Asymmetric Extended Route Optimization (AERO)Boeing Research & TechnologyP.O. Box 3707SeattleWA98124USAfltemplin@acm.orgI-DInternet-DraftThis document specifies an Asymmetric Extended Route Optimization
(AERO) service for IP internetworking over Overlay Multilink Network
(OMNI) interfaces. AERO/OMNI use an IPv6 link-local address format that
supports operation of the IPv6 Neighbor Discovery (ND) protocol and
links ND to IP forwarding. Prefix delegation/registration services are
employed for network admission and to manage the routing system. Secure
multilink operation, mobility management, multicast, traffic selector
signaling and route optimization are naturally supported through dynamic
neighbor cache updates. AERO is a widely-applicable mobile
internetworking service especially well-suited to aviation services,
intelligent transportation systems, mobile end user devices and many
other applications.Asymmetric Extended Route Optimization (AERO) fulfills the
requirements of Distributed Mobility Management (DMM) and route optimization for
aeronautical networking and other network mobility use cases including
intelligent transportation systems and enterprise mobile device users.
AERO is a secure internetworking and mobility management service that
employs the Overlay Multilink Network Interface (OMNI) Non-Broadcast, Multiple Access (NBMA)
virtual link model. The OMNI link is a virtual overlay configured over
one or more underlying Internetworks, and nodes on the link can exchange
original IP packets as single-hop neighbors. The OMNI Adaptation Layer
(OAL) supports multilink operation for increased reliability and path
optimization while providing fragmentation and reassembly services to
support Maximum Transmission Unit (MTU) diversity. In terms of
precedence, readers may appreciate reading this specification first to
gain an understanding of the overall architecture and mobility services
then return to the OMNI specification for a deeper analysis of the NBMA
link model.The AERO service comprises Clients, Proxy/Servers and Relays that are
seen as OMNI link neighbors as well as Bridges that interconnect diverse
Internetworks as OMNI link segments through OAL forwarding at a layer
below IP. Each node's OMNI interface uses an IPv6 link-local address
format that supports operation of the IPv6 Neighbor Discovery (ND)
protocol and links ND to IP forwarding. A
node's OMNI interface can be configured over multiple underlying
interfaces, and therefore appears as a single interface with multiple
link-layer addresses. Each link-layer address is subject to change due
to mobility and/or 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 any Proxy/Server acting as a Mobility Anchor Point (MAP) and
fixed nodes may use any Relay on the link for efficient communications.
Fixed nodes forward original IP packets destined to other AERO nodes via
the nearest Relay, which forwards them through the cloud. Mobile node
Clients discover shortest paths to OMNI link neighbors through AERO
route optimization. Both unicast and multicast communications are
supported, and Clients may efficiently move between locations while
maintaining continuous communications with correspondents and without
changing their IP Address.AERO Bridges peer with Proxy/Servers in a secured private BGP overlay
routing instance to provide a Segment Routing Topology (SRT) that allows
the OAL to span the underlying Internetworks of multiple disjoint
administrative domains as a single unified OMNI link at a layer below
IP. Each OMNI link instance is characterized by the set of Mobility
Service Prefixes (MSPs) common to all mobile nodes. Relays provide an
optimal route from (fixed) correspondent nodes on the underlying
Internetwork to (mobile or fixed) nodes on the OMNI link. To the
underlying Internetwork, the Relay is the source of a route to the MSP;
hence uplink traffic to the mobile node is naturally routed to the
nearest Relay. A Relay can be considered as a simple case of a
Proxy/Server that provides only forwarding and not proxying
services.AERO can be used with OMNI links that span private-use Internetworks
and/or public Internetworks such as the global Internet. In the latter
case, some end systems may be located behind global Internet Network
Address Translators (NATs). A means for robust traversal of NATs while
avoiding "triangle routing" and Proxy/Server traffic concentration is
therefore provided.AERO assumes the use of PIM Sparse Mode in support of multicast
communication. In support of Source Specific Multicast (SSM) when a
Mobile Node is the source, AERO route optimization ensures that a
shortest-path multicast tree is established with provisions for mobility
and multilink operation. In all other multicast scenarios there are no
AERO dependencies.AERO provides a secure aeronautical internetworking service for both
manned and unmanned aircraft, where the aircraft is treated as a mobile
node that can connect an Internet of Things (IoT). AERO is also
applicable to a wide variety of other use cases. For example, it can be
used to coordinate the links of mobile nodes (e.g., cellphones, tablets,
laptop computers, etc.) that connect into a home enterprise network via
public access networks with VPN or non-VPN services enabled according to
the appropriate security model. AERO can also be used to facilitate
terrestrial vehicular and urban air mobility (as well as pedestrian
communication services) for future intelligent transportation systems
. Other applicable use cases are
also in scope.Along with OMNI, AERO provides secured optimal routing support for
the "6M's" of modern Internetworking, including:Multilink – a mobile node’s ability to coordinate
multiple diverse underlying data links as a single logical unit
(i.e., the OMNI interface) to achieve the required communications
performance and reliability objectives.Multinet – the ability to span the OMNI link over a segment
routing topology with multiple diverse network administrative
domains while maintaining seamless end-to-end communications between
mobile Clients and correspondents such as air traffic controllers,
fleet administrators, etc.Mobility – a mobile node’s ability to change network
points of attachment (e.g., moving between wireless base stations)
which may result in an underlying interface address change, but
without disruptions to ongoing communication sessions with peers
over the OMNI link.Multicast – the ability to send a single network
transmission that reaches multiple nodes belonging to the same
interest group, but without disturbing other nodes not subscribed to
the interest group.Multihop – a mobile node vehicle-to-vehicle relaying
capability useful when multiple forwarding hops between vehicles may
be necessary to “reach back” to an infrastructure access
point connection to the OMNI link.MTU assurance – the ability to deliver packets of various
robust sizes between peers without loss due to a link size
restriction, and to dynamically adjust packets sizes to achieve the
optimal performance for each independent traffic flow.The following numbered sections present the AERO specification. The
appendices at the end of the document are non-normative.The terminology in the normative references applies; especially, the
terminology in the OMNI specification is used extensively throughout. The
following terms are defined within the scope of this document:a control
message service for coordinating neighbor relationships between
nodes connected to a common link. AERO uses the IPv6 ND messaging
service specified in .a networking service
for delegating IPv6 prefixes to nodes on the link. The nominal
service is DHCPv6 , however alternate
services (e.g., based on 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 IPv6 source address of an ND message.a node's first-hop data
link service network (e.g., a radio access network, cellular service
provider network, corporate enterprise network, etc.) that often
provides link-layer security services such as IEEE 802.1X and
physical-layer security (e.g., "protected spectrum") to prevent
unauthorized access internally and with border network-layer
security services such as firewalls and proxys that prevent
unauthorized outside access.a node's attachment to a link
in an ANET.a network topology with a
coherent IP routing and addressing plan and that provides a transit
backbone service for its connected end systems. INETs also provide
an underlay service over which the AERO virtual link is configured.
Example INETs include corporate enterprise networks, aviation
networks, and the public Internet itself. When there is no
administrative boundary between an ANET and the INET, the ANET and
INET are one and the same.a node's attachment to a link
in an INET.a "wildcard" term referring to either
ANET or INET when it is not necessary to draw a distinction between
the two.a node's attachment to a link
in a *NET.frequently, *NETs such as
large corporate enterprise networks are sub-divided internally into
separate isolated partitions (a technique also known as "network
segmentation"). Each partition is fully connected internally but
disconnected from other partitions, and there is no requirement that
separate partitions maintain consistent Internet Protocol and/or
addressing plans. (Each *NET partition is seen as a separate OMNI
link segment as discussed below.)an IP address assigned to a
node's interface connection to a *NET.the encapsulation of a
packet in an outer header or headers that can be routed within the
scope of the local *NET partition.the same as defined in , and manifested by IPv6
encapsulation . The OMNI link spans
underlying *NET segments joined by intermediate nodes in a spanning
tree 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 multiple underlying *NET hops; AERO nodes can
use Segment Routing to cause packets to
visit selected waypoints on the link.a node's attachment to an OMNI
link. Since OMNI interface addresses are managed for uniqueness,
OMNI interfaces do not require Duplicate Address Detection (DAD) and
therefore set the administrative variable 'DupAddrDetectTransmits'
to zero .an OMNI interface
service that subjects original IP packets admitted into the
interface to mid-layer IPv6 header encapsulation followed by
fragmentation and reassembly. The OAL is also responsible for
generating MTU-related control messages as necessary, and for
providing addressing context for spanning multiple segments of a
bridged OMNI link.a whole IP packet or
fragment admitted into the OMNI interface by the network layer prior
to OAL encapsulation and fragmentation, or an IP packet delivered to
the network layer by the OMNI interface following OAL decapsulation
and reassembly.an original IP packet encapsulated
in OAL headers and trailers before OAL fragmentation, or following
OAL reassembly.a portion of an OAL packet
following fragmentation but prior to *NET encapsulation, or
following *NET encapsulation but prior to OAL reassembly.an OAL packet that does
not require fragmentation is always encapsulated as an "atomic
fragment" and includes a Fragment Header with Fragment Offset and
More Fragments both set to 0, but with a valid Identification
value.an encapsulated OAL
fragment following *NET encapsulation or prior to *NET
decapsulation. OAL sources and destinations exchange carrier packets
over underlying interfaces, and may be separated by one or more OAL
intermediate nodes. OAL intermediate nodes re-encapsulate carrier
packets during forwarding by removing the *NET headers of the
previous hop underlying network and replacing them with new *NET
headers for the next hop underlying network.an OMNI interface acts as an OAL
source when it encapsulates original IP packets to form OAL packets,
then performs OAL fragmentation and *NET encapsulation to create
carrier packets.an OMNI interface acts as an
OAL destination when it decapsulates carrier packets, then performs
OAL reassembly and decapsulation to derive the original IP
packet.an OMNI interface acts
as an OAL intermediate node when it removes the *NET headers of
carrier packets received on a first segment, then re-encapsulates
the carrier packets in new *NET headers and forwards them into the
next segment. OAL intermediate nodes decrement the Hop Limit of the
OAL IPv6 header during re-encapsulation, and discard the packet if
the Hop Limit reaches 0. OAL intermediate nodes do not decrement the
Hop Limit/TTL of the original IP packet.a *NET interface over
which an OMNI interface is configured.an aggregated
IP Global Unicast Address (GUA) prefix (e.g., 2001:db8::/32,
192.0.2.0/24, etc.) assigned to the OMNI link and from which
more-specific Mobile Network Prefixes (MNPs) are delegated. OMNI
link administrators typically obtain MSPs from an Internet address
registry, however private-use prefixes can alternatively be used
subject to certain limitations (see: ). OMNI links that connect to the
global Internet advertise their MSPs to their interdomain routing
peers.a longer IP
prefix delegated from an MSP (e.g., 2001:db8:1000:2000::/56,
192.0.2.8/30, etc.) and delegated to an AERO Client or Relay.an
IPv6 Link Local Address that embeds the most significant 64 bits of
an MNP in the lower 64 bits of fe80::/64, as specified in .an
IPv6 Unique-Local Address derived from an MNP-LLA.an
IPv6 Link Local Address that embeds a 32-bit
administratively-assigned identification value in the lower 32 bits
of fe80::/96, as specified in .an
IPv6 Unique-Local Address derived from an ADM-LLA.a node that is connected to an OMNI
link and participates in the AERO internetworking and mobility
service.an AERO node
that connects over one or more underlying interfaces and requests
MNP delegation/registration service from AERO Proxy/Servers. The
Client assigns an MNP-LLA to the OMNI interface for use in ND
exchanges with other AERO nodes and forwards original IP packets to
correspondents according to OMNI interface neighbor cache state.a
node that provides a proxying service between AERO Clients and
external peers on its Client-facing ANET interfaces (i.e., in the
same fashion as for an enterprise network proxy) as well as default
forwarding and Mobility Anchor Point (MAP) services for coordination
with correspondents on its INET-facing interfaces. (Proxy/Servers in
the open INET instead configure only an INET interface and no ANET
interfaces.) The Proxy/Server configures an OMNI interface and
assigns an ADM-LLA to support the operation of IPv6 ND services,
while advertising all of its associated MNPs via BGP peerings with
Bridges. Note that the Proxy and Server functions can be considered
logically separable, but since each Proxy/Server must be informed of
all of the Client's other multilink Proxy/Server affiliations the
AERO service is best supported when the two functions are coresident
on the same physical or logical platform.a Proxy/Server
that provides forwarding services between nodes reached via the OMNI
link and correspondents on connected downstream networks and links.
AERO Relays configure an OMNI interface and assign an ADM-LLA the
same as Proxy/Servers, and also run a dynamic routing protocol to
discover any non-MNP IP GUA routes in service on its connected
downstream network links. The Relay advertises the MSP(s) to its
downstream networks, and redistributes downstream network routes
into the OMNI link routing system the same as for Proxy/Servers.a BGP hub
autonomous system node that also provides OAL forwarding services
(as well as a security trust anchor) for nodes on an OMNI link. The
Bridge forwards carrier packets between OMNI link segments as an OAL
intermediate node while decrementing the OAL IPv6 header Hop Limit
but without decrementing the network layer IP TTL/Hop Limit. Bridges
peer with Proxy/Servers and other Bridges over an OMNI link secured
spanning tree to discover the full set of MNPs for the link as well
as any non-MNP IP GUA routes reached via Relays.a
Proxy/Server for an underlying interface of the source Client that
forwards packets sent by the source Client over that interface into
the segment routing topology.a
Proxy/Server for an underlying interface of the target Client that
forwards packets received from the segment routing topology to the
target Client over that interface.a multinet
forwarding region between the FHS Proxy/Server and LHS Proxy/Server.
FHS/LHS Proxy/Servers and SRT Bridges span the OMNI link on behalf
of source/target Client pairs. The SRT maintains a spanning tree
established through BGP peerings between Bridges and Proxy/Servers.
Each SRT segment includes Bridges in a "hub" and Proxy/Servers in
"spokes", while adjacent segments are interconnected by
Bridge-Bridge peerings. The BGP peerings are configured over both
secured and unsecured underlying network paths such that a secured
spanning tree is available for critical control messages while other
messages can use the unsecured spanning tree.an IP address used as an
encapsulation header source or destination address from the
perspective of the OMNI interface. When an upper layer protocol
(e.g., UDP) is used as part of the encapsulation, the port number is
also considered as part of the link-layer address.the source or
destination address of an original IP packet presented to the OMNI
interface.an internal virtual or
external edge IP network that an AERO Client or Relay connects to
the rest of the network via the OMNI interface. The Client/Relay
sees each EUN as a "downstream" network, and sees the OMNI interface
as the point of attachment to the "upstream" network.an AERO Client and all of
its downstream-attached networks that move together as a single
unit, i.e., an end system that connects an Internet of Things.a MN's on-board router
that forwards original IP packets between any downstream-attached
networks and the OMNI link. The MR is the MN entity that hosts the
AERO Client.the AERO node
nearest the source that initiates route optimization. The ROS may be
a FHS Proxy/Server or Relay for the source, or may be the source
Client itself.the AERO
node that responds to route optimization requests on behalf of the
target. The ROR may be an LHS Proxy/Server for a target MNP Client
or an LHS Relay for a non-MNP target.a geographically and/or
topologically referenced list of addresses of all Proxy/Servers
within the same OMNI link. Each OMNI link has its own MAP list.a
BGP-based overlay routing service coordinated by Proxy/Servers and
Bridges that tracks all Proxy/Server-to-Client associations.the collective set of
all Proxy/Servers, Bridges and Relays that provide the AERO Service
to Clients.an individual
Proxy/Server, Bridge or Relay in the Mobility Service.Throughout the document, the simple terms "Client",
"Proxy/Server", "Bridge" and "Relay" refer to "AERO Client", "AERO
Proxy/Server", "AERO Bridge" and "AERO Relay", respectively.
Capitalization is used to distinguish these terms from other common
Internetworking uses in which they appear without capitalization.The terminology of IPv6 ND and DHCPv6 (including the names of node variables, messages and
protocol constants) is used throughout this document. The terms
"All-Routers multicast", "All-Nodes multicast", "Solicited-Node
multicast" and "Subnet-Router anycast" are defined in . Also, the term "IP" is used to generically refer to
either Internet Protocol version, i.e., IPv4 or
IPv6 .The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP 14
when, and only when,
they appear in all capitals, as shown here.The following sections specify the operation of IP over OMNI links
using the AERO service:AERO Clients are Mobile Nodes (MNs) that configure OMNI interfaces
over underlying interfaces with addresses that may change when the
Client moves to a new network connection point. AERO Clients register
their Mobile Network Prefixes (MNPs) with the AERO service, and
distribute the MNPs to nodes on EUNs. AERO Bridges, Proxy/Servers and
Relays are critical infrastructure elements in fixed (i.e.,
non-mobile) INET deployments and hence have permanent and unchanging
INET addresses. Together, they constitute the AERO service which
provides an OMNI link virtual overlay for connecting AERO Clients.AERO Bridges (together with Proxy/Servers) provide the secured
backbone supporting infrastructure for a Segment Routing Topology
(SRT) that spans the OMNI link. Bridges forward carrier packets both
within the same SRT segment and between disjoint SRT segments based on
an IPv6 encapsulation mid-layer known as the OMNI Adaptation Layer
(OAL) . The OMNI interface and
OAL provide a virtual bridging service, since the inner IP TTL/Hop
Limit is not decremented. Each Bridge also peers with Proxy/Servers
and other Bridges in a dynamic routing protocol instance to provide a
Distributed Mobility Management (DMM) service for the list of active
MNPs (see ). Bridges present the OMNI link as
a set of one or more Mobility Service Prefixes (MSPs) and configure
secured tunnels with Proxy/Servers, Relays and other Bridges; they
further maintain IP forwarding table entries for each MNP and any
other reachable non-MNP prefixes.AERO Proxy/Servers in distributed SRT segments provide default
forwarding and mobility/multilink services for AERO Client mobile
nodes. Each Proxy/Server also peers with Bridges in a dynamic routing
protocol instance to advertise its list of associated MNPs (see ). Proxy/Servers facilitate prefix
delegation/registration exchanges with Clients, where each delegated
prefix becomes an MNP taken from an MSP. Proxy/Servers forward carrier
packets between OMNI interface neighbors and track each Client's
mobility profiles. Proxy/Servers at ANET/INET boundaries provide a
conduit for ANET Clients to associate with peers reached through
external INETs. Proxy/Servers in the open INET support INET Clients
through authenticated IPv6 ND message exchanges. Source Clients employ
First-Hop Segment (FHS) Proxy/Servers to forward packets over the SRT
to Last-Hop Segment (LHS) Proxy/Servers which finally forward to
target Clients.AERO Relays are Proxy/Servers that provide forwarding services to
exchange original IP packets between the OMNI interface and INET/EUN
interfaces. Relays are provisioned with MNPs the same as for an AERO
Client, and also run a dynamic routing protocol to discover any
non-MNP IP routes. The Relay advertises the MSP(s) to its connected
networks, and distributes all of its associated MNP and non-MNP routes
via BGP peerings with Bridges presents the basic OMNI link
reference model: In this model:the OMNI link is an overlay network service configured over
one or more underlying SRT segments which may be managed by
different administrative authorities and have incompatible
protocols and/or addressing plans.AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1,
discovers Mobile Network Prefixes (MNPs) X* and advertises the
MSP via BGP peerings over secured tunnels to Proxy/Servers (S1,
S2). Bridges provide the backbone for an SRT that spans the OMNI
link.AERO Proxy/Servers S1 and S2 configure secured tunnels with
Bridge B1 and also provide mobility, multilink, multicast and
default router services for the MNPs of their associated Clients
C1 and C2. (Proxy/Servers that act as Relays can also advertise
non-MNP routes for non-mobile correspondent nodes the same as
for MNP Clients.)AERO Clients C1 and C2 associate with Proxy/Servers S1 and
S2, respectively. They receive MNP delegations X1 and X2, and
also act as default routers for their associated physical or
internal virtual EUNs. Simple hosts H1 and H2 attach to the EUNs
served by Clients C1 and C2, respectively.An OMNI link configured over a single *NET appears as a single
unified link with a consistent underlying network addressing plan;
all nodes on the link can exchange carrier packets via simple *NET
encapsulation (i.e., following any necessary NAT traversal) since
the underlying *NET is connected. In common practice, however, OMNI
links often traverse an SRT spanning tree that connects multiple
distinct *NET segments that may be managed under different
administrative authorities (e.g., as for worldwide aviation service
providers such as ARINC, SITA, Inmarsat, etc.). Individual *NETs may
also be partitioned internally, in which case each internal
partition is seen as a separate segment.The addressing plan of each SRT segment is consistent internally
but will often bear no relation to the addressing plans of other
segments. Each segment is also likely to be separated from others by
network security devices (e.g., firewalls, proxys, packet filtering
gateways, etc.), and disjoint segments often have no common physical
link connections. Therefore, nodes can only be assured of exchanging
carrier packets directly with correspondents in the same segment,
and not with those in other segments. The only means for joining the
segments therefore is through inter-domain peerings between AERO
Bridges.The same as for traditional campus LANs, the OMNI link spans
multiple SRT segments that can be joined into a single unified link
using the OMNI Adaptation Layer (OAL) . The OAL is an OMNI interface
sublayer that inserts a mid-layer IPv6 encapsulation header for
inter-segment forwarding (i.e., bridging) without decrementing the
network-layer TTL/Hop Limit of the original IP packet. An example
OMNI link SRT is shown in :Bridge, Proxy/Server and Relay OMNI interfaces are configured
over both secured tunnels and open INET underlying interfaces within
their respective SRT segments. Within each segment, Bridges
configure "hub-and-spokes" BGP peerings with Proxy/Server/Relays as
"spokes". Adjacent SRT segments are joined by Bridge-to-Bridge
peerings to collectively form a spanning tree over the entire SRT.
