Commentary on Inter-Domain Routing in the Internet
RFC 3221

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Network Working Group                                          G. Huston
Request for Comments: 3221                   Internet Architecture Board
Category: Informational                                    December 2001

                             Commentary on
                  Inter-Domain Routing in the Internet

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 (2001).  All Rights Reserved.

Abstract

   This document examines the various longer term trends visible within
   the characteristics of the Internet's BGP table and identifies a
   number of operational practices and protocol factors that contribute
   to these trends.  The potential impacts of these practices and
   protocol properties on the scaling properties of the inter-domain
   routing space are examined.

   This document is the outcome of a collaborative exercise on the part
   of the Internet Architecture Board.

Table of Contents

   1.   Introduction.................................................  2
   2.   Network Scaling and Inter-Domain Routing  ...................  2
   3.   Measurements of the total size of the BGP Table  ............  4
   4.   Related Measurements derived from BGP Table  ................  7
   5.   Current State of inter-AS routing in the Internet  .......... 11
   6.   Future Requirements for the Exterior Routing System  ........ 14
   7.   Architectural Approaches to a scalable Exterior
          Routing Protocol........................................... 15
   8.   Directions for Further Activity  ............................ 21
   9.   Security Considerations  .................................... 22
   10.  References  ................................................. 23
   11.  Acknowledgements  ........................................... 24
   12.  Author's Address  ........................................... 24
   13.  Full Copyright Statement  ................................... 25

Huston                       Informational                      [Page 1]
RFC 3221           Commentary on Inter-Domain Routing      December 2001

1.  Introduction

   This document examines the various longer term trends visible within
   the characteristics of the Internet's BGP table and identifies a
   number of operational practices and protocol factors that contribute
   to these trends.  The potential impacts of these practices and
   protocol properties on the scaling properties of the inter-domain
   routing space are examined.

   These impacts include the potential for exhaustion of the existing
   Autonomous System number space, increasing convergence times for
   selection of stable alternate paths following withdrawal of route
   announcements, the stability of table entries, and the average prefix
   length of entries in the BGP table.  The larger long term issue is
   that of an increasingly denser inter-connectivity mesh between ASes,
   causing a finer degree of granularity of inter-domain policy and
   finer levels of control to undertake inter-domain traffic
   engineering.

   Various approaches to a refinement of the inter-domain routing
   protocol and associated operating practices that may provide superior
   scaling properties are identified as an area for further
   investigation.

   This document is the outcome of a collaborative exercise on the part
   of the Internet Architecture Board.

2.   Network Scaling and Inter-Domain Routing

   Are there inherent scaling limitations in the technology of the
   Internet or its architecture of deployment that may impact on the
   ability of the Internet to meet escalating levels of demand? There
   are a number of potential areas to search for such limitations.
   These include the capacity of transmission systems, packet switching
   capacity, the continued availability of protocol addresses, and the
   capability of the routing system to produce a stable view of the
   overall topology of the network.  In this study we will look at this
   latter capability with the objective of identifying some aspects of
   the scaling properties of the Internet's routing system.

   The basic structure of the Internet is a collection of networks, or
   Autonomous Systems (ASes) that are interconnected to form a connected
   domain.  Each AS uses an interior routing system to maintain a
   coherent view of the topology within the AS, and uses an exterior
   routing system to maintain adjacency information with neighboring
   ASes to create a view of the connectivity of the entire system.

Huston                       Informational                      [Page 2]
RFC 3221           Commentary on Inter-Domain Routing      December 2001

   This network-wide connectivity is described in the routing table used
   by the BGP4 protocol (referred to as the Routing Information Base, or