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, enterprise wireless devices, etc.)
communicate with networked correspondents over multiple access network
data links and configure mobile routers to connect end user networks. A
multilink interface specification is therefore needed for coordination
with the network-based mobility service. This document specifies the
transmission of IPv6 packets over Overlay Multilink Network (OMNI)
Interfaces.Mobile Nodes (MNs) (e.g., aircraft of various configurations,
terrestrial vehicles, seagoing vessels, enterprise wireless devices,
etc.) often have multiple data links for communicating with networked
correspondents. These data links may have diverse performance, cost and
availability properties that can change dynamically according to
mobility patterns, flight phases, proximity to infrastructure, etc. MNs
coordinate their data links in a discipline known as "multilink", in
which a single virtual interface is configured over the underlying data
links.The MN configures a virtual interface (termed the "Overlay Multilink
Network (OMNI) interface") as a thin layer over the underlying Access
Network (ANET) interfaces. The OMNI interface is therefore the only
interface abstraction exposed to the 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 one or more Internetworks
that may include private-use infrastructures and/or the global public
Internet itself.Each MN receives a Mobile Network Prefix (MNP) for numbering
downstream-attached End User Networks (EUNs) independently of the access
network data links selected for data transport. The MN performs router
discovery over the OMNI interface (i.e., similar to IPv6 customer edge
routers ) 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 ).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.MNs may connect to multiple distinct OMNI links by configuring
multiple OMNI interfaces, e.g., omni0, omni1, omni2, etc. Each OMNI
interface is configured over a set of underlying interfaces and provides
a nexus for Safety-Based Multilink (SBM) operation. The IP layer selects
an OMNI interface based on SBM routing considerations, then the selected
interface applies Performance-Based Multilink (PBM) to select the
correct underlying interface. Applications can apply Segment Routing
to select independent SBM topologies for fault
tolerance.The OMNI interface interacts with a network-based Mobility Service
(MS) through IPv6 Neighbor Discovery (ND) control message exchanges
. 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 terms "All-Routers multicast",
"All-Nodes multicast" and "Subnet-Router anycast" are the same as
defined in (with Link-Local scope assumed).The following terms are defined within the scope of this
document:an end system with a mobile
router having multiple distinct upstream data link connections that
are grouped together in one or more logical units. The MN's data
link connection parameters can change over time due to, e.g., node
mobility, link quality, etc. The MN further connects a
downstream-attached End User Network (EUN). The term MN used here is
distinct from uses in other documents, and does not imply a
particular mobility protocol.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.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 entity in
the MS (either singular or aggregate) that coordinates the mobility
events of one or more MN.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 an 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, wifi network, etc.)
that connects MNs. Physical and/or data link level security between
the MN and ANET are assumed.a first-hop router in the
ANET for connecting MNs to correspondents in outside
Internetworks.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 Non-Broadcast, Multiple Access
(NBMA) virtual overlay configured over one or more INETs and their
connected ANETs. An OMNI link can comprise multiple INET segments
joined by bridges the same as for any link; the addressing plans in
each segment may be mutually exclusive and managed by different
administrative entities.a node's attachment to an OMNI
link, and configured over one or more underlying ANET/INET
interfaces.a link local
IPv6 address per constructed as specified
in .a unique
local IPv6 address per constructed as
specified in . OMNI ULAs are
statelessly derived from OMNI LLAs, and vice-versa.an IPv6 Neighbor Discovery option
providing multilink parameters for the OMNI interface as specified
in .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.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.Each
MSE and AR is assigned a unique 32-bit Identification (MSID) as
specified in .A means for
ensuring fault tolerance through redundancy by connecting multiple
independent OMNI interfaces to independent routing topologies (i.e.,
multiple independent OMNI links).A means for
selecting underlying interface(s) for packet trasnmission and
reception within a single OMNI interface.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 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.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 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 therefore sees the OMNI
interface as a single L3 interface with multiple underlying 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) or Muticast Listener Discovery (MLD)
messaging is necessary.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. (An alternative would be to also
assign the same OMNI LLA to all ANET interfaces.)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 L3 traffic shaping 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.Multiple independent OMNI interfaces can be used for increased
fault tolerance through Safety-Based Multilink (SBM), with
Performance-Based Multilink (PBM) applied within each interface.Other opportunities are discussed in . 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.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 one or more underlying Internetwork via a mid-layer
overlay encapsulation based on and using addressing. Each OMNI link corresponds to a different
overlay (differentiated by an address codepoint) which may be carried
over a completely separate underlying topology. Each MN can facilitate
SBM by connecting to multiple OMNI links using a distinct OMNI interface
for each link.The OMNI interface observes the link nature of tunnels, including the
Maximum Transmission Unit (MTU) and the role of fragmentation and
reassembly. The OMNI
interface is configured over one or more underlying interfaces that may
have diverse MTUs.IPv6 underlying interfaces are REQUIRED to configure a minimum MTU of
1280 bytes . The network therefore MUST forward
packets of at least 1280 bytes without generating an IPv6 Path MTU
Discovery (PMTUD) Packet Too Big (PTB) message .
