Network Working Group F. Templin, Ed.
Internet-Draft The Boeing Company
Intended status: Informational A. Whyman
Expires: December 6, 2021 MWA Ltd c/o Inmarsat Global Ltd
June 4, 2021
Transmission of IP Packets over Overlay Multilink Network (OMNI)
Interfaces
draft-templin-6man-omni-23
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 presented that
enables mobile nodes to coordinate with a network-based mobility
service and/or with other mobile node peers. This document specifies
the transmission of IP packets over Overlay Multilink Network (OMNI)
Interfaces.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 6, 2021.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 12
4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 12
5. OMNI Interface Maximum Transmission Unit (MTU) . . . . . . . 18
6. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 19
6.1. OAL Source Encapsulation and Fragmentation . . . . . . . 19
6.2. OAL *NET Encapsulation and Re-Encapsulation . . . . . . . 24
6.3. OAL Destination Decapsulation and Reassembly . . . . . . 26
6.4. OAL Header Compression . . . . . . . . . . . . . . . . . 26
6.5. OAL Identification Window Maintenance . . . . . . . . . . 29
6.6. OAL Fragment Retransmission . . . . . . . . . . . . . . . 34
6.7. OAL MTU Feedback Messaging . . . . . . . . . . . . . . . 35
6.8. OAL Requirements . . . . . . . . . . . . . . . . . . . . 37
6.9. OAL Fragmentation Security Implications . . . . . . . . . 39
6.10. OAL Super-Packets . . . . . . . . . . . . . . . . . . . . 40
7. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 42
8. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 42
9. Unique-Local Addresses (ULAs) . . . . . . . . . . . . . . . . 43
10. Global Unicast Addresses (GUAs) . . . . . . . . . . . . . . . 45
11. Node Identification . . . . . . . . . . . . . . . . . . . . . 46
12. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 46
12.1. The OMNI Option . . . . . . . . . . . . . . . . . . . . 47
12.2. OMNI Sub-Options . . . . . . . . . . . . . . . . . . . . 49
12.2.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 50
12.2.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 51
12.2.3. Interface Attributes (Types 1 through 3) . . . . . . 51
12.2.4. Interface Attributes (Type 4) . . . . . . . . . . . 52
12.2.5. MS-Register . . . . . . . . . . . . . . . . . . . . 55
12.2.6. MS-Release . . . . . . . . . . . . . . . . . . . . . 56
12.2.7. Geo Coordinates . . . . . . . . . . . . . . . . . . 56
12.2.8. Dynamic Host Configuration Protocol for IPv6
(DHCPv6) Message . . . . . . . . . . . . . . . . . . 57
12.2.9. Host Identity Protocol (HIP) Message . . . . . . . . 58
12.2.10. PIM-SM Message . . . . . . . . . . . . . . . . . . . 59
12.2.11. Reassembly Limit . . . . . . . . . . . . . . . . . . 60
12.2.12. Fragmentation Report . . . . . . . . . . . . . . . . 61
12.2.13. Node Identification . . . . . . . . . . . . . . . . 62
12.2.14. ICMPv6 Error . . . . . . . . . . . . . . . . . . . . 64
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12.2.15. Sub-Type Extension . . . . . . . . . . . . . . . . . 64
13. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 68
14. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 68
14.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 69
14.2. Client-Proxy/Server Loop Prevention . . . . . . . . . . 69
15. Router Discovery and Prefix Registration . . . . . . . . . . 70
15.1. Window Synchronization . . . . . . . . . . . . . . . . . 74
15.2. Router Discovery in IP Multihop and IPv4-Only Networks . 75
15.3. MS-Register and MS-Release List Processing . . . . . . . 77
15.4. DHCPv6-based Prefix Registration . . . . . . . . . . . . 79
16. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 80
17. Proxy/Server Resilience . . . . . . . . . . . . . . . . . . . 80
18. Detecting and Responding to Proxy/Server Failures . . . . . . 81
19. Transition Considerations . . . . . . . . . . . . . . . . . . 81
20. OMNI Interfaces on Open Internetworks . . . . . . . . . . . . 82
21. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 85
22. (H)HITs and Temporary ULAs . . . . . . . . . . . . . . . . . 85
23. Address Selection . . . . . . . . . . . . . . . . . . . . . . 86
24. Error Messages . . . . . . . . . . . . . . . . . . . . . . . 87
25. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 87
25.1. "IEEE 802 Numbers" Registry . . . . . . . . . . . . . . 87
25.2. "IPv6 Neighbor Discovery Option Formats" Registry . . . 87
25.3. "Ethernet Numbers" Registry . . . . . . . . . . . . . . 87
25.4. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry . 87
25.5. "OMNI Option Sub-Type Values" (New Registry) . . . . . . 88
25.6. "OMNI Geo Coordinates Type Values" (New Registry) . . . 88
25.7. "OMNI Node Identification ID-Type Values" (New Registry) 89
25.8. "OMNI Option Sub-Type Extension Values" (New Registry) . 89
25.9. "OMNI RFC4380 UDP/IP Header Option" (New Registry) . . . 90
25.10. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry) . . 90
25.11. Additional Considerations . . . . . . . . . . . . . . . 90
26. Security Considerations . . . . . . . . . . . . . . . . . . . 91
27. Implementation Status . . . . . . . . . . . . . . . . . . . . 92
28. Document Updates . . . . . . . . . . . . . . . . . . . . . . 92
29. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 93
30. References . . . . . . . . . . . . . . . . . . . . . . . . . 94
30.1. Normative References . . . . . . . . . . . . . . . . . . 94
30.2. Informative References . . . . . . . . . . . . . . . . . 96
Appendix A. OAL Checksum Algorithm . . . . . . . . . . . . . . . 104
Appendix B. VDL Mode 2 Considerations . . . . . . . . . . . . . 105
Appendix C. Client-Proxy/Server Isolation Through L2 Address
Mapping . . . . . . . . . . . . . . . . . . . . . . 106
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 106
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 110
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1. Introduction
Mobile network platforms and devices (e.g., aircraft of various
configurations, terrestrial vehicles, seagoing vessels, enterprise
wireless devices, pedestrians with cellphones, etc.) configure mobile
routers with multiple interface connections to wireless and/or wired-
line data links. These data links may have diverse performance, cost
and availability properties that can change dynamically according to
mobility patterns, flight phases, proximity to infrastructure, etc.
The mobile router acts as a Client to the network-based mobility
service to coordinate its data links in a discipline known as
"multilink", in which a single virtual interface is configured over
the Client's underlying interface data link connections.
Each Client configures a virtual interface (termed the "Overlay
Multilink Network Interface (OMNI)") as a thin layer over its
underlying interfaces. The OMNI interface is therefore the only
interface abstraction exposed to the IP layer and behaves according
to the Non-Broadcast, Multiple Access (NBMA) interface principle,
while underlying interfaces appear as link layer communication
channels in the architecture. The OMNI interface internally employs
the "OMNI Adaptation Layer (OAL)" to ensure that original IP packets
are delivered without loss due to size restrictions. The OMNI
interface connects to a virtual overlay service known as the "OMNI
link". The OMNI link spans one or more Internetworks that may
include private-use infrastructures and/or the global public Internet
itself.
Each Client receives a Mobile Network Prefix (MNP) through mobility
service control message exchanges with Proxy/Servers which also
configure OMNI interfaces. The Client uses the MNP for numbering
downstream-attached End User Networks (EUNs) independently of the
access network data links selected for data transport. The Client
acts as a mobile router on behalf of its EUNs, and uses OMNI
interface control messaging to coordinate with Proxy/Servers (and/or
other Clients). The Client iterates its router discovery process
over each of the OMNI interface's underlying interfaces in order to
register per-link parameters (see Section 15).
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 MNPs are derived. If there are multiple OMNI
links, the IPv6 layer will see multiple OMNI interfaces.
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Clients may connect to multiple distinct OMNI links within the same
OMNI domain by configuring multiple OMNI interfaces, e.g., omni0,
omni1, omni2, etc. Each OMNI interface is configured over a set of
underlying interfaces and provides a nexus for Safety-Based Multilink
(SBM) operation. Each OMNI interface within the same OMNI domain
configures a common ULA prefix [ULA]::/48, and configures a unique
16-bit Subnet ID '*' to construct the sub-prefix [ULA*]::/64 (see:
Section 9). The IP layer applies SBM routing to select a specific
OMNI interface, and the OMNI interface then applies Performance-Based
Multilink (PBM) internally to select appropriate underlying
interfaces. Applications can apply Segment Routing [RFC8402] to
select independent SBM topologies for fault tolerance, while the OMNI
interface orchestrates PBM.
The OMNI interface interacts with a network-based Mobility Service
(MS) and/or other Clients through IPv6 Neighbor Discovery (ND)
control message exchanges [RFC4861]. The MS provides includes Proxy/
Servers (and other infrastructure elements) that track Client
movements and represent their MNPs in a global routing or mapping
system. An example MS appears (along with definitions of its other
required mobility service elements) appears in
[I-D.templin-6man-aero].
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
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.
In addition to many other aspects, OMNI supports the "6M's" of modern
Internetworking including:
1. Multilink - a Client's ability to coordinate multiple diverse
underlying data links as a single logical unit (i.e., the OMNI
interface) to achieve the required communications performance and
reliability objectives.
2. Multinet - the ability to span the OMNI link across multiple
diverse network administrative segments while maintaining
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seamless end-to-end communications between mobile Clients and
correspondents such as air traffic controllers, fleet
administrators, etc.
3. Mobility - a Client's ability to change network points of
attachment (e.g., moving between wireless base stations) which
may result in an underlying interface address change, but without
disruptions to ongoing communication sessions with peers over the
OMNI link.
4. Multicast - the ability to send a single network transmission
that reaches multiple Clients belonging to the same interest
group, but without disturbing other Clients not subscribed to the
interest group.
5. Multihop - a mobile Client vehicle-to-vehicle relaying capability
useful when multiple forwarding hops between vehicles may be
necessary to "reach back" to an infrastructure access point
connection to the OMNI link.
6. MTU assurance - the ability to deliver packets of various robust
sizes between peers without loss due to a link size restriction,
and to dynamically adjust packets sizes to achieve the optimal
performance for each independent traffic flow.
This document specifies the transmission of IP packets and control
messages over OMNI interfaces. The OMNI interface supports either IP
protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) as the
network layer in the data plane, while using IPv6 ND messaging as the
control plane independently of the data plane IP protocol(s). The
OAL operates as a sublayer between L3 and L2 based on IPv6
encapsulation [RFC2473] as discussed in the following sections.
2. Terminology
The terminology in the normative references applies; especially, the
terms "link" and "interface" are the same as defined in the IPv6
[RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications.
Additionally, this document assumes the following IPv6 ND message
types: Router Solicitation (RS), Router Advertisement (RA), Neighbor
Solicitation (NS), Neighbor Advertisement (NA) and Redirect. Clients
and Proxy/Servers that implement IPv6 ND maintain per-neighbor state
in Neighbor Cache Entries (NCEs). Each NCE is indexed by the
neighbor's Link-Local Address (LLA), while the Unique-Local Address
(ULA) used for encapsulation provides context for Identification
verification.
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The Protocol Constants defined in Section 10 of [RFC4861] are used in
their same format and meaning in this document. The terms "All-
Routers multicast", "All-Nodes multicast" and "Subnet-Router anycast"
are the same as defined in [RFC4291] (with Link-Local scope assumed).
The term "IP" is used to refer collectively to either Internet
Protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) when a
specification at the layer in question applies equally to either
version.
The following terms are defined within the scope of this document:
Client
a mobile network platform/device mobile router that has one or
more distinct upstream data link connections grouped together into
one or more logical units. The Client's data link connection
parameters can change over time due to, e.g., node mobility, link
quality, etc. The Client further connects downstream-attached End
User Networks (EUNs).
End User Network (EUN)
a simple or complex downstream-attached mobile network that
travels with the Client as a single logical unit. The IP
addresses assigned to EUN devices remain stable even if the
Client's upstream data link connections change.
Mobility Service (MS)
a mobile routing service that tracks Client movements and ensures
that Clients remain continuously reachable even across mobility
events. The MS consists of the set of all Proxy/Servers for the
OMNI link as well as any other OMNI link supporting infrastructure
nodes. Specific MS details are out of scope for this document,
with an example MS found in [I-D.templin-6man-aero].
Proxy/Server
a router that provides an entry point into the MS and coordinates
Client mobility events. As a server, the Proxy/Server responds
directly to some Client IPv6 ND messages. As a proxy, the Proxy/
Server forwards other Client IPv6 ND messages to other Proxy/
Servers and Clients. As a router, the Proxy/Server forwards
ordinary data packets between OMNI interface Clients and networked
correspondent nodes.
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
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Internet address registry, however private-use prefixes can
alternatively be used subject to certain limitations (see:
Section 10). OMNI links that connect to the global Internet
advertise their MSPs to their interdomain routing peers.
Mobile Network Prefix (MNP)
a longer IP prefix delegated from an MSP (e.g.,
2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a
Client. Clients sub-delegate the MNP to devices located in EUNs.
Note that OMNI link Relay nodes may also service non-MNP routes
(i.e., GUA prefixes not covered by an MSP) but that these
correspond to fixed correspondent nodes and not Clients. Other
than this distinction, MNP and non-MNP routes are treated exactly
the same by the OMNI routing system.
Access Network (ANET)
a data link service network (e.g., an aviation radio access
network, satellite service provider network, cellular operator
network, WiFi network, etc.) that connects Clients. Physical and/
or data link level security is assumed, and sometimes referred to
as "protected spectrum". Private enterprise networks and ground
domain aviation service networks may provide multiple secured IP
hops between the Client's point of connection and the nearest
Proxy/Server.
ANET interface
a Client's attachment to a link in an ANET.
Internetwork (INET)
a connected network region with a coherent IP addressing plan that
provides transit forwarding services between ANETs and nodes that
connect directly to the open INET via unprotected media. No
physical and/or data link level security is assumed, therefore
security must be applied by upper layers. The global public
Internet itself is an example.
INET interface
a node's attachment to a link in an INET.
*NET
a "wildcard" term used when a given specification applies equally
to both ANET and INET cases.
OMNI link
a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured
over one or more INETs and their connected ANETs. An OMNI link
may comprise multiple INET segments joined by bridges the same as
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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 sublayer service whereby original IP packets
admitted into the interface are wrapped in an IPv6 header and
subject to fragmentation and reassembly. The OAL is also
responsible for generating MTU-related control messages as
necessary, and for providing addressing context for spanning
multiple segments of a bridged OMNI link.
original IP packet
a whole IP packet or fragment admitted into the OMNI interface by
the network layer prior to OAL encapsulation and fragmentation, or
an IP packet delivered to the network layer by the OMNI interface
following OAL decapsulation and reassembly.
OAL packet
an original IP packet encapsulated in OAL headers and trailers,
which is then submitted for OAL fragmentation and reassembly.
OAL fragment
a portion of an OAL packet following fragmentation but prior to
*NET encapsulation, or following *NET encapsulation but prior to
OAL reassembly.
(OAL) atomic fragment
an OAL packet that does not require fragmentation is always
encapsulated as an "atomic fragment" with a Fragment Header with
Fragment Offset and More Fragments both set to 0, but with a valid
Identification value.
(OAL) carrier packet
an encapsulated OAL fragment following *NET encapsulation or prior
to *NET decapsulation. OAL sources and destinations exchange
carrier packets over underlying interfaces, and may be separated
by one or more OAL intermediate nodes. OAL intermediate nodes may
perform re-encapsulation on carrier packets by removing the *NET
headers of the first hop network and replacing them with new *NET
headers for the next hop network.
OAL source
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an OMNI interface acts as an OAL source when it encapsulates
original IP packets to form OAL packets, then performs OAL
fragmentation and *NET encapsulation to create carrier packets.
OAL destination
an OMNI interface acts as an OAL destination when it decapsulates
carrier packets, then performs OAL reassembly and decapsulation to
derive the original IP packet.
OAL intermediate node
an OMNI interface acts as an OAL intermediate node when it removes
the *NET headers of carrier packets received on a first segment,
then re-encapsulates the carrier packets in new *NET headers and
forwards them into the next segment.
OMNI Option
an IPv6 Neighbor Discovery option providing multilink parameters
for the OMNI interface as specified in Section 12.
Mobile Network Prefix Link Local Address (MNP-LLA)
an IPv6 Link Local Address that embeds the most significant 64
bits of an MNP in the lower 64 bits of fe80::/64, as specified in
Section 8.
Mobile Network Prefix Unique Local Address (MNP-ULA)
an IPv6 Unique-Local Address derived from an MNP-LLA.
Administrative Link Local Address (ADM-LLA)
an IPv6 Link Local Address that embeds a 32-bit administratively-
assigned identification value in the lower 32 bits of fe80::/96,
as specified in Section 8.
Administrative Unique Local Address (ADM-ULA)
an IPv6 Unique-Local Address derived from an ADM-LLA.
Multilink
an OMNI interface's manner of managing diverse underlying
interface connections to data links as a single logical unit. The
OMNI interface provides a single unified interface to upper
layers, while underlying interface selections are performed on a
per-packet basis considering traffic selectors such as DSCP, flow
label, application policy, signal quality, cost, etc.
Multilinking decisions are coordinated in both the outbound and
inbound directions.
Multinet
an OAL intermediate node's manner of bridging multiple diverse IP
Internetworks and/or private enterprise networks at the OAL layer
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below IP. Through intermediate node concatenation of bridged
network segments in this way, multiple diverse Internetworks (such
as the global public IPv4 and IPv6 Internets) can serve as transit
segments in a bridged path for forwarding IP packets end-to-end.
This bridging capability provide benefits such as supporting IPv4/
IPv6 transition and coexistence, joining multiple diverse operator
networks into a cooperative single service network, etc.
Multihop
an iterative relaying of IP packets between Client's over an OMNI
underlying interface technology (such as omnidirectional wireless)
without support of fixed infrastructure. Multihop services entail
Client-to-Client relaying within a Mobile/Vehicular Ad-hoc Network
(MANET/VANET) for Vehicle-to-Vehicle (V2V) communications and/or
for Vehicle-to-Infrastructure (V2I) "range extension" where
Clients within range of communications infrastructure elements
provide forwarding services for other Clients.
L2
The second layer in the OSI network model. Also known as "layer-
2", "link-layer", "sub-IP layer", "data link layer", etc.
L3
The third layer in the OSI network model. Also known as "layer-
3", "network-layer", "IP layer", etc.
underlying interface
a *NET interface over which an OMNI interface is configured. The
OMNI interface is seen as a L3 interface by the IP layer, and each
underlying interface is seen as a L2 interface by the OMNI
interface. The underlying interface either connects directly to
the physical communications media or coordinates with another node
where the physical media is hosted.
Mobility Service Identification (MSID)
Each Proxy/Server is assigned a unique 32-bit Identification
(MSID) (see: Section 8). IDs are assigned according to MS-
specific guidelines (e.g., see: [I-D.templin-6man-aero]).
Safety-Based Multilink (SBM)
A means for ensuring fault tolerance through redundancy by
connecting multiple affiliated OMNI interfaces to independent
routing topologies (i.e., multiple independent OMNI links).
Performance Based Multilink (PBM)
A means for selecting underlying interface(s) for packet
transmission and reception within a single OMNI interface.
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OMNI Domain
The set of all SBM/PBM OMNI links that collectively provides
services for a common set of MSPs. Each OMNI domain consists of a
set of affiliated OMNI links that all configure the same ::/48 ULA
prefix with a unique 16-bit Subnet ID as discussed in Section 9.
3. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
An implementation is not required to internally use the architectural
constructs described here so long as its external behavior is
consistent with that described in this document.
4. Overlay Multilink Network (OMNI) Interface Model
An OMNI interface is a virtual interface configured over one or more
underlying interfaces, which may be physical (e.g., an aeronautical
radio link, etc.) or virtual (e.g., an Internet or higher-layer
"tunnel"). The OMNI interface architectural layering model is the
same as in [RFC5558][RFC7847], and augmented as shown in Figure 1.
The IP layer therefore sees the OMNI interface as a single L3
interface nexus for multiple underlying interfaces that appear as L2
communication channels in the architecture.
+----------------------------+
| Upper Layer Protocol |
Session-to-IP +---->| |
Address Binding | +----------------------------+
+---->| IP (L3) |
IP Address +---->| |
Binding | +----------------------------+
+---->| OMNI Interface |
Logical-to- +---->| (OMNI Adaptation Layer) |
Physical | +----------------------------+
Interface +---->| L2 | L2 | | L2 |
Binding |(IF#1)|(IF#2)| ..... |(IF#n)|
+------+------+ +------+
| L1 | L1 | | L1 |
| | | | |
+------+------+ +------+
Figure 1: OMNI Interface Architectural Layering Model
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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 a Proxy/Server. The ANET interface may be either
on the same L2 link segment as the Proxy/Server, or separated from
the Proxy/Server 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.
The OMNI interface forwards original IP packets from the network
layer (L3) using the OMNI Adaptation Layer (OAL) (see: Section 5) as
an encapsulation and fragmentation sublayer service. This "OAL
source" then further encapsulates the resulting OAL packets/fragments
in *NET headers to create OAL carrier packets for transmission over
underlying interfaces (L2/L1). The target OMNI interface receives
the carrier packets from underlying interfaces (L1/L2) and discards
the *NET headers. If the resulting OAL packets/fragments are
addressed to itself, the OMNI interface acts as an "OAL destination"
and performs reassembly if necessary, discards the OAL encapsulation,
and delivers the original IP packet to the network layer (L3). If
the OAL fragments are addressed to another node, the OMNI interface
instead acts as an "OAL intermediate node" by re-encapsulating in new
*NET headers and forwarding the new carrier packets over an
underlying interface without reassembling or discarding the OAL
encapsulation. The OAL source and OAL destination are seen as
"neighbors" on the OMNI link, while OAL intermediate nodes are seen
as "bridges" capable of multinet concatenation.
