RFC 2791 (rfc2791) - Page 2 of 26

Scalable Routing Design Principles

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



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