Network Working Group F. Templin, Ed.
Internet-Draft The Boeing Company
Intended status: Standards Track A. Whyman
Expires: October 24, 2020 MWA Ltd c/o Inmarsat Global Ltd
April 22, 2020

Transmission of IPv6 Packets over Overlay Multilink Network (OMNI) Interfaces


Mobile nodes (e.g., aircraft of various configurations, terrestrial vehicles, seagoing vessels, mobile enterprise devices, etc.) communicate with networked correspondents over multiple access network data links and configure mobile routers to connect end user networks. A multilink interface specification is therefore needed for coordination with the network-based mobility service. This document specifies the transmission of IPv6 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 October 24, 2020.

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Table of Contents

1. Introduction

Mobile Nodes (MNs) (e.g., aircraft of various configurations, terrestrial vehicles, seagoing vessels, mobile enterprise devices, etc.) often have multiple data links for communicating with networked correspondents. These data links may have diverse performance, cost and availability properties that can change dynamically according to mobility patterns, flight phases, proximity to infrastructure, etc. MNs coordinate their data links in a discipline known as "multilink", in which a single virtual interface is configured over the underlying data links.

The MN configures a virtual interface (termed the "Overlay Multilink Network (OMNI) interface") as a thin layer over the underlying Access Network (ANET) interfaces. The OMNI interface is therefore the only interface abstraction exposed to the IPv6 layer and behaves according to the Non-Broadcast, Multiple Access (NBMA) interface principle, while underlying interfaces appear as link layer communication channels in the architecture. The OMNI interface connects to a virtual overlay service known as the "OMNI link". The OMNI link spans a worldwide Internetwork that may include private-use infrastructures and/or the global public Internet itself.

Each MN receives a Mobile Network Prefix (MNP) for numbering downstream-attached End User Networks (EUNs) independently of the access network data links selected for data transport. The MN performs router discovery over the OMNI interface (i.e., similar to IPv6 customer edge routers [RFC7084]) and acts as a mobile router on behalf of its EUNs. The router discovery process is iterated over each of the OMNI interface's underlying interfaces in order to register per-link parameters (see Section 12).

The OMNI interface provides a multilink nexus for exchanging inbound and outbound traffic via the correct underlying interface(s). The IPv6 layer sees the OMNI interface as a point of connection to the OMNI link. Each OMNI link has one or more associated Mobility Service Prefixes (MSPs) from which OMNI link MNPs are derived. If there are multiple OMNI links, the IPv6 layer will see multiple OMNI interfaces.

The OMNI interface interacts with a network-based Mobility Service (MS) through IPv6 Neighbor Discovery (ND) control message exchanges [RFC4861]. The MS provides Mobility Service Endpoints (MSEs) that track MN movements and represent their MNPs in a global routing or mapping system.

This document specifies the transmission of IPv6 packets [RFC8200] and MN/MS control messaging over OMNI interfaces.

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. Also, 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 defined in [RFC4291] (with Link-Local scope assumed).

The following terms are defined within the scope of this document:

Mobile Node (MN)

an end system with multiple distinct upstream data link connections that are managed together as a single logical unit. The MN's data link connection parameters can change over time due to, e.g., node mobility, link quality, etc. The MN further connects a downstream-attached End User Network (EUN). The term MN used here is distinct from uses in other documents, and does not imply a particular mobility protocol.
End User Network (EUN)

a simple or complex downstream-attached mobile network that travels with the MN as a single logical unit. The IPv6 addresses assigned to EUN devices remain stable even if the MN's upstream data link connections change.
Mobility Service (MS)

a mobile routing service that tracks MN movements and ensures that MNs remain continuously reachable even across mobility events. Specific MS details are out of scope for this document.
Mobility Service Endpoint (MSE)

an entity in the MS (either singluar or aggregate) that coordinates the mobility events of one or more MN.
Mobility Service Prefix (MSP)

an aggregated IPv6 prefix (e.g., 2001:db8::/32) advertised to the rest of the Internetwork by the MS, and from which more-specific Mobile Network Prefixes (MNPs) are derived.
Mobile Network Prefix (MNP)

a longer IPv6 prefix taken from an MSP (e.g., 2001:db8:1000:2000::/56) and assigned to a MN. MNs sub-delegate the MNP to devices located in EUNs.
Access Network (ANET)

a data link service network (e.g., an aviation radio access network, satellite service provider network, cellular operator network, wifi network, etc.) that connects MNs. Physical and/or data link level security between the MN and ANET are assumed.
Access Router (AR)

a first-hop router in the ANET for connecting MNs to correspondents in outside Internetworks.
ANET interface

a MN's attachment to a link in an ANET.
Internetwork (INET)

a connected network region with a coherent IP addressing plan that provides transit forwarding services for ANET MNs and INET correspondents. Examples include private enterprise networks, ground domain aviation service networks and the global public Internet itself.
INET interface

a node's attachment to a link in an INET.
OMNI link

a virtual overlay configured over one or more INETs and their connected ANETs. An OMNI link can comprise multiple INET segments joined by bridges the same as for any link; the addressing plans in each segment may be mutually exclusive and managed by different administrative entities.
OMNI interface

a node's attachment to an OMNI link, and configured over one or more underlying ANET/INET interfaces.
OMNI link local address (LLA)

an IPv6 link-local address constructed as specified in Section 7, and assigned to an OMNI interface.
OMNI Option

an IPv6 Neighbor Discovery option providing multilink parameters for the OMNI interface as specified in Section 9.

an OMNI interface's manner of managing diverse underlying data link interfaces as a single logical unit. The OMNI interface provides a single unified interface to upper layers, while underlying data link selections are performed on a per-packet basis considering factors such as DSCP, flow label, application policy, signal quality, cost, etc. Multilinking decisions are coordinated in both the outbound (i.e. MN to correspondent) and inbound (i.e., correspondent to MN) directions.

