Automatic Extended Route Optimization (AERO)Boeing Research & TechnologyP.O. Box 3707SeattleWA98124USAfltemplin@acm.orgI-DInternet-DraftThis document specifies an Automatic 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 (IPv6 ND) protocol.
Prefix delegation/registration services are employed for network
admission and to manage the IP forwarding and routing systems. Secure
multilink operation, mobility management, multicast, traffic path
selection 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 end user devices and many
other applications.Automatic 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 multilink operation for increased reliability and path
optimization while providing fragmentation and reassembly services to
support Maximum Transmission Unit (MTU) diversity. In terms of
precedence, this specification may provide first-principle insights into
a representative mobility service architecture as context for
understanding the OMNI specification.The AERO service connects Clients over Proxy/Servers and Relays that
are seen as OMNI link neighbors, and includes 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
(IPv6 ND) protocol . 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 multilink
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 Proxy/Servers acting as proxys and/or designated routers while
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. Mobile node
Clients discover shortest paths to OMNI link neighbors through AERO
route optimization. Both unicast and multicast communications are
supported, and Clients may efficiently move between locations while
maintaining continuous communications with correspondents and without
changing their IP Address.AERO Bridges peer with Proxy/Servers in a secured private BGP overlay
routing instance to establish a Segment Routing Topology (SRT) spanning
tree over the underlying Internetworks of one or more disjoint
administrative domains as a single unified OMNI link. 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 (fixed)
correspondent nodes on the underlying Internetwork to (mobile or fixed)
nodes on the OMNI link. To the underlying Internetwork, the Relay is the
source of a route to the MSP; hence uplink traffic to mobile nodes 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 both cases,
Clients may be located behind Network Address Translators (NATs) on the
path to their associated Proxy/Servers. A means for robust traversal of
NATs while avoiding "triangle routing" and critical infrastructure
traffic concentration 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 provides 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 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 over a segment
routing topology with multiple diverse administrative domain network
segments while maintaining seamless end-to-end communications
between mobile Clients 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 while including the
OMNI option extensions 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 IPv6 ND messaging) are also in scope. 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 source address of an IPv6 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 network topology with a
coherent IP routing and addressing plan and that provides a transit
backbone service for its connected 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 throughout this document.)the encapsulation of a
packet in an outer header or headers that can be routed within the
scope of the local *NET partition.the IP address (and also UDP
port number when UDP is used) that appears in *NET encapsulations
sent over a node's interface connection to a *NET.the same as defined for "*NET" address
above, with both terms used interchangeably throughout the
document.the same as defined in . The OMNI link employs IPv6
encapsulation to traverse intermediate
nodes in a spanning tree over underlying *NET segments the same as a
bridged campus LAN. AERO nodes on the OMNI link appear as single-hop
neighbors at the network layer even though they may be separated by
many underlying *NET hops; AERO nodes can employ Segment Routing
to navigate between different OMNI links,
and/or to cause packets to visit selected waypoints within the same
OMNI link.a node's attachment to an OMNI
link. Since OMNI interface addresses 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
service that subjects original IP packets admitted into the
interface to mid-layer IPv6 header encapsulation followed by
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 decapsulation but prior to OAL reassembly.an OAL packet that can
be forwarded without fragmentation, but still includes a Fragment
Header with a valid Identification value and with Fragment Offset
and More Fragments both set to 0.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 re-encapsulate carrier
packets during forwarding by removing the *NET headers of the
previous hop underlying network and replacing them with new *NET
headers for the next hop underlying 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 from a previous hop, then re-encapsulates
the carrier packets in new *NET headers and forwards them to the
next hop. 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. OAL intermediate nodes do not decrement the Hop
Limit/TTL of the original IP packet.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 IPv6 ND
exchanges with other AERO nodes and forwards original IP packets to
correspondents according to OMNI interface neighbor cache state.a
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
designated router services for coordination with correspondents on
its INET-facing interfaces. (Proxy/Servers in the open INET instead
configure only a single INET interface and no ANET interfaces.) The
Proxy/Server configures an OMNI interface and assigns an ADM-LLA to
support the operation of IPv6 ND services, while advertising any
associated MNPs for which it is acting as a hub via BGP peerings
with Bridges.a Proxy/Server
that provides forwarding services between nodes reached via the OMNI
link and correspondents on other links/networks. AERO Relays
configure an OMNI interface, assign an ADM-LLA and maintain BGP
peerings with Bridges the same as Proxy/Servers and run a dynamic
routing protocol to discover any non-MNP IP GUA routes in service on
other links/networks. The Relay advertises the MSP(s) to its other
links/networks, and redistributes routes discovered on other
links/networks into the OMNI link BGP routing system the same as for
Proxy/Servers. (Relays that connect to major Internetworks such as
the global IPv6 or IPv4 Internet can also be configured to advertise
"default" routes into the OMNI link BGP routing system.)a BGP hub
autonomous system node that also provides OAL forwarding services
for nodes on an OMNI link. Bridges 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. Bridges peer with Proxy/Servers and other Bridges
to form a spanning tree over all OMNI link segments and to discover
the set of all MNP and non-MNP prefixes in service. Bridges process
carrier packets received over the secured spanning tree that are
addressed to themselves, while forwarding all other carrier packets
to the next hop also via the secured spanning tree. Bridges forward
carrier packets received over the unsecured spanning tree to the
next hop either via the unsecured spanning tree or via direct
encapsulation if the next hop is on the same OMNI link segment.a
Proxy/Server for a source Client's underlying interface that
forwards the Client's packets into the segment routing topology. FHS
Proxy/Servers also act as intermediate forwarding nodes to
facilitate RS/RA exchanges between a Client and its Hub
Proxy/Server.a single Proxy/Server
selected by a Client that provides a designated router service for
all of the Client's underlying interfaces. Clients often select the
first FHS Proxy/Server they coordinate with to serve in the Hub role
(as all FHS Proxy/Servers are equally capable candidates to serve in
that capacity), however the Client can also select any available
Proxy/Server for the OMNI link (as there is no requirement that the
Hub must also be one of the Client's FHS Proxy/Servers).a
Proxy/Server for an underlying interface of the target Client that
forwards packets received from the segment routing topology to the
target Client over that interface.a multinet
OMNI link forwarding region between FHS and LHS Proxy/Servers.
FHS/LHS Proxy/Servers and SRT Bridges span the OMNI link on behalf
of source/target Client pairs. The SRT maintains a spanning tree
established through BGP peerings between Bridges and Proxy/Servers.
Each SRT segment includes Bridges in a "hub" and Proxy/Servers in
"spokes", while adjacent segments are interconnected by
Bridge-Bridge peerings. The BGP peerings are configured over both
secured and unsecured underlying network paths such that a secured
spanning tree is available for critical control messages while other
messages can use the unsecured spanning tree.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 FHS Proxy/Server or Relay for the source, or may be the source
Client itself. If the Client engages the Hub Proxy/Server in
"mobility anchor" mode, the Hub Proxy/Server may be the ROS (see:
).the AERO
node that responds to route optimization requests on behalf of the
target. The ROR may be either the target MNP Client itself or a
Relay for a non-MNP target. If the Client engages the Hub
Proxy/Server in "mobility anchor" mode, the Hub Proxy/Server may be
the ROR (see: ).a geographically
and/or topologically referenced list of addresses of all
Proxy/Servers within the same OMNI link. Each OMNI link has its own
PRL.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.A
forwarding table on each AERO/OMNI source, destination and
intermediate node that includes Multilink Forwarding Vectors (MFV)
with both next hop forwarding instructions and context for
reconstructing compressed headers for specific underlying interface
pairs used to communicate with peers.An MFIB
entry that includes soft state for each underlying interface
pairwise communication session between peer OMNI nodes. MFVs are
identified by both a next-hop and previous-hop MFV Index (MFVI),
with the next-hop established based on an IPv6 ND solicitation and
the previous hop established based on the solicited IPv6 ND
advertisement response.A 4
octet value selected by an AERO/OMNI node when it creates an MFV,
then advertises to either a next-hop or previous-hop. AERO/OMNI
intermediate nodes assign two distinct local MFVIs for each MFV and
advertise one to the next-hop and the other to the previous-hop.
AERO/OMNI end systems assign and advertise a single MFVI. AERO/OMNI
nodes also discover the remote MFVIs advertised by other nodes that
indicate a value the remote node is willing to accept.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 IPv6 ND and DHCPv6 (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 can be deployed as fixed infrastructure nodes close to
end systems, or as Mobile Nodes (MNs) that can change their network
attachment points dynamically. AERO Clients configure OMNI interfaces
over underlying interfaces with addresses that may change due to
mobility. 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 (together with Proxy/Servers) provide the secured
backbone supporting infrastructure for a Segment Routing Topology
(SRT) spanning tree for the OMNI link. Bridges forward carrier packets
both within the same SRT segment and between disjoint SRT segments
based on an IPv6 encapsulation mid-layer known as the OMNI Adaptation
Layer (OAL) . The OMNI interface
and OAL provide 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 assign one or more
Mobility Service Prefixes (MSPs) to the OMNI link and configure
secured tunnels with Proxy/Servers, Relays and other Bridges; they
further maintain forwarding table entries for each MNP or non-MNP
prefix in service on the OMNI link.AERO Proxy/Servers distributed across one or more SRT segments
provide default forwarding and mobility/multilink services for AERO
Client mobile nodes. Each Proxy/Server also peers with Bridges in a
dynamic routing protocol instance to advertise its list of associated
MNPs (see ). Hub Proxy/Servers provide prefix
delegation/registration services and track the mobility/multilink
profiles of each of their associated Clients, where each delegated
prefix becomes an MNP taken from an MSP. Proxy/Servers at ANET/INET
boundaries provide a forwarding service for ANET Clients to
communicate with peers in external INETs, while Proxy/Servers in the
open INET provide an authentication service for INET Client IPv6 ND
messages but only a secondary forwarding service when the Client
cannot forward directly to a peer or Bridge. Source Clients securely
coordinate with target Clients by sending control messages via a
First-Hop Segment (FHS) Proxy/Server which forwards them over the SRT
spanning tree to a Last-Hop Segment (LHS) Proxy/Server which finally
forwards them to the target.AERO Relays are Proxy/Servers that provide forwarding services to
exchange original IP packets between the OMNI link and nodes on other
links/networks. Relays run a dynamic routing protocol to discover any
non-MNP prefixes in service on other links/networks, and Relays that
connect to larger Internetworks (such as the Internet) may originate
default routes. The Relay redistributes OMNI link MSP(s) into other
links/networks, and redistributes non-MNP prefixes via OMNI link
Bridge BGP peerings. presents the basic OMNI link
reference model: In this model:the OMNI link is an overlay network service configured over
one or more underlying SRT segments 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 provide the backbone for an SRT spanning tree for
the 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. (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;
all nodes on the link can exchange carrier packets via simple *NET
encapsulation (i.e., following any necessary NAT traversal) since
the underlying *NET is connected. In common practice, however, OMNI
links are often configured over an SRT spanning tree that bridges
multiple distinct *NET segments managed under different
administrative authorities (e.g., as for worldwide aviation service
providers such as ARINC, SITA, Inmarsat, etc.). Individual *NETs may
also be partitioned internally, in which case each internal
partition appears as a separate segment.The addressing plan of each SRT 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 disjoint segments often have no 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 OMNI link spans multi-segment SRT topologies using the OMNI
Adaptation Layer (OAL) to
provide the network layer with a virtual abstraction similar to a
bridged campus LAN. The OAL is an OMNI interface sublayer that
inserts a mid-layer IPv6 encapsulation header for inter-segment
forwarding (i.e., bridging) without decrementing the network-layer
TTL/Hop Limit of the original IP packet. An example OMNI link SRT is
shown in :Bridge, Proxy/Server and Relay OMNI interfaces are configured
over both secured tunnels and open INET underlying interfaces within
their respective SRT segments. Within each segment, Bridges
configure "hub-and-spokes" BGP peerings with Proxy/Server/Relays as
"spokes". Adjacent SRT segments are joined by Bridge-to-Bridge
peerings to collectively form a spanning tree over the entire SRT.
The "secured" spanning tree supports authentication and integrity
for critical control plane messages. The "unsecured" spanning tree
conveys ordinary carrier packets without security codes and that
must be treated by destinations according to data origin
authentication procedures. AERO nodes can employ route optimization
to cause carrier packets to take more direct paths between OMNI link
neighbors without having to follow strict spanning tree paths.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 based on 32-bit Mobility
Service ID (MSID) values ("ADM-LLAs") per . Non-MNP routes are also
represented the same as for MNP-LLAs, but may include a prefix that
is not properly covered by an 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. A GUA block is also reserved for OMNI link
anycast purposes. 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 Border Gateway
Protocol (BGP) service coordinated between
Bridges and Proxy/Servers. The service supports carrier packet
forwarding at a layer below IP and does not interact with the public
Internet BGP routing system, but supports redistribution of
information for other links and networks discovered by Relays.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 SRT segment in the OMNI link must include one or
more Bridges in a "hub" AS, which peer with the Proxy/Servers within
that segment as "spoke" ASes. All Bridges within the same segment
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 segments 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 also maintain black-hole routes for the OMNI link MSPs so that
carrier packets destined to non-existent MNP-ULAs are dropped with a
Destination Unreachable message returned. In this way, Proxy/Servers
and Relays have only partial topology knowledge (i.e., they only
maintain routing information for 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 known as the "SRT prefix". 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 SRT 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 SRT segments into a unified OMNI link
over multiple diverse network administrative domains. They support a
virtual bridging service 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 appear 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 rarely change, since they
correspond to fixed infrastructure elements in their respective
segments.MNP (and non-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 .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 bridged campus LAN 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 OMNI IPv6 anycast address
used for OMNI interface determination in Safety-Based Multilink
(SBM) as discussed in . Each
OMNI interface further applies Performance-Based Multilink (PBM)
internally.The Bridges and Proxy/Servers of each independent SRT engage in
BGP peerings to form a spanning tree with the Bridges in non-leaf
nodes and the Proxy/Servers in leaf nodes. The spanning tree is
configured over both secured and unsecured underlying network paths.
The secured spanning tree is used to convey secured control messages
between Proxy/Servers and Bridges, while the unsecured spanning tree
forwards data messages and/or unsecured control messages.Each SRT segment is identified by a unique ADM-ULA prefix used by
all Proxy/Servers and Bridges in the segment. Each AERO node must
therefore discover an SRT prefix that correspondents can use to
determine the correct segment, and must publish the SRT prefix in
IPv6 ND messages.Original IPv6 source can direct IPv6 packets to an AERO node by
including a standard IPv6 Segment Routing Header (SRH) with the OMNI IPv6 anycast address for the
selected OMNI link as either the IPv6 destination or as an
intermediate hop within the SRH. This allows the original source to
determine the specific OMNI link SRT an original IPv6 packet will
traverse when there may be multiple alternatives.When an 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).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 with the outermost NAT providing
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 an FHS Proxy/Server. Clients can issue control
messages over the ANET without including an authentication
signature since the ANET is secured at the network layer or below.
