Transmission of IPv6 Packets
over Overlay Multilink Network (OMNI) InterfacesThe Boeing CompanyP.O. Box 3707SeattleWA98124USAfltemplin@acm.orgMWA Ltd c/o Inmarsat Global Ltd99 City RoadLondonEC1Y 1AXEnglandtony.whyman@mccallumwhyman.comI-DInternet-DraftMobile 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.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 characteristics 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
link interfaces.The MN configures a virtual interface (termed the "Overlay Multilink
Network (OMNI) interface") as a thin layer over the underlying access
network 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 access network 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 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 ) 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 access network data links in order to register
per-link parameters (see Section 12).The OMNI interface provides a multilink nexus for guiding inbound and
outbound traffic to the correct underlying Access Network (ANET)
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 an Internetwork Mobility Service
(MS) through IPv6 Neighbor Discovery (ND) control message exchanges
. 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 and MN/MS control messaging over OMNI interfaces.The terminology in the normative references applies; especially, the
terms "link" and "interface" are the same as defined in the IPv6 and IPv6 Neighbor Discovery (ND) specifications. Also, the Protocol Constants defined
in Section 10 of are used in their same format
and meaning in this document.The following terms are defined within the scope of this
document:an end system with multiple
distinct data link connections that are managed together as a single
logical unit. The MN connects an EUN, and its data link connection
parameters can change over time due to, e.g., node mobility, link
quality, etc. The term MN used here is distinct from uses in other
documents, and does not imply a particular mobility protocol.a simple or complex
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 data link connections change.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.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.a longer IPv6
prefix taken from the MSP (e.g., 2001:db8:1000:2000::/56) and
assigned to a MN. MNs sub-delegate the MNP to devices located in
EUNs.a data link service
network (e.g., an aviation radio access network, satellite service
provider network, cellular operator network, etc.) that provides an
Access Router (AR) for connecting MNs to correspondents in outside
Internetworks. Physical and/or data link level security between the
MN and AR are assumed.a MN's attachment to a link in
an ANET.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.a node's attachment to a link
in an INET.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.a node's attachment to an OMNI
link, and configured over one or more underlying ANET/INET
interfaces.an IPv6
link-local address constructed as specified in , and assigned to an OMNI interface.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.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
when, and only when,
they appear in all capitals, as shown here.An OMNI interface is a MN virtual interface configured over one or
more ANET 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 and assigns the LLA to the OMNI interface.The OMNI interface architectural layering model is the same as in
, and augmented as shown in . The IP layer (L3) therefore sees the OMNI interface
as a single network layer interface with multiple underlying ANET
interfaces that appear as L2 communication channels in the
architecture.The OMNI virtual interface model gives rise to a number of
opportunities:since OMNI LLAs are uniquely derived from an MNP, no Duplicate
Address Detection (DAD) messaging is necessary over the OMNI
interface.ANET interfaces do not require any L3 addresses (i.e., not even
link-local) in environments where communications are coordinated
entirely over the OMNI interface.as ANET interface properties change (e.g., link quality, cost,
availability, etc.), any active ANET interface can be used to update
the profiles of multiple additional ANET interfaces in a single
message. This allows for timely adaptation and service continuity
under dynamically changing conditions.coordinating ANET interfaces in this way allows them to be
represented in a unified MS profile with provisions for mobility and
multilink operations.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 queuing at the L3 based on, e.g., DSCP, flow label,
etc.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.Other opportunities are discussed in . depicts the architectural model for a MN
connecting to the MS via multiple independent ANETs. When an ANET
interface becomes active, the MN sends native (i.e., unencapsulated)
IPv6 ND messages via the underlying ANET 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.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.All IPv6 interfaces MUST configure an MTU of at least 1280 bytes
. The OMNI interface configures its MTU based on
the largest MTU among all underlying ANET interfaces. The value MAY be
overridden if an RA message with an MTU option is received.The OMNI interface returns internally-generated IPv6 Path MTU
