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 selector
signaling and route optimization are naturally supported through dynamic
neighbor cache updates. AERO is a widely-applicable mobile
internetworking service especially well-suited to aviation services,
intelligent transportation systems, mobile 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 comprises Clients, Proxy/Servers and Relays that are
seen as OMNI link neighbors as well as Bridges that interconnect diverse
Internetworks as OMNI link segments through OAL forwarding at a layer
below IP. Each node's OMNI interface uses an IPv6 link-local address
format that supports operation of the IPv6 Neighbor Discovery (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 default routers and mobility anchor
points 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 multiple 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 the mobile node is
naturally routed to the nearest Relay.AERO can be used with OMNI links that span private-use Internetworks
and/or public Internetworks such as the global Internet. In the latter
case, some end systems may be located behind global Internet Network
Address Translators (NATs). A means for robust traversal of NATs while
avoiding "triangle routing" 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 network administrative
domains 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 .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 below.)an IP address assigned to a
node's interface connection to a *NET.the encapsulation of a
packet in an outer header or headers that can be routed within the
scope of the local *NET partition.the same as defined in . 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 encapsulation 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 first 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 default
forwarding and mobility anchor point services for coordination with
correspondents on its INET-facing interfaces. (Proxy/Servers in the
open INET instead configure only an 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 all of its associated MNPs 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 and assign an ADM-LLA the same as
Proxy/Servers, and also run a dynamic routing protocol to discover
any non-MNP IP GUA routes in service on its 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 routing system the same as for Proxy/Servers.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 single Proxy/Server
selected by the Client that provides a designated router and
mobility anchor point service for all of the Client's underlying
interfaces. Clients normally 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.a
Proxy/Server for an underlying interface of the source Client that
forwards packets sent by the source Client over that interface into
the segment routing topology. FHS Proxy/Servers act as intermediate
forwarding nodes to facilitate RS/RA exchanges between a Client and
its Hub Proxy/Server.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 the FHS Proxy/Server and LHS
Proxy/Server. 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.the AERO
node that responds to route optimization requests on behalf of the
target. The ROR may be a Proxy/Server for a target MNP Client or a
Relay for a non-MNP target.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.an individual
Proxy/Server, Bridge or Relay in the Mobility Service.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 advertised 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 other 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 present the OMNI link as
a set of one or more Mobility Service Prefixes (MSPs) and configure
secured tunnels with Proxy/Servers, Relays and other Bridges; they
further maintain forwarding table entries for each MNP or non-MNP
prefix in service on the OMNI link.AERO Proxy/Servers in distributed 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 limited forwarding services. 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 other
links/networks. Relays run a dynamic routing protocol to discover any
non-MNP prefixes in service on other links/networks. 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 from administrative
identification values ("ADM-LLAs") as specified in . Non-MNP routes are also
represented the same as for MNP-LLAs, but may include a prefix that
is not properly covered by 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,
while carrier packets destined to all other MNP-ULAs are dropped
with a Destination Unreachable message returned due to the
black-hole route. 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 are as follows:[ULA*]::1000/116->local,
[ULA*]::2000/116->B, [ULA*]::3000/116->C[ULA*]::1000/116->A,
[ULA*]::2000/116->local, [ULA*]::3000/116->C[ULA*]::1000/116->A, [ULA*]::2000/116->B,
[ULA*]::3000/116->localThese forwarding table entries 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 .When the network layer forwards an original IP packet into an
OMNI interface, the OMNI Adaptation Layer (OAL) encapsulates the
packet to produce an OAL packet . This OAL source then fragments the
OAL packet 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 also
includes an identical Compressed Routing Header with 32-bit ID
fields (CRH-32) with
each fragment if necessary as discussed in
and . 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 original IP header and packet body/fragment
are encapsulated 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 both Client
MNP-ULA prefix information that may change dynamically due to
regional node mobility 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 "shortcuts" instead
of always following 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.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 Hub, FHS and LHS Proxy/Servers, 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 include a supplemental forwarding table termed
the Multilink Forwarding Information Base (MFIB) that provides
shorter paths for 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).OMNI interface "OAL source", "OAL intermediate" and "OAL
destination" nodes create MFVs/MFVIs when they process an IPv6 ND
solicitation message with a Multilink Forwarding Parameters
sub-option with Job code "00" (Initialize; Build B) or a solicited
advertisement with Job code "01" (Follow B; Build A) (see: ). The OAL source of the
solicitation (and OAL destination of the solicited advertisement)
are considered to reside in the "First Hop Segment (FHS)", while the
OAL destination of the solicitation (and OAL source of the solicited
advertisement) are considered to reside in the "Last Hop Segment
(LHS)".When an OAL node processes a solicitation with Job code "00", it
creates an MFV, records the solicitation's source and destination
LLAs and assigns a "B" MFVI. When the "B" MVFI is referenced, the
MVF presents the LLAs in (dst,src) order the opposite of how they
appeared in the original solicitation.When an OAL node processes a solicited advertisement with Job
code "01", it locates the MFV created by the solicitation and
assigns an "A" MFVI. When the "A" MFVI is referenced, the MFV
presents the LLAs in (src,dst) order the same as they appeared in
the original solicitation.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
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.) An MFVI generated by a first OAL node SHOULD NOT
be 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 LHS
intermediate node before the OAL destination. The OAL node
generates and assigns a "B1" MFVI to a newly-created MFV when it
processes a solicitation 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 FHS
intermediate node before the 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
advertisement 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
advertisement 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 a
solicitation 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, (i.e., one for which there is no existing NCE)
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 a solicitation 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 creates a NCE for the selected destination {ADM,MNP}-LLA
in the INCOMPLETE state. The OAL source next creates an MFV based on
the solicitation 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
solicitation Multilink Forwarding Parameters based on any FHS/LHS
information it knows locally. OAL intermediate nodes on the path to
the OAL destination may populate addtional 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 LHS
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/fragmentation, sets the source to its own ADM-ULA and
sets the destination to the ADM-ULA of the FHS Proxy/Server. The FHS
Client then selects an appropriate Identification value and *NET
headers and 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
solicitation then verifies the authentication signature. 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 then 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 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 re-encapsulates/re-fragments while setting the
source to its own ADM-ULA and destination address to the FHS Subnet
Router Anycast ULA. The FHS Proxy/Server finally includes an
appropriate Identification value and *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 solicitation. 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 solicitation 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 solicitation'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 solicitation LHS
information and writes its ADM-ULA suffix and LHS INADDR into the
solicitation OMNI Multilink Forwarding Parameters LHS fields. The
FHS/LHS Bridge then re-encapsulates the solicitation with its own
ADM-ULA as the source and with the ADM-ULA of the LHS Proxy/Server
as the destination. If the FHS and LHS prefixes are different, the
FHS Bridge instead re-encapsulates with its own ADM-ULA as the
source and with the LHS Subnet Router Anycast ULA as the
destination. The FHS Bridge 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
solicitation then 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 as the spanning tree address for "B2", caches the
solicitation 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 re-encapsulates with its own ADM-ULA as the
source and the ADM-ULA of the LHS Proxy/Server as the destination,
then selects an appropriate Identification and *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
solicitation 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 solicitation 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 solicitation destination is its own ADM-LLA, the LHS
Proxy/Server next prepares to return a solicited advertisement with
Job code "01". If the solicitation 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 solicitation 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 advertisement with Job code
"01" while copying the solicitation OMNI Multilink Forwarding
Parameters FHS/LHS information into the corresponding fields in the
advertisement. 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
advertisement'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 Tunnel block (if necessary). The LHS
Proxy/Server then encapsulates the advertisement, 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 solicitation destination was the MNP-LLA of the LHS
Client, the LHS Proxy/Server instead includes an authentication
signature in the solicitation, then re-encapsulates/re-fragments
with its own ADM-ULA as the source and the MNP-ULA of the LHS Client
as the destination. The LHS Proxy/Server then selects an appropriate
Identification value and *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 solicitation. The LHS Client then creates a NCE for
the solicitation LLA source address in the STALE state. If LHS
FMT-Forward is set, FHS FMT-Forward is clear and the solicitation
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
