# RIP - Routing Information Protocol ## What is RIP RIP stands for Routing Information Protocol. It is one of the oldest dynamic routing protocols still in use. RIP is a distance vector routing protocol that uses hop count as its metric to determine the best path to a destination. Hop count is the number of routers a packet must pass through to reach the destination. RIP is simple to configure and is suitable for small networks but is not appropriate for large or complex networks due to its limitations. ## How RIP Works Each router running RIP maintains a routing table that lists all known networks and the hop count to reach each one. Routers exchange their complete routing tables with directly connected neighbors every 30 seconds. When a router receives a routing update from a neighbor, it adds one to each hop count to account for the hop to that neighbor, then compares the updated information with its existing routing table. If a new or shorter path is found, the routing table is updated. ## RIP Metric and Maximum Hop Count RIP uses hop count as its only metric. A directly connected network has a hop count of zero. A network reachable through one router has a hop count of one. RIP defines a maximum hop count of 15. Any destination with a hop count of 16 is considered unreachable. This limits RIP networks to a diameter of 15 hops, making it unsuitable for large networks. ## RIP Versions RIP version 1 is a classful routing protocol that does not include subnet mask information in routing updates. This means all interfaces in the same major network must use the same subnet mask and VLSM is not supported. RIP version 2 is a classless routing protocol that includes subnet mask information in routing updates. This supports VLSM and CIDR. RIP version 2 also supports authentication to prevent unauthorized routers from injecting false routing information. RIPng is the version of RIP designed for IPv6 networks. ## RIP Timers RIP uses several timers. The update timer controls how often routing updates are sent, defaulting to 30 seconds. The invalid timer marks a route as invalid if no update is received for 180 seconds. The holddown timer prevents a router from accepting new information about an invalid route for 180 seconds, helping to prevent routing loops. The flush timer removes an invalid route from the table after 240 seconds. ## Limitations of RIP RIP converges slowly when network topology changes because updates are sent only every 30 seconds. The 15 hop limit restricts RIP to small networks. RIP uses only hop count as its metric and does not consider bandwidth, delay, or reliability when choosing paths. A slow one hop link is preferred over a fast two hop link. RIP generates significant network overhead by sending complete routing table updates every 30 seconds.