The minimum MTU for IPv4 underlying interfaces is only 68 bytes , meaning that a packet smaller than the IPv6 minimum
MTU may require fragmentation when IPv4 encapsulation is used.
Therefore, the Don't Fragment (DF) bit in the IPv4 encapsulation header
MUST be set to 0The OMNI interface configures an MTU of 9180 bytes ; 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 packets as large as the OMNI interface MTU while generating
IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) messages as necessary (see below). For IPv4 packets with DF=0,
the IP layer performs IPv4 fragmentation if necessary to admit the
fragments into the OMNI interface. The interface may then internally
apply further IPv4 fragmentation prior to encapsulation to ensure that
the IPv4 fragments are delivered to the final destination.OMNI interfaces internally employ OMNI link encapsulation and
fragmentation/reassembly per . The encapsulation
inserts a mid-layer IPv6 header between the inner IP packet and any
outer IP encapsulation headers. 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 encapsulation and fragmentation/reassembly as
follows:When an OMNI interface sends a packet toward a final destination
via an ANET peer, it sends without OMNI link encapsulation if the
packet is no larger than the underlying interface MTU. Otherwise, it
inserts an IPv6 header with source address set to the node's own
OMNI Unique Local Address (ULA) (see: )
and destination set to the OMNI ULA of the ANET peer. The OMNI
interface then uses IPv6 fragmentation to break the packet into a
minimum number of non-overlapping fragments, where the largest
fragment size is determined by the underlying interface MTU and the
smallest fragment is no smaller than 640 bytes. The OMNI interface
then sends the fragments to the ANET peer, which reassembles before
forwarding toward the final destination.When an OMNI interface sends a packet toward a final destination
via an INET interface, it sends packets no larger than 1280 bytes
(including any INET encapsulation headers) without inserting a
mid-layer IPv6 header if the destination is reached via an INET
address within the same OMNI link segment. Otherwise, it inserts an
IPv6 header with source address set to the node's OMNI ULA,
destination set to the ULA of the next hop OMNI node toward the
final destination and (if necessary) with a Segment Routing Header
with the remaining Segment IDs on the path to the final destination.
The OMNI interface then uses IPv6 fragmentation to break the
encapsulated packet into a minimum number of non-overlapping
fragments, where the largest fragment size (including both the OMNI
mid-layer IPv6 and outer-layer INET encapsulations) is 1280 bytes
and the smallest fragment is no smaller than 640 bytes. The OMNI
interface then encapsulates the fragments in any INET headers and
sends them to the OMNI link neighbor, which reassembles before
forwarding toward the final destination.OMNI interfaces unconditionally drop all OMNI link fragments smaller
than 640 bytes. In order to set the correct context for reassembly, the
OMNI interface that inserts the IPv6 header MUST also be the one that
inserts the IPv6 Fragment Header Identification value. While not
strictly required, sending all fragments of the same fragmented
mid-layer packet consecutively over the same underlying interface with
minimal inter-fragment delay may increase the likelihood of successful
reassembly.Note that the OMNI interface can forward large packets via
encapsulation and fragmentation while at the same time returning
"advisory" PTB messages (subject to rate limiting). The receiving node
that performs reassembly can also send advisory PTB messages if
reassembly conditions become unfavorable. The OMNI interface can
therefore continuously forward large packets without loss while
returning advisory PTB messages recommending a smaller size.OMNI interfaces that send advisory PTB messages set the ICMPv6
message header Code field to the value 1. Receiving nodes that recognize
the code reduce their estimate of the path MTU the same as for ordinary
"diagnistic" PTBs but do not regard the message as a loss indication.