solicitation OMNI header window synchronization parameters and
Multilink Forwarding Parameters in the NCE corresponding to the
solicitation 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 advertisement - 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 advertisement using exactly the
same procedures as for the LHS Proxy/Server above, except that it
uses its MNP-LLA as the source. The LHS Client also includes an
authentication signature, then encapsulates the advertisement with
source set to its own ADM-ULA and destination set to the ADM-ULA of
the LHS Proxy/Server. The LHS Client then 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 advertisement, verifies the authentication signature,
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 re-encapsulates/re-fragments the advertisement,
sets 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 advertisement 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 solicitation. The FHS/LHS Bridge then
re-encapsulates the solicitation with its own ADM-ULA as the source
and with the ADM-ULA of the FHS Proxy/Server as the destination. If
the FHS and LHS prefixes are different, the FHS Bridge instead
re-encapsulates/re-fragments with its own ADM-ULA as the source and
with the ADM-ULA of the FHS Bridge as the destination. 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
advertisement, 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
advertisement FHS Bridge fields. The FHS Bridge then
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
advertisement 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
advertisement destination is its own ADM-LLA, the FHS Proxy/Server
then caches the advertisement 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 advertisement 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 advertisement 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 in the advertisement message. The FHS
Proxy/Server then re-encapsulates/re-fragments with its own ADM-ULA
as the source, with the MNP-ULA of the FHS Client as the
destination, 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 advertisement
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
advertisement 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 advertisement 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).When either the FHS Client or FHS Proxy/Server needs to return an
NA acknowledgement to complete window synchronization, it prepares
an acknowledgement message with an OMNI Multilink Forwarding
Parameters sub-option with Job code set to "10" (Follow A; Record
B). The FHS node then includes Tunnel Window Synchronization
parameters if necessary and sets the MFVI List to the cached list of
A entries received in the LHS advertisement, but need not set any
other FHS/LHS information. If the FHS node is the Client, it next
includes an authentication signature then encapsulates/fragments
with its own MNP-ULA as the source and 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 to the FHS Proxy/Server. The FHS Proxy/Server then verifies
the Identification, reassembles/decapsulates, verifies the
authentication signature and 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 solicitation.The FHS Proxy/Server then re-encapsulates/re-fragments with 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 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. The FHS Bridge then re-encapsulates/re-fragments
with its own ADM-ULA as the source and the ADM-ULA of the LHS
Proxy/Server as the 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 then selects an appropriate Identification and *NET
headers and 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 source to its own ADM-ULA and 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 NA acknowledgement message.
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 solicitation. 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 in the NA. If the NA
destination is its own ADM-LLA, the LHS Proxy/Server next updates
the NCE for the NA 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
solicitation.If the NA 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,
re-encapsulates/re-fragments with 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 NA acknowledgement, verifies
the authentication signature then processes the message exactly the
same as for the LHS Proxy/Server case above.Following the solicitation/advertisement/acknowledgement
exchange, 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 compressed headers (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 advertisement 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 a compressed OAL 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 employs NAT traversal procedures to enable direct carrier
packet forwarding while bypassing the local Proxy/Server based on
the Client's advertised MFVIs and discovered NATed L2ADDR
information. 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 MVF
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. 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 header with an MNP-ULA source
or a compressed header with an MFVI that matches an MFV, the ingress
encapsulates the carrier packet in a new OAL full or compressed
header with the inner header containing Identification values
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 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 L2ADDR information) while
bypassing the Proxy/Server. 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 L2ADDR
addresses through NAT traversal, they can exchange carrier packets
directly with header compression using MFVIs discovered as above.
The FHS Client will have cached the A MFVI for the LHS Client, which
will have cached the B MVFI for the FHS Client.OMNI interfaces are virtual interfaces configured over one or more
underlying interfaces classified as follows:INET interfaces connect to an INET either natively or through
one or more NATs. Native INET interfaces have global IP addresses
that are reachable from any INET correspondent. The INET-facing
interfaces of Proxy/Servers are native interfaces, as are Relay
and Bridge interfaces. NATed INET interfaces connect to a private
network behind one or more NATs that provide INET access. Clients
that are behind a NAT are required to send periodic keepalive
messages to keep NAT state alive when there are no carrier packets
flowing.ANET interfaces connect to an ANET that is separated from the
open INET by 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.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, 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
Multilink Forwarding Parameters sub-options with different underlying
interface indexes.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 BGP protocol TCP sessions 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 returns an RA
message with corresponding parameters. The RS/RA messages may pass
through one or more NATs in the case of a Client's INET interface.
(Note: if the Client used a Temporary ULA in its initial RS message,
it will discover an MNP-{LLA, ULA} in the corresponding RA that it
receives from the 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 provide 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(WIN) route optimization. When a Bridge creates/updates
a NCE for a local segment Client based on NS/NA(WIN) route
optimization, it also maintains MVFI and L2ADDR state for messages
destined to this local segment Client.Hub 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 location instead. When DepartTime
decrements to 0, the NCE is deleted. It is RECOMMENDED that
DEPART_TIME be set to the default constant value REACHABLE_TIME plus
10 seconds (40 seconds by default) to allow a window for carrier
packets in flight to be delivered while stale route optimization state
may be present.Hub Proxy/Servers act as RORs on behalf of their associated Clients
according to the Proxy Neighbor Advertisement specification in Section
7.2.8 of . When a Hub Proxy/Server ROR
receives an authentic NS(AR) message, it first searches for a NCE for
the target Client and accepts the message only if there is an entry.
The Hub Proxy/Server then returns a solicited NA(AR) message while
creating or updating a "Report List" entry in the target Client's NCE
that caches both the LLA and ULA of ROS with a "ReportTime" variable
set to REPORT_TIME seconds. The ROR resets ReportTime when it receives
a new authentic NS(AR) message, and otherwise decrements ReportTime
while no authentic NS(AR) messages have been received. It is
RECOMMENDED that REPORT_TIME be set to the default constant value
REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow a
window for route optimization to converge before ReportTime decrements
below REACHABLE_TIME.When the ROS receives a solicited NA(AR) message response to its
NS(AR), it 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 message (beginning with a pseudo-header of the IPv6 header) but
does not then proceed to calculate the IPv6 ND message checksum
itself. If the OMNI interface forwards the message to a next hop
over the secured spanning tree path, it omits both the
authentication signature and checksum since lower layers already
ensure authentication and integrity. In all other cases, the OMNI
interface calculates the standard IPv6 ND message checksum 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 Nonce
and/or Timestamp options 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 solicitation message includes a Timestamp
option, the advertisement reply should also include a Timestamp
option.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 only. The
ROS sends an NS(AR) to the solicited-node multicast address of
the target, and the current ROR with addressing information for
the target returns a unicast NA(AR). The NA(AR) contains
current, consistent and authentic target address resolution
information, but only an implicit third-party assertion of
target reachability. NS/NA(AR) messages must be secured.NS/NA(WIN) messages are used for establishing and maintaining
window synchronization state (and/or any other state such as
Interface Attributes). The source sends an NS(WIN) to the
unicast address of the target, and the target returns a unicast
NA(WIN). The NS/NA(WIN) exchange synchronizes the sequence
number windows for Identification values the neighbors will
include in subsequent carrier packets, and asserts reachability
for the target without necessarily testing a specific underlying
interface pair. NS/NA(WIN) messages must be secured.NS/NA(NUD) messages are used for determining 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 be secured but should include an IPv6 ND
message checksum. NS/NA(NUD) messages may also be used in
combination with window synchronization (i.e., NUD+WIN), 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 include state update information must
be secured.NS/NA(DAD) messages are not used in AERO, since Duplicate
Address Detection is not required.Additionally, nodes may send NA/RA messages with the OMNI
option PNG flag set to receive a solicited NA response from the
neighbor. The solicited NA response MUST set the ACK flag (without
also setting the SYN or PNG flags) and include the Identification
used in the PNG message in the Acknowledgement.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(WIN) message
exchanges to maintain send/receive window state in their respective
neighbor cache entries as specified in .The OMNI interface admits original IP packets then acts as an OAL
source to perform OAL encapsulation and fragmentation as specified in
while including a CRH-32 if
necessary as specified in . The OAL
encapsulates original IP packets to form OAL packets subject to
fragmentation, then encapsulates the resulting OAL fragments in *NET
headers as carrier packets.For carrier packets undergoing re-encapsulation at an OAL
intermediate node, the OMNI interface decrements the OAL IPv6 header
Hop Limit and discards the carrier packet if the Hop Limit reaches 0.