Discovery (PMTUD) Packet Too Big (PTB) messages
for packets admitted into the OMNI interface that are too large for the
outbound underlying ANET interface. Similarly, the OMNI interface
performs PMTUD even if the destination appears to be on the same link
since a proxy on the path could return a PTB message. PMTUD therefore
ensures that the OMNI interface MTU is adaptive and reflects the current
path used for a given data flow.Applications that cannot tolerate loss due to MTU restrictions SHOULD
refrain from sending packets larger than 1280 bytes, since dynamic path
changes can reduce the path MTU at any time. Applications that may
benefit from sending larger packets even though the path MTU may change
dynamically MAY use larger sizes.The OMNI interface transmits IPv6 packets according to the native
frame format of each underlying ANET interface. For example, for
Ethernet-compatible interfaces the frame format is specified in , 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 , etc.OMNI interfaces assign IPv6 Link-Local Addresses (LLAs) using the
following constructs:MN OMNI LLAs encode the most-significant 64 bits of a MNP within
the least-significant 64 bits (i.e., the interface ID) of a
Link-Local IPv6 Unicast Address (see: ,
Section 2.5.6). For example, for the MNP 2001:db8:1000:2000::/56 the
corresponding LLA is fe80::2001:db8:1000:2000.MSE OMNI LLAs are allocated from the range fe80::/96, and MUST be
managed for uniqueness by the collective OMNI link administrative
authorities. The lower 32 bits of the LLA includes a unique integer
value between '1' and 'fffffffe', e.g., as in fe80::1, fe80::2,
fe80::3, etc., fe80::ffff:fffe. The address fe80:: is the IPv6
link-local Subnet Router Anycast address
and the address fe80::ffff:ffff is reserved.IPv4-compatible MN OMNI LLAs are allocated as
fe80::ffff:[v4addr], i.e., fe80::/10, followed by 70 '0' bits,
followed by 16 '1' bits, followed by a 32bit IPv4 address. For
example, the IPv4-Compatible MN OMNI LLA for 192.0.2.1 is
fe80::ffff:192.0.2.1 (also written as fe80::ffff:c000:0201).Since the prefix 0000::/8 is "Reserved by the IETF" , no MNPs can be allocated from that block ensuring
that there is no possibility for overlap between the different OMNI LLA
constructs.Since MN OMNI LLAs are based on the distribution of administratively
assured unique MNPs, and since MSE OMNI LLAs are guaranteed unique
through administrative assignment, OMNI interfaces set the
autoconfiguration variable DupAddrDetectTransmits to 0 .OMNI interfaces maintain a neighbor cache for tracking per-neighbor
state and use the link-local address format specified in . IPv6 Neighbor Discovery (ND) messages on MN OMNI interfaces observe the native
Source/Target Link-Layer Address Option (S/TLLAO) formats of the
underlying ANET interfaces (e.g., for Ethernet the S/TLLAO is specified
in ).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 ANET interfaces in a single
IPv6 ND message exchange.OMNI interfaces use an IPv6 ND option called the "OMNI option"
formatted as shown in :In this format:Type is set to TBD.Length is set to the number of 8 octet blocks in the option.Prefix Length is set according to the IPv6 source LLA type. For
MN OMNI LLAs, the value is set to the length of the embedded MNP.
For MSE OMNI LLAs, the value is set to 128.R (the "Register" bit) is set to '1' to assert MNP registration
or set to '0' to cancel MNP registration.N (the "Notify" bit) is set to '1' if the option includes a
trailing 4 byte "Notification ID" (see below); set to '0'
otherwise.Reserved is set to the value '0' on transmission and ignored on
reception.A set of N ANET interface "ifIndex-tuples" are included as
follows:ifIndex[i] is set to an 8-bit integer value corresponding to
a specific underlying ANET interface. The first ifIndex-tuple
MUST correspond to the ANET interface over which the message is
sent. IPv6 ND messages originating from a MN may include
multiple ifIndex-tuples, and MUST number each ifIndex with a
distinct value between '1' and '255' that represents a
MN-specific 8-bit mapping for the actual ifIndex value assigned
to the ANET interface by network management . IPv6 ND messages originating from the MS
include a single ifIndex-tuple with ifIndex set to the value
'0'.ifType[i] is set to an 8-bit integer value corresponding to
the underlying ANET interface identified by ifIndex. 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].Reserved[i] is set to the value '0' on transmission and
ignored on reception.Link[i] 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").QoS[i] encodes the number of 4-byte blocks (between '0' and
'15') of two-bit P[*] values that follow. The first 4 blocks
correspond to the 64 Differentiated Service Code Point (DSCP)
values P00 - P63 . If additional 4-byte
P[i] blocks follow, their values correspond to "pseudo-DSCP"
values P64, P65, P66, etc. numbered consecutively. The
pseudo-DSCP values correspond to ancillary QoS information
defined for the specific OMNI interface (e.g., see Appendix
A).P[*] includes zero or more per-ifIndex 4-byte blocks of
two-bit Preferences. Each P[*] field is set to the value '0'
("disabled"), '1' ("low"), '2' ("medium") or '3' ("high") to
indicate a QoS preference level for ANET interface selection
purposes. The first four blocks always correspond to the 64 DSCP
