Asymmetric Extended Route Optimization (AERO)Boeing Research & TechnologyP.O. Box 3707SeattleWA98124USAfltemplin@acm.orgI-DInternet-DraftThis document specifies an Asymmetric Extended Route Optimization
(AERO) service for IP internetworking over Overlay Multilink Network
(OMNI) interfaces. AERO/OMNI use an IPv6 link-local address format that
supports operation of the IPv6 Neighbor Discovery (ND) protocol and
links ND to IP forwarding. Prefix delegation/registration services are
employed for network admission and to manage the routing system. Secure
multilink operation, mobility management, multicast, quality of service
(QoS) signaling and route optimization are naturally supported through
dynamic neighbor cache updates. AERO is a widely-applicable mobile
internetworking service especially well-suited to aviation services,
intelligent transportation systems, mobile Virtual Private Networks
(VPNs) and many other applications.Asymmetric Extended Route Optimization (AERO) fulfills the
requirements of Distributed Mobility Management (DMM) and route optimization for
aeronautical networking and other network mobility use cases including
intelligent transportation systems and enterprise mobile device users.
AERO is a secure internetworking and mobility management service that
employs the Overlay Multilink Network Interface (OMNI) Non-Broadcast, Multiple Access (NBMA)
virtual link model. The OMNI link is a virtual overlay configured over
one or more underlying Internetworks, and nodes on the link can exchange
original IP packets as single-hop neighbors. The OMNI Adaptation Layer
(OAL) supports end system multilink operation for increased reliability,
bandwidth optimization and traffic path selection while performing
fragmentation and reassembly to support Internetwork segment routing and
Maximum Transmission Unit (MTU) diversity.The AERO service comprises Clients, Proxy/Servers and Relays that are
seen as OMNI link neighbors as well as Bridges that interconnect diverse
Internetworks as OMNI link segments through OAL forwarding at a layer
below IP. Each node's OMNI interface uses an IPv6 link-local address
format that supports operation of the IPv6 Neighbor Discovery (ND)
protocol and links ND to IP forwarding. A
node's OMNI interface can be configured over multiple underlying
interfaces, and therefore appears as a single interface with multiple
link-layer addresses. Each link-layer address is subject to change due
to mobility and/or QoS fluctuations, and link-layer address changes are
signaled by ND messaging the same as for any IPv6 link.AERO provides a secure cloud-based service where mobile node Clients
may use any Proxy/Server acting as a Mobility Anchor Point (MAP) and
fixed nodes may use any Relay on the link for efficient communications.
Fixed nodes forward original IP packets destined to other AERO nodes via
the nearest Relay, which forwards them through the cloud. A mobile
node's initial packets are forwarded through the Proxy/Server, and
direct routing is supported through route optimization while packets are
flowing. Both unicast and multicast communications are supported, and
mobile nodes may efficiently move between locations while maintaining
continuous communications with correspondents and without changing their
IP Address.AERO Bridges are interconnected in a secured private BGP overlay
routing instance to provide an OAL routing/bridging service that joins
the underlying Internetworks of multiple disjoint administrative domains
into a single unified OMNI link at a layer below IP. Each OMNI link
instance is characterized by the set of Mobility Service Prefixes (MSPs)
common to all mobile nodes. Relays provide an optimal route from
correspondent nodes on the underlying Internetwork to nodes on the OMNI
link. To the underlying Internetwork, the Relay is the source of a route
to the MSP, and hence uplink traffic to the mobile node is naturally
routed to the nearest Relay.AERO can be used with OMNI links that span private-use Internetworks
and/or public Internetworks such as the global Internet. In the latter
case, some end systems may be located behind global Internet Network
Address Translators (NATs). A means for robust traversal of NATs while
avoiding "triangle routing" is therefore provided.AERO assumes the use of PIM Sparse Mode in support of multicast
communication. In support of Source Specific Multicast (SSM) when a
Mobile Node is the source, AERO route optimization ensures that a
shortest-path multicast tree is established with provisions for mobility
and multilink operation. In all other multicast scenarios there are no
AERO dependencies.AERO was designed as a secure aeronautical internetworking service
for both manned and unmanned aircraft, where the aircraft is treated as
a mobile node that can connect an Internet of Things (IoT). AERO is also
applicable to a wide variety of other use cases. For example, it can be
used to coordinate the links of mobile nodes (e.g., cellphones, tablets,
laptop computers, etc.) that connect into a home enterprise network via
public access networks using tunneling software such as OpenVPN with VPN or non-VPN services enabled according to the
appropriate security model. AERO can also be used to facilitate
terrestrial vehicular and urban air mobility (as well as pedestrian
communication services) for future intelligent transportation systems
. Other applicable use cases are
also in scope.Along with OMNI, AERO provides secured optimal routing support for
the "6M's" of modern Internetworking, including:Multilink – a mobile node’s ability to coordinate
multiple diverse underlying data links as a single logical unit
(i.e., the OMNI interface) to achieve the required communications
performance and reliability objectives.Multinet – the ability to span the OMNI link across
multiple diverse network administrative segments while maintaining
seamless end-to-end communications between mobile nodes and
correspondents such as air traffic controllers, fleet
administrators, etc.Mobility – a mobile node’s ability to change network
points of attachment (e.g., moving between wireless base stations)
which may result in an underlying interface address change, but
without disruptions to ongoing communication sessions with peers
over the OMNI link.Multicast – the ability to send a single network
transmission that reaches multiple nodes belonging to the same
interest group, but without disturbing other nodes not subscribed to
the interest group.Multihop – a mobile node vehicle-to-vehicle relaying
capability useful when multiple forwarding hops between vehicles may
be necessary to “reach back” to an infrastructure access
point connection to the OMNI link.MTU assurance – the ability to deliver packets of various
robust sizes between peers without loss due to a link size
restriction, and to dynamically adjust packets sizes to achieve the
optimal performance for each independent traffic flow.The following numbered sections present the AERO specification. The
appendices at the end of the document are non-normative.The terminology in the normative references applies; especially, the
terminology in the OMNI specification is used extensively throughout. The
following terms are defined within the scope of this document:a control
message service for coordinating neighbor relationships between
nodes connected to a common link. AERO uses the IPv6 ND messaging
service specified in .a networking service
for delegating IPv6 prefixes to nodes on the link. The nominal
service is DHCPv6 , however alternate
services (e.g., based on ND messaging) are also in scope. Most
notably, a minimal form of prefix delegation known as "prefix
registration" can be used if the Client knows its prefix in advance
and can represent it in the IPv6 source address of an ND
message.a node's first-hop data
link service network (e.g., a radio access network, cellular service
provider network, corporate enterprise network, etc.) that often
provides link-layer security services such as IEEE 802.1X and
physical-layer security (e.g., "protected spectrum") to prevent
unauthorized access internally and with border network-layer
security services such as firewalls and proxys that prevent
unauthorized outside access.a node's attachment to a link
in an ANET.a connected IP network
topology with a coherent routing and addressing plan and that
provides a transit backbone service for ANET end systems. INETs also
provide an underlay service over which the AERO virtual link is
configured. Example INETs include corporate enterprise networks,
aviation networks, and the public Internet itself. When there is no
administrative boundary between an ANET and the INET, the ANET and
INET are one and the same.a node's attachment to a link
in an INET.a "wildcard" term referring to either
ANET or INET when it is not necessary to draw a distinction between
the two.a node's attachment to a link
in a *NET.frequently, *NETs such as
large corporate enterprise networks are sub-divided internally into
separate isolated partitions (a technique also known as "network
segmentation"). Each partition is fully connected internally but
disconnected from other partitions, and there is no requirement that
separate partitions maintain consistent Internet Protocol and/or
addressing plans. (Each *NET partition is seen as a separate OMNI
link segment as discussed below.)an IP address assigned to a
node's interface connection to a *NET.the encapsulation of a
packet in an outer header or headers that can be routed within the
scope of the local *NET partition.the same as defined in , and manifested by IPv6
encapsulation . The OMNI link spans
underlying *NET segments joined by virtual bridges in a spanning
tree the same as a bridged campus LAN. AERO nodes on the OMNI link
appear as single-hop neighbors even though they may be separated by
multiple underlying *NET hops, and can use Segment Routing to cause packets to visit selected waypoints on
the link.a node's attachment to an OMNI
link. Since the addresses assigned to an OMNI interface are managed
for uniqueness, OMNI interfaces do not require Duplicate Address
Detection (DAD) and therefore set the administrative variable
'DupAddrDetectTransmits' to zero .an OMNI interface
process whereby original IP packets admitted into the interface are
wrapped in a mid-layer IPv6 header and subject to fragmentation and
reassembly. The OAL is also responsible for generating MTU-related
control messages as necessary, and for providing addressing context
for spanning multiple segments of a bridged OMNI link.a whole IP packet or
fragment admitted into the OMNI interface by the network layer prior
to OAL encapsulation and fragmentation, or an IP packet delivered to
the network layer by the OMNI interface following OAL decapsulation
and reassembly.an original IP packet encapsulated
in OAL headers and trailers before OAL fragmentation, or following
OAL reassembly.a portion of an OAL packet
following fragmentation but prior to *NET encapsulation, or
following *NET encapsulation but prior to OAL reassembly.an OAL packet that does
not require fragmentation is always encapsulated as an "atomic
fragment" with a Fragment Header with Fragment Offset and More
Fragments both set to 0, but with a valid Identification value.an encapsulated OAL
fragment following *NET encapsulation or prior to *NET
decapsulation. OAL sources and destinations exchange carrier packets
over underlying interfaces, and may be separated by one or more OAL
intermediate nodes. OAL intermediate nodes may perform
re-encapsulation on carrier packets by removing the *NET headers of
the first hop network and replacing them with new *NET headers for
the next hop network.an OMNI interface acts as an OAL
source when it encapsulates original IP packets to form OAL packets,
then performs OAL fragmentation and *NET encapsulation to create
carrier packets.an OMNI interface acts as an
OAL destination when it decapsulates carrier packets, then performs
OAL reassembly and decapsulation to derive the original IP
packet.an OMNI interface acts
as an OAL intermediate node when it removes the *NET headers of
carrier packets received on a first segment, then re-encapsulates
the carrier packets in new *NET headers and forwards them into the
next segment. OAL intermediate nodes decrement the Hop Limit of the
OAL IPv6 header during re-encapsulation, and discard the packet if
the Hop Limit reaches 0.a *NET interface over
which an OMNI interface is configured.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 delegated to an AERO Client or Relay.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.a node that is connected to an OMNI
link and participates in the AERO internetworking and mobility
service.an AERO node
that connects over one or more underlying interfaces and requests
MNP delegation/registration service from AERO Proxy/Servers. The
Client assigns an MNP-LLA to the OMNI interface for use in ND
exchanges with other AERO nodes and forwards original IP packets to
correspondents according to OMNI interface neighbor cache state.a
dual-function node that provides a proxying service between AERO
Clients and external peers on its Client-facing ANET interfaces
(i.e., in the same fashion as for an enterprise network proxy) as
well as default forwarding and Mobility Anchor Point (MAP) services
for coordination with correspondents on its INET-facing interfaces
(Proxy/Servers in the open Internetwork instead have a single INET
interface). The Proxy/Server configures an OMNI interface and
assigns an ADM-LLA to support the operation of IPv6 ND services,
while advertising all of its associated MNPs via BGP peerings with
Bridges. Note that the Proxy and Server functions can be considered
logically separable, but since each Proxy/Server must be informed of
all of the Client's other multilink Proxy/Server affiliations the
AERO service is best supported when the two functions are coresident
on the same physical or logical platform.a Proxy/Server
that provides forwarding services between nodes reached via the OMNI
link and correspondents on connected downstream links. AERO Relays
configure an OMNI interface and assign an ADM-LLA the same as
Proxy/Servers. AERO Relays also run a dynamic routing protocol to
discover any non-MNP IP GUA routes in service on its connected
downstream network links. In both cases, the Relay advertises the
MSP(s) to its downstream networks, and distributes all of its
associated non-MNP IP GUA routes via BGP peerings with Bridges
(i.e., the same as for Proxy/Servers).a node that
provides hybrid routing/bridging services (as well as a security
trust anchor) for nodes on an OMNI link. The Bridge forwards carrier
packets between OMNI link segments as OAL intermediate nodes while
decrementing the OAL IPv6 header Hop Limit but without decrementing
the network layer IP TTL/Hop Limit. AERO Bridges peer with
Proxy/Servers and other Bridges over secured tunnels to discover the
full set of MNPs for the link as well as any non-MNP IP GUA routes
that are reachable via Relays.an IP address used as an
encapsulation header source or destination address from the
perspective of the OMNI interface. When an upper layer protocol
(e.g., UDP) is used as part of the encapsulation, the port number is
also considered as part of the link-layer address.the source or
destination address of an original IP packet presented to the OMNI
interface.an internal virtual or
external edge IP network that an AERO Client or Relay connects to
the rest of the network via the OMNI interface. The Client/Relay
sees each EUN as a "downstream" network, and sees the OMNI interface
as the point of attachment to the "upstream" network.an AERO Client and all of
its downstream-attached networks that move together as a single
unit, i.e., an end system that connects an Internet of Things.a MN's on-board router
that forwards original IP packets between any downstream-attached
networks and the OMNI link. The MR is the MN entity that hosts the
AERO Client.the AERO node
nearest the source that initiates route optimization. The ROS may be
a Proxy/Server or Relay acting on behalf of the source, or may be
the source Client itself.the AERO
node nearest the target destination that responds to route
optimization requests. The ROR may be a Proxy/Server acting on
behalf of a target MNP Client, a Relay for a non-MNP destination or
may be the target Client itself.a geographically and/or
topologically referenced list of addresses of all Proxy/Servers
within the same OMNI link. There is a single MAP list for the entire
OMNI link.a
BGP-based overlay routing service coordinated by Proxy/Servers and
Bridges that tracks all Proxy/Server-to-Client associations.the collective set of
all Proxy/Servers, Bridges and Relays that provide the AERO Service
to Clients.an individual
Proxy/Server, Bridge or Relay in the Mobility Service.Throughout the document, the simple terms "Client",
"Proxy/Server", "Bridge" and "Relay" refer to "AERO Client", "AERO
Proxy/Server", "AERO Bridge" and "AERO Relay", respectively.
Capitalization is used to distinguish these terms from other common
Internetworking uses in which they appear without capitalization.The terminology of DHCPv6 and IPv6 ND (including the names of node variables, messages and
protocol constants) is used throughout this document. The terms
"All-Routers multicast", "All-Nodes multicast", "Solicited-Node
multicast" and "Subnet-Router anycast" are defined in . Also, the term "IP" is used to generically refer to
either Internet Protocol version, i.e., IPv4 or
IPv6 .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.The following sections specify the operation of IP over OMNI links
using the AERO service:AERO Clients are Mobile Nodes (MNs) that configure OMNI interfaces
over underlying interfaces with addresses that may change when the
Client moves to a new network connection point. AERO Clients register
their Mobile Network Prefixes (MNPs) with the AERO service, and
distribute the MNPs to nodes on EUNs. AERO Bridges, Proxy/Servers and
Relays are critical infrastructure elements in fixed (i.e.,
non-mobile) INET deployments and hence have permanent and unchanging
INET addresses. Together, they constitute the AERO service which
provides an OMNI link virtual overlay for connecting AERO Clients.AERO Bridges provide hybrid routing/bridging services (as well as a
security trust anchor) for nodes on an OMNI link. Bridges use standard
IPv6 routing to forward carrier packets both within the same *NET
partition and between disjoint *NET partitions based on an IPv6
encapsulation mid-layer known as the OMNI Adaptation Layer (OAL) . During forwarding, the inner IP
layer experiences a virtual bridging service since the inner IP
TTL/Hop Limit is not decremented. Each Bridge also peers with
Proxy/Servers and other Bridges in a dynamic routing protocol instance
to provide a Distributed Mobility Management (DMM) service for the
list of active MNPs (see ). Bridges present
the OMNI link as a set of one or more Mobility Service Prefixes (MSPs)
and configure secured tunnels with Proxy/Servers, Relays and other
Bridges; they further maintain IP forwarding table entries for each
MNP and any other reachable non-MNP prefixes.AERO Proxy/Servers in distributed *NET locations provide default
forwarding and mobility/multilink services for AERO Client Mobile
Nodes (MNs). Each Proxy/Server also peers with Bridges in a dynamic
routing protocol instance to advertise its list of associated MNPs
(see ). Proxy/Servers facilitate prefix
delegation/registration exchanges with Clients, where each delegated
prefix becomes an MNP taken from an MSP. Proxy/Servers forward carrier
packets between OMNI interface neighbors and track each Client's
mobility profiles. Proxy/Servers at ANET/INET boundaries provide a
conduit for ANET Clients to associate with peers reached through
external INETs. Proxy/Servers in the open INET support INET Clients
through authenticated IPv6 ND message exchanges.AERO Relays are Proxy/Servers that provide forwarding services to
exchange original IP packets between the OMNI interface and INET/EUN
interfaces. Relays are provisioned with MNPs the same as for an AERO
Client, and also run a dynamic routing protocol to discover any
non-MNP IP routes. The Relay advertises the MSP(s) to its connected
networks, and distributes all of its associated MNP and non-MNP routes
via BGP peerings with Bridges presents the basic OMNI link
reference model: In this model:the OMNI link is an overlay network service configured over
one or more underlying *NET partitions which may be managed by
different administrative authorities and have incompatible
protocols and/or addressing plans.AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1,
discovers Mobile Network Prefixes (MNPs) X* and advertises the
MSP via BGP peerings over secured tunnels to Proxy/Servers (S1,
S2). Bridges connect the disjoint segments of a partitioned OMNI
link.AERO Proxy/Servers S1 and S2 configure secured tunnels with
Bridge B1 and also provide mobility, multilink, multicast and
default router services for the MNPs of their associated Clients
C1 and C2. (AERO Proxy/Servers that act as Relays can also
advertise non-MNP routes for non-mobile correspondent nodes the
same as for MNP Clients.)AERO Clients C1 and C2 associate with Proxy/Servers S1 and
S2, respectively. They receive MNP delegations X1 and X2, and
also act as default routers for their associated physical or
internal virtual EUNs. Simple hosts H1 and H2 attach to the EUNs
served by Clients C1 and C2, respectively.An OMNI link configured over a single *NET appears as a single
unified link with a consistent underlying network addressing plan.
In that case, all nodes on the link can exchange carrier packets via
simple *NET encapsulation, since the underlying *NET is connected.
