One document matched: draft-templin-ironbis-02.xml
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<front>
<title abbrev="IRON">The Internet Routing Overlay Network (IRON)</title>
<author fullname="Fred L. Templin" initials="F." role="editor"
surname="Templin">
<organization>Boeing Research & Technology</organization>
<address>
<postal>
<street>P.O. Box 3707 MC 7L-49</street>
<city>Seattle</city>
<region>WA</region>
<code>98124</code>
<country>USA</country>
</postal>
<email>fltemplin@acm.org</email>
</address>
</author>
<date day="19" month="August" year="2011" />
<workgroup>Network Working Group</workgroup>
<keyword>I-D</keyword>
<keyword>Internet-Draft</keyword>
<abstract>
<t>Since the Internet must continue to support escalating growth due to
increasing demand, it is clear that current routing architectures and
operational practices must be updated. This document proposes an
Internet Routing Overlay Network (IRON) architecture that supports
sustainable growth while requiring no changes to end systems and no
changes to the existing routing system. IRON further addresses other
important issues including routing scaling, mobility management, mobile
networks, multihoming, traffic engineering and NAT traversal. While
business considerations are an important determining factor for
widespread adoption, they are out of scope for this document.</t>
</abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t>Growth in the number of entries instantiated in the Internet routing
system has led to concerns regarding unsustainable routing scaling <xref
target="RADIR"></xref>. Operational practices such as the increased use
of multihoming with Provider-Independent (PI) addressing are resulting
in more and more fine-grained prefixes being injected into the routing
system from more and more end user networks. Furthermore, depletion of
the public IPv4 address space has raised concerns for both increased
address space fragmentation (leading to yet further routing table
entries) and an impending address space run-out scenario. At the same
time, the IPv6 routing system is beginning to see growth <xref
target="BGPMON"></xref> 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 routing methodologies and operational practices are needed.</t>
<t>Several related works have investigated routing scaling issues.
Virtual Aggregation (VA) <xref target="GROW-VA"></xref> and Aggregation
in Increasing Scopes (AIS) <xref target="EVOLUTION"></xref> 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) <xref target="RFC5720"></xref> examines recursive arrangements
of enterprise networks that can apply to a very broad set of use-case
scenarios <xref target="RFC6139"></xref>. IRON specifically adopts the
RANGER Non-Broadcast, Multiple Access (NBMA) tunnel virtual-interface
model, and uses Virtual Enterprise Traversal (VET) <xref
target="INTAREA-VET"></xref> and the Subnetwork Adaptation and
Encapsulation Layer (SEAL) <xref target="INTAREA-SEAL"></xref> as its
functional building blocks.</t>
<t>This document proposes an Internet Routing Overlay Network (IRON)
architecture with goals of supporting scalable routing and addressing
while requiring no changes to the Internet's Border Gateway Protocol
(BGP) routing system <xref target="RFC4271"></xref>. IRON observes the
Internet Protocol standards <xref target="RFC0791"></xref><xref
target="RFC2460"></xref>, while other network-layer protocols that can
be encapsulated within IP packets (e.g., OSI/CLNP (Connectionless
Network Protocol) <xref target="RFC1070"></xref>, etc.) are also within
scope.</t>
<t>IRON borrows concepts from VA and AIS, and further borrows concepts
from the Internet Vastly Improved Plumbing (Ivip) <xref
target="IVIP-ARCH"></xref> architecture proposal along with its
associated Translating Tunnel Router (TTR) mobility extensions <xref
target="TTRMOB"></xref>. 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 <xref
target="SAMPLE"></xref>.</t>
<t>IRON is a global virtual routing system comprising Virtual Service
Provider (VSP) overlay networks that service Virtual Prefixes (VPs) from
which End User Network (EUN) prefixes (EPs) are delegated to customer
sites. IRON is motivated by a growing customer demand for mobility
management, mobile networks, multihoming and traffic engineering while
using stable addressing to minimize dependence on network renumbering
<xref target="RFC4192"></xref><xref target="RFC5887"></xref>. IRON VSP
overlay network instances use the existing IPv4 and IPv6 global Internet
routing systems as virtual NBMA links for tunneling inner network
protocol packets within outer IPv4 or IPv6 headers (see Section 3). Each
IRON instance requires deployment of a small number of new Autonomous
System Border Routers (ASBRs) and supporting servers, as well as
IRON-aware clients that connect customer EUNs. No modifications to
hosts, and no modifications to most routers, are required. The following
sections discuss details of the IRON architecture.</t>
</section>
<section title="Terminology">
<t>This document makes use of the following terms:</t>
<t><list style="hanging">
<t hangText="End User Network (EUN):"><vspace />an edge network that
connects an organization's devices (e.g., computers, routers,
printers, etc.) to the Internet. IRON EUNs are mobile networks, and
can change their ISP attachments without having to renumber.</t>
<t hangText="End User Network Prefix (EP):"><vspace />a more
specific inner network-layer prefix (e.g., an IPv4 /28, an IPv6 /56,
etc.) derived from an aggregated Virtual Prefix (VP) and delegated
to an EUN by a Virtual Service Provider (VSP).</t>
<t hangText="End User Network Prefix Address (EPA):"><vspace />a
network-layer address belonging to an EP and assigned to the
interface of an end system in an EUN.</t>
<t hangText="Forwarding Information Base (FIB):"><vspace />a data
structure containing network prefixes to next-hop mappings; usually
maintained in a router's fast-path processing lookup tables.</t>
<t hangText="Internet Routing Overlay Network (IRON):"><vspace />the
union of all VSP overlay network instances. Each such IRON instance
supports routing within the overlay through encapsulation of inner
packets with EPA addresses within outer headers that use locator
addresses. Each IRON instance connects to the global Internet the
same as for any Autonomous System (AS).</t>
<t
hangText="IRON Client Router/Host ("Client"):"><vspace />a
customer's router or host that logically connects the customer's
EUNs and their associated EPs to an IRON instance via an NBMA tunnel
virtual interface.</t>
<t hangText="IRON Serving Router ("Server"):"><vspace />a
VSP's IRON instance router that provides forwarding and mapping
services for the EPs owned by customer Clients.</t>
<t hangText="IRON Relay Router ("Relay"):"><vspace />a
VSP's IRON instance router that acts as a relay between the IRON and
the native Internet.</t>
<t hangText="IRON Agent (IA):"><vspace />generically refers to any
of an IRON Client/Server/Relay.</t>
<t hangText="IRON Instance:"><vspace />a set of IRON Agents deployed
by a VSP to service customer EUNs through automatic tunneling over
an underlying Internetwork (e.g., the global Internet).</t>
<t hangText="Internet Service Provider (ISP):"><vspace />a service
provider that connects customer EUNs to the underlying Internetwork.