values. If one or more of the blocks are absent (e.g., for QoS
values 0,1,2,3) the P[*] values for the missing blocks default
to "medium".Zero-padding added if necessary to produce an integral number of
8 octet blocks.Notification ID (present only if N = '1') contains the
least-significant 32 bits of an MSE OMNI LLA to notify. For example,
for the LLA fe80::dead:beef the field contains 0xdeadbeef.The multicast address mapping of the native underlying ANET interface
applies. The mobile router on board the aircraft also serves as an
IGMP/MLD Proxy for its EUNs and/or hosted applications per while using the L2 address of the router as the L2
address for all multicast packets.Per , IPv6 ND messages may be sent to either
a multicast or unicast link-scoped IPv6 destination address. However,
IPv6 ND messaging is coordinated between the MN and MS only without
invoking other nodes on the ANET.For this reason, ANET links maintain unicast L2 addresses ("MSADDR")
for the purpose of supporting MN/MS IPv6 ND messaging. For
Ethernet-compatible ANETs, this specification reserves one Ethernet
unicast address TBD2. 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 an 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 MS devices that are configured to accept
packets destined to MSADDR. Note that multiple MS devices 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) .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 default routes and neighbor cache entries for MSEs, and may
also include additional neighbor cache entries created through other
means (e.g., Address Resolution, static configuration, etc.).After a packet enters the OMNI interface, an outbound ANET 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 ANET interfaces for increased reliability at the expense of
packet duplication.OMNI interface multilink service designers MUST observe the BCP
guidance in Section 15 in terms of implications
for reordering when packets from the same flow may be spread across
multiple ANET interfaces having diverse properties.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 ANET 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.ARs process IPv6 ND messages destined to all-routers multicast
(ff02::2), the subnet router anycast LLA (fe80::) and unicast IPv6 LLAs.
ARs configure the L2 address MSADDR (see: )
and act as a proxy for MSE OMNI LLAs in the range fe80::1 through
fe80::ffff:fffe.MNs interface with the MS by sending RS messages with OMNI options.
For each ANET interface, the MN sends an RS message with an OMNI option,
with L2 destination address set to MSADDR and with L3 destination
address set to either a specific MSE OMNI LLA, subnet router anycast
LLA, or all-routers multicast. The MN discovers MSE OMNI LLAs either
through an RA message response to an initial anycast/multicast RS or
before sending an initial RS message. provides
example MSE address discovery methods, including information conveyed
during data link login, name service lookups, static configuration,
etc.The AR receives the RS messages and coordinates with the
corresponding MSE in a manner outside the scope of this document. The AR
returns an RA message with source address set to the MSE OMNI LLA, with
an OMNI option and with any information for the link that would normally
be delivered in a solicited RA message. (Note that if all MSEs share
common state, the AR can instead return an RA with source address set to
the subnet router anycast LLA.)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 initial RS
messages to register its MNP and an initial set of underlying ANET
interfaces that are also UP. The MN sends additional RS messages to
refresh lifetimes and to register/deregister underlying ANET interfaces
as they transition to UP or DOWN.ARs return RA messages with configuration information in response to
a MN's RS messages. The RAs include a Router Lifetime value and any
necessary options, such as:PIOs with (A; L=0) that include MSPs for the link .RIOs with more-specific routes.an MTU option that specifies the maximum acceptable packet size
for the OMNI linkThe AR coordinates with the MSE and sends immediate unicast RA
responses 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, but is
not required to do so for unicast advertisements .The MN sends RS messages from within the OMNI interface while using
an UP underlying ANET interface as the outbound interface. Each RS
message is formatted as though it originated from the IPv6 layer, but
the process is coordinated wholly from within the OMNI interface and is
therefore opaque to the IPv6 layer. The MN sends initial RS messages
over an UP underlying interface with its OMNI LLA as the source. The RS
messages include an OMNI option with a valid Prefix Length as well as
ifIndex-tuples appropriate for underlying ANET interfaces. The AR
processes RS message and conveys the OMNI option information to the
MSE.When the MSE processes the OMNI information, if the prefix
registration was accepted the MSE injects the MNP into the
routing/mapping system then caches the new Prefix Length, MNP and
ifIndex-tuples. The MSE then directs the AR to return an RA message to
the MN with an OMNI option and with a non-zero Router Lifetime if the
prefix assertion was acceptable; otherwise, with a zero Router Lifetime.
