One document matched: draft-templin-ironbis-00.xml
<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
<?rfc comments="yes"?>
<?rfc inline="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<?rfc strict='no'?>
<?rfc iprnotified='no'?>
<rfc category="info" docName="draft-templin-ironbis-00.txt" ipr="trust200902">
<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="03" 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,
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 sustainable growth while requiring
no changes to the existing routing system. 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 supports scalable addressing without changing the current BGP
<xref target="RFC4271"></xref> routing system. IRON observes the
Internet Protocol standards <xref target="RFC0791"></xref><xref
target="RFC2460"></xref>. 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 is a global 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 multihoming, mobility
management, 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 BGP core routers
and supporting servers, as well as IRON-aware clients in 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.</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.</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="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 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 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 />a specialized set of
routers deployed by a VSP to service customer EUNs through an IRON
instance configured over an underlying Internetwork (e.g., the
global Internet).</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 network instances connected to a common
Internetwork. 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 route redirections, indications of
Path Maximum Transmission Unit (PMTU) limitations, destination
unreachables, etc. IAs appear as neighbors on an NBMA virtual link, and
form bidirectional and/or unidirectional tunnel-neighbor
relationships.</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 lease 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 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 the VSP IRON instance via tunnels, as shown in <xref
target="IREP"></xref>. Client routers obtain EPs from VSPs and use
them to number subnets and interfaces within their EUNs. 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 that forms
bidirectional tunnel-neighbor relationships with each of its Client
customers and also servers as the tunnel egress of dynamically
discovered unidirectional tunnel-neighbors. Each Server also
associates with a set of Relays that can forward packets from the IRON
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 VSP's overlay
network router that acts as a relay between the IRON instance and the
native Internet. Therefore, it 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 all of the VSP's overlay network Servers, e.g.,
via tunnels over the IRON instance, via a direct interconnect such as
an Ethernet cable, etc. The Relay role (as well as its relationship
with overlay network Servers) 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
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, where each patch coordinates its activities independently of all
others.</t>
<t>Each VSP IRON instance maintains a set of Relays and Servers that
provide services to Client customers. In order to ensure adequate
customer service levels, the VSP should conduct a traffic scaling
analysis and distribute sufficient Relays and Servers for the overlay
network globally throughout the Internet. <xref target="VON"></xref>
depicts the logical arrangement of Relays, Servers, and Clients in an
IRON virtual overlay network.</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
underlying IPv4 and IPv6 Internets. 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
direct them toward EPA-addressed end systems connected to the VSP's IRON
instance.</t>
<t>Each VSP also manages a set of Servers that connect their Clients and
associated EUNs to the IRON instance and to the IPv6 and IPv4 Internets
via their associations with Relays. IRON Servers therefore need not be
BGP routers themselves; they can be simple commodity hardware platforms.
Moreover, the Server and Relay functions can be deployed together on the
same physical platform as a unified gateway, or they may be deployed on
separate platforms (e.g., for load balancing purposes).</t>
<t>Each Server maintains a working set of bidirectional tunnel-neighbor
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 each of the Relays in the IRON instance via
a dynamic routing protocol (e.g., an overlay network internal BGP
instance that carries only the EP-to-Server mappings and does not
interact with the external BGP routing system). 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 mapping table that
represents reachability information for all EPs in the VSP overlay
network.</t>
<t>Customers establish Clients that obtain their basic Internet
connectivity from ISPs and connect to 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 through an anycast
discovery process (described below). It then selects one of these nearby
Servers and forms a bidirectional tunnel-neighbor relationship with the
server through an initial exchange followed by periodic keepalives.</t>
<t>After the Client selects a Server, it forwards initial outbound
packets from its EUNs by tunneling them to the Server, which, in turn,
forwards them to the nearest 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 Server in turn provides a unidirectional
tunnel-neighbor egress for route optimization purposes,.</t>
<t>The 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 Initialization">
<t>IRON instance initialization entails the startup actions of IAs and
customer EUNs. The following sub-sections discuss these startup
procedures.</t>
<section title="IRON Relay Router Initialization">
<t>Before its first operational use, each IRON Relay is provisioned
with the list of VPs that it will serve as well as the locators for
all Servers within the IRON instance. The Relay is also provisioned
with external BGP interconnections -- the same as for any BGP
router.</t>
<t>Upon startup, the Relay engages in BGP routing exchanges with its
peers in the IPv4 and IPv6 Internets the same as for any BGP router.
It then connects to all of the Servers in the overlay network (e.g.,
via a TCP connection over a bidirectional tunnel, via an Internal BGP
(IBGP) route reflector, etc.) for the purpose of discovering
EP-to-Server mappings. After the Relay has fully populated its
EP-to-Server mapping information database, it is said to be
"synchronized" with regard to its VPs.</t>
<t>After this initial synchronization procedure, the Relay then
advertises the overlay network's VPs externally. 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. The Relay
additionally advertises an IPv4 /24 companion prefix (e.g.,
192.0.2.0/24) into the IPv4 routing system and an IPv6 ::/64 companion
prefix (e.g., 2001:DB8::/64) into the IPv6 routing system (note that
these may also be sub-prefixes taken from a VP). 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 it assigns the resulting addresses
as "Relay anycast" addresses for the IRON instance. (See Appendix A
for more information on the discovery and use of companion prefixes.)
The Relay then engages in ordinary packet-forwarding operations.</t>
</section>
<section title="IRON Serving Router Initialization">
<t>Before its first operational use, each IRON Server is provisioned
with the locators for all Relays within the IRON instance. Upon
startup, each Server must connect to all of the Relays within the IRON
instance (e.g., via a TCP connection, via an IBGP route reflector,
etc.) for the purpose of reporting its EP-to-Server mappings. The
Server then actively listens for Client customers that register their
EP prefixes as part of establishing a bidirectional tunnel-neighbor
relationship. When a new Client connects, the Server announces the new
EP additions to all Relays; when an existing Client disconnects, the
Server withdraws its announcements.</t>
</section>
<section anchor="EUN" title="IRON Client Initialization">
<t>Before its first operational use, each Client must obtain one or
more EPs from its VSP as well as the companion prefixes associated
with the VSP's IRON instance (see Section 5.1). The Client must also
obtain a certificate and a public/private key pair from the VSP that
it can later use to prove ownership of its EPs. This implies that each
VSP must run its own public key infrastructure to be used only for the
purpose of verifying its customers' claimed right to use an EP. Hence,
the VSP need not coordinate its public key infrastructure with any
other organization.</t>
<t>Upon startup, the Client sends an SCMP Router Solicitation (SRS)
message to the VSP overlay network Relay anycast address to discover
the nearest Relay. The Relay will return an SCMP Router Advertisement
(SRA) message that lists the locator addresses of one or more nearby
Servers. (This list is analogous to the Intra-Site Automatic Tunnel
Addressing Protocol (ISATAP) Potential Router List (PRL) <xref
target="RFC5214"></xref>.)</t>
<t>After the Client receives an SRA message from the nearby Relay
listing the locator addresses of nearby Servers, it initiates a short
transaction with one of the Servers carried by a reliable transport
protocol such as TCP in order to establish a bidirectional
tunnel-neighbor relationship. The protocol details of the transaction
are specific to the VSP, and hence out of scope for this document.</t>
<t>Note that it is essential that the Client select one and only one
Server. This is to allow the VSP overlay network mapping system to
have one and only one active EP-to-Server mapping at any point in
time, which shares fate with the Server itself. If this Server fails,
the Client can select a new one that will automatically update the VSP
overlay network mapping system with a new EP-to-Server mapping.</t>
</section>
</section>
<section anchor="operation" title="IRON Operation">
<t>Following the initialization operations detailed in Section 5, IAs
engage in the steady-state process of receiving and forwarding packets.
All 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. (Note however that an
IA must not send an SCMP message in response to an SCMP error message.)
Each IA operates as specified in the following sub-sections.</t>
<section title="IRON Client Operation">
<t>After selecting its Server as specified in Section 5.3, the Client
registers each of its active ISP connections with its IRON instance
Server. To do so, it sends periodic beacons (e.g., cryptographically
signed SRS messages) to the Server via each active ISP 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
updated. Although the client may connect via multiple ISPs, a single
tunnel-neighbor identifier ("NBR_ID") is used to represent the set of
all ISP paths between the Client and the Server. The NBR_ID therefore
names this "bundle" of tunnel-neighbor ISP connections.</t>
<t>If the Client ceases to receive acknowledgements from its 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
marks the Server as unusable and quickly attempts to register with a
new Server. The act of registering with a new Server will
automatically purge the stale mapping state associated with the old
Server, since dynamic routing will soon propagate the new
Client/Server relationship among the IRON instance's Relay
Routers.</t>
<t>When an end system in an EUN sends a flow of packets to a
correspondent, the packets are forwarded through the EUN via normal
routing until they reach the Client, which then tunnels the initial
packets to its Server as the next hop. In particular, the Client
encapsulates each packet in an outer header with its locator as the
source address and the locator of its Server as the destination
address. Note that after sending the initial packets of a flow, the
Client may receive important control messages, such as indications of
PMTU limitations, redirect messages that indicate a better
tunnel-neighbor next hop, etc.</t>
<t>The Client uses the mechanisms specified in VET and SEAL to
encapsulate each forwarded packet. The Client further uses the SCMP
protocol to coordinate with Servers, including accepting redirects and
other control messages. When the Client receives an SCMP message, it
checks the NBR_ID field of the encapsulated packet-in-error to verify
that the message corresponds to the tunnel-neighbor state for its
Server.</t>
</section>
<section title="IRON Serving Router Operation">
<t>After the Server is initialized, it responds to SRS messages from
tunnel-neighbor Clients by sending SRAs.</t>
<t>When the Server receives a SEAL-encapsulated data packet from one
of its bidirectional tunnel-neighbor 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 tunnel-neighbor
Client; 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
either a Relay or from a unidirectional tunnel-neighbor Client, it
again locates a FIB entry that matches the packet's inner destination
address. If the matching FIB entry is more-specific than default, the
server re-encapsulates the packet and forwards it to the correct
bidirectional tunnel-neighbor Client. If the Client has recently moved
to a different Server, however, the Server also returns an SCMP
redirect message listing a NULL next hop which informs the source that
the Client has moved.</t>
<t>After forwarding the packet into the tunnel, the Server may receive
SCMP error or redirect messages. The Server then re-encapsulates the
SCMP message and forwards it to the source of the original packet.</t>
</section>
<section title="IRON Relay Router Operation">
<t>After each Relay has synchronized its VPs (see Section 5.1) it
advertises the full set of the company's VPs and companion prefixes
into 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 the
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 the Internet destined to one of
its Relay anycast addresses, it discards the packet if it is not SEAL
encapsulated. If the packet is an SCMP SRS message, the Relay instead
sends an SRA message back to the source listing the locator addresses
of nearby Servers then discards the message. The Relay otherwise
discards all other SCMP messages.</t>
</section>
<section title="IRON Reference Operating Scenarios">
<t>IRON supports communications when one or both hosts are located
within EP-addressed EUNs. When both hosts are within the EUNs of the
same VSP IRON instance, route redirections that eliminate unnecessary
Servers and Relays from the path are possible. When only one host is
within an IRON EUN, however, route optimization cannot be used. The
following sections discuss the two scenarios.</t>
<section title="Both Hosts within Same IRON Instance">
<t>When both hosts are within EUNs served by the same VSP 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.</t>
<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 Relay of
the destination host, 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[ ________________________________________
.-( .-. )-.
.-( ,-( _)-. )-.
.-( +========+(_ (_ +=====+ )-.
.( || (_|| Internet ||_) || ).
.( || ||-(______)-|| vv ).
.( +--------++--+ || || +------------+ ).
( +==>| Server(A) | vv || | Server(B) |====+ )
( // +---------|\-+ +--++----++--+ +------------+ \\ )
( // .-. | \ | Relay(R) | .-. \\ )
( //,-( _)-. | \ +-v----------+ ,-( _)-\\ )
( .||_ (_ )-. | \____| .-(_ (_ ||. )
( _|| ISP A .) | (__ ISP B ||_))
( ||-(______)-' | (redirect) `-(______)|| )
( || | | | vv )
( +-----+-----+ | +-----+-----+ )
| Client(A) | <--+ | Client(B) |
+-----+-----+ VSP IRON Instance +-----+-----+
| ( (Overlaid on the Native Internet) ) |
.-. .-( .-) .-.
,-( _)-. .-(________________________)-. ,-( _)-.
.-(_ (_ )-. .-(_ (_ )-.
(_ IRON EUN A ) (_ IRON EUN B )
`-(______)-' `-(______)-'
| |
+---+----+ +---+----+
| Host A | | Host B |
+--------+ +--------+]]></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 uses VET and
SEAL to encapsulate them in outer headers with its locator address
as the outer source address and the locator address of Server(A) as
the outer destination address. 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(A).</t>
<t>Server(A) receives the encapsulated packets from Client(A) then
rewrites the outer source address to one of its own locator
addresses and rewrites the outer destination address to the address
of a nearby IRON instance Relay(R). Server(A) then forwards the
revised encapsulated packets into the Internet, where routing will
direct them to Relay(R).</t>
<t>Relay(R) will intercept the encapsulated packets from Server(A)
then check its FIB to discover an entry that covers inner
destination address B with Server(B) as the next hop. Relay(B) then
returns SCMP redirect messages to Server(A) (*), rewrites the outer
destination address of the encapsulated packets to the locator
address of Server(B), and forwards these revised packets to
Server(B).</t>
<t>Server(B) will receive the encapsulated packets from Relay(R)
then check 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>(*) Note that after the initial flow of packets, Server(A) will
have received one or more SCMP redirect messages from Relay(R)
listing Server(B) as a better next hop. Server(A) will, in turn,
forward the redirects to Client(A), which will establish
unidirectional tunnel-neighbor state and thereafter forward 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[ ________________________________________
.-( .-. )-.
.-( ,-( _)-. )-.
.-( +=============> .-(_ (_ )-.======+ )-.
.( // (__ Internet _) || ).
.( // `-(______)-' vv ).
.( // +------------+ ).
( // | Server(B) |====+ )
( // +------------+ \\ )
( // .-. .-. \\ )
( //,-( _)-. ,-( _)-\\ )
( .||_ (_ )-. .-(_ (_ ||. )
( _|| ISP A .) (__ ISP B ||_))
( ||-(______)-' `-(______)|| )
( || | | vv )
( +-----+-----+ IRON Instance +-----+-----+ )
| Client(A) | (Overlaid on the native Internet) | Client(B) |
+-----+-----+ +-----+-----+
| ( ) |
.-. .-( .-) .-.
,-( _)-. .-(________________________)-. ,-( _)-.
.-(_ (_ )-. .-(_ (_ )-.
(_ IRON EUN A ) (_ IRON EUN B )
`-(______)-' `-(______)-'
| |
+---+----+ +---+----+
| Host A | | Host B |
+--------+ +--------+]]></artwork>
</figure></t>
</section>
<section title="Mixed IRON and Non-IRON Hosts">
<t>When 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), the IA elements involved depend on the packet-flow
directions. The cases 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)
`-(______)-' `-(______)-'
| |
+---+----+ +---+----+
| Host A | | 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 uses VET and SEAL to encapsulate
them in outer headers with its locator address as the outer source
address and the locator address of Server(A) as the outer
destination address. 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, routing 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>
<t>This scenario always involves a Server and Relay owned by the
VSP that provides service to IRON EUN A.</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)
`-(______)-' `-(_______)-'
| |
+---+----+ +---+----+
| Host A | | 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. 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>
<t>This scenario always involves a Server and Relay owned by the
VSP that provides service 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 from host A in an IRON
instance B to 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 and 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 )
`-(______)-' `-(______)-'
| |
+---+----+ +---+----+
| Host A | | Host B |
+--------+ +--------+]]></artwork>
</figure></t>
</section>
</section>
<section title="Mobility, Multihoming, and Traffic Engineering Considerations">
<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">
<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.</t>
<t>If the Client has moved far away from its previous network point
of attachment, however, it re-issues the anycast discovery procedure
described in Section 6.1 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.</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 reliable transaction. The former Server
will then retain the (stale) FIB entries until their lifetime
expires, allowing it to continue delivering packets to the Client
for the short term while informing existing correspondents that the
Client has moved.</t>
</section>
<section title="Multihoming">
<t>A Client may register multiple locators with its Server. It can
assign metrics with its registrations to inform the Server of
preferred locators, and it can select outgoing locators according to
its local preferences. Therefore, multihoming is naturally
supported.</t>
</section>
<section title="Inbound Traffic Engineering">
<t>A Client can dynamically adjust the priorities of its prefix
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>
</section>
<section title="Outbound Traffic Engineering">
<t>A Client can select outgoing locators, e.g., based on current
Quality-of-Service (QoS) considerations such as minimizing one-way
delay or one-way delay 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 EP prefixes from a VSP, it can change
between ISPs seamlessly and without need to renumber. 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 confront a renumbering scenario.</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, e.g., it can 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 Client customers, it can
discover locator information for each Client by examining the UDP port
number and IP address in the outer headers of the Client's
encapsulated SRS 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 UDP 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>IRON does not 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.) will be discussed in a separate 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>
<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 virtual overlay network 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 virtual overlay networks also work seamlessly with existing and
emerging services within the native Internet. In particular, customers
serviced by IRON virtual overlay networks 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 IRON virtual overlay network customers.</t>
<t>The IRON system operates between routers 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, IRON routers have a method for
naturally detecting and tuning out all 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 an
in-built mobility management and multihoming capability that allows 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>
</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 customer EUNs coordinate with Servers is different and based on
the redirection model associated with NBMA links.</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>
</section>
<section anchor="secure" title="Security Considerations">
<t>Security considerations that apply to tunneling in general are
discussed in <xref target="V6OPS-TUN-SEC"></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>
</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.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="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"?> -->
<reference anchor="V6OPS-TUN-SEC">
<front>
<title>Security Concerns With IP Tunneling</title>
<author fullname="Suresh Krishnan" initials="S" surname="Krishnan">
<organization></organization>
</author>
<author fullname="Dave Thaler" initials="D" surname="Thaler">
<organization></organization>
</author>
<author fullname="James Hoagland" initials="J" surname="Hoagland">
<organization></organization>
</author>
<date day="25" month="October" year="2010" />
<abstract>
<t>A number of security concerns with IP tunnels are documented in
this memo. The intended audience of this document includes network
administrators and future protocol developers. The primary intent
of this document is to raise the awareness level regarding the
security issues with IP tunnels as deployed today.</t>
</abstract>
</front>
<seriesInfo name="Work in" value="Progress" />
</reference>
<!-- <?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>
</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 mapping database is required to allow Servers to map VPs 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>Every VP in the IRON must therefore 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 Server discovers the full set of VPs for the IRON
by reading the MVPd. The Server 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 Server has a full list of
VP-to-companion prefix mappings.</t>
<t>The Server can then forward packets toward EPAs covered by a VP by
encapsulating them in an outer header of the VP's companion prefix
address family and using any address taken from the companion prefix as
the outer destination address. The companion prefix therefore serves as
an anycast prefix.</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.) Each VP also has an associated anycast companion prefix; hence,
there will be one anycast prefix advertised into the global routing
system for each 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 vast
majority of traffic packets. 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 overlay network's 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 VSP overlay network 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 VSP overlay network. Sizing the
Relay to accommodate state information for all EUNs is therefore
required during VSP overlay network planning. In terms of state
requirements for Servers, each Server maintains tunnel-neighbor state
for each of the customer EUNs it serves, but it need not keep state for
all EUNs in the VSP overlay network. 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 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 15:52:05 |