Boeing's Interior Routing Overlay Network
(IRON)Boeing Research & TechnologyP.O. Box 3707 MC 7L-49SeattleWA98124USAfltemplin@acm.orgNetwork Working GroupI-DInternet-DraftSince large-scale Internetworks such as the public Internet must
continue to support escalating growth due to increasing demand, it is
clear that Autonomous Systems (ASes) must avoid injecting excessive
de-aggregated prefixes into the interdomain routing system and instead
mitigate de-aggregation internally. This document describes an Interior
Routing Overlay Network (IRON) architecture developed by Boeing that
supports sustainable growth within AS-interior routing domains while
requiring no changes to end systems and no changes to the exterior
routing system. In addition to routing scaling, IRON further addresses
other important issues including mobility management, mobile networks,
multihoming, traffic engineering, NAT traversal and security. While
business considerations are an important determining factor for
widespread adoption, they are out of scope for this document.Growth in the number of prefix entries instantiated in the Internet
routing system has led to concerns regarding unsustainable routing
scaling . Operational practices
such as de-aggregation and the increased use of multihoming with
Provider-Independent (PI) addressing are resulting in more and more
prefixes being injected into the Internet routing system. Furthermore,
depletion of the public IPv4 address space has raised concerns for both
increased de-aggregation and an impending address space run-out
scenario. At the same time, the IPv6 routing system is beginning to see
growth which must be managed in order to avoid
the same routing scaling issues the IPv4 Internet now faces. Since the
Internet must continue to scale to accommodate increasing demand, it is
clear that new methodologies and operational practices for managing
Autonomous System (AS) interior routing systems are needed in order to
avoid excessive routing scaling due to de-aggregation.These same issues apply also to Internetworks other than the public
Internet, including critical infrastructure networks such as corporate
enterprise networks, civil aviation networks, emergency response
networks, power grid networks, medical care networks, etc. The
architectural principles presented in this document therefore apply
equally to any such Internetwork.Several related works have investigated routing scaling issues.
Virtual Aggregation (VA) and Aggregation in
Increasing Scopes (AIS) are global routing
proposals that introduce routing overlays with Virtual Prefixes (VPs) to
reduce the number of entries required in each router's Forwarding
Information Base (FIB) and Routing Information Base (RIB). Routing and
Addressing in Networks with Global Enterprise Recursion (RANGER) examines recursive arrangements of enterprise
networks that can apply to a very broad set of use-case scenarios . IRON specifically adopts the RANGER Non-Broadcast,
Multiple Access (NBMA) tunnel virtual-interface model, and uses Virtual
Enterprise Traversal (VET) the Subnetwork
Adaptation and Encapsulation Layer (SEAL)
and Asymmetric Extended Route Optimization as
its functional building blocks.This document introduces an Interior Routing Overlay Network (IRON)
architecture developed by Boeing with goals of supporting scalable
routing and addressing while requiring no changes to the Internetwork's
interdomain routing system . IRON observes the
Internet Protocol standards , while other network-layer protocols that can be
encapsulated within IP packets (e.g., OSI/CLNP ,
etc.) are also within scope.IRON borrows concepts from VA and AIS, and further borrows concepts
from the Internet Vastly Improved Plumbing (Ivip) architecture proposal along with its associated
Translating Tunnel Router (TTR) mobility extensions . Indeed, the TTR model to a great degree inspired the
IRON mobility architecture design discussed in this document. The
Network Address Translator (NAT) traversal techniques adapted for IRON
were inspired by the Simple Address Mapping for Premises Legacy
Equipment (SAMPLE) proposal and by Teredo .IRON is specifically adapted for Virtual Service Provider (VSP)
overlay networks that connect to the Internetwork as an AS and service
Aggregated Prefixes (APs) from which more-specific Client Prefixes (CPs)
are delegated. IRON is motivated by a growing end user demand for
mobility management, mobile networks, multihoming, traffic engineering,
NAT traversal and security while using stable addressing to minimize
dependence on network renumbering . IRON VSP overlay network instances use the existing
IPv4 and/or IPv6 Internetwork as virtual NBMA links for tunneling inner
network layer packets within outer network layer headers (see Section
4). Each IRON instance requires deployment of a small number of relays
and servers in the Internetwork, as well as client devices that connect
End User Networks (EUNs). No modifications to hosts, and no
modifications to existing routers, are required. The following sections
discuss details of the IRON architecture.An earlier version of IRON was published as RFC6179. This version
clarifies that IRON operates at the intradomain level within an AS, and
is therefore not intended as an interdomain solution. IRON is therefore
complimentary with the approaches documented in interdomain solutions
such as the Identifier / Locator Network Protocol (ILNP) and the Locator I/D Split Protocol (LISP) . This version of IRON further introduces significant
improvements in security and route optimization, as well as a direct
client-to-client route optimization capability not found in RFC6179.Some terminology has been changed for greater clarification,
including Virtual Service Provier (VSP), Aggregated Prefix (AP) and
Client Prefix (CP). This document further introduces Asymmetric Extended
Route Optimization (AERO) as the primary route
discovery mechanism. The document finally adds a new section on
renumbering considerations and adds enhanced security
considerations.This document makes use of the following terms:a short network-layer
prefix (e.g., an IPv4 /16, an IPv6 /20, an OSI Network Service
Access Protocol (NSAP) prefix, etc.) that is owned and managed by a
Virtual Service Provider (VSP).a more-specific
network-layer prefix (e.g., an IPv4 /28, an IPv6 /56, etc.) derived
from an AP and delegated to a client end user network.a network-layer
address belonging to a CP and assigned to an interface in an End
User Network (EUN).an edge network that
connects an end user's devices (e.g., computers, routers, printers,
etc.) to the Internetwork. IRON EUNs are mobile networks, and can
change their ISP attachments without having to renumber.an
AS-interior overlay network instance that appears as a virtual
enterprise network, and connects to the Internetwork the same as for
any AS.a
customer device that logically connects EUNs to an IRON instance via
an NBMA tunnel virtual interface. The device is normally a router,
but may instead be a host if the "EUN" is a singleton end
system.a
VSP's IRON instance router that provides forwarding and mapping
services for Clients.a
VSP's router that acts as a relay between the IRON instance and the
Internetwork.generically refers to any of
an IRON Client/Server/Relay.a set of IRON Agents deployed
by a VSP to service EUNs through automatic tunneling over the
Internetwork.a
service provider that connects an IA to the Internetwork. In other
words, an ISP is responsible for providing IAs with data link
services for basic connectivity.an IP address assigned to the
interface of a router or end system connected to a public or private
network over which tunnels are formed. Locators taken from public IP
prefixes are routable on a global basis, while locators taken from
private IP prefixes are made public via
Network Address Translation (NAT).