The second layer in the OSI network model. Also known as "layer-2", "link-layer", "sub-IP layer", "data link layer", etc.

The third layer in the OSI network model. Also known as "layer-3", "network-layer", "IPv6 layer", etc.
underlying interface

an ANET/INET interface over which an OMNI interface is configured. The OMNI interface is seen as a L3 interface by the IP layer, and each underlying interface is seen as a L2 interface by the OMNI interface.
Mobility Service Identification (MSID)

Each MSE and AR is assigned a unique 32-bit Identification (MSID) as specified in Section 7.
Spanning Partitioned Administrative Networks (SPAN)

A means for bridging disjoint INET partitions as segments of a unified OMNI link the same as for a bridged campus LAN. The SPAN is a mid-layer IPv6 encapsulation service that supports a unified OMNI link view for all segments.

3. Requirements

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119][RFC8174] when, and only when, they appear in all capitals, as shown here.

An implementation is not required to internally use the architectural constructs described here so long as its external behavior is consistent with that described in this document.

4. Overlay Multilink Network (OMNI) Interface Model

An OMNI interface is a MN virtual interface configured over one or more underlying interfaces, which may be physical (e.g., an aeronautical radio link) or virtual (e.g., an Internet or higher-layer "tunnel"). The MN receives a MNP from the MS, and coordinates with the MS through IPv6 ND message exchanges. The MN uses the MNP to construct a unique OMNI LLA through the algorithmic derivation specified in Section 7 and assigns the LLA to the OMNI interface.

The OMNI interface architectural layering model is the same as in [RFC7847], and augmented as shown in Figure 1. The IP layer therefore sees the OMNI interface as a single L3 interface with multiple underlying interfaces that appear as L2 communication channels in the architecture.

                                  |    Upper Layer Protocol    |
           Session-to-IP    +---->|                            |
           Address Binding  |     +----------------------------+
                            +---->|           IP (L3)          |
           IP Address       +---->|                            |
           Binding          |     +----------------------------+
                            +---->|       OMNI Interface       |
           Logical-to-      +---->|         (OMNI LLA)         |
           Physical         |     +----------------------------+
           Interface        +---->|  L2  |  L2  |       |  L2  |
           Binding                |(IF#1)|(IF#2)| ..... |(IF#n)|
                                  +------+------+       +------+
                                  |  L1  |  L1  |       |  L1  |
                                  |      |      |       |      |
                                  +------+------+       +------+

Figure 1: OMNI Interface Architectural Layering Model

The OMNI virtual interface model gives rise to a number of opportunities:


Other opportunities are discussed in

Figure 2 depicts the architectural model for a MN connecting to the MS via multiple independent ANETs. When an underlying interface becomes active, the MN's OMNI interface sends native (i.e., unencapsulated) IPv6 ND messages via the underlying interface. IPv6 ND messages traverse the ground domain ANETs until they reach an Access Router (AR#1, AR#2, .., AR#n). The AR then coordinates with a Mobility Service Endpoint (MSE#1, MSE#2, ..., MSE#m) in the INET and returns an IPv6 ND message response to the MN. IPv6 ND messages traverse the ANET at layer 2; hence, the Hop Limit is not decremented.

                        |      MN      |
                        |OMNI interface|
               +--------|IF#1|IF#2|IF#n|------ +
              /         +----+----+----+        \
             /                 |                 \
            /    <---- Native  |  IP ---->        \
           v                   v                   v
        (:::)-.              (:::)-.              (:::)-.
   .-(::ANET:::)        .-(::ANET:::)        .-(::ANET:::)
     `-(::::)-'           `-(::::)-'           `-(::::)-'
       +----+               +----+               +----+
 ...   |AR#1|  ..........   |AR#2|   .........   |AR#n|  ...
.      +-|--+               +-|--+               +-|--+     .
.        |                    |                    |
.        v                    v                    v        .
.               <-----  Encapsulation ----->                .
.                                                           .
.      +-----+               (:::)-.                        .
.      |MSE#2|           .-(::::::::)          +-----+      .
.      +-----+       .-(:::   INET  :::)-.     |MSE#m|      .
.                  (:::::    Routing  ::::)    +-----+      .
.                     `-(::: System :::)-'                  .
.  +-----+                `-(:::::::-'                      .
.  |MSE#1|          +-----+               +-----+           .
.  +-----+          |MSE#3|               |MSE#4|           .
.                   +-----+               +-----+           .
.                                                           .
.                                                           .
.       <----- Worldwide Connected Internetwork ---->       .

Figure 2: MN/MS Coordination via Multiple ANETs

After the initial IPv6 ND message exchange, the MN can send and receive unencapsulated IPv6 data packets over the OMNI interface. OMNI interface multilink services will forward the packets via ARs in the correct underlying ANETs. The AR encapsulates the packets according to the capabilities provided by the MS and forwards them to the next hop within the worldwide connected Internetwork via optimal routes.

