Transmission of IP 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 IP packets over Overlay Multilink Network (OMNI)
Interfaces.Mobile Nodes (MNs) (e.g., aircraft of various configurations,
terrestrial vehicles, seagoing vessels, enterprise wireless devices,
pedestrians with cellphones, etc.) often have multiple interface
connections to wireless and/or wired-link data links used for
communicating with networked correspondents. These data links may have
diverse performance, cost and availability properties that can change
dynamically according to mobility patterns, flight phases, proximity to
infrastructure, etc. MNs coordinate their data links in a discipline
known as "multilink", in which a single virtual interface is configured
over the node's underlying interface connections to the data links.The MN configures a virtual interface (termed the "Overlay Multilink
Network Interface (OMNI)") as a thin layer over the underlying
interfaces. The OMNI interface is therefore the only interface
abstraction exposed to the IP layer and behaves according to the
Non-Broadcast, Multiple Access (NBMA) interface principle, while
underlying interfaces appear as link layer communication channels in the
architecture. The OMNI interface internally employs the "OMNI Adaptation
Layer (OAL)" to ensure that packets are delivered without loss due to
size restrictions. The OMNI interface connects to a virtual overlay
service known as the "OMNI link". The OMNI link spans one or more
Internetworks that may include private-use infrastructures and/or the
global public Internet itself.Each 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 IP
layer sees the OMNI interface as a point of connection to the OMNI link.
Each OMNI link has one or more associated Mobility Service Prefixes
(MSPs), which are typically IP Global Unicast Address (GUA) prefixes
from which OMNI link MNPs are derived. If there are multiple OMNI links,
the IPv6 layer will see multiple OMNI interfaces.MNs may connect to multiple distinct OMNI links within the same OMNI
domain by configuring multiple OMNI interfaces, e.g., omni0, omni1,
omni2, etc. Each OMNI interface is configured over a set of underlying
interfaces and provides a nexus for Safety-Based Multilink (SBM)
operation. Each OMNI interface within the same OMNI domain configures a
common ULA prefix [ULA]::/48, and configures a unique 16-bit Subnet ID
'*' to construct the sub-prefix [ULA*]::/64 (see: ). The IP layer applies SBM routing to select an
OMNI interface, which then applies Performance-Based Multilink (PBM) to
select the correct underlying interface. Applications can apply Segment
Routing 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.Many OMNI use cases have been proposed. In particular, the
International Civil Aviation Organization (ICAO) Working Group-I
Mobility Subgroup is developing a future Aeronautical Telecommunications
Network with Internet Protocol Services (ATN/IPS) and has issued a
liaison statement requesting IETF adoption in
support of ICAO Document 9896 . The IETF IP
Wireless Access in Vehicular Environments (ipwave) working group has
further included problem statement and use case analysis for OMNI in a
document now in AD evaluation for RFC publication . Still other communities
of interest include AEEC, RTCA Special Committee 228 (SC-228) and NASA
programs that examine commercial aviation, Urban Air Mobility (UAM) and
Unmanned Air Systems (UAS). Pedestrians with handheld devices represent
another large class of potential OMNI users.This document specifies the transmission of IP packets and MN/MS
control messages over OMNI interfaces. The OMNI interface supports
either IP protocol version (i.e., IPv4 or IPv6
) as the network layer in the data plane, while
using IPv6 ND messaging as the control plane independently of the data
plane IP protocol(s). The OAL operates as a mid-layer between L3 and L2
based on IP-in-IPv6 encapsulation per as
discussed in the following sections. OMNI interfaces enable multilink,
mobility, multihop and multicast services, with provisions for both
Vehicle-to-Infrastructure (V2I) communications and Vehicle-to-Vehicle
(V2V) communications outside the context of infrastructure.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. Additionally, this document assumes
the following IPv6 ND message types: Router Solicitation (RS), Router
Advertisement (RA), Neighbor Solicitation (NS), Neighbor Advertisement
(NA) and Redirect.The Protocol Constants defined in Section 10 of 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 term "IP" is used to refer collectively to either Internet
Protocol version (i.e., IPv4 or IPv6 ) when a specification at the layer in question
applies equally to either version.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 IP 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
IP Global Unicast Address (GUA) prefix (e.g., 2001:db8::/32,
192.0.2.0/24, etc.) assigned to the OMNI link and from which
more-specific Mobile Network Prefixes (MNPs) are delegated. OMNI
link administrators typically obtain MSPs from an Internet address
registry, however private-use prefixes can alternatively be used
subject to certain limitations (see: ). OMNI
links that connect to the global Internet advertise their MSPs to
their interdomain routing peers.a longer IP
prefix delegated from an MSP (e.g., 2001:db8:1000:2000::/56,
192.0.2.8/30, etc.) and assigned to a MN. MNs sub-delegate the MNP
to devices located in EUNs.a data link service
network (e.g., an aviation radio access network, satellite service
provider network, cellular operator network, WiFi network, etc.)
that connects MNs. Physical and/or data link level security is
assumed, and sometimes referred to as "protected spectrum". Private
enterprise networks and ground domain aviation service networks may
provide multiple secured IP hops between the MN's point of
connection and the nearest Access Router.a router in the ANET for
connecting MNs to correspondents in outside Internetworks. The AR
may be located on the same physical link as the MN, or may be
located multiple IP hops away. In the latter case, the MN uses
encapsulation to communicate with the AR as though it were on the
same physical link.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 between ANETs and nodes that connect directly to
the open INET via unprotected media. No physical and/or data link
level security is assumed, therefore security must be applied by
upper layers. The global public Internet itself is an example.a node's attachment to a link
in an INET.a "wildcard" term used when a given
specification applies equally to both ANET and INET cases.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 *NET interfaces. If
there are multiple OMNI links in an OMNI domain, a separate OMNI
interface is configured for each link.an OMNI interface
process whereby packets admitted into the interface are wrapped in a
mid-layer IPv6 header and fragmented/reassembled if necessary to
support the OMNI link Maximum Transmission Unit (MTU). The OAL is
also responsible for generating MTU-related control messages as
necessary, and for providing addressing context for spanning
multiple segments of a bridged OMNI link.an IPv6 Neighbor Discovery option
providing multilink parameters for the OMNI interface as specified
in .an
IPv6 Link Local Address that embeds the most significant 64 bits of
an MNP in the lower 64 bits of fe80::/64, as specified in .an
IPv6 Unique-Local Address derived from an MNP-LLA.an
IPv6 Link Local Address that embeds a 32-bit
administratively-assigned identification value in the lower 32 bits
of fe80::/96, as specified in .an
IPv6 Unique-Local Address derived from an ADM-LLA.an OMNI interface's manner of
managing diverse underlying interface connections to data links as a
single logical unit. The OMNI interface provides a single unified
interface to upper layers, while underlying interface selections are
performed on a per-packet basis considering factors such as DSCP,
flow label, application policy, signal quality, cost, etc.
Multilinking decisions are coordinated in both the outbound (i.e. MN
to correspondent) and inbound (i.e., correspondent to MN)
directions.an iterative relaying of IP packets
between MNs over an OMNI underlying interface technology (such as
omnidirectional wireless) without support of fixed infrastructure.
Multihop services entail node-to-node relaying within a
Mobile/Vehicular Ad-hoc Network (MANET/VANET) for MN-to-MN
communications and/or for "range extension" where MNs within range
of communications infrastructure elements provide forwarding
services for other MNs.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", "IP layer", etc.a *NET interface over
which an OMNI interface is configured. The OMNI interface is seen as
a L3 interface by the IP layer, and each underlying interface is
seen as a L2 interface by the OMNI interface. The underlying
interface either connects directly to the physical communications
media or coordinates with another node where the physical media is
hosted.Each
MSE and AR is assigned a unique 32-bit Identification (MSID) (see:
). IDs are assigned according to
MS-specific guidelines (e.g., see: ).A means for
ensuring fault tolerance through redundancy by connecting multiple
affiliated OMNI interfaces to independent routing topologies (i.e.,
multiple independent OMNI links).A means for
selecting underlying interface(s) for packet transmission and
reception within a single OMNI interface.The set of all SBM/PBM OMNI links
that collectively provides services for a common set of MSPs. Each
OMNI domain consists of a set of affiliated OMNI links that all
configure the same ::/48 ULA prefix with a unique 16-bit Subnet ID
as discussed in .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
Link-Local Address (MNP-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.| |
Address Binding | +----------------------------+
+---->| IP (L3) |
IP Address +---->| |
Binding | +----------------------------+
+---->| OMNI Interface |
Logical-to- +---->| (LLA) |
Physical | +----------------------------+
Interface +---->| L2 | L2 | | L2 |
Binding |(IF#1)|(IF#2)| ..... |(IF#n)|
+------+------+ +------+
| L1 | L1 | | L1 |
| | | | |
+------+------+ +------+
]]>Each underlying interface provides an L2/L1 abstraction according to
one of the following models:INET interfaces connect to an INET either natively or through one
or several IPv4 Network Address Translators (NATs). Native INET
interfaces have global IP addresses that are reachable from any INET
correspondent. NATed INET interfaces typically have private IP
addresses and connect to a private network behind one or more NATs
that provide INET access.ANET interfaces connect to a protected ANET that is separated
from the open INET by an AR acting as a proxy. The ANET interface
may be either on the same L2 link segment as the AR, or separated
from the AR by multiple IP hops.VPNed interfaces use security encapsulation over a *NET to a
Virtual Private Network (VPN) gateway. Other than the link-layer
encapsulation format, VPNed interfaces behave the same as for Direct
interfaces.Direct (aka "point-to-point") interfaces connect directly to a
peer without crossing any *NET paths. An example is a line-of-sight
link between a remote pilot and an unmanned aircraft.The OMNI virtual interface model gives rise to a number of
opportunities:since MNP-LLAs are uniquely derived from an MNP, no Duplicate
Address Detection (DAD) or Multicast Listener Discovery (MLD)
messaging is necessary.since Temporary ULAs are statistically unique, they can be used
without DAD, e.g. for MN-to-MN communications until an MNP-LLA is
obtained.*NET interfaces on the same L2 link segment as an AR do not
require any L3 addresses (i.e., not even link-local) in environments
where communications are coordinated entirely over the OMNI
interface. (An alternative would be to also assign the same LLA to
all *NET interfaces.)as underlying interface properties change (e.g., link quality,
cost, availability, etc.), any active interface can be used to
update the profiles of multiple additional interfaces in a single
message. This allows for timely adaptation and service continuity
under dynamically changing conditions.coordinating underlying 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.the OMNI interface allows inter-INET traversal when nodes located
in different INETs need to communicate with one another. This mode
of operation would not be possible via direct communications over
the underlying interfaces themselves.the OMNI Adaptation Layer (OAL) within the OMNI interface
supports lossless and adaptive path MTU mitigations not available
for communications directly over the underlying interfaces
themselves. The OAL supports "packing" of multiple IP payload
packets within a single OAL packet.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 .
Note that even when the OMNI virtual interface is present, applications
can still access underlying interfaces either through the network
protocol stack using an Internet socket or directly using a raw socket.
This allows for intra-network (or point-to-point) communications without
invoking the OMNI interface and/or OAL. For example, when an IPv6 OMNI
interface is configured over an underlying IPv4 interface, applications
can still invoke IPv4 intra-network communications as long as the
communicating endpoints are not subject to mobility dynamics. However,
the opportunities discussed above are not available when the
architectural layering is bypassed in this way. depicts the architectural model for a MN
with an attached EUN connecting to the MS via multiple independent
*NETs. When an underlying interface becomes active, the MN's OMNI
interface sends IPv6 ND messages without encapsulation if the first-hop
Access Router (AR) is on the same underlying link; otherwise, the
interface uses IP-in-IP encapsulation. The IPv6 ND messages traverse the
ground domain *NETs until they reach an AR (AR#1, AR#2, ..., AR#n),
which then coordinates with an INET Mobility Service Endpoint (MSE#1,
MSE#2, ..., MSE#m) and returns an IPv6 ND message response to the MN.
The Hop Limit in IPv6 ND messages is not decremented due to
encapsulation; hence, the OMNI interface appears to be attached to an
ordinary link..-(::EUN:::)
+--------------+ `-(::::)-'
|OMNI interface|
+----+----+----+
+--------|IF#1|IF#2|IF#n|------ +
/ +----+----+----+ \
/ | \
/ | \
v v v
(:::)-. (:::)-. (:::)-.
.-(::*NET:::) .-(::*NET:::) .-(::*NET:::)
`-(::::)-' `-(::::)-' `-(::::)-'
+----+ +----+ +----+
... |AR#1| .......... |AR#2| ......... |AR#n| ...
. +-|--+ +-|--+ +-|--+ .
. | | |
. v v v .
. <----- INET Encapsulation -----> .
. .
. +-----+ (:::)-. .
. |MSE#2| .-(::::::::) +-----+ .
. +-----+ .-(::: INET :::)-. |MSE#m| .
. (::::: Routing ::::) +-----+ .
. `-(::: System :::)-' .
. +-----+ `-(:::::::-' .
. |MSE#1| +-----+ +-----+ .
. +-----+ |MSE#3| |MSE#4| .
. +-----+ +-----+ .
. .
. .
. <----- Worldwide Connected Internetwork ----> .
...........................................................
]]>After the initial IPv6 ND message exchange, the MN (and/or any nodes
on its attached EUNs) can send and receive IP data packets over the OMNI
interface. OMNI interface multilink services will forward the packets
via ARs in the correct underlying *NETs. The AR encapsulates the packets
according to the capabilities provided by the MS and forwards them to
the next hop within the worldwide connected Internetwork via optimal
routes.OMNI links span one or more underlying Internetwork via the OMNI
Adaptation Layer (OAL) which is based on a mid-layer overlay
encapsulation using . 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.Note: OMNI interface underlying interfaces often connect directly to
physical media on the local platform (e.g., a laptop computer with WiFi,
etc.), but in some configurations the physical media may be hosted on a
separate Local Area Network (LAN) node. In that case, the OMNI interface
can establish a Layer-2 VLAN or a point-to-point tunnel (at a layer
below the underlying interface) to the node hosting the physical media.
