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 unique-local address format for
IPv6 Neighbor Discovery (IPv6 ND) messaging over the OMNI virtual link.
Router discovery and neighbor coordination are employed for network
admission and to manage the OMNI link forwarding and routing systems.
Secure multilink operation, mobility management, multicast, traffic path
selection and route optimization are naturally supported through dynamic
neighbor cache updates. AERO is a widely-applicable mobile
internetworking service especially well-suited to aviation, 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 manifested by
IPv6 encapsulation and configured over a network-of-networks
concatenation of underlay Internetworks. Nodes on the link can exchange
original IP packets or parcels as single-hop neighbors on the
link - both IP protocol versions (IPv4 and IPv6) are supported. The OMNI
Adaptation Layer (OAL) supports multilink operation for increased
reliability and path optimization while providing fragmentation and
reassembly services to support improved performance and Maximum
Transmission Unit (MTU) diversity. This specification provides a
mobility service architecture companion to the OMNI specification.The AERO service connects Hosts and Clients as OMNI link neighbors
via Proxy/Servers and Relays as intermediate nodes as necessary; AERO
further provides Gateways that interconnect diverse Internetworks as
OMNI link segments through OAL forwarding at a layer below IP. Each
node's OMNI interface uses an IPv6 unique-local address format that
supports operation of the IPv6 Neighbor Discovery (IPv6 ND) protocol
. A Client's OMNI interface can be configured
over multiple underlay interfaces, and therefore appears as a single
interface with multiple link-layer addresses. Each link-layer address is
subject to change due to mobility and/or multilink fluctuations, and
link-layer address changes are signaled by ND messaging the same as for
any IPv6 link.AERO provides a secure cloud-based service where mobile node Clients
may use Proxy/Servers acting as proxys and/or designated routers while
fixed nodes may use any Relay on the link for efficient communications.
Fixed nodes forward original IP packets/parcels 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 using stable IP Addresses not subject to dynamic
fluctuations.AERO Gateways peer with Proxy/Servers in a secured private BGP
overlay routing instance to establish a Segment Routing Topology (SRT)
spanning tree over the underlay Internetworks of one or more disjoint
administrative domains concatenated 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 underlay Internetworks to
(mobile or fixed) nodes on the OMNI link. From the perspective of
underlay Internetworks, each Relay appears as the source of a route to
the MSP; hence uplink traffic to mobile nodes is naturally routed to the
nearest Relay.AERO can be used with OMNI links that span private-use Internetworks
and/or public Internetworks such as the global Internet. In both cases,
Clients may be located behind Network Address Translators (NATs) on the
path to their associated Proxy/Servers. A means for robust traversal of
NATs while avoiding "triangle routing" and critical infrastructure
traffic concentration through a service known as "route optimization" 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 "6 M's" of modern Internetworking, including:Multilink – a mobile node’s ability to coordinate
multiple diverse underlay data links as a single logical unit (i.e.,
the OMNI interface) to achieve the required communications
performance and reliability objectives.Multinet – the ability to span the OMNI link over a segment
routing topology with multiple diverse administrative domain network
segments while maintaining seamless end-to-end communications
between mobile Clients and correspondents such as air traffic
controllers, fleet administrators, other mobile Clients, 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 underlay 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/parcels of
various robust sizes between peers without loss due to a link size
restriction, and to dynamically adjust packet/parcel 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 in conjunction with
the OMNI extensions specified in .a networking service
for delegating IPv6 prefixes to nodes on the link. The nominal
service is DHCPv6 , however alternate
services (e.g., based on IPv6 ND messaging) are also in scope. A
minimal form of prefix delegation known as "prefix registration" can
be used if the Client knows its prefix in advance and can represent
it in the source address of an IPv6 ND message.The Data Link layer in the OSI network
model. Also known as "layer-2", "link-layer", "sub-IP layer",
etc.The Network layer in the OSI network
model. Also known as "layer-3", "IP layer", etc.A mid-layer that adapts L3
to a diverse collection of L2 underlay interfaces and their
encapsulations. (No layer number is assigned, since numbering was an
artifact of the legacy reference model that need not carry forward
in the modern architecture.) The adaptation layer sees the upper
layer as "L3" and sees all lower layer encapsulations as "L2
encapsulations", which may include UDP, IP and true link-layer
(e.g., Ethernet, etc.) headers.a connected network
region (e.g., an aviation radio access network, satellite service
provider network, cellular operator network, WiFi network, etc.)
that joins Clients to the Mobility Service. Physical and/or data
link level security is assumed, and sometimes referred to as
"protected spectrum". Private enterprise networks and ground domain
aviation service networks may provide multiple secured IP hops
between the Client's point of connection and the nearest
Proxy/Server.a connected network
region with a coherent IP addressing plan that provides transit
forwarding services between ANETs and AERO/OMNI nodes that
coordinate with the Mobility Service over unprotected media. No
physical and/or data link level security is assumed, therefore
security must be applied by upper layers. The global public Internet
itself is an example.a simple or complex
"downstream" network that travels with the Client as a single
logical unit. The ENET could be as simple as a single link
connecting a single Host, or as complex as a large network with many
links, routers, bridges and Hosts. The ENET could also provide an
"upstream" link in a recursively-descending chain of additional
Clients and ENETs. In this way, an ENET of an upstream Client is
seen as the ANET of a downstream Client.a node's attachment to a
link in an {A,I,E}NET.an ANET/INET/ENET
network/interface over which an OMNI interface is configured. The
OMNI interface is seen as a network layer (L3) interface by the IP
layer, and the OMNI adaptation layer sees the underlay interface as
a data link layer (L2) interface. The underlay interface either
connects directly to the physical communications media or
coordinates with another node where the physical media is
hosted.the same as defined in . The OMNI link employs IPv6
encapsulation to traverse intermediate
nodes in a spanning tree over underlay network 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 underlay network hops; AERO nodes can employ
Segment Routing to navigate between
different OMNI links, and/or to cause packets/parcels to visit
selected waypoints within the same OMNI link.an OMNI interface
sublayer service that encapsulates original IP packets/parcels
admitted into the interface in an IPv6 header and/or subjects them
to fragmentation and reassembly. The OAL is also responsible for
generating MTU-related control messages as necessary, and for
providing addressing context for spanning multiple segments of an
extended OMNI link.a node's attachment to an OMNI
link (i.e., the same as defined in ). 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 .frequently, underlay
networks 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 partition is seen as a
separate OMNI link segment as discussed throughout this
document.)the OMNI protocol
encapsulation of OAL packets/fragments in an outer header or headers
to form carrier packets that can be routed within the scope of the
local {A,I,E}NET underlay network partition. Common L2 encapsulation
combinations include UDP/IP/Ethernet, etc. using a port/protocol/type
number for OMNI.an address that appears
in the L2 encapsulation for an underlay interface and also in
IPv6 ND message OMNI options. L2ADDR can be either an IP address for
IP encapsulations or an IEEE EUI address for
direct data link encapsulation. (When UDP/IP encapsulation is used,
the UDP port number is considered an ancillary extension of the IP
L2ADDR.)a whole IP
packet/parcel 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/parcel
encapsulated in an OAL IPv6 header before OAL fragmentation, or
following OAL reassembly.a portion of an OAL packet
following fragmentation but prior to L2 encapsulation, or following
L2 decapsulation but prior to OAL reassembly.an OAL packet that can
be forwarded without fragmentation, but still includes a Fragment
Header with a valid Identification value and with Fragment Offset
and More Fragments both set to 0.an encapsulated OAL
fragment following L2 encapsulation or prior to L2 decapsulation.
OAL sources and destinations exchange carrier packets over underlay
interfaces, and may be separated by one or more OAL intermediate
nodes. OAL intermediate nodes re-encapsulate OAL packets/fragments
during forwarding by removing the L2 headers of the previous hop
underlay network and replacing them with new L2 headers for the
next hop underlay network.an OMNI interface acts as an OAL
source when it encapsulates original IP packets/parcels to form OAL
packets, then performs OAL fragmentation and L2 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/parcel.an OMNI interface acts
as an OAL intermediate node when it removes the L2 headers of
carrier packets received from a previous hop, then re-encapsulates
the enclosed OAL packets/fragments in new L2 headers and sends
them to the next hop. OAL intermediate nodes decrement the OAL Hop
Limit during forwarding, and discard the OAL packet/fragment if the
Hop Limit reaches 0. OAL intermediate nodes do not decrement the
TTL/Hop Limit of the original IP packet/parcel.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.the least
significant 64 bits of an IPv6 address, as specified in the IPv6
addressing architecture .an IPv6 address
beginning with fe80::/64 per the IPv6 addressing architecture and with either a 64-bit MNP (LLA-MNP) or a
56-bit random value (LLA-RND) encoded in the IID as specified in
.an IPv6 address
beginning with fd00::/8 followed by a 40-bit Global ID followed by a
16-bit Subnet ID per and with either a
64-bit MNP (ULA-MNP) or a 56-bit random value (ULA-RND) encoded in
the IID as specified in .
(Note that specifies a second form of ULAs
based on the prefix fc00::/8, which are referred to as "ULA-C"
throughout this document to distinguish them from the ULAs defined
here.)a ULA beginning
with fd00::/16 followed by a 48-bit randomly-initialized value
followed by an MNP-based (TLA-MNP) or random (TLA-RND) IID as
specified in . Clients use
TLAs to bootstrap autoconfiguration in the presence of OMNI link
infrastructure or for sustained communications in the absence of
infrastructure. (Note that in some environments Clients can instead
use a (Hierarchical) Host Identity Tag ((H)HIT) instead of a TLA -
see: .)a ULA beginning
with fd00::/64 followed by an MNP-based (XLA-MNP) or random
(XLA-RND) IID as specified in . An XLA can be used to supply a
stable address for IPv6 ND messaging, a routing table entry for the
OMNI link routing system, etc. (Note that XLAs can also be
statelessly formed from LLAs (and vice-versa) simply by inverting
prefix bits 7 and 8.)a node that is connected to an OMNI
link and participates in the AERO internetworking and mobility
service.an AERO node
that configures an OMNI interface over an ENET underlying interface
serviced by an upstream Client. The Host does not assign an LLA or
ULA to the OMNI interface, but instead assigns the address taken
from the ENET underlying interface. (As an implementation matter,
the Host may instead configure the "OMNI interface" as a virtual
sublayer of the underlay interface itself.) When an AERO host
forwards an original IP packet/parcel to another AERO node on the
same ENET, it uses simple IP-in-IP encapsulation without including
an OAL encapsulation header. The Host is therefore an OMNI link
termination endpoint.an AERO node
that configures an OMNI interface over one or more underlay
interfaces and requests MNP delegation/registration service from
AERO Proxy/Servers. The Client assigns an XLA-MNP (as well as
Proxy/Server-specific ULA-MNPs) to the OMNI interface for use in
IPv6 ND exchanges with other AERO nodes and forwards original IP
packets/parcels to correspondents according to OMNI interface
neighbor cache state. The Client coordinates with Proxy/Servers
and/or other Clients over upstream ANET/INET interfaces and may also
provide Proxy/Server services for Hosts and/or other Clients over
downstream ENET interfaces.a
node that provides a proxying service between AERO Clients and
external peers on its Client-facing ANET interfaces (i.e., in the
same fashion as for an enterprise network proxy) as well as
designated router services for coordination with correspondents on
its INET-facing interfaces. (Proxy/Servers in the open INET instead
configure only a single INET interface and no ANET interfaces.) The
Proxy/Server configures an OMNI interface and assigns a ULA-RND to
support the operation of IPv6 ND services, while advertising any
associated MNPs for which it is acting as a hub via BGP peerings
with AERO Gateways.a Proxy/Server
that provides forwarding services between nodes reached via the OMNI
link and correspondents on other links/networks. AERO Relays assign
a ULA-RND to an OMNI interface and maintain BGP peerings with
Gateways the same as Proxy/Servers. Relays also run a dynamic
routing protocol to discover any non-MNP IP GUA routes in service on
other links/networks, advertise OMNI link MSP(s) to other
links/networks, and redistribute routes discovered on other
links/networks into the OMNI link BGP routing system. (Relays that
connect to major Internetworks such as the global IPv6 or IPv4
Internet can also be configured to advertise "default" routes into
the OMNI link BGP routing system.)a BGP hub
autonomous system node that also provides OAL forwarding services
for nodes on an OMNI link. Gateways forward OAL packets/fragments 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. Gateways peer with Proxy/Servers and other
Gateways to form an IPv6-based OAL spanning tree over all OMNI link
segments and to discover the set of all MNP and non-MNP prefixes in
service. Gateways process OAL packets/fragments received over the secured
spanning tree that are addressed to themselves, while forwarding all
other OAL packets/fragments to the next hop also via the secured spanning
tree. Gateways forward OAL packets/fragments 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 Client that
initiates communications with a target peer by sending an NS message
to establish reverse-path multilink forwarding state in OMNI link
intermediate nodes on the path to the target. Note that in some
arrangements the Client's (FHS) Proxy/Server (and not the Client
itself) initiates the NS.a Client that
responds to a communications request from a source peer's NS by
returning an NA response to establish forward-path multilink
forwarding state in OMNI link intermediate nodes on the path to the
source. Note that in some arrangements the Client's (LHS)
Proxy/Server (and not the Client itself) returns the NA.a
Proxy/Server for an FHS Client's underlay interface that forwards
the Client's OAL packets into the segment routing topology. FHS
Proxy/Servers also act as intermediate forwarding nodes to
facilitate RS/RA exchanges between a Client and its Hub
Proxy/Server.a
Proxy/Server for an underlay interface of an LHS Client that
forwards OAL packets received from the segment routing topology to
the Client over that interface.a single Proxy/Server
selected by a Client that injects the Client's XLA-MNP into the BGP
routing system and provides a designated router service for all of
the Client's underlay interfaces. Clients often select the first FHS
Proxy/Server they coordinate with to serve in the Hub role (as all
FHS Proxy/Servers are equally capable candidates to serve as a Hub),
however the Client can also select any available Proxy/Server for
the OMNI link (as there is no requirement that the Hub must also be
one of the Client's FHS Proxy/Servers).a Multinet
OMNI link forwarding region between FHS and LHS Proxy/Servers.
FHS/LHS Proxy/Servers and SRT Gateways span the OMNI link on behalf
of FHS/LHS Client pairs. The SRT maintains a spanning tree
established through BGP peerings between Gateways and Proxy/Servers.
Each SRT segment includes Gateways in a "hub" and Proxy/Servers in
"spokes", while adjacent segments are interconnected by
Gateway-Gateway peerings. The BGP peerings are configured over both
secured and unsecured underlay network paths such that a secured
spanning tree is available for critical control messages while other
messages can use the unsecured spanning tree.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/parcels between any
downstream-attached networks and the OMNI link. The MR is the MN
entity that hosts the AERO Client.the node
nearest the original source that initiates OMNI link address
resolution. The ARS may be a Proxy/Server or Relay for the source,
or may be the source Client itself. The ARS is often (but not
always) also the same node that becomes the FHS source during route
optimization.the node
toward which address resolution is directed. The ART may be a Relay
or the target Client itself. The ART is often (but not always) also
the same node that becomes the LHS target during route
optimization.the node
that responds to address resolution requests on behalf of the ART.
The ARR may be a Relay, the ART itself, or the ART's current Hub
Proxy/Server. Note that a Hub Proxy/Server can assume the ARR role
even if it is located on a different SRT segment than the ART. The
Hub Proxy/Server assumes the ARR role only when it receives an RS
message from the ART that has the Neighbor Coordination sub-option
'A' flag set (see: ).a geographically
and/or topologically referenced list of addresses of all
Proxy/Servers within the same OMNI link. Each OMNI link has its own
PRL.a
BGP-based overlay routing service coordinated by Proxy/Servers and
Gateways that tracks all Proxy/Server-to-Client associations.the collective set of
all Proxy/Servers, Gateways and Relays that provide the AERO Service
to Clients.A
forwarding table on each OAL source, destination and intermediate
node that includes AERO Forwarding Vectors (AFV) with both multilink
forwarding instructions and context for reconstructing compressed
headers for specific communicating peer underlay interface pairs.
The AFIB also supports route optimization where one or more OAL
intermediate nodes in the path can be "skipped" to reduce path
stretch and decrease load on critical infrastructure elements.An AFIB entry
that includes soft state for each underlay interface pairwise
communication session between peer OAL nodes. AFVs are identified by
both a forward and reverse path AFV Index (AFVI). OAL nodes
establish reverse path AFVIs when they forward an IPv6 ND unicast
Neighbor Solicitation (NS) message and establish forward path AFVIs
when they forward the solicited IPv6 ND unicast Neighbor
Advertisement (NA) response.A
locally-unique 4 octet value automatically generated by an OAL node
when it creates an AFV. OAL intermediate nodes assign two distinct
AFVIs (called "A" and "B") to each AFV, with "A" representing the
forward path and "B" representing the reverse path. Meanwhile, the
OAL source assigns a single "B" AFVI, and the OAL destination
assigns a single "A" AFVI. Each OAL node advertises its "A" AFVI to
previous hop nodes on the reverse path toward the source and
advertises its "B" AFVI to next hop nodes on the forward path toward
the destination.An OMNI
option sub-option that appears in IPv6 ND NS/NA messages and
includes all parameters necessary for establishing AFV state in OAL
nodes in the path (see: ).Throughout the document, the simple terms "Host", "Client",
"Proxy/Server", "Gateway" and "Relay" refer to "AERO/OMNI Host",
"AERO/OMNI Client", "AERO/OMNI Proxy/Server", "AERO/OMNI Gateway" and
"AERO/OMNI Relay", respectively. Capitalization is used to distinguish
these terms from other common Internetworking uses in which they appear
without capitalization, and implies that the node in question both
configures an OMNI interface and engages the OMNI Adaptation Layer.The terminology of IPv6 ND , DHCPv6 and OMNI
(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 Hosts configure an OMNI interface over an underlay interface
connected to a Client's ENET and coordinate with both other AERO Hosts
and Clients over the ENET. As an implementation matter, the Host
either assigns the same (MNP-based) IP address from the underlay
interface to the OMNI interface, or configures the "OMNI interface" as
a virtual sublayer of the underlay interface itself. AERO Hosts treat
the ENET as an ANET, and treat the upstream Client for the ENET as a
Proxy/Server. AERO Hosts are seen as OMNI link termination
endpoints.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 underlay 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 ENETs (which may
connect AERO Hosts and other Clients). AERO Clients provide
Proxy/Server-like services for Hosts and other Clients on
downstream-attached ENETs.AERO Gateways, 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 and Hosts. AERO Gateways (together with
Proxy/Servers) provide the secured backbone supporting infrastructure
for a Segment Routing Topology (SRT) spanning tree for the OMNI
link.AERO Gateways forward 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
an adaptation layer forwarding service that upper layers perceive as
L2 bridging, since the inner IP TTL/Hop Limit is not decremented. Each
Gateway also peers with Proxy/Servers and other Gateways in a dynamic
routing protocol instance to provide a Distributed Mobility Management
(DMM) service for the list of active MNPs (see ). Gateways assign one or more Mobility Service
Prefixes (MSPs) to the OMNI link and configure secured tunnels with
Proxy/Servers, Relays and other Gateways; they further maintain
forwarding table entries for each MNP or non-MNP prefix in service on
the OMNI link.AERO Proxy/Servers distributed across one or more SRT segments
provide default forwarding and mobility/multilink services for AERO
Client mobile nodes. Each Proxy/Server also peers with Gateways in an
adaptation layer 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 and Hosts to communicate with peers in external INETs,
while Proxy/Servers in the open INET provide an authentication service
for INET Client IPv6 ND messages but only a secondary forwarding
service when the Client cannot forward directly to a peer or Gateway.