The intermediate node next removes the *NET encapsulation headers from
the first segment and re-encapsulates the packet in new *NET
encapsulation headers for the next segment.When an FHS Bridge receives a carrier packet with a compressed
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,
the OMNI interface discards the NET encapsulation headers and
reassembles as discussed in .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 . 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 match, the Client selects one or more
"reachable" neighbor interfaces in the entry for forwarding
purposes. If there is no NCE, the Client instead either enqueues the
original IP packet and invokes route optimization while forwarding
the original IP packet toward an FHS Proxy/Server. The Client
(acting as an OAL source) performs OAL encapsulation and sets the
OAL destination address to the MNP-ULA of the target if there is a
matching NCE; otherwise, it sets the OAL destination to the ADM-ULA
of the FHS Proxy/Server. If the Client has multiple original IP
packets to send to the same neighbor, it can concatenate them in a
single super-packet . The OAL
source then performs fragmentation to create OAL fragments (see:
), appends any *NET encapsulation, and sends
the resulting carrier packets over underlying interfaces to the
neighbor acting as an OAL destination.If the neighbor interface selected for forwarding is located on
the same OMNI link segment and not behind a NAT, the Client forwards
the carrier packets directly according to the L2ADDR information for
the neighbor. If the neighbor interface is behind a NAT on the same
OMNI link segment, the Client instead forwards the initial carrier
packets to the LHS Proxy/Server (while inserting an CRH-32 if
necessary) and initiates NAT traversal procedures. If the Client's
intended source underlying interface is also behind a NAT and
located on the same OMNI link segment, it sends a "direct bubble"
over the interface per to the L2ADDR found in the neighbor cache in
order to establish state in its own NAT by generating traffic toward
the neighbor (note that no response to the bubble is expected).The Client next sends an NS(NUD) message toward the MNP-ULA of
the neighbor via the LHS Proxy/Server as discussed in . If the Client receives an NA(NUD) from the neighbor
over the underlying interface, it marks the neighbor interface as
"trusted" and sends future carrier packets directly to the L2ADDR
information for the neighbor instead of indirectly via the LHS
Proxy/Server. The Client must honor the neighbor cache maintenance
procedure by sending additional direct bubbles and/or NS/NA(NUD)
messages as discussed in in order to keep NAT state alive as long as
carrier packets are still flowing.When 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: When a Client performs an NS/NA(WIN) exchange with a peer
over the spanning tree, MFIB information will be established in all
FHS and LHS intermediate nodes in the path. The Client can then
opportunistically "skip ahead" in the chain of hops to bypass
intermediate nodes that are not required to forward packets. The
Client will have the map of MFVIs held at each hop, and can include
the MFVI for the first hop it visits in a compressed OMNI header or
in a CRH-32 routing header.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 the Proxy/Server receives an original IP packet from the
network layer, it drops the packet if routing indicates that it
should be forwarded back to the network layer to avoid looping.
Otherwise, the Proxy/Server regards the original IP packet the same
as if it had arrived as carrier packets with OAL destination set to
its own ADM-ULA. When the Proxy/Server receives carrier packets on
underlying interfaces with OAL destination set to its own ADM-ULA,
it performs OAL reassembly if necessary to obtain the original IP
packet.The Proxy/Server next searches for a NCE that matches the
original IP destination and proceeds as follows:if the packet is an NA(WIN) message for a local Client NCE,
the Proxy/Server examines the Multilink Forwarding Parameters
information and rewrites the fields if the NA(WIN) was not
already processed by a (local segment) Bridge as discussed in
.else, if the original IP packet destination matches a NCE,
the Proxy/Sever uses one or more "reachable" neighbor interfaces
in the entry for packet forwarding using OAL encapsulation and
fragmentation according to the cached link-layer address
information. If the neighbor interface is in a different OMNI
link segment, the Proxy/Server performs OAL encapsulation and
fragmentation, inserts an CRH-32 if necessary and forwards the
resulting carrier packets via the spanning tree to a Bridge;
otherwise, it forwards the carrier packets directly to the
neighbor via INET encapsulation. If the neighbor is behind a
NAT, this FHS Proxy/Server instead forwards initial carrier
packets via a Bridge (or more directly via an LHS Proxy/Server)
while sending an NS(NUD) to the neighbor. When the Proxy/Server
receives the NA(NUD), it can begin forwarding carrier packets
directly to the neighbor the same as discussed in while sending additional NS(NUD) messages as
necessary to maintain NAT state. Note that no direct bubbles are
necessary since the Proxy/Server is by definition not located
behind a NAT.else, if the original IP destination matches a non-MNP route
in the IP forwarding table or an ADM-LLA assigned to the
Proxy/Server's OMNI interface, the Proxy/Server acting as a
Relay presents the original IP packet to the network layer for
local delivery or IP forwarding.else, the Proxy/Server initiates address resolution as
discussed in , while submitting the
original IP packets for OAL encapsulation and forwarding the
resulting carrier packets into the secured spanning tree subject
to rate limiting.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.FHS Clients maintain a single Hub Proxy/Server and one or more
FHS Proxy/Servers. FHS Clients can forward carrier packets to the
FHS Proxy/Server for a specific outbound underlying interface while
also initiating route optimization, and the FHS Proxy/Server will
reassemble, re-encapsulate and re-fragment then send the resulting
carrier packets into the secured spanning tree subject to rate
limiting while route optimization is in progress. The secured
spanning tree carrier packets will arrive at the Hub LHS
Proxy/Server for an LHS Client, which reassembles, re-encapsulates,
re-fragments and forwards to the LHS Client. Once route optimization
has converged, the FHS and LHS Clients can enact "shortcuts" to
avoid slow-path forwarding of carrier packets over the secured
spanning tree.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
process carrier packets with their ADM-ULA as the destination by
first examining the packet for a CRH-32 header or a compressed OAL
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.Note: Proxy/Servers may receive carrier packets 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. For a full
discussion see: .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 verifies any upper layer
authentication signatures and/or forwards the unsecured message
toward the destination which must apply data origin
authentication.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 secured spanning tree, and may convey other carrier packets via
the 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 CRH-32 header or a compressed OAL 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.Bridges forward carrier packets received from a first segment via
the SRT 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).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 INET on the path to the neighbor or by the neighbor
itself. The message includes an IP header with the address of the node
that generated the error as the source address and with the link-layer
address of the AERO node as the destination address.The IP header is followed by an ICMP header that includes an error
Type, Code and Checksum. Valid type values include "Destination
Unreachable", "Time Exceeded" and "Parameter Problem" . (OMNI interfaces ignore
link-layer IPv4 "Fragmentation Needed" and IPv6 "Packet Too Big"
messages for carrier packets that are no larger than the minimum/path
MPS as discussed in , however these messages
may provide useful hints of probe failures during path MPS
probing.)The ICMP header is followed by the leading portion of the carrier
packet that generated the error, also known as the "packet-in-error".
