Routing Information Protocol

Routing information protocol (RIP) is a true distance-vector routing protocol. RIP sends the complete routing table out to all active interfaces every 30 seconds. RIP only uses hop count to determine the best way to remote network, but it has a maximum allowable hop count of 15 unreachable. RIP works well in small networks, but i,s inefficient on large networks with slow WAN links or on networks with a large number of routers installed.

   RIP Version 1 uses only classful routing, which means that all devices in the network must use the same subnet mask. This is because RIP version 1 doesn't send updates with subnet mask information in tow. RIP version 2 provides something called prefix routing and does send subnet mask information with the route updates. This is called classless routing.

RIP Timers: RIP uses four different kinds of timers to regulate its performance:

Route Update Timer Sets the interval (typically 30 seconds) between periodic routing updates in which the router sends a complete copy of its routing table out to all neighbors.

Route Invalid Timer Determines the length of time that must elapse (180 seconds) before a router determines that a route has become invalid. It will come to this conclusion if it hasn't heard any updates about a particular route for that period. When that happens, the router will send out updates to all its neighbors letting them know that the route is invalid.

Holddown Timer This sets the amount of time during which routing information is suppressed. Routes will enter into the holddown state when an update packet is received that indicates the route is unreachable. This continues either until an update packet is received with a better metric, the original route comes back up, or the holddown timer expires. The default is 180 seconds.

Route Flush Timer Sets the time between a route becoming invalid and its removal from the routing table (240 seconds). Before it's removed from the table, the router notifies its neighbors of that route's impending demise. The value of the route invalid timer must be less than that of the route flush timer. This gives the router enough time to tell its neighbors about the invalid route before the local routing table is updated.

Configuring RIP Routing: To configure RIP routing, just turn on the protocol with the router rip command and tell the RIP routing protocol which networks to advertise.

You can add the RIP routing protocol  by using the router rip command and the network command. The network command tells the routing protocol which classful network to advertise. By doing this process, you activate the RIP routing process on the interfaces whose addressing falls within the specified classful networks configured with the network command under the RIP routing process.
example: Router(config)# router rip
Router(config)#network 10.0.0.0

Verifying the RIP Routing Tables Each routing table should now have all directly connected routers as well as RIP-injected routes received from neighboring routers. Now we can go back to the Corp router and check it out.

example: 10.0.0.0/24 is subnetted, 5 subnets

C 10.1.1.0 is directly connected, serial0/0/0

C 10.1.2.0 is directly connected, serial0/0/1

172.16.0.0/16 is varibly subnetted,2 subnets, 2 masks

R 172.16.0.0/16 [120/1] via 10.1.5.2 00:00:19, fastethernet0/0

S  172.16.10.0/24 [150/0] via 10.1.5.2

Holding Down RIP Propagations You probably don't want you RIP network advere on your LAN and WAN. There's not a whole lot to be gained by advertising your RIP network to the Internet.

  There are a few different ways to stop unwanted RIP updates from propagating across your LANs and WANs, and the easiest one is through the passive-interface command. This command prevents RIP update broadcasts from being sent out a specified interface, yet that same interface can still receive RIP updates.