If the MN's OMNI option included a Notification ID, the new MSE also
notifies the former MSE (with reliable confirmation).When the MN receives the RA message, it creates a default route with
L3 next hop address set to the address found in the RA source address
and with L2 address set to MSADDR. The AR will then forward packets
between the MN and the MS.The MN then manages its underlying ANET interfaces according to their
states as follows:When an underlying ANET interface transitions to UP, the MN sends
an RS over the ANET interface with an OMNI option. The OMNI option
contains a first ifIndex-tuple with values specific to this ANET
interface, and may contain additional ifIndex-tuples specific to
other ANET interfaces.When an underlying ANET interface transitions to DOWN, the MN
sends an RS or unsolicited NA message over any UP ANET interface
with an OMNI option containing an ifIndex-tuple for the DOWN ANET
interface with Link(i) set to '0'. The MN sends an RS when an
acknowledgement is required, or an unsolicited NA when reliability
is not thought to be a concern (e.g., if redundant transmissions are
sent on multiple ANET interfaces).When a MN wishes to release from a current MSE, it sends an RS or
unsolicited NA message over any UP ANET interfaces with an OMNI
option with R set to 0. The corresponding MSE then withdraws the MNP
from the routing/mapping system and (for RS responses) returns an RA
message with an OMNI option and with Router Lifetime set to 0.When a MN wishes to transition to a new MSE, it sends an RS or
unsolicited NA message over any UP ANET interfaces with an OMNI
option with R set to 1, with the new MSE OMNI LLA set in the
destination address, and (optionally) with a Notification ID for the
former MSE.When all of a MNs underlying interfaces have transitioned to
DOWN, the MSE withdraws the MNP the same as if it had received a
message with an OMNI option with R set to 0.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 multiple UP
ANET interfaces, the MN declares this MSE unreachable and tries a
different MSE.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 (such as Router Lifetime, MTU, etc.)
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.ANETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP)
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.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) 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 aeronautical radio links) and can therefore be tuned for
rapid response.ARs employ proactive NUD with MSEs for which there are currently
active ANET MNs. If an MSE fails, ARs can quickly inform MNs of the
outage by sending RA messages on the ANET interface. The AR sends RA
messages to the MN via the ANET interface with source address set to the
MSEs OMNI LLA, destination address set to all-nodes multicast, and
Router Lifetime set to 0.The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated
by small delays . 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.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 .The IANA is instructed to allocate one Ethernet unicast address TBD2
(suggest 00-00-5E-00-52-14 ) in the registry
"IANA Ethernet Address Block - Unicast Use".Security considerations for IPv6 and IPv6
Neighbor Discovery apply. OMNI interface IPv6
ND messages SHOULD include Nonce and Timestamp options when synchronized transaction confirmation is
needed.Security considerations for specific access network interface types
are covered under the corresponding IP-over-(foo) specification (e.g.,
).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:
Pavel Drasil, Zdenek Jaron, Michael Matyas, Madhu Niraula, Greg Saccone,
Stephane Tamalet, Eric Vyncke. Naming of the IPv6 ND option was
discussed on the 6man mailing list.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.Adaptation of the OMNI interface to specific Internetworks such as
the Aeronautical Telecommunications Network with Internet Protocol
Services (ATN/IPS) includes link selection preferences based on
transport port numbers in addition to the existing DSCP-based
preferences. ATN/IPS nodes maintain a map of transport port numbers to
additional "pseudo-DSCP" P[*] preference fields beyond the first 64. For
example, TCP port 22 maps to pseudo-DSCP value P67, TCP port 443 maps to
P70, UDP port 8060 maps to P76, etc. shows an
example OMNI option with extended P[*] values beyond the base 64 used
for DSCP mapping (i.e., for QoS values 5 or greater):The 64-bit boundary in IPv6 addresses
determines the MN OMNI LLA format for encoding the most-significant 64
MNP bits into the least-significant 64 bits of the prefix fe80::/64 as