The OMNI interface may also apply encapsulation at a layer above the
underlying interface such that packets would appear
"double-encapsulated" on the LAN; the node hosting the physical media in
turn removes the LAN encapsulation prior to transmission or inserts it
following reception. Finally, the underlying interface must monitor the
node hosting the physical media (e.g., through periodic keepalives) so
that it can convey up/down/status information to the OMNI interface.The OMNI interface observes the link nature of tunnels, including the
Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and the
role of fragmentation and reassembly . The OMNI interface is configured
over one or more underlying interfaces as discussed in , where the interfaces (and their associated *NET
paths) may have diverse MTUs. The OMNI interface accommodates MTU
diversity by encapsulating original IP packets using the OMNI Adaptation
Layer (OAL) mid-layer encapsulation and fragmentation/reassembly
service. The OAL then further encapsulates the resulting OAL
packets/fragments in *NET headers for transmission over underlying
interfaces. OMNI interface considerations for accommodating original IP
packets of various sizes are discussed in the following sections.IPv6 underlying interfaces are REQUIRED to configure a minimum MTU
of 1280 bytes and a minimum MRU of 1500 bytes . Therefore, the minimum IPv6 path MTU is 1280 bytes
since routers on the path are not permitted to perform network
fragmentation even though the destination is required to reassemble
more. The network therefore MUST forward packets of at least 1280
bytes without generating an IPv6 Path MTU Discovery (PMTUD) Packet Too
Big (PTB) message . (Note: the source can
apply "source fragmentation" for locally-generated IPv6 packets up to
1500 bytes and larger still if it if has a way to determine that the
destination configures a larger MRU, but this does not affect the
minimum IPv6 path MTU.)IPv4 underlying interfaces are REQUIRED to configure a minimum MTU
of 68 bytes and a minimum MRU of 576 bytes
. Therefore, when the
Don't Fragment (DF) bit in the IPv4 header is set to 0 the minimum
IPv4 path MTU is 576 bytes since routers on the path support network
fragmentation and the destination is required to reassemble at least
that much. The OMNI interface therefore MUST set DF to 0 in the IPv4
encapsulation headers of OAL/*NET packets that are no larger than 576
bytes, and MUST set DF to 1 in larger packets. (Note: even if the
encapsulation source has a way to determine that the encapsulation
destination configures an MRU larger than 576 bytes, it should not
assume a larger minimum IPv4 path MTU without careful consideration of
the issues discussed in .)The OMNI interface configures both an MTU and MRU of 9180 bytes
; the size is therefore not a reflection of
the underlying interface or *NET path MTUs, but rather determines the
largest original "inner-layer" IP packet the OMNI interface can
forward or reassemble. The OMNI interface employs the OAL as a
"mid-layer" encapsulation, fragmentation and reassembly service for
original IP packets, and the OAL in turn uses "outer-layer" *NET
encapsulation to forward OAL/*NET packets/fragments over the
underlying interfaces (see: ).When the network layer admits an original inner IP packet/fragment
into the OMNI interface, the OAL inserts a mid-layer IPv6
encapsulation per if fragmentation, integrity
verification and/or explicit OAL addressing is required. In other
cases (e.g., for packet transmissions between ANET peers that share a
common underlying link), the OAL MAY omit the encapsulation. When OAL
encapsulation is used, the OAL sets the header fields per standard
IPv6 procedures but does not decrement the inner IP header Hop
Limit/TTL since encapsulation occurs at a layer below IP forwarding.
The OAL next inserts a 2 octet trailer (initialized to 0) at the end
of the packet while incrementing the OAL header Payload Length to
reflect the addition of the trailer. The OAL then calculates the 2's
complement (mod 256) Fletcher's checksum over the entire OAL packet
beginning with an IPv6 pseudo-header based on the OAL header Payload
Length (see Section 8.1 of ), then writes the
results over the trailer octets. The OAL then inserts a single OMNI
Routing Header (ORH) if necessary (see: ) while incrementing Payload
Length to reflect the addition of the ORH, then fragments the OAL
packet if necessary. The OAL finally forwards the packet/fragments
over an underlying interface while adding any necessary *NET
encapsulations. The formats of OAL packets and fragments are shown in
.When an OMNI interface receives a *NET encapsulated packet from an
underlying interface, the OAL discards the *NET encapsulation headers
and examines the OAL header if present. If the packet is addressed to
a different node, the OAL re-encapsulates and forwards as discussed
below; otherwise, the OAL performs reassembly if necessary then
removes the ORH if present while decrementing Payload Length to
reflect the removal of the ORH. If the OAL header is present, the OAL
next verifies the checksum and discards the packet if the checksum is
incorrect. If the packet was accepted, the OAL then removes the OAL
header/trailer, then delivers the original packet to the IP layer.
Note that link layers include a CRC-32 integrity check which provides
effective hop-by-hop error detection in the underlying network for
packet/fragment sizes up to the OMNI interface MTU , but that some hops may traverse intermediate layers
such as tunnels over IPv4 that do not include integrity checks. The
OAL source therefore includes a trailing Fletcher checksum to allow
the OAL destination to detect packet splicing errors for fragmented
OAL packets and/or to verify integrity for packets that may have
traversed unprotected underlying network hops .
The Fletcher checksum also provides diversity with respect to both
lower layer CRCs and upper layer Internet checksums as part of a
complimentary multi-layer integrity assurance architecture.The OMNI interface assumes the IPv4 minimum path MTU (i.e., 576
bytes) as the worst case for OAL fragmentation regardless of the
underlying interface IP protocol version since IPv6/IPv4 protocol
translation and/or IPv6-in-IPv4 encapsulation may occur in any *NET
path. By always assuming the IPv4 minimum even for IPv6 underlying
interfaces, the OAL may produce smaller fragments with additional
encapsulation overhead but will always interoperate and never run the
risk of loss due to an MTU restriction or due to presenting a
destination interface with a packet that exceeds its MRU.
Additionally, the OAL path could traverse multiple *NET "segments"
with intermediate OAL forwarding nodes performing re-encapsulation
where the *NET encapsulation of the previous segment is replaced by
the *NET encapsulation of the next segment which may be based on a
different IP protocol version and/or encapsulation sizes.The OAL therefore assumes a default minimum path MTU of 576 bytes
at each *NET segment for the purpose of generating OAL fragments. In
the worst case, each successive *NET segment may re-encapsulate with
either a 20 byte IPv4 or 40 byte IPv6 header, an 8 byte UDP header and
in some cases an IP security encapsulation (40 bytes maximum assumed).
Any *NET segment may also insert a maximum-length (40 byte) ORH as an
extension to the existing 40 byte OAL IPv6 header plus 8 byte Fragment
Header if an ORH was not already present. Assuming therefore an
absolute worst case of (40 + 40 + 8) = 88 bytes for *NET encapsulation
plus (40 + 40 + 8) = 88 bytes for OAL encapsulation leaves (576 - 88 -
88) = 400 bytes to accommodate a portion of the original IP
packet/fragment. OMNI interfaces therefore set a minimum Maximum
Payload Size (MPS) of 400 bytes as the basis for the minimum-sized OAL
fragment that can be assured of traversing all segments without loss
due to an MTU/MRU restriction. The OAL fragmentation Maximum Fragment
Size (MFS) is therefore determined by the MPS plus the size of the OAL
encapsulation headers. (Note that the OAL source must include the 2
octet trailer as part of the payload during fragmentation, and the OAL
destination must regard it as ordinary payload until reassembly and
checksum verification are complete.)In light of the above, OAL source, intermediate and destination
nodes observe the following normative requirements:OAL sources MUST NOT send OAL packets/fragments including
original IP packets larger than the OMNI interface MTU, i.e.,
whether or not fragmentation is needed.OAL sources MUST NOT perform OAL fragmentation for original IP
packets smaller than the minimum MPS minus the trailer size, and
MUST produce non-final fragments that contain a payload no smaller
than the minimum MPS when performing fragmentation.OAL sources MUST NOT send OAL packets/fragments that include
any extension headers other than a single ORH and a single
Fragment Header.OAL intermediate nodes SHOULD and OAL destinations MUST
unconditionally drop OAL packets/fragments including original IP
packets larger than the OMNI interface MRU, i.e., whether or not
reassembly is needed.OAL intermediate nodes SHOULD and OAL destinations MUST
unconditionally drop any non-final OAL fragments containing a
payload smaller than the minimum MPS.OAL intermediate nodes SHOULD and OAL destinations MUST
unconditionally drop OAL packets/fragments that include any
extension headers other than a single ORH and a single Fragment
Header.The OAL source MAY maintain "path MPS" values for selected OAL
destinations initialized to the minimum MPS and increased to larger
values (up to the OMNI interface MTU) if better information is known
or discovered. For example, when *NET peers share a common underlying
link or a fixed path with a known larger MTU, the OAL can base path
MPS on this larger size (i.e., instead of 576 bytes) as long as the
*NET peer reassembles before re-encapsulating and forwarding (while
re-fragmenting if necessary). Also, if the OAL source has a way of
knowing the maximum *NET encapsulation size for all segments along the
path it may be able to increase path MPS to reserve additional room
for payload data.The OAL source can also actively probe OAL destinations to discover
larger path MPS values (e.g., per ), but care must be taken to avoid setting static
values for dynamically changing paths leading to black holes. The
probe involves sending an OAL packet larger than the current path MPS
and receiving a small acknowledgement message in response. For this
purpose, the OAL source can send a large NS message with OMNI options
with PadN sub-options (see: ) in order to
receive a small NA response from the OAL destination. While observing
the minimum MPS will always result in robust and secure behavior, the
OAL should optimize path MPS values when more efficient utilization
may result in better performance (e.g. for wireless aviation data
links).Under the minimum MPS, a common 1500 byte inner IP packet would
require 4 OAL fragments, with each non-final fragment containing 400
payload bytes and the final fragment containing 302 payload bytes
(i.e., the final 300 bytes of the original IP packet plus the 2 octet
trailer). For all packet sizes, the likelihood of successful
reassembly may improve when the OMNI interface sends all fragments of
the same fragmented OAL packet consecutively over the same underlying
interface. Finally, an assured minimum/path MPS allows continuous
operation over all paths including those that traverse bridged L2
media with dissimilar MTUs.Note: Some early network hardware of the past millennium was unable
to accept packet "bursts" resulting from an IP fragmentation event -
even to the point that the hardware would reset itself when presented
with a burst. This does not seem to be a common problem in the modern
era, where fragmentation and reassembly can be readily demonstrated at
line rate (e.g., using tools such as 'iperf3') even over fast links on
average hardware platforms. Even so, the OAL source could impose an
inter-fragment delay while the OAL destination is reporting reassembly
timeouts (see: ) and decrease the delay when
timeout reports subside.The OMNI interface performs OAL encapsulation and selects source
and destination addresses for the OAL IPv6 header according to the
node's *NET orientation. The OMNI interface sets the OAL IPv6 header
addresses to Unique Local Addresses (ULAs) based on either
Administrative (ADM-ULA) or Mobile Network Prefix (MNP-ULA) values
(see: ). When an ADM-ULA or MNP-ULA is
not available, the OMNI interface can use Temporary ULAs and/or Host
Identity Tags (HITs) instead (see: ). The
following sections discuss the addressing considerations for OMNI
Interfaces configured over *NET interfaces.When an OMNI interface sends an original IP packet toward a final
destination via an ANET interface, it sends without OAL encapsulation
if the packet (including any outer-layer ANET encapsulations) is no
larger than the underlying interface MTU for on-link ANET peers or the
minimum ANET path MTU for peers separated by multiple IP hops.