Proxy/Servers can actively issue control messages over the INET on
behalf of ANET Clients to reduce ANET congestion. The same as for
INET interfaces, there may be NATs on the path from the Client to
its FHS Proxy/Server.VPNed interfaces use security encapsulation over the INET to a
Virtual Private Network (VPN) server that also acts as an FHS
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 an FHS 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
FHS 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 FHS 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 IPv6 ND
messages including Router Solicitation (RS), Router Advertisement
(RA), Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for
neighbor cache management. In environments where spoofing may be a
threat, OMNI neighbors should employ OAL Identification window
synchronization in their IPv6 ND message exchanges.OMNI interfaces send IPv6 ND messages with an OMNI option formatted
as specified in . The OMNI
option includes prefix registration information, Interface Attributes
and/or Multilink Forwarding Parameters containing link information
parameters for the OMNI interface's underlying interfaces and any
other per-neighbor information.A Client's OMNI interface may be configured over multiple
underlying interfaces. 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 successive IPv6 ND messages all include
OMNI option Multilink Forwarding Parameters sub-options with the same
underlying interface index. In that case, the Client would appear to
have a single underlying interface but with a dynamically changing
link-layer address.If the Client has multiple active underlying interfaces, then from
the perspective of IPv6 ND it would appear to have multiple link-layer
addresses. In that case, IPv6 ND message OMNI options MAY include
Interface Attributes and/or Multilink Forwarding Parameters
sub-options with different underlying interface indexes.Proxy/Servers on the open Internet include only a single INET
underlying interface. INET Clients therefore discover only the INADDR
information for the Proxy/Server's INET interface. Proxy/Servers on an
ANET/INET boundary include both an ANET and INET underlying interface.
ANET Clients therefore must discover both the ANET and INET INADDR
information for the Proxy/Server.Bridge and Proxy/Server OMNI interfaces are configured over
underlying interfaces that provide both secured tunnels for carrying
IPv6 ND and BGP protocol control plane messages and open INET access
for carrying unsecured messages. The OMNI interface configures both an
ADM-LLA and its corresponding ADM-ULA, and acts as an OAL source to
encapsulate and fragment original IP packets while presenting the
resulting carrier packets over the secured or unsecured underlying
paths. Note that Bridge and Proxy/Server end-to-end transport protocol
sessions used by the BGP are run directly over the OMNI interface and
use ADM-ULA source and destination addresses. The OMNI interface
employs the OAL to encapsulate the original IP packets for these
sessions as carrier packets (i.e., even though the OAL header may use
the same ADM-ULAs as the original IP header) and forwards them over
the secured underlying path.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 associated with another interface are directed
to an 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 SRT segment. The
Proxy/Server also configures secured tunnels with one or more
neighboring Bridges and engages in BGP routing protocol sessions
with one or more Bridges.The OMNI interface provides a single interface abstraction to the
IP layer, but internally includes an NBMA nexus for sending carrier
packets to OMNI interface neighbors over underlying INET interfaces
and secured tunnels. The Proxy/Server further configures a service
to facilitate IPv6 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 over its
underlying interfaces to an FHS Proxy/Server, which coordinates with
a Hub Proxy/Server that returns an RA message with corresponding
parameters. The RS/RA messages may pass through one or more NATs in
the path between the Client and FHS Proxy/Server. (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 FHS 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 delegate an MNP.)AERO Bridges configure an OMNI interface and assign an ADM-ULA
and corresponding Subnet Router Anycast address for each OMNI link
SRT segment they connect to. Bridges configure secured tunnels with
Proxy/Servers in the same SRT segment and other Bridges in the same
(or an adjacent) SRT segment. Bridges then engage in a BGP routing
protocol session with neighbors over the secured spanning tree (see:
).Each OMNI interface maintains a conceptual neighbor cache that
includes a Neighbor Cache Entry (NCE) for each of its active neighbors
on the OMNI link per . Each NCE is indexed by
the LLA of the neighbor, while the OAL encapsulation ULA determines
the context for Identification verification. Clients and Proxy/Servers
maintain NCEs through RS/RA exchanges, and also maintain NCEs for any
active correspondent peers through NS/NA exchanges.Bridges also maintain NCEs for Clients within their local segments
based on NS/NA route optimization messaging (see: ). When a Bridge creates/updates a NCE for a local
segment Client based on NS/NA route optimization, it also maintains
MVFI and INADDR state for messages destined to this local segment
Client.Proxy/Servers add an additional state DEPARTED to the list of NCE
states found in Section 7.3.2 of . When a
Client terminates its association, the Proxy/Server OMNI interface
sets a "DepartTime" variable for the NCE to "DEPART_TIME" seconds.
DepartTime is decremented unless a new IPv6 ND message causes the
state to return to REACHABLE. While a NCE is in the DEPARTED state,
the Proxy/Server forwards carrier packets destined to the target
Client to the Client's new FHS/Hub Proxy/Server instead. It is
RECOMMENDED that DEPART_TIME be set to the default constant value 10
seconds to accept any carrier packets that may be in flight. When
DepartTime decrements to 0, the NCE is deleted.Clients and their Hub Proxy/Servers have full knowledge of the
Client's current underlying Interface Attributes, while FHS
Proxy/Servers acting in "proxy" mode have knowledge of only the
individual Client underlying interfaces they service. When the Client
is configured to create NCEs on its own behalf, it is responsible for
sending mobility signaling messages to its current correspondents. If
the Client is unable to provide mobility signaling on its own behalf,
it should instead engage its Proxy/Servers in "mobility anchor" mode
described in .Clients act as RORs on their own behalf when they receive an NS(AR)
from an ROS via their Hub Proxy/Server (Relays instead act as RORs on
behalf of non-MNP targets specific to other links/networks that the
Relay services and/or "default"). The ROR returns and NA(AR) response
to the ROS, which creates or updates a NCE for the target
network-layer and link-layer addresses. The ROS then (re)sets
ReachableTime for the NCE to REACHABLE_TIME seconds and performs
reachability tests over specific underlying interface pairs to
determine paths for forwarding carrier packets directly to the target.
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 messages 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 the above constants 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 interfaces prepare IPv6 ND messages the same as for standard
IPv6 ND, but also include a new option type termed the OMNI option
. OMNI interfaces prepare IPv6
ND messages the same as for standard IPv6 ND, and include one or
more OMNI options and any other options then completely populate all
option information. If the OMNI interface includes an authentication
signature, it sets the IPv6 ND message Checksum field to 0 and
calculates the authentication signature over the entire length of
the OAL packet or super-packet (beginning with a pseudo-header of
the IPv6 header up to but not including the trailing OAL checksum)
but does not then proceed to calculate the IPv6 ND message checksum
itself. Otherwise, the OMNI interface calculates the standard IPv6
ND message checksum over the OAL packet or super-packet and writes
the value in the Checksum field. OMNI interfaces verify
authentication and integrity of each IPv6 ND message received
according to the specific check(s) included, and process the message
further only following verification.OMNI options include per-neighbor information that provides
multilink forwarding, link-layer address and traffic selector
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 IPv6 ND messages received from the
neighbor; it is therefore not required that each IPv6 ND message
contain all neighbor information.The OMNI option is distinct from any Source/Target Link-Layer
Address Options (S/TLLAOs) that may appear in an IPv6 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 mediaOMNI interface IPv6 ND messages may also include other IPv6 ND
options. In particular, solicitation messages may include a Nonce
option if required for verification of advertisement replies. If an
OMNI IPv6 ND solicitation message includes a Nonce option, the
advertisement reply must echo the same Nonce. If an OMNI IPv6 ND
advertisement message includes a Timestamp option, the recipient
should check the Timestamp to determine if the message is
current.AERO Clients send RS messages to the link-scoped All-Routers
multicast address or an ADM-LLA while using unicast link-layer
addresses. AERO Proxy/Servers respond by returning unicast RA
messages. During the RS/RA exchange, AERO Clients and Proxy/Servers
include state synchronization parameters to establish Identification
windows and other state.AERO nodes use NS/NA messages for the following purposes:NS/NA(AR) messages are used for address resolution and
optionally to establish sequence number windows. The ROS sends
an NS(AR) to the solicited-node multicast address of the target,
and an ROR with addressing information for the target returns a
unicast NA(AR) that contains current, consistent and authentic
target address resolution information. NS/NA(AR) messages must
be secured.NS/NA(NUD) messages are used to establish multilink
forwarding state and determine target reachability. The source
sends an NS(NUD) to the unicast address of the target while
naming a specific underlying interface pair, and the target
returns a unicast NA(NUD). NS/NA(NUD) messages that use an
in-window sequence number and do not update any other state need
not include an authentication signature but instead must include
an IPv6 ND message checksum. NS/NA(NUD) messages may also be
used to establish window synchronization and/or MFIB state, in
which case the messages must be secured.Unsolicited NA (uNA) messages are used to signal addressing
and/or other neighbor state changes (e.g., address changes due
to mobility, signal degradation, traffic selector updates,
etc.). uNA messages that update state information must be
secured.NS/NA(DAD) messages are not used in AERO, since Duplicate
Address Detection is not required.Additionally, nodes may sent the OMNI option PNG flag in
NA/RA messages to receive a uNA response from the neighbor. The uNA
response MUST set the ACK flag (without also setting the SYN or PNG
flags) with the Acknowledgement field set to the Identification used
in the PNG message.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 uNAs (both unicast and
multicast).O: The O ("Override") flag is set to 0 for solicited 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
IPv6 ND protocol operation, however, no role is currently seen
for assigning the same MNP-LLA to multiple Clients.In secured environments (e.g., between secured spanning tree
neighbors, between neighbors on the same secured ANET, etc.), OMNI
interface neighbors can exchange OAL packets using
randomly-initialized and monotonically-increasing Identification
values (modulo 2**32) without window synchronization. In
environments where spoofing is considered a threat, OMNI interface
neighbors instead invoke window synchronization in NS/NA message
exchanges to maintain send/receive window state in their respective
neighbor cache entries as specified in .When the network layer forwards an original IP packet into an OMNI
interface, the interface locates or creates a Neighbor Cache Entry
(NCE) that matches the destination. The OMNI interface then invokes
the OMNI Adaptation Layer (OAL) as discussed in which encapsulates the packet in an
IPv6 header, and IPv6 Fragment Header and 2-octet Checksum trailer to
produce an OAL packet. This OAL source then calculates the checksum
and fragments the OAL packet (and invokes OAL header compression when
appropriate) while including an identical Identification value for
each fragment that must be within the window for the LHS Proxy/Server
or the target Client itself.The OAL source next includes an identical Compressed Routing Header
with 32-bit ID fields (CRH-32) with each fragment if
necessary containing one or more Multilink Forwarding Vector Indices
(MFVIs) as discussed in . (The OAL source
can then optionally invoke OAL header compression by replacing the OAL
IPv6 header and CRH-32 with an OAL Compressed Header (OCH), Type 0 or
1.)The OAL source finally encapsulates each resulting OAL fragment in
*NET headers 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 the next hop OAL intermediate node or destination
(e.g., 192.0.2.1). The carrier packet encapsulation format in the
above example is shown in :In this format, the OAL source encapsulates the original IP header
and packet body/fragment in an OAL IPv6 header prepared according to
, the CRH-32 is a Routing Header extension of
the OAL header, the Fragment Header identifies each fragment, and the
*NET header is prepared as discussed in . The OAL source transmits each such
carrier packet into the SRT spanning tree, where they are forwarded
over possibly multiple OAL intermediate nodes until they arrive at the
OAL destination.The OMNI link control plane service distributes Client MNP-ULA
prefix information that may change dynamically due to regional node
mobility as well as Relay non-MNP-ULA and per-segment ADM-ULA prefix
information that rarely changes. OMNI link Bridges and Proxy/Servers
use the information to establish and maintain a forwarding plane
spanning tree that connects all nodes on the link. The spanning tree
supports a carrier packet virtual bridging service according to
link-layer (instead of network-layer) information, but may often
include longer paths than necessary.Each OMNI interface therefore also includes a Multilink Forwarding
Information Base (MFIB) with Multilink Forwarding Vectors (MFVs) that
can often provide more direct forwarding "shortcuts" that avoid strict
spanning tree paths. As a result, the spanning tree is always
available but OMNI interfaces can often use the MFIB to greatly
improve performance and reduce load on critical infrastructure
elements.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 an FHS Bridge receives a carrier packet with an OCH-0/1 header
that must be forwarded to an LHS Bridge over the unsecured spanning
tree, it reconstructs the headers based on MFV state, inserts a CRH-32
immediately following the OAL header and adjusts the OAL payload
length and destination address field. The FHS Bridge includes a single
MFVI in the CRH-32 that will be meaningful to the LHS Bridge. When the
LHS Bridge receives the carrier packet, it locates the MFV for the
next hop based on the CRH-32 MFVI then re-applies header compression
(resulting in the removal of the CRH-32) and forwards the carrier
packet to the next hop.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 addressed to itself arrive,
this OAL destination discards the NET encapsulation headers and
reassembles to obtain the OAL packet or super-packet (see: ). The OAL destination then verifies
the OAL checksum, discards the OAL encapsulations to obtain the
original IP packet(s) and finally forwards them to either the network
layer or a next-hop on the OMNI link.AERO nodes employ simple data origin authentication procedures. In
particular:AERO Bridges and Proxy/Servers accept carrier packets 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, Proxy/Servers and Bridges verify carrier
packet UDP/IP encapsulation addresses according to .AERO nodes accept carrier packets addressed to themselves with
Identification values within the current window for the OAL source
neighbor (when window synchronization is used) and drop any
carrier packets with out-of-window Identification values. (AERO
nodes may forward carrier packets not addressed to themselves
without verifying the Identification value.)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
potentially larger per-path MPS 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 . (If the super-packet begins with an
IPv6 ND message that includes and authentication signature, the
signature is calculated over the entire length of the super-packet up
to but not including the trailing Checksum.)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: Although a CRH-32 may be inserted or removed by a Bridge in
the path (see: ), this does not interfere with
the destination's ability to reassemble since the CRH-32 is not
included in the fragmentable part and its removal/transformation does
not invalidate fragment header information.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 original IP packet 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 Selectors (e.g., port number, flow
specification, etc.) to select an outbound underlying interface for
each OAL packet and also to select segment routing and/or link-layer
destination addresses based on the neighbor's underlying interfaces.