For ICMPv6, specifies that the
packet-in-error includes: "As much of invoking packet as possible
without the ICMPv6 packet exceeding the minimum IPv6 MTU" (i.e., no
more than 1280 bytes). For ICMPv4, specifies
that the packet-in-error includes: "Internet Header + 64 bits of
Original Data Datagram", however Section
4.3.2.3 updates this specification by stating: "the ICMP datagram
SHOULD contain as much of the original datagram as possible without
the length of the ICMP datagram exceeding 576 bytes".The link-layer error message format is shown in :The AERO node rules for processing these link-layer error
messages are as follows:When an AERO node receives a link-layer Parameter Problem
message, it processes the message the same as described as for
ordinary ICMP errors in the normative references .When an AERO node receives persistent link-layer Time Exceeded
messages, the IP ID field may be wrapping before earlier fragments
awaiting reassembly have been processed. In that case, the node
should begin including integrity checks and/or institute rate
limits for subsequent packets.When an AERO node receives persistent link-layer Destination
Unreachable messages in response to carrier packets that it sends
to one of its neighbor correspondents, the node should process the
message as an indication that a path may be failing, and
optionally initiate NUD over that path. If it receives Destination
Unreachable messages over multiple paths, the node should allow
future carrier packets destined to the correspondent to flow
through a default route and re-initiate route optimization.When an AERO Client receives persistent link-layer Destination
Unreachable messages in response to carrier packets that it sends
to one of its neighbor Proxy/Servers, the Client should mark the
path as unusable and use another path. If it receives Destination
Unreachable messages on many or all paths, the Client should
associate with a new Proxy/Server and release its association with
the old Proxy/Server as specified in .When an AERO Proxy/Server receives persistent link-layer
Destination Unreachable messages in response to carrier packets
that it sends to one of its neighbor Clients, the Proxy/Server
should mark the underlying path as unusable and use another
underlying path.When an AERO Proxy/Server receives link-layer Destination
Unreachable messages in response to a carrier packet that it sends
to one of its permanent neighbors, it treats the messages as an
indication that the path to the neighbor may be failing. However,
the dynamic routing protocol should soon reconverge and correct
the temporary outage.When an AERO Bridge receives a carrier packet for which the
network-layer destination address is covered by an MSP, the Bridge
drops the packet if there is no more-specific routing information for
the destination and returns 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 Router Discovery, Prefix Delegation and Autoconfiguration are
coordinated as discussed in the following Sections.Each AERO Proxy/Server on the OMNI link is configured to
facilitate Client prefix delegation/registration requests. Each
Proxy/Server is provisioned with a database of MNP-to-Client ID
mappings for all Clients enrolled in the AERO service, as well as
any information necessary to authenticate each Client. The Client
database is maintained by a central administrative authority for the
OMNI link and securely distributed to all Proxy/Servers, e.g., via
the Lightweight Directory Access Protocol (LDAP) , via static configuration, etc. Clients receive
the same service regardless of the Proxy/Servers they select.Clients associate each of their underlying interfaces with a FHS
Proxy/Server. Each FHS Proxy/Server may locally service one or more
of the Client's underlying interfaces, and the Client selects one
among them to serve as the Hub Proxy/Server. The Hub Proxy/Server is
responsible for short-term packet forwarding, for acting as a
mobility anchor point and for acting as an ROR for NS(AR) messages
directed to the Client. 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 FHS 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 (see ). The IPv6 ND messages are
exchanged between the Client and Hub Proxy/Server (via any FHS
Proxy/Servers acting as proxies) 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 specify the Client and Proxy/Server
behavior.AERO Clients discover the addresses of candidate FHS
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 a unicast RA response to a multicast/anycast RS as
described below. In the absence of other information, the Client can
resolve the DNS Fully-Qualified Domain Name (FQDN)
"linkupnetworks.[domainname]" where "linkupnetworks" is a constant
text string and "[domainname]" is a DNS suffix for the OMNI link
(e.g., "example.com").To associate with a Hub Proxy/Server over a first underlying
interface, the Client acts as a requesting router to request MNPs by
preparing an RS message with prefix management parameters. If the
Client already knows the Proxy/Server's ADM-LLA, it includes the LLA
as the network-layer destination address; otherwise, the Client
includes link-scoped All-Routers multicast as the network-layer
destination. The Client can use its MNP-LLA as the network-layer
source address and include an OMNI option with prefix registration
information. If the Client does not yet have an MNP-LLA, it instead
sets the network-layer source address to unspecified (::) and
includes prefix delegation parameters in the OMNI option (see: ).The Client next includes an authentication sub-option if
necessary and Multilink Forwarding Parameters corresponding to the
underlying interface over which it will send the RS message. Next,
the Client submits the RS for OAL encapsulation and fragmentation if
necessary with its own MNP-ULA and the Proxy/Server's ADM-ULA or an
OMNI IPv6 anycast address as the OAL addresses while selecting an
Identification value and invoking window synchronization as
specified in .The Client then sends the 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) then
waits up to RetransTimer milliseconds for an RA message reply (see
) (retrying up to
MAX_RTR_SOLICITATIONS). 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 Hub Proxy/Server and
try another FHS Proxy/Server. Otherwise, the Client processes the
prefix information found in the RA message.When the Client processes an RA, it first performs OAL reassembly
and decapsulation if necessary then creates a NCE with the Hub
Proxy/Server's ADM-LLA as the network-layer address and the Hub
Proxy/Server's encapsulation and/or link-layer addresses as the
link-layer address. The Client then caches the Multilink Forwarding
Parameters information. The Client next records the RA Router
Lifetime field value in the NCE as the time for which the Hub
Proxy/Server has committed to maintaining the MNP in the routing
system via this underlying interface, and caches the other RA
configuration information including Cur Hop Limit, M and O flags,
Reachable Time and Retrans Timer. The Client then autoconfigures
MNP-LLAs for any delegated MNPs and assigns them to the OMNI
interface. The Client also caches any MSPs included in Route
Information Options (RIOs) as MSPs to
associate with the OMNI link, and assigns the MTU value in the MTU
option to the underlying interface.The Client then registers its additional underlying interfaces
with FHS Proxy/Servers for those interfaces discovered by sending RS
messages via each additional interface but with the ADM-LLA of the
Hub Proxy/Server as the destination. The additional FHS
Proxy/Servers will assume the proxy role and forward proxyed copies
of the RS/RA exchanges between the Client and Hub Proxy/Server. The
Client finally sub-delegates the MNPs to its attached EUNs and/or
the Client's own internal virtual interfaces as described in to support the Client's
downstream attached "Internet of Things (IoT)". The Client then
sends additional RS messages over each underlying interface before
the Router Lifetime received for that interface expires.After the Client registers its underlying interfaces, it may wish
to change one or more registrations, e.g., if an interface changes
address or becomes unavailable, if 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 Multilink
Forwarding Parameters specific to the selected underlying interface.
When the Client receives the Hub Proxy/Server's RA response, it has
assurance that the Proxy/Server has been updated with the new
information.If the Client wishes to discontinue use of a Hub Proxy/Server it
issues an RS message over any underlying interface with an OMNI
option with a prefix release indication. 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.AERO Proxy/Servers act as both IP routers and IPv6 ND proxies,
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 an FHS 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, the Proxy/Server performs OAL reassembly if
necessary, then decapsulates and authenticates the RS message. If
the RS message destination is link-scoped All-Routers multicast or
the Proxy/Server's own ADM-LLA, the Proxy/Server assumes the Hub
role. If the RS message destination is the ADM-LLA of another node,
the Proxy/Server assumes the proxy role and forwards the RS to the
Hub Proxy/server via the secured spanning tree. (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.)The Hub Proxy/Server then 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. 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 next creates a NCE for the Client using the
base MNP-LLA as the network-layer address. Next, the Hub
Proxy/Server updates the NCE by recording the information in the
Multilink Forwarding Parameters sub-option in the RS OMNI option.
The Hub Proxy/Server also records the actual OAL/*NET addresses and
RS message window synchronization parameters (if any) in the
NCE.Next, the Hub Proxy/Server prepares an RA message using its
ADM-LLA as the network-layer source address and the network-layer
source address of the RS message as the network-layer destination
address. The Hub Proxy/Server sets the Router Lifetime to the time
for which it will maintain both this underlying interface
individually and the NCE as a whole. The Hub Proxy/Server also sets
Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer to
values appropriate for the OMNI link. The Hub Proxy/Server includes
the MNPs, any other prefix management parameters and an OMNI option
with a Multilink Forwarding Parameters sub-option with FHS
addressing information filled out. The Hub Proxy/Server then
includes one or more RIOs that encode the MSPs for the OMNI link,
plus an MTU option (see ). The Hub
Proxy/Server finally forwards the message to the Client using OAL
encapsulation/fragmentation if necessary while including an
acknowledgement if the RS invoked window synchronization.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 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 and returns an NA/RA reply in response to solicitations.