In common practice, however, an OMNI link may be partitioned into
multiple "segments", where each segment is a distinct *NET
potentially managed under a different administrative authority
(e.g., as for worldwide aviation service providers such as ARINC,
SITA, Inmarsat, etc.). Individual *NETs may also themselves be
partitioned internally, in which case each internal partition is
seen as a separate segment.The addressing plan of each segment is consistent internally but
will often bear no relation to the addressing plans of other
segments. Each segment is also likely to be separated from others by
network security devices (e.g., firewalls, proxys, packet filtering
gateways, etc.), and in many cases disjoint segments may not even
have any common physical link connections. Therefore, nodes can only
be assured of exchanging carrier packets directly with
correspondents in the same segment, and not with those in other
segments. The only means for joining the segments therefore is
through inter-domain peerings between AERO Bridges.The same as for traditional campus LANs, multiple OMNI link
segments can be joined into a single unified link via a virtual
bridging service using the OMNI Adaptation Layer (OAL) which inserts a mid-layer IPv6
encapsulation header that supports inter-segment forwarding (i.e.,
bridging) without decrementing the network-layer TTL/Hop Limit. This
bridging of OMNI link segments is shown in :Bridges, Proxy/Servers and Relays connect via secured INET
tunnels over their respective segments in a spanning tree topology
rooted at the Bridges. The secured spanning tree supports strong
authentication for IPv6 ND control messages and may also be used to
convey the initial carrier packets in a flow. Route optimization can
then be employed to cause carrier packets to take more direct paths
between OMNI link neighbors without having to strictly follow the
spanning tree.AERO nodes on OMNI links use the Link-Local Address (LLA) prefix
fe80::/64 to assign LLAs used for
network-layer addresses in link-scoped IPv6 ND and data messages.
AERO Clients use LLAs constructed from MNPs (i.e., "MNP-LLAs") while
other AERO nodes use LLAs constructed from administrative
identification values ("ADM-LLAs") as specified in . Non-MNP routes are also
represented the same as for MNP-LLAs, but may include a prefix that
is not properly covered by the MSP.AERO nodes also use the Unique Local Address (ULA) prefix
fd00::/8 followed by a pseudo-random 40-bit OMNI domain identifier
to form the prefix [ULA]::/48, then include a 16-bit OMNI link
identifier '*' to form the prefix [ULA*]::/64 . The AERO node then uses the prefix [ULA*]::/64
to form "MNP-ULAs" or "ADM-ULA"s as specified in to support OAL addressing. (The
prefix [ULA*]::/64 appearing alone and with no suffix represents
"default".) AERO Clients also use Temporary ULAs constructed per
, where the addresses are
typically used only in initial control message exchanges until a
stable MNP-LLA/ULA is assigned.AERO MSPs, MNPs and non-MNP routes are typically based on Global
Unicast Addresses (GUAs), but in some cases may be based on
private-use addresses. See
for a full specification of LLAs, ULAs and GUAs used by AERO nodes
on OMNI links.Finally, AERO Clients and Proxy/Servers configure node
identification values as specified in .The AERO routing system comprises a private instance of the
Border Gateway Protocol (BGP) that is
coordinated between Bridges and Proxy/Servers and does not interact
with either the public Internet BGP routing system or any underlying
INET routing systems.In a reference deployment, each Proxy/Server is configured as an
Autonomous System Border Router (ASBR) for a stub Autonomous System
(AS) using a 32-bit AS Number (ASN) that is
unique within the BGP instance, and each Proxy/Server further uses
eBGP to peer with one or more Bridges but does not peer with other
Proxy/Servers. Each *NET of a multi-segment OMNI link must include
one or more Bridges, which peer with the Proxy/Servers within that
*NET. All Bridges within the same *NET are members of the same hub
AS, and use iBGP to maintain a consistent view of all active routes
currently in service. The Bridges of different *NETs peer with one
another using eBGP.Bridges maintain forwarding table entries only for the MNP-ULAs
corresponding to MNP and non-MNP routes that are currently active,
and carrier packets destined to all other MNP-ULAs will correctly
incur Destination Unreachable messages due to the black-hole route.
In this way, Proxy/Servers and Relays have only partial topology
knowledge (i.e., they know only about the routes their directly
associated Clients and non-AERO links) and they forward all other
carrier packets to Bridges which have full topology knowledge.Each OMNI link segment assigns a unique ADM-ULA sub-prefix of
[ULA*]::/96. For example, a first segment could assign
[ULA*]::1000/116, a second could assign [ULA*]::2000/116, a third
could assign [ULA*]::3000/116, etc. Within each segment, each
Proxy/Server configures an ADM-ULA within the segment's prefix,
e.g., the Proxy/Servers within [ULA*]::2000/116 could assign the
ADM-ULAs [ULA*]::2011/116, [ULA*]::2026/116, [ULA*]::2003/116,
etc.The administrative authorities for each segment must therefore
coordinate to assure mutually-exclusive ADM-ULA prefix assignments,
but internal provisioning of ADM-ULAs an independent local
consideration for each administrative authority. For each ADM-ULA
prefix, the Bridge(s) that connect that segment assign the
all-zero's address of the prefix as a Subnet Router Anycast address.
For example, the Subnet Router Anycast address for [ULA*]::1023/116
is simply [ULA*]::1000.ADM-ULA prefixes are statically represented in Bridge forwarding
tables. Bridges join multiple segments into a unified OMNI link over
multiple diverse administrative domains. They support a bridging
function by first establishing forwarding table entries for their
ADM-ULA prefixes either via standard BGP routing or static routes.
For example, if three Bridges ('A', 'B' and 'C') from different
segments serviced [ULA*]::1000/116, [ULA*]::2000/116 and
[ULA*]::3000/116 respectively, then the forwarding tables in each
Bridge are as follows:[ULA*]::1000/116->local,
[ULA*]::2000/116->B, [ULA*]::3000/116->C[ULA*]::1000/116->A,
[ULA*]::2000/116->local, [ULA*]::3000/116->C[ULA*]::1000/116->A, [ULA*]::2000/116->B,
[ULA*]::3000/116->localThese forwarding table entries are permanent and never
change, since they correspond to fixed infrastructure elements in
their respective segments.MNP ULAs are instead dynamically advertised in the AERO routing
system by Proxy/Servers and Relays that provide service for their
corresponding MNPs. For example, if three Proxy/Servers ('D', 'E'
and 'F') service the MNPs 2001:db8:1000:2000::/56,
2001:db8:3000:4000::/56 and 2001:db8:5000:6000::/56 then the routing
system would include:[ULA*]:2001:db8:1000:2000/120[ULA*]:2001:db8:3000:4000/120[ULA*]:2001:db8:5000:6000/120A full discussion of the BGP-based routing system used by AERO is
found in .With the Client and partition prefixes in place in Bridge
forwarding tables, the OMNI interface sends control and data
messages toward AERO destination nodes located in different OMNI
link segments over the spanning tree. The OMNI interface uses the
OMNI Adaptation Layer (OAL) encapsulation service , and includes an OMNI Routing
Header (ORH) as an extension to the OAL header if final segment
forwarding information is available, e.g., in the neighbor cache.
(For nodes located in the same OMNI link segment, or when no final
segment forwarding information is available, the ORH may be
omitted.) The ORH is formatted as shown in :In this format:Next Header identifies the type of header immediately
following the ORH.Hdr Ext Len is the length of the Routing header in 8-octet
units (not including the first 8 octets), with trailing padding
added if necessary to produce an integral number of 8-octet
units.Routing Type is set to TBD1 (see IANA Considerations).Segments Left is omitted, and replaced by a 5-bit SRT and
3-bit FMT field.SRT - a 5-bit Segment Routing Topology prefix length value
that (when added to 96) determines the prefix length to apply to
the ADM-ULA formed from concatenating [ULA*]::/96 with the 32
bit LHS 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 *NET encapsulation address for the
target Client itself; otherwise L2ADDR is the address of the
Proxy/Server named in the LHS.When the next most significant bit (i.e., "Mode") is set
to 1, the Framework node is (likely) located behind a *NET
Network Address Translator (NAT); otherwise, it is on the
open *NET.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 ID of a node in the Last Hop Segment that
services the target. When SRT and LHS are both set to 0, the LHS
is considered unspecified. When SRT is set to 0 and LHS is
non-zero, the prefix length is set to 128. SRT and LHS provide
guidance to the OMNI interface forwarding algorithm.
Specifically, if SRT/LHS is located in the local OMNI link
segment, the OAL source can omit the ORH and (following any
necessary NAT traversal messaging) send directly to the OAL
destination according to FMT/L2ADDR. Otherwise, it includes the
ORH and forwards according to the OMNI link spanning tree.Link Layer Address (L2ADDR) - Formatted according to FMT, and
identifies the link-layer address (i.e., the encapsulation
address) of the target. The UDP Port Number appears in the first
two 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
*NET encapsulation address for local forwarding when SRT/LHS is
located in the same OMNI link segment. Note that if the target
is behind a NAT, L2ADDR will contain the mapped *NET address
stored in the NAT; otherwise, L2ADDR will contain the native
*NET information of the target itself.Destination Suffix is a 64-bit field included only for OAL
non-first-fragments. Present only when Hdr Ext Len indicates
that at least 8 bytes follow L2ADDR. When present, encodes the
64-bit MNP-ULA suffix for the target Client.Null Padding contains zero-valued octets as necessary to pad
the ORH to an integral number of 8-octet units.AERO neighbors use OAL encapsulation and fragmentation to
exchange OAL packets as specified in . When an AERO node's OMNI interface
(acting as an OAL source) uses OAL encapsulation for an original IP
packet with source address 2001:db8:1:2::1 and destination address
2001:db8:1234:5678::1, it sets the OAL header source address to its
own ULA (e.g., [ULA*]::2001:db8:1:2), sets the destination address
to the MNP-ULA corresponding to the IP destination address (e.g.,
[ULA*]::2001:db8:1234:5678), sets the Traffic Class, Flow Label, Hop
Limit and Payload Length as discussed in , then finally selects an
Identification and appends an OAL checksum.If the neighbor cache information indicates that the target is in
a different segment, the OAL source next inserts an ORH immediately
following the OAL header while including the correct SRT, FMT, LHS,
L2ADDR and Destination Suffix if fragmentation if needed (in this
case, the Destination Suffix is 2001:db8:1234:5678). Next, the OAL
source overwrites the OAL header destination address with the LHS
Subnet Router Anycast address (for example, for LHS 3000:4567 with
SRT 16, the Subnet Router Anycast address is [ULA*]::3000:0000).
(Note: if the ADM-ULA of the last-hop Proxy/Server is known but the
SRT, FMT, LHS and L2ADDR are not (yet) known, the OAL source instead
overwrites the OAL header destination address with the ADM-ULA.)The OAL source then fragments the OAL packet, with each resulting
OAL fragment including the OAL/ORH headers while only the first
fragment includes the original IPv6 header. (Note that if no actual
fragmentation is required the OAL packet is still prepared as an
"atomic" fragment that includes a Fragment Header with Offset and
More Fragments both set to 0.) The OAL source finally encapsulates
each resulting OAL fragment in an *NET header to form an OAL carrier
packet, with source address set to its own *NET address (e.g.,
192.0.2.100) and destination set to the *NET address of a Bridge
(e.g., 192.0.2.1).The carrier packet encapsulation format in the above example is
shown in :In this format, the original IP header and packet body/fragment
are from the original IP packet, the OAL header is an IPv6 header
prepared according to , the ORH is a Routing
Header extension of the OAL header, the Fragment Header identifies
each fragment, and the INET header is prepared as discussed in . When the OAL source transmits the resulting
carrier packets, they are forwarded over possibly multiple OAL
intermediate nodes in the OMNI link spanning tree until they arrive
at the OAL destination.This gives rise to a routing system that contains both Client
MNP-ULA routes that may change dynamically due to regional node
mobility and per-partition ADM-ULA routes that rarely if ever
change. The Bridges can therefore provide link-layer bridging by
sending carrier packets over the spanning tree instead of
network-layer routing according to MNP routes. As a result,
opportunities for loss due to node mobility between different
segments are mitigated.In normal operations, IPv6 ND messages are conveyed over secured
paths between OMNI link neighbors so that specific Proxy/Servers or
Relays can be addressed without being subject to mobility events.
Conversely, only the first few carrier packets destined to Clients
need to traverse secured paths until route optimization can
determine a more direct path.Note: When the OAL source and destination are on the same INET
segment, the ORH is not needed and OAL header compression can be
used to significantly reduce encapsulation overhead .Note: When the OAL source has multiple original IP packets to
send to the same OAL destination, it can perform "packing" to
generate a "super-packet" . In
that case, the OAL/ORH super-packet may include up to N original IP
packets as long as the total length of the super-packet does not
exceed the OMNI interface MTU.Note: Use of an IPv6 "minimal encapsulation" format (i.e., an
IPv6 variant of ) based on extensions to the
ORH was considered and abandoned. In the approach, the ORH would be
inserted as an extension header to the original IPv6 packet header.
The IPv6 destination address would then be written into the ORH, and
the ULA corresponding to the destination would be overwritten in the
IPv6 destination address. This would seemingly convey enough
forwarding information so that OAL encapsulation could be avoided.
However, this "minimal encapsulation" IPv6 packet would then have a
non-ULA source address and ULA destination address, an incorrect
value in upper layer protocol checksums, and a Hop Limit that is
decremented within the spanning tree when it should not be. The
insertion and removal of the ORH would also entail rewriting the
Payload Length and Next Header fields - again, invalidating upper
layer checksums. These irregularities would result in implementation
challenges and the potential for operational issues, e.g., since
actionable ICMPv6 error reports could not be delivered to the
original source. In order to address the issues, still more
information such as the original IPv6 source address could be
written into the ORH. However, with the additional information the
benefit of the "minimal encapsulation" savings quickly diminishes,
and becomes overshadowed by the implementation and operational
irregularities.The 64-bit sub-prefixes of [ULA]::/48 identify up to 2^16
distinct Segment Routing Topologies (SRTs). Each SRT is a
mutually-exclusive OMNI link overlay instance using a distinct set
of ULAs, and emulates a Virtual LAN (VLAN) service for the OMNI
link. In some cases (e.g., when redundant topologies are needed for
fault tolerance and reliability) it may be beneficial to deploy
multiple SRTs that act as independent overlay instances. A
communication failure in one instance therefore will not affect
communications in other instances.Each SRT is identified by a distinct value in bits 48-63 of
[ULA]::/48, i.e., as [ULA0]::/64, [ULA1]::/64, [ULA2]::/64, etc.
Each OMNI interface is identified by a unique interface name (e.g.,
omni0, omni1, omni2, etc.) and assigns an anycast ADM-ULA
corresponding to its SRT prefix length. The anycast ADM-ULA is used
for OMNI interface determination in Safety-Based Multilink (SBM) as
discussed in . Each OMNI
interface further applies Performance-Based Multilink (PBM)
internally.An original IPv6 source can direct an IPv6 packet to an AERO node
by including a standard IPv6 Segment Routing Header (SRH) with the anycast ADM-ULA for the selected SRT as
either the IPv6 destination or as an intermediate hop within the
SRH. This allows the original source to determine the specific OMNI
link topology an original IPv6 packet will traverse when there may
be multiple alternatives.When the AERO node processes the SRH and forwards the original
IPv6 packet to the correct OMNI interface, the OMNI interface writes
the next IPv6 address from the SRH into the IPv6 destination address
and decrements Segments Left. If decrementing would cause Segments
Left to become 0, the OMNI interface deletes the SRH before
forwarding. This form of Segment Routing supports Safety-Based
Multilink (SBM).OAL sources can insert an ORH for Segment Routing within the OMNI
link to influence the paths of OAL packets sent to OAL destinations
in remote segments without requiring all carrier packets to traverse
strict spanning tree paths.When an AERO node's OMNI interface has an original IP packet to
send to a target discovered through route optimization located in
the same OMNI link segment, it acts as an OAL source to perform OAL
encapsulation and fragmentation. The node then uses the target's
Link Layer Address (L2ADDR) information for *NET encapsulation.When an AERO node's OMNI interface has an original IP packet to
send to a route optimization target located in a remote OMNI link
segment, it acts as an OAL source the same as above but also
includes an ORH while setting the OAL destination to the Subnet
Router Anycast address for the final OMNI link segment, then
forwards the resulting carrier packets to a Bridge.When a Bridge receives a carrier packet destined to its Subnet
Router Anycast address with an ORH with SRT/LHS values corresponding
to the local segment, it examines the L2ADDR according to FMT and
removes the ORH from the carrier packet. The Bridge then writes the
MNP-ULA corresponding to the ORH Destination Suffix into the OAL
destination address, decrements the OAL IPv6 header Hop Limit (and
discards the packet if the Hop Limit reaches 0), re-encapsulates the
carrier packet according to L2ADDR and forwards the carrier packet
either to the LHS Proxy/Server or directly to the target Client
itself. In this way, the Bridge participates in route optimization
to reduce traffic load and suboptimal routing through strict
spanning tree paths.OMNI interfaces are virtual interfaces configured over one or more
underlying interfaces classified as follows:INET interfaces connect to an INET either natively or through
one or more NATs. Native INET interfaces have global IP addresses
that are reachable from any INET correspondent. The INET-facing
interfaces of Proxy/Servers are native interfaces, as are Relay
and Bridge interfaces. NATed INET interfaces connect to a private
network behind one or more NATs that provide INET access. Clients
that are behind a NAT are required to send periodic keepalive
messages to keep NAT state alive when there are no carrier packets
flowing.ANET interfaces connect to an ANET that is separated from the
open INET by a Proxy/Server. Proxy/Servers can actively issue
control messages over the INET on behalf of the Client to reduce
ANET congestion.VPNed interfaces use security encapsulation over the INET to a
Virtual Private Network (VPN) server that also acts as a
Proxy/Server. Other than the link-layer encapsulation format,
VPNed interfaces behave the same as Direct interfaces.Direct (i.e., single-hop point-to-point) interfaces connect a
Client directly to a Proxy/Server without crossing any ANET/INET
paths. An example is a line-of-sight link between a remote pilot
and an unmanned aircraft. The same Client considerations apply as
for VPNed interfaces.OMNI interfaces use OAL encapsulation and fragmentation as
discussed in . OMNI interfaces use
*NET encapsulation (see: ) to exchange
carrier packets with OMNI link neighbors over INET or VPNed interfaces
as well as over ANET interfaces for which the Client and Proxy/Server
may be multiple IP hops away. OMNI interfaces do not use link-layer
encapsulation over Direct underlying interfaces or ANET interfaces
when the Client and Proxy/Server are known to be on the same
underlying link.OMNI interfaces maintain a neighbor cache for tracking per-neighbor
state the same as for any interface. OMNI interfaces use ND messages
including Router Solicitation (RS), Router Advertisement (RA),
Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for
neighbor cache management.OMNI interfaces send ND messages with an OMNI option formatted as
specified in . The OMNI option
includes prefix registration information and Interface Attributes
containing link information parameters for the OMNI interface's
underlying interfaces. Each OMNI option may include multiple Interface
Attributes sub-options, each identified by an ifIndex value.A Client's OMNI interface may be configured over multiple
underlying interface connections. For example, common mobile handheld
devices have both wireless local area network ("WLAN") and cellular
wireless links. These links are often used "one at a time" with
low-cost WLAN preferred and highly-available cellular wireless as a
standby, but a simultaneous-use capability could provide benefits. In
a more complex example, aircraft frequently have many wireless data
link types (e.g. satellite-based, cellular, terrestrial, air-to-air
directional, etc.) with diverse performance and cost properties.If a Client's multiple underlying interfaces are used "one at a
time" (i.e., all other interfaces are in standby mode while one
interface is active), then ND message OMNI options include only a
single Interface Attributes sub-option set to constant values. In that
case, the Client would appear to have a single interface but with a
dynamically changing link-layer address.If the Client has multiple active underlying interfaces, then from
the perspective of ND it would appear to have multiple link-layer
addresses. In that case, ND message OMNI options MAY include multiple
Interface Attributes sub-options - each with values that correspond to
a specific interface. Every ND message need not include Interface
Attributes for all underlying interfaces; for any attributes not
included, the neighbor considers the status as unchanged.Bridge and Proxy/Server OMNI interfaces may be configured over one
or more secured tunnel interfaces. The OMNI interface configures both
an ADM-LLA and its corresponding ADM-ULA, while the underlying secured
tunnel interfaces are either unnumbered or configure the same ULA. The
OMNI interface acting as an OAL source encapsulates and fragments each
original IP packet, then and presents the resulting carrier packets to
the underlying secured tunnel interface. Routing protocols such as BGP
that run over the OMNI interface do not employ OAL encapsulation, but
rather present the routing protocol messages directly to the
underlying secured tunnels while using the ULA as the source address.