Nodes that do not recognize the code treat the message the same as a
diagnostic PTB, but should heed the advice in
regarding retransmissions. This document therefore updates and .As discussed in Section 3.7 of , there are four basic threats
concerning IPv6 fragmentation; each of which is addressed by a
suitable mitigation as follows:Overlapping fragment attacks - reassembly of overlapping
fragments is forbidden by ; therefore,
this threat does not apply to OMNI interfaces.Resource exhaustion attacks - this threat is mitigated by
providing a sufficiently large OMNI interface reassembly cache and
instituting “fast discard” of incomplete reassemblies
that may be part of a buffer exhaustion attack. The reassembly
cache should be sufficiently large so that a sustained attack does
not cause excessive loss of good reassemblies but not so large
that (timer-based) data structure management becomes
computationally expensive.Attacks based on predictable fragment identification values -
this threat is mitigated by selecting a suitably random ID value
per .Evasion of Network Intrusion Detection Systems (NIDS) - this
threat is mitigated by disallowing “tiny fragments”
per the OMNI interface fragmentation procedures specified
above.Additionally, IPv4 fragmentation includes a 16-bit
Identification (IP ID) field with only 65535 unique values, meaning
that for even moderately high data rates the field could wrap and
apply to new packets while the fragments of old packets using the same
ID are still alive in the network . Since IPv6
provides a 32-bit Identification value, however, this is not a concern
for IPv6 fragmentation.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 , 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 construct IPv6 Link-Local Addresses (i.e., "OMNI
LLAs") as follows:IPv6 MN OMNI LLAs encode the most-significant 112 bits of a MNP
within the least-significant 112 bits of the IPv6 link-local prefix
fe80::/16. For example, for the MNP 2001:db8:1000:2000::/56 the
corresponding LLA is fe80:2001:db8:1000:2000::. This updates the
IPv6 link-local address format specified in Section 2.5.6 of by defining a use for bits 11 - 63.IPv4-compatible MN OMNI LLAs are constructed as
fe80::ffff:[v4addr], i.e., the most significant 16 bits of the
prefix fe80::/16, followed by 64 '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).MS OMNI LLAs are assigned to ARs and MSEs from the range
fe80::/96, and MUST be managed for uniqueness. The lower 32 bits of
the LLA includes a unique integer "MSID" value between 0x00000001
and 0xfeffffff, e.g., as in fe80::1, fe80::2, fe80::3, etc.,
fe80::feff:ffff. The MSID 0x00000000 corresponds to the link-local
Subnet-Router anycast address (fe80::) . The
MSID range 0xff000000 through 0xffffffff is reserved for future
use.The OMNI LLA range fe80::/32 is used as the service prefix for
the address format specified in Section 4 of (see for further
discussion).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 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 .OMNI links use IPv6 Unique Local Addresses (i.e., "OMNI ULAs") as the source and destination addresses in OMNI link
IPv6 encapsulation headers. This document updates by reserving the ULA prefix fc80::/10 for mapping
OMNI LLAs to routable OMNI ULAs.Each OMNI link instance is identified by bits 10-15 of the OMNI
service prefix fc80::/10. For example, OMNI ULAs associated with
instance 0 are configured from the prefix fc80::/16, instance 1 from
fc81::/16, etc., up to instance 63 from fcbf::/16. OMNI ULAs are
configured in one-to-one correspondence with OMNI LLAs through stateless
prefix translation. For example, for OMNI link instance fc80::/16:the OMNI ULA corresponding to fe80:2001:db8:1:2:: is simply
fc80:2001:db8:1:2::the OMNI ULA corresponding to fe80::ffff:192.0.2.1 is simply
fc80::ffff:192.0.2.1the OMNI ULA corresponding to fe80::1000 is simply fc80::1000the OMNI ULA corresponding to fe80:: is simply fc80::Each OMNI interface assigns the Anycast OMNI ULA specific to the OMNI
link instance, e.g., the OMNI interface connected to instance 3 assigns
the Anycast OMNI ULA fc83:. Routers that configure OMNI interfaces
advertise the OMNI service prefix (e.g., fc83::/16) into the local
routing system so that applications can direct traffic according to SBM
requirements.The OMNI ULA 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 . The OMNI link extends across one or more underling
Internetworks to include all ARs and MSEs. All MNs are also considered
to be connected to the OMNI link, however OMNI link encapsulation is
omitted over ANET links when possible to conserve bandwidth (see: ).The OMNI link can be subdivided into "segments" that often correspond
to different administrative domains or physical partitions. OMNI nodes
can use IPv6 Segment Routing when necessary to
support efficient packet forwarding to destinations located in other
OMNI link segments. A full discussion of Segment Routing over the OMNI
link appears in .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 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 underlying 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 address type.