an architectural examination of virtual overlay networks applied to
enterprise network scenarios, with implications for a wider variety
of use cases.an
encapsulation sublayer that provides extended identification fields
and control messages to ensure deterministic network-layer
feedback.a method
for discovering border routers and forming dynamic tunnel neighbor
relationships over enterprise networks (or sites) with varying
properties.a
means for a destination IA to securely inform a source IA of a more
direct path.a company
that owns and manages a set of APs from which it delegates CPs to
EUNs.the same as defined
above for IRON Instance.The Interior Routing Overlay Network (IRON) operates at the AS level
and provides a number of important services to End User Networks (EUNs)
that are not well supported in the current architecture, including
routing scaling, mobility management, mobile networks, multihoming,
traffic engineering and NAT traversal. This is accomplisehd through the
establishment of IRON instances as overlays configured over the
underlying Internetwork.Each IRON instance consists of IRON Agents (IAs) that automatically
tunnel the packets of end-to-end communication sessions within
encapsulating headers used for Internetwork routing. IAs use the Virtual
Enterprise Traversal (VET) virtual NBMA
link model in conjunction with the Subnetwork Encapsulation and
Adaptation Layer (SEAL) to encapsulate
inner network-layer packets within outer network layer headers, as shown
in .VET specifies automatic tunneling and tunnel neighbor coordination
mechanisms, where IAs appear as neighbors on an NBMA tunnel virtual
link. SEAL specifies the format and usage of the SEAL encapsulating
header. Additionally, Asymmetric Extended Route Optimization (AERO)
specifies the method for route optimization to
reduce routing path stretch. Together, these documents specify a set of
control messages used to deterministically exchange and authenticate
neighbor discovery messages, route redirections, indications of Path
Maximum Transmission Unit (PMTU) limitations, destination unreachables,
etc.Each IRON instance comprises a set of IAs distributed throughout the
Internetwork to provide routing services for a set of Aggregated
Prefixes (APs). (The APs may be owned either by the VSP, or by an
enterprise network customer that hires the VSP to manage its APs.) VSPs
delegate sub-prefixes from APs, which they provide to end users as
Client Prefixes (CPs). In turn, end users assign CPs to Client IAs which
connect their End User Networks (EUNs) to the VSP IRON instance.VSPs may have no affiliation with the ISP networks from which end
users obtain their basic Internetwork connectivity. In that case, the
VSP can service its end users without the need to coordinate its
activities with ISPs or other VSPs. Further details on VSP business
considerations are out of scope for this document.IRON requires no changes to end systems or to existing routers.
Instead, IAs are deployed either as new platforms or as modifications to
existing platforms. IAs may be deployed incrementally without disturbing
the existing Internetwork routing system, and act as waypoints (or
"cairns") for navigating VSP overly networks. The functional roles for
IAs are described in the following sections.An IRON Client (or, simply, "Client") is a router that logically
connects EUNs to the VSP's IRON instance via tunnels, as shown in
. Clients obtain CPs from their VSPs and use them
to number subnets and interfaces within the EUNs.Each Client connects to one or more Servers in the IRON instance
which serve as default routers. The Servers in turn consider this
class of Clients as "dependent" Clients. Clients also dynamically
discover destination-specific Servers through the receipt of
redirection messages. These destination-specific Servers in turn
consider this class of Clients as "visiting" Clients.A Client can be deployed on the same physical platform that also
connects EUNs to the end user's ISPs, but it may also be deployed as a
separate router within the EUN. (This model applies even if the EUN
connects to the ISP via a Network Address Translator (NAT) -- see
Section 7.7). Finally, a Client may also be a simple end system that
connects a singleton EUN and exhibits the outward appearance of a
host.An IRON serving router (or, simply, "Server") is a VSP's router
that provides forwarding and mapping services within the IRON instance
for the CPs that have been delegated to end user Clients. In typical
deployments, a VSP will deploy many Servers for the IRON instance in a
globally distributed fashion (e.g., as depicted in ) around the Internetwork so that Clients can discover
those that are nearby.Each Server acts as a tunnel-endpoint router. The Server
forms bidirectional tunnel neighbor relationships with each of its
dependent Clients, and can also serve as the unidirectional tunnel
neighbor egress for dynamically discovered visiting Clients. (The
Server can also form bidirectional tunnel neighbor relationships with
visiting Clients, e.g., if a symmetric security association is
necessary.) Each Server also forms bidirectional tunnel neighbor
relationships with a set of Relays that can forward packets from the
IRON instance out to the native Internetwork and vice versa, as
discussed in the next section.An IRON Relay Router (or, simply, "Relay") is a router that
connects the VSP's IRON instance to the Internetwork as an AS. The
Relay therefore also serves as an Autonomous System Border Router
(ASBR) that is owned and managed by the VSP.Each VSP configures one or more Relays that advertise the VSP's APs
into the IPv4 and/or IPv6 Internetwork routing systems. Each Relay
associates with the VSP's IRON instance Servers, e.g., via tunnel
virtual links over the IRON instance, via a physical interconnect such
as an Ethernet cable, etc. The Relay role is depicted in .Each IRON instance represents a distinct "patch" on the underlying
Internetwork "quilt", where the patches are stitched together by
standard routing. When a new IRON instance is deployed, it becomes yet
another patch on the quilt and coordinates its internal routing system
independently of all other patches.Each IRON instance connects to the Internetwork as an AS in the
interdomain routing system using a public Border Gateway Protocol (BGP)
Autonomous System Number (ASN). The IRON instance maintains a set of
Relays that serve as ASBRs as well as a set of Servers that provide
routing and addressing services to Clients. depicts
the logical arrangement of Relays, Servers, and Clients in an IRON
instance.Each Relay connects the IRON instance directly to the
underlying IPv4 and/or IPv6 Internetworks via external BGP (eBGP)
peerings with neighboring ASes. It also advertises the IPv4 APs managed
by the VSP into the IPv4 Internetwork routing system and advertises the
IPv6 APs managed by the VSP into the IPv6 Internetwork routing system.
Relays will therefore receive packets with CPA destination addresses
sent by end systems in the Internetwork and forward them to a Server
that connects the Client to which the corresponding CP has been
delegated. Finally, the IRON instance Relays maintain synchronization by
running interior BGP (iBGP) between themselves the same as for ordinary
ASBRs.In a simple VSP overlay network arrangement, each Server can be
configured as an ASBR for a stub AS using a private ASN to peer with each IRON instance Relay the same as for
an ordinary eBGP neighbor. (The Server and Relay functions can instead
be deployed together on the same physical platform as a unified
gateway.) Each Server maintains a working set of dependent Clients for
which it caches CP-to-Client mappings in its forwarding table. Each
Server also, in turn, propagates the list of CPs in its working set to
its neighboring Relays via eBGP. Therefore, each Server only needs to
track the CPs for its current working set of dependent Clients, while
each Relay will maintain a full CP-to-Server forwarding table that
represents reachability information for all CPs in the IRON
instance.Each Client obtains its basic Internetwork connectivity from ISPs,
and connects to Servers to attach its EUNs to the IRON instance. Each
EUN can further connect to the IRON instance via multiple Clients as
long as the Clients coordinate with one another, e.g., to mitigate EUN
partitions. Clients may additionaly use private addresses behind one or
several layers of NATs. Each Client initially discovers a list of nearby
Servers then forms a bidirectional tunnel neighbor relationship with one
or more Servers through an initial exchange followed by periodic
keepalives.After a Client connects to Servers, it forwards initial outbound
packets from its EUNs by tunneling them to a Server, which may, in turn,
forward them to a nearby Relay within the IRON instance. The Client may
subsequently receive redirection messages informing it of a more direct
route through a different IA within the IRON instance that serves the
final destination EUN.IRON can also be used to support APs of network-layer address
families that cannot be routed natively in the underlying Internetwork
(e.g., OSI/CLNP over the public Internet, IPv6 over IPv4-only
Internetworks, IPv4 over IPv6-only Internetworks, etc.). Further details
for the support of IRON APs of one address family over Internetworks
based on different address families are discussed in Appendix A.Each IRON instance supports routing through the control plane startup
and runtime dynamic routing operation of IAs. The following sub-sections
discuss control plane considerations for initializing and maintaining
the IRON instance routing system.Each Client obtains one or more CPs in a secured exchange with the
VSP as part of the initial end user registration. Upon startup, the
Client discovers a list of nearby VSP Servers via, e.g., a location
broker, a well known website, a static map, etc.After the Client obtains a list of nearby Servers, it initiates
short transactions to connect to one or more Servers, e.g., via
secured TCP connections. During the transaction, each Server provides
the Client with a CP and a symmetric secret key that the Client will
use to sign and authenticate messages. The Client in turn provides the
Server with a set of link identifiers ("LINK_ID"s) that represent the
Client's ISP connections. Finally, the Client provides a "willingness"
indication as to whether or not it will accept direct Client-to-Client
communications without involving the Server as an intermediary. The
protocol details of the connection transaction are specific to the
VSP, and hence out of scope for this document.After the Client connects to Servers, it configures default routes
that list the Servers as next hops on the tunnel virtual interface.
The Client may subsequently discover more-specific routes through
receipt of redirection messages.In a simple VSP overlay network arrangement, each IRON Server is
provisioned with the locators for Relays within the IRON instance. The
Server is further configured as an ASBR for a stub AS and uses eBGP
with a private ASN to peer with each Relay.Upon startup, the Server uses eBGP to announce the list of CPs it
is currently serving to the overlay network Relays. The Server then
actively listens for Clients that register their CPs as part of the
connection establishment procedure described in Section 6.1. When a
new Client connects, the Server uses eBGP to announce the new CP
routes to its neighboring Relays; when an existing Client disconnects,
the Server withdraws its CP announcements. This process can often be
accommodated through standard eBGP router configurations, e.g., on
routers that can announce and withdraw prefixes based on kernel route
additions and deletions.Each IRON Relay is provisioned with the list of APs that it will
serve, as well as the locators for Servers within the IRON instance.
The Relay is also provisioned with eBGP peerings with neighboring ASes
in the Internetwork -- the same as for any ASBR.In a simple VSP overlay network arrangement, each Relay connects to
each Server via IRON instance-internal eBGP peerings for the purpose
of discovering CP-to-Server mappings, and connects to all other Relays
using iBGP either in a full mesh or using route reflectors. (The Relay
only uses iBGP to announce those prefixes it has learned from AS
peerings external to the IRON instance, however, since all Relays will
already discover all CPs in the IRON instance via their eBGP peerings
with Servers.) The Relay then engages in eBGP routing exchanges with
peer ASes in the IPv4 and/or IPv6 Internetworks the same as for any
ASBR.After this initial synchronization procedure, the Relay advertises
the APs to its eBGP peers in the Internetwork. In particular, the
Relay advertises the IPv6 APs into the IPv6 interdomain routing system
and advertises the IPv4 APs into the IPv4 interdomain routing system,
but it does not advertise the full list of the IRON overlay's CPs to
any of its eBGP peers. The Relay further advertises "default" via eBGP
to its associated Servers, then engages in ordinary packet-forwarding
operations.Following control plane initialization, IAs engage in the cooperative
process of receiving and forwarding packets. IAs forward encapsulated
packets over the IRON instance using the mechanisms of VET , SEAL and AERO
, while Relays additionally forward packets to
and from the native IPv6 and/or IPv4 Internetworks. IAs also use VET,
SEAL and AERO control messages to coordinate with other IAs, including
the process of sending and receiving redirection messages, error
messages, etc. Each IA operates as specified in the following
sub-sections.After connecting to Servers as specified in Section 6.1, the Client
registers its active ISP connections with each of its connected
Servers. Thereafter, the Client sends periodic beacons (e.g.,
cryptographically signed SEAL Control Message Protocol (SCMP) Router
Solicitation (SRS) messages) to the Server via each ISP connection to
maintain tunnel neighbor address mapping state. The beacons should be
sent at no more than 60 second intervals (subject to a small random
delay) so that state in NATs on the path as well as on the Server
itself is refreshed regularly. Although the Client may connect via
multiple ISPs (each represented by a different LINK_ID), the CP itself
is used to represent the bidirectional Client-to-Server tunnel
neighbor association. The CP therefore names this "bundle" of ISP
connections.If the Client ceases to receive acknowledgements from a Server via
a specific ISP connection, it marks the Server as unreachable from
that ISP. (The Client should also inform the Server of this outage via
one of its working ISP connections.) If the Client ceases to receive
acknowledgements from the Server via multiple ISP connections, it
disconnects from the failing Server and connects to a different nearby
Server. The act of disconnecting from old servers and connecting to
new servers will soon propagate the appropriate routing information
among the IRON instance's Relays.When an end system in an EUN sends a flow of packets to a
correspondent in a different network, the packets are forwarded
through the EUN via normal routing until they reach the Client, which
then tunnels the initial packets to one of its connected Servers as
its default router. In particular, the Client encapsulates each packet
in outer headers with its locator as the source address and the
locator of the Server as the destination address.The Client uses the mechanisms specified in VET and SEAL to
encapsulate each packet to be forwarded, and uses the redirection
procedures described in AERO to coordinate route optimization. The
Client further accepts control messages from its Servers, including
neighbor coordination exchanges, indications of PMTU limitations,
redirections and other control messages. When the Client is redirected
to a foreign Server that serves a destination CP, it forms a
unidirectional tunnel neighbor association with the foreign Server as
the new next hop toward the CP. (The visiting Client can also form a
bidirectional tunnel neighbor association with the foreign Server,
e.g., if a symmetric security association is necessary.)Note that Client-to-Client tunneling is also enabled when the
foreign Client has indicated its willingness to accept
Client-to-Client communications. In that case, the foreign Server can
allow the final destination Client to return the redirection message,
which removes the foreign Server from the fowarding path.After the Server associates with nearby Relays, it accepts Client
connections and authenticates the SRS messages it receives from its
already-connected Clients. The Server discards any SRS messages that
failed authentication, and responds to authentic SRS messages by
returning signed SCMP Router Advertisement (SRA) messages.When the Server receives a SEAL-encapsulated data packet from one
of its dependent Clients, it uses normal longest-prefix-match rules to
locate a forwarding table entry that matches the packet's inner
destination address. The Server then re-encapsulates the packet (i.e.,
it removes the outer header and replaces it with a new outer header),
sets the outer destination address to the locator address of the next
hop and forwards the packet to the next hop.When the Server receives a SEAL-encapsulated data packet from a
visiting Client, it accepts the packet only if the packet's signature
is correct; otherwise, it silently drops the packet. The Server then
locates a forwarding table entry that matches the packet's inner
destination address. If the destination does not correspond to one of
the Server's dependent Clients, the Server silently drops the packet.
Otherwise, the Server re-encapsulates the packet and forwards it to
the correct dependent Client. If the Client is in the process of
disconnecting (e.g., due to mobility), the Server also returns a
redirection message listing a NULL next hop to inform the visiting
Client that the dependent Client has moved.When the Server receives a SEAL-encapsulated data packet from a
Relay, it again locates a forwarding table entry that matches the
packet's inner destination. If the destination does not correspond to
one of the Server's dependent Clients, the Server drops the packet and
sends a destination unreachable message. Otherwise, the Server
re-encapsulates the packet and forwards it to the correct dependent
Client.After each Relay has synchronized its APs (see Section 6.3) it
advertises them in the IPv4 and/or IPv6 interdomain routing systems.
These APs will be represented as ordinary routing information in the
interdomain routing system, and any packets originating from the IPv4
or IPv6 Internetwork destined to an address covered by one of the APs
will be forwarded to one of the VSP's Relays.When a Relay receives a packet from the Internetwork destined to a
CPA covered by one of its APs, it behaves as an ordinary IP router.
Specifically, the Relay looks in its forwarding table to discover a
locator of a Server that serves the CP covering the destination
address. The Relay then simply forwards the packet to the Server,
e.g., via SEAL encapsulation over a tunnel virtual link, via a
physical interconnect, etc.When a Relay receives a packet from a Server destined to a CPA
serviced by a different Server, the Relay forwards the packet toward
the correct Server while also sending a "predirect" indication as the
initial leg in the AERO redirection procedure. When the target IA
returns a redirection message, the Relay proxies the message by
re-encapsulating it and forwarding it to the previous hop.The following sections discuss the IRON reference operating
scenarios.When both hosts are within EUNs served by the same IRON instance,
it is sufficient to consider the scenario in a unidirectional fashion,
i.e., by tracing packet flows only in the forward direction from
source host to destination host. The reverse direction can be
considered separately and incurs the same considerations as for the
forward direction. The simplest case occurs when the EUNs that service
the source and destination hosts are connected to the same server,
while the general case occurs when the EUNs are connected to different
Servers. The two cases are discussed in the following sections.In this scenario, the packet flow from the source host is
forwarded through the EUN to the source's IRON Client. The Client
then tunnels the packets to the Server, which simply re-encapsulates
and forwards the tunneled packets to the destination's Client. The
destination's Client then removes the packets from the tunnel and
forwards them over the EUN to the destination. depicts the sustained flow of packets from Host
A to Host B within EUNs serviced by the same Server via a
"hairpinned" route:With reference to , Host A sends
packets destined to Host B via its network interface connected to
EUN A. Routing within EUN A will direct the packets to Client(A) as
a default router for the EUN, which then encapsulates them in outer
IP/*/SEAL headers with its locator address as the outer source
address, the locator address of Server(S) as the outer destination
address, and the identifying information associated with its tunnel
neighbor state as the identity. Client(A) then simply forwards the
encapsulated packets into the ISP network connection that provided
its locator. The ISP will forward the encapsulated packets into the
Internetwork without filtering since the (outer) source address is
topologically correct. Once the packets have been forwarded into the
Internetwork, routing will direct them to Server(S).Server(S) will receive the encapsulated packets from Client(A)
then check its forwarding table to discover an entry that covers
destination address B with Client(B) as the next hop. Server(S) then
re-encapsulates the packets in a new outer header that uses the
source address, destination address, and identification parameters
associated with the tunnel neighbor state for Client(B). Server(S)
then forwards these re-encapsulated packets into the Internetwork,
where routing will direct them to Client(B). Client(B) will, in
turn, decapsulate the packets and forward the inner packets to Host
B via EUN B.In this scenario, the initial packets of a flow produced by a
source host within an EUN connected to the IRON instance by a Client
must flow through both the Server of the source host and a nearby
Relay, but route optimization can eliminate these elements from the
path for subsequent packets in the flow.
shows the flow of initial packets from Host A to Host B within EUNs
of the same IRON instance:With reference to , Host A sends
packets destined to Host B via its network interface connected to
EUN A. Routing within EUN A will direct the packets to
Client(A) as a default router for the EUN, which then encapsulates
them in outer IP/*/SEAL headers that use the source address,
destination address, and identification parameters associated with
the tunnel neighbor state for Server(A). Client(A) then forwards the
encapsulated packets into the ISP network connection that provided
its locator, which will forward the encapsulated packets into the
Internetwork where routing will direct them to Server(A).Server(A) receives the encapsulated packets from Client(A) and
consults its forwarding table to determine that the most-specific
matching route is via Relay(R) as the next hop. Server(A) then
re-encapsulates the packets in outer headers that use the source
address, destination address, and identification parameters
associated with Relay (R), and forwards them into the Internetwork
where routing will direct them to Relay(R). (Note that the Server
could instead forward the packets directly to the Relay without
encapsulation when the Relay is directly connected, e.g., via a
physical interconnect.)Relay(R) receives the forwarded packets from Server(A) then
checks its forwarding table to discover a CP entry that covers inner
destination address B with Server(B) as the next hop. Relay(R) then
sends a "predirect" indication forward to Server(B) to inform the
server that a redirection message must be returned. Relay(R) finally
re-encapsulates the packets in outer headers that use the source
address, destination address, and identification parameters
associated with Server(B), then forwards them into the Internetwork
where routing will direct them to Server(B). (Note again that the
Relay could instead forward the packets directly to the Server,
e.g., via a physical interconnect.)Server(B) receives the "predirect" and forwarded packets from
Relay(R), then checks its forwarding table to discover a CP entry
that covers destination address B with Client(B) as the next hop.
Server(B) returns a redirection message to Relay(R), which proxies
the message back to Server(A), which then proxies the message back
to Client(A).Server(B) then re-encapsulates the packets in outer headers that
use the source address, destination address, and identification
parameters associated with Client(B), then forwards them into the
Internetwork where routing will direct them to Client(B). Client(B)
will, in turn, decapsulate the packets and forward the inner packets
to Host B via EUN B.After the initial flow of packets, Client(A) will have received
one or more redirection messages listing Server(B) as a better next
hop, and will establish unidirectional tunnel neighbor state listing
Server(B) as the next hop toward the CP that covers Host B.
Client(A) thereafter forwards its encapsulated packets directly to
the locator address of Server(B) without involving either Server(A)
or Relay(B), as shown in .In the scenarios shown in Sections 8.1.1 and 8.1.2, if the
foreign Client has indicated its willingness to accept
Client-to-Client communications, then the foreign Server can allow
the foreign Client to return the redirection message, i.e., by
passing the "predirect" message on to the Client. In that case, the
two Clients become peers in either a unidirectional or bidirectional
tunnel neighbor relationship as shown in :The cases in which one host is within an IRON EUN and the other is
in a non-IRON EUN (i.e., one that connects to the native Internetwork
instead of the IRON) are described in the following sub-sections. depicts the IRON reference operating
scenario for packets flowing from Host A in an IRON EUN to Host B in
a non-IRON EUN.In this scenario, Host A sends packets destined to Host B via its
network interface connected to IRON EUN A. Routing within EUN
A will direct the packets to Client(A) as a default router for the
EUN, which then encapsulates them and forwards them into the
Internetwork routing system where they will be directed to
Server(A).Server(A) receives the encapsulated packets from Client(A) then
forwards them to Relay(A), which simply forwards the unencapsulated
packets into the Internetwork. Once the packets are released into
the Internetwork, routing will direct them to the final destination
B. (Note that for simplicity Server(A) and Relay(A) are depicted in
as two concatenated "half-routers", and
the forwarding between the two halves is via encapsulation, via a
physical interconnect, via a shared memory operation when the two
halves are within the same physical platform, etc.) depicts the IRON reference operating
scenario for packets flowing from Host B in an Non-IRON EUN to Host
A in an IRON EUN.In this scenario, Host B sends packets destined to Host A via its
network interface connected to non-IRON EUN B. Interdomain routing
will direct the packets to Relay(A), which then forwards them to
Server(A).Server(A) will then check its forwarding table to discover an
entry that covers destination address A with Client(A) as the next
hop. Server(A) then (re-)encapsulates the packets and forwards them
into the Internetwork, where routing will direct them to Client(A).
Client(A) will, in turn, decapsulate the packets and forward the
inner packets to Host A via its network interface connected to IRON
EUN A. depicts the IRON reference operating
scenario for packets flowing between Host A in an IRON instance A and
Host B in a different IRON instance B. In that case, forwarding
between hosts A and B always involves the Servers and Relays of both
IRON instances, i.e., the scenario is no different than if one of the
hosts was serviced by an IRON EUN and the other was serviced by a
non-IRON EUN. While IRON Servers and Relays are typically arranged as fixed
infrastructure, Clients may need to move between different network
points of attachment, connect to multiple ISPs, or explicitly manage
their traffic flows. The following sections discuss mobility,
multihoming, and traffic engineering considerations for IRON
Clients.When a Client changes its network point of attachment (e.g., due to
a mobility event), it configures one or more new locators. If the
Client has not moved far away from its previous network point of
attachment, it simply informs its connected Server and any Client
neighbors of any locator changes. This operation is performance
sensitive and should be conducted immediately to avoid packet loss.
This aspect of mobility can be classified as a "localized mobility
event".If the Client has moved far away from its previous network point of
attachment, however, it re-issues the Server discovery procedure
described in Section 6.3. If the Client's current Server is no longer
close by, the Client may wish to move to a new Server in order to
reduce routing stretch. This operation is not performance critical,
and therefore can be conducted over a matter of minutes/seconds
instead of milliseconds/microseconds. This aspect of mobility can be
classified as a "global mobility event".To move to a new Server, the Client first engages in the CP
registration process with the new Server, as described in Section 6.3.
The Client then informs its former Server that it has departed; again,
via a VSP-specific secured reliable transport connection. The former
Server will then withdraw its CP advertisements from the IRON instance
routing system and retain the (stale) forwarding table entries until
their lifetime expires. In the interim, the former Server continues to
deliver packets to the Client's last-known locator addresses for the
short term while informing any unidirectional tunnel neighbors that
the Client has moved.Note that the Client may be either a mobile host or a mobile
router. In the case of a mobile router, the Client's EUN becomes a
mobile network, and can continue to use the Client's CPs without
renumbering even as it moves between different network attachment
points.A Client may register multiple ISP connections with each Server
such that multiple interfaces are naturally supported. This feature
results in the Client "harnessing" its multiple ISP connections into a
"bundle" that is represented as a single entity at the network layer,
and therefore allows for ISP independence at the link-layer.A Client may further register with multiple Servers for fault
tolerance and reduced routing stretch. In that case, the Client should
register its full bundle of ISP connections with each of its Servers
unless it has a reason for carefully coordinating its individual
ISP-to-Server mappings.Client registration with multiple Servers results in
"pseudo-multihoming", in which the multiple homes are within the same
VSP IRON instance and hence share fate with the health of the IRON
instance itself.A Client can dynamically adjust its ISP-to-Server mappings in order
to influence inbound traffic flows. It can also change between Servers
when multiple Servers are available, but should strive for stability
in its Server selection in order to limit VSP network routing
churn.A Client can select outgoing ISPs, e.g., based on current
Quality-of-Service (QoS) considerations such as minimizing delay or
variance.As new link-layer technologies and/or service models emerge, end
users will be motivated to select their basic Internetwork connectivity
solutions through healthy competition between ISPs. If an end user's
network-layer addresses are tied to a specific ISP, however, they may be
forced to undergo a painstaking renumbering even if they wish to change
to a different ISP .When an end user Client obtains CPs from a VSP, it can change between
ISPs seamlessly and without need to renumber the CPs. IRON therefore
provides ISP independence at the link layer. If the end user is later
compelled to change to a different VSP, however, it would be obliged to
abandon its CPs and obtain new ones from the new VSP. In that case, the
Client would again be required to engage in a painstaking renumbering
event.In order to avoid any future renumbering headaches, a Client that is
part of a cooperative collective (e.g., a large enterprise network)
could join together with the collective to obtain a suitably large PI
prefix then and hire a VSP to manage the prefix on behalf of the
collective. If the collective later decides to switch to a new VSP, it
simply revokes its PI prefix registration with the old VSP and activates
its registration with the new VSP.The Internet today consists of a global public IPv4 routing and
addressing system with non-IRON EUNs that use either public or private
IPv4 addressing. The latter class of EUNs connect to the public Internet
via Network Address Translators (NATs). When an IRON Client is located
behind a NAT, it selects Servers using the same procedures as for
Clients with public addresses and can then send SRS messages to Servers
in order to get SRA messages in return. The only requirement is that the
Client must configure its encapsulation format to use a transport
protocol that supports NAT traversal, e.g., UDP, TCP, etc.Since the Server maintains state about its dependent Clients, it can
discover locator information for each Client by examining the transport
port number and IP address in the outer headers of the Client's
encapsulated packets. When there is a NAT in the path, the transport
port number and IP address in each encapsulated packet will correspond
to state in the NAT box and might not correspond to the actual values
assigned to the Client. The Server can then encapsulate packets destined
to hosts in the Client's EUN within outer headers that use this IP
address and transport port number. The NAT box will receive the packets,
translate the values in the outer headers, then forward the packets to
the Client. In this sense, the Server's "locator" for the Client
consists of the concatenation of the IP address and transport port
number.In order to keep NAT and Server connection state alive, the Client
sends periodic beacons to the server, e.g., by sending an SRS message to
elicit an SRA message from the Server. IRON does not otherwise introduce
any new complications for NAT traversal or for applications embedding
address referrals in their payload.IRON Servers and Relays are topologically positioned to provide
Internet Group Management Protocol (IGMP) / Multicast Listener Discovery
(MLD) proxying for their Clients . Further
multicast considerations for IRON (e.g., interactions with multicast
routing protocols, traffic scaling, etc.) are out of scope and will be
discussed in a future document.Each Client configures a locator that may be taken from an ordinary
non-CPA address assigned by an ISP or from a CPA address taken from a CP
assigned to another Client. In that case, the Client is said to be
"nested" within the EUN of another Client, and recursive nestings of
multiple layers of encapsulations may be necessary.For example, in the network scenario depicted in , Client(A) configures a locator CPA(B) taken from the CP
assigned to EUN(B). Client(B) in turn configures a locator CPA(C) taken
from the CP assigned to EUN(C). Finally, Client(C) configures a locator
ISP(D) taken from a non-CPA address delegated by an ordinary ISP(D).Using this example, the "nested-IRON" case must be examined in which
a Host A, which configures the address CPA(A) within EUN(A), exchanges
packets with Host Z located elsewhere in a different IRON instance
EUN(Z).The two cases of Host A sending packets to Host Z, and Host Z sending
packets to Host A, must be considered separately, as described
below.Host A first forwards a packet with source address CPA(A) and
destination address Z into EUN(A). Routing within EUN(A) will direct
the packet to Client(A), which encapsulates it in an outer header with
CPA(B) as the outer source address and Server(A) as the outer
destination address then forwards the once-encapsulated packet into
EUN(B).Routing within EUN(B) will direct the packet to Client(B), which
encapsulates it in an outer header with CPA(C) as the outer source
address and Server(B) as the outer destination address then forwards
the twice-encapsulated packet into EUN(C). Routing within EUN(C) will
direct the packet to Client(C), which encapsulates it in an outer
header with ISP(D) as the outer source address and Server(C) as the
outer destination address. Client(C) then sends this
triple-encapsulated packet into the ISP(D) network, where it will be
routed via the Internetwork to Server(C).When Server(C) receives the triple-encapsulated packet, it forwards
it to Relay(C) which removes the outer layer of encapsulation and
forwards the resulting twice-encapsulated packet into the Internetwork
to Server(B). Next, Server(B) forwards the packet to Relay(B) which
removes the outer layer of encapsulation and forwards the resulting
once-encapsulated packet into the Internetwork to Server(A). Next,
Server(A) forwards the packet to Relay(A), which decapsulates it and
forwards the resulting inner packet via the Internetwork to Relay(Z).
Relay(Z), in turn, forwards the packet to Server(Z), which
encapsulates and forwards the packet to Client(Z), which decapsulates
it and forwards the inner packet to Host Z.When Host Z sends a packet to Host A, forwarding in EUN(Z) will
direct it to Client(Z), which encapsulates and forwards the packet to
Server(Z). Server(Z) will forward the packet to Relay(Z), which will
then decapsulate and forward the inner packet into the Internetwork.
Interdomain will convey the packet to Relay(A) as the next-hop towards
CPA(A), which then forwards it to Server(A).Server (A) encapsulates the packet and forwards it to Relay(B) as
the next-hop towards CPA(B) (i.e., the locator for CPA(A)). Relay(B)
then forwards the packet to Server(B), which encapsulates it a second
time and forwards it to Relay(C) as the next-hop towards CPA(C) (i.e.,
the locator for CPA(B)). Relay(C) then forwards the packet to
Server(C), which encapsulates it a third time and forwards it to
Client(C).Client(C) then decapsulates the packet and forwards the resulting
twice-encapsulated packet via EUN(C) to Client(B). Client(B) in turn
decapsulates the packet and forwards the resulting once-encapsulated
packet via EUN(B) to Client(A). Client(A) finally decapsulates and
forwards the inner packet to Host A.For IRON instances configured over the public Internet as the
underlying Internetwork, the IRON system requires a VSP deployment of
new routers/servers throughout the Internet to maintain well-balanced
virtual overlay networks. These routers/servers can be deployed
incrementally without disruption to existing Internet infrastructure as
long as they are appropriately managed to provide acceptable service
levels to end users.End-to-end traffic that traverses an IRON instance may experience
delay variance between the initial packets and subsequent packets of a
flow. This is due to the IRON system allowing a longer path stretch for
initial packets followed by timely route optimizations to utilize better
next hop routers/servers for subsequent packets.IRON instances work seamlessly with existing and emerging services
within the native Internet. In particular, end users serviced by an IRON
instance will receive the same service enjoyed by end users serviced by
non-IRON service providers. Internet services already deployed within
the native Internet also need not make any changes to accommodate IRON
end users.The IRON system operates between IAs within the Internet and EUNs.
Within these networks, the underlying paths traversed by the virtual
overlay networks may comprise links that accommodate varying MTUs. While
the IRON system imposes an additional per-packet overhead that may cause
the size of packets to become slightly larger than the underlying path
can accommodate, IAs have a method for naturally detecting and tuning
out instances of path MTU underruns. In some cases, these MTU underruns
may need to be reported back to the original hosts; however, the system
will also allow for MTUs much larger than those typically available in
current Internet paths to be discovered and utilized as more links with
larger MTUs are deployed.Finally, and perhaps most importantly, the IRON system provides
in-built mobility management, mobile networks, multihoming and traffic
engineering capabilities that allow end user devices and networks to
move about freely while both imparting minimal oscillations in the
routing system and maintaining generally shortest-path routes. This
mobility management is afforded through the very nature of the IRON
service model, and therefore requires no adjunct mechanisms. The
mobility management and multihoming capabilities are further supported
by forward-path reachability detection that provides "hints of forward
progress" in the same spirit as for IPv6 Neighbor Discovery (ND).Considerations for the scalability of interdomain routing due to
multihoming, traffic engineering, and provider-independent addressing
are discussed in . Other scaling
considerations specific to IRON are discussed in Appendix B.Route optimization considerations for mobile networks are found in
.In order to ensure acceptable end user service levels, the VSP should
conduct a capacity analysis and distribute sufficient Relays and Servers
for the IRON instance globally throughout the Internet. As for common
practices in the Internet today, such capacity analysis can be conducted
in parallel with actual deployment of the service.IRON builds upon the concepts of the RANGER architecture , and therefore inherits the same set of related
initiatives. The Internet Research Task Force (IRTF) Routing Research
Group (RRG) mentions IRON in its recommendation for a routing
architecture .Virtual Aggregation (VA) and Aggregation in
Increasing Scopes (AIS) provide the basis for
the Virtual Prefix concepts.Internet Vastly Improved Plumbing (Ivip)
has contributed valuable insights, including the use of real-time
mapping. The use of Servers as mobility anchor points is directly
influenced by Ivip's associated TTR mobility extensions .
discusses a route optimization approach using a Correspondent Router
(CR) model. The IRON Server construct is similar to the CR concept
described in this work; however, the manner in which Clients coordinate
with Servers is different and based on the NBMA virtual link model .Numerous publications have proposed NAT traversal techniques. The NAT
traversal techniques adapted for IRON were inspired by the Simple
Address Mapping for Premises Legacy Equipment (SAMPLE) proposal .The IRON Client-Server relationship is managed in essentially the
same way as for the Tunnel Broker model .
Numerous existing provider networks that provide service similar to
tunnel broker (e.g., Hurricane Electric, SixXS, freenet6, etc.) provide
existence proofs that IRON-like overlay network services can be deployed
and managed on a global basis .IRON is further related to the Identifier-Locator Network Protocol
(ILNP) and Locator / ID Split Protocol (LISP)
proposals which address routing scaling aspects
at the interdomain level. IRON is therefore complimentary to these
approaches.There are no IANA considerations for this document.Security considerations that apply to tunneling in general are
discussed in . Additional considerations that
apply also to IRON are discussed in RANGER , VET and SEAL .The IRON system further depends on mutual authentication of IRON
Clients to Servers and Servers to Relays. As for all Internet
communications, the IRON system also depends on Relays acting with
integrity and not injecting false advertisements into the interdomain
routing system (e.g., to mount traffic siphoning attacks).IRON Agents must perform message origin authentication on the packets
they accept from correspondents. IAs must therefore include a signature
on each packet that the destination can use to verify that the IA is
authorized to use the source address.IRON Servers must ensure that any changes in a Client's locator
addresses are communicated only through an authenticated exchange that
is not subject to replay. For this reason, Clients periodically send
digitally-signed SRS messages to the Server. If the Client's locator
address stays the same, the Server can accept the SRS message without
verifying the signature. If the Client's locator address changes, the
Server must verify the SRS message's signature before accepting the
message. Once the message has been authenticated, the Server updates the
Client's locator address to the new address.Each IRON instance requires a means for assuring the integrity of the
interior routing system so that all Relays and Servers in the overlay
have a consistent view of CP<->Server bindings. Also,
Denial-of-Service (DoS) attacks on IRON Relays and Servers can occur
when packets with spoofed source addresses arrive at high data rates.
However, this issue is no different than for any border router in the
public Internet today.Middleboxes can interfere with tunneled packets within an IRON
instance in various ways. For example, a middlebox may alter a packet's
contents, change a packet's locator addresses, inject spurious packets,
replay old packets, etc. These issues are no different than for
middlebox interactions with ordinary Internet communications. If
man-in-the-middle attacks are a matter for concern in certain
deployments, however, IRON Agents can use IPsec
or TLS/SSL to protect the authenticity,
integrity and (if necessary) privacy of their tunneled packets.The ideas behind this work have benefited greatly from discussions
with colleagues; some of which appear on the RRG and other IRTF/IETF
mailing lists. Robin Whittle and Steve Russert co-authored the TTR
mobility architecture, which strongly influenced IRON. Eric Fleischman
pointed out the opportunity to leverage anycast for discovering
topologically close Servers. Thomas Henderson recommended a quantitative
analysis of scaling properties.The following individuals provided essential review input: Jari
Arkko, Mohamed Boucadair, Stewart Bryant, John Buford, Ralph Droms,
Wesley Eddy, Adrian Farrel, Dae Young Kim, and Robin Whittle.Discussions with colleagues following the publication of RFC6179 have
provided useful insights that have resulted in significant improvements
to this, the Second Edition of IRON.This document received substantial review input from the IESG and
IETF area directorates in the February 2013 timeframe. IESG members and
IETF area directorate representatives who contributed helpful comments
and suggestions are gratefully acknowledged.The Subnetwork Encapsulation and Adaptation Layer
(SEAL)For the purpose of this document, a subnetwork is defined as a
virtual topology configured over a connected IP network routing
region and bounded by encapsulating border nodes. These virtual
topologies are manifested by tunnels that may span multiple IP
and/or sub-IP layer forwarding hops, and can introduce failure
modes due to packet duplication and/or links with diverse Maximum
Transmission Units (MTUs). This document specifies a Subnetwork
Encapsulation and Adaptation Layer (SEAL) that accommodates such
virtual topologies over diverse underlying link technologies.Virtual Enterprise Traversal (VET)Enterprise networks connect hosts and routers over various link
types, and often also connect to provider networks and/or the
global Internet. Enterprise network nodes require a means to
automatically provision addresses/prefixes and support
internetworking operation in a wide variety of use cases including
Small Office, Home Office (SOHO) networks, Mobile Ad hoc Networks
(MANETs), ISP networks, multi-organizational corporate networks
and the interdomain core of the global Internet itself. This
document specifies a Virtual Enterprise Traversal (VET)
abstraction for autoconfiguration and operation of nodes in
enterprise networks.FIB Suppression with Virtual AggregationThe continued growth in the Default Free Routing Table (DFRT)
stresses the global routing system in a number of ways. One of the
most costly stresses is FIB size: ISPs often must upgrade router
hardware simply because the FIB has run out of space, and router
vendors must design routers that have adequate FIB. FIB
suppression is an approach to relieving stress on the FIB by NOT
loading selected RIB entries into the FIB. Virtual Aggregation
(VA) allows ISPs to shrink the FIBs of any and all routers, easily
by an order of magnitude with negligible increase in path length
and load. FIB suppression deployed autonomously by an ISP
(cooperation between ISPs is not required), and can co-exist with
legacy routers in the ISP. There are no changes from the 03
version.Evolution Towards Global Routing ScalabilityInternet routing scalability has long been considered a serious
problem. Although many efforts have been devoted to address this
problem over the years, the IETF community as a whole is yet to
achieve a shared understanding on what is the best way forward. In
this draft, we step up a level to re-examine the problem and the
ongoing efforts. we conclude that, to effectively solve the
routing scalability problem, we first need a clear understanding
on how to introduce solutions to the Internet which is a global
scale deployed system. In this draft we sketch out our reasoning
on the need for an evolutionary path towards scaling the global
routing system, instead of attempting to introduce a brand new
design.Ivip (Internet Vastly Improved Plumbing) ArchitectureIvip (Internet Vastly Improved Plumbing) is a Core-Edge
Separation solution to the routing scaling problem, for both IPv4
and IPv6. It provides portable address "edge" address space which
is suitable for multihoming and inbound traffic engineering (TE)
to end-user networks of all types and sizes - in a manner which
imposes far less load on the DFZ control plane than the only
current method of achieving these benefits: separately advertised
PI prefixes. Ivip includes two extensions for ITR-to-ETR tunneling
without encapsulation and the Path MTU Discovery problems which
result from encapsulation - one for IPv4 and the other for IPv6.
Both involve modifying the IP header and require most DFZ routers
to be upgraded. Ivip is a good basis for the TTR (Translating
Tunnel Router) approach to mobility, in which mobile hosts retain
an SPI micronet of one or more IPv4 addresses (or IPv6 /64s) no
matter what addresses or access network they are using, including
behind NAT and on SPI addresses. TTR mobility for both IPv4 and
IPv6 involves generally optimal paths, works with unmodified
correspondent hosts and supports all application protocols.On the Scalability of Internet RoutingThere has been much discussion over the last years about the
overall scalability of the Internet routing system. Some have
argued that the resources required to maintain routing tables in
the core of the Internet are growing faster than available
technology will be able to keep up. Others disagree with that
assessment. This document attempts to describe the factors that
are placing pressure on the routing system and the growth trends
behind those factors.Legacy NAT Traversal for IPv6: Simple Address Mapping for
Premises Legacy Equipment (SAMPLE)IPv6 deployment is delayed by the existence of millions of
subscriber network address translators (NATs) that cannot be
upgraded to support IPv6. This document specifies a mechanism for
traversal of such NATs. It is based on an address mapping and on a
mechanism whereby suitably upgraded hosts behind a NAT may obtain
IPv6 connectivity via a stateless server, known as a SAMPLE
server, operated by their Internet Service Provider. SAMPLE is an
alternative to the Teredo protocol.Correspondent Router based Route Optimisation for NEMO
(CRON)The Network Mobility Basic Support protocol enables networks to
roam and attach to different access networks without disrupting
the ongoing sessions that nodes of the network may have. By
extending the Mobile IPv6 support to Mobile Routers, nodes of the
network are not required to support any kind of mobility, since
packets must go through the Mobile Router-Home Agent (MRHA)
bi-directional tunnel. Communications from/to a mobile network
have to traverse the Home Agent, and therefore better paths may be
available. Additionally, this solution adds packet overhead, due
to the encapsulation. This document describes an approach to the
Route Optimisation for NEMO, based on the well-known concept of
Correspondent Router. The solution aims at meeting the currently
identified NEMO Route Optimisation requirements for Operational
Use in Aeronautics and Space Exploration. Based on the ideas that
have been proposed in the past, as well as some other extensions,
this document describes a Correspondent Router based solution,
trying to identify the most important open issues. The main goal
of this first version of the document is to describe an initial
NEMO RO solution based on the deployment of Correspondent Routers
and trigger the discussion within the MEXT WG about this kind of
solution. This document (in an appendix) also analyses how a
Correspondent Router based solution fits each of the currently
identified NEMO Route Optimisation requirements for Operational
Use in Aeronautics and Space Exploration.BGPmon.net - Monitoring Your Prefixes,
http://bgpmon.net/stat.phpTTR Mobility Extensions for Core-Edge Separation Solutions to
the Internet's Routing Scaling Problem,
http://www.firstpr.com.au/ip/ivip/TTR-Mobility.pdfList of IPv6 Tunnel Brokers,
http://en.wikipedia.org/wiki/List_of_IPv6_tunnel_brokersThe IRON architecture leverages the routing system by providing
generally shortest-path routing for packets with CPA addresses from APs
that match the address family of the underlying Internetwork. When the
APs are of an address family that is not routable within the underlying
Internetwork, however, (e.g., when OSI/NSAP APs
are used over an IPv4 Internetwork) a global Master AP mapping database
(MAP) is required. The MAP allows the Relays of the local IRON instance
to map APs belonging to other IRON instances to addresses taken from
companion prefixes of address families that are routable within the
Internetwork. For example, an IPv6 AP (e.g., 2001:DB8::/32) could be
paired with one or more companion IPv4 prefixes (e.g., 192.0.2.0/24) so
that encapsulated IPv6 packets can be forwarded over IPv4-only
Internetworks. (In the limiting case, the companion prefixes could
themselves be singleton addresses, e.g., 192.0.2.1/32).The MAP is maintained by a globally managed authority, e.g. in the
same manner as the Internet Assigned Numbers Authority (IANA) currently
maintains the master list of all top-level IPv4 and IPv6 delegations.
The MAP can be replicated across multiple servers for load balancing
using common Internetworking server hierarchies, e.g., the DNS caching
resolvers, ftp mirror servers, etc.Upon startup, each Relay advertises IPv4 companion prefixes (e.g.,
192.0.2.0/24) into the IPv4 Internetwork routing system and/or IPv6
companion prefixes (e.g., 2001:DB8::/64) into the IPv6 Internetwork
routing system for the IRON instance that it serves. The Relay then
selects singleton host numbers within the IPv4 companion prefixes (e.g.,
192.0.2.1) and/or IPv6 companion prefixes (e.g., as 2001:DB8::0), and
assigns the resulting addresses to its Internetwork interfaces. (When
singleton companion prefixes are used (e.g., 192.0.2.1/32), the Relay
does not advertise a the companion prefixes but instead simply assigns
them to its Internetwork interfaces and allows standard Internet routing
to direct packets to the interfaces.)The Relay then discovers the APs for other IRON instances by reading
the MAP, either a priori or on-demand of data packets addressed to other
AP destinations. The Relay reads the MAP from a nearby MAP server and
periodically checks the server for deltas since the database was last
read. The Relay can then forward packets toward CPAs belonging to other
IRON instances by encapsulating them in an outer header of the companion
prefix address family and using the Relay anycast address as the outer
destination address.Possible encapsulations in this model include IPv6-in-IPv4,
IPv4-in-IPv6, OSI/CLNP-in-IPv6, OSI/CLNP-in-IPv4, etc. Details of how
the DNS can be used as a MAP are given in Section 5.4 of VET .Scaling aspects of the IRON architecture have strong implications for
its applicability in practical deployments. Scaling must be considered
along multiple vectors, including interdomain core routing scaling,
scaling to accommodate large numbers of EUNs, traffic scaling, state
requirements, etc.In terms of routing scaling, each VSP will advertise one or more APs
into the interdomain routing system from which CPs are delegated to end
users. Routing scaling will therefore be minimized when each AP covers
many CPs. For example, the IPv6 prefix 2001:DB8::/32 contains 2^24 ::/56
CP prefixes for assignment to EUNs; therefore, the VSP could accommodate
2^32 ::/56 CPs with only 2^8 ::/32 APs advertised in the interdomain
routing core. (When even longer CP prefixes are used, e.g., /64s
assigned to individual handsets in a cellular provider network, many
more EUNs can be represented within only a single AP.)In terms of traffic scaling for Relays, each Relay represents an ASBR
of a "shell" enterprise network that simply directs arriving traffic
packets with CPA destination addresses towards Servers that service the
corresponding Clients. Moreover, the Relay sheds traffic destined to
CPAs through redirection, which removes it from the path for the
majority of traffic packets between Clients within the same IRON
instance. On the other hand, each Relay must handle all traffic packets
forwarded between the CPs it manages and the rest of the Internetwork.
The scaling concerns for this latter class of traffic are no different
than for ASBR routers that connect large enterprise networks to the
Internet. In terms of traffic scaling for Servers, each Server services
a set of CPs. The Server services all traffic packets destined to its
own CPs but only services the initial packets of flows initiated from
its own CPs and destined to other CPs. Therefore, traffic scaling for
CPA-addressed traffic is an asymmetric consideration and is proportional
to the number of CPs each Server serves. When possible, the Server can
also be removed from the path in order to allow direct Client-to-Client
communications as described in Section 8.1.3. In that case, the Server's
burden in handling data packets is greatly reduced.In terms of state requirements for Relays, each Relay maintains a
list of Servers in the IRON instance as well as forwarding table entries
for the CPs that each Server handles. This Relay state is therefore
dominated by the total number of CPs handled by the Relay's associated
Servers. Keeping in mind that current day core router technologies are
only capable of handling fast-path FIB cache sizes of O(1M) entries, a
large-scale deployment may require that the total CP database for the
VSP overlay be spread between the FIBs of a mesh of Relays rather than
fully-resident in the FIB of each Relay. In that case, the techniques of
Virtual Aggregation (VA) may be useful in bridging together the mesh of
Relays. Alternatively, each Relay could elect to keep some or all CP
prefixes out of the FIB and maintain them only in a slow-path forwarding
table. In that case, considerably more CP entries could be kept in each
Relay at the cost of incurring slow-path processing for the initial
packets of a flow.In terms of state requirements for Servers, each Server maintains
state only for the CPs it serves, and not for the CPs handled by other
Servers in the IRON instance. Finally, neither Relays nor Servers need
keep state for final destinations of outbound traffic.Clients source and sink all traffic packets originating from or
destined to the CP. Therefore, traffic scaling considerations for
Clients are the same as for any site border router. Clients also retain
tunnel neighbor state for final destinations of outbound traffic flows.
This can be managed as soft state, since stale entries purged from the
cache will be refreshed when new traffic packets are sent.