AERO implementations SHOULD permit network management to dynamically
adjust Traffic Selector values at runtime.If an OAL packet matches the Traffic Selectors of multiple outgoing
interfaces and/or neighbor interfaces, the OMNI interface replicates
the packet and sends one copy via each of the (outgoing / neighbor)
interface pairs; otherwise, it sends a single copy of the OAL packet
via an interface with the best matching Traffic Selector. (While not
strictly required, the likelihood of successful reassembly may improve
when the OMNI interface sends all fragments of the same fragmented OAL
packet consecutively over the same underlying interface pair to avoid
complicating factors such as delay variance and reordering.) 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 NCE that matches the
destination. If there is a matching NCE, the Client selects one or
more "reachable" neighbor interfaces in the entry for forwarding
purposes. Otherwise, the Client invokes route optimization per and follows the multilink forwarding procedures
outlined there.When a carrier packet enters a Client's OMNI interface from the
link-layer, if the OAL destination matches one of the Client's ULAs
the Client (acting as an OAL destination) verifies that the
Identification is in-window for this OAL source, then reassembles
and decapsulates as necessary and delivers the original IP packet to
the network layer. If the OAL destination does not match, 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 FHS 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 either the OAL integrity check or per-packet Identification
values that can be used for data origin authentication and
link-layer retransmissions. The tradeoff therefore involves an
assessment of the per-packet encapsulation overhead saved by
bypassing the OAL vs. inheritance of classical network
"brittleness". (Note however that ANET peers can send small original
IP packets without invoking the OAL, while invoking the OAL for
larger packets. This presents the beneficial aspects of both small
packet efficiency and large packet robustness, with delay variance
and reordering as possible side effects.)When a 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 then supports multilink forwarding
procedures as specified in and/or acts as
an ROS to initiate route optimization as specified in .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 then acts as a Relay
to present it to the network layer where it will be delivered
according to standard IP forwarding.When a Proxy/Server receives a carrier packet from one of its
Client neighbors with OAL destination set to another node, it
forwards the packets via a matching NCE or via the spanning tree if
there is no matching entry. When the Proxy/Server receives a carrier
packet with OAL destination set to the MNP-ULA of one of its Client
neighbors established through RS/RA exchanges, it accepts the
carrier packet only if data origin authentication succeeds. If the
NCE state is DEPARTED, the Proxy/Server 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 some of the carrier packets of
the same original IP packet could be forwarded through a different
Proxy/Server.) In that case, the Client may receive fragments that
are smaller than its link MTU but that can still be reassembled.Proxy/Servers process carrier packets with OAL destinations that
do not match their ADM-ULA in the same manner as for traditional IP
forwarding within the OAL, i.e., nodes use IP forwarding to forward
packets not explicitly addressed to themselves. (Proxy/Servers
include a special case that accepts and reassembles carrier packets
destined to the MNP-ULA of one of their Clients received over the
secured spanning tree.) Proxy/Servers process carrier packets with
their ADM-ULA as the destination by first examining the packet for a
CRH-32 header or an OCH-0/1 header. In that case, the Proxy/Server
examines the next MFVI in the carrier packet to locate the MFV entry
in the MFIB for next hop forwarding (i.e., without examining IP
addresses). When the Proxy/Server forwards the carrier packet, it
changes the destination address according to the MFVI value for the
next hop found either in the CRH-32 header or in the node's own
MFIB. Proxy/Servers must verify that the *NET addresses of carrier
packets not received from the secured spanning tree are "trusted"
before forwarding according to an MFV (otherwise, the carrier packet
must be dropped).Note: Proxy/Servers may receive carrier packets addressed to
their own ADM-ULA with CRH-32s that include additional forwarding
information. Proxy/Servers use the forwarding information to
determine the correct NCE and underlying interface for forwarding to
the target Client, then remove the CRH-32 and forward the carrier
packet. If necessary, the Proxy/Server reassembles first before
re-encapsulating (and possibly also re-fragmenting) then forwards to
the target Client.Note: Clients and their FHS 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 either
the OAL integrity check or per-packet Identification values that can
be used for data origin authentication and link-layer
retransmissions. The tradeoff therefore involves an assessment of
the per-packet encapsulation overhead saved by bypassing the OAL vs.
inheritance of classical network "brittleness". (Note however that
ANET peers can send small original IP packets without invoking the
OAL, while invoking the OAL for larger packets. This presents the
beneficial aspects of both small packet efficiency and large packet
robustness.)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; Proxy/Servers drop any original IP packets (received either
directly from an ANET Client or following reassembly of carrier
packets received from an ANET/INET Client) with a destination that
corresponds to the Client's delegated MNP. Similarly, Proxy/Servers
drop any carrier packet received with both a source and destination
that correspond to the Client's delegated MNP regardless of their
OMNI link point of origin. These checks are necessary to prevent
Clients from either accidentally or intentionally establishing
endless loops that could congest Proxy/Servers and/or ANET/INET
links.Note: Proxy/Servers forward secure control plane carrier packets
via the SRT secured spanning tree and forward other carrier packets
via the unsecured spanning tree. When a Proxy/Server receives a
carrier packet from the secured spanning tree, it considers the
message as authentic without having to verify upper layer
authentication signatures. When a Proxy/Server receives a carrier
packet from the unsecured spanning tree, it applies data origin
authentication itself and/or forwards the unsecured message toward
the destination which must apply data origin authentication on its
own behalf.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 spanning tree carrier packets while decrementing
the OAL header Hop Count but not the original IP header Hop
Count/TTL. Bridges convey carrier packets that encapsulate critical
IPv6 ND control messages or routing protocol control messages via
the SRT secured spanning tree, and may convey other carrier packets
via the secured/unsecured spanning tree or via more direct paths
according to MFIB information. When the Bridge receives a carrier
packet, it removes the outer *NET header and searches for an MFIB
entry that matches an MFVI or an IP forwarding table entry that
matches the OAL destination address.Bridges process carrier packets with OAL destinations that do not
match their ADM-ULA or the SRT Subnet Router Anycast address in the
same manner as for traditional IP forwarding within the OAL, i.e.,
nodes use IP forwarding to forward packets not explicitly addressed
to themselves. Bridges process carrier packets with their ADM-ULA or
the SRT Subnet Router Anycast address as the destination by first
examining the packet for a full OAL header with a CRH-32 extension
or an OCH-0/1 header. In that case, the Bridge examines the next
MFVI in the carrier packet to locate the MFV entry in the MFIB for
next hop forwarding (i.e., without examining IP addresses). When the
Bridge forwards the carrier packet, it changes the destination
address according to the MFVI value for the next hop found either in
the CRH-32 header or in the node's own MFIB. If the Bridge has a NCE
for the target Client with an entry for the target underlying
interface and current *NET addresses, the Bridge instead forwards
directly to the target Client while using the final hop MFVI instead
of the next hop (see: ).Bridges forward carrier packets received from a first segment via
the secured spanning tree to the next segment also via the secured
spanning tree. Bridges forward carrier packets received from a first
segment via the unsecured spanning tree to the next segment also via
the unsecured spanning tree. Bridges use a single IPv6 routing table
that always determines the same next hop for a given OAL
destination, where the secured/unsecured spanning tree is determined
through the selection of the underlying interface to be used for
transmission (i.e., a secured tunnel or an open INET interface).As for Proxy/Servers, Bridges must verify that the *NET addresses
of carrier packets not received from the secured spanning tree are
"trusted" before forwarding according to an MFV (otherwise, the
carrier packet must be dropped).When an AERO node admits an original IP packet into the OMNI
interface, it may receive link-layer or network-layer error
indications. The AERO node may also receive OMNI link error
indications in OAL-encapsulated uNA messages that include
authentication signatures.A link-layer error indication is an ICMP error message generated by
a router in the *NET 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 :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 assigned to a
black-hole route, the Bridge drops the packet if there is no
more-specific routing information for the destination and returns an
OMNI interface Destination Unreachable message subject to rate
limiting.When an AERO node receives a carrier packet for which reassembly is
currently congested, it returns an OMNI interface Packet Too Big (PTB)
message as discussed in (note
that the PTB messages could indicate either "hard" or "soft"
errors).AERO nodes include ICMPv6 error messages intended for the OAL
source as sub-options in the OMNI option of secured uNA messages. When
the OAL source receives the uNA message, it can extract the ICMPv6
error message enclosed in the OMNI option and either process it
locally or translate it into a network-layer error to return to the
original source.AERO nodes observes the Router Discovery and Prefix Registration
specifications found in Section 15 of . AERO nodes further coordinate their
autoconfiguration actions with the mobility service 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.Clients associate each of their underlying interfaces with a FHS
Proxy/Server. Each FHS Proxy/Server locally services one or more of
the Client's underlying interfaces, and the Client typically selects
one among them to serve as the Hub Proxy/Server (the Client may
instead select a "third-party" Hub Proxy/Server that does not
directly service any of its underlying interfaces). All of the
Client's other FHS Proxy/Servers forward proxyed copies of RS/RA
messages between the Hub Proxy/Server and Client without assuming
the Hub role functions themselves.Each Client associates with a single Hub Proxy/Server at a time,
while all other Proxy/Servers are candidates for providing the Hub
role for other Clients. An FHS Proxy/Server assumes the Hub role
when it receives an RS message with its own ADM-LLA or link-scoped
All-Routers multicast as the destination. An FHS Proxy/Server
assumes the proxy role when it receives an RS message with the
ADM-LLA of another Proxy/Server as the destination. (An FHS
Proxy/Server can also assume the proxy role when it receives an RS
message addressed to link-scoped All-Routers multicast if it can
determine the ADM-LLA of another Proxy/Server to serve as a
Hub.)AERO Clients and Proxy/Servers use IPv6 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 Hub Proxy/Servers include prefix delegation
and/or registration parameters in RS/RA messages. The IPv6 ND
messages are exchanged between the Client and Hub Proxy/Server (via
any FHS Proxy/Servers acting as proxys) 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 Hub 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 outlines Client and Proxy/Server behaviors
based on the Router Discovery and Prefix Registration specifications
found in Section 15 of . These
sections observe all of the OMNI specifications, and include
additional specifications of the interactions of Client-Proxy/Server
RS/RA exchanges with the AERO mobility service.AERO Clients discover the addresses of candidate Proxy/Servers by
resolving the Potential Router List (PRL) in a similar manner as
described in . Discovery methods include
static configuration (e.g., 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 an 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").The Client then performs RS/RA exchanges over each of its
underlying interfaces to associate with (possibly multiple) FHS
Proxy/Serves and a single Hub Proxy/Server as specified in Section
15 of . The Client then sends
each RS (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) and waits up to RetransTimer
milliseconds for an RA message reply (see ) while retrying up to MAX_RTR_SOLICITATIONS
if necessary. 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 candidate Proxy/Server and try another
Proxy/Server.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 traffic selectors 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 and with an Interface
Attributes sub-option specific to the selected underlying interface.
When the Client receives the Hub Proxy/Server's RA response, it has
assurance that both the Hub and FHS Proxy/Servers have been updated
with the new information.If the Client wishes to discontinue use of a Hub Proxy/Server it
issues an RS message over any underlying interface with an OMNI
option with a prefix release indication (i.e., by setting Preflen to
0). When the Hub Proxy/Server processes the message, it releases the
MNP, sets the NCE 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 Hub Proxy/Server withdraws the MNP from the routing
system. (Alternatively, when the Client associates with a new
FHS/Hub Proxy/Server it can include an OMNI "Proxy/Server Departure"
sub-option in RS messages with the MSIDs of the Old FHS/Hub
Proxy/Server.)AERO Proxy/Servers act as both IP routers and IPv6 ND proxys, and
support a prefix delegation/registration service for Clients.
Proxy/Servers arrange to add their ADM-LLAs to the PRL maintained in
a static map of Proxy/Server addresses for the link, the DNS
resource records for the FQDN "linkupnetworks.[domainname]", etc.
before entering service. The PRL should be arranged such that
Clients can discover the addresses of Proxy/Servers that are
geographically and/or topologically "close" to their underlying
network connections.When a FHS/Hub Proxy/Server receives a prospective Client's RS
message, 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, it processes the RS as specified in Section
15 of . When the Hub
Proxy/Server receives the RS, it 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 Hub Proxy/Server returns
the MNPs, it also creates a forwarding table entry for the MNP-ULA
corresponding to each MNP resulting in a BGP update (see: ). For IPv6, the Hub Proxy/Server creates an IPv6
forwarding table entry for each MNP-ULA. For IPv4, the Hub
Proxy/Server creates an IPv6 forwarding table entry with the
IPv4-compatibility MNP-ULA prefix corresponding to the IPv4 address.
