One document matched: draft-templin-ironbis-00.txt
Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Informational August 03, 2011
Expires: February 4, 2012
The Internet Routing Overlay Network (IRON)
draft-templin-ironbis-00.txt
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) 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.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on February 4, 2012.
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
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
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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 . . . . . . . . . . . . . . . . . . . 9
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 . . . . . . . . . . . . . . . . 14
6. IRON Operation . . . . . . . . . . . . . . . . . . . . . . . . 15
6.1. IRON Client Operation . . . . . . . . . . . . . . . . . . 15
6.2. IRON Serving Router Operation . . . . . . . . . . . . . . 16
6.3. IRON Relay Router Operation . . . . . . . . . . . . . . . 17
6.4. IRON Reference Operating Scenarios . . . . . . . . . . . . 18
6.4.1. Both Hosts within Same IRON Instance . . . . . . . . . 18
6.4.2. Mixed IRON and Non-IRON Hosts . . . . . . . . . . . . 21
6.4.3. Hosts within Different IRON Instances . . . . . . . . 24
6.5. Mobility, Multihoming, and Traffic Engineering
Considerations . . . . . . . . . . . . . . . . . . . . . . 25
6.5.1. Mobility Management . . . . . . . . . . . . . . . . . 25
6.5.2. Multihoming . . . . . . . . . . . . . . . . . . . . . 26
6.5.3. Inbound Traffic Engineering . . . . . . . . . . . . . 26
6.5.4. Outbound Traffic Engineering . . . . . . . . . . . . . 26
6.6. Renumbering Considerations . . . . . . . . . . . . . . . . 26
6.7. NAT Traversal Considerations . . . . . . . . . . . . . . . 27
6.8. Multicast Considerations . . . . . . . . . . . . . . . . . 27
6.9. Nested EUN Considerations . . . . . . . . . . . . . . . . 28
6.9.1. Host A Sends Packets to Host Z . . . . . . . . . . . . 29
6.9.2. Host Z Sends Packets to Host A . . . . . . . . . . . . 30
7. Implications for the Internet . . . . . . . . . . . . . . . . 31
8. Additional Considerations . . . . . . . . . . . . . . . . . . 32
9. Related Initiatives . . . . . . . . . . . . . . . . . . . . . 32
10. Security Considerations . . . . . . . . . . . . . . . . . . . 33
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 33
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
12.1. Normative References . . . . . . . . . . . . . . . . . . . 34
12.2. Informative References . . . . . . . . . . . . . . . . . . 34
Appendix A. IRON VPs over Internetworks with Different
Address Families . . . . . . . . . . . . . . . . . . 36
Appendix B. Scaling Considerations . . . . . . . . . . . . . . . 37
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 38
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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) [RFC5720] examines
recursive arrangements of enterprise networks that can apply to a
very broad set of use-case scenarios [RFC6139]. 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)
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) [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].
IRON supports scalable addressing without changing the current BGP
[RFC4271] routing system. IRON observes the Internet Protocol
standards [RFC0791][RFC2460]. Other network-layer protocols that can
be encapsulated within IP packets (e.g., OSI/CLNP (Connectionless
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Network Protocol) [RFC1070], etc.) are also within scope.
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
[RFC4192][RFC5887]. 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.
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 (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).
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.
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):
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.
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IRON Client Router/Host ("Client"):
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.
IRON Serving Router ("Server"):
a VSP's IRON instance router that provides forwarding and mapping
services for the EPs owned by customer Clients.
IRON Relay Router ("Relay"):
a VSP's IRON instance 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.
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 Service Provider (VSP).
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Virtual Service Provider (VSP):
a company that owns and manages a set of VPs from which it
delegates EPs to EUNs.
VSP Overlay Network:
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).
3. The Internet Routing Overlay Network
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.
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) [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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+-------------------------+
| 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.
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.
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.
IRON requires no changes to end systems or to most routers in the
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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.
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 VSP IRON instance via tunnels, as shown in Figure 2. 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.