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. Finally, If the NCE is in
the DEPARTED state, the Hub Proxy/Server deletes the entry after
DepartTime expires.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. Although these fragments will have traversed the
secured spanning tree, the security only assures correct reassembly
and does not assure message content security.Note: Clients SHOULD 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.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 coded in the OMNI option.
When the Client receives the RA, it creates a default route,
assigns the Subnet Router Anycast address and sets its MNP-LLA
based on the delegated MNP.Note: See for an MNP
delegation alternative that avoids including a DHCPv6 message
sub-option in the RS. Namely, when the Client requests a single
MNP it can set the RS source to the unspecified address (::) and
include a Node Identification sub-option and Preflen in the OMNI
option (but with no DHCPv6 message sub-option). When the Hub
Proxy/Server receives the RS message, it forwards a self-generated
DHCPv6 Solicit message to the DHCPv6 server on behalf of the
Client. When the Hub Proxy/Server receives the DHCPv6 Reply, it
prepares an RA message with an OMNI option with Preflen
information (but with no DHCPv6 message sub-option), then places
the (newly-created) MNP-LLA in the RA destination address and
returns the message to the Client.OMNI link 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 all of the Client's additional
underlying interfaces. 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 "A" processes a
Client registration, it must either assume the Hub role or forward a
proxyed registration to another FHS Proxy/Server acting as the Hub.
Proxy/Servers satisfy these requirements as follows:when Proxy/Server "A" 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 "A
instead creates one in the STALE state and returns an RA message
with an authentication signature if necessary and any window
synchronization parameters.) Proxy/Server "A" then examines the
network-layer destination address. If the destination address is
the ADM-LLA of a different Proxy/Server "B", Proxy/Server "A"
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 "A" also writes its own
information over the Multilink Forwarding Parameters sub-option
supplied by the Client then sets the S/T-omIndex to the value for
this Client underlying interface, then forwards the message into
the OMNI link secured spanning tree.when Proxy/Server "B" receives the RS, it assume the Hub role
and creates or updates a NCE for the Client with FHS Proxy/Server
"A"'s Multilink Forwarding Parameters as the link-layer address
information for this S/T-omIndex and caches any window
synchronization parameters supplied by the Client. Hub
Proxy/Server "B" then prepares an RA message with source set to
its own LLA and destination set to the Client's MNP-LLA, and with
any window synchronization acknowledgements. Hub Proxy/Server "B"
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
"A, performs fragmentation if necessary, then sends the resulting
carrier packets into the secured spanning tree.when Proxy/Server "A" reassembles the RA, it locates the Client
NCE based on the RA destination LLA. Proxy/Server "A" 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,
includes an authentication signature if necessary, and echoes the
Multilink Forwarding Parameters sub-option. Proxy/Server "A" sets
the P flag in the RA flags field to indicate that the message has
passed through a proxy , 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 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 each FHS Proxy/Server
"A", "A" can send NS, RS and/or unsolicited NA messages to update the
neighbor cache entries of other AERO nodes on behalf of the Client
and/or to convey Multilink Forwarding Parameter updates. This allows
for higher-frequency Proxy-initiated RS/RA messaging over
well-connected INET infrastructure supplemented by lower-frequency
Client-initiated RS/RA messaging over constrained ANET data links.If the Hub Proxy/Server "A" ceases to send solicited RAs,
Proxy/Servers "B", "C", "D" 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 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 Proxy/Server
"A".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. This
can be very beneficial, e.g., if the Client connects to the ANET via
low-end data links such as some aviation wireless links.If the ANET first-hop access router is on the same underlying link
as the Client and recognizes the AERO/OMNI protocol, the Client can
avoid OAL encapsulation for both its control and data messages. When
the Client connects to the link, it can send an unencapsulated RS
message with source address set to its own MNP-LLA (or to a Temporary
LLA), and with destination address set to the ADM-LLA of the Client's
selected Proxy/Server or to link-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
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 IPv6 ND message checksum and/or authentication signature are
invalidated. If the Proxy/Server forwards the message over the secured
spanning tree, however, it need not re-calculate the
checksum/signature since they will not be examined by the next
hop.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 in rapid succession, 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).AERO nodes invoke route optimization when they need to forward
packets to new target destinations. Route optimization is based on
IPv6 ND Address Resolution messaging between a Route Optimization
Source (ROS) and the target Client's 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.The route optimization procedure is conducted between the ROS and
the LHS Hub Proxy/Server/Relay for the target selected by routing as
the ROR. In this arrangement, the ROS is always the Client or
Proxy/Server (or Relay) nearest the source over the selected source
underlying interface, while the ROR is always the target's current Hub
Proxy/Server.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.The procedures are specified in the following sections.When an original IP packet from a source node destined to a
target node arrives, the ROS checks for a 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 invokes the OAL and forwards the resulting carrier
packets into the secured spanning tree, then sends an NS message for
Address Resolution (NS(AR)) to receive a solicited NA(AR) message
from the ROR. While route optimization is in progress, the ROS may
forward additional original IP packets into the secured spanning
tree but if so must impose rate limiting to minimize secured
spanning tree traffic as well as ROR reassembly.The 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 then
selects an Identification value and submits the NS(AR) message for
OAL encapsulation with OAL source set to its own ULA and OAL
destination set to the ULA corresponding to the target. (The ROS
does not include any window synchronization parameters, since it
will not exchange other packet types with the ROR.) The ROS then
sends the resulting carrier packet into the SRT secured spanning
tree without decrementing the network-layer TTL/Hop Limit field.When the ROS is an INET Client, it must instead forward the
resulting carrier packet to the ADM-ULA of one of its current
Proxy/Servers. The Proxy/Server then verifies the NS(AR)
authentication signature, then re-encapsulates with the OAL source
set to its own ADM-ULA and OAL destination set to the ULA
corresponding to the target and forwards the resulting carrier
packets into the secured spanning tree on behalf of the Client.When the Bridge receives the carrier packet containing the RS
from the ROS, it discards the *NET headers and determines the next
hop by consulting its standard IPv6 forwarding table for the OAL
header destination address. The Bridge then decrements the OAL
header Hop-Limit, then re-encapsulates and forwards the carrier
packet(s) via the secured spanning tree the same as for any IPv6
router, where it may traverse multiple OMNI link segments. The
final-hop Bridge will deliver the carrier packet via the secured
spanning tree to the ROR for the target.When the ROR for the target receives the secured carrier packet,
it examines the NS(AR) target to determine whether it has a matching
NCE and/or non-MNP route. If there is no match, the ROR drops the
message. Otherwise, the ROR continues processing as follows:if the NS(AR) target matches a Client NCE in the DEPARTED
state, the ROR re-encapsulates while setting the OAL source to
the ULA of the ROS and OAL destination address to the ADM-ULA of
the Client's new Proxy/Server. The ROR then forwards the
resulting carrier packet over the secured spanning tree then
returns from processing.If the NS(AR) target matches the MNP-LLA of a Client NCE in
the REACHABLE state, the ROR notes whether the NS (AR) arrived
from the secured spanning tree then provides route optimization
information on behalf of the Client. If the message arrived via
the secured spanning tree the ROR need not perform further
authentication; otherwise, it must verify the message
authentication signature before accepting.If the NS(AR) target matches one of its non-MNP routes, the