OMNI links span the underlying Internetwork via a mid-layer overlay known as "The SPAN" - see Section 8. Each OMNI link corresponds to a different SPAN overlay which may be carried over a completely separate Internetwork topology and/or differentiated by a SPAN header codepoint. The same as for VLANs, each MN can connect to multiple OMNI links (i.e., multipe SPANs) by configuring a distinct OMNI interface for each link.

5. Maximum Transmission Unit (MTU) and Fragmentation

All IPv6 interfaces are REQUIRED to configure a minimum Maximum Transmission Unit (MTU) of 1280 bytes [RFC8200]. The network therefore MUST forward packets of at least 1280 bytes without generating an IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) message [RFC8201].

The OMNI interface configures an MTU of 9180 bytes [RFC2492]; the size is therefore not a reflection of the underlying interface MTUs, but rather determines the largest packet the OMNI interface can forward or reassemble. The OMNI interface therefore accommodates IP packets up to 9180 bytes while generating IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) messages [RFC8201] as necessary (see below).

OMNI interfaces employ mid-layer IPv6 encapsulation and fragmentation/reassembly per [RFC2473] (also known as "SPAN encapsulation" - see Section 8) to accommodate the 9180 byte MTU. The OMNI interface returns internally-generated PTB messages for packets admitted into the interface that it deems too large (e.g., according to link performance characteristics, reassembly cost, etc.) while either dropping or forwarding the packet as necessary. The OMNI interface performs PMTUD even if the destination appears to be on the same link since an OMNI link node on the path may return a PTB. This ensures that the path MTU is adaptive and reflects the current path used for a given data flow.

OMNI interfaces perform SPAN encapsulation and fragmentation/reassembly as follows:

In order to avoid a "tiny fragment" attack, OMNI interfaces unconditionally drop all SPAN fragments smaller than 640 bytes. In order to set the correct context for reassembly, the OMNI interface that inserts a SPAN header MUST also be the one that inserts the IPv6 Fragment Header Identification value. Although all fragmnets of the same fragmented SPAN packet are typically sent via the same underlying interface, this is not strictly required since all fragments will arrive at the OMNI interface that performs reassembly even if they travel over different paths.

Note that the OMNI interface can forward large packets via encapsulation and fragmentation while at the same time returning advisory PTB messages, e.g., subject to rate limiting. The receiving node that performs reassembly can also send advisory PTB messages if reassembly conditions become unfavorable. The AERO interface can therefore continuously forward large packets without loss while returning advisory messages recommending a smaller size (but no smaller than 1280). Advisory PTB messages are differentiated from PTB messages that report loss by setting the Code field in the ICMPv6 message header to the value 1. This document therefore updates [RFC4443] and [RFC8201].

6. Frame Format

The OMNI interface transmits IPv6 packets according to the native frame format of each underlying interface. For example, for Ethernet-compatible interfaces the frame format is specified in [RFC2464], for aeronautical radio interfaces the frame format is specified in standards such as ICAO Doc 9776 (VDL Mode 2 Technical Manual), for tunnels over IPv6 the frame format is specified in [RFC2473], etc.

7. Link-Local Addresses

OMNI interfaces assign IPv6 Link-Local Addresses (i.e., "OMNI LLAs") using the following constructs:

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 above OMNI LLA constructs.

Since MN OMNI LLAs are based on the distribution of administratively assured unique MNPs, and since MS OMNI LLAs are guaranteed unique through administrative assignment, OMNI interfaces set the autoconfiguration variable DupAddrDetectTransmits to 0 [RFC4862].

8. The SPAN

OMNI links employ an overlay network instance called "The SPAN" (Spanning Partitioned Administrative Networks) that supports forwarding of encapsulated link-scoped messages over an IPv6 overlay routing instance that spans the entire link without decrementing the (link-local) Hop Limit. The OMNI link reserves the Unique Local Address (ULA) prefix fd80::/10 [RFC4193] used for mapping OMNI LLAs to routable SPAN addresses.

SPAN addresses are configured in one-to-one correspondence with MN/MS OMNI LLAs through stateless translation of the prefix. For example, for the SPAN sub-prefix fd80::/16:

The SPAN address presents an IPv6 address format that is routable within the OMNI link routing system and can be used to convey link-scoped messages across multiple hops using IPv6 encapsulation [RFC2473]. The SPAN extends over the entire OMNI link to include all ARs and MSEs. All MNs are also consideed to be "on the SPAN", however SPAN encapsulation is omitted over ANET links when possible to conserve bandwidth (see: Section 11).

The SPAN allows the OMNI link to be subdivided into "segments" that often correspond to administrative domains or physical partitions. OMNI nodes can use IPv6 Segment Routing [RFC8754][RFC8402] when necessary to support efficient packet forwarding to destinations located in other SPAN segments. A full discussion of Segment Routing over the SPAN appears in [I-D.templin-intarea-6706bis].

9. Address Mapping - Unicast

OMNI interfaces maintain a neighbor cache for tracking per-neighbor state and use the link-local address format specified in Section 7. IPv6 Neighbor Discovery (ND) [RFC4861] messages on MN OMNI interfaces observe the native Source/Target Link-Layer Address Option (S/TLLAO) formats of the underlying interfaces (e.g., for Ethernet the S/TLLAO is specified in [RFC2464]).