The Hub Proxy/Server then returns an RA to the Client via an FHS
Proxy/Server if necessary.After the initial RS/RA exchange, the Hub Proxy/Server maintains
a ReachableTime timer for each of the Client's underlying interfaces
individually (and for the Client's NCE collectively) set to expire
after ReachableTime seconds. If the Client (or an FHS Proxy/Server)
issues additional RS messages, the Hub Proxy/Server sends an RA
response and resets ReachableTime. If the Hub Proxy/Server receives
an IPv6 ND message with a prefix release indication it sets the
Client's NCE to the DEPARTED state and withdraws the MNP-ULA route
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 Hub Proxy/Server marks the interface as
DOWN. If ReachableTime expires before any new RS is received on any
individual underlying interface, the Hub Proxy/Server sets the NCE
state to STALE and sets a 10 second timer. If the Hub Proxy/Server
has not received a new RS or uNA message with a prefix release
indication before the 10 second timer expires, it deletes the NCE
and withdraws the MNP from the routing system.The Hub Proxy/Server processes any IPv6 ND messages pertaining to
the Client while forwarding to the Client or responding on the
Client's behalf as necessary. The Hub 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. The Hub Proxy/Server may also receive carrier packets via the
secured spanning tree that contain initial data packets sent while
route optimization is in progress. The Hub Proxy/Server reassembles,
then re-encapsulates/re-fragments and forwards the packets to the
target Client via an FHS Proxy/Server if necessary. Finally, If the
NCE is in the DEPARTED state, the old Hub Proxy/Server forwards any
carrier packets it receives from the secure spanning tree and
destined to the Client to the new Hub Proxy/Server, then deletes the
entry after DepartTime expires.Note: Clients SHOULD arrange to notify former Hub Proxy/Servers
of their departures, but Hub 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). Hub 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 FHS 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.AERO Clients register with FHS Proxy/Servers for each
underlying interface. Each of the Client's FHS Proxy/Servers must
inform a single Hub Proxy/Server of the Client's underlying
interface(s) that it services. For Clients on Direct and VPNed
underlying interfaces, the FHS Proxy/Server for each interface is
directly connected, for Clients on ANET underlying interfaces the
FHS Proxy/Server is located on the ANET/INET boundary, and for
Clients on INET underlying interfaces the FHS Proxy/Server is
located somewhere in the connected Internetwork. When FHS
Proxy/Server "B" processes a Client registration, it must either
assume the Hub role or forward a proxyed registration to another
Proxy/Server "A" acting as the Hub. Proxy/Servers satisfy these
requirements as follows:when FHS Proxy/Server "B" receives a Client RS message, it
first verifies that the OAL Identification is within the
window for the NCE that matches the MNP-ULA for this Client
neighbor and authenticates the message. If no NCE was found,
Proxy/Server "B" instead creates one in the STALE state and
caches the Client-supplied Interface Attributes, Origin
Indication and Window Synchronization parameters as well as
the Client's observed *NET addresses (noting that they may
differ from the Origin addresses if there were NATs on the
path). Proxy/Server "B" then examines the network-layer
destination address. If the destination address is the ADM-LLA
of a different Proxy/Server "A", Proxy/Server "B" prepares a
separate proxyed version of the RS message with an OAL header
with source set to its own ADM-ULA and destination set to
Proxy/Server B's ADM-ULA. Proxy/Server "B" also writes its own
information over the Interface Attributes sub-option supplied
by the Client, omits or zeros the Origin Indication sub-option
then forwards the message into the OMNI link secured spanning
tree.when Hub Proxy/Server "A" receives the RS, it assume the
Hub role and creates or updates a NCE for the Client with FHS
Proxy/Server "B"'s Interface Attributes as the link-layer
address information for this FHS omIndex. Hub Proxy/Server "A"
then prepares an RA message with source set to its own LLA and
destination set to the Client's MNP-LLA, then encapsulates the
RA in an OAL header with source set to its own ADM-ULA and
destination set to the ADM-ULA of FHS Proxy/Server "B". Hub
Proxy/Server "A" then performs fragmentation if necessary and
sends the resulting carrier packets into the secured spanning
tree.when FHS Proxy/Server "B" reassembles the RA, it locates
the Client NCE based on the RA destination LLA. If the RA
message includes an OMNI "Proxy/Server Departure" sub-option,
Proxy/Server "B" first sends a uNA to the old FHS/Hub
Proxy/Servers named in the sub-option. Proxy/Server "B" then
re-encapsulates the RA message with OAL source set to its own
ADM-ULA and OAL destination set to the MNP-ULA of the Client,
with an appropriate Identification value, with an
authentication signature if necessary, with the Client's
Interface Attributes sub-option echoed and with the cached
observed *NET addresses written into an Origin Indication
sub-option. Proxy/Server "B" sets the P flag in the RA flags
field to indicate that the message has passed through a proxy
, includes responsive Window
Synchronization parameters, then fragments the RA if necessary
and returns the fragments to the Client.The Client repeats this process over each of its additional
underlying interfaces while treating each additional FHS
Proxy/Server "C", "D", "E", etc. as a proxy to facilitate
RS/RA exchanges between the Hub and the Client.After the initial RS/RA exchanges each FHS Proxy/Server
forwards any of the Client's carrier packets with OAL destinations
for which there is no matching NCE to a Bridge using OAL
encapsulation with its own ADM-ULA as the source and with
destination determined by the Client. 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 FHS Proxy/Servers
"B", "C", "D", etc., each FHS Proxy/Server can send NS, RS and/or
unsolicited NA messages to update the neighbor cache entries of
other AERO nodes on behalf of the Client based on changes in
Interface Attributes, Traffic Selectors, etc. 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 the Hub Proxy/Server "A" ceases to send solicited RAs, FHS
Proxy/Servers "B", "C", "D" can send unsolicited RAs over the
Client's underlying interface with destination set to (link-local)
All-Nodes multicast and with Router Lifetime set to zero to inform
Clients that the Hub Proxy/Server has failed. Although FHS
Proxy/Servers "B", "C" and "D" can engage in IPv6 ND exchanges on
behalf of the Client, the Client can also send IPv6 ND messages on
its own behalf, e.g., if it is in a better position to convey
state changes. The IPv6 ND messages sent by the Client include the
Client's MNP-LLA as the source in order to differentiate them from
the IPv6 ND messages sent by a FHS Proxy/Server.If the Client becomes unreachable over all underlying interface
it serves, the Hub Proxy/Server sets the NCE state to DEPARTED and
retains the entry for DepartTime seconds. While the state is
DEPARTED, the Hub Proxy/Server forwards any carrier packets
destined to the Client to a Bridge via OAL encapsulation. When
DepartTime expires, the Hub Proxy/Server deletes the NCE and
discards any further carrier packets destined to the former
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/Server. This can be 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-scoped 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 ANET 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: When a Proxy/Server alters the IPv6 ND message contents
before forwarding (e.g., such as altering the OMNI option
contents), the original IPv6 ND message checksum or authentication
signature is invalidated, and a new checksum or authentication
signature must be calculated and included.Note: When a Proxy/Server receives a secured Client NS message,
it performs the same proxying procedures as for described for RS
messages above. The proxying procedures for NS/NA message
exchanges is specified in .In environments where fast recovery from Proxy/Server failure
is required, FHS Proxy/Servers SHOULD use proactive Neighbor
Unreachability Detection (NUD) to track Hub Proxy/Server
reachability in a similar fashion as for Bidirectional Forwarding
Detection (BFD) . Each FHS Proxy/Server
can then quickly detect and react to failures so that cached
information is re-established through alternate paths. The
NS/NA(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.FHS Proxy/Servers perform continuous NS/NA(NUD) exchanges with
the Hub Proxy/Server, e.g., one exchange per second. The FHS
Proxy/Server sends the NS(NUD) message via the spanning tree with
its own ADM-LLA as the source and the ADM-LLA of the Hub
Proxy/Server as the destination, and the Hub Proxy/Server responds
with an NA(NUD). When the FHS Proxy/Server is also sending RS
messages to a Hub Proxy/Server on behalf of Clients, the resulting
RA responses can be considered as equivalent hints of forward
progress. This means that the FHS Proxy/Server need not also send
a periodic NS(NUD) if it has already sent an RS within the same
period. If the Hub Proxy/Server fails (i.e., if the FHS
Proxy/Server ceases to receive advertisements), the FHS
Proxy/Server can quickly inform Clients by sending unsolicited RA
messagesThe FHS Proxy/Server sends unsolicited RA messages with source
address set to the Hub Proxy/Server's address, destination address
set to (link-local) All-Nodes multicast, and Router Lifetime set
to 0. The FHS Proxy/Server SHOULD send
MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays
. Any Clients that had been using the
failed Hub Proxy/Server will receive the RA messages and select
one of its other FHS Proxy/Servers to assume the Hub role (i.e.,
by sending an RS with destination set to the ADM-LLA of the new
Hub).When a Client is not pre-provisioned with an MNP-LLA, it will
need for the Hub 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 Hub
Proxy/Server to select additional MNPs.) The DHCPv6 service is used to support this requirement.When a Client needs to have the Hub 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 Hub Proxy/Server receives the RS message, it
extracts the DHCPv6-PD message from the OMNI option.The Hub 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 Hub
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 Hub 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 Hub 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 and Preflen 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: Further details of the DHCPv6-PD based MNP registration
(as well as a minimal MNP delegation alternative that avoids
including a DHCPv6 message sub-option in the RS) are found in
.AERO nodes invoke route optimization when they need to forward
initial packets to new target destinations and for ongoing multilink
forwarding for current destinations. Route optimization is based on
IPv6 ND Address Resolution messaging between a Route Optimization
Source (ROS) and a Relay or the target Client itself (reached via the
current Hub Proxy/Server) acting as a Route Optimization Responder
(ROR). Route optimization is initiated by the first eligible ROS
closest to the source as follows:For Clients on VPNed and Direct interfaces, the Client's FHS
Proxy/Server is the ROS.For Clients on ANET interfaces, either the Client or the FHS
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.For Clients that engage the Hub Proxy/Server in "mobility
anchor" mode, the Hub Proxy/Server is the ROS.The AERO routing system directs a route optimization request sent
by the ROS to the ROR, which returns a route optimization reply which
must include information that is current, consistent and authentic.
The ROS is responsible for periodically refreshing the route
optimization, and the ROR is responsible for quickly informing the ROS
of any changes. Following address resolution, the ROS and ROR perform
ongoing multilink route optimizations to maintain optimal forwarding
profiles.The route optimization procedures are specified in the following
sections.When one or more original IP packets from a source node destined
to a target node arrives, the ROS checks for a NCE with an MNP-LLA
that matches the target destination. If there is a NCE in the
REACHABLE state, the ROS invokes the OAL and forwards the resulting
carrier packets according to the cached state then returns from
processing. Otherwise, if there is no NCE the ROS creates one in the
INCOMPLETE state.The ROS next prepares an NS message for Address Resolution
(NS(AR)) to send toward an ROR while including the original IP
packet(s) as trailing data following the NS(AR) in an OAL
super-packet . The resulting
NS(AR) message must be sent securely, and 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(AR) destination address is
ff02:0:0:0:0:1:ff10:2000.The NS(AR) message also includes an OMNI option with an
authentication sub-option if necessary and with Preflen set to the
prefix length associated with the NS(AR) source. The ROS also
includes Interface Attributes and Traffic Selectors for all of the
source Client's underlying interfaces, calculates the authentication
signature or checksum, then selects an Identification value and
submits the NS(AR) message for OAL encapsulation with OAL source set
to its own {ADM,MNP}-ULA and OAL destination set to the MNP-ULA
corresponding to the target and with window synchronization
parameters. The ROS then inserts a fragment header, performs
fragmentation and *NET encapsulation, then sends the resulting
carrier packets into the SRT secured spanning tree without
decrementing the network-layer TTL/Hop Limit field.When the ROS is a Client, it must instead use the ADM-ULA of one
of its FHS Proxy/Servers as the destination. The ROS Client then
fragments, performs *NET encapsulation and forwards the carrier
packets to the FHS Proxy/Server. The FHS Proxy/Server then
reassembles, verifies the NS(AR) authentication signature or
checksum, changes the OAL source to its own ADM-ULA, changes the OAL
destination to the MNP-ULA corresponding to the target, selects an
appropriate Identification, then re-fragments and forwards the
resulting carrier packets into the secured spanning tree on behalf
of the Client.Note: both the target Client and its Hub Proxy/Server include
current and accurate information for the Client's multilink
Interface Attributes profile. The Hub Proxy/Server can be trusted to
provide an authoritative response on behalf of the Client should the
need arise. While the Client has no such trust basis, any attempt by
the Client to mount an attack by providing false Interface
Attributes information would only result in black-holing of return
traffic, i.e., the "attack" could only result in denial of service
to the Client itself. Therefore, the Client's asserted Interface
Attributes need not be validated by the Hub Proxy/Server.When the Bridge receives carrier packets containing the NS(AR),
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, then re-encapsulates and forwards the carrier packet(s)
via the secured spanning tree the same as for any IPv6 router,
where they may traverse multiple OMNI link segments. The final-hop
Bridge will deliver the carrier packet via the secured spanning
tree to the Hub Proxy/Server (or Relay) that services the
target.When the Hub Proxy/Server for the target receives the NS(AR)
secured carrier packets with the MNP-ULA of the target as the OAL
destination, it reassembles then forwards the message to the
target Client (while including an authentication signature and
encapsulation if necessary) or processes the NS(AR) locally if it
is acting as a Relay or IP router: The Hub Proxy/Server processes
the message as follows:if the NS(AR) target matches a Client NCE in the DEPARTED
state, the (old) Hub Proxy/Server re-encapsulates by setting
the OAL destination address to the ADM-ULA of the Client's new
Hub Proxy/Server. The old Hub Proxy/Server then re-fragments
and re-encapsulates, then forwards the resulting carrier
packets over the secured spanning tree.If the NS(AR) target matches the MNP-LLA of a Client NCE in
the REACHABLE state, the Hub Proxy/Server notes whether the
NS(AR) arrived from the secured spanning tree then sets the
OAL destination address to the MNP-ULA of the Client or the
ADM-ULA of the selected FHS Proxy/Server for the Client. If
the message arrived via the secured spanning tree the Hub
Proxy/Server verifies the checksum; otherwise, it must verify
the message authentication signature before forwarding. When
the Hub Proxy/Server determines the underlying interface for
the target Client, it then changes the OAL destination to the
ADM-ULA of the target Client's FHS Proxy/Server, re-fragments
and forwards the resulting carrier packets into the secured
spanning tree. When the FHS Proxy/Server receives the carrier
packets, it reassembles and verifies the checksum, then
includes an authentication signature if necessary, changes the
OAL source to its own ADM-ULA and destination to the MNP-ULA
of the target Client, includes an Identification value within
the current window, then re-fragments and forwards the
resulting carrier packets to the target Client ROR. (Note that
if the Hub and FHS Proxy/Server are one and the same the Hub
itself will perform the FHS procedures.)If the NS(AR) target matches one of its non-MNP routes, the
Hub Proxy/Server serves as both a Relay and a ROR, since the
Relay forwards IP packets toward the (fixed network) target at
the network layer.The ROR then creates a NCE for the NS(AR) LLA source address if
necessary, processes the window synchronization parameters, caches
all Interface Attributes and Traffic Selector information, and
prepares a (solicited) NA(AR) message to return to the ROS with
the source address set to its own MNP-LLA, the destination address
set to the NS(AR) LLA source address and the Target Address set to
the same value that appeared in the NS(AR) Target Address. The ROR
includes an OMNI option with Preflen set to the prefix length
associated with the NA(AR) source address.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 1 (as an authoritative responder). The ROR finally submits
the NA(AR) for OAL encapsulation with source set to its own ULA
and destination set to either the ULA corresponding to the NS(AR)
source or the ADM-ULA of its FHS Proxy/Server, selects an
appropriate Identification, and includes window synchronization
parameters and authentication signature or checksum. The ROR then
includes Interface Attributes and Traffic Selector sub-options for
all of the target's underlying interfaces with current information
for each interface, fragments and encapsulates each fragment in
appropriate *NET headers, then forwards the resulting
(*NET-encapsulated) carrier packets to the FHS Proxy/Server.When the FHS Proxy/Server receives the carrier packets, it
reassembles if necessary and verifies the authentication signature
or checksum. The FHS Proxy/Server then changes the OAL source
address to its own ADM-ULA, changes the destination to the
{ADM,MNP}-ULA corresponding to the NA(AR) LLA destination,
includes an appropriate Identification, then fragments and
forwards the carrier packets into the secured spanning tree.When the Bridge receives NA(AR) carrier packets, 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 SRT
secured spanning tree, where it may traverse multiple OMNI link
segments. The final-hop Bridge will deliver the carrier packet via
the secured spanning tree to a Proxy/Server for the ROS.When the ROS receives the NA(AR) message, it first searches for
a NCE that matches the NA(AR) target address. The ROS then
processes the message the same as for standard IPv6 Address
Resolution . In the process, it caches all
OMNI option information in the target NCE (including all Interface
Attributes), and caches the NA(AR) MNP-LLA source address as the
address of the target Client.When the ROS is a Client, the SRT secured spanning tree will
first deliver the solicited NA(AR) message to the FHS
Proxy/Server, which re-encapsulates and forwards the message to
the Client. If the Client is on a well-managed ANET, physical
security and protected spectrum ensures security for the NA(AR)
without needing an additional authentication signature; if the
Client is on the open INET the Proxy/Server must instead include
an authentication signature (while adjusting the OMNI option size,
if necessary). The Proxy/Server uses its own ADM-ULA as the OAL
source and the MNP-ULA of the Client as the OAL destination.Following address resolution, the ROS and ROR can assert
multilink paths through underlying interface pairs serviced by the
same source/destination LLAs by sending unicast NS/NA messages with
Multilink Forwarding Parameters and window synchronization
parameters when necessary. The unicast NS/NA messages establish
multilink forwarding state in intermediate nodes in the path between
the ROS and ROR.To support multilink route optimization, OMNI interfaces include
an additional forwarding table termed the Multilink Forwarding
Information Base (MFIB) that supports carrier packet forwarding
based on OMNI neighbor underlying interface pairs. The MFIB contains
Multilink Forwarding Vectors (MFVs) indexed by 4-octet values known
as MFV Indexes (MFVIs).OAL source, intermediate and destination nodes create MFVs/MFVIs
when they process an NS message with a Multilink Forwarding
Parameters sub-option with Job code "00" (Initialize; Build B) or a
solicited NA with Job code "01" (Follow B; Build A) (see: ). The OAL source of the NS (and OAL
destination of the solicited NA) are considered to reside in the
"First Hop Segment (FHS)", while the OAL destination of the NS (and
OAL source of the solicited NA) are considered to reside in the
"Last Hop Segment (LHS)".When an OAL node processes an NS with Job code "00", it creates
an MFV, records the NS source and destination ULAs and assigns a "B"
MFVI. When the "B" MVFI is referenced, the MVF retains the ULAs in
(dst,src) order the opposite of how they appeared in the original NS
to support full header reconstruction. (If the NS message included a
nested OAL encapsulation, the ULAs of both OAL headers are
retained.)When an OAL node processes a solicited NA with Job code "01", it
locates the MFV created by the NS and assigns an "A" MFVI. When the
"A" MFVI is referenced, the MFV retains the ULAs in (src,dst) order
the same as they appeared in the original NS to support full header
reconstruction. (If the NS message included a nested OAL
encapsulation, the ULAs of both OAL headers are retained.)OAL nodes generate random 32-bit values as candidate A/B MFVIs
which must first be tested for local uniqueness. If a candidate MFVI
s already in use (or if the value is 0), the OAL node repeats the
random generation process until it obtains a unique non-zero value.