The OMNI interface can send/receive original IP packets to/from
underlying interfaces while including/omitting various encapsulations
including OAL, UDP, IP and L2. The network layer can also access the
underlying interfaces directly while bypassing the OMNI interface
entirely when necessary. This architectural flexibility may be
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beneficial for underlying interfaces (e.g., some aviation data links)
for which encapsulation overhead may be a primary consideration.
OMNI interfaces that send original IP packets directly over
underlying interfaces without invoking the OAL can only reach peers
located on the same OMNI link segment. However, an ANET Proxy/Server
that receives the original IP packet can forward it further by
performing OAL encapsulation with source set to its own address and
destination set to the OAL destination corresponding to the final
destination (i.e., even if the OAL destination is on a different OMNI
link segment).
Original IP packets sent directly over underlying interfaces are
subject to the same path MTU related issues as for any
Internetworking path, and do not include per-packet identifications
that can be used for data origin verification and/or link-layer
retransmissions. Original IP packets presented directly to an
underlying interface that exceed the underlying network path MTU are
dropped with an ordinary ICMPv6 Packet Too Big (PTB) message
returned. These PTB messages are subject to loss [RFC2923] the same
as for any non-OMNI IP interface.
The OMNI interface encapsulation/decapsulation layering possibilities
are shown in Figure 2 below. Imaginary vertical lines drawn between
the Network Layer and Underlying interfaces in the figure denote the
encapsulation/decapsulation layering combinations possible. Common
combinations include NULL (i.e., direct access to underlying
interfaces with or without using the OMNI interface), OMNI/IP,
OMNI/UDP/IP, OMNI/UDP/IP/L2, OMNI/OAL/UDP/IP, OMNI/OAL/UDP/L2, etc.
+------------------------------------------------------------+
| Network Layer |
+--+---------------------------------------------------------+
| OMNI Interface |
+--------------------------+------------------------------+
| OAL Encaps/Decaps |
+------------------------------+
| OAL Frag/Reass |
+------------+---------------+--------------+
| UDP Encaps/Decaps/Compress |
+----+---+------------+--------+--+ +--------+
| IP E/D | | IP E/D | | IP E/D |
+---+------+-+----+ +--+---+----+ +----+---+--+
|L2 E/D| |L2 E/D| |L2 E/D| |L2 E/D|
+-------+------+---+------+----+------+---------------+------+
| Underlying Interfaces |
+------------------------------------------------------------+
Figure 2: OMNI Interface Layering
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The OMNI/OAL model gives rise to a number of opportunities:
o Clients receive MNPs from the MS, and coordinate with the MS
through IPv6 ND message exchanges with Proxy/Servers. Clients use
the MNP to construct a unique Link-Local Address (MNP-LLA) through
the algorithmic derivation specified in Section 8 and assign the
LLA to the OMNI interface. Since MNP-LLAs are uniquely derived
from an MNP, no Duplicate Address Detection (DAD) or Multicast
Listener Discovery (MLD) messaging is necessary.
o since Temporary ULAs are statistically unique, they can be used
without DAD until an MNP-LLA is obtained.
o underlying interfaces on the same L2 link segment as a Proxy/
Server do not require any L3 addresses (i.e., not even link-local)
in environments where communications are coordinated entirely over
the OMNI interface.
o as underlying interface properties change (e.g., link quality,
cost, availability, etc.), any active interface can be used to
update the profiles of multiple additional interfaces in a single
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 OAL supports lossless and adaptive path MTU mitigations not
available for communications directly over the underlying
interfaces themselves. The OAL supports "packing" of multiple IP
payload packets within a single OAL packet.
o the OAL applies per-packet identification values that allow for
link-layer reliability and data origin authentication.
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o L3 sees the OMNI interface as a point of connection to the OMNI
link; if there are multiple OMNI links (i.e., multiple MS's), L3
will see multiple OMNI interfaces.
o Multiple independent OMNI interfaces can be used for increased
fault tolerance through Safety-Based Multilink (SBM), with
Performance-Based Multilink (PBM) applied within each interface.
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.
Figure 3 depicts the architectural model for a Client with an
attached EUN connecting to the MS via multiple independent *NETs.
When an underlying interface becomes active, the Client's OMNI
interface sends IPv6 ND messages without encapsulation if the first-
hop Proxy/Server 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 a local Proxy/Server (LPS#1,
LPS#2, ..., LPS#n), which returns an IPv6 ND message response and/or
forwards a proxyed version of the message to remote INET Proxy/
Servers (RPS#1, RPS#2, ..., RPS#m). 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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+--------------+ (:::)-.
| Client |<-->.-(::EUN:::)
+--------------+ `-(::::)-'
|OMNI interface|
+----+----+----+
+--------|IF#1|IF#2|IF#n|------ +
/ +----+----+----+ \
/ | \
/ | \
v v v
(:::)-. (:::)-. (:::)-.
.-(::*NET:::) .-(::*NET:::) .-(::*NET:::)
`-(::::)-' `-(::::)-' `-(::::)-'
+-----+ +-----+ +-----+
... |LPS#1| ......... |LPS#2| ......... |LPS#n| ...
. +--|--+ +--|--+ +--|--+ .
. | | |
. v v v .
. <----- INET Encapsulation -----> .
. .
. +-----+ (:::)-. .
. |RPS#2| .-(::::::::) +-----+ .
. +-----+ .-(::: INET :::)-. |RPS#m| .
. (::::: Routing ::::) +-----+ .
. `-(::: System :::)-' .
. +-----+ `-(:::::::-' .
. |RPS#1| +-----+ +-----+ .
. +-----+ |RPS#3| |RPS#4| .
. +-----+ +-----+ .
. .
. .
. <----- Worldwide Connected Internetwork ----> .
...........................................................
Figure 3: MN/MS Coordination via Multiple *NETs
After the initial IPv6 ND message exchange, the Client (and/or any
nodes on its attached EUNs) can send and receive original IP packets
over the OMNI interface. OMNI interface multilink services will
forward the packets via Proxy/Servers in the correct underlying
*NETs. The Proxy/Server 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.
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5. OMNI Interface Maximum Transmission Unit (MTU)
The OMNI interface observes the link nature of tunnels, including the
Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and
the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels].
The OMNI interface is configured over one or more underlying
interfaces as discussed in Section 4, where the interfaces (and their
associated *NET paths) may have diverse MTUs. OMNI interface
considerations for accommodating original IP packets of various sizes
are discussed in the following sections.
IPv6 underlying interfaces are REQUIRED to configure a minimum MTU of
1280 bytes and a minimum MRU of 1500 bytes [RFC8200]. Therefore, the
minimum IPv6 path MTU is 1280 bytes since routers on the path are not
permitted to perform network fragmentation even though the
destination is required to reassemble more. The network therefore
MUST forward original IP packets of at least 1280 bytes without
generating an IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB)
message [RFC8201]. (While the source can apply "source
fragmentation" for locally-generated IPv6 packets up to 1500 bytes
and larger still if it knows the destination configures a larger MRU,
this does not affect the minimum IPv6 path MTU.)
IPv4 underlying interfaces are REQUIRED to configure a minimum MTU of
68 bytes [RFC0791] and a minimum MRU of 576 bytes [RFC0791][RFC1122].
Therefore, when the Don't Fragment (DF) bit in the IPv4 header is set
to 0 the minimum IPv4 path MTU is 576 bytes since routers on the path
support network fragmentation and the destination is required to
reassemble at least that much. The OMNI interface therefore MUST set
DF to 0 in the IPv4 encapsulation headers of carrier packets that are
no larger than 576 bytes, and SHOULD set DF to 1 in larger carrier
packets unless it has a way to determine the encapsulation
destination MRU and has carefully considered the issues discussed in
Section 6.9.
The OMNI interface configures an MTU and MRU of 9180 bytes [RFC2492];
the size is therefore not a reflection of the underlying interface or
*NET path MTUs, but rather determines the largest original IP packet
the OAL (and/or underlying interface) can forward or reassemble. For
each OAL destination (i.e., for each OMNI link neighbor), the OAL
source may discover "hard" or "soft" Reassembly Limit values smaller
than the MRU based on receipt of IPv6 ND messages with OMNI
Reassembly Limit sub-options (see: Section 12.2.11). The OMNI
interface employs the OAL as an encapsulation sublayer service to
transform original IP packets into OAL packets/fragments, and the OAL
in turn uses *NET encapsulation to forward carrier packets over the
underlying interfaces (see: Section 6).
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6. The OMNI Adaptation Layer (OAL)
When an OMNI interface forwards an original IP packet from the
network layer for transmission over one or more underlying
interfaces, the OMNI Adaptation Layer (OAL) acting as the OAL source
drops the packet and returns a PTB message if the packet exceeds the
MRU and/or the hard Reassembly Limit for the intended OAL
destination. Otherwise, the OAL source applies encapsulation to form
OAL packets subject to fragmentation producing OAL fragments suitable
for *NET encapsulation and transmission as carrier packets over
underlying interfaces as described in Section 6.1.
These carrier packets travel over one or more underlying networks
bridged by OAL intermediate nodes, which re-encapsulate by removing
the *NET headers of the first underlying network and appending *NET
headers appropriate for the next underlying network in succession.
(This process supports the multinet concatenation capability needed
for joining multiple diverse networks.) After re-encapsulation by
zero or more OAL intermediate nodes, the carrier packets arrive at
the OAL destination.
When the OAL destination receives the carrier packets, it discards
the *NET headers and reassembles the resulting OAL fragments into an
OAL packet as described in Section 6.3. The OAL destination then
decapsulates the OAL packet to obtain the original IP packet, which
it then delivers to the network layer.
The OAL presents an OMNI sublayer abstraction similar to ATM
Adaptation Layer 5 (AAL5). Unlike AAL5 which performs segmentation
and reassembly with fixed-length 53 octet cells over ATM networks,
however, the OAL uses IPv6 encapsulation, fragmentation and
reassembly with larger variable-length cells over heterogeneous
underlying networks. Detailed operations of the OAL are specified in
the following sections.
6.1. OAL Source Encapsulation and Fragmentation
When the network layer forwards an original IP packet into the OMNI
interface, the OAL source inserts an IPv6 encapsulation header but
does not decrement the Hop Limit/TTL of the original IP packet since
encapsulation occurs at a layer below IP forwarding [RFC2473]. The
OAL source copies the "Type of Service/Traffic Class" [RFC2983] and
"Congestion Experienced" [RFC3168] values in the original packet's IP
header into the corresponding fields in the OAL header, then sets the
OAL header "Flow Label" as specified in [RFC6438]. The OAL source
finally sets the OAL header IPv6 Hop Limit to a conservative value
sufficient to enable loop-free forwarding over multiple concatenated
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OMNI link segments and sets the Payload Length to the length of the
original IP packet.
The OAL next selects source and destination addresses for the IPv6
header of the resulting OAL packet. Client OMNI interfaces set the
OAL IPv6 header source address to a Unique Local Address (ULA) based
on the Mobile Network Prefix (MNP-ULA), while Proxy/Server OMNI
interfaces set the source address to an Administrative ULA (ADM-ULA)
(see: Section 9). When a Client OMNI interface does not (yet) have
an MNP-ULA, it can use a Temporary ULA and/or Host Identity Tag (HIT)
instead (see: Section 22).
When the OAL source forwards an original IP packet toward a final
destination via an ANET underlying interface, it sets the OAL IPv6
header source address to its own ULA and sets the destination 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 source then fragments the OAL
packet if necessary, encapsulates the OAL fragments in any ANET
headers and sends the resulting carrier packets to the ANET peer
which either reassembles before forwarding if the OAL destination is
its own ULA or forwards the fragments toward the true OAL destination
without first reassembling otherwise.
When the OAL source forwards an original IP packet toward a final
destination via an INET underlying interface, it sets the OAL IPv6
header source address to its own ULA and sets the destination to the
ULA of an OAL destination node on the final *NET segment. The OAL
source then fragments the OAL packet if necessary, encapsulates the
OAL fragments in any *NET headers and sends the resulting carrier
packets toward the OAL destination on the final segment OMNI node
which reassembles before forwarding the original IP packets toward
the final destination.
Following OAL IPv6 encapsulation and address selection, the OAL
source next appends a 2 octet trailing Checksum (initialized to 0) at
the end of the original IP packet while incrementing the OAL header
IPv6 Payload Length field to reflect the addition of the trailer.
The format of the resulting OAL packet following encapsulation is
shown in Figure 4:
+----------+-----+-----+-----+-----+-----+-----+----+
| OAL Hdr | Original IP packet |Csum|
+----------+-----+-----+-----+-----+-----+-----+----+
Figure 4: OAL Packet Before Fragmentation
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The OAL source next selects a 32-bit Identification value for the
packet as specified in Section 6.5 then calculates the checksum per
the 8-bit Fletcher algorithm specified in Appendix A. The OAL source
calculates the checksum over the entire OAL packet beginning with a
pseudo-header of the IPv6 header similar to that found in Section 8.1
of [RFC8200] and extending to the end of the (0-initialized) checksum
trailer. The OAL IPv6 pseudo-header is formed as shown in Figure 5:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ OAL Source Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ OAL Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL Payload Length | zero | Next Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: OAL IPv6 Pseudo-Header
After calculating the checksum, the OAL source writes the results
over the (0-initialized) trailing checksum octets. The OAL source
then inserts a single OMNI Routing Header (ORH) if necessary (see:
[I-D.templin-6man-aero]) while incrementing Payload Length to reflect
the addition of the ORH, where the late addition of the ORH is not
covered by the checksum. (Alternatively, the OAL source can defer
ORH insertion until after fragmentation, then manually insert an
identical copy of the ORH between the IPv6 header and Fragment Header
of each fragment while resetting the IPv6 Payload Length and Next
Header fields accordingly.)
The OAL source next fragments the OAL packet if necessary while
assuming the IPv4 minimum path MTU (i.e., 576 bytes) as the worst
case for OAL fragmentation regardless of the underlying interface IP
protocol version since IPv6/IPv4 protocol translation and/or IPv6-in-
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IPv4 encapsulation may occur in any *NET path. By always assuming
the IPv4 minimum even for IPv6 underlying interfaces, the OAL source
may produce smaller fragments with additional encapsulation overhead
but will always interoperate and never run the risk of loss due to an
MTU restriction or due to presenting an underlying interface with a
carrier packet that exceeds its MRU. Additionally, the OAL path
could traverse multiple *NET "segments" with intermediate OAL
forwarding nodes performing re-encapsulation where the *NET
encapsulation of the previous segment is replaced by the *NET
encapsulation of the next segment which may be based on a different
IP protocol version and/or encapsulation sizes.
The OAL source therefore assumes a default minimum path MTU of 576
bytes at each *NET segment for the purpose of generating OAL
fragments for *NET encapsulation and transmission as carrier packets.
In the worst case, each successive *NET segment may re-encapsulate
with either a 20 byte IPv4 or 40 byte IPv6 header, an 8 byte UDP
header and in some cases an IP security encapsulation (40 bytes
maximum assumed). Any *NET segment may also insert a maximum-length
(40 byte) ORH as an extension to the existing 40 byte OAL IPv6 header
plus 8 byte Fragment Header if an ORH was not already present.
Assuming therefore an absolute worst case of (40 + 40 + 8) = 88 bytes
for *NET encapsulation plus (40 + 40 + 8) = 88 bytes for OAL
encapsulation leaves (576 - 88 - 88) = 400 bytes to accommodate a
portion of the original IP packet/fragment. The OAL source therefore
sets a minimum Maximum Payload Size (MPS) of 400 bytes as the basis
for the minimum-sized OAL fragment that can be assured of traversing
all segments without loss due to an MTU/MRU restriction. The Maximum
Fragment Size (MFS) for OAL fragmentation is therefore determined by
the MPS plus the size of the OAL encapsulation headers. (Note that
the OAL source includes the 2 octet trailer as part of the payload
during fragmentation, and the OAL destination regards it as ordinary
payload until reassembly and checksum verification are complete.)
The OAL source SHOULD maintain "path MPS" values for individual OAL
destinations initialized to the minimum MPS and increased to larger
values (up to the OMNI interface MTU) if better information is known
or discovered. For example, when *NET peers share a common
underlying link or a fixed path with a known larger MTU, the OAL
source can base path MPS on this larger size (i.e., instead of 576
bytes) as long as the *NET peer reassembles before re-encapsulating
and forwarding (while re-fragmenting if necessary). Also, if the OAL
source has a way of knowing the maximum *NET encapsulation size for
all segments along the path it may be able to increase path MPS to
reserve additional room for payload data. The OAL source must
include the uncompressed OAL header size in its path MPS calculation,
since a full header could be included at any time.
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The OAL source can also actively probe individual OAL destinations to
discover larger path MPS values using packetization layer probes in a
similar fashion as [RFC4821][RFC8899], but care must be taken to
avoid setting static values for dynamically changing paths leading to
black holes. The probe involves sending an OAL packet larger than
the current path MPS and receiving a small acknowledgement message in
response (with the possible receipt of link-layer error message in
case the probe was lost). For this purpose, the OAL source can send
an NS message with one or more OMNI options with large PadN sub-
options (see: Section 12) in order to receive a small NA response
from the OAL destination. While observing the minimum MPS will
always result in robust and secure behavior, the OAL source should
optimize path MPS values when more efficient utilization may result
in better performance (e.g. for wireless aviation data links). (If
so, the OAL source should maintain separate path MPS values for each
(source, target) underlying interface pair for the same OAL
destination, since each underlying interface pair may support a
different path MPS.)
When the OAL source performs fragmentation, it SHOULD produce the
minimum number of non-overlapping fragments under current MPS
constraints, where each non-final fragment MUST be at least as large
as the minimum MPS, while the final fragment MAY be smaller. The OAL
source also converts all original IP packets no larger than the
current MPS into "atomic fragments" by including a Fragment Header
with Fragment Offset and More Fragments both set to 0.
For each fragment produced, the OAL source writes an ordinal number
for the fragment into the Reserved field in the IPv6 Fragment Header.
In particular, the OAL source writes the ordinal number '0' for the
first fragment, '1' for the second fragment, '2' for the third
fragment, etc. up to and including the final fragment. Since the
minMPS is 400 and the MTU is 9180, at most 23 fragments will be
produced for each OAL packet.
The OAL source finally encapsulates the fragments in *NET headers to
form carrier packets and forwards them over an underlying interface,
while retaining the fragments and their ordinal numbers (i.e., #0,
#1, #2, etc.) for a link persistence period in case link-layer
retransmission is requested (see: Section 6.6). The formats of OAL
fragments and carrier packets are shown in Figure 6.
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+----------+--+-------------+
| OAL Hdr |FH| Frag #0 |
+----------+--+-------------+
+----------+--+-------------+
| OAL Hdr |FH| Frag #1 |
+----------+--+-------------+
+----------+--+-------------+
| OAL Hdr |FH| Frag #2 |
+----------+--+-------------+
....
+----------+--+-------------+----+
| OAL Hdr |FH| Frag #(N-1) |Csum|
+----------+--+-------------+----+
a) OAL fragments after fragmentation
(FH = Fragment Header; Csum appears only in final fragment)
+--------+--+-----+-----+-----+-----+-----+----+
|OAL Hdr |FH| Original IP packet |Csum|
+--------+--+-----+-----+-----+-----+-----+----+
b) An OAL atomic fragment with FH but no fragmentation.
+--------+----------+--+-------------+
|*NET Hdr| OAL Hdr |FH| Frag #i |
+--------+----------+--+-------------+
c) OAL carrier packet after *NET encapsulation
Figure 6: OAL Fragments and Carrier Packets
6.2. OAL *NET Encapsulation and Re-Encapsulation
During *NET encapsulation, the OAL source first encapsulates each OAL
fragment in a UDP header as the first *NET encapsulation sublayer if
NAT traversal, packet filtering middlebox traversal and/or OAL header
compression are necessary. The OAL source then appends any
additional encapsulation sublayer headers necessary and presents the
*NET packet to an underlying interface (see: Figure 2).
When a UDP header is included, the OAL source next sets the UDP
source port to a constant value that it will use in each successive
carrier packet it sends to the next OAL hop. For packets sent to an
Proxy/Server, the OAL source sets the UDP destination port to 8060,
i.e., the IANA-registered port number for AERO. For packets sent to
a peer Client, the source sets the UDP destination port to the cached
port value for this peer. The OAL source then sets the UDP length to
the total length of the OAL fragment in correspondence with the OAL
header Payload Length (i.e., the UDP length and IPv6 Payload Length
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must agree). The OAL source finally sets the UDP checksum to 0
[RFC6935][RFC6936] since the only fields not already covered by the
OAL checksum or underlying *NET CRCs are the Fragment Header fields,
and any corruption in those fields will be garbage collected by the
reassembly algorithm (however, see Section 20 for additional
considerations). The UDP encapsulation header is often used in
association with IP encapsulation, but may also be used between
neighbors on a shared physical link with a true L2 header format such
as for transmission over IEEE 802 Ethernet links. This document
therefore requests a new Ether Type code assignment TBD1 in the IANA
'ieee-802-numbers' registry for direct User Datagram Protocol (UDP)
encapsulation over IEEE 802 Ethernet links (see: Section 25).
For *NET encapsulations over IP, the OAL source next copies the "Type
of Service/Traffic Class" [RFC2983] and "Congestion Experienced"
[RFC3168] values in the OAL IPv6 header into the corresponding fields
in the *NET IP header, then (for IPv6) sets the *NET IPv6 header
"Flow Label" as specified in [RFC6438]. The OAL source then sets the
*NET IP TTL/Hop Limit the same as for any *NET host, i.e., it does
not copy the Hop Limit value from the OAL header. For carrier
packets undergoing OAL intermediate node re-encapsulation, the node
decrements the OAL IPv6 header Hop Limit and discards the carrier
packet if the value reaches 0. The node then copies the "Type of
Service/Traffic Class" and "Congestion Experienced" values from the
previous hop *NET encapsulation header into the OAL IPv6 header
before setting the next hop *NET IP encapsulation header values the
same as specified for the OAL source above.