MNs such as aircraft typically have many wireless data link types (e.g. satellite-based, cellular, terrestrial, air-to-air directional, etc.) with diverse performance, cost and availability properties. The OMNI interface would therefore appear to have multiple L2 connections, and may include information for multiple underlying interfaces in a single IPv6 ND message exchange.

OMNI interfaces use an IPv6 ND option called the "OMNI option" formatted as shown in Figure 3:

      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    | Prefix Length |R|   Reserved  |
     |                                                               |
     ~                          Sub-Options                          ~
     |                                                               |

Figure 3: OMNI Option Format

9.1. Sub-Options

      0                   1                   2  
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5  
     |   Sub-Type    |  Sub-length   | Sub-Option Data ...  

Figure 4: Sub-Option Format

     Option Name            Sub-Type
     Pad1                        0
     PadN                        1
     ifIndex-tuple (Type 1)      2
     ifIndex-tuple (Type 2)      3
     MS-Register                 4
     MS-Release                  5

Figure 5

The OMNI option includes zero or more Sub-Options, some of which may appear multiple times in the same message. Each consecutive Sub-Option is concatenated immediately after its predecessor. All Sub-Options except Pad1 (see below) are type-length-value (TLV) encoded in the following format:

During processing, unrecognized Sub-Options are ignored and the next Sub-Option processed until the end of the OMNI option.

The following Sub-Option types and formats are defined in this document:

9.1.1. Pad1

      0 1 2 3 4 5 6 7 
     |   Sub-Type=0  |

Figure 6: Pad1

9.1.2. PadN

      0                   1                   2
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
     |   Sub-Type=1  |Sub-length=N-2 | N-2 padding bytes ...

Figure 7: PadN

9.1.3. ifIndex-tuple (Type 1)

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |   Sub-Type=2  | Sub-length=4+N|    ifIndex    |    ifType     |
     |  Provider ID  | Link  |S|I|RSV| Bitmap(0)=0xff|P00|P01|P02|P03|
     |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff|
     |P32|P33|P34|P35|P36|P37|P38|P39| ...

Figure 8: ifIndex-tuple (Type 1)

     |   Index=i     |   Bitmap(i)   |P[*] values ...

Figure 9

9.1.4. ifIndex-tuple (Type 2)

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |   Sub-Type=3  | Sub-length=4+N|    ifIndex    |    ifType     |
     |  Provider ID  | Link  |S|Resvd|                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               ~
     ~                                                               ~
     ~                RFC 6088 Format Traffic Selector               ~
     ~                                                               ~

Figure 10: ifIndex-tuple (Type 2)

9.1.5. MS-Register

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |   Sub-Type=4  | Sub-length=4  |        MSID (bits 0 - 15)     |
     |      MSID (bits 16 - 32)      |

Figure 11: MS-Register Sub-option

9.1.6. 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
     |   Sub-Type=5  | Sub-length=4  |        MSID (bits 0 - 15)     |
     |      MSID (bits 16 - 32)      |

Figure 12: MS-Release Sub-option

10. Address Mapping - Multicast

The multicast address mapping of the native underlying interface applies. The mobile router on board the aircraft also serves as an IGMP/MLD Proxy for its EUNs and/or hosted applications per [RFC4605] while using the L2 address of the router as the L2 address for all multicast packets.

11. Conceptual Sending Algorithm

The MN's IPv6 layer selects the outbound OMNI interface according to standard IPv6 requirements when forwarding data packets from local or EUN applications to external correspondents. The OMNI interface maintains a neighbor cache the same as for any IPv6 interface, but with additional state for multilink coordination.

After a packet enters the OMNI interface, an outbound underlying interface is selected based on multilink parameters such as DSCP, application port number, cost, performance, message size, etc. OMNI interface multilink selections could also be configured to perform replication across multiple underlying interfaces for increased reliability at the expense of packet duplication.

When an OMNI interface sends a packet over a selected outbound underlying interface, it omits SPAN encapsulation if the packet does not require fragmentation and the neighbor can determine the SPAN addresses through other means (e.g., the packet's destination, neighbor cache information, etc.). Otherwise, the OMNI interface inserts a SPAN header and performs fragmentation if necessary.

OMNI interface multilink service designers MUST observe the BCP guidance in Section 15 [RFC3819] in terms of implications for reordering when packets from the same flow may be spread across multiple underlying interfaces having diverse properties.

11.1. Multiple OMNI Interfaces

MNs may associate with multiple MS instances concurrently. Each MS instance represents a distinct OMNI link distinguished by its associated MSPs. The MN configures a separate OMNI interface for each link so that multiple interfaces (e.g., omni0, omni1, omni2, etc.) are exposed to the IPv6 layer.

Depending on local policy and configuration, an MN may choose between alternative active OMNI interfaces using a packet's DSCP, routing information or static configuration. Interface selection based on per-packet source addresses is also enabled when the MSPs for each OMNI interface are known (e.g., discovered through Prefix Information Options (PIOs) and/or Route Information Options (RIOs)).

Each OMNI interface can be configured over the same or different sets of underlying interfaces. Each ANET distinguishes between the different OMNI links based on the MSPs represented in per-packet IPv6 addresses.