Otherwise, the OAL inserts an IPv6 header per
with source address set to the node's own ULA and destination set to
either the Administrative ULA (ADM-ULA) of the ANET peer or the Mobile
Network Prefix ULA (MNP-ULA) corresponding to the final destination
(see below). The OAL then fragments if necessary, encapsulates the OAL
packet/fragments in any ANET headers and sends them to the ANET peer
which either reassembles before forwarding if the OAL destination is
its own ULA or forwards the fragments toward the final destination
without first reassembling otherwise.When an OMNI interface sends an original IP packet toward a final
destination via an INET interface, it sends packets (including any
outer-layer INET encapsulations) no larger than the minimum INET path
MTU without OAL encapsulation if the destination is reached via an
INET address within the same OMNI link segment. Otherwise, the OAL
inserts an IPv6 header per with source
address set to the node's ULA and destination set to the ULA of an
OMNI node on the final *NET segment. The OAL then fragments if
necessary, encapsulates the OAL packet/fragments in any INET headers
and sends them toward the final segment OMNI node, which reassembles
before forwarding toward the final destination.When the OMNI interface admits original IP packets, it invokes the
OAL and returns internally-generated ICMPv4 Fragmentation Needed or ICMPv6 Path MTU Discovery (PMTUD) Packet Too Big
(PTB) messages as necessary. This document
refers to both of these ICMPv4/ICMPv6 message types simply as "PTBs",
and introduces a distinction between PTB "hard" and "soft" errors as
discussed below.Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6
header Code field value 0 are hard errors that always indicate that a
packet has been dropped due to a real MTU restriction. However, the
OMNI interface can also forward large original IP packets via OAL
encapsulation and fragmentation while at the same time returning PTB
soft error messages (subject to rate limiting) if it deems the
original IP packet too large according to factors such as link
performance characteristics, reassembly congestion, etc. This ensures
that the path MTU is adaptive and reflects the current path used for a
given data flow. The OMNI interface can therefore continuously forward
packets without loss while returning PTB soft error messages
recommending a smaller size if necessary. Original sources that
receive the soft errors in turn reduce the size of the packets they
send, i.e., the same as for hard errors.The OMNI interface sets the ICMPv4 header "unused" field or ICMPv6
header Code field to the value 1 in PTB soft error messages. The OMNI
interface sets the PTB destination address to the source address of
the original packet, and sets the source address to the MNP Subnet
Router Anycast address of the MN. The OMNI interface then sets the MTU
field to a value no smaller than 576 for ICMPv4 or 1280 for ICMPv6,
and returns the PTB soft error to the original source.When the original source receives the PTB, it reduces its path MTU
estimate the same as for hard errors but does not regard the message
as a loss indication. (If the original source does not recognize the
soft error code, it regards the PTB the same as a hard error but
should heed the retransmission advice given in suggesting retransmission based on normal
packetization layer retransmission timers.) This document therefore
updates and . Furthermore, implementations of must be aware that PTB hard or soft errors may
arrive at any time even if after a successful MTU probe (this is the
same consideration as for an ordinary path fluctuation following a
successful probe).An OMNI interface that reassembles OAL fragments may experience
congestion-oriented loss in its reassembly cache and can optionally
send PTB soft errors to the original source and/or ICMP "Time
Exceeded" messages to the source of the OAL fragments. In environments
where the messages may contribute to unacceptable additional
congestion, however, the OMNI interface can refrain from sending PTB
soft errors and simply regard the loss as an ordinary unreported
congestion event for which the original source will eventually
compensate.Applications that receive PT soft errors can dynamically tune the
size of the packets they to send to produce the best possible
throughput and latency, with the understanding that these parameters
may change over time due to factors such as congestion, mobility,
network path changes, etc. The receipt or absence of soft errors
should be seen as hints of when increasing or decreasing packet sizes
may be beneficial.In summary, the OMNI interface supports continuous transmission and
reception of packets of various sizes in the face of dynamically
changing network conditions. Moreover, since PTB soft errors do not
indicate loss, original sources that receive soft errors can quickly
scan for path MTU increases without waiting for the minimum 10 minutes
specified for loss-oriented PTB hard errors . The OMNI interface
therefore provides a lossless and adaptive service that accommodates
MTU diversity especially well-suited for dynamic multilink
environments.As discussed in Section 3.7 of , there are
four basic threats concerning IPv6 fragmentation; each of which is
addressed by effective mitigations as follows:Overlapping fragment attacks - reassembly of overlapping
fragments is forbidden by ; therefore,
this threat does not apply to the OAL.Resource exhaustion attacks - this threat is mitigated by
providing a sufficiently large OAL reassembly cache and
instituting “fast discard” of incomplete reassemblies
that may be part of a buffer exhaustion attack. The reassembly
cache should be sufficiently large so that a sustained attack does
not cause excessive loss of good reassemblies but not so large
that (timer-based) data structure management becomes
computationally expensive. The cache should also be indexed based
on the arrival underlying interface such that congestion
experienced over a first underlying interface does not cause
discard of incomplete reassemblies for uncongested underlying
interfaces.Attacks based on predictable fragment identification values -
this threat is mitigated by selecting a suitably random ID value
per . Additionally, inclusion of the
trailing Fletcher checksum would make it very difficult for an
attacker who could somehow predict a fragment identification value
to inject malicious fragments resulting in undetected reassemblies
of bad data.Evasion of Network Intrusion Detection Systems (NIDS) - this
threat is mitigated by setting a minimum MPS for OAL
fragmentation, which defeats all "tiny fragment"-based
attacks.Additionally, IPv4 fragmentation includes a 16-bit
Identification (IP ID) field with only 65535 unique values such that
at high data rates the field could wrap and apply to new packets while
the fragments of old packets using the same ID are still alive in the
network . However, since the largest OAL
fragment that will be sent via an IPv4 *NET path with DF = 0 is 576
bytes any IPv4 fragmentation would occur only on links with an IPv4
MTU smaller than this size, and
recommendations suggest that such links will have low data rates.
Since IPv6 provides a 32-bit Identification value, IP ID wraparound at
high data rates is not a concern for IPv6 fragmentation.Finally, documents fragmentation security
concerns for large IPv6 ND messages. These concerns are addressed when
the OMNI interface employs the OAL instead of directly fragmenting the
IPv6 ND message itself. For this reason, OMNI interfaces MUST NOT
admit IPv6 ND messages larger than the OMNI interface MTU, and MUST
employ the OAL for IPv6 ND messages admitted into the OMNI interface
the same as discussed above.By default, the OAL source includes a 40-byte IPv6 encapsulation
header for each original IP packet during OAL encapsulation. The OAL
source also calculates and appends a 2 octet trailing Fletcher
checksum then performs fragmentation such that a copy of the 40-byte
IPv6 header plus an 8-byte IPv6 Fragment Header is included in each
OAL fragment (when an ORH is added, the OAL encapsulation headers
become larger still). However, these encapsulations may represent
excessive overhead in some environments. A technique known as
"packing" discussed in is
therefore supported so that multiple original IP packets can be
included within a single OAL "super-packet".When the OAL source has multiple original IP packets with total
length no larger than the OMNI interface MTU to send to the same
destination, it can concatenate them into a super-packet encapsulated
in a single OAL header and trailing checksum. Within the OAL
super-packet, the IP header of the first original packet (iHa)
followed by its data (iDa) is concatenated immediately following the
OAL header, then the IP header of the next original packet (iHb)
followed by its data (iDb) is concatenated immediately following the
first original packet, etc. with the trailing checksum included last.
The OAL super-packet format is transposed from and shown in :
+-----+-----+
| iHa | iDa |
+-----+-----+
|
| +-----+-----+
| | iHb | iDb |
| +-----+-----+
| |
| | +-----+-----+
| | | iHc | iDc |
| | +-----+-----+
| | |
v v v
+----------+-----+-----+-----+-----+-----+-----+----+
| OAL Hdr | iHa | iDa | iHb | iDb | iHc | iDc |Csum|
+----------+-----+-----+-----+-----+-----+-----+----+
<--- OAL "Super-Packet" with single OAL Hdr/Csum --->
]]>When the OAL source prepares a super-packet, it applies OAL
fragmentation if necessary then sends the packet or fragments to the
OAL destination. When the OAL destination receives the super-packet it
reassembles if necessary, verifies and removes the trailing checksum,
then regards the remaining OAL header Payload Length as the sum of the
lengths of all payload packets. The OAL destination then selectively
extracts each original IP packet (e.g., by setting pointers into the
super-packet buffer and maintaining a reference count, by copying each
packet into a separate buffer, etc.) and forwards each packet or
processes it locally as appropriate. During extraction, the OAL
determines the IP protocol version of each successive original IP
packet 'j' by examining the four most-significant bits of iH(j), and
determines the length of the packet by examining the rest of iH(j)
according to the IP protocol version.Note that OMNI interfaces must take care to avoid processing
super-packet payload elements that would subvert security.
Specifically, if a super-packet contains a mix of data and control
payload packets (which could include critical security codes), the
node MUST NOT process the data packets before processing the control
packetsThe OMNI interface transmits original IP packets by first invoking
the OAL, next including any *NET encapsulations and finally engaging the
native frame format of the 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 various forms of tunnels the frame format is found in the
appropriate tunneling specification, etc.The OMNI interface SHOULD minimize the amount of *NET encapsulation
for increased efficiency. For example, while an OMNI node may need to
use UDP/IP as a *NET encapsulation over underlying interfaces connected
to an open Internetwork, it may be able to omit the UDP header over
underlying interfaces connected to *NETs that do not include NATs or
packet filtering gateways. Similarly, when an OMNI MN shares a common
underlying link with an AR, the MN may be able to avoid including any
*NET encapsulations and instead directly engage the underlying interface
native frame format. Further considerations for *NET encapsulation are
discussed throughout the document and in .OMNI nodes are assigned OMNI interface IPv6 Link-Local Addresses
(LLAs) through pre-service administrative actions. "MNP-LLAs" embed the
MNP assigned to the mobile node, while "ADM-LLAs" include an
administratively-unique ID that is guaranteed to be unique on the link.
LLAs are configured as follows:IPv6 MNP-LLAs encode the most-significant 64 bits of a MNP within
the least-significant 64 bits of the IPv6 link-local prefix
fe80::/64, i.e., in the LLA "interface identifier" portion. The
prefix length for the LLA is determined by adding 64 to the MNP
prefix length. For example, for the MNP 2001:db8:1000:2000::/56 the
corresponding MNP-LLA is fe80::2001:db8:1000:2000/120.IPv4-compatible MNP-LLAs are constructed as fe80::ffff:[IPv4],
i.e., the interface identifier consists of 16 '0' bits, followed by
16 '1' bits, followed by a 32bit IPv4 address/prefix. The prefix
length for the LLA is determined by adding 96 to the MNP prefix
length. For example, the IPv4-Compatible MN OMNI LLA for
192.0.2.0/24 is fe80::ffff:192.0.2.0/120 (also written as
fe80::ffff:c000:0200/120).ADM-LLAs are assigned to ARs and MSEs and MUST be managed for
uniqueness. The lower 32 bits of the LLA includes a unique integer
"MSID" value between 0x00000001 and 0xfeffffff, e.g., as in fe80::1,
fe80::2, fe80::3, etc., fe80::feffffff. The ADM-LLA prefix length is
determined by adding 96 to the MSID prefix length. For example, if
the prefix length for MSID 0x10012001 is 16 then the ADM-LLA prefix
length is set to 112 and the LLA is written as fe80::1001:2001/112.
The "zero" address for each ADM-LLA prefix is the Subnet-Router
anycast address for that prefix ; for
example, the Subnet-Router anycast address for fe80::1001:2001/112
is simply fe80::1001:2000. The MSID range 0xff000000 through
0xffffffff is reserved for future use.Since the prefix 0000::/8 is "Reserved by the IETF" , no MNPs can be allocated from that block ensuring
that there is no possibility for overlap between the different MNP- and
ADM-LLA constructs discussed above.Since MNP-LLAs are based on the distribution of administratively
assured unique MNPs, and since ADM-LLAs are guaranteed unique through
administrative assignment, OMNI interfaces set the autoconfiguration
variable DupAddrDetectTransmits to 0 .Note: If future protocol extensions relax the 64-bit boundary in IPv6
addressing, the additional prefix bits of an MNP could be encoded in
bits 16 through 63 of the MNP-LLA. (The most-significant 64 bits would
therefore still be in bits 64-127, and the remaining bits would appear
in bits 16 through 48.) However, the analysis provided in suggests that the 64-bit boundary will remain in the
IPv6 architecture for the foreseeable future.Note: Even though this document honors the 64-bit boundary in IPv6
addressing, it specifies prefix lengths longer than /64 for routing
purposes. This effectively extends IPv6 routing determination into the
interface identifier portion of the IPv6 address, but it does not
redefine the 64-bit boundary. Modern routing protocol implementations
honor IPv6 prefixes of all lengths, up to and including /128.OMNI domains use IPv6 Unique-Local Addresses (ULAs) as the source and
destination addresses in OAL IPv6 encapsulation headers. ULAs are only
routable within the scope of a an OMNI domain, and are derived from the
IPv6 Unique Local Address prefix fc00::/7 followed by the L bit set to 1
(i.e., as fd00::/8) followed by a 40-bit pseudo-random Global ID to
produce the prefix [ULA]::/48, which is then followed by a 16-bit Subnet
ID then finally followed by a 64 bit Interface ID as specified in
Section 3 of . All nodes in the same OMNI domain
configure the same 40-bit Global ID as the OMNI domain identifier. The
statistic uniqueness of the 40-bit pseudo-random Global ID allows
different OMNI domains to be joined together in the future without
requiring renumbering.Each OMNI link instance is identified by a value between 0x0000 and
0xfeff in bits 48-63 of [ULA]::/48; the values 0xff00 through 0xfffe are
reserved for future use, and the value 0xffff denotes the presence of a
Temporary ULA (see below). For example, OMNI ULAs associated with
instance 0 are configured from the prefix [ULA]:0000::/64, instance 1
from [ULA]:0001::/64, instance 2 from [ULA]:0002::/64, etc. ULAs and
their associated prefix lengths are configured in correspondence with
LLAs through stateless prefix translation where "MNP-ULAs" are assigned
in correspondence to MNP-LLAs and "ADM-ULAs" are assigned in
correspondence to ADM-LLAs. For example, for OMNI link instance
[ULA]:1010::/64:the MNP-ULA corresponding to the MNP-LLA fe80::2001:db8:1:2 with
a 56-bit MNP length is derived by copying the lower 64 bits of the
LLA into the lower 64 bits of the ULA as [ULA]:1010:2001:db8:1:2/120
(where, the ULA prefix length becomes 64 plus the IPv6 MNP
length).the MNP-ULA corresponding to fe80::ffff:192.0.2.0 with a 28-bit
MNP length is derived by simply writing the LLA interface ID into
the lower 64 bits as [ULA]:1010:0:ffff:192.0.2.0/124 (where, the ULA
prefix length is 64 plus 32 plus the IPv4 MNP length).the ADM-ULA corresponding to fe80::1000/112 is simply
[ULA]:1010::1000/112.the ADM-ULA corresponding to fe80::/128 is simply
[ULA]:1010::/128.etc.Each OMNI interface assigns the Anycast ADM-ULA specific to the OMNI
link instance. For example, the OMNI interface connected to instance 3
assigns the Anycast address [ULA]:0003::/128. Routers that configure
OMNI interfaces advertise the OMNI service prefix (e.g.,
[ULA]:0003::/64) into the local routing system so that applications can
direct traffic according to SBM requirements.The ULA presents an IPv6 address format that is routable within the
OMNI routing system and can be used to convey link-scoped IPv6 ND
messages across multiple hops using IPv6 encapsulation . 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 OAL encapsulation is omitted
whenever possible to conserve bandwidth (see: ).Each OMNI link can be subdivided into "segments" that often
correspond to different administrative domains or physical partitions.