The "secured" spanning tree supports authentication and integrity
for critical control plane messages. The "unsecured" spanning tree
conveys ordinary carrier packets without security codes and that
must be treated by destinations according to data origin
authentication procedures. AERO nodes can employ route optimization
to cause carrier packets to take more direct paths between OMNI link
neighbors without having to follow strict SRT spanning tree
paths.AERO nodes on OMNI links use the Link-Local Address (LLA) prefix
fe80::/64 to assign LLAs used for
network-layer addresses in link-scoped IPv6 ND and data messages.
AERO Clients use LLAs constructed from MNPs (i.e., "MNP-LLAs") while
other AERO nodes use LLAs constructed from administrative
identification values ("ADM-LLAs") as specified in . Non-MNP routes are also
represented the same as for MNP-LLAs, but may include a prefix that
is not properly covered by the MSP.AERO nodes also use the Unique Local Address (ULA) prefix
fd00::/8 followed by a pseudo-random 40-bit OMNI domain identifier
to form the prefix [ULA]::/48, then include a 16-bit OMNI link
identifier '*' to form the prefix [ULA*]::/64 . The AERO node then uses the prefix [ULA*]::/64
to form "MNP-ULAs" or "ADM-ULA"s as specified in to support OAL addressing. (The
prefix [ULA*]::/64 appearing alone and with no suffix represents
"default".) AERO Clients also use Temporary ULAs constructed per
, where the addresses are
typically used only in initial control message exchanges until a
stable MNP-LLA/ULA is assigned.AERO MSPs, MNPs and non-MNP routes are typically based on Global
Unicast Addresses (GUAs), but in some cases may be based on
private-use addresses. See
for a full specification of LLAs, ULAs and GUAs used by AERO nodes
on OMNI links.Finally, AERO Clients and Proxy/Servers configure node
identification values as specified in .The AERO routing system comprises a private Border Gateway
Protocol (BGP) service coordinated between
Bridges and Proxy/Servers. The service supports carrier packet
forwarding at a layer below IP, and does not interact with either
the public Internet BGP routing system or any underlying INET
routing systems.In a reference deployment, each Proxy/Server is configured as an
Autonomous System Border Router (ASBR) for a stub Autonomous System
(AS) using a 32-bit AS Number (ASN) that is
unique within the BGP instance, and each Proxy/Server further uses
eBGP to peer with one or more Bridges but does not peer with other
Proxy/Servers. Each SRT segment in the OMNI link must include one or
more Bridges in a "hub" AS, which peer with the Proxy/Servers within
that segment as "spoke" ASes. All Bridges within the same segment
are members of the same hub AS, and use iBGP to maintain a
consistent view of all active routes currently in service. The
Bridges of different segments peer with one another using eBGP.Bridges maintain forwarding table entries only for the MNP-ULAs
corresponding to MNP and non-MNP routes that are currently active,
while carrier packets destined to all other MNP-ULAs are dropped
with a Destination Unreachable message returned due to the
black-hole route. In this way, Proxy/Servers and Relays have only
partial topology knowledge (i.e., they only maintain routing
information for their directly associated Clients and non-AERO
links) and they forward all other carrier packets to Bridges which
have full topology knowledge.Each OMNI link SRT segment assigns a unique ADM-ULA sub-prefix of
[ULA*]::/96 known as the "SRT prefix". For example, a first segment
could assign [ULA*]::1000/116, a second could assign
[ULA*]::2000/116, a third could assign [ULA*]::3000/116, etc. Within
each segment, each Proxy/Server configures an ADM-ULA within the
segment's SRT prefix, e.g., the Proxy/Servers within
[ULA*]::2000/116 could assign the ADM-ULAs [ULA*]::2011/116,
[ULA*]::2026/116, [ULA*]::2003/116, etc.The administrative authorities for each segment must therefore
coordinate to assure mutually-exclusive ADM-ULA prefix assignments,
but internal provisioning of ADM-ULAs an independent local
consideration for each administrative authority. For each ADM-ULA
prefix, the Bridge(s) that connect that segment assign the
all-zero's address of the prefix as a Subnet Router Anycast address.
For example, the Subnet Router Anycast address for [ULA*]::1023/116
is simply [ULA*]::1000.ADM-ULA prefixes are statically represented in Bridge forwarding
tables. Bridges join multiple SRT segments into a unified OMNI link
over multiple diverse network administrative domains. They support a
bridging function by first establishing forwarding table entries for
their ADM-ULA prefixes either via standard BGP routing or static
routes. For example, if three Bridges ('A', 'B' and 'C') from
different segments serviced [ULA*]::1000/116, [ULA*]::2000/116 and
[ULA*]::3000/116 respectively, then the forwarding tables in each
Bridge are as follows:[ULA*]::1000/116->local,
[ULA*]::2000/116->B, [ULA*]::3000/116->C[ULA*]::1000/116->A,
[ULA*]::2000/116->local, [ULA*]::3000/116->C[ULA*]::1000/116->A, [ULA*]::2000/116->B,
[ULA*]::3000/116->localThese forwarding table entries are permanent and never
change, since they correspond to fixed infrastructure elements in
their respective segments.MNP ULAs are instead dynamically advertised in the AERO routing
system by Proxy/Servers and Relays that provide service for their
corresponding MNPs. For example, if three Proxy/Servers ('D', 'E'
and 'F') service the MNPs 2001:db8:1000:2000::/56,
2001:db8:3000:4000::/56 and 2001:db8:5000:6000::/56 then the routing
system would include:[ULA*]:2001:db8:1000:2000/120[ULA*]:2001:db8:3000:4000/120[ULA*]:2001:db8:5000:6000/120A full discussion of the BGP-based routing system used by AERO is
found in .With the Client and SRT segment prefixes in place in Bridge
forwarding tables, the OMNI interface sends control and data carrier
packets toward AERO destination nodes located in different OMNI link
segments over the SRT spanning tree. The OMNI interface uses the
OMNI Adaptation Layer (OAL) encapsulation service , and includes an OMNI Routing
Header (ORH) as an OAL header extension. Each carrier packet
includes at most one ORH in compressed or uncompressed form (with
the uncompressed form shown in ):The ORH includes the following fields, in consecutive
order:Next Header identifies the type of header immediately
following the ORH.Hdr Ext Len is the length of the Routing header in 8-octet
units (not including the first 8 octets). The field must encode
a value between 0 and 4 (all other values indicate a parameter
problem).Routing Type is set to TBD1 (see IANA Considerations).Segments Left encodes the value 0 or 1 (all other values
indicate a parameter problem).NIndex - a 3-octet "Neighbor Index" value corresponding to a
Client NCE maintained by a Proxy/Server or Bridge. Values
between 1 and 2**24 represent a specific NCE, while the value 0
represents "unspecified". The Proxy/Server or Bridge assigns a
unique NIndex value when it creates a new Client NCE, and
maintains the assignment until the NCE is deleted.omIndex - a 1-octet field that identifies a specific Client
underlying interface when there are multiple alternatives. When
FMT-Forward is clear, omIndex determines the interface for
forwarding the ORH packet following reassembly; when FMT-Forward
is set, omIndex determines the interface for forwarding the raw
carrier packets without first reassembling. When omIndex is 0
(or when no ORH is present), the LHS Proxy/Server selects among
any of the Client's available underlying interfaces that it
services locally (i.e., and not those serviced by another
Proxy/Server).FMT - a 3-bit "Forward/Mode/Trailer" code corresponding to
the included Link Layer Address as follows:When the most significant bit (i.e., "FMT-Forward") is
clear, the LHS Proxy/Server must reassemble. When
FMT-Forward is set, the LHS Proxy/Server must forward the
fragments to the Client (while changing the OAL destination
address to the MNP-ULA of the Client if necessary) without
reassembling.When the next most significant bit (i.e., "FMT-Mode") is
clear, L2ADDR is the INET address of the LHS Proxy/Server
and the Client must be reached through the LHS Proxy/Server.
When FMT-Mode is set, the Client is eligible for route
optimization over the open INET where it may be located
behind one or more NATs, and L2ADDR is either the INET
address of the LHS Proxy/Server (when FMT-Forward is set) or
the native INET address of the Client itself (when
FMT-Forward is clear).The least significant bit (i.e., "FMT-Type") is consulted
only when Hdr Ext Len is 3 and ignored otherwise. If
FMT-Type is clear, the remainder includes an IPv4 L2ADDR
followed by null padding followed by an 8-octet (IPv6)
Destination Suffix. If FMT-Type is set, the remainder
instead contains an IPv6 L2ADDR followed by null padding and
no Destination Suffix.SRT - a 5-bit Segment Routing Topology prefix length
consulted only when Segments Left is 1, and encodes a value that
(when added to 96) determines the prefix length to apply to the
ADM-ULA formed from concatenating [ULA*]::/96 with the 32 bit
LHS value (for example, the value 16 corresponds to the prefix
length 112).LHS - a 4-octet field consulted only when Segments Left is 1.
The field encodes the 32-bit ADM-ULA suffix of an LHS
Proxy/Server for the target. When SRT is non-zero, SRT and LHS
together determine the ADM-ULA of the LHS Proxy/Server over the
spanning tree. When SRT is 0, LHS instead encodes an NIndex
value and the LHS Proxy/Server or Client must be reached
directly via INET encapsulation instead of over the spanning
tree. Link Layer Address (L2ADDR) - an IP encapsulation address
consulted only when Segments Left is 1. The ORH length also
determines the L2ADDR IP version since the field will always
contain exactly 6 octets for UDP/IPv4 or 18 octets for UDP/IPv6.
When present, provides the link-layer address (i.e., the
encapsulation address) of the LHS Proxy/Server or the target
Client itself. The UDP Port Number appears in the first two
octets and the IP address appears in the remaining octets. The
Port Number and IP address are recorded in network byte order,
and in ones-compliment "obfuscated" form per . The OMNI interface forwarding algorithm uses
L2ADDR as the INET encapsulation address for forwarding when
SRT/LHS is located in the local OMNI link segment. If direct
INET encapsulation is not permitted, L2ADDR is instead set to
all-zeros and the packet must be forwarded to the LHS
Proxy-Server via the spanning tree.Null Padding - zero-valued octets added as necessary to pad
the portion of the ORH included up to this point to an even
8-octet boundary.Destination Suffix - a trailing 8-octet field present only
when indicated by the ORH length and FMT-Type (see below). When
present, encodes the 64-bit MNP-ULA suffix for the target
Client. (For first-fragments, the MNP-LLA is already encoded in
the original IP packet header and Destination Suffix may be
omitted.)The ORH Hdr Ext Len field value also serves as an implicit ORH
"Type", with 5 distinct Types possible (i.e., ORH-0 through ORH-4).
All ORH-* Types include the same 8-octet preamble beginning with
Next Header up to and including NIndex/omIndex, followed by a
Type-specific remainder as follows: ORH-0 - The preamble Hdr Ext Len and Segments Left must both
be 0. All other fields are omitted.ORH-1 - The preamble Hdr Ext Len is set to 1 and Segments
Left must be 0. Destination Suffix is included and all other
fields are omitted.ORH-2 - The preamble Hdr Ext Len is set to 2. FMT/SRT/LHS and
L2ADDR for IPv4 are included, and Destination Suffix is
omitted.ORH-3 - The preamble Hdr Ext Len is set to 3. FMT/SRT/LHS are
included. If FMT-Type is clear, L2ADDR for IPv4 and Destination
Suffix is included. If FMT-Type is set, L2ADDR for IPv6 is
included and Destination Suffix is omitted.ORH-4 - The preamble Hdr Ext Len is set to 4. FMT/SRT/LHS,
L2ADDR for IPv6 and Destination Suffix are included.AERO neighbors use OAL encapsulation and fragmentation to
exchange OAL packets as specified in . When an AERO node's OMNI interface
(acting as an OAL source) uses OAL encapsulation for an original IP
packet with source address 2001:db8:1:2::1 and destination address
2001:db8:1234:5678::1, it sets the OAL header source address to its
own ULA (e.g., [ULA*]::2001:db8:1:2), sets the destination address
to the MNP-ULA corresponding to the IP destination address (e.g.,
[ULA*]::2001:db8:1234:5678), sets the Traffic Class, Flow Label, Hop
Limit and Payload Length as discussed in , then finally selects an
Identification and appends an OAL checksum.If the neighbor cache information indicates that the target is in
a different segment, the OAL source next inserts an ORH immediately
following the OAL header while including Destination Suffix only
when necessary (in this case, the Destination Suffix is
2001:db8:1234:5678). Next, to direct the packet to an LHS Bridge,
the source prepares an ORH with Segments Left set to 1 and with
NIndex/omIndex and FMT/SRT/LHS/L2ADDR included, then overwrites the
OAL header destination address with the LHS Subnet Router Anycast
address (for example, for LHS 3000:4567 with SRT 16, the Subnet
Router Anycast address is [ULA*]::3000:0000). To direct the packet
to the LHS Proxy/Server (either directly in the local segment or in
a remote segment via the spanning tree), the OAL source instead
includes an ORH (Type 0 or 1) with Segments Left set to 0 and
FMT/SRT/LHS/L2ADDR omitted, and overwrites the OAL header
destination address with either the LHS Proxy/Server ADM-ULA or the
MNP-ULA of the Client itself.The OAL source then fragments the OAL packet, with each resulting
OAL fragment including the OAL/ORH headers while only the first
fragment includes the original IPv6 header. If FMT-Forward is set,
the Identification used for fragmentation must be within the window
for the Client and a Destination Suffix must be included when
necessary; otherwise the Identification must be within the window
for the LHS Proxy/Server and no Destination Suffix is needed. (Note
that if no actual fragmentation is required the OAL source still
prepares the packet as an "atomic" fragment that includes a Fragment
Header with Offset and More Fragments both set to 0.) The OAL source
finally encapsulates each resulting OAL fragment in an *NET header
to form an OAL carrier packet, with source address set to its own
*NET address (e.g., 192.0.2.100) and destination set to the *NET
address of the last hop itself or the next hop in the spanning tree
(e.g., 192.0.2.1).The carrier packet encapsulation format in the above example is
shown in :In this format, the original IP header and packet body/fragment
are encapsulated in an OAL IPv6 header prepared according to , the ORH is a Routing Header extension of the OAL
header, the Fragment Header identifies each fragment, and the *NET
header is prepared as discussed in . The
OAL source transmits each such carrier packet into the SRT spanning
tree, where they are forwarded over possibly multiple OAL
intermediate nodes until they arrive at the OAL destination.The SRT forwarding system therefore contains both Client MNP-ULA
prefix information that may change dynamically due to regional node
mobility and per-segment ADM-ULA prefix information that rarely if
ever changes. The spanning tree can therefore provide link-layer
bridging by sending carrier packets over the spanning tree instead
of network-layer routing according to MNP routes. As a result,
opportunities for loss due to node mobility between different
segments are mitigated.Note: The document recommends that AERO nodes transform ORHs with
Segments Left set to 1 into ORH-0/1 during forwarding. While this
may yield encapsulation overhead savings in some cases, the AERO
node can instead simply decrement Segments Left and leave the
original ORH in place. The LHS Proxy/Server or destination Client
that processes the ORH will receive the same information in both
cases.Note: When the OAL source sets a carrier packet destination
address to a target's MNP-ULA but does not assert a specific target
underlying interface, it may omit the ORH whether forwarding to the
LHS Proxy/Server or directly to the target itself. When the LHS
Proxy/Server receives a carrier packet with OAL destination set to
the target MNP-ULA but with no ORH, it forwards over any available
underlying interface for the target that it services locally.Note: When the OAL source and destination are on the same INET
segment, OAL header compression can be used to significantly reduce
encapsulation overhead as discussed in .Note: Use of an IPv6 "minimal encapsulation" format (i.e., an
IPv6 variant of ) based on extensions to the
ORH was considered and abandoned. In the approach, the ORH would be
inserted as an extension header to the original IPv6 packet header.
The IPv6 destination address would then be written into the ORH, and
the ULA corresponding to the destination would be overwritten in the
IPv6 destination address. This would seemingly convey enough
forwarding information so that OAL encapsulation could be avoided.
However, this "minimal encapsulation" IPv6 packet would then have a
non-ULA source address and ULA destination address, an incorrect
value in upper layer protocol checksums, and a Hop Limit that is
decremented within the spanning tree when it should not be. The
insertion and removal of the ORH would also entail rewriting the
Payload Length and Next Header fields - again, invalidating upper
layer checksums. These irregularities would result in implementation
challenges and the potential for operational issues, e.g., since
actionable ICMPv6 error reports could not be delivered to the
original source. In order to address the issues, still more
information such as the original IPv6 source address could be
written into the ORH. However, with the additional information the
benefit of the "minimal encapsulation" savings quickly diminishes,
and becomes overshadowed by the implementation and operational
irregularities.The 64-bit sub-prefixes of [ULA]::/48 identify up to 2^16
distinct Segment Routing Topologies (SRTs). Each SRT is a
mutually-exclusive OMNI link overlay instance using a distinct set
of ULAs, and emulates a Virtual LAN (VLAN) service for the OMNI
link. In some cases (e.g., when redundant topologies are needed for
fault tolerance and reliability) it may be beneficial to deploy
multiple SRTs that act as independent overlay instances. A
communication failure in one instance therefore will not affect
communications in other instances.Each SRT is identified by a distinct value in bits 48-63 of
[ULA]::/48, i.e., as [ULA0]::/64, [ULA1]::/64, [ULA2]::/64, etc.
Each OMNI interface is identified by a unique interface name (e.g.,
omni0, omni1, omni2, etc.) and assigns an anycast ADM-ULA
corresponding to its SRT prefix length. The anycast ADM-ULA is used
for OMNI interface determination in Safety-Based Multilink (SBM) as
discussed in . Each OMNI
interface further applies Performance-Based Multilink (PBM)
internally.The Bridges and Proxy/Servers of each independent SRT engage in
BGP peerings to form a spanning tree with the Bridges in non-leaf
nodes and the Proxy/Servers in leaf nodes. The spanning tree is
configured over both secured and unsecured underlying network paths.
The secured spanning tree is used to convey secured control messages
between FHS and LHS Proxy/Servers, while the unsecured spanning tree
forwards data messages and/or unsecured control messages.Each SRT segment is identified by a unique ADM-ULA prefix used by
all Proxy/Servers and Bridges in the segment. Each AERO node must
therefore discover an SRT prefix that correspondents can use to
determine the correct segment, and must publish the SRT prefix in
IPv6 ND messages and carrier packet ORHs.Original IPv6 source can direct IPv6 packets to an AERO node by
including a standard IPv6 Segment Routing Header (SRH) with the anycast ADM-ULA for the selected OMNI
link as either the IPv6 destination or as an intermediate hop within
the SRH. This allows the original source to determine the specific
OMNI link SRT an original IPv6 packet will traverse when there may
be multiple alternatives.When an AERO node processes the SRH and forwards the original
IPv6 packet to the correct OMNI interface, the OMNI interface writes
the next IPv6 address from the SRH into the IPv6 destination address
and decrements Segments Left. If decrementing would cause Segments
Left to become 0, the OMNI interface deletes the SRH before
forwarding. This form of Segment Routing supports Safety-Based
Multilink (SBM).OAL sources can insert an ORH for Segment Routing within the same
OMNI link to influence the paths of carrier packets sent to OAL
destinations in remote SRT segments without requiring all carrier
packets to traverse strict SRT spanning tree paths. (OAL sources can
also insert an ORH in carrier packets sent to OAL destinations in
the local segment if additional last-hop forwarding information is
required.)When an AERO node's OMNI interface has an original IP packet to
send to a target discovered through route optimization located in
the same SRT segment, it acts as an OAL source to perform OAL
encapsulation and fragmentation. The node then uses L2ADDR for INET
encapsulation while including an ORH-0 when sending the resulting
carrier packets to the ADM-ULA of the LHS Proxy/Server, or
optionally omitting the ORH-0 when sending to the MNP-ULA of the
target Client itself. When the node sends carrier packets with an
ORH-0 to the LHS Proxy/Server, it sets the OAL destination to the
ADM-ULA of the Proxy/Server if the Proxy/Server is responsible for
reassembly; otherwise, it sets the OAL destination to the MNP-ULA of
the target Client to cause the Proxy/Server to forward without
reassembling. The node also sets omIndex to select a specific target
Client underlying interface, or sets omIndex to 0 when no preference
is selected.When an AERO node's OMNI interface has an original IP packet to
send to a route optimization target located in a remote OMNI link
segment, it acts as an OAL source the same as above but also
includes an appropriate ORH type with Segments Left set to 1 and
with (NIndex/omIndex) and FMT/SRT/LHS/L2ADDR information while
setting the OAL destination to the Subnet Router Anycast address for
the LHS OMNI link segment. (The OAL source can alternatively include
an ORH with Segments Left set to 0 while setting the OAL destination
to the ADM-ULA of the LHS Proxy/Server, but this would cause the
carrier packets to follow strict spanning tree paths.) The OMNI
interface then forwards the resulting carrier packets into the
spanning tree.When a Bridge receives carrier packest destined to its Subnet
Router Anycast address with an ORH with Segments Left set to 1 and
with FMT/SRT/LHS/L2ADDR values corresponding to the local segment,
it first reassembles if necessary. If the reassembled packet arrived
over the secured spanning tree and contains an NS(WIN) or NA(WIN)
(see: and ), the
Bridge creates or updates a NCE for the NS/NA target address and
caches the ULA/LLA source/destination addresses and receive window
information. For NS(WIN), the Bridge also caches the omIndex and
FMT/SRT/LHS/L2ADDR information found in the ORH. For NA(WIN), the
Bridge instead caches the omIndex and FMT/SRT/LHS/L2ADDR information
found in the OMNI option Interface Attributes. The Bridge then
selects a unique NIndex value for this NCE and, for NA(WIN),
rewrites the Interface Attributes SRT to 0 and LHS to
(NIndex/omIndex) and rewrites L2ADDR to its own INET address. The
Bridge then forwards the NS/NA(WIN) to the LHS Proxy/Server over the
secured spanning tree.For all other carrier packets addressed to the Subnet Router
Anycast address, the Bridge next examines FMT-Mode to determine
whether the target Client can accept packets directly (i.e.,
following any NAT traversal procedures necessary) while bypassing
the LHS Proxy/Server. If the Client can be reached directly and NAT
traversal has converged, the Bridge then writes the MNP-ULA (found
in the inner IPv6 header for first fragments or the ORH Destination
Suffix for non-first fragments) into the OAL destination address,
decrements the OAL IPv6 header Hop Limit (and discards the packet if
Hop Limit reaches 0), removes the ORH, re-encapsulates the carrier
packet according to L2ADDR then forwards the carrier packets
directly to the target Client. If the Client cannot be reached
directly (or if NAT traversal has not yet converged), the Bridge
instead transforms the ORH into an ORH-0, re-encapsulates the packet
according to L2ADDR, changes the OAL destination to the ADM-ULA of
the LHS Proxy/Server if FMT-Forward is clear or the MNP-ULA of the
Client if FMT-Forward is set and forwards the carrier packet to the
LHS Proxy/Server.When a Bridge receives a carrier packet destined to another
ADM-ULA or MNP-ULA address (i.e., and not the Subnet Router Anycast
address) the Bridge forwards the packet via spanning tree. If the
carrier packet arrived via the secured spanning tree, the Bridge
forwards to the next hop also via the secured spanning tree. If the
carrier packet arrived via the unsecured spanning tree, the Bridge
forwards to the next hop also via the unsecured spanning tree.When an LHS Proxy/Server receives carrier packets with any ORH
type with Segments Left set to 0 and with OAL destination set to its
own ADM-ULA, it first determines if the carrier packet contains an
NA(WIN). If so, and if the OMNI option Interface Attributes SRT code
is non-zero (i.e., meaning that it was not processed by a Bridge)
the LHS Proxy/Server creates or updates a NCE for the NA target
address while assigning a unique NIndex value and caches the ULA/LLA
source/destination addresses and receive window information. The LHS
Proxy/Server also caches the omIndex and FMT/SRT/LHS/L2ADDR
information found in the OMNI option Interface Attributes, rewrites
the Interface Attributes SRT to 0 and LHS to (NIndex/omIndex) and
rewrites L2ADDR to its own INET address The LHS Proxy/Server then
proceeds according to FMT-Forward and omIndex, while including an
authentication signature in any IPv6 ND messages. If FMT-Forward is
set, the LHS Proxy/Server changes the OAL destination to the MNP-ULA
of the target Client found in the IPv6 header for first fragments or
in the ORH Destination Suffix for non-first-fragments, removes the
ORH and forwards to the target Client interface identified by
omIndex. If FMT-Forward is clear, the LHS Proxy/Server instead
reassembles then re-encapsulates while refragmenting if necessary,
removes the ORH and forwards to the target Client according to
omIndex.When an LHS Proxy/Server receives carrier packets with any ORH
type with Segments Left set to 0 and with OAL destination set to the
MNP-ULA of the target Client, it removes the ORH and forwards to the
target Client according to omIndex. During forwarding, the LHS
Proxy/Server must first verify that the omIndex corresponds to a
target underlying interface that it services locally and must not
forward to other target underlying interfaces. If omIndex is 0 (or
if no ORH is included) the LHS Proxy/Server instead selects among
any of the target underlying interfaces it services.When a target Client receives carrier packets with OAL
destination set to is MNP-ULA, it reassembles to obtain the OAL
packet then decapsulates and delivers the original IP packet to
upper layers.Note: Special handling procedures are employed for the exchange
of IPv6 ND messages used to establish neighbor cache state as
discussed in . The procedures call for
hop-by-hop authentication and neighbor cache state establishment
based on the encapsulation ULA, with next-hop determination based on
the IPv6 ND message LLA.OMNI interfaces are virtual interfaces configured over one or more
underlying interfaces classified as follows:INET interfaces connect to an INET either natively or through
one or more NATs. Native INET interfaces have global IP addresses
that are reachable from any INET correspondent. The INET-facing
interfaces of Proxy/Servers are native interfaces, as are Relay
and Bridge interfaces. NATed INET interfaces connect to a private
network behind one or more NATs that provide INET access. Clients
that are behind a NAT are required to send periodic keepalive
messages to keep NAT state alive when there are no carrier packets
flowing.ANET interfaces connect to an ANET that is separated from the
open INET by an FHS Proxy/Server. Clients can issue control
messages over the ANET without including an authentication
signature since the ANET is secured at the network layer or below.
Proxy/Servers can actively issue control messages over the INET on
behalf of ANET Clients to reduce ANET congestion.VPNed interfaces use security encapsulation over the INET to a
Virtual Private Network (VPN) server that also acts as an FHS
Proxy/Server. Other than the link-layer encapsulation format,
VPNed interfaces behave the same as Direct interfaces.Direct (i.e., single-hop point-to-point) interfaces connect a
Client directly to an FHS Proxy/Server without crossing any
ANET/INET paths. An example is a line-of-sight link between a
remote pilot and an unmanned aircraft. The same Client
considerations apply as for VPNed interfaces.OMNI interfaces use OAL encapsulation and fragmentation as
discussed in . OMNI interfaces use
*NET encapsulation (see: ) to exchange
carrier packets with OMNI link neighbors over INET or VPNed interfaces
as well as over ANET interfaces for which the Client and FHS
Proxy/Server may be multiple IP hops away. OMNI interfaces do not use
link-layer encapsulation over Direct underlying interfaces or ANET
interfaces when the Client and FHS Proxy/Server are known to be on the
same underlying link.OMNI interfaces maintain a neighbor cache for tracking per-neighbor
state the same as for any interface. OMNI interfaces use ND messages
including Router Solicitation (RS), Router Advertisement (RA),
Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for
neighbor cache management. In environments where spoofing may be a
threat, OMNI neighbors should employ OAL Identification window
synchronization in their ND message exchanges.OMNI interfaces send ND messages with an OMNI option formatted as
specified in . The OMNI option
includes prefix registration information, Interface Attributes
containing link information parameters for the OMNI interface's
underlying interfaces and any other per-neighbor information. Each
OMNI option may include multiple Interface Attributes sub-options
identified by omIndex values.A Client's OMNI interface may be configured over multiple
underlying interfaces. For example, common mobile handheld devices
have both wireless local area network ("WLAN") and cellular wireless
links. These links are often used "one at a time" with low-cost WLAN
preferred and highly-available cellular wireless as a standby, but a
simultaneous-use capability could provide benefits. In a more complex
example, aircraft frequently have many wireless data link types (e.g.
satellite-based, cellular, terrestrial, air-to-air directional, etc.)
with diverse performance and cost properties.If a Client's multiple underlying interfaces are used "one at a
time" (i.e., all other interfaces are in standby mode while one
interface is active), then successive ND messages all include OMNI
option Interface Attributes sub-options with the same underlying
interface index. In that case, the Client would appear to have a
single underlying interface but with a dynamically changing link-layer
address.If the Client has multiple active underlying interfaces, then from
the perspective of ND it would appear to have multiple link-layer
addresses. In that case, ND message OMNI options MAY include Interface
Attributes sub-options with different underlying interface indexes.
Every ND message need not include Interface Attributes for all
underlying interfaces; for any attributes not included, the neighbor
considers the status as unchanged.Bridge and Proxy/Server OMNI interfaces are configured over
underlying interfaces that provide both secured tunnels for carrying
IPv6 ND and BGP protocol control plane messages and open INET access
for carrying unsecured messages. The OMNI interface configures both an
ADM-LLA and its corresponding ADM-ULA, and acts as an OAL source to
encapsulate and fragment original IP packets while presenting the
resulting carrier packets over the secured or unsecured underlying
paths. Note that Bridge and Proxy/Server BGP protocol TCP sessions are
run directly over the OMNI interface and use ADM-ULA source and
destination addresses. The OMNI interface employs the OAL to
encapsulate the original IP packets for these sessions as carrier
packets (i.e., even though the OAL header may use the same ADM-ULAs as
the original IP header) and forwards them over the secured underlying
path.AERO Proxy/Servers and Clients configure OMNI interfaces as their
point of attachment to the OMNI link. AERO nodes assign the MSPs for
the link to their OMNI interfaces (i.e., as a "route-to-interface") to
ensure that original IP packets with destination addresses covered by
an MNP not explicitly associated with another interface are directed
to an OMNI interface.OMNI interface initialization procedures for Proxy/Servers, Clients
and Bridges are discussed in the following sections.When a Proxy/Server enables an OMNI interface, it assigns an
ADM-{LLA,ULA} appropriate for the given OMNI link SRT segment. The
Proxy/Server also configures secured tunnels with one or more
neighboring Bridges and engages in a BGP routing protocol session
with each Bridge.The OMNI interface provides a single interface abstraction to the
IP layer, but internally includes an NBMA nexus for sending carrier
packets to OMNI interface neighbors over underlying INET interfaces
and secured tunnels. The Proxy/Server further configures a service
to facilitate ND exchanges with AERO Clients and manages per-Client
neighbor cache entries and IP forwarding table entries based on
control message exchanges.Relays are simply Proxy/Servers that run a dynamic routing
protocol to redistribute routes between the OMNI interface and
INET/EUN interfaces (see: ). The Relay
provisions MNPs to networks on the INET/EUN interfaces (i.e., the
same as a Client would do) and advertises the MSP(s) for the OMNI
link over the INET/EUN interfaces. The Relay further provides an
attachment point of the OMNI link to a non-MNP-based global
topology.When a Client enables an OMNI interface, it assigns either an
MNP-{LLA, ULA} or a Temporary ULA and sends RS messages with ND
parameters over its underlying interfaces to an FHS Proxy/Server,
which returns an RA message with corresponding parameters. The RS/RA
messages may pass through one or more NATs in the case of a Client's
INET interface. (Note: if the Client used a Temporary ULA in its
initial RS message, it will discover an MNP-{LLA, ULA} in the
corresponding RA that it receives from the FHS Proxy/Server and
begin using these new addresses. If the Client is operating outside
the context of AERO infrastructure such as in a Mobile Ad-hoc
Network (MANET), however, it may continue using Temporary ULAs for
Client-to-Client communications until it encounters an
infrastructure element that can provide an MNP.)AERO Bridges configure an OMNI interface and assign the ADM-ULA
Subnet Router Anycast address for each OMNI link SRT segment they
connect to. Bridges configure secured tunnels with Proxy/Servers in
the same SRT segment and other Bridges in the same (or an adjacent)
SRT segment. Bridges then engage in a BGP routing protocol session
with neighbors over the secured spanning tree (see: ).Each OMNI interface maintains a conceptual neighbor cache that
includes a Neighbor Cache Entry (NCE) for each of its active neighbors
on the OMNI link per . Each NCE is indexed by
the LLA of the neighbor, while the OAL encapsulation ULA determines
the context for Identification verification.Proxy/Servers maintain NCEs for each of their associated local
Clients discovered through RS/RA exchanges. Proxy/Servers and Bridges
also maintain NCEs for non-local target Clients associated with other
Proxy/Servers through NS/NA(WIN) route optimization. When a
Proxy/Server or Bridge creates a NCE for a local or target Client, it
assigns a unique "Neighbor Index" value between (1 - 2**24) that
remains associated with the NCE until the NCE is deleted.To the list of NCE states in Section 7.3.2 of , Proxy/Server OMNI interfaces add an additional
state DEPARTED that applies to Clients that have recently departed.
The interface sets a "DepartTime" variable for the NCE to
"DEPART_TIME" seconds. DepartTime is decremented unless a new ND
message causes the state to return to REACHABLE. While a NCE is in the
DEPARTED state, the Proxy/Server forwards carrier packets destined to
the target Client to the Client's new location instead. When
DepartTime decrements to 0, the NCE is deleted. It is RECOMMENDED that
DEPART_TIME be set to the default constant value REACHABLE_TIME plus
10 seconds (40 seconds by default) to allow a window for carrier
packets in flight to be delivered while stale route optimization state
may be present.Proxy/Servers can act as RORs on behalf of their associated Clients
according to the Proxy Neighbor Advertisement specification in Section
7.2.8 of . When a Proxy/Server ROR receives an
authentic NS message used for route optimization, it first searches
for a NCE for the target Client and accepts the message only if there
is an entry. The Proxy/Server then returns a solicited NA message
while creating or updating a "Report List" entry in the target
Client's NCE that caches both the LLA and ULA of ROS with a
"ReportTime" variable set to REPORT_TIME seconds. The ROR resets
ReportTime when it receives a new authentic NS message, and otherwise
decrements ReportTime while no authentic NS messages have been
received. It is RECOMMENDED that REPORT_TIME be set to the default
constant value REACHABLE_TIME plus 10 seconds (40 seconds by default)
to allow a window for route optimization to converge before ReportTime
decrements below REACHABLE_TIME.When the ROS receives a solicited NA message response to its NS
message used for route optimization, it creates or updates a NCE for
the target network-layer and link-layer addresses. The ROS then
(re)sets ReachableTime for the NCE to REACHABLE_TIME seconds and
performs reachability tests over specific underlying interface pairs
to determine paths for forwarding carrier packets directly to the
target. The ROS otherwise decrements ReachableTime while no further
solicited NA messages arrive. It is RECOMMENDED that REACHABLE_TIME be
set to the default constant value 30 seconds as specified in .AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the
number of NS messages sent when a correspondent may have gone
unreachable, the value MAX_RTR_SOLICITATIONS to limit the number of RS
messages sent without receiving an RA and the value
MAX_NEIGHBOR_ADVERTISEMENT to limit the number of unsolicited NAs that
can be sent based on a single event. It is RECOMMENDED that
MAX_UNICAST_SOLICIT, MAX_RTR_SOLICITATIONS and
MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the same as specified in .Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME,
MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and
MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if
different values are chosen, all nodes on the link MUST consistently
configure the same values. Most importantly, DEPART_TIME and
REPORT_TIME SHOULD be set to a value that is sufficiently longer than
REACHABLE_TIME to avoid packet loss due to stale route optimization
state.OMNI interfaces prepare IPv6 ND messages the same as for standard
IPv6 ND, but also include a new option type termed the OMNI option
. OMNI interfaces prepare IPv6
ND messages the same as for standard IPv6 ND, and include one or
more OMNI options and any other options then completely populate all
option information. If the OMNI interface includes an authentication
signature, it sets the IPv6 ND message Checksum field to 0 and
calculates the authentication signature over the entire length of
the message (beginning with a pseudo-header of the IPv6 header) but
does not then proceed to calculate the IPv6 ND message checksum
itself. If the OMNI interface forwards the message to a next hop
over the secured spanning tree path, it omits both the
authentication signature an checksum since lower layers already
ensure authentication and integrity. In all other cases, the OMNI
interface calculates the standard IPv6 ND message checksum and
writes the value in the Checksum field. OMNI interfaces verify
authentication and integrity of each IPv6 ND message received
according to the specific check(s) included, and process the message
further only following verification.OMNI options include per-neighbor information such as Interface
Attributes that provide link-layer address and traffic selector
information for the neighbor's underlying interfaces. This
information is stored in the neighbor cache and provides the basis
for the forwarding algorithm specified in .
The information is cumulative and reflects the union of the OMNI
information from the most recent ND messages received from the
neighbor; it is therefore not required that each ND message contain
all neighbor information.The OMNI option Interface Attributes for each underlying
interface includes a two-part "Link-Layer Address" consisting of an
INET encapsulation address determined by the FMT and L2ADDR fields
and an ADM-ULA determined by the SRT and LHS fields. Underlying
interfaces are further selected based on their associated traffic
selectors.The OMNI option is distinct from any Source/Target Link-Layer
Address Options (S/TLLAOs) that may appear in an ND message
according to the appropriate IPv6 over specific link layer
specification (e.g., ). If both an OMNI
option and S/TLLAO appear, the former pertains to encapsulation
addresses while the latter pertains to the native L2 address format
of the underlying mediaOMNI interface IPv6 ND messages may also include other IPv6 ND
options. In particular, solicitation messages may include Nonce
and/or Timestamp options if required for verification of
advertisement replies. If an OMNI ND solicitation message includes a
Nonce option, the advertisement reply must echo the same Nonce. If
an OMNI ND solicitation message includes a Timestamp option, the
advertisement reply should also include a Timestamp option.AERO Clients send RS messages to the All-Routers multicast
address while using unicast link-layer addresses. AERO Proxy/Servers
respond by returning unicast RA messages. During the RS/RA exchange,
AERO Clients and Servers include state synchronization parameters to
establish Identification windows and other state.AERO nodes use NS/NA messages for the following purposes:NS/NA(AR) messages are used for address resolution only. The
ROS sends an NS(AR) to the solicited-node multicast address of
the target, and an ROR in the network with addressing
information for the target returns a unicast NA(AR). The NA(AR)
contains current, consistent and authentic target address
resolution information, but only an implicit third-party
assertion of target reachability. NS/NA(AR) messages must be
secured.NS/NA(WIN) messages are used for establishing and maintaining
window synchronization state (and/or any other state such as
Interface Attributes). The source sends an NS(WIN) to the
unicast address of the target, and the target returns a unicast
NA(WIN). The NS/NA(WIN) exchange synchronizes the sequence
number windows for Identification values the neighbors will
include in subsequent carrier packets, and asserts reachability
for the target without necessarily testing a specific underlying
interface pair. NS/NA(WIN) messages must be secured.NS/NA(NUD) messages are used for determining target
reachability. The source sends an NS(NUD) to the unicast address
of the target while naming a specific underlying interface pair,
and the target returns a unicast NA(NUD). NS/NA(NUD) messages
that use an in-window sequence number and do not update any
other state need not be secured but should include an IPv6 ND
message checksum. NS/NA(NUD) messages may also be used in
combination with window synchronization (i.e., NUD+WIN), in
which case the messages must be secured.Unsolicited NA (uNA) messages are used to signal addressing
and/or other neighbor state changes (e.g., address changes due
to mobility, signal degradation, traffic selector updates,
etc.). uNA messages that include state update information must
be secured.NS/NA(DAD) messages are not used in AERO, since Duplicate
Address Detection is not required.Additionally, nodes may send NA/RA messages with the OMNI
option PNG flag set to receive a solicited NA response from the
neighbor. The solicited NA response MUST set the ACK flag (without
also setting the SYN or PNG flags) and include the Identification
used in the PNG message in the Acknowledgement.As discussed in Section 4.4 of NA
messages include three flag bits R, S and O. OMNI interface NA
messages treat the flags as follows:R: The R ("Router") flag is set to 1 in the NA messages sent
by all AERO/OMNI node types. Simple hosts that would set R to 0
do not occur on the OMNI link itself, but may occur on the
downstream links of Clients and Relays.S: The S ("Solicited") flag is set exactly as specified in
Section 4.4. of , i.e., it is set to 1
for Solicited NAs and set to 0 for uNAs (both unicast and
multicast).O: The O ("Override") flag is set to 0 for solicited NAs
returned by a Proxy/Server ROR and set to 1 for all other
solicited and unsolicited NAs. For further study is whether
solicited NAs for anycast targets apply for OMNI links. Since
MNP-LLAs must be uniquely assigned to Clients to support correct
ND protocol operation, however, no role is currently seen for
assigning the same MNP-LLA to multiple Clients.In secured environments (e.g., such as between nodes on the same
secured ANET), OMNI interface neighbors can exchange OAL packets
using randomly-initialized and monotonically-increasing
Identification values (modulo 2*32) without window synchronization.
In environments where spoofing is considered a threat, OMNI
interface neighbors instead invoke window synchronization in ND
message exchanges to maintain send/receive window state in their
respective neighbor cache entries as specified in .In the asymmetric window synchronization case, the initial ND
message exchange establishes only the initiator's send window and
the responder's receive window such that a corresponding exchange
would be needed to establish the reverse direction. In the symmetric
case, the initiator and responder engage in a three-way handshake to
symmetrically establish the send/receive windows of both
parties.The OMNI interface admits original IP packets then acts as an OAL
source to perform OAL encapsulation and fragmentation as specified in
while including an ORH if
necessary as specified in . The OAL
encapsulates original IP packets to form OAL packets subject to
fragmentation, then encapsulates the resulting OAL fragments in *NET
headers as carrier packets.For carrier packets undergoing re-encapsulation at an OAL
intermediate node, the OMNI interface decrements the OAL IPv6 header
Hop Limit and discards the carrier packet if the Hop Limit reaches 0.
The intermediate node next removes the *NET encapsulation headers from
the first segment and re-encapsulates the packet in new *NET
encapsulation headers for the next segment.When an FHS Proxy/Server re-encapsulates a carrier packet received
from a Client that includes an OAL but no ORH, it inserts an ORH
immediately following the OAL header and adjusts the OAL payload
length and destination address field. The ORH may be removed by an LHS
Bridge or Proxy/Server, but its insertion and removal will not
interfere with reassembly at the final destination. For this reason,
Clients must reserve 40 bytes for a maximum-length ORH when they
perform OAL encapsulation (see: ).OMNI interfaces (acting as OAL destinations) decapsulate and
reassemble OAL packets into original IP packets destined either to the
AERO node itself or to a destination reached via an interface other
than the OMNI interface the original IP packet was received on. When
carrier packets containing OAL fragments addressed to itself arrive,
the OMNI interface discards the NET encapsulation headers and
reassembles as discussed in .AERO nodes employ simple data origin authentication procedures. In
particular:AERO Bridges and Proxy/Servers accept carrier packets received
from secured underlying interfaces.AERO Proxy/Servers and Clients accept carrier packets and
original IP packets that originate from within the same secured
ANET.AERO Clients and Relays accept original IP packets from
downstream network correspondents based on ingress filtering.AERO Clients, Relays and Proxy/Servers verify carrier packet
UDP/IP encapsulation addresses according to .AERO nodes accept carrier packets addressed to themselves with
Identification values within the current window for the OAL source
neighbor (when window synchronization is used) and drop any
carrier packets with out-of-window Identification values. (AERO
nodes may forward carrier packets not addressed to themselves
without verifying the Identification value.)AERO nodes silently drop any packets that do not satisfy the
above data origin authentication procedures. Further security
considerations are discussed in .The OMNI interface observes the link nature of tunnels, including
the Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and
the role of fragmentation and reassembly . The OMNI interface employs an
OMNI Adaptation Layer (OAL) that accommodates multiple underlying
links with diverse MTUs while observing both a minimum and per-path
Maximum Payload Size (MPS). The functions of the OAL and the OMNI
interface MTU/MRU/MPS are specified in with MTU/MRU both set to the constant
value 9180 bytes, with minimum MPS set to 400 bytes, and with
potentially larger per-path MPS values depending on the underlying
path.When the network layer presents an original IP packet to the OMNI
interface, the OAL source encapsulates and fragments the original IP
packet if necessary. When the network layer presents the OMNI
interface with multiple original IP packets bound to the same OAL
destination, the OAL source can concatenate them together into a
single OAL super-packet as discussed in . The OAL source then fragments the
OAL packet if necessary according to the minimum/path MPS such that
the OAL headers appear in each fragment while the original IP packet
header appears only in the first fragment. The OAL source then
encapsulates each OAL fragment in *NET headers for transmission as
carrier packets over an underlying interface connected to either a
physical link (such as Ethernet, WiFi and the like) or a virtual link
such as an Internet or higher-layer tunnel (see the definition of link
in ).Note: A Client that does not (yet) have neighbor cache state for a
target may omit the ORH in carrier packets with the understanding that
a Proxy/Server may insert an ORH on its behalf. For this reason,
Clients reserve 40 bytes for the largest possible ORH in their OAL
fragment size calculations.Note: Although the ORH may be removed or replaced by a Bridge or
Proxy/Server on the path (see: ), this does not
interfere with the destination's ability to reassemble since the ORH
is not included in the fragmentable part and its
removal/transformation does not invalidate fragment header
information.Original IP packets enter a node's OMNI interface either from the
network layer (i.e., from a local application or the IP forwarding
system) while carrier packets enter from the link layer (i.e., from an
OMNI interface neighbor). All original IP packets and carrier packets
entering a node's OMNI interface first undergo data origin
authentication as discussed in . Those that
satisfy data origin authentication are processed further, while all
others are dropped silently.Original IP packets that enter the OMNI interface from the network
layer are forwarded to an OMNI interface neighbor using OAL
encapsulation and fragmentation to produce carrier packets for
transmission over underlying interfaces. (If routing indicates that
the original IP packet should instead be forwarded back to the network
layer, the packet is dropped to avoid looping). Carrier packets that
enter the OMNI interface from the link layer are either
re-encapsulated and re-admitted into the OMNI link, or reassembled and
forwarded to the network layer where they are subject to either local
delivery or IP forwarding. In all cases, the OAL MUST NOT decrement
the network layer TTL/Hop-count since its forwarding actions occur
below the network layer.OMNI interfaces may have multiple underlying interfaces and/or
neighbor cache entries for neighbors with multiple underlying
interfaces (see ). The OAL uses Interface
Attributes traffic selectors (e.g., port number, flow specification,
etc.) to select an outbound underlying interface for each OAL packet
based on the node's own interface attributes, and also to select a
destination link-layer address based on the neighbor's underlying
interface attributes. AERO implementations SHOULD permit network
management to dynamically adjust traffic selector values at
runtime.If an OAL packet matches the traffic selectors of multiple outgoing
interfaces and/or neighbor interfaces, the OMNI interface replicates
the packet and sends one copy via each of the (outgoing / neighbor)
interface pairs; otherwise, it sends a single copy of the OAL packet
via an interface with the best matching traffic selector. (While not
strictly required, the likelihood of successful reassembly may improve
when the OMNI interface sends all fragments of the same fragmented OAL
packet consecutively over the same underlying interface pair to avoid
complicating factors such as delay variance and reordering.) AERO
nodes keep track of which underlying interfaces are currently
"reachable" or "unreachable", and only use "reachable" interfaces for
forwarding purposes.The following sections discuss the OMNI interface forwarding
algorithms for Clients, Proxy/Servers and Bridges. In the following
discussion, an original IP packet's destination address is said to
"match" if it is the same as a cached address, or if it is covered by
a cached prefix (which may be encoded in an MNP-LLA).When an original IP packet enters a Client's OMNI interface from
the network layer the Client searches for a NCE that matches the
destination. If there is a match, the Client selects one or more
"reachable" neighbor interfaces in the entry for forwarding
purposes. If there is no NCE, the Client instead either enqueues the
original IP packet and invokes route optimization or forwards the
original IP packet toward a Proxy/Server. The Client (acting as an
OAL source) performs OAL encapsulation and sets the OAL destination
address to the MNP-ULA of the target if there is a matching NCE;
otherwise, it sets the OAL destination to the ADM-ULA of the
Proxy/Server. If the Client has multiple original IP packets to send
to the same neighbor, it can concatenate them in a single
super-packet . The OAL source
then performs fragmentation to create OAL fragments (see: ), appends any *NET encapsulation, and sends the
resulting carrier packets over underlying interfaces to the neighbor
acting as an OAL destination.If the neighbor interface selected for forwarding is located on
the same OMNI link segment and not behind a NAT, the Client forwards
the carrier packets directly according to the L2ADDR information for
the neighbor. If the neighbor interface is behind a NAT on the same
OMNI link segment, the Client instead forwards the initial carrier
packets to the LHS Proxy/Server (while inserting an ORH-0 if
necessary) and initiates NAT traversal procedures. If the Client's
intended source underlying interface is also behind a NAT and
located on the same OMNI link segment, it sends a "direct bubble"
over the interface per to the L2ADDR found in the neighbor cache in
order to establish state in its own NAT by generating traffic toward
the neighbor (note that no response to the bubble is expected).The Client next sends an NS(NUD) message toward the MNP-ULA of
the neighbor via the LHS Proxy/Server as discussed in . If the Client receives an NA(NUD) from the neighbor
over the underlying interface, it marks the neighbor interface as
"trusted" and sends future carrier packets directly to the L2ADDR
information for the neighbor instead of indirectly via the LHS
Proxy/Server. The Client must honor the neighbor cache maintenance
procedure by sending additional direct bubbles and/or NS/NA(NUD)
messages as discussed in in order to keep NAT state alive as long as
carrier packets are still flowing.When a carrier packet enters a Client's OMNI interface from the
link-layer, if the OAL destination matches one of the Client's ULAs
the Client (acting as an OAL destination) verifies that the
Identification is in-window for this OAL source, then reassembles
and decapsulates as necessary and delivers the original IP packet to
the network layer. Otherwise, the Client drops the original IP
packet and MAY return a network-layer ICMP Destination Unreachable
message subject to rate limiting (see: ).Note: Clients and their FHS Proxy/Server (and other Client) peers
can exchange original IP packets over ANET underlying interfaces
without invoking the OAL, since the ANET is secured at the link and
physical layers. By forwarding original IP packets without invoking
the OAL, however, the ANET peers can engage only in classical path
MTU discovery since the packets are subject to loss and/or
corruption due to the various per-link MTU limitations that may
occur within the ANET. Moreover, the original IP packets do not
include either the OAL integrity check or per-packet Identification
values that can be used for data origin authentication and
link-layer retransmissions. The tradeoff therefore involves an
assessment of the per-packet encapsulation overhead saved by
bypassing the OAL vs. inheritance of classical network
"brittleness". (Note however that ANET peers can send small original
IP packets without invoking the OAL, while invoking the OAL for
larger packets. This presents the beneficial aspects of both small
packet efficiency and large packet robustness, with delay variance
and reordering as possible side effects.)When the Proxy/Server receives an original IP packet from the
network layer, it drops the packet if routing indicates that it
should be forwarded back to the network layer to avoid looping.
Otherwise, the Proxy/Server regards the original IP packet the same
as if it had arrived as carrier packets with OAL destination set to
its own ADM-ULA. When the Proxy/Server receives carrier packets on
underlying interfaces with OAL destination set to its own ADM-ULA,
it performs OAL reassembly if necessary to obtain the original IP
packet.The Proxy/Server next searches for a NCE that matches the
original IP destination and proceeds as follows:if the packet is an NA(WIN) message for a local Client NCE,
the Proxy/Server examines the Interface Attributes information
and rewrites the fields if the NA(WIN) was not already processed
by a (local segment) Bridge as discussed in .else, if the original IP packet destination matches a NCE,
the Proxy/Sever uses one or more "reachable" neighbor interfaces
in the entry for packet forwarding using OAL encapsulation and
fragmentation according to the cached link-layer address
information. If the neighbor interface is in a different OMNI
link segment, the Proxy/Server performs OAL encapsulation and
fragmentation, inserts an ORH and forwards the resulting carrier
packets via the spanning tree to a Bridge; otherwise, it
forwards the carrier packets directly to the neighbor. If the
neighbor is behind a NAT, the Proxy/Server instead forwards
initial carrier packets via a Bridge while sending an NS(NUD) to
the neighbor. When the Proxy/Server receives the NA(NUD), it can
begin forwarding carrier packets directly to the neighbor the
same as discussed in while sending
additional NS(NUD) messages as necessary to maintain NAT state.
Note that no direct bubbles are necessary since the Proxy/Server
is by definition not located behind a NAT.else, if the original IP destination matches a non-MNP route
in the IP forwarding table or an ADM-LLA assigned to the
Proxy/Server's OMNI interface, the Proxy/Server acting as a
Relay presents the original IP packet to the network layer for
local delivery or IP forwarding.else, the Proxy/Server initiates address resolution as
discussed in , while retaining initial
original IP packets in a small queue awaiting address resolution
completion.When the Proxy/Server receives a carrier packet with OAL
destination set to an MNP-ULA that does not match the MSP, it
accepts the carrier packet only if data origin authentication
succeeds and if there is a network layer routing table entry for a
GUA route that matches the MNP-ULA. If there is no route, the
Proxy/Server drops the carrier packet; otherwise, it reassembles and
decapsulates to obtain the original IP packet then acts as a Relay
to present it to the network layer where it will be delivered
according to standard IP forwarding.When a Proxy/Server receives a carrier packet from one of its
Client neighbors with OAL destination set to another node, it
forwards the packets via a matching NCE or via the spanning tree if
there is no matching entry. When the Proxy/Server receives a carrier
packet with OAL destination set to the MNP-ULA of one of its Client
neighbors established through RS/RA exchanges, it accepts the
carrier packet only if data origin authentication succeeds. If the
NCE state is DEPARTED, the Proxy/Server inserts an ORH that encodes
the MNP-ULA destination suffix and changes the OAL destination
address to the ADM-ULA of the new Proxy/Server, then re-encapsulates
the carrier packet and forwards it to a Bridge which will eventually
deliver it to the new Proxy/Server.If the neighbor cache state for the MNP-ULA is REACHABLE, the
Proxy/Server forwards the carrier packets to the Client which then
must reassemble. (Note that the Proxy/Server does not reassemble
carrier packets not explicitly addressed to its own ADM-ULA, since
some of the carrier packets of the same original IP packet could be
forwarded through a different Proxy/Server.) In that case, the
Client may receive fragments that are smaller than its link MTU but
that can still be reassembled.Note: Proxy/Servers may receive carrier packets with ORHs that
include additional forwarding information. Proxy/Servers use the
forwarding information to determine the correct NCE and underlying
interface for forwarding to the target Client, then remove the ORH
and forward the carrier packet. If the ORH information instead
indicates that the Proxy/Server is responsible for reassembly, the
Proxy/Server reassembles first before re-encapsulating (and possibly
also re-fragmenting) then forwards to the target Client. For a full
discussion of cases when the Proxy/Server may receive carrier
packets with ORHs, see: .Note: Clients and their FHS Proxy/Server peers can exchange
original IP packets over ANET underlying interfaces without invoking
the OAL, since the ANET is secured at the link and physical layers.
By forwarding original IP packets without invoking the OAL, however,
the Client and Proxy/Server can engage only in classical path MTU
discovery since the packets are subject to loss and/or corruption
due to the various per-link MTU limitations that may occur within
the ANET. Moreover, the original IP packets do not include either
the OAL integrity check or per-packet Identification values that can
be used for data origin authentication and link-layer
retransmissions. The tradeoff therefore involves an assessment of
the per-packet encapsulation overhead saved by bypassing the OAL vs.
inheritance of classical network "brittleness". (Note however that
ANET peers can send small original IP packets without invoking the
OAL, while invoking the OAL for larger packets. This presents the
beneficial aspects of both small packet efficiency and large packet
robustness.)Note: When a Proxy/Server receives a (non-OAL) original IP packet
from an ANET Client, or a carrier packet with OAL destination set to
its own ADM-ULA from any Client, the Proxy/Server reassembles if
necessary then performs ROS functions on behalf of the Client. The
Client may at some later time begin sending carrier packets to the
OAL address of the actual target instead of the Proxy/Server, at
which point it may begin functioning as an ROS on its own behalf and
thereby "override" the Proxy/Server's ROS role.Note; Proxy/Servers drop any original IP packets (received either
directly from an ANET Client or following reassembly of carrier
packets received from an ANET/INET Client) with a destination that
corresponds to the Client's delegated MNP. Similarly, Proxy/Servers
drop any carrier packet received with both a source and destination
that correspond to the Client's delegated MNP regardless of their
OMNI link point of origin. These checks are necessary to prevent
Clients from either accidentally or intentionally establishing
endless loops that could congest Proxy/Servers and/or ANET/INET
links.Note: Proxy/Servers forward secure control plane carrier packets
via the SRT secured spanning tree and forwards other carrier packets
via the unsecured spanning tree. When a Proxy/Server receives a
carrier packet from the secured spanning tree, it considers the
message as authentic without having to verify upper layer
authentication signatures. When a Proxy/Server receives a carrier
packet from the unsecured spanning tree, it verifies any upper layer
authentication signatures and/or forwards the unsecured message
toward the destination which must apply data origin
authentication.Note: If the Proxy/Server has multiple original IP packets to
send to the same neighbor, it can concatenate them in a single OAL
super-packet .Bridges forward carrier packets while decrementing the OAL header
Hop Count but not the original IP header Hop Count/TTL. Bridges
convey carrier packets that encapsulate IPv6 ND control messages or
routing protocol control messages via the secured spanning tree, and
may convey carrier packets that encapsulate ordinary data via the
unsecured spanning tree. When the Bridge receives a carrier packet,
it removes the outer *NET header and searches for a forwarding table
entry that matches the OAL destination address. The Bridge then
processes the packet as follows:if the carrier packet destination matches its ADM-ULA or the
corresponding ADM-ULA Subnet Router Anycast address and the OAL
header is followed by an ORH, the Bridge reassembles if
necessary then sets aside the ORH and processes the carrier
packet locally before forwarding. If the carrier packet contains
an NS/NA(WIN) message, the Bridge creates/updates an NCE for the
target and rewrites the Interface Attributes as discussed in
. The Bridge next examines the ORH, and
if FMT-Mode indicates the destination is a Client on the open
*NET (or, a Client behind a NAT for which NAT traversal
procedures have already converged) the Bridge writes the MNP-ULA
formed from the ORH Destination Suffix into the OAL destination.
The Bridge then removes the ORH and forwards the packet using
encapsulation based on L2ADDR. If the LHS Proxy/Server will
forward to the Client without reassembly, the Bridge writes the
MNP-ULA into the OAL destination then replaces the ORH with an
ORH-0 and forwards the carrier packet to the LHS Proxy/Server
while also invoking NAT traversal procedures if necessary
(noting that no direct bubbles are necessary since only the
target Client and not the Bridge is behind a NAT). If the LHS
Proxy/Server must perform reassembly before forwarding to the
Client, the Bridge instead writes the ADM-ULA formed from the
ORH SRT/LHS into the OAL destination address, replaces the ORH
with an ORH-0 and forwards the carrier packet to the LHS
Proxy/Server. (Note: for NA/NA(WIN) messages, the Bridge must
forward the message to the LHS Proxy/Server over the secured
spanning tree instead of directly to the Client itself even if
NAT traversal has converged.)else, if the carrier packet destination matches its ADM-ULA
or the corresponding ADM-ULA Subnet Router Anycast address and
the OAL header is not followed by an ORH with Segments Left set
to 1, the Bridge submits the packet for reassembly. When
reassembly is complete, the Bridge submits the original IP
packet to the network layer to support local applications such
as BGP routing protocol sessions.else, if the carrier packet destination matches a forwarding
table entry the Bridge forwards the carrier packet to the next
hop. (If the destination matches an MSP without matching an MNP,
however, the Bridge instead drops the packet and returns a
Destination Unreachable message subject to rate limiting - see:
).else, the Bridge drops the packet and returns an Destination
Unreachable as above.The Bridge decrements the OAL IPv6 header Hop Limit when it
forwards the carrier packet and drops the packet if the Hop Limit
reaches 0. Therefore, only the Hop Limit in the OAL header is
decremented and not the TTL/Hop Limit in the original IP packet
header. Bridges do not insert OAL/ORH headers themselves; instead,
they simply forward carrier packets based on their destination
addresses while also possibly transforming larger ORHs into an ORH-0
(or removing the ORH altogether).Bridges forward carrier packets received from a first segment via
the SRT secured spanning tree to the next segment also via the
secured spanning tree. Bridges forward carrier packets received from
a first segment via the unsecured spanning tree to the next segment
also via the unsecured spanning tree. Bridges use a single IPv6
routing table that always determines the same next hop for a given
OAL destination, where the secured/unsecured spanning tree is
determined through the selection of the underlying interface to be
used for transmission (i.e., a secured tunnel or an open INET
interface).When an AERO node admits an original IP packet into the OMNI
interface, it may receive link-layer or network-layer error
indications. The AERO node may also receive OMNI link error
indications in OAL-encapsulated uNA messages that include
authentication signatures.A link-layer error indication is an ICMP error message generated by
a router in the INET on the path to the neighbor or by the neighbor
itself. The message includes an IP header with the address of the node
that generated the error as the source address and with the link-layer
address of the AERO node as the destination address.The IP header is followed by an ICMP header that includes an error
Type, Code and Checksum. Valid type values include "Destination
Unreachable", "Time Exceeded" and "Parameter Problem" . (OMNI interfaces ignore
link-layer IPv4 "Fragmentation Needed" and IPv6 "Packet Too Big"
messages for carrier packets that are no larger than the minimum/path
MPS as discussed in , however these messages
may provide useful hints of probe failures during path MPS
probing.)The ICMP header is followed by the leading portion of the carrier
packet that generated the error, also known as the "packet-in-error".
For ICMPv6, specifies that the
packet-in-error includes: "As much of invoking packet as possible
without the ICMPv6 packet exceeding the minimum IPv6 MTU" (i.e., no
more than 1280 bytes). For ICMPv4, specifies
that the packet-in-error includes: "Internet Header + 64 bits of
Original Data Datagram", however Section
4.3.2.3 updates this specification by stating: "the ICMP datagram
SHOULD contain as much of the original datagram as possible without
the length of the ICMP datagram exceeding 576 bytes".The link-layer error message format is shown in :The AERO node rules for processing these link-layer error
messages are as follows:When an AERO node receives a link-layer Parameter Problem
message, it processes the message the same as described as for
ordinary ICMP errors in the normative references .When an AERO node receives persistent link-layer Time Exceeded
messages, the IP ID field may be wrapping before earlier fragments
awaiting reassembly have been processed. In that case, the node
should begin including integrity checks and/or institute rate
limits for subsequent packets.When an AERO node receives persistent link-layer Destination
Unreachable messages in response to carrier packets that it sends
to one of its neighbor correspondents, the node should process the
message as an indication that a path may be failing, and
optionally initiate NUD over that path. If it receives Destination
Unreachable messages over multiple paths, the node should allow
future carrier packets destined to the correspondent to flow
through a default route and re-initiate route optimization.When an AERO Client receives persistent link-layer Destination
Unreachable messages in response to carrier packets that it sends
to one of its neighbor Proxy/Servers, the Client should mark the
path as unusable and use another path. If it receives Destination
Unreachable messages on many or all paths, the Client should
associate with a new Proxy/Server and release its association with
the old Proxy/Server as specified in .When an AERO Proxy/Server receives persistent link-layer
Destination Unreachable messages in response to carrier packets
that it sends to one of its neighbor Clients, the Proxy/Server
should mark the underlying path as unusable and use another
underlying path.When an AERO Proxy/Server receives link-layer Destination
Unreachable messages in response to a carrier packet that it sends
to one of its permanent neighbors, it treats the messages as an
indication that the path to the neighbor may be failing. However,
the dynamic routing protocol should soon reconverge and correct
the temporary outage.When an AERO Bridge receives a carrier packet for which the
network-layer destination address is covered by an MSP, the Bridge
drops the packet if there is no more-specific routing information for
the destination and returns an OMNI interface Destination Unreachable
message subject to rate limiting.When an AERO node receives a carrier packet for which reassembly is
currently congested, it returns an OMNI interface Packet Too Big (PTB)
message as discussed in (note
that the PTB messages could indicate either "hard" or "soft"
errors).AERO nodes include ICMPv6 error messages intended for the OAL
source as sub-options in the OMNI option of secured uNA messages. When
the OAL source receives the uNA message, it can extract the ICMPv6
error message enclosed in the OMNI option and either process it
locally or translate it into a network-layer error to return to the
original source.AERO Router Discovery, Prefix Delegation and Autoconfiguration are
coordinated as discussed in the following Sections.Each AERO Proxy/Server on the OMNI link is configured to
facilitate Client prefix delegation/registration requests. Each
Proxy/Server is provisioned with a database of MNP-to-Client ID
mappings for all Clients enrolled in the AERO service, as well as
any information necessary to authenticate each Client. The Client
database is maintained by a central administrative authority for the
OMNI link and securely distributed to all Proxy/Servers, e.g., via
the Lightweight Directory Access Protocol (LDAP) , via static configuration, etc. Clients receive
the same service regardless of the Proxy/Servers they select.AERO Clients and Proxy/Servers use ND messages to maintain
neighbor cache entries. AERO Proxy/Servers configure their OMNI
interfaces as advertising NBMA interfaces, and therefore send
unicast RA messages with a short Router Lifetime value (e.g.,
ReachableTime seconds) in response to a Client's RS message.
Thereafter, Clients send additional RS messages to keep Proxy/Server
state alive.AERO Clients and Proxy/Servers include prefix delegation and/or
registration parameters in RS/RA messages (see ). The ND messages are exchanged
between Client and FHS Proxy/Servers according to the prefix
management schedule required by the service. If the Client knows its
MNP in advance, it can employ prefix registration by including its
MNP-LLA as the source address of an RS message and with an OMNI
option with valid prefix registration information for the MNP. If
the Proxy/Server accepts the Client's MNP assertion, it injects the
MNP into the routing system and establishes the necessary neighbor
cache state. If the Client does not have a pre-assigned MNP, it can
instead employ prefix delegation by including the unspecified
address (::) as the source address of an RS message and with an OMNI
option with prefix delegation parameters to request an MNP.The following sections specify the Client and Proxy/Server
behavior.AERO Clients discover the addresses of candidate FHS
Proxy/Servers in a similar manner as described in . Discovery methods include static configuration
(e.g., from a flat-file map of Proxy/Server addresses and
locations), or through an automated means such as Domain Name System
(DNS) name resolution . Alternatively, the
Client can discover Proxy/Server addresses through a layer 2 data
link login exchange, or through a unicast RA response to a
multicast/anycast RS as described below. In the absence of other
information, the Client can resolve the DNS Fully-Qualified Domain
Name (FQDN) "linkupnetworks.[domainname]" where "linkupnetworks" is
a constant text string and "[domainname]" is a DNS suffix for the
OMNI link (e.g., "example.com").To associate with a FHS Proxy/Server over an underlying
interface, the Client acts as a requesting router to request MNPs by
preparing an RS message with prefix management parameters. If the
Client already knows the Proxy/Server's ADM-LLA, it includes the LLA
as the network-layer destination address; otherwise, the Client
includes the (link-local) All-Routers multicast as the network-layer
destination. The Client can use its MNP-LLA as the network-layer
source address and include an OMNI option with prefix registration
information. If the Client does not yet have an MNP-LLA, it instead
sets the network-layer source address to unspecified (::) and
includes prefix delegation parameters in the OMNI option (see: ).The Client next includes an authentication sub-option if
necessary, Interface Attributes corresponding to the underlying
interface over which it will send the RS message, and optionally any
additional Interface Attributes corresponding to other underlying
interfaces. Next, the Client submits the RS for OAL encapsulation
and fragmentation if necessary with its own MNP-ULA and the
Proxy/Server's ADM-ULA or (site-scoped) All-Routers multicast as the
OAL addresses while selecting an Identification value and invoking
window synchronization as specified in .The Client then sends the RS (either directly via Direct
interfaces, via a VPN for VPNed interfaces, via an access router for
ANET interfaces or via INET encapsulation for INET interfaces) then
waits up to RetransTimer milliseconds for an RA message reply (see
) (retrying up to
MAX_RTR_SOLICITATIONS). If the Client receives no RAs, or if it
receives an RA with Router Lifetime set to 0, the Client SHOULD
abandon attempts through the first candidate FHS Proxy/Server and
try another Proxy/Server. Otherwise, the Client processes the prefix
information found in the RA message.When the Client processes an RA, it first performs OAL reassembly
and decapsulation if necessary then creates a NCE with the
Proxy/Server's ADM-LLA as the network-layer address and the
Proxy/Server's encapsulation and/or link-layer addresses as the
link-layer address. The Client then caches the FMT/SRT/LHS/L2ADDR
information from the Interface Attributes for omIndex 0 included in
the RA as an SRT point-of-reference for this Proxy/Server. The
Client next records the RA Router Lifetime field value in the NCE as
the time for which the Proxy/Server has committed to maintaining the
MNP in the routing system via this underlying interface, and caches
the other RA configuration information including Cur Hop Limit, M
and O flags, Reachable Time and Retrans Timer. The Client then
autoconfigures MNP-LLAs for any delegated MNPs and assigns them to
the OMNI interface. The Client also caches any MSPs included in
Route Information Options (RIOs) as MSPs to
associate with the OMNI link, and assigns the MTU value in the MTU
option to the underlying interface.The Client then registers its additional underlying interfaces
with FHS Proxy/Servers for those interfaces discovered by sending RS
messages via each additional interface as described above. The RS
messages include the same parameters as for the initial RS/RA
exchange, but with destination address set to the Proxy/Server's
ADM-LLA. The Client finally sub-delegates the MNPs to its attached
EUNs and/or the Client's own internal virtual interfaces as
described in to support
the Client's downstream attached "Internet of Things (IoT)". The
Client then sends additional RS messages over each underlying
interface before the Router Lifetime received for that interface
expires.After the Client registers its underlying interfaces, it may wish
to change one or more registrations, e.g., if an interface changes
address or becomes unavailable, if traffic selectors change, etc. To
do so, the Client prepares an RS message to send over any available
underlying interface as above. The RS includes an OMNI option with
prefix registration/delegation information, with Interface
Attributes specific to the selected underlying interface, and with
any additional Interface Attributes specific to other underlying
interfaces. When the Client receives the Proxy/Server's RA response,
it has assurance that the Proxy/Server has been updated with the new
information.If the Client wishes to discontinue use of a Proxy/Server it
issues an RS message over any underlying interface with an OMNI
option with a prefix release indication. When the Proxy/Server
processes the message, it releases the MNP, sets the NCE state for
the Client to DEPARTED and returns an RA reply with Router Lifetime
set to 0. After a short delay (e.g., 2 seconds), the Proxy/Server
withdraws the MNP from the routing system.AERO Proxy/Servers act as both IP routers and ND proxies, and
support a prefix delegation/registration service for Clients.
Proxy/Servers arrange to add their ADM-LLAs to a static map of
Proxy/Server addresses for the link and/or the DNS resource records
for the FQDN "linkupnetworks.[domainname]" before entering service.
The static map and/or DNS resource records should be arranged such
that Clients can discover the addresses of Proxy/Servers that are
geographically and/or topologically "close" to their underlying
network connections.When an FHS Proxy/Server receives a prospective Client's RS
message, it SHOULD return an immediate RA reply with Router Lifetime
set to 0 if it is currently too busy or otherwise unable to service
the Client. Otherwise, the Proxy/Server performs OAL reassembly if
necessary, then decapsulates and authenticates the RS message before
processing the prefix delegation/registration parameters. The
Proxy/Server then determines the correct MNPs to provide to the
Client by processing the MNP-LLA prefix parameters and/or the DHCPv6
OMNI sub-option. When the Proxy/Server returns the MNPs, it also
creates a forwarding table entry for the MNP-ULA corresponding to
each MNP resulting in a BGP update (see: ).
For IPv6, the Proxy/Server creates an IPv6 forwarding table entry
for each MNP. For IPv4, the Proxy/Server creates an IPv6 forwarding
table entry with the IPv4-compatibility MNP-ULA prefix corresponding
to the IPv4 address.The Proxy/Server next creates a NCE for the Client using the base
MNP-LLA as the network-layer address. Next, the Proxy/Server updates
the NCE by recording the information in each Interface Attributes
sub-option in the RS OMNI option. The Proxy/Server also records the
actual OAL/*NET addresses and RS message window synchronization
parameters (if any) in the NCE.Next, the Proxy/Server prepares an RA message using its ADM-LLA
as the network-layer source address and the network-layer source
address of the RS message as the network-layer destination address.
The Proxy/Server sets the Router Lifetime to the time for which it
will maintain both this underlying interface individually and the
NCE as a whole. The Proxy/Server also sets Cur Hop Limit, M and O
flags, Reachable Time and Retrans Timer to values appropriate for
the OMNI link. The Proxy/Server includes the MNPs, any other prefix
management parameters and an OMNI option with an Interface
Attributes sub-option with omIndex 0 and FMT/SRT/LHS/L2ADDR
information for its INET interface and an Origin Indication
sub-option with the mapped and obfuscated Port Number and IP address
corresponding to the Client's RS encapsulation addresses. The
Proxy/Server then includes one or more RIOs that encode the MSPs for
the OMNI link, plus an MTU option (see ).
The Proxy/Server finally forwards the message to the Client using
OAL encapsulation/fragmentation if necessary while including an
acknowledgement if the RS invoked window synchronization.After the initial RS/RA exchange, the Proxy/Server maintains a
ReachableTime timer for each of the Client's underlying interfaces
individually (and for the Client's NCE collectively) set to expire
after ReachableTime seconds. If the Client (or Proxy) issues
additional RS messages, the Proxy/Server sends an RA response and
resets ReachableTime. If the Proxy/Server receives an ND message
with a prefix release indication it sets the Client's NCE to the
DEPARTED state and withdraws the MNP from the routing system after a
short delay (e.g., 2 seconds). If ReachableTime expires before a new
RS is received on an individual underlying interface, the
Proxy/Server marks the interface as DOWN. If ReachableTime expires
before any new RS is received on any individual underlying
interface, the Proxy/Server sets the NCE state to STALE and sets a
10 second timer. If the Proxy/Server has not received a new RS or ND
message with a prefix release indication before the 10 second timer
expires, it deletes the NCE and withdraws the MNP from the routing
system.The Proxy/Server processes any ND messages pertaining to the
Client and returns an NA/RA reply in response to solicitations. The
Proxy/Server may also issue unsolicited RA messages, e.g., with
reconfigure parameters to cause the Client to renegotiate its prefix
delegation/registrations, with Router Lifetime set to 0 if it can no
longer service this Client, etc. Finally, If the NCE is in the
DEPARTED state, the Proxy/Server deletes the entry after DepartTime
expires.Note: Clients SHOULD notify former Proxy/Servers of their
departures, but Proxy/Servers are responsible for expiring neighbor
cache entries and withdrawing routes even if no departure
notification is received (e.g., if the Client leaves the network
unexpectedly). Proxy/Servers SHOULD therefore set Router Lifetime to
ReachableTime seconds in solicited RA messages to minimize
persistent stale cache information in the absence of Client
departure notifications. A short Router Lifetime also ensures that
proactive RS/RA messaging between Clients and Proxy/Servers will
keep any NAT state alive (see above).Note: All Proxy/Servers on an OMNI link MUST advertise consistent
values in the RA Cur Hop Limit, M and O flags, Reachable Time and
Retrans Timer fields the same as for any link, since unpredictable
behavior could result if different Proxy/Servers on the same link
advertised different values.When a Client is not pre-provisioned with an MNP-LLA, it will
need for the FHS Proxy/Server to select one or more MNPs on its
behalf and set up the correct state in the AERO routing service.
(A Client with a pre-provisioned MNP may also request the
Proxy/Server to select additional MNPs.) The DHCPv6 service is used to support this requirement.When a Client needs to have the FHS Proxy/Server select MNPs,
it sends an RS message with source address set to the unspecified
address (::) and with an OMNI option that includes a DHCPv6
message sub-option with DHCPv6 Prefix Delegation (DHCPv6-PD)
parameters. When the Proxy/Server receives the RS message, it
extracts the DHCPv6-PD message from the OMNI option.The Proxy/Server then acts as a "Proxy DHCPv6 Client" in a
message exchange with the locally-resident DHCPv6 server, which
delegates MNPs and returns a DHCPv6-PD Reply message. (If the
Proxy/Server wishes to defer creation of MN state until the
DHCPv6-PD Reply is received, it can instead act as a Lightweight
DHCPv6 Relay Agent per by encapsulating
the DHCPv6-PD message in a Relay-forward/reply exchange with Relay
Message and Interface ID options.)When the Proxy/Server receives the DHCPv6-PD Reply, it adds a
route to the routing system and creates an MNP-LLA based on the
delegated MNP. The Proxy/Server then sends an RA back to the
Client with the (newly-created) MNP-LLA as the destination address
and with the DHCPv6-PD Reply message coded in the OMNI option.
When the Client receives the RA, it creates a default route,
assigns the Subnet Router Anycast address and sets its MNP-LLA
based on the delegated MNP.Note: See for an MNP
delegation alternative that avoids including a DHCPv6 message
sub-option in the RS. Namely, when the Client requests a single
MNP it can set the RS source to the unspecified address (::) and
include a Node Identification sub-option and Preflen in the OMNI
option (but with no DHCPv6 message sub-option). When the
Proxy/Server receives the RS message, it forwards a self-generated
DHCPv6 Solicit message to the DHCPv6 server on behalf of the
Client. When the Proxy/Server receives the DHCPv6 Reply, it
prepares an RA message with an OMNI option with Preflen
information (but with no DHCPv6 message sub-option), then places
the (newly-created) MNP-LLA in the RA destination address and
returns the message to the Client.OMNI link Clients register with one or more FHS Proxy/Servers for
each underlying interface. Each of the Client's FHS Proxy/Servers must
be informed of all of the Client's additional underlying interfaces.
For Clients on Direct and VPNed underlying interfaces, the FHS
Proxy/Server for each interface is directly connected, for Clients on
ANET underlying interfaces the Proxy/Server is located on the
ANET/INET boundary, and for Clients on INET underlying interfaces the
FHS Proxy/Server is located somewhere in the connected Internetwork.
When FHS Proxy/Server "A" processes a Client registration, it must
also forward a proxyed registration to any Proxy/Servers "B", "C",
"D", etc. for the Client's other underlying interfaces, which it
perceives as LHS Proxy/Servers (i.e., and not FHS) from its own
reference point. Proxy/Servers satisfies these requirements as
follows:when FHS Proxy/Server "A" receives a Client RS message, it
first verifies that the OAL Identification is within the window
for the NCE that matches the MNP-ULA for this Client neighbor and
authenticates the message. (If no NCE was found, Proxy/Server "A
instead creates one in the STALE state and returns an RA message
with an authentication signature if necessary and any window
synchronization parameters.) Proxy/Server "A" then examines the
network-layer destination address. If the destination address is
the ADM-LLA of a different Proxy/Server "B" (or, if the OMNI
option included MS-Register/Release sub-options with the ADM-LLAs
of one or more different LHS Proxy/Servers "B", "C", "D", etc.),
Proxy/Server "A" prepares a separate proxyed version of the RS
message with an OAL header with source set to its own ADM-ULA and
destination set to the LHS Proxy/Server's ADM-ULA. Proxy/Server
"A" also writes its own FMT/SRT/LHS/L2ADDR information over the
first Interface Attributes supplied by the Client (i.e., by
inserting the FMT/SRT/LHS/L2ADDR fields if not already present, or
increasing/decreasing the L2ADDR field size if the IP version of
the Client underlying interface differs from its own INET
interface). Proxy/Server "A" then sets the S/T-omIndex to the
value for this Client underlying interface, then forwards the
message into the OMNI link secured spanning tree.when LHS Proxy/Server "B" receives the RS, it authenticates the
message then creates or updates a NCE for the Client with FHS
Proxy/Server "A"'s Interface Attributes as the link-layer address
information for this S/T-omIndex and caches any window
synchronization parameters supplied by the Client. LHS
Proxy/Server "B" then prepares an RA message with source set to
its own LLA and destination set to the Client's MNP-LLA, and with
any window synchronization acknowledgements. Proxy/Server "B" then
encapsulates the RA in an OAL header with source set to its own
ADM-ULA and destination set to the ADM-ULA of Proxy/Server "A,
performs fragmentation if necessary, then sends the resulting
carrier packets into the secured spanning tree.when Proxy/Server "A" reassembles the RA, it locates the Client
NCE based on the RA destination LLA. Proxy/Server "A" then
re-encapsulates the RA message with OAL source set to its own
ADM-ULA and OAL destination set to the MNP-ULA of the Client,
includes an authentication signature if necessary, and includes an
Interface Attributes sub-option with omIndex 0 and with
FMT/SRT/LHS/L2ADDR information for its INET interface.
Proxy/Server "A" then fragments if necessary and returns the
fragments to the Client.The Client repeats this process over each of its additional
underlying interfaces while treating each "B", "C", "D" as a FHS
Proxy/Server while providing MS-Register//Release information for
the others as LHS Proxy/Servers.After the initial RS/RA exchanges each Proxy/Server forwards
any of the Client's carrier packets with OAL destinations for which
there is no matching NCE to a Bridge using OAL encapsulation with its
own ADM-ULA as the source and the destination determined by the ORH
supplied by the Client. The Proxy/Server instead forwards any carrier
packets destined to a neighbor cache target directly to the target
according to the OAL/link-layer information - the process of
establishing neighbor cache entries is specified in .While the Client is still associated with each Proxy/Server "A",
"A" can send NS, RS and/or unsolicited NA messages to update the
neighbor cache entries of other AERO nodes on behalf of the Client
and/or to convey Interface Attributes updates. This allows for
higher-frequency Proxy-initiated RS/RA messaging over well-connected
INET infrastructure supplemented by lower-frequency Client-initiated
RS/RA messaging over constrained ANET data links.If any Proxy/Server "B", "C", "D" ceases to send solicited RAs,
Proxy/Server "A" sends unsolicited RAs over the Client's underlying
interface with destination set to (link-local) All-Nodes multicast and
with Router Lifetime set to zero to inform Clients that another
Proxy/Server has failed. Although Proxy/Server "A" can engage in ND
exchanges on behalf of the Client, the Client can also send ND
messages on its own behalf, e.g., if it is in a better position than
"A" to convey Interface Attribute changes, etc. The ND messages sent
by the Client include the Client's MNP-LLA as the source in order to
differentiate them from the ND messages sent by Proxy/Server "A".If the Client becomes unreachable over all underlying interface it
serves, Proxy/Server "A" sets the NCE state to DEPARTED and retains
the entry for DepartTime seconds. While the state is DEPARTED,
Proxy/Server "A" forwards any carrier packets destined to the Client
to a Bridge via OAL/ORH encapsulation. When DepartTime expires,
Proxy/Server "A" deletes the NCE and discards any further carrier
packets destined to the former Client.In some ANETs that employ a Proxy/Server, the Client's MNP can be
injected into the ANET routing system. In that case, the Client can
send original IP packets without invoking the OAL so that the ANET
routing system transports the original IP packets to the Proxy. This
can be very beneficial, e.g., if the Client connects to the ANET via
low-end data links such as some aviation wireless links.If the ANET first-hop access router is on the same underlying link
as the Client and recognizes the AERO/OMNI protocol, the Client can
avoid OAL encapsulation for both its control and data messages. When
the Client connects to the link, it can send an unencapsulated RS
message with source address set to its own MNP-LLA (or to a Temporary
LLA), and with destination address set to the ADM-LLA of the Client's
selected Proxy/Server or to (link-local) All-Routers multicast. The
Client includes an OMNI option formatted as specified in . The Client then sends the
unencapsulated RS message, which will be intercepted by the AERO-Aware
access router.The ANET access router then performs OAL encapsulation on the RS
message and forwards it to a Proxy/Server at the ANET/INET boundary.
When the access router and Proxy/Server are one and the same node, the
Proxy/Server would share and underlying link with the Client but its
message exchanges with outside correspondents would need to pass
through a security gateway at the ANET/INET border. The method for
deploying access routers and Proxys (i.e. as a single node or multiple
nodes) is an ANET-local administrative consideration.Note: When a Proxy/Server alters the IPv6 ND message contents
before forwarding (e.g., such as altering the OMNI option contents),
the IPv6 ND message checksum and/or authentication signature are
invalidated. If the Proxy/Server forwards the message over the secured
spanning tree, however, it need not re-calculate the
checksum/signature since they will not be examined by the next
hop.Note: When a Proxy/Server receives a secured Client NS message, it
performs the same proxying procedures as for described for RS messages
above. The proxying procedures for NS/NA message exchanges is
specified in .In environments where fast recovery from Proxy/Server failure is
required, Proxy/Server "A" SHOULD use proactive Neighbor
Unreachability Detection (NUD) to track each peer Proxy/Server "B"
reachability in a similar fashion as for Bidirectional Forwarding
Detection (BFD) . Proxy/Server "A" can then
quickly detect and react to failures so that cached information is
re-established through alternate paths. The NS/NA(NUD) control
messaging is carried only over well-connected ground domain networks
(i.e., and not low-end aeronautical radio links) and can therefore
be tuned for rapid response.Proxy/Server "A" performs continuous NS/NA(NUD) exchanges with
peer Proxy/Server "B" for which there are currently active Clients
in rapid succession, e.g., one exchange per second. Proxy/Server "A"
sends the NS(NUD) message via the spanning tree with its own ADM-LLA
as the source and the ADM-LLA of the peer Proxy/Server "B" as the
destination, and Proxy/Server "B" responds with an NA(NUD). When
Proxy/Server "A" is also sending RS messages to the peer
Proxy/Server "B" on behalf of Clients, the resulting RA responses
can be considered as equivalent hints of forward progress. This
means that Proxy/Server "B" need not also send a periodic NS(NUD) if
it has already sent an RS within the same period. If the peer
Proxy/Server "B" fails (i.e., if "A" ceases to receive
advertisements), Proxy/Server "A" can quickly inform Clients by
sending unsolicited RA messagesProxy/Server "A" sends unsolicited RA messages with source
address set to Proxy/Server "B"'s address, destination address set
to (link-local) All-Nodes multicast, and Router Lifetime set to 0.
Proxy/Server "A" SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA
messages separated by small delays . Any
Clients that had been using the failed Proxy/Server "B" will receive
the RA messages and associate with a new Proxy/Server.In environments where Client messaging over ANETs is
bandwidth-limited and/or expensive, Clients can enlist the services
of FHS Proxy/Server "A" to coordinate with multiple LHS
Proxy/Servers "B", "C", "D" etc. in a single RS/RA message exchange.
The Client can send a single RS message to (link-local) All-Routers
multicast that includes the ID's of multiple Proxy/Servers in
MS-Register/MS-Release OMNI sub-options.When FHS Proxy/Server "A" receives the RS and processes the OMNI
option, it sends a separate RS to each MS-Register/MS-Release LHS
Proxy/Server "B", "C", "D", etc. When FHS Proxy/Server "A" receives
an LHS Proxy/Server RA, it can optionally return an immediate
"singleton" RA to the Client or record the LHS Proxy/Server's MSID
for inclusion in a pending "aggregate" RA message. FHS Proxy/Server
"A" can then return aggregate RA messages to the Client including
multiple LHS Proxy/Server MSIDs in order to conserve bandwidth. Each
RA includes a proper subset of the LHS Proxy/Server MSIDs from the
original RS message, and FHS Proxy/Server "A" must ensure that the
message contents of each RA are consistent with the information
received from the (aggregated) LHS Proxy/Servers.Clients can thereafter employ efficient point-to-multipoint LHS
Proxy/Server coordination under the assistance of FHS Proxy/Server
"A" to reduce the number of messages sent over the *NET. Clients can
further include MS-Release sub-options in IPv6 ND messages to
request FHS Proxy/Server "A" to release from former LHS
Proxy/Servers via the procedures discussed in .The OMNI interface specification provides further discussion of the
RS/RA messaging involved in point-to-multipoint coordination.AERO nodes invoke route optimization when they need to forward
packets to new target destinations. Route optimization is based on
IPv6 ND Address Resolution messaging between a Route Optimization
Source (ROS) and Route Optimization Responder (ROR). Route
optimization is initiated by the first eligible ROS closest to the
source as follows:For Clients on VPNed and Direct interfaces, the Client's FHS
Proxy/Server is the ROS.For Clients on ANET interfaces, either the Client or the FHS
Proxy/Server may be the ROS.For Clients on INET interfaces, the Client itself is the
ROS.For correspondent nodes on INET/EUN interfaces serviced by a
Relay, the Relay is the ROS.The route optimization procedure is conducted between the ROS and
an LHS Proxy/Server/Relay for the target selected by routing as the
ROR. In this arrangement, the ROS is always the Client or
Proxy/Server/Relay nearest the source over the selected source
underlying interface, while the ROR is always an LHS
Proxy/Server/Relay for the target regardless of the target underlying
interface.The AERO routing system directs a route optimization request sent
by the ROS to the nearest available ROR, which returns a route
optimization reply. The exact ROR selected is unimportant as long as
the information returned is current, consistent and authentic. The ROS
is responsible for periodically refreshing the route optimization, and
the ROR is responsible for quickly informing the ROS of any
changes.The procedures are specified in the following sections.When an original IP packet from a source node destined to a
target node arrives, the ROS checks for a NCE with an MNP-LLA that
matches the target destination. If there is a NCE in the REACHABLE
state, the ROS invokes the OAL and forwards the resulting carrier
packets according to the cached state then returns from processing.
Otherwise, if there is no NCE the ROS creates one in the INCOMPLETE
state.The ROS next places the original IP packet on a short queue then
sends an NS message for Address Resolution (NS(AR)) to receive a
solicited NA(AR) message from an ROR. The NS(AR) message must be
sent securely, and includes:the LLA of the ROS as the source address.the MNP-LLA corresponding to the original IP packet's
destination as the Target Address, e.g., for
2001:db8:1:2::10:2000 the Target Address is
fe80::2001:db8:1:2.the Solicited-Node multicast address
formed from the lower 24 bits of the original IP packet's
destination as the destination address, e.g., for
2001:db8:1:2::10:2000 the NS(AR) destination address is
ff02:0:0:0:0:1:ff10:2000.The NS(AR) message also includes an OMNI option with an
authentication sub-option if necessary, an Interface Attributes
sub-option for the underlying interface, with S/T-omIndex set to the
underlying interface index and with Preflen set to the prefix length
associated with the NS(AR) source. The ROS then selects an
Identification value submits the NS(AR) message for OAL
encapsulation with OAL source set to its own ULA and OAL destination
set to the ULA corresponding to the target. (The ROS does not
include any window synchronization parameters, since it will not
exchange other packet types with the ROR.) The ROS then sends the
resulting carrier packet(s) into the SRT secured spanning tree
without decrementing the network-layer TTL/Hop Limit field.When the ROS is an INET Client, it must instead forward the
resulting carrier packets to the ADM-ULA of one of its current
Proxy/Servers. The Proxy/Server reassembles if necessary, then
verifies the NS(AR) authentication signature and writes its
FMT/SRT/LHS/L2ADDR information into the Interface Attributes
sub-option the same as described for RS messages in . The Proxy/Server then re-encapsulates the
NS(AR) with the OAL source set to its own ADM-ULA and OAL
destination set to the ULA corresponding to the target, fragments if
necessary and forwards the resulting carrier packets into the
secured spanning tree on behalf of the Client.When the Bridge receives the carrier packet(s) containing the RS
from the ROS, it discards the *NET headers and determines the next
hop by consulting its standard IPv6 forwarding table for the OAL
header destination address. The Bridge then decrements the OAL
header Hop-Limit, then re-encapsulates and forwards the carrier
packet(s) via the secured spanning tree the same as for any IPv6
router, where it may traverse multiple OMNI link segments. The
final-hop Bridge will deliver the carrier packet(s) via the secured
spanning tree to a Proxy/Server or Relay that services the
target.When an LHS Proxy/Server (or Relay) for the target receives the
secured carrier packet(s), it reassembles if necessary then examines
the NS(AR) target to determine whether it has a matching NCE and/or
non-MNP route. If there is no match, the Proxy/Server drops the
message. Otherwise, the LHS Proxy/Server/Relay continues processing
as follows:if the NS(AR) target matches a Client NCE in the DEPARTED
state, the Proxy/Server re-encapsulates while setting the OAL
source to the ULA of the ROS and OAL destination address to the
ADM-ULA of the Client's new Proxy/Server. The (old) Proxy/Server
then fragments if necessary and forwards the resulting carrier
packet(s) over the secured spanning tree then returns from
processing.If the NS(AR) target matches the MNP-LLA of a Client NCE in
the REACHABLE state, the Proxy/Server notes whether the NS (AR)
arrived from the secured or unsecured spanning tree then acts as
an ROR to provide route optimization information on behalf of
the Client. If the message arrived via the secured spanning tree
the ROR need not perform further authentication; otherwise, it
must verify the message authentication signature before
accepting.If the NS(AR) target matches one of its non-MNP routes, the
Relay acts as both an ROR and a route optimization target, since
the Relay forwards IP packets toward the (fixed network) target
at the network layer.The ROR next checks the target NCE for a Report List entry that
matches the NS(AR) source LLA/ULA of the ROS. If there is a Report
List entry, the ROR refreshes ReportTime for this ROR; otherwise,
the ROR creates a new entry for the ROS and records both the LLA and
ULA.The ROR then prepares a (solicited) NA(AR) message to return to
the ROS with the source address set to its own ADM-LLA, the
destination address set to the NS(AR) LLA source address and the
Target Address set to the target Client's MNP-LLA. The ROR includes
an OMNI option with Preflen set to the prefix length associated with
the NA(AR) source address as well as Interface Attributes
sub-options for all of the target's underlying interfaces with
current information for each interface.For each Interface Attributes sub-option, the ROR sets the L2ADDR
according to its own INET address for VPNed, Direct, ANET and NATed
Client interfaces, or to the Client's INET address for native Client
interfaces. The ROR then includes the lower 32 bits of the
Proxy/Server's ADM-ULA as the LHS, encodes the ADM-ULA SRT prefix
length in the SRT field and sets FMT as specified in .The ROR then sets the NA(AR) message R flag to 1 (as a router)
and S flag to 1 (as a response to a solicitation) and sets the O
flag to 0 (as a proxy) and sets the OMNI header S/T-omIndex to 0.
The ROR finally submits the NA(AR) for OAL encapsulation with source
set to its own ULA and destination set to the same ULA that appeared
in the NS(AR) OAL source, then performs OAL encapsulation and
fragmentation using the same Identification value that appeared in
the NS(AR) and finally forwards the resulting (*NET-encapsulated)
carrier packets via the secured spanning tree without decrementing
the network-layer TTL/Hop Limit field.When the Bridge receives NA(AR) carrier packets from the ROR, it
discards the *NET header and determines the next hop by consulting
its standard IPv6 forwarding table for the OAL header destination
address. The Bridge then decrements the OAL header Hop-Limit,
re-encapsulates the carrier packet and forwards it via the SRT
secured spanning tree the same as for any IPv6 router, where it may
traverse multiple OMNI link segments. The final-hop Bridge will
deliver the carrier packet via the secured spanning tree to a
Proxy/Server for the ROS.When the ROS receives the NA(AR) message from the ROR, it first
searches for a NCE that matches the NA(AR) target address. The ROS
then processes the message the same as for standard IPv6 Address
Resolution . In the process, it caches all
OMNI option information in the target NCE (including all Interface
Attributes), and caches the NA(AR) ADM-{LLA,ULA} source addresses as
the addresses of the ROR. If the ROS receives additional NA(AR) or
uNA messages for this target Client with the same ADM-LLA source
address but a different ADM-ULA source address, it caches the new
MSID as the new ADM-{LLA,ULA} and deprecates the former
ADM-{LLA,ULA}.When the ROS is a Client, the solicited NA(AR) message will first
be delivered via the SRT secured spanning tree to the Proxy/Server
that forwarded the NS(AR), which reassembles if necessary. The
Proxy/Server then forwards the message to the Client while
re-encapsulating and re-fragmenting if necessary. If the Client is
on a well-managed ANET, physical security and protected spectrum
ensures security for the unmodified NA(AR); if the Client is on the
open INET the Proxy/Server must instead include an authentication
signature (while adjusting the OMNI option size, if necessary). The
Proxy/Server uses its own ADM-ULA as the OAL source and the MNP-ULA
of the Client as the OAL destination.After the ROS receives the route optimization NA(AR) and updates
the target NCE, it sends additional NS(AR) messages to the ADM-ULA
of the ROR to refresh the NCE ReachableTime before expiration while
it still has sustained interest in this target. While the NCE
remains REACHABLE, the ROS can forward packets along the best
underlying interface paths based on the target's Interface
Attributes. The ROS selects target underlying interfaces according
to traffic selectors and/or any other traffic discriminators,
however each underlying interface selected must first establish
window synchronization state if necessary.To establish window synchronization state, the ROS performs a
secured unicast NS/NA(WIN) exchange with window synchronization
parameters according to the Interface Attributes FMT code. If
FMT-Forward is set, the ROS prepares an NS(WIN) with its own LLA as
the source and the MNP-LLA of the target Client as the destination;
otherwise, it sets the ADM-LLA of the LHS Proxy/Server as the
destination. The ROS then encapsulates the NS(WIN) in an OAL header
with its own ULA as the source and includes an ORH with Segments
Left set to 1 and with FMT/SRT/LHSL2ADDR addressing information for
the LHS Proxy/Server. If the ROS is the Client, it sets the OAL
destination to the ADM-ULA of its FHS Proxy/Server, includes an
authentication signature if necessary, includes an Interface
Attributes sub-option for its underlying interface and, then
forwards the NS(WIN) to its FHS Proxy/Server which must reassemble,
verify the authentication signature and rewrite the Interface
Attributes FMT/SRT/LHS/L2ADDR information if necessary. The FHS
Proxy/Server then re-encapsulates, re-fragments and forwards the
NS(WIN) carrier packets into the secured spanning tree with its own
ADM-ULA as the OAL source and the Subnet Router Anycast address for
the LHS as the OAL destination.When an LHS Bridge that configures the Subnet Router Anycast
address receives the NS(WIN) carrier packets over the secured
spanning tree, it reassembles if necessary then creates a NCE for
the NS(WIN) target and assigns an NIndex value as discussed in . The Bridge then re-encapsulates, re-fragments
and forwards the NS(WIN) carrier packets into the secured spanning
tree with the ADM-ULA of the LHS Proxy/Server as the OAL
destination.When the LHS Proxy/Server receives the NS(WIN) carrier packets it
first reassembles if necessary. If the NS(WIN) destination is its
own ADM-LLA, the LHS Proxy/Server creates an NCE based on the
NS(WIN) source LLA, caches the window synchronization information,
and prepares an NA(WIN) while using its own ADM-LLA as the source
and the ROS LLA as the destination. The LHS Proxy/Server then
encapsulates the NA(WIN) in an OAL header with source set to its own
ADM-ULA and destination set to the Subnet Router Anycast address for
the NS(WIN) OAL source. The LHS Proxy/Server then fragments if
necessary, includes an ORH with FMT/SRT/LHS/L2ADDR found in the
NS(WIN) OMNI option, then forwards the resulting carrier packets
into the secured spanning tree which will deliver them to a FHS
Bridge on the ROS Proxy/Server segment.If the NS(WIN) destination is the MNP-LLA of the target Client,
the LHS Proxy/Server instead removes the ORH, re-encapsulates using
the same OAL source and the MNP-ULA of the target as the OAL
destination and includes an authentication signature (while
adjusting the OMNI option size) if necessary. The LHS Proxy/Server
then forwards the NS(WIN) to the target Client over the underlying
interface identified by the ORH omIndex (or, over any underlying
interface if omIndex is 0). When the target Client receives the
NS(WIN), it verifies the authentication signature if necessary then
creates an NCE for the ROS LLA, caches the window synchronization
information and prepares an NA(WIN) to return to the ROS with its
MNP-LLA as the source and the LLA of the ROS as the destination, and
with an Interface Attributes sub-option and an authentication
signature if necessary. The target Client then encapsulates the
NA(WIN) in an OAL header with its own MNP-ULA as the source, the
ADM-ULA of the LHS Proxy/Server as the destination, and with an ORH
with FMT/SRT/LHS/L2ADDR information copied from the NS(WIN)
Interface Attributes. The target Client then sets the ORH omIndex to
the S/T-omIndex value found in the NS(WIN) OMNI option, then
forwards the NA(WIN) message to the LHS Proxy/Server.When the LHS Proxy/Server receives the message, it reassembles if
necessary, verifies the authentication signature and rewrites the
Interface Attributes FMT/SRT/LHS/L2ADDR information if necessary,
then re-encapsulates using its own ADM-ULA as the source and the
Subnet Router Anycast address for the FHS Proxy/Server as the
destination. The LHS Proxy/Server then re-fragments and forwards the
NA(WIN) carrier packets into the secured spanning tree.When an FHS Bridge that configures the Subnet Router Anycast
address receives the NA(WIN) carrier packets, it reassembles if
necessary then creates a NCE for the NA(WIN) target, assigns an
NIndex value and rewrites the Interface Attributes
FMT/SRT/LHS/L2ADDR information as discussed in . The Bridge then re-encapsulates, re-fragments
and forwards the NA(WIN) carrier packets into the secured spanning
tree with the ADM-ULA of the FHS Proxy/Server as the OAL
destination.When the FHS Proxy/Server receives the NA(WIN), it reassembles if
necessary then updates the NCE for the NA(WIN) target based on the
message contents if the Proxy/Server itself is the ROS. If the
NA(WIN) source was the ADM-LLA of the LHS Proxy/Server, the ROS must
also create and maintain a NCE for the LHS Proxy/Server which it
must regard as a companion to the existing target Client NCE. (The
NCE for the LHS Proxy/Server can also be shared by multiple target
Client NCEs if the ROS communicates with multiple active targets
located behind the same LHS Proxy/Server.)If the Client is the ROS, the FHS Proxy/Server instead inserts an
authentication signature (while adjusting the OMNI option size) if
necessary, removes the ORH then re-encapsulates and re-fragments if
necessary while changing the OAL destination to the MNP-ULA of the
ROS Client. The FHS Proxy/Server then forwards the NA(WIN) to the
ROS Client over the underlying interface identified by the ORH
omIndex which then updates its own NCE based on the target Client
MNP-LLA or LHS Proxy/Server ADM-LLA. The ROS (whether the
Proxy/Server or the Client itself) finally arranges to return an
acknowledgement if requested by the NA(WIN) by sending an NA(WIN)
acknowledgement in the reverse path over the secured spanning tree,
where it will first visit the LHS Bridge which updates the taregt
Client NCE and securely forwards the NA(WIN) toward the target
itself.After window synchronization state has been established, the ROS
and taget Client can begin forwarding carrier packets as specified
in while performing additional NS/NA(WIN)
exchanges as above to update window state and/or test reachability.
The ROS sends carrier packets to the FHS Bridge discovered through
the NS/NA(WIN) exhange which verifies the Identification is in
window. The FHS Bridge then forwards the carrier packets over the
unsecured spanning tree to the LHS Bridge, whch forwards them via
LHS encapsulation to the LHS Proxy/Server or directly to the target
Client itself. The target Client in turn sends packes to the ROS in
the reverse direction while forwarding through the Bridges to
minimize Proxy/Server load whenever possible.The above forwarding procedures apply to the case where the
selected target interface SRT/LHS codes indicate that the interface
is located in a foreign OMNI link segment. If the SRT/LHS codes
indicate that the interface is in the local OMNI link segment, the
ROS can instead forward carrier packets directly to the LHS
Proxy/Server using the L2ADDR for encapsulation following the
initial secured NS/NA(WIN) exchange (or even directly to the target
Client itself while invoking NAT traversal if necessary). When the
ROS sends packets directly to the LHS Proxy/Server, it includes an
ORH if necessary to inform the Proxy/Server as to whether it must
reassemble and/or the correct target Client (NIndex/omIndex) for
(re)forwarding. If the LHS Proxy/Server is required to reassemble,
the ROS sets the OAL destination to the ADM-ULA of the LHS
Proxy/Server; otherwise, it sets the OAL destination to the MNP-ULA
of the target Client itself. When the ROS sends packets directly to
the target Client, it need not include an ORH. The LHS Proxy/Server
(or target Client) then saves the L2ADDR and full OAL addresses in
the ROS NCE.While the ROS continues to actively forward packets to the target
Client, it is responsible for updating window synchronization state
and per-interface reachability before expiration. Window
synchronization state is shared by all underlying interfaces in the
ROS' NCE that use the same destination LLA so that a single
NS/NA(NUD) exchange applies for all interfaces regardless of the
(single) interface used to conduct the exchange. However, the window
synchronization exchange only confirms target Client reachability
over the specific interface used to conduct the exchange.
Reachability for other underlying interfaces that share the same
window synchronization state must be determined individually using
NS/NA(NUD) messages which need not be secured as long as they use
in-window Identifications and do not update other state
information.AERO nodes perform Neighbor Unreachability Detection (NUD) per
either reactively in response to persistent
link-layer errors (see ) or proactively to
confirm reachability. The NUD algorithm is based on periodic control
message exchanges and may further be seeded by ND hints of forward
progress, but care must be taken to avoid inferring reachability based
on spoofed information. For example, IPv6 ND message exchanges that
include authentication codes and/or in-window Identifications may be
considered as acceptable hints of forward progress, while spurious
random carrier packets should be ignored.AERO nodes can perform NS/NA(NUD) exchanges over the OMNI link
secured spanning tree (i.e. the same as described above for
NS/NA(WIN)) to test reachability without risk of DoS attacks from
nodes pretending to be a neighbor. These NS/NA(NUD) messages use the
unicast LLAs and ULAs of the parties involved in the NUD test the same
as for standard IPv6 ND over the secured spanning tree. When only
reachability information is required without updating any other NCE
state, AERO nodes can instead perform NS/NA(NUD) exchanges directly
between neighbors without employing the secured spanning tree as long
as they include in-window Identifications and either an authentication
signature or checksum.When an ROR directs an ROS to a target neighbor with one or more
link-layer addresses, the ROS probes each unsecured target underlying
interface either proactively or on-demand of carrier packets directed
to the path by multilink forwarding to maintain the interface's state
as reachable. Probing is performed through NS(NUD) messages over the
SRT secured or unsecured spanning tree, or through NS(NUD) messages
sent directly to an underlying interface of the target itself. While
testing a target underlying interface, the ROS can optionally continue
to forward carrier packets via alternate interfaces and/or maintain a
small queue of carrier packets until target reachability is
confirmed.NS(NUD) messages are encapsulated, fragmented and transmitted as
carrier packets the same as for ordinary original IP data packets,
however the encapsulated destinations are the LLA of the ROS and
either the ADM-LLA of the LHS Proxy/Server or the MNP-LLA of the
target itself. The ROS encapsulates the NS(NUD) message the same as
described in , however Destination Suffixes
(if present) are set according to the LLA destination (i.e., and not
the ULA/GUA destination). The ROS sets the NS(NUD) OMNI header
S/T-omIndex to identify the underlying interface used for forwarding
(or to 0 if any underlying interface can be used). The ROS also
includes an ORH with FMT/SRT/LHS/L2ADDR information the same as for
ordinary data packets, but does not include an authentication
signature. The ROS then fragments the OAL packet and forwards the
resulting carrier packets into the unsecured spanning tree or directly
to the target (or LHS Proxy/Server) if it is in the local segment.When the target (or LHS Proxy/Server) receives the NS(NUD) carrier
packets, it verifies that it has a NCE for this ROS and that the
Identification is in-window, then submits the carrier packets for
reassembly. The node then verifies the authentication signature or
checksum, then searches for Interface Attributes in its NCE for the
ROS that match the NS(NUD) S/T-omIndex and uses the FMT/SRT/LHS/L2ADDR
information to prepare an ORH for the NA(NUD) reply. The node then
prepares the NA(NUD) with the source and destination LLAs reversed,
encapsulates and sets the OAL source and destination, sets the NA(NUD)
S/T-omIndex to the index of the underlying interface the NS(NUD)
arrived on and sets the Target Address to the same value included in
the NS(NUD). The target next sets the R flag to 1, the S flag to 1 and
the O flag to 1, then selects an in-window Identification for the ROS
and performs fragmentation. The node then forwards the carrier packets
into the unsecured spanning tree, directly to the ROS if it is in the
local segment or directly to a Bridge in the local segment.When the ROS receives the NA(NUD), it marks the target underlying
interface tested as "reachable". Note that underlying interface states
are maintained independently of the overall NCE REACHABLE state, and
that a single NCE may have multiple target underlying interfaces in
various states "reachable" and otherwise while the NCE state as a
whole remains REACHABLE.Note also that the exchange of NS/NA(NUD) messages has the useful
side-benefit of opening holes in NATs that may be useful for NAT
traversal.AERO is a Distributed Mobility Management (DMM) service. Each
Proxy/Server is responsible for only a subset of the Clients on the
OMNI link, as opposed to a Centralized Mobility Management (CMM)
service where there is a single network mobility collective entity for
all Clients. Clients coordinate with their associated Proxy/Servers
via RS/RA exchanges to maintain the DMM profile, and the AERO routing
system tracks all current Client/Proxy/Server peering
relationships.Proxy/Servers provide default routing and mobility/multilink
services for their dependent Clients. Clients are responsible for
maintaining neighbor relationships with their Proxy/Servers through
periodic RS/RA exchanges, which also serves to confirm neighbor
reachability. When a Client's underlying Interface Attributes change,
the Client is responsible for updating the Proxy/Server with this new
information. Note that when there is a Proxy/Server in the path, the
Proxy function can also perform some RS/RA exchanges on the Client's
behalf.Mobility management messaging is based on the transmission and
reception of unsolicited Neighbor Advertisement (uNA) messages. Each
uNA message sets the IPv6 source address to the LLA of the ROR and the
destination address to the unicast LLA of the ROS.Mobility management considerations are specified in the following
sections.RORs accommodate Client mobility and/or multilink change events
by sending secured uNA messages to each ROS in the target Client's
Report List. When an ROR sends a uNA message, it sets the IPv6
source address to the its own LLA, sets the destination address to
the ROS LLA (i.e., an MNP-LLA if the ROS is a Client and an ADM-LLA
if the ROS is a Proxy/Server) and sets the Target Address to the
Client's MNP-LLA. The ROR also includes an OMNI option with Preflen
set to the prefix length associated with the Client's MNP-LLA, with
Interface Attributes for the target Client's underlying interfaces
and with the OMNI header S/T-omIndex set to 0. The ROR then sets the
uNA R flag to 1, S flag to 0 and O flag to 1, then encapsulates the
message in an OAL header with source set to its own ADM-ULA and
destination set to the ROS ULA (i.e., the ADM-ULA of the ROS
Proxy/Server) and sends the message into the secured spanning
tree.As discussed in Section 7.2.6 of , the
transmission and reception of uNA messages is unreliable but
provides a useful optimization. In well-connected Internetworks with
robust data links uNA messages will be delivered with high
probability, but in any case the Proxy/Server can optionally send up
to MAX_NEIGHBOR_ADVERTISEMENT uNAs to each ROS to increase the
likelihood that at least one will be received. Alternatively, the
Proxy/Server can set the PNG flag in the uNA OMNI option header to
request a solicited NA acknowledgement as specified in .When the ROS Proxy/Server receives a uNA message prepared as
above, it ignores the message if the destination is not its own
ADM-ULA or the MNP-ULA of the ROS Client. If the destination was its
own ADM-ULA, the ROS Proxy/Server uses the included OMNI option
information to update its NCE for the target but does not reset
ReachableTime since the receipt of an unsolicited NA message from
the ROR does not provide confirmation that any forward paths to the
target Client are working. If the destination was the MNP-ULA of the
ROS Client, the Proxy/Server instead re-encapsulates with the OAL
source set to its own ADM-ULA, OAL destination set to the MNP-ULA of
the ROS Client with an authentication signature if necessary, and
with an in-window Identification for this Client. Finally, if the
uNA message PNG flag was set, the ROS returns a solicited NA
acknowledgement as specified in .In addition to sending uNA messages to the current set of ROSs
for the target Client, the ROR also sends uNAs to the former
Proxy/Server associated with the underlying interface for which the
link-layer address has changed. These uNA messages update former
Proxy/Servers that cannot easily detect (e.g., without active
probing) when a formerly-active Client has departed. When the ROR
sends the uNA, it sets the IPv6 source address to its LLA, sets the
destination address to the former Proxy/Server's ADM-LLA, and sets
the Target Address to the Client's MNP-LLA. The ROR also includes an
OMNI option with Preflen set to the prefix length associated with
the Client's MNP-LLA, with Interface Attributes for the changed
underlying interface, and with the OMNI header S/T-omIndex set to 0.
The ROR then sets the uNA R flag to 1, S flag to 0 and O flag to 1,
then encapsulates the message in an OAL header with source set to
its own ULA and destination set to the ADM-ULA of the former
Proxy/Server and sends the message into the secured spanning
tree.When a Client needs to change its underlying Interface Attributes
(e.g., due to a mobility event), the Client requests one of its
Proxy/Servers to send RS messages to all of its other Proxy/Servers
via the secured spanning tree with an OMNI option that includes
Interface Attributes with the new link quality and address
information.Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel
with sending carrier packets containing user data in case one or
more RAs are lost. If all RAs are lost, the Client SHOULD
re-associate with a new Proxy/Server.When the Proxy/Server receives the Client's changes, it sends uNA
messages to all nodes in the Report List the same as described in
the previous section.When a Client needs to bring new underlying interfaces into
service (e.g., when it activates a new data link), it sends an RS
message to the Proxy/Server via the underlying interface with an
OMNI option that includes Interface Attributes with appropriate link
quality values and with link-layer address information for the new
link.When a Client needs to deactivate an existing underlying
interface, it sends an RS message to an FHS Proxy/Server with an
OMNI option with appropriate Interface Attribute values for the
deactivated link - in particular, the link quality value 0 assures
that neighbors will cease to use the link.If the Client needs to send RS messages over an underlying
interface other than the one being deactivated, it MUST include
Interface Attributes with appropriate link quality values for any
underlying interfaces being deactivated.Note that when a Client deactivates an underlying interface,
neighbors that have received the RS/uNA messages need not purge all
references for the underlying interface from their neighbor cache
entries. The Client may reactivate or reuse the underlying interface
and/or its omIndex at a later point in time, when it will send new
RS messages to an FHS Proxy/Server with fresh Interface Attributes
to update any neighbors.The Client performs the procedures specified in when it first associates with a new FHS
Proxy/Server or renews its association with an existing
Proxy/Server. The Client also includes MS-Release identifiers in the
RS message OMNI option per if
it wants the new Proxy/Server to notify any old Proxy/Servers from
which the Client is departing.When the new FHS Proxy/Server receives the Client's RS message,
it returns an RA as specified in and
sends RS messages to any old Proxy/Servers listed in OMNI option
MS-Release identifiers. When the new Proxy/Server sends an RS
message, it sets the source to the MNP-LLA of the Client and sets
the destination to the ADM-LLA of the old Proxy/Server. The new
Proxy/Server also includes an OMNI option with Preflen set to the
prefix length associated with the Client's MNP-LLA, with Interface
Attributes for its INET underlying interface, and with the OMNI
header S/T-omIndex set to 0. The new Proxy/Server then encapsulates
the message in an OAL header with source set to its own ADM-ULA and
destination set to the ADM-ULA of the old Proxy/Server and sends the
message into the secured spanning tree.When an old Proxy/Server receives the RS, it notices that the
message appears to have originated from the Client's MNP-LLA but
that it includes an Interface Attributes sub-option for the new
Proxy/Server and with S/T-omIndex set to 0. The old Proxy/Server
then changes the Client's NCE state to DEPARTED, sets the
FMT/SRT/LHS/L2ADDR information for the Client to point to the new
Proxy/Server, and resets DepartTime. The old Proxy/Server then
returns an RA message with zero Router Lifetime via the secured
spanning tree by reversing the LLA and ULA addresses found in the RS
message. After a short delay (e.g., 2 seconds) the old Proxy/Server
withdraws the Client's MNP from the routing system. After DepartTime
expires, the old Proxy/Server deletes the Client's NCE.The old Proxy/Server also iteratively sends uNA messages to each
ROS in the Client's Report List with OAL source address set to the
ADM-ULA of the new Proxy/Server and OAL destination address set to
the ULA of the ROS. When the ROS receives the uNA, it examines the
uNA Target Address to locate the target Client's NCE and the LLA
source address to identify the old Proxy/Server. The ROS then caches
the ULA source address as the ADM-{LLA/ULA} for the new Proxy/Server
for this target NCE and marks the entry as STALE. While in the STALE
state, the ROS sends new NS(AR) messages using its own ULA as the
OAL source and the ADM-ULA of the new Proxy/Server as the OAL
destination address. The new Proxy/Server will then process the
NS(AR) and return an NA(AR) response.Clients SHOULD NOT move rapidly between Proxy/Servers in order to
avoid causing excessive oscillations in the AERO routing system.
Examples of when a Client might wish to change to a different
Proxy/Server include a Proxy/Server that has gone unreachable,
topological movements of significant distance, movement to a new
geographic region, movement to a new OMNI link segment, etc.The AERO Client provides an IGMP (IPv4) or
MLD (IPv6) proxy service for its EUNs and/or
hosted applications . Proxy/Servers act as a
Protocol Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM")
Designated Router (DR) . AERO Relays also act
as PIM routers (i.e., the same as AERO Proxys/Servers) on behalf of
nodes on INET/EUN networks.Clients on ANET underlying interfaces for which the ANET has
deployed native multicast services forward IGMP/MLD messages into the
ANET. The IGMP/MLD messages may be further forwarded by a first-hop
ANET access router acting as an IGMP/MLD-snooping switch , then ultimately delivered to an ANET FHS
Proxy/Server.Clients on ANET underlying interfaces without native multicast
services instead send NS(AR) messages to cause their FHS Proxy/Server
to act as an ROS and forward the message to an LHS Proxy/Server ROR.
Clients on INET interfaces act as an ROS on their own behalf and
forward NS(AR) messages directly to the LHS Proxy/Server ROR (i.e.,
via the FHS Proxy/Server as a proxy). When the Client receives an
NA(AR) response, it initiates PIM protocol messaging according to the
Source-Specific Multicast (SSM) and Any-Source Multicast (ASM)
operational modes as discussed in the following sections.When an ROS "X" (i.e., either a ROS Client or its FHS Proxy
Server) acting as PIM router receives a Join/Prune message from a
node on its downstream interfaces containing one or more ((S)ource,
(G)roup) pairs, it updates its Multicast Routing Information Base
(MRIB) accordingly. For each S belonging to a prefix reachable via
X's non-OMNI interfaces, X then forwards the (S, G) Join/Prune to
any PIM routers on those interfaces per .For each S belonging to a prefix reachable via X's OMNI
interface, X sends an NS(AR) message (see: ) using its own LLA as the source address and
the LLA of S as the destination address. X then encapsulates the
NS(AR) in an OAL header with source address set to the ULA of X and
destination address set to the solicited node multicast address for
S, then forwards the message into the secured spanning tree, which
delivers it to ROR "Y" that services S. The resulting NA(AR) will
return the LLA for the prefix that matches S as the network-layer
source address and with an OMNI option with interface attributes for
any underlying interfaces that are currently servicing S.When X processes the NA(AR) it selects one or more underlying
interfaces for S and performs an NS/NA(WIN) exchange while including
a PIM Join/Prune message for each multicast group of interest in the
OMNI option. If S is located behind any Proxys "Z"*, each Z* then
updates its MRIB accordingly and maintains the LLA of X as the next
hop in the reverse path. Since the Bridges do not examine network
layer control messages, 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.At some later time, Client C that holds an MNP for source S may
depart from a first Proxy/Server Z1 and/or connect via a new
Proxy/Server Z2. In that case, Y sends a uNA message to X the same
as specified for unicast mobility in . When
X receives the uNA message, it updates its NCE for the LLA for
source S and sends new Join messages to any new Proxys Z2. There is
no requirement to send any Prune messages to old Proxy/Server Z1
since source S will no longer source any multicast data traffic via
Z1. Instead, the multicast state for (S,G) in Proxy/Server Z1 will
soon time out since no new Joins will arrive.After some later time, C may move to a new Proxy/Server Y2 and
depart from old Sever Y1. In that case, Y1 sends Join messages for
any of C's active (S,G) groups to Y2 while including its own LLA as
the source address. This causes Y2 to include Y1 in the multicast
forwarding tree during the interim time that Y1's NCE for C is in
the DEPARTED state. At the same time, Y1 sends a uNA message to X
with an OMNI option with S/T-omIndex set to 0 and a release
indication to cause X to release its NCE for S. X then sends a new
Join message to S via the secured spanning tree and re-initiates
route optimization the same as if it were receiving a fresh Join
message from a node on a downstream link.When an ROS X acting as a PIM router receives a Join/Prune from a
node on its downstream interfaces containing one or more (*,G)
pairs, it updates its Multicast Routing Information Base (MRIB)
accordingly. X then forwards a copy of the message within the OMNI
option of an NS(WIN) message to the Rendezvous Point (RP) R for each
G over the secured spanning tree. X uses its own LLA as the source
address and the LLA for R as the destination address, then
encapsulates the NS(WIN) message in an OAL header with source
address set to the ULA of X and destination address set to the ULA
of R's Proxy/Server then sends the message into the secured spanning
tree.For each source S that sends multicast traffic to group G via R,
the Proxy/Server Z* for the Client that aggregates S encapsulates
the original IP packets in PIM Register messages and forwards them
to R via the secured spanning tree, which may then elect to send a
PIM Join to Z*. This will result in an (S,G) tree rooted at Z* with
R as the next hop so that R will begin to receive two copies of the
original IP packet; one native copy from the (S, G) tree and a
second copy from the pre-existing (*, G) tree that still uses PIM
Register encapsulation. R can then issue a PIM Register-stop message
to suppress the Register-encapsulated stream. At some later time, if
C moves to a new Proxy/Server Z*, it resumes sending original IP
packets via PIM Register encapsulation via the new Z*.At the same time, as multicast listeners discover individual S's
for a given G, they can initiate an (S,G) Join for each S under the
same procedures discussed in . Once the
(S,G) tree is established, the listeners can send (S, G) Prune
messages to R so that multicast original IP packets for group G
sourced by S will only be delivered via the (S, G) tree and not from
the (*, G) tree rooted at R. All mobility considerations discussed
for SSM apply.Bi-Directional PIM (BIDIR-PIM) provides
an alternate approach to ASM that treats the Rendezvous Point (RP)
as a Designated Forwarder (DF). Further considerations for BIDIR-PIM
are out of scope.An AERO Client can connect to multiple OMNI links the same as for
any data link service. In that case, the Client maintains a distinct
OMNI interface for each link, e.g., 'omni0' for the first link,
'omni1' for the second, 'omni2' for the third, etc. Each OMNI link
would include its own distinct set of Bridges and Proxy/Servers,
thereby providing redundancy in case of failures.Each OMNI link could utilize the same or different ANET
connections. The links can be distinguished at the link-layer via the
SRT prefix in a similar fashion as for Virtual Local Area Network
(VLAN) tagging (e.g., IEEE 802.1Q) and/or through assignment of
distinct sets of MSPs on each link. This gives rise to the opportunity
for supporting multiple redundant networked paths (see: ).The Client's IP layer can select the outgoing OMNI interface
appropriate for a given traffic profile while (in the reverse
direction) correspondent nodes must have some way of steering their
original IP packets destined to a target via the correct OMNI
link.In a first alternative, if each OMNI link services different MSPs
the Client can receive a distinct MNP from each of the links. IP
routing will therefore assure that the correct OMNI link is used for
both outbound and inbound traffic. This can be accomplished using
existing technologies and approaches, and without requiring any
special supporting code in correspondent nodes or Bridges.In a second alternative, if each OMNI link services the same MSP(s)
then each link could assign a distinct "OMNI link Anycast" address
that is configured by all Bridges on the link. Correspondent nodes can
then perform Segment Routing to select the correct SRT, which will
then direct the original IP packet over multiple hops to the
target.AERO Client MNs and INET correspondent nodes consult the Domain
Name System (DNS) the same as for any Internetworking node. When
correspondent nodes and Client MNs use different IP protocol versions
(e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain A
records for IPv4 address mappings to MNs which must then be populated
in Relay NAT64 mapping caches. In that way, an IPv4 correspondent node
can send original IPv4 packets to the IPv4 address mapping of the
target MN, and the Relay will translate the IPv4 header and
destination address into an IPv6 header and IPv6 destination address
of the MN.When an AERO Client registers with an AERO Proxy/Server, the
Proxy/Server can return the address(es) of DNS servers in RDNSS
options . The DNS server provides the IP
addresses of other MNs and correspondent nodes in AAAA records for
IPv6 or A records for IPv4.OAL encapsulation ensures that dissimilar INET partitions can be
joined into a single unified OMNI link, even though the partitions
themselves may have differing protocol versions and/or incompatible
addressing plans. However, a commonality can be achieved by
incrementally distributing globally routable (i.e., native) IP
prefixes to eventually reach all nodes (both mobile and fixed) in all
OMNI link segments. This can be accomplished by incrementally
deploying AERO Bridges on each INET partition, with each Bridge
distributing its MNPs and/or discovering non-MNP IP GUA prefixes on
its INET links.This gives rise to the opportunity to eventually distribute native
IP addresses to all nodes, and to present a unified OMNI link view
even if the INET partitions remain in their current protocol and
addressing plans. In that way, the OMNI link can serve the dual
purpose of providing a mobility/multilink service and a
transition/coexistence service. Or, if an INET partition is
transitioned to a native IP protocol version and addressing scheme
that is compatible with the OMNI link MNP-based addressing scheme, the
partition and OMNI link can be joined by Bridges.Relays that connect INETs/EUNs with dissimilar IP protocol versions
may need to employ a network address and protocol translation function
such as NAT64 .In environments where rapid failure recovery is required,
Proxy/Servers and Bridges SHOULD use Bidirectional Forwarding
Detection (BFD) . Nodes that use BFD can
quickly detect and react to failures so that cached information is
re-established through alternate nodes. BFD control messaging is
carried only over well-connected ground domain networks (i.e., and not
low-end radio links) and can therefore be tuned for rapid
response.Proxy/Servers and Bridges maintain BFD sessions in parallel with
their BGP peerings. If a Proxy/Server or Bridge fails, BGP peers will
quickly re-establish routes through alternate paths the same as for
common BGP deployments. Similarly, Proxys maintain BFD sessions with
their associated Bridges even though they do not establish BGP
peerings with them.AERO Clients that connect to the open Internet via INET interfaces
can establish a VPN or direct link to securely connect to a FHS
Proxy/Server in a "tethered" arrangement with all of the Client's
traffic transiting the Proxy/Server which acts as a router.
Alternatively, the Client can associate with an INET FHS Proxy/Server
using UDP/IP encapsulation and control message securing services as
discussed in the following sections.When a Client's OMNI interface enables an INET underlying
interface, it first examines the INET address. For IPv4, the Client
assumes it is on the open Internet if the INET address is not a
special-use IPv4 address per . Similarly for
IPv6, the Client assumes it is on the open Internet if the INET
address is a Global Unicast Address (GUA) .
Otherwise, the Client should assume it is behind one or several
NATs.The Client then prepares an RS message with IPv6 source address set
to its MNP-LLA, with IPv6 destination set to (link-local) All-Routers
multicast and with an OMNI option with underlying interface
attributes. If the Client believes that it is on the open Internet, it
SHOULD include its IP address and UDP port number in the Interface
Attributes sub-option corresponding to the underlying interface
(otherwise it may omit the FMT/SRT/LHS/L2ADDR fields). If the
underlying address is IPv4, the Client includes the Port Number and
IPv4 address written in obfuscated form as
discussed in . If the underlying interface
address is IPv6, the Client instead includes the Port Number and IPv6
address in obfuscated form. The Client finally includes an
authentication signature per to
provide message authentication, selects an Identification value and
window synchronization parameters, and submits the RS for OAL
encapsulation. The Client then encapsulates the OAL fragment in UDP/IP
headers to form a carrier packet, sets the UDP/IP source to its INET
address and UDP port, sets the UDP/IP destination to the FHS
Proxy/Server's INET address and the AERO service port number (8060),
then sends the carrier packet to the Proxy/Server.When the FHS Proxy/Server receives the RS, it discards the OAL
encapsulation, authenticates the RS message, creates a NCE and
registers the Client's MNP, window synchronization state and INET
interface information according to the OMNI option parameters. If the
Interface Attributes sub-option includes an L2ADDR, the Proxy/Server
compares the encapsulation IP address and UDP port number with the
(unobfuscated) values. If the values are the same, the Proxy/Server
caches the Client's information as an "INET" address meaning that the
Client is likely to accept direct messages without requiring NAT
traversal exchanges. If the values are different (or, if the OMNI
option did not include an L2ADDR) the Proxy/Server instead caches the
Client's information as a "mapped" address meaning that NAT traversal
exchanges may be necessary.The FHS Proxy/Server then prepares an RA message with IPv6 source
and destination set corresponding to the addresses in the RS, and with
an OMNI option with an Origin Indication sub-option per with the mapped and obfuscated Port
Number and IP address observed in the encapsulation headers. The
Proxy/Server also includes an Interface Attributes sub-option with
omIndex 0 and FMT/SRT/LHS/L2ADDR information appropriate for its INET
interface, an authentication signature sub-option per and/or a symmetric window
synchronization/acknowledgement if necessary. The Proxy/Server then
performs OAL encapsulation and fragmentation if necessary and
encapsulates each fragment in UDP/IP headers with addresses set per
the L2ADDR information in the NCE for the Client.When the Client receives the RA, it authenticates the message then
process the window synchronization/acknowledgement and compares the
mapped Port Number and IP address from the Origin Indication
sub-option with its own address. If the addresses are the same, the
Client assumes the open Internet / Cone NAT principle; if the
addresses are different, the Client instead assumes that further
qualification procedures are necessary to detect the type of NAT and
proceeds according to standard procedures . The Client also caches the
RA Interface Attributes FMT/SRT/LHS/L2ADDR information to discover the
Proxy/Server's spanning tree orientation. The Client finally arranges
to return an explicit/implicit acknowledgement, and sends periodic RS
messages to receive fresh RA messages before the Router Lifetime
received on each INET interface expires.When the Client sends messages to target IP addresses, it also
invokes route optimization per . For route
optimized targets in the same OMNI link segment, if the target's
L2ADDR is on the open INET, the Client forwards carrier packets
directly to the target INET address. If the target is behind a NAT,
the Client first establishes NAT state for the L2ADDR using the
"direct bubble" and NUD mechanisms discussed in . The Client continues to send carrier packets via its
Proxy/Server until NAT state is populated, then begins forwarding
carrier packets via the direct path through the NAT to the target. For
targets in different OMNI link segments, the Client uses OAL/ORH
encapsulation and forwards carrier packets to the Bridge that returned
the NA(AR) message.The Client can send original IP packets to route-optimized
neighbors in the same OMNI link segment no larger than the
minimum/path MPS in one piece and with OAL encapsulation as atomic
fragments. For larger original IP packets, the Client applies OAL
encapsulation then fragments if necessary according to , with OAL header with source set to its own MNP-ULA
and destination set to the MNP-ULA of the target, and with an
in-window Identification value. The Client then encapsulates each
resulting carrier packet in UDP/IP *NET headers and sends them to the
next hop.Note: The NAT traversal procedures specified in this document are
applicable for Cone, Address-Restricted and Port-Restricted NATs only.
While future updates to this document may specify procedures for other
NAT variations (e.g., hairpinning and various forms of Symmetric
NATs), it should be noted that continuous communications are always
possible through Proxy/Server forwarding even for these other NAT
variations.In some use cases, it is desirable, beneficial and efficient for
the Client to receive a constant MNP that travels with the Client
wherever it moves. For example, this would allow air traffic
controllers to easily track aircraft, etc. In other cases, however
(e.g., intelligent transportation systems), the MN may be willing to
sacrifice a modicum of efficiency in order to have time-varying MNPs
that can be changed every so often to defeat adversarial tracking.The DHCPv6 service offers a way for Clients that desire
time-varying MNPs to obtain short-lived prefixes (e.g., on the order
of a small number of minutes). In that case, the identity of the
Client would not be bound to the MNP but rather to a Node
Identification value (see: ) to
be used as the Client ID seed for MNP prefix delegation. The Client
would then be obligated to renumber its internal networks whenever its
MNP (and therefore also its MNP-LLA) changes. This should not present
a challenge for Clients with automated network renumbering services,
however presents limits for the durations of ongoing sessions that
would prefer to use a constant address.An early AERO implementation based on OpenVPN (https://openvpn.net/)
was announced on the v6ops mailing list on January 10, 2018 and an
initial public release of the AERO proof-of-concept source code was
announced on the intarea mailing list on August 21, 2015.AERO Release-3.2 was tagged on March 30, 2021, and is undergoing
internal testing. Additional internal releases expected within the
coming months, with first public release expected end of 1H2021.Many AERO/OMNI functions are implemented and undergoing final
integration. OAL fragmentation/reassembly buffer management code has
been cleared for public release and will be presented at the June 2021
ICAO mobility subgroup meeting.The IANA is instructed to assign a new type value TBD1 in the IPv6
Routing Types registry (IANA registration procedure is IETF Review or
IESG Approval).The IANA has assigned the UDP port number "8060" for an earlier
experimental first version of AERO . This
document together with reclaims
UDP port number "8060" for 'aero' as the service port for UDP/IP
encapsulation. This document makes no request of IANA, since already provides instructions. (Note:
although was not widely implemented or
deployed, it need not be obsoleted since its messages use the invalid
ICMPv6 message type number '0' which implementations of this
specification can easily distinguish and ignore.)No further IANA actions are required.AERO Bridges configure secured tunnels with AERO Proxy/Servers and
Relays within their local OMNI link segments. Applicable secured tunnel
alternatives include IPsec , TLS/SSL , DTLS , WireGuard , etc. The AERO Bridges of all OMNI link segments in turn
configure secured tunnels for their neighboring AERO Bridges in a
secured spanning tree topology. Therefore, control messages exchanged
between any pair of OMNI link neighbors over the secured spanning tree
are already protected.To prevent spoofing vectors, Proxy/Servers MUST discard without
responding to any unsecured NS(AR) messages. Also, Proxy/Servers MUST
discard without forwarding any original IP packets received from one of
their own Clients (whether directly or following OAL reassembly) with a
source address that does not match the Client's MNP and/or a destination
address that does match the Client's MNP. Finally, Proxy/Servers MUST
discard without forwarding any carrier packets with an OAL source and
destination that both match the same MNP (i.e., after consulting the ORH
if present).For INET partitions that require strong security in the data plane,
two options for securing communications include 1) disable route
optimization so that all traffic is conveyed over secured tunnels, or 2)
enable on-demand secure tunnel creation between Client neighbors. Option
1) would result in longer routes than necessary and impose traffic
concentration on critical infrastructure elements. Option 2) could be
coordinated between Clients using NS/NA messages with OMNI Host Identity
Protocol (HIP) "Initiator/Responder" message sub-options to create a
secured tunnel on-demand.AERO Clients that connect to secured ANETs need not apply security to
their ND messages, since the messages will be authenticated and
forwarded by a perimeter Proxy/Server that applies security on its
INET-facing interface as part of the spanning tree (see above). AERO
Clients connected to the open INET can use network and/or transport
layer security services such as VPNs or can by some other means
establish a direct link to a Proxy/Server. When a VPN or direct link may
be impractical, however, INET Clients and Proxy/Servers SHOULD include
and verify authentication signatures for their IPv6 ND messages as
specified in .Application endpoints SHOULD use transport-layer (or higher-layer)
security services such as TLS/SSL, DTLS or SSH
to assure the same level of protection as for critical secured Internet
services. AERO Clients that require host-based VPN services SHOULD use
network and/or transport layer security services such as IPsec, TLS/SSL,
DTLS, etc. AERO Proxys and Proxy/Servers can also provide a
network-based VPN service on behalf of the Client, e.g., if the Client
is located within a secured enclave and cannot establish a VPN on its
own behalf.AERO Proxy/Servers and Bridges present targets for traffic
amplification Denial of Service (DoS) attacks. This concern is no
different than for widely-deployed VPN security gateways in the
Internet, where attackers could send spoofed packets to the gateways at
high data rates. This can be mitigated through the AERO/OMNI data origin
authentication procedures, as well as connecting Proxy/Servers and
Bridges over dedicated links with no connections to the Internet and/or
when connections to the Internet are only permitted through well-managed
firewalls. Traffic amplification DoS attacks can also target an AERO
Client's low data rate links. This is a concern not only for Clients
located on the open Internet but also for Clients in secured enclaves.
AERO Proxy/Servers and Proxys can institute rate limits that protect
Clients from receiving packet floods that could DoS low data rate
links.AERO Relays must implement ingress filtering to avoid a spoofing
attack in which spurious messages with ULA addresses are injected into
an OMNI link from an outside attacker. AERO Clients MUST ensure that
their connectivity is not used by unauthorized nodes on their EUNs to
gain access to a protected network, i.e., AERO Clients that act as
routers MUST NOT provide routing services for unauthorized nodes. (This
concern is no different than for ordinary hosts that receive an IP
address delegation but then "share" the address with other nodes via
some form of Internet connection sharing such as tethering.)The MAP list MUST be well-managed and secured from unauthorized
tampering, even though the list contains only public information. The
MAP list can be conveyed to the Client in a similar fashion as in (e.g., through layer 2 data link login messaging,
secure upload of a static file, DNS lookups, etc.).The AERO service for open INET Clients depends on a public key
distribution service in which Client public keys and identities are
maintained in a shared database accessible to all open INET
Proxy/Servers. Similarly, each Client must be able to determine the
public key of each Proxy/Server, e.g. by consulting an online database.
When AERO nodes register their public keys indexed by a unique Host
Identity Tag (HIT) in a distributed database
such as the DNS, and use the HIT as an identity for applying IPv6 ND
message authentication signatures, a means for determining public key
attestation is available.Security considerations for IPv6 fragmentation and reassembly are
discussed in . In environments
where spoofing is considered a threat, OMNI nodes SHOULD employ
Identification window synchronization and OAL destinations SHOULD
configure an (end-system-based) firewall.SRH authentication facilities are specified in . Security considerations for accepting link-layer
ICMP messages and reflected packets are discussed throughout the
document.Discussions in the IETF, aviation standards communities and private
exchanges helped shape some of the concepts in this work. Individuals
who contributed insights include Mikael Abrahamsson, Mark Andrews, Fred
Baker, Bob Braden, Stewart Bryant, Scott Burleigh, Brian Carpenter,
Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, Sri
Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom Herbert,
Bob Hinden, Sascha Hlusiak, Lee Howard, Christian Huitema, Zdenek Jaron,
Andre Kostur, Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima,
Tomek Mrugalski, Thomas Narten, Madhu Niraula, Alexandru Petrescu,
Behcet Saikaya, Michal Skorepa, Dave Thaler, Joe Touch, Bernie Volz,
Ryuji Wakikawa, Tony Whyman, Lloyd Wood and James Woodyatt. Members of
the IESG also provided valuable input during their review process that
greatly improved the document. Special thanks go to Stewart Bryant, Joel
Halpern and Brian Haberman for their shepherding guidance during the
publication of the AERO first edition.This work has further been encouraged and supported by Boeing
colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam
Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish,
Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad
Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, Greg
Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, Gene
MacLean III, Kyle Mikos, Rob Muszkiewicz, Sean O'Sullivan, Vijay
Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, Mike
Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia Wilson, Julie
Wulff, Yueli Yang, Eric Yeh and other members of the Boeing mobility,
networking and autonomy teams. Kyle Bae, Wayne Benson, Madhuri Madhava
Badgandi, Vijayasarathy Rajagopalan, Katie Tran and Eric Yeh are
especially acknowledged for their work on the AERO implementation. Chuck
Klabunde is honored and remembered for his early leadership, and we
mourn his untimely loss.This work was inspired by the support and encouragement of countless
outstanding colleagues, managers and program directors over the span of
many decades. Beginning in the late 1980s,' the Digital Equipment
Corporation (DEC) Ultrix Engineering and DECnet Architects groups
identified early issues with fragmentation and bridging links with
diverse MTUs. In the early 1990s, engagements at DEC Project Sequoia at
UC Berkeley and the DEC Western Research Lab in Palo Alto included
investigations into large-scale networked filesystems, ATM vs Internet
and network security proxies. In the mid-1990s to early 2000s employment
at the NASA Ames Research Center (Sterling Software) and SRI
International supported early investigations of IPv6, ONR UAV
Communications and the IETF. An employment at Nokia where important IETF
documents were published gave way to a present-day engagement with The
Boeing Company. The work matured at Boeing through major programs
including Future Combat Systems, Advanced Airplane Program, DTN for the
International Space Station, Mobility Vision Lab, CAST, Caravan, the
NASA UAS/CNS program, the FAA/ICAO ATN/IPS program and many others. An
attempt to name all who gave support and encouragement would double the
current document size and result in many unintentional omissions - but
to all a humble thanks.Earlier works on NBMA tunneling approaches are found in .Many of the constructs presented in this second edition of AERO are
based on the author's earlier works, including:The Internet Routing Overlay Network (IRON) Virtual Enterprise Traversal (VET) The Subnetwork Encapsulation and Adaptation Layer (SEAL) AERO, First Edition Note that these works cite numerous earlier efforts that are
not also cited here due to space limitations. The authors of those
earlier works are acknowledged for their insights.This work is aligned with the NASA Safe Autonomous Systems Operation
(SASO) program under NASA contract number NNA16BD84C.This work is aligned with the FAA as per the SE2025 contract number
DTFAWA-15-D-00030.This work is aligned with the Boeing Commercial Airplanes (BCA)
Internet of Things (IoT) and autonomy programs.This work is aligned with the Boeing Information Technology (BIT)
MobileNet program.http://openvpn.netBGP in 2015, http://potaroo.netWireGuard, https://www.wireguard.comWireguardAERO can be applied to a multitude of Internetworking scenarios, with
each having its own adaptations. The following considerations are
provided as non-normative guidance:Route optimization as discussed in
results in the route optimization source (ROS) creating a NCE for the
target neighbor. The NCE state is set to REACHABLE for at most
ReachableTime seconds. In order to refresh the NCE lifetime before the
ReachableTime timer expires, the specification requires
implementations to issue a new NS/NA(AR) exchange to reset
ReachableTime while data packets are still flowing. However, the
decision of when to initiate a new NS/NA(AR) exchange and to
perpetuate the process is left as an implementation detail.One possible strategy may be to monitor the NCE watching for data
packets for (ReachableTime - 5) seconds. If any data packets have been
sent to the neighbor within this timeframe, then send an NS(AR) to
receive a new NA(AR). If no data packets have been sent, wait for 5
additional seconds and send an immediate NS(AR) if any data packets
are sent within this "expiration pending" 5 second window. If no
additional data packets are sent within the 5 second window, reset the
NCE state to STALE.The monitoring of the neighbor data packet traffic therefore
becomes an ongoing process during the NCE lifetime. If the NCE
expires, future data packets will trigger a new NS/NA(AR) exchange
while the packets themselves are delivered over a longer path until
route optimization state is re-established.OMNI interface neighbors MAY provide a configuration option that
allows them to perform implicit mobility management in which no ND
messaging is used. In that case, the Client only transmits packets
over a single interface at a time, and the neighbor always observes
packets arriving from the Client from the same link-layer source
address.If the Client's underlying interface address changes (either due to
a readdressing of the original interface or switching to a new
interface) the neighbor immediately updates the NCE for the Client and
begins accepting and sending packets according to the Client's new
address. This implicit mobility method applies to use cases such as
cellphones with both WiFi and Cellular interfaces where only one of
the interfaces is active at a given time, and the Client automatically
switches over to the backup interface if the primary interface
fails.When a Client's OMNI interface is configured over a Direct
interface, the neighbor at the other end of the Direct link can
receive packets without any encapsulation. In that case, the Client
sends packets over the Direct link according to traffic selectors. If
the Direct interface is selected, then the Client's IP packets are
transmitted directly to the peer without going through an ANET/INET.
If other interfaces are selected, then the Client's IP packets are
transmitted via a different interface, which may result in the
inclusion of Proxy/Servers and Bridges in the communications path.
Direct interfaces must be tested periodically for reachability, e.g.,
via NUD.AERO Bridges can be either Commercial off-the Shelf (COTS) standard
IP routers or virtual machines in the cloud. Bridges must be
provisioned, supported and managed by the INET administrative
authority, and connected to the Bridges of other INETs via
inter-domain peerings. Cost for purchasing, configuring and managing
Bridges is nominal even for very large OMNI links.AERO INET Proxy/Servers can be standard dedicated server platforms,
but most often will be deployed as virtual machines in the cloud. The
only requirements for INET Proxy/Servers are that they can run the
AERO/OMNI code and have at least one network interface connection to
the INET. INET Proxy/Servers must be provisioned, supported and
managed by the INET administrative authority. Cost for purchasing,
configuring and managing cloud Proxy/Servers is nominal especially for
virtual machines.AERO ANET Proxy/Servers are most often standard dedicated server
platforms with one underlying interface connected to the ANET and a
second interface connected to an INET. As with INET Proxy/Servers, the
only requirements are that they can run the AERO/OMNI code and have at
least one interface connection to the INET. ANET Proxy/Servers must be
provisioned, supported and managed by the ANET administrative
authority. Cost for purchasing, configuring and managing Proxys is
nominal, and borne by the ANET administrative authority.AERO Relays are simply Proxy/Servers connected to INETs and/or EUNs
that provide forwarding services for non-MNP destinations. The Relay
connects to the OMNI link and engages in eBGP peering with one or more
Bridges as a stub AS. The Relay then injects its MNPs and/or non-MNP
prefixes into the BGP routing system, and provisions the prefixes to
its downstream-attached networks. The Relay can perform ROS/ROR
services the same as for any Proxy/Server, and can route between the
MNP and non-MNP address spaces.AERO Proxy/Servers may appear as a single point of failure in the
architecture, but such is not the case since all Proxy/Servers on the
link provide identical services and loss of a Proxy/Server does not
imply immediate and/or comprehensive communication failures.
Proxy/Server failure is quickly detected and conveyed by Bidirectional
Forward Detection (BFD) and/or proactive NUD allowing Clients to
migrate to new Proxy/Servers.If a Proxy/Server fails, ongoing packet forwarding to Clients will
continue by virtue of the neighbor cache entries that have already
been established in route optimization sources (ROSs). If a Client
also experiences mobility events at roughly the same time the
Proxy/Server fails, uNA messages may be lost but neighbor cache
entries in the DEPARTED state will ensure that packet forwarding to
the Client's new locations will continue for up to DepartTime
seconds.If a Client is left without a Proxy/Server for a considerable
length of time (e.g., greater than ReachableTime seconds) then
existing neighbor cache entries will eventually expire and both
ongoing and new communications will fail. The original source will
continue to retransmit until the Client has established a new
Proxy/Server relationship, after which time continuous communications
will resume.Therefore, providing many Proxy/Servers on the link with high
availability profiles provides resilience against loss of individual
Proxy/Servers and assurance that Clients can establish new
Proxy/Server relationships quickly in event of a Proxy/Server
failure.The AERO architectural model is client / server in the control
plane, with route optimization in the data plane. The same as for
common Internet services, the AERO Client discovers the addresses of
AERO Proxy/Servers and connects to one or more of them. The AERO
service is analogous to common Internet services such as google.com,
yahoo.com, cnn.com, etc. However, there is only one AERO service for
the link and all Proxy/Servers provide identical services.Common Internet services provide differing strategies for
advertising server addresses to clients. The strategy is conveyed
through the DNS resource records returned in response to name
resolution queries. As of January 2020 Internet-based 'nslookup'
services were used to determine the following:When a client resolves the domainname "google.com", the DNS
always returns one A record (i.e., an IPv4 address) and one AAAA
record (i.e., an IPv6 address). The client receives the same
addresses each time it resolves the domainname via the same DNS
resolver, but may receive different addresses when it resolves the
domainname via different DNS resolvers. But, in each case, exactly
one A and one AAAA record are returned.When a client resolves the domainname "ietf.org", the DNS
always returns one A record and one AAAA record with the same
addresses regardless of which DNS resolver is used.When a client resolves the domainname "yahoo.com", the DNS
always returns a list of 4 A records and 4 AAAA records. Each time
the client resolves the domainname via the same DNS resolver, the
same list of addresses are returned but in randomized order (i.e.,
consistent with a DNS round-robin strategy). But, interestingly,
the same addresses are returned (albeit in randomized order) when
the domainname is resolved via different DNS resolvers.When a client resolves the domainname "amazon.com", the DNS
always returns a list of 3 A records and no AAAA records. As with
"yahoo.com", the same three A records are returned from any
worldwide Internet connection point in randomized order.The above example strategies show differing approaches to
Internet resilience and service distribution offered by major Internet
services. The Google approach exposes only a single IPv4 and a single
IPv6 address to clients. Clients can then select whichever IP protocol
version offers the best response, but will always use the same IP
address according to the current Internet connection point. This means
that the IP address offered by the network must lead to a
highly-available server and/or service distribution point. In other
words, resilience is predicated on high availability within the
network and with no client-initiated failovers expected (i.e., it is
all-or-nothing from the client's perspective). However, Google does
provide for worldwide distributed service distribution by virtue of
the fact that each Internet connection point responds with a different
IPv6 and IPv4 address. The IETF approach is like google
(all-or-nothing from the client's perspective), but provides only a
single IPv4 or IPv6 address on a worldwide basis. This means that the
addresses must be made highly-available at the network level with no
client failover possibility, and if there is any worldwide service
distribution it would need to be conducted by a network element that
is reached via the IP address acting as a service distribution
point.In contrast to the Google and IETF philosophies, Yahoo and Amazon
both provide clients with a (short) list of IP addresses with Yahoo
providing both IP protocol versions and Amazon as IPv4-only. The order
of the list is randomized with each name service query response, with
the effect of round-robin load balancing for service distribution.
With a short list of addresses, there is still expectation that the
network will implement high availability for each address but in case
any single address fails the client can switch over to using a
different address. The balance then becomes one of function in the
network vs function in the end system.The same implications observed for common highly-available services
in the Internet apply also to the AERO client/server architecture.
When an AERO Client connects to one or more ANETs, it discovers one or
more AERO Proxy/Server addresses through the mechanisms discussed in
earlier sections. Each Proxy/Server address presumably leads to a
fault-tolerant clustering arrangement such as supported by Linux-HA,
Extended Virtual Synchrony or Paxos. Such an arrangement has
precedence in common Internet service deployments in lightweight
virtual machines without requiring expensive hardware deployment.
Similarly, common Internet service deployments set service IP
addresses on service distribution points that may relay requests to
many different servers.For AERO, the expectation is that a combination of the Google/IETF
and Yahoo/Amazon philosophies would be employed. The AERO Client
connects to different ANET access points and can receive 1-2
Proxy/Server ADM-LLAs at each point. It then selects one AERO
Proxy/Server address, and engages in RS/RA exchanges with the same
Proxy/Server from all ANET connections. The Client remains with this
Proxy/Server unless or until the Proxy/Server fails, in which case it
can switch over to an alternate Proxy/Server. The Client can likewise
switch over to a different Proxy/Server at any time if there is some
reason for it to do so. So, the AERO expectation is for a balance of
function in the network and end system, with fault tolerance and
resilience at both levels.<< RFC Editor - remove prior to publication >>Changes from draft-templin-6man-aero-16 to
draft-templin-6man-aero-17:Final editorial review pass resulting in multiple changes.
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draft-templin-6man-aero-05:Changed to use traffic selectors instead of the former multilink
selection strategy.Changes from draft-templin-6man-aero-03 to
draft-templin-6man-aero-04:Removed documents from "Obsoletes" list.Introduced the concept of "secured" and "unsecured" spanning
tree.Additional security considerations.Additional route optimization considerations.Changes from draft-templin-6man-aero-02 to
draft-templin-6man-aero-03:Support for extended route optimization from ROR to target over
target's underlying interfaces.Changes from draft-templin-6man-aero-01 to
draft-templin-6man-aero-02:Changed reference citations to "draft-templin-6man-omni".Several important updates to IPv6 ND cache states and route
optimization message addressing.Included introductory description of the "6M's".Updated Multicast specification.Changes from draft-templin-6man-aero-00 to
draft-templin-6man-aero-01:Changed category to "Informational".Updated implementation status.Changes from earlier versions to
draft-templin-6man-aero-00:Established working baseline reference.