For MN OMNI LLAs, the value is set to the length of the embedded
MNP. For IPv4-compatible MN OMNI LLAs, the value is set to 96 plus
the length of the embedded IPv4 prefix. For MS OMNI LLAs, the value
is set to 128.R (the "Register/Release" bit) is set to 1/0 to request the
message recipient to register/release a MN's MNP. The OMNI option
may additionally include MSIDs for the recipient to contact to also
register/release the MNP.Reserved is set to the value '0' on transmission and ignored on
reception.Sub-Options is a Variable-length field, of length such that the
complete OMNI Option is an integer multiple of 8 octets long.
Contains one or more options, as described in .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: Sub-Type is a 1-byte field that encodes the Sub-Option type.
Sub-Options defined in this document are:Sub-Types 253 and 254 are reserved for experimentation,
as recommended in .Sub-Length is a 1-byte field that encodes the length of the
Sub-Option Data, in bytesSub-Option Data is a byte string with format determined by
Sub-TypeDuring 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:Sub-Type is set to 0.No Sub-Length or Sub-Option Data follows (i.e., the
"Sub-Option" consists of a single zero octet).Sub-Type is set to 1.Sub-Length is set to N-2 being the number of padding bytes
that follow.Sub-Option Data consists of N-2 zero-valued octets.Sub-Type is set to 2.Sub-Length is set to 4+N (the number of Sub-Option Data bytes
that follow).Sub-Option Data contains an "ifIndex-tuple" (Type 1) encoded
as follows (note that the first four bytes must be
present):ifIndex is set to an 8-bit integer value corresponding to
a specific underlying interface. OMNI options MAY include
multiple ifIndex-tuples, and MUST number each with an
ifIndex value between '1' and '255' that represents a
MN-specific 8-bit mapping for the actual ifIndex value
assigned to the underlying interface by network management
(the ifIndex value '0' is reserved
for use by the MS). Multiple ifIndex-tuples with the same
ifIndex value MAY appear in the same OMNI option.ifType is set to an 8-bit integer value corresponding to
the underlying 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].Provider ID is set to an OMNI interface-specific 8-bit ID
value for the network service provider associated with this
ifIndex.Link encodes a 4-bit link metric. The value '0' means the
link is DOWN, and the remaining values mean the link is UP
with metric ranging from '1' ("lowest") to '15'
("highest").S is set to '1' if this ifIndex-tuple corresponds to the
underlying interface that is the source of the ND message.
Set to '0' otherwise.I is set to '0' ("Simplex") if the index for each
singleton Bitmap byte in the Sub-Option Data is inferred
from its sequential position (i.e., 0, 1, 2, ...), or set to
'1' ("Indexed") if each Bitmap is preceded by an Index byte.
shows the simplex case for I
set to '0'. For I set to '1', each Bitmap is instead
preceded by an Index byte that encodes a value "i" = (0 -
255) as the index for its companion Bitmap as
follows:RSV is set to the value 0 on transmission and ignored on
reception.The remainder of the Sub-Option Data contains N = (0 -
251) bytes of traffic classifier preferences consisting of a
first (indexed) Bitmap (i.e., "Bitmap(i)") followed by 0-8
1-byte blocks of 2-bit P[*] values, followed by a second
Bitmap (i), followed by 0-8 blocks of P[*] values, etc.
Reading from bit 0 to bit 7, the bits of each Bitmap(i) that
are set to '1'' indicate the P[*] blocks from the range
P[(i*32)] through P[(i*32) + 31] that follow; if any
Bitmap(i) bits are '0', then the corresponding P[*] block is
instead omitted. For example, if Bitmap(0) contains 0xff
then the block with P[00]-P[03], followed by the block with
P[04]-P[07], etc., and ending with the block with
P[28]-P[31] are included (as shown in ). The next Bitmap(i) is then
consulted with its bits indicating which P[*] blocks follow,
etc. out to the end of the Sub-Option. The first 16 P[*]
blocks correspond to the 64 Differentiated Service Code
Point (DSCP) values P[00] - P[63] .