.-.
,-( _)-.
+--------+ .-(_ (_ )-.
| Client |--(_ ISP )
+---+----+ `-(______)-'
| <= T \ .-.
.-. u \ ,-( _)-.
,-( _)-. n .-(_ (- )-.
.-(_ (_ )-. n (_ Internet )
(_ EUN ) e `-(______)-
`-(______)-' l ___
| s => (:::)-.
+----+---+ .-(::::::::)
| Host | .-(::: IRON :::)-.
+--------+ (:::: Instance ::::)
`-(::::::::::::)-'
`-(::::::)-'
Figure 2: IRON Client Router Connecting EUN to IRON Instance
3.2. IRON Serving Router
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 Figure 3) so that Clients
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can discover those that are nearby.
+--------+ +--------+
| Boston | | Tokyo |
| Server | | Server |
+--+-----+ ++-------+
+--------+ \ /
| Seattle| \ ___ /
| Server | \ (:::)-. +--------+
+------+-+ .-(::::::::)------+ Paris |
\.-(::: IRON :::)-. | Server |
(:::: Instance ::::) +--------+
`-(::::::::::::)-'
+--------+ / `-(::::::)-' \ +--------+
| Moscow + | \--- + Sydney |
| Server | +----+---+ | Server |
+--------+ | Cairo | +--------+
| Server |
+--------+
Figure 3: IRON Serving Router Global Distribution Example
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.
3.3. IRON Relay Router
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.
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 Figure 4.
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.-.
,-( _)-.
.-(_ (_ )-.
(_ Internet )
`-(______)-' | +--------+
| |--| Server |
+----+---+ | +--------+
| Relay |----| +--------+
+--------+ |--| Server |
_|| | +--------+
(:::)-. (Ethernet)
.-(::::::::)
+--------+ .-(::: IRON :::)-. +--------+
| Server |=(:::: Instance ::::)=| Server |
+--------+ `-(::::::::::::)-' +--------+
`-(::::::)-'
|| (Tunnels)
+--------+
| Server |
+--------+
Figure 4: IRON Relay Router Connecting IRON Instance to Native
Internet
4. IRON Organizational Principles
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.
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. Figure 5 depicts the
logical arrangement of Relays, Servers, and Clients in an IRON
virtual overlay network.
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.-.
,-( _)-.
.-(_ (_ )-.
(__ Internet _)
`-(______)-'
<------------ Relays ------------>
________________________
(::::::::::::::::::::::::)-.
.-(:::::::::::::::::::::::::::::)
.-(:::::::::::::::::::::::::::::::::)-.
(::::::::::: IRON Instance :::::::::::::)
`-(:::::::::::::::::::::::::::::::::)-'
`-(::::::::::::::::::::::::::::)-'
<------------ Servers ------------>
.-. .-. .-.
,-( _)-. ,-( _)-. ,-( _)-.
.-(_ (_ )-. .-(_ (_ )-. .-(_ (_ )-.
(__ ISP A _) (__ ISP B _) ... (__ ISP x _)
`-(______)-' `-(______)-' `-(______)-'
<----------- NATs ------------>
<----------- Clients and EUNs ----------->
Figure 5: IRON Organization
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.
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).
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
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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.
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.
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,.
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 instance initialization entails the startup actions of IAs and
customer EUNs. The following sub-sections discuss these startup
procedures.
5.1. IRON Relay Router Initialization
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
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Servers within the IRON instance. The Relay is also provisioned with
external BGP interconnections -- the same as for any BGP router.
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 "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.
5.2. IRON Serving Router Initialization
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.
5.3. IRON Client Initialization
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
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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.
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) [RFC5214].)
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.
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.
6. IRON Operation
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 [INTAREA-VET] and SEAL [INTAREA-SEAL],
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.
6.1. IRON Client Operation
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
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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.
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.
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.
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.
6.2. IRON Serving Router Operation
After the Server is initialized, it responds to SRS messages from
tunnel-neighbor Clients by sending SRAs.
