Scalable Routing Design Principles
RFC 2791

Document Type RFC - Informational (July 2000; No errata)
Was draft-yu-routing-scaling (individual)
Last updated 2013-03-02
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Network Working Group                                              J. Yu
Request for Comments: 2791                         CoSine Communications
Category: Informational                                        July 2000

                   Scalable Routing Design Principles

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 (2000).  All Rights Reserved.

Abstract

   Routing is essential to a network. Routing scalability is essential
   to a large network. When routing does not scale, there is a direct
   impact on the stability and performance of a network. Therefore,
   routing scalability is an important issue, especially for a large
   network. This document identifies major factors affecting routing
   scalability as well as basic principles of designing scalable routing
   for large networks.

Yu                           Informational                      [Page 1]
RFC 2791           Scalable Routing Design Principles          July 2000

Table of Contents

   1           Introduction  ..................................      2
   2           Common Routing Design Goals  ...................      3
   3           Characteristics of Today's Large Networks  .....      3
   4           Routing Scaling Issues  ..........................    3
   4.1         Router Resource Consumption  .....................    4
   4.2         Routing Complexity  ..............................    5
   5           Routing Protocol Scalability .....................    6
   5.1         IS-IS and OSPF  ..................................    6
   5.2         BGP  .............................................    8
   6           Scalable Routing Design Principles  ..............    9
   6.1         Building Hierarchy  ..............................   10
   6.2         Compartmentalization  ............................   13
   6.3         Making Proper Trade-offs  ........................   13
   6.4         Reduce Burdens of Routing Information Process  ...   14
   6.4.1       Routing Intelligence Placement  ..................   14
   6.4.2       Reduce Routes and Routing Information  ...........   15
   6.4.2.1     CIDR and Route Aggregation  ......................   15
   6.4.2.2     Utilize Default Routing where it's Possible  .....   15
   6.4.2.3     Reduce Alternative Paths  ........................   16
   6.4.3       Use Static Route at Edge  .........................  16
   6.4.4       Minimize the Impact of Route Flapping  ............  16
   6.5         Scalable Routing Policy and Scalable Implementation  17
   6.6         Out-of-band Process  ..............................  19
   7           Conclusion and Discussion  ........................  19
   8           Security Considerations  ..........................  20
   9           Acknowledgement  ..................................  21
   10          References  .......................................  21
   Author's Address ..............................................  22
   Appendix A  Out-of-Band Routing Processes  ....................  23
   Full Copyright Statement  .....................................  26

1. Introduction

   Routing is essential to a network. Without routing, packets cannot be
   delivered to desired destinations and the network would be non-
   functional. The challenge of designing the routing for a large
   network, such as a large ISP backbone network, is not only to make it
   work, but also to make it scale. Without a scalable routing system, a
   network may suffer from severe performance penalties, as
   unfortunately proven by disastrous events in large networks. This
   document attempts to analyze routing scalability issues and define a
   set of principles for designing scalable routing system for large
   networks.

   The organization of this document is as follows: Section 2 describes
   routing functions and design goals. Sections 3 and 4 discuss the

Yu                           Informational                      [Page 2]
RFC 2791           Scalable Routing Design Principles          July 2000

   characteristics of today's large networks and the associated routing
   scaling issues. Section 5 explores routing protocol scalability, and
   Section 6 presents scalable routing design principles. Section 7
   provides a conclusion to the document.

2. Common Routing Design Goals

   The basic goals a routing system should achieve are as follows:

      o Stability
      o Redundancy and robustness
      o Reasonable convergency time
      o Routing information integrity
      o Sensible and manageable routing policy

   The challenge of designing routing in a large network is not only to
   achieve these basic goals but also to make the routing system scale.

3. Characteristics of Today's Large Networks

   Today's large networks typically possess the following features:
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