(Since the number of MFVs in service at each OAL node is likely to
be much smaller than 2**32, the process will generate a unique value
after a small number of tries; also, an MFVI generated by a first
OAL node is never tested for uniqueness on other OAL nodes, since
the uniqueness property is node-local only.)OAL nodes maintain A/B MFVIs as follows: "B1" - a locally-unique MFVI maintained independently by each
OAL node on the path from the FHS OAL source to the last OAL
intermediate node before the LHS OAL destination. The OAL node
generates and assigns a "B1" MFVI to a newly-created MFV when it
processes an NS message with Job code "00". When the OAL node
receives future carrier packets that include this value, it can
unambiguously locate the correct MFV and determine
directionality without examining addresses."A1" - a locally unique MFVI maintained independently by each
OAL node on the path from the LHS OAL source to the last OAL
intermediate node before the FHS OAL destination. The OAL node
generates and assigns an "A1" MFVI to the MVF that configures
the corresponding "B1" MFVI when it processes a solicited NA
message with Job code "01". When the OAL node receives future
carrier packets that include this value, it can unambiguously
locate the correct MFV and determine directionality without
examining addresses."A2" - the A1 MFVI of a remote OAL node discovered by an FHS
OAL source or OAL intermediate node when it processes an NA
message with Job code "01" that originated from an LHS OAL
source. A2 values MUST NOT be tested for uniqueness within the
OAL node's local context."B2" - the B1 MFVI of a remote OAL node discovered by an LHS
OAL source or OAL intermediate node when it processes an NS
message with Job code "00" that originated from an FHS OAL
source. B2 values MUST NOT be tested for uniqueness within the
OAL node's local context.When an FHS OAL source has an original IP packet to send to an
LHS OAL destination discovered via multilink address resolution, it
first selects a source and target underlying interface pair. The OAL
source uses its cached information for the target underlying
interface as LHS information then prepares an NS message with an
OMNI Multilink Forwarding Parameters sub-option with Job code "00"
and with source set to its own {ADM,MNP}-LLA. If the LHS FMT-Forward
and FMT-Mode bits are both clear, the OAL source sets the
destination to the ADM-LLA of the LHS Proxy/Server; otherwise, it
sets the destination to the MNP-LLA of the target Client. The OAL
source then sets window synchronization information in the OMNI
header and updates/creates a NCE for the selected destination
{ADM,MNP}-LLA in the INCOMPLETE state. The OAL source next creates
an MFV based on the NS source and destination LLAs, then generates a
"B1" MFVI and assigns it to the MFV while also including it as the
first B entry in the MFVI List. The OAL source then populates the NS
Multilink Forwarding Parameters based on any FHS/LHS information it
knows locally. OAL intermediate nodes on the path to the OAL
destination may populate additional FHS/LHS information on a
hop-by-hop basis.If the OAL source is the FHS Proxy/Server, it then performs OAL
encapsulation/fragmentation while setting the source to its own
ADM-ULA and setting the destination to the FHS Subnet Router Anycast
ULA determined by applying the FHS SRT prefix length to its ADM-ULA.
The FHS Proxy/Server next examines the LHS FMT code. If FMT-Forward
is clear and FMT-Mode is set, the FHS Proxy/Server checks for a NCE
for the ADM-LLA of the LHS Proxy/Server. If there is no NCE, the FHS
Proxy/Server creates one in the INCOMPLETE state. If a new NCE was
created (or if the existing NCE requires fresh window
synchronization), the FHS Proxy/Server then writes window
synchronization parameters into the OMNI Multilink Forwarding
Parameters Tunnel Window Synchronization fields. The FHS
Proxy/Server then selects an appropriate Identification value and
*NET headers and forwards the resulting carrier packets into the
secured spanning tree which will deliver them to a Bridge interface
that assigns the FHS Subnet Router Anycast ULA.If the OAL source is the FHS Client, it instead includes an
authentication signature if necessary, performs OAL encapsulation,
sets the source to its own MNP-ULA, sets the destination to
{ADM,MNP}-ULA of the FHS Proxy/Server and selects an appropriate
Identification value for the FHS Proxy/Server. If FHS FMT-Forward is
set and LHS FMT-Forward is clear, the FHS Client creates/updates a
NCE for the ADM-LLA of the LHS Proxy/Server as above and includes
Tunnel Window Synchronization parameters. The FHS Client then
fragments and encapsulates in appropriate *NET headers then forwards
the carrier packets to the FHS Proxy/Server. When the FHS
Proxy/Server receives the carrier packets, it verifies the
Identification, reassembles/decapsulates to obtain the NS then
verifies the authentication signature or checksum. The FHS
Proxy/Server then creates an MFV (i.e., the same as the FHS Client
had done) while assigning the current B entry in the MFVI List
(i.e., the one included by the FHS Client) as the "B2" MFVI for this
MVF. The FHS Proxy/Server next generates a new unique "B1" MFVI,
then both assigns it to the MFV and writes it as the next B entry in
the OMNI Multilink Forwarding Parameters MFVI List (while also
writing any FHS Client and Proxy/Server addressing information). The
FHS Proxy/Server then checks FHS/LHS FMT-Forward/Mode to determine
whether to create a NCE for the LHS Proxy/Server ADM-LLA and include
Tunnel Window Synchronization parameters the same as above. The FHS
Proxy/Server then calculates the checksum, re-fragments while
setting the OAL source address to its own ADM-ULA and destination
address to the FHS Subnet Router Anycast ULA, and includes an
Identification appropriate for the secured spanning tree. The FHS
Proxy/Server finally includes appropriate *NET headers and forwards
the carrier packets into the secured spanning tree the same as
above.Bridges in the spanning tree forward carrier packets not
explicitly addressed to themselves, while forwarding those that
arrived via the secured spanning tree to the next hop also via the
secured spanning tree and forwarding all others via the unsecured
spanning tree. When an FHS Bridge receives a carrier packet over the
secured spanning tree addressed to its ADM-ULA or the FHS Subnet
Router Anycast ULA, it instead reassembles/decapsulates to obtain
the NS then verifies the checksum. The FHS Bridge next creates an
MFV (i.e., the same as the FHS Proxy/Server had done) while
assigning the current B entry in the MFVI List as the MFV "B2"
index. The FHS Bridge also caches the NS Multilink Forwarding
Parameters FHS information in the MFV, and also caches the first B
entry in the MFVI List as "FHS-Client" when FHS FMT-Forward/Mode are
both set to enable future direct forwarding to this FHS Client. The
FHS Bridge then generates a "B1" MFVI for the MFV and also writes it
as the next B entry in the NS's MFVI List.The FHS Bridge then examines the SRT prefixes corresponding to
both FHS and LHS. If the FHS Bridge has a local interface connection
to both the FHS and LHS (whether they are the same or different
segments), the FHS/LHS Bridge caches the NS LHS information, writes
its ADM-ULA suffix and LHS INADDR into the NS OMNI Multilink
Forwarding Parameters LHS fields, then sets its own ADM-ULA as the
source and the ADM-ULA of the LHS Proxy/Server as the destination
while selecting an appropriate identification. If the FHS and LHS
prefixes are different, the FHS Bridge instead sets the LHS Subnet
Router Anycast ULA as the destination. The FHS Bridge then
recalculates the NS checksum, selects an appropriate Identification
and *NET headers as above then forwards the carrier packets into the
secured spanning tree.When the FHS and LHS Bridges are different, the LHS Bridge will
receive carrier packets over the secured spanning tree from the FHS
Bridge. The LHS Bridge reassembles/decapsulates to obtain the NS
then verifies the checksum and creates an MFV (i.e., the same as the
FHS Bridge had done) while assigning the current B entry in the MFVI
List as the MFV "B2" index. The LHS Bridge also caches the ADM-ULA
of the FHS Bridge found in the Multilink Forwarding Parameters as
the spanning tree address for "B2", caches the NS Multilink
Forwarding Parameters LHS information then generates a "B1" MFVI for
the MFV while also writing it as the next B entry in the MFVI List.
The LHS Bridge also writes its own ADM-ULA suffix and LHS INADDR
into the OMNI Multilink Forwarding Parameters. The LHS Bridge then
sets the its own ADM-ULA as the source and the ADM-ULA of the LHS
Proxy/Server as the OAL destination, recalculates the checksum,
selects an appropriate Identification, then fragments while
including appropriate *NET headers and forwards the carrier packets
into the secured spanning tree.When the LHS Proxy/Server receives the carrier packets from the
secured spanning tree, it reassembles/decapsulates to obtain the NS,
verifies the checksum then verifies that the LHS information
supplied by the FHS source is consistent with its own cached
information. If the information is consistent, the LHS Proxy/Server
then creates an MFV and assigns the current B entry in the MFVI List
as the "B2" MFVI the same as for the prior hop. If the NS
destination is the MNP-LLA of the target Client, the LHS
Proxy/Server also generates a "B1" MFVI and assigns it both to the
MFVI and as the next B entry in the MFVI List. The LHS Proxy/Server
then examines FHS FMT; if FMT-Forward is clear and FMT-Mode is set,
the LHS Proxy/Server creates a NCE for the ADM-LLA of the FHS
Proxy/Server (if necessary) and sets the state to STALE, then caches
any Tunnel Window Synchronization parameters.If the NS destination is its own ADM-LLA, the LHS Proxy/Server
next prepares to return a solicited NA with Job code "01". If the NS
source was the MNP-LLA of the FHS Client, the LHS Proxy/Server first
creates or updates an NCE for the MNP-LLA with state set to STALE.
The LHS Proxy/Server next caches the NS OMNI header window
synchronization parameters and Multilink Forwarding Parameters
information (including the MFVI List) in the NCE corresponding to
the LLA source. When the LHS Proxy/Server forwards future carrier
packets based on the NCE, it can populate reverse-path forwarding
information in a CRH-32 routing header to enable forwarding based on
the cached MFVI List B entries instead of ULA addresses.The LHS Proxy/Server then creates an NA with Job code "01" while
copying the NS OMNI Multilink Forwarding Parameters FHS/LHS
information into the corresponding fields in the NA. The LHS
Proxy/Server then generates an "A1" MFVI and both assigns it to the
MFV and includes it as the first A entry in NA's MFVI List (see:
for details on MFVI List A/B
processing). The LHS Proxy/Server then includes end-to-end window
synchronization parameters in the OMIN header (if necessary) and
also tunnel window synchronization parameters in the Multilink
Forwarding Parameters (if necessary). The LHS Proxy/Server then
encapsulates the NA, calculates the checksum, sets the source to its
own ADM-ULA, sets the destination to the ADM-ULA of the LHS Bridge,
selects an appropriate Identification value and *NET headers then
forwards the carrier packets into the secured spanning tree.If the NS destination was the MNP-LLA of the LHS Client, the LHS
Proxy/Server instead includes an authentication signature in the NS
if necessary (otherwise recalculates the checksum), then changes the
OAL source to its own ADM-ULA and changes the destination to the
MNP-ULA of the LHS Client. The LHS Proxy/Server then selects an
appropriate Identification value, fragments if necessary, includes
appropriate *NET headers and forwards the carrier packets to the LHS
Client. When the LHS Client receives the carrier packets, it
verifies the Identification and reassembles/decapsulates to obtain
the NS then verifies the authentication signature or checksum. The
LHS Client then creates a NCE for the NS LLA source address in the
STALE state. If LHS FMT-Forward is set, FHS FMT-Forward is clear and
the NS source was an MNP-LLA, the Client also creates a NCE for the
ADM-LLA of the FHS Proxy/Server in the STALE state and caches any
Tunnel Window Synchronization parameters. The Client then caches the
NS OMNI header window synchronization parameters and Multilink
Forwarding Parameters in the NCE corresponding to the NS LLA source,
then creates an MFV and assigns both the current MFVI List B entry
as "B2" and a locally generated "A1" MFVI the same as for previous
hops (the LHS Client also includes the "A1" value in the solicited
NA - see above and below). The LHS Client also caches the previous
MFVI List B entry as "LHS-Bridge" since it can include this value
when it sends future carrier packets directly to the Bridge
(following appropriate neighbor coordination).The LHS Client then prepares an NA using exactly the same
procedures as for the LHS Proxy/Server above, except that it uses
its MNP-LLA as the source and the {ADM,MNP}-LLA of the FHS
correspondent as the destination. The LHS Client also includes an
authentication signature if necessary (otherwise calculates the
checksum), then encapsulates the NA with OAL source set to its own
MNP-ULA and destination set to the ADM-ULA of the LHS Proxy/Server,
includes an appropriate Identification and *NET headers and forwards
the carrier packets to the LHS Proxy/Server. When the LHS
Proxy/Server receives the carrier packets, it verifies the
Identifications, reassembles/decapsulates to obtain the NA, verifies
the authentication signature or checksum, then uses the current MVFI
List B entry to locate the MFV. The LHS Proxy/Server then writes the
current MFVI List A entry as the "A2" value for the MVF, generates
an "A1" MFVI and both assigns it to the MFV and writes it as the
next MFVI List A entry. The LHS Proxy/Server then examines the
FHS/LHS FMT codes to determine if it needs to include Tunnel Window
Synchronization parameters. The LHS Proxy/Server then recalculates
the checksum, re-fragments the NA while setting the OAL source to
its own ADM-ULA and destination to the ADM-ULA of the LHS Bridge,
includes an appropriate Identification and *NET headers and forwards
the carrier packets into the secured spanning tree.When the LHS Bridge receives the carrier packets, it
reassembles/decapsulates to obtain the NA while verifying the
checksum then uses the current MFVI List B entry to locate the MFV.