Any additional P[*] blocks that follow correspond to
"pseudo-DSCP" traffic classifier values P[64], P[65], P[66],
etc. See Appendix A for further discussion and examples.Each 2-bit P[*] field is set to the value '0'
("disabled"), '1' ("low"), '2' ("medium") or '3' ("high") to
indicate a QoS preference level for underlying interface
selection purposes. Not all P[*] values need to be included
in all OMNI option instances of a given ifIndex-tuple. Any
P[*] values represented in an earlier OMNI option but
omitted in the current OMNI option remain unchanged. Any
P[*] values not yet represented in any OMNI option default
to "medium".Sub-Type is set to 3.Sub-Length is set to 4+N (the number of Sub-Option Data bytes
that follow).Sub-Option Data contains an "ifIndex-tuple" (Type 2) encoded
as follows (note that the first four bytes must be
present):ifIndex, ifType, Provider ID, Link and S are set exactly
as for Type 1 ifIndex-tuples as specified in .the remainder of the Sub-Option body encodes a
variable-length traffic selector formatted per , beginning with the "TS Format"
field.Sub-Type is set to 4.Sub-Length is set to 4.MSID contains the 32 bit ID of an MSE or AR, in network byte
order. OMNI options contain zero or more MS-Register
sub-options.Sub-Type is set to 5.Sub-Length is set to 4.MSIID contains the 32 bit ID of an MS or AR, in network byte
order. OMNI options contain zero or more MS-Release
sub-options.Sub-Type is set to 6.Sub-Length is set to N.Network Access Identifier (NAI) is coded per , and is up to 253 bytes in length.Sub-Type is set to 7.Sub-Length is set to N.A set of Geo Coordinates up to 253 bytes in length (format
TBD). Includes Latitude/Longitude at a minimum; may also include
additional attributes such as altitude, heading, speed,
etc.).The multicast address mapping of the native underlying interface
applies. The mobile router on board the MN also serves as an IGMP/MLD
Proxy for its EUNs and/or hosted applications per while using the L2 address of the AR as the L2
address for all multicast packets.The MN uses Multicast Listener Discovery (MLDv2) to coordinate with the AR, and ANET L2 elements use
MLD snooping .The MN's IPv6 layer selects the outbound OMNI interface according to
SBM considerations when forwarding data packets from local or EUN
applications to external correspondents. Each OMNI interface maintains a
neighbor cache the same as for any IPv6 interface, but with additional
state for multilink coordination.After a packet enters the OMNI interface, an outbound underlying
interface is selected based on PBM traffic selectors 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 OMNI link encapsulation if the packet
does not require fragmentation and the neighbor can determine the OMNI
ULAs through other means (e.g., the packet's destination, neighbor cache
information, etc.). Otherwise, the OMNI interface inserts an IPv6 header
with the OMNI ULAs and performs fragmentation if necessary. The OMNI
interface also performs enacpsulation when the nearest AR is located
multiple hops away as discussed in .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 underlying interfaces having diverse properties.MNs may connect to multiple independent OMNI links concurrently in
support of SBM. Each OMNI interface is distinguished by its Anycast
OMNI ULA (e.g., fc80::, fc81::, fc82::). The MN configures a separate
OMNI interface for each link so that multiple interfaces (e.g., omni0,
omni1, omni2, etc.) are exposed to the IPv6 layer. A different Anycast
OMNI ULA is assigned to each interface, and the MN injects the service
prefixes for the OMNI link instances into the EUN routing system.Applications in EUNs can use Segment Routing to select the desired
OMNI interface based on SBM considerations. The Anycast OMNI ULA is
written into the IPv6 destination address, and the actual destination
(along with any additional intermediate hops) is written into the
Segment Routing Header. Standard IP routing directs the packets to the
MN's mobile router entity, and the Anycast OMNI ULA identifies the
OMNI interface to be used for transmission to the next hop. When the
MN receives the message, it replaces the IPv6 destination address with
the next hop found in the routing header and transmits the message
over the OMNI interface identified by the Anycast OMNI ULA.Multiple distinct OMNI links can therefore be used to support fault
tolerance, load balancing, reliability, etc. The architectural model
is similar to Layer 2 Virtual Local Area Networks (VLANs).MNs interface with the MS by sending RS messages with OMNI options
under the assumption that a single AR on the ANET will process 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 (however, considerations for
ANETs that do not provide ARs that recognize the OMNI option are
discussed in ).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 link-scoped All-Routers multicast (ff02::2) . Example MSID discovery methods are given in , including data link login parameters, name service
lookups, static configuration, etc. Alternatively, MNs can discover
individual 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 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 either as an
MSE themselves or as a proxy for another MSE. ARs receive RS messages
and create a neighbor cache entry for the MN, then coordinate with any
named MSEs in a manner outside the scope of this document. The AR
returns RA messages with destination address set to the MN OMNI LLA
(i.e., unicast), with source address set to the MSE OMNI LLA, with an
OMNI option with valid prefix registration information, ifIndex-tuples,
and with any information for the link that would normally be delivered
in a solicited RA message. 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: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 this ANET interface.The AR coordinates with each Register/Release MSID then 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. If the AR is not itself the MSID named in an MS-Register
option, it also sets the P(roxy) bit in the RA flags . The AR MAY also send
periodic and/or event-driven unsolicited RA messages according to the
standard .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 returns an RA message with an OMNI option
per .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:When an underlying interface transitions to UP, the MN sends an
RS over the underlying interface with an OMNI option with R set to
1. The OMNI option contains at least one ifIndex-tuple with values
specific to this underlying interface, and may contain additional
ifIndex-tuples specific to this and/or other underlying interfaces.