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/parcels between the OMNI link and nodes
on other links/networks. Relays run a dynamic routing protocol to
discover any non-MNP prefixes in service on other links/networks, and
Relays that connect to larger Internetworks (such as the Internet) may
originate default routes. The Relay redistributes OMNI link MSP(s)
into other links/networks, and redistributes non-MNP prefixes via OMNI
link Gateway 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 underlay SRT segments which may be managed by
different administrative authorities and have incompatible
protocols and/or addressing plans.AERO Gateway G1 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). Gateways provide the backbone for an SRT spanning tree for
the OMNI link.AERO Proxy/Servers S1 and S2 configure secured tunnels with
Gateway G1 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 ENETs.AERO Hosts H1 and H2 attach to the ENETs served by Clients C1
and C2, respectively.An OMNI link configured over a single underlay network appears as
a single unified link with a consistent addressing plan; all nodes
on the link can exchange carrier packets via simple L2 encapsulation
(i.e., following any necessary NAT traversal) since the underlay is
connected. In common practice, however, OMNI links are often
configured over an SRT spanning tree that bridges multiple distinct
underlay network segments managed under different administrative
authorities (e.g., as for worldwide aviation service providers such
as ARINC, SITA, Inmarsat, etc.). Individual underlay networks 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
Gateways.The OMNI link spans multiple SRT segments 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/parcel. An example OMNI link
SRT is shown in :Gateway, Proxy/Server and Relay OMNI interfaces are configured
over both secured tunnels and open INET underlay interfaces within
their respective SRT segments. Within each segment, Gateways
configure "hub-and-spokes" BGP peerings with Proxy/Servers and
Relays as "spokes". Adjacent SRT segments are joined by
Gateway-to-Gateway peerings to collectively form a spanning tree
over the entire SRT. The "secured" spanning tree supports
authentication and integrity for critical control plane messages
(and any trailing data plane message extensions). 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.The AERO Multinet service concatenates SRT segments to form a
larger network through Gateway-to-Gateway peerings as originally
suggested in the "Catenet Model for Internetworking" ; especially follows
directly from the illustrations in . The
Catenet concept suggested a "network-of-networks" concatenation of
independent and diverse Internetwork "segments" to form a much
larger network supporting end-to-end services.The Catenet concept first articulated in the 1970's was distorted
through the evolution of the Internet in later decades, since a
critical element was missing from the architecture. As a result, the
Internet evolved as a single, large public routing and addressing
domain interconnecting private domains (i.e., instead of a true
network-of-networks) which has impeded flexibility and inhibited
end-to-end services. With the advent of the adaptation layer
established by the AERO/OMNI services, however, the original Catenet
"network-of-networks" vision is now made possible.AERO nodes on OMNI links use the Link-Local Address (LLA) prefix
fe80::/64 to assign LLAs to the OMNI
interface to satisfy the requirements of .
AERO Clients configure LLAs constructed from MNPs (i.e., "LLA-MNPs")
while AERO infrastructure nodes construct LLAs based on 56-bit
random values ("LLA-RNDs") per . Non-MNP routes are also
represented the same as for MNPs, 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 Global ID to form the
prefix {ULA}::/48, then include a 16-bit Subnet ID '*' to form the
prefix {ULA*}::/64 . The AERO node then uses
the prefix {ULA*}::/64 to form "ULA-MNPs" or "ULA-RNDs" as specified
in to support OAL addressing.
(The prefix {ULA*}::/64 appearing alone and with no suffix
represents "default" for that prefix.)AERO Clients also use Temporary Local Addresses (TLAs) and
eXtended Local Addresses (XLAs) constructed per , where TLAs are distinguished from
ordinary ULAs based on the prefix fd00::/16 and XLAs are
distinguished from ULAs/TLAs based on the prefix fd00::/64. Clients
use TLA-RNDs only in initial control message exchanges until a
stable MNP is assigned, but may sometimes also use them for
sustained communications within a local routing region. AERO nodes
use XLA-MNPs to provide forwarding information for the global
routing table as well as IPv6 ND message addressing information.AERO MSPs, MNPs and non-MNP routes are typically based on Global
Unicast Addresses (GUAs), but in some cases may be based on IPv4
private addresses or IPv6 ULA-C's . A GUA block is also reserved for OMNI link
anycast purposes. See for a
full specification of LLAs, ULAs, TLAs, XLAs, GUAs and anycast
addresses 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
Gateways and Proxy/Servers (Relays also engage in the routing system
as simplified Proxy/Servers). The service supports OAL packet/fragment
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 connected 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 Gateways but does not peer with other
Proxy/Servers. Each SRT segment in the OMNI link must include one or
more Gateways in a "hub" AS, which peer with the Proxy/Servers
within that segment as "spoke" ASes. All Gateways 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
Gateways of different segments peer with one another using eBGP.Gateways maintain forwarding table entries only for ULA prefixes
for infrastructure elements and XLA-MNPs corresponding to MNP and
non-MNP routes that are currently active; Gateways also maintain
black-hole routes for the OMNI link MSPs so that OAL packets/fragments
destined to non-existent more-specific routes are dropped with a
Destination Unreachable message returned. In this way, Proxy/Servers
and Relays have only partial topology knowledge (i.e., they only
maintain routing information for their directly associated Clients
and non-AERO links) and they forward all other OAL packets/fragments
to Gateways which have full topology knowledge.Each OMNI link segment assigns a unique sub-prefix of {ULA}::/48
known as the "SRT prefix". For example, a first segment could assign
{ULA}:1000::/56, a second could assign {ULA}:2000::/56, a third
could assign {ULA}:3000::/56, etc. Within each segment, each
Proxy/Server configures a ULA-RND within the segment's SRT prefix
with a 56-bit random value in the interface identifier as specified
in .The administrative authorities for each segment must therefore
coordinate to assure mutually-exclusive ULA prefix assignments, but
internal provisioning of ULAs is an independent local consideration
for each administrative authority. For each ULA prefix, the
Gateway(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::/64 is simply
{ULA}:1023::/64.ULA prefixes are statically represented in Gateway forwarding
tables. Gateways 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 ULA prefixes either via standard BGP routing or
static routes. For example, if three Gateways ('A', 'B' and 'C')
from different segments serviced {ULA}:1000::/60, {ULA}:2000::/56
and {ULA}:3000::/56 respectively, then the forwarding tables in each
Gateway appear as follows:{ULA}:1000::/56->local,
{ULA}:2000::/56->B, {ULA}:3000::/56->C{ULA}:1000::/56->A,
{ULA}:2000::/56->local, {ULA}:3000::/56->C{ULA}:1000::/56->A, {ULA}:2000::/56->B,
{ULA}:3000::/56->localThese forwarding table entries rarely change, since they
correspond to fixed infrastructure elements in their respective
segments.MNP (and non-MNP) routes are instead dynamically advertised in
the AERO routing system by Proxy/Servers and Relays that provide
service for their corresponding MNPs. The routes are advertised as
XLA-MNP prefixes, i.e., as fd00::{MNP} (see: ). 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:fd00::2001:db8:1000:2000/120fd00::2001:db8:3000:4000/120fd00::2001:db8:5000:6000/120A full discussion of the BGP-based routing system used by AERO is
found in .The distinct {ULA}::/48 prefixes in an OMNI link domain identify
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 the 40-bit ULA
Global ID field 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 Gateways and Proxy/Servers of each independent SRT engage in
BGP peerings to form a spanning tree with the Gateways in non-leaf
nodes and the Proxy/Servers in leaf nodes. The spanning tree is
configured over both secured and unsecured underlay network paths.
The secured spanning tree is used to convey secured control messages
(and sometimes data message extensions) between Proxy/Servers and
Gateways, while the unsecured spanning tree forwards bulk data
messages and/or unsecured control messages.Each SRT segment is identified by a unique ULA prefix used by all
Proxy/Servers and Gateways 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.Note: The distinct ULA prefixes in an OMNI link domain can be
carried either in a common BGP routing protocol instance for all
OMNI links or in distinct BGP routing protocol instances for
different OMNI links. In some SBM environments, such separation may
be necessary to ensure that distinct OMNI links do not include any
common infrastructure elements as single points of failure. In other
environments, carrying the ULAs of multiple OMNI links within a
common routing system may be acceptable.Original IPv6 sources can direct IPv6 packets/parcels 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/parcel
will traverse when there may be multiple alternatives.When an AERO node processes the SRH and forwards the original
IPv6 packet/parcel to the correct OMNI interface, the OMNI interface
writes the next IPv6 address from the SRH into the IPv6 destination
address and decrements Segments Left. If decrementing would cause
Segments Left to become 0, the OMNI interface deletes the SRH before
forwarding. This form of Segment Routing supports Safety-Based
Multilink (SBM).OMNI interfaces are virtual interfaces configured over one or more
underlay interfaces classified as follows:ANET interfaces connect to a protected and secured ANET that is
separated from the open INET by Proxy/Servers. The ANET interface
may be either on the same L2 link segment as a Proxy/Server, or
separated from a Proxy/Server by multiple IP hops. (Note that NATs
may appear internally within an ANET and may require NAT traversal
on the path to the Proxy/Server the same as for the INET
case.)INET interfaces connect to an INET either natively or through
one or several IPv4 Network Address Translators (NATs). Native
INET interfaces have global IP addresses that are reachable from
any INET correspondent. NATed INET interfaces typically have
private IP addresses and connect to a private network behind one
or more NATs with the outermost NAT providing INET access.ENET interfaces connect a Client's downstream-attached
networks, where the Client provides forwarding services for ENET
Host and Client communications to remote peers. An ENET can be as
simple as a small stub network that travels with a mobile Client
(e.g., an Internet-of-Things) to as complex as a large private
enterprise network that the Client connects to a larger ANET or
INET.VPNed interfaces use security encapsulation over an underlay
network to a Client or Proxy/Server acting as a Virtual Private
Network (VPN) gateway. Other than the link-layer encapsulation
format, VPNed interfaces behave the same as for Direct
interfaces.Direct (aka "point-to-point") interfaces connect directly to a
Client or Proxy/Server without crossing any networked paths. An
example is a line-of-sight link between a remote pilot and an
unmanned aircraft.OMNI interfaces use OAL encapsulation and fragmentation as
discussed in . OMNI interfaces use L2
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 use
link-layer encapsulation only (i.e., and no other L2 encapsulations)
over Direct underlay interfaces or ANET interfaces when the Client and
FHS Proxy/Server are known to be on the same underlay 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), Neighbor Advertisement (NA) and
Redirect for neighbor cache management. In environments where spoofing
may be a threat, OMNI neighbors should invoke OAL Identification
window synchronization in their IPv6 ND message exchanges.OMNI interfaces send IPv6 ND messages with an OMNI option formatted
as specified in . The OMNI
option includes prefix registration information, Interface Attributes
and/or AERO Forwarding Parameters (AFPs) containing link information
parameters for the OMNI interface's underlay interfaces and any other
per-neighbor information.A Host's OMNI interface is configured over an underlay interface
connected to an ENET provided by an upstream Client. From the Host's
perspective, the ENET appears as an ANET and the upstream Client
appears as a Proxy/Server. The Host does not provide OMNI intermediate
node services and is therefore a logical termination point for the
OMNI link.A Client's OMNI interface may be configured over multiple ANET/INET
underlay 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 ANET/INET underlay 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 Interface Attributes, Traffic Selector and/or AFP
sub-options with the same underlay interface ifIndex. In that case,
the Client would appear to have a single underlay interface but with a
dynamically changing link-layer address.If the Client has multiple active ANET/INET underlay 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 sub-options with different underlay interface ifIndexes.Proxy/Servers on the open Internet include only a single INET
underlay interface. INET Clients therefore discover only the L2ADDR
information for the Proxy/Server's INET interface. Proxy/Servers on an
ANET/INET boundary include both an ANET and INET underlay interface.
ANET Clients therefore must discover both the ANET and INET L2ADDR
information for their Proxy/Servers.Gateway and Proxy/Server OMNI interfaces are configured over
underlay 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 a
ULA-RND and acts as an OAL source to encapsulate original IP
packets/parcels, then fragments the resulting OAL packets, performs
L2 encapsulation and sends
the resulting carrier packets over the secured or unsecured underlay
paths. Note that Gateway and Proxy/Server end-to-end transport
protocol sessions used by the BGP run directly over the OMNI interface
and use ULA-RND source and destination addresses. The ULA-RND
addresses that appear in BGP protocol session original IP
packets/parcels may therefore be the same as those that appear in the
OAL IPv6 encapsulation header.AERO Proxy/Servers, Clients and Hosts 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/parcels 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
Hosts and Gateways are discussed in the following sections.When a Proxy/Server enables an OMNI interface, it assigns a
ULA-RND appropriate for the given OMNI link SRT segment. The
Proxy/Server also configures secured underlay interface tunnels and
engages in BGP routing protocol sessions over the OMNI interface
with one or more neighboring Gateways.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 underlay interfaces and/or
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/ENET interfaces (see: ). The Relay
provisions MNPs to networks on the INET/ENET interfaces (i.e., the
same as a Client would do) and advertises the MSP(s) for the OMNI
link over the INET/ENET 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
XLA-MNP or a TLA and sends OMNI-encapsulated RS messages over its
ANET/INET underlay interfaces to an FHS Proxy/Server, which
coordinates with a Hub Proxy/Server that returns an RA message with
corresponding parameters. The RS/RA messages may pass through one or
more NATs in the path between the Client and FHS Proxy/Server.
(Note: if the Client used a TLA in its initial RS messages, it may
discover ULA-MNPs in the corresponding RAs that it receives from FHS
Proxy/Servers 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 TLAs
for Client-to-Client communications at least until it encounters an
infrastructure element that can delegate MNPs.)A Client can further extend the OMNI link over its (downstream)
ENET interfaces where it provides a first-hop router for Hosts and
other AERO Clients connected to the ENET. A downstream Client that
connects via the ENET serviced by an upstream Client can in turn
service further downstream ENETs that connect other Hosts and
Clients. This OMNI link extension can be applied recursively over a
"chain" of ENET Clients.When a Host enables an OMNI interface, it assigns an address
taken from the ENET underlay interface which may itself be a GUA
delegated by the upstream Client. The Host does not assign a
link-local address to the OMNI interface, since no autoconfiguration
is necessary on that interface. (As an implementation matter, the
Host could instead configure the "OMNI interface" as a virtual
sublayer of the ENET underlay interface itself.)The Host sends OMNI-encapsulated RS messages over its ENET
underlay interface to the upstream Client, which returns
encapsulated RAs and provides routing services in the same fashion
that Proxy/Servers provides services for Clients. Hosts represent
the leaf end systems in recursively-nested chain of concatenated
ENETs, i.e., they represent terminating endpoints for the OMNI
link.AERO Gateways configure an OMNI interface and assign a ULA-RND
and corresponding Subnet Router Anycast address for each OMNI link
SRT segment they connect to. Gateways configure underlay interface
secured tunnels with Proxy/Servers in the same SRT segment and other
Gateways in the same (or an adjacent) SRT segment. Gateways then
engage in a BGP routing protocol session with neighbors over the
secured spanning tree (see: ).Each Client, Proxy/Server and Gateway OMNI interface maintains a
network layer conceptual neighbor cache per
or the same as for any IP interface. The OMNI
interface network layer neighbor cache is maintained through static
and/or dynamic neighbor cache entry configurations.Each OMNI interface also maintains a separate internal adaptation
layer conceptual neighbor cache that includes a Neighbor Cache Entry
(NCE) for each of its active OAL neighbors per . Throughout this document, the terms "neighbor
cache" and "NCE" refer to this adaptation layer neighbor cache unless
otherwise specified.Each OMNI interface NCE is indexed by the ULA of the neighbor found
in the ND message IPv6 header and determines the context for
Identification verification. Clients and Proxy/Servers maintain NCEs
through dynamic RS/RA message exchanges, and also maintain NCEs for
any active correspondent peers through dynamic NS/NA message
exchanges.Hosts also maintain NCEs for Clients and other Hosts through the
exchange of RS/RA, NS/NA or Redirect messages. Each NCE is indexed by
the IP address assigned to the Host ENET interface, which is the same
address used for L2 encapsulation (i.e., without the insertion of
an OAL header). This encapsulation format identifies the NCE as a
Host-based entry where the Host is a leaf end system in the
recursively extended OMNI link.Gateways also maintain NCEs for Clients within their local segments
based on NS/NA route optimization messaging (see: ). When a Gateway creates/updates a NCE for a local
segment Client based on NS/NA route optimization, it also maintains
AFIB state for messages destined to this local segment Client.Proxy/Servers add an additional state DEPARTED to the list of NCE
states found in Section 7.3.2 of . When a
Client terminates its association, the Proxy/Server OMNI interface
sets a "DepartTime" variable for the NCE to "DEPART_TIME" seconds.
DepartTime is decremented unless a new IPv6 ND message causes the
state to return to REACHABLE. While a NCE is in the DEPARTED state,
the Proxy/Server forwards OAL packets/fragments destined to the target
Client to the Client's new FHS/Hub Proxy/Server instead. It is
RECOMMENDED that DEPART_TIME be set to the default constant value 10
seconds to accept any carrier packets that may be in flight. When
DepartTime decrements to 0, the NCE is deleted.Clients determine the service profiles for their FHS and Hub
Proxy/Servers by setting the N/A/U flags in a Neighbor Coordination
sub-option of the first OMNI option in RS messages. When the N/A/U
flags are clear, Proxy/Servers forward all NS/NA messages to the
Client, while the Client performs mobility update signaling through
the transmission of uNA messages to all active neighbors following a
mobility event. However, in some environments this may result in
excessive NS/NA control message overhead especially for Clients
connected to low-end data links.To minimize NS/NA message overhead, Clients can set the N/A/U flags
in the OMNI Neighbor Coordination sub-option of RS messages they send.
If the N flag is set, the FHS Proxy/Server that forwards the RS
message assumes the role of responding to NS messages and maintains
peer NCEs associated with the NCE for this Client. If the A flag is
set, the Hub Proxy/Server that processes the RS message assumes the
role of responding to NS(AR) messages on behalf of this Client NCE. If
the U flag is set, the Hub Proxy/Server that processes the RS message
becomes responsible for maintaining a "Report List" of sources/targets
for NS(AR) messages it forwards on behalf of this Client NCE. The Hub
Proxy/Server maintains each Report List entry for REPORT_TIME seconds,
and sends uNA messages to each member of the Report List when it
receives a Client mobility update indication (e.g., through receipt of
an RS with updated Interface Attributes and/or Traffic Selectors).Both the Client and its Hub Proxy/Server have full knowledge of the
Client's current underlay Interface Attributes and Traffic Selectors,
while FHS Proxy/Servers acting in "proxy" mode have knowledge of only
the individual Client underlay interfaces they service. Clients
determine their FHS and Hub Proxy/Server service models by setting the
N/A/U flags in the RS messages they send as discussed above.When an Address Resolution Source (ARS) sends an NS(AR) message
toward an Address Resolution Target (ART) Client/Relay, the OMNI link
routing system directs the NS(AR) to a Hub Proxy/Server for the ART.
The Hub then either acts as an Address Resolution Responder (ARR) on
behalf of the ART or forwards the NS(AR) to the ART which acts as an
ARR on its own behalf. The ARR returns an NA(AR) response to the ARS,
which creates or updates a NCE for the ART while caching L3 and L2
addressing information. The ARS then (re)sets ReachableTime for the
NCE to REACHABLE_TIME seconds and performs unicast NS/NA exchanges
over specific underlay interface pairs to determine paths for
sending carrier packets directly to the ART. The ARS 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 use ULAs
instead of LLAs as IPv6 ND message source and destination addresses.