The LHS Bridge then writes the current MFVI List A entry as the MFV
"A2" index and generates a new "A1" value which it both assigns the
MFV and writes as the next MFVI List A entry. (The LHS Bridge also
caches the first A entry in the MFVI List as "LHS-Client" when LHS
FMT-Forward/Mode are both set to enable future direct forwarding to
this LHS Client.) If the LHS Bridge is connected directly to both
the FHS and LHS segments (whether the segments are the same or
different), the FHS/LHS Bridge will have already cached the FHS/LHS
information based on the original NS. The FHS/LHS Bridge
recalculates the checksum then re-fragments the NA while setting the
OAL source to its own ADM-ULA and destination to the ADM-ULA of the
FHS Proxy/Server. If the FHS and LHS prefixes are different, the FHS
Bridge instead re-fragments while setting the destination to the
ADM-ULA of the FHS Bridge. The LHS Bridge selects an appropriate
Identification and *NET headers then forwards the carrier packets
into the secured spanning tree.When the FHS and LHS Bridges are different, the FHS Bridge will
receive the carrier packets from the LHS Bridge over the secured
spanning tree. The FHS Bridge reassembles/decapsulates to obtain the
NA while verifying the checksum, then locates the MFV based on the
current MFVI List B entry. The FHS Bridge then assigns the current
MFVI List A entry as the MFV "A2" index and caches the ADM-ULA of
the LHS Bridge as the spanning tree address for "A2". The FHS Bridge
then generates an "A1" MVFI and both assigns it to the MVF and
writes it as the next MFVI List A entry while also writing its
ADM-ULA and INADDR in the NA FHS Bridge fields. The FHS Bridge then
recalculates the checksum, re-encapsulates/re-fragments with its own
ADM-ULA as the source, with the ADM-ULA of the FHS Proxy/Server as
the destination, then selects an appropriate Identification value
and *NET headers and forwards the carrier packets into the secured
spanning tree.When the FHS Proxy/Server receives the carrier packets from the
secured spanning tree, it reassembles/decapsulates to obtain the NA
while verifying the checksum then locates the MFV based on the
current MFVI List B entry. The FHS Proxy/Server then assigns the
current MFVI List A entry as the "A2" MFVI the same as for the prior
hop. If the NA destination is its own ADM-LLA, the FHS Proxy/Server
then caches the NA Multilink Forwarding Parameters with the MFV and
examines LHS FMT. If FMT-Forward is clear, the FHS Proxy/Server
locates the NCE for the ADM-LLA of the LHS Proxy/Server and sets the
state to REACHABLE then caches any Tunnel Window Synchronization
parameters. If the NA source is the MNP-LLA of the LHS Client, the
FHS Proxy/Server then locates the LHS Client NCE and sets the state
to REACHABLE then caches the OMNI header window synchronization
parameters and prepares to return an NA acknowledgement, if
necessary.If the NA destination is the MNP-LLA of the FHS Client, the FHS
Proxy/Server also searches for and updates the NCE for the ADM-LLA
of the LHS Proxy/Server if necessary the same as above. The FHS
Proxy/Server then generates an "A1" MFVI and assigns it both to the
MFVI and as the next MFVI List A entry, then includes an
authentication signature or checksum in the NA message. The FHS
Proxy/Server then sets the OAL source to its own ADM-LA and sets the
destination to the MNP-ULA of the FHS Client, then selects an
appropriate Identification value and *NET headers and forwards the
carrier packets to the FHS Client.When the FHS Client receives the carrier packets, it verifies the
Identification, reassembles/decapsulates to obtain the NA, verifies
the authentication signature or checksum, then locates the MFV based
on the current MFVI List B entry. The FHS Client then assigns the
current MFVI List A entry as the "A2" MFVI the same as for the prior
hop. The FHS Client then caches the NA Multilink Forwarding
Parameters (including the MFVI List) with the MFV and examines LHS
FMT. If FMT-Forward is clear, the FHS Client locates the NCE for the
ADM-LLA of the LHS Proxy/Server and sets the state to REACHABLE then
caches any Tunnel Window Synchronization parameters. If the NA
source is the MNP-LLA of the LHS Client, the FHS Proxy/Server then
locates the LHS Client NCE and sets the state to REACHABLE then
caches the OMNI header window synchronization parameters and
prepares to return an NA acknowledgement, if necessary. The FHS
Client also caches the previous MFVI List A entry as "FHS-Bridge"
since it can include this value when it sends future carrier packets
directly to the Bridge (following appropriate neighbor
coordination).If either the FHS Client or FHS Proxy/Server needs to return an
acknowledgement to complete window synchronization, it prepares a
uNA message with an OMNI Multilink Forwarding Parameters sub-option
with Job code set to "10" (Follow A; Record B) (note that this step
is unnecessary when Rapid Commit route optimization is used per
). The FHS node sets the source to its own
{ADM,MNP}-LLA, sets the destination to the {ADM,MNP}-LLA of the LHS
node then includes Tunnel Window Synchronization parameters if
necessary. The FHS node next sets the MFVI List to the cached list
of A entries received in the Job code "01" NA, but need not set any
other FHS/LHS information. The FHS node then encapsulates the uNA
message in an OAL header with its own {ADM,MNP}-ULA as the source.
If the FHS node is the Client, it next sets the ADM-ULA of the FHS
Proxy/Server as the OAL destination, includes an authentication
signature or checksum, selects an appropriate Identification value
and *NET headers and forwards the carrier packets to the FHS
Proxy/Server. The FHS Proxy/Server then verifies the Identification,
reassembles/decapsulates, verifies the authentication signature or
checksum, then uses the current MFVI List A entry to locate the MFV.
The FHS Proxy/Server then writes its "B1" MFVI as the next MFVI List
B entry and determines whether it needs to include Tunnel Window
Synchronization parameters the same as it had done when it forwarded
the original NS.The FHS Proxy/Server recalculates the uNA checksum then
re-fragments while setting its own ADM-ULA as the source and the
ADM-ULA of the FHS Bridge as the destination, then selects an
appropriate Identification and *NET headers and forwards the carrier
packets into the secured spanning tree. When the FHS Bridge receives
the carrier packets, it reassembles/decapsulates to obtain the uNA
while verifying the checksum then uses the current MFVI List A entry
to locate the MFV. The FHS Bridge then writes its "B1" MFVI as the
next MFVI List B entry, then re-fragments while setting the OAL
source and destination. If the FHS Bridge is also the LHS Bridge, it
sets the ADM-ULA of the LHS Proxy/Server as the destination;
otherwise it sets the ADM-ULA of the LHS Bridge. The FHS Bridge
recalculates the checksum then selects an appropriate Identification
and *NET headers, re-fragments/forwards the carrier packets into the
secured spanning tree. If an LHS Bridge receives the carrier
packets, it processes them exactly the same as the FHS Bridge had
done while setting the carrier packet destination to the ADM-ULA of
the LHS Proxy/Server.When the LHS Proxy/Server receives the carrier packets, it
reassembles/decapsulates to obtain the uNA message while verifying
the checksum. The LHS Proxy/Server then locates the MFV based on the
current MFVI List A entry then determines whether it is a tunnel
ingress the same as for the original NS. If it is a tunnel ingress,
the LHS Proxy/Server updates the NCE for the tunnel far-end based on
the Tunnel Window Synchronization parameters. If the uNA destination
is its own ADM-LLA, the LHS Proxy/Server next updates the NCE for
the source LLA based on the OMNI header Window Synchronization
parameters and MAY compare the MVFI List to the version it had
cached in the MFV based on the original NS.If the uNA destination is the MNP-LLA of the LHS Client, the LHS
Proxy/Server instead writes its "B1" MFV as the next MFVI List B
entry, includes an authentication signature or checksum, writes its
own ADM-ULA as the source and the MNP-ULA of the Client as the
destination then selects an appropriate Identification and *NET
headers and forwards the resulting carrier packets to the LHS
Client. When the LHS Client receives the carrier packets, it
verifies the Identification, reassembles/decapsulates to obtain the
uNA, verifies the authentication signature or checksum then
processes the message exactly the same as for the LHS Proxy/Server
case above.Following the NS/NA exchange with Multilink Forwarding
Parameters, OAL end systems and tunnel endpoints can begin
exchanging ordinary carrier packets with Identification values
within their respective send/receive windows without requiring
security signatures and/or secured spanning tree traversal. Either
peer can refresh window synchronization parameters and/or send other
carrier packets requiring security at any time using the same
secured procedures described above. OAL end systems and intermediate
nodes can also use their own A1/B1 MFVIs when they receive carrier
packets to unambiguously locate the correct MFV and determine
directionality and can use any discovered A2/B2 MFVIs to forward
carrier packets to other OAL nodes that configure the corresponding
A1/B1 MFVIs. When an OAL node uses an MFVI included in a carrier
packet to locate an MFV, it need not also examine the carrier packet
addresses.OAL sources can also begin including CRH-32s in carrier packets
with a list of A/B MFVIs that OAL intermediate nodes can use for
shortest-path carrier packet forwarding based on MFVIs instead of
spanning tree addresses. OAL sources and intermediate nodes can also
begin forwarding carrier packets with OAL compressed headers termed
"OCH-0/1" (Type 0 or 1) (see: ) that include only a single A/B
MFVI meaningful to the next hop, since all nodes in the path up to
(and sometimes including) the OAL destination have already
established MFV forwarding information. Note that when an FHS OAL
source receives a solicited NA with Job code "01', the message will
contain an MFVI List with A entries populated in the reverse order
needed for populating a CRH-32 routing header. The FHS OAL source
must therefore write the MFVI List A entries last-to-first when it
populates a CRH-32, or must select the correct A entry to include in
an OCH-0/1 header based on the intended OAL intermediate node or
destination.When a Bridge receives unsecured carrier packets destined to a
local segment Client that has asserted direct reachability, the
Bridge performs direct carrier packet forwarding while bypassing the
local Proxy/Server based on the Client's advertised MFVIs and
discovered NATed INADDR information (see: ). If the Client cannot be reached directly (or
if NAT traversal has not yet converged), the Bridge instead forwards
carrier packets directly to the local Proxy/Server.When a Proxy/Server receives carrier packets destined to a local
Client or forwards carrier packets received from a local Client, it
first locates the correct MFV. If the carrier packets include a
secured IPv6 ND message, the Proxy/Server uses the Client's NCE
established through RS/RA exchanges to re-encapsulate/re-fragment
while forwarding outbound secured carrier packets via the secured
spanning tree and forwarding inbound secured carrier packets while
including an authentication signature or checksum. For ordinary
carrier packets, the Proxy/Server uses the same MFV if directed by
MFVI and/or OAL addressing. Otherwise it locates an MFV established
through an NS/NA exchange between the Client and the remote peer,
and forwards the carrier packets without first
reassembling/decapsulating.When a Proxy/Server or Client configured as a tunnel ingress
receives a carrier packet with a full OAL header with an MNP-ULA
source and CRH-32 routing header, or an OCH-0/1 header with an MFVI
that matches an MFV, the ingress encapsulates the carrier packet in
a new full OAL header or an OCH-0/1 header containing the next hop
MVFI and an Identification value appropriate for the end-to-end
window and the outer header containing an Identification value
appropriate for the tunnel endpoints. When a Proxy/Server or Client
configured as a tunnel egress receives an encapsulated carrier
packet, it verifies the Identification in the outer header, then
discards the outer header and forwards the inner carrier packet to
the final destination.When a Proxy/Server with FMT-Forward/Mode set to 0/1 for a source
Client receives carrier packets from the source Client, it first
reassembles to obtain the original OAL packet then re-fragments if
necessary to cause the Client's packets to match the MPS on the path
from the Proxy/Server as a tunnel ingress to the tunnel egress. The
Proxy/Server then performs OAL-in-OAL encapsulation and forwards the
resulting carrier packets to the tunnel egress. When a Proxy/Server
with FMT-Forward/Mode set to 0/1 for a target Client receives
carrier packets from a tunnel ingress, it first decapsulates to
obtain the original fragments then reassembles to obtain the
original OAL packet. The Proxy/Server then re-fragments if necessary
to cause the fragments to match the target Client's underlying
interface (Path) MTU and forwards the resulting carrier packets to
the target Client.When a source Client forwards carrier packets it can employ
header compression according to the MFVIs established through an
NS/NA exchange with a remote or local peer. When the source Client
forwards to a remote peer, it can forward carrier packets to a local
SRT Bridge (following the establishment of INADDR information) while
bypassing the Proxy/Server (see: ). When a
target Client receives carrier packets that match a local MFV, the
Client first verifies the Identification then decompresses the
headers if necessary, reassembles if necessary to obtain the OAL
packet then decapsulates and delivers the IP packet to upper
layers.When synchronized peer Clients in the same SRT segment with
FMT-Forward and FMT-Mode set discover each other's NATed INADDR
addresses, they can exchange carrier packets directly with header
compression using MFVIs discovered as above (see: ). The FHS Client will have cached the A MFVI for
the LHS Client, which will have cached the B MVFI for the FHS
Client.After window synchronization state has been established, the ROS
and ROR can begin forwarding carrier packets while performing
additional NS/NA exchanges as above to update window state, register
new interface pairs for optimized multilink forwarding and/or
confirm reachability. The ROS sends carrier packets to the FHS
Bridge discovered through the NS/NA exchange. The FHS Bridge then
forwards the carrier packets over the unsecured spanning tree to the
LHS Bridge, which forwards them via LHS encapsulation to the LHS
Proxy/Server or directly to the target Client itself. The target
Client in turn sends packets to the ROS in the reverse direction
while forwarding through the Bridges to minimize Proxy/Server load
whenever possible.While the ROS continues to actively forward packets to the target
Client, it is responsible for updating window synchronization state
and per-interface reachability before expiration. Window
synchronization state is shared by all underlying interfaces in the
ROS' NCE that use the same destination LLA so that a single NS/NA
exchange applies for all interfaces regardless of the specific
interface used to conduct the exchange. However, the window
synchronization exchange only confirms target Client reachability
over the specific underlying interface pair. Reachability for other
underlying interfaces that share the same window synchronization