The option also includes any Register/Release MSIDs.When an underlying interface transitions to DOWN, the MN sends an
RS or unsolicited NA message over any UP underlying interface with
an OMNI option containing an ifIndex-tuple for the DOWN underlying
interface with Link set to '0'. The MN sends an RS when an
acknowledgement is required, or an unsolicited NA when reliability
is not thought to be a concern (e.g., if redundant transmissions are
sent on multiple underlying interfaces).When the Router Lifetime for a specific AR nears expiration, the
MN sends an RS over the underlying interface to receive a fresh RA.
If no RA is received, the MN marks the underlying interface as
DOWN.When a MN wishes to release from one or more current MSIDs, it
sends an RS or unsolicited NA message over any UP underlying
interfaces with an OMNI option with a Release MSID. Each MSID then
withdraws the MNP from the routing/mapping system and informs the AR
that the release was successful.When all of a MNs underlying interfaces have transitioned to DOWN
(or if the prefix registration lifetime expires), any associated
MSEs withdraw the MNP the same as if they had received a message
with a release indication.The MN is responsible for retrying each RS exchange up to
MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL
seconds until an RA is received. If no RA is received over 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.Note: On multicast-capable underlying interfaces, MNs should send
periodic unsolicited multicast NA messages and ARs should send periodic
unsolicited multicast RA messages as "beacons" that can be heard by
other nodes on the link. If a node fails to receive a beacon after a
timeout value specific to the link, it can initiate a unicast exchange
to test reachability.On some ANET types (e.g., omni-directional ad-hoc wireless) a MN
may be located multiple hops away from a node which has connectivity
to the nearest ANET/INET service. Forwarding through these multiple
hops would be conducted through the application of a Mobile Ad-hoc
Network (MANET) routing protocol operating across the ANET
interfaces.A MN located potentially multiple ANET hops away from the nearst AR
prepares an RS message as normal then encapsulates the message in an
IPv6 header with source address set to the ULA corresponding to the RS
LLA source address, and with destination set to site-scoped
All-Routers multicast (ff05::2). The MN
then sends the encapsulated RS message via the ANET interface, where
it will be received by zero or more nearby intermediate MNs.When an intermediate MN that particpates in the MANET routing
protocol receives the encapsulated RS, it forwards the message
according to its (ULA-based) MANET routing tables. This process
repeats iteratively until the RS message is received by an ultimate MN
that is within communications range of an AR, which forwards the
message to the AR.When the AR receives the RS message, it coordinates with the MS the
same as if the message were received as an ordinary link-local RS,
since the inner Hop Limit will not have been decremented by the MANET
multihop forwarding process. The AR then prepares an RA message with
source address set to its own LLA and destination address set to the
LLA of the original MN, then encapsulates the message in an IPv6
header with source and destination set to the ULAs corresponding to
the inner header.The AR then forwards the message to an MN within communications
range, which forwards the message according to its MANET routing
tables to an intermediate MN. The MANET forwarding process continues
repetitively until the message is delivered to the original MN, which
decapsulates the message and performs autoconfiguration the same as if
it had received the RA directly from an AR.Note: An alternate approach to encapsulation of IPv6 ND messages
for multihop forwarding would be to statelessly translate the IPv6
LLAs into ULAs and forward the messages without encapsulation. This
would violate the requirement that certain
IPv6 ND messages must use link-local addresses and must not be
accepted if received with Hop Limit less than 255. This document
therefore advocates encapsulation since the overhead is nominal
considering the infrequent nature and small size of IPv6 ND messages.