This allows multiple different OMNI links to be joined into a single
link at some future time without requiring a global renumbering
event.For each IPv6 ND message, the OMNI interface includes one or more
OMNI options (and any other ND message options) then completely
populates all option information. If the OMNI interface includes an
authentication signature, it sets the IPv6 ND message Checksum field
to 0 and calculates the authentication signature over the entire
length of the OAL packet or super-packet beginning with a
pseudo-header of the IPv6 header. Otherwise, the OMNI interface
calculates the standard IPv6 ND message checksum over the OAL packet
or super-packet and writes the value in the Checksum field. OMNI
interfaces verify authentication and integrity of each IPv6 ND
message received according to the specific check(s) included, and
process the message further only following verification.OMNI options include per-neighbor information that provides
multilink forwarding, link-layer address and traffic selector
information for the neighbor's underlay 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.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 OMNI options
and S/TLLAOs appear, the former pertains to adaptation layer to
underlay interface address mappings while the latter pertains to the
native L2 address format of the underlay media.OMNI interface IPv6 ND messages may also include other IPv6 ND
options. In particular, solicitation messages may include a Nonce
option if required for verification of advertisement replies. If an
OMNI IPv6 ND solicitation message includes a Nonce option, the
advertisement reply must echo the same Nonce. If an OMNI IPv6 ND
solicitation message includes a Timestamp option, the recipient must
include a Timestamp option in its advertisement reply. All
unsolicited advertisement and redirect messages should include a
Timestamp option.AERO Clients send RS messages to the link-scoped All-Routers
multicast address or a ULA-RND while using unicast or anycast OAL/L2
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 Hosts and Clients on ENET underlay networks send RS messages
to the link-scoped All-Routers multicast address, a ULA-RND of a
remote Hub Proxy/Server or the ULA-MNP of an upstream Client while
using unicast or anycast OAL/L2 addresses. The upstream AERO Client
responds by returning a unicast RA message.AERO nodes use NS/NA messages for the following purposes:NS/NA(AR) messages are used for address resolution and
optionally to establish sequence number windows. The ARS sends
an NS(AR) to the solicited-node multicast address of the ART,
and an ARR with addressing information for the ART returns a
unicast NA(AR) that contains current, consistent and authentic
target address resolution information. NS(AR) messages include a
solicited-node multicast destination address to distinguish them
from ordinary NS messages. NS/NA(AR) messages must be
secured.Ordinary NS/NA messages are used determine target
reachability, establish and maintain NAT state, and/or establish
AFIB state. The source sends an NS to the unicast address of the
target while optionally including an OMNI AERO Forwarding
Parameters (AFP) sub-option naming a specific underlay interface
pair, and the target returns a unicast NA that includes a
responsive AFP if necessary. NS/NA messages that use an
in-window sequence number and do not update any other state need
not include an authentication signature but instead must include
an IPv6 ND message checksum. NS/NA messages used to establish
window synchronization and/or AFIB state must be secured.Unsolicited NA (uNA) messages are used to signal addressing
and/or other neighbor state changes (e.g., address changes due
to mobility, signal degradation, traffic selector updates,
etc.). uNA messages that update state information must be
secured.NS/NA(DAD) messages are not used in AERO, since Duplicate
Address Detection is not required.Additionally, nodes may set the OMNI option PNG flag in
NA/RA messages to receive a uNA response from the neighbor. The uNA
response MUST set the ACK flag (without also setting the SYN or PNG
flags) with the Acknowledgement field set to the Identification used
in the PNG message.As discussed in Section 4.4 of NA
messages include three flag bits R, S and O. OMNI interface NA
messages treat the flags as follows:R: The R ("Router") flag is set to 1 in the NA messages sent
by all AERO/OMNI node types. Simple hosts that would set R to 0
do not occur on the OMNI link itself, but may occur on the
downstream links of Clients and Relays.S: The S ("Solicited") flag is set exactly as specified in
Section 4.4. of , i.e., it is set to 1
for Solicited NAs and set to 0 for uNAs (both unicast and
multicast).O: The O ("Override") flag is set to 0 for solicited NAs
returned by a Proxy/Server ARR 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
XLA-MNPs must be uniquely assigned to Clients to support correct
IPv6 ND protocol operation, however, no role is currently seen
for assigning the same XLA-MNP 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 by including OMNI
Neighbor Coordination sub-options in RS/RA or NS/NA message
exchanges to maintain send/receive window state in their respective
neighbor cache entries as specified in .When the network layer forwards an original IP packet/parcel into
an OMNI interface, the interface locates or creates a Neighbor Cache
Entry (NCE) that matches the destination. The OMNI interface then
invokes the OMNI Adaptation Layer (OAL) as discussed in which encapsulates the packet/parcel
in an IPv6 header to produce an OAL packet. For example, an original
IP packet/parcel with source address 2001:db8:1:2::1 and destination
address 2001:db8:1234:5678::1 might cause the OAL encapsulation header
to include source address {XLA*}::2001:db8:1:2 (i.e., an XLA-MNP) and
destination address {ULA*}::0012:3456:789a:bcde (i.e., a ULA-RND).Following encapsulation, the OAL source then calculates and
includes a 2-octet OAL checksum, then fragments the OAL packet while
including an identical Identification value for each fragment that
must be within the window for the neighbor. This fragmentation causes
the OAL checksum to appear as the final 2 octets of the final
fragment, i.e., as a "trailer".The OAL source next includes an identical Compressed Routing Header
with 32-bit ID fields (CRH-32) with each fragment containing
one or more AERO Forwarding Vector Indices (AFVIs) if necessary as
discussed in . The OAL source can instead
invoke OAL header compression by replacing the OAL IPv6 header, CRH-32
and Fragment Header with an OAL Compressed Header (OCH).The OAL source finally encapsulates each resulting OAL fragment in
L2 headers to form a carrier packet, with source address set to its
own L2 address (e.g., 192.0.2.100) and destination set to the L2
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 :Note: that carrier packets exchanged by Hosts on ENETs do
not include the OAL IPv6 or CRH-32 headers, i.e., the OAL
encapsulation is NULL and only the Fragment Header and L2
encapsulations are included.In this format, the OAL source encapsulates the original IP header
and packet/parcel body/fragment in an OAL IPv6 header prepared
according to , the CRH-32 is a Routing Header
extension of the OAL header, the Fragment Header identifies each
fragment, and the L2 headers are prepared as discussed in . The OAL source sends each such
carrier packet into the SRT spanning tree, where they are forwarded
over possibly multiple OAL intermediate nodes until they arrive at the
OAL destination.The OMNI link control plane service distributes Client XLA-MNP
prefix information that may change occasionally due to regional node
mobility, as well as XLA-MNP prefix information for Relay non-MNPs and
per-segment ULA prefix information that rarely changes. OMNI link
Gateways 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 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 an AERO Forwarding
Information Base (AFIB) that caches AERO Forwarding Vectors (AFVs)
which can provide more direct forwarding "shortcuts" that avoid strict
spanning tree paths. As a result, the spanning tree is always
available but OMNI interfaces can often use the AFIB to greatly
improve performance and reduce load on critical infrastructure
elements.For OAL packets/fragments undergoing L2 re-encapsulation at an OAL
intermediate node, the OMNI interface removes the L2 encapsulation
headers and reassembles if necessary to obtain the OAL packet. The
OMNI interface then decrements the OAL IPv6 header Hop Limit and
discards the packet/fragment if the Hop Limit reaches 0. Otherwise, the
OMNI interface updates the OAL addresses if necessary, recalculates
the OAL checksum, re-fragments and re-encapsulates each fragment in
new L2 encapsulation headers to form carrier packets appropriate for
next segment forwarding.When an FHS Gateway forwards an OAL packet/fragment to an LHS Gateway
over the unsecured spanning tree, it reconstructs the OAL header based
on AFV state, inserts a CRH-32 immediately following the OAL header
and adjusts the OAL payload length and destination address field. The
FHS Gateway includes a single AFVI in the CRH-32 that will be
meaningful to the LHS Gateway, then forwards the OAL packet/fragment over
the unsecured spanning tree. When the LHS Gateway receives the OAL
packet/fragment, it locates the AFV for the next hop based on the CRH-32
AFVI then re-applies header compression (resulting in the removal of the
CRH-32) and forwards the OAL packet/fragment to the next hop.When an OAL node receives OAL packets/fragments
addressed to another node, it discards the L2 headers and includes new
L2 headers appropriate for the next hop in the forwarding path to the
OAL destination. The node then sends these new carrier packets into
the next hop underlay interface.When an OAL node receives OAL packets/fragments
addressed to itself, it discards the L2 headers, verifies the
Identification, reassembles to obtain the original OAL packet (or
super-packet - see: ) then
finally verifies the OAL checksum. Next, if the enclosed original IP
packet(s)/parcel(s) are destined either to itself or to a destination
reached via an interface other than the OMNI interface, the OAL node
discards the OAL encapsulation and forwards the original IP
packet(s)/parcel(s) to the network layer.If the original IP packet(s)/parcel(s) are destined to another node
reached by the OMNI interface, the OAL node instead changes the OAL
source to its own address, changes the OAL destination to the ULA of
the next-hop node over the OMNI interface, decrements the Hop Limit,
recalculates the OAL checksum, refragments if necessary, includes new
L2 headers appropriate for the next hop, then sends these new
carrier packets into the next hop underlay interface.AERO nodes employ simple data origin authentication procedures. In
particular:AERO Gateways and Proxy/Servers accept carrier packets received
from the secured spanning tree.AERO Proxy/Servers and Clients accept carrier packets and
original IP packets/parcels that originate from within the same
secured ANET.AERO Clients and Relays accept original IP packets/parcels from
downstream network correspondents based on ingress filtering.AERO Hosts, Clients, Relays, Proxy/Servers and Gateways verify
carrier packet L2 encapsulation addresses according to .AERO nodes accept OAL packets/fragments addressed to themselves
with Identification values within the current window for the OAL
source neighbor and drop any packets with out-of-window
Identification values. (AERO nodes may forward OAL packets/fragments
not addressed to themselves without verifying the Identification
value.)AERO nodes silently drop any packets/parcels 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 underlay links
with diverse MTUs while observing both a minimum and per-path Maximum
Payload Size (MPS). The functions of the OAL and OMNI interface
MTU/MRU/MPS considerations are specified in . (Note that the OMNI interface
accommodates an assured MTU of 65535 octets due to the use of
fragmentation, and can optionally expose larger MTUs to upper layers
for best-effort Jumbogram services.)When the network layer presents an original IP packet/parcel to the
OMNI interface, the OAL source encapsulates and fragments the
packet/parcel if necessary. When the network layer presents the OMNI
interface with multiple original IP packets/parcels bound to the same
OAL destination, the OAL source can concatenate them as a single OAL
super-packet as discussed in
before applying fragmentation. The OAL source then encapsulates each
OAL fragment in L2 headers for transmission as carrier packets over an
underlay interface connected to either a physical link (e.g.,
Ethernet, WiFi, Cellular, etc.) 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 Gateway 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/parcels 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/parcels 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/parcels 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 underlay interfaces. (If forwarding state indicates
that the original IP packet/parcel should instead be forwarded back to
the network layer, the packet/parcel 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 link layer, or
reassembled and forwarded to the network layer where they are subject
to either local delivery or IP forwarding.When the network layer forwards an original IP packet/parcel into
the OMNI interface, it decrements the TTL/Hop Limit following standard
IP router conventions. Once inside the OMNI interface, however, the
OAL does not further decrement the original IP packet/parcel TTL/Hop
Limit since its forwarding actions occur below the network layer. The
original IP packet/parcel's TTL/Hop Limit will therefore be the same
when it exits the destination OMNI interface as when it first entered
the source OMNI interface.When an OAL intermediate node receives a carrier packet, it discards
the L2 headers to obtain the enclosed OAL packet/fragment. When the
intermediate node forwards an OAL packet/fragment
not addressed to itself, it decrements the OAL Hop Limit
without decrementing the network layer IP TTL/Hop Limit. If
decrementing would cause the OAL Hop Limit to become 0, the OAL
intermediate node drops the OAL packet/fragment. This ensures
that original IP packet(s)/parcel(s) cannot enter an endless loop.OMNI interfaces may have multiple underlay interfaces and/or
neighbor cache entries for neighbors with multiple underlay interfaces
(see ). The OAL uses Interface Attributes
and/or Traffic Selectors to select an outbound underlay interface for
each OAL packet and also to select segment routing and/or link-layer
destination addresses based on the neighbor's target underlay
interfaces. AERO implementations SHOULD permit network management to
dynamically adjust Traffic Selector values at runtime.If an OAL packet/fragment matches the Interface Attributes and/or
Traffic Selectors of multiple outgoing interfaces and/or neighbor interfaces,
the OMNI interface replicates the packet and sends a separate copy via
each of the (outgoing / neighbor) interface pairs; otherwise, it sends
a single copy via an interface with the best matching
attributes/selectors. (While not strictly required, the likelihood of
successful reassembly may improve when the OMNI interface sends all
fragments of the same fragmented OAL packet/fragment consecutively over the
same underlay interface pair to avoid complicating factors such as
delay variance and reordering.) AERO nodes keep track of which
underlay interfaces are currently "reachable" or "unreachable", and
only use "reachable" interfaces for forwarding purposes.The ULA Subnet ID value is used only for subnet coordination within
a local OMNI link segment. When a node forwards an OAL packet/fragment
addressed to a ULA with a foreign Global and/or Subnet ID value, it
forwards the OAL packet/fragment based solely on the OMNI link routing
information. For this reason, OMNI link routing and forwarding table
entries always include both ULA-RNDs with their associated prefix
lengths and XLA-MNPs which encode an MNP while leaving the Global and
Subnet ID values set to 0.The following sections discuss the OMNI interface-specific
forwarding algorithms for Hosts, Clients, Proxy/Servers and Gateways.
In the following discussion, an original IP packet/parcel'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 {ULA,XLA}-MNP).When an original IP packet/parcel enters a Host's OMNI interface
from the network layer the Host searches for a NCE that matches the
destination. If there is a matching NCE, the Host performs OMNI L2
encapsulation, fragments if necessary as discussed in Section 6.13
of then sends the
resulting carrier packets into the ENET addressed to the L2 address
of the neighbor. If there is no match, the host instead sends the
carrier packets to its upstream Client.After sending the carrier packet, the Host may receive an OAL
Redirect message from its upstream Client to inform it of another
AERO node on the same ENET that would provide a better first hop.
The Host authenticates the Redirect message, then updates its
neighbor cache accordingly.When an original IP packet/parcel enters a Client's OMNI
interface from the network layer the Client searches for a NCE that
matches the destination. If there is a matching NCE for a neighbor
reached via an ANET/INET interface (i.e., an upstream interface),
the Client selects one or more "reachable" neighbor interfaces in
the entry for forwarding purposes. Otherwise, the Client performs
OAL encapsulation and fragmentation, forwards the resulting OAL
packet/fragment to an FHS
Proxy/Server, then either invokes address resolution and multilink
forwarding procedures per or allows the
FHS Proxy/Server to invoke these procedures on its behalf. If there
is a matching NCE for a neighbor reached via an ENET interface
(i.e., a downstream interface), the Client instead forwards the
original IP packet/parcel to the downstream Host or Client using
encapsulation and fragmentation if necessary.When a carrier packet enters a Client's OMNI interface from the
link layer, the Client discards the L2 headers to obtain the OAL
packet/fragment then examines the OAL destination. 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,
then delivers the original IP packet/parcel to the network layer. If
the OAL destination matches a NCE for a peer Client on an ENET interface,
the Client instead forwards the OAL packet/fragment to the peer while
decrementing the OAL Hop Limit. If the OAL destination matches a NCE
for a Host on an ENET interface, the Client instead reassembles then
forwards the original IP packet/parcel to the Host while using
L2 encapsulation and fragmentation (i.e., without invoking the OAL)
if necessary. If the OAL destination does not match, the Client drops
the original IP packet/parcel and MAY return a network-layer ICMP
Destination Unreachable message subject to rate limiting (see: ).When a Client forwards an OAL packet/fragment from an ENET Host
to a neighbor connected to the same ENET, it also returns a Redirect
message to inform the Host that it can reach the neighbor directly
as an ENET peer.Note: Clients and their FHS Proxy/Server (and other Client) peers
can exchange original IP packets/parcels over ANET underlay
interfaces using L2 encapsulation without invoking the OAL,
since the ANET is secured at the link and physical layers. By
forwarding original IP packets/parcels without invoking the OAL,
the ANET peers use the same L2 encapsulation and fragmentation
procedures as specified for Hosts above.Note: The forwarding table entries established in peer Clients of
a multihop forwarding region are based on ULA-MNPs and/or TLAs used
to seed the multihop routing protocols. When ULA-MNPs are used, the
ULA /64 prefix provides topological relevance for the multihop
forwarding region, while the 64-bit Interface Identifier encodes the
Client MNP. Therefore, Clients can forward atomic fragments with
compressed OAL headers that do not include ULA or AFVI information
by examining the MNP-based addresses in the original IP
packet/parcel header. In other words, each forwarding table entry
contains two pieces of forwarding information - the ULA information
in the prefix and the MNP information in the interface
identifier.When the network layer admits an original IP packet/parcel into a
Proxy/Server's OMNI interface, the OAL drops the packet/parcel to
avoid looping if forwarding state indicates that it should be
forwarded back to the network layer. Otherwise, the OAL examines the
IP destination address to determine if it matches the ULA of a
neighboring Gateway found in the OMNI interface's network layer
neighbor cache. If so, the Proxy/Server performs OAL encapsulation
and fragmentation followed by L2 encapsulation then
sends the resulting carrier packets to the neighboring
Gateway over a secured tunnel to support the operation of the BGP
routing protocol. If the destination is a non-ULA, the Proxy/Server
instead assumes the Relay role and forwards the original IP
packet/parcel in a similar manner as for Clients. Specifically, if
there is a matching NCE the Proxy/Server selects one or more
"reachable" neighbor interfaces in the entry for forwarding
purposes; otherwise, the Proxy/Server performs OAL
encapsulation/fragmentation followed by L2 encapsulation and
sends the resulting carrier packets while invoking address
resolution and multilink forwarding procedures per
.When the Proxy/Server receives carrier packets on underlay
interfaces that contain OAL packets/fragments with both a source
and destination OAL address that
correspond to the same Client's delegated MNP, the Proxy/Server
drops the carrier packets regardless of their OMNI link point of
origin. The Proxy/Server also drops original IP packets/parcels
received on underlay interfaces either directly from an ANET Client
or following reassembly of carrier packets received from an
ANET/INET Client if the original IP destination corresponds to the
same Client's delegated MNP. Proxy/Servers also drop carrier packets
that contain OAL packets/fragments with foreign OAL destinations that
do not match their own ULA, the ULA of one of their Clients or a
ULA corresponding to one of their GUA routes. These checks are
essential to prevent forwarding inconsistencies from accidentally
or intentionally establishing endless loops that could congest
nodes and/or ANET/INET links.Proxy/Servers process carrier packets that contain OAL
packets/fragments with OCH headers or with
destinations that match their ULA and also include a CRH-32 header
that encodes one or more AFVIs. The Proxy/Server examines the next
AFVI in the OAL headers to locate the corresponding AFV entry in
the AFIB. If the carrier packets were not received from the secured
spanning tree, the Proxy/Server must then verify that the L2
addresses are "trusted" according to the AFV. If the carrier packets
were trusted, the Proxy/Server then forwards them according to the
AFV state while decrementing the OAL packet/fragment Hop Limit.For OAL packets/fragments with destinations that match their ULA
but do not include a CRH-32/OCH, the Proxy/Server instead discards
the L2 headers and performs OAL reassembly if necessary to obtain the
original IP packet/parcel. For data packets/parcels addressed to
their own ULA that arrived via the secured spanning tree, the
Proxy/Server delivers the original IP packet/parcel to the network
layer to support secured BGP routing protocol control messaging. For
data packets/parcels originating from one of its dependent Clients,
the Proxy/Server instead performs OAL encapsulation/fragmentation
then performs L2 encapsulation and sends the resulting
carrier packets while invoking address resolution and multilink
forwarding procedures per . For IPv6 ND
control messages, the Proxy/Server instead authenticates the message
and processes it as specified in later sections of this document
while updating neighbor cache and/or AFIB state accordingly.When the Proxy/Server receives a carrier packet that contains
an OAL packet/fragment with OAL
destination set to a {ULA,XLA}-MNP 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 ULA of the new Proxy/Server, decrements the OAL Hop Limit, then
supplies new OMNI L2 headers and forwards the resulting carrier
packet into the spanning tree which will eventually deliver it to
the new Proxy/Server. If the neighbor cache state for the Client is
REACHABLE and the Proxy/Server is a Hub responsible for serving as
the Client's address resolution responder and/or default router, it
submits the OAL packet/fragment for reassembly then decapsulates and
processes the resulting IPv6 ND message or original IP packet/parcel
accordingly. Otherwise, the Proxy/Server decrements the OAL Hop
Limit, supplies new OMNI L2 headers and sends the carrier packets
to the Client which must then perform data origin verification and
reassembly. (In the latter case, the Client may receive fragments of
the same original IP packet/parcel from different Proxy/Servers but
this will not interfere with reassembly.)When the Proxy/Server receives a carrier packet that contains an
OAL packet/fragment with OAL
destination set to a {ULA,XLA}-MNP that does not match the MSP, it
accepts the carrier packet only if data origin authentication
succeeds and if there is a network layer forwarding table entry for
a GUA route that matches the MNP. The Proxy/Server then discards the
L2 headers, performs OAL reassembly and decapsulation to obtain the
original IP packet/parcel, then presents it to the network layer
(as a Relay) where it will be delivered according to standard IP
forwarding.Clients and their FHS Proxy/Server peers can exchange original IP
packets/parcels over ANET underlay interfaces using L2 encapsulation
without invoking the
OAL, since the ANET is secured at the link and physical layers. By
forwarding original IP packets/parcels without invoking the OAL,
however, the Client and Proxy/Server can engage only in classical
path MTU discovery since loss and/or corruption due to various
per-link MTU limitations may occur within the ANET. Moreover, the
original IP packets/parcels 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/parcels without invoking the OAL, while invoking
the OAL for larger packets/parcels. This presents the beneficial
aspects of both small packet efficiency and large packet
robustness.)Proxy/Servers forward OAL packets/fragments received in secure
control plane carrier packets via the SRT secured spanning tree and
forward other OAL packets/fragments via
the unsecured spanning tree. When a Proxy/Server receives a carrier
packet from the secured spanning tree, it considers the message as
authentic without having to verify upper layer authentication
signatures. When a Proxy/Server receives a carrier packet from the
unsecured spanning tree, it applies data origin authentication
itself and/or forwards the enclosed unsecured OAL contents toward
the destination which must apply data origin authentication on its
own behalf.If the Proxy/Server has multiple original IP packets/parcels to
send to the same neighbor, it can concatenate them as a single OAL
super-packet . If the
super-packet begins with an IPv6 ND control message to be sent over
the secured spanning tree, the remainder of the super-packet also
traverses the secured spanning tree.Note: Clients and their FHS Proxy/Server (and other Client) peers
can exchange original IP packets/parcels over ANET underlay
interfaces without invoking the OAL, since the ANET is secured at
the link and physical layers. By forwarding original IP
packets/parcels without invoking the OAL, the ANET peers use the
same L2 encapsulation and fragmentation procedures as specified
for Hosts above.When the network layer admits an original IP packet/parcel into
the Gateway's OMNI interface, the OAL drops the packet if routing
indicates that it should be forwarded back to the network layer to
avoid looping. Otherwise, the Gateway examines the IP destination
address to determine if it matches the ULA of a neighboring Gateway
or Proxy/Server by examining the OMNI interface's network layer
neighbor cache. If so, the Gateway performs OAL encapsulation/fragmentation
followed by L2 encapsulation and forwards the resulting carrier
packets to the neighboring Gateway or Proxy/Server over a secured
tunnel to support the operation of the BGP routing protocol between
OAL neighbors.Gateways forward OAL packets/fragments received in spanning tree
carrier packets while decrementing the OAL Hop Limit but not the
original IP header TTL/Hop Limit. Gateways send carrier packets
that contain OAL packets/fragments with critical IPv6 ND control
messages or BGP routing protocol control messages via the SRT secured
spanning tree, and may send other carrier packets via the secured/unsecured
spanning tree or via more direct paths according to AFIB information. When
the Gateway receives a carrier packet, it removes the L2 headers to obtain
the OAL packet/fragment then searches for an AFIB entry that matches
the OAL header AFVI or an IP forwarding table entry that matches
the OAL destination address.Gateways process carrier packets that contain OAL packets/fragments
with OAL destinations that do not match their ULA or the SRT Subnet
Router Anycast address in the
same manner as for traditional IP forwarding within the OAL, i.e.,
they forward packets not explicitly addressed to themselves.