This distinction must be honored consistently according to each node's
configuration so that the IP forwarding table will associate
discovered IP routes with the correct interface.AERO Proxy/Servers and Clients configure OMNI interfaces as their
point of attachment to the OMNI link. AERO nodes assign the MSPs for
the link to their OMNI interfaces (i.e., as a "route-to-interface") to
ensure that original IP packets with destination addresses covered by
an MNP not explicitly assigned to a non-OMNI interface are directed to
the OMNI interface.OMNI interface initialization procedures for Proxy/Servers, Clients
and Bridges are discussed in the following sections.When a Proxy/Server enables an OMNI interface, it assigns an
ADM-{LLA,ULA} appropriate for the given OMNI link segment. The
Proxy/Server also configures secured tunnels with one or more
neighboring Bridges and engages in a BGP routing protocol session
with each Bridge.The OMNI interface provides a single interface abstraction to the
IP layer, but internally includes one or more secured tunnels as
well as an NBMA nexus as underlying interfaces for sending carrier
packets to OMNI interface neighbors. The Proxy/Server further
configures a service to facilitate ND exchanges with AERO Clients
and manages per-Client neighbor cache entries and IP forwarding
table entries based on control message exchanges.Relays are simply Proxy/Servers that run a dynamic routing
protocol to redistribute routes between the OMNI interface and
INET/EUN interfaces (see: ). The Relay
provisions MNPs to networks on the INET/EUN interfaces (i.e., the
same as a Client would do) and advertises the MSP(s) for the OMNI
link over the INET/EUN interfaces. The Relay further provides an
attachment point of the OMNI link to a non-MNP-based global
topology.When a Client enables an OMNI interface, it assigns either an
MNP-{LLA, ULA} or a Temporary ULA and sends RS messages with ND
parameters over its underlying interfaces to a Proxy/Server, which
returns an RA message with corresponding parameters. The RS/RA
messages may pass through one or more NATs in the case of a Client's
INET interface. (Note: if the Client used a Temporary ULA in its
initial RS message, it will discover an MNP-{LLA, ULA} in the
corresponding RA that it receives from the Proxy/Server and begin
using these new addresses. If the Client is operating outside the
context of AERO infrastructure such as in a Mobile Ad-hoc Network
(MANET), however, it may continue using Temporary ULAs for
Client-to-Client communications until it encounters an
infrastructure element that can provide an MNP.)AERO Bridges configure an OMNI interface and assign the ADM-ULA
Subnet Router Anycast address for each OMNI link segment they
connect to. Bridges configure secured tunnels with Proxy/Servers and
other Bridges, and engage in a BGP routing protocol session with
neighbors on the spanning tree (see: ).Each OMNI interface maintains a conceptual neighbor cache that
includes an entry for each neighbor it communicates with on the OMNI
link per . In addition to ordinary neighbor
cache entries, proxy neighbor cache entries are created and maintained
by AERO Proxy/Servers when they proxy Client ND message exchanges
. AERO Proxy/Servers maintain proxy neighbor
cache entries for each of their associated Clients.To the list of neighbor cache entry states in Section 7.3.2 of
, Proxy/Server OMNI interfaces add an
additional state DEPARTED that applies to Clients that have recently
departed. The interface sets a "DepartTime" variable for the neighbor
cache entry to "DEPART_TIME" seconds. DepartTime is decremented unless
a new ND message causes the state to return to REACHABLE. While a
neighbor cache entry is in the DEPARTED state, the Proxy/Server
forwards carrier packets destined to the target Client to the Client's
new location instead. When DepartTime decrements to 0, the neighbor
cache entry is deleted. It is RECOMMENDED that DEPART_TIME be set to
the default constant value REACHABLE_TIME plus 10 seconds (40 seconds
by default) to allow a window for carrier packets in flight to be
delivered while stale route optimization state may be present.Proxy/Servers can act as RORs on behalf of disadvantaged Clients
according to the Proxy Neighbor Advertisement specification in Section
7.2.8 of , while well-connected Clients can
act as an ROR on their own behalf. When a Proxy/Server ROR receives an
authentic NS message used for route optimization, it first searches
for a proxy neighbor cache entry for the target Client and accepts the
message only if there is an entry. The Proxy/Server (or the actual
target Client acting as an ROR) then returns a solicited NA message
while creating a neighbor cache entry for the ROS and caching the
Identification value found in the NS message carrier packet as the
starting window Identification value for this ROS. Proxy/Servers
acting as proxy RORs also create or update a "Report List" entry for
the ROS in the target Client's proxy neighbor cache entry with a
"ReportTime" variable set to REPORT_TIME seconds. The ROR resets
ReportTime when it receives a new authentic NS message, and otherwise
decrements ReportTime while no authentic NS messages have been
received. It is RECOMMENDED that REPORT_TIME be set to the default
constant value REACHABLE_TIME plus 10 seconds (40 seconds by default)
to allow a window for route optimization to converge before ReportTime
decrements below REACHABLE_TIME.When the ROS receives a solicited NA message response to its NS
message used for route optimization, it creates or updates a neighbor
cache entry for the target network-layer and link-layer addresses. The
ROS then (re)sets ReachableTime for the neighbor cache entry to
REACHABLE_TIME seconds and uses this value to determine whether
carrier packets can be forwarded directly to the target, i.e., instead
of via a default route. The ROS also maintains a window start
Identification value that is monotonically incremented for each OAL
packet sent to this target, and sets new window start Identification
values when it sends a new NS. The ROS otherwise decrements
ReachableTime while no further solicited NA messages arrive. It is
RECOMMENDED that REACHABLE_TIME be set to the default constant value
30 seconds as specified in .AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the
number of NS keepalives sent when a correspondent may have gone
unreachable, the value MAX_RTR_SOLICITATIONS to limit the number of RS
messages sent without receiving an RA and the value
MAX_NEIGHBOR_ADVERTISEMENT to limit the number of unsolicited NAs that
can be sent based on a single event. It is RECOMMENDED that
MAX_UNICAST_SOLICIT, MAX_RTR_SOLICITATIONS and
MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the same as specified in .Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME,
MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and
MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if
different values are chosen, all nodes on the link MUST consistently
configure the same values. Most importantly, DEPART_TIME and
REPORT_TIME SHOULD be set to a value that is sufficiently longer than
REACHABLE_TIME to avoid packet loss due to stale route optimization
state.OMNI interface IPv6 ND messages include OMNI options with Interface Attributes that
provide Link-Layer Address and QoS Preference information for the
neighbor's underlying interfaces. This information is stored in the
neighbor cache and provides the basis for the forwarding algorithm
specified in . The information is cumulative
and reflects the union of the OMNI information from the most recent
ND messages received from the neighbor; it is therefore not required
that each ND message contain all neighbor information.The OMNI option Interface Attributes for each underlying
interface includes a two-part "Link-Layer Address" consisting of a
simple IP encapsulation address determined by the FMT and L2ADDR
fields and an ADM-ULA determined by the SRT and LHS fields.
Underlying interfaces are further selected based on their associated
preference values "high", "medium", "low" or "disabled".Note: the OMNI option is distinct from any Source/Target
Link-Layer Address Options (S/TLLAOs) that may appear in an ND
message according to the appropriate IPv6 over specific link layer
specification (e.g., ). If both an OMNI
option and S/TLLAO appear, the former pertains to encapsulation
addresses while the latter pertains to the native L2 address format
of the underlying media.As discussed in Section 4.4 of NA
messages include three flag bits R, S and O. OMNI interface NA
messages treat the flags as follows:R: The R ("Router") flag is set to 1 in the NA messages sent
by all AERO/OMNI node types. Simple hosts that would set R to 0
do not occur on the OMNI link itself, but may occur on the
downstream links of Clients and Relays.S: The S ("Solicited") flag is set exactly as specified in
Section 4.4. of , i.e., it is set to 1
for Solicited NAs and set to 0 for Unsolicited NAs (both unicast
and multicast).O: The O ("Override") flag is set to 0 for solicited proxy
NAs returned by a Proxy/Server ROR and set to 1 for all other
solicited and unsolicited NAs. For further study is whether
solicited NAs for anycast targets apply for OMNI links. Since
MNP-LLAs must be uniquely assigned to Clients to support correct
ND protocol operation, however, no role is currently seen for
assigning the same MNP-LLA to multiple Clients.The OMNI interface admits original IP packets then (acting as an
OAL source) performs OAL encapsulation and fragmentation as specified
in while including an ORH if
necessary as specified in . OAL
encapsulation produces OAL packets, while OAL fragmentation turns them
into OAL fragments which are then encapsulated in *NET headers as
carrier packets.For carrier packets undergoing re-encapsulation at an OAL
intermediate node, the OMNI interface decrements the OAL IPv6 header
Hop Limit and discards the carrier packet if the Hop Limit reaches 0.
The intermediate node next removes the *NET encapsulation headers from
the first segment and re-encapsulates the packet in new *NET
encapsulation headers for the next segment.When a Proxy/Server or Relay re-encapsulates a carrier packet
received from a Client that includes an OAL but no ORH, it inserts an
ORH immediately following the OAL header and adjusts the OAL payload
length and destination address field. The inserted ORH will be removed
by the final-hop Bridge, but its insertion and removal will not
interfere with reassembly at the final destination. For this reason,
Clients must reserve 40 bytes for a maximum-length ORH when they
perform OAL encapsulation (see: ).OMNI interfaces (acting as OAL destinations) decapsulate and
reassemble OAL packets into original IP packets destined either to the
AERO node itself or to a destination reached via an interface other
than the OMNI interface the original IP packet was received on. When
carrier packets containing OAL fragments arrive, the OMNI interface
reassembles as discussed in .AERO nodes employ simple data origin authentication procedures. In
particular:AERO Bridges and Proxy/Servers accept carrier packets
(including either data or control messages) received from the
(secured) spanning tree.AERO Proxy/Servers and Clients accept carrier packets and
original IP packets that originate from within the same secured
ANET.AERO Clients and Relays accept original IP packets from
downstream network correspondents based on ingress filtering.AERO Clients, Relays and Proxy/Servers verify carrier packet
UDP/IP encapsulation addresses according to .AERO Clients (as well as Proxy/Servers and Relays when acting
as OAL destinations) accept OAL packets/fragments with
Identification values within the current window for the OAL
source.AERO nodes silently drop any packets that do not satisfy the
above data origin authentication procedures. Further security
considerations are discussed in .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 employs an
OMNI Adaptation Layer (OAL) that accommodates multiple underlying
links with diverse MTUs while observing both a minimum and per-path
Maximum Payload Size (MPS). The functions of the OAL and the OMNI
interface MTU/MRU/MPS are specified in with MTU/MRU both set to the constant
value 9180 bytes, with minimum MPS set to 400 bytes, and with per-path
MPS set to potentially larger values depending on the underlying
path.When the network layer presents an original IP packet to the OMNI
interface, the OAL source encapsulates and fragments the original IP
packet if necessary. When the network layer presents the OMNI
interface with multiple original IP packets bound to the same OAL
destination, the OAL source can concatenate them together into a
single OAL super-packet as discussed in . The OAL source then fragments the
OAL packet if necessary according to the minimum/path MPS such that
the OAL headers appear in each fragment while the original IP packet
header appears only in the first fragment. The OAL source then
encapsulates each OAL fragment in *NET headers for transmission as
carrier packets over an underlying interface connected to either a
physical link such as Ethernet, WiFi and the like or a virtual link
such as an Internet or higher-layer tunnel (see the definition of link
in ).Note: A Client that does not (yet) have neighbor cache state for a
target may omit the ORH in carrier packets with the understanding that
a Proxy/Server may insert an ORH on its behalf. For this reason,
Clients reserve 40 bytes for the largest possible ORH in their OAL
fragment size calculations.Note: Although the ORH may be removed by a Bridge on the path (see:
), this does not interfere with the
destination's ability to reassemble. This is due to the fact that the
ORH is not included in the fragmentable part; therefore, its removal
does not invalidate the offset values in any fragment headers.Original IP packets enter a node's OMNI interface either from the
network layer (i.e., from a local application or the IP forwarding
system) while carrier packets enter from the link layer (i.e., from an
OMNI interface neighbor). All original IP packets and carrier packets
entering a node's OMNI interface first undergo data origin
authentication as discussed in . Those that
satisfy data origin authentication are processed further, while all
others are dropped silently.Original IP packets that enter the OMNI interface from the network
layer are forwarded to an OMNI interface neighbor using OAL
encapsulation and fragmentation to produce carrier packets for
transmission over underlying interfaces. (If routing indicates that
the original IP packet should instead be forwarded back to the network
layer, the packet is dropped to avoid looping). Carrier packets that
enter the OMNI interface from the link layer are either
re-encapsulated and re-admitted into the OMNI link, or reassembled and
forwarded to the network layer where they are subject to either local
delivery or IP forwarding. In all cases, the OAL MUST NOT decrement
the network layer TTL/Hop-count since its forwarding actions occur
below the network layer.OMNI interfaces may have multiple underlying interfaces and/or
neighbor cache entries for neighbors with multiple underlying
interfaces (see ). The OAL uses interface
attributes and/or traffic classifiers (e.g., DSCP value, port number,
flow specification, etc.) to select an outgoing underlying interface
for each OAL packet based on the node's own QoS preferences, and also
to select a destination link-layer address based on the neighbor's
underlying interface with the highest preference. AERO implementations
SHOULD allow for QoS preference values to be modified at runtime
through network management.If multiple outgoing interfaces and/or neighbor interfaces have a
preference of "high", the AERO node replicates the OAL packet and
sends one copy via each of the (outgoing / neighbor) interface pairs;
otherwise, the node sends a single copy of the OAL packet via an
interface with the highest preference. (While not strictly required,
successful delivery may be more likely when all OAL fragments of the
same OAL packet are sent over the same underlying interface.) AERO
nodes keep track of which underlying interfaces are currently
"reachable" or "unreachable", and only use "reachable" interfaces for
forwarding purposes.The following sections discuss the OMNI interface forwarding
algorithms for Clients, Proxy/Servers and Bridges. In the following
discussion, an original IP packet's destination address is said to
"match" if it is the same as a cached address, or if it is covered by
a cached prefix (which may be encoded in an MNP-LLA).When an original IP packet enters a Client's OMNI interface from
the network layer the Client searches for a neighbor cache entry
that matches the destination. If there is a match, the Client
selects one or more "reachable" neighbor interfaces in the entry for
forwarding purposes. If there is no neighbor cache entry, the Client
instead forwards the original IP packet toward a Proxy/Server. The
Client (acting as an OAL source) performs OAL encapsulation and sets
the OAL destination address to the MNP-ULA if there is a matching
neighbor cache entry; otherwise, it sets the OAL destination to the
ADM-ULA of the Proxy/Server. If the Client has multiple original IP
packets to send to the same neighbor, it can concatenate them in a
single super-packet . The OAL
source then performs fragmentation to create OAL fragments (see:
), appends any *NET encapsulation, and sends
the resulting carrier packets over underlying interfaces to the
neighbor acting as an OAL destination.If the neighbor interface selected for forwarding is located on
the same OMNI link segment and not behind a NAT, the Client forwards
the carrier packets directly according to the L2ADDR information for
the neighbor. If the neighbor interface is behind a NAT on the same
OMNI link segment, the Client instead forwards the initial carrier
packets to its Proxy/Server and initiates NAT traversal procedures.
If the Client's intended source underlying interface is also behind
a NAT and located on the same OMNI link segment, it sends a "direct
bubble" over the interface per to the L2ADDR found in the neighbor cache in
order to establish state in its own NAT by generating traffic toward
the neighbor (note that no response to the bubble is expected).The Client next sends an NS(NUD) message toward the MNP-ULA of
the neighbor via its Proxy/Server as discussed in . If the Client receives an NA(NUD) from the neighbor
over the underlying interface, it marks the neighbor interface as
"trusted" and sends future carrier packets directly to the L2ADDR
information for the neighbor instead of indirectly via the
Proxy/Server. The Client must honor the neighbor cache maintenance
procedure by sending additional direct bubbles and/or NS/NA(NUD)
messages as discussed in in order to keep NAT state alive as long as
carrier packets are still flowing.When an carrier packet enters a Client's OMNI interface from the
link-layer, if the OAL destination matches one of the Client's MNPs
or LLAs the Client (acting as an OAL destination) reassembles and
decapsulates as necessary and delivers the original IP packet to the
network layer. Otherwise, the Client drops the original IP packet
and MAY return a network-layer ICMP Destination Unreachable message
subject to rate limiting (see: ).Note: Clients and their Proxy/Server (and other Client) peers can
exchange original IP packets over ANET underlying interfaces without
invoking the OAL, since the ANET is secured at the link and physical
layers. By forwarding original IP packets without invoking the OAL,
however, the ANET peers can engage only in classical path MTU
discovery since the packets are subject to loss and/or corruption
due to the various per-link MTU limitations that may occur within
the ANET. Moreover, the original IP packets do not include
per-packet Identification values that can be used for data origin
authentication and link-layer retransmission purposes, nor the OAL
integrity check. The tradeoff therefore involves an assessment of
the per-packet encapsulation overhead saved by bypassing the OAL vs.
inheritance of classical network "brittleness".When the Proxy/Server receives an original IP packet from the
network layer, it drops the packet if routing indicates that it
should be forwarded back to the network layer to avoid looping.
Otherwise, the Proxy/Server regards the original IP packet the same
as if it had arrived as carrier packets with OAL destination set to
its own ADM-ULA. When the Proxy/Server receives carrier packets on
underlying interfaces with OAL destination set to its own ADM-ULA,
it performs OAL reassembly if necessary to obtain the original IP
packet.The Proxy/Server next searches for a neighbor cache entry that
matches the original IP destination and proceeds as follows:if the original IP packet destination matches a neighbor
cache entry, the Proxy/Sever uses one or more "reachable"
neighbor interfaces in the entry for packet forwarding using OAL
encapsulation and fragmentation according to the cached
link-layer address information. If the neighbor interface is in
a different OMNI link segment, the Proxy/Server forwards the
resulting carrier packets to a Bridge; otherwise, it forwards
the carrier packets directly to the neighbor. If the neighbor is
behind a NAT, the Proxy/Server instead forwards initial carrier
packets via a Bridge while sending an NS(NUD) to the neighbor.
When the Proxy/Server receives the NA(NUD), it can begin
forwarding carrier packets directly to the neighbor the same as
discussed in while sending additional
NS(NUD) messages as necessary to maintain NAT state. Note that
no direct bubbles are necessary since the Proxy/Server is by
definition not located behind a NAT.else, if the original IP destination matches a non-MNP route
in the IP forwarding table or an ADM-LLA assigned to the
Proxy/Server's OMNI interface, the Proxy/Server acting as a
Relay presents the original IP packet to the network layer for
local delivery or IP forwarding.else, the Proxy/Server initiates address resolution as
discussed in , while retaining initial
original IP packets in a small queue awaiting address resolution
completion.When the Proxy/Server receives a carrier packet with OAL
destination set to an MNP-ULA that does not match the MSP, it
accepts the carrier packet only if data origin authentication
succeeds and if there is a network layer routing table entry for a
GUA route that matches the MNP-ULA. If there is no route, the
Proxy/Server drops the carrier packet; otherwise, it reassembles and
decapsulates to obtain the original IP packet and acts as a Relay to
present it to the network layer where it will be delivered according
to standard IP forwarding.When the Proxy/Server receives a carrier packet with OAL
destination set to an MNP-ULA, it accepts the carrier packet only if
data origin authentication succeeds and if there is a neighbor cache
entry that matches the OAL destination. If the neighbor cache entry
state is DEPARTED, the Proxy/Server inserts an ORH that encodes the
MNP-ULA destination suffix and changes the OAL destination address
to the ADM-ULA of the new Proxy/Server, then re-encapsulates the
carrier packet and forwards it to a Bridge which will eventually
deliver it to the new Proxy/Server.If the neighbor cache state for the MNP-ULA is REACHABLE, the
Proxy/Server forwards the carrier packets to the Client which then
must reassemble. (Note that the Proxy/Server does not reassemble
carrier packets not explicitly addressed to its own ADM-ULA, since
routing could direct some of the carrier packet of the same original
IP packet through a different Proxy/Server.) In that case, the
Client may receive fragments that are smaller than its link MTU but
can still be reassembled; if this proves inefficient, the Client can
in the future elect to employ the Proxy/Server as a ROR instead of
serving in that role on its own behalf.Note: Clients and their Proxy/Server peers can exchange original
IP packets over ANET underlying interfaces without invoking the OAL,
since the ANET is secured at the link and physical layers. By
forwarding original IP packets without invoking the OAL, however,
the Client and Proxy/Server can engage only in classical path MTU
discovery since the packets are subject to loss and/or corruption
due to the various per-link MTU limitations that may occur within
the ANET. Moreover, the original IP packets do not include
per-packet Identification values that can be used for data origin
authentication and link-layer retransmission purposes, nor the OAL
integrity check. The tradeoff therefore involves an assessment of
the per-packet encapsulation overhead saved by bypassing the OAL vs.
inheritance of classical network "brittleness".Note: When a Proxy/Server receives a (non-OAL) original IP packet
from an ANET Client, or a carrier packet with OAL destination set to
its own ADM-ULA from any Client, the Proxy/Server reassembles if
necessary then performs ROS functions on behalf of the Client. The
Client may at some later time begin sending carrier packets to the
OAL address of the actual target instead of the Proxy/Server, at
which point it may begin functioning as an ROS on its own behalf and
thereby "override" the Proxy/Server's ROS role.Note: If the Proxy/Server has multiple original IP packets to
send to the same neighbor, it can concatenate them in a single OAL
super-packet .Bridges forward carrier packets the same as any IPv6 router.
Bridges convey carrier packets and original IP packets that
encapsulate IPv6 ND control messages or routing protocol control
messages using security encapsulations, and may convey packets that
encapsulate ordinary data without including security encapsulations.
When the Bridge receives a carrier packet or an original IP packet,
it removes the outer *NET header and searches for a forwarding table
entry that matches the OAL destination address. The Bridge then
processes the packet as follows:if the packet is a carrier packet with a destination that
matches its ADM-ULA Subnet Router Anycast address the Bridge
processes the carrier packet locally before forwarding. The
Bridge drops the carrier packet if it does not include an ORH;
otherwise, for NA(NUD) messages the Bridge replaces the OMNI
option Interface Attributes sub-option with information for its
own interface while retaining the ifIndex value supplied by the
NA(NUD) message source. The Bridge next examines the ORH FMT
code. If the code indicates the destination is a Client on the
open *NET (or, a Client behind a NAT for which NAT traversal
procedures have already converged) the Bridge removes the ORH
then writes the MNP-ULA formed from the ORH Destination Suffix
into the OAL destination. The Bridge then re-encapsulates the
carrier packet and forwards it to the ORH L2ADDR. For all other
destination cases, the Bridge instead writes the ADM-ULA formed
from the ORH SRT/LHS into the OAL destination address and
forwards the carrier packet to the ADM-ULA Proxy/Server while
invoking NAT traversal procedures the same as for Proxy/Servers
if necessary, noting that no direct bubbles are necessary since
only the target Client and not the Bridge is behind a NAT.else, if the packet is a carrier packet with a destination
that matches a forwarding table entry the Bridge forwards the
carrier packet via a secured tunnel to the next hop. (If the
destination matches an MSP without matching an MNP, however, the
Bridge instead drops the packet and returns an ICMP Destination
Unreachable message subject to rate limiting - see: ).else, if the packet is an original IP packet with a
destination that matches one of the Bridge's own addresses, the
Bridge submits the original IP packet for local delivery to
support local applications such as routing protocols.else, the Bridge drops the packet and returns an ICMP
Destination Unreachable as above.As for any IP router, the Bridge decrements the OAL IPv6
header Hop Limit when it forwards the carrier packet and drops the
packet if the Hop Limit reaches 0. Therefore, when an OAL header is
present only the Hop Limit in the OAL header is decremented and not
the TTL/Hop Limit in the original IP packet header. Bridges do not
insert OAL/ORH headers themselves; instead, they act as IPv6 routers
and forward carrier packets based on their destination
addresses.Bridges forward packets received from a first segment without
security encapsulations to the next segment also without including
security encapsulations. Bridges forward packets received from a
first segment with security encapsulations to the next segment also
including security encapsulations. Bridges use a single IPv6 routing
table that always determines the same next hop for a given OAL
destination whether or not security encapsulation is included.When an AERO node admits an original IP packet into the OMNI
interface, it may receive link-layer or network-layer error
indications.A link-layer error indication is an ICMP error message generated by
a router in the INET on the path to the neighbor or by the neighbor
itself. The message includes an IP header with the address of the node
that generated the error as the source address and with the link-layer
address of the AERO node as the destination address.The IP header is followed by an ICMP header that includes an error
Type, Code and Checksum. Valid type values include "Destination
Unreachable", "Time Exceeded" and "Parameter Problem" . (OMNI interfaces ignore
link-layer IPv4 "Fragmentation Needed" and IPv6 "Packet Too Big"
messages for carrier packets that are no larger than the minimum/path
MPS as discussed in , however these messages
may provide useful hints of probe failures during path MPS
probing.)The ICMP header is followed by the leading portion of the carrier
packet that generated the error, also known as the "packet-in-error".
For ICMPv6, specifies that the
packet-in-error includes: "As much of invoking packet as possible
without the ICMPv6 packet exceeding the minimum IPv6 MTU" (i.e., no
more than 1280 bytes). For ICMPv4, specifies
that the packet-in-error includes: "Internet Header + 64 bits of
Original Data Datagram", however Section
4.3.2.3 updates this specification by stating: "the ICMP datagram
SHOULD contain as much of the original datagram as possible without
the length of the ICMP datagram exceeding 576 bytes".The link-layer error message format is shown in (where, "L2" and "L3" refer to link-layer and
network-layer, respectively):The AERO node rules for processing these link-layer error
messages are as follows:When an AERO node receives a link-layer Parameter Problem
message, it processes the message the same as described as for
ordinary ICMP errors in the normative references .When an AERO node receives persistent link-layer Time Exceeded
messages, the IP ID field may be wrapping before earlier fragments
awaiting reassembly have been processed. In that case, the node
should begin including integrity checks and/or institute rate
limits for subsequent packets.When an AERO node receives persistent link-layer Destination
Unreachable messages in response to carrier packets that it sends
to one of its neighbor correspondents, the node should process the
message as an indication that a path may be failing, and
optionally initiate NUD over that path. If it receives Destination
Unreachable messages over multiple paths, the node should allow
future carrier packets destined to the correspondent to flow
through a default route and re-initiate route optimization.When an AERO Client receives persistent link-layer Destination
Unreachable messages in response to carrier packets that it sends
to one of its neighbor Proxy/Servers, the Client should mark the
path as unusable and use another path. If it receives Destination
Unreachable messages on many or all paths, the Client should
associate with a new Proxy/Server and release its association with
the old Proxy/Server as specified in .When an AERO Proxy/Server receives persistent link-layer
Destination Unreachable messages in response to carrier packets
that it sends to one of its neighbor Clients, the Proxy/Server
should mark the underlying path as unusable and use another
underlying path.When an AERO Proxy/Server receives link-layer Destination
Unreachable messages in response to a carrier packet that it sends
to one of its permanent neighbors, it treats the messages as an
indication that the path to the neighbor may be failing. However,
the dynamic routing protocol should soon reconverge and correct
the temporary outage.When an AERO Bridge receives a carrier packet for which the
network-layer destination address is covered by an MSP, the Bridge
drops the packet if there is no more-specific routing information for
the destination and returns a network-layer Destination Unreachable
message subject to rate limiting. The Bridge writes the network-layer
source address of the original IP packet as the destination address
and uses one of its non link-local addresses as the source address of
the message.When an AERO node receives a carrier packet for which reassembly is
currently congested, it returns a network-layer Packet Too Big (PTB)
message as discussed in (note
that the PTB messages could indicate either "hard" or "soft"
errors).AERO Router Discovery, Prefix Delegation and Autoconfiguration are
coordinated as discussed in the following Sections.Each AERO Proxy/Server on the OMNI link is configured to
facilitate Client prefix delegation/registration requests. Each
Proxy/Server is provisioned with a database of MNP-to-Client ID
mappings for all Clients enrolled in the AERO service, as well as
any information necessary to authenticate each Client. The Client
database is maintained by a central administrative authority for the
OMNI link and securely distributed to all Proxy/Servers, e.g., via
the Lightweight Directory Access Protocol (LDAP) , via static configuration, etc. Clients receive
the same service regardless of the Proxy/Servers they select.AERO Clients and Proxy/Servers use ND messages to maintain
neighbor cache entries. AERO Proxy/Servers configure their OMNI
interfaces as advertising NBMA interfaces, and therefore send
unicast RA messages with a short Router Lifetime value (e.g.,
ReachableTime seconds) in response to a Client's RS message.
Thereafter, Clients send additional RS messages to keep Proxy/Server
state alive.AERO Clients and Proxy/Servers include prefix delegation and/or
registration parameters in RS/RA messages (see ). The ND messages are exchanged
between Client and Proxy/Server according to the prefix management
schedule required by the service. If the Client knows its MNP in
advance, it can employ prefix registration by including its MNP-LLA
as the source address of an RS message and with an OMNI option with
valid prefix registration information for the MNP. If the
Proxy/Server accepts the Client's MNP assertion, it injects the MNP
into the routing system and establishes the necessary neighbor cache
state. If the Client does not have a pre-assigned MNP, it can
instead employ prefix delegation by including the unspecified
address (::) as the source address of an RS message and with an OMNI
option with prefix delegation parameters to request an MNP.The following sections specify the Client and Proxy/Server
behavior.AERO Clients discover the addresses of Proxy/Servers in a similar
manner as described in . Discovery methods
include static configuration (e.g., from a flat-file map of
Proxy/Server addresses and locations), or through an automated means
such as Domain Name System (DNS) name resolution . Alternatively, the Client can discover
Proxy/Server addresses through a layer 2 data link login exchange,
or through a unicast RA response to a multicast/anycast RS as
described below. In the absence of other information, the Client can
resolve the DNS Fully-Qualified Domain Name (FQDN)
"linkupnetworks.[domainname]" where "linkupnetworks" is a constant
text string and "[domainname]" is a DNS suffix for the OMNI link
(e.g., "example.com").To associate with a Proxy/Server, the Client acts as a requesting
router to request MNPs. The Client prepares an RS message with
prefix management parameters and includes a Nonce and Timestamp
option if the Client needs them to correlate RA replies. If the
Client already knows the Proxy/Server's ADM-LLA, it includes the LLA
as the network-layer destination address; otherwise, the Client
includes the (link-local) All-Routers multicast as the network-layer
destination. If the Client already knows its own MNP-LLA, it can use
the MNP-LLA as the network-layer source address and include an OMNI
option with prefix registration information. Otherwise, the Client
uses the unspecified address (::) as the network-layer source
address and includes prefix delegation parameters in the OMNI option
(see: ). The Client includes
Interface Attributes corresponding to the underlying interface over
which it will send the RS message, and MAY include additional
Interface Attributes specific to other underlying interfaces.For INET Clients, the Client must ensure that the RS message is
no larger than the minimum/path MPS for the chosen Proxy/Server and
must include a security signature that the Proxy/Server can verify.
The Client next applies OAL encapsulation such that the entire RS
message fits within an OAL First Fragment (i.e., as an atomic
fragment) while including an unpredictable OAL Identification number
selected per that will serve as the window
start Identification value for future packets it will send/accept
with its own MNP-ULA and the Proxy/Server's ADM-ULA as the OAL
addresses. (The Proxy/Server in turn caches the Identification
number as start value for future packets it will accept/send with
its own ADM-ULA and the Client's MNP-ULA as the OAL addresses.)The Client then sends the RS message (either directly via Direct
interfaces, via a VPN for VPNed interfaces, via an access router for
ANET interfaces or via INET encapsulation for INET interfaces) while
using OAL encapsulation/fragmentation, then waits for an RA message
reply (see ). The Client retries up to
MAX_RTR_SOLICITATIONS times until an RA is received. If the Client
receives no RAs, or if it receives an RA with Router Lifetime set to
0, the Client SHOULD abandon attempts through the first Proxy/Server
and try another Proxy/Server. Otherwise, the Client processes the
prefix information found in the RA message.When the Client processes an RA, it first performs OAL reassembly
and decapsulation then creates a neighbor cache entry with the
Proxy/Server's ADM-LLA as the network-layer address and the
Proxy/Server's encapsulation and/or link-layer addresses as the
link-layer address. The Client next records the RA Router Lifetime
field value in the neighbor cache entry as the time for which the
Proxy/Server has committed to maintaining the MNP in the routing
system via this underlying interface, and caches the other RA
configuration information including Cur Hop Limit, M and O flags,
Reachable Time and Retrans Timer. The Client then autoconfigures
MNP-LLAs for any delegated MNPs and assigns them to the OMNI
interface. The Client also caches any MSPs included in Route
Information Options (RIOs) as MSPs to
associate with the OMNI link, and assigns the MTU value in the MTU
option to the underlying interface.The Client then registers additional underlying interfaces with
the Proxy/Server by sending RS messages via each additional
interface as described above. The RS messages include the same
parameters as for the initial RS/RA exchange, but with destination
address set to the Proxy/Server's ADM-LLA. The Client finally
sub-delegates the MNPs to its attached EUNs and/or the Client's own
internal virtual interfaces as described in to support the Client's
downstream attached "Internet of Things (IoT)". The Client then
sends additional RS messages over each underlying interface before
the Router Lifetime received for that interface expires.After the Client registers its underlying interfaces, it may wish
to change one or more registrations, e.g., if an interface changes
address or becomes unavailable, if QoS preferences change, etc. To
do so, the Client prepares an RS message to send over any available
underlying interface as above. The RS includes an OMNI option with
prefix registration/delegation information, with Interface
Attributes specific to the selected underlying interface, and with
any additional Interface Attributes specific to other underlying
interfaces. When the Client receives the Proxy/Server's RA response,
it has assurance that the Proxy/Server has been updated with the new
information.If the Client wishes to discontinue use of a Proxy/Server it
issues an RS message over any underlying interface with an OMNI
option with a prefix release indication. When the Proxy/Server
processes the message, it releases the MNP, sets the neighbor cache
entry state for the Client to DEPARTED and returns an RA reply with
Router Lifetime set to 0. After a short delay (e.g., 2 seconds), the
Proxy/Server withdraws the MNP from the routing system.AERO Proxy/Servers act as IP routers and support a prefix
delegation/registration service for Clients. Proxy/Servers arrange
to add their ADM-LLAs to a static map of Proxy/Server addresses for
the link and/or the DNS resource records for the FQDN
"linkupnetworks.[domainname]" before entering service. Proxy/Server
addresses should be geographically and/or topologically referenced,
and made available for discovery by Clients on the OMNI link.When a Proxy/Server receives a prospective Client's RS message on
its OMNI interface, it SHOULD return an immediate RA reply with
Router Lifetime set to 0 if it is currently too busy or otherwise
unable to service the Client. Otherwise, the Proxy/Server performs
OAL reassembly and decapsulation, then authenticates the RS message
and processes the prefix delegation/registration parameters. The
Proxy/Server first determines the correct MNPs to provide to the
Client by processing the MNP-LLA prefix parameters and/or the DHCPv6
OMNI sub-option. When the Proxy/Server returns the MNPs, it also
creates a forwarding table entry for the MNP-ULA corresponding to
each MNP so that the MNPs are propagated into the routing system
(see: ). For IPv6, the Proxy/Server creates
an IPv6 forwarding table entry for each MNP. For IPv4, the
Proxy/Server creates an IPv6 forwarding table entry with the
IPv4-compatibility MNP-ULA prefix corresponding to the IPv4
address.The Proxy/Server next creates a neighbor cache entry for the
Client using the base MNP-LLA as the network-layer address and with
lifetime set to no more than the smallest prefix lifetime. Next, the
Proxy/Server updates the neighbor cache entry by recording the
information in each Interface Attributes sub-option in the RS OMNI
option. The Proxy/Server also records the actual OAL/*NET addresses
in the neighbor cache entry. For RS messages encapsulated as carrier
packets, the Proxy/Server also records the OAL Identification number
as the starting value for the window of future packets it will
send/accept with its own ADM-ULA and the Client's MNP-ULA as the OAL
addresses. (The Client in turn caches the Identification number as
start value for future packets it will accept/send with its own
MNP-ULA and the Proxy/Server's ADM-ULA as the OAL addresses.)Next, the Proxy/Server prepares an RA message using its ADM-LLA
as the network-layer source address and the network-layer source
address of the RS message as the network-layer destination address.
The Proxy/Server sets the Router Lifetime to the time for which it
will maintain both this underlying interface individually and the
neighbor cache entry as a whole. The Proxy/Server also sets Cur Hop
Limit, M and O flags, Reachable Time and Retrans Timer to values
appropriate for the OMNI link. The Proxy/Server includes the MNPs,
any other prefix management parameters and an OMNI option with no
Interface Attributes but with an Origin Indication sub-option per
with the mapped and
obfuscated Port Number and IP address corresponding to the Client's
own INET address in the case of INET Clients or to the
Proxy/Server's INET-facing address for all other Clients. The
Proxy/Server then includes one or more RIOs that encode the MSPs for
the OMNI link, plus an MTU option (see ).
The Proxy/Server finally forwards the message to the Client using
OAL encapsulation/fragmentation as necessary with an OAL
Identification value that matches the RS.After the initial RS/RA exchange, the Proxy/Server maintains a
ReachableTime timer for each of the Client's underlying interfaces
individually (and for the Client's neighbor cache entry
collectively) set to expire after ReachableTime seconds. If the
Client (or Proxy) issues additional RS messages, the Proxy/Server
sends an RA response and resets ReachableTime. If the Proxy/Server
receives an ND message with a prefix release indication it sets the
Client's neighbor cache entry to the DEPARTED state and withdraws
the MNP from the routing system after a short delay (e.g., 2
seconds). If ReachableTime expires before a new RS is received on an
individual underlying interface, the Proxy/Server marks the
interface as DOWN. If ReachableTime expires before any new RS is
received on any individual underlying interface, the Proxy/Server
sets the neighbor cache entry state to STALE and sets a 10 second
timer. If the Proxy/Server has not received a new RS or ND message
with a prefix release indication before the 10 second timer expires,
it deletes the neighbor cache entry and withdraws the MNP from the
routing system.The Proxy/Server processes any ND messages pertaining to the
Client and returns an NA/RA reply in response to solicitations. The
Proxy/Server may also issue unsolicited RA messages, e.g., with
reconfigure parameters to cause the Client to renegotiate its prefix
delegation/registrations, with Router Lifetime set to 0 if it can no
longer service this Client, etc. Finally, If the neighbor cache
entry is in the DEPARTED state, the Proxy/Server deletes the entry
after DepartTime expires.Note: Clients SHOULD notify former Proxy/Servers of their
departures, but Proxy/Servers are responsible for expiring neighbor
cache entries and withdrawing routes even if no departure
notification is received (e.g., if the Client leaves the network
unexpectedly). Proxy/Servers SHOULD therefore set Router Lifetime to
ReachableTime seconds in solicited RA messages to minimize
persistent stale cache information in the absence of Client
departure notifications. A short Router Lifetime also ensures that
proactive RS/RA messaging between Clients and Proxy/Servers will
keep any NAT state alive (see above).Note: All Proxy/Servers on an OMNI link MUST advertise consistent
values in the RA Cur Hop Limit, M and O flags, Reachable Time and
Retrans Timer fields the same as for any link, since unpredictable
behavior could result if different Proxy/Servers on the same link
advertised different values.When a Client is not pre-provisioned with an MNP-LLA, it will
need for the Proxy/Server to select one or more MNPs on its behalf
and set up the correct state in the AERO routing service. (A
Client with a pre-provisioned MNP may also request the
Proxy/Server to select additional MNPs.) The DHCPv6 service is used to support this requirement.When a Client needs to have the Proxy/Server select MNPs, it
sends an RS message with source address set to the unspecified
address (::) and with an OMNI option that includes a DHCPv6
message sub-option with DHCPv6 Prefix Delegation (DHCPv6-PD)
parameters. When the Proxy/Server receives the RS message, it
extracts the DHCPv6-PD message from the OMNI option.The Proxy/Server then acts as a "Proxy DHCPv6 Client" in a
message exchange with the locally-resident DHCPv6 server, which
delegates MNPs and returns a DHCPv6-PD Reply message. (If the
Proxy/Server wishes to defer creation of MN state until the
DHCPv6-PD Reply is received, it can instead act as a Lightweight
DHCPv6 Relay Agent per by encapsulating
the DHCPv6-PD message in a Relay-forward/reply exchange with Relay
Message and Interface ID options.)When the Proxy/Server receives the DHCPv6-PD Reply, it adds a
route to the routing system and creates an MNP-LLA based on the
delegated MNP. The Proxy/Server then sends an RA back to the
Client with the (newly-created) MNP-LLA as the destination address
and with the DHCPv6-PD Reply message coded in the OMNI option.
When the Client receives the RA, it creates a default route,
assigns the Subnet Router Anycast address and sets its MNP-LLA
based on the delegated MNP.Note: See for an MNP
delegation alternative in which the Client can optionally avoid
including a DHCPv6 message sub-option. Namely, when the Client
requests a single MNP it can set the RS source to the unspecified
address (::) and include a Node Identification sub-option and
Preflen in the OMNI option (but with no DHCPv6 message
sub-option). When the Proxy/Server receives the RS message, it
forwards a self-generated DHCPv6 Solicit message to the DHCPv6
server on behalf of the Client. When the Proxy/Server receives the
DHCPv6 Reply, it prepares an RA message with an OMNI option with
Preflen information (but with no DHCPv6 message sub-option), then
places the (newly-created) MNP-LLA in the RA destination address
and returns the message to the Client.Clients connect to the OMNI link via Proxy/Servers, with one
Proxy/Server for each underlying interface. Each of the Client's
Proxy/Servers must be informed of all of the Client's additional
underlying interfaces. For Clients on Direct and VPNed underlying
interfaces the Proxy/Server "A" for that interface is directly
connected, for Clients on ANET underlying interfaces Proxy/Server "A"
is located on the ANET/INET boundary, and for Clients on INET
underlying interfaces Proxy/Server "A" is located somewhere in the
connected Internetwork. When the Client registers with Proxy/Server
"A", it must also report the registration to any other Proxy/Servers
for other underlying interfaces "B", "C", "D", etc. for which an
underlying interface relationship has already been established. The
Proxy/Server satisfies these requirements as follows:when Proxy/Server "A" receives an RS message from a new Client,
it first authenticates the message then examines the network-layer
destination address. If the destination address is Proxy/Server
"A"'s ADM-LLA or (link-local) All-Routers multicast, Proxy/Server
"A" creates a proxy neighbor cache entry and caches the Client
link-layer addresses along with the OMNI option information and
any other identifying information including OAL Identification
values, Client Identifiers, Nonce values, etc. If the RS message
destination was the ADM-LLA of a different Proxy/Server "B" (or,
if the OMNI option included an MS-Register sub-option with the
ADM-LLA of a different Proxy/Server "B"), Proxy/Server "A"
encapsulates a proxyed version of the RS message in an OAL header
with source set to Proxy/Server "A"'s ADM-ULA and destination set
to Proxy/Server "B"'s ADM-ULA. Proxy/Server "A" also includes an
OMNI header with an Interface Attributes option that includes its
own INET address plus a unique UDP Port Number for this Client,
then forwards the message into the OMNI link spanning tree. (Note:
including a unique Port Number allows Proxy/Server "B" to
distinguish different Clients located behind the same Proxy/Server
"A" at the link-layer, whereas the link-layer addresses would
otherwise be indistinguishable.)when the Proxy/Server "B" receives the RS, it authenticates the
message then creates or updates a neighbor cache entry for the
Client with Proxy/Server "A"'s ADM-ULA, INET address and UDP Port
Number as the link-layer address information. Proxy/Server "B"
then sends an RA message back to Proxy/Server "A" via the spanning
tree.when Proxy/Server "A" receives the RA, it authenticates the
message and matches it with the proxy neighbor cache entry created
by the RS. Proxy/Server "A" then caches the prefix information as
a mapping from the Client's MNPs to the Client's link-layer
address, caches the Proxy/Server's advertised Router Lifetime and
sets the neighbor cache entry state to REACHABLE. The Proxy/Server
then optionally rewrites the Router Lifetime and forwards the
(proxyed) message to the Client. The Proxy/Server finally includes
an MTU option (if necessary) with an MTU to use for the underlying
ANET interface.The Client repeats this process with each Proxy/Server "B",
"C", "D" for each of its additional underlying interfaces.After the initial RS/RA exchanges each Proxy/Server forwards
any of the Client's carrier packets for which there is no matching
neighbor cache entry to a Bridge using OAL encapsulation with its own
ADM-ULA as the source and the MNP-ULA corresponding to the Client as
the destination. The Proxy/Server instead forwards any carrier packets
destined to a neighbor cache target directly to the target according
to the OAL/link-layer information - the process of establishing
neighbor cache entries is specified in .While the Client is still associated with each Proxy/Server "A",
"A" can send NS, RS and/or unsolicited NA messages to update the
neighbor cache entries of other AERO nodes on behalf of the Client
and/or to convey QoS updates. This allows for higher-frequency
Proxy-initiated RS/RA messaging over well-connected INET
infrastructure supplemented by lower-frequency Client-initiated RS/RA
messaging over constrained ANET data links.If any Proxy/Server "B", "C", "D" ceases to send solicited
advertisements, Proxy/Server "A" sends unsolicited RAs to the Client
with destination set to (link-local) All-Nodes multicast and with
Router Lifetime set to zero to inform Clients that a Proxy/Server has
failed. Although Proxy/Server "A" can engage in ND exchanges on behalf
of the Client, the Client can also send ND messages on its own behalf,
e.g., if it is in a better position than "A" to convey QoS changes,
etc. The ND messages sent by the Client include the Client's MNP-LLA
as the source in order to differentiate them from the ND messages sent
by Proxy/Server "A".If the Client becomes unreachable over an underlying interface,
Proxy/Server "A" sets the neighbor cache entry state to DEPARTED and
retains the entry for DepartTime seconds. While the state is DEPARTED,
Proxy/Server "A" forwards any carrier packets destined to the Client
to a Bridge via OAL/ORH encapsulation. When DepartTime expires,
Proxy/Server "A" deletes the neighbor cache entry and discards any
further carrier packets destined to this (now forgotten) Client.In some ANETs that employ a Proxy/Server, the Client's MNP can be
injected into the ANET routing system. In that case, the Client can
send original IP packets without invoking the OAL so that the ANET
routing system transports the original IP packets to the Proxy. This
can be very beneficial, e.g., if the Client connects to the ANET via
low-end data links such as some aviation wireless links.If the ANET first-hop access router is on the same underlying link
as the Client and recognizes the AERO/OMNI protocol, the Client can
avoid OAL encapsulation for both its control and data messages. When
the Client connects to the link, it can send an unencapsulated RS
message with source address set to its own MNP-LLA (or to a Temporary
LLA), and with destination address set to the ADM-LLA of the Client's
selected Proxy/Server or to (link-local) All-Routers multicast. The
Client includes an OMNI option formatted as specified in . The Client then sends the
unencapsulated RS message, which will be intercepted by the AERO-Aware
access router.The ANET access router then performs OAL encapsulation on the RS
message and forwards it to a Proxy/Server at the ANET/INET boundary.
When the access router and Proxy/Server are one and the same node, the
Proxy/Server would share and underlying link with the Client but its
message exchanges with outside correspondents would need to pass
through a security gateway at the ANET/INET border. The method for
deploying access routers and Proxys (i.e. as a single node or multiple
nodes) is an ANET-local administrative consideration.Note: The Proxy/Server can apply packing as discussed in if an opportunity arises to
concatenate multiple original IP packets that will be destined to the
same neighbor.In environments where fast recovery from Proxy/Server failure is
required, Proxy/Server "A" SHOULD use proactive Neighbor
Unreachability Detection (NUD) to track peer Proxy/Server "B"
reachability in a similar fashion as for Bidirectional Forwarding
Detection (BFD) . Proxy/Server "A" can then
quickly detect and react to failures so that cached information is
re-established through alternate paths. The NUD control messaging is
carried only over well-connected ground domain networks (i.e., and
not low-end aeronautical radio links) and can therefore be tuned for
rapid response.Proxy/Server "A" performs proactive NUD with peer Proxy/Server
"B" for which there are currently active Clients by sending
continuous NS messages in rapid succession, e.g., one message per
second. Proxy/Server "A" sends the NS message via the spanning tree
with its own ADM-LLA as the source and the ADM-LLA of the peer
Proxy/Server "B" as the destination. When Proxy/Server "A" is also
sending RS messages to the peer Proxy/Server "B" on behalf of ANET
Clients, the resulting RA responses can be considered as equivalent
hints of forward progress. This means that Proxy/Server "B" need not
also send a periodic NS if it has already sent an RS within the same
period. If the peer Proxy/Server "B" fails (i.e., if "A" ceases to
receive advertisements), Proxy/Server "A" can quickly inform Clients
by sending multicast RA messages on the ANET interface.Proxy/Server "A" sends RA messages on the ANET interface with
source address set to Proxy/Server "B"'s address, destination
address set to (link-local) All-Nodes multicast, and Router Lifetime
set to 0. Proxy/Server "A" SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS
RA messages separated by small delays . Any
Clients on the ANET that had been using the failed Proxy/Server "B"
will receive the RA messages and associate with a new
Proxy/Server.In environments where Client messaging over ANETs is
bandwidth-limited and/or expensive, Clients can enlist the services
of Proxy/Server "A" to coordinate with multiple Proxy/Servers "B",
"C", "D" etc. in a single RS/RA message exchange. The Client can
send a single RS message to (link-local) All-Routers multicast that
includes the ID's of multiple Proxy/Servers in MS-Register
sub-options of the OMNI option.When Proxy/Server "A" receives the RS and processes the OMNI
option, it sends a separate RS to each MS-Register Proxy/Server ID.
When Proxy/Server "A" receives an RA, it can optionally return an
immediate "singleton" RA to the Client or record the Proxy/Server's
ID for inclusion in a pending "aggregate" RA message. Proxy/Server
"A" can then return aggregate RA messages to the Client including
multiple Proxy/Server IDs in order to conserve bandwidth. Each RA
includes a proper subset of the Proxy/Server IDs from the original
RS message, and Proxy/Server "A" must ensure that the message
contents of each RA are consistent with the information received
from the (aggregated) additional Proxy/Servers.Clients can thereafter employ efficient point-to-multipoint
Proxy/Server coordination under the assistance of Proxy/Server "A"
to reduce the number of messages sent over the ANET while enlisting
the support of multiple Proxy/Servers for fault tolerance. Clients
can further include MS-Release sub-options in IPv6 ND messages to
request Proxy/Server "A" to release from former Proxy/Servers via
the procedures discussed in .The OMNI interface specification provides further discussion of the
RS/RA messaging involved in point-to-multipoint coordination.While AERO nodes can always send data packets over strict spanning
tree paths, route optimization should be performed while carrier
packets are flowing between a source and target node. Route
optimization is based on asymmetric IPv6 ND Address Resolution
messaging between a Route Optimization Source (ROS) and Route
Optimization Responder (ROR), and later extended to the target using
IPv6 ND Neighbor Unreachability Detection messaging. Route
optimization is initiated by the first eligible ROS closest to the
source as follows:For Clients on VPNed and Direct interfaces, the Proxy/Server is
the ROS.For Clients on ANET interfaces, either the Client or the
Proxy/Server may be the ROS.For Clients on INET interfaces, the Client itself is the
ROS.For correspondent nodes on INET/EUN interfaces serviced by a
Relay, the Relay is the ROS.The route optimization procedure is conducted between the ROS and
the target Proxy/Server/Relay acting as an ROR (the target may either
be a MNP Client serviced by a Proxy/Server or a non-MNP correspondent
reachable via a Relay). Note that in this arrangement the ROS is
always the Client or Proxy/Server/Relay nearest the source over the
selected source underlying interface, while the ROR is always a
Proxy/Server/Relay that services the target regardless of the target
underlying interface.The procedures are specified in the following sections.When an original IP packet from a source node destined to a
target node arrives, the ROS checks for a neighbor cache entry for
an MNP-LLA that matches the target destination. If there is a
neighbor cache entry in the REACHABLE state, the ROS invokes the OAL
and forwards the resulting carrier packets according to the cached
state and returns from processing. Otherwise, if there is no
neighbor cache entry the ROS creates one in the INCOMPLETE
state.The ROS next places the original IP packet on a short queue then
sends an NS message for Address Resolution (NS(AR)) to receive a
solicited NA(AR) message from a ROR. The NS(AR) message must be no
larger than the minimum/path MPS so that its entire contents will
fit in an OAL first fragment (i.e., as an atomic fragment). The ROS
prepares an NS(AR) that includes:the LLA of the ROS as the source address.the MNP-LLA corresponding to the original IP packet's
destination as the Target Address, e.g., for
2001:db8:1:2::10:2000 the Target Address is
fe80::2001:db8:1:2.the Solicited-Node multicast address
formed from the lower 24 bits of the original IP packet's
destination as the destination address, e.g., for
2001:db8:1:2::10:2000 the NS destination address is
ff02:0:0:0:0:1:ff10:2000.The NS(AR) message also includes an OMNI option with an
Interface Attributes entry for the sending interface, and with
Preflen set to the prefix length associated with the NS(AR) source.
The ROS then submits the NS(AR) message for OAL encapsulation and
fragmentation, with OAL source set to its own ULA and OAL
destination set to the ULA corresponding to the target, and with an
unpredictable initial Identification value. The ROS caches the
initial Identification value in the (newly-created) neighbor cache
entry as the starting sequence number for the "send" window for
future carrier packets sent to this target via the responding
ROR.The ROS then sends the resulting carrier packet into the spanning
tree without decrementing the network-layer TTL/Hop Limit field.
(When the ROS is an INET Client, it instead must first sign the
NS(AR) message and send the resulting carrier packet to the ADM-ULA
of one of its current Proxy/Servers which then verifies the NS(AR)
signature and forwards the carrier packet into the spanning tree on
behalf of the Client.)When the Bridge receives the carrier packet containing the RS
from the ROS, it discards the *NET headers and determines the next
hop by consulting its standard IPv6 forwarding table for the OAL
header destination address. The Bridge then decrements the OAL
header Hop-Limit, re-encapsulates the carrier packet and forwards it
via the spanning tree the same as for any IPv6 router, where it may
traverse multiple OMNI link segments. The final-hop Bridge in the
spanning tree will deliver the carrier packet via a secured tunnel
to a Proxy/Server or Relay that services the target.When the target Proxy/Server (or Relay) receives the carrier
packet, it examines the enclosed atomic fragment to determine that
it contains an NS(AR) then examines the NS(AR) target to determine
whether it has a matching neighbor cache entry and/or non-MNP route.
If there is no match, the Proxy/Server drops the message. Otherwise,
the Proxy/Server/Relay continues processing as follows:if the NS(AR) target matches a Client neighbor cache entry in
the DEPARTED state, the Proxy/Server inserts an ORH with
destination prefix set to the lower 64 bits of the Client's
MNP-ULA and sets the destination address to the ADM-ULA of the
Client's new Proxy/Server. The (old) Proxy/Server then
re-encapsulates the carrier packet, forwards it into the
spanning tree and returns from processing.If the NS(AR) target matches the MNP-LLA of a Client neighbor
cache entry in the REACHABLE state, the Proxy/Server acts as an
ROR to provide route optimization information on behalf of the
Client.If the NS(AR) target matches one of its non-MNP routes, the
Relay acts as an ROR since it serves as a router to forward IP
packets toward the (fixed network) target at the network
layer.The ROR next checks the target neighbor cache entry for a Report
List entry that matches the NS(AR) source LLA/ULA of the ROS. If
there is a Report List entry, the ROR accepts the NS(AR) only if the
OAL Identification value is within the "accept" window for this ROS
or if the NS(AR) was forwarded over the secured spanning tree. If
the NS(AR) is authentic and the OAL Identification is outside of the
current "accept" window for this ROS, the ROR resets the current
"accept" window start to the new OAL Identification value. If the
NS(AR) is authentic but the target neighbor cache entry does not
already include a Report List entry for this ROS, the ROR creates a
new entry and caches the ROS information. The Report List cache
entry therefore includes the LLA and ULA of the ROS, the new
"accept" Identification number for the ROS and the previous "accept"
Identification number in case any packets sent under the previous
window are still in flight.The ROR then prepares a (solicited) NA(AR) message to send back
to the ROS using the same Identification value received in the
NS(AR) (unlike the NS(AR), the NA(AR) need not fit in a single OAL
fragment). The ROR sets the NA(AR) source address to the target's
MNP-LLA, sets the destination address to the NS(AR) LLA source
address and sets the Target Address to the same value that appeared
in the NS(AR). The ROR then includes an OMNI option with Preflen set
to the prefix length associated with the NA(AR) source address. If
the NS(AR) target was an MNP Client, the ROR next includes Interface
Attributes in the OMNI option for each of the target's underlying
interfaces with current information for each interface and includes
an authentication signature if necessary. The ROR then sets the
S/T-ifIndex field in the OMNI header to 0.For each Interface Attributes sub-option, the ROR sets the L2ADDR
according to the Proxy/Server's INET address for VPNed or Direct
interfaces, to the INET address of the Proxy/Server for proxyed
interfaces or to the Client's INET address for INET interfaces. The
ROR then includes the lower 32 bits of the Proxy/Server's ADM-ULA as
the LHS, encodes the ADM-ULA prefix length code in the SRT field and
sets the FMT code accordingly as specified in .The ROR then sets the NA(AR) message R flag to 1 (as a router)
and S flag to 1 (as a response to a solicitation) and sets the O
flag to 0 (as a proxy). The ROR finally submits the NA(AR) for OAL
encapsulation with source set to its own ULA and destination set to
the ULA of the ROS, then performs OAL fragmentation using the same
Identification value that appeared in the NS(AR) and forwards the
resulting (*NET-encapsulated) carrier packets via the spanning tree
without decrementing the network-layer TTL/Hop Limit field.When the Bridge receives the carrier packets from the ROR, it
discards the *NET header and determines the next hop by consulting
its standard IPv6 forwarding table for the OAL header destination
address. The Bridge then decrements the OAL header Hop-Limit,
re-encapsulates the carrier packet and forwards it via the spanning
tree the same as for any IPv6 router, where it may traverse multiple
OMNI link segments. The final-hop Bridge in the spanning tree will
deliver the carrier packet via a secured tunnel to a Proxy/Server
for the ROS.When the ROS receives the NA(AR) message, it first searches for a
neighbor cache entry that matches the NA(AR) LLA source address. If
there is an entry in the INCOMPLETE or STALE state, the ROS matches
the OAL Identification value with the value it had included in the
corresponding NS(AR). If the values match, the ROS processes the
message the same as for standard IPv6 Address Resolution . In the process, it caches the NA(AR) LLA source
address and all information found in the OMNI option in the neighbor
cache entry for the target. The ROS finally sets the neighbor cache
entry state to REACHABLE and sets its lifetime to ReachableTime
seconds. (When the ROS is a Client, the solicited NA(AR) message
will first be delivered via the spanning tree to one of its current
Proxy/Servers, which then securely forwards the message to the
Client. If the Client is on an ANET, ANET physical security and
protected spectrum ensures security; if the Client is on the open
ANET, the Proxy/Server must include an authentication
signature.)Following route optimization, the ROS forwards future carrier
packets with user data destined to the target via the addresses
found in the cached link-layer information and with a
monotonically-incrementing Identification value for each OAL packet.
The route optimization is shared by all sources that send original
IP packets to the target via the ROS, i.e., and not just the source
on behalf of which the route optimization was initiated. Note that
route optimization is performed only for original IP packets that
contain user data, and not for those that contain other IPv6 ND
control messages.While the ROS continues to forward additional original IP packets
destined to the target, it sends additional NS(AR) messages to the
ROR before ReachableTime expires to receive a fresh NA(AR) message
the same as described in the previous sections (route optimization
refreshment strategies are an implementation matter, with a
non-normative example given in ). The ROS
may supply a new unpredictable Identification value if it wishes to
reset the neighbor's "accept" Identification window. If the ROS is
an INET Client, it must include an authentication signature with the
NS(AR) message so that the Proxy/Server can authenticate.The ROS uses its own ULA as the NS(AR) OAL source address and the
ULA of the ROR as the NS(AR) OAL destination address, and sends up
to MAX_MULTICAST_SOLICIT NS(AR) messages separated by 1 second until
an NA(AR) is received. If no NA(AR) is received, the ROS assumes
that the current ROR has become unreachable and deletes the target
neighbor cache entry. Subsequent original IP packets will trigger a
new route optimization event (see: ) which
may discover a different ROR that services the same target.If an NA(AR) is received, the ROS then updates the neighbor cache
entry for the target to refresh ReachableTime, while (for MNP
targets) the ROR adds or updates the ROS address to the target's
Report List and with time set to ReportTime. While no carrier
packets are flowing, the ROS instead allows ReachableTime for the
target neighbor cache entry to expire. When ReachableTime expires,
the ROS places the target neighbor cache entry back in the STALE
state. Any future carrier packets flowing through the ROS will again
trigger a new route optimization.The ROS may also receive unsolicited NA (uNA) messages from the
ROR at any time (see: ). If there is a
neighbor cache entry for the target and the carrier packet(s)
containing the uNA is received securely, the ROS updates the
link-layer information but does not update ReachableTime since the
receipt of a uNA does not confirm that any forward paths are
working. If there is no neighbor cache entry or the message cannot
be authenticated, the ROS simply discards the uNA.In this arrangement, the ROS holds a neighbor cache entry for the
target in the REACHABLE state with a "send" Identification window
starting value, while the ROR's target neighbor cache entry holds a
Report List entry for the ROS with an "accept" Identification window
starting value for the ULA of the ROS. The route optimization
neighbor relationship is therefore asymmetric and unidirectional. If
the target node also has carrier packets to send back to the source
node, then a separate route optimization procedure is performed in
the reverse direction, but there is no requirement that the forward
and reverse paths be symmetric.AERO nodes perform Neighbor Unreachability Detection (NUD) per
either reactively in response to persistent
link-layer errors (see ) or on-demand to
confirm reachability and/or initiate route optimizations from the ROS
to the target via the ROR. The NUD algorithm is based on periodic
control message exchanges. The algorithm may further be seeded by ND
hints of forward progress, but care must be taken to avoid inferring
reachability based on spoofed information. For example, authentic IPv6
ND message exchanges may be considered as acceptable hints of forward
progress, while spurious random packets should not be.AERO nodes can use standard NS/NA(NUD) exchanges sent over the OMNI
link spanning tree to securely test reachability without risk of DoS
attacks from nodes pretending to be a neighbor. These NS/NA(NUD)
messages use the unicast LLAs and ULAs of the two parties involved in
the NUD test the same as for standard IPv6 ND over the secured
spanning tree, however a means for an ROS to test the unsecured target
route optimized paths is also necessary.When an ROR directs an ROS to a target neighbor with one or more
link-layer addresses, the ROS performs extended route optimization for
each unsecured target underlying interface either proactively or
on-demand of carrier packets directed to the path by multilink
forwarding. The route optimization is performed through secured
NS(NUD) messages over the spanning tree in the forward path that
invoke an unsecured NA(NUD) reply over the target underlying interface
on return path. (The NS(NUD) messages must therefore include
Identification values (and optionally Nonce and Timestamp options)
that will be echoed in the unsecured NA(NUD) replies.) While testing a
target underlying interface, the ROS can optionally continue to send
carrier packets via the ROR or maintain a small queue of carrier
packets until target reachability is confirmed.When the ROS sends an NS(NUD) message, it sets the IPv6 source to
its own LLA and sets both the destination and Target Address to the
LLA of the target. The ROS also includes an OMNI option with a single
Interface Attributes sub-option with the SRT, FMT, LHS and L2ADDR
information for its own underlying interface it wishes to test, but
sets the S/T-ifIndex field to the index for target's underlying
interface to be tested. The ROS includes an Identification value
within the current "send" window for this ROR (and optionally Nonce
and Timestamp options), then encapsulates the message in OAL/INET
headers with its own ULA as the source and the ULA of the ROR as the
destination. The ROS then forwards the NS(NUD) message toward the ROR
(and ultimately the target itself) via the spanning tree.When the ROR receives the NS(NUD) message, it examines the
S/T-ifIndex field to determine the underlying interface target of the
NS(NUD) test. If the underlying interface is a Direct or VPNed
interface, the ROR acts as the target. If the underlying interface is
a Proxyed interface, the ROR changes the OAL destination to the ULA of
the Proxy and forwards the NS(NUD) to the Proxy which either acts as
the target itself or forwards the message to the target Client. If the
underlying interface is an INET interface, the ROR changes the OAL
destination address to the ULA of the target Client and forwards the
NS(NUD) over the underlying interface to the target Client while
including an authentication signature.The target then creates a neighbor cache entry for the ROS LLA
address if necessary and caches the Identification value as the start
of the "accept" window for this ROS. The target then creates an
NA(NUD) by reversing the OAL and IPv6 addresses from the NS(NUD) while
copying the Identification value, and next including an Interface
Attributes sub-option with attributes for its own interface identified
by the NS(NUD) S/T-ifIndex. The target sets the NA(NUD) S/T-ifIndex to
the index of the ROS, sets the Target Address to the same value that
was in the NS(NUD), sets R flag to 1, the S flag to 0 and the O flag
to 1, and returns the message using its own underlying interface
identified by NS(NUD) S/T-ifIndex and destined to the ROS's interface
identified by the original Interface Attributes sub-option.When the ROS receives the NA(NUD) message, it can determine from
the Identification value and Target Address (and optionally the Nonce
and Timestamp) that the message matched its NS(NUD) and that it
transited the direct path from the ROR using the selected underlying
interface pair. The ROS marks route optimization target paths that
pass these NUD tests as "reachable", and those that do not as
"unreachable". These markings inform the OMNI interface forwarding
algorithm specified in .Note: If the target determines that the OMNI option Interface
Attributes in the NS(NUD) is located in a different OMNI link segment
than its own interface named in the S/T-ifIndex, it instead returns
the NA(NUD) via the spanning tree while including an ORH and setting
the OAL destination address to the Subnet Router Anycast address used
by Bridges on the ROS segment. When a Bridge on the ROS segment
receives the NA(NUD), it replaces the Interface Attributes with
information for its own interface while using the ifIndex value
specific to the target.AERO is a Distributed Mobility Management (DMM) service. Each
Proxy/Server is responsible for only a subset of the Clients on the
OMNI link, as opposed to a Centralized Mobility Management (CMM)
service where there is a single network mobility collective entity for
all Clients. Clients coordinate with their associated Proxy/Servers
via RS/RA exchanges to maintain the DMM profile, and the AERO routing
system tracks all current Client/Proxy/Server peering
relationships.Proxy/Servers provide default routing and mobility/multilink
services for their dependent Clients. Clients are responsible for
maintaining neighbor relationships with their Proxy/Servers through
periodic RS/RA exchanges, which also serves to confirm neighbor
reachability. When a Client's underlying interface address and/or QoS
information changes, the Client is responsible for updating the
Proxy/Server with this new information. Note that when there is a
Proxy/Server in the path, the Proxy function can also perform some
RS/RA exchanges on the Client's behalf.Mobility management messaging is based on the transmission and
reception of unsolicited Neighbor Advertisement (uNA) messages. Each
uNA message sets the IPv6 destination address to (link-local)
All-Nodes multicast to convey a general update of Interface Attributes
to (possibly) multiple recipients, or to a specific unicast LLA to
announce a departure event to a specific recipient. Implementations
must therefore examine the destination address to determine the nature
of the mobility event (i.e., update vs departure).Mobility management considerations are specified in the following
sections.RORs accommodate Client mobility, multilink and/or QoS change
events by sending unsolicited NA (uNA) messages to each ROS in the
target Client's Report List. When an ROR sends a uNA message, it
sets the IPv6 source address to the its own LLA, sets the
destination address to (link-local) All-Nodes multicast and sets the
Target Address to the Client's MNP-LLA. The ROR also includes an
OMNI option with Preflen set to the prefix length associated with
the Client's MNP-LLA, with Interface Attributes for the target
Client's underlying interfaces and with the OMNI header S/T-ifIndex
set to 0. The ROR then sets the NA R flag to 1, the S flag to 0 and
the O flag to 1, then encapsulates the message in an OAL header with
source set to its own ULA and destination set to the ULA of the ROS
and sends the message into the spanning tree.As discussed in Section 7.2.6 of , the
transmission and reception of uNA messages is unreliable but
provides a useful optimization. In well-connected Internetworks with
robust data links uNA messages will be delivered with high
probability, but in any case the Proxy/Server can optionally send up
to MAX_NEIGHBOR_ADVERTISEMENT uNAs to each ROS to increase the
likelihood that at least one will be received.When the ROS receives a uNA message prepared as above, it ignores
the message if there is no existing neighbor cache entry for the
target Client. Otherwise, it uses the included OMNI option
information to update the neighbor cache entry, but does not reset
ReachableTime since the receipt of an unsolicited NA message from
the ROR does not provide confirmation that any forward paths to the
target Client are working.If uNA messages are lost, the ROS may be left with stale address
and/or QoS information for the Client for up to ReachableTime
seconds. During this time, the ROS can continue sending carrier
packets according to its stale neighbor cache information. When
ReachableTime is close to expiring, the ROS will re-initiate route
optimization and receive fresh link-layer address information.In addition to sending uNA messages to the current set of ROSs
for the Client, the ROR also sends uNAs to the MNP-ULA associated
with the link-layer address for any underlying interface for which
the link-layer address has changed. These uNA messages update an old
Proxy/Server that cannot easily detect (e.g., without active
probing) when a formerly-active Client has departed. When the ROR
sends the uNA, it sets the IPv6 source address to its LLA, sets the
destination address to the old Proxy/Server's ADM-LLA, and sets the
Target Address to the Client's MNP-LLA. The ROR also includes an
OMNI option with Preflen set to the prefix length associated with
the Client's MNP-LLA, with Interface Attributes for the changed
underlying interface, and with the OMNI header S/T-ifIndex set to
its own omIndex if the ROR is a Client or 0 if the ROR is a
Proxy/Server. The ROR then sets the NA R flag to 1, the S flag to 0
and the O flag to 1, then encapsulates the message in an OAL header
with source set to its own ULA and destination set to the ADM-ULA of
the old Proxy/Server and sends the message into the spanning
tree.When a Client needs to change its underlying interface addresses
and/or QoS preferences (e.g., due to a mobility event), the Client
requests one of its Proxy/Servers to send RS messages to all of its
other Proxy/Servers via the spanning tree with an OMNI option that
includes Interface attributes with the new link quality and address
information.Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel
with sending carrier packets containing user data in case one or
more RAs are lost. If all RAs are lost, the Client SHOULD
re-associate with a new Proxy/Server.When the Proxy/Server receives the Client's changes, it sends uNA
messages to all nodes in the Report List the same as described in
the previous section.When a Client needs to bring new underlying interfaces into
service (e.g., when it activates a new data link), it sends an RS
message to the Proxy/Server via the underlying interface with an
OMNI option that includes Interface Attributes with appropriate link
quality values and with link-layer address information for the new
link.When a Client needs to deactivate an existing underlying
interface, it sends an RS or uNA message to its Proxy/Server with an
OMNI option with appropriate Interface Attribute values - in
particular, the link quality value 0 assures that neighbors will
cease to use the link.If the Client needs to send RS/uNA messages over an underlying
interface other than the one being deactivated, it MUST include
Interface Attributes with appropriate link quality values for any
underlying interfaces being deactivated.Note that when a Client deactivates an underlying interface,
neighbors that have received the RS/uNA messages need not purge all
references for the underlying interface from their neighbor cache
entries. The Client may reactivate or reuse the underlying interface
and/or its ifIndex at a later point in time, when it will send
RS/uNA messages with fresh Interface Attributes to update any
neighbors.The Client performs the procedures specified in when it first associates with a new
Proxy/Server or renews its association with an existing
Proxy/Server. The Client also includes MS-Release identifiers in the
RS message OMNI option per if
it wants the new Proxy/Server to notify any old Proxy/Servers from
which the Client is departing.When the new Proxy/Server receives the Client's RS message, it
returns an RA as specified in and
sends up to MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old
Proxy/Servers listed in OMNI option MS-Release identifiers. When the
new Proxy/Server sends a uNA message, it sets the IPv6 source
address to the Client's MNP-LLA, sets the destination address to the
old Proxy/Server's ADM-LLA, and sets the Target Address to the
Client's LLA. The new Proxy/Server also includes an OMNI option with
Preflen set to the prefix length associated with the Client's
MNP-LLA, with Interface Attributes for its own underlying interface,
and with the OMNI header S/T-ifIndex set to 0. The new Proxy/Server
then sets the NA R flag to 1, the S flag to 0 and the O flag to 1,
then encapsulates the message in an OAL header with source set to
its own ADM-ULA and destination set to the ADM-ULA of the old
Proxy/Server and sends the message into the spanning tree.When an old Proxy/Server receives the uNA, it changes the
Client's neighbor cache entry state to DEPARTED, sets the link-layer
address of the Client to the new Proxy/Server's ADM-ULA, and resets
DepartTime. After a short delay (e.g., 2 seconds) the old
Proxy/Server withdraws the Client's MNP from the routing system.
After DepartTime expires, the old Proxy/Server deletes the Client's
neighbor cache entry.The old Proxy/Server also iteratively forwards a copy of the uNA
message to each ROS in the Client's Report List by changing the OAL
destination address to the ULA of the ROS while leaving all other
fields of the message unmodified. When the ROS receives the uNA, it
examines the Target address to determine the correct neighbor cache
entry and verifies that the IPv6 destination address matches the old
Proxy/Server. The ROS then caches the IPv6 source address as the new
Proxy/Server for the existing neighbor cache entry and marks the
entry as STALE. While in the STALE state, the ROS allows new carrier
packets to flow according to any existing cached link-layer
information and sends new NS(AR) messages using its own ULA as the
OAL source and the ADM-ULA of the new Proxy/Server as the OAL
destination address to elicit NA messages that reset the neighbor
cache entry state to REACHABLE. If no new NA message is received for
10 seconds while in the STALE state, the ROS deletes the neighbor
cache entry.Clients SHOULD NOT move rapidly between Proxy/Servers in order to
avoid causing excessive oscillations in the AERO routing system.
Examples of when a Client might wish to change to a different
Proxy/Server include a Proxy/Server that has gone unreachable,
topological movements of significant distance, movement to a new
geographic region, movement to a new OMNI link segment, etc.When a Client moves to a new Proxy/Server, some of the fragments
of a multiple fragment OAL packet may have already arrived at the
old Proxy/Server while others are en route to the new Proxy/Server,
however no special attention in the reassembly algorithm is
necessary since all fragments will eventually be delivered to the
Client which can then reassemble.The AERO Client provides an IGMP (IPv4) or
MLD (IPv6) proxy service for its EUNs and/or
hosted applications . The Client forwards
IGMP/MLD messages over any of its underlying interfaces for which
group membership is required. The IGMP/MLD messages may be further
forwarded by a first-hop ANET access router acting as an
IGMP/MLD-snooping switch , then ultimately
delivered to an AERO Proxy/Server acting as a Protocol Independent
Multicast - Sparse-Mode (PIM-SM, or simply "PIM") Designated Router
(DR) . AERO Relays also act as PIM routers
(i.e., the same as AERO Proxys/Servers) on behalf of nodes on INET/EUN
networks. The behaviors identified in the following sections
correspond to Source-Specific Multicast (SSM) and Any-Source Multicast
(ASM) operational modes.When an ROS "X" acting as PIM router receives a Join/Prune
message from a node on its downstream interfaces containing one or
more ((S)ource, (G)roup) pairs, it updates its Multicast Routing
Information Base (MRIB) accordingly. For each S belonging to a
prefix reachable via X's non-OMNI interfaces, X then forwards the
(S, G) Join/Prune to any PIM routers on those interfaces per .For each S belonging to a prefix reachable via X's OMNI
interface, X includes a PIM Join/Prune for each (S,G) in the OMNI
option of an NS(AR) message (see: ) using
its own LLA as the source address and ALL-PIM-ROUTERS as the
destination address. X then encapsulates the NS(AR) in an OAL header
with source address set to the ULA of X and destination address set
to S then forwards the message into the spanning tree, which
delivers it to ROR "Y" that services S. The resulting NA(AR) will
return the LLA for the prefix that matches S as the network-layer
source address and with an OMNI option with the ULA corresponding to
any underlying interfaces that are currently servicing S.When Y processes the NS(AR) it examines the PIM Join/Prune
message. If S is located behind any INET, Direct, or VPNed
interfaces Y acts as a PIM router and updates its MRIB to list X as
the next hop in the reverse path. If S is located behind any Proxys
"Z"*, X then sends an NS(NUD) message containing the PIM message to
each Z* via Y with addressing and encapsulation details the same as
specified in . Each Z* then updates its MRIB
accordingly and maintains the LLA of X as the next hop in the
reverse path. Since the Bridges do not examine network layer control
messages, this means that the (reverse) multicast tree path is
simply from each Z* (and/or Y) to X with no other multicast-aware
routers in the path.Following the initial combined Join/Prune and NS/NA messaging, X
maintains a neighbor cache entry for each S the same as if X was
sending unicast data traffic to S. In particular, X performs
additional NS/NA exchanges to keep the neighbor cache entry alive
for up to t_periodic seconds . If no new
Joins are received within t_periodic seconds, X allows the neighbor
cache entry to expire. Finally, if X receives any additional
Join/Prune messages for (S,G) it forwards the messages in NS/NA
exchanges with each Y and Z* in the neighbor cache entry over the
spanning tree.At some later time, Client C that holds an MNP for source S may
depart from a first Proxy/Server Z1 and/or connect via a new
Proxy/Server Z2. In that case, Y sends a uNA message to X the same
as specified for unicast mobility in . When
X receives the uNA message, it updates its neighbor cache entry for
the LLA for source S and sends new Join messages to any new Proxys
Z2. There is no requirement to send any Prune messages to old
Proxy/Server Z1 since source S will no longer source any multicast
data traffic via Z1. Instead, the multicast state for (S,G) in
Proxy/Server Z1 will soon time out since no new Joins will
arrive.After some later time, C may move to a new Proxy/Server Y2 and
depart from old Sever Y1. In that case, Y1 sends Join messages for
any of C's active (S,G) groups to Y2 while including its own LLA as
the source address. This causes Y2 to include Y1 in the multicast
forwarding tree during the interim time that Y1's neighbor cache
entry for C is in the DEPARTED state. At the same time, Y1 sends a
uNA message to X with an OMNI option with S/T-ifIndex in the header
set to 0 and a release indication to cause X to release its neighbor
cache entry for S. X then sends a new Join message to S via the
spanning tree and re-initiates route optimization the same as if it
were receiving a fresh Join message from a node on a downstream
link.When an ROS X acting as a PIM router receives a Join/Prune from a
node on its downstream interfaces containing one or more (*,G)
pairs, it updates its Multicast Routing Information Base (MRIB)
accordingly. X then forwards a copy of the message within the OMNI
option of an NS(AR) message to the Rendezvous Point (RP) R for each
G over the spanning tree. X uses its own LLA as the source address
and ALL-PIM-ROUTERS as the destination address, then encapsulates
the NS(AR) message in an OAL header with source address set to the
ULA of X and destination address set to R, then sends the message
into the spanning tree.For each source S that sends multicast traffic to group G via R,
the Proxy/Server Z* for the Client that aggregates S encapsulates
the original IP packets in PIM Register messages and forwards them
to R via the spanning tree, which may then elect to send a PIM Join
to Z*. This will result in an (S,G) tree rooted at Z* with R as the
next hop so that R will begin to receive two copies of the original
IP packet; one native copy from the (S, G) tree and a second copy
from the pre-existing (*, G) tree that still uses PIM Register
encapsulation. R can then issue a PIM Register-stop message to
suppress the Register-encapsulated stream. At some later time, if C
moves to a new Proxy/Server Z*, it resumes sending original IP
packets via PIM Register encapsulation via the new Z*.At the same time, as multicast listeners discover individual S's
for a given G, they can initiate an (S,G) Join for each S under the
same procedures discussed in . Once the
(S,G) tree is established, the listeners can send (S, G) Prune
messages to R so that multicast original IP packets for group G
sourced by S will only be delivered via the (S, G) tree and not from
the (*, G) tree rooted at R. All mobility considerations discussed
for SSM apply.Bi-Directional PIM (BIDIR-PIM) provides
an alternate approach to ASM that treats the Rendezvous Point (RP)
as a Designated Forwarder (DF). Further considerations for BIDIR-PIM
are out of scope.An AERO Client can connect to multiple OMNI links the same as for
any data link service. In that case, the Client maintains a distinct
OMNI interface for each link, e.g., 'omni0' for the first link,
'omni1' for the second, 'omni2' for the third, etc. Each OMNI link
would include its own distinct set of Bridges and Proxy/Servers,
thereby providing redundancy in case of failures.Each OMNI link could utilize the same or different ANET
connections. The links can be distinguished at the link-layer via the
SRT prefix in a similar fashion as for Virtual Local Area Network
(VLAN) tagging (e.g., IEEE 802.1Q) and/or through assignment of
distinct sets of MSPs on each link. This gives rise to the opportunity
for supporting multiple redundant networked paths, with each VLAN
distinguished by a different SRT "color" (see: ).The Client's IP layer can select the outgoing OMNI interface
appropriate for a given traffic profile while (in the reverse
direction) correspondent nodes must have some way of steering their
original IP packets destined to a target via the correct OMNI
link.In a first alternative, if each OMNI link services different MSPs,
then the Client can receive a distinct MNP from each of the links. IP
routing will therefore assure that the correct OMNI link is used for
both outbound and inbound traffic. This can be accomplished using
existing technologies and approaches, and without requiring any
special supporting code in correspondent nodes or Bridges.In a second alternative, if each OMNI link services the same MSP(s)
then each link could assign a distinct "OMNI link Anycast" address
that is configured by all Bridges on the link. Correspondent nodes can
then perform Segment Routing to select the correct SRT, which will
then direct the original IP packet over multiple hops to the
target.AERO Client MNs and INET correspondent nodes consult the Domain
Name System (DNS) the same as for any Internetworking node. When
correspondent nodes and Client MNs use different IP protocol versions
(e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain A
records for IPv4 address mappings to MNs which must then be populated
in Relay NAT64 mapping caches. In that way, an IPv4 correspondent node
can send original IPv4 packets to the IPv4 address mapping of the
target MN, and the Relay will translate the IPv4 header and
destination address into an IPv6 header and IPv6 destination address
of the MN.When an AERO Client registers with an AERO Proxy/Server, the
Proxy/Server can return the address(es) of DNS servers in RDNSS
options . The DNS server provides the IP
addresses of other MNs and correspondent nodes in AAAA records for
IPv6 or A records for IPv4.OAL encapsulation ensures that dissimilar INET partitions can be
joined into a single unified OMNI link, even though the partitions
themselves may have differing protocol versions and/or incompatible
addressing plans. However, a commonality can be achieved by
incrementally distributing globally routable (i.e., native) IP
prefixes to eventually reach all nodes (both mobile and fixed) in all
OMNI link segments. This can be accomplished by incrementally
deploying AERO Bridges on each INET partition, with each Bridge
distributing its MNPs and/or discovering non-MNP IP GUA prefixes on
its INET links.This gives rise to the opportunity to eventually distribute native
IP addresses to all nodes, and to present a unified OMNI link view
even if the INET partitions remain in their current protocol and
addressing plans. In that way, the OMNI link can serve the dual
purpose of providing a mobility/multilink service and a
transition/coexistence service. Or, if an INET partition is
transitioned to a native IP protocol version and addressing scheme
that is compatible with the OMNI link MNP-based addressing scheme, the
partition and OMNI link can be joined by Bridges.Relays that connect INETs/EUNs with dissimilar IP protocol versions
may need to employ a network address and protocol translation function
such as NAT64 .In environments where rapid failure recovery is required,
Proxy/Servers and Bridges SHOULD use Bidirectional Forwarding
Detection (BFD) . Nodes that use BFD can
quickly detect and react to failures so that cached information is
re-established through alternate nodes. BFD control messaging is
carried only over well-connected ground domain networks (i.e., and not
low-end radio links) and can therefore be tuned for rapid
response.Proxy/Servers and Bridges maintain BFD sessions in parallel with
their BGP peerings. If a Proxy/Server or Bridge fails, BGP peers will
quickly re-establish routes through alternate paths the same as for
common BGP deployments. Similarly, Proxys maintain BFD sessions with
their associated Bridges even though they do not establish BGP
peerings with them.AERO Clients that connect to the open Internet via INET interfaces
can establish a VPN or direct link to securely connect to a
Proxy/Server in a "tethered" arrangement with all of the Client's
traffic transiting the Proxy/Server. Alternatively, the Client can
associate with an INET Proxy/Server using UDP/IP encapsulation and
control message securing services as discussed in the following
sections.When a Client's OMNI interface enables an INET underlying
interface, it first determines whether the interface is likely to be
behind a NAT. For IPv4, the Client assumes it is on the open Internet
if the INET address is not a special-use IPv4 address per . Similarly for IPv6, the Client assumes it is on
the open Internet if the INET address is a Global Unicast Address
(GUA) . Otherwise, the Client assumes it may
be behind one or several NATs.The Client then prepares an RS message with IPv6 source address set
to its MNP-LLA, with IPv6 destination set to (link-local) All-Routers
multicast and with an OMNI option with underlying interface
attributes. If the Client believes that it is on the open Internet, it
SHOULD include an L2ADDR in the Interface Attributes sub-option
corresponding to the underlying interface; otherwise, it MAY omit
L2ADDR. If the underlying address is IPv4, the Client includes the
Port Number and IPv4 address written in obfuscated form as discussed in . If the
underlying interface address is IPv6, the Client instead includes the
Port Number and IPv6 address in obfuscated form. The Client finally
includes an authentication signature sub-option in the OMNI option
to provide message
authentication and submits the RS for OAL encapsulation as an atomic
fragment using an unpredictable Identification value to establish the
start of the "send/accept" window for this Proxy/Server. The Client
then encapsulates the OAL fragment in UDP/IP headers to form a carrier
packet, sets the UDP/IP source to its INET address and UDP port, sets
the UDP/IP destination to the Proxy/Server's INET address and the AERO
service port number (8060), then sends the carrier packet to the
Proxy/Server.When the Proxy/Server receives the RS, it discards the OAL
encapsulation, authenticates the RS message, creates a neighbor cache
entry and registers the Client's MNP, Identification and INET
interface information according to the OMNI option parameters. If the
RS message OMNI option includes Interface Attributes with an L2ADDR,
the Proxy/Server compares the encapsulation IP address and UDP port
number with the (unobfuscated) values. If the values are the same, the
Proxy/Server caches the Client's information as "INET" addresses
meaning that the Client is likely to accept direct messages without
requiring NAT traversal exchanges. If the values are different (or, if
the OMNI option did not include an L2ADDR) the Proxy/Server instead
caches the Client's information as "mapped" addresses meaning that NAT
traversal exchanges may be necessary.The Proxy/Server then prepares an RA message with IPv6 source and
destination set corresponding to the addresses in the RS, and with an
OMNI option with an Origin Indication sub-option per with the mapped and obfuscated Port
Number and IP address observed in the encapsulation headers. The
Proxy/Server also includes an authentication signature sub-option per
that contains an
acknowledgement of the update sent by the Client. The Proxy/Server
then performs OAL encapsulation and fragmentation if necessary using
the same Identification value that appeared in the RS, and
encapsulates each fragment in UDP/IP headers with addresses set per
the L2ADDR information in the neighbor cache entry for the Client.When the Client receives the RA message, it verifies the OAL
Identification value, performs OAL reassembly if necessary,
authenticates the message, then compares the mapped Port Number and IP
address from the Origin Indication sub-option with its own address. If
the addresses are the same, the Client assumes the open Internet /
Cone NAT principle; if the addresses are different, the Client instead
assumes that further qualification procedures are necessary to detect
the type of NAT and proceeds according to standard procedures .After the Client has registered its INET interfaces in such RS/RA
exchanges it sends periodic RS messages to receive fresh RA messages
before the Router Lifetime received on each INET interface expires.
The Client also maintains default routes via its Proxy/Servers, i.e.,
the same as described in earlier sections.When the Client sends messages to target IP addresses, it also
invokes route optimization per using IPv6
ND address resolution messaging. The Client first creates a neighbor
cache entry for the target in the INCOMPLETE state, then sends the
NS(AR) message to the Proxy/Server with an OMNI option with an
authentication signature sub-option. The Client sets the NS source
address to its own MNP-LLA, destination address to the target
solicited node multicast address and target address to the LLA of the
target. The Client then wraps the NS message in OAL headers (i.e., as
an atomic fragment) with an unpredictable Identification value to
establish the "send" window for this target, with source address set
to its own MNP-ULA and destination address set to the target's
MNP-ULA. The Client then wraps the atomic fragment in a UDP/IP header
and sends the resulting carrier packet to the Proxy/Server.When the Client's Proxy/Server receives the OAL-encapsulated NS, it
authenticates the message by processing the authentication signature
sub-option and forwards the message over the spanning tree on behalf
of the Client. When the ROR receives the NS(AR), it creates a neighbor
cache entry for the ROS in the STALE state and caches the
Identification value as the start of the "accept" window for packets
originating from this ROS (if the ROR is a Proxy/Server, it also
creates a Report List entry for this ROS in the target Client's
neighbor cache entry). The ROR then returns an NA(AR) with OMNI option
information for the target including all of the target's Interface
Attributes.The ROR sets the NA(AR) source address to its own LLA, sets the
destination address to the ROS LLA and sets the target address to the
LLA of the target. The ROR then performs OAL encapsulation using the
same Identification value that appeared in the NS(AR), then sets the
OAL source address to the ROR's ULA and destination address to ULA
source of the NS(AR). If the ROR is an INET Client, it includes an
authentication signature and sends the NA(AR) to its Proxy/Sever which
verifies the authentication signature and forwards the NA(AR) into the
secured spanning tree. If the ROR is an ANET Client or a Proxy/Server,
it simply forwards the NA(AR) into the secured spanning tree.When the Proxy/Sever for the ROS Client receives the NA(AR) message
contained in one or more carrier packets, it verifies the OAL
Identification matches the same value that was used in the NS(AR) then
reassembles if necessary. When reassembly is complete, the
Proxy/Server includes an authentication signature and forwards the
NA(AR) to the ROS Client. The ROS Client then verifies the
authentication signature and changes the neighbor cache entry state
for this target to REACHABLE.Following route optimization for targets in the same OMNI link
segment, if the target's L2ADDR is on the open INET, the Client
forwards carrier packets directly to the target INET address. If the
target is behind a NAT, the Client first establishes NAT state for the
L2ADDR using the "direct bubble" and NUD mechanisms discussed in . The Client continues to send carrier packets via its
Proxy/Server until NAT state is populated, then begins forwarding
carrier packets via the direct path through the NAT to the target. For
targets in different OMNI link segments, the Client uses OAL/ORH
encapsulation and forwards carrier packets to the Bridge that returned
the NA message.The ROR may return uNAs via the ROS Proxy/Server if the target
moves, and the Proxy/Server will send corresponding uNAs to the Client
with an OMNI authentication sub-option. The Client can also send NUD
messages to test forward path reachability even though there is no
security association between the Client and the target.The Client can send original IP packets to route-optimized
neighbors in the same OMNI link segment no larger than the
minimum/path MPS in one piece and with OAL encapsulation but without
fragmentation. For larger original IP packets, the Client applies OAL
encapsulation and fragmentation if necessary according to , with OAL header with source set to its own MNP-ULA
and destination set to the MNP-ULA of the target. The Client then
encapsulates each original IP packet or OAL fragment in UDP/IP *NET
headers and sends them to the next hop.Note: The NAT traversal procedures specified in this document are
applicable for Cone, Address-Restricted and Port-Restricted NATs only.
