Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 274
Route Reports

Unicast routing information is sent between neighbors using a special packet called a route report. Contained in the route report is a listing of unicast (source) subnets and their masks, and the metric (cost) associated with each subnet. A route learned through route reports should be refreshed within 140 seconds (2 × report interval + 20), after which it can be replaced with the next best route to the same source. If no update and no alternative route exists and 200 seconds have passed, the route is discarded from the routing table.

A route report is sent out every 60 seconds, and any number of route reports can be sent at any time during this interval. In this way, a router is not consumed by a periodic update like RIP that could consist of thousands of routes. At any time during this interval, “flash updates” can be sent. These reports indicate changes in the network but only contain the source subnet that changed. This reduces the loop changes and other catastrophes when paths for source networks change.

Route Reports