Gateways locally process OAL packets/fragments with OCH headers or full
OAL headers with their ULA or the SRT Subnet Router Anycast address
as the OAL destination. If the OAL packet/fragment contains an OCH or a
full OAL header with a CRH-32 extension, the Gateway examines the
next AFVI in the CRH-32 to locate the AFV entry in the AFIB for next
hop forwarding. If an AFV is found, the Gateway uses the next hop
AFVI to forward the OAL packet/fragment to the next hop while
decrementing the OAL Hop Limit but without reassembling. If the
Gateway has a NCE for the target Client with an entry for the target
underlay interface and current L2 addresses, the Gateway instead
forwards the OAL packet/fragment directly to the target Client while
using the final hop AFVI instead of the next hop (see: ).If the OAL packet/fragment includes a full OAL header addressed to
itself but does not include an AFVI, the Gateway instead reassembles
if necessary, verifies the OAL checksum, and processes the OAL
packet further. The Gateway first determines whether the OAL packet
includes an NS/NA message then processes the message according to
the multilink forwarding procedures discussed in . If the carrier packets arrived over the
secured spanning tree and the enclosed OAL packets/fragments are
addressed to its ULA, the Gateway instead reassembles then discards
the OAL header and forwards the original IP packet/parcel to the
network layer to support secured BGP routing protocol control
messaging. The Gateway instead drops all other OAL packets.Gateways forward OAL packets/fragments received in carrier packets
that arrived from a first segment via the secured spanning tree to the
next segment also via the secured spanning tree. Gateways forward OAL
packets/fragments received in carrier packets that arrived
from a first segment via the unsecured spanning tree to the next
segment also via the unsecured spanning tree. Gateways 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 underlay interface to be
used for transmission (i.e., a secured tunnel or an open INET
interface).As for Proxy/Servers, Gateways must verify that the L2 addresses
of carrier packets not received from the secured spanning tree are
"trusted" before forwarding according to an AFV (otherwise, the
carrier packet must be dropped).When an AERO node admits an original IP packet/parcel 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 an underlay network 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 carrier 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 underlay path as unusable and use another underlay
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 Gateway receives a carrier packet for which the
network-layer destination address is covered by an MSP assigned to a
black-hole route, the Gateway drops the carrier 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 OAL 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 an OAL source
as sub-options in the OMNI option of secured uNA messages. When the
OAL source receives the uNA message, it can extract the ICMPv6 error
message enclosed in the OMNI option and either process it locally or
translate it into a network-layer error to return to the original
source.AERO nodes observes the Router Discovery and Prefix Registration
specifications found in Section 15 of . AERO nodes further coordinate their
autoconfiguration actions with the mobility service as discussed in
the following sections.Each AERO Proxy/Server on the OMNI link is configured to
facilitate Client prefix delegation/registration requests. Each
Proxy/Server is provisioned with a database of MNP-to-Client ID
mappings for all Clients enrolled in the AERO service, as well as
any information necessary to authenticate each Client. The Client
database is maintained by a central administrative authority for the
OMNI link and securely distributed to all Proxy/Servers, e.g., via
the Lightweight Directory Access Protocol (LDAP) , via static configuration, etc. Clients receive
the same service regardless of the Proxy/Servers they select.Clients associate each of their ANET/INET underlay interfaces
with a FHS Proxy/Server. Each FHS Proxy/Server locally services one
or more of the Client's underlay interfaces, and the Client
typically selects one among them to serve as the Hub Proxy/Server
(the Client may instead select a "third-party" Hub Proxy/Server that
does not directly service any of its underlay interfaces). All of
the Client's other FHS Proxy/Servers forward proxyed copies of RS/RA
messages between the Hub Proxy/Server and Client without assuming
the Hub role functions themselves.Each Client associates with a single Hub Proxy/Server at a time,
while all other Proxy/Servers are candidates for providing the Hub
role for other Clients. An FHS Proxy/Server assumes the Hub role
when it receives an RS message with its own ULA 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 ULA
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 ULA of
another Proxy/Server to serve as a Hub.)Hosts and Clients on ENET interfaces associate with an upstream
Client on the ENET the same as a Client would associate with an ANET
Proxy/Server. In particular, the Host/Client sends an RS message via
the ENET which directs the message to the upstream Client. The
upstream Client returns an RA message. In this way, the downstream
nodes see the ENET as an ANET and see the upstream Client as a
Proxy/Server for that ANET.AERO Hosts, Clients and Proxy/Servers use IPv6 ND messages to
maintain neighbor cache entries. AERO Proxy/Servers configure their
OMNI interfaces as advertising NBMA interfaces, and therefore send
unicast RA messages with a short Router Lifetime value (e.g.,
ReachableTime seconds) in response to a Client's RS message.
Thereafter, Clients send additional RS messages to keep Proxy/Server
state alive.AERO Clients and Hub Proxy/Servers include prefix delegation
and/or registration parameters in RS/RA messages. The IPv6 ND
messages are exchanged between the Client and Hub Proxy/Server (via
any FHS Proxy/Servers acting as proxys) according to the prefix
management schedule required by the service. If the Client knows its
MNP in advance, it can employ prefix registration by including its
XLA-MNP 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 a TLA as
the source address of an RS message and with an OMNI option with
prefix delegation parameters to request an MNP.The following sections outlines Host, Client and Proxy/Server
behaviors based on the Router Discovery and Prefix Registration
specifications found in Section 15 of . These sections observe all of the
OMNI specifications, and include additional specifications of the
interactions of Client-Proxy/Server RS/RA exchanges with the AERO
mobility service.AERO Hosts and Clients discover the addresses of candidate
Proxy/Servers by resolving the Potential Router List (PRL) in a
similar manner as described in . Discovery
methods include static configuration (e.g., a flat-file map of
Proxy/Server addresses and locations), or through an automated means
such as Domain Name System (DNS) name resolution . Alternatively, the Host/Client can discover
Proxy/Server addresses through a layer 2 data link login exchange,
or through an RA response to a multicast/anycast RS as described
below. In the absence of other information, the Host/Client can
resolve the DNS Fully-Qualified Domain Name (FQDN)
"linkupnetworks.[domainname]" where "linkupnetworks" is a constant
text string and "[domainname]" is a DNS suffix for the OMNI link
(e.g., "example.com"). The name resolution returns a set of resource
records with Proxy/Server address information.The Host/Client then performs RS/RA exchanges over each of its
underlay interfaces to associate with (possibly multiple) FHS
Proxy/Serves and a single Hub Proxy/Server as specified in Section
15 of . The Host/Client then
sends each RS (either directly via Direct interfaces, via a VPN for
VPNed interfaces, via an access router for ANET interfaces or via
INET encapsulation for INET interfaces) and waits up to RetransTimer
milliseconds for an RA message reply (see ) while retrying up to MAX_RTR_SOLICITATIONS
if necessary. If the Host/Client receives no RAs, or if it receives
an RA with Router Lifetime set to 0, the Client SHOULD abandon
attempts through the first candidate Proxy/Server and try another
Proxy/Server.After the Host/Client registers its underlay 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 Host/Client prepares an RS message to send over
any available underlay interface as above. The RS includes an OMNI
option with prefix registration/delegation information and with an
Interface Attributes sub-option specific to the selected underlay
interface. When the Host/Client receives the Hub Proxy/Server's RA
response, it has assurance that both the Hub and FHS Proxy/Servers
have been updated with the new information.If the Host/Client wishes to discontinue use of a Hub
Proxy/Server it issues an RS message over any underlay interface
with an OMNI option with a prefix release indication (i.e., by
setting the OMNI Neighbor Coordination sub-option Preflen to 0).
When the Hub Proxy/Server processes the message, it releases the
MNP, sets the NCE state for the Host/Client to DEPARTED and returns
an RA reply with Router Lifetime set to 0. After a short delay
(e.g., 2 seconds), the Hub Proxy/Server withdraws the MNP from the
routing system. (Alternatively, when the Host/Client associates with
a new FHS/Hub Proxy/Server it can include an OMNI "Proxy/Server
Departure" sub-option in RS messages with the ULAs of the Old
FHS/Hub Proxy/Servers.)AERO Proxy/Servers act as both IP routers and IPv6 ND proxys, and
support a prefix delegation/registration service for Clients.
Proxy/Servers arrange to add their ULAs 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 underlay network
connections.When a FHS/Hub Proxy/Server receives a prospective Client's RS
message, it SHOULD return an immediate RA reply with Router Lifetime
set to 0 if it is currently too busy or otherwise unable to service
the Client; otherwise, it processes the RS as specified in Section
15 of . When the Hub
Proxy/Server receives the RS, it determines the correct MNPs to
provide to the Client by processing the XLA-MNP prefix parameters
and/or the DHCPv6 OMNI sub-option. When the Hub Proxy/Server returns
the MNPs, it also creates an XLA-MNP forwarding table entry for the
MNP resulting in a BGP update (see: ). The
Hub Proxy/Server then returns an RA to the Client with destination
set to the source of the RS (if an FHS Proxy/Server on the return
path proxys the RA, it changes the destination to the Client's
ULA-MNP).After the initial RS/RA exchange, the Hub Proxy/Server maintains
a ReachableTime timer for each of the Client's underlay 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 route from
the routing system after a short delay (e.g., 2 seconds). If
ReachableTime expires before a new RS is received on an individual
underlay interface, the Hub Proxy/Server marks the interface as
DOWN. If ReachableTime expires before any new RS is received on any
individual underlay 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 XLA-MNP from the routing system.The Hub Proxy/Server processes any IPv6 ND messages pertaining to
the Client while forwarding to the Client or responding on the
Client's behalf as necessary. The Hub Proxy/Server may also issue
unsolicited RA messages, e.g., with reconfigure parameters to cause
the Client to renegotiate its prefix delegation/registrations, with
Router Lifetime set to 0 if it can no longer service this Client,
etc. The Hub Proxy/Server may also receive carrier packets via the
secured spanning tree that contain initial data sent while route
optimization is in progress. The Hub Proxy/Server reassembles the
enclosed OAL packets/fragments, then re-encapsulates/re-fragments
and sends the carrier packets to the target Client via an FHS
Proxy/Server if necessary. Finally, If the NCE is in the DEPARTED
state, the old Hub Proxy/Server forwards any OAL packets/fragments it
receives from the secured spanning tree and destined to the Client
to the new Hub Proxy/Server, then deletes the entry after DepartTime
expires.Note: Clients SHOULD arrange to notify former Hub Proxy/Servers
of their departures, but Hub Proxy/Servers are responsible for
expiring neighbor cache entries and withdrawing XLA-MNP routes even
if no departure notification is received (e.g., if the Client leaves
the network unexpectedly). Hub Proxy/Servers SHOULD therefore set
Router Lifetime to ReachableTime seconds in solicited RA messages to
minimize persistent stale cache information in the absence of Client
departure notifications. A short Router Lifetime also ensures that
proactive RS/RA messaging between Clients and FHS Proxy/Servers will
keep any NAT state alive (see above).Note: All Proxy/Servers on an OMNI link MUST advertise consistent
values in the RA Cur Hop Limit, M and O flags, Reachable Time and
Retrans Timer fields the same as for any link, since unpredictable
behavior could result if different Proxy/Servers on the same link
advertised different values.AERO Clients register with FHS Proxy/Servers for each underlay
interface. Each of the Client's FHS Proxy/Servers must inform a
single Hub Proxy/Server of the Client's underlay interface(s) that
it services. For Clients on Direct and VPNed underlay interfaces,
the FHS Proxy/Server for each interface is directly connected, for
Clients on ANET underlay interfaces the FHS Proxy/Server is
located on the ANET/INET boundary, and for Clients on INET
underlay interfaces the FHS Proxy/Server is located somewhere in
the connected Internetwork. When FHS Proxy/Server "B" processes a
Client registration, it must either assume the Hub role or forward
a proxyed registration to another Proxy/Server "A" acting as the
Hub. Proxy/Servers satisfy these requirements as follows:when FHS Proxy/Server "B" receives a Client RS message, it
first verifies that the OAL Identification is within the
window for the NCE that matches the {UAL,XLA}-MNP in the RS
source address for this Client neighbor and authenticates the
message. If no NCE was found, Proxy/Server "B" instead creates
one in the STALE state and caches the Client-supplied
Interface Attributes, Origin Indication and OMNI Neighbor
Coordination sub-option window synchronization parameters as
well as the Client's observed L2 addresses (noting that they
may differ from the Origin addresses if there were NATs on the
path). Proxy/Server "B" then examines the RS destination
address. If the destination address is the ULA of a different
Proxy/Server "A", Proxy/Server "B" prepares a separate proxyed
version of the RS message with an OAL header with source set
to its own ULA and destination set to Proxy/Server B's ULA.
Proxy/Server "B" also writes its own information over the
Interface Attributes sub-option supplied by the Client, omits
or zeros the Origin Indication sub-option then forwards the
message into the OMNI link secured spanning tree.when Hub Proxy/Server "A" receives the RS, it assume the
Hub role, delegates an MNP for the Client if necessary, and
creates/updates a NCE indexed by the Client's XLA-MNP with FHS
Proxy/Server "B"'s Interface Attributes as the link-layer
address information for this FHS ifIndex. Hub Proxy/Server "A"
then prepares an RA message with source set to its own ULA and
destination set to the source of the RS message, then
encapsulates the RA in an OAL header with source set to its
own ULA and destination set to the ULA of FHS Proxy/Server
"B". Hub Proxy/Server "A" then performs fragmentation if
necessary and sends the resulting carrier packets into the
secured spanning tree.when FHS Proxy/Server "B" reassembles the RA, it locates
the Client NCE based on the RA destination. If the RA message
includes an OMNI "Proxy/Server Departure" sub-option,
Proxy/Server "B" first sends a uNA to the old FHS/Hub
Proxy/Servers named in the sub-option. If the RA message
delegates a new XLA-MNP, Proxy/Server "B" then resets the RA
destination to the corresponding ULA-MNP for this interface.
Proxy/Server "B" then re-encapsulates the message with OAL
source set to its own ULA and OAL destination set to ULA that
appeared in the Client's RS message OAL source, with an
appropriate Identification value, with an authentication
signature if necessary, with the Client's Interface Attributes
sub-option echoed and with the cached observed L2 addresses
written into an Origin Indication sub-option. Proxy/Server "B"
sets the P flag in the RA flags field to indicate that the
message has passed through a proxy ,
includes responsive window synchronization parameters, then
fragments the RA if necessary and returns the fragments to the
Client.The Client repeats this process over each of its additional
underlay interfaces while treating each additional FHS
Proxy/Server "C", "D", "E", etc. as a proxy to facilitate
RS/RA exchanges between the Hub and the Client. The Client
creates/updates NCEs for each such FHS Proxy/Server as well as
the Hub Proxy/Server in the process.After the initial RS/RA exchanges each FHS Proxy/Server
forwards any of the Client's carrier packets that contain OAL
packets/fragments with destinations
for which there is no matching NCE to a Gateway using OAL
encapsulation with its own ULA as the source and with destination
determined by the Client. The Proxy/Server instead forwards any
OAL packets/fragments destined to a neighbor cache target directly to
the target according to the OAL/link-layer information - the
process of establishing neighbor cache entries is specified in
.While the Client is still associated with FHS Proxy/Servers
"B", "C", "D", etc., each FHS Proxy/Server can send NS, RS and/or
unsolicited NA messages to update the neighbor cache entries of
other AERO nodes on behalf of the Client based on changes in
Interface Attributes, Traffic Selectors, etc. This allows for
higher-frequency Proxy-initiated RS/RA messaging over
well-connected INET infrastructure supplemented by lower-frequency
Client-initiated RS/RA messaging over constrained ANET data
links.If the Hub Proxy/Server "A" ceases to send solicited RAs, FHS
Proxy/Servers "B", "C", "D" can send unsolicited RAs over the
Client's underlay interface with destination set to (link-local)
All-Nodes multicast and with Router Lifetime set to zero to inform
Clients that the Hub Proxy/Server has failed. Although FHS
Proxy/Servers "B", "C" and "D" can engage in IPv6 ND exchanges on
behalf of the Client, the Client can also send IPv6 ND messages on
its own behalf, e.g., if it is in a better position to convey
state changes. The IPv6 ND messages sent by the Client include the
Client's XLA-MNP as the source in order to differentiate them from
the IPv6 ND messages sent by a FHS Proxy/Server.If the Client becomes unreachable over all underlay 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 OAL packets/fragments
destined to the Client to a Gateway via OAL encapsulation. When
DepartTime expires, the Hub Proxy/Server deletes the NCE,
withdraws the XLA-MNP route and discards any further carrier
packets that contain OAL packets/fragments 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/parcels without invoking the OAL so
that the ANET routing system transports the original IP
packets/parcels to the Proxy/Server. This can be beneficial, e.g.,
if the Client connects to the ANET via low-end data links such as
some aviation wireless links.If the ANET first-hop access router is on the same underlay
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
XLA-MNP (or to a TLA), and with destination address set to the ULA
of the Client's selected Proxy/Server or to link-scoped
All-Routers multicast. The Client includes an OMNI option
formatted as specified in .