OMNI nodes can use IPv6 Segment Routing 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 .Temporary ULAs are constructed per based on
the prefix [ULA]:ffff::/64 and used by MNs when they have no other
addresses. Temporary ULAs can be used for MN-to-MN communications
outside the context of any supporting OMNI link infrastructure, and can
also be used as an initial address while the MN is in the process of
procuring an MNP. Temporary ULAs are not routable within the OMNI
routing system, and are therefore useful only for OMNI link "edge"
communications. Temporary ULAs employ optimistic DAD principles since they are probabilistically unique.Note: IPv6 ULAs taken from the prefix fc00::/7 followed by the L bit
set to 0 (i.e., as fc00::/8) are never used for OMNI OAL addressing,
however the range could be used for MSP and MNP addressing under certain
limiting conditions (see: ).OMNI domains use IP Global Unicast Address (GUA) prefixes as Mobility Service Prefixes (MSPs) from which Mobile
Network Prefixes (MNP) are delegated to Mobile Nodes (MNs).For IPv6, GUA prefixes are assigned by IANA
and/or an associated regional assigned numbers authority such that the
OMNI domain can be interconnected to the global IPv6 Internet without
causing inconsistencies in the routing system. An OMNI domain could
instead use ULAs with the 'L' bit set to 0 (i.e., from the prefix
fc00::/8), however this would require
IPv6 NAT if the domain were ever connected to the global IPv6
Internet.For IPv4, GUA prefixes are assigned by IANA
and/or an associated regional assigned numbers authority such that the
OMNI domain can be interconnected to the global IPv4 Internet without
causing routing inconsistencies. An OMNI domain could instead use
private IPv4 prefixes (e.g., 10.0.0.0/8, etc.) ,
however this would require IPv4 NAT if the domain were ever connected to
the global IPv4 Internet.OMNI MNs and MSEs that connect over open Internetworks generate a
Host Identity Tag (HIT) as specified in and use
the value as a robust general-purpose node identification value.
Hierarchical HITs (HHITs) may provide
a useful alternative in certain domains such as the Unmanned (Air)
Traffic Management (UTM) service for Unmanned Air Systems (UAS). MNs and
MSEs can then use their (H)HITs in IPv6 ND control message
exchanges.When a MN is truly outside the context of any infrastructure, it may
have no MNP information at all. In that case, the MN can use its (H)HIT
as an IPv6 source/destination address for sustained communications in
Vehicle-to-Vehicle (V2V) and (multihop) Vehicle-to-Infrastructure (V2I)
scenarios. The MN can also propagate the (H)HIT into the multihop
routing tables of (collective) Mobile/Vehicular Ad-hoc Networks
(MANETs/VANETs) using only the vehicles themselves as communications
relays.When a MN connects to ARs over (non-multihop) protected-spectrum
ANETs, an alternate form of node identification (e.g., MAC address,
serial number, airframe identification value, VIN, etc.) may be
sufficient. In that case, the MN should still generate a (H)HIT and
maintain it in conjunction with any other node identifiers. The MN can
then include OMNI "Node Identification" sub-options (see: ) in IPv6 ND messages should the need to transmit
identification information over the network arise.OMNI interfaces maintain a neighbor cache for tracking per-neighbor
state and use the link-local address format specified in . OMNI interface IPv6 Neighbor Discovery (ND)
messages sent over physical underlying
interfaces without encapsulation observe the native underlying interface
Source/Target Link-Layer Address Option (S/TLLAO) format (e.g., for
Ethernet the S/TLLAO is specified in ). OMNI
interface IPv6 ND messages sent over underlying interfaces via
encapsulation do not include S/TLLAOs which were intended for encoding
physical L2 media address formats and not encapsulation IP addresses.
Furthermore, S/TLLAOs are not intended for encoding additional interface
attributes needed for multilink coordination. Hence, this document does
not define an S/TLLAO format but instead defines a new option type
termed the "OMNI option" designed for these purposes.MNs such as aircraft typically have many wireless data link types
(e.g. satellite-based, cellular, terrestrial, air-to-air directional,
etc.) with diverse performance, cost and availability properties. 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 TBD1.Length is set to the number of 8 octet blocks in the option. The
value 0 is invalid, while the values 1 through 255 (i.e., 8 through
2040 octets, respectively) indicate the total length of the OMNI
option.Preflen is an 8 bit field that determines the length of prefix
associated with an LLA. Values 0 through 128 specify a valid prefix
length (all other values are invalid). For IPv6 ND messages sent
from a MN to the MS, Preflen applies to the IPv6 source LLA and
provides the length that the MN is requesting or asserting to the
MS. For IPv6 ND messages sent from the MS to the MN, Preflen applies
to the IPv6 destination LLA and indicates the length that the MS is
granting to the MN. For IPv6 ND messages sent between MS endpoints,
Preflen provides the length associated with the source/target MN
that is subject of the ND message.S/T-omIndex is an 8 bit field corresponds to the omIndex value
for source or target underlying interface used to convey this IPv6
ND message. OMNI interfaces MUST number each distinct underlying
interface with an omIndex value between '1' and '255' that
represents a MN-specific 8-bit mapping for the actual ifIndex value
assigned by network management (the omIndex
value '0' is reserved for use by the MS). For RS and NS messages,
S/T-omIndex corresponds to the source underlying interface the
message originated from. For RA and NA messages, S/T-omIndex
corresponds to the target underlying interface that the message is
destined to. (For NS messages used for Neighbor Unreachability
Detection (NUD), S/T-omIndex instead identifies the neighbor's
underlying interface to be used as the target interface to return
the NA.)Sub-Options is a Variable-length field, of length such that the
complete OMNI Option is an integer multiple of 8 octets long.
Contains one or more Sub-Options, as described in .The OMNI option may appear in any IPv6 ND message type; it is
processed by interfaces that recognize the option and ignored by all
other interfaces. If multiple OMNI option instances appear in the same
IPv6 ND message, the interface processes the Preflen and S/T-omIndex
fields in the first instance and ignores those fields in all other
instances. The interface processes the Sub-Options of all OMNI option
instances in the same IPv6 ND message in the consecutive order in which
they appear.The OMNI option(s) in each IPv6 ND message may include full or
partial information for the neighbor. The union of the information in
the most recently received OMNI options is therefore retained, and the
information is aged/removed in conjunction with the corresponding
neighbor cache entry.Each OMNI option includes zero or more Sub-Options. Each
consecutive Sub-Option is concatenated immediately after its
predecessor. All Sub-Options except Pad1 (see below) are in
type-length-value (TLV) encoded in the following format: Sub-Type is a 5-bit field that encodes the Sub-Option type.
Sub-Options defined in this document are:Sub-Types 11-29 are available for future assignment for
major protocol functions. Sub-Type 31 is reserved by IANA.Sub-Length is an 11-bit field that encodes the length of the
Sub-Option Data ranging from 0 to 2034 octets.Sub-Option Data is a block of data with format determined by
Sub-Type and length determined by Sub-Length.During transmission, the OMNI interface codes Sub-Type and
Sub-Length together in network byte order in 2 consecutive octets,
where Sub-Option Data may be up to 2034 octets in length. This allows
ample space for coding large objects (e.g., ASCII strings, domain
names, protocol messages, security codes, etc.), while a single OMNI
option is limited to 2040 octets the same as for any IPv6 ND option.
If the Sub-Options to be coded would cause an OMNI option to exceed
2040 octets, the OMNI interface codes any remaining Sub-Options in
additional OMNI option instances in the intended order of processing
in the same IPv6 ND message. Implementations must therefore observe
size limitations, and must refrain from sending IPv6 ND messages
larger than the OMNI interface MTU. If the available OMNI information
would cause a single IPv6 ND message to exceed the OMNI interface MTU,
the OMNI interface codes as much as possible in a first IPv6 ND
message and codes the remainder in additional IPv6 ND messages.During reception, the OMNI interface processes each OMNI option
Sub-Option while skipping over and ignoring any unrecognized
Sub-Options. The OMNI interface processes the Sub-Options of all OMNI
option instances in the consecutive order in which they appear in the
IPv6 ND message, beginning with the first instance and continuing
through any additional instances to the end of the message. If a
Sub-Option length would cause processing to exceed the OMNI option
total length, the OMNI interface accepts any Sub-Options already
processed and ignores the final Sub-Option. The interface then
processes any remaining OMNI options in the same fashion to the end of
the IPv6 ND message.Note: large objects that exceed the Sub-Option Data limit of 2034
octets are not supported under the current specification; if this
proves to be limiting in practice, future specifications may define
support for fragmenting large objects across multiple OMNI options
within the same IPv6 ND message.The following Sub-Option types and formats are defined in this
document:Sub-Type is set to 0. If multiple instances appear in OMNI
options of the same message all are processed.Sub-Type is followed by 3 'x' bits, set to any value on
transmission (typically all-zeros) and ignored on receipt. Pad1
therefore consists of 1 octet with the most significant 5 bits
set to 0, and with no Sub-Length or Sub-Option Data fields
following.Sub-Type is set to 1. If multiple instances appear in OMNI
options of the same message all are processed.Sub-Length is set to N (from 0 to 2034) that encodes the
number of padding octets that follow.Sub-Option Data consists of N octets, set to any value on
transmission (typically all-zeros) and ignored on receipt.The Interface Attributes (Type 1) sub-option provides a basic set
of attributes for underlying interfaces. Interface Attributes (Type
1) is deprecated throughout the rest of this specification, and
Interface Attributes (Type 2) (see: ) are
indicated wherever the term "Interface Attributes" appears without
an associated Type designation.Nodes SHOULD NOT include Interface Attributes (Type 1)
sub-options in IPv6 ND messages they send, and MUST ignore any in
IPv6 ND messages they receive. If an Interface Attributes (Type 1)
is included, it must have the following format:Sub-Type is set to 2. If multiple instances with different
omIndex values appear in OMNI option of the same message all are
processed; if multiple instances with the same omIndex value
appear, the first is processed and all others are ignoredSub-Length is set to N (from 4 to 2034) that encodes the
number of Sub-Option Data octets that follow.omIndex is a 1-octet field containing a value from 0 to 255
identifying the underlying interface for which the attributes
apply.omType is a 1-octet field containing a value from 0 to 255
corresponding to the underlying interface identified by
omIndex.Provider ID is a 1-octet field containing a value from 0 to
255 corresponding to the underlying interface identified by
omIndex.Link encodes a 4-bit link metric. The value '0' means the
link is DOWN, and the remaining values mean the link is UP with
metric ranging from '1' ("lowest") to '15' ("highest").Resvd is reserved for future use. Set to 0 on transmission
and ignored on reception.A 16-octet ""Preferences" field immediately follows 'Resvd',
with values P[00] through P[63] corresponding to the 64
Differentiated Service Code Point (DSCP) values . Each 2-bit P[*] field is set to the value
'0' ("disabled"), '1' ("low"), '2' ("medium") or '3' ("high") to
indicate a QoS preference for underlying interface selection
purposes.The Interface Attributes (Type 2) sub-option provides L2
forwarding information for the multilink conceptual sending
algorithm discussed in . The L2 information
is used for selecting among potentially multiple candidate
underlying interfaces that can be used to forward packets to the
neighbor based on factors such as DSCP preferences and link quality.
Interface Attributes (Type 2) further includes link-layer address
information to be used for either OAL encapsulation or direct UDP/IP
encapsulation (when OAL encapsulation can be avoided).Interface Attributes (Type 2) are the sole Interface Attributes
format in this specification that all OMNI nodes must honor.
Wherever the term "Interface Attributes" occurs throughout this
specification without a "Type" designation, the format given below
is indicated:Sub-Type is set to 3. If multiple instances with different
omIndex values appear in OMNI options of the same message all
are processed; if multiple instances with the same omIndex value
appear, the first is processed and all others are ignored.Sub-Length is set to N (from 4 to 2034) that encodes the
number of Sub-Option Data octets that follow. The 'omIndex',
'omType', 'Provider ID', 'Link', 'R' and 'API' fields are always
present; hence, the remainder of the Sub-Option Data is limited
to 2030 octets.Sub-Option Data contains an "Interface Attributes (Type 2)"
option encoded as follows:omIndex is set to an 8-bit integer value corresponding to
a specific underlying interface the same as specified above
for the OMNI option S/T-omIndex field. The OMNI options of a
same message may include multiple Interface Attributes
Sub-Options, with each distinct omIndex value pertaining to
a different underlying interface. The OMNI option will often
include an Interface Attributes Sub-Option with the same
omIndex value that appears in the S/T-omIndex. In that case,
the actual encapsulation address of the received IPv6 ND
message should be compared with the L2ADDR encoded in the
Sub-Option (see below); if the addresses are different (or,
if L2ADDR is absent) the presence of a NAT is assumed.omType is set to an 8-bit integer value corresponding to
the underlying interface identified by omIndex. The value
represents an OMNI interface-specific 8-bit mapping for the
actual IANA ifType value registered in the 'IANAifType-MIB'
registry [http://www.iana.org].Provider ID is set to an OMNI interface-specific 8-bit ID
value for the network service provider associated with this
omIndex.Link encodes a 4-bit link metric. The value '0' means the
link is DOWN, and the remaining values mean the link is UP
with metric ranging from '1' ("lowest") to '15'
("highest").R is reserved for future use.API - a 3-bit "Address/Preferences/Indexed" code that
determines the contents of the remainder of the sub-option
as follows:When the most significant bit (i.e., "Address") is
set to 1, the SRT, FMT, LHS and L2ADDR fields are
included immediately following the API code; else, they
are omitted.When the next most significant bit (i.e.,
"Preferences") is set to 1, a preferences block is
included next; else, it is omitted. (Note that if
"Address" is set the preferences block immediately
follows L2ADDR; else, it immediately follows the API
code.)When a preferences block is present and the least
significant bit (i.e., "Indexed") is set to 0, the block
is encoded in "Simplex" form as shown in ; else it is encoded in
"Indexed" form as discussed below.When API indicates that an "Address" is included, the
following fields appear in consecutive order (else, they are
omitted):SRT - a 5-bit Segment Routing Topology prefix length
value that (when added to 96) determines the prefix
length to apply to the ULA formed from concatenating
[ULA*]::/96 with the 32 bit LHS MSID value that follows.