Following *NET encapsulation/re-encapsulation, the OAL source sends
the resulting carrier packets over one or more underlying interfaces.
The underlying interfaces often connect directly to physical media on
the local platform (e.g., a laptop computer with WiFi, etc.), but in
some configurations the physical media may be hosted on a separate
Local Area Network (LAN) node. In that case, the OMNI interface can
establish a Layer-2 VLAN or a point-to-point tunnel (at a layer below
the underlying interface) to the node hosting the physical media.
The OMNI interface may also apply encapsulation at the underlying
interface layer (e.g., as for a tunnel virtual interface) such that
carrier packets would appear "double-encapsulated" on the LAN; the
node hosting the physical media in turn removes the LAN encapsulation
prior to transmission or inserts it following reception. Finally,
the underlying interface must monitor the node hosting the physical
media (e.g., through periodic keepalives) so that it can convey
up/down/status information to the OMNI interface.
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6.3. OAL Destination Decapsulation and Reassembly
When an OMNI interface receives a carrier packet from an underlying
interface, it discards the *NET encapsulation headers and examines
the OAL header of the enclosed OAL fragment. If the OAL fragment is
addressed to a different node, the OMNI interface (acting as an OAL
intermediate node) re-encapsulates and forwards as discussed below.
If the OAL fragment is addressed to itself, the OMNI interface
(acting as an OAL destination) accepts or drops the fragment based on
the (Source, Destination, Identification)-tuple. The OAL destination
next drops all non-final OAL fragments smaller than the minimum MPS
and all fragments that would overlap or leave "holes" smaller than
the minimum MPS with respect to other fragments already received.
The OAL destination records the ordinal number of each accepted
fragment of the same OAL packet (i.e., as Frag #0, Frag #1, Frag #2,
etc.) and admits them into the reassembly cache.
When reassembly is complete, the OAL destination removes the ORH if
present while decrementing Payload Length to reflect the removal of
the ORH. The OAL destination next verifies the resulting OAL
packet's checksum and discards the packet if the checksum is
incorrect. If the OAL packet was accepted, the OAL destination then
removes the OAL header/trailer, then delivers the original IP packet
to the network layer. Note that link layers include a CRC-32
integrity check which provides effective hop-by-hop error detection
in the underlying network for payload sizes up to the OMNI interface
MTU [CRC], but that some hops may traverse intermediate layers such
as tunnels over IPv4 that do not include integrity checks. The
trailing Fletcher checksum therefore allows the OAL destination to
detect OAL packet splicing errors due to reassembly misassociations
and/or to verify the integrity of OAL packets whose fragments may
have traversed unprotected underlying network hops [CKSUM]. The
Fletcher checksum algorithm also provides diversity with respect to
both lower layer CRCs and upper layer Internet checksums as part of a
complimentary multi-layer integrity assurance architecture.
6.4. OAL Header Compression
When the OAL source and destination are on the same *NET segment,
carrier packet header compression is possible. When the OAL source
and destination exchange IPv6 ND messages, each caches the observed
*NET UDP source port and source IP (or L2) address associated with
the OAL IPv6 source address found in the full-length OAL IPv6 header.
After the initial IPv6 ND message exchange, the OAL source can apply
OAL Header Compression for subsequent carrier packets to
significantly reduce encapsulation overhead.
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When the OAL source uses INET encapsulation to send carrier packets
directly to an OAL destination with NCE state, it can begin omitting
significant portions of the IPv6 header, Fragment Header and OMNI
Routing Header (ORH). (Conversely, the OAL source must still include
full headers for destinations that can only be reached via an OAL
intermediate node.) For OAL first-fragments (including atomic
fragments), the OAL source uses OMNI Compressed Header - Type 0 (OCH-
0) as shown in Figure 7:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ *
| Source port | Destination port | U
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ D
| Length | Checksum | P
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ *
|Vers=0 | Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hop Limit |M| Identification (0 -1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification (2-3) | omIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: OMNI Compressed Header - Type 0 (OCH-0)
In this format, the UDP header appears in its entirety in the first 8
octets and is followed by a compressed IPv6 header with Version set
to 0 (to distinguish OCH-0 from both OCH-1 and a true IP protocol
version number), followed by the uncompressed (Traffic Class, Flow
Label, Next Header) fields and a 7-bit compressed Hop Limit that
encodes the minimum of the uncompressed Hop Limit and 127. (Note:
the OAL source sets Next Header to the protocol number of the header
following the final extension header, and not to the protocol number
for the extension header itself.) The compressed IPv6 header is then
followed by a compressed Fragment Header beginning with a (M)ore
Fragments bit followed by a 4-octet Identification and with all other
fields omitted. The compressed Fragment Header is followed by a
compressed ORH consisting of a 1-octet omIndex that encodes an
underlying interface index for the target Client (or 0 if the target
underlying interface is unspecified). The OCH-0 header is then
followed by the OAL fragment body, and the UDP length field is
reduced by the difference in length between the compressed headers
and full-length (IPv6, Fragment, ORH) headers. The OCH-0 format
applies only for first fragments, which are always regarded as
ordinal fragment 0 even though the OCH-0 does not include an explicit
Ordinal field.
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For OAL non-first fragments (i.e., those with non-zero Fragment
Offsets), the OAL uses OMNI Compressed Header - Type 1 (OCH-1) as
shown in Figure 8:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ *
| Source port | Destination port | U
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ D
| Length | Checksum | P
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ *
|Vers=1 | Ordinal |R|M| Fragment Offset | ID (0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification (1-3) | omIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: OMNI Compressed Header - Type 1 (OCH-1)
In this format, the UDP header appears in its entirety in the first 8
octets, but all IPv6 header fields except for Version are omitted.
Version is set to 1 (to distinguish OCH-1 from both OCH-0 and a true
IP protocol version number) and is followed by a compressed IPv6
Fragment Header that includes a 5-bit Ordinal number for this
fragment. a (R)eserved bit set to 0, and with (M)ore Fragments/
Fragment Offset/Identification copied from the uncompressed fragment
header. The compressed ORH includes a 1-octet omIndex that encodes
an underlying interface index for the target Client (or 0 if the
target underlying interface is unspecified). The OCH-1 header is
then followed by the OAL fragment body, while the UDP length field is
reduced by the difference in length between the compressed headers
and full-length (IPv6, Fragment, ORH) headers. The OCH-1 format
applies only for non-first fragments, therefore Ordinal is set to a
value beginning with 1 for the first non-first fragment and
monotonically incremented for each successive non-first fragment up
to and including the final fragment.
When the OAL destination receives a carrier packet with an OCH, it
first determines the OAL IPv6 source and destination addresses by
examining the UDP source port and L2 source address, then determines
the length by examining the UDP length. The OAL destination then
examines the Version field immediately following the UDP header. If
Version encodes the value 0, the OAL destination processes the
remainder of the header as an OCH-0, then reconstitutes the full-
sized IPv6 and Fragment Headers and adds this OAL fragment to the
reassembly buffer if the fragment is acceptable. If Version encodes
the value 1, the OAL destination instead processes the remainder of
the header as an OCH-1, then reconstitutes the full-sized IPv6 and
Fragment Headers. Note that, since OCH-1 does not include Traffic
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Class, Flow Label, Next Header or Hop Limit information, the OAL
destination writes the value 0 into those fields when it
reconstitutes the full headers. The values will be correctly
populated during reassembly after an OAL first fragment with an OCH-0
or uncompressed OAL header arrives.
When the OAL destination is an LHS Proxy/Server, it examines the
destination address after re-constituting the OAL header. If the
destination address is its own ADM-ULA, the Proxy/Server submits the
resulting OAL fragment for local reassembly. Following reassembly,
the Proxy/Server re-encapsulates the OAL packet (while re-fragmenting
if necessary) and forwards the packet/fragments to the Client
underlying interface identified by omIndex. If the destination
address is the MNP-ULA of one of its Clients, the Proxy/Server
instead forwards the OAL fragment via the Client underlying interface
identified by omIndex. If the header compression state and/or
destination address are not recognized, the Proxy/Server instead
drops the packet.
When the OAL destination is the Client, it examines the destination
address after re-constituting the OAL header. If the destination
address is its own MNP-ULA, the Client submits the resulting OAL
fragment for local reassembly. Otherwise, the Client drops the
packet.
Note: OAL header compression does not interfere with checksum
calculation and verification, which must be applied according to the
full OAL pseudo-header per Section 6.1 even when compression is used.
Carrier packets may further include uncompressed headers at any time
even after header compression state has been established.
6.5. OAL Identification Window Maintenance
The OAL encapsulates each original IP packet as an OAL packet then
performs fragmentation to produce one or more carrier packets with
the same 32-bit Identification value. In environments were spoofing
is not considered a threat, OAL nodes can send OAL packets beginning
with a random initial Identification value and incremented (modulo
2**32) for each successive packet. In other environments, OMNI
interfaces should maintain explicit per-neighbor send and receive
windows to exclude spurious carrier packets that might clutter the
reassembly cache. OMNI interface neighbors maintain windows using
TCP-like synchronization [RFC0793] with Identification sequence
numbers beginning with an unpredictable initial value [RFC7739] and
incremented (modulo 2 *32) for each successive OAL packet.
OMNI interface neighbors exchange IPv6 ND messages with OMNI options
that include TCP-like information fields to manage streams of OAL
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packets instead of streams of octets. As a link-layer service, the
OAL provides low-persistence best-effort retransmission with no
mitigations for duplication, reordering or deterministic delivery.
Since the service model is best-effort and only control message
sequence numbers are acknowledged, OAL nodes can select unpredictable
new initial sequence numbers outside of the current window without
delaying for the Maximum Segment Lifetime (MSL).
OMNI interface neighbors maintain current and previous window state
in IPv6 ND neighbor cache entries (NCEs) to support dynamic rollover
to a new window while still sending OAL packets and accepting carrier
packets from the previous windows. Each NCE is indexed by the
neighbor's LLA, which must also match the ULA used for OAL
encapsulation. OMNI interface neighbors synchronize windows through
asymmetric and/or symmetric IPv6 ND message exchanges. When a node
receives an IPv6 ND message with new window information, it resets
the previous window state based on the current window then resets the
current window based on new and/or pending information.
The IPv6 ND message OMNI option header includes TCP-like information
fields including Sequence Number, Acknowledgement Number, Window and
flags (see: Section 12). OMNI interface neighbors maintain the
following TCP-like state variables in the NCE:
Send Sequence Variables (current, previous and pending)
SND.NXT - send next
SND.WND - send window
ISS - initial send sequence number
Receive Sequence Variables (current and previous)
RCV.NXT - receive next
RCV.WND - receive window
IRS - initial receive sequence number
OMNI interface neighbors "OAL A" and "OAL B" exchange IPv6 ND
messages per [RFC4861] with OMNI options that include TCP-like
information fields. When OAL A synchronizes with OAL B, it maintains
both a current and previous SND.WND beginning with a new
unpredictable ISS and monotonically increments SND.NXT for each
successive OAL packet transmission. OAL A initiates synchronization
by including the new ISS in the Sequence Number of an authentic IPv6
ND NS/RS message with the SYN flag set and with Window set to M as a
tentative receive window size while creating a NCE in the INCOMPLETE
state if necessary. OAL A caches the new ISS as pending, uses the
new ISS as the Identification for OAL encapsulation, then sends the
resulting OAL packet to OAL B and waits up to RetransTimer
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milliseconds to receive a solicited NA/RA ACK response
(retransmitting up to MAX_UNICAST_SOLICIT times if necessary).
When OAL B receives the carrier packets containing the NS/RS SYN, it
creates a NCE in the STALE state if necessary, resets its RCV
variables, caches the tentative (send) window size M, and selects a
(receive) window size N (up to 2^24) to indicate the number of OAL
packets it is willing to accept under the current RCV.WND. (The
RCV.WND should be large enough to minimize control message overhead
yet small enough to provide an effective filter for spurious carrier
packets.) OAL B then prepares a solicited NA/RA message with the ACK
flag set, with the Acknowledgement Number set to OAL A's next
sequence number, and with Window set to N. Since OAL B does not
assert an ISS of its own, it uses OAL A's IRS as the Identification
for OAL encapsulation then sends the resulting OAL packet to OAL A.
When OAL A receives the carrier packets containing the solicited NA/
RA, it notes that their Identification matches its pending ISS. OAL
A then sets the NCE state to REACHABLE and resets its SND variables
based on the Window size and Acknowledgement Number (which must
include the sequence number following the pending ISS). OAL A can
then begin sending OAL packets to OAL B with Identification values
within the (new) current SND.WND for up to ReachableTime milliseconds
or until the NCE is updated by a new IPv6 ND message exchange. This
implies that OAL A must send a new NS/RS SYN message before sending
more than N OAL packets within the current SND.WND, i.e., even if
ReachableTime is not nearing expiration.
After OAL B returns the solicited NA/RA, it accepts carrier packets
received from OAL A within either the current or previous RCV.WND as
well as any new authentic NS/RS SYN messages received from OAL A even
if outside the windows. IPv6 ND messages used for window
synchronization must therefore fit within a single carrier packet
(i.e., within current MPS constraints), since the carrier packets of
fragmented IPv6 ND messages with out-of-window Identification values
could be part of a DoS attack and should not be admitted into the
reassembly cache. OAL B discards all other carrier packets received
from OAL A with out-of-window Identifications.
OMNI interface neighbors can employ asymmetric window synchronization
as described above using two independent [(NS/RS SYN) -> (NA/RA ACK)]
exchanges (i.e., a four-message exchange), or they can employ
symmetric window synchronization using a modified version of the TCP
three-way handshake as follows:
o OAL A prepares an NS/RS SYN message with an unpredictable ISS not
within the current SND.WND and with Window set to M as a tentative
receive window size. OAL A caches the new ISS and Window size as
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pending information, uses the pending ISS as the Identification
for OAL encapsulation, then sends the resulting OAL packet to OAL
B and waits up to RetransTimer milliseconds to receive a solicited
NA/RA ACK response (retransmitting up to MAX_UNICAST_SOLICIT times
if necessary).
o OAL B receives the carrier packets containing the NS/RS SYN, then
resets its RCV variables based on the Sequence Number while
caching OAL A's tentative receive Window size M and a new
unpredictable ISS outside of its current window as pending
information. OAL B then prepares a solicited NA/RA response with
Sequence Number set to the pending ISS and Acknowledgement Number
set to OAL A's next sequence number. OAL B then sets both the SYN
and ACK flags, sets Window to N and sets the OPT flag according to
whether an explicit NS ACK is optional or mandatory. OAL B then
uses the pending ISS as the Identification for OAL encapsulation,
sends the resulting OAL packet to OAL A and waits up to
RetransTimer milliseconds to receive an acknowledgement
(retransmitting up to MAX_UNICAST_SOLICIT times if necessary).
o OAL A receives the carrier packets containing the NA/RA SYN/ACK,
then resets its SND variables based on the Acknowledgement Number
(which must include the sequence number following the pending ISS)
and OAL B's advertised Window N. OAL A then resets its RCV
variables based on the Sequence Number and marks the NCE as
REACHABLE. If the OPT flag is clear, OAL A next prepares an
immediate solicited NA message with the ACK flag set, the
Acknowledgement Number set to OAL B's next sequence number, with
Window set a value that may be the same as or different than M,
and with the OAL encapsulation Identification to SND.NXT, then
sends the resulting OAL packet to OAL B. If the OPT flag is set
and OAL A has OAL packets queued to send to OAL B, it can
optionally begin sending their carrier packets under the (new)
current SND.WND as implicit acknowledgements instead of returning
an explicit NA ACK. In that case, the tentative Window size M
becomes the current receive window size.
o OAL B receives the implicit/explicit acknowledgement(s) then
resets its SND state based on the pending/advertised values and
marks the NCE as REACHABLE. If OAL B receives an explicit
acknowledgement, it uses the advertised Window size and abandons
the tentative size. (Note that OAL B sets the OPT flag in the NA
SYN/ACK to assert that it will interpret timely receipt of carrier
packets within the (new) current window as an implicit
acknowledgement. Potential benefits include reduced delays and
control message overhead, but use case analysis is outside the
scope of this specification.)
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Following synchronization, OAL A and OAL B hold updated NCEs and can
exchange OAL packets with Identifications set to SND.NXT while the
state remains REACHABLE and there is available window capacity.
Either neighbor may at any time send a new NS/RS SYN to assert a new
ISS. For example, if OAL A's current SND.WND for OAL B is nearing
exhaustion and/or ReachableTime is nearing expiration, OAL A
continues to send OAL packets under the current SND.WND while also
sending an NS/RS SYN with a new unpredictable ISS. When OAL B
receives the NS/RS SYN, it resets its RCV variables and may
optionally return either an asymmetric NA/RA ACK or a symmetric NA/RA
SYN/ACK to also assert a new ISS. While sending IPv6 ND SYNs, both
neighbors continue to send OAL packets with Identifications set to
the current SND.NXT then reset the SND variables after an
acknowledgement is received.
While the optimal symmetric exchange is efficient, anomalous
conditions such as receipt of old duplicate SYNs can cause confusion
for the algorithm as discussed in Section 3.4 of [RFC0793]. For this
reason, the OMNI option header includes an RST flag which OAL nodes
set in solicited NA responses to ACKs received with incorrect
acknowledgement numbers. The RST procedures (and subsequent
synchronization recovery) are conducted exactly as specified in
[RFC0793].
OMNI interfaces may set the PNG ("ping") flag in IPv6 ND
advertisement messages when a reachability confirmation is needed.
(OMNI interfaces therefore most often set the PNG flag in
(unsolicited) advertisement messages and ignore it in solicitation
messages.) When an OMNI interface receives a PNG, it returns a
solicited NA ACK with the PNG message Identification in the
Acknowledgment, but without updating RCV state variables. OMNI
interfaces return unicast solicited NA ACKs even for multicast PNG
destination addresses, since OMNI link multicast is based on unicast
emulation. OMNI interfaces may also send unsolicited NA messages to
request selective retransmissions (see: Section 12.2.12).
OMNI interfaces that employ the window synchronization procedures
described above observe the following requirements:
o OMNI interfaces MUST select new unpredictable ISS values that are
outside of the current SND.WND.
o OMNI interfaces MUST set the initial NS SYN message Window field
to a tentative value to be used only if no concluding NA ACK is
sent.
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o OMNI interfaces that receive NA/RA messages with the PNG and/or
SYN flag set MUST NOT set the PNG and/or SYN flag in solicited NA
responses.
o OMNI interfaces that send NA/RA messages with the PNG and/or SYN
flag set MUST ignore solicited NA responses with the PNG and/or
SYN flag set.
o OMNI interfaces MUST include authentication signatures in IPv6 ND
messages while using unpredictable Identification values until
window synchronization is complete.
When an OMNI interface sends an RS SYN to the All-Routers multicast
address, it may receive multiple unicast RA ACK or SYN/ACK replies -
each with a distinct LLA source address. The OMNI interface then
creates a separate NCE for each distinct neighbor and completes
window synchronization through independent message exchanges with
each neighbor. The fact that all neighbors receive the same ISS in
the original RS SYN is not a matter for concern, as further window
synchronization will be conducted on a per-neighbor basis.
Note: Although OMNI interfaces employ TCP-like window synchronization
and support solicited NA ACK responses to NA/RA SYNs and PNGs, all
other aspects of the IPv6 ND protocol (e.g., control message
exchanges, NCE state management, timers, retransmission limits, etc.)
are honored exactly per [RFC4861].
Note: Recipients of OAL-encapsulated IPv6 ND messages index the NCE
based on the ULA source address, which also determines the carrier
packet Identification window. However, IPv6 ND messages may contain
an LLA source address that does not match the ULA source address when
the recipient acts as a proxy.
6.6. OAL Fragment Retransmission
When the OAL source sends carrier packets to an OAL destination, it
should cache recently sent packets in case best-effort selective
retransmission is requested. The OAL destination in turn maintains a
checklist for the (Source, Destination, Identification)-tuple of
recently received carrier packets and notes the ordinal numbers of
OAL packet fragments already received (i.e., as Frag #0, Frag #1,
Frag #2, etc.). The timeframe for maintaining the OAL source and
destination caches determines the link persistence (see: [RFC3366]).
If the OAL destination notices some fragments missing after most
other fragments within the same link persistence timeframe have
already arrived, it may send a uNA message to the OAL source. The
OAL destination creates a uNA message with an OMNI option containing
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an authentication sub-option to provide authentication (if the OAL
source is on an open Internetwork) and one or more Fragmentation
Report sub-options that include a list of (Identification, Bitmap)-
tuples for fragments received and missing from this OAL source (see:
Section 12). The OAL destination signs the message if an
authentication sub-option is included, performs OAL encapsulation
(with the its own address as the OAL source and the source address of
the message that prompted the uNA as the OAL destination) and sends
the message to the OAL source.
When the OAL source receives the uNA message, it authenticates the
message using the authentication sub-option (if present) then
examines the Fragmentation Report. For each (Source, Destination,
Identification)-tuple, the OAL source determines whether it still
holds the corresponding carrier packets in its cache and retransmits
any for which the Bitmap indicates a loss event. For example, if the
Bitmap indicates that ordinal fragments #3, #7, #10 and #13 from the
same OAL packet are missing the OAL source only retransmits carrier
packets containing those fragments and no others. When the OAL
destination receives the retransmitted carrier packets, it admits the
enclosed fragments into the reassembly cache and updates its
checklist. If some fragments are still missing, the OAL destination
may repeat the request in a small number of additional uNAs within
the link persistence timeframe.
Note that the OAL provides a link-layer low persistence Automatic
Repeat Request (ARQ) service based on Selective Repeat (SR)
capability consistent with [RFC3366] and Section 8.1 of [RFC3819].
The service provides the benefit of timely best-effort link-layer
retransmissions which may reduce packet loss and avoid some
unnecessary end-to-end delays.