Future documents may consider encapsulation avoidance through
translation while updating .If the ANET link model is multiple access, the AR is responsible for
assuring that address duplication cannot corrupt the neighbor caches of
other nodes on the link. When the MN sends an RS message on a multiple
access ANET link, the AR verifies that the MN is authorized to use the
address and returns an RA with a non-zero Router Lifetime only if the MN
is authorized.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.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 ANET links such as aeronautical radios) and can therefore be
tuned for rapid response.ARs perform proactive NUD for MSEs for which there are currently
active MNs on the ANET. If an MSE fails, ARs can quickly inform MNs of
the outage by sending multicast RA messages on the ANET interface. The
AR sends RA messages to MNs via the ANET interface with an OMNI option
with a Release ID for the failed MSE, and with destination address set
to All-Nodes multicast (ff02::1) .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.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 . 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 . This arrangement imparts a
(virtual) point-to-point link model over the (physical) multiple access
link.OMNI interfaces configured over IPv6-enabled underlying interfaces on
the open Internet without an OMNI-aware first-hop AR receive RA messages
that do not include an OMNI option, while OMNI interfaces configured
over IPv4-only underlying interfaces do not receive any (IPv6) RA
messages at all. OMNI interfaces that receive RA messages without an
OMNI option configure addresses, on-link prefxies, etc. on the
underlying interface that received the RA according to standard IPv6 ND
and address resolution conventions . OMNI interfaces configured over IPv4-only underlying
interfaces configure IPv4 address information on the underlying
interfaces using mechanisms such as DHCPv4 .OMNI interfaces configured over underlying interfaces that connect to
the open Internet can apply security services such as VPNs to connect to
an MSE or establish a direct link to an MSE through some other means. In
environments where an explicit VPN or direct link may be impractical,
OMNI interfaces can instead use UDP/IP encapsulation per . (SEcure Neighbor Discovery
(SEND) and Cryptographically Generated Addresses (CGA) or other protocol-specific
security services can can also be used if additional authentication is
necessary.)After estabishing a VPN or preparing for UDP/IP encapsulation, OMNI
interfaces send control plane messages to interface with the MS. The
control plane messages must be authenticated while data plane messages
are delivered the same as for ordinary best-effort Internet traffic with
basic source address-based data origin verification. Data plane
communications via OMNI interfaces that connect over the open Internet
without an explicit VPN should therefore employ transport- or
higher-layer security to ensure integrity and/or confidentiality.OMNI interfaces in the open Internet are often located behind Network
Address Translators (NATs). The OMNI interface accommodates NAT
traversal using UDP/IP encapsulation and the mechanisms discussed in
.In some use cases, it is desirable, beneficial and efficient for the
MN to receive a constant MNP that travels with the MN wherever it moves.
For example, this would allow air traffic controllers to easily track
aircraft, etc. In other cases, however (e.g., intelligent transportation
systems), the MN may be willing to sacrifice a modicum of efficiency in
order to have time-varying MNPs that can be changed every so often to
defeat adversarial tracking.Prefix delegation services such as those discussed in and allow OMNI MNs that desire
time-varying MNPs to obtain short-lived prefixes. In that case, the
identity of the MN can be used as a prefix delegation seed (e.g., a
DHCPv6 Device Unique IDentifier (DUID) ). 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.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 assign a new Code value "1" in the "ICMPv6
Code Fields: Type 2 - Packet Too Big" registry. The registry should read
as follows: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".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 .Security considerations for IPv6 and IPv6
Neighbor Discovery apply. OMNI interface IPv6
ND messages SHOULD include Nonce and Timestamp options when transaction confirmation and/or time
synchronization is needed.OMNI interfaces configured over secured ANET interfaces inherit the
physical and/or link-layer security properties of the connected ANETs.