For example, the value 16 corresponds to the prefix
length 112.FMT - a 3-bit "Framework/Mode/Type" code
corresponding to the included Link Layer Address as
follows:When the most significant bit (i.e., "Framework")
is set to 1, L2ADDR is the INET encapsulation
address for the Source/Target Client itself;
otherwise L2ADDR is the address of the Server/Proxy
named in the LHS.When the next most significant bit (i.e., "Mode")
is set to 1, the Framework node is (likely) located
behind an INET Network Address Translator (NAT);
otherwise, it is on the open INET.When the least significant bit (i.e., "Type") is
set to 0, L2ADDR includes a UDP Port Number followed
by an IPv4 address; otherwise, it includes a UDP
Port Number followed by an IPv6 address.LHS - the 32 bit MSID of the Last Hop Server/Proxy on
the path to the target. When SRT and LHS are both set to
0, the LHS is considered unspecified in this IPv6 ND
message. When SRT is set to 0 and LHS is non-zero, the
prefix length is set to 128. SRT and LHS together
provide guidance to the OMNI interface forwarding
algorithm. Specifically, if SRT/LHS is located in the
local OMNI link segment then the OMNI interface can
encapsulate according to FMT/L2ADDR (following any
necessary NAT traversal messaging); else, it must
forward according to the OMNI link spanning tree. See
for further
discussion.Link Layer Address (L2ADDR) - Formatted according to
FMT, and identifies the link-layer address (i.e., the
encapsulation address) of the source/target. The UDP
Port Number appears in the first 2 octets and the IP
address appears in the next 4 octets for IPv4 or 16
octets for IPv6. The Port Number and IP address are
recorded in network byte order, and in ones-compliment
"obfuscated" form per . The OMNI
interface forwarding algorithm uses FMT/L2ADDR to
determine the encapsulation address for forwarding when
SRT/LHS is located in the local OMNI link segment. Note
that if the target is behind a NAT, L2ADDR will contain
the mapped INET address stored in the NAT; otherwise,
L2ADDR will contain the native INET information of the
target itself.When API indicates that "Preferences" are included, a
preferences block appears as the remainder of the Sub-Option
as a series of Bitmaps and P[*] values. In "Simplex" form,
the index for each singleton Bitmap octet is inferred from
its sequential position (i.e., 0, 1, 2, ...) as shown in
. In "Indexed" form, each
Bitmap is preceded by an Index octet that encodes a value
"i" = (0 - 255) as the index for its companion Bitmap as
follows:The preferences consist of a first (simplex/indexed)
Bitmap (i.e., "Bitmap(i)") followed by 0-8 single-octet
blocks of 2-bit P[*] values, followed by a second Bitmap
(i), followed by 0-8 blocks of P[*] values, etc. Reading
from bit 0 to bit 7, the bits of each Bitmap(i) that are set
to '1'' indicate the P[*] blocks from the range P[(i*32)]
through P[(i*32) + 31] that follow; if any Bitmap(i) bits
are '0', then the corresponding P[*] block is instead
omitted. For example, if Bitmap(0) contains 0xff then the
block with P[00]-P[03], followed by the block with
P[04]-P[07], etc., and ending with the block with
P[28]-P[31] are included (as shown in ). The next Bitmap(i) is then
consulted with its bits indicating which P[*] blocks follow,
etc. out to the end of the Sub-Option.Each 2-bit P[*] field is set to the value '0'
("disabled"), '1' ("low"), '2' ("medium") or '3' ("high") to
indicate a QoS preference for underlying interface selection
purposes. Not all P[*] values need to be included in the
OMNI option of each IPv6 ND message received. Any P[*]
values represented in an earlier OMNI option but omitted in
the current OMNI option remain unchanged. Any P[*] values
not yet represented in any OMNI option default to
"medium".The first 16 P[*] blocks correspond to the 64
Differentiated Service Code Point (DSCP) values P[00] -
P[63] . 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.Sub-Type is set to 4. If multiple instances appear in OMNI
options of the same message all are processed, i.e., even if the
same omIndex value appears multiple times.Sub-Length is set to N (from 1 to 2034) that encodes the
number of Sub-Option Data octets that follow.Sub-Option Data contains a 1 octet omIndex encoded exactly as
specified in , followed by an N-1 octet
traffic selector formatted per
beginning with the "TS Format" field. The largest traffic
selector for a given omIndex is therefore 2033 octets.Sub-Type is set to 5. If multiple instances appear in OMNI
options of the same message all are processed. Only the first
MAX_MSID values processed (whether in a single instance or
multiple) are retained and all other MSIDs are ignored.Sub-Length is set to 4n, with 508 as the maximum value for n.
The length of the Sub-Option Data section is therefore limited
to 2032 octets.A list of n 4 octet MSIDs is included in the following 4n
octets. The Anycast MSID value '0' in an RS message MS-Register
sub-option requests the recipient to return the MSID of a nearby
MSE in a corresponding RA response.Sub-Type is set to 6. If multiple instances appear in OMNI
options of the same message all are processed. Only the first
MAX_MSID values processed (whether in a single instance or
multiple) are retained and all other MSIDs are ignored.Sub-Length is set to 4n, with 508 as the maximum value for n.
The length of the Sub-Option Data section is therefore limited
to 2032 octets.A list of n 4 octet MSIDs is included in the following 4n
octets. The Anycast MSID value '0' is ignored in MS-Release
sub-options, i.e., only non-zero values are processed.Sub-Type is set to 7. If multiple instances appear in OMNI
options of the same message the first is processed and all
others are ignored.Sub-Length is set to N (from 0 to 2034) that encodes the
number of Sub-Option Data octets that follow.A set of Geo Coordinates of maximum length 2034 octets.
Format(s) to be specified in future documents; should include
Latitude/Longitude, plus any additional attributes such as
altitude, heading, speed, etc.The Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
sub-option may be included in the OMNI options of RS messages sent
by MNs and RA messages returned by MSEs. ARs that act as proxys to
forward RS/RA messages between MNs and MSEs also forward DHCPv6
sub-options unchanged and do not process DHCPv6 sub-options
themselves. Sub-Type is set to 8. If multiple instances appear in OMNI
options of the same message the first is processed and all
others are ignored.Sub-Length is set to N (from 4 to 2034) that encodes the
number of Sub-Option Data octets that follow. The 'msg-type' and
'transaction-id' fields are always present; hence, the length of
the DHCPv6 options is restricted to 2030 octets.'msg-type' and 'transaction-id' are coded according to
Section 8 of .A set of DHCPv6 options coded according to Section 21 of
follows.The Host Identity Protocol (HIP) Message sub-option may be
included in the OMNI options of RS messages sent by MNs and RA
messages returned by ARs. ARs that act as proxys authenticate and
remove HIP messages in RS messages they forward from a MN to an MSE.
ARs that act as proxys insert and sign HIP messages in the RA
messages they forward from an MSE to a MN.Sub-Type is set to 9. If multiple instances appear in OMNI
options of the same message the first is processed and all
others are ignored.Sub-Length is set to N, i.e., the length of the option in
octets beginning immediately following the Sub-Length field and
extending to the end of the HIP parameters. The length of the
entire HIP message is therefore restricted to 2034 octets.The HIP message is coded exactly as specified in Section 5 of
, except that the OMNI "Sub-Type" and
"Sub-Length" fields replace the first 2 octets of the HIP
message header (i.e., the Next Header and Header Length
fields).Sub-Type is set to 10. If multiple instances appear in OMNI
options of the same IPv6 ND message the first instance of a
specific ID-Type is processed and all other instances of the
same ID-Type are ignored. (Note therefore that it is possible
for a single IPv6 ND message to convey multiple Node
Identifications - each having a different ID-Type.)Sub-Length is set to N (from 1 to 2034) that encodes the
number of Sub-Option Data octets that follow. The ID-Type field
is always present; hence, the maximum Node Identification Value
length is 2033 octets.ID-Type is a 1 octet field that encodes the type of the Node
Identification Value. The following ID-Type values are currently
defined:0 - Universally Unique IDentifier (UUID) . Indicates that Node Identification Value
contains a 16 octet UUID.1 - Host Identity Tag (HIT) .
Indicates that Node Identification Value contains a 16 octet
HIT.2 - Hierarchical HIT (HHIT) . Indicates that Node
Identification Value contains a 16 octet HHIT.3 - Network Access Identifier (NAI) . Indicates that Node Identification Value
contains an N-1 octet NAI.4 - Fully-Qualified Domain Name (FQDN) . Indicates that Node Identification Value
contains an N-1 octet FQDN.5 - 252 - Unassigned.253-254 - Reserved for experimentation, as recommended in
.255 - reserved by IANA.Node Identification Value is an (N - 1) octet field encoded
according to the appropriate the "ID-Type" reference above.When a Node Identification Value is needed for DHCPv6 messaging
purposes, it is encoded as a DHCP Unique IDentifier (DUID) using the
"DUID-EN for OMNI" format with enterprise number 45282 (see: ) as shown in :In this format, the ID-Type and Node Identification Value fields
are coded exactly as in following the 6
octet DUID-EN header, and the entire "DUID-EN for OMNI" is included
in a DHCPv6 message per .Since the Sub-Type field is only 5 bits in length, future
specifications of major protocol functions may exhaust the remaining
Sub-Type values available for assignment. This document therefore
defines Sub-Type 30 as an "extension", meaning that the actual
sub-option type is determined by examining a 1 octet
"Extension-Type" field immediately following the Sub-Length field.
The Sub-Type Extension is formatted as shown in :Sub-Type is set to 30. If multiple instances appear in OMNI
options of the same message all are processed, where each
individual extension defines its own policy for processing
multiple of that type.Sub-Length is set to N (from 1 to 2034) that encodes the
number of Sub-Option Data octets that follow. The Extension-Type
field is always present; hence, the maximum Extension-Type Body
length is 2033 octets.Extension-Type contains a 1 octet Sub-Type Extension value
between 0 and 255.Extension-Type Body contains an N-1 octet block with format
defined by the given extension specification.Extension-Type values 2 through 252 are available for
assignment by future specifications, which must also define the
format of the Extension-Type Body and its processing rules.
Extension-Type values 253 and 254 are reserved for experimentation,
as recommended in , and value 255 is
reserved by IANA. Extension-Type values 0 and 1 are defined in the
following subsections:Sub-Type is set to 30.Sub-Length is set to N (from 2 to 2034) that encodes the
number of Sub-Option Data octets that follow. The
Extension-Type and Header Type fields are always present;
hence, the maximum-length Header Option Value is 2032
octets.Extension-Type is set to 0. Each instance encodes exactly
one header option per Section 5.1.1 of , with the leading '0' octet omitted and the
following octet coded as Header Type. If multiple instances of
the same Header Type appear in OMNI options of the same
message the first instance is processed and all others are
ignored.Header Type and Header Option Value are coded exactly as
specified in Section 5.1.1 of ; the
following types are currently defined:0 - Origin Indication (IPv4) - value coded per Section
5.1.1 of .1 - Authentication Encapsulation - value coded per
Section 5.1.1 of .2 - Origin Indication (IPv6) - value coded per Section
5.1.1 of , except that the address
is a 16-octet IPv6 address instead of a 4-octet IPv4
address.Header Type values 3 through 252 are available for
assignment by future specifications, which must also define
the format of the Header Option Value and its processing
rules. Header Type values 253 and 254 are reserved for
experimentation, as recommended in ,
and value 255 is Reserved by IANA.Sub-Type is set to 30.Sub-Length is set to N (from 2 to 2034) that encodes the
number of Sub-Option Data octets that follow. The
Extension-Type and Trailer Type fields are always present;
hence, the maximum-length Trailer Option Value is 2032
octets.Extension-Type is set to 1. Each instance encodes exactly
one trailer option per Section 4 of .
If multiple instances of the same trailer type appear in OMNI
options of the same message the first instance is processed
and all others ignored.Trailer Type and Trailer Option Value are coded exactly as
specified in Section 4 of ; the
following Trailer Types are currently defined:0 - Unassigned1 - Nonce Trailer - value coded per Section 4.2 of
.2 - Unassigned3 - Alternate Address Trailer (IPv4) - value coded per
Section 4.3 of .4 - Neighbor Discovery Option Trailer - value coded per
Section 4.4 of .5 - Random Port Trailer - value coded per Section 4.5
of .6 - Alternate Address Trailer (IPv6) - value coded per
Section 4.3 of , except that each
address is a 16-octet IPv6 address instead of a 4-octet
IPv4 address.Trailer Type values 7 through 252 are available for
assignment by future specifications, which must also define
the format of the Trailer Option Value and its processing
rules. Trailer Type values 253 and 254 are reserved for
experimentation, as recommended in ,
and value 255 is Reserved by IANA.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 *NET 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. Each OMNI interface maintains default
routes via ARs discovered as discussed in , and
may configure more-specific routes discovered through means outside the
scope of this specification.After a packet enters the OMNI interface, one or more outbound
underlying interfaces are selected based on PBM traffic attributes, and
one or more neighbor underlying interfaces are selected based on the
receipt of Interface Attributes sub-options in IPv6 ND messages (see:
). Underlying interface selection for the
nodes own local interfaces are based on attributes such as DSCP,
application port number, cost, performance, message size, etc. OMNI
interface multilink selections could also be configured to perform
replication across multiple underlying interfaces for increased
reliability at the expense of packet duplication. The set of all
Interface Attributes received in IPv6 ND messages determines the
multilink forwarding profile for selecting the neighbor's underlying
interfaces.When the OMNI interface sends a packet over a selected outbound
underlying interface, the OAL includes or omits a mid-layer
encapsulation header as necessary as discussed in and as determined by the L2 address information
received in Interface Attributes. The OAL also performs encapsulation
when the nearest AR is located multiple hops away as discussed in . (Note that the OAL MAY employ packing when multiple
packets are available for forwarding to the same destination.)OMNI interface multilink service designers MUST observe the BCP
guidance in Section 15 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
ULA (e.g., [ULA]:0002::, [ULA]:1000::, [ULA]:7345::, etc.). The MN
configures a separate OMNI interface for each link so that multiple
interfaces (e.g., omni0, omni1, omni2, etc.) are exposed to the IPv6
layer. A different Anycast ULA is assigned to each interface, and the
MN injects the service prefixes for the OMNI link instances into the
EUN routing system.Applications in EUNs can use Segment Routing to select the desired
OMNI interface based on SBM considerations. The Anycast ULA is written
into the IPv6 destination address, and the actual destination (along
with any additional intermediate hops) is written into the Segment
Routing Header. Standard IP routing directs the packets to the MN's
mobile router entity, and the Anycast ULA identifies the OMNI
interface to be used for transmission to the next hop. When the MN
receives the message, it replaces the IPv6 destination address with
the next hop found in the routing header and transmits the message
over the OMNI interface identified by the Anycast ULA.Multiple distinct OMNI links can therefore be used to support fault
tolerance, load balancing, reliability, etc. The architectural model
is similar to Layer 2 Virtual Local Area Networks (VLANs).After an AR has registered an MNP for a MN (see: ), the AR will forward packets destined to an address
within the MNP to the MN. The MN will under normal circumstances then
forward the packet to the correct destination within its internal
networks.If at some later time the MN loses state (e.g., after a reboot), it
may begin returning packets destined to an MNP address to the AR as
its default router. The AR therefore must drop any packets originating
from the MN and destined to an address within the MN's registered MNP.
To do so, the AR institutes the following check:if the IP destination address belongs to a neighbor on the same
OMNI interface, and if the link-layer source address is the same
as one of the neighbor's link-layer addresses, drop the
packet.MNs interface with the MS by sending RS messages with OMNI options
under the assumption that one or more AR on the *NET will process the
message and respond. The MN then configures default routes for the OMNI
interface via the discovered ARs as the next hop. The manner in which
the *NET ensures AR coordination is link-specific and outside the scope
of this document (however, considerations for *NETs that do not provide
ARs that recognize the OMNI option are discussed in ).For each underlying interface, the MN sends an RS message with an
OMNI option to coordinate with MSEs identified by MSID values. Example
MSID discovery methods are given in and include
data link login parameters, name service lookups, static configuration,
a static "hosts" file, etc. The MN can also send an RS with an
MS-Register sub-option that includes the Anycast MSID value '0', i.e.,
instead of or in addition to any non-zero MSIDs. When the AR receives an
RS with a MSID '0', it selects a nearby MSE (which may be itself) and
returns an RA with the selected MSID in an MS-Register sub-option. The
AR selects only a single wildcard MSE (i.e., even if the RS MS-Register
sub-option included multiple '0' MSIDs) while also soliciting the MSEs
corresponding to any non-zero MSIDs.MNs configure OMNI interfaces that observe the properties discussed
in the previous section. The OMNI interface and its underlying
interfaces are said to be in either the "UP" or "DOWN" state according
to administrative actions in conjunction with the interface connectivity
status. An OMNI interface transitions to UP or DOWN through
administrative action and/or through state transitions of the underlying
interfaces. When a first underlying interface transitions to UP, the
OMNI interface also transitions to UP. When all underlying interfaces
transition to DOWN, the OMNI interface also transitions to DOWN.When an OMNI interface transitions to UP, the MN sends RS messages to
register its MNP and an initial set of underlying interfaces that are
also UP. The MN sends additional RS messages to refresh lifetimes and to
register/deregister underlying interfaces as they transition to UP or
DOWN. The MN's OMNI interface sends initial RS messages over an UP
underlying interface with its MNP-LLA as the source and with destination
set to link-scoped All-Routers multicast (ff02::2) . The OMNI interface includes an OMNI option per with a Preflen assertion, Interface Attributes
appropriate for underlying interfaces, MS-Register/Release sub-options
containing MSID values, and with any other necessary OMNI sub-options
(e.g., a Node Identification sub-option as an identity for the MN). The
OMNI interface then sets the S/T-omIndex field to the index of the
underlying interface over which the RS message is sent. The OMNI
interface then sends the RS over the underlying interface, using OAL
encapsulation and fragmentation if necessary. If OAL encapsulation is
used, the OMNI interface sets the OAL source address to the ULA
corresponding to the RS source and sets the OAL destination to
site-scoped All-Routers multicast (ff05::2).ARs process IPv6 ND messages with OMNI options and act as an MSE
themselves and/or as a proxy for other MSEs. ARs receive RS messages
(while performing OAL reassembly if necessary) and create a neighbor
cache entry for the MN, then coordinate with any MSEs named in the
Register/Release lists in a manner outside the scope of this document.
When an MSE processes the OMNI information, it first validates the
prefix registration information then injects/withdraws the MNP in the
routing/mapping system and caches/discards the new Preflen, MNP and
Interface Attributes. The MSE then informs the AR of registration
success/failure, and the AR returns an RA message to the MN with an OMNI
option per .The AR's OMNI interface returns the RA message via the same
underlying interface of the MN over which the RS was received, and with
destination address set to the MNP-LLA (i.e., unicast), with source
address set to its own LLA, and with an OMNI option with S/T-omIndex set
to the value included in the RS. The OMNI option also includes a Preflen
confirmation, Interface Attributes, MS-Register/Release and any other
necessary OMNI sub-options (e.g., a Node Identification sub-option as an
identity for the AR). The RA also includes any information for the link,
including RA Cur Hop Limit, M and O flags, Router Lifetime, Reachable
Time and Retrans Timer values, and includes any necessary options such
as: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 underlying interface.The OMNI interface then sends the RA, using OAL encapsulation and
fragmentation if necessary. If OAL encapsulation is used, the OMNI
interface sets the OAL source address to the ULA corresponding to the RA
source and sets the OAL destination to the ULA corresponding to the RA
destination. The AR MAY also send periodic and/or event-driven
unsolicited RA messages per . In that case, the
S/T-omIndex field in the OMNI option of the unsolicited RA message
identifies the target underlying interface of the destination MN.The AR can combine the information from multiple MSEs into one or
more "aggregate" RAs sent to the MN in order conserve *NET bandwidth.
Each aggregate RA includes an OMNI option with MS-Register/Release
sub-options with the MSEs represented by the aggregate. If an aggregate
is sent, the RA message contents must consistently represent the
combined information advertised by all represented MSEs. Note that since
the AR uses its own ADM-LLA as the RA source address, the MN determines
the addresses of the represented MSEs by examining the
MS-Register/Release OMNI sub-options.When the MN receives the RA message, it creates an OMNI interface
neighbor cache entry for each MSID that has confirmed MNP registration
via the L2 address of this AR. If the MN connects to multiple *NETs, it
records the additional L2 AR addresses in each MSID neighbor cache entry
(i.e., as multilink neighbors). The MN then configures a default route
via the MSE that returned the RA message, and assigns the Subnet Router
Anycast address corresponding to the MNP (e.g., 2001:db8:1:2::) to the
OMNI interface. The MN then manages its underlying interfaces according
to their states as follows:When an underlying interface transitions to UP, the MN sends an
RS over the underlying interface with an OMNI option. The OMNI
option contains at least one Interface Attribute sub-option with
values specific to this underlying interface, and may contain
additional Interface Attributes specific to other underlying
interfaces. The option also includes any MS-Register/Release
sub-options.When an underlying interface transitions to DOWN, the MN sends an
RS or unsolicited NA message over any UP underlying interface with
an OMNI option containing an Interface Attribute sub-option for the
DOWN underlying interface with Link set to '0'. The MN sends an RS
when an acknowledgement is required, or an unsolicited NA when
reliability is not thought to be a concern (e.g., if redundant
transmissions are sent on multiple underlying interfaces).When the Router Lifetime for a specific AR nears expiration, the
MN sends an RS over the underlying interface to receive a fresh RA.
If no RA is received, the MN can send RS messages to an alternate
MSID in case the current MSID has failed. If no RS messages are
received even after trying to contact alternate MSIDs, the MN marks
the underlying interface as DOWN.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 an UP
underlying interface (i.e., even after attempting to contact alternate
MSEs), 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. Still other deployments may elect to
administratively disable the ordinary RS/RA messaging used by the IPv6
layer over the OMNI interface, since they are not required to drive the
internal RS/RA processing. (Note that this same logic applies to IPv4
implementations that employ ICMP-based Router Discovery per .)Note: The Router Lifetime value in RA messages indicates the time
before which the MN must send another RS message over this underlying
interface (e.g., 600 seconds), however that timescale may be
significantly longer than the lifetime the MS has committed to retain
the prefix registration (e.g., REACHABLETIME seconds). ARs are therefore
responsible for keeping MS state alive on a shorter timescale than the
MN is required to do on its own behalf.Note: On multicast-capable underlying interfaces, MNs should send
periodic unsolicited multicast NA messages and ARs should send periodic
unsolicited multicast RA messages as "beacons" that can be heard by
other nodes on the link. If a node fails to receive a beacon after a
timeout value specific to the link, it can initiate a unicast exchange
to test reachability.Note: if an AR acting as a proxy forwards a MN's RS message to
another node acting as an MSE using UDP/IP encapsulation, it must use a
distinct UDP source port number for each MN. This allows the MSE to
distinguish different MNs behind the same AR at the link-layer, whereas
the link-layer addresses would otherwise be indistinguishable.Note: when an AR acting as an MSE returns an RA to an INET Client, it
includes an OMNI option with an Interface Attributes sub-option with
omIndex set to 0 and with SRT, FMT, LHS and L2ADDR information for its
INET interface. This provides the Client with partition prefix context
regarding the local OMNI link segment.On some *NETs, a MN may be located multiple IP hops away from the
nearest AR. Forwarding through IP multihop *NETs is conducted through
the application of a routing protocol (e.g., a MANET/VANET routing
protocol over omni-directional wireless interfaces, an inter-domain
routing protocol in an enterprise network, etc.). These *NETs could be
either IPv6-enabled or IPv4-only, while IPv4-only *NETs could be
either multicast-capable or unicast-only (note that for IPv4-only
*NETs the following procedures apply for both single-hop and multihop
cases).A MN located potentially multiple *NET hops away from the nearest
AR prepares an RS message with source address set to its MNP-LLA (or
to the unspecified address (::) if it does not yet have an MNP-LLA),
and with destination set to link-scoped All-Routers multicast the same
as discussed above. If OAL encapsulation and fragmentation are
necessary, the OMNI interface sets the OAL source address to the ULA
corresponding to the RS source (or to a Temporary ULA if the RS source
was the unspecified address (::)) and sets the OAL destination to
site-scoped All-Routers multicast (ff05::2). For IPv6-enabled *NETs,
the MN then encapsulates the message in UDP/IPv6 headers with source
address set to the underlying interface address (or to the ULA that
would be used for OAL encapsulation if the underlying interface does
not yet have an address) and sets the destination to either a unicast
or anycast address of an AR. For IPv4-only *NETs, the MN instead
encapsulates the RS message in an IPv4 header with source address set
to the IPv4 address of the underlying interface and with destination
address set to either the unicast IPv4 address of an AR or an IPv4 anycast address reserved for OMNI. The
MN then sends the encapsulated RS message via the *NET interface,
where it will be forwarded by zero or more intermediate *NET hops.When an intermediate *NET hop that participates in the routing
protocol receives the encapsulated RS, it forwards the message
according to its routing tables (note that an intermediate node could
be a fixed infrastructure element or another MN). This process repeats
iteratively until the RS message is received by a penultimate *NET hop
within single-hop communications range of an AR, which forwards the
message to the AR.When the AR receives the message, it decapsulates the RS (while
performing OAL reassembly, if necessary) and coordinates with the MS
the same as for an ordinary link-local RS, since the inner Hop Limit
will not have been decremented by the multihop forwarding process. The
AR then prepares an RA message with source address set to its own
ADM-LLA and destination address set to the LLA of the original MN. The
AR then performs OAL encapsulation and fragmentation if necessary,
with OAL source set to its own ADM-ULA and destination set to the ULA
corresponding to the RA source. The AR then encapsulates the message
in an IPv4/IPv6 header with source address set to its own IPv4/ULA
address and with destination set to the encapsulation source of the
RS.The AR then forwards the message to an *NET node within
communications range, which forwards the message according to its
routing tables to an intermediate node. The multihop forwarding
process within the *NET continues repetitively until the message is
delivered to the original MN, which decapsulates the message and
performs autoconfiguration the same as if it had received the RA
directly from the AR as an on-link neighbor.Note: An alternate approach to multihop forwarding via IPv6
encapsulation would be for the MN and AR to statelessly translate the
IPv6 LLAs into ULAs and forward the RS/RA messages without
encapsulation. This would violate the
requirement that certain IPv6 ND messages must use link-local
addresses and must not be accepted if received with Hop Limit less
than 255. This document therefore mandates encapsulation since the
overhead is nominal considering the infrequent nature and small size
of IPv6 ND messages. Future documents may consider encapsulation
avoidance through translation while updating .Note: An alternate approach to multihop forwarding via IPv4
encapsulation would be to employ IPv6/IPv4 protocol translation.
However, for IPv6 ND messages the LLAs would be truncated due to
translation and the OMNI Router and Prefix Discovery services would
not be able to function. The use of IPv4 encapsulation is therefore
indicated.Note: An IPv4 anycast address for OMNI in IPv4 networks could be
part of a new IPv4 /24 prefix allocation, but this may be difficult to
obtain given IPv4 address exhaustion. An alternative would be to
re-purpose the prefix 192.88.99.0 which has been set aside from its
former use by .OMNI links maintain a constant value "MAX_MSID" selected to provide
MNs with an acceptable level of MSE redundancy while minimizing
control message amplification. It is RECOMMENDED that MAX_MSID be set
to the default value 5; if a different value is chosen, it should be
set uniformly by all nodes on the OMNI link.When a MN sends an RS message with an OMNI option via an underlying
interface to an AR, the MN must convey its knowledge of its
currently-associated MSEs. Initially, the MN will have no associated
MSEs and should therefore include an MS-Register sub-option with the
single "anycast" MSID value 0 which requests the AR to select and
assign an MSE. The AR will then return an RA message with source
address set to the ADM-LLA of the selected MSE.As the MN activates additional underlying interfaces, it can
optionally include an MS-Register sub-option with MSID value 0, or
with non-zero MSIDs for MSEs discovered from previous RS/RA exchanges.
The MN will thus eventually begin to learn and manage its currently
active set of MSEs, and can register with new MSEs or release from
former MSEs with each successive RS/RA exchange. As the MN's MSE
constituency grows, it alone is responsible for including or omitting
MSIDs in the MS-Register/Release lists it sends in RS messages. The
inclusion or omission of MSIDs determines the MN's interface to the MS
and defines the manner in which MSEs will respond. The only limiting
factor is that the MN should include no more than MAX_MSID values in
each list per each IPv6 ND message, and should avoid duplication of
entries in each list unless it wants to increase likelihood of control
message delivery.When an AR receives an RS message sent by a MN with an OMNI option,
the option will contain zero or more MS-Register and MS-Release
sub-options containing MSIDs. After processing the OMNI option, the AR
will have a list of zero or more MS-Register MSIDs and a list of zero
or more of MS-Release MSIDs. The AR then processes the lists as
follows:For each list, retain the first MAX_MSID values in the list and
discard any additional MSIDs (i.e., even if there are duplicates
within a list).Next, for each MSID in the MS-Register list, remove all
matching MSIDs from the MS-Release list.Next, proceed according to whether the AR's own MSID or the
value 0 appears in the MS-Register list as follows:If yes, send an RA message directly back to the MN and send
a proxy copy of the RS message to each additional MSID in the
MS-Register list with the MS-Register/Release lists omitted.
Then, send an unsolicited NA (uNA) message to each MSID in the
MS-Release list with the MS-Register/Release lists omitted and
with an OMNI option with S/T-omIndex set to 0.If no, send a proxy copy of the RS message to each
additional MSID in the MS-Register list with the MS-Register
list omitted. For the first MSID, include the original
MS-Release list; for all other MSIDs, omit the MS-Release
list.Each proxy copy of the RS message will include an OMNI option
and OAL encapsulation header with the ADM-ULA of the AR as the source
and the ADM-ULA of the Register MSE as the destination. When the
Register MSE receives the proxy RS message, if the message includes an
MS-Release list the MSE sends a uNA message to each additional MSID in
the Release list with an OMNI option with S/T-omIndex set to 0. The
Register MSE then sends an RA message back to the (Proxy) AR wrapped
in an OAL encapsulation header with source and destination addresses
reversed, and with RA destination set to the MNP-LLA of the MN. When
the AR receives this RA message, it sends a proxy copy of the RA to
the MN.Each uNA message (whether sent by the first-hop AR or by a Register
MSE) will include an OMNI option and an OAL encapsulation header with
the ADM-ULA of the Register MSE as the source and the ADM-ULA of the
Release MSE as the destination. The uNA informs the Release MSE that
its previous relationship with the MN has been released and that the
source of the uNA message is now registered. The Release MSE must then
note that the subject MN of the uNA message is now "departed", and
forward any subsequent packets destined to the MN to the Register
MSE.Note that it is not an error for the MS-Register/Release lists to
include duplicate entries. If duplicates occur within a list, the AR
will generate multiple proxy RS and/or uNA messages - one for each
copy of the duplicate entries.When a MN is not pre-provisioned with an MNP-LLA (or, when the MN
requires additional MNP delegations), it requests the MSE to select
MNPs on its behalf and set up the correct routing state within the MS.
The DHCPv6 service supports this
requirement.When an MN needs to have the MSE select MNPs, it sends an RS
message with source set to the unspecified address (::) if it has no
MNP_LLAs. If the MN requires only a single MNP delegation, it can then
include a Node Identification sub-option in the OMNI option and set
Preflen to the length of the desired MNP. If the MN requires multiple
MNP delegations and/or more complex DHCPv6 services, it instead
includes a DHCPv6 Message sub-option containing a Client Identifier,
one or more IA_PD options and a Rapid Commit option then sets the
'msg-type' field to "Solicit", and includes a 3 octet
'transaction-id'. The MN then sets the RS destination to All-Routers
multicast and sends the message using OAL encapsulation and
fragmentation if necessary as discussed above.When the MSE receives the RS message, it performs OAL reassembly if
necessary. Next, if the RS source is the unspecified address (::)
and/or the OMNI option includes a DHCPv6 message sub-option, the MSE
acts as a "Proxy DHCPv6 Client" in a message exchange with the
locally-resident DHCPv6 server. If the RS did not contain a DHCPv6
message sub-option, the MSE generates a DHCPv6 Solicit message on
behalf of the MN using an IA_PD option with the prefix length set to
the OMNI header Preflen value and with a Client Identifier formed from
the OMNI option Node Identification sub-option; otherwise, the MSE
uses the DHCPv6 Solicit message contained in the OMNI option. The MSE
then sends the DHCPv6 message to the DHCPv6 Server, which delegates
MNPs and returns a DHCPv6 Reply message with PD parameters. (If the
MSE wishes to defer creation of MN state until the DHCPv6 Reply is
received, it can instead act as a Lightweight DHCPv6 Relay Agent per
by encapsulating the DHCPv6 message in a
Relay-forward/reply exchange with Relay Message and Interface ID
options. In the process, the MSE packs any state information needed to
return an RA to the MN in the Relay-forward Interface ID option so
that the information will be echoed back in the Relay-reply.)When the MSE receives the DHCPv6 Reply, it adds routes to the
routing system and creates MNP-LLAs based on the delegated MNPs. The
MSE then sends an RA back to the MN with the DHCPv6 Reply message
included in an OMNI DHCPv6 message sub-option if and only if the RS
message had included an explicit DHCPv6 Solicit. If the RS message
source was the unspecified address (::), the MSE includes one of the
(newly-created) MNP-LLAs as the RA destination address and sets the
OMNI option Preflen accordingly; otherwise, the MSE includes the RS
source address as the RA destination address. The MSE then sets the RA
source address to its own ADM-LLA then performs OAL encapsulation and
fragmentation if necessary and sends the RA to the MN. When the MN
receives the RA, it reassembles and discards the OAL encapsulation if
necessary, then creates a default route, assigns Subnet Router Anycast
addresses and uses the RA destination address as its primary MNP-LLA.
The MN will then use this primary MNP-LLA as the source address of any
IPv6 ND messages it sends as long as it retains ownership of the
MNP.Note: After a MN performs a DHCPv6-based prefix registration
exchange with a first MSE, it would need to repeat the exchange with
each additional MSE it registers with. In that case, the MN supplies
the MNP delegation information received from the first MSE when it
engages the additional MSEs.If the *NET link model is multiple access, the AR is responsible for
assuring that address duplication cannot corrupt the neighbor caches of
other nodes on the link. When the MN sends an RS message on a multiple
access *NET link, the AR verifies that the MN is authorized to use the
address and returns an RA with a non-zero Router Lifetime only if the MN
is authorized.After verifying MN authorization and returning an RA, the AR MAY
return IPv6 ND Redirect messages to direct MNs located on the same *NET
link to exchange packets directly without transiting the AR. In that
case, the MNs can exchange packets according to their unicast L2
addresses discovered from the Redirect message instead of using the
dogleg path through the AR. In some *NET links, however, such direct
communications may be undesirable and continued use of the dogleg path
through the AR may provide better performance. In that case, the AR can
refrain from sending Redirects, and/or MNs can ignore them.*NETs 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 *NET 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 *NET. If an MSE fails, ARs can quickly inform MNs of
the outage by sending multicast RA messages on the *NET interface. The
AR sends RA messages to MNs via the *NET interface with an OMNI option
with a Release ID for the failed MSE, and with destination address set
to All-Nodes multicast (ff02::1) .The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated
by small delays . Any MNs on the *NET interface
that have been using the (now defunct) MSE will receive the RA messages
and associate with a new MSE.When a MN connects to an *NET link for the first time, it sends an RS
message with an OMNI option. If the first hop AR recognizes the option,
it returns an RA with its ADM-LLA as the source, the MNP-LLA as the
destination and with an OMNI option included. The MN then engages the AR
according to the OMNI link model specified above. If the first hop AR is
a legacy IPv6 router, however, it instead returns an RA message with no
OMNI option and with a non-OMNI unicast source LLA as specified in . In that case, the MN engages the *NET according to
the legacy IPv6 link model and without the OMNI extensions specified in
this document.If the *NET link model is multiple access, there must be assurance
that address duplication cannot corrupt the neighbor caches of other
nodes on the link. When the MN sends an RS message on a multiple access
*NET link with an LLA source address and an OMNI option, ARs that
recognize the option ensure that the MN is authorized to use the address
and return an RA with a non-zero Router Lifetime only if the MN is
authorized. ARs that do not recognize the option instead return an RA
that makes no statement about the MN's authorization to use the source
address. In that case, the MN should perform Duplicate Address Detection
to ensure that it does not interfere with other nodes on the link.An alternative approach for multiple access *NET links to ensure
isolation for MN / AR communications is through L2 address mappings as
discussed in . 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
an open Internetwork without an OMNI-aware first-hop AR receive RA
messages that do not include an OMNI option, while OMNI interfaces
configured over IPv4-only underlying interfaces do not receive any
(IPv6) RA messages at all. OMNI interfaces that receive RA messages
without an OMNI option configure addresses, on-link prefixes, etc. on
the underlying interface that received the RA according to standard IPv6
ND and address resolution conventions . 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
an open Internetwork can apply security services such as VPNs to connect
to an MSE, or can establish a direct link to an MSE through some other
means (see ). In environments where an explicit
VPN or direct link may be impractical, OMNI interfaces can instead use
UDP/IP encapsulation per and HIP-based message authentication per .OMNI interfaces use UDP service port number 8060 (see: and Section 3.6 of ) according to the simple UDP/IP
encapsulation format specified in for both IPv4
and IPv6 underlying interfaces. OMNI interfaces do not include the
UDP/IP header/trailer extensions specified in , but may include them as OMNI
sub-options instead when necessary. Since the OAL includes an integrity
check over the OAL packet, OAL sources selectively disable UDP checksums
for OAL packets that do not require UDP/IP address integrity, but enable
UDP checksums for others including non-OAL packets, IPv6 ND messages
used to establish link-layer addresses, etc. If the OAL source discovers
that packets with UDP checksums disabled are being dropped in the path
it should enable UDP checksums in future packets. Further considerations
for UDP encapsulation checksums are found in .For "Vehicle-to-Infrastructure (V2I)" coordination, the MN codes a
HIP "Initiator" message in an OMNI option of an IPv6 RS message and the
AR responds with a HIP "Responder" message coded in an OMNI option of an
IPv6 RA message. HIP security services are applied per , using the RS/RA messages as simple "shipping
containers" to convey the HIP parameters. In that case, a "two-message
HIP exchange" through a single RS/RA exchange may be sufficient for
mutual authentication. For "Vehicle-to-Vehicle (V2V)" coordination, two
MNs can coordinate directly with one another with HIP
"Initiator/Responder" messages coded in OMNI options of IPv6 NS/NA
messages. In that case, a four-message HIP exchange (i.e., two
back-to-back NS/NA exchanges) may be necessary for the two MNs to attain
mutual authentication.After establishing a VPN or preparing for UDP/IP encapsulation, OMNI
interfaces send control plane messages to interface with the MS,
including RS/RA messages used according to and
NS/NA messages used for route optimization and mobility (see: ). The control plane messages must
be authenticated while data plane messages are delivered the same as for
ordinary best-effort traffic with basic source address-based data origin
verification. Data plane communications via OMNI interfaces that connect
over open Internetworks without an explicit VPN should therefore employ
transport- or higher-layer security to ensure integrity and/or
confidentiality.OMNI interfaces configured over open Internetworks are often located
behind NATs. The OMNI interface accommodates NAT traversal using UDP/IP
encapsulation and the mechanisms discussed in . To support NAT determination,
ARs include an Origin Indication sub-option in RA messages sent in
response to RS messages received from a Client via UDP/IP
encapsulation.Note: Following the initial HIP Initiator/Responder exchange, OMNI
interfaces configured over open Internetworks maintain HIP associations
through the transmission of IPv6 ND messages that include OMNI options
with HIP "Update" and "Notify" messages. OMNI interfaces use the HIP
"Update" message when an acknowledgement is required, and use the
"Notify" message in unacknowledged isolated IPv6 ND messages (e.g.,
unsolicited NAs).Note: ARs that act as proxys on an open Internetwork authenticate and
remove HIP message OMNI sub-options from RSes they forward from a MN to
an MSE, and insert and sign HIP message and Origin Indication
sub-options in RAs they forward from an MSE to an MN. Conversely, ARs
that act as proxys forward without processing any DHCPv6 information in
RS/RA message exchanges between MNs and MSEs. The AR is therefore
responsible for MN authentication while the MSE is responsible for
registering/delegating MNPs.In some use cases, it is desirable, beneficial and efficient for the
MN to receive a constant MNP that travels with the MN wherever it moves.