6.7. OAL MTU Feedback Messaging
When the OMNI interface forwards original IP packets from the network
layer, it invokes the OAL and returns internally-generated ICMPv4
Fragmentation Needed [RFC1191] or ICMPv6 Path MTU Discovery (PMTUD)
Packet Too Big (PTB) [RFC8201] messages as necessary. This document
refers to both of these ICMPv4/ICMPv6 message types simply as "PTBs",
and introduces a distinction between PTB "hard" and "soft" errors as
discussed below.
Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6
header Code field value 0 are hard errors that always indicate that a
packet has been dropped due to a real MTU restriction. In
particular, the OAL source drops the packet and returns a PTB hard
error if the packet exceeds the OAL destination MRU. However, the
OMNI interface can also forward large original IP packets via OAL
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encapsulation and fragmentation while at the same time returning PTB
soft error messages (subject to rate limiting) if it deems the
original IP packet too large according to factors such as link
performance characteristics, reassembly congestion, etc. This
ensures that the path MTU is adaptive and reflects the current path
used for a given data flow. The OMNI interface can therefore
continuously forward packets without loss while returning PTB soft
error messages recommending a smaller size if necessary. Original
sources that receive the soft errors in turn reduce the size of the
packets they send (i.e., the same as for hard errors), but can soon
resume sending larger packets if the soft errors subside.
An OAL source sends PTB soft error messages by setting the ICMPv4
header "unused" field or ICMPv6 header Code field to the value 1 if a
original IP packet was deemed lost (e.g., due to reassembly timeout)
or to the value 2 otherwise. The OAL source sets the PTB destination
address to the original IP packet source, and sets the source address
to one of its OMNI interface unicast/anycast addresses that is
routable from the perspective of the original source. The OAL source
then sets the MTU field to a value smaller than the original packet
size but no smaller than 576 for ICMPv4 or 1280 for ICMPv6, writes
the leading portion of the original IP packet into the "packet in
error" field, and returns the PTB soft error to the original source.
When the original source receives the PTB soft error, it temporarily
reduces the size of the packets it sends the same as for hard errors
but may seek to increase future packet sizes dynamically while no
further soft errors are arriving. (If the original source does not
recognize the soft error code, it regards the PTB the same as a hard
error but should heed the retransmission advice given in [RFC8201]
suggesting retransmission based on normal packetization layer
retransmission timers.)
An OAL destination may experience reassembly cache congestion, and
can return uNA messages to the OAL source that originated the
fragments (subject to rate limiting) to advertise reduced hard/soft
Reassembly Limits and/or to report individual reassembly failures.
The OAL destination creates a uNA message with an OMNI option
containing an authentication message sub-option (if the OAL source is
on an open Internetwork) followed optionally by at most one hard and
one soft Reassembly Limit sub-options with reduced hard/soft values,
and with one of them optionally including the leading portion an OAL
first fragment containing the header of an original IP packet whose
source must be notified (see: Section 12). The OAL destination
encapsulates the leading portion of the OAL first fragment (beginning
with the OAL header) in the "OAL First Fragment" field of sub-option,
signs the message if an authentication sub-option is included,
performs OAL encapsulation (with the its own address as the OAL
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source and the source address of the message that prompted the uNA as
the OAL destination) and sends the message to the OAL source.
When the OAL source receives the uNA message, it records the new
hard/soft Reassembly Limit values for this OAL destination if the
OMNI option includes Reassembly Limit sub-options. If a hard or soft
Reassembly Limit sub-option includes an OAL First Fragment, the OAL
source next sends a corresponding network layer PTB hard or soft
error to the original source to recommend a smaller size. For hard
errors, the OAL source sets the PTB Code field to 0. For soft
errors, the OAL source sets the PTB Code field to 1 if the L flag in
the Reassembly Limit sub-option is 1; otherwise, the OAL source sets
the Code field to 2. The OAL source crafts the PTB by extracting the
leading portion of the original IP packet from the OAL First Fragment
field (i.e., not including the OAL header) and writes it in the
"packet in error" field of a PTB with destination set to the original
IP packet source and source set to one of its OMNI interface unicast/
anycast addresses that is routable from the perspective of the
original source. For future transmissions, if the original IP packet
is larger than the hard Reassembly Limit for this OAL destination the
OAL source drops the packet and returns a PTB hard error with MTU set
to the hard Reassembly Limit. If the packet is no larger than the
current hard Reassembly Limit but larger than the current soft limit,
the OAL source can also return a PTB soft error (subject to rate
limiting) with Code set to 2 and MTU set to the current soft limit
while still forwarding the packet to the OMNI destination.
Original sources that receive PTB soft errors can dynamically tune
the size of the original IP packets they to send to produce the best
possible throughput and latency, with the understanding that these
parameters may change over time due to factors such as congestion,
mobility, network path changes, etc. The receipt or absence of soft
errors should be seen as hints of when increasing or decreasing
packet sizes may be beneficial. The OMNI interface supports
continuous transmission and reception of packets of various sizes in
the face of dynamically changing network conditions. Moreover, since
PTB soft errors do not indicate a hard limit, original sources that
receive soft errors can begin sending larger packets without waiting
for the recommended 10 minutes specified for PTB hard errors
[RFC1191][RFC8201]. The OMNI interface therefore provides an
adaptive service that accommodates MTU diversity especially well-
suited for dynamic multilink environments.
6.8. OAL Requirements
In light of the above, OAL sources, destinations and intermediate
nodes observe the following normative requirements:
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o OAL sources MUST NOT send OAL fragments including original IP
packets larger than the OMNI interface MTU or the OAL destination
hard Reassembly Limit, i.e., whether or not fragmentation is
needed.
o OAL sources MUST NOT fragment original IP packets smaller than the
minimum MPS minus the trailer size, but must instead encapsulate
them as atomic fragments.
o OAL sources MUST produce non-final fragments with payloads no
smaller than the minimum MPS during fragmentation.
o OAL sources MUST NOT send OAL fragments that include any extension
headers other than a single ORH and a single Fragment Header.
o OAL intermediate nodes SHOULD and OAL destinations MUST
unconditionally drop any OAL fragments with offset and length that
would cause the reassembled packet to exceed the OMNI interface
MRU and/or OAL destination hard Reassembly Limit.
o OAL intermediate nodes SHOULD and OAL destinations MUST
unconditionally drop any non-final OAL fragments with payloads
smaller than the minimum MPS.
o OAL intermediate nodes SHOULD and OAL destinations MUST
unconditionally drop OAL fragments that include any extension
headers other than a single ORH and a single Fragment Header.
o OAL destinations MUST drop any new OAL fragments with Offset and
Payload length that would overlap with other fragments and/or
leave holes smaller than the minimum MPS between fragments that
have already been received.
Note: Under the minimum MPS, ordinary 1500 byte original IP packets
would require at most 4 OAL fragments, with each non-final fragment
containing 400 payload bytes and the final fragment containing 302
payload bytes (i.e., the final 300 bytes of the original IP packet
plus the 2 octet trailer). Likewise, maximum-length 9180 byte
original IP packets would require at most 23 fragments. For all
packet sizes, the likelihood of successful reassembly may improve
when the OMNI interface sends all fragments of the same fragmented
OAL packet consecutively over the same underlying interface pair
instead of spread across multiple underlying interface pairs.
Finally, an assured minimum/path MPS allows continuous operation over
all paths including those that traverse bridged L2 media with
dissimilar MTUs.
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Note: Certain legacy network hardware of the past millennium was
unable to accept packet "bursts" resulting from an IP fragmentation
event - even to the point that the hardware would reset itself when
presented with a burst. This does not seem to be a common problem in
the modern era, where fragmentation and reassembly can be readily
demonstrated at line rate (e.g., using tools such as 'iperf3') even
over fast links on ordinary hardware platforms. Even so, the OAL
source could impose an inter-fragment delay while the OAL destination
is reporting reassembly congestion (see: Section 6.7) and decrease
the delay when reassembly congestion subsides.
6.9. OAL Fragmentation Security Implications
As discussed in Section 3.7 of [RFC8900], there are four basic
threats concerning IPv6 fragmentation; each of which is addressed by
effective mitigations as follows:
1. Overlapping fragment attacks - reassembly of overlapping
fragments is forbidden by [RFC8200]; therefore, this threat does
not apply to the OAL.
2. Resource exhaustion attacks - this threat is mitigated by
providing a sufficiently large OAL reassembly cache and
instituting "fast discard" of incomplete reassemblies that may be
part of a buffer exhaustion attack. The reassembly cache should
be sufficiently large so that a sustained attack does not cause
excessive loss of good reassemblies but not so large that (timer-
based) data structure management becomes computationally
expensive. The cache should also be indexed based on the arrival
underlying interface such that congestion experienced over a
first underlying interface does not cause discard of incomplete
reassemblies for uncongested underlying interfaces.
3. Attacks based on predictable fragment identification values - in
environments where spoofing is possible, this threat is mitigated
through the use of Identification windows per Section 6.5. By
maintaining windows of acceptable Identifications beginning with
unpredictable values, OAL neighbors can quickly discard spurious
carrier packets that might otherwise clutter the reassembly
cache. The OAL additionally provides an integrity check to
detect corruption that may be caused by spurious fragments
received with in-window Identification values.
4. Evasion of Network Intrusion Detection Systems (NIDS) - since the
OAL source employs a robust MPS, network-based firewalls can
inspect and drop OAL fragments containing malicious data thereby
disabling reassembly by the OAL destination. However, since OAL
fragments may take different paths through the network (some of
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which may not employ a firewall) each OAL destination must also
employ a firewall.
IPv4 includes a 16-bit Identification (IP ID) field with only 65535
unique values such that at high data rates the field could wrap and
apply to new carrier packets while the fragments of old packets using
the same IP ID are still alive in the network [RFC4963]. Since
carrier packets sent via an IPv4 path with DF=0 are normally no
larger than 576 bytes, IPv4 fragmentation is possible only at small-
MTU links in the path which should support data rates low enough for
safe reassembly [RFC3819]. (IPv4 carrier packets larger than 576
bytes with DF=0 may incur high data rate reassembly errors in the
path, with the OAL destination checksum providing a last-resort
integrity verification.) Since IPv6 provides a 32-bit Identification
value, IP ID wraparound at high data rates is not a concern for IPv6
fragmentation.
Fragmentation security concerns for large IPv6 ND messages are
documented in [RFC6980]. These concerns are addressed when the OMNI
interface employs the OAL instead of directly fragmenting the IPv6 ND
message itself. For this reason, OMNI interfaces MUST NOT send IPv6
ND messages larger than the OMNI interface MTU, and MUST employ OAL
encapsulation and fragmentation for IPv6 ND messages larger than the
current MPS for this OAL destination.
Unless the path is secured at the network-layer or below (i.e., in
environments where spoofing is possible), OMNI interfaces MUST NOT
send ordinary carrier packets with Identification values outside the
current window and MUST secure IPv6 ND messages used for address
resolution or window state synchronization. OAL destinations SHOULD
therefore discard without reassembling any out-of-window OAL
fragments received over an unsecured path.
6.10. OAL Super-Packets
By default, the OAL source includes a 40-byte IPv6 encapsulation
header for each original IP packet during OAL encapsulation. The OAL
source also calculates and appends a 2 octet trailing checksum then
performs fragmentation such that a copy of the 40-byte IPv6 header
plus an 8-byte IPv6 Fragment Header is included in each OAL fragment
(when an ORH is added, the OAL encapsulation headers become larger
still). However, these encapsulations may represent excessive
overhead in some environments. OAL header compression can
dramatically reduce the amount of encapsulation overhead, however a
complimentary technique known as "packing" (see:
[I-D.ietf-intarea-tunnels]) is also supported so that multiple
original IP packets and/or control messages can be included within a
single OAL "super-packet".
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When the OAL source has multiple original IP packets to send to the
same OAL destination with total length no larger than the OAL
destination MRU, it can concatenate them into a super-packet
encapsulated in a single OAL header and trailing checksum. Within
the OAL super-packet, the IP header of the first original IP packet
(iHa) followed by its data (iDa) is concatenated immediately
following the OAL header, then the IP header of the next original
packet (iHb) followed by its data (iDb) is concatenated immediately
following the first original packet, etc. with the trailing checksum
included last. The OAL super-packet format is transposed from
[I-D.ietf-intarea-tunnels] and shown in Figure 9:
<------- Original IP packets ------->
+-----+-----+
| iHa | iDa |
+-----+-----+
|
| +-----+-----+
| | iHb | iDb |
| +-----+-----+
| |
| | +-----+-----+
| | | iHc | iDc |
| | +-----+-----+
| | |
v v v
+----------+-----+-----+-----+-----+-----+-----+----+
| OAL Hdr | iHa | iDa | iHb | iDb | iHc | iDc |Csum|
+----------+-----+-----+-----+-----+-----+-----+----+
<--- OAL "Super-Packet" with single OAL Hdr/Csum --->
Figure 9: OAL Super-Packet Format
When the OAL source prepares a super-packet, it applies OAL
fragmentation and *NET encapsulation then sends the carrier packets
to the OAL destination. When the OAL destination receives the super-
packet it reassembles if necessary, verifies and removes the trailing
checksum, then regards the remaining OAL header Payload Length as the
sum of the lengths of all payload packets. The OAL destination then
selectively extracts each original IP packet (e.g., by setting
pointers into the super-packet buffer and maintaining a reference
count, by copying each packet into a separate buffer, etc.) and
forwards each packet to the network layer. During extraction, the
OAL determines the IP protocol version of each successive original IP
packet 'j' by examining the four most-significant bits of iH(j), and
determines the length of the packet by examining the rest of iH(j)
according to the IP protocol version.
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7. Frame Format
When the OMNI interface forwards original IP packets from the network
layer it first invokes the OAL to create OAL packets/fragments if
necessary, then includes any *NET encapsulations and finally engages
the native frame format of the underlying interface. For example,
for Ethernet-compatible interfaces the frame format is specified in
[RFC2464], for aeronautical radio interfaces the frame format is
specified in standards such as ICAO Doc 9776 (VDL Mode 2 Technical
Manual), for various forms of tunnels the frame format is found in
the appropriate tunneling specification, etc.
See Figure 2 for a map of the various *NET layering combinations
possible. For any layering combination, the final layer (e.g., UDP,
IP, Ethernet, etc.) must have an assigned number and frame format
representation that is compatible with the selected underlying
interface.
8. Link-Local Addresses (LLAs)
OMNI interfaces assign IPv6 Link-Local Addresses (LLAs) through pre-
service administrative actions. Clients assign "MNP-LLAs" with
interface identifiers that embed the MNP, while Proxy/Servers assign
"ADM-LLAs" that include an administrative ID guaranteed to be unique
on the link. LLAs are configured as follows:
o IPv6 MNP-LLAs encode the most-significant 64 bits of 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. Non-
MNP routes are also represented the same as for MNP-LLAs, but
include a GUA prefix that is not properly covered by the MSP.
o IPv4-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 MNP-LLA for
192.0.2.0/24 is fe80::ffff:192.0.2.0/120 (also written as
fe80::ffff:c000:0200/120).
o ADM-LLAs are assigned to Proxy/Servers 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
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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.
9. Unique-Local Addresses (ULAs)
OMNI domains use IPv6 Unique-Local Addresses (ULAs) as the source and
destination addresses in OAL packet IPv6 encapsulation headers. ULAs
are only routable within the scope of a an OMNI domain, and are
derived from the IPv6 Unique Local Address prefix fc00::/7 followed
by the L bit set to 1 (i.e., as fd00::/8) followed by a 40-bit
pseudo-random Global ID to produce the prefix [ULA]::/48, which is
then followed by a 16-bit Subnet ID then finally followed by a 64 bit
Interface ID as specified in Section 3 of [RFC4193]. All nodes in
the same OMNI domain configure the same 40-bit Global ID as the OMNI
domain identifier. The statistic uniqueness of the 40-bit pseudo-
random Global ID allows different OMNI domains to be joined together
in the future without requiring renumbering.
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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
include all Proxy/Servers. All Clients are also considered to be
connected to the OMNI link, however unnecessary encapsulations are
omitted whenever possible to conserve bandwidth (see: Section 14).
Each OMNI link may be subdivided into "segments" that often
correspond to different administrative domains or physical
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partitions. OMNI nodes can use IPv6 Segment Routing [RFC8402] when
necessary to support efficient forwarding to destinations located in
other OMNI link segments. A full discussion of Segment Routing over
the OMNI link appears in [I-D.templin-6man-aero].
Temporary ULAs are constructed per [RFC8981] based on the prefix
[ULA]:ffff::/64 and used by Clients when they have no other
addresses. Temporary ULAs can be used for Client-to-Client
communications outside the context of any supporting OMNI link
infrastructure, and can also be used as an initial address while the
Client is in the process of procuring an MNP. Temporary ULAs are not
routable within the OMNI routing system, and are therefore useful
only for OMNI link "edge" communications. Temporary ULAs employ
optimistic DAD principles [RFC4429] since they are probabilistically
unique.
Note: IPv6 ULAs taken from the prefix fc00::/7 followed by the L bit
set to 0 (i.e., as fc00::/8) are never used for OMNI OAL addressing,
however the range could be used for MSP/MNP addressing under certain
limiting conditions (see: Section 10).
10. Global Unicast Addresses (GUAs)
OMNI domains use IP Global Unicast Address (GUA) prefixes [RFC4291]
as Mobility Service Prefixes (MSPs) from which Mobile Network
Prefixes (MNP) are delegated to Clients. Fixed correspondent node
networks reachable from the OMNI domain are represented by non-MNP
GUA prefixes that are not derived from the MSP, but are treated in
all other ways the same as for MNPs.
For IPv6, GUA 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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11. Node Identification
OMNI Clients and Proxy/Servers that connect over open Internetworks
include a unique node identification value for themselves in the OMNI
options of their IPv6 ND messages (see: Section 12.2.13). One useful
identification value alternative is the Host Identity Tag (HIT) as
specified in [RFC7401], while Hierarchical HITs (HHITs)
[I-D.ietf-drip-rid] may provide an alternative more appropriate for
certain domains such as the Unmanned (Air) Traffic Management (UTM)
service for Unmanned Air Systems (UAS). Another alternative is the
Universally Unique IDentifier (UUID) [RFC4122] which can be self-
generated by a node without supporting infrastructure with very low
probability of collision.
When a Client is truly outside the context of any infrastructure, it
may have no MNP information at all. In that case, the Client can use
an IPv6 temporary ULA or (H)HIT as an IPv6 source/destination address
for sustained communications in Vehicle-to-Vehicle (V2V) and
(multihop) Vehicle-to-Infrastructure (V2I) scenarios. The Client can
also propagate the ULA/(H)HIT into the multihop routing tables of
(collective) Mobile/Vehicular Ad-hoc Networks (MANETs/VANETs) using
only the vehicles themselves as communications relays.
When a Client connects to Proxy/Servers 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. The Client can then include OMNI "Node
Identification" sub-options (see: Section 12.2.13) in IPv6 ND
messages should the need to transmit identification information over
the network arise.
12. Address Mapping - Unicast
OMNI interfaces maintain a neighbor cache for tracking per-neighbor
state and use the link-local address format specified in Section 8.
IPv6 Neighbor Discovery (ND) [RFC4861] messages sent over OMNI
interfaces without encapsulation observe the native underlying
interface Source/Target Link-Layer Address Option (S/TLLAO) format
(e.g., for Ethernet the S/TLLAO is specified in [RFC2464]). IPv6 ND
messages sent over OMNI interfaces using encapsulation do not include
S/TLLAOs, but instead include a new option type that encodes
encapsulation addresses, interface attributes and other OMNI link
information. (Note that OMNI interface IPv6 ND messages sent without
encapsulation may include both OMNI options and S/TLLAOs, but the
information conveyed in each is mutually exclusive.) 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.
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Clients such as aircraft typically have many wireless data link types
(e.g. satellite-based, cellular, terrestrial, air-to-air directional,
etc.) with diverse performance, cost and availability properties.
The OMNI interface would therefore appear to have multiple L2
connections, and may include information for multiple underlying
interfaces in a single IPv6 ND message exchange. OMNI interfaces
manage their dynamically-changing multilink profiles by including
OMNI options in IPv6 ND messages as discussed in the following
subsections.
12.1. The OMNI Option
The first OMNI option appearing in an IPv6 ND message is formatted as
shown in Figure 10:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Acknowledgment Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|A|R|O|P| | |
|Y|C|S|P|N| Res | Window |
|N|K|T|T|G| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Sub-Options ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: OMNI Option Format
In this format:
o Type is set to TBD2.
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 Client to the MS, Preflen applies to the IPv6
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source LLA and provides the length that the Client is requesting
or asserting to the MS. For IPv6 ND messages sent from the MS to
the Client, Preflen applies to the IPv6 destination LLA and
indicates the length that the MS is granting to the Client. For
IPv6 ND messages sent between MS endpoints, Preflen provides the
length associated with the source/target Client MNP that is
subject of the ND message.
o S/T-omIndex is an 8 bit field that includes an omIndex value for
the source or target underlying interface for this IPv6 ND
message. Client OMNI interfaces MUST number each distinct
underlying interface with an omIndex value between '1' and '255'
that represents a Client-specific 8-bit mapping for the actual
ifIndex value assigned by network management [RFC2863], then set
S/T-omIndex to either a specific omIndex value or '0' to denote
"unspecified". Proxy/Server OMNI interfaces use the omIndex value
'0' to denote an INET underlying interface.
o The remaining header fields before the Sub-Options begin are
modeled from the Transmission Control Protocol (TCP) header
specified in Section 3.1 of [RFC0793] and include a 32 bit
Sequence Number followed by a 32 bit Acknowledgement Number
followed by 8 flags bits followed by a 24-bit Window. The (SYN,
ACK, RST) flags are used when TCP-like window synchronization is
used, while the TCP (URG, PSH, FIN) flags are never used and
therefore omitted. The (OPT, PNG) flags are OMNI-specific, and
the remaining flags are Reserved. Together, these fields support
the asymmetric and symmetric OAL window synchronization services
specified in Section 6.5.
o Sub-Options is a Variable-length field such that the complete OMNI
Option is an integer multiple of 8 octets long. Sub-Options
contains zero or more sub-options as specified in Section 12.2.
