Washington Elementary School District
Routing Updates on the WAN

In order for a network to dynamically respond to changes in topology, a routing protocol must be implemented. Routing protocols allow routers to exchange information about available routes, and receive updates when changes occur to ensure that packets are being delivered in the most efficient way. However, these updates consume network bandwidth, so the network designer must balance the advantages of dynamic updates with the disadvantage of reduced bandwidth for data.

The routing protocol chosen for the Washington Elementary School District network is IGRP. IGRP is a Cisco-proprietary distance-vector routing protocol, which means that it periodically sends its full routing table to its neighbors. By default, IGRP sends its table every 90 seconds. If the router does not receive an update about a route after 270 seconds, it marks it as down, and flushes the route from its table if it does not receive an update after 630 seconds. On the Washington Elementary School District network, the default values will be used. The configuration of IGRP on the Phoenix C.O. WAN core router can be seen here.

It is not anticipated that the routing updates will have a significant negative effect on WAN core throughput. Even with 39 total routers on the network, routing tables should be relatively small, and therefore should not take up much bandwidth when updates are sent. In addition, each core router has four T1 connections to each of its neighbors, which should ensure that routing updates have minimal impact on core bandwidth.