state must be determined individually using additional NS/NA
messages.When the ROR receives an NS(AR) with a set of Interface
Attributes for the source Client, it can perform "rapid commit" by
immediately invoking multilink route optimization as above instead
of returning an NA(AR). In order to perform rapid commit, the ROR
prepares a unicast NS message with an OMNI option with Window
Synchronization information responsive to the NS(AR), with a
Multilink Forwarding Parameters sub-option selected for a specific
underlying interface pair and with Interface Attributes for all of
the ROR's other underlying interfaces. The ROR can also include
ordinary IP packets as OAL super-packet trailers to the NS message
if it has immediate data to send to the ROS. The ROR then returns
the NS to the ROS the same as for the NA(AR) case.When the NS message traverses the return path to the ROR, all
intermediate nodes in the path establish state exactly the same as
for an ordinary NS/NA multilink route optimization exchange. When
the NS message arrives at the ROS, the Window Synchronization
parameters confirm that the NS is taking the place of the NA(AR),
thereby eliminating an extraneous message transmission and
associated delay. The ROS then completes the route optimization by
returning a responsive NA.Note: The ROS must accept unicast NS messages with an ACK
matching the SYN included in the NS(AR) as an equivalent message
replacement for the NA(AR). Address resolution and multilink
forwarding coordination can therefore be coordinated in a single
three-way handshake connection with minimal messaging and delay
(i.e., as opposed to a four-message exchange).Following multilink route optimization for specific underlying
interface pairs, ROS/ROR Clients located on open INETs can invoke
Client/Bridge route optimization to improve performance and reduce
load and congestion on their respective FHS/LHS Proxy/Servers. To
initiate Client/Bridge route optimization, the Client prepares an NS
message with its own MNP-LLA address as the source and the ADM-LLA
of its Bridge as the destination while creating a NCE for the Bridge
if necessary. The NS message must be no larger than the minimum MPS
and encapsulated as an atomic fragment.The Client then includes an Interface Attributes sub-option for
its underlying interface as well as an authentication signature but
does not include Window Synchronization parameters. The Client then
performs OAL encapsulation with its own MNP-ULA as the source and
the ADM-ULA of the Bridge as the destination while including a
randomly-chosen Identification value, then performs *NET
encapsulation on the atomic fragment and sends the resulting carrier
packet directly to the Bridge.When the Bridge receives the carrier packet, it verifies the
authentication signature then creates a NCE for the Client. The
Bridge then caches the *NET encapsulation addresses (which may have
been altered by one or more NATs on the path) as well as the
Interface Attributes for this Client omIndex, and marks this Client
underlying interface as "trusted". The Bridge then prepares an NA
reply with its own ADM-LLA as the source and the MNP-LLA of the
Client as the destination where the NA again must be no larger than
the minimum MPS.The Bridge then echoes the Client's Interface Attributes,
includes an Origin Indication with the Client's observed *NET
addresses and includes an authentication signature. The Bridge then
performs OAL encapsulation with its own ADM-ULA as the source and
the MNP-ULA of the Client as the destination while using the same
Identification value that appeared in the NS, then performs *NET
encapsulation on the atomic fragment and sends the resulting carrier
packet directly to the Client.When the Client receives the NA reply, it caches the carrier
packet *NET source address information as the Bridge target address
via this underlying interface while marking the interface as
"trusted". The Client also caches the Origin Indication *NET address
information as its own (external) source address for this underlying
interface.After the Client and Bridge have established NCEs as well as
"trusted" status for a particular underlying interface pair, each
node can begin forwarding ordinary carrier packets intended for this
multilink route optimization directly to one another while omitting
the Proxy/Server from the forwarding path while the status is
"trusted". The NS/NA messaging will have established the correct
state in any NATs in the path so that NAT traversal is naturally
supported. The Client and Bridge must maintain a timer that watches
for activity on the path; if no carrier packets and/or NS/NA
messages are sent or received over the path before NAT state is
likely to have expired, the underlying interface pair status becomes
"untrusted".Thereafter, when the Client forwards a carrier packet with an
MFVI toward the Bridge as the next hop, the Client uses the MFVI for
the Bridge (discovered during multilink route optimization) instead
of the MFVI for its Proxy/Server; the Bridge will accept the packet
from the Client if and only if the underlying interface status is
trusted and if the MFVI is correct for the next hop toward the final
destination. (The same is true in the reverse direction when the
Bridge sends carrier packets directly to the Client.)Note that the Client and Bridge each maintain a single NCE, but
that the NCE may aggregate multiple underlying interface pairs. Each
underlying interface pair may use differing source and target *NET
addresses according to NAT mappings, and the "trusted/untrusted"
status of each pair must be tested independently. When no "trusted"
pairs remain, the NCE is deleted.Note that the above method requires Bridges to participate in
NS/NA message authentication signature application and verification.
In an alternate approach, the Client could instead exchange NS/NA
messages with authentication signatures via its Proxy/Server but
addressed to the ADM-LLA of the Bridge, and the Proxy/Server and
Bridge could relay the messages over the secured spanning tree.
However, this would still require the Client to send additional
messages toward the *NET address of the Bridge to populate NAT
state; hence the savings in complexity for Bridges would result in
increased message overhead for Clients.When the ROS/ROR Clients are both located on the same SRT
segment, Client-to-Client route optimization is possible following
the establishment of any necessary state in NATs in the path. Both
Clients will have already established state via their respective
shared segment Proxy/Servers (and possibly also the shared segment
Bridge) and can begin forwarding packets directly via NAT traversal
while avoiding any Proxy/Server and/or Bridge hops.When the ROR/ROS Clients on the same SRT segment perform the
initial NS/NA exchange to establish Multilink Forwarding state, they
also include an Origin Indication (i.e., in addition to Multilink
Forwarding Parameters) with the mapped addresses discovered during
the RS/RA exchanges with their respective Proxy/Servers. After the
MFV paths have been established, both Clients can begin sending
packets via strict MFV paths while establishing a direct path for
Client-to-Client route optimization.To establish the direct path, either Client (acting as the
source) transmits a bubble to the mapped *NET address for the target
Client which primes its local chain of NATs for reception of future
packets from that *NET address (see: and
). The source Client then
prepares an NS message with its own MNP-LLA as the source, with the
MNP-LLA of the target as the destination and with an OMNI option
with an Interface Attributes sub-option. The source Client then
encapsulates the NS in an OAL header with its own MNP-ULA as the
source, with the MNP-ULA of the target Client as the destination and
with an in-window Identification for the target. The source Client
then fragments and encapsulates in *NET headers addressed to its FHS
Proxy/Server then forwards the resulting carrier packets to the
Proxy/Server.When the FHS Proxy/Server receives the carrier packets, it
re-encapsulates and forwards them as unsecured carrier packets
according to MFV state where they will eventually arrive at the
target Client which can verify that the identifications are within
the acceptable window and reassemble if necessary. Following
reassembly, the target Client prepares an NA message with its own
MNP-LLA as the source, with the MNP-LLA of the source Client as the
destination and with an OMNI option with an Interface Attributes
sub-option. The target Client then encapsulates the NA in an OAL
header with its own MNP-ULA as the source, with the MNP-ULA of the
source Client as the destination and with an in-window
Identification for the source Client. The target Client then
fragments and encapsulates in *NET headers addressed to the source
Client's Origin addresses then forwards the resulting carrier
packets directly to the source Client.Following the initial NS/NA exchange, both Clients mark their
respective (source, target) underlying interface pairs as "trusted"
for no more than ReachableTime seconds. While the Clients continue
to exchange carrier packets via the direct path avoiding all
Proxy/Servers and Bridges, they should perform additional NS/NA
exchanges via their local Proxy/Servers to refresh NCE state as well
as send additional bubbles to the peer's Origin address information
if necessary to refresh NAT state.Note that these procedures are suitable for a widely-deployed but
basic class of NATs. Procedures for advanced NAT classes are
outlined in , which provides mechanisms that
can be employed equally for AERO using the corresponding sub-options
specified by OMNI.Note also that each communicating pair of Clients may need to
maintain NAT state for peer to peer communications via multiple
underlying interface pairs. It is therefore important that Origin
Indications are maintained with the correct peer interface and that
the NCE may cache information for multiple peer interfaces.Note that the source and target Client exchange Origin
information during the secured NS/NA multilink route optimization
exchange. This allows for subsequent NS/NA exchanges to proceed
using only the Identification value as a data origin confirmation.
However, Client-to-Client peerings that require stronger security
may also include authentication signatures for mutual
authentication.AERO nodes perform Neighbor Unreachability Detection (NUD) per
either reactively in response to persistent
link-layer errors (see ) or proactively to
confirm reachability. The NUD algorithm is based on periodic control
message exchanges and may further be seeded by IPv6 ND hints of
forward progress, but care must be taken to avoid inferring
reachability based on spoofed information. For example, IPv6 ND
message exchanges that include authentication codes and/or in-window
Identifications may be considered as acceptable hints of forward
progress, while spurious random carrier packets should be ignored.AERO nodes can perform NS/NA(NUD) exchanges over the OMNI link
secured spanning tree (i.e. the same as described above) to 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 parties involved in the NUD test. When only reachability
information is required without updating any other NCE state, AERO
nodes can instead perform NS/NA(NUD) exchanges directly between
neighbors without employing the secured spanning tree as long as they
include in-window Identifications and either an authentication
signature or checksum.After an ROR directs an ROS to a target neighbor with one or more
link-layer addresses, either node may invoke multilink forwarding
state initialization to establish authentic intermediate node state
between specific underlying interface pairs which also tests their
reachability. Thereafter, either node acting as the source may perform
additional reachability probing through NS(NUD) messages over the SRT
secured or unsecured spanning tree, or through NS(NUD) messages sent
directly to an underlying interface of the target itself. While
testing a target underlying interface, the source can optionally
continue to forward carrier packets via alternate interfaces, maintain
a small queue of carrier packets until target reachability is
confirmed or include them as trailing data with the NS(NUD) in an OAL
super-packet .NS(NUD) messages are encapsulated, fragmented and transmitted as
carrier packets the same as for ordinary original IP data packets,
however the encapsulated destinations are the LLA of the source and
either the ADM-LLA of the LHS Proxy/Server or the MNP-LLA of the
target itself. The source encapsulates the NS(NUD) message the same as
described in and includes an Interface
Attributes sub-option with omIndex set to identify its underlying
interface used for forwarding. The source then includes an in-window
Identification, fragments the OAL packet and forwards the resulting
carrier packets into the unsecured spanning tree, directly to the
target if it is in the local segment or directly to a Bridge in the
local segment.When the target receives the NS(NUD) carrier packets, it verifies
that it has a NCE for this source and that the Identification is
in-window, then submits the carrier packets for reassembly. The target
then verifies the authentication signature or checksum, then searches
for Interface Attributes in its NCE for the source that match the
NS(NUD) for the NA(NUD) reply. The target then prepares the NA(NUD)
with the source and destination LLAs reversed, encapsulates and sets
the OAL source and destination, includes an Interface Attributes
sub-option in the NA(NUD) to identify the omIndex of the underlying
interface the NS(NUD) arrived on and sets the Target Address to the
same value included in the NS(NUD). The target next sets the R flag to
1, the S flag to 1 and the O flag to 1, then selects an in-window
Identification for the source and performs fragmentation. The node
then forwards the carrier packets into the unsecured spanning tree,
directly to the source if it is in the local segment or directly to a
Bridge in the local segment.When the source receives the NA(NUD), it marks the target
underlying interface tested as "trusted". Note that underlying
interface states are maintained independently of the overall NCE
REACHABLE state, and that a single NCE may have multiple target
underlying interfaces in various "trusted/untrusted" states while the
NCE state as a whole remains REACHABLE.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 FHS and Hub
Proxy/Servers via RS/RA exchanges to maintain the DMM profile, and the
AERO routing system tracks all current Client/Proxy/Server peering
relationships.Hub Proxy/Servers provide a designated router service for their
dependent Clients, while FHS Proxy/Servers provide a proxy conduit
between the Client and both the Hub and OMNI link in general. 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
attributes change, the Client is responsible for updating the Hub
Proxy/Server through new RS/RA exchanges using the FHS Proxy/Server as
a first-hop conduit. The FHS Proxy/Server can also act as a proxy to
perform some IPv6 ND exchanges on the Client's behalf without
consuming bandwidth on the Client underlying interface.Mobility management considerations are specified in the following
sections.RORs and ROSs accommodate Client mobility and/or multilink change
events by sending secured uNA messages to each active neighbor. When
an ROR/ROS sends a uNA message, it sets the IPv6 source address to
the its own LLA, sets the destination address to the neighbor's
{ADM,MNP}-LLA and sets the Target Address to the Client's MNP-LLA.