The OMNI option is included in all OMNI interface IPv6 ND messages;
the option is processed by receiving interfaces that recognize it and
otherwise ignored. If multiple OMNI option instances appear in the
same IPv6 ND message, only the first option includes the OMNI header
fields before the Sub-Options while all others are coded as follows:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Type | Length | Sub-Options ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The OMNI interface processes the Sub-Options of all OMNI option
instances received in the same IPv6 ND message in the consecutive
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order in which they appear. The OMNI option(s) included in each IPv6
ND message may include full or partial information for the neighbor.
The union of the information in the most recently received OMNI
options is therefore retained and aged/removed in conjunction with
the corresponding NCE.
12.2. OMNI Sub-Options
Each OMNI option includes a Sub-Options block containing zero or more
individual sub-options. Each consecutive sub-option is concatenated
immediately after its predecessor. All sub-options except Pad1 (see
below) are in type-length-value (TLV) format encoded as follows:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Sub-Type| Sub-length | Sub-Option Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 11: Sub-Option Format
o Sub-Type is a 5-bit field that encodes the Sub-Option type. Sub-
options defined in this document are:
Sub-Option Name Sub-Type
Pad1 0
PadN 1
Interface Attributes (Type 1) 2
Interface Attributes (Type 2) 3
Interface Attributes (Type 4) 4
MS-Register 5
MS-Release 6
Geo Coordinates 7
DHCPv6 Message 8
HIP Message 9
PIM-SM Message 10
Reassembly Limit 11
Fragmentation Report 12
Node Identification 13
ICMPv6 Error 14
Sub-Type Extension 30
Figure 12
Sub-Types 14-29 are available for future assignment for major
protocol functions. Sub-Type 31 is reserved by IANA.
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o Sub-Length is an 11-bit field that encodes the length of the Sub-
Option Data in octets.
o Sub-Option Data is a block of data with format determined by Sub-
Type and length determined by Sub-Length.
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 2040 octets minus the length of the OMNI
option header octets preceding the Sub-Options. This allows ample
space for coding large objects (e.g., ASCII strings, domain names,
protocol messages, security codes, etc.), while a single OMNI option
is limited to 2040 octets the same as for any IPv6 ND option. The
OMNI interface codes initial sub-options in a first OMNI option
instance and subsequent sub-options in additional instances in the
same IPv6 ND message in the intended order of processing. The OMNI
interface can then code any remaining sub-options in additional IPv6
ND messages if necessary. Implementations must observe these size
limits and refrain from sending IPv6 ND messages larger than the OMNI
interface MTU.
During reception, the OMNI interface processes the OMNI option Sub-
Options while skipping over and ignoring any unrecognized sub-
options. The OMNI interface processes the Sub-Options of all OMNI
option instances in the consecutive order in which they appear in the
IPv6 ND message, beginning with the first instance and continuing
through any additional instances to the end of the message. If an
individual sub-option length would cause processing to exceed the
OMNI option total length, the OMNI interface accepts any sub-options
already processed and ignores the final sub-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 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:
12.2.1. Pad1
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0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| S-Type=0|x|x|x|
+-+-+-+-+-+-+-+-+
Figure 13: Pad1
o Sub-Type is set to 0. If multiple instances appear in OMNI
options of the same message all are processed.
o Sub-Type is followed by 3 'x' bits, set to any value on
transmission (typically all-zeros) and ignored on receipt. Pad1
therefore consists of 1 octet with the most significant 5 bits set
to 0, and with no Sub-Length or Sub-Option Data fields following.
12.2.2. PadN
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| S-Type=1| Sub-length=N | N padding octets ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 14: 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 that encodes the number of padding octets
that follow.
o Sub-Option Data consists of N octets, set to any value on
transmission (typically all-zeros) and ignored on receipt.
12.2.3. Interface Attributes (Types 1 through 3)
Interface Attributes (Type 1) and (Type 2) were defined in
[I-D.templin-6man-omni-interface] and have been moved to historic
status. Their sub-option types (2 and 3) are reserved for future
use.
Interface Attributes (Type 3) was never defined; the number was
skipped to bring (Type 4) into agreement with the corresponding sub-
option Type value.
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12.2.4. Interface Attributes (Type 4)
The Interface Attributes (Type 4) sub-option provides L2 forwarding
information for the multilink conceptual sending algorithm discussed
in Section 14. The L2 information is used for selecting among
potentially multiple candidate underlying interfaces that can be used
to forward carrier packets to the neighbor based on factors such as
traffic selectors and link quality. Interface Attributes (Type 4)
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 4) must be honored by all implementations.
Throughout the remainder of this specification, when the term
"Interface Attributes" appears without a "Type" designation the below
format is indicated:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=4| Sub-length=N | omIndex | TS Format |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| omType | Provider ID | Link | Resvd | FMT | SRT |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LHS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Link Layer Address (L2ADDR) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ RFC 6088 Format Traffic Selector ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: Interface Attributes (Type 4)
o Sub-Type is set to 4. 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 Traffic Selectors of all are processed while the
remaining information is processed only for the first instance and
ignored in all other instances.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. All fields beginning with omIndex up to and
including TS Format are always present, while the 'A' and 'T'
flags determine the remaining Sub-Option Data format.
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o Sub-Option Data contains an "Interface Attributes (Type 4)" option
encoded as follows:
* omIndex is a 1-octet 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 the presence of a NAT is
indicated.
* TS Format is a 1-octet field that encodes a Traffic Selector
version per [RFC6088] when T is 1. If TS Format encodes the
value 1, the Traffic Selector includes IPv4 information. If it
encodes the value 2, the Traffic Selector includes IPv6
information. If it encodes the value 0, the Traffic Selector
field is omitted.
* 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").
* Resvd is 4-bit field reserved for future use, set to 0 on
transmit and ignored on receipt.
* The following address-related fields appear next in consecutive
order:
+ FMT - a 3-bit "Forward/Mode/Type" code corresponding to the
included Link Layer Address as follows:
- When the most significant bit (i.e., "FMT-Forward") is
clear, the Proxy/Server must reassemble. When the bit is
set, the Proxy/Server must forward the fragments to the
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Client (while changing the OAL destination address)
without reassembling.
- When the next most significant bit (i.e., "FMT-Mode") is
clear, L2ADDR is the address of the Proxy/Server and the
Client must be reached through the Proxy/Server. When
the bit is set, the Client can be reached on the open
*NET where it may be located behind one or more NATs and
L2ADDR is either the address of the Proxy/Server (when
FMT-Forward is set) or the native INET address of the
Client itself (when FMT-Forward is clear).
- The least significant bit (i.e., "FMT-Type") determines
the IP address version encoded in L2ADDR. If FMT-Type is
clear, L2ADDR includes a 4-octet IPv4 address. If FMT-
Type is set, L2ADDR includes a 16-octet IPv6 address.
+ SRT - a 5-bit Segment Routing Topology prefix length value
that (when added to 96) determines the prefix length to
apply to the ULA formed from concatenating [ULA*]::/96 with
the 32 bit LHS MSID value that follows. For example, the
value 16 corresponds to the prefix length 112.
+ LHS - the 32 bit MSID of the Last Hop Proxy/Server 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-6man-aero] for further discussion.
+ Link Layer Address (L2ADDR) - identifies the link-layer
address (i.e., the encapsulation address) of the source/
target according to FMT. 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.
* When TS Format is non-zero, the remainder of the sub-option
includes a traffic selector formatted per [RFC6088] beginning
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with the "Flags (A-N)" field, and with the Traffic Selector IP
protocol version coded in the TS Format field. Note that each
Interface Attributes sub-option includes at most one IPv4 or
IPv6 Traffic Selector block. If a single interface identified
by omIndex requires traffic selectors for multiple IP protocol
versions, or if a traffic selector block would exceed the space
available in a single Interface Attributes sub-option, the
remaining information is coded in additional sub-options all
having the same omIndex in 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=4| Sub-length=N | omIndex | TS Format |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ RFC 6088 Format Traffic Selector ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
12.2.5. MS-Register
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 16: 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.
o Sub-Length is set to 4n, with n representing the number of MSIDs
included.
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
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requests the recipient to return the MSID of a nearby Proxy/Server
in a corresponding RA response.
12.2.6. 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 17: 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 n representing the number of MSIDs
included.
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.
12.2.7. Geo Coordinates
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=7| Sub-length=N | Geo Type |Geo Coordinates
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 18: Geo Coordinates Sub-option
o Sub-Type is set to 7. If multiple instances appear in OMNI
options of the same message all are processed.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
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o Geo Type is a 1 octet field that encodes a type designator that
determines the format and contents of the Geo Coordinates field
that follows. The following types are currently defined:
* 0 - NULL, i.e., the Geo Coordinates field is zero-length.
o A set of Geo Coordinates of length up to the remaining available
space for this OMNI option. New formats to be specified in future
documents and may include attributes such as latitude/longitude,
altitude, heading, speed, etc.
12.2.8. Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Message
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) sub-option
may be included in the OMNI options of Client RS messages and Proxy/
Server RA messages. Proxy/Servers that forward RS/RA messages
between a Client and other Proxy/Servers also forward DHCPv6 Sub-
Options unchanged. Note that DHCPv6 messages do not include a
Checksum field, but integrity is protected by the IPv6 ND message
Checksum.
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 19: 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.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The 'msg-type' and 'transaction-id' fields
are always present; hence, the length of the DHCPv6 options is
limited by the remaining available space for this OMNI option.
o 'msg-type' and 'transaction-id' are coded according to Section 8
of [RFC8415].
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o A set of DHCPv6 options coded according to Section 21 of [RFC8415]
follows.
12.2.9. Host Identity Protocol (HIP) Message
The Host Identity Protocol (HIP) Message sub-option may be included
in the OMNI options of IPv6 ND messages exchanged between Clients and
Proxy/Servers over an open Internetwork. Proxy/Servers authenticate
the HIP signatures of Client IPv6 ND messages before securely
forwarding them to other OMNI nodes. Proxy/Servers that receive
secured IPv6 ND messages from other OMNI nodes insert HIP signatures
before forwarding them to the Client..
The HIP message sub-option should be included in any OMNI IPv6 ND
message that traverses an open Internetwork, i.e., where link-layer
authentication is not already assured by lower layers.
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|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Controls |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ HIP Parameters /
/ /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: 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.
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
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to the end of the HIP parameters. The length of the entire HIP
message is therefore limited by the remaining available space for
this OMNI option.
o The HIP message is coded per Section 5 of [RFC7401], except that
the OMNI "Sub-Type" and "Sub-Length" fields replace the first 2
octets of the HIP message header (i.e., the Next Header and Header
Length fields). Also, since the IPv6 ND message header already
includes a Checksum the HIP message Checksum field is replaced by
a Reserved field set to 0 on transmission and ignored on
reception.
Note: In some environments, maintenance of a Host Identity Tag (HIT)
namespace may be unnecessary for securely associating an OMNI node
with an IPv6 address-based identity. In that case, other types of
IPv6 addresses (e.g., a Client's MNP-LLA, etc.) can be used instead
of HITs in the authentication signature as long as the address can be
uniquely associated with the Sender/Receiver.
12.2.10. PIM-SM Message
The Protocol Independent Multicast - Sparse Mode (PIM-SM) Message
sub-option may be included in the OMNI options of IPv6 ND messages.
PIM-SM messages are formatted as specified in Section 4.9 of
[RFC7761], with the exception that the Checksum field is replaced by
a Reserved field (set to 0) since the IPv6 ND message header already
includes a Checksum. The PIM-SM message sub-option format is shown
in Figure 21:
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 |PIM Ver| Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ PIM-SM Message /
/ /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: PIM-SM Message Option Format
o Sub-Type is set to 10. If multiple instances appear in OMNI
options of the same message all are processed.
o Sub-Length is set to N, i.e., the length of the option in octets
beginning immediately following the Sub-Length field and extending
to the end of the PIM-SM message. The length of the entire PIM-SM
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message is therefore limited by the remaining available space for
this OMNI option.
o The PIM-SM message is coded exactly as specified in Section 4.9 of
[RFC7761], except that the Checksum field is replaced by a
Reserved field set to 0 on transmission and ignored on reception.
The "PIM Ver" field MUST encode the value 2, and the "Type" field
encodes the PIM message type. (See Section 4.9 of [RFC7761] for a
list of PIM-SM message types and formats.)
12.2.11. Reassembly Limit
The Reassembly Limit sub-option may be included in the OMNI options
of IPv6 ND messages. The message consists of a 15-bit Reassembly
Limit value, followed by a flag bit (H) optionally followed by an (N-
2)-octet leading portion of an OAL First Fragment that triggered the
message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=11| Sub-length=N | Reassembly Limit |H|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL First Fragment (As much of invoking packet |
+ as possible without causing the IPv6 ND message +
| to exceed the minimum IPv6 MTU) |
+ +
Figure 22: Reassembly Limit
o Sub-Type is set to 11. If multiple instances appear in OMNI
options of the same message the first occurring "hard" and "soft"
Reassembly Limit values are accepted, and any additional
Reassembly Limit values are ignored.
o Sub-Length is set to 2 if no OAL First Fragment is included, or to
a value N greater than 2 if an OAL First Fragment is included.
o A 15-bit Reassembly Limit follows, and includes a value between
1500 and 9180. If any other value is included, the sub-option is
ignored. The value indicates the hard or soft limit for original
IP packets that the source of the message is currently willing to
reassemble; the source may increase or decrease the hard or soft
limit at any time through the transmission of new IPv6 ND
messages. Until the first IPv6 ND message with a Reassembly Limit
sub-option arrives, OMNI nodes assume initial default hard/soft
limits of 9180 (I.e., the OMNI interface MRU). After IPv6 ND
messages with Reassembly Limit sub-options arrive, the OMNI node
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retains the most recent hard/soft limit values until new IPv6 ND
messages with different values arrive.
o The 'H' flag is set to 1 if the Reassembly Limit is a "Hard"
limit, and set to 0 if the Reassembly Limit is a "Soft" limit.
o If N is greater than 2, the remainder of the Reassembly Limit sub-
option encodes the leading portion of an OAL First Fragment that
prompted this IPv6 ND message. The first fragment is included
beginning with the OAL IPv6 header, and continuing with as much of
the fragment payload as possible without causing the IPv6 ND
message to exceed the minimum IPv6 MTU.
12.2.12. Fragmentation Report
The Fragmentation Report may be included in the OMNI options of uNA
messages sent from an OAL destination to an OAL source. The message
consists of (N / 8)-many (Identification, Bitmap)-tuples which
include the Identification values of OAL fragments received plus a
Bitmap marking the ordinal positions of individual fragments received
and fragments missing.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=12| Sub-Length = N | Identification #1 (bits 0 -15)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification #1 (bits 15-31)| Bitmap #1 (bits 0 - 15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bitmap #1 (bits 16-31) | Identification #2 (bits 0 -15)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification #2 (bits 15-31)| Bitmap #2 (bits 0 - 15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bitmap #2 (bits 16-31) | Identification #3 (bits 0 -15)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification #3 (bits 15-31)| Bitmap #3 (bits 0 - 15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bitmap #3 (bits 16-31) | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +
| ... |
+ ... +
Figure 23: Fragmentation Report
o Sub-Type is set to 12. If multiple instances appear in OMNI
options of the same message all are processed.
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o Sub-Length is set to N, i.e., the length of the option in octets
beginning immediately following the Sub-Length field and extending
to the end of the sub-option. If N is not an integral multiple of
8 octets, the sub-option is ignored. The length of the entire
sub-option should not cause the entire IPv6 ND message to exceed
the minimum MPS.
o Identification (i) includes the IPv6 Identification value found in
the Fragment Header of a received OAL fragment. (Only those
Identification values included represent fragments for which loss
was unambiguously observed; any Identification values not included
correspond to fragments that were either received in their
entirety or may still be in transit.)
o Bitmap (i) includes an ordinal checklist of fragments, with each
bit set to 1 for a fragment received or 0 for a fragment missing.
(Each OAL packet may consist of at most 23 fragments, therefore
Bitmp bits 0-22 are consulted while bits 23-31 are reserved for
future use and ignored.) For example, for a 20-fragment OAL
packet with ordinal fragments #3, #10, #13 and #17 missing and all
other fragments received, Bitmap would encode:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|1|1|1|0|1|1|1|1|1|1|0|1|1|0|1|1|1|0|1|1|0|0|0|...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 24
(Note that loss of an OAL atomic fragment is indicated by a
Bitmap(i) with all bits set to 0.)
12.2.13. 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=13| Sub-length=N | ID-Type | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ Node Identification Value (N-1 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 25: Node Identification
o Sub-Type is set to 13. 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
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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 that encodes the number of Sub-Option Data
octets that follow. The ID-Type field is always present; hence,
the maximum Node Identification Value length is limited by the
remaining available space in this OMNI option.
o ID-Type is a 1 octet field that encodes the type of the Node
Identification Value. The following ID-Type values are currently
defined:
* 0 - Universally Unique IDentifier (UUID) [RFC4122]. Indicates
that Node Identification Value contains a 16 octet UUID.
* 1 - Host Identity Tag (HIT) [RFC7401]. Indicates that Node
Identification Value contains a 16 octet HIT.
* 2 - Hierarchical HIT (HHIT) [I-D.ietf-drip-rid]. Indicates
that Node Identification Value contains a 16 octet HHIT.
* 3 - Network Access Identifier (NAI) [RFC7542]. Indicates that
Node Identification Value contains an N-1 octet NAI.
* 4 - Fully-Qualified Domain Name (FQDN) [RFC1035]. Indicates
that Node Identification Value contains an N-1 octet FQDN.
* 5 - IPv6 Address. Indicates that Node Identification contains
a 16-octet IPv6 address that is not a (H)HIT. The IPv6 address
type is determined according to the IPv6 addressing
architecture [RFC4291].
* 6 - 252 - Unassigned.
* 253-254 - Reserved for experimentation, as recommended in
[RFC3692].
* 255 - reserved by IANA.
o Node Identification Value is an (N - 1) octet field encoded
according to the appropriate the "ID-Type" reference above.
When a Node Identification Value is used 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 25) as shown in Figure 26:
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DUID-Type (2) | EN (high bits == 0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EN (low bits = 45282) | ID-Type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. Node Identification Value .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 26: DUID-EN for OMNI Format
In this format, the ID-Type and Node Identification Value fields are
coded exactly as in Figure 25 following the 6 octet DUID-EN header,
and the entire "DUID-EN for OMNI" is included in a DHCPv6 message per
[RFC8415].
12.2.14. ICMPv6 Error
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=14| Sub-length=N | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ~
~ RFC4443 Error Message Body ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 27: ICMPv6 Error
o Sub-Type is set to 14. If multiple instances appear in OMNI
options of the same IPv6 ND message all are processed
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
o RFC4443 Error Message Body is an N-octet field encoding the body
of an ICMPv6 Error Message per Section 2.1 of [RFC4443]. ICMPv6
error messages are processed exactly per the standard, while
ICMPv6 informational messages must not be included and are ignored
if received. OMNI interfaces include as much of the ICMPv6 error
message body in the sub-option as possible without causing the
IPv6 ND message to exceed the minimum IPv6 MTU.
12.2.15. Sub-Type Extension
Since the Sub-Type field is only 5 bits in length, future
specifications of major protocol functions may exhaust the remaining
Sub-Type values available for assignment. This document therefore
defines Sub-Type 30 as an "extension", meaning that the actual Sub-
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Option type is determined by examining a 1 octet "Extension-Type"
field immediately following the Sub-Length field. The Sub-Type
Extension is formatted as shown in Figure 28:
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 28: Sub-Type Extension
o Sub-Type is set to 30. If multiple instances appear in OMNI
options of the same message all are processed, where each
individual extension defines its own policy for processing
multiple of that type.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The Extension-Type field is always present,
and the maximum Extension-Type Body length is limited by the
remaining available space in this OMNI option.
o Extension-Type contains a 1 octet Sub-Type Extension value between
0 and 255.
o Extension-Type Body contains an N-1 octet block with format
defined by the given extension specification.
Extension-Type values 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:
12.2.15.1. RFC4380 UDP/IP Header Option
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Ext-Type=0 | Header Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Header Option Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 29: RFC4380 UDP/IP Header Option (Extension-Type 0)
o Sub-Type is set to 30.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The Extension-Type and Header Type fields are
always present, and the Header Option Value is limited by the
remaining available space in this OMNI option.
o Extension-Type is set to 0. Each instance encodes exactly one
header option per Section 5.1.1 of [RFC4380], with 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.
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12.2.15.2. 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 30: RFC6081 UDP/IP Trailer Option (Extension-Type 1)
o Sub-Type is set to 30.
o Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The Extension-Type and Trailer Type fields
are always present, and the maximum-length Trailer Option Value is
limited by the remaining available space in this OMNI option.
o Extension-Type is set to 1. Each instance encodes exactly one
trailer option per Section 4 of [RFC6081]. If multiple instances
of the same Trailer Type appear in OMNI options of the same
message the first instance is processed and all others ignored.
o Trailer Type and Trailer Option Value are coded exactly as
specified in Section 4 of [RFC6081]; the following Trailer Types
are currently defined:
* 0 - Unassigned
* 1 - Nonce Trailer - value coded per Section 4.2 of [RFC6081].
* 2 - Unassigned
* 3 - Alternate Address Trailer (IPv4) - value coded per
Section 4.3 of [RFC6081].
* 4 - Neighbor Discovery Option Trailer - value coded per
Section 4.4 of [RFC6081].
* 5 - Random Port Trailer - value coded per Section 4.5 of
[RFC6081].
* 6 - Alternate Address Trailer (IPv6) - value coded per
Section 4.3 of [RFC6081], except that each address is a
16-octet IPv6 address instead of a 4-octet IPv4 address.
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o Trailer Type values 7 through 252 are available for assignment by
future specifications, which must also define the format of the
Trailer Option Value and its processing rules. Trailer Type
values 253 and 254 are reserved for experimentation, as
recommended in [RFC3692], and value 255 is Reserved by IANA.