Multiple distinct OMNI links can therefore be used to support fault tolerance, load balancing, reliability, etc. The architectural model parallels Layer 2 Virtual Local Area Networks (VLANs), where the MSPs serve as (virtual) VLAN tags.

12. Router Discovery and Prefix Registration

MNs interface with the MS by sending RS messages with OMNI options under the assumption that a single AR on the ANET will proocess the message and respond. This places a requirement on each ANET, which may be enforced by physical/logical partitioning, L2 AR beaconing, etc. The manner in which the ANET ensures single AR coordination is link-specific and outside the scope of this document.

For each underlying interface, the MN sends an RS message with an OMNI option with prefix registration information, ifIndex-tuples, MS-Register/Release suboptions containing MSIDs, and with destination address set to All-Routers multicast (ff02::2) [RFC4291]. Example MSID discovery methods are given in [RFC5214], including data link login parameters, name service lookups, static configuration, etc. Alternatively, MNs can discover indiviual MSIDs by sending an initial RS with MS-Register MSID set to 0x00000000.

MNs configure OMNI interfaces that observe the properties discussed in the previous section. The OMNI interface and its underlying interfaces are said to be in either the "UP" or "DOWN" state according to administrative actions in conjunction with the interface connectivity status. An OMNI interface transitions to UP or DOWN through administrative action and/or through state transitions of the underlying interfaces. When a first underlying interface transitions to UP, the OMNI interface also transitions to UP. When all underlying interfaces transition to DOWN, the OMNI interface also transitions to DOWN.

When an OMNI interface transitions to UP, the MN sends RS messages to register its MNP and an initial set of underlying interfaces that are also UP. The MN sends additional RS messages to refresh lifetimes and to register/deregister underlying interfaces as they transition to UP or DOWN. The MN sends initial RS messages over an UP underlying interface with its OMNI LLA as the source and with destination set to All-Routers multicast. The RS messages include an OMNI option per Section 9 with valid prefix registration information, ifIndex-tuples appropriate for underlying interfaces and MS-Register/Release sub-options.

ARs process IPv6 ND messages with OMNI options and act as a proxy for MSEs. ARs receive RS messages and create a neighbor cache entry for the MN, then coordinate with any named MSIDs in a manner outside the scope of this document. The AR returns an RA message with destination address set to the MN OMNI LLA (i.e., unicast), with source address set to its MS OMNI LLA, with the P(roxy) bit set in the RA flags [RFC4389], with an OMNI option with valid prefix registration information, ifIndex-tuples, MS-Register/Release sub-options, and with any information for the link that would normally be delivered in a solicited RA message. ARs return RA messages with configuration information in response to a MN's RS messages. The AR sets the RA Cur Hop Limit, M and O flags, Router Lifetime, Reachable Time and Retrans Timer values, and includes any necessary options such as:

The AR coordinates with each Register/Release MSID then sends an immediate unicast RA response without delay; therefore, the IPv6 ND MAX_RA_DELAY_TIME and MIN_DELAY_BETWEEN_RAS constants for multicast RAs do not apply. The AR MAY send periodic and/or event-driven unsolicited RA messages according to the standard [RFC4861].

When the MSE processes the OMNI information, it first validates the prefix registration information. The MSE then injects/withdraws the MNP in the routing/mapping system and caches/discards the new Prefix Length, MNP and ifIndex-tuples. The MSE then informs the AR of registration success/failure, and the AR adds the MSE to the list of Register/Release MSIDs to return in an RA message OMNI option per Section 9.

When the MN receives the RA message, it creates an OMNI interface neighbor cache entry with the AR's address as an L2 address and records the MSIDs that have confirmed MNP registration via this AR. If the MN connects to multiple ANETs, it establishes additional AR L2 addresses (i.e., as a Multilink neighbor). The MN then manages its underlying interfaces according to their states as follows:

The MN is responsible for retrying each RS exchange up to MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL seconds until an RA is received. If no RA is received over a an UP underlying interface, the MN declares this underlying interface as DOWN.

The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. Therefore, when the IPv6 layer sends an RS message the OMNI interface returns an internally-generated RA message as though the message originated from an IPv6 router. The internally-generated RA message contains configuration information that is consistent with the information received from the RAs generated by the MS. Whether the OMNI interface IPv6 ND messaging process is initiated from the receipt of an RS message from the IPv6 layer is an implementation matter. Some implementations may elect to defer the IPv6 ND messaging process until an RS is received from the IPv6 layer, while others may elect to initiate the process proactively.

Note: The Router Lifetime value in RA messages indicates the time before which the MN must send another RS message over this underlying interface (e.g., 600 seconds), however that timescale may be significantly longer than the lifetime the MS has committed to retain the prefix registration (e.g., REACHABLETIME seconds). ARs are therefore responsible for keeping MS state alive on a shorter timescale than the MN is required to do on its own behalf.

13. Secure Redirection

If the ANET link model is multiple access, the AR is responsible for assuring that address duplication cannot corrupt the neighbor caches of other nodes on the link. When the MN sends an RS message on a multiple access ANET link, the AR verifys that the MN is authorized to use the address and returns an RA with a non-zero Router Lifetime only if the MN is authorized.