The Client then sends the unencapsulated RS message, which will be
intercepted by the AERO-aware ANET access router.The ANET access router then performs OAL encapsulation on the
RS message and forwards it to a Proxy/Server at the ANET/INET
boundary. When the access router and Proxy/Server are one and the
same node, the Proxy/Server would share an underlay link with the
Client but its message exchanges with outside correspondents would
need to pass through a security gateway at the ANET/INET border.
The method for deploying access routers and Proxys (i.e. as a
single node or multiple nodes) is an ANET-local administrative
consideration.Note: When a Proxy/Server alters the IPv6 ND message contents
before forwarding (e.g., such as altering the OMNI option
contents), the original IPv6 ND message checksum or authentication
signature is invalidated, and a new checksum or authentication
signature must be calculated and included.Note: When a Proxy/Server receives a secured Client NS message,
it performs the same proxying procedures as for described for RS
messages above. The proxying procedures for NS/NA message
exchanges is specified in .In environments where fast recovery from Proxy/Server failure
is required, FHS Proxy/Servers SHOULD use proactive Neighbor
Unreachability Detection (NUD) to track Hub Proxy/Server
reachability in a fashion that parallels 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
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 exchanges with the
Hub Proxy/Server, e.g., one exchange per second. The FHS
Proxy/Server sends the NS message via the spanning tree with its
own ULA as the source and the ULA of the Hub Proxy/Server as the
destination, and the Hub Proxy/Server responds with an NA. 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 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 a
different Proxy/Server to assume the Hub role (i.e., by sending an
RS with destination set to the ULA of the new Hub).When a Client is not pre-provisioned with an MNP, 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 a TLA 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
creates an XLA based on the delegated MNP adds an XLA-MNP route to
the routing system. The Hub Proxy/Server then sends an RA back to
the Client either directly or via an FHS Proxy/Server acting as a
proxy. The Proxy/Server that returns the RA directly to the Client
sets the (newly-created) ULA-MNP as the destination address and
with the DHCPv6-PD Reply message and OMNI Neighbor Coordination
sub-option Preflen coded in the OMNI option. When the Client
receives the RA, it creates a default route, assigns the Subnet
Router Anycast address and sets its {ULA,XLA}-MNP based on the
delegated MNP.Note: Further details of the DHCPv6-PD based MNP registration
(as well as a minimal MNP delegation alternative that avoids
including a DHCPv6 message sub-option in the RS) are found in
.Note: when the Hub Proxy/Server forwards an RA to the Client
via a different node acting as a FHS Proxy/Server, the Hub sets
the RA destination to the same address that appeared in the RS
source. The FHS Proxy/Server then subsequently sets the RA
destination to the ULA-MNP when it forwards the Proxyed version of
the RA to the Client - see
for further details.AERO nodes invoke address resolution, multilink forwarding and
route optimization when they need to forward initial original IP
packets/parcels to new neighbors over ANET/INET interfaces and for
ongoing multilink forwarding coordination with existing neighbors.
Address resolution is based on an IPv6 ND NS/NA(AR) messaging exchange
between an Address Resolution Source (ARS) and the target neighbor as
the Address Resolution Target (ART). Either the ART itself or the
ART's current Hub Proxy/Server serves as the Address Resolution
Responder (ARR).Address resolution is initiated by the first eligible ARS closest
to the original source as follows:For Clients on VPNed and Direct interfaces, the Client's FHS
Proxy/Server is the ARS.For Clients on ANET interfaces, either the Client or the FHS
Proxy/Server may be the ARS.For Clients on INET interfaces, the Client itself is the
ARS.For correspondent nodes on INET/ENET interfaces serviced by a
Relay, the Relay is the ARS.For Clients that engage the Hub Proxy/Server in "mobility
anchor" mode, the Hub Proxy/Server is the ARS.For peers within the same ANET/ENET, route optimization is
through receipt of Redirect messages.The AERO routing system directs an address resolution request sent
by the ARS to the ARR. The ARR then returns an address resolution
reply which must include information that is current, consistent and
authentic. Both the ARS and ARR are then jointly responsible for
periodically refreshing the address resolution, and for quickly
informing each other of any changes. Following address resolution, the
ARS and ART perform continuous unicast multilink forwarding and route
optimization exchanges to maintain optimal forwarding profiles.The address resolution, multilink forwarding and route optimization
procedures are specified in the following sections.When one or more original IP packets/parcels from a source node
destined to a target node arrives, the ARS checks for a NCE with an
XLA-MNP that matches the target destination. If there is a NCE in
the REACHABLE state, the ARS invokes the OAL and sends the
resulting carrier packets according to the cached state then returns
from processing.Otherwise, if there is no NCE the ARS creates one in the
INCOMPLETE state. The ARS then prepares an NS message for Address
Resolution (NS(AR)) to send toward an ART while including the
original IP packet(s)/parcel(s) as trailing data following the
NS(AR) in an OAL super-packet . The resulting NS(AR) message must
be sent securely, and includes:the ULA of the ARS as the source address.the XLA corresponding to the original IP packet/parcel's
destination as the Target Address, e.g., for
2001:db8:1:2::10:2000 the Target Address is
fd00::2001:db8:1:2.the Solicited-Node multicast address
formed from the lower 24 bits of the original IP packet/parcel'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 an OMNI Neighbor
Coordination sub-option with Preflen set to the prefix length
associated with the NS(AR) source. The ARS also includes Interface
Attributes and/or Traffic Selectors for all of the source Client's
underlay interfaces, calculates the authentication signature or
checksum, includes window synchronization parameters then submits
the NS(AR) message for OAL encapsulation. The ARS sets the OAL
source to its own ULA and sets the OAL destination according to the
Client's RS message Neighbor Coordination 'U' flag (see: ). If the 'U' flag was set, the ARS
sets the OAL destination to the ULA of its Hub Proxy/Server which
maintains a Report List; otherwise, the ARS sets the destination to
the XLA-MNP corresponding to the ART. The ARS then selects an
identification value, inserts a fragment header, calculates the OAL
checksum, performs fragmentation and L2 encapsulation, then sends
the resulting carrier packets into the SRT secured spanning tree
without decrementing the network-layer TTL/Hop Limit field.When the ARS is a Client, it must instead use the ULA of one of
its FHS Proxy/Servers as the OAL destination. The ARS Client then
fragments, performs L2 encapsulation and forwards the carrier
packets to the FHS Proxy/Server. The FHS Proxy/Server then discards
the L2 headers, verifies the Identification, reassembles if necessary,
verifies the NS(AR) authentication signature or checksum, changes the
OAL source to its own ULA and changes the OAL destination to the ULA
of the Hub Proxy/Server or XLA-MNP
corresponding to the ART as specified above. The FHS Proxy/Server
then selects an appropriate Identification, calculates the OAL
checksum, re-fragments, performs L2 encapsulation and sends
the resulting carrier packets into the secured spanning tree on
behalf of the Client.Note: both the source and target Client/Relay and their Hub
Proxy/Servers include current and accurate information for their
multilink Interface Attributes profile. The Hub Proxy/Servers can be
trusted to provide an authoritative ARR response and/or mobility
update message on behalf of the source/target should the need arise.
While the source or target itself has no such trust basis, any
attempt to mount an attack by providing false Interface Attributes
information would only result in black-holing of return traffic,
i.e., the "attack" could only result in denial of service to the
source/target itself. Therefore, the source/target's asserted
Interface Attributes need not be validated by the Hub
Proxy/Server.If the ARS Client's Hub Proxy/Server maintains a Report List,
the carrier packets containing the NS(AR) will first arrive at the
at the Hub due to the OAL destination address supplied by the ARS
(see above). This source Hub then discards the L2 headers,
reassembles then records the NS Target Address in the Report List
for this source Client. The Hub then leaves the OAL source address
unchanged, but changes the OAL destination address to the XLA
corresponding to the NS Target Address. The Hub then decrements
the OAL header Hop Limit, includes an appropriate Identification,
recalculates the OAL checksum, refragments, performs L2 encapsulation
and sends the resulting carrier packets into the secured spanning
tree.When a Gateway receives carrier packets containing the NS(AR),
it discards the L2 headers and determines the next hop by
consulting its standard IPv6 forwarding table for the OAL header
XLA destination address. The Gateway next decrements the OAL
header Hop Limit, then performs L2 encapsulation and sends the
carrier packet(s) via the secured spanning tree the same as for
any IPv6 router, where they may traverse multiple OMNI link
segments. The final-hop Gateway will deliver the carrier packets
via the secured spanning tree to the Hub Proxy/Server (or Relay)
that services the ART.When the ART's Hub Proxy/Server receives the NS(AR) secured
carrier packets with the XLA-MNP of the ART as the OAL
destination, it discards the L2 headers, verifies the Identification,
reassembles if necessary, verifies the
OAL checksum then either forwards the NS(AR) to the ART or
processes it locally if it is acting as a Relay or as the ART's
designated ARR. The Hub Proxy/Server processes the message as
follows:if the NS(AR) target matches a Client NCE in the DEPARTED
state, the (old) Hub Proxy/Server resets the OAL destination
address to the ULA of the Client's new Hub Proxy/Server. The
old Hub Proxy/Server then decrements the OAL header Hop Limit,
recalculates the OAL checksum, re-fragments, includes
appropriate L2 headers then forwards the resulting carrier
packets over the secured spanning tree.If the NS(AR) target matches a Client NCE in the REACHABLE
state, the Hub Proxy/Server notes whether the NS(AR) arrived
from the secured spanning tree. If the message arrived via the
secured spanning tree the Hub Proxy/Server verifies the NS
checksum; otherwise, it must verify the message authentication
signature. If the Hub Proxy/Server maintains a Report List for
the ART, it next records the NS source address in the Report
List for this ART. If the Hub Proxy/Server is the ART's
designated ARR, it prepares to return an NA(AR) as discussed
below; otherwise, the Hub Proxy/Server determines the underlay
interface for the ART and proceeds as follows:If the Hub Proxy/Server is also the FHS Proxy/Server on
the underlay interface used to convey the NS(AR) to the
ART, it either recalculates the NS(AR) checksum or
includes an authentication signature as necessary. The Hub
then changes the OAL source to its own ULA and OAL
destination to the ULA-MNP of the ART, decrements the OAL
Hop Limit, includes a suitable identification value,
recalculates the OAL checksum, re-fragments if necessary,
includes appropriate L2 headers and sends the resulting
carrier packets over the underlay interface to the
ART.If the Hub Proxy/Server is not the FHS Proxy/Server on
the underlay interface used to convey the NS(AR) to the
ART, it instead recalculates the NS(AR) checksum, changes
the OAL source to its own ULA and changes the OAL
destination to the ULA of the FHS Proxy/Server for this
ART interface. The Hub Proxy/Server next decrements the
OAL Hop Limit, includes a suitable Identification value,
recalculates the OAL checksum, re-fragments if necessary,
includes appropriate L2 headers and sends the resulting
carrier packets over the secured spanning tree.When the FHS Proxy/Server receives the carrier packets,
it discards the L2 headers, reassembles and verifies the OAL
and NS(AR) checksums, then forwards to the ART the same as
described above.If the NS(AR) target matches one of its non-MNP routes, the
Hub Proxy/Server serves as both a Relay and an ARR, since the
Relay forwards original IP packets/parcels toward the (fixed
network) target at the network layer.If the ARR is a Relay or the ART itself, it first creates or
updates a NCE for the NS(AR) source address while processing the
window synchronization parameters and caching all Interface
Attributes and Traffic Selector information. Next, the ARR
prepares a (solicited) NA(AR) message to return to the ARS with
the source address set to the ART's XLA, the destination address
set to the NS(AR) ULA source address and the Target Address set to
the same value that appeared in the NS(AR) Target Address. The ARR
includes an OMNI option with OMNI Neighbor Coordination sub-option
Preflen set to the prefix length associated with the NA(AR) source
address.The ARR then includes Interface Attributes and Traffic Selector
sub-options for all of the ART's underlay interfaces with current
information for each interface. The ARR also includes either an
authentication signature or an NA message checksum as necessary.
The ARR next sets the NA(AR) message R flag to 1 (as a router) and
S flag to 1 (as a response to a solicitation) and sets the O flag
to 1 (as an authoritative responder). The ARR then submits the
NA(AR) for OAL encapsulation with source set to its own ULA and
destination set to the ULA that appeared in the NS(AR) OAL source,
selects an appropriate Identification, and includes window
synchronization parameters if necessary. The ARR then includes an
authentication signature or checksum, calculates the OAL checksum,
fragments, includes appropriate L2 headers and sends the
resulting (L2-encapsulated) carrier packets.When the Proxy/Server for the ART receives the carrier packets
sent by an ART acting as an ARR on its own behalf, it reassembles
if necessary, verifies the authentication signature or checksum
and includes a new authentication signature or checksum. The
Proxy/Server then changes the OAL source address to its own ULA,
changes the OAL destination to the ULA corresponding to the NA(AR)
destination, decrements the OAL Hop Limit, includes an appropriate
Identification, recalculates the NA and OAL checksums and
fragments if necessary. The Proxy/Server finally includes
appropriate L2 headers and sends the carrier packets into the
secured spanning tree.Note: If the Hub Proxy/Server is acting as the ARR but not as a
Relay, it prepares the NA(AR) with the R flag set to 0 but without
setting the SYN/ACK flags in the OMNI Neighbor Coordination
sub-option window synchronization parameters. This informs the ARS
that it must initiate multilink route optimization to synchronize
with the target either directly or via an LHS Proxy/Server (see:
). In all other ways, the Hub Proxy/Server
prepares and returns the NA(AR) the same as for the ART
Proxy/Server case above.When a Gateway receives NA(AR) carrier packets, it discards the
L2 headers and determines the next hop by consulting its standard
IPv6 forwarding table for the OAL header destination address. The
Gateway then decrements the OAL header Hop Limit, re-encapsulates
the carrier packets with new L2 headers and forwards them via the
SRT secured spanning tree where they may traverse multiple OMNI
link segments. The final-hop Gateway will deliver the carrier
packets via the secured spanning tree to a Proxy/Server for the
ARS.When the ARS receives the NA(AR) message, it first searches for
a NCE that matches the NA(AR) target address. The ARS then
processes the message the same as for standard IPv6 Address
Resolution . In the process, it caches all
OMNI option information in the NCE for the ART (including
Interface Attributes, Traffic Selectors, etc.), and caches the
NA(AR) XLA source address as the address of the ART.When the ARS is a Client, the SRT secured spanning tree will
first deliver the solicited NA(AR) message to the FHS
Proxy/Server, which re-adjusts the OAL header and forwards the
message to the Client. If the Client is on a well-managed ANET,
physical security and protected spectrum ensures security for the
NA(AR) without needing an additional authentication signature; if
the Client is on the open INET the Proxy/Server must instead
include an authentication signature (while adjusting the OMNI
option size, if necessary). The Proxy/Server uses its own ULA as
the OAL source and the ULA-MNP of the Client as the OAL
destination when it forwards the NA(AR). The Proxy/Server then
decrements the OAL Hop Limit, includes an appropriate
Identification, recalculates the OAL checksum, re-fragments,
includes appropriate L2 headers and sends the carrier packets
over the underlay interface to the Client.After the ARS transmits the first NS(AR), it should wait up to
RETRANS_TIMER seconds to receive a responsive NA(AR). The ARR can
then retransmit the NS(AR) up to MAX_UNICAST_SOLICIT times before
giving up.Following address resolution, the ARS and ART can assert
multilink forwarding paths through underlay interface pairs serviced
by the same source/destination ULAs by sending unicast NS/NA
messages with OMNI AERO Forwarding Parameter (AFP) and/or Neighbor
Coordination sub-options. The unicast NS/NA messages establish
multilink forwarding state in OAL intermediate nodes in the path
between the ARS and ART. Note that either the ARS or ART can
independently initiate multilink forwarding by sending unicast NS
messages on behalf of specific underlay interface pairs.Nodes that configure OMNI interfaces include an additional
forwarding table termed the AERO Forwarding Information Base (AFIB)
that supports OAL packet/fragment forwarding based on OMNI neighbor
underlay interface pairs. The AFIB contains AERO Forwarding Vectors
(AFVs) identified by locally-unique 4-octet values known as AFV
Indexes (AFVIs). The AFVs cache uncompressed OAL header information
as well as the previous/next-hop addressing and AFVI
information.OAL source, intermediate and target nodes create AFVs/AFVIs when
they process an NS message with an AFP sub-option with Job code '00'
(Initialize; Build B) or a solicited NA message with Job code '01'
(Follow B; Build A) (see: ).
The OAL source of the NS (which is also the OAL destination of the
solicited NA) is considered to reside in the "First Hop Segment
(FHS)", while the OAL destination of the NS (which is also the OAL
source of the solicited NA) is considered to reside in the "Last Hop
Segment (LHS)".The FHS and LHS roles are determined on a per-interface-pair
basis. After address resolution, either peer is equally entitled to
initiate multilink forwarding on behalf of a specific FHS/LHS
underlay interface pair. The peer that sends the initiating NS with
Job code '00' message for a specific pair becomes the FHS peer while
the one that returns the NA response becomes the LHS peer for that
pair only. It is therefore quite possible (and even commonplace)
that both peers may assume the FHS role for some pairs while
assuming the LHS role for other pairs, i.e., even though each peer
maintains only a single NCE.When an OAL node initiates or forwards an NS with Job code '00',
it creates an AFV, records the NS source and destination ULAs then
generates and assigns a locally-unique "B" AFVI (while also caching
the "B" values for all previous OAL hops on the path from the FHS
OAL source). When the OAL node receives future OAL packets/fragments
that include "B", it can unambiguously locate the correct AFV and
determine directionality without examining addresses. When the AFV
is indexed by its "B" AFVI, it returns the ULAs in (dst,src) order
the opposite of how they appeared in the OAL header of the original
NS to support full header reconstruction for reverse-path
forwarding. (If the NS message included a nested OAL encapsulation,
the ULAs of both OAL headers are returned.)When an OAL node initiates or forwards a solicited NA with Job
code '01', it uses the "B" AFVI to locate the AFV created by the NS
then generates and assigns a locally-unique "A" AFVI (while also
caching the "A" values for all previous OAL hops on the path from
the LHS OAL source). When the OAL node receives future carrier
packets that include "A", it can unambiguously locate the correct
AFV and determine directionality without examining addresses. When
the AFV is indexed by its "A" AFVI, it returns the ULAs in (src,dst)
order the same as they appeared in the OAL header of the original NS
to support full header reconstruction for forward-path forwarding.