13. Address Mapping - Multicast
The multicast address mapping of the native underlying interface
applies. The Client mobile router also serves as an IGMP/MLD Proxy
for its EUNs and/or hosted applications per [RFC4605] while using the
L2 address of a Proxy/Server as the L2 address for all multicast
packets.
The Client uses Multicast Listener Discovery (MLDv2) [RFC3810] to
coordinate with Proxy/Servers, and *NET L2 elements use MLD snooping
[RFC4541].
Since the OMNI link model is NBMA, OMNI links support link-scoped
multicast through iterative unicast transmissions to individual
multicast group members (i.e., unicast/multicast emulation).
14. Multilink Conceptual Sending Algorithm
The Client's IPv6 layer selects the outbound OMNI interface according
to SBM considerations when forwarding original IP packets from local
or EUN applications to external correspondents. Each OMNI interface
maintains a neighbor cache the same as for any IPv6 interface, but
with additional state for multilink coordination. Each OMNI
interface maintains default routes via Proxy/Servers discovered as
discussed in Section 15, and may configure more-specific routes
discovered through means outside the scope of this specification.
After an original IP 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: Section 12.2.4). Underlying interface
selection for the node's own local interfaces are based on traffic
selectors, cost, performance, message size, etc. Both node-local and
neighbor underlying interface traffic selectors may also be
configured to indicate replication 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 an original IP packet over a selected
outbound underlying interface, the OAL employs encapsulation and
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fragmentation as discussed in Section 5, then performs *NET
encapsulation as determined by the L2 address information received in
Interface Attributes. The OAL also performs encapsulation when the
nearest Proxy/Server is located multiple hops away as discussed in
Section 15.2. (Note that the OAL MAY employ packing when multiple
original IP packets and/or control messages are available for
forwarding to the same OAL destination.)
OMNI interface multilink service designers MUST observe the BCP
guidance in Section 15 [RFC3819] in terms of implications for
reordering when original IP packets from the same flow may be spread
across multiple underlying interfaces having diverse properties.
14.1. Multiple OMNI Interfaces
Clients may connect to multiple independent OMNI links concurrently
in support of SBM. Each OMNI interface is distinguished by its
Anycast ULA (e.g., [ULA]:0002::, [ULA]:1000::, [ULA]:7345::, etc.).
The Client 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 the Client 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 an original IP packet's 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 packet to the Client's mobile router entity, and the
Anycast ULA identifies the OMNI interface to be used for transmission
to the next hop. When the Client receives the packet, 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).
14.2. Client-Proxy/Server Loop Prevention
After a Proxy/Server has registered an MNP for a Client (see:
Section 15), the Proxy/Server will forward all packets destined to an
address within the MNP to the Client. The Client will under normal
circumstances then forward the packet to the correct destination
within its internal networks.
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If at some later time the Client loses state (e.g., after a reboot),
it may begin returning packets destined to an MNP address to the
Proxy/Server as its default router. The Proxy/Server therefore must
drop any packets originating from the Client with a destination
address that matches the Client's registered MNP. To do so, the
Proxy/Server 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.
15. Router Discovery and Prefix Registration
Clients interface with the MS by sending RS messages with OMNI
options under the assumption that one or more Proxy/Servers on the
*NET will process the message and respond. The RS message is
received by a first-hop Proxy/Server nearest the Client, which may in
turn forward a proxyed copy of the RS to other Proxy/Servers. The
Client then configures default routes for the OMNI interface based on
any Proxy/Server RA message responses.
For each underlying interface, the Client sends an RS message with an
OMNI option to coordinate with Proxy/Servers identified by MSID
values. Example MSID discovery methods are given in [RFC5214] and
include data link login parameters, name service lookups, static
configuration, a static "hosts" file, etc. When the first-hop Proxy/
Server receives the RS, it returns an RA with the selected MSID in an
MS-Register sub-option while also forwarding the RS to other Proxy/
Servers corresponding to any non-zero MSIDs.
Clients 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 a Client OMNI interface transitions to UP, it sends RS messages
to register its MNP and an initial set of underlying interfaces that
are also UP. The Client sends additional RS messages to refresh
lifetimes and to register/deregister underlying interfaces as they
transition to UP or DOWN. The Client's OMNI interface sends initial
RS messages over an UP underlying interface with its MNP-LLA as the
source (or with the unspecified address (::) as the source if it does
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not yet have an MNP-LLA) and with destination set to link-scoped All-
Routers multicast (ff02::2) [RFC4291]. The OMNI interface includes
an OMNI option per Section 12 with a Preflen assertion, Interface
Attributes appropriate for underlying interfaces, MS-Register/Release
sub-options containing MSID values, Reassembly Limits, an
authentication sub-option and with any other necessary OMNI sub-
options. 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 the
Client uses OAL encapsulation for RS messages sent over an INET
interface, the entire RS message must fit within a single carrier
packet (i.e., an atomic fragment) so that the first-hop Proxy/Server
can verify the authentication signature without having to reassemble.
The OMNI interface selects an Identification value (see:
Section 6.5), sets the OAL source address to the ULA corresponding to
the RS source (or a Temporary ULA if the RS source is the unspecified
address (::)) and sets the OAL destination to site-scoped All-Routers
multicast (ff05::2) then sends the message.
First-hop Proxy/Servers receive IPv6 ND messages with OMNI options
and create a NCE for the Client if necessary while forwarding proxied
versions to other Proxy/Servers named in the Register/Release list.
When each Proxy/Server processes the RS OMNI information, it first
validates the prefix registration information then injects/withdraws
the MNP in the MS and caches/discards the new Preflen, MNP and
Interface Attributes. The Proxy/Server then returns an RA message
with an OMNI option per Section 12.
Remote Proxy/Servers return RAs to the first-hop Proxy/server, and
the first-hop Proxy/Server forwards them to the Client via the same
underlying interface over which the RS was received. Each RA message
includes the Client's MNP-LLA (i.e., unicast) as the destination, the
ADM-LLA of source Proxy/Server as the source, and 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. 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.
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The first-hop Proxy/Server prepares the RA using OAL encapsulation/
fragmentation with an Identification value selected per Section 6.5,
with source set to its own ADM-ULA and destination set to the MNP-ULA
or temporary ULA of the Client. The first-hop Proxy/Server then
sends initial RA messages to the Client and MAY later send additional
periodic and/or event-driven unsolicited RA messages per [RFC4861].
In that case, the S/T-omIndex field in the OMNI option of each
unsolicited RA message identifies the target underlying interface of
the destination Client.
The first-hop Proxy/Server can combine the information from multiple
other Proxy/Servers by sending one or more "aggregate" RAs to the
Client in order conserve *NET bandwidth. Each aggregate RA includes
an OMNI option with MS-Register/Release sub-options with the MSIDs of
all Proxy/Servers represented by the aggregate. Each such aggregate
RA message must consistently represent the combined information
advertised by all represented Proxy/Servers. Note that since the
first-hop Proxy/Server uses its own ADM-LLA as the RA source address,
the Client determines the addresses of the represented Proxy/Servers
by examining the MS-Register/Release OMNI sub-options. Note also
that the first-hop Proxy/Server must return any next-hop Proxy/Server
RA messages that set window synchronization flags directly to the
Client, i.e., and without including them in an aggregate.
When the Client receives the RA message, it creates an OMNI interface
NCE for each MSID that has confirmed MNP registration via the L2
address of the first-hop Proxy/Server. If the Client connects to
multiple *NETs, it records the additional L2 Proxy/Server addresses
in each MSID NCE (i.e., as multilink neighbors). The Client then
configures default routes and assigns the Subnet Router Anycast
address corresponding to the MNP (e.g., 2001:db8:1:2::) to the OMNI
interface. The Client then manages its underlying interfaces
according to their states as follows:
o When an underlying interface transitions to UP, the Client sends
an RS over the underlying interface with an OMNI option. 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 Client 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
Client sends isolated unsolicited NAs when reliability is not
thought to be a concern (e.g., if redundant transmissions are sent
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on multiple underlying interfaces), or may instead set the SYN
flag in the OMNI header to trigger a reliable solicited NA reply.
o When the Router Lifetime for a first-hop Proxy/Server nears
expiration, the Client sends an RS over the underlying interface
to receive a fresh RA. If no RA messages are received (i.e.,
after retrying), the Client marks the underlying interface as
DOWN.
o When a Client 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 Proxy/Server that the release was successful.
o When all of a Client's underlying interfaces have transitioned to
DOWN (or if the prefix registration lifetime expires), all
associated Proxy/Servers withdraw the MNP the same as if they had
received a message with a release indication.
The Client is responsible for retrying each RS exchange up to
MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL
seconds until an RA is received. If no RA is received over an UP
underlying interface (i.e., even after attempting to contact
alternate Proxy/Servers), the Client declares this underlying
interface as DOWN.
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 or independently of 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 Client must send another RS message over this
underlying interface (e.g., 600 seconds), however that timescale may
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be significantly longer than the lifetime the MS has committed to
retain the prefix registration (e.g., REACHABLETIME seconds). Proxy/
Servers are therefore responsible for keeping MS state alive on a
shorter timescale than the Client is required to do on its own
behalf.
Note: On multicast-capable underlying interfaces, Clients should send
periodic unsolicited multicast NA messages and Proxy/Servers should
send periodic unsolicited multicast RA messages as "beacons" that can
be heard by other nodes on the link. If a node fails to receive a
beacon after a timeout value specific to the link, it can initiate a
unicast exchange to test reachability.
Note: When a Proxy/Server forwards a Client's RS message to another
Proxy/Server using UDP/IP encapsulation, it must use a distinct UDP
source port number for each Client. This allows the next-hop Proxy/
Server to distinguish different Clients behind the same first-hop
Proxy/Server at the link-layer, whereas the link-layer addresses
would otherwise be indistinguishable.
Note: When a Proxy/Server 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.
15.1. Window Synchronization
In environments where Identification window synchronization is
necessary, the RS/RA exchanges discussed above observe the procedures
specified in Section 6.5. In the asymmetric case, the initial RS/RA
exchange establishes only the Client's send window and Proxy/Server's
receive window such that a corresponding NS/NA exchange would be
needed in the reverse direction. In the symmetric case, the Client
returns an explicit/implicit acknowledgement response to the RA to
symmetrically establish the send/receive windows of both parties.
The initial RS/RA exchange between a Client and Proxy/Server over a
first underlying interface must invoke window synchronization, while
subsequent RS/RA exchanges performed over additional underlying
interfaces within ReachableTime and with in-window Identification
values need not also invoke window synchronization. Following the
initial exchange, future window (re)synchronizations can occur over
any underlying interface, i.e., and not necessarily only over the one
used for the initial exchange.
When a Client sends an RS SYN that includes an OMNI MS-Register sub-
option with multiple MSIDs, it may receive multiple RA SYN/ACKs -
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each with their own synchronization parameters. The resulting
"multi-three-way" handshake would require the Client to establish
separate NCE SND/RCV state and return explicit/implicit
acknowledgements for each responding Proxy/Server.
15.2. Router Discovery in IP Multihop and IPv4-Only Networks
On some *NETs, a Client may be located multiple IP hops away from the
nearest Proxy/Server. Forwarding through IP multihop *NETs is
conducted through the application of a routing protocol (e.g., a
MANET/VANET routing protocol over omni-directional wireless
interfaces, an inter-domain routing protocol in an enterprise
network, etc.). 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 Client located potentially multiple *NET hops away from the nearest
Proxy/Server 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. The OMNI interface then
employs OAL encapsulation and fragmentation, and 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 Client 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 a Proxy/Server.
For IPv4-only *NETs, the Client instead encapsulates the RS message
in UDP/IPv4 headers with source address set to the IPv4 address of
the underlying interface and with destination address set to either
the unicast IPv4 address of a Proxy/Server [RFC5214] or an IPv4
anycast address reserved for OMNI. The Client 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 Client). This process
repeats iteratively until the RS message is received by a penultimate
*NET hop within single-hop communications range of a Proxy/Server,
which forwards the message to the Proxy/Server.
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When the Proxy/Server 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 network
layer Hop Limit will not have been decremented by the multihop
forwarding process. The Proxy/Server then prepares an RA message
with source address set to its own ADM-LLA and destination address
set to the LLA of the original Client. The Proxy/Server then
performs OAL encapsulation and fragmentation, with OAL source set to
its own ADM-ULA and destination set to the ULA corresponding to the
RA source. The Proxy/Server then encapsulates the message in UDP/
IPv4 or UDP/IPv6 headers with source address set to its own address
and with destination set to the encapsulation source of the RS.
The Proxy/Server then forwards the message to a *NET node within
communications range, which forwards the message according to its
routing tables to an intermediate node. The multihop forwarding
process within the *NET continues repetitively until the message is
delivered to the original Client, which decapsulates the message and
performs autoconfiguration the same as if it had received the RA
directly from a Proxy/Server on the same physical link.
Note: An alternate approach to multihop forwarding via IPv6
encapsulation would be for the Client and Proxy/Server 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. OMNI therefore proposes to re-
claim the prefix 192.88.99.0 [RFC7526] for this purpose (see IANA
considerations).
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15.3. MS-Register and MS-Release List Processing
OMNI links maintain a constant value "MAX_MSID" selected to provide
Clients with an acceptable level of Proxy/Server 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 Client sends an RS message with an OMNI option via an
underlying interface to a first-hop Proxy/Server, the Client must
convey its knowledge of its other currently-associated Proxy/Servers.
Initially, the Client will have no associated Proxy/Servers and
should therefore send its initial RS messages to the link-scoped All-
Routers multicast address. A first-hop Proxy/Server will then return
an RA message with source address set to its own ADM-LLA.
As the Client activates additional underlying interfaces, it can
optionally include an MS-Register sub-option with MSIDs for other
Proxy/Servers discovered from previous RS/RA exchanges. The Client
will thus eventually begin to learn and manage its currently active
set of Proxy/Servers, and can register with new Proxy/Servers or
release from former Proxy/Servers with each successive RS/RA
exchange. As the Client's Proxy/Server 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 Client's interface to the MS and defines the
manner in which Proxy/Servers will respond. The only limiting factor
is that the Client 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 first-hop Proxy/Server receives an RS message sent by a
Client 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 Proxy/Server will have a list of zero
or more MS-Register MSIDs and a list of zero or more of MS-Release
MSIDs. The Proxy/Server 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 as follows:
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* If the Proxy/Server's own MSID appears in the MS-Register list,
send an RA message directly back to the Client 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.
* Otherwise, send a proxy copy of the RS message to each
additional MSID in the MS-Register list with the MS-Register
list omitted. For the first MSID, include the original MS-
Release list; for all other MSIDs, omit the MS-Release list.
Each proxy copy of the RS message will include an OMNI option and OAL
encapsulation header with the ADM-ULA of the first-hop Proxy/Server
as the source and the ADM-ULA of the next-hop Proxy/Server as the
destination. When the next-hop Proxy/Server receives the proxy RS
message, if the message includes an MS-Release list the Proxy/Server
sends a uNA message to each additional MSID in the Release list with
an OMNI option with S/T-omIndex set to 0. The Proxy/Server then
sends an RA message back to the first-hop Proxy/Server with an OAL
header with source and destination addresses reversed, and with RA
destination set to the MNP-LLA of the Client. When the first-hop
Proxy/Server receives this RA message, it sends a proxy copy of the
RA to the Client.
Each uNA message (whether sent by the first-hop Proxy/Server or a
next-hop Proxy/Server) will include an OMNI option and an OAL header
with the ADM-ULA of the uNA source Proxy/Server as the source and the
ADM-ULA of uNA target Proxy/Server as the destination. The uNA
informs the target Proxy/Server that its previous relationship with
the Client has been released and that the source of the uNA message
is now registered. The uNA target must then note that the subject
Client of the uNA message is now "departed", and forward any
subsequent packets destined to the Client to the uNA source Proxy/
Server.
Note: It is not an error for the MS-Register/Release lists to include
duplicate entries. If duplicates occur within a list, the first-hop
Proxy/Server will generate multiple proxy RS and/or uNA messages -
one for each copy of the duplicate entries.
Note: the Client is responsible for honoring the window
synchronization protocol for each responding Proxy/Server when it
sends a single RS message with synchronization parameters and an MS-
Register option with multiple MSIDs. Each responding Proxy/Server
will cache identical RCV state information based on the single RS
message, then respond with its own unique SND parameters.
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15.4. DHCPv6-based Prefix Registration
When a Client is not pre-provisioned with an MNP-LLA (or, when the
Client requires additional MNP delegations), it requests the MS to
select MNPs on its behalf and set up the correct routing state. The
DHCPv6 service [RFC8415] supports this requirement.
When a Client requires the MS to select MNPs, it sends an RS message
with source set to the unspecified address (::) if it has no
MNP_LLAs. If the Client requires only a single MNP delegation, it
can then include a Node Identification sub-option in the OMNI option
and set Preflen to the length of the desired MNP. If the Client
requires multiple MNP delegations and/or more complex DHCPv6
services, it instead includes a DHCPv6 Message sub-option containing
a Client Identifier, one or more IA_PD options and a Rapid Commit
option then sets the 'msg-type' field to "Solicit", and includes a 3
octet 'transaction-id'. The Client then sets the RS destination to
All-Routers multicast and sends the message using OAL encapsulation
and fragmentation if necessary as discussed above.
When a Proxy/Server receives the RS message, it performs OAL
reassembly if necessary. Next, if the RS source is the unspecified
address (::) and/or the OMNI option includes a DHCPv6 message sub-
option, the Proxy/Server acts as a "Proxy DHCPv6 Client" in a message
exchange with the locally-resident DHCPv6 server. If the RS did not
contain a DHCPv6 message sub-option, the Proxy/Server generates a
DHCPv6 Solicit message on behalf of the Client using an IA_PD option
with the prefix length set to the OMNI header Preflen value and with
a Client Identifier formed from the OMNI option Node Identification
sub-option; otherwise, the Proxy/Server uses the DHCPv6 Solicit
message contained in the OMNI option. The Proxy/Server then sends
the DHCPv6 message to the DHCPv6 Server, which delegates MNPs and
returns a DHCPv6 Reply message with PD parameters. (If the Proxy/
Server wishes to defer creation of Client state until the DHCPv6
Reply is received, it can instead act as a Lightweight DHCPv6 Relay
Agent per [RFC6221] by encapsulating the DHCPv6 message in a Relay-
forward/reply exchange with Relay Message and Interface ID options.
In the process, the Proxy/Server packs any state information needed
to return an RA to the Client in the Relay-forward Interface ID
option so that the information will be echoed back in the Relay-
reply.)
When the Proxy/Server receives the DHCPv6 Reply, it adds routes to
the routing system and creates MNP-LLAs based on the delegated MNPs.
The Proxy/Server then sends an RA back to the Client with the DHCPv6
Reply message included in an OMNI DHCPv6 message sub-option if and
only if the RS message had included an explicit DHCPv6 Solicit. If
the RS message source was the unspecified address (::), the Proxy/
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Server includes one of the (newly-created) MNP-LLAs as the RA
destination address and sets the OMNI option Preflen accordingly;
otherwise, the Proxy/Server includes the RS source address as the RA
destination address. The Proxy/Server then sets the RA source
address to its own ADM-LLA then performs OAL encapsulation and
fragmentation and sends the RA to the Client. When the Client
receives the RA, it reassembles and discards the OAL encapsulation,
then creates a default route, assigns Subnet Router Anycast addresses
and uses the RA destination address as its primary MNP-LLA. The
Client will then use this primary MNP-LLA as the source address of
any IPv6 ND messages it sends as long as it retains ownership of the
MNP.
Note: After a Client performs a DHCPv6-based prefix registration
exchange with a first Proxy/Server, it would need to repeat the
exchange with each of its additional Proxy/Servers. In that case,
the Client supplies the MNP delegation information received from the
first Proxy/Server when it engages the additional Proxy/Servers.
16. Secure Redirection
If the *NET link model is multiple access, the first-hop Proxy/Server
is responsible for assuring that address duplication cannot corrupt
the neighbor caches of other nodes on the link. When the Client
sends an RS message on a multiple access *NET link, the Proxy/Server
verifies that the Client is authorized to use the address and returns
an RA with a non-zero Router Lifetime only if the Client is
authorized.
After verifying Client authorization and returning an RA, the Proxy/
Server MAY return IPv6 ND Redirect messages to direct Clients located
on the same *NET link to exchange packets directly without transiting
the Proxy/Server. In that case, the Clients can exchange packets
according to their unicast L2 addresses discovered from the Redirect
message instead of using the dogleg path through the Proxy/Server.
In some *NET links, however, such direct communications may be
undesirable and continued use of the dogleg path through the Proxy/
Server may provide better performance. In that case, the Proxy/
Server can refrain from sending Redirects, and/or Clients can ignore
them.
17. Proxy/Server Resilience
*NETs SHOULD deploy Proxy/Servers in Virtual Router Redundancy
Protocol (VRRP) [RFC5798] configurations so that service continuity
is maintained even if one or more Proxy/Servers fail. Using VRRP,
the Client is unaware which of the (redundant) Proxy/Servers is
currently providing service, and any service discontinuity will be
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limited to the failover time supported by VRRP. Widely deployed
public domain implementations of VRRP are available.
Proxy/Servers SHOULD use high availability clustering services so
that multiple redundant systems can provide coordinated response to
failures. As with VRRP, widely deployed public domain
implementations of high availability clustering services are
available. Note that special-purpose and expensive dedicated
hardware is not necessary, and public domain implementations can be
used even between lightweight virtual machines in cloud deployments.
18. Detecting and Responding to Proxy/Server Failures
In environments where fast recovery from Proxy/Server failure is
required, first-hop Proxy/Servers SHOULD use proactive Neighbor
Unreachability Detection (NUD) in a manner that parallels
Bidirectional Forwarding Detection (BFD) [RFC5880] to track next-hop
Proxy/Server reachability. First-hop Proxy/Servers can then quickly
detect and react to failures so that cached information is re-
established through alternate paths. Proactive NUD control messaging
is carried only over well-connected ground domain networks (i.e., and
not low-end *NET links such as aeronautical radios) and can therefore
be tuned for rapid response.
