RIP (Routing Information Protocol)
A protocol for exchanging routing table information. RIP table entries provide a cost for each destination called hops. In the illustration above, data traveling from LAN X requires two hops to reach LAN Y. Only the segments between the routers counts as a hop. To maintain routing information, RIP-based routers:
- * update their internal routing tables by requesting information from other routers about every 30 seconds
- * respond to route requests from other routers
- * broadcast their presence less than every 180 seconds
- * broadcast information about down routes -- if a router doesn't broadcast its presence after 180 seconds, its routes are considered down
When a router receives RIP updates from another router, each new route added to get to a destination adds to the hop count which is the sum of each leg of the route. If a packet needs to make more than 15 hops, its destination is considered unreachable and the packet is discarded.
In the illustration above it would appear that using Router E would be the shortest path; however, it may be that Routers B and C are on higher speed lines and actually route data faster; or are lower cost lines, and more economical. There are a number of factors that can determine the best route.
RIP version 1 has been made obsolete and replaced by RIP version 2. RIP version 2 recognizes subnets, where version 1 did not. RIP is published as an RFC.