(If the NS message included a nested OAL encapsulation, the ULAs of
both OAL headers are returned.)OAL nodes generate random non-zero 32-bit values as candidate
AFVIs which must first be tested for local uniqueness. If a
candidate AFVI s already in use, the OAL node repeats the random
generation process until it obtains a unique non-zero value. Since
the number of AFVs 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. Since the uniqueness property is node-local
only, an AFVI locally generated by a first OAL node must not be
tested for uniqueness by other OAL nodes.OAL nodes cache AFVs for up to ReachableTime seconds following
their initial creation. If the node processes another NS or NA
message specific to an AFV, it resets ReachableTime to
REACHABLE_TIME seconds, i.e., the same as for NCEs. If ReachableTime
expires, the node deletes the AFV and frees its associated AFVIs so
they can be reused for future AFVs.The following sections provide the detailed specifications of
these NS/NA exchanges for all nodes along the forward and reverse
paths.When an FHS OAL source has an original IP packet/parcel to send
to an LHS OAL target following multilink address resolution, it
first selects a source and target underlay interface pair. The FHS
source uses its cached information for the target underlay
interface as LHS information then prepares an NS message with an
AFP sub-option with Job code '00' and with the NS source set to
its own ULA or XLA and the NS destination set to the ULA or XLA of
the LHS target. The FHS source then sets window synchronization
information in the OMNI Neighbor Coordination sub-option and
creates a NCE for the selected target ULA or XLA in the INCOMPLETE
state. The FHS source next creates an AFV then generates and
assigns a locally-unique "B" AFVI to the AFV while also including
it as the first "B" entry in the AFP AFVI List. The FHS source
then includes any FHS/LHS addressing information it knows locally
in the AFP sub-option, i.e., based on information discovered
through address resolution.If the FHS source is the FHS Proxy/Server, it then 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 ULA of the LHS Proxy/Server.
If there is no NCE, the FHS Proxy/Server creates one in the
INCOMPLETE state. If a new NCE was created (or if the existing NCE
requires fresh window synchronization), the FHS Proxy/Server then
writes window synchronization parameters into the AFP Tunnel
Window Synchronization fields. The FHS Proxy/Server then performs
OAL encapsulation while setting the OAL source to its own ULA and
setting the OAL destination to the FHS Subnet Router Anycast ULA
determined by applying the FHS SRT prefix length to its ULA. The
FHS Proxy/Server then selects an appropriate Identification value,
calculates the OAL checksum, fragments if necessary, encapsulates
in appropriate L2 headers then sends the carrier packets into
the secured spanning tree which will deliver them to a Gateway
interface that assigns the FHS Subnet Router Anycast ULA.If the FHS source is the FHS Client, it instead includes an
authentication signature if necessary. If FHS FMT-Forward is set
and LHS FMT-Forward is clear, the FHS Client creates/updates a NCE
for the ULA of the LHS Proxy/Server as above and includes Tunnel
Window Synchronization parameters. The FHS Client then performs
OAL encapsulation, sets the OAL source to its own ULA-MNP and sets
the OAL destination to the ULA of the FHS Proxy/Server. The FHS
Client finally selects an appropriate Identification value for the
FHS Proxy/Server, calculates the OAL checksum, fragments if
necessary, encapsulates in appropriate L2 headers then sends
the carrier packets to the FHS Proxy/Server.When the FHS Proxy/Server receives the carrier packets, it
discards the L2 headers then verifies the Identification,
reassembles if necessary, verifies the OAL checksum and verifies
the NS authentication
signature or checksum. The FHS Proxy/Server then creates an AFV
(i.e., the same as the FHS Client had done) while caching the AFP
AFVI List "B" entry along with the FHS Client addressing
information as previous hop information for this AFV. The FHS
Proxy/Server next generates a new locally-unique "B" AFVI, then
both assigns it as the AFV index and writes it as the next "B"
entry in the AFP AFVI List (while also writing any FHS Client and
Proxy/Server addressing information). The FHS Proxy/Server then
checks FHS/LHS FMT-Forward/Mode to determine whether to create a
NCE for the LHS Proxy/Server ULA and include Tunnel Window
Synchronization parameters the same as above. The FHS Proxy/Server
then calculates the NS checksum and sets the OAL source address to
its own ULA and destination address to the FHS Subnet Router
Anycast ULA. The FHS Proxy/Server finally decrements the OAL Hop
Limit, includes an Identification appropriate for the secured
spanning tree, calculates the OAL checksum and re-fragments if
necessary. The FHS Proxy/Server finally includes appropriate L2
headers and sends the carrier packets into the secured spanning
tree.Gateways in the spanning tree forward OAL packets/fragments 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 Gateway receives an OAL packet/fragment
over the secured spanning tree addressed to its ULA or the FHS Subnet
Router Anycast ULA, it instead reassembles to obtain the NS then
verifies the OAL and NS checksums. The FHS Gateway next creates an
AFV (i.e., the same as the FHS Proxy/Server had done) while
caching the AFP FHS Client and Proxy/Server addressing information
and corresponding AFVI List "B" list values in the AFV to enable
future reverse path forwarding to this FHS Client. The FHS Gateway
then generates a locally-unique "B" AFVI for the AFV and also
writes it as the next "B" entry in the NS AFP AFVI List.The FHS Gateway then examines the SRT prefixes corresponding to
both FHS and LHS. If the FHS Gateway has a local interface
connection to both the FHS and LHS (whether they are the same or
different segments), the FHS/LHS Gateway caches the NS AFP LHS
information in the AFV, writes its LHS ULA and L2ADDR into the NS
AFP LHS fields, then sets its LHS ULA as the OAL source and the
ULA of the LHS Proxy/Server as the OAL destination. If the FHS and
LHS prefixes are different, the FHS Gateway instead sets its FHS
ULA as the OAL source and the LHS Subnet Router Anycast ULA as the
OAL destination. The FHS Gateway then decrements the OAL Hop
Limit, selects an appropriate Identification, recalculates the NS
and OAL checksums, re-fragments if necessary, then finally
includes appropriate L2 headers and sends the carrier packets
into the secured spanning tree.When the FHS and LHS Gateways are different, the LHS Gateway
will receive carrier packets over the secured spanning tree from
the FHS Gateway, noting there may be many intermediate Gateways in
the path between FHS and LHS which will simply forward the enclosed
OAL packets/fragments without further processing. The LHS Gateway then
reassembles to obtain the NS, verifies the OAL and NS checksums
then creates an AFV (i.e., the same as the FHS Gateway had done)
while caching the AFP "B" AFVIs and addressing information of
previous OAL forwarding hops. In particular, the LHS Gateway
caches the ULA of the FHS Gateway as the spanning tree address for
the previous-hop, caches the LHS information then generates a
locally-unique "B" AFVI for the AFV. The LHS Gateway then writes
its own LHS ULA and L2ADDR into the AFP sub-option while also
writing "B" as the next entry in the AFP AFVI List. The LHS
Gateway then sets its own ULA as the OAL source and the ULA of the
LHS Proxy/Server as the OAL destination, decrements the OAL Hop
Limit selects an appropriate Identification, recalculates the NS
and OAL checksums, re-fragments if necessary, then finally
includes appropriate L2 headers and sends the carrier packets
into the secured spanning tree.When the LHS Proxy/Server receives the carrier packets from the
secured spanning tree, it discards the L2 headers, reassembles if
necessary, verifies the OAL and NS checksums 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 AFV and caches the AFP "B" AFVIs and
addressing information of previous OAL forwarding hops the same as
for the prior hop. If the NS destination is the XLA of the LHS
Client, the LHS Proxy/Server also generates a locally-unique "B"
AFVI and assigns it both to the AFVI and as the next "B" entry in
the AFVI 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 ULA of the FHS Proxy/Server (if necessary)
and sets the state to STALE, then caches any Tunnel Window
Synchronization parameters.If the NS destination matches its own ULA, the LHS Proxy/Server
next prepares to return a solicited NA with Job code '01'. If the
NS source was the XLA of the FHS Client, the LHS Proxy/Server
first creates or updates an NCE for the XLA with state set to
STALE. The LHS Proxy/Server next caches the NS OMNI Neighbor
Coordination sub-option window synchronization parameters and AFP
information (including the AFVI List) in the NCE corresponding to
the ULA source. When the LHS Proxy/Server forwards future carrier
packets based on the NCE, it can populate forwarding information
in a CRH-32 routing header to enable forwarding based on the
cached AFVI List "B" entries instead of ULA addresses.The LHS Proxy/Server then creates an NA with Job code '01'
while copying the NS AFP sub-option into the NA. The LHS
Proxy/Server then generates a locally-unique "A" AFVI and both
assigns it to the AFV and includes it as the first "A" entry in
the AFP sub-option AFVI List (see: for details on AFVI List A/B
processing). The LHS Proxy/Server then includes end-to-end window
synchronization parameters in the OMNI Neighbor Coordination
sub-option (if necessary) and also tunnel window synchronization
parameters in the AFP sub-option (if necessary). The LHS
Proxy/Server then encapsulates the NA with OAL source set to its
own ULA and OAL destination set to the ULA of the LHS Gateway. The
LHS Proxy/Server then selects an appropriate Identification value,
calculates the NA and OAL checksums, fragments if necessary then
finally includes appropriate L2 headers and forwards the carrier
packets into the secured spanning tree.If the NS destination was the XLA of the LHS Client, the LHS
Proxy/Server instead includes an authentication signature in the
NS if necessary (otherwise recalculates the checksum), then
changes the OAL source to its own ULA and changes the OAL
destination to the ULA-MNP of the LHS Client. The LHS Proxy/Server
then decrements the OAL Hop Limit, selects an appropriate
Identification value, calculates the OAL checksum, fragments if
necessary then finally includes appropriate L2 headers and
sends the carrier packets to the LHS Client. When the LHS
Client receives the carrier packets, it discards the L2 headers,
verifies the Identification, reassembles if necessary, then verifies
the OAL checksum and NS authentication signature or checksum. The
LHS Client then creates a NCE for the NS ULA source address in the
STALE state and examines the AFP sub-option. If LHS FMT-Forward is
set, FHS FMT-Forward is clear and the NS source was an XLA, the
Client also creates a NCE for the ULA of the FHS Proxy/Server in
the STALE state and caches any Tunnel Window Synchronization
parameters. The Client then caches the NS OMNI Neighbor
Coordination and AFP sub-options in the NCE corresponding to the
NS ULA source, then creates an AFV, caches the addressing
information and "B" entries of the previous OAL hops then finally
generates and assigns a locally-unique "A" AFVI the same as for
previous hops.The LHS Client then prepares an NA using exactly the same
procedures as for the LHS Proxy/Server above, except that it uses
its XLA as the NA source and the NS source as the NA destination.
The LHS Client also includes an authentication signature if
necessary (otherwise calculates the checksum), then encapsulates
the NA with OAL source set to its own ULA-MNP and OAL destination
set to the ULA of the LHS Proxy/Server. The LHS Client finally
includes an appropriate Identification, calculates the OAL
checksum, fragments if necessary then includes appropriate L2
headers and sends the carrier packets to the LHS Proxy/Server.
When the LHS Proxy/Server receives the carrier packets, it discards
the L2 headers verifies the Identifications, reassembles if necessary,
verifies the OAL checksum and NA authentication signature or
checksum, then uses the current AFP AFVI List "B" entry to locate
the AFV. The LHS Proxy/Server then caches the addressing and "A"
information for the LHS Client in the AFV, then generates a
locally-unique "A" AFVI and both assigns it to the AFV and writes
it as the next AFP AFVI 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 calculates the NA checksum, sets the OAL source to its own
ULA and destination to the ULA of the LHS Gateway, decrements the
OAL Hop Limit, includes an appropriate Identification, calculates
the OAL checksum, re-fragments if necessary then finally includes
appropriate L2 headers and sends the carrier packets into the
secured spanning tree.When the LHS Gateway receives the carrier packets containing
the NA message, it discards the L2 headers, reassembles if necessary,
verifies the OAL and NA checksums then uses the current NA AFP AFVI
List "B" entry to locate the AFV. The LHS Gateway then caches the AFP
addressing and
AFVI List "A" information for the previous hops in the AFV, then
generates a locally-unique "A" AFVI and both assigns it to the AFV
and writes it as the next AFP AFVI List "A" entry. The LHS Gateway
then recalculates the NA checksum. If the LHS Gateway is connected
directly to both the FHS and LHS segments (whether the segments
are the same or different), the LHS Gateway will have already
cached the FHS/LHS information based on the original NS; the LHS
Gateway then sets the OAL source to its FHS ULA and OAL
destination to the ULA of the FHS Proxy/Server. Otherwise, the LHS
Gateway sets the OAL source to its LHS ULA and OAL destination to
the ULA of the FHS Gateway. The LHS Gateway then decrements the
OAL Hop Limit, selects an appropriate Identification, recalculates
the OAL checksum, re-fragments if necessary, includes appropriate
L2 headers and finally sends the carrier packets into the
secured spanning tree.When the FHS and LHS Gateways are different, the FHS Gateway
will receive carrier packets containing the NA message from the
LHS Gateway over the secured spanning tree, where there may have
been many intermediate Gateway forwarding hops. The FHS Gateway
then discards the L2 headers, reassembles if necessary, verifies
the OAL and NA checksums and locates the AFV based on the current
AFP AFVI List "B" entry. The FHS Gateway then caches the addressing
and "A" information for the previous hops in the AFV and generates a
locally-unique "A" AFVI. The FHS Gateway then assigns the new "A"
value to the AFV, records "A" in the AFP AFVI List then writes its
FHS ULA and L2ADDR into the AFP FHS Gateway fields. The FHS
Gateway then recalculates the NA checksum, sets its FHS ULA as the
OAL source and sets the ULA of the FHS Proxy/Server as the OAL
destination. The FHS Gateway then decrements the OAL Hop Limit,
selects an appropriate Identification value, recalculates the OAL
checksum, re-fragments if necessary, includes appropriate L2
headers and finally sends the carrier packets into the secured
spanning tree.When the FHS Proxy/Server receives the carrier packets from the
secured spanning tree, it discards the L2 headers, reassembles if
necessary, verifies
the OAL and NA checksums then locates the AFV based on the current
AFP AFVI List "B" entry. The FHS Proxy/Server then caches the AFP
addressing and "A" information for the previous hops. If the NA
destination matches its own ULA, the FHS Proxy/Server then
examines LHS FMT. If FMT-Forward is clear, the FHS Proxy/Server
locates the NCE for the ULA of the LHS Proxy/Server and sets the
state to REACHABLE then caches any Tunnel Window Synchronization
parameters. If the NA source is the XLA of the LHS Client, the FHS
Proxy/Server then locates the LHS Client NCE and sets the state to
REACHABLE then caches the OMNI Neighbor Coordination window
synchronization parameters and prepares to return an
acknowledgement, if necessary.If the NA destination is the XLA of the FHS Client, the FHS
Proxy/Server also searches for and updates the NCE for the ULA of
the LHS Proxy/Server if necessary the same as above. The FHS
Proxy/Server then generates a locally-unique "A" AFVI and assigns
it both to the AFV and as the next AFP AFVI List "A" entry, then
includes an authentication signature or checksum in the NA
message. The FHS Proxy/Server then sets the OAL source to its own
ULA and sets the OAL destination to the ULA-MNP of the FHS Client.
The FHS Proxy/Server then decrements the OAL Hop Limit, selects an
appropriate Identification value, recalculates the OAL checksum,
re-fragments if necessary, includes appropriate L2 headers and
finally sends the carrier packets to the FHS Client.When the FHS Client receives the carrier packets, it discards
the L2 headers, verifies the Identification, reassembles if necessary,
verifies the OAL checksum and NA authentication signature or checksum,
then locates the AFV based on the current AFP AFVI List "B" entry. The
FHS Client then caches the previous hop addressing and "A" information
the same as for prior hops. The FHS Client then examines LHS FMT.
If FMT-Forward is clear, the FHS Client locates the NCE for the
ULA of the LHS Proxy/Server and sets the state to REACHABLE then
caches any Tunnel Window Synchronization parameters. If the NA
source is the XLA of the LHS Client, the FHS Client then locates
the LHS Client NCE and sets the state to REACHABLE then caches the
OMNI Neighbor Coordination window synchronization parameters and
prepares to return an unsolicited NA (uNA) acknowledgement, if
necessary.If either the FHS Client or FHS Proxy/Server needs to return an
acknowledgement to complete window synchronization, it prepares a
uNA message with an AFP sub-option with Job code set to '10'
(Follow A; Record B) (note that this step is unnecessary when
Rapid Commit route optimization is used per ). The FHS node sets the uNA source to its own
ULA or XLA, sets the uNA destination to the ULA or XLA of the LHS
node then includes Tunnel Window Synchronization parameters if
necessary. The FHS node next sets the AFP AFVI List to the cached
list of "A" entries received in the Job code '01' NA, but need not
set any other FHS/LHS information. The FHS node then encapsulates
the uNA message in an OAL header with its own ULA as the OAL
source. If the FHS node is the Client, it next sets the ULA of the
FHS Proxy/Server as the OAL destination, includes an
authentication signature or checksum, selects an appropriate
Identification value, calculates the OAL checksum, fragments if
necessary, includes appropriate L2 headers and finally sends
the carrier packets to the FHS Proxy/Server. The FHS Proxy/Server
then verifies the Identification, reassembles if necessary,
verifies the OAL checksum and uNA authentication signature or
checksum, then uses the current AFVI List "A" entry to locate the
AFV. The FHS Proxy/Server then writes its "B" AFVI as the next AFP
AFVI List "B" entry and determines whether it needs to include
Tunnel Window Synchronization parameters the same as it had done
when it forwarded the original NS with Job code '00'.The FHS Proxy/Server recalculates the uNA checksum then sets
its own ULA as the OAL source and the ULA of the FHS Gateway as
the OAL destination, The FHS Proxy/Server finally decrements the
OAL Hop Limit, selects an appropriate Identification, recalculates
the OAL checksum, includes appropriate L2 headers and finally
sends the carrier packets into the secured spanning tree. When
the FHS Gateway receives the carrier packets, it discards the L2
headers, reassembles if necessary, verifies the OAL and uNA checksums
then uses the current AFVI List "A" entry to locate the AFV. The FHS
Gateway
then writes its "B" AFVI as the next AFP AFVI List "B" entry, then
sets the OAL source to its own ULA. If the FHS Gateway is also the
LHS Gateway, it sets the OAL destination to the ULA of the LHS
Proxy/Server; otherwise it sets the OAL destination to the ULA of
the LHS Gateway. The FHS Gateway recalculates the uNA checksum
then decrements the OAL Hop Limit, selects an appropriate
Identification, recalculates the OAL checksum, re-fragments if
necessary, includes appropriate L2 headers and finally sends
the carrier packets into the secured spanning tree. If an LHS
Gateway receives the carrier packets, it processes them exactly
the same as the FHS Gateway had done while re-setting the OAL
destination to the ULA of the LHS Proxy/Server.When the LHS Proxy/Server receives the carrier packets, it
discards the L2 headers, verifies the Identification, reassembles
if necessary then verifies the OAL and
uNA checksums. The LHS Proxy/Server then locates the AFV based on
the current AFP AFVI List "A" entry then determines whether it is
a tunnel ingress the same as for the original NS. If so, the LHS
Proxy/Server updates the NCE for the tunnel far-end based on the
Tunnel Window Synchronization parameters. If the uNA destination
matches its own ULA, the LHS Proxy/Server next updates the NCE for
the source ULA based on the OMNI Neighbor Coordination sub-option
window synchronization parameters and MAY compare the AFVI List to
the version it had cached in the AFV based on the original NS.If the uNA destination is the XLA of the LHS Client, the LHS
Proxy/Server instead writes its "B" AFVI as the next AFP AFVI List
"B" entry and includes an authentication signature or checksum.