After verifying MN authorization and returning an RA, the AR MAY return IPv6 ND Redirect messages to direct MNs located on the same ANET link to exchange packets directly without transiting the AR. In that case, the MNs can exchange packets according to their unicast L2 addresses discovered from the Redirect message instead of using the dogleg path through the AR. In some ANET links, however, such direct communications may be undesirable and continued use of the dogleg path through the AR may provide better performance. In that case, the AR can refrain from sending Redirects, and/or MNs can ignore them.

14. AR and MSE Resilience

ANETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) [RFC5798] configurations so that service continuity is maintained even if one or more ARs fail. Using VRRP, the MN is unaware which of the (redundant) ARs is currently providing service, and any service discontinuity will be limited to the failover time supported by VRRP. Widely deployed public domain implementations of VRRP are available.

MSEs SHOULD use high availability clustering services so that multiple redundant systems can provide coordinated response to failures. As with VRRP, widely deployed public domain implementations of high availability clustering services are available. Note that special-purpose and expensive dedicated hardware is not necessary, and public domain implementations can be used even between lightweight virtual machines in cloud deployments.

15. Detecting and Responding to MSE Failures

In environments where fast recovery from MSE failure is required, ARs SHOULD use proactive Neighbor Unreachability Detection (NUD) in a manner that parallels Bidirectional Forwarding Detection (BFD) [RFC5880] to track MSE reachability. ARs can then quickly detect and react to failures so that cached information is re-established through alternate paths. Proactive NUD control messaging is carried only over well-connected ground domain networks (i.e., and not low-end ANET links such as aeronautical radios) and can therefore be tuned for rapid response.

ARs perform proactive NUD for MSEs for which there are currently active MNs on the ANET. If an MSE fails, ARs can quickly inform MNs of the outage by sending multicast RA messages on the ANET interface. The AR sends RA messages to the MN via the ANET interface with an OMNI option with a Release ID for the failed MSE, and with destination address set to All-Nodes multicast (ff02::1) [RFC4291].

The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays [RFC4861]. Any MNs on the ANET interface that have been using the (now defunct) MSE will receive the RA messages and associate with a new MSE.

16. Transition Considerations

When a MN connects to an ANET link for the first time, it sends an RS message with an OMNI option. If the first hop AR recognizes the option, it returns an RA with its MS OMNI LLA as the source, the MN OMNI LLA as the destination, the P(roxy) bit set in the RA flags and with an OMNI option included. The MN then engages the AR according to the OMNI link model specified above. If the first hop AR is a legacy IPv6 router, however, it instead returns an RA message with no OMNI option and with a non-OMNI unicast source LLA as specified in [RFC4861]. In that case, the MN engages the ANET according to the legacy IPv6 link model and without the OMNI extensions specified in this document.

If the ANET link model is multiple access, there must be assurance that address duplication cannot corrupt the neighbor caches of other nodes on the link. When the MN sends an RS message on a multiple access ANET link with an OMNI LLA source address and an OMNI option, ARs that recognize the option ensure that the MN is authorized to use the address and return an RA with a non-zero Router Lifetime only if the MN is authorized. ARs that do not recognize the option instead return an RA that makes no statement about the MN's authorization to use the source address. In that case, the MN should perform Duplicate Address Detection to ensure that it does not interfere with other nodes on the link.

An alternative approach for multiple access ANET links to ensure isolation for MN / AR communications is through L2 address mappings as discussed in Appendix C. This arrangement imparts a (virtual) point-to-point link model over the (physical) multiple access link.

17. OMNI Interfaces on the Open Internet

OMNI interfaces that connect to the open Internet via INET interfaces can apply symmetric security services such as VPNs to establish secured tunnels to MSEs. In environments where an explicit VPN may be too restrictive, OMNI interfaces can instead ensure neighbor cache integrity using SEcure Neighbor Discovery (SEND) [RFC3971] and Cryptographically Generated Addresses (CGAs) [RFC3972].

When SEND/CGA are used, the IPv6 ND control plane messages used to establish neighbor cache state are authenticated while data plane messages are delivered the same as for ordinary best-effort Internet traffic. Instead, data plane communications via OMNI interfaces that connect over the open Internet without an explicit VPN must emply transport- or higher-layer security to ensure integrity and/or confidentiality.

In addition to secured OMNI interface RS/RA exchanges, SEND/CGA supports safe address resolution and neighbor unreachability detection as discused in Asymmetric Extended Route Optimization (AERO) [I-D.templin-intarea-6706bis]. This allows for efficient multilink operations over the open Internet with assured neighbor cache integrity.

OMNI interfaces in the open Internet are often located behind Network Address Translators (NATs). The OMNI interface accommodates NAT traversal using the OMNI LLA prefix fe80::/32 for Teredo IPv6 addresses formatted as discussed in Section 4 of [RFC4380]. Further specifications for NAT traversal are discussed in [I-D.templin-intarea-6706bis][RFC6081][RFC4380].

18. Time-Varying MNPs

In some use cases, it is desireable, beneficial and efficient for the MN to receive a contstant MNP that travels with the MN wherever it moves. For example, this would allow air traffic controllers to easily track aircraft, etc. In other cases, however (e.g., intelligent transportation systems), the MN may be willing to sacrifice a modicum of efficiency in order to have time-varying MNPs that can be changed every so often to defeat adversarial tracking.