In other words, an ISP is responsible for providing basic Internet
connectivity for customer EUNs.</t>
<t hangText="Locator"><vspace />an IP address assigned to the
interface of a router or end system within a public or private
network. Locators taken from public IP prefixes are routable on a
global basis, while locators taken from private IP prefixes
<xref target="RFC1918"></xref> are made public via Network
Address Translation (NAT).</t>
<t
hangText="Routing and Addressing in Networks with Global Enterprise Recursion (RANGER):"><vspace />
an architectural examination of virtual overlay networks applied to
enterprise network scenarios, with implications for a wider variety
of use cases.</t>
<t
hangText="Subnetwork Encapsulation and Adaptation Layer (SEAL):"><vspace />an
encapsulation sublayer that provides extended packet identification
and a Control Message Protocol to ensure deterministic network-layer
feedback.</t>
<t hangText="Virtual Enterprise Traversal (VET):"><vspace />a method
for discovering border routers and forming dynamic tunnel-neighbor
relationships over enterprise networks (or sites) with varying
properties.</t>
<t hangText="Virtual Prefix (VP):"><vspace />a large prefix block
(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).</t>
<t hangText="Virtual Service Provider (VSP):"><vspace />a company
that owns and manages a set of VPs from which it delegates EPs to
EUNs.</t>
<t hangText="VSP Overlay Network:"><vspace />the same as defined
above for IRON Instance.</t>
</list></t>
</section>
<section anchor="iron" title="The Internet Routing Overlay Network">
<t>The Internet Routing Overlay Network (IRON) is a union of Virtual
Service Provider (VSP) overlay networks (also known as "IRON instances")
configured over a common Internetwork. IRON provides a number of
important services to End User Networks (EUNs) that are not well
supported in the current Internet architecture, including routing
scaling, mobility management, mobile networks, multihoming, traffic
engineering and NAT traversal. While the principles presented in this
document are discussed within the context of the public global Internet,
they can also be applied to any autonomous Internetwork. The rest of
this document therefore refers to the terms "Internet" and
"Internetwork" interchangeably except in cases where specific
distinctions must be made.</t>
<t>Each IRON instance consists of IRON Agents (IAs) that automatically
tunnel the packets of end-to-end communication sessions within
encapsulating headers used for Internet routing. IAs use the Virtual
Enterprise Traversal (VET) <xref target="INTAREA-VET"></xref> virtual
NBMA link model in conjunction with the Subnetwork Encapsulation and
Adaptation Layer (SEAL) <xref target="INTAREA-SEAL"></xref> to
encapsulate inner network-layer packets within outer headers, as shown
in <xref target="encaps"></xref>.</t>
<t><figure anchor="encaps"
title="Encapsulation of Inner Packets within Outer IP Headers">
<artwork><![CDATA[ +-------------------------+
| Outer headers with |
~ locator addresses ~
| (IPv4 or IPv6) |
+-------------------------+
| SEAL Header |
+-------------------------+ +-------------------------+
| Inner Packet Header | --> | Inner Packet Header |
~ with EP addresses ~ --> ~ with EP addresses ~
| (IPv4, IPv6, OSI, etc.) | --> | (IPv4, IPv6, OSI, etc.) |
+-------------------------+ +-------------------------+
| | --> | |
~ Inner Packet Body ~ --> ~ Inner Packet Body ~
| | --> | |
+-------------------------+ +-------------------------+
Inner packet before Outer packet after
encapsulation encapsulation]]></artwork>
</figure></t>
<t>VET specifies the automatic tunneling mechanisms used for
encapsulation, while SEAL specifies the format and usage of the SEAL
header as well as a set of control messages. Most notably, IAs use the
SEAL Control Message Protocol (SCMP) to deterministically exchange and
authenticate control messages such as router solicitations, route
redirections, indications of Path Maximum Transmission Unit (PMTU)
limitations, destination unreachables, etc. IAs appear as neighbors on
an NBMA tunnel virtual link.</t>
<t>Each IRON instance comprises a set of IAs distributed throughout the
Internet to serve highly aggregated Virtual Prefixes (VPs). VSPs
delegate sub-prefixes from their VPs, which they provide to customers as
End User Network Prefixes (EPs). In turn, the customers assign the EPs
to their customer edge IAs, which connect their End User Networks (EUNs)
to the VSP IRON instance.</t>
<t>VSPs may have no affiliation with the ISP networks from which
customers obtain their basic Internet connectivity. Therefore, a
customer could procure its summary network and data link services either
through a common provider or through separate entities. In that case,
the VSP can open for business and begin serving its customers
immediately without the need to coordinate its activities with ISPs or
other VSPs. Further details on business considerations are out of scope
for this document.</t>
<t>IRON requires no changes to end systems or to most routers in the
Internet. Instead, IAs are deployed either as new platforms or as
modifications to existing platforms. IAs may be deployed incrementally
without disturbing the existing Internet routing system, and act as
waypoints (or "cairns") for navigating VSP overly networks. The
functional roles for IAs are described in the following sections.</t>
<section title="IRON Client">
<t>An IRON client (or, simply, "Client") is a customer's router or
host that logically connects the customer's EUNs and their associated
EPs to its VSP's IRON instance via tunnels, as shown in <xref
target="IREP"></xref>. Client routers obtain EPs from their VSPs and
use them to number subnets and interfaces within their EUNs.</t>
<t>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 "connected Clients". Clients also dynamically
discover destination-specific Servers through the receipt of redirect
messages. These destination-specific Servers consider this class of
Clients as "foreign Clients".</t>
<t>A Client can be deployed on the same physical platform that also
connects the customer's EUNs to its ISPs, but it may also be a
separate router or even a standalone server system located within the
EUN. (This model applies even if the EUN connects to the ISP via a
Network Address Translator (NAT) -- see Section 6.7). Finally, a
Client may also be a simple end system that connects a singleton EUN
and exhibits the outward appearance of a host.</t>
<figure anchor="IREP"
title="IRON Client Router Connecting EUN to IRON Instance">
<artwork><![CDATA[ .-.
,-( _)-.
+--------+ .-(_ (_ )-.
| Client |--(_ ISP )
+---+----+ `-(______)-'
| <= T \ .-.
.-. u \ ,-( _)-.
,-( _)-. n .-(_ (- )-.
.-(_ (_ )-. n (_ Internet )
(_ EUN ) e `-(______)-
`-(______)-' l ___
| s => (:::)-.
+----+---+ .-(::::::::)
| Host | .-(::: IRON :::)-.
+--------+ (:::: Instance ::::)
`-(::::::::::::)-'
`-(::::::)-']]></artwork>
</figure>
<t></t>
</section>
<section title="IRON Serving Router">
<t>An IRON serving router (or, simply, "Server") is a VSP's router
that provides forwarding and mapping services within the IRON instance
for the EPs owned by customer Client routers. In typical deployments,
a VSP will deploy many Servers around the IRON instance in a globally
distributed fashion (e.g., as depicted in <xref target="IRVE"></xref>)
so that Clients can discover those that are nearby.</t>
<t><figure anchor="IRVE"
title="IRON Serving Router Global Distribution Example">
<artwork><![CDATA[ +--------+ +--------+
| Boston | | Tokyo |
| Server | | Server |
+--+-----+ ++-------+
+--------+ \ /
| Seattle| \ ___ /
| Server | \ (:::)-. +--------+
+------+-+ .-(::::::::)------+ Paris |
\.-(::: IRON :::)-. | Server |
(:::: Instance ::::) +--------+
`-(::::::::::::)-'
+--------+ / `-(::::::)-' \ +--------+
| Moscow + | \--- + Sydney |
| Server | +----+---+ | Server |
+--------+ | Cairo | +--------+
| Server |
+--------+]]></artwork>
</figure>Each Server acts as a tunnel-endpoint router. The Server
forms bidirectional tunnel-neighbor relationships with each of its
connected Clients, and also serves as the unidirectional
tunnel-neighbor egress for dynamically discovered foreign Clients.
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 Internet and vice versa, as discussed in the next
section.</t>
</section>
<section title="IRON Relay Router">
<t>An IRON Relay Router (or, simply, "Relay") is a router that
connects the VSP's IRON instance to the Internet as an Autonomous
System (AS). The Relay therefore also serves as an Autonomous System
Border Router (ASBR) that is owned and managed by the VSP.</t>
<t>Each VSP configures one or more Relays that advertise the company's
VPs into the IPv4 and IPv6 global Internet BGP routing systems. Each
Relay associates with the VSP's IRON instance Servers, e.g., via
bidirectional tunnel-neighbor relationships over the IRON instance,
via a direct interconnect such as an Ethernet cable, etc. The Relay
role is depicted in <xref target="IRGW"></xref>.</t>
<t><figure anchor="IRGW"
title="IRON Relay Router Connecting IRON Instance to Native Internet ">
<artwork><![CDATA[
.-.
,-( _)-.
.-(_ (_ )-.
(_ Internet )
`-(______)-' | +--------+
| |--| Server |
+----+---+ | +--------+
| Relay |----| +--------+
+--------+ |--| Server |
_|| | +--------+
(:::)-. (Ethernet)
.-(::::::::)
+--------+ .-(::: IRON :::)-. +--------+
| Server |=(:::: Instance ::::)=| Server |
+--------+ `-(::::::::::::)-' +--------+
`-(::::::)-'
|| (Tunnels)
+--------+
| Server |
+--------+]]></artwork>
</figure></t>
</section>
</section>
<section anchor="IBM" title="IRON Organizational Principles">
<t>The IRON consists of the union of all VSP overlay networks configured
over a common Internetwork (e.g., the public Internet). Each such IRON
instance represents a distinct "patch" on the Internet "quilt", where
the patches are stitched together by standard Internet 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.</t>
<t>Each IRON instance connects to the Internet as an AS in the BGP
routing system using a public 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 Client
customers. <xref target="VON"></xref> depicts the logical arrangement of
Relays, Servers, and Clients in an IRON instance.</t>
<t><figure anchor="VON" title="IRON Organization">
<artwork><![CDATA[ .-.
,-( _)-.
.-(_ (_ )-.
(__ Internet _)
`-(______)-'
<------------ Relays ------------>
________________________
(::::::::::::::::::::::::)-.
.-(:::::::::::::::::::::::::::::)
.-(:::::::::::::::::::::::::::::::::)-.
(::::::::::: IRON Instance :::::::::::::)
`-(:::::::::::::::::::::::::::::::::)-'
`-(::::::::::::::::::::::::::::)-'
<------------ Servers ------------>
.-. .-. .-.
,-( _)-. ,-( _)-. ,-( _)-.
.-(_ (_ )-. .-(_ (_ )-. .-(_ (_ )-.
(__ ISP A _) (__ ISP B _) ... (__ ISP x _)
`-(______)-' `-(______)-' `-(______)-'
<----------- NATs ------------>
<----------- Clients and EUNs ----------->]]></artwork>
</figure>Each Relay connects the IRON instance directly to the IPv4
and IPv6 Internets via external BGP (eBGP) peerings with neighboring
ASes. It also advertises the VSP's IPv4 VPs into the IPv4 BGP routing
system and advertises the VSP's IPv6 VPs into the IPv6 BGP routing
system. Relays will therefore receive packets with EPA destination
addresses sent by end systems in the Internet and forward them to a
server that connects the EPA-addressed end system to the VSP's IRON
instance. Finally, the IRON instance Relays maintain synchronization by
running interior BGP (iBGP) between themselves the same as for ordinary
ASBRs.</t>
<t>Each Server is configured as an ASBR for a stub AS, and uses a
private ASN <xref target="RFC1930"></xref> 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 connected Clients for which it caches EP-to-Client mappings in
its Forwarding Information Base (FIB). Each Server also, in turn,
propagates the list of EPs in its working set to its neighboring Relays
via eBGP. Therefore, each Server only needs to track the EPs for its
current working set of Clients, while each Relay will maintain a full
EP-to-Server Routing Information Base (RIB) that represents reachability
information for all EPs in the IRON instance.</t>
<t>Customer Clients obtain their basic Internet connectivity from ISPs,
and connect to VSP Servers to attach their 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. Unlike Relays and Servers, Clients may 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.</t>
<t>After the 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 redirect messages informing it of a more direct
route through a different Server within the IRON instance that serves
the final destination EUN. This foreign Server in turn provides the
Client with a unidirectional tunnel-neighbor egress for route
optimization purposes,.</t>
<t>IRON can also be used to support VPs 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 VPs of one address family over Internetworks
based on other address families are discussed in Appendix A.</t>
</section>
<section anchor="initialization" title="IRON Control Plane Operation">
<t>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.</t>
<section anchor="EUN" title="IRON Client Operation">
<t>Each Client obtains one or more EPs in a secured exchange with the
VSP as part of the initial customer signup agreement. Upon startup,
the Client connects to a location broker (e.g., a well known website
run by the VSP) to discover a list of nearby Servers.</t>
<t>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 tunnel-neighbor identifier ("NBR_ID") and a Shared
Secret that the Client will use to sign and authenticate certain
control messages. The protocol details of the transaction are specific
to the VSP, and hence out of scope for this document.</t>
<t>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 redirect messages.</t>
</section>
<section title="IRON Server Operation">
<t>Each IRON Server is provisioned with the locators for Relays within
the IRON instance. Unless the Server shares the same physical platform
as a Relay, the Server is further configured as an ASBR for a stub AS
and uses eBGP with a private ASN to peer with each Relay.</t>
<t>Upon startup, the Server connects to each Relay via eBGP peerings
for the purpose of reporting the list of EPs it is currently serving.
The Server then actively listens for Client customers that register
their EP prefixes as part of a connection establishment procedure.
When a new Client connects, the Server announces the new EP routes to
its neighboring Relays; when an existing Client disconnects, the
Server withdraws its EP announcements.</t>
</section>
<section title="IRON Relay Operation">
<t>Each IRON Relay is provisioned with the list of VPs that it will
serve, as well as the locators for Servers within the IRON instance.
The Relay is also provisioned with eBGP interconnections with peering
ASes in the Internet -- the same as for any BGP router.</t>
<t>Upon startup, the Relay connects to each Server via IRON
instance-internal eBGP peerings for the purpose of discovering
EP-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 have already
discovered all EPs 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 Internets the same as for any BGP
router.</t>
<t>After this initial synchronization procedure, the Relay advertises
the VPs to its eBGP peers in the Internet. In particular, the Relay
advertises the IPv6 VPs into the IPv6 BGP routing system and
advertises the IPv4 VPs into the IPv4 BGP routing system, but it does
not advertise any of the IRON overlay's EPs to any of its eBGP peers.
The Relay further advertises "default" via eBGP to its associated
Servers, then engages in ordinary packet-forwarding operations.</t>
</section>
</section>
<section anchor="operation" title="IRON Forwarding Plane Operation">
<t>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 <xref
target="INTAREA-VET"></xref> and SEAL <xref
target="INTAREA-SEAL"></xref>, while Relays additionally forward packets
to and from the native IPv6 and IPv4 Internets. IAs also use SCMP to
coordinate with other IAs, including the process of sending and
receiving redirect messages, error messages, etc. Each IA operates as
specified in the following sub-sections.</t>
<section title="IRON Client Operation">
<t>After connecting to Servers as specified in Section 5.1, the Client
registers one or more active ISP connections with each Server. To do
so, it sends periodic beacons (e.g., cryptographically signed 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, a single NBR_ID is used to represent the set of all ISP paths
the Client has registered with this Server. The NBR_ID therefore names
this "bundle" of ISP connections.</t>
<t>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 this server and connects to a new 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 Relay Routers.</t>
<t>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 a Server as its default router. In
particular, the Client encapsulates each packet in an outer header
with its locator as the source address and the locator of the Server
as the destination address.</t>
<t>The Client uses the mechanisms specified in VET and SEAL to
encapsulate each packet to be forwarded. The Client further accepts
SCMP protocol messages from its Servers, including indications of PMTU
limitations, redirects and other control messages. When the Client is
redirected to a foreign Server that serves a destination EP, it sends
future packets toward that destination EP directly to the foreign
Server instead of via one of its connected Servers.</t>
<t>Note that Client-to-Client tunneling is not permitted, since this
could result in unpredictable behavior when one or both Clients are
located behind a NAT, or when one or both Clients are mobile.
Therefore, Client-to-Client mobility binding updates are not required
in the IRON model.</t>
</section>
<section title="IRON Server Operation">
<t>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 SRAs.</t>
<t>When the Server receives a SEAL-encapsulated data packet from one
of its connected Clients, it uses normal longest-prefix-match rules to
locate a FIB entry that matches the packet's inner destination
address. If the matching FIB entry is more-specific than default, the
next hop is another of its connected Clients; otherwise, the next-hop
is a Relay which serves as a default router. The Server then
re-encapsulates the packet (i.e., it removes the outer header and
replaces it with a new outer header of the same address family), sets
the outer destination address to the locator address of the next hop
and tunnels the packet to the next hop.</t>
<t>When the Server receives a SEAL-encapsulated data packet from a
foreign Client, it accepts the packet only if there is a matching
ingress filter table entry; otherwise, it silently drops the packet.
The Server then locates a FIB entry that matches the packet's inner
destination address. If there is no matching FIB entry more-specific
than default (i.e., the destination does not correspond to a connected
Client), the Server silently drops the packet. Otherwise, the Server
re-encapsulates the packet and forwards it to the correct connected
Client. If the Client is in the process of disconnecting (e.g., due to
mobility), the Server also returns a redirect message listing a NULL
next hop to inform the foreign Client that the connected Client has
moved.</t>
<t>When the Server receives a SEAL-encapsulated data packet from a
Relay, it again locates a FIB entry that matches the packet's inner
destination. If there is no matching FIB entry more-specific than
default, the Server drops the packet and sends a destination
unreachable message. Otherwise, the Server re-encapsulates the packet
and forwards it to the correct connected Client.</t>
<t>Note that Server-to-Server tunneling is not permitted, since this
could result in sustained routing loops in which Server A has a route
to Server B, and Server B has a route to Server A. This implies that a
Server must never accept and process a redirect message, but must
instead relay the redirect message to the appropriate Client.</t>
<t>The permissible data flow paths for tunneled packets that flow
through a Server are therefore:</t>
<t><list style="symbols">
<t>From a connected Client to another connected Client (i.e., a
hairpin route)</t>
<t>From a connected Client to a default Relay router</t>
<t>From a foreign Client to a connected Client</t>
<t>From a default Relay router to a connected Client</t>
</list></t>
</section>
<section title="IRON Relay Operation">
<t>After each Relay has synchronized its VPs (see Section 5.3) it
advertises them in the IPv4 and IPv6 Internet BGP routing systems.
These prefixes will be represented as ordinary routing information in
the BGP, and any packets originating from the IPv4 or IPv6 Internet
destined to an address covered by one of the prefixes will be
forwarded to one of the VSP's Relays.</t>
<t>When a Relay receives a packet from the Internet destined to an EPA
covered by one of its VPs, it behaves as an ordinary IP router. In
particular, the Relay looks in its FIB to discover a locator of a
Server that serves the EP covering the destination address. The Relay
then simply encapsulates the packet with its own locator as the outer
source address and the locator of the Server as the outer destination
address and forwards the packet to the Server.</t>
<t>When a Relay receives a packet from a Server destined to an EPA
covered by an EP serviced by a different Server, the Relay forwards
the packet to the correct Server and initiates a redirection
procedure. The procedure used is termed "Asymmetric Extended Route
Optimization" <xref target="AERO"></xref>, which both establishes the
necessary ingress filtering state in the target Server and conveys a
better next hop to the source Client.</t>
</section>
</section>
<section title="IRON Reference Operating Scenarios">
<t>IRON supports communications when one or both hosts are located
within EP-addressed EUNs. The following sections discuss the reference
operating scenarios.</t>
<section title="Both Hosts within Same IRON Instance">
<t>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.</t>
<section title="EUNs Served by Same Server">
<t>In this scenario, the packet flow from the source host is
forwarded through the EUN to the source's 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. <xref
target="example0"></xref> depicts the sustained flow of packets from
Host A to Host B within EUNs serviced by the same Server(S) via a
"hairpinned" route:</t>
<t><figure anchor="example0"
title="Sustained Packet Flow via Hairpinned Route">
<artwork><![CDATA[ ________________________________________
.-( )-.
.-( )-.
.-( )-.
.( ).
.( ).
.( +------------+ ).
( +===================>| Server(S) |=====================+ )
( // +------------+ \\ )
( // .-. .-. \\ )
( //,-( _)-. ,-( _)-\\ )
( .||_ (_ )-. .-(_ (_ ||. )
((_|| ISP A .) (__ ISP B ||_))
( ||-(______)-' `-(______)|| )
( || | | vv )
( +-----+-----+ +-----+-----+ )
| Client(A) | | Client(B) |
+-----+-----+ VSP IRON Instance +-----+-----+
^ | ( (Overlaid on the Native Internet) ) | |
| .-. .-( .-) .-. |
| ,-( _)-. .-(________________________)-. ,-( _)-. |
.|(_ (_ )-. .-(_ (_ )|
(_| IRON EUN A ) (_ IRON EUN B|)
|`-(______)-' `-(______)-|
| | Legend: | |
| +---+----+ <---> == Native +----+---+ |
+-| Host A | <===> == Tunnel | Host B |<+
+--------+ +--------+]]></artwork>
</figure>With reference to <xref target="example0"></xref>, 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 uses VET and
SEAL to encapsulate them in outer headers with its locator address
as the outer source address, the locator address of Server(S) as the
outer destination address, and the NBR_ID parameters associated with
its tunnel-neighbor state as the identity. Client(A) then simply
forwards the encapsulated packets into its ISP network connection
that provided its locator. The ISP will forward the encapsulated
packets into the Internet without filtering since the (outer) source
address is topologically correct. Once the packets have been
forwarded into the Internet, routing will direct them to
Server(S).</t>
<t>Server(S) will receive the encapsulated packets from Client(A)
then check its FIB 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 NBR_ID parameters
associated with the tunnel-neighbor state for Client(B). Server(S)
then forwards these re-encapsulated packets into the Internet, 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.</t>
</section>
<section title="EUNs Served by Different Servers">
<t>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. <xref
target="example1"></xref> shows the flow of initial packets from
Host A to Host B within EUNs of the same IRON instance:</t>
<t><figure anchor="example1"
title="Initial Packet Flow Before Redirects">
<artwork><![CDATA[ ________________________________________
.-( )-.
.-( +------------+ )-.
.-( +======>| Relay(R) |=======+ )-.
.( || +*-----------+ || ).
.( || * vv ).
.( +--------++--+* +--++--------+ ).
( +==>| Server(A) *| | Server(B) |====+ )
( // +----------*-+ +------------+ \\ )
( // .-. * .-. \\ )
( //,-( _)-. * ,-( _)-\\ )
( .||_ (_ )-. * .-(_ (_ ||. )
((_|| ISP A .) * (__ ISP B ||_))
( ||-(______)-' * `-(______)|| )
( || | * | vv )
( +-----+-----+ * +-----+-----+ )
| Client(A) |<* | Client(B) |
+-----+-----+ VSP IRON Instance +-----+-----+
^ | ( (Overlaid on the Native Internet) ) | |
| .-. .-( .-) .-. |
| ,-( _)-. .-(________________________)-. ,-( _)-. |
.|(_ (_ )-. .-(_ (_ )|
(_| IRON EUN A ) (_ IRON EUN B|)
|`-(______)-' `-(______)-|
| | Legend: | |
| +---+----+ <---> == Native +----+---+ |
+-| Host A | <===> == Tunnel | Host B |<+
+--------+ ****> == Redirect +--------+]]></artwork>
</figure>With reference to <xref target="example1"></xref>, 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 headers and forwards the encapsulated packets into the
ISP network connection that provided its locator. The ISP will
forward the encapsulated packets into the Internet, where routing
will direct them to Server(A).</t>
<t>Server(A) receives the encapsulated packets from Client(A) and
consults its FIB to determine that the most-specific matching route
is "default" with Relay(R) as the next hop. Server(A) then
re-encapsulates the packets and forwards them into the Internet
where routing will direct them to Relay(R).</t>
<t>Relay(R) receives the encapsulated packets from Server(A) then
checks its FIB to discover an entry that covers inner destination
address B with Server(B) as the next hop. Relay(R) then returns
redirect messages to Server(A), which forwards (or, "proxies") the
redirects to Client(A). Relay(R) finally re-encapsulates the packets
and forwards them to Server(B).</t>
<t>Server(B) receives the encapsulated packets from Relay(R) then
checks its FIB to discover an entry that covers destination address
B with Client(B) as the next hop. Server(B) then re-encapsulates the
packets in a new outer header that uses the source address,
destination address, and NBR_ID parameters associated with the
tunnel-neighbor state for Client(B). Server(B) then forwards these
re-encapsulated packets into the Internet, 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.</t>
<t>After the initial flow of packets, Server(A) will have received
one or more redirect messages from Relay(R) listing Server(B) as a
better next hop. Server(A) will, in turn, proxy the redirects to
Client(A), which will establish unidirectional tunnel-neighbor state
listing Server(B) as the next hop toward the EP 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 <xref target="example2"></xref>.</t>
<t><figure anchor="example2"
title="Sustained Packet Flow After Redirects">
<artwork><![CDATA[ ________________________________________
.-( )-.
.-( )-.
.-( )-.
.( ).
.( ).
.( +------------+ ).
( +====================================>| Server(B) |====+ )
( // +------------+ \\ )
( // .-. .-. \\ )
( //,-( _)-. ,-( _)-\\ )
( .||_ (_ )-. .-(_ (_ ||. )
((_|| ISP A .) (__ ISP B ||_))
( ||-(______)-' `-(______)|| )
( || | | vv )
( +-----+-----+ +-----+-----+ )
| Client(A) | | Client(B) |
+-----+-----+ IRON Instance +-----+-----+
^ | ( (Overlaid on the Native Internet) ) | |
| .-. .-( .-) .-. |
| ,-( _)-. .-(________________________)-. ,-( _)-. |
.|(_ (_ )-. .-(_ (_ )|
(_| IRON EUN A ) (_ IRON EUN B|)
|`-(______)-' `-(______)-|
| | Legend: | |
| +---+----+ <---> == Native +----+---+ |
+-| Host A | <===> == Tunnel | Host B |<+
+--------+ +--------+]]></artwork>
</figure></t>
</section>
</section>
<section title="Mixed IRON and Non-IRON Hosts">
<t>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 Internet
instead of the IRON) are described in the following sub-sections.</t>
<section title="From IRON Host A to Non-IRON Host B">
<t><xref target="example5"></xref> depicts the IRON reference
operating scenario for packets flowing from Host A in an IRON EUN to
Host B in a non-IRON EUN.</t>
<t><figure anchor="example5"
title="From IRON Host A to Non-IRON Host B">
<artwork><![CDATA[ _________________________________________
.-( )-. )-.
.-( +-------)----+ )-.
.-( | Relay(A) |--------------------------+ )-.
.( +------------+ \ ).
.( +=======>| Server(A) | \ ).
.( // +--------)---+ \ ).
( // ) \ )
( // IRON ) \ )
( // .-. Instance ) .-. \ )
( //,-( _)-. ) ,-( _)-. \ )
( .||_ (_ )-. ) The Native Internet .- _ (_ )-| )
( _|| ISP A ) ) (_ ISP B |))
( ||-(______)-' ) `-(______)-' | )
( || | )-. | v )
( +-----+ ----+ )-. +-----+-----+ )
| Client(A) |)-. | Router(B) |
+-----+-----+ +-----+-----+
^ | ( ) | |
| .-. .-( .-) .-. |
| ,-( _)-. .-(________________________)-. ,-( _)-. |
.|(_ (_ )-. .-(_ (_ )|
(_| IRON EUN A ) (non-IRON EUN B|)
|`-(______)-' `-(______)-|
| | Legend: | |
| +---+----+ <---> == Native +----+---+ |
+-| Host A | <===> == Tunnel | Host B |<+
+--------+ +--------+]]></artwork>
</figure></t>
<t>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 sends them into the ISP
network. The ISP will pass the packets without filtering since the
(outer) source address is topologically correct. Once the packets
have been released into the native Internet, the Internet routing
system will direct them to Server(A).</t>
<t>Server(A) receives the encapsulated packets from Client(A) then
re-encapsulates and forwards them to Relay(A), which simply
decapsulates them and forwards the unencapsulated packets into the
Internet. Once the packets are released into the Internet, routing
will direct them to the final destination B. (Note that Server(A)
and Relay(A) are depicted in <xref target="example5"></xref> as two
halves of a unified gateway. In that case, the "forwarding" between
Server(A) and Relay(A) is a zero-instruction imaginary operation
within the gateway.)</t>
</section>
<section title="From Non-IRON Host B to IRON Host A">
<t><xref target="example6"></xref> depicts the IRON reference
operating scenario for packets flowing from Host B in an Non-IRON
EUN to Host A in an IRON EUN.</t>
<t><figure anchor="example6"
title="From Non-IRON Host B to IRON Host A">
<artwork><![CDATA[ _________________________________________
.-( )-. )-.
.-( +-------)----+ )-.
.-( | Relay(A) |<-------------------------+ )-.
.( +------------+ \ ).
.( +========| Server(A) | \ ).
.( // +--------)---+ \ ).
( // ) \ )
( // IRON ) \ )
( // .-. Instance ) .-. \ )
( //,-( _)-. ) ,-( _)-. \ )
( .||_ (_ )-. ) The Native Internet .- _ (_ )-| )
( _|| ISP A ) ) (_ ISP B |))
( ||-(______)-' ) `-(______)-' | )
( vv | )-. | | )
( +-----+ ----+ )-. +-----+-----+ )
| Client(A) |)-. | Router(B) |
+-----+-----+ +-----+-----+
| | ( ) | |
| .-. .-( .-) .-. |
| ,-( _)-. .-(________________________)-. ,-( _)-. |
.|(_ (_ )-. .-(_ (_ )|
(_| IRON EUN A ) (Non-IRON EUN B|)
|`-(______)-' `-(______)-|
| | Legend: | |
| +---+----+ <---> == Native +----+---+ |
+>| Host A | <===> == Tunnel | Host B |-+
+--------+ +--------+]]></artwork>
</figure></t>
<t>In this scenario, Host B sends packets destined to Host A via its
network interface connected to non-IRON EUN B. Internet routing will
direct the packets to Relay(A), which then forwards them to
Server(A) using encapsulation if necessary.</t>
<t>Server(A) will then check its FIB to discover an entry that
covers destination address A with Client(A) as the next hop.
Server(A) then (re-)encapsulates the packets in an outer header that
uses the source address, destination address, and NBR_ID parameters
associated with the tunnel-neighbor state for Client(A). Next,
Server(A) forwards these (re-)encapsulated packets into the
Internet, 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.</t>
</section>
</section>
<section title="Hosts within Different IRON Instances ">
<t><xref target="example7"></xref> 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. <figure anchor="example7"
title="Hosts within Different IRON Instances">
<artwork><![CDATA[ _________________________________________
.-( )-. .-( )-.
.-( +-------)----+ +---(--------+ )-.
.-( | Relay(A) | <---> | Relay(B) | )-.
.( +------------+ +------------+ ).
.( +=======>| Server(A) | | Server(B) |<======+ ).
.( // +--------)---+ +---(--------+ \\ ).
( // ) ( \\ )
( // IRON ) ( IRON \\ )
( // .-. Instance A ) ( Instance B .-. \\ )
( //,-( _)-. ) ( ,-( _). || )
( .||_ (_ )-. ) ( .-'_ (_ )|| )
( _|| ISP A ) ) ( (_ ISP B ||))
( ||-(______)-' ) ( '-(______)-|| )
( vv | )-. .-( | vv )
( +-----+ ----+ )-. .-( +-----+-----+ )
| Client(A) |)-. .-(| Client(B) |
+-----+-----+ The Native Internet +-----+-----+
^ | ( ) | ^
| .-. .-( .-) .-. |
| ,-( _)-. .-(________________________)-. ,-( _)-. |
.|(_ (_ )-. .-(_ (_ )|
(_| IRON EUN A ) (_ IRON EUN B|)
|`-(______)-' `-(______)-|
| | Legend: | |
| +---+----+ <---> == Native +----+---+ |
+>| Host A | <===> == Tunnel | Host B |<+
+--------+ +--------+]]></artwork>
</figure></t>
</section>
</section>
<section title="Mobility, Multiple Interfaces, Multihoming, and Traffic Engineering">
<t>While IRON Servers and Relays can be considered 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 Client
routers.</t>
<section title="Mobility Management and Mobile Networks">
<t>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 Server of any locator additions or
deletions. This operation is performance sensitive and should be
conducted immediately to avoid packet loss. This form of mobility can
be classified as a "localized mobility event".</t>
<t>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 5.3 to discover whether its candidate set of
Servers has changed. If the Client's current Server is also included
in the new list received from the VSP, this provides indication that
the Client has not moved far enough to warrant changing to a new
Server. Otherwise, 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
seconds/minutes instead of milliseconds/microseconds. This form of
mobility can be classified as a "global mobility event".</t>
<t>To move to a new Server, the Client first engages in the EP
registration process with the new Server, as described in Section 5.3.
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 EP advertisements from the VSP routing
system and retain the (stale) FIB 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.</t>
<t>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 EPs without
renumbering even as it moves between different network attachment
points.</t>
</section>
<section title="Multiple Interfaces and Multihoming">
<t>A Client may register multiple ISP connections with each Server.
Therefore, multiple interfaces are naturally supported. This feature
results in the Client considering its multiple ISP connections as a
"bundle" of interfaces that are represented as a single entity at the
network layer, and therefore allows for ISP independence at the
link-layer.</t>
<t>A Client may further register with multiple Servers for fault
tolerance and reduced routing stretch. In that case, the Client should
register each of its ISP connections with each of its Servers unless
it has a way of carefully coordinating its ISP-to-Server mappings.
(However, unpredictable performance may result if the Client registers
only preferred ISP connections with Server A and backup ISP
connections with Server B.)</t>
<t>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.</t>
</section>
<section title="Traffic Engineering">
<t>A Client can dynamically adjust the priorities of its ISP
registrations with its Server 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.</t>
<t>A Client can select outgoing ISPs, e.g., based on current
Quality-of-Service (QoS) considerations such as minimizing delay or
variance.</t>
</section>
</section>
<section title="Renumbering Considerations">
<t>As new link-layer technologies and/or service models emerge,
customers will be motivated to select their service providers through
healthy competition between ISPs. If a customer's EUN addresses are tied
to a specific ISP, however, the customer may be forced to undergo a
painstaking EUN renumbering process if it wishes to change to a
different ISP <xref target="RFC4192"></xref><xref
target="RFC5887"></xref>.</t>
<t>When a customer obtains EPs from a VSP, it can change between ISPs
seamlessly and without need to renumber. IRON therefore provides ISP
independence at the link layer. If the VSP itself applies unreasonable
costing structures for use of the EPs, however, the customer may be
compelled to seek a different VSP and would again be required to engage
in a network layer renumbering event.</t>
</section>
<section title="NAT Traversal Considerations">
<t>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 a 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 SEAL encapsulation to use a transport protocol that
supports NAT traversal, e.g., UDP, TCP, SSL, etc.</t>
<t>Since the Server maintains state about its connected 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.</t>
<t>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 issues to complications raised for NAT traversal or for
applications embedding address referrals in their payload.</t>
</section>
<section title="Multicast Considerations">
<t>IRON Servers and Relays are topologically positioned to provide
Internet Group Management Protocol (IGMP) / Multicast Listener Discovery
(MLD) proxying for their Clients <xref target="RFC4605"></xref>. 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.</t>
</section>
<section title="Nested EUN Considerations">
<t>Each Client configures a locator that may be taken from an ordinary
non-EPA address assigned by an ISP or from an EPA address taken from an
EP 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.</t>
<t>For example, in the network scenario depicted in <xref
target="nest"></xref>, Client(A) configures a locator EPA(B) taken from
the EP assigned to EUN(B). Client(B) in turn configures a locator EPA(C)
taken from the EP assigned to EUN(C). Finally, Client(C) configures a
locator ISP(D) taken from a non-EPA 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 EPA(A) within EUN(A),
exchanges packets with Host Z located elsewhere in the Internet.</t>
<t><figure anchor="nest" title="Nested EUN Example">
<artwork><![CDATA[ .-.
ISP(D) ,-( _)-.
+-----------+ .-(_ (_ )-.
| Client(C) |--(_ ISP(D) )
+-----+-----+ `-(______)-'
| <= T \ .-.
.-. u \ ,-( _)-.
,-( _)-. n .-(_ (- )-.
.-(_ (_ )-. n (_ Internet )
(_ EUN(C) ) e `-(______)-'
`-(______)-' l ___
| EPA(C) s => (:::)-.
+-----+-----+ .-(::::::::)
| Client(B) | .-(::: IRON :::)-. +-----------+
+-----+-----+ (:::: Instance ::::) | Relay(Z) |
| `-(::::::::::::)-' +-----------+
.-. `-(::::::)-' +-----------+
,-( _)-. | Server(Z) |
.-(_ (_ )-. +-----------+ +-----------+
(_ EUN(B) ) | Server(C) | +-----------+
`-(______)-' +-----------+ | Client(Z) |
| EPA(B) +-----------+ +-----------+
+-----+-----+ | Server(B) | +--------+
| Client(A) | +-----------+ | Host Z |
+-----------+ +-----------+ +--------+
| | Server(A) |
.-. +-----------+
,-( _)-. EPA(A)
.-(_ (_ )-. +--------+
(_ EUN(A) )---| Host A |
`-(______)-' +--------+]]></artwork>
</figure></t>
<t>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.</t>
<section title="Host A Sends Packets to Host Z">
<t>Host A first forwards a packet with source address EPA(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
EPA(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 EPA(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 into the Internet to Server(C).</t>
<t>When Server(C) receives the triple-encapsulated packet, it removes
the outer layer of encapsulation and forwards the resulting
twice-encapsulated packet into the Internet to Server(B). Next,
Server(B) removes the outer layer of encapsulation and forwards the
resulting once-encapsulated packet into the Internet to Server(A).
Next, Server(A) checks the address type of the inner address 'Z'. If Z
is a non-EPA address, Server(A) simply decapsulates the packet and
forwards it into the Internet. Otherwise, Server(A) rewrites the outer
source and destination addresses of the once-encapsulated packet and
forwards it to Relay(Z). Relay(Z), in turn, rewrites the outer
destination address of the packet to the locator for Server(Z), then
forwards the packet and sends a redirect to Server(A) (which forwards
the redirect to Client(A)). Server(Z) then re-encapsulates the packet
and forwards it to Client(Z), which decapsulates it and forwards the
inner packet to Host Z. Subsequent packets from Client(A) will
then use Server(Z) as the next hop toward Host Z, which eliminates
Server(A) and Relay(Z) from the path.</t>
</section>
<section title="Host Z Sends Packets to Host A">
<t>Whether or not Host Z configures an EPA address, its packets
destined to Host A will eventually reach Server(A). Server(A) will
have a mapping that lists Client(A) as the next hop toward EPA(A).
Server(A) will then encapsulate the packet with EPA(B) as the outer
destination address and forward the packet into the Internet. Internet
routing will convey this once-encapsulated packet to Server(B), which
will have a mapping that lists Client(B) as the next hop toward
EPA(B). Server(B) will then encapsulate the packet with EPA(C) as the
outer destination address and forward the packet into the Internet.
Internet routing will then convey this twice-encapsulated packet to
Server(C), which will have a mapping that lists Client(C) as the next
hop toward EPA(C). Server(C) will then encapsulate the packet with
ISP(D) as the outer destination address and forward the packet into
the Internet. Internet routing will then convey this
triple-encapsulated packet to Client(C).</t>
<t>When the triple-encapsulated packet arrives at Client(C), it strips
the outer layer of encapsulation and forwards the twice-encapsulated
packet to EPA(C), which is the locator address of Client(B). When
Client(B) receives the twice-encapsulated packet, it strips the outer
layer of encapsulation and forwards the once-encapsulated packet to
EPA(B), which is the locator address of Client(A). When Client(A)
receives the once-encapsulated packet, it strips the outer layer of
encapsulation and forwards the unencapsulated packet to EPA(A), which
is the host address of Host A.</t>
</section>
</section>
<section title="Implications for the Internet">
<t>The IRON architecture envisions a hybrid routing/mapping system that
benefits from both the shortest-path routing afforded by pure dynamic
routing systems and the routing-scaling suppression afforded by pure
mapping systems. Therefore, IRON targets the elusive "sweet spot" that
pure routing and pure mapping systems alone cannot satisfy.</t>
<t>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 and appropriately managed
to provide acceptable service levels to customers.</t>
<t>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.</t>
<t>IRON instances work seamlessly with existing and emerging services
within the native Internet. In particular, customers serviced by an IRON
instance will receive the same service enjoyed by customers serviced by
non-IRON service providers. Internet services already deployed within
the native Internet also need not make any changes to accommodate VSP
customers.</t>
<t>The IRON system operates between IAs within provider networks and end
user networks. 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.</t>
<t>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
customer/provider relationship, 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).</t>
</section>
<section anchor="research" title="Additional Considerations">
<t>Considerations for the scalability of Internet Routing due to
multihoming, traffic engineering, and provider-independent addressing
are discussed in <xref target="RADIR"></xref>. Other scaling
considerations specific to IRON are discussed in Appendix B.</t>
<t>Route optimization considerations for mobile networks are found in
<xref target="RFC5522"></xref>.</t>
<t>In order to ensure acceptable customer service levels, the VSP should
conduct a traffic scaling analysis and distribute sufficient Relays and
Servers for the IRON instance globally throughout the Internet.</t>
</section>
<section anchor="init" title="Related Initiatives">
<t>IRON builds upon the concepts of the RANGER architecture <xref
target="RFC5720"></xref> , 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 <xref target="RFC6115"></xref>.</t>
<t>Virtual Aggregation (VA) <xref target="GROW-VA"></xref> and
Aggregation in Increasing Scopes (AIS) <xref target="EVOLUTION"></xref>
provide the basis for the Virtual Prefix concepts.</t>
<t>Internet Vastly Improved Plumbing (Ivip) <xref
target="IVIP-ARCH"></xref> 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 <xref target="TTRMOB"></xref>.</t>
<t><xref target="RO-CR"></xref> 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
redirection model associated with NBMA links <xref
target="RFC5214"></xref>.</t>
<t>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 <xref
target="SAMPLE"></xref>.</t>
<t>The IRON Client-Server relationship is managed in essentially the
same way as for the Tunnel Broker model <xref target="RFC3053"></xref>.
Numerous existing tunnel broker provider networks (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
<xref target="BROKER"></xref>.</t>
</section>
<section anchor="secure" title="Security Considerations">
<t>Security considerations that apply to tunneling in general are
discussed in <xref target="RFC6169"></xref>. Additional considerations
that apply also to IRON are discussed in RANGER <xref
target="RFC5720"></xref> , VET <xref target="INTAREA-VET"></xref> and
SEAL <xref target="INTAREA-SEAL"></xref>.</t>
<t>The IRON system further depends on mutual authentication of IRON
Clients to Servers and Servers to Relays. This is accomplished through
initial authentication exchanges that establish tunnel-neighbor NBR_ID
values that can be used to detect off-path attacks. As for all Internet
communications, the IRON system also depends on Relays acting with
integrity and not injecting false advertisements into the BGP (e.g., to
mount traffic siphoning attacks).</t>
<t>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 as long as the NBR_ID of the SRS matches the
Client. 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.</t>
<t>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 Client<->Server bindings. Finally,
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.</t>
<t>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 to protect the
authenticity, integrity and (if necessary) privacy of their tunneled
packets.</t>
</section>
<section anchor="ack" title="Acknowledgements">
<t>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.</t>
<t>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.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc rfcedstyle="no" ?>
<?rfc include="reference.RFC.0791"?>
<?rfc include="reference.RFC.2460"?>
</references>
<references title="Informative References">
<!-- <?rfc include="reference.I-D.ietf-grow-va"?> -->
<reference anchor="GROW-VA">
<front>
<title>FIB Suppression with Virtual Aggregation</title>
<author fullname="Paul Francis" initials="P" surname="Francis">
<organization></organization>
</author>
<author fullname="Xiaohu Xu" initials="X" surname="Xu">
<organization></organization>
</author>
<author fullname="Hitesh Ballani" initials="H" surname="Ballani">
<organization></organization>
</author>
<author fullname="Dan Jen" initials="D" surname="Jen">
<organization></organization>
</author>
<author fullname="Robert Raszuk" initials="R" surname="Raszuk">
<organization></organization>
</author>
<author fullname="Lixia Zhang" initials="L" surname="Zhang">
<organization></organization>
</author>
<date day="22" month="February" year="2011" />
<abstract>
<t>The 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.</t>
</abstract>
</front>
<seriesInfo name="Work in" value="Progress" />
</reference>
<!-- <?rfc include="reference.I-D.zhang-evolution"?> -->
<reference anchor="EVOLUTION">
<front>
<title>Evolution Towards Global Routing Scalability</title>
<author fullname="Beichuan Zhang" initials="B" surname="Zhang">
<organization></organization>
</author>
<author fullname="Lixia Zhang" initials="L" surname="Zhang">
<organization></organization>
</author>
<author fullname="L. Wang" initials="L" surname="Wang">
<organization></organization>
</author>
<date day="26" month="October" year="2009" />
<abstract>
<t>Internet 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.</t>
</abstract>
</front>
<seriesInfo name="Work in" value="Progress" />
</reference>
<!-- <?rfc include="reference.I-D.whittle-ivip-arch"?> -->
<reference anchor="IVIP-ARCH">
<front>
<title>Ivip (Internet Vastly Improved Plumbing) Architecture</title>
<author fullname="Robin Whittle" initials="R" surname="Whittle">
<organization></organization>
</author>
<date day="8" month="March" year="2010" />
<abstract>
<t>Ivip (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.</t>
</abstract>
</front>
<seriesInfo name="Work in" value="Progress" />
</reference>
<?rfc include="reference.RFC.1070"?>
<?rfc include="reference.RFC.1918"?>
<?rfc include="reference.RFC.1930"?>
<?rfc include="reference.RFC.3053"?>
<?rfc include="reference.RFC.4192"?>
<?rfc include="reference.RFC.4271"?>
<?rfc include="reference.RFC.4548"?>
<?rfc include="reference.RFC.5214"?>
<?rfc include="reference.RFC.5522"?>
<!-- <?rfc include="reference.I-D.templin-intarea-seal"?> -->
<reference anchor="AERO">
<front>
<title>Asymmetric Extended Route Optimization (AERO)</title>
<author fullname="Fred Templin" initials="F" role="editor"
surname="Templin">
<organization></organization>
</author>
<date day="23" month="June" year="2011" />
<abstract>
<t>Nodes (i.e., gateways, routers and hosts) attached to link
types such as multicast-capable, shared media and non-broadcast
multiple access (NBMA), etc. can exchange packets as neighbors on
the link. Each node should therefore be able to discover a
neighboring gateway that can provide default routing services to
reach off-link destinations, and should also accept redirection
messages from the gateway informing it of a neighbor that is
closer to the final destination. This redirect function can
provide a useful route optimization, since the triangular path
from the ingress link neighbor, to the gateway, and finally to the
egress link neighbor may be considerably longer than the direct
path between the neighbors. However, ordinary redirection may lead
to operational issues on certain link types and/or in certain
deployment scenarios. This document therefore introduces an
Asymmetric Extended Route Optimization (AERO) capability that
addresses the issues.</t>
</abstract>
</front>
<seriesInfo name="Work in" value="Progress" />
</reference>
<reference anchor="INTAREA-SEAL">
<front>
<title>The Subnetwork Encapsulation and Adaptation Layer
(SEAL)</title>
<author fullname="Fred Templin" initials="F" role="editor"
surname="Templin">
<organization></organization>
</author>
<date day="8" month="February" year="2011" />
<abstract>
<t>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.</t>
</abstract>
</front>
<seriesInfo name="Work in" value="Progress" />
</reference>
<!-- <?rfc include="reference.I-D.templin-intarea-vet"?> -->
<reference anchor="INTAREA-VET">
<front>
<title>Virtual Enterprise Traversal (VET)</title>
<author fullname="Fred Templin" initials="F" role="editor"
surname="Templin">
<organization></organization>
</author>
<date day="19" month="January" year="2011" />
<abstract>
<t>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.</t>
</abstract>
</front>
<seriesInfo name="Work in" value="Progress" />
</reference>
<?rfc include="reference.RFC.5720"?>
<?rfc include="reference.RFC.5743"?>
<?rfc include="reference.RFC.5887"?>
<?rfc include="reference.RFC.4605"?>
<!-- <?rfc include="reference.I-D.irtf-rrg-recommendation"?> -->
<?rfc include="reference.RFC.6115"?>
<!-- <?rfc include="reference.I-D.russert-rangers"?> -->
<?rfc include="reference.RFC.6139"?>
<!-- <?rfc include="reference.I-D.ietf-v6ops-tunnel-security-concerns"?> -->
<?rfc include="reference.RFC.6169"?>
<!-- <?rfc include="reference.I-D.narten-radir-problem-statement"?> -->
<reference anchor="RADIR">
<front>
<title>On the Scalability of Internet Routing</title>
<author fullname="Thomas Narten" initials="T" surname="Narten">
<organization></organization>
</author>
<date day="17" month="February" year="2010" />
<abstract>
<t>There 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.</t>
</abstract>
</front>
<seriesInfo name="Work in" value="Progress" />
</reference>
<!-- <?rfc include="reference.I-D.carpenter-softwire-sample"?> -->
<reference anchor="SAMPLE">
<front>
<title>Legacy NAT Traversal for IPv6: Simple Address Mapping for
Premises Legacy Equipment (SAMPLE)</title>
<author fullname="Brian Carpenter" initials="B" surname="Carpenter">
<organization></organization>
</author>
<author fullname="Sheng Jiang" initials="S" surname="Jiang">
<organization></organization>
</author>
<date day="7" month="June" year="2010" />
<abstract>
<t>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.</t>
</abstract>
</front>
<seriesInfo name="Work in" value="Progress" />
</reference>
<!-- <?rfc include="reference.I-D.bernardos-mext-nemo-ro-cr"?> -->
<reference anchor="RO-CR">
<front>
<title>Correspondent Router based Route Optimisation for NEMO
(CRON)</title>
<author fullname="Carlos Bernardos" initials="C"
surname="Bernardos">
<organization></organization>
</author>
<author fullname="Maria Calderon" initials="M" surname="Calderon">
<organization></organization>
</author>
<author fullname="Ignacio Soto" initials="I" surname="Soto">
<organization></organization>
</author>
<date day="7" month="July" year="2008" />
<abstract>
<t>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.</t>
</abstract>
</front>
<seriesInfo name="Work in" value="Progress" />
</reference>
<reference anchor="BGPMON">
<front>
<title>BGPmon.net - Monitoring Your Prefixes,
http://bgpmon.net/stat.php</title>
<author fullname="BGPmon.net" initials="B" surname="net">
<organization></organization>
</author>
<date month="June" year="2010" />
</front>
</reference>
<reference anchor="TTRMOB">
<front>
<title>TTR Mobility Extensions for Core-Edge Separation Solutions to
the Internet's Routing Scaling Problem,
http://www.firstpr.com.au/ip/ivip/TTR-Mobility.pdf</title>
<author fullname="Robin Whittle" initials="R" surname="Whittle">
<organization></organization>
</author>
<author fullname="Steven Russert" initials="S" surname="Russert">
<organization></organization>
</author>
<date month="August" year="2008" />
</front>
</reference>
<reference anchor="BROKER">
<front>
<title>List of IPv6 Tunnel Brokers,
http://en.wikipedia.org/wiki/List_of_IPv6_tunnel_brokers</title>
<author fullname="Wikipedia" initials="W" surname="Wikipedia">
<organization></organization>
</author>
<date month="August" year="2011" />
</front>
</reference>
</references>
<?rfc rfcedstyle="yes" ?>
<section title="IRON VPs over Internetworks with Different Address Families">
<t>The IRON architecture leverages the routing system by providing
generally shortest-path routing for packets with EPA addresses from VPs
that match the address family of the underlying Internetwork. When the
VPs are of an address family that is not routable within the underlying
Internetwork, however, (e.g., when OSI/NSAP <xref
target="RFC4548"></xref> VPs are used within an IPv4 Internetwork) a
global VP mapping database is required. The mapping database allows the
Relays of the local IRON instance to map VPs belonging to other IRON
instances to companion prefixes taken from address families that are
routable within the Internetwork. For example, an IPv6 VP (e.g.,
2001:DB8::/32) could be paired with a companion IPv4 prefix (e.g.,
192.0.2.0/24) so that encapsulated IPv6 packets can be forwarded over
IPv4-only Internetworks.</t>
<t>In that case, every VP must be represented in a globally distributed
Master VP database (MVPd) that maintains VP-to-companion prefix mappings
for all VPs in the IRON. The MVPd is maintained by a globally managed
assigned numbers authority 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 database can be replicated
across multiple servers for load balancing, much in the same way that
FTP mirror sites are used to manage software distributions.</t>
<t>Upon startup, each Relay advertises an IPv4 companion prefix (e.g.,
192.0.2.0/24) into the internetwork IPv4 routing system and/or an IPv6
companion prefix (e.g., 2001:DB8::/64) into the internetwork IPv6
routing system for the IRON instance that it serves. The Relay then
configures the host number '1' in the IPv4 companion prefix (e.g., as
192.0.2.1) and the interface identifier '0' in the IPv6 companion prefix
(e.g., as 2001:DB8::0), and assigns the resulting addresses as "Relay
anycast" addresses for the IRON instance.</t>
<t>The Relay then discovers the full set of VPs for all other IRON
instances by reading the MVPd. The Relay reads the MVPd from a nearby
server and periodically checks the server for deltas since the database
was last read. After reading the MVPd, the Relay has a full list of
VP-to-companion prefix mappings. The Relay can then forward packets
toward EPAs 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.</t>
<t>Possible encapsulations in this model include IPv6-in-IPv4,
IPv4-in-IPv6, OSI/CLNP-in-IPv6, OSI/CLNP-in-IPv4, etc.</t>
</section>
<section title="Scaling Considerations">
<t>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 customer EUNs, traffic scaling,
state requirements, etc.</t>
<t>In terms of routing scaling, each VSP will advertise one or more VPs
into the global Internet routing system from which EPs are delegated to
customer EUNs. Routing scaling will therefore be minimized when each VP
covers many EPs. For example, the IPv6 prefix 2001:DB8::/32 contains
2^24 ::/56 EP prefixes for assignment to EUNs; therefore, the IRON could
accommodate 2^32 ::/56 EPs with only 2^8 ::/32 VPs advertised in the
interdomain routing core. (When even longer EP prefixes are used, e.g.,
/64s assigned to individual handsets in a cellular provider network,
considerable numbers of EUNs can be represented within only a single
VP.)</t>
<t>In terms of traffic scaling for Relays, each Relay represents an ASBR
of a "shell" enterprise network that simply directs arriving traffic
packets with EPA destination addresses towards Servers that service
customer EUNs. Moreover, the Relay sheds traffic destined to EPAs
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
its customer EUNs and the non-IRON Internet. 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 the VSP customer
EUNs. The Server services all traffic packets destined to its EUNs but
only services the initial packets of flows initiated from the EUNs and
destined to EPAs. Therefore, traffic scaling for EPA-addressed traffic
is an asymmetric consideration and is proportional to the number of EUNs
each Server serves.</t>
<t>In terms of state requirements for Relays, each Relay maintains a
list of all Servers in the IRON instance as well as FIB entries for all
customer EUNs that each Server serves. This state is therefore dominated
by the number of EUNs in the IRON instance. Sizing the Relay to
accommodate state information for all EUNs is therefore required during
overlay network planning. In terms of state requirements for Servers,
each Server maintains state only for the customer EUNs it serves, and
not for the customers served by other Servers in the IRON instance.
Finally, neither Relays nor Servers need keep state for final
destinations of outbound traffic.</t>
<t>Clients source and sink all traffic packets originating from or
destined to the customer EUN. Therefore, traffic scaling considerations
for Clients are the same as for any site border router. Clients also
retain unidirectional tunnel-neighbor state for the Servers 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.</t>
</section>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-24 12:06:57 |