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Routing Information Protocol (RIP) is a relatively simple interior gateway protocol 
(IGP), which is mainly applied to small scale networks.

It is easy to implement RIP. You can configure and maintain RIP more easily than 
OSPF and IS-IS, so RIP still has a wide application in actual networking.

RIP is a kind of Distance-Vector (D-V) algorithm-based protocol and exchanges 
routing information via UDP packets.

It employs Hop Count to measure the distance to the destination host, which is 
called Routing Cost. In RIP, the hop count from a router to its directly connected 
network is 0, and that to a network which can be reached through another router 
is 1, and so on. To restrict the time to converge, RIP prescribes that the cost value 
is an integer ranging from 0 to 15. The hop count equal to or exceeding 16 is 
defined as infinite, that is, the destination network or the host is unreachable.

To improve the performance and avoid route loop, RIP supports Split Horizon and 
allows importing the routes discovered by other routing protocols.

Each router running RIP manages a route database, which contains routing entries 
to all the reachable