ROR serves as both a Relay and a route optimization target,
since the Relay forwards IP packets toward the (fixed network)
target at the network layer.The ROR next checks the target NCE for a Report List entry that
matches the NS(AR) source LLA/ULA of the ROS. If there is a Report
List entry, the ROR refreshes ReportTime for this ROR; otherwise,
the ROR creates a new entry for the ROS and records both the LLA and
ULA.The ROR then prepares a (solicited) NA(AR) message to return to
the ROS with the source address set to its own ADM-LLA, the
destination address set to the NS(AR) LLA source address and the
Target Address set to the target Client's MNP-LLA. The ROR includes
an OMNI option with Preflen set to the prefix length associated with
the NA(AR) source address, with S/T-omIndex set to the value that
appeared in the NS(AR) and with Interface Attributes sub-options for
all of the target's underlying interfaces with current information
for each interface.For each Interface Attributes sub-option, the ROR sets the L2ADDR
according to its own INET address for VPNed, Direct, ANET and NATed
Client interfaces, or to the Client's INET address for native Client
interfaces. The ROR then includes the lower 32 bits of its ADM-ULA
as the LHS, encodes the ADM-ULA SRT prefix length in the SRT field
and sets FMT as specified in .The ROR then sets the NA(AR) message R flag to 1 (as a router)
and S flag to 1 (as a response to a solicitation) and sets the O
flag to 0 (as a proxy). The ROR finally submits the NA(AR) for OAL
encapsulation with source set to its own ULA and destination set to
the same ULA that appeared in the NS(AR) OAL source, then performs
OAL encapsulation using the same Identification value that appeared
in the NS(AR) and finally forwards the resulting (*NET-encapsulated)
carrier packet via the secured spanning tree without decrementing
the network-layer TTL/Hop Limit field.When the Bridge receives NA(AR) carrier packet from the ROR, it
discards the *NET header and determines the next hop by consulting
its standard IPv6 forwarding table for the OAL header destination
address. The Bridge then decrements the OAL header Hop-Limit,
re-encapsulates the carrier packet and forwards it via the 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) ADM-{LLA,ULA} source addresses as the
addresses of the ROR. If the ROS receives additional NA(AR) or uNA
messages for this target Client with the same ADM-LLA source address
but a different ADM-ULA source address, it configures the ADM-LLA
corresponding to the new ADM-ULA, then caches the new ADM-{LLA,ULA}
and deprecates the former ADM-{LLA,ULA}.When the ROS is a Client, the SRT secured spanning tree will
first deliver the solicited NA(AR) message to the local
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 unmodified NA(AR);
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.After the ROS receives the route optimization NA(AR) and updates
the target NCE, it sends additional NS(AR) messages to the ADM-ULA
of the ROR to refresh the NCE ReachableTime before expiration while
it still has sustained interest in this target. While the NCE
remains REACHABLE, the ROS can forward packets along paths that use
best underlying interface pairs based on local preferences and
target Interface Attributes. The ROS selects target underlying
interfaces according to traffic selectors and/or any other traffic
discriminators, but must first establish window synchronization
state for each target if necessary.The ROS initiates window synchronization through a secured uncast
NS/NA(WIN) exchange as specified in . The
NS/NA(WIN) exchange is conducted over a first underlying interface
pair and registers only those interfaces. If the ROS and target have
additional underlying interface pairs serviced by the same
source/destination LLAs, they may register new interfaces by sending
additional NS/NA(WIN) messages but need not include window
synchronization parameters. If the ROS and target have additional
underlying interface pairs services by different source/destination
LLAs, they must include window synchronization parameters when they
send NS/NA(WIN) messages to establish NCE state for the new
source/destination LLAs.After window synchronization state has been established, the ROS
and target Client can begin forwarding carrier packets while
performing additional NS/NA(WIN) exchanges as above to update window
state, register new interfaces and/or test reachability. The ROS
sends carrier packets to the FHS Bridge discovered through the
NS/NA(WIN) exchange which verifies the Identification is in window
for the target Client. 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(WIN) exchange applies for all interfaces regardless of the
(single) interface used to conduct the exchange. However, the window
synchronization exchange only confirms target Client reachability
over the specific interface used to conduct the exchange.
Reachability for other underlying interfaces that share the same
window synchronization state must be determined individually using
NS/NA(NUD) messages which need not be secured as long as they use
in-window Identifications and do not update other state
information.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 for
NS/NA(WIN)) 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.When an ROR directs an ROS to a target neighbor with one or more
link-layer addresses, the ROS probes each unsecured target underlying
interface either proactively or on-demand of carrier packets directed
to the path by multilink forwarding to maintain the interface's state
as reachable. Probing is performed 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 ROS can optionally continue
to forward carrier packets via alternate interfaces and/or maintain a
small queue of carrier packets until target reachability is
confirmed.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 ROS and
either the ADM-LLA of the LHS Proxy/Server or the MNP-LLA of the
target itself. The ROS encapsulates the NS(NUD) message the same as
described in and sets the NS(NUD) OMNI header
S/T-omIndex to identify the underlying interface used for forwarding
(or to 0 if any underlying interface can be used). The ROS then
fragments the OAL packet and forwards the resulting carrier packets
into the unsecured spanning tree or via direct encapsulation for local
segment targets.When the target receives the NS(NUD) carrier packets, it verifies
that it has a NCE for this ROS and that the Identification is
in-window, then submits the carrier packets for reassembly. The node
then verifies the authentication signature or checksum, then searches
for Interface Attributes in its NCE for the ROS that match the NS(NUD)
S/T-omIndex for the NA(NUD) reply. The node then prepares the NA(NUD)
with the source and destination LLAs reversed, encapsulates and sets
the OAL source and destination, sets the NA(NUD) S/T-omIndex to the
index 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 ROS and performs
fragmentation. The node then forwards the carrier packets into the
unsecured spanning tree, directly to the ROS if it is in the local
segment or directly to a Bridge in the local segment.When the ROS receives the NA(NUD), it marks the target underlying
interface tested as "reachable". 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 states "reachable" and otherwise while the NCE state as a
whole remains REACHABLE.Note also that the exchange of NS/NA(NUD) messages has the useful
side-benefit of opening holes in NATs that may be useful for NAT
traversal. For example, a Client that discovers the address of a
Bridge on the local SRT segment during an NS/NA(WIN) exchange with a
peer that established MFIB state can send an NS(NUD) message directly
to the INET address of the Bridge while including an authentication
signature. The NS(NUD) will open a hole in any NATs on the path from
the Client to the Bridge, and the Bridge can verify the authentication
signature before returning a direct NA(NUD) to the Client's NATed
L2ADDR while also including an authentication signature. Future
carrier packets exchanged between the Client and peer can then be
forwarded directly via the Bridge while bypassing the Client's FHS
Proxy/Server.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 ROR, default routing and mobility anchor
point services for their dependent Clients, while FHS Proxy/Servers
provide a proxy conduit between the Client and the Hub. 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 with this new information while 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 accommodate Client mobility and/or multilink change events
by sending secured uNA messages to each ROS in the target Client's
Report List. When an ROR sends a uNA message, it sets the IPv6
source address to the its own ADM-LLA, sets the destination address
to the ROS LLA (i.e., an MNP-LLA if the ROS is a Client and an
ADM-LLA if the ROS is a Proxy/Server) and sets the Target Address to
the Client's MNP-LLA. The ROR also includes an OMNI option with
Preflen set to the prefix length associated with the Client's
MNP-LLA, with Interface Attributes for the target Client's
underlying interfaces and with the OMNI header S/T-omIndex set to 0.