First-hop Proxy/Servers perform proactive NUD for next-hop Proxy/
Servers for which there are currently active Clients on the *NET. If
a next-hop Proxy/Server fails, the first-hop Proxy/Server can quickly
inform Clients of the outage by sending multicast RA messages on the
*NET interface. The first-hop Proxy/Server sends RA messages to
Clients via the *NET interface with an OMNI option with a Release ID
for the failed next-hop Proxy/Server, and with destination address
set to All-Nodes multicast (ff02::1) [RFC4291].
The first-hop Proxy/Server SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS
RA messages separated by small delays [RFC4861]. Any Clients on the
*NET interface that have been using the (now defunct) next-hop Proxy/
Server will receive the RA messages.
19. Transition Considerations
When a Client connects to an *NET link for the first time, it sends
an RS message with an OMNI option. If the first hop router
recognizes the option, it returns an RA with its ADM-LLA as the
source, the MNP-LLA as the destination and with an OMNI option
included. The Client then engages this first-hop Proxy/Sever
according to the OMNI link model specified above. If the first hop
router is a legacy IPv6 router, however, it instead returns an RA
message with no OMNI option and with a non-OMNI unicast source LLA as
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specified in [RFC4861]. In that case, the Client engages the *NET
according to the legacy IPv6 link model and without the OMNI
extensions specified in this document.
If the *NET link model is multiple access, there must be assurance
that address duplication cannot corrupt the neighbor caches of other
nodes on the link. When the Client sends an RS message on a multiple
access *NET link with an LLA source address and an OMNI option, first
hop routers that recognize the OMNI option ensure that the Client is
authorized to use the address and return an RA with a non-zero Router
Lifetime only if the Client is authorized. First hop routers that do
not recognize the OMNI option instead return an RA that makes no
statement about the Client's authorization to use the source address.
In that case, the Client should perform Duplicate Address Detection
to ensure that it does not interfere with other nodes on the link.
An alternative approach for multiple access *NET links to ensure
isolation for Client-Proxy/Server communications is through L2
address mappings as discussed in Appendix C. This arrangement
imparts a (virtual) point-to-point link model over the (physical)
multiple access link.
20. OMNI Interfaces on Open Internetworks
Client OMNI interfaces configured over IPv6-enabled underlying
interfaces on an open Internetwork without an OMNI-aware first-hop
router receive RA messages that do not include an OMNI option, while
OMNI interfaces configured over IPv4-only underlying interfaces do
not receive any (IPv6) RA messages at all (although they may receive
IPv4 RA messages [RFC1256]). Client 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]. Client OMNI interfaces configured over
IPv4-only underlying interfaces configure IPv4 address information on
the underlying interfaces using mechanisms such as DHCPv4 [RFC2131].
Client OMNI interfaces configured over underlying interfaces that
connect to an open Internetwork can apply security services such as
VPNs to connect to a Proxy/Server, or can establish a direct link to
the Proxy/Server through some other means (see Section 4). In
environments where an explicit VPN or direct link may be impractical,
Client OMNI interfaces can instead use UDP/IP encapsulation while
including authentication signatures in IPv6 ND messages.
OMNI interfaces use UDP service port number 8060 (see: Section 25.11
and Section 3.6 of [I-D.templin-6man-aero]), and use simple UDP/IP
encapsulation for both IPv4 and IPv6 underlying interfaces. The OMNI
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interface encapsulates the original IP packet or OAL packet
immediately following the UDP header, with the IP protocol version
identified by the first four bits. (When the first four bits include
a value other than 4 or 6, the UDP message body is interpreted
according to the OCH-0, OCH-1 or other header formats as discussed in
previous sections.) The OMNI interface sets the UDP length to the
exact length of the encapsulated IP or OAL packet, i.e., and must not
set a larger value to imply surplus space following the packet.
Since the OAL includes an integrity check over the OAL packet, OAL
sources selectively disable UDP checksums for OAL packets that do not
require ORH and/or UDP/IP address integrity, but enable UDP checksums
for others including non-OAL packets, IPv6 ND messages used to
establish link-layer addresses, etc. If the OAL source discovers
that packets with UDP checksums disabled are being dropped in the
path it should enable UDP checksums in future packets. Further
considerations for UDP encapsulation checksums are found in
[RFC6935][RFC6936].
For Client-Proxy/Server (e.g., "Vehicle-to-Infrastructure (V2I)")
neighbor exchanges, the source must include an OMNI option with an
authentication sub-option in all IPv6 ND messages. The source can
apply HIP security services per [RFC7401] using the IPv6 ND message
OMNI option as a "shipping container" to convey an authentication
signature in a (unidirectional) HIP "Notify" message. For Client-
Client (e.g., "Vehicle-to-Vehicle (V2V)") neighbor exchanges, two
Clients can exchange HIP "Initiator/Responder" messages coded in OMNI
options of multiple IPv6 NS/NA messages for mutual authentication
according to the HIP protocol. (Note: a simple Hashed Message
Authentication Code (HMAC) such as specified in [RFC4380] can be used
as an alternate authentication service in some environments.)
When HIP authentication is used, the IPv6 ND message source should
include an OMNI option with a HIP message containing a valid
authentication signature. When the source prepares the HIP message,
it includes its own (H)HIT as the Sender's HIT and the neighbor's
(H)HIT if known as the Receiver's HIT (otherwise 0). If (H)HITs are
not available within the OMNI operational environment, the source can
instead use ordinary IPv6 addresses instead of (H)HITs as long as the
Sender and Receiver have some way to associate the addresses with the
neighbor (e.g., via a node identifier embedded in the address).
Before calculating the HIP signature, the source sets both the ICMPv6
Checksum field and HIP signature fields to 0. The source then
calculates the HIP authentication signature over the full length of
the IPv6 ND message beginning with the ICMPv6 message header and
extending over all included IPv6 ND message options including the
OMNI option itself. The source next writes the authentication
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signature into the HIP signature field, then calculates the ICMPv6
message checksum and writes the value into the ICMPv6 Checksum field.
After establishing a VPN or preparing for UDP/IP encapsulation, OMNI
interfaces send RS/RA messages for Client-Proxy/Server coordination
(see: Section 15) and NS/NA messages for route optimization and
mobility management (see: [I-D.templin-6man-aero]). These control
plane messages must be authenticated while data plane messages are
delivered the same as for ordinary best-effort traffic with source
address and/or Identification window-based data 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.
Client 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-6man-aero]. To support NAT determination, Proxy/Servers
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 IPv6 ND message exchange, OMNI interfaces
configured over open Internetworks maintain neighbor relationships by
transmitting periodic IPv6 ND messages with OMNI options that include
HIP "Update" and/or "Notify" messages. When HMAC authentication is
used instead of HIP, the Client and Proxy/Server exchange all IPv6 ND
messages with HMAC signatures included based on a shared-secret.
Note: The [RFC4380] HMAC and/or HIP message [RFC7401] authentication
sub-options appear in the OMNI option, which may occur anywhere
within the IPv6 ND message body. When a node that inserts an
authentication sub-option generates the authentication signature, it
calculates the signature over the entire length of the IPv6 ND
message but with the sub-option authentication field itself set to 0.
The node then writes the resulting signature into the authentication
field then continues to prepare the message for transmission. For
this reason, if an IPv6 ND message includes multiple authentication
sub-options, the first sub-option is consulted and any additional
sub-options are ignored.
Note: OMNI interfaces on open Internetworks should employ the
Identification window synchronization mechanisms specified in
Section 6.5 in order to reject spurious carrier packets that might
otherwise clutter the reassembly cache. This is especially important
in environments where carrier packet spoofing is a threat.
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21. Time-Varying MNPs
In some use cases, it is desirable, beneficial and efficient for the
Client to receive a constant MNP that travels with the Client
wherever it moves. For example, this would allow air traffic
controllers to easily track aircraft, etc. In other cases, however
(e.g., intelligent transportation systems), the Client may be willing
to sacrifice a modicum of efficiency in order to have time-varying
MNPs that can be changed every so often to defeat adversarial
tracking.
The prefix delegation services discussed in Section 15.4 allows
Clients that desire time-varying MNPs to obtain short-lived prefixes
to send RS messages with source set to the unspecified address (::)
and/or with an OMNI option with DHCPv6 Option sub-options. The
Client would then be obligated to renumber its internal networks
whenever its MNP (and therefore also its OMNI address) changes. This
should not present a challenge for Clients with automated network
renumbering services, but may present limits for the durations of
ongoing sessions that would prefer to use a constant address.
22. (H)HITs and Temporary ULAs
Clients that generate (H)HITs but do not have pre-assigned MNPs can
request MNP delegations by issuing IPv6 ND messages that use the
(H)HIT instead of a Temporary ULA. In particular, when a Client
creates an RS message it can set the source to the unspecified
address (::) and destination to link-scoped All-Routers multicast.
The IPv6 ND message includes an OMNI option with a HIP message sub-
option, and need not include a Node Identification sub-option since
the Client's HIT appears in the HIP message. The Client 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 Client then sends the message to the Proxy/
Server as specified in Section 15.2.
When the Proxy/Server receives the RS message, it notes that the
source was the unspecified address (::), then examines the
encapsulation source address to determine that the source is a (H)HIT
and not a Temporary ULA. The Proxy/Server next invokes the DHCPv6
protocol to request an MNP prefix delegation while using the HIT as
the Client Identifier, then prepares an RA message with source
address set to its own ADM-LLA and destination set to the MNP-LLA
corresponding to the delegated MNP. The Proxy/Server next includes
an OMNI option with a HIP message sub-option and any DHCPv6 prefix
delegation parameters. The Proxy/Server finally encapsulates the RA
in an IPv6 header with source address set to its own ADM-ULA and
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destination set to the (H)HIT from the RS encapsulation source
address, then returns the encapsulated RA to the Client.
Clients can also use (H)HITs and/or Temporary ULAs for direct Client-
to-Client communications outside the context of any OMNI link
supporting infrastructure. When two Clients encounter one another
they can use their (H)HITs and/or Temporary ULAs as original IPv6
packet source and destination addresses to support direct
communications. Clients can also inject their (H)HITs and/or
Temporary ULAs into a MANET/VANET routing protocol to enable multihop
communications. Clients can further exchange IPv6 ND messages (such
as NS/NA) using their (H)HITs and/or Temporary ULAs as source and
destination addresses. Note that the HIP security protocols for
establishing secure neighbor relationships are based on (H)HITs.
IPv6 ND messages that use Temporary ULAs instead use the HMAC
authentication service specified in [RFC4380].
Lastly, when Clients are within the coverage range of OMNI link
infrastructure a case could be made for injecting (H)HITs and/or
Temporary ULAs into the global MS routing system. For example, when
the Client sends an RS to a Proxy/Server it could include a request
to inject the (H)HIT / Temporary ULA into the routing system instead
of requesting an MNP prefix delegation. This would potentially
enable OMNI link-wide communications using only (H)HITs or Temporary
ULAs, and not MNPs. This document notes the opportunity, but makes
no recommendation.
23. Address Selection
Clients use LLAs only for link-scoped communications on the OMNI
link. Typically, Clients use LLAs as source/destination IPv6
addresses of IPv6 ND messages, but may also use them for addressing
ordinary original IP packets exchanged with an OMNI link neighbor.
Clients use MNP-ULAs as source/destination IPv6 addresses in the
encapsulation headers of OAL packets. Clients use Temporary ULAs for
OAL addressing when an MNP-ULA is not available, or as source/
destination IPv6 addresses for communications within a MANET/VANET
local area. Clients can also use HITs instead of Temporary ULAs when
operation outside the context of a specific ULA domain and/or source
address attestation is necessary.
Clients use MNP-based GUAs as original IP packet source and
destination addresses for communications with Internet destinations
when they are within range of OMNI link supporting infrastructure
that can inject the MNP into the routing system.
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24. Error Messages
An OAL destination or intermediate node may need to return
ICMPv6-like error messages (e.g., Destination Unreachable, Packet Too
Big, Time Exceeded, etc.) [RFC4443] to an OAL source. Since ICMPv6
error messages do not themselves include authentication codes, OAL
nodes that return error messages can include them as an OMNI ICMPv6
Error sub-option in a secured IPv6 ND uNA message.
25. IANA Considerations
The following IANA actions are requested in accordance with [RFC8126]
and [RFC8726]:
25.1. "IEEE 802 Numbers" Registry
The IANA is instructed to allocate an official Ethertype number TBD1
from the 'ieee-802-numbers' registry for User Datagram Protocol (UDP)
encapsulation on Ethernet networks. Guidance is found in [RFC7042]
(registration procedure is Expert Review).
25.2. "IPv6 Neighbor Discovery Option Formats" Registry
The IANA is instructed to allocate an official Type number TBD2 from
the "IPv6 Neighbor Discovery Option Formats" registry for the OMNI
option (registration procedure is RFC required). Implementations set
Type to 253 as an interim value [RFC4727].
25.3. "Ethernet Numbers" Registry
The IANA is instructed to allocate one Ethernet unicast address TBD3
(suggested value '00-52-14') in the 'ethernet-numbers' registry under
"IANA Unicast 48-bit MAC Addresses" (registration procedure is Expert
Review). The registration should appear as follows:
Addresses Usage Reference
--------- ----- ---------
00-52-14 Overlay Multilink Network (OMNI) Interface [RFCXXXX]
Figure 31: IANA Unicast 48-bit MAC Addresses
25.4. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry
The IANA is instructed to assign two new Code values in the "ICMPv6
Code Fields: Type 2 - Packet Too Big" registry (registration
procedure is Standards Action or IESG Approval). The registry should
appear as follows:
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Code Name Reference
--- ---- ---------
0 PTB Hard Error [RFC4443]
1 PTB Soft Error (loss) [RFCXXXX]
2 PTB Soft Error (no loss) [RFCXXXX]
Figure 32: ICMPv6 Code Fields: Type 2 - Packet Too Big Values
(Note: this registry also to be used to define values for setting the
"unused" field of ICMPv4 "Destination Unreachable - Fragmentation
Needed" messages.)
25.5. "OMNI Option Sub-Type Values" (New Registry)
The OMNI option defines a 5-bit Sub-Type field, for which IANA is
instructed to create and maintain a new registry entitled "OMNI
Option Sub-Type Values". Initial values are given below
(registration procedure is RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 Pad1 [RFCXXXX]
1 PadN [RFCXXXX]
2 Interface Attributes (Type 1) [RFCXXXX]
3 Interface Attributes (Type 2) [RFCXXXX]
4 Interface Attributes (Type 4) [RFCXXXX]
5 MS-Register [RFCXXXX]
6 MS-Release [RFCXXXX]
7 Geo Coordinates [RFCXXXX]
8 DHCPv6 Message [RFCXXXX]
9 HIP Message [RFCXXXX]
11 PIM-SM Message [RFCXXXX]
11 Reassembly Limit [RFCXXXX]
12 Fragmentation Report [RFCXXXX]
13 Node Identification [RFCXXXX]
14 ICMPv6 Error [RFCXXXX]
15-29 Unassigned
30 Sub-Type Extension [RFCXXXX]
31 Reserved by IANA [RFCXXXX]
Figure 33: OMNI Option Sub-Type Values
25.6. "OMNI Geo Coordinates Type Values" (New Registry)
The OMNI Geo Coordinates sub-option (see: Section 12.2.7) contains an
8-bit Type field, for which IANA is instructed to create and maintain
a new registry entitled "OMNI Geo Coordinates Type Values". Initial
values are given below (registration procedure is RFC required):
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Value Sub-Type name Reference
----- ------------- ----------
0 NULL [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 34: OMNI Geo Coordinates Type
25.7. "OMNI Node Identification ID-Type Values" (New Registry)
The OMNI Node Identification sub-option (see: Section 12.2.13)
contains an 8-bit ID-Type field, for which IANA is instructed to
create and maintain a new registry entitled "OMNI Node Identification
ID-Type Values". Initial values are given below (registration
procedure is RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 UUID [RFCXXXX]
1 HIT [RFCXXXX]
2 HHIT [RFCXXXX]
3 Network Access Identifier [RFCXXXX]
4 FQDN [RFCXXXX]
5 IPv6 Address [RFCXXXX]
6-252 Unassigned [RFCXXXX]
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 35: OMNI Node Identification ID-Type Values
25.8. "OMNI Option Sub-Type Extension Values" (New Registry)
The OMNI option defines an 8-bit Extension-Type field for Sub-Type 30
(Sub-Type Extension), for which IANA is instructed to create and
maintain a new registry entitled "OMNI Option Sub-Type Extension
Values". Initial values are given below (registration procedure is
RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 RFC4380 UDP/IP Header Option [RFCXXXX]
1 RFC6081 UDP/IP Trailer Option [RFCXXXX]
2-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 36: OMNI Option Sub-Type Extension Values
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25.9. "OMNI RFC4380 UDP/IP Header Option" (New Registry)
The OMNI Sub-Type Extension "RFC4380 UDP/IP Header Option" defines an
8-bit Header Type field, for which IANA is instructed to create and
maintain a new registry entitled "OMNI RFC4380 UDP/IP Header Option".
Initial registry values are given below (registration procedure is
RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 Origin Indication (IPv4) [RFC4380]
1 Authentication Encapsulation [RFC4380]
2 Origin Indication (IPv6) [RFCXXXX]
3-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 37: OMNI RFC4380 UDP/IP Header Option
25.10. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry)
The OMNI Sub-Type Extension for "RFC6081 UDP/IP Trailer Option"
defines an 8-bit Trailer Type field, for which IANA is instructed to
create and maintain a new registry entitled "OMNI RFC6081 UDP/IP
Trailer Option". Initial registry values are given below
(registration procedure is RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 Unassigned
1 Nonce [RFC6081]
2 Unassigned
3 Alternate Address (IPv4) [RFC6081]
4 Neighbor Discovery Option [RFC6081]
5 Random Port [RFC6081]
6 Alternate Address (IPv6) [RFCXXXX]
7-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 38: OMNI RFC6081 Trailer Option
25.11. 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-6man-aero] reclaims the UDP port number "8060" for
'aero' as the service port for UDP/IP encapsulation. (Note that,
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although [RFC6706] was not widely implemented or deployed, any
messages coded to that specification can be easily distinguished and
ignored since they use an invalid ICMPv6 message type number '0'.)
The IANA is therefore instructed to update the reference for UDP port
number "8060" from "RFC6706" to "RFCXXXX" (i.e., this document).
The IANA has assigned a 4 octet Private Enterprise Number (PEN) code
"45282" in the "enterprise-numbers" registry. This document is the
normative reference for using this code in DHCP Unique IDentifiers
based on Enterprise Numbers ("DUID-EN for OMNI Interfaces") (see:
Section 11). The IANA is therefore instructed to change the
enterprise designation for PEN code "45282" from "LinkUp Networks" to
"Overlay Multilink Network Interface (OMNI)".
The IANA has assigned the ifType code "301 - omni - Overlay Multilink
Network Interface (OMNI)" in accordance with Section 6 of [RFC8892].
The registration appears under the IANA "Structure of Management
Information (SMI) Numbers (MIB Module Registrations) - Interface
Types (ifType)" registry.
The IANA is instructed to re-purpose the prefix 192.88.99.0 which has
been set aside from its former use by [RFC7526] as an IPv4 OMNI
interface anycast address.
No further IANA actions are required.
26. Security Considerations
Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6
Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages
SHOULD include Nonce and Timestamp options [RFC3971] when transaction
confirmation and/or time synchronization is needed. (Note however
that when OAL encapsulation is used the (echoed) OAL Identification
value can provide sufficient transaction confirmation.)
Client OMNI interfaces configured over secured ANET interfaces
inherit the physical and/or link-layer security properties (i.e.,
"protected spectrum") of the connected ANETs. Client OMNI interfaces
configured over open INET interfaces can use symmetric securing
services such as VPNs or can by some other means establish a direct
link. When a VPN or direct link may be impractical, however, the
security services specified in [RFC7401] and/or [RFC4380] can be
employed. While the OMNI link protects control plane messaging,
applications must still employ end-to-end transport- or higher-layer
security services to protect the data plane.
Strong network layer security for control plane messages and
forwarding path integrity for data plane messages between Proxy/
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Servers MUST be supported. In one example, the AERO service
[I-D.templin-6man-aero] constructs a spanning tree between Proxy/
Servers and secures the spanning tree links 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. Additionally, the OAL Identification value provides
a first level of data origin authentication that mitigates off-path
spoofing.
Identity-based key verification infrastructure services such as iPSK
may be necessary for verifying the identities claimed by Clients.
This requirement should be harmonized with the manner in which
(H)HITs are attested in a given operational environment.
Security considerations for specific access network interface types
are covered under the corresponding IP-over-(foo) specification
(e.g., [RFC2464], [RFC2492], etc.).
Security considerations for IPv6 fragmentation and reassembly are
discussed in Section 6.9. In environments where spoofing is
considered a threat, OMNI nodes SHOULD employ Identification window
synchronization and OAL destinations SHOULD configure an (end-system-
based) firewall.
27. Implementation Status
AERO/OMNI Release-3.2 was tagged on March 30, 2021, and is undergoing
internal testing. Additional internal releases expected within the
coming months, with first public release expected end of 1H2021.
28. Document Updates
This document does not itself update other RFCs, but suggests that
the following could be updated through future IETF initiatives:
o [RFC1191]
o [RFC4443]
o [RFC8201]
o [RFC7526]
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Updates can be through, e.g., standards action, the errata process,
etc. as appropriate.
29. Acknowledgements
The first version of this document was prepared per the consensus
decision at the 7th Conference of the International Civil Aviation
Organization (ICAO) Working Group-I Mobility Subgroup on March 22,
2019. Consensus to take the document forward to the IETF was reached
at the 9th Conference of the Mobility Subgroup on November 22, 2019.
Attendees and contributors included: Guray Acar, Danny Bharj,
Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo,
Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu
Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg
Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane
Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman,
Fryderyk Wrobel and Dongsong Zeng.
The following individuals are acknowledged for their useful comments:
Stuart Card, Michael Matyas, Robert Moskowitz, Madhu Niraula, Greg
Saccone, Stephane Tamalet, Eduard Vasilenko, Eric Vyncke. Pavel
Drasil, Zdenek Jaron and Michal Skorepa are especially recognized for
their many helpful ideas and suggestions. Madhuri Madhava Badgandi,
Sean Dickson, Don Dillenburg, Joe Dudkowski, Vijayasarathy
Rajagopalan, Ron Sackman and Katherine Tran are acknowledged for
their hard work on the implementation and technical insights that led
to improvements for the spec.
Discussions on the IETF 6man and atn mailing lists during the fall of
2020 suggested additional points to consider. The authors gratefully
acknowledge the list members who contributed valuable insights
through those discussions. Eric Vyncke and Erik Kline were the
intarea ADs, while Bob Hinden and Ole Troan were the 6man WG chairs
at the time the document was developed; they are all gratefully
acknowledged for their many helpful insights. Many of the ideas in
this document have further built on IETF experiences beginning as
early as Y2K, with insights from colleagues including Brian
Carpenter, Ralph Droms, Christian Huitema, Thomas Narten, Dave
Thaler, Joe Touch, and many others who deserve recognition.
Early observations on IP fragmentation performance implications were
noted in the 1986 Digital Equipment Corporation (DEC) "qe reset"
investigation, where fragment bursts from NFS UDP traffic triggered
hardware resets resulting in communication failures. Jeff Chase,
Fred Glover and Chet Juzsczak of the Ultrix Engineering Group led the
investigation, and determined that setting a smaller NFS mount block
size reduced the amount of fragmentation and suppressed the resets.
Early observations on L2 media MTU issues were noted in the 1988 DEC
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FDDI investigation, where Raj Jain, KK Ramakrishnan and Kathy Wilde
represented architectural considerations for FDDI networking in
general including FDDI/Ethernet bridging. Jeff Mogul (who led the
IETF Path MTU Discovery working group) and other DEC colleagues who
supported these early investigations are also acknowledged.
Throughout the 1990's and into the 2000's, many colleagues supported
and encouraged continuation of the work. Beginning with the DEC
Project Sequoia effort at the University of California, Berkeley,
then moving to the DEC research lab offices in Palo Alto CA, then to
the NASA Ames Research Center, then to SRI in Menlo Park, CA, then to
Nokia in Mountain View, CA and finally to the Boeing Company in 2005
the work saw continuous advancement through the encouragement of
many. Those who offered their support and encouragement are
gratefully acknowledged.
This work is aligned with the NASA Safe Autonomous Systems Operation
(SASO) program under NASA contract number NNA16BD84C.
This work is aligned with the FAA as per the SE2025 contract number
DTFAWA-15-D-00030.
This work is aligned with the Boeing Information Technology (BIT)
Mobility Vision Lab (MVL) program.
30. References
30.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
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[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <https://www.rfc-editor.org/info/rfc4191>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4,
ICMPv6, UDP, and TCP Headers", RFC 4727,
DOI 10.17487/RFC4727, November 2006,
<https://www.rfc-editor.org/info/rfc4727>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont,
"Traffic Selectors for Flow Bindings", RFC 6088,
DOI 10.17487/RFC6088, January 2011,
<https://www.rfc-editor.org/info/rfc6088>.
[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>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
30.2. Informative References
[ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground
Interface for Civil Aviation, IETF Liaison Statement
#1676, https://datatracker.ietf.org/liaison/1676/", March
2020.
[ATN-IPS] WG-I, ICAO., "ICAO Document 9896 (Manual on the
Aeronautical Telecommunication Network (ATN) using
Internet Protocol Suite (IPS) Standards and Protocol),
Draft Edition 3 (work-in-progress)", December 2020.
[CKSUM] Stone, J., Greenwald, M., Partridge, C., and J. Hughes,
"Performance of Checksums and CRC's Over Real Data, IEEE/
ACM Transactions on Networking, Vol. 6, No. 5", October
1998.
[CRC] Jain, R., "Error Characteristics of Fiber Distributed Data
Interface (FDDI), IEEE Transactions on Communications",
August 1990.
[I-D.ietf-drip-rid]
Moskowitz, R., Card, S. W., Wiethuechter, A., and A.
Gurtov, "UAS Remote ID", draft-ietf-drip-rid-07 (work in
progress), January 2021.
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[I-D.ietf-intarea-tunnels]
Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", draft-ietf-intarea-tunnels-10 (work in
progress), September 2019.
[I-D.ietf-ipwave-vehicular-networking]
(editor), J. (. J., "IPv6 Wireless Access in Vehicular
Environments (IPWAVE): Problem Statement and Use Cases",
draft-ietf-ipwave-vehicular-networking-20 (work in
progress), March 2021.
[I-D.ietf-tsvwg-udp-options]
Touch, J., "Transport Options for UDP", draft-ietf-tsvwg-
udp-options-12 (work in progress), May 2021.
[I-D.templin-6man-aero]
Templin, F. L., "Automatic Extended Route Optimization
(AERO)", draft-templin-6man-aero-01 (work in progress),
April 2021.
[I-D.templin-6man-dhcpv6-ndopt]
Templin, F. L., "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. L., "The IPv6 Link-Local Address Type Field",
draft-templin-6man-lla-type-02 (work in progress),
November 2020.
[I-D.templin-6man-omni-interface]
Templin, F. L. and T. Whyman, "Transmission of IP Packets
over Overlay Multilink Network (OMNI) Interfaces", draft-
templin-6man-omni-interface-99 (work in progress), March
2021.
[IPV4-GUA]
Postel, J., "IPv4 Address Space Registry,
https://www.iana.org/assignments/ipv4-address-space/ipv4-
address-space.xhtml", December 2020.
[IPV6-GUA]
Postel, J., "IPv6 Global Unicast Address Assignments,
https://www.iana.org/assignments/ipv6-unicast-address-
assignments/ipv6-unicast-address-assignments.xhtml",
December 2020.
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[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC1146] Zweig, J. and C. Partridge, "TCP alternate checksum
options", RFC 1146, DOI 10.17487/RFC1146, March 1990,
<https://www.rfc-editor.org/info/rfc1146>.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/info/rfc1191>.
[RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages",
RFC 1256, DOI 10.17487/RFC1256, September 1991,
<https://www.rfc-editor.org/info/rfc1256>.
[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>.
[RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery",
RFC 2923, DOI 10.17487/RFC2923, September 2000,
<https://www.rfc-editor.org/info/rfc2923>.
[RFC2983] Black, D., "Differentiated Services and Tunnels",
RFC 2983, DOI 10.17487/RFC2983, October 2000,
<https://www.rfc-editor.org/info/rfc2983>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330,
DOI 10.17487/RFC3330, September 2002,
<https://www.rfc-editor.org/info/rfc3330>.
[RFC3366] Fairhurst, G. and L. Wood, "Advice to link designers on
link Automatic Repeat reQuest (ARQ)", BCP 62, RFC 3366,
DOI 10.17487/RFC3366, August 2002,
<https://www.rfc-editor.org/info/rfc3366>.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692,
DOI 10.17487/RFC3692, January 2004,
<https://www.rfc-editor.org/info/rfc3692>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, DOI 10.17487/RFC3819, July 2004,
<https://www.rfc-editor.org/info/rfc3819>.
[RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local
Addresses", RFC 3879, DOI 10.17487/RFC3879, September
2004, <https://www.rfc-editor.org/info/rfc3879>.
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[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>.
[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>.
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[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>.
[RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
Version 3 for IPv4 and IPv6", RFC 5798,
DOI 10.17487/RFC5798, March 2010,
<https://www.rfc-editor.org/info/rfc5798>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC6081] Thaler, D., "Teredo Extensions", RFC 6081,
DOI 10.17487/RFC6081, January 2011,
<https://www.rfc-editor.org/info/rfc6081>.
[RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A.
Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221,
DOI 10.17487/RFC6221, May 2011,
<https://www.rfc-editor.org/info/rfc6221>.
[RFC6247] Eggert, L., "Moving the Undeployed TCP Extensions RFC
1072, RFC 1106, RFC 1110, RFC 1145, RFC 1146, RFC 1379,
RFC 1644, and RFC 1693 to Historic Status", RFC 6247,
DOI 10.17487/RFC6247, May 2011,
<https://www.rfc-editor.org/info/rfc6247>.
[RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based
DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355,
DOI 10.17487/RFC6355, August 2011,
<https://www.rfc-editor.org/info/rfc6355>.
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[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>.
[RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for
Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May
2012, <https://www.rfc-editor.org/info/rfc6543>.
[RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization
(AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012,
<https://www.rfc-editor.org/info/rfc6706>.
[RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
UDP Checksums for Tunneled Packets", RFC 6935,
DOI 10.17487/RFC6935, April 2013,
<https://www.rfc-editor.org/info/rfc6935>.
[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, DOI 10.17487/RFC6936, April 2013,
<https://www.rfc-editor.org/info/rfc6936>.
[RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation
with IPv6 Neighbor Discovery", RFC 6980,
DOI 10.17487/RFC6980, August 2013,
<https://www.rfc-editor.org/info/rfc6980>.
[RFC7042] Eastlake 3rd, D. and J. Abley, "IANA Considerations and
IETF Protocol and Documentation Usage for IEEE 802
Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042,
October 2013, <https://www.rfc-editor.org/info/rfc7042>.
[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>.
[RFC7323] Borman, D., Braden, B., Jacobson, V., and R.
Scheffenegger, Ed., "TCP Extensions for High Performance",
RFC 7323, DOI 10.17487/RFC7323, September 2014,
<https://www.rfc-editor.org/info/rfc7323>.
[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<https://www.rfc-editor.org/info/rfc7401>.
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[RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S.,
Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit
Boundary in IPv6 Addressing", RFC 7421,
DOI 10.17487/RFC7421, January 2015,
<https://www.rfc-editor.org/info/rfc7421>.
[RFC7526] Troan, O. and B. Carpenter, Ed., "Deprecating the Anycast
Prefix for 6to4 Relay Routers", BCP 196, RFC 7526,
DOI 10.17487/RFC7526, May 2015,
<https://www.rfc-editor.org/info/rfc7526>.
[RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542,
DOI 10.17487/RFC7542, May 2015,
<https://www.rfc-editor.org/info/rfc7542>.
[RFC7739] Gont, F., "Security Implications of Predictable Fragment
Identification Values", RFC 7739, DOI 10.17487/RFC7739,
February 2016, <https://www.rfc-editor.org/info/rfc7739>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface
Support for IP Hosts with Multi-Access Support", RFC 7847,
DOI 10.17487/RFC7847, May 2016,
<https://www.rfc-editor.org/info/rfc7847>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8726] Farrel, A., "How Requests for IANA Action Will Be Handled
on the Independent Stream", RFC 8726,
DOI 10.17487/RFC8726, November 2020,
<https://www.rfc-editor.org/info/rfc8726>.
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[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8892] Thaler, D. and D. Romascanu, "Guidelines and Registration
Procedures for Interface Types and Tunnel Types",
RFC 8892, DOI 10.17487/RFC8892, August 2020,
<https://www.rfc-editor.org/info/rfc8892>.
[RFC8899] Fairhurst, G., Jones, T., Tuexen, M., Ruengeler, I., and
T. Voelker, "Packetization Layer Path MTU Discovery for
Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
September 2020, <https://www.rfc-editor.org/info/rfc8899>.
[RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
and F. Gont, "IP Fragmentation Considered Fragile",
BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,
<https://www.rfc-editor.org/info/rfc8900>.
[RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves,
"Temporary Address Extensions for Stateless Address
Autoconfiguration in IPv6", RFC 8981,
DOI 10.17487/RFC8981, February 2021,
<https://www.rfc-editor.org/info/rfc8981>.
Appendix A. OAL Checksum Algorithm
The OAL Checksum Algorithm adopts the 8-bit Fletcher Checksum
Algorithm specified in Appendix I of [RFC1146] as also analyzed in
[CKSUM]. [RFC6247] declared [RFC1146] historic for the reason that
the algorithms had never seen widespread use with TCP, however this
document adopts the 8-bit Fletcher algorithm for a different purpose.
Quoting from Appendix I of [RFC1146], the OAL Checksum Algorithm
proceeds as follows:
"The 8-bit Fletcher Checksum Algorithm is calculated over a
sequence of data octets (call them D[1] through D[N]) by
maintaining 2 unsigned 1's-complement 8-bit accumulators A and B
whose contents are initially zero, and performing the following
loop where i ranges from 1 to N:
A := A + D[i]
B := B + A
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It can be shown that at the end of the loop A will contain the
8-bit 1's complement sum of all octets in the datagram, and that B
will contain (N)D[1] + (N-1)D[2] + ... + D[N]."
To calculate the OAL checksum, the above algorithm is applied over
the N-octet concatenation of the OAL pseudo-header, the encapsulated
IP packet and the two-octet trailing checksum field initialized to 0.
Specifically, the algorithm is first applied over the 40 octets of
the OAL pseudo-header as data octets D[1] through D[40], then
continues over the entire length of the original IP packet as data
octets D[41] through D[N-2] and finally concludes with the two
trailing 0 octets as data octets D[N-1] and D[N].
Appendix B. VDL Mode 2 Considerations
ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2"
(VDLM2) that specifies an essential radio frequency data link service
for aircraft and ground stations in worldwide civil aviation air
traffic management. The VDLM2 link type is "multicast capable"
[RFC4861], but with considerable differences from common multicast
links such as Ethernet and IEEE 802.11.
First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of
magnitude less than most modern wireless networking gear. Second,
due to the low available link bandwidth only VDLM2 ground stations
(i.e., and not aircraft) are permitted to send broadcasts, and even
so only as compact layer 2 "beacons". Third, aircraft employ the
services of ground stations by performing unicast RS/RA exchanges
upon receipt of beacons instead of listening for multicast RA
messages and/or sending multicast RS messages.
This beacon-oriented unicast RS/RA approach is necessary to conserve
the already-scarce available link bandwidth. Moreover, since the
numbers of beaconing ground stations operating within a given spatial
range must be kept as sparse as possible, it would not be feasible to
have different classes of ground stations within the same region
observing different protocols. It is therefore highly desirable that
all ground stations observe a common language of RS/RA as specified
in this document.
Note that links of this nature may benefit from compression
techniques that reduce the bandwidth necessary for conveying the same
amount of data. The IETF lpwan working group is considering possible
alternatives: [https://datatracker.ietf.org/wg/lpwan/documents].
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Appendix C. Client-Proxy/Server Isolation Through L2 Address Mapping
Per [RFC4861], IPv6 ND messages may be sent to either a multicast or
unicast link-scoped IPv6 destination address. However, IPv6 ND
messaging should be coordinated between the Client and Proxy/Server
only without invoking other nodes on the *NET. This implies that
Client-Proxy/Server control messaging should be isolated and not
overheard by other nodes on the link.
To support Client-Proxy/Server isolation on some *NET links, Proxy/
Servers can maintain an OMNI-specific unicast L2 address ("MSADDR").
For Ethernet-compatible *NETs, this specification reserves one
Ethernet unicast address TBD3 (see: Section 25). For non-Ethernet
statically-addressed *NETs, MSADDR is reserved per the assigned
numbers authority for the *NET addressing space. For still other
*NETs, MSADDR may be dynamically discovered through other means,
e.g., L2 beacons.
Clients map the L3 addresses of all IPv6 ND messages they send (i.e.,
both multicast and unicast) to MSADDR instead of to an ordinary
unicast or multicast L2 address. In this way, all of the Client's
IPv6 ND messages will be received by Proxy/Servers that are
configured to accept packets destined to MSADDR. Note that multiple
Proxy/Servers on the link could be configured to accept packets
destined to MSADDR, e.g., as a basis for supporting redundancy.
Therefore, Proxy/Servers must accept and process packets destined to
MSADDR, while all other devices must not process packets destined to
MSADDR. This model has well-established operational experience in
Proxy Mobile IPv6 (PMIP) [RFC5213][RFC6543].
Appendix D. Change Log
<< RFC Editor - remove prior to publication >>
Differences from draft-templin-6man-omni-22 to draft-templin-6man-
omni-23:
o Final editorial review pass resulting in multiple changes.
Document now submit for final approval (with reference to rfcdiff
from previous version).
Differences from draft-templin-6man-omni-21 to draft-templin-6man-
omni-22:
o Final editorial review pass resulting in multiple changes.
Document now submit for final approval (with reference to rfcdiff
from previous version).
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Differences from draft-templin-6man-omni-20 to draft-templin-6man-
omni-21:
o Final editorial review pass resulting in multiple changes.
Document now submit for final approval (with reference to rfcdiff
from previous version).
Differences from draft-templin-6man-omni-19 to draft-templin-6man-
omni-20:
o Final editorial review pass resulting in multiple changes.
Document now submit for final approval (with reference to rfcdiff
from previous version).
Differences from draft-templin-6man-omni-18 to draft-templin-6man-
omni-19:
o Final editorial review pass resulting in multiple changes.
Document now submit for final approval (with reference to rfcdiff
from previous version).
Differences from draft-templin-6man-omni-17 to draft-templin-6man-
omni-18:
o Final editorial review pass resulting in multiple changes.
Document now submit for final approval (with reference to rfcdiff
from previous version).
Differences from draft-templin-6man-omni-16 to draft-templin-6man-
omni-17:
o Final editorial review pass resulting in multiple changes.
Document now submit for final approval (with reference to rfcdiff
from previous version).
Differences from draft-templin-6man-omni-15 to draft-templin-6man-
omni-16:
o Final editorial review pass resulting in multiple changes.
Document now submit for final approval.
Differences from draft-templin-6man-omni-14 to draft-templin-6man-
omni-15:
o Text restructuring to remove ambiguities, eliminate extraneous
text and improve readability.
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o Clarified that the OMNI link model is NBMA and that link-scoped
multicast is through iterative unicast.
Differences from draft-templin-6man-omni-13 to draft-templin-6man-
omni-14:
o Brought back the optional two-message exchange feature.
o Added TCP RST flag and new (OPT, PNG) flags to the OMNI option
header.
o Require the OAL node that initiates the symmetric connection to
include its (future) receive window size in the initial SYN.
o Require OAL nodes to select new ISS values that are outside of the
current SND.WND.
o Text clarifications for improved readability.
Differences from draft-templin-6man-omni-12 to draft-templin-6man-
omni-13:
o Complete revision of OAL Identification Window Maintenance section
to incorporate well-known protocol conventions and terminology.
Differences from draft-templin-6man-omni-11 to draft-templin-6man-
omni-12:
o Expanded on details of symmetric window synchronization.
Differences from draft-templin-6man-omni-10 to draft-templin-6man-
omni-11:
o Included an Ordinal Number field in the Compressed Header format
for non-final fragments
o Clarified that the window coordination protocol is based on the
IPv6 ND connectionless protocol using TCP constructs, and not
based on the TCP connection-oriented protocol.
o Removed unneeded fields from the OMNI option header.
Differences from draft-templin-6man-omni-09 to draft-templin-6man-
omni-10:
o Fixed sizing considerations for OMNI option fields.
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o Updated handling of multiple OMNI options in the same IPv6 ND
message. Only the first option includes the header, while all
other options include only sub-options.
Differences from draft-templin-6man-omni-08 to draft-templin-6man-
omni-09:
o Included reference to RFC3366 and updated section on Fragment
Retransmission.
o Added "ordinal number" marking in Fragment Header reserved field.
Differences from draft-templin-6man-omni-07 to draft-templin-6man-
omni-08:
o Included TCP state variables; window scale
Differences from draft-templin-6man-omni-06 to draft-templin-6man-
omni-07:
o Moved Interface Attributes, Type 1 and Type 2 to historic status.
o Incorporated Traffic Selector into Interface Attributes, Type 4.
Differences from draft-templin-6man-omni-05 to draft-templin-6man-
omni-06:
o Adopted TCP as an OAL packet-based connection-oriented protocol.
o Three-Way handshake for establishing symmetric send/receive
windows
o Window length specified, plus "current" and "previous" windows
o New appendix on checksum algorithm, with citations changed
o Security architecture considerations.
o More details on HIP message signatures.
o Require firewalls at OAL destinations.
o Removed "equal-length" requirement for OAL non-final fragments.
Differences from draft-templin-6man-omni-04 to draft-templin-6man-
omni-05:
o Change to S/T-omIndex definition.
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Differences from draft-templin-6man-omni-03 to draft-templin-6man-
omni-04:
o Changed reference citations to "draft-templin-6man-aero".
o Included introductory description of the "6M's".
o Included new OMNI sub-option for PIM-SM.
Differences from draft-templin-6man-omni-02 to draft-templin-6man-
omni-03:
o Added citation of RFC8726.
Differences from draft-templin-6man-omni-01 to draft-templin-6man-
omni-02:
o Updated IANA registration policies for OMNI registries.
Differences from draft-templin-6man-omni-00 to draft-templin-6man-
omni-01:
o Changed intended document status to Informational, and removed
documents from "updates" category.
o Updated implementation status.
o Minor edits to HIP message specifications.
o Clarified OAL and *NET IP header field settings during
encapsulation and re-encapsulation.
Differences from earlier versions to draft-templin-6man-omni-00:
o Established working baseline reference.
Authors' Addresses
Fred L. Templin (editor)
The Boeing Company
P.O. Box 3707
Seattle, WA 98124
USA
Email: fltemplin@acm.org
Templin & Whyman Expires December 6, 2021 [Page 110]
Internet-Draft IPv6 over OMNI Interfaces June 2021
Tony Whyman
MWA Ltd c/o Inmarsat Global Ltd
99 City Road
London EC1Y 1AX
England
Email: tony.whyman@mccallumwhyman.com
Templin & Whyman Expires December 6, 2021 [Page 111]