discussed in . defines the link-local address format as
fe80::/10, followed by 54 unused bits, followed by the least-significant
64 bits of the address. If the 64-bit boundary is relaxed through future
standards activity, then the 54 unused bits can be employed for extended
coding of MNPs of length /65 up to /118.The extended coding format would continue to encode MNP bits 0-63 in
bits 64-127 of the OMNI LLA, while including MNP bits 64-117 in bits
10-63. For example, the OMNI LLA corresponding to the MNP
2001:db8:1111:2222:3333:4444:5555::/112 would be
fe8c:ccd1:1115:5540:2001:db8:1111:2222, and would still be a valid IPv6
LLA per .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" , 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].<< RFC Editor - remove prior to publication >>Differences from draft-templin-atn-aero-interface-12 to
draft-templin-atn-aero-interface-13:Minor re-work on "Notify-MSE" (changed to Notification ID).Differences from draft-templin-atn-aero-interface-11 to
draft-templin-atn-aero-interface-12:Removed "Request/Response" OMNI option formats. Now, there is
only one OMNI option format that applies to all ND messages.Added new OMNI option field and supporting text for
"Notify-MSE".Differences from draft-templin-atn-aero-interface-10 to
draft-templin-atn-aero-interface-11:Changed name from "aero" to "OMNI"Resolved AD review comments from Eric Vyncke (posted to atn
list)Differences from draft-templin-atn-aero-interface-09 to
draft-templin-atn-aero-interface-10:Renamed ARO option to AERO optionRe-worked Section 13 text to discuss proactive NUD.Differences from draft-templin-atn-aero-interface-08 to
draft-templin-atn-aero-interface-09:Version and reference updateDifferences from draft-templin-atn-aero-interface-07 to
draft-templin-atn-aero-interface-08:Removed "Classic" and "MS-enabled" link model discussionAdded new figure for MN/AR/MSE model.New Section on "Detecting and responding to MSE failure".Differences from draft-templin-atn-aero-interface-06 to
draft-templin-atn-aero-interface-07:Removed "nonce" field from AR option format. Applications that
require a nonce can include a standard nonce option if they want
to.Various editorial cleanups.Differences from draft-templin-atn-aero-interface-05 to
draft-templin-atn-aero-interface-06:New Appendix C on "VDL Mode 2 Considerations"New Appendix D on "RS/RA Messaging as a Single Standard API"Various significant updates in Section 5, 10 and 12.Differences from draft-templin-atn-aero-interface-04 to
draft-templin-atn-aero-interface-05:Introduced RFC6543 precedent for focusing IPv6 ND messaging to a
reserved unicast link-layer addressIntroduced new IPv6 ND option for Aero RegistrationSpecification of MN-to-MSE message exchanges via the ANET access
router as a proxyIANA Considerations updated to include registration requests and
set interim RFC4727 option type value.Differences from draft-templin-atn-aero-interface-03 to
draft-templin-atn-aero-interface-04:Removed MNP from aero option format - we already have RIOs and
PIOs, and so do not need another option type to include a
Prefix.Clarified that the RA message response must include an aero
option to indicate to the MN that the ANET provides a MS.MTU interactions with link adaptation clarified.Differences from draft-templin-atn-aero-interface-02 to
draft-templin-atn-aero-interface-03:Sections re-arranged to match RFC4861 structure.Multiple aero interfacesConceptual sending algorithmDifferences from draft-templin-atn-aero-interface-01 to
draft-templin-atn-aero-interface-02:Removed discussion of encapsulation (out of scope)Simplified MTU sectionChanged to use a new IPv6 ND option (the "aero option") instead
of S/TLLAOExplained the nature of the interaction between the mobility
management service and the air interfaceDifferences from draft-templin-atn-aero-interface-00 to
draft-templin-atn-aero-interface-01:Updates based on list review comments on IETF 'atn' list from
4/29/2019 through 5/7/2019 (issue tracker established)added list of opportunities afforded by the single virtual link
modeladded discussion of encapsulation considerations to Section 6noted that DupAddrDetectTransmits is set to 0removed discussion of IPv6 ND options for prefix assertions. The
aero address already includes the MNP, and there are many good
reasons for it to continue to do so. Therefore, also including the
MNP in an IPv6 ND option would be redundant.Significant re-work of "Router Discovery" section.New Appendix B on Prefix Length considerationsFirst draft version (draft-templin-atn-aero-interface-00):Draft based on consensus decision of ICAO Working Group I
Mobility Subgroup March 22, 2019.