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 ADM-ULA and destination set to the ROS ULA (i.e., the
ADM-ULA of the ROS Proxy/Server) and sends the message 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 can optionally send up to
MAX_NEIGHBOR_ADVERTISEMENT uNAs to each ROS to increase the
likelihood that at least one will be received. Alternatively, the
ROR can set the PNG flag in the uNA OMNI option header to request a
solicited NA acknowledgement as specified in .When the ROS Proxy/Server receives a uNA message prepared as
above, it ignores the message if the OAL destination is not its own
ADM-ULA. If the uNA destination was its own ADM-LLA, the ROS
Proxy/Server uses the included OMNI option information to update its
NCE for the target but does not reset ReachableTime since the
receipt of an unsolicited NA message from the ROR does not provide
confirmation that any forward paths to the target Client are
working. If the destination was the MNP-LLA of the ROS Client, the
Proxy/Server instead re-encapsulates with the OAL source set to its
own ADM-ULA, OAL destination set to the MNP-ULA of the ROS Client
with an authentication signature if necessary, and with an in-window
Identification for this Client. Finally, if the uNA message PNG flag
was set, the ROS returns a solicited NA acknowledgement as specified
in .In addition to sending uNA messages to the current set of ROSs
for the target Client, the ROR also sends uNAs to the former
Proxy/Server associated with the underlying interface for which the
link-layer address has changed. These uNA messages update former
Proxy/Servers that cannot easily detect (e.g., without active
probing) when a formerly-active Client has departed. When the ROR
sends the uNA, it sets the source address to its ADM-LLA, sets the
destination address to the former Proxy/Server's ADM-LLA, and sets
the Target Address to the Client's MNP-LLA. The ROR also includes an
OMNI option with Preflen set to the prefix length associated with
the Client's MNP-LLA, with Interface Attributes for the changed
underlying interface, and with the OMNI header S/T-omIndex set to 0.
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 ADM-ULA and destination set to the ADM-ULA of the former
Proxy/Server and sends the message into the secured spanning
tree.When a Client needs to change its underlying Interface Attributes
(e.g., due to a mobility event), the Client sends an RS message to
its Hub Proxy/Server (i.e., the ROR) via a first-hop FHS
Proxy/Server, if necessary. The RS includes an OMNI option with a
Multilink Forwarding Parameters sub-option with the new link quality
and address information. Note that the first FHS Proxy/Server may
change due to the underlying interface change; any stale state in
former FHS Proxy/Servers 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.When the Proxy/Server receives the Client's changes, it sends uNA
messages to all nodes in the Report List the same as described in
the previous section.When a Client needs to bring new underlying interfaces into
service (e.g., when it activates a new data link), it sends an RS
message to the Hub Proxy/Server via a FHS Proxy/Server for the
underlying interface (if necessary) with an OMNI option that
includes Multilink Forwarding Parameters with appropriate link
quality values and with link-layer address information for the new
link.When a Client needs to deactivate an existing underlying
interface, it sends an RS message to an FHS Proxy/Server with an
OMNI option with appropriate Multilink Forwarding Parameter 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 RS messages over an underlying
interface other than the one being deactivated, it MUST include
Interface Attributes with appropriate link quality values for any
underlying interfaces being deactivated.Note that when a Client deactivates an underlying interface,
neighbors that have received the RS/uNA messages need not purge all
references for the underlying interface from their neighbor cache
entries. The Client may reactivate or reuse the underlying interface
and/or its 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 an FHS Proxy/Server receives the Client's RS message
destined to a new Hub Proxy/Server, it forwards the RS and also
sends uNA messages to inform the old Hub Proxy/Server that the
Client has DEPARTED. The FHS Proxy/Server sets the uNA source to the
ADM-LLA of the new Hub Proxy/Server, sets the destination to the
ADM-LLA of the old Hub Proxy/Server, sets the OAL source to its own
ADM-ULA and sets the OAL destination to the ADM-ULA of the old Hub
Proxy/Server. The FHS Proxy/Server then submits the uNA for OAL
encapsulation and fragmentation, then forwards the resulting carrier
packets into the secured spanning tree.When the old Hub Proxy/Server receives the uNA, it changes the
Client's NCE state to DEPARTED, sets the interface attributes
information for the Client to point to the new Hub Proxy/Server, and
resets DepartTime. After a short delay (e.g., 2 seconds) the old Hub
Proxy/Server withdraws the Client's MNP from the routing system.
After DepartTime expires, the old Hub Proxy/Server deletes the
Client's NCE.The old Hub Proxy/Server also iteratively sends uNA messages to
each ROS in the Client's Report List with its own ADM-LLA as the
source and the LLA of the ROS as the destination. The old
Proxy/Server then encapsulates the uNA with OAL source address set
to the ADM-ULA of the new Hub Proxy/Server and OAL destination
address set to the ADM-ULA of the ROS Proxy/Server and sends the
carrier packets over the secured spanning tree. When the ROS
Proxy/Server receives the uNA, it forwards the message to the ROS
Client if the destination is an MNP-LLA. The ROS then examines the
uNA Target Address to locate the target Client's NCE and the ADM-LLA
source address to identify the old Hub Proxy/Server. The ROS then
caches the ULA source address as the ADM-{LLA/ULA} for the new Hub
Proxy/Server for this target NCE and marks the entry as STALE. While
in the STALE state, the ROS sends new NS(AR) messages using its own
ULA as the OAL source and the ADM-ULA of the new Hub Proxy/Server as
the OAL destination address. The new Hub Proxy/Server will then
process the NS(AR) and return an NA(AR) response.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 Proxy/Server then acts as an ROS to send NS(AR)
messages to an ROR. Clients on INET and ANET underlying interfaces
without native multicast services instead send NS(AR) messages as an
ROS to cause their 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(WIN) 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(WIN)
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(WIN) 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(WIN) 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(WIN) message with its own LLA as the source
address and the LLA for R as the destination address, then
encapsulates the NS(WIN) 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.AERO Clients that connect to the open Internet via INET interfaces
can establish a VPN or direct link to securely connect to a FHS/Hub
Proxy/Server in a "tethered" arrangement with all of the Client's
traffic transiting the Proxy/Server which acts as a router.
Alternatively, the Client can associate with an INET FHS/Hub
Proxy/Server using UDP/IP encapsulation and control message securing
services as discussed in the following sections.When a Client's OMNI interface enables an INET underlying
interface, it first examines the INET address. For IPv4, the Client
assumes it is on the open Internet if the INET address is not a
special-use IPv4 address per . Similarly for
IPv6, the Client assumes it is on the open Internet if the INET
address is a Global Unicast Address (GUA) .
