IPv4 Multihoming Practices and Limitations
RFC 4116
Network Working Group J. Abley
Request for Comments: 4116 ISC
Category: Informational K. Lindqvist
Netnod Internet Exchange
E. Davies
Independent Researcher
B. Black
Layer8 Networks
V. Gill
AOL
July 2005
IPv4 Multihoming Practices and Limitations
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
Multihoming is an essential component of service for many Internet
sites. This document describes some implementation strategies for
multihoming with IPv4 and enumerates features for comparison with
other multihoming proposals (particularly those related to IPv6).
Abley, et al. Informational [Page 1]
RFC 4116 IPv4 Multihoming July 2005
Table of Contents
1. Introduction ....................................................3
2. Terminology .....................................................3
3. IPv4 Multihoming Practices ......................................4
3.1. Multihoming with BGP .......................................4
3.1.1. Addressing Considerations ...........................4
3.1.2. AS Number Considerations ............................6
3.2. Multiple Attachments to a Single Transit Provider ..........6
3.3. NAT- or RFC2260-based Multihoming ..........................7
4. Features of IPv4 Multihoming ....................................7
4.1. Redundancy .................................................7
4.2. Load Sharing ...............................................8
4.3. Performance ................................................8
4.4. Policy .....................................................8
4.5. Simplicity .................................................9
4.6. Transport-Layer Survivability ..............................9
4.7. Impact on DNS ..............................................9
4.8. Packet Filtering ...........................................9
4.9. Scalability ................................................9
4.10. Impact on Routers ........................................10
4.11. Impact on Hosts ..........................................10
4.12. Interactions between Hosts and the Routing System ........10
4.13. Operations and Management ................................10
4.14. Cooperation between Transit Providers ....................10
5. Security Considerations ........................................10
6. Acknowledgements ...............................................10
7. Informative References .........................................11
Abley, et al. Informational [Page 2]
RFC 4116 IPv4 Multihoming July 2005
1. Introduction
Multihoming is an important component of service for many Internet
sites. Current IPv4 multihoming practices have been added on to the
Classless Inter Domain Routing (CIDR) architecture [RFC1519], which
assumes that routing table entries can be aggregated based upon a
hierarchy of customers and service providers.
Multihoming is a mechanism by which sites can satisfy a number of
high-level requirements. It is widely used in the IPv4 Internet.
There are some practical limitations, however, including concerns as
to how it would scale with future Internet growth. This document
aims to document common IPv4 multihoming practices and enumerate
their features for comparison with other multihoming approaches.
There are a number of different ways to route and manage traffic in
and out of a multihomed site: the majority rely on the routing policy
capabilities of the inter-domain routing protocol, the Border Gateway
Protocol, version 4 (BGP) [RFC1771]. This document also discusses a
multi-homing strategy which does not rely on the capabilities of BGP.
2. Terminology
A "site" is an entity autonomously operating a network using IP, and
in particular, determining the addressing plan and routing policy for
that network. This definition is intended to be equivalent to
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