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
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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.
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.
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.
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 VSP'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 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.
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6.4. IRON Reference Operating Scenarios
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.
6.4.1. Both Hosts within Same IRON Instance
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.
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. Figure 6 shows the
flow of initial packets from host A to host B within EUNs of the same
IRON instance:
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________________________________________
.-( .-. )-.
.-( ,-( _)-. )-.
.-( +========+(_ (_ +=====+ )-.
.( || (_|| 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 |
+--------+ +--------+
Figure 6: Initial Packet Flow before Redirects
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 address of a nearby
IRON instance Relay(R). Server(A) then forwards the revised
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encapsulated packets into the Internet, where routing will direct
them to Relay(R).
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).
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.
(*) 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 Figure 7.
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________________________________________
.-( .-. )-.
.-( ,-( _)-. )-.
.-( +=============> .-(_ (_ )-.======+ )-.
.( // (__ 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 |
+--------+ +--------+
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.
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_________________________________________
.-( )-. )-.
.-( +-------)----+ )-.
.-( | 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 |
+--------+ +--------+
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
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-
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instruction imaginary operation within the gateway.)
This scenario always involves a Server and Relay owned by the VSP
that provides service to IRON EUN A.
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) | \ ).
.( // +--------)---+ \ ).
( // ) \ )
( // 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 |
+--------+ +--------+
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.
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
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(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.
This scenario always involves a Server and Relay owned by the VSP
that provides service to IRON EUN A.
6.4.3. Hosts within Different IRON Instances
Figure 10 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.
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_________________________________________
.-( )-. )-.
.-( +-------)----+ +---(--------+ )-.
.-( | 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 |
+--------+ +--------+
Figure 10: Hosts within Different IRON Instances
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.
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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.
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.
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 VSP 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
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undergo a painstaking EUN renumbering process if it wishes to change
to a different ISP [RFC4192][RFC5887].
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.
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, e.g., UDP, TCP, SSL, etc.
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.
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 [RFC4605]. Further
multicast considerations for IRON (e.g., interactions with multicast
routing protocols, traffic scaling, etc.) will be discussed in a
separate document.
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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.
For example, in the network scenario depicted in Figure 11, 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.
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.-.
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 |
`-(______)-' +--------+
Figure 11: 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.
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
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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
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)
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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 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.
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
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.
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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
[RFC5522].
9. Related Initiatives
IRON builds upon the concepts of the RANGER architecture [RFC5720] ,
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
[RFC6115].
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].
[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
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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 [RFC5720] , 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 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).
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.
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.
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.
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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.
12. References
12.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC2460] 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.
[RFC1070] 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.
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[RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for
Renumbering an IPv6 Network without a Flag Day", RFC 4192,
September 2005.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4548] Gray, E., Rutemiller, J., and G. Swallow, "Internet Code
Point (ICP) Assignments for NSAP Addresses", RFC 4548,
May 2006.
[RFC4605] 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.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
[RFC5522] 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.
[RFC5720] Templin, F., "Routing and Addressing in Networks with
Global Enterprise Recursion (RANGER)", RFC 5720,
February 2010.
[RFC5743] Falk, A., "Definition of an Internet Research Task Force
(IRTF) Document Stream", RFC 5743, December 2009.
[RFC5887] Carpenter, B., Atkinson, R., and H. Flinck, "Renumbering
Still Needs Work", RFC 5887, May 2010.
[RFC6115] Li, T., "Recommendation for a Routing Architecture",
RFC 6115, February 2011.
[RFC6139] 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.
[SAMPLE] Carpenter, B. and S. Jiang, "Legacy NAT Traversal for
IPv6: Simple Address Mapping for Premises Legacy Equipment
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(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.
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 [RFC4548] 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.
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Possible encapsulations in this model include IPv6-in-IPv4, IPv4-in-
IPv6, OSI/CLNP-in-IPv6, OSI/CLNP-in-IPv4, etc.
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 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.
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.
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
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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.
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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