Otherwise, the Client should assume it is behind one or several
NATs.The Client then prepares an RS message with IPv6 source address set
to its MNP-LLA, with IPv6 destination set to link-scoped All-Routers
multicast and with an OMNI option with underlying interface
attributes. If the Client believes that it is on the open Internet, it
SHOULD include its IP address and UDP port number in the Multilink
Forwarding Parameters sub-option corresponding to the underlying
interface. If the underlying address is IPv4, the Client includes the
Port Number and IPv4 address written in obfuscated form as discussed in . If the
underlying interface address is IPv6, the Client instead includes the
Port Number and IPv6 address in obfuscated form. The Client finally
includes an authentication signature per to provide message authentication,
selects an Identification value and window synchronization parameters,
and submits the RS for OAL encapsulation. The Client then encapsulates
the OAL atomic fragment in UDP/IP headers to form a carrier packet,
sets the UDP/IP source to its INET address and UDP port, sets the
UDP/IP destination to the FHS Proxy/Server's INET address and the AERO
service port number (8060), then sends the carrier packet to the
Proxy/Server.When the FHS Proxy/Server receives the RS, it discards the OAL
encapsulation, authenticates the RS message, and examines the
destination address. If the destination is the ADM-LLA of another
Proxy/Server, the FHS Proxy/Server assumes the proxy role and forwards
the message into the secured spanning tree. If the destination is its
own ADM-LLA, the FHS Proxy/Server instead assumes the Hub role,
creates a NCE and registers the Client's MNP, window synchronization
state and INET interface information according to the OMNI option
parameters. (If the destination is link-scoped All-Routers multicast,
the FHS Proxy/Server can assume either the proxy or Hub role.)If the Multilink Forwarding Paramters sub-option includes a
non-zero L2ADDR, the Hub Proxy/Server compares the encapsulation IP
address and UDP port number with the (unobfuscated) values. If the
values are the same, the Hub Proxy/Server caches the Client's
information as an "INET" address meaning that the Client is likely to
accept direct messages without requiring NAT traversal exchanges. If
the values are different (or, if the OMNI option did not include an
L2ADDR) the Hub Proxy/Server instead caches the Client's information
as a "mapped" address meaning that NAT traversal exchanges may be
necessary.The Hub Proxy/Server then prepares an RA message with IPv6 source
and destination set corresponding to the addresses in the RS, and with
an OMNI option with an Origin Indication sub-option per with the mapped and obfuscated Port
Number and IP address observed in the encapsulation headers. The
Proxy/Server also includes a Multilink Forwarding Parameters
sub-option, an authentication signature sub-option per and/or a symmetric window
synchronization/acknowledgement if necessary. The Hub Proxy/Server
then performs OAL encapsulation then encapsulates the carrier packet
in UDP/IP headers with addresses set per the L2ADDR information in the
NCE for the Client.When the Client receives the RA, it authenticates the message then
process the window synchronization/acknowledgement and compares the
mapped Port Number and IP address from the Multilink Forwarding
Parameters sub-option with its own address. If the addresses are the
same, the Client assumes the open Internet / Cone NAT principle; if
the addresses are different, the Client instead assumes that further
qualification procedures are necessary to detect the type of NAT and
performs NAT traversal on-demand according to standard procedures
. The Client also
caches the RA rest of the Multilink Forwarding Parameters information
to discover the FHS Proxy/Server's local spanning tree segment. The
Client finally arranges to return an explicit/implicit
acknowledgement, and sends periodic RS messages to receive fresh RA
messages before the Router Lifetime received on each INET interface
expires.When the Client sends messages to target IP addresses, it also
invokes route optimization per . For route
optimized targets in the same OMNI link segment, if the target's
L2ADDR is on the open INET, the Client forwards carrier packets
directly to the target INET address. If the target is behind a NAT,
the Client first establishes NAT state for the L2ADDR using the
"direct bubble" and NS/NA(NUD) mechanisms discussed in . The Client continues to send carrier packets via the
local Bridge discovered during window synchronization until NAT state
is populated, then begins forwarding carrier packets via the direct
path through the NAT to the target. For targets in different OMNI link
segments, the Client forwards carrier packets to the local Bridge.The Client can send original IP packets to route-optimized
neighbors in the same OMNI link segment no larger than the
minimum/path MPS in one piece and with OAL encapsulation as atomic
fragments. For larger original IP packets, the Client applies OAL
encapsulation then fragments if necessary according to , with OAL header with source set to its own MNP-ULA
and destination set to the MNP-ULA of the target, and with an
in-window Identification value. The Client then encapsulates each
resulting carrier packet in UDP/IP *NET headers and sends them to the
neighbor.INET Clients exchange NS/NA(WIN) messages to associate with a new
peer as discussed in . The exchange
establishes MFIB state in the Client, peer and all OMNI intermediate
nodes in the path. After MFIB state is established, INET Clients and
peers can exchange carrier packets with compressed headers that
include an MFVI which is updated on a hop-by-hop basis, while
employing "shortcuts" to skip any unnecessary hops.Note: The NAT traversal procedures specified in this document are
applicable for Cone, Address-Restricted and Port-Restricted NATs only.
While future updates to this document may specify procedures for other
NAT variations (e.g., hairpinning and various forms of Symmetric
NATs), it should be noted that continuous communications are always
possible through Proxy/Server forwarding even for these other NAT
variations.In some use cases, it is desirable, beneficial and efficient for
the Client to receive a constant MNP that travels with the Client
wherever it moves. For example, this would allow air traffic
controllers to easily track aircraft, etc. In other cases, however
(e.g., intelligent transportation systems), the MN may be willing to
sacrifice a modicum of efficiency in order to have time-varying MNPs
that can be changed every so often to defeat adversarial tracking.The DHCPv6 service offers a way for Clients that desire
time-varying MNPs to obtain short-lived prefixes (e.g., on the order
of a small number of minutes). In that case, the identity of the
Client would not be bound to the MNP but rather to a Node
Identification value (see: ) to
be used as the Client ID seed for MNP prefix delegation. The Client
would then be obligated to renumber its internal networks whenever its
MNP (and therefore also its MNP-LLA) changes. This should not present
a challenge for Clients with automated network renumbering services,
however presents limits for the durations of ongoing sessions that
would prefer to use a constant address.An early AERO implementation based on OpenVPN (https://openvpn.net/)
was announced on the v6ops mailing list on January 10, 2018 and an
initial public release of the AERO proof-of-concept source code was
announced on the intarea mailing list on August 21, 2015.AERO Release-3.2 was tagged on March 30, 2021, and is undergoing
internal testing. Additional internal releases expected within the
coming months, with first public release expected end of 1H2021.Many AERO/OMNI functions are implemented and undergoing final
integration. OAL fragmentation/reassembly buffer management code has
been cleared for public release and will be presented at the June 2021
ICAO mobility subgroup meeting.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(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.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 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 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 proxies. 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 route optimization source (ROS) creating a NCE for the
target neighbor. 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.<< RFC Editor - remove prior to publication >>Changes from draft-templin-6man-aero-21 to
draft-templin-6man-aero-22:That's it, folks.Changes from draft-templin-6man-aero-20 to
draft-templin-6man-aero-21:Major updates to Hub-and-Spokes Proxy/Server coordination.Changes from draft-templin-6man-aero-19 to
draft-templin-6man-aero-20:Major updates especially in Section 3.2.7.Changes from draft-templin-6man-aero-18 to
draft-templin-6man-aero-19:Major revision update for review.Changes from draft-templin-6man-aero-17 to
draft-templin-6man-aero-18:Interim version with extensive new text - cleanup planned for
next release.Changes from draft-templin-6man-aero-16 to
draft-templin-6man-aero-17:Final editorial review pass resulting in multiple changes.
Document now submit for final approval (with reference to rfcdiff
from previous version).Changes from draft-templin-6man-aero-15 to
draft-templin-6man-aero-16:Final editorial review pass resulting in multiple changes.
Document now submit for final approval (with reference to rfcdiff
from previous version).Changes from draft-templin-6man-aero-14 to
draft-templin-6man-aero-15:Final editorial review pass resulting in multiple changes.
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draft-templin-6man-aero-13:Final editorial review pass resulting in multiple changes.
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draft-templin-6man-aero-12:Final editorial review pass resulting in multiple changes.
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from previous version).Changes from draft-templin-6man-aero-10 to
draft-templin-6man-aero-11:Final editorial review pass resulting in multiple changes.
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from previous version).Changes from draft-templin-6man-aero-09 to
draft-templin-6man-aero-10:Final editorial review pass resulting in multiple changes.
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from previous version).Changes from draft-templin-6man-aero-08 to
draft-templin-6man-aero-09:Final editorial review pass resulting in multiple changes.
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from previous version).Changes from draft-templin-6man-aero-07 to
draft-templin-6man-aero-08:Final editorial review pass resulting in multiple changes.
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from previous version).Changes from draft-templin-6man-aero-06 to
draft-templin-6man-aero-07:Final editorial review pass resulting in multiple changes.
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from previous version).Changes from draft-templin-6man-aero-05 to
draft-templin-6man-aero-06:Final editorial review pass resulting in multiple changes.
Document now submit for final approval.Changes from draft-templin-6man-aero-04 to
draft-templin-6man-aero-05:Changed to use traffic selectors instead of the former multilink
selection strategy.Changes from draft-templin-6man-aero-03 to
draft-templin-6man-aero-04:Removed documents from "Obsoletes" list.Introduced the concept of "secured" and "unsecured" spanning
tree.Additional security considerations.Additional route optimization considerations.Changes from draft-templin-6man-aero-02 to
draft-templin-6man-aero-03:Support for extended route optimization from ROR to target over
target's underlying interfaces.Changes from draft-templin-6man-aero-01 to
draft-templin-6man-aero-02:Changed reference citations to "draft-templin-6man-omni".Several important updates to IPv6 ND cache states and route
optimization message addressing.Included introductory description of the "6M's".Updated Multicast specification.Changes from draft-templin-6man-aero-00 to
draft-templin-6man-aero-01:Changed category to "Informational".Updated implementation status.Changes from earlier versions to
draft-templin-6man-aero-00:Established working baseline reference.