RIP or the Routing Information Protocol was standardized in RFC1058 in 1988. It was developed from earlier routing protocols developed at Xerox. RIP has three major versions RIPv1 (1988), RIPv2 (RFC2453 1998), and RIPng (RFC2080 1997). RIP version 2 added support for VLSM and CIDR and version ng or next generation adds support for IPv6.
1. Classful routing – RIP is a classful routing protocol, it does not send or receive subnet masks, it assumes classful subnet masks
2. Periodic updates – RIP broadcasts routing updates every 30 seconds. It broadcasts the entire routing table in the update.
3. Triggered updates – RIP also broadcasts updates when there is a change in the topology, like a network going up or down.
4. Metric – RIP’s metric is hop count. A hop is a router, so a RIP route with metric of 2 means the network is two routers away. RIP’s maximum distance is 15 hops. 16 hops is infinity and is used to mark a route as dead. A router that receives a packet then removed from the routing table.
5. Administrative Distance – RIP’s administrative distance is 120. AD ranks the trustworthiness, or reliability of the route, the lower the administrative distance the better the route.
6. Hold Down Timer – RIP uses a hold down timer of 180 seconds so that it does not propagate bad routes and does not have a count-to-infinity routing loop. Route is flushed at 240 seconds
7. Load Balancing – Default load balancing across 4 equal cost routes. Can go up to 6 routes.
8. Count to infinity – is prevented by hold down timers and by RIPs maximum metric of 15 hops.
9. Routing Loops – are prevented by: Hold Down Timer, Split Horizon Rule, Route Poisoning, Route Poisoning with Poison Reverse, as well as TTL.
10. Automatic Route Summarization. RIP automatically summarizes routes into classful network ranges because it will not allow non-classful network configuration or the propagation of non-classful subnet masks. It can only advertise classful networks. This can cause problems if subnetted networks are configured on multiple router interfaces in a discontiguous manner (see the video tutorials below for a demonstration).
11. Transport Layer – RIP sends out updates on UDP port 520
IOS CLI commands to use with RIP
router(config)#router rip //to activate RIP
router(config-router)#network <network ip address> //to add a participating network and interface
router(config-router)#passive-interface <interface type> <interface number> //to stop RIP from sending updates out of an interface
router#show running-config //to verify your configuration
router#show ip route //to verify your routing table
router#show ip protocols //to verify your RIP configuration
router#copy running-config startup-config //to save your configuration
In this part, I prepare the network and configure the network interfaces
In this part, I demonstrate how RIP auto-summarizes classless subnets
In this part, I demonstrate how auto-summary can create a problem if the networks are discontiguous