishing secure neighbor relationships are based on
(H)HITs; therefore, Temporary ULAs would presumably utilize some
alternate form of message authentication such as the [RFC4380]
authentication service.
Lastly, when MNs are within the coverage range of OMNI link
infrastructure a case could be made for injecting (H)HITs and/or
Temporary ULAs into the global MS routing system. For example, when
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the MN sends an RS to a MSE it could include a request to inject the
(H)HIT / Temporary ULA into the routing system instead of requesting
an MNP prefix delegation. This would potentially enable OMNI link-
wide communications using only (H)HITs or Temporary ULAs, and not
MNPs. This document notes the opportunity, but makes no
recommendation.
22. IANA Considerations
The following IANA actions are requested:
22.1. "IPv6 Neighbor Discovery Option Formats" Registry
The IANA is instructed to allocate an official Type number TBD1 from
the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI
option. Implementations set Type to 253 as an interim value
[RFC4727].
22.2. "Ethernet Numbers" Registry
The IANA is instructed to allocate one Ethernet unicast address TBD2
(suggested value '00-52-14') in the 'ethernet-numbers' registry under
"IANA Unicast 48-bit MAC Addresses" as follows:
Addresses Usage Reference
--------- ----- ---------
00-52-14 Overlay Multilink Network (OMNI) Interface [RFCXXXX]
Figure 23: IANA Unicast 48-bit MAC Addresses
22.3. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry
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
appear as follows:
Code Name Reference
--- ---- ---------
0 Diagnostic Packet Too Big [RFC4443]
1 Advisory Packet Too Big [RFCXXXX]
Figure 24: ICMPv6 Code Fields: Type 2 - Packet Too Big Values
22.4. "OMNI Option Sub-Type Values" (New Registry)
The OMNI option defines a 5-bit Sub-Type field, for which IANA is
instructed to create and maintain a new registry entitled "OMNI
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Option Sub-Type Values". Initial values are given below (future
assignments are to be made through Standards Action [RFC8126]):
Value Sub-Type name Reference
----- ------------- ----------
0 Pad1 [RFCXXXX]
1 PadN [RFCXXXX]
2 Interface Attributes (Type 1) [RFCXXXX]
3 Interface Attributes (Type 2) [RFCXXXX]
4 Traffic Selector [RFCXXXX]
5 MS-Register [RFCXXXX]
6 MS-Release [RFCXXXX]
7 Geo Coordinates [RFCXXXX]
8 DHCPv6 Message [RFCXXXX]
9 HIP Message [RFCXXXX]
10 Node Identification [RFCXXXX]
11-29 Unassigned
30 Sub-Type Extension [RFCXXXX]
31 Reserved by IANA [RFCXXXX]
Figure 25: OMNI Option Sub-Type Values
22.5. "OMNI Node Identification ID-Type Values" (New Registry)
The OMNI Node Identification Sub-Option (see: Section 11.1.11)
contains an 8-bit ID-Type field, for which IANA is instructed to
create and maintain a new registry entitled "OMNI Node Identification
ID-Type Values". Initial values are given below (future assignments
are to be made through Expert Review [RFC8126]):
Value Sub-Type name Reference
----- ------------- ----------
0 UUID [RFCXXXX]
1 HIT [RFCXXXX]
2 HHIT [RFCXXXX]
3 Network Access Identifier [RFCXXXX]
4 FQDN [RFCXXXX]
5-252 Unassigned [RFCXXXX]
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 26: OMNI Node Identification ID-Type Values
22.6. "OMNI Option Sub-Type Extension Values" (New Registry)
The OMNI option defines an 8-bit Extension-Type field for Sub-Type 30
(Sub-Type Extension), for which IANA is instructed to create and
maintain a new registry entitled "OMNI Option Sub-Type Extension
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Values". Initial values are given below (future assignments are to
be made through Expert Review [RFC8126]):
Value Sub-Type name Reference
----- ------------- ----------
0 RFC4380 UDP/IP Header Option [RFCXXXX]
1 RFC6081 UDP/IP Trailer Option [RFCXXXX]
2-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 27: OMNI Option Sub-Type Extension Values
22.7. "OMNI RFC4380 UDP/IP Header Option" (New Registry)
The OMNI Sub-Type Extension "RFC4380 UDP/IP Header Option" defines an
8-bit Header Type field, for which IANA is instructed to create and
maintain a new registry entitled "OMNI RFC4380 UDP/IP Header Option".