Prefix delegation services such as those discussed in [I-D.templin-6man-dhcpv6-ndopt] and [I-D.templin-intarea-6706bis] allow OMNI MNs that desire time-varying MNPs to obtain short-lived prefixes. In that case, the identity of the MN would not be bound to the MNP but rather to the prefix delegation ID and used as the seed for Prefix Delegation. The MN would then be obligated to renumber its internal networks whenever its MNP (and therefore also its OMNI address) changes. This should not present a challenge for MNs with automated network renumbering services, however presents limits for the durations of ongoing sessions that would prefer to use a constant address.

19. IANA Considerations

The IANA is instructed to allocate an official Type number TBD from the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI option. Implementations set Type to 253 as an interim value [RFC4727].

The IANA is instructed to allocate one Ethernet unicast address TBD2 (suggest 00-00-5E-00-52-14 [RFC5214]) in the registry "IANA Ethernet Address Block - Unicast Use".

The OMNI option also defines an 8-bit Sub-Type field, for which IANA is instructed to create and maintain a new registry entitled "OMNI option Sub-Type values". Initial values for the OMNI option Sub-Type values registry are given below; future assignments are to be made through Expert Review [RFC8126].

   Value    Sub-Type name              Reference  
   -----    -------------              ----------  
   0        Pad1                       [RFCXXXX]  
   1        PadN                       [RFCXXXX]  
   2        ifIndex-tuple (Type 1)     [RFCXXXX]
   3        ifIndex-tuple (Type 2)     [RFCXXXX]  
   4        MS-Register                [RFCXXXX]
   5        MS-Release                 [RFCXXXX]
   6-252    Unassigned  
   253-254  Experimental               [RFCXXXX]  
   255      Reserved                   [RFCXXXX]

Figure 13: OMNI Option Sub-Type Values

20. Security Considerations

Security considerations for IPv6 [RFC8200] and IPv6 Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages SHOULD include Nonce and Timestamp options [RFC3971] when synchronized transaction confirmation is needed.

OMNI interfaces configured over secured underlying ANET interfaces inherit the physical and/or link-layer security aspects of the connected ANETs. OMNI interfaces configured over open Internet interfaces must use symmetric securing services such as VPNs or asymmetric services such as SEND/CGA [RFC3971][RFC3972].

Security considerations for specific access network interface types are covered under the corresponding IP-over-(foo) specification (e.g., [RFC2464], [RFC2492], etc.).

21. Acknowledgements

The first version of this document was prepared per the consensus decision at the 7th Conference of the International Civil Aviation Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 2019. Consensus to take the document forward to the IETF was reached at the 9th Conference of the Mobility Subgroup on November 22, 2019. Attendees and contributors included: Guray Acar, Danny Bharj, Francois D´Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, Fryderyk Wrobel and Dongsong Zeng.

The following individuals are acknowledged for their useful comments: Michael Matyas, Madhu Niraula, Greg Saccone, Stephane Tamalet, Eric Vyncke. Pavel Drasil, Zdenek Jaron and Michal Skorepa are recognized for their many helpful ideas and suggestions.

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.

22. References

22.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[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.
[RFC3971] Arkko, J., Kempf, J., Zill, B. and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, DOI 10.17487/RFC3971, March 2005.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", RFC 3972, DOI 10.17487/RFC3972, March 2005.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, November 2005.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006.
[RFC4443] Conta, A., Deering, S. and M. Gupta, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", STD 89, RFC 4443, DOI 10.17487/RFC4443, March 2006.
[RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers", RFC 4727, DOI 10.17487/RFC4727, November 2006.
[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.
[RFC4862] Thomson, S., Narten, T. and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, DOI 10.17487/RFC4862, September 2007.
[RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H. and N. Montavont, "Traffic Selectors for Flow Bindings", RFC 6088, DOI 10.17487/RFC6088, January 2011.
[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.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017.
[RFC8201] McCann, J., Deering, S., Mogul, J. and R. Hinden, "Path MTU Discovery for IP version 6", STD 87, RFC 8201, DOI 10.17487/RFC8201, July 2017.

22.2. Informative References

[I-D.templin-6man-dhcpv6-ndopt] Templin, F., "A Unified Stateful/Stateless Configuration Service for IPv6", Internet-Draft draft-templin-6man-dhcpv6-ndopt-09, January 2020.
[I-D.templin-intarea-6706bis] Templin, F., "Asymmetric Extended Route Optimization (AERO)", Internet-Draft draft-templin-intarea-6706bis-45, April 2020.
[RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, December 1998.
[RFC2492] Armitage, G., Schulter, P. and M. Jork, "IPv6 over ATM Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999.
[RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers Considered Useful", BCP 82, RFC 3692, DOI 10.17487/RFC3692, January 2004.
[RFC3819] Karn, P., 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.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through Network Address Translations (NATs)", RFC 4380, DOI 10.17487/RFC4380, February 2006.
[RFC4389] Thaler, D., Talwar, M. and C. Patel, "Neighbor Discovery Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 2006.
[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.
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K. and B. Patil, "Proxy Mobile IPv6", RFC 5213, DOI 10.17487/RFC5213, August 2008.
[RFC5214] Templin, F., Gleeson, T. and D. Thaler, "Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, DOI 10.17487/RFC5214, March 2008.
[RFC5798] Nadas, S., "Virtual Router Redundancy Protocol (VRRP) Version 3 for IPv4 and IPv6", RFC 5798, DOI 10.17487/RFC5798, March 2010.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010.
[RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, DOI 10.17487/RFC6081, January 2011.
[RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 2012.
[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.
[RFC7421] Carpenter, B., 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.
[RFC7847] Melia, T. and S. Gundavelli, "Logical-Interface Support for IP Hosts with Multi-Access Support", RFC 7847, DOI 10.17487/RFC7847, May 2016.
[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.
[RFC8402] Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S. and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018.
[RFC8754] Filsfils, C., Dukes, D., Previdi, S., Leddy, J., Matsushima, S. and D. Voyer, "IPv6 Segment Routing Header (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020.

