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IETF RFC 6179
The Internet Routing Overlay Network (IRON)
Last modified on Saturday, March 12th, 2011
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Internet Research Task Force (IRTF) F. Templin, Ed.
Request for Comments: 6179 Boeing Research & Technology
Category: Experimental March 2011
ISSN: 2070-1721
The Internet Routing Overlay Network (IRON)
 Abstract
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) 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. This document is a product of the
IRTF Routing Research Group.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Research Task
Force (IRTF). The IRTF publishes the results of Internet-related
research and development activities. These results might not be
suitable for deployment. This RFC represents the individual
opinion(s) of one or more members of the Internet Research Task Force
(IRTF) Research Group of the Internet Research Task Force (IRTF).
Documents approved for publication by the IRSG are not a candidate
for any level of Internet Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 6179.
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RFC 6179 IRON March 2011
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
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RFC 6179 IRON March 2011
Table of Contents
1. Introduction ....................................................4
2. Terminology .....................................................5
3. The Internet Routing Overlay Network ............................7
3.1. IRON Client ................................................9
3.2. IRON Serving Router .......................................10
3.3. IRON Relay Router .........................................10
4. IRON Organizational Principles .................................11
5. IRON Initialization ............................................13
5.1. IRON Relay Router Initialization ..........................13
5.2. IRON Serving Router Initialization ........................14
5.3. IRON Client Initialization ................................15
6. IRON Operation .................................................15
6.1. IRON Client Operation .....................................16
6.2. IRON Serving Router Operation .............................17
6.3. IRON Relay Router Operation ...............................18
6.4. IRON Reference Operating Scenarios ........................18
6.4.1. Both Hosts within IRON EUNs ........................19
6.4.2. Mixed IRON and Non-IRON Hosts ......................21
6.5. Mobility, Multihoming, and Traffic Engineering
Considerations ............................................24
6.5.1. Mobility Management ................................24
6.5.2. Multihoming ........................................25
6.5.3. Inbound Traffic Engineering ........................25
6.5.4. Outbound Traffic Engineering .......................25
6.6. Renumbering Considerations ................................25
6.7. NAT Traversal Considerations ..............................26
6.8. Multicast Considerations ..................................26
6.9. Nested EUN Considerations .................................26
6.9.1. Host A Sends Packets to Host Z .....................28
6.9.2. Host Z Sends Packets to Host A .....................28
7. Implications for the Internet ..................................29
8. Additional Considerations ......................................30
9. Related Initiatives ............................................30
10. Security Considerations .......................................31
11. Acknowledgements ..............................................31
12. References ....................................................32
12.1. Normative References .....................................32
12.2. Informative References ...................................32
Appendix A. IRON VPs over Internetworks with Different
Address Families ......................................35
Appendix B. Scaling Considerations ................................36
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RFC 6179 IRON March 2011
1. Introduction
Growth in the number of entries instantiated in the Internet routing
system has led to concerns regarding unsustainable routing scaling
[RADIR]. 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 [BGPMON] 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.
Several related works have investigated routing scaling issues.
Virtual Aggregation (VA) [GROW-VA] and Aggregation in Increasing
Scopes (AIS) [EVOLUTION] 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) [RFC 5720] examines
recursive arrangements of enterprise networks that can apply to a
very broad set of use-case scenarios [RFC 6139]. IRON specifically
adopts the RANGER Non-Broadcast, Multiple Access (NBMA) tunnel
virtual-interface model, and uses Virtual Enterprise Traversal (VET)
[INTAREA-VET] and the Subnetwork Adaptation and Encapsulation Layer
(SEAL) [INTAREA-SEAL] as its functional building blocks.
This document proposes an Internet Routing Overlay Network (IRON)
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) [IVIP-ARCH] architecture proposal along with
its associated Translating Tunnel Router (TTR) mobility extensions
[TTRMOB]. 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 [SAMPLE].
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IRON supports scalable addressing without changing the current BGP
[RFC 4271] routing system. IRON observes the Internet Protocol
standards [RFC 791][RFC 2460]. Other network-layer protocols that can
be encapsulated within IP packets (e.g., OSI/CLNP (Connectionless
Network Protocol) [RFC 1070], etc.) are also within scope.
The IRON is a global routing system comprising virtual overlay
networks managed by Virtual Prefix Companies (VPCs) that own and
manage Virtual Prefixes (VPs) from which End User Network (EUN)
prefixes (EPs) are delegated to customer sites. The 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 [RFC 4192][RFC 5887]. The
IRON uses 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). The IRON requires
deployment of a small number of new BGP core routers and supporting
servers, as well as IRON-aware routers/servers in customer EUNs. No
modifications to hosts, and no modifications to most routers, are
required.
Note: This document is offered in compliance with Internet Research
Task Force (IRTF) document stream procedures [RFC 5743]; it is not an
IETF product and is not a standard. The views in this document were
considered controversial by the IRTF Routing Research Group (RRG),
but the RG reached a consensus that the document should still be
published. The document will undergo a period of review within the
RRG and through selected expert reviewers prior to publication. The
following sections discuss details of the IRON architecture.
2. Terminology
This document makes use of the following terms:
End User Network (EUN):
an edge network that connects an organization's devices (e.g.,
computers, routers, printers, etc.) to the Internet.
End User Network Prefix (EP):
a more specific inner network-layer prefix derived from a Virtual
Prefix (VP) (e.g., an IPv4 /28, an IPv6 /56, etc.) and delegated
to an EUN by a Virtual Prefix Company (VPC).
End User Network Prefix Address (EPA):
a network-layer address belonging to an EP and assigned to the
interface of an end system in an EUN.
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RFC 6179 IRON March 2011
Forwarding Information Base (FIB):
a data structure containing network prefixes to next-hop mappings;
usually maintained in a router's fast-path processing lookup
tables.
Internet Routing Overlay Network (IRON):
a composite virtual overlay network that comprises the union of
all VPC overlay networks configured over a common Internetwork.
The IRON supports routing through encapsulation of inner packets
with EPA addresses within outer headers that use locator
addresses.
IRON Client Router/Host ("Client"):
a customer's router or host that logically connects the customer's
EUNs and their associated EPs to the IRON via an NBMA tunnel
virtual interface.
IRON Serving Router ("Server"):
a VPC's overlay network router that provides forwarding and
mapping services for the EPs owned by customer Clients.
IRON Relay Router ("Relay"):
a VPC's overlay network router that acts as a relay between the
IRON and the native Internet.
IRON Agent (IA):
generically refers to any of an IRON Client/Server/Relay.
Internet Service Provider (ISP):
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.
Locator
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).
Routing and Addressing in Networks with Global Enterprise Recursion
(RANGER):
an architectural examination of virtual overlay networks applied
to enterprise network scenarios, with implications for a wider
variety of use cases.
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RFC 6179 IRON March 2011
Subnetwork Encapsulation and Adaptation Layer (SEAL):
an encapsulation sublayer that provides extended packet
identification and a Control Message Protocol to ensure
deterministic network-layer feedback.
Virtual Enterprise Traversal (VET):
a method for discovering border routers and forming dynamic
tunnel-neighbor relationships over enterprise networks (or sites)
with varying properties.
Virtual Prefix (VP):
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 Prefix Company (VPC).
Virtual Prefix Company (VPC):
a company that owns and manages a set of VPs from which it
delegates EPs to EUNs.
VPC Overlay Network
a specialized set of routers deployed by a VPC to service customer
EUNs through a virtual overlay network configured over an
underlying Internetwork (e.g., the global Internet).
3. The Internet Routing Overlay Network
The Internet Routing Overlay Network (IRON) is a system of virtual
overlay networks configured over 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.
The IRON 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) [INTAREA-VET] virtual NBMA link model in conjunction
with the Subnetwork Encapsulation and Adaptation Layer (SEAL)
[INTAREA-SEAL] to encapsulate inner network-layer packets within
outer headers, as shown in Figure 1.
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RFC 6179 IRON March 2011
+-------------------------+
| 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
Figure 1: Encapsulation of Inner Packets within Outer IP Headers
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.
The IRON is the union of all virtual overlay networks that are
configured over a common underlying Internet and are owned and
managed by Virtual Prefix Companies (VPCs). Each such virtual
overlay network comprises a set of IAs distributed throughout the
Internet to serve highly aggregated Virtual Prefixes (VPs). VPCs
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 IRON.
VPCs 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 broker or through separate entities. In that case, the VPC
can open for business and begin serving its customers immediately
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RFC 6179 IRON March 2011
without the need to coordinate its activities with ISPs or other
VPCs. Further details on business considerations are out of scope
for this document.
The IRON requires no changes to end systems or to most routers in the
Internet. Instead, the IRON comprises IAs that 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 the
IRON. The functional roles for IAs are described in the following
sections.
3.1. IRON Client
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 IRON via tunnels, as shown in Figure 2. Client routers obtain
EPs from VPCs 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 EPA and exhibits the outward appearance of a host.
.-.
,-( _)-.
+--------+ .-(_ (_ )-.
| Client |--(_ ISP )
+---+----+ `-(______)-'
| <= T \ .-.
.-. u \ ,-( _)-.
,-( _)-. n .-(_ (- )-.
.-(_ (_ )-. n (_ Internet )
(_ EUN ) e `-(______)-
`-(______)-' l ___
| s => (:::)-.
+----+---+ .-(::::::::)
| Host | .-(::::::::::::)-.
+--------+ (:::: The IRON ::::)
`-(::::::::::::)-'
`-(::::::)-'
Figure 2: IRON Client Router Connecting EUN to the IRON
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RFC 6179 IRON March 2011
3.2. IRON Serving Router
An IRON serving router (or, simply, "Server") is a VPC's overlay
network router that provides forwarding and mapping services for the
EPs owned by customer Client routers. In typical deployments, a VPC
will deploy many Servers around the IRON in a globally distributed
fashion (e.g., as depicted in Figure 3) so that Clients can discover
those that are nearby.
+--------+ +--------+
| Boston | | Tokyo |
| Server | | Server |
+--+-----+ ++-------+
+--------+ \ /
| Seattle| \ ___ /
| Server | \ (:::)-. +--------+
+------+-+ .-(::::::::)------+ Paris |
\.-(::::::::::::)-. | Server |
(:::: The IRON ::::) +--------+
`-(::::::::::::)-'
+--------+ / `-(::::::)-' \ +--------+
| Moscow + | \--- + Sydney |
| Server | +----+---+ | Server |
+--------+ | Cairo | +--------+
| Server |
+--------+
Figure 3: IRON Serving Router Global Distribution Example
Each Server acts as a tunnel-endpoint router that forms a
bidirectional tunnel-neighbor relationship with each of its Client
customers. 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.
3.3. IRON Relay Router
An IRON Relay Router (or, simply, "Relay") is a VPC's overlay network
router that acts as a relay between the IRON and the native Internet.
Therefore, it also serves as an Autonomous System Border Router
(ASBR) that is owned and managed by the VPC.
Each VPC 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 VPC's overlay network Servers, e.g.,
via tunnels over the IRON, 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 Figure 4.
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RFC 6179 IRON March 2011
.-.
,-( _)-.
.-(_ (_ )-.
(_ Internet )
`-(______)-' | +--------+
| |--| Server |
+----+---+ | +--------+
| Relay |----| +--------+
+--------+ |--| Server |
_|| | +--------+
(:::)-. (Ethernet)
.-(::::::::)
+--------+ .-(::::::::::::)-. +--------+
| Server |=(:::: The IRON ::::)=| Server |
+--------+ `-(::::::::::::)-' +--------+
`-(::::::)-'
|| (Tunnels)
+--------+
| Server |
+--------+
Figure 4: IRON Relay Router Connecting IRON to Native Internet
4. IRON Organizational Principles
The IRON consists of the union of all VPC overlay networks configured
over a common Internetwork (e.g., the public Internet). Each such
overlay network represents a distinct "patch" on the Internet
"quilt", where the patches are stitched together by tunnels over the
links, routers, bridges, etc. that connect the underlying
Internetwork. When a new VPC overlay network is deployed, it becomes
yet another patch on the quilt. The IRON is therefore a composite
overlay network consisting of multiple individual patches, where each
patch coordinates its activities independently of all others (with
the exception that the Servers of each patch must be aware of all VPs
in the IRON). In order to ensure mutual cooperation between all VPC
overlay networks, sufficient address space portions of the inner
network-layer protocol (e.g., IPv4, IPv6, etc.) should be set aside
and designated as VP space.
Each VPC overlay network in the IRON maintains a set of Relays and
Servers that provide services to their Client customers. In order to
ensure adequate customer service levels, the VPC should conduct a
traffic scaling analysis and distribute sufficient Relays and Servers
for the overlay network globally throughout the Internet. Figure 5
depicts the logical arrangement of Relays, Servers, and Clients in an
IRON virtual overlay network.
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RFC 6179 IRON March 2011
.-.
,-( _)-.
.-(_ (_ )-.
(__ Internet _)
`-(______)-'
<------------ Relays ------------>
________________________
(::::::::::::::::::::::::)-.
.-(:::::::::::::::::::::::::::::)
.-(:::::::::::::::::::::::::::::::::)-.
(::::::::::: The IRON :::::::::::::::)
`-(:::::::::::::::::::::::::::::::::)-'
`-(::::::::::::::::::::::::::::)-'
<------------ Servers ------------>
.-. .-. .-.
,-( _)-. ,-( _)-. ,-( _)-.
.-(_ (_ )-. .-(_ (_ )-. .-(_ (_ )-.
(__ ISP A _) (__ ISP B _) ... (__ ISP x _)
`-(______)-' `-(______)-' `-(______)-'
<----------- NATs ------------>
<----------- Clients and EUNs ----------->
Figure 5: Virtual Overlay Network Organization
Each Relay in the VPC overlay network connects the overlay directly
to the underlying IPv4 and IPv6 Internets. It also advertises the
VPC overlay network's IPv4 VPs into the IPv4 BGP routing system and
advertises the overlay network'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 VPC overlay network.
Each VPC overlay network also manages a set of Servers that connect
their Clients and associated EUNs to the IRON 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).
Each Server maintains a working set of 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 VPC overlay network via a dynamic
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RFC 6179 IRON March 2011
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 VPC overlay network.
Customers establish Clients that obtain their basic Internet
connectivity from ISPs and connect to Servers to attach their EUNs to
the IRON. Each EUN can connect to the IRON via one or 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.
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 that serves
the final destination. The Client will subsequently receive redirect
messages informing it of a more direct route through a Server that
serves the final destination EUN.
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.
5. IRON Initialization
IRON initialization entails the startup actions of IAs within the VPC
overlay network and customer EUNs. The following sub-sections
discuss these startup procedures.
5.1. IRON Relay Router Initialization
Before its first operational use, each Relay in a VPC overlay network
is provisioned with the list of VPs that it will serve as well as the
locators for all Servers that belong to the same overlay network.
The Relay is also provisioned with external BGP interconnections --
the same as for any BGP router.
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RFC 6179 IRON March 2011
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.
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 subnet-router anycast addresses
[RFC 3068][RFC 2526] for the VPC overlay network. (See Appendix A for
more information on the discovery and use of companion prefixes.)
The Relay then engages in ordinary packet-forwarding operations.
5.2. IRON Serving Router Initialization
Before its first operational use, each Server in a VPC overlay
network is provisioned with the locators for all Relays that
aggregate the overlay network's VPs. In order to support route
optimization, the Server must also be provisioned with the list of
all VPs in the IRON (i.e., not just the VPs of its own overlay
network) so that it can discern EPA and non-EPA addresses.
(Therefore, the Server could be greatly simplified if the list of VPs
could be covered within a small number of very short prefixes, e.g.,
one or a few IPv6 ::/20's). The Server must also discover the VP
companion prefix relationships discussed in Section 5.1, e.g., via a
global database such as discussed in Appendix A.
Upon startup, each Server must connect to all of the Relays within
its overlay network (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 registers its EP
prefixes, the Server announces the new EP additions to all Relays;
when an existing Client unregisters its EP prefixes, the Server
withdraws its announcements.
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RFC 6179 IRON March 2011
5.3. IRON Client Initialization
Before its first operational use, each Client must obtain one or more
EPs from its VPC as well as the companion prefixes associated with
the VPC overlay network (see Section 5.1). The Client must also
obtain a certificate and a public/private key pair from the VPC that
it can later use to prove ownership of its EPs. This implies that
each VPC 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 VPC need not coordinate its public key infrastructure
with any other organization.
Upon startup, the Client sends an SCMP Router Solicitation (SRS)
message to the VPC overlay network subnet-router 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) [RFC 5214].)
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 VPC, and hence out of scope for this document.
Note that it is essential that the Client select one and only one
Server. This is to allow the VPC 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 VPC overlay network mapping system with a new EP-to-Server
mapping.
6. IRON Operation
Following the IRON initialization detailed in Section 5, IAs engage
in the steady-state process of receiving and forwarding packets. All
IAs forward encapsulated packets over the IRON using the mechanisms
of VET [INTAREA-VET] and SEAL [INTAREA-SEAL], while Relays (and in
some cases Servers) 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.
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RFC 6179 IRON March 2011
6.1. IRON Client Operation
After selecting its Server as specified in Section 5.3, the Client
should register each of its ISP connections with the Server for
multihoming purposes. To do so, it sends periodic beacons (e.g., SRS
messages) to its Server via each of its ISPs to establish additional
tunnel-neighbor state. This implies that a single tunnel-neighbor
identifier (i.e., a "nonce") is used to represent the set of all ISP
paths between the Client and the Server. Therefore, the nonce names
this "bundle" of ISP paths.
If the Client ceases to receive acknowledgements from its Server via
a specific ISP connection, it marks the Server as unreachable from
that address and therefore over that ISP connection. (The Client
should also inform its Server of this outage via one of its working
ISP connections.) If the Client ceases to receive acknowledgements
from its 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 propagate the new client/server relationship to the VPC overlay
network Relay Routers.
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 SCMP messages, such as indications of
PMTU limitations, redirects that point to a better next hop, etc.
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 SCMP messages. When the Client receives an SCMP message,
it checks the nonce field of the encapsulated packet-in-error to
verify that the message corresponds to the tunnel-neighbor state for
its Server and accepts the message if the nonce matches. (Note
however that the outer source and destination addresses of the
packet-in-error may be different than those in the original packet
due to possible Server and/or Relay address rewritings.)
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RFC 6179 IRON March 2011
6.2. IRON Serving Router Operation
After the Server is initialized, it responds to SRSs from Clients by
sending SRAs. When the Server receives a SEAL-encapsulated packet
from one of its Client tunnel neighbors, it examines the inner
destination address. If the inner destination address is not an EPA,
the Server decapsulates the packet and forwards it unencapsulated
into the Internet if it is able to do so without loss due to ingress
filtering. Otherwise, the Server re-encapsulates the packet (i.e.,
it removes the outer header and replaces it with a new outer header
of the same address family) and sets the outer destination address to
the locator address of a Relay within its VPC overlay network. It
then forwards the re-encapsulated packet to the Relay, which will, in
turn, decapsulate it and forward it into the Internet.
If the inner destination address is an EPA, however, the Server
rewrites the outer source address to one of its own locator addresses
and rewrites the outer destination address to the subnet-router
anycast address taken from the companion prefix associated with the
inner destination address (where the companion prefix of the same
address family as the outer IP protocol is used). The Server then
forwards the revised encapsulated packet into the Internet via a
default or more specific route, where it will be directed to the
closest Relay within the destination VPC overlay network. After
sending the packet, the Server may then receive an SCMP error or
redirect message from a Relay/Server within the destination VPC
overlay network. In that case, the Server verifies that the nonce in
the message matches the Client that sent the original inner packet
and discards the message if the nonce does not match. Otherwise, the
Server re-encapsulates the SCMP message in a new outer header that
uses the source address, destination address, and nonce parameters
associated with the Client's tunnel-neighbor state; it then forwards
the message to the Client. This arrangement is necessary to allow
SCMP messages to flow through any NATs on the path.
When a Server ('A') receives a SEAL-encapsulated packet from a Relay
or from the Internet, if the inner destination address matches an EP
in its FIB, 'A' re-encapsulates the packet in a new outer header and
forwards it to a Client ('B'), which, in turn, decapsulates the
packet and forwards it to the correct end system in the EUN.
However, if 'B' has left notice with 'A' that it has moved to a new
Server ('C'), 'A' will instead forward the packet to 'C' and also
send an SCMP redirect message back to the source of the packet. In
this way, 'B' can leave behind forwarding information when changing
between Servers 'A' and 'C' (e.g., due to mobility events) without
exposing packets to loss.
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RFC 6179 IRON March 2011
6.3. IRON Relay Router Operation
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 VPC overlay network's Relays.
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.
When a Relay receives a packet from the Internet destined to one of
its subnet-router 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.
If the packet is an ordinary SEAL packet (i.e., one that encapsulates
an inner packet), the Relay sends an SCMP redirect message of the
same address family back to the source with the locator of the Server
that serves the EPA destination in the inner packet as the redirected
target. The source and destination addresses of the SCMP redirect
message use the outer destination and source addresses of the
original packet, respectively. After sending the redirect message,
the Relay then rewrites the outer destination address of the SEAL-
encapsulated packet to the locator of the Server and forwards the
revised packet to the Server. Note that in this arrangement, any
errors that occur on the path between the Relay and the Server will
be delivered to the original source but with a different destination
address due to this Relay address rewriting.
6.4. IRON Reference Operating Scenarios
The IRON supports communications when one or both hosts are located
within EP-addressed EUNs, regardless of whether the EPs are
provisioned by the same VPC or by different VPCs. When both hosts
are within IRON EUNs, 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.
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RFC 6179 IRON March 2011
6.4.1. Both Hosts within IRON EUNs
When both hosts are within IRON EUNs, 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.
In this scenario, the initial packets of a flow produced by a source
host within an EUN connected to the IRON 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. Figure 6 shows the
flow of initial packets from host A to host B within two IRON EUNs
(the same scenario applies whether the two EUNs are within the same
VPC overlay network or different overlay networks).
________________________________________
.-( .-. )-.
.-( ,-( _)-. )-.
.-( +========+(_ (_ +=====+ )-.
.( || (_|| Internet ||_) || ).
.( || ||-(______)-|| vv ).
.( +--------++--+ || || +------------+ ).
( +==>| Server(A) | vv || | Server(B) |====+ )
( // +---------|\-+ +--++----++--+ +------------+ \\ )
( // .-. | \ | Relay(B) | .-. \\ )
( //,-( _)-. | \ +-v----------+ ,-( _)-\\ )
( .||_ (_ )-. | \____| .-(_ (_ ||. )
( _|| ISP A .) | (__ ISP B ||_))
( ||-(______)-' | (redirect) `-(______)|| )
( || | | | vv )
( +-----+-----+ | +-----+-----+ )
| Client(A) | <--+ | Client(B) |
+-----+-----+ The IRON +-----+-----+
| ( (Overlaid on the Native Internet) ) |
.-. .-( .-) .-.
,-( _)-. .-(________________________)-. ,-( _)-.
.-(_ (_ )-. .-(_ (_ )-.
(_ IRON EUN A ) (_ IRON EUN B )
`-(______)-' `-(______)-'
| |
+---+----+ +---+----+
| Host A | | Host B |
+--------+ +--------+
Figure 6: Initial Packet Flow before Redirects
Templin Experimental PAGE 19
RFC 6179 IRON March 2011
With reference to Figure 6, 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).
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 subnet-router
anycast address of the appropriate address family associated with the
inner destination address. Server(A) then forwards the revised
encapsulated packets into the Internet, where routing will direct
them to Relay(B), which services the VPC overlay network associated
with host B.
Relay(B) 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).
Server(B) will receive the encapsulated packets from Relay(B) 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 nonce 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.
(*) Note that after the initial flow of packets, Server(A) will have
received one or more SCMP redirect messages from Relay(B) 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 Figure 7.
Templin Experimental PAGE 20
RFC 6179 IRON March 2011
________________________________________
.-( .-. )-.
.-( ,-( _)-. )-.
.-( +=============> .-(_ (_ )-.======+ )-.
.( // (__ Internet _) || ).
.( // `-(______)-' vv ).
.( // +------------+ ).
( // | Server(B) |====+ )
( // +------------+ \\ )
( // .-. .-. \\ )
( //,-( _)-. ,-( _)-\\ )
( .||_ (_ )-. .-(_ (_ ||. )
( _|| ISP A .) (__ ISP B ||_))
( ||-(______)-' `-(______)|| )
( || | | vv )
( +-----+-----+ The IRON +-----+-----+ )
| Client(A) | (Overlaid on the native Internet) | Client(B) |
+-----+-----+ +-----+-----+
| ( ) |
.-. .-( .-) .-.
,-( _)-. .-(________________________)-. ,-( _)-.
.-(_ (_ )-. .-(_ (_ )-.
(_ IRON EUN A ) (_ IRON EUN B )
`-(______)-' `-(______)-'
| |
+---+----+ +---+----+
| Host A | | Host B |
+--------+ +--------+
Figure 7: Sustained Packet Flow after Redirects
6.4.2. Mixed IRON and Non-IRON Hosts
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.
6.4.2.1. From IRON Host A to Non-IRON Host B
Figure 8 depicts the IRON reference operating scenario for packets
flowing from host A in an IRON EUN to host B in a non-IRON EUN.
Templin Experimental PAGE 21
RFC 6179 IRON March 2011
_________________________________________
.-( )-. )-.
.-( +-------)----+ )-.
.-( | Relay(A) |--------------+ )-.
.( +------------+ \ ).
.( +=======>| Server(A) | \ ).
.( // +--------)---+ \ ).
( // ) \ )
( // The IRON ) \ )
( // .-. ) \ .-. )
( //,-( _)-. ) \ ,-( _)-. )
( .||_ (_ )-. ) The Native Internet .-|_ (_ )-. )
( _|| ISP A ) ) (_ | ISP B ))
( ||-(______)-' ) |-(______)-' )
( || | )-. v | )
( +-----+ ----+ )-. +-----+-----+ )
| Client(A) |)-. | Router B |
+-----+-----+ +-----+-----+
| ( ) |
.-. .-(____________________________________)-. .-.
,-( _)-. ,-( _)-.
.-(_ (_ )-. .-(_ (_ )-.
(_ IRON EUN A ) (_non-IRON EUN B)
`-(______)-' `-(______)-'
| |
+---+----+ +---+----+
| Host A | | Host B |
+--------+ +--------+
Figure 8: From IRON Host A to Non-IRON Host B
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).
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
Templin Experimental PAGE 22
RFC 6179 IRON March 2011
depicted in Figure 8 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.)
This scenario always involves a Server and Relay owned by the VPC
that provides service to IRON EUN A. Therefore, it imparts a cost
that would need to be borne by either the VPC or its customers.
6.4.2.2. From Non-IRON Host B to IRON Host A
Figure 9 depicts the IRON reference operating scenario for packets
flowing from host B in an Non-IRON EUN to host A in an IRON EUN.
_______________________________________
.-( )-. )-.
.-( +-------)----+ )-.
.-( | Relay(A) |<-------------+ )-.
.( +------------+ \ ).
.( +========| Server(A) | \ ).
.( // +--------)---+ \ ).
( // ) \ )
( // The IRON ) \ )
( // .-. ) \ .-. )
( //,-( _)-. ) \ ,-( _)-. )
( .||_ (_ )-. ) The Native Internet .-|_ (_ )-. )
( _|| ISP A ) ) (_ | ISP B ))
( ||-(______)-' ) |-(______)-' )
( vv | )-. | | )
( +-----+ ----+ )-. +-----+-----+ )
| Client(A) |)-. | Router B |
+-----+-----+ +-----+-----+
| ( ) |
.-. .-(____________________________________)-. .-.
,-( _)-. ,-( _)-.
.-(_ (_ )-. .-(_ (_ )-.
(_ IRON EUN A ) (_non-IRON EUN B)
`-(______)-' `-(_______)-'
| |
+---+----+ +---+----+
| Host A | | Host B |
+--------+ +--------+
Figure 9: From Non-IRON Host B to IRON Host A
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.
Templin Experimental PAGE 23
RFC 6179 IRON March 2011
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 nonce 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.
This scenario always involves a Server and Relay owned by the VPC
that provides service to IRON EUN A. Therefore, it imparts a cost
that would need to be borne by either the VPC or its customers.
6.5. Mobility, Multihoming, and Traffic Engineering Considerations
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.
6.5.1. Mobility Management
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.
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 VPC, 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.
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 moved by
Templin Experimental PAGE 24
RFC 6179 IRON March 2011
providing it with the locator address of the new Server; again, via a
VPC-specific reliable transaction. The former Server will then
garbage-collect the stale FIB entries when their lifetime expires.
This will allow the former Server to redirect existing correspondents
to the new Server so that no packets are lost.
6.5.2. Multihoming
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.
6.5.3. Inbound Traffic Engineering
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 VPC network routing churn.
6.5.4. Outbound Traffic Engineering
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.
6.6. Renumbering Considerations
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 [RFC 4192][RFC 5887].
When a customer obtains EP prefixes from a VPC, it can change between
ISPs seamlessly and without need to renumber. If the VPC itself
applies unreasonable costing structures for use of the EPs, however,
the customer may be compelled to seek a different VPC and would again
be required to confront a renumbering scenario. The IRON approach to
renumbering avoidance therefore depends on VPCs conducting ethical
business practices and offering reasonable rates.
Templin Experimental PAGE 25
RFC 6179 IRON March 2011
6.7. NAT Traversal Considerations
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, namely UDP.
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 packets. When there is a NAT in the path, the UDP 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 UDP port
number.
IRON does not introduce any new issues to complications raised for
NAT traversal or for applications embedding address referrals in
their payload.
6.8. Multicast Considerations
IRON Servers and Relays are topologically positioned to provide
Internet Group Management Protocol (IGMP) / Multicast Listener
Discovery (MLD) proxying for their Clients [RFC 4605]. Further
multicast considerations for IRON (e.g., interactions with multicast
routing protocols, traffic scaling, etc.) will be discussed in a
separate document.
6.9. Nested EUN Considerations
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.
Templin Experimental PAGE 26
RFC 6179 IRON March 2011
For example, in the network scenario depicted in Figure 10, 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.
.-.
ISP(D) ,-( _)-.
+-----------+ .-(_ (_ )-.
| Client(C) |--(_ ISP(D) )
+-----+-----+ `-(______)-'
| <= T \ .-.
.-. u \ ,-( _)-.
,-( _)-. n .-(_ (- )-.
.-(_ (_ )-. n (_ Internet )
(_ EUN(C) ) e `-(______)-'
`-(______)-' l ___
| EPA(C) s => (:::)-.
+-----+-----+ .-(::::::::)
| Client(B) | .-(::::::::::::)-. +-----------+
+-----+-----+ (:::: The IRON ::::) | 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 |
`-(______)-' +--------+
Figure 10: Nested EUN Example
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.
Templin Experimental PAGE 27
RFC 6179 IRON March 2011
6.9.1. Host A Sends Packets to Host Z
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).
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.
6.9.2. Host Z Sends Packets to Host A
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
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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).
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.
7. Implications for the Internet
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.
The IRON system requires a deployment of new routers/servers
throughout the Internet and/or provider networks 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.
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.
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.
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
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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.
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).
8. Additional Considerations
Considerations for the scalability of Internet Routing due to
multihoming, traffic engineering, and provider-independent addressing
are discussed in [RADIR]. Other scaling considerations specific to
IRON are discussed in Appendix B.
Route optimization considerations for mobile networks are found in
[RFC 5522].
9. Related Initiatives
IRON builds upon the concepts of the RANGER architecture [RFC 5720]
[RFC 6139], 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 [RFC 6115].
Virtual Aggregation (VA) [GROW-VA] and Aggregation in Increasing
Scopes (AIS) [EVOLUTION] provide the basis for the Virtual Prefix
concepts.
Internet Vastly Improved Plumbing (Ivip) [IVIP-ARCH] 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 [TTRMOB].
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RFC 6179 IRON March 2011
[RO-CR] 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.
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
[SAMPLE].
10. Security Considerations
Security considerations that apply to tunneling in general are
discussed in [V6OPS-TUN-SEC]. Additional considerations that apply
also to IRON are discussed in RANGER [RFC 5720] [RFC 6139], VET
[INTAREA-VET] and SEAL [INTAREA-SEAL].
The IRON system further depends on mutual authentication of IRON
Clients to Servers and Servers to Relays. This is accomplished
through initial authentication exchanges followed by tunnel-neighbor
nonces 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).
Each VPC overlay network 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.
11. Acknowledgements
The ideas behind this work have benefited greatly from discussions
with colleagues; some of which appear on the RRG and other IRTF/IETF
mailing lists. Robin Whittle and Steve Russert co-authored the TTR
mobility architecture, which strongly influenced IRON. Eric
Fleischman pointed out the opportunity to leverage anycast for
discovering topologically close Servers. Thomas Henderson
recommended a quantitative analysis of scaling properties.
The following individuals provided essential review input: Jari
Arkko, Mohamed Boucadair, Stewart Bryant, John Buford, Ralph Droms,
Wesley Eddy, Adrian Farrel, Dae Young Kim, and Robin Whittle.
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RFC 6179 IRON March 2011
12. References
12.1. Normative References
[RFC 791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC 2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
12.2. Informative References
[BGPMON] net, B., "BGPmon.net - Monitoring Your Prefixes,
http://bgpmon.net/stat.php", June 2010.
[EVOLUTION]
Zhang, B., Zhang, L., and L. Wang, "Evolution Towards
Global Routing Scalability", Work in Progress,
October 2009.
[GROW-VA] Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and
L. Zhang, "FIB Suppression with Virtual Aggregation", Work
in Progress, February 2011.
[INTAREA-SEAL]
Templin, F., Ed., "The Subnetwork Encapsulation and
Adaptation Layer (SEAL)", Work in Progress, February 2011.
[INTAREA-VET]
Templin, F., Ed., "Virtual Enterprise Traversal (VET)",
Work in Progress, January 2011.
[IVIP-ARCH]
Whittle, R., "Ivip (Internet Vastly Improved Plumbing)
Architecture", Work in Progress, March 2010.
[RADIR] Narten, T., "On the Scalability of Internet Routing", Work
in Progress, February 2010.
[RFC 1070] Hagens, R., Hall, N., and M. Rose, "Use of the Internet as
a subnetwork for experimentation with the OSI network
layer", RFC 1070, February 1989.
[RFC 2526] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast
Addresses", RFC 2526, March 1999.
[RFC 3068] Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
RFC 3068, June 2001.
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RFC 6179 IRON March 2011
[RFC 4192] Baker, F., Lear, E., and R. Droms, "Procedures for
Renumbering an IPv6 Network without a Flag Day", RFC 4192,
September 2005.
[RFC 4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC 4548] Gray, E., Rutemiller, J., and G. Swallow, "Internet Code
Point (ICP) Assignments for NSAP Addresses", RFC 4548,
May 2006.
[RFC 4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, August 2006.
[RFC 5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
[RFC 5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility
Route Optimization Requirements for Operational Use in
Aeronautics and Space Exploration Mobile Networks",
RFC 5522, October 2009.
[RFC 5720] Templin, F., "Routing and Addressing in Networks with
Global Enterprise Recursion (RANGER)", RFC 5720,
February 2010.
[RFC 5743] Falk, A., "Definition of an Internet Research Task Force
(IRTF) Document Stream", RFC 5743, December 2009.
[RFC 5887] Carpenter, B., Atkinson, R., and H. Flinck, "Renumbering
Still Needs Work", RFC 5887, May 2010.
[RFC 6115] Li, T., "Recommendation for a Routing Architecture",
RFC 6115, February 2011.
[RFC 6139] Russert, S., Fleischman, E., and F. Templin, "Routing and
Addressing in Networks with Global Enterprise Recursion
(RANGER) Scenarios", RFC 6139, February 2011.
[RO-CR] Bernardos, C., Calderon, M., and I. Soto, "Correspondent
Router based Route Optimisation for NEMO (CRON)", Work
in Progress, July 2008.
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RFC 6179 IRON March 2011
[SAMPLE] Carpenter, B. and S. Jiang, "Legacy NAT Traversal for
IPv6: Simple Address Mapping for Premises Legacy Equipment
(SAMPLE)", Work in Progress, June 2010.
[TTRMOB] Whittle, R. and S. Russert, "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",
August 2008.
[V6OPS-TUN-SEC]
Krishnan, S., Thaler, D., and J. Hoagland, "Security
Concerns With IP Tunneling", Work in Progress,
October 2010.
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RFC 6179 IRON March 2011
Appendix A. IRON VPs over Internetworks with Different Address Families
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 [RFC 4548] 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.
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.
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.
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.
Possible encapsulations in this model include IPv6-in-IPv4, IPv4-in-
IPv6, OSI/CLNP-in-IPv6, OSI/CLNP-in-IPv4, etc.
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Appendix B. Scaling Considerations
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.
In terms of routing scaling, each VPC 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.
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 VPC 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.
In terms of state requirements for Relays, each Relay maintains a
list of all Servers in the VPC 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 VPC overlay network.
Sizing the Relay to accommodate state information for all EUNs is
therefore required during VPC 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
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state for all EUNs in the VPC overlay network. Finally, neither
Relays nor Servers need keep state for final destinations of outbound
traffic.
Clients source and sink all traffic packets originating from or
destined to the 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.
Author's Address
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707 MC 7L-49
Seattle, WA 98124
USA
EMail: fltemplin@acm.org
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The Internet Routing Overlay Network (IRON)
RFC TOTAL SIZE: 92638 bytes
PUBLICATION DATE: Saturday, March 12th, 2011
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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