While future updates to this document may specify procedures for other
NAT variations (e.g., hairpinning and various forms of Symmetric
NATs), it should be noted that continuous communications are always
possible through forwarding via a Proxy/Server even if NAT traversal
is not employed.In some use cases, it is desirable, beneficial and efficient for
the Client to receive a constant MNP that travels with the Client
wherever it moves. For example, this would allow air traffic
controllers to easily track aircraft, etc. In other cases, however
(e.g., intelligent transportation systems), the 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 DHCPv6 service offers a way for Clients that desire
time-varying MNPs to obtain short-lived prefixes (e.g., on the order
of a small number of minutes). In that case, the identity of the
Client would not be bound to the MNP but rather to a Node
Identification value (see: ) to
be used as the Client ID seed for MNP prefix delegation. The Client
would then be obligated to renumber its internal networks whenever its
MNP (and therefore also its MNP-LLA) changes. This should not present
a challenge for Clients with automated network renumbering services,
however presents limits for the durations of ongoing sessions that
would prefer to use a constant address.An early AERO implementation based on OpenVPN (https://openvpn.net/)
was announced on the v6ops mailing list on January 10, 2018 and an
initial public release of the AERO proof-of-concept source code was
announced on the intarea mailing list on August 21, 2015.AERO Release-3.2 was tagged on March 30, 2021, and is undergoing
internal testing. Additional internal releases expected within the
coming months, with first public release expected end of 1H2021.The IANA is instructed to assign a new type value TBD1 in the IPv6
Routing Types registry (IANA registration procedure is IETF Review or
IESG Approval).The IANA has assigned the UDP port number "8060" for an earlier
experimental first version of AERO . This
document obsoletes , and 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'.) This document makes no request of IANA, since already provides instructions.No further IANA actions are required.AERO Bridges configure secured tunnels with AERO Proxy/Servers and
Relays within their local OMNI link segments. Applicable secured tunnel
alternatives include IPsec , TLS/SSL , DTLS , WireGuard , etc. The AERO Bridges of all OMNI link segments in turn
configure secured tunnels for their neighboring AERO Bridges in a
spanning tree topology. Therefore, control messages exchanged between
any pair of OMNI link neighbors on the spanning tree are already
secured.AERO nodes acting as Route Optimization Responders (RORs) may also
receive packets directly from arbitrary nodes in INET partitions instead
of via the secured spanning tree. For INET partitions that apply
effective ingress filtering to defeat source address spoofing, the
simple data origin authentication procedures in can be applied.For INET partitions that require strong security in the data plane,
two options for securing communications include 1) disable route
optimization so that all traffic is conveyed over secured tunnels, or 2)
enable on-demand secure tunnel creation between INET partition
neighbors. Option 1) would result in longer routes than necessary and
traffic concentration on critical infrastructure elements. Option 2)
could be coordinated by establishing a secured tunnel on-demand instead
of performing an NS/NA exchange in the route optimization
procedures.AERO Clients that connect to secured ANETs need not apply security to
their ND messages, since the messages will be intercepted by a perimeter
Proxy/Server that applies security on its INET-facing interface as part
of the spanning tree (see above). AERO Clients connected to the open
INET can use network and/or transport layer security services such as
VPNs or can by some other means establish a direct link to a
Proxy/Server. When a VPN or direct link may be impractical, however,
INET Clients and Proxy/Servers SHOULD include and verify authentication
signatures for their IPv6 ND messages as specified in .Application endpoints SHOULD use application-layer security services
such as TLS/SSL, DTLS or SSH to assure the same
level of protection as for critical secured Internet services. AERO
Clients that require host-based VPN services SHOULD use network and/or
transport layer security services such as IPsec, TLS/SSL, DTLS, etc.
AERO Proxys and Proxy/Servers can also provide a network-based VPN
service on behalf of the Client, e.g., if the Client is located within a
secured enclave and cannot establish a VPN on its own behalf.AERO Proxy/Servers and Bridges present targets for traffic
amplification Denial of Service (DoS) attacks. This concern is no
different than for widely-deployed VPN security gateways in the
Internet, where attackers could send spoofed packets to the gateways at
high data rates. This can be mitigated by connecting Proxy/Servers and
Bridges over dedicated links with no connections to the Internet and/or
when connections to the Internet are only permitted through well-managed
firewalls. Traffic amplification DoS attacks can also target an AERO
Client's low data rate links. This is a concern not only for Clients
located on the open Internet but also for Clients in secured enclaves.
AERO Proxy/Servers and Proxys can institute rate limits that protect
Clients from receiving packet floods that could DoS low data rate
links.AERO Relays must implement ingress filtering to avoid a spoofing
attack in which spurious messages with ULA addresses are injected into
an OMNI link from an outside attacker. AERO Clients MUST ensure that
their connectivity is not used by unauthorized nodes on their EUNs to
gain access to a protected network, i.e., AERO Clients that act as
routers MUST NOT provide routing services for unauthorized nodes. (This
concern is no different than for ordinary hosts that receive an IP
address delegation but then "share" the address with other nodes via
some form of Internet connection sharing such as tethering.)The MAP list MUST be well-managed and secured from unauthorized
tampering, even though the list contains only public information. The
MAP list can be conveyed to the Client in a similar fashion as in (e.g., through layer 2 data link login messaging,
secure upload of a static file, DNS lookups, etc.).SRH authentication facilities are specified in .Security considerations for accepting link-layer ICMP messages and
reflected packets are discussed throughout the document.Security considerations for IPv6 fragmentation and reassembly are
discussed in .Discussions in the IETF, aviation standards communities and private
exchanges helped shape some of the concepts in this work. Individuals
who contributed insights include Mikael Abrahamsson, Mark Andrews, Fred
Baker, Bob Braden, Stewart Bryant, Brian Carpenter, Wojciech Dec, Pavel
Drasil, Ralph Droms, Adrian Farrel, Nick Green, Sri Gundavelli, Brian
Haberman, Bernhard Haindl, Joel Halpern, Tom Herbert, Sascha Hlusiak,
Lee Howard, Zdenek Jaron, Andre Kostur, Hubert Kuenig, Ted Lemon, Andy
Malis, Satoru Matsushima, Tomek Mrugalski, Madhu Niraula, Alexandru
Petrescu, Behcet Saikaya, Michal Skorepa, Joe Touch, Bernie Volz, Ryuji
Wakikawa, Tony Whyman, Lloyd Wood and James Woodyatt. Members of the
IESG also provided valuable input during their review process that
greatly improved the document. Special thanks go to Stewart Bryant, Joel
Halpern and Brian Haberman for their shepherding guidance during the
publication of the AERO first edition.This work has further been encouraged and supported by Boeing
colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam
Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish,
Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad
Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, Greg
Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, Gene
MacLean III, Kyle Mikos, Rob Muszkiewicz, Sean O'Sullivan, Vijay
Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, Mike
Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia Wilson, Julie
Wulff, Yueli Yang, Eric Yeh and other members of the Boeing mobility,
networking and autonomy teams. Kyle Bae, Wayne Benson, Madhuri Madhava
Badgandi, Vijayasarathy Rajagopalan, Katie Tran and Eric Yeh are
especially acknowledged for implementing the AERO functions as
extensions to the public domain OpenVPN distribution. Chuck Klabunde is
honored and remembered for his early leadership, and we mourn his
untimely loss.Earlier works on NBMA tunneling approaches are found in .Many of the constructs presented in this second edition of AERO are
based on the author's earlier works, including:The Internet Routing Overlay Network (IRON) Virtual Enterprise Traversal (VET) The Subnetwork Encapsulation and Adaptation Layer (SEAL) AERO, First Edition Note that these works cite numerous earlier efforts that are
not also cited here due to space limitations. The authors of those
earlier works are acknowledged for their insights.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 Commercial Airplanes (BCA)
Internet of Things (IoT) and autonomy programs.This work is aligned with the Boeing Information Technology (BIT)
MobileNet program.http://openvpn.netBGP in 2015, http://potaroo.netWireguard, https://www.wireguard.comWireguardAERO can be applied to a multitude of Internetworking scenarios, with
each having its own adaptations. The following considerations are
provided as non-normative guidance:Route optimization as discussed in
results in the route optimization source (ROS) creating a neighbor
cache entry for the target neighbor. The neighbor cache entry state is
set to REACHABLE for at most ReachableTime seconds. In order to
refresh the neighbor cache entry lifetime before the ReachableTime
timer expires, the specification requires implementations to issue a
new NS/NA exchange to reset ReachableTime while data packets are still
flowing. However, the decision of when to initiate a new NS/NA
exchange and to perpetuate the process is left as an implementation
detail.One possible strategy may be to monitor the neighbor cache entry
watching for data packets for (ReachableTime - 5) seconds. If any data
packets have been sent to the neighbor within this timeframe, then
send an NS to receive a new NA. If no data packets have been sent,
wait for 5 additional seconds and send an immediate NS if any data
packets are sent within this "expiration pending" 5 second window. If
no additional data packets are sent within the 5 second window, reset
the neighbor cache entry state to STALE.The monitoring of the neighbor data packet traffic therefore
becomes an ongoing process during the neighbor cache entry lifetime.
If the neighbor cache entry expires, future data packets will trigger
a new NS/NA exchange while the packets themselves are delivered over a
longer path until route optimization state is re-established.OMNI interface neighbors MAY provide a configuration option that
allows them to perform implicit mobility management in which no ND
messaging is used. In that case, the Client only transmits packets
over a single interface at a time, and the neighbor always observes
packets arriving from the Client from the same link-layer source
address.If the Client's underlying interface address changes (either due to
a readdressing of the original interface or switching to a new
interface) the neighbor immediately updates the neighbor cache entry
for the Client and begins accepting and sending packets according to
the Client's new address. This implicit mobility method applies to use
cases such as cellphones with both WiFi and Cellular interfaces where
only one of the interfaces is active at a given time, and the Client
automatically switches over to the backup interface if the primary
interface fails.When a Client's OMNI interface is configured over a Direct
interface, the neighbor at the other end of the Direct link can
receive packets without any encapsulation. In that case, the Client
sends packets over the Direct link according to QoS preferences. If
the Direct interface has the highest QoS preference, then the Client's
IP packets are transmitted directly to the peer without going through
an ANET/INET. If other interfaces have higher QoS preferences, then
the Client's IP packets are transmitted via a different interface,
which may result in the inclusion of Proxy/Servers and Bridges in the
communications path. Direct interfaces must be tested periodically for
reachability, e.g., via NUD.AERO Bridges can be either Commercial off-the Shelf (COTS) standard
IP routers or virtual machines in the cloud. Bridges must be
provisioned, supported and managed by the INET administrative
authority, and connected to the Bridges of other INETs via
inter-domain peerings. Cost for purchasing, configuring and managing
Bridges is nominal even for very large OMNI links.AERO cloud Proxy/Servers can be standard dedicated server
platforms, but most often will be deployed as virtual machines in the
cloud. The only requirements for cloud Proxy/Servers are that they can
run the AERO user-level code and have at least one network interface
connection to the INET. Cloud Proxy/Servers must be provisioned,
supported and managed by the INET administrative authority. Cost for
purchasing, configuring and managing cloud Proxy/Servers is nominal
especially for virtual machines.AERO ANET Proxy/Servers are most often standard dedicated server
platforms with one underlying interface connected to the ANET and a
second interface connected to an INET. As with cloud Proxy/Servers,
the only requirements are that they can run the AERO user-level code
and have at least one interface connection to the INET. ANET
Proxy/Servers must be provisioned, supported and managed by the ANET
administrative authority. Cost for purchasing, configuring and
managing Proxys is nominal, and borne by the ANET administrative
authority.AERO Relays are simply Proxy/Servers connected to INETs and/or EUNs
that provide forwarding services for non-MNP destinations. The Relay
connects to the OMNI link and engages in eBGP peering with one or more
Bridges as a stub AS. The Relay then injects its MNPs and/or non-MNP
prefixes into the BGP routing system, and provisions the prefixes to
its downstream-attached networks. The Relay can perform ROS/ROR
services the same as for any Proxy/Server, and can route between the
MNP and non-MNP address spaces.AERO Proxy/Servers may appear as a single point of failure in the
architecture, but such is not the case since all Proxy/Servers on the
link provide identical services and loss of a Proxy/Server does not
imply immediate and/or comprehensive communication failures.
Proxy/Server failure is quickly detected and conveyed by Bidirectional
Forward Detection (BFD) and/or proactive NUD allowing Clients to
migrate to new Proxy/Servers.If a Proxy/Server fails, ongoing packet forwarding to Clients will
continue by virtue of the neighbor cache entries that have already
been established in route optimization sources (ROSs). If a Client
also experiences mobility events at roughly the same time the
Proxy/Server fails, unsolicited NA messages may be lost but neighbor
cache entries in the DEPARTED state will ensure that packet forwarding
to the Client's new locations will continue for up to DepartTime
seconds.If a Client is left without a Proxy/Server for a considerable
length of time (e.g., greater than ReachableTime seconds) then
existing neighbor cache entries will eventually expire and both
ongoing and new communications will fail. The original source will
continue to retransmit until the Client has established a new
Proxy/Server relationship, after which time continuous communications
will resume.Therefore, providing many Proxy/Servers on the link with high
availability profiles provides resilience against loss of individual
Proxy/Servers and assurance that Clients can establish new
Proxy/Server relationships quickly in event of a Proxy/Server
failure.The AERO architectural model is client / server in the control
plane, with route optimization in the data plane. The same as for
common Internet services, the AERO Client discovers the addresses of
AERO Proxy/Servers and connects to one or more of them. The AERO
service is analogous to common Internet services such as google.com,
yahoo.com, cnn.com, etc. However, there is only one AERO service for
the link and all Proxy/Servers provide identical services.Common Internet services provide differing strategies for
advertising server addresses to clients. The strategy is conveyed
through the DNS resource records returned in response to name
resolution queries. As of January 2020 Internet-based 'nslookup'
services were used to determine the following:When a client resolves the domainname "google.com", the DNS
always returns one A record (i.e., an IPv4 address) and one AAAA
record (i.e., an IPv6 address). The client receives the same
addresses each time it resolves the domainname via the same DNS
resolver, but may receive different addresses when it resolves the
domainname via different DNS resolvers. But, in each case, exactly
one A and one AAAA record are returned.When a client resolves the domainname "ietf.org", the DNS
always returns one A record and one AAAA record with the same
addresses regardless of which DNS resolver is used.When a client resolves the domainname "yahoo.com", the DNS
always returns a list of 4 A records and 4 AAAA records. Each time
the client resolves the domainname via the same DNS resolver, the
same list of addresses are returned but in randomized order (i.e.,
consistent with a DNS round-robin strategy). But, interestingly,
the same addresses are returned (albeit in randomized order) when
the domainname is resolved via different DNS resolvers.When a client resolves the domainname "amazon.com", the DNS
always returns a list of 3 A records and no AAAA records. As with
"yahoo.com", the same three A records are returned from any
worldwide Internet connection point in randomized order.The above example strategies show differing approaches to
Internet resilience and service distribution offered by major Internet
services. The Google approach exposes only a single IPv4 and a single
IPv6 address to clients. Clients can then select whichever IP protocol
version offers the best response, but will always use the same IP
address according to the current Internet connection point. This means
that the IP address offered by the network must lead to a
highly-available server and/or service distribution point. In other
words, resilience is predicated on high availability within the
network and with no client-initiated failovers expected (i.e., it is
all-or-nothing from the client's perspective). However, Google does
provide for worldwide distributed service distribution by virtue of
the fact that each Internet connection point responds with a different
IPv6 and IPv4 address. The IETF approach is like google
(all-or-nothing from the client's perspective), but provides only a
single IPv4 or IPv6 address on a worldwide basis. This means that the
addresses must be made highly-available at the network level with no
client failover possibility, and if there is any worldwide service
distribution it would need to be conducted by a network element that
is reached via the IP address acting as a service distribution
point.In contrast to the Google and IETF philosophies, Yahoo and Amazon
both provide clients with a (short) list of IP addresses with Yahoo
providing both IP protocol versions and Amazon as IPv4-only. The order
of the list is randomized with each name service query response, with
the effect of round-robin load balancing for service distribution.
With a short list of addresses, there is still expectation that the
network will implement high availability for each address but in case
any single address fails the client can switch over to using a
different address. The balance then becomes one of function in the
network vs function in the end system.The same implications observed for common highly-available services
in the Internet apply also to the AERO client/server architecture.
When an AERO Client connects to one or more ANETs, it discovers one or
more AERO Proxy/Server addresses through the mechanisms discussed in
earlier sections. Each Proxy/Server address presumably leads to a
fault-tolerant clustering arrangement such as supported by Linux-HA,
Extended Virtual Synchrony or Paxos. Such an arrangement has
precedence in common Internet service deployments in lightweight
virtual machines without requiring expensive hardware deployment.
Similarly, common Internet service deployments set service IP
addresses on service distribution points that may relay requests to
many different servers.For AERO, the expectation is that a combination of the Google/IETF
and Yahoo/Amazon philosophies would be employed. The AERO Client
connects to different ANET access points and can receive 1-2
Proxy/Server ADM-LLAs at each point. It then selects one AERO
Proxy/Server address, and engages in RS/RA exchanges with the same
Proxy/Server from all ANET connections. The Client remains with this
Proxy/Server unless or until the Proxy/Server fails, in which case it
can switch over to an alternate Proxy/Server. The Client can likewise
switch over to a different Proxy/Server at any time if there is some
reason for it to do so. So, the AERO expectation is for a balance of
function in the network and end system, with fault tolerance and
resilience at both levels.<< RFC Editor - remove prior to publication >>Changes from draft-templin-6man-aero-01 to
draft-templin-6man-aero-02:Changed reference citations to "draft-templin-6man-omni".Several important updates to IPv6 ND cache states and route
optimization message addressing.Included introductory description of the "6M's".Updated Multicast specification.Changes from draft-templin-6man-aero-00 to
draft-templin-6man-aero-01:Changed category to "Informational".Updated implementation status.Changes from earlier versions to
draft-templin-6man-aero-00:Established working baseline reference.