OMNI interfaces configured over open INET interfaces can use symmetric
securing services such as VPNs or can by some other means establish a
direct link. When a VPN or direct link may be impractical, however, an
asymmetric security service such as SEcure Neighbor Discovery (SEND)
with Cryptographically Generated Addresses
(CGAs) , the authentication option specified in
or other protocol control message security
mechanisms may be necessary.While the OMNI link protects control plane messaging as discussed
above, applications should still employ transport- or higher-layer
security services to protect the data plane.Security considerations for specific access network interface types
are covered under the corresponding IP-over-(foo) specification (e.g.,
, , etc.).Security considerations for IPv6 fragmentation and reassembly are
discussed in .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.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: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].Per , IPv6 ND messages may be sent to either
a multicast or unicast link-scoped IPv6 destination address. However,
IPv6 ND messaging should be coordinated between the MN and AR only
without invoking other nodes on the ANET. This implies that MN / AR
control messaging should be isolated and not overheard by other nodes on
the link.To support MN / AR isolation on some ANET links, ARs can maintain an
OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible
ANETs, this specification reserves one Ethernet unicast address TBD2
(see: ). 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) .<< RFC Editor - remove prior to publication >>Differences from draft-templin-6man-omni-interface-20 to
draft-templin-6man-omni-interface-21:Safety-Based Multilink (SBM) and Performance-Based Multilink
(PBM).Differences from draft-templin-6man-omni-interface-18 to
draft-templin-6man-omni-interface-19:SEND/CGA.Differences from draft-templin-6man-omni-interface-17 to
draft-templin-6man-omni-interface-18:TeredoDifferences from draft-templin-6man-omni-interface-14 to
draft-templin-6man-omni-interface-15:Prefix length discussions removed.Differences from draft-templin-6man-omni-interface-12 to
draft-templin-6man-omni-interface-13:TeredoDifferences from draft-templin-6man-omni-interface-11 to
draft-templin-6man-omni-interface-12:Major simplifications and clarifications on MTU and
fragmentation.Document now updates RFC4443 and RFC8201.Differences from draft-templin-6man-omni-interface-10 to
draft-templin-6man-omni-interface-11:Removed /64 assumption, resulting in new OMNI address format.Differences from draft-templin-6man-omni-interface-07 to
draft-templin-6man-omni-interface-08:OMNI MNs in the open InternetDifferences from draft-templin-6man-omni-interface-06 to
draft-templin-6man-omni-interface-07:Brought back L2 MSADDR mapping text for MN / AR isolation based
on L2 addressing.Expanded "Transition Considerations".Differences from draft-templin-6man-omni-interface-05 to
draft-templin-6man-omni-interface-06:Brought back OMNI option "R" flag, and discussed its use.Differences from draft-templin-6man-omni-interface-04 to
draft-templin-6man-omni-interface-05:Transition considerations, and overhaul of RS/RA addressing with
the inclusion of MSE addresses within the OMNI option instead of as
RS/RA addresses (developed under FAA SE2025 contract number
DTFAWA-15-D-00030).Differences from draft-templin-6man-omni-interface-02 to
draft-templin-6man-omni-interface-03:Added "advisory PTB messages" under FAA SE2025 contract number
DTFAWA-15-D-00030.Differences from draft-templin-6man-omni-interface-01 to
draft-templin-6man-omni-interface-02:Removed "Primary" flag and supporting text.Clarified that "Router Lifetime" applies to each ANET interface
independently, and that the union of all ANET interface Router
Lifetimes determines MSE lifetime.Differences from draft-templin-6man-omni-interface-00 to
draft-templin-6man-omni-interface-01:"All-MSEs" OMNI LLA defined. Also reserved fe80::ff00:0000/104
for future use (most likely as "pseudo-multicast").Non-normative discussion of alternate OMNI LLA construction form
made possible if the 64-bit assumption were relaxed.Differences from draft-templin-atn-aero-interface-21 to
draft-templin-6man-omni-interface-00:Minor clarification on Type-2 ifIndex-tuple encoding.Draft filename change (replaces
draft-templin-atn-aero-interface).Differences from draft-templin-atn-aero-interface-20 to
draft-templin-atn-aero-interface-21:OMNI option formatMTUDifferences from draft-templin-atn-aero-interface-19 to
draft-templin-atn-aero-interface-20:MTUDifferences from draft-templin-atn-aero-interface-18 to
draft-templin-atn-aero-interface-19:MTUDifferences from draft-templin-atn-aero-interface-17 to
draft-templin-atn-aero-interface-18:MTU and RA configuration information updated.Differences from draft-templin-atn-aero-interface-16 to
draft-templin-atn-aero-interface-17:New "Primary" flag in OMNI option.Differences from draft-templin-atn-aero-interface-15 to
draft-templin-atn-aero-interface-16:New note on MSE OMNI LLA uniqueness assurance.General cleanup.Differences from draft-templin-atn-aero-interface-14 to
draft-templin-atn-aero-interface-15:General cleanup.Differences from draft-templin-atn-aero-interface-13 to
draft-templin-atn-aero-interface-14:General cleanup.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.