Initial registry values are given below (future assignments are to be
made through Expert Review [RFC8126]):
Value Sub-Type name Reference
----- ------------- ----------
0 Origin Indication (IPv4) [RFC4380]
1 Authentication Encapsulation [RFC4380]
2 Origin Indication (IPv6) [RFCXXXX]
3-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 28: OMNI RFC4380 UDP/IP Header Option
22.8. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry)
The OMNI Sub-Type Extension for "RFC6081 UDP/IP Trailer Option"
defines an 8-bit Trailer Type field, for which IANA is instructed to
create and maintain a new registry entitled "OMNI RFC6081 UDP/IP
Trailer Option". Initial registry values are given below (future
assignments are to be made through Expert Review [RFC8126]):
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Value Sub-Type name Reference
----- ------------- ----------
0 Unassigned
1 Nonce [RFC6081]
2 Unassigned
3 Alternate Address (IPv4) [RFC6081]
4 Neighbor Discovery Option [RFC6081]
5 Random Port [RFC6081]
6 Alternate Address (IPv6) [RFCXXXX]
7-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 29: OMNI RFC6081 Trailer Option
22.9. Additional Considerations
The IANA has assigned the UDP port number "8060" for an earlier
experimental version of AERO [RFC6706]. This document together with
[I-D.templin-intarea-6706bis] reclaims the UDP port number "8060" for
'aero' as the service port for UDP/IP encapsulation. (Note that,
although [RFC6706] was not widely implemented or deployed, any
messages coded to that specification can be easily distinguished and
ignored since they use the invalid ICMPv6 message type number '0'.)
The IANA is therefore instructed to update the reference for UDP port
number "8060" from "RFC6706" to "RFCXXXX" (i.e., this document).
The IANA has already assigned a 4 octet Private Enterprise Number
(PEN) code "45282" in the "enterprise-numbers" registry. This
document is the normative reference for using this code in DHCP
Unique IDentifiers based on Enterprise Numbers ("DUID-EN for OMNI
Interfaces") (see: Section 10). The IANA is therefore instructed to
change the enterprise designation for PEN code "45282" from "LinkUp
Networks" to "Overlay Multilink Network Interface (OMNI)".
An application for an Interface Type (ifType) registration was
submitted to IANA on February 8, 2021 in accordance with Section 6 of
[RFC8892]. The application requests registration of an ifType for
"omni" (Overlay Multilink Network Interface (OMNI)), with the OMNI
Adaptation Layer (OAL) as a sublayer. No further IANA actions are
required.
23. 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.
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MN OMNI interfaces configured over secured ANET interfaces inherit
the physical and/or link-layer security properties (i.e., "protected
spectrum") of the connected ANETs. MN OMNI interfaces configured
over open INET interfaces can use symmetric securing services such as
VPNs or can by some other means establish a direct link. When a VPN
or direct link may be impractical, however, the security services
specified in [RFC7401] and/or [RFC4380] can be employed. While the
OMNI link protects control plane messaging, applications must still
employ end-to-end transport- or higher-layer security services to
protect the data plane.
Strong network layer security for control plane messages and
forwarding path integrity for data plane messages between MSEs MUST
be supported. In one example, the AERO service
[I-D.templin-intarea-6706bis] constructs a spanning tree between MSEs
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.
Identity-based key verification infrastructure services such as iPSK
may be necessary for verifying the identities claimed by MNs. This
requirement should be harmonized with the manner in which (H)HITs are
attested in a given operational environment.
Security considerations for specific access network interface types
are covered under the corresponding IP-over-(foo) specification
(e.g., [RFC2464], [RFC2492], etc.).
Security considerations for IPv6 fragmentation and reassembly are
discussed in Section 5.1.
24. Implementation Status
AERO/OMNI Release-3.0.2 was tagged on October 15, 2020, and is
undergoing internal testing. Additional internal releases expected
within the coming months, with first public release expected end of
1H2021.
25. Acknowledgements
The first version of this document was prepared per the consensus
decision at the 7th Conference of the International Civil Aviation
Organization (ICAO) Working Group-I Mobility Subgroup on March 22,
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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:
Stuart Card, Michael Matyas, Robert Moskowitz, Madhu Niraula, Greg
Saccone, Stephane Tamalet, Eric Vyncke. Pavel Drasil, Zdenek Jaron
and Michal Skorepa are especially recognized for their many helpful
ideas and suggestions. Madhuri Madhava Badgandi, Sean Dickson, Don
Dillenburg, Joe Dudkowski, Vijayasarathy Rajagopalan, Ron Sackman and
Katherine Tran are acknowledged for their hard work on the
implementation and technical insights that led to improvements for
the spec.
Discussions on the IETF 6man and atn mailing lists during the fall of
2020 suggested additional points to consider. The authors gratefully
acknowledge the list members who contributed valuable insights
through those discussions. Eric Vyncke and Erik Kline were the
intarea ADs, while Bob Hinden and Ole Troan were the 6man WG chairs
at the time the document was developed; they are all gratefully
acknowledged for their many helpful insights.
This work is aligned with the NASA Safe Autonomous Systems Operation
(SASO) program under NASA contract number NNA16BD84C.