The ROR/ROS also includes an OMNI option with Preflen set to the
prefix length associated with the Client's MNP-LLA, includes
Interface Attributes and Traffic Selectors for the Client's
underlying interfaces and includes an authentication signature if
necessary. The ROR then sets the uNA R flag to 1, S flag to 0 and O
flag to 1, then encapsulates the message in an OAL header with
source set to its own ULA and destination set to its FHS
Proxy/Server's ADM-ULA. When the FHS Proxy/Server receives the uNA,
it reassembles, verifies the authentication signature, then changes
the destination to the ULA corresponding to the LLA destination and
forwards the uNA into the secured 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 ROR/ROS can optionally send up to
MAX_NEIGHBOR_ADVERTISEMENT uNAs to each neighbor to increase the
likelihood that at least one will be received. Alternatively, the
ROR/ROS can set the PNG flag in the uNA OMNI option header to
request a uNA acknowledgement as specified in .When the ROR/ROS Proxy/Server receives a uNA message prepared as
above, if the uNA destination was its own ADM-LLA the Proxy/Server
uses the included OMNI option information to update its NCE for the
target but does not reset ReachableTime since the receipt of a uNA
message does not provide confirmation that any forward paths to the
target Client are working. If the destination was the MNP-LLA of the
ROR/ROS Client, the Proxy/Server instead changes the OAL source to
its own ADM-ULA, includes an authentication signature if necessary,
and includes an in-window Identification for this Client. Finally,
if the uNA message PNG flag was set, the node that processes the uNA
returns a uNA acknowledgement as specified in .When a Client needs to change its underlying Interface Attributes
and/or Traffic Selectors (e.g., due to a mobility event), the Client
sends an RS message to its Hub Proxy/Server via a first-hop FHS
Proxy/Server, if necessary. The RS includes an OMNI option with an
Interface Attributes sub-option with the omIndex and with new link
quality and any other information.Note that the first FHS Proxy/Server may change due to the
underlying interface change. If the Client supplies the address of
the former FHS Proxy/Server, the new FHS Proxy/Server can send a
departure indication (see below); otherwise, any stale state in the
former FHS Proxy/Server will simply expire after ReachableTime
expires with no effect on the Hub Proxy/Server.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.After performing the RS/RA exchange, the Client sends uNA
messages to all neighbors 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 Hub Proxy/Server via a FHS Proxy/Server for the
underlying interface (if necessary) with an OMNI option that
includes an Interface Attributes sub-option with appropriate link
quality values and with link-layer address information for the new
link. The Client then again sends uNA messages to all neighbors the
same as described above.When a Client needs to deactivate an existing underlying
interface, it sends a uNA message toward the Hub Proxy/Server via an
FHS Proxy/Server with an OMNI option with appropriate Interface
Attributes values for the deactivated link - in particular, the link
quality value 0 assures that neighbors will cease to use the
link.If the Client needs to send 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. The Client then again sends
uNA messages to all neighbors the same as described above.Note that when a Client deactivates an underlying interface,
neighbors that receive the ensuing 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 omIndex at a later point in time, when it will send new
RS messages to an FHS Proxy/Server with fresh interface parameters
to update any neighbors.The Client performs the procedures specified in when it first associates with a new Hub
Proxy/Server or renews its association with an existing Hub
Proxy/Server.When a Client associates with a new Hub Proxy/Server, it sends RS
messages to register its underlying interfaces with the new Hub
while including the 32 least significant bits of the old Hub's
ADM-LLA in the "Old Hub Proxy/Server MSID" field of a Proxy/Server
Departure OMNI sub-option. When the new Hub Proxy/Server returns the
RA message via the FHS Proxy/Server (acting as a Proxy), the FHS
Proxy/Server sends a uNA to the old Hub Proxy/Server (i.e., if the
MSID is non-zero and different from its own). The uNA has the
MNP-LLA of the Client as the source and the ADM-LLA of the old hub
as the destination and with Preflen set to 0. The FHS Proxy/Server
encapsulates the uNA in an OAL header with the ADM-ULA of the new
Hub as the source and the ADM-ULA of the old Hub as the destination,
the fragments and sends the carrier packets via the secured spanning
tree.When the old Hub Proxy/Server receives the uNA, it changes the
Client's NCE state to DEPARTED, resets DepartTime and caches the new
Hub Proxy/Server ADM-ULA. After a short delay (e.g., 2 seconds) the
old Hub Proxy/Server withdraws the Client's MNP from the routing
system. While in the DEPARTED state, the old Hub Proxy/Server
forwards any carrier packets received via the secured spanning tree
destined to the Client's MNP-ULA to the new Hub Proxy/Server's
ADM-ULA. After DepartTime expires, the old Hub Proxy/Server deletes
the Client's NCE.Mobility events may also cause a Client to change to a new FHS
Proxy/Server over a specific underlying interface at any time such
that a Client RS/RA exchange over the underlying interface will
engage the new FHS Proxy/Server instead of the old. The Client can
arrange to inform the old FHS Proxy/Server of the departure by
including a Proxy/Server Departure sub-option with an MSID for the
"Old FHS Proxy/Server MSID", and the new FHS Proxy/Server will issue
a uNA using the same procedures as outlined for the Hub above while
using its own ADM-ULA as the source address. This can often result
in successful delivery of packets that would otherwise be lost due
to the mobility event.Clients SHOULD NOT move rapidly between Hub 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 Hub Proxy/Server include a Hub 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.Clients provide an IGMP (IPv4) or MLD
(IPv6) proxy service for its EUNs and/or
hosted applications and act as a Protocol
Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM")
Designated Router (DR) on the OMNI link.
Proxy/Servers act as OMNI link PIM routers for Clients on ANET, VPNed
or Direct interfaces, and Relays also act as OMNI link PIM routers on
behalf of nodes on other links/networks.Clients on VPNed, Direct or ANET underlying interfaces for which
the ANET has deployed native multicast services forward IGMP/MLD
messages into the ANET. 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 ANET
Proxy/Server. The FHS Proxy/Server then acts as an ROS to send NS(AR)
messages to an ROR for the multicast source. Clients on INET and ANET
underlying interfaces without native multicast services instead send
NS(AR) messages as an ROS to cause their FHS Proxy/Server forward the
message to an ROR. When the ROR receives an NA(AR) response, it
initiates PIM protocol messaging according to the Source-Specific
Multicast (SSM) and Any-Source Multicast (ASM) operational modes as
discussed in the following sections.When an ROS "X" (i.e., either a Client or Proxy/Server) 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 sends an NS(AR) message (see: ) using its own LLA as the source address, the
solicited node multicast address corresponding to S as the
destination and the LLA of S as the target address. X then
encapsulates the NS(AR) in an OAL header with source address set to
its own ULA and destination address set to the ULA for S, then
forwards the message into the secured spanning tree which delivers
it to ROR "Y" that services S. The resulting NA(AR) will return an
OMNI option with Interface Attributes for any underlying interfaces
that are currently servicing S.When X processes the NA(AR) it selects one or more underlying
interfaces for S and performs an NS/NA multilink route optimization
exchange over the secured spanning tree while including a PIM
Join/Prune message for each multicast group of interest in the OMNI
option. If S is located behind any Proxys "Z"*, each Z* then updates
its MRIB accordingly and maintains the LLA of X as the next hop in
the reverse path. Since Bridges forward messages not addressed to
themselves without examining them, this means that the (reverse)
multicast tree path is simply from each Z* (and/or S) to X with no
other multicast-aware routers in the path.Following the initial combined Join/Prune and NS/NA messaging, X
maintains a NCE 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 NCE alive for up to t_periodic seconds . If no new Joins are received within t_periodic
seconds, X allows the NCE to expire. Finally, if X receives any
additional Join/Prune messages for (S,G) it forwards the messages
over the secured spanning tree.Client C that holds an MNP for source S may later 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 NCE for the LLA for source S and sends
new Join messages in NS/NA exchanges addressed to the new target
Client underlying interface connection for S. 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
expire since no new Joins will arrive.When an ROS X acting as a PIM router receives Join/Prune messages
from a node on its downstream interfaces containing one or more
(*,G) pairs, it updates its Multicast Routing Information Base
(MRIB) accordingly. X first performs an NS/NA(AR) exchange to
receive route optimization information for Rendezvous Point (RP) R
for each G. X then includes a copy of each Join/Prune message in the
OMNI option of an NS message with its own LLA as the source address
and the LLA for R as the destination address, then encapsulates the
NS message in an OAL header with its own ULA as the source and the
ADM-ULA of R's Proxy/Server as the destination then sends the
message into the secured spanning tree.For each source S that sends multicast traffic to group G via R,
Client S* that aggregates S (or its Proxy/Server) encapsulates the
original IP packets in PIM Register messages, includes the PIM
Register messages in the OMNI options of uNA messages, performs OAL
encapsulation and fragmentation then forwards the resulting carrier
packets with Identification values within the receive window for
Client R* that aggregates R. Client R* may then elect to send a PIM
Join to S* in the OMNI option of a uNA over the secured spanning
tree. This will result in an (S,G) tree rooted at S* 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 uNA PIM Register
encapsulation. R can then issue a uNA PIM Register-stop message over
the secured spanning tree to suppress the Register-encapsulated
stream. At some later time, if Client S* moves to a new
Proxy/Server, it resumes sending original IP packets via uNA PIM
Register encapsulation via the new Proxy/Server.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 (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
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.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.Many AERO/OMNI functions are implemented and undergoing final
integration. OAL fragmentation/reassembly buffer management code has
been cleared for public release.The IANA has assigned the UDP port number "8060" for an earlier
experimental first version of AERO . This
document together with reclaims
UDP port number "8060" as the service port for UDP/IP encapsulation.
This document makes no request of IANA, since already provides instructions. (Note:
although was not widely implemented or
deployed, it need not be obsoleted since its messages use the invalid
ICMPv6 message type number '0' which implementations of this
specification can easily distinguish and ignore.)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
secured spanning tree topology. Therefore, control messages exchanged
between any pair of OMNI link neighbors over the secured spanning tree
are already protected.To prevent spoofing vectors, Proxy/Servers MUST discard without
responding to any unsecured NS/NA(AR) messages. Also, Proxy/Servers MUST
discard without forwarding any original IP packets received from one of
their own Clients (whether directly or following OAL reassembly) with a
source address that does not match the Client's MNP and/or a destination
address that does match the Client's MNP. Finally, Proxy/Servers MUST
discard without forwarding any carrier packets with an OAL source and
destination that both match the same MNP.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 Client neighbors. Option
1) would result in longer routes than necessary and impose traffic
concentration on critical infrastructure elements. Option 2) could be
coordinated between Clients using NS/NA messages with OMNI Host Identity
Protocol (HIP) "Initiator/Responder" message sub-options to create a
secured tunnel on-demand, or to use the QUIC-TLS protocol to establish a
secured connection .AERO Clients that connect to secured ANETs need not apply security to
their IPv6 ND messages, since the messages will be authenticated and
forwarded by a perimeter Proxy/Server that applies security on its
INET-facing interface as part of the secured 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 transport-layer (or higher-layer)
security services such as QUIC-TLS, 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 through the AERO/OMNI data origin
authentication procedures, as well as 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 PRL MUST be well-managed and secured from unauthorized tampering,
even though the list contains only public information. The PRL 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.).The AERO service for open INET Clients depends on a public key
distribution service in which Client public keys and identities are
maintained in a shared database accessible to all open INET
Proxy/Servers. Similarly, each Client must be able to determine the
public key of each Proxy/Server, e.g. by consulting an online database.
When AERO nodes register their public keys indexed by a unique Host
Identity Tag (HIT) in a distributed database
such as the DNS, and use the HIT as an identity for applying IPv6 ND
message authentication signatures, a means for determining public key
attestation is available.Security considerations for IPv6 fragmentation and reassembly are
discussed in . In environments
where spoofing is considered a threat, OMNI nodes SHOULD employ
Identification window synchronization and OAL destinations SHOULD
configure an (end-system-based) firewall.SRH authentication facilities are specified in . Security considerations for accepting link-layer
ICMP messages and reflected packets are discussed throughout the
document.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, Scott Burleigh, Brian Carpenter,
Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, Sri
Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom Herbert,
Bob Hinden, Sascha Hlusiak, Lee Howard, Christian Huitema, Zdenek Jaron,
Andre Kostur, Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima,
Tomek Mrugalski, Thomas Narten, Madhu Niraula, Alexandru Petrescu,
Behcet Saikaya, Michal Skorepa, Dave Thaler, 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 their work on the AERO implementation. Chuck
Klabunde is honored and remembered for his early leadership, and we
mourn his untimely loss.This work was inspired by the support and encouragement of countless
outstanding colleagues, managers and program directors over the span of
many decades. Beginning in the late 1980s,' the Digital Equipment
Corporation (DEC) Ultrix Engineering and DECnet Architects groups
identified early issues with fragmentation and bridging links with
diverse MTUs. In the early 1990s, engagements at DEC Project Sequoia at
UC Berkeley and the DEC Western Research Lab in Palo Alto included
investigations into large-scale networked filesystems, ATM vs Internet
and network security proxys. In the mid-1990s to early 2000s employment
at the NASA Ames Research Center (Sterling Software) and SRI
International supported early investigations of IPv6, ONR UAV
Communications and the IETF. An employment at Nokia where important IETF
documents were published gave way to a present-day engagement with The
Boeing Company. The work matured at Boeing through major programs
including Future Combat Systems, Advanced Airplane Program, DTN for the
International Space Station, Mobility Vision Lab, CAST, Caravan,
Airplane Internet of Things, the NASA UAS/CNS program, the FAA/ICAO
ATN/IPS program and many others. An attempt to name all who gave support
and encouragement would double the current document size and result in
many unintentional omissions - but to all a humble thanks.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 creation of NCEs. The NCE state is set to REACHABLE for
at most ReachableTime seconds. In order to refresh the NCE lifetime
before the ReachableTime timer expires, the specification requires
implementations to issue a new NS/NA(AR) exchange to reset
ReachableTime while data packets are still flowing. However, the
decision of when to initiate a new NS/NA(AR) exchange and to
perpetuate the process is left as an implementation detail.One possible strategy may be to monitor the NCE 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(AR) to
receive a new NA(AR). If no data packets have been sent, wait for 5
additional seconds and send an immediate NS(AR) 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
NCE state to STALE.The monitoring of the neighbor data packet traffic therefore
becomes an ongoing process during the NCE lifetime. If the NCE
expires, future data packets will trigger a new NS/NA(AR) 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 IPv6
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 NCE 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 traffic selectors. If
the Direct interface is selected, then the Client's IP packets are
transmitted directly to the peer without going through an ANET/INET.
If other interfaces are selected, 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 INET Proxy/Servers can be standard dedicated server platforms,
but most often will be deployed as virtual machines in the cloud. The
only requirements for INET Proxy/Servers are that they can run the
AERO/OMNI code and have at least one network interface connection to
the INET. INET 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 INET Proxy/Servers, the
only requirements are that they can run the AERO/OMNI 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, uNA 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.AERO Proxy/Servers by default forward NS/NA messages to their
dependent Clients which create neighbor cache entries for
correspondents. The Client then becomes responsible for initiating
mobility update signaling through the transmission of uNA messages to
all active neighbors following a mobility event. However, in some
environments this may constitute excessive control message overhead
especially for Clients connected to low-end data links.To avoid this NS/NA overhead, such disadvantaged Clients can engage
their Hub Proxy/Servers according to the mobility anchor model. In
this model, the Hub Proxy/Server is responsible for tracking all of
the Client's active neighbors and the FHS Proxy/Servers for all of the
Client's underlying interfaces are responsible for terminating the
Client's multilink route optimization requests. The Hub is therefore
responsible for reporting Client mobility events to neighbors through
the transmission of uNA messages on behalf of the Client. To engage
this model, the Client must consistently set the Code field in all RS
messages it sends to the value 1.<< RFC Editor - remove prior to publication >>Changes from earlier versions to draft-templin-6man-aero-33:New baseline version with corrections and section reorganizations
to improve document flow.