For example, this would allow air traffic controllers to easily track
aircraft, etc. In other cases, however (e.g., intelligent transportation
systems), the MN may be willing to sacrifice a modicum of efficiency in
order to have time-varying MNPs that can be changed every so often to
defeat adversarial tracking.The prefix delegation services discussed in
allows OMNI MNs that desire time-varying MNPs to obtain short-lived
prefixes to send RS messages with source set to the unspecified address
(::) and/or with an OMNI option with DHCPv6 Option sub-options. The MN
would then be obligated to renumber its internal networks whenever its
MNP (and therefore also its OMNI address) changes. This should not
present a challenge for MNs with automated network renumbering services,
however presents limits for the durations of ongoing sessions that would
prefer to use a constant address.MNs that generate (H)HITs but do not have pre-assigned MNPs can
request MNP delegations by issuing IPv6 ND messages that use the (H)HIT
instead of a Temporary ULA. In particular, when a MN creates an RS
message it can set the source to the unspecified address (::) and
destination to All-Routers multicast. The IPv6 ND message includes an
OMNI option with a HIP "Initiator" message sub-option, and need not
include a Node Identification sub-option since the MN's HIT appears in
the HIP message. The MN then encapsulates the message in an IPv6 header
with the (H)HIT as the source address and with destination set to either
a unicast or anycast ADM-ULA. The MN then sends the message to the AR as
specified in .When the AR receives the message, it notes that the RS source was the
unspecified address (::), then examines the RS encapsulation source
address to determine that the source is a (H)HIT and not a Temporary
ULA. The AR next invokes the DHCPv6 protocol to request an MNP prefix
delegation while using the HIT as the Client Identifier, then prepares
an RA message with source address set to its own ADM-LLA and destination
set to the MNP-LLA corresponding to the delegated MNP. The AR next
includes an OMNI option with a HIP "Responder" message and any DHCPv6
prefix delegation parameters. The AR then finally encapsulates the RA in
an IPv6 header with source address set to its own ADM-ULA and
destination set to the (H)HIT from the RS encapsulation source address,
then returns the encapsulated RA to the MN.MNs can also use (H)HITs and/or Temporary ULAs for direct MN-to-MN
communications outside the context of any OMNI link supporting
infrastructure. When two MNs encounter one another they can use their
(H)HITs and/or Temporary ULAs as IPv6 packet source and destination
addresses to support direct communications. MNs can also inject their
(H)HITs and/or Temporary ULAs into a MANET/VANET routing protocol to
enable multihop communications. MNs can further exchange IPv6 ND
messages (such as NS/NA) using their (H)HITs and/or Temporary ULAs as
source and destination addresses. Note that the HIP security protocols
for establishing secure neighbor relationships are based on (H)HITs;
therefore, Temporary ULAs would presumably utilize some alternate form
of message authentication such as the
authentication service.Lastly, when MNs are within the coverage range of OMNI link
infrastructure a case could be made for injecting (H)HITs and/or
Temporary ULAs into the global MS routing system. For example, when the
MN sends an RS to a MSE it could include a request to inject the (H)HIT
/ Temporary ULA into the routing system instead of requesting an MNP
prefix delegation. This would potentially enable OMNI link-wide
communications using only (H)HITs or Temporary ULAs, and not MNPs. This
document notes the opportunity, but makes no recommendation.OMNI MNs use LLAs only for link-scoped communications on the OMNI
link. Typically, MNs use LLAs as source/destination IPv6 addresses of
IPv6 ND messages, but may also use them for addressing ordinary data
packets exchanged with an OMNI link neighbor.OMNI MNs use MNP-ULAs as source/destination IPv6 addresses in the OAL
headers of OAL-encapsulated packets. OMNI MNs use Temporary ULAs for OAL
addressing when an MNP-ULA is not available, or as source/destination
IPv6 addresses for communications within a MANET/VANET local area. OMNI
MNs use HITs instead of Temporary ULAs when operation outside the
context of a specific ULA domain and/or source address attestation is
necessary.OMNI MNs use MNP-based GUAs for communications with Internet
destinations when they are within range of OMNI link supporting
infrastructure that can inject the MNP into the routing system.The following IANA actions are requested:The IANA is instructed to allocate an official Type number TBD1
from the registry "IPv6 Neighbor Discovery Option Formats" for the
OMNI option. Implementations set Type to 253 as an interim value .The IANA is instructed to allocate one Ethernet unicast address
TBD2 (suggested value '00-52-14') in the 'ethernet-numbers' registry
under "IANA Unicast 48-bit MAC Addresses" as follows:The IANA is instructed to assign a new Code value "1" in the
"ICMPv6 Code Fields: Type 2 - Packet Too Big" registry. The registry
should appear as follows:The OMNI option defines a 5-bit Sub-Type field, for which IANA is
instructed to create and maintain a new registry entitled "OMNI Option
Sub-Type Values". Initial values are given below (future assignments
are to be made through Standards Action ):The OMNI Node Identification Sub-Option (see: ) contains an 8-bit ID-Type field, for which IANA is
instructed to create and maintain a new registry entitled "OMNI Node
Identification ID-Type Values". Initial values are given below (future
assignments are to be made through Expert Review ):The OMNI option defines an 8-bit Extension-Type field for Sub-Type
30 (Sub-Type Extension), for which IANA is instructed to create and
maintain a new registry entitled "OMNI Option Sub-Type Extension
Values". Initial values are given below (future assignments are to be
made through Expert Review ):The OMNI Sub-Type Extension "RFC4380 UDP/IP Header Option" defines
an 8-bit Header Type field, for which IANA is instructed to create and
maintain a new registry entitled "OMNI RFC4380 UDP/IP Header Option".
Initial registry values are given below (future assignments are to be
made through Expert Review ):The OMNI Sub-Type Extension for "RFC6081 UDP/IP Trailer Option"
defines an 8-bit Trailer Type field, for which IANA is instructed to
create and maintain a new registry entitled "OMNI RFC6081 UDP/IP
Trailer Option". Initial registry values are given below (future
assignments are to be made through Expert Review ):The IANA has assigned the UDP port number "8060" for an earlier
experimental version of AERO . This document
together with reclaims
the UDP port number "8060" for 'aero' as the service port for UDP/IP
encapsulation. (Note that, although was not
widely implemented or deployed, any messages coded to that
specification can be easily distinguished and ignored since they use
the invalid ICMPv6 message type number '0'.) The IANA is therefore
instructed to update the reference for UDP port number "8060" from
"RFC6706" to "RFCXXXX" (i.e., this document).The IANA has assigned a 4 octet Private Enterprise Number (PEN)
code "45282" in the "enterprise-numbers" registry. This document is
the normative reference for using this code in DHCP Unique IDentifiers
based on Enterprise Numbers ("DUID-EN for OMNI Interfaces") (see:
). The IANA is therefore instructed to change
the enterprise designation for PEN code "45282" from "LinkUp Networks"
to "Overlay Multilink Network Interface (OMNI)".The IANA has assigned the ifType code "301 - omni - Overlay
Multilink Network Interface (OMNI)" in accordance with Section 6 of
. The registration appears under the IANA
"Structure of Management Information (SMI) Numbers (MIB Module
Registrations) - Interface Types (ifType)" registry.No further IANA actions are required.Security considerations for IPv4 , 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.MN OMNI interfaces configured over secured ANET interfaces inherit
the physical and/or link-layer security properties (i.e., "protected
spectrum") of the connected ANETs. MN OMNI interfaces configured over
open INET interfaces can use symmetric securing services such as VPNs or
can by some other means establish a direct link. When a VPN or direct
link may be impractical, however, the security services specified in
and/or can be
employed. While the OMNI link protects control plane messaging,
applications must still employ end-to-end transport- or higher-layer
security services to protect the data plane.Strong network layer security for control plane messages and
forwarding path integrity for data plane messages between MSEs MUST be
supported. In one example, the AERO service constructs a spanning tree
between MSEs and secures the links in the spanning tree with network
layer security mechanisms such as IPsec or
Wireguard. Control plane messages are then constrained to travel only
over the secured spanning tree paths and are therefore protected from
attack or eavesdropping. Since data plane messages can travel over route
optimized paths that do not strictly follow the spanning tree, however,
end-to-end transport- or higher-layer security services are still
required.Identity-based key verification infrastructure services such as iPSK
may be necessary for verifying the identities claimed by MNs. This
requirement should be harmonized with the manner in which (H)HITs are
attested in a given operational environment.Security considerations for specific access network interface types
are covered under the corresponding IP-over-(foo) specification (e.g.,
, , etc.).Security considerations for IPv6 fragmentation and reassembly are
discussed in .AERO/OMNI Release-3.0.2 was tagged on October 15, 2020, and is
undergoing internal testing. Additional internal releases expected
within the coming months, with first public release expected end of
1H2021.The first version of this document was prepared per the consensus
decision at the 7th Conference of the International Civil Aviation
Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 2019.
Consensus to take the document forward to the IETF was reached at the
9th Conference of the Mobility Subgroup on November 22, 2019. Attendees
and contributors included: Guray Acar, Danny Bharj, Francois
D´Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo,
Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu
Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg
Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane Tamalet,
Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, Fryderyk
Wrobel and Dongsong Zeng.The following individuals are acknowledged for their useful comments:
Stuart Card, Michael Matyas, Robert Moskowitz, Madhu Niraula, Greg
Saccone, Stephane Tamalet, Eric Vyncke. Pavel Drasil, Zdenek Jaron and
Michal Skorepa are especially recognized for their many helpful ideas
and suggestions. Madhuri Madhava Badgandi, Sean Dickson, Don Dillenburg,
Joe Dudkowski, Vijayasarathy Rajagopalan, Ron Sackman and Katherine Tran
are acknowledged for their hard work on the implementation and technical
insights that led to improvements for the spec.Discussions on the IETF 6man and atn mailing lists during the fall of
2020 suggested additional points to consider. The authors gratefully
acknowledge the list members who contributed valuable insights through
those discussions. Eric Vyncke and Erik Kline were the intarea ADs,
while Bob Hinden and Ole Troan were the 6man WG chairs at the time the
document was developed; they are all gratefully acknowledged for their
many helpful insights.Early observations on IP fragmentation performance implications were
noted in the 1986 Digital Equipment Corporation (DEC) "qe reset"
investigation, where fragment bursts from NFS UDP traffic triggered
hardware resets resulting in communication failures. Jeff Chase and Chet
Juzsczak of the Ultrix Engineering Group led the investigation, and
determined that setting a smaller NFS mount block size reduced the
amount of fragmentation and suppressed the resets. Early observations on
L2 media MTU issues were noted in the 1988 DEC FDDI investigation, where
Raj Jain and KK Ramakrishnan represented architectural considerations
for FDDI networking in general including FDDI/Ethernet bridging. Jeff
Mogul (who led the IETF Path MTU Discovery working group) and other DEC
colleagues who supported these early investigations are also
acknowledged.This work is aligned with the NASA Safe Autonomous Systems Operation
(SASO) program under NASA contract number NNA16BD84C.This work is aligned with the FAA as per the SE2025 contract number
DTFAWA-15-D-00030.This work is aligned with the Boeing Information Technology (BIT)
Mobility Vision Lab (MVL) program.Error Characteristics of Fiber Distributed Data Interface
(FDDI), IEEE Transactions on CommunicationsPerformance of Checksums and CRC's Over Real Data, IEEE/ACM
Transactions on Networking, Vol. 6, No. 5The OMNI Interface - An IPv6 Air/Ground Interface for Civil
Aviation, IETF Liaison Statement #1676,
https://datatracker.ietf.org/liaison/1676/ICAO Document 9896 (Manual on the Aeronautical
Telecommunication Network (ATN) using Internet Protocol Suite (IPS)
Standards and Protocol), Draft Edition 3 (work-in-progress)IPv4 Address Space Registry,
https://www.iana.org/assignments/ipv4-address-space/ipv4-address-space.xhtmlIPv6 Global Unicast Address Assignments,
https://www.iana.org/assignments/ipv6-unicast-address-assignments/ipv6-unicast-address-assignments.xhtmlAdaptation of the OMNI option Interface Attributes Preferences Bitmap
encoding 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 Interface Attribute the
same format must be used for the entire Interface Attribute sub-option.
Different sub-options may use different formats.The following figures show coding examples for various Simplex and
Indexed formats: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 *NET. This implies that MN / AR
control messaging should be isolated and not overheard by other nodes on
the link.To support MN / AR isolation on some *NET links, ARs can maintain an
OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible
*NETs, this specification reserves one Ethernet unicast address TBD2
(see: ). For non-Ethernet statically-addressed
*NETs, MSADDR is reserved per the assigned numbers authority for the
*NET addressing space. For still other *NETs, MSADDR may be dynamically
discovered through other means, e.g., L2 beacons.MNs map the L3 addresses of all IPv6 ND messages they send (i.e.,
both multicast and unicast) to MSADDR instead of to an ordinary unicast
or multicast L2 address. In this way, all of the MN's IPv6 ND messages
will be received by ARs that are configured to accept packets destined
to MSADDR. Note that multiple ARs on the link could be configured to
accept packets destined to MSADDR, e.g., as a basis for supporting
redundancy.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-35 to
draft-templin-6man-omni-interface-36:Major clarifications on aspects such as "hard/soft" PTB error
messagesMade generic so that either IP protocol version (IPv4 or IPv6)
can be used in the data plane.Differences from draft-templin-6man-omni-interface-31 to
draft-templin-6man-omni-interface-32:MTUSupport for multi-hop ANETS such as ISATAP.Differences from draft-templin-6man-omni-interface-29 to
draft-templin-6man-omni-interface-30:Moved link-layer addressing information into the OMNI option on a
per-ifIndex basisRenamed "ifIndex-tuple" to "Interface Attributes"Differences from draft-templin-6man-omni-interface-27 to
draft-templin-6man-omni-interface-28:Updates based on implementation experience.Differences from draft-templin-6man-omni-interface-25 to
draft-templin-6man-omni-interface-26:Further clarification on "aggregate" RA messages.Expanded Security Considerations to discuss expectations for
security in the Mobility Service.Differences from draft-templin-6man-omni-interface-20 to
draft-templin-6man-omni-interface-21: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.First draft version (draft-templin-atn-aero-interface-00):Draft based on consensus decision of ICAO Working Group I
Mobility Subgroup March 22, 2019.