This work is aligned with the FAA as per the SE2025 contract number
DTFAWA-15-D-00030.
This work is aligned with the Boeing Information Technology (BIT)
Mobility Vision Lab (MVL) program.
26. References
26.1. 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>.
[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<https://www.rfc-editor.org/info/rfc7401>.
[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>.
26.2. Informative References
[ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground
Interface for Civil Aviation, IETF Liaison Statement
#1676, https://datatracker.ietf.org/liaison/1676/", 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.
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[CRC] Jain, R., "Error Characteristics of Fiber Distributed Data
Interface (FDDI), IEEE Transactions on Communications",
August 1990.
[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-drip-rid]
Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov,
"UAS Remote ID", draft-ietf-drip-rid-06 (work in
progress), December 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-11
(work in progress), January 2021.
[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-87 (work in
progress), January 2021.
[IPV4-GUA]
Postel, J., "IPv4 Address Space Registry,
https://www.iana.org/assignments/ipv4-address-space/ipv4-
address-space.xhtml", December 2020.
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[IPV6-GUA]
Postel, J., "IPv6 Global Unicast Address Assignments,
https://www.iana.org/assignments/ipv6-unicast-address-
assignments/ipv6-unicast-address-assignments.xhtml",
December 2020.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[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>.
[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>.
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[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>.
[RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330,
DOI 10.17487/RFC3330, September 2002,
<https://www.rfc-editor.org/info/rfc3330>.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692,
DOI 10.17487/RFC3692, January 2004,
<https://www.rfc-editor.org/info/rfc3692>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, DOI 10.17487/RFC3819, July 2004,
<https://www.rfc-editor.org/info/rfc3819>.
[RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local
Addresses", RFC 3879, DOI 10.17487/RFC3879, September
2004, <https://www.rfc-editor.org/info/rfc3879>.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/info/rfc4122>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
DOI 10.17487/RFC4380, February 2006,
<https://www.rfc-editor.org/info/rfc4380>.
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[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
2006, <https://www.rfc-editor.org/info/rfc4389>.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
<https://www.rfc-editor.org/info/rfc4429>.
[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605,
August 2006, <https://www.rfc-editor.org/info/rfc4605>.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
<https://www.rfc-editor.org/info/rfc4821>.
[RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly
Errors at High Data Rates", RFC 4963,
DOI 10.17487/RFC4963, July 2007,
<https://www.rfc-editor.org/info/rfc4963>.
[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>.
[RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)",
RFC 5558, DOI 10.17487/RFC5558, February 2010,
<https://www.rfc-editor.org/info/rfc5558>.
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[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>.
[RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization
(AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012,
<https://www.rfc-editor.org/info/rfc6706>.
[RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation
with IPv6 Neighbor Discovery", RFC 6980,
DOI 10.17487/RFC6980, August 2013,
<https://www.rfc-editor.org/info/rfc6980>.
[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>.
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[RFC7526] Troan, O. and B. Carpenter, Ed., "Deprecating the Anycast
Prefix for 6to4 Relay Routers", BCP 196, RFC 7526,
DOI 10.17487/RFC7526, May 2015,
<https://www.rfc-editor.org/info/rfc7526>.
[RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542,
DOI 10.17487/RFC7542, May 2015,
<https://www.rfc-editor.org/info/rfc7542>.
[RFC7739] Gont, F., "Security Implications of Predictable Fragment
Identification Values", RFC 7739, DOI 10.17487/RFC7739,
February 2016, <https://www.rfc-editor.org/info/rfc7739>.
[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>.
[RFC8892] Thaler, D. and D. Romascanu, "Guidelines and Registration
Procedures for Interface Types and Tunnel Types",
RFC 8892, DOI 10.17487/RFC8892, August 2020,
<https://www.rfc-editor.org/info/rfc8892>.
[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)
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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
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=3| Sub-length=N | omIndex | omType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 30: 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=3| Sub-length=N | omIndex | omType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 31: 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=3| Sub-length=N | omIndex | omType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 32: 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 *NET. 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 *NET links, ARs can maintain an
OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible
*NETs, this specification reserves one Ethernet unicast address TBD2
(see: Section 22). For non-Ethernet statically-addressed *NETs,
MSADDR is reserved per the assigned numbers authority for the *NET
addressing space. For still other *NETs, MSADDR may be dynamically
discovered through other means, e.g., L2 beacons.
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 experience.
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
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Fred L. Templin (editor)
The Boeing Company
P.O. Box 3707
Seattle, WA 98124
USA
Email: fltemplin@acm.org
Tony Whyman
MWA Ltd c/o Inmarsat Global Ltd
99 City Road
London EC1Y 1AX
England
Email: tony.whyman@mccallumwhyman.com
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