RFC 2791 (rfc2791) - Page 3 of 26

Scalable Routing Design Principles

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:

      o They are composed of a large number of nodes (routers and/or
        switches), typically in the hundreds. Some provider networks
        include customer CPE routers within their administrative domain,
        which increases the number of nodes to thousands.

      o They have rich connectivity to meet redundancy and robustness
        requirements, and they consequently have complex topologies.

      o They are default-free; that is, they carry all the routes known
        to the entire Internet. Currently, the total number is
        approximately 70,000.

      o The customer aggregation routers inside the large networks
        connect sometimes hundreds of customer routers.

   These characteristics impose a direct challenge to the routing
   scalability of the network.

4. Routing Scaling Issues

   Today, the main issues surrounding routing scaling are: i) excessive
   router resource consumption, which can potentially increase routing
   convergency difficulties thus destabilize a network; and ii) routing
   complexity, resulting in poor management of network, producing low
   service quality.




Yu                           Informational