The LHS Proxy/Server then writes its own ULA as the OAL source and
the ULA-MNP of the Client as the OAL destination, then decrements
the OAL Hop Limit, selects an appropriate Identification and
recalculates the OAL checksum. The LHS Proxy/Server finally
re-fragments if necessary, includes appropriate L2 headers and
sends the resulting carrier packets to the LHS Client. When the
LHS Client receives the carrier packets, it discards the L2 headers,
verifies the Identification, reassembles if necessary, verifies the
OAL checksum and uNA authentication signature or checksum then
processes the message exactly the same as for the LHS Proxy/Server
case above.Following the initial NS/NA exchange with AFP sub-options, OAL
end systems and tunnel endpoints can begin exchanging ordinary
carrier packets that include "A/B" AFVIs and with Identification
values within their respective send/receive windows without
requiring security signatures and/or secured spanning tree
traversal. OAL end systems and intermediate nodes can also consult
their AFIBs when they receive carrier packets that contain OAL
packets/fragments with "A/B" AFVIs to unambiguously locate the
correct AFV and can use any discovered "A/B" values of other OAL
nodes to forward OAL packets/fragments to nodes that configure the
corresponding AFVIs. OAL end systems must then perform continuous
NS/NA exchanges to update window state, register new interface pairs
for optimized multilink forwarding, confirm reachability and/or
refresh AFIB cache state in the path before ReachableTime expires.While the OAL end systems continue to actively exchange OAL
packets, they are jointly responsible for updating cache state and
per-interface reachability before expiration. Window
synchronization state is shared by all underlay interfaces in the
FHS peer's NCE that use the same destination ULA so that a single
NS/NA exchange applies for all interfaces regardless of the
specific interface used to conduct the exchange. However, the
window synchronization exchange only confirms target Client
reachability over the specific underlay interface pair.
Reachability for other underlay interfaces that share the same
window synchronization state must be determined individually using
additional NS/NA messages.To update AFIB state in the path, the FHS node that sent the
original NS message with AFP Job code '00' can send additional NS
messages with Job code '10' (Follow "A"; Record "B"). The message
will be processed by all intermediate OAL nodes which will refresh
AFV timers and forward the NS onward toward the LHS node that
returned the original NA message. When the LHS node receives the
NS, it returns an NA message with AFP Job code '11' (Follow "B";
Record "A").At the same time, the LHS node that received the original NS
message with Job code '00' can send additional NS messages with
Job code '11' in order to cause the FHS node to return an NA
message with AFP Job code '10'. The process can therefore be
coordinated asynchronously with the FHS/LHS nodes initiating an
NS/NA exchange independently of one another. The exchanges will
succeed as long as the AFIB state in the path remains active. Note
that all intermediate node processing of Job code '10' and '11'
NS/NA messages is conducted the same as for the initial NS/NA
exchange according to the detailed specifications above.OAL sources can also begin including CRH-32s in OAL packets/fragments
with a list of "A/B" AFVIs that OAL intermediate nodes can use for
shortest-path forwarding based on AFVIs instead of
spanning tree addresses. OAL sources and intermediate nodes can
instead forward OAL packets/fragments with OAL compressed headers termed
"OCH" (see: ) that include
only a single "A/B" AFVI meaningful to the next hop, since all OAL
nodes in the path up to (and sometimes including) the OAL
destination have already established AFVs. Note that when an FHS
OAL source receives a solicited NA with Job code '01', the AFP
sub-option will contain an AFVI 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 AFP AFVI List "A"
entries last-to-first when it populates a CRH-32, or must select
the correct "A" entry to include in an OCH header based on the
intended OAL intermediate node or destination.When a Gateway receives unsecured carrier packets that contain
OAL packets/fragments destined to a
local SRT segment Client that has asserted direct reachability,
the Gateway performs direct forwarding while
bypassing the local Proxy/Server based on the Client's advertised
AFVIs and discovered NATed L2ADDR information (see: ). If the Client cannot be reached directly (or
if NAT traversal has not yet converged), the Gateway instead
forwards OAL packets/fragments directly to the local segment
Proxy/Server.When a Proxy/Server receives OAL packets/fragments destined to a
local SRT segment Client or forwards OAL packets/fragments received
from a local segment Client, it first locates the correct AFV. If
the OAL packet/fragment includes a secured IPv6 ND message, the
Proxy/Server uses the Client's NCE established through RS/RA
exchanges to re-encapsulate/re-fragment while sending outbound
secured carrier packets via the secured spanning tree and
sending inbound secured carrier packets while including an
authentication signature or checksum. For ordinary OAL packets/fragments,
the Proxy/Server uses the same AFV if directed by AFVI and/or OAL
addressing. Otherwise it locates an AFV established through an NS/NA
exchange between the Client and the remote SRT segment peer, and
forwards the OAL packet/fragments without first
reassembling/decapsulating.When a Proxy/Server or Client configured as a tunnel ingress
receives a carrier packet that includes an OAL packet/fragment
with a full OAL header with a ULA-MNP
source and CRH-32 routing header, or an OCH header with an AFVI
that matches an AFV, the ingress re-encapsulates the OAL packet/fragment
in a new full OAL header or an OCH header containing the next hop
AFVI and an Identification value appropriate for the end-to-end
window and the outer header containing an Identification value
appropriate for the tunnel endpoints. When a Proxy/Server or
Client configured as a tunnel egress receives an encapsulated
OAL packet/fragment, it verifies the Identification in the outer
header, then discards the outer header and forwards the inner
OAL packet/fragment to the final destination.When a Proxy/Server with FMT-Forward/Mode set to 0/1 for a
source Client receives carrier packets from the source Client, it
discards the L2 headers, verifies the Identification, reassembles
if necessary, then re-fragments if necessary to cause the new
fragments to fit within the MPS on the path from the Proxy/Server
as a tunnel ingress to the tunnel egress. The Proxy/Server then
performs OAL-in-OAL
encapsulation, performs L2 encapsulation and sends the resulting
carrier packets to the tunnel egress. When a Proxy/Server with
FMT-Forward/Mode set to 0/1 for a target Client receives carrier
packets from a tunnel ingress, it first decapsulates to obtain
the original fragments then reassembles to obtain the OAL packet.
The Proxy/Server then re-fragments if necessary to cause the OAL
fragments to match the target Client's underlay interface (Path)
MTU, then performs L2 encapsulation and sends the resulting
carrier packets to the target Client.When a source Client forwards OAL packets/fragments it can employ
header compression according to the AFVIs established through an
NS/NA exchange with a remote or local peer. When the source Client
forwards to a remote peer, it can forward OAL packets/fragments
to a local SRT Gateway (following the establishment of L2ADDR
information) while bypassing the Proxy/Server following route
optimization (see: ). When a target
Client receives carrier packets that contain OAL packets/fragments
that match a local AFV, 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 original
IP packet/parcel 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, they can exchange carrier packets that contain OAL
packets/fragments directly with header compression using AFVIs
discovered as above (see: ). The FHS Client
will have cached the "A" AFVI for the LHS Client, which will have
cached the "B" AFVI for the FHS Client.When the FHS Client or FHS Proxy/Server sends an NS for the
purpose of establishing multilink forwarding state, it should wait
up to RETRANS_TIMER seconds to receive a responsive NA. The FHS
node can then retransmit the NS up to MAX_UNICAST_SOLICIT times
before giving up. Note that each successive attempt establishes
new AFV state in the OAL intermediate nodes, but that any
abandoned stale AFV state will be quickly reclaimed.Multilink forwarding can often be invoked simultaneously with
Address Resolution in order to reduce control message overhead and
round-trip delays. When an ART acting as an ARR receives an NS(AR)
with a set of Interface Attributes for the ARS source Client, it
can perform "rapid commit" by immediately invoking multilink
forwarding as above at the same time as returning the NA(AR).In order to perform rapid commit, the ARR includes an AFP
sub-option with Job code '00' as the first OMNI sub-option in the
NA(AR) as though it were initiating a multilink coordination NS/NA
exchange as specified above. The ARR then includes any Interface
Attributes and/or Traffic Selector sub-options as necessary to
satisfy the address resolution request, and can also include
ordinary original IP packets/parcels as additional super-packet
extensions to this NA(AR) message if it has immediate data to send
to the ARS. The ARR then returns the NA(AR) to the ARS using the
same hop-by-hop OAL addressing disciplines as specified above for
an ordinary multilink NS/NA exchange. This will cause the NA(AR)
to visit all OAL intermediate nodes on the path towards the
ARS.When the NA(AR) traverses the return path to the ARS, OAL
intermediate nodes in the path process the NS AFP information
exactly the same as for an ordinary multilink forwarding exchange
as specified above, i.e., without examining the remaining NA(AR)
message contents. This results in the ARR node now assuming the
FHS role and the ARS assuming the LHS role from the perspective of
multilink forwarding coordination. When the NA(AR) arrives, the
ARS processes the window synchronization parameters while also
processing all other NA(AR) OMNI option information, thereby
eliminating an extraneous message transmission and associated
delay. The ARS (now acting as an LHS peer) then completes the
exchange by returning a responsive NA; if no NA response is
received within RETRANS_TIMER seconds, the ARR can retransmit the
NA(AR) up to MAX_NEIGHBOR_ADVERTISEMENT times before giving
up.This very importantly implies that the type of IPv6 ND message
used to convey an AFP with Job codes '00' and '01' (i.e., NS or
NA) is unimportant from the perspective of multilink forwarding.
This means that Job code '00' serves as the solicitation
indication and Job code '01' serves as the response such that
either an NS or NA message carrying an AFP with Job code '00' will
invoke a responsive NA message carrying an AFP with Job code '01'.
Also importantly, this condition does not apply for Job codes '10'
and '11'; for those job codes, an NA is only sent in response to
an NS and never in response to another NA.Following multilink route optimization for specific underlay
interface pairs, FHS/LHS Clients located on open INETs can invoke
Client/Gateway route optimization to improve performance and reduce
load and congestion on their respective Proxy/Servers. To initiate
Client/Gateway route optimization, the Client prepares an NS message
with its own XLA address as the source and the ULA of its Gateway as
the destination while creating a NCE for the Gateway if necessary.
The NS message must be no larger than the minimum MPS and
encapsulated as an atomic fragment.The Client then includes an Interface Attributes sub-option for
its underlay interface as well as an authentication signature but
does not include window synchronization parameters. The Client then
performs OAL encapsulation with its own ULA-MNP as the source and
the ULA of the Gateway as the destination while including a
randomly-chosen Identification value, then performs L2 encapsulation
on the atomic fragment and sends the resulting carrier packet
directly to the Gateway.When the Gateway receives the carrier packet, it removes the
L2 headers, verifies the NS
authentication signature then creates a NCE for the Client. The
Gateway then caches the L2 encapsulation addresses (which may have
been altered by one or more NATs on the path) as well as the
Interface Attributes for this Client ifIndex, and marks this Client
underlay interface as "trusted". The Gateway then prepares an NA
reply with its own ULA as the source and the XLA of the Client as
the destination where the NA again must be no larger than the
minimum MPS.The Gateway then echoes the Client's Interface Attributes,
includes an Origin Indication with the Client's observed L2
addresses and includes an authentication signature. The Gateway then
performs OAL encapsulation with its own ULA as the source and the
ULA-MNP of the Client as the destination while using the same
Identification value that appeared in the NS, then performs L2
encapsulation on the atomic fragment and sends the resulting carrier
packet directly to the Client.When the Client receives the NA reply, it caches the carrier
packet L2 source address information as the Gateway target address
via this underlay interface while marking the interface as
"trusted". The Client also caches the Origin Indication L2 address
information as its own (external) source address for this underlay
interface.After the Client and Gateway have established NCEs as well as
"trusted" status for a particular underlay interface pair, each node
can begin sending ordinary carrier packets intended for this
multilink route optimization directly to one another while omitting
the Proxy/Server from the forwarding path while the status is
"trusted". The NS/NA messaging will have established the correct
state in any NATs in the path so that NAT traversal is naturally
supported. The Client and Gateway must maintain a timer that watches
for activity on the path; if no carrier packets and/or NS/NA
messages are sent or received over the path before NAT state is
likely to have expired, the underlay interface pair status becomes
"untrusted".Thereafter, when the Client sends a carrier packet that contains
an OAL packet/fragment toward the Gateway as the next hop, the Client
includes the AFVI
for the Gateway (discovered during multilink route optimization)
instead of the AFVI for its Proxy/Server; the Gateway will accept
the OAL packet/fragment from the Client if and only if the AFVI matches
the correct AFV and the underlay interface status is trusted. (The
same is true in the reverse direction when the Gateway sends carrier
packets directly to the Client.)Note that the Client and Gateway each maintain a single NCE, but
that the NCE may aggregate multiple underlay interface pairs. Each
underlay interface pair may use differing source and target L2
addresses according to NAT mappings, and the "trusted/untrusted"
status of each pair must be tested independently. When no "trusted"
pairs remain, the NCE is deleted.Note that the above method requires Gateways to participate in
NS/NA message authentication signature application and verification.
In an alternate approach, the Client could instead exchange NS/NA
messages with authentication signatures via its Proxy/Server but
addressed to the ULA of the Gateway, and the Proxy/Server and
Gateway could relay the messages over the secured spanning tree.
However, this would still require the Client to send additional
messages toward the L2 address of the Gateway to populate NAT state;
hence the savings in complexity for Gateways would result in
increased message overhead for Clients.When the FHS/LHS Clients are both located on the same SRT
segment, Client-to-Client route optimization is possible following
the establishment of any necessary state in NATs in the path. Both
Clients will have already established state via their respective
shared segment Proxy/Servers (and possibly also the shared segment
Gateway) and can begin sending carrier packets directly via NAT
traversal while avoiding any Proxy/Server and/or Gateway hops.When the FHS/LHS Clients on the same SRT segment perform the
initial NS/NA exchange to establish AFIB state, they also include an
Origin Indication (i.e., in addition to an AFP sub-option) with the
mapped addresses discovered during the RS/RA exchanges with their
respective Proxy/Servers. After the AFV paths have been established,
both Clients can begin sending carrier packets via strict AFV paths
while establishing a direct path for Client-to-Client route
optimization.To establish the direct path, either Client (acting as the
source) transmits a bubble to the mapped L2 address for the target
Client which primes its local chain of NATs for reception of future
carrier packets from that L2 address (see:
and ). The source Client then
prepares an NS message with its own XLA as the source, with the XLA
of the target as the destination and with an OMNI option with an
Interface Attributes sub-option. The source Client then encapsulates
the NS in an OAL header with its own ULA-MNP as the source, with the
ULA-MNP of the target Client as the destination and with an
in-window Identification for the target. The source Client then
fragments and encapsulates in L2 headers addressed to its
Proxy/Server then sends the resulting carrier packets to the
Proxy/Server.When the Proxy/Server receives the carrier packets, it
re-encapsulates and sends them as unsecured carrier packets
according to AFIB state where they will eventually arrive at the
target Client which can verify that the identifications are within
the acceptable window and reassemble if necessary. Following
reassembly, the target Client prepares an NA message with its own
XLA as the source, with the XLA of the source Client as the
destination and with an OMNI option with an Interface Attributes
sub-option. The target Client then encapsulates the NA in an OAL
header with its own ULA-MNP as the source, with the ULA-MNP of the
source Client as the destination and with an in-window
Identification for the source Client. The target Client then
fragments and encapsulates in L2 headers addressed to the source
Client's Origin addresses then forwards the resulting carrier
packets directly to the source Client.Following the initial NS/NA exchange, both Clients mark their
respective (source, target) underlay interface pairs as "trusted"
for no more than ReachableTime seconds. While the Clients continue
to exchange carrier packets via the direct path avoiding all
Proxy/Servers and Gateways, they should perform additional NS/NA
exchanges via their local Proxy/Servers to refresh NCE state as well
as send additional bubbles to the peer's Origin address information
if necessary to refresh NAT state.Note that these procedures are suitable for a widely-deployed but
basic class of NATs. Procedures for advanced NAT classes are
outlined in , which provides mechanisms that
can be employed equally for AERO using the corresponding sub-options
specified by OMNI.Note also that each communicating pair of Clients may need to
maintain NAT state for peer to peer communications via multiple
underlay interface pairs. It is therefore important that Origin
Indications are maintained with the correct peer interface and that
the NCE may cache information for multiple peer interfaces.Note that the source and target Client exchange Origin
information during the secured NS/NA multilink route optimization
exchange. This allows for subsequent NS/NA exchanges to proceed
using only the Identification value as a data origin confirmation.
However, Client-to-Client peerings that require stronger security
may also include authentication signatures for mutual
authentication.Clients may be recursively nested within the ENETs of other
Clients. When a Client is the downstream-attached ENET neighbor of
an upstream Client, it still supports the route optimization
functions discussed above by maintaining an AFIB and assigning AFVI
values. When the Client processes an IPv6 ND NS/NA message that
includes an AFP sub-option, it writes its AFVI information as the
first/last AFVI list entry the same as for the single Client case
discussed above.The Client then forwards the NS/NA message to the next Client in
the extended OMNI link toward the FHS/LHS Proxy/Server, which
records the AFVI value then overwrites the AFVI list entry with its
own AFVI value. This process iteratively continues until the Client
that will forward the NS/NA message to the FHS/LHS Proxy/Server is
reached, at which point the NS/NA AFVI list entries are populated by
the intermediate nodes on the path to the LHS/FHS the same as
discussed above.In this way, each Client in the extended OMNI link discovers the
A/B AFVIs of the next/previous Client without intruding into the AFP
sub-option AFVI list. Therefore the list can remain fixed at 5
entries even though the Client-to-Client OMNI link extension can be
arbitrarily long. Therefore, route optimization is not possible
between consecutive Client members of the extended OMNI link but
becomes possible at the Internetworking border that separates the
FHS and LHS elements.When a Client forwards an OAL packet (or original IP
packet/parcel) from a Host or another Client connected to one of its
downstream ENETs to a peer within the same downstream ENET, the
Client returns an IPv6 ND Redirect message to inform the source that
that target can be reached directly. The contents of the Redirect
message are the same as specified in .In the same fashion, when a Proxy/Server forwards an OAL packet
(or original IP packet/parcel) from a Host or Client connected to
one of its downstream ANETs to a peer within the same downstream
ANET, the Proxy/Server returns an IPv6 ND Redirect message.All other route optimization functions are conducted per the
NS/NA messaging discussed in the previous sections.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 exchanges over the OMNI link secured
spanning tree (i.e. the same as described above) to test reachability
without risk of DoS attacks from nodes pretending to be a neighbor.
These NS/NA messages use the unicast XLAs/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 exchanges directly between neighbors without employing the
secured spanning tree as long as they include in-window
Identifications and either an authentication signature or
checksum.After route optimization directs a source FHS peer to a target LHS
peer with one or more link-layer addresses, either node may invoke
multilink forwarding state initialization to establish authentic
intermediate node state between specific underlay interface pairs
which also tests their reachability. Thereafter, either node acting as
the source may perform additional reachability probing through NS
messages over the SRT secured or unsecured spanning tree, or through
NS messages sent directly to an underlay interface of the target
itself. While testing a target underlay interface, the source can
optionally continue to forward OAL packets/fragments via alternate
interfaces, maintain a small queue of carrier packets until target
reachability is confirmed or include them as trailing data with the NS
in an OAL super-packet .NS messages are encapsulated, fragmented and transmitted as carrier
packets the same as for ordinary original IP data packets/parcels,
however the encapsulated destinations are either the ULA or XLA of the
source and either the ULA of the LHS Proxy/Server or the XLA of the
target itself. The source encapsulates the NS message the same as
described in and includes an Interface
Attributes sub-option with ifIndex set to identify its underlay
interface used for forwarding. The source then includes an in-window
Identification, fragments the OAL packet, includes L2 encapsulations
and sends the resulting carrier packets into the unsecured spanning
tree, either directly to the target if it is in the local segment or
directly to a Gateway in the local segment.When the target receives the NS carrier packets, it discards the L2
headers, verifies that it has a NCE for this source and that the
Identification is in-window then reassembles if necessary. The target
next verifies the NS authentication signature or checksum, then searches
for Interface Attributes in its NCE for the source that match the NS for
the NA reply. The target then prepares the NA with the source and
destination addresses reversed, encapsulates and sets the OAL source
and destination, includes an Interface Attributes sub-option in the NA
to identify the ifIndex of the underlay interface the NS arrived on
and sets the Target Address to the same value included in the NS. The
target next sets the R flag to 1, the S flag to 1 and the O flag to 1,
then selects an in-window Identification for the source and performs
fragmentation. The node then performs L2 encapsulation and sends
the carrier packets into the unsecured spanning tree either directly
to the source if it is in the local segment or directly to a Gateway
in the local segment.When the source receives the NA, it marks the target underlay
interface tested as "trusted". Note that underlay interface states are
maintained independently of the overall NCE REACHABLE state, and that
a single NCE may have multiple target underlay interfaces in various
"trusted/untrusted" states while the NCE state as a whole remains
REACHABLE.AERO is a fully Distributed Mobility Management (DMM) service in
which each Proxy/Server is responsible for only a small subset of the
Clients on the OMNI link. This is in contrast to a Centralized
Mobility Management (CMM) service where there are only one or a few
network mobility collective entities for large Client populations.
Clients coordinate with their associated FHS and Hub Proxy/Servers via
RS/RA exchanges to maintain the DMM profile, and the AERO routing
system tracks all current Client/Proxy/Server peering
relationships.Hub Proxy/Servers provide a designated router service for their
dependent Clients, while FHS Proxy/Servers provide a proxy conduit
between the Client and both the Hub and OMNI link in general. Clients
are responsible for maintaining neighbor relationships with their
Proxy/Servers through periodic RS/RA exchanges, which also serves to
confirm neighbor reachability. When a Client's underlay interface
attributes change, the Client is responsible for updating the Hub
Proxy/Server through new RS/RA exchanges using the FHS Proxy/Server as
a first-hop conduit. The FHS Proxy/Server can also act as a proxy to
perform some IPv6 ND exchanges on the Client's behalf without
consuming bandwidth on the Client underlay interface.Mobility management considerations are specified in the following
sections.Mobile Clients (and/or their Hub Proxy/Servers) accommodate
mobility and/or multilink change events by sending secured uNA
messages to each active neighbor. When a node sends a uNA message to
each specific neighbor on behalf of a mobile Client, it sets the
IPv6 source address to its own ULA or XLA, sets the destination
address to the neighbor's ULA or XLA and sets the Target Address to
the mobile Client's XLA. The uNA also includes an OMNI option with
OMNI Neighbor Coordination sub-option Preflen set to the prefix
length associated with the mobile Client's XLA, includes Interface
Attributes and Traffic Selectors for the mobile Client's underlay
interfaces and includes an authentication signature if necessary.
The node then sets the uNA R flag to 1, S flag to 0 and O flag to 1,
then encapsulates the message in an OAL header with source set to
its own ULA and destination set to either the specific neighbor's
ULA or the FHS Proxy/Server's ULA. The uNA message will then follow
the secured spanning tree and arrive at the specific neighbor.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 node can optionally send up to
MAX_NEIGHBOR_ADVERTISEMENT uNAs to each neighbor to increase the
likelihood that at least one will be received. Alternatively, the
node can set the PNG flag in the uNA OMNI option header to request a
uNA acknowledgement as specified in .When the FHS/LHS Proxy/Server receives a secured uNA message
prepared as above, if the uNA destination was its own ULA the
Proxy/Server uses the included OMNI option information to update its
NCE for the target but does not reset ReachableTime since the
receipt of a uNA message does not provide confirmation that any
forward paths to the target Client are working. If the destination
was the XLA of the FHS/LHS Client, the Proxy/Server instead changes
the OAL source to its own ULA, includes an authentication signature
if necessary, and includes an in-window Identification for this
Client. Finally, if the uNA message PNG flag was set, the node that
processes the uNA returns a uNA acknowledgement as specified in
.When a Client needs to change its underlay Interface Attributes
and/or Traffic Selectors for one or more underlay interfaces (e.g.,
due to a mobility event), the Client sends RS messages to its Hub
Proxy/Server (via first-hop FHS Proxy/Servers if necessary). Each RS
includes an OMNI option with Interface Attributes and/or Traffic
Selector sub-options for the ifIndex in question.Note that the first FHS Proxy/Server may change due to the
underlay interface change. If the Client RS includes an OMNI
Proxy/Server Departure sub-option for the former FHS Proxy/Server,
the new FHS Proxy/Server can send a departure indication (see ); otherwise, any stale state in the former FHS
Proxy/Server will simply expire after ReachableTime expires with no
effect on the Hub Proxy/Server.Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel
with sending carrier packets containing user data in case one or
more RAs are lost. If all RAs are lost, the Client SHOULD
re-associate with a new Proxy/Server.After performing the RS/RA exchange, the Client sends uNA
messages to all neighbors the same as described in the previous
section.When a Client needs to bring new underlay 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 underlay
interface (if necessary) with an OMNI option that includes an
Interface Attributes sub-option with appropriate link quality values
and with link-layer address information for the new link. The Client
then again sends uNA messages to all neighbors the same as described
above.When a Client needs to deactivate an existing underlay interface,
it sends a uNA message toward the Hub Proxy/Server via an FHS
Proxy/Server with an OMNI option with appropriate Interface
Attributes values for the deactivated link - in particular, the link
quality value 0 assures that neighbors will cease to use the
link.If the Client needs to send uNA messages over an underlay
interface other than the one being deactivated, it MUST include
Interface Attributes with appropriate link quality values for any
underlay interfaces being deactivated. The Client then again sends
uNA messages to all neighbors the same as described above.Note that when a Client deactivates an underlay interface,
neighbors that receive the ensuing uNA messages need not purge all
references for the underlay interface from their neighbor cache
entries. The Client may reactivate or reuse the underlay interface
and/or its ifIndex at a later point in time, when it will send new
RS messages to an FHS Proxy/Server with fresh interface parameters
to update any neighbors.The Client performs the procedures specified in when it first associates with a new Hub
Proxy/Server or renews its association with an existing Hub
Proxy/Server.When a Client associates with a new Hub Proxy/Server, it sends RS
messages to register its underlay interfaces with the new Hub while
including the old Hub's ULA in the "Old Hub Proxy/Server ULA" field
of a Proxy/Server Departure OMNI sub-option. When the new Hub
Proxy/Server returns the RA message via the FHS Proxy/Server (acting
as a proxy), the FHS Proxy/Server sends a uNA to the old Hub
Proxy/Server (i.e., if the ULA is non-zero and different from its
own). The uNA has the XLA of the Client as the source and the ULA of
the old hub as the destination and with OMNI Neighbor Coordination
sub-option Preflen set to 0. The FHS Proxy/Server encapsulates the
uNA in an OAL header with the ULA of the new Hub as the source and
the ULA of the old Hub as the destination, the fragments, performs
L2 encapsulation and sends the resulting carrier packets via the
secured spanning tree.When the old Hub Proxy/Server receives the carrier packets, it
decapsulates and reassembles if necessary to obtain the uNA then
changes the Client's NCE state to
DEPARTED, resets DepartTime and caches the new Hub Proxy/Server ULA.
After a short delay (e.g., 2 seconds) the old Hub Proxy/Server
withdraws the Client's MNP from the routing system. While in the
DEPARTED state, the old Hub Proxy/Server forwards any carrier
packets received via the secured spanning tree destined to the
Client's ULA-MNP to the new Hub Proxy/Server's ULA. After DepartTime
expires, the old Hub Proxy/Server deletes the Client's NCE.Mobility events may also cause a Client to change to a new FHS
Proxy/Server over a specific underlay interface at any time such
that a Client RS/RA exchange over the underlay interface will engage
the new FHS Proxy/Server instead of the old. The Client can arrange
to inform the old FHS Proxy/Server of the departure by including a
Proxy/Server Departure sub-option with a ULA for the "Old FHS
Proxy/Server ULA", and the new FHS Proxy/Server will issue a uNA
using the same procedures as outlined for the Hub above while using
its own ULA as the source address. This can often result in
successful delivery of carrier packets that would otherwise be lost
due to the mobility event.Clients SHOULD NOT move rapidly between Hub Proxy/Servers in
order to avoid causing excessive oscillations in the AERO routing
system. Examples of when a Client might wish to change to a
different Hub Proxy/Server include a Hub Proxy/Server that has
become unresponsive, 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 ENETs 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 underlay interfaces for which the
ANET has deployed native multicast services forward IGMP/MLD messages
into the ANET. The IGMP/MLD messages may be further forwarded by a
first-hop ANET access router acting as an IGMP/MLD-snooping switch
, then ultimately delivered to an ANET
Proxy/Server. The FHS Proxy/Server then acts as an ARS to send NS(AR)
messages to an ARR for the multicast source. Clients on INET and ANET
underlay interfaces without native multicast services instead send
NS(AR) messages as an ARS to cause their FHS Proxy/Server to forward
the message to an ARR. When the ARR prepares 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 ARS "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 ULA or XLA as the source
address, the solicited node multicast address corresponding to S as
the destination and the XLA 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 ARR "Y" that services S. Y will then return an NA(AR) that
includes an OMNI option with Interface Attributes for any underlay
interfaces that are currently servicing S.When X processes the NA(AR) it selects one or more underlay
interfaces for S and performs an NS/NA multilink forwarding 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 XLA of X as the next hop in the
reverse path. Since Gateways forward messages not addressed to
themselves without examining them, this means that the (reverse)
multicast tree path is simply from each Z* (and/or S) to X with no
other multicast-aware routers in the path.Following the initial combined Join/Prune and NS/NA messaging, X
maintains a NCE for each S the same as if X was sending unicast data
traffic to S. In particular, X performs additional NS/NA exchanges
to keep the NCE alive for up to t_periodic seconds . If no new Joins are received within t_periodic
seconds, X allows the NCE to expire. Finally, if X receives any
additional Join/Prune messages for (S,G) it forwards the messages
over the secured spanning tree.Client C that holds an MNP for source S may later depart from a
first Proxy/Server Z1 and/or connect via a new Proxy/Server Z2. In
that case, Y sends a uNA message to X the same as specified for
unicast mobility in . When X receives the
uNA message, it updates its NCE for the XLA for source S and sends
new Join messages in NS/NA exchanges addressed to the new target
Client underlay 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 ARS "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 address resolution information for Rendezvous Point (RP) "R"
for each G. X then includes a copy of each Join/Prune message in the
OMNI option of an NS message with its own ULA or XLA as the source
address and the ULA or XLA for R as the destination address, then
encapsulates the NS message in an OAL header with its own ULA as the
source and the 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/parcels in PIM Register messages, includes
the PIM Register messages in the OMNI options of uNA messages,
performs OAL encapsulation and fragmentation with Identification
values within the receive window for Client R* that aggregates R,
then performs L2 encapsulation and sends the resulting carrier packets.
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/parcel; 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/parcels 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/parcels 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 Gateways 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/parcels 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 Gateways.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 Gateways on the link. Correspondent nodes
can then perform Segment Routing to select the correct SRT, which will
then direct the original IP packet/parcel 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/parcels 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 Gateways on each INET partition, with each Gateway
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 Gateways.Relays that connect INETs/ENETs 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 Gateways 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 Gateways maintain BFD sessions in parallel with
their BGP peerings. If a Proxy/Server or Gateway fails, BGP peers will
quickly re-establish routes through alternate paths the same as for
common BGP deployments.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 XLA) changes. This should not present a
challenge for Clients with automated network renumbering services,
however presents limits for the durations of ongoing sessions that
would prefer to use a constant address.An early AERO implementation based on OpenVPN (https://openvpn.net/)
was announced on the v6ops mailing list on January 10, 2018 and an
initial public release of the AERO proof-of-concept source code was
announced on the intarea mailing list on August 21, 2015.Many AERO/OMNI functions are implemented and undergoing final
integration. OAL fragmentation/reassembly buffer management code has
been cleared for public release.The IANA has assigned the UDP port number "8060" for an earlier
experimental first version of AERO . This
document together with reclaims
UDP port number "8060" as the service port for UDP/IP encapsulation.
This document makes no request of IANA, since already provides instructions. (Note:
although was not widely implemented or
deployed, it need not be obsoleted since its messages use the invalid
ICMPv6 message type number '0' which implementations of this
specification can easily distinguish and ignore.)No further IANA actions are required.AERO Gateways configure underlay interface 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
Gateways of all OMNI link segments in turn configure underlay interface
secured tunnels with neighboring AERO Gateways for other OMNI link
segments 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. (Note that this
inter-segment Gateway arrangement mirrors the "half-gateway" model
discussed in the original Catenet proposal.)To prevent unauthorized local applications from congesting the
secured spanning tree, Proxy/Servers and Gateways should configure local
firewall settings to permit only the BGP protocol service daemon to
source routing protocol control messages with the ULA assigned to the
OMNI interface as the source and the ULA of a neighboring Proxy/Server
or Gateway as the destination. This could be implemented as a
port/address filtering configuration that permits only TCP port 179 (as
defined in the IANA "Service Names and Port Numbers" registry) when
using the ULA assigned to the OMNI interface. To prevent malicious
Clients from congesting the secured spanning tree, Proxy/Servers should
also rate-limit the secured IPv6 ND NS/NA messages they process for the
same (source, target) pair, e.g., by applying IPv6 ND
MAX_UNICAST_SOLICIT; MAX_NEIGHBOR_ADVERTISEMENT limits. This is
especially true for NS/NA messages that include ordinary original IP
data packets/parcels as part of a super-packet.To prevent spoofing vectors, Proxy/Servers MUST discard without
responding to any unsecured IPv6 ND messages that include OMNI
sub-options that would affect state. Also, Proxy/Servers MUST discard
without forwarding any original IP packets/parcels 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 sending any carrier packets that include an OAL
packet/fragment with 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 the secured spanning
tree, or 2) enable on-demand secure tunnel creation between Client
neighbors. Option 1) would result in longer routes than necessary and
impose traffic concentration on critical infrastructure elements. Option
2) could be coordinated between Clients using NS/NA messages with OMNI
Host Identity Protocol (HIP) "Initiator/Responder" message sub-options
to create
a secured tunnel on-demand, or to use the QUIC-TLS protocol to establish
a secured connection .AERO Clients that connect to secured ANETs need not apply security to
their IPv6 ND messages, since the messages will be authenticated and
forwarded by a perimeter Proxy/Server that applies security on its
INET-facing interface as part of the secured spanning tree (see above).
AERO Clients connected to the open INET can use network and/or transport
layer security services such as VPNs or can by some other means
establish a direct link to a Proxy/Server. When a VPN or direct link may
be impractical, however, INET Clients and Proxy/Servers SHOULD include
and verify authentication signatures for their IPv6 ND messages as
specified in .Application endpoints SHOULD use transport-layer (or higher-layer)
security services such as QUIC-TLS, TLS/SSL, DTLS or SSH to assure the same level of protection as for
critical secured Internet services. AERO Clients that require host-based
VPN services SHOULD use network and/or transport layer security services
such as IPsec, TLS/SSL, DTLS, etc. AERO Proxys and Proxy/Servers can
also provide a network-based VPN service on behalf of the Client, e.g.,
if the Client is located within a secured enclave and cannot establish a
VPN on its own behalf.AERO Proxy/Servers and Gateways 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
Gateways 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 carrier 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 ENETs 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, OAL 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 carrier 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, Eliot Lear, 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 Akash Agarwal, Kyle Bae, M. Wayne Benson, Dave
Bernhardt, Cam Brodie, John Bush, Balaguruna Chidambaram, Irene Chin,
Bruce Cornish, Claudiu Danilov, Sean Dickson, 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, Satish Raghavendran, Vijay Rajagopalan, Kristina Ross, Greg
Saccone, Bhargava Raman Sai Prakash, Rod Santiago, Madhanmohan
Savadamuthu, 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.
Akash Agarwal, Kyle Bae, Wayne Benson, Madhuri Madhava Badgandi,
Vijayasarathy Rajagopalan, Bhargava Raman Sai Prakash, Katie Tran and
Eric Yeh are especially acknowledged for their work on the AERO
implementation. Chuck Klabunde is honored for his support and
guidance, and we mourn his untimely loss.This work was inspired by the support and encouragement of countless
outstanding colleagues, managers and program directors over the span of
many decades. Beginning in the late 1980s,' the Digital Equipment
Corporation (DEC) Ultrix Engineering and DECnet Architects groups
identified early issues with fragmentation and bridging links with
diverse MTUs. In the early 1990s, engagements at DEC Project Sequoia at
UC Berkeley and the DEC Western Research Lab in Palo Alto included
investigations into large-scale networked filesystems, ATM vs Internet
and network security proxys. In the mid-1990s to early 2000s employment
at the NASA Ames Research Center (Sterling Software) and SRI
International supported early investigations of IPv6, ONR UAV
Communications and the IETF. An employment at Nokia where important IETF
documents were published gave way to a present-day engagement with The
Boeing Company. The work matured at Boeing through major programs
including Future Combat Systems, Advanced Airplane Program, DTN for the
International Space Station, Mobility Vision Lab, CAST, Caravan,
Airplane Internet of Things, the NASA UAS/CNS program, the FAA/ICAO
ATN/IPS program and many others. An attempt to name all who gave support
and encouragement would double the current document size and result in
many unintentional omissions - but to all a humble thanks.Earlier works on NBMA tunneling approaches are found in .Many of the constructs presented in this second edition of AERO are
based on the author's earlier works, including:The Internet Routing Overlay Network (IRON) Virtual Enterprise Traversal (VET) The Subnetwork Encapsulation and Adaptation Layer (SEAL) AERO, First Edition Note that these works cite numerous earlier efforts that are
not also cited here due to space limitations. The authors of those
earlier works are acknowledged for their insights.This work is aligned with the NASA Safe Autonomous Systems Operation
(SASO) program under NASA contract number NNA16BD84C.This work is aligned with the FAA as per the SE2025 contract number
DTFAWA-15-D-00030.This work is aligned with the Boeing Commercial Airplanes (BCA)
Internet of Things (IoT) and autonomy programs.This work is aligned with the Boeing Information Technology (BIT)
MobileNet program.http://openvpn.netBGP in 2015, http://potaroo.netThe Catenet Model For Internetworking,
https://www.rfc-editor.org/ien/ien48.txtThe Catenet Model For Internetworking (with figures),
http://www.postel.org/ien/pdf/ien048.pdfWireGuard, https://www.wireguard.comWireguardGuidelines for Use of Extended Unique Identifier (EUI),
Organizationally Unique Identifier (OUI), and Company ID,
https://standards.ieee.org/wp-content/uploads/import/documents/tutorials/eui.pdfAERO can be applied to a multitude of Internetworking scenarios, with
each having its own adaptations. The following considerations are
provided as non-normative guidance:Address resolution and route optimization as discussed in results in the creation of NCEs. The NCE state is
set to REACHABLE for at most ReachableTime seconds. In order to
refresh the NCE lifetime before the ReachableTime timer expires, the
specification requires implementations to issue a new NS/NA(AR)
exchange to reset ReachableTime while data messages 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
messages for (ReachableTime - 5) seconds. If any data messages have
been sent to the neighbor within this timeframe, then send an NS(AR)
to receive a new NA(AR). If no data messages 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 messages are sent within the 5 second window, reset
the NCE state to STALE.The monitoring of the neighbor data traffic therefore becomes an
ongoing process during the NCE lifetime. If the NCE expires, future
data messages will trigger a new NS/NA(AR) exchange while the messages
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 carrier
packets over a single interface at a time, and the neighbor always
observes carrier packets arriving from the Client from the same
L2 source address.If the Client's underlay 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 carrier 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 original IP packets/parcels without any encapsulation. In that
case, the Client sends packets/parcels over the Direct link according
to traffic selectors. If the Direct interface is selected, then the
Client's packets/parcels are transmitted directly to the peer without
traversing an ANET/INET. If other interfaces are selected, then the
Client's packets/parcels are transmitted via a different interface,
which may result in the inclusion of Proxy/Servers and Gateways in the
communications path. Direct interfaces must be tested periodically for
reachability, e.g., via NUD.AERO Gateways can be either Commercial off-the Shelf (COTS)
standard IP routers or virtual machines in the cloud. Gateways must be
provisioned, supported and managed by the INET administrative
authority, and connected to the Gateways of other INETs via
inter-domain peerings. Cost for purchasing, configuring and managing
Gateways 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 underlay 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
ENETs that provide forwarding services for non-MNP destinations. The
Relay connects to the OMNI link and engages in eBGP peering with one
or more Gateways 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
ARS/ARR 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, peer carrier packet forwarding to Clients
will continue by virtue of the neighbor cache entries that have
already been established through address resolution and route
optimization. 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 carrier
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 ULAs 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 earlier versions:Submit for RFC publication.