Appendix A. Type 1 ifIndex-tuple Traffic Classifier Preference Encoding

Adaptation of the OMNI option Type 1 ifIndex-tuple's traffic classifier Bitmap to specific Internetworks such as the Aeronautical Telecommunications Network with Internet Protocol Services (ATN/IPS) may include link selection preferences based on other traffic classifiers (e.g., transport port numbers, etc.) in addition to the existing DSCP-based preferences. Nodes on specific Internetworks maintain a map of traffic classifiers to additional P[*] preference fields beyond the first 64. For example, TCP port 22 maps to P[67], TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc.

Implementations use Simplex or Indexed encoding formats for P[*] encoding in order to encode a given set of traffic classifiers in the most efficient way. Some use cases may be more efficiently coded using Simplex form, while others may be more efficient using Indexed. Once a format is selected for preparation of a single ifIndex-tuple the same format must be used for the entire Sub-Option. Different Sub-Options may use different formats.

The following figures show coding examples for various Simplex and Indexed formats:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |   Sub-Type=2  | Sub-length=4+N|    ifIndex    |    ifType     |
     |  Provider ID  | Link  |S|0|RSV| Bitmap(0)=0xff|P00|P01|P02|P03|
     |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff|
     | Bitmap(2)=0xff|P64|P65|P67|P68| ...

Figure 14: Example 1: Dense Simplex Encoding

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |   Sub-Type=2  | Sub-length=4+N|    ifIndex    |    ifType     |
     |  Provider ID  | Link  |S|0|RSV| Bitmap(0)=0x00| Bitmap(1)=0x0f|
     | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00|
     | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203|
     |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275|
     |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00|
     |Bitmap(10)=0x00| ...

Figure 15: Example 2: Sparse Simplex Encoding

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |   Sub-Type=2  | Sub-length=4+N|    ifIndex    |    ifType     |
     |  Provider ID  | Link  |S|1|RSV|  Index = 0x00 | Bitmap = 0x80 |
     |P00|P01|P02|P03|  Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63|
     |  Index = 0x10 | Bitmap = 0x80 |512|513|514|515|  Index = 0x18 |
     | Bitmap = 0x01 |796|797|798|799| ...

Figure 16: Example 3: Indexed Encoding

Appendix B. VDL Mode 2 Considerations

ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" (VDLM2) that specifies an essential radio frequency data link service for aircraft and ground stations in worldwide civil aviation air traffic management. The VDLM2 link type is "multicast capable" [RFC4861], but with considerable differences from common multicast links such as Ethernet and IEEE 802.11.

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: [].

Appendix C. MN / AR Isolation Through L2 Address Mapping

Per [RFC4861], IPv6 ND messages may be sent to either a multicast or unicast link-scoped IPv6 destination address. However, IPv6 ND messaging should be coordinated between the MN and AR only without invoking other nodes on the ANET. This implies that MN / AR coordinations should be isolated and not overheard by other nodes on the link.

To support MN / AR isolation on some ANET links, ARs can maintain an OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible ANETs, this specification reserves one Ethernet unicast address TBD2 (see: Section 19). For non-Ethernet statically-addressed ANETs, MSADDR is reserved per the assigned numbers authority for the ANET addressing space. For still other ANETs, MSADDR may be dynamically discovered through other means, e.g., L2 beacons.

MNs map the L3 addresses of all IPv6 ND messages they send (i.e., both multicast and unicast) to MSADDR instead of to an ordinary unicast or multicast L2 address. In this way, all of the MN's IPv6 ND messages will be received by ARs that are configured to accept packets destined to MSADDR. Note that multiple ARs on the link could be configured to accept packets destined to MSADDR, e.g., as a basis for supporting redundancy.

Therefore, ARs must accept and process packets destined to MSADDR, while all other devices must not process packets destined to MSADDR. This model has well-established operational experience in Proxy Mobile IPv6 (PMIP) [RFC5213][RFC6543].

Appendix D. Change Log

<< RFC Editor - remove prior to publication >>

Differences from draft-templin-6man-omni-interface-14 to draft-templin-6man-omni-interface-15:

Differences from draft-templin-6man-omni-interface-12 to draft-templin-6man-omni-interface-13:

Differences from draft-templin-6man-omni-interface-11 to draft-templin-6man-omni-interface-12:

Differences from draft-templin-6man-omni-interface-10 to draft-templin-6man-omni-interface-11:

Differences from draft-templin-6man-omni-interface-07 to draft-templin-6man-omni-interface-08:

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First draft version (draft-templin-atn-aero-interface-00):

Authors' Addresses

Fred L. Templin (editor) The Boeing Company P.O. Box 3707 Seattle, WA 98124 USA EMail:
Tony Whyman MWA Ltd c/o Inmarsat Global Ltd 99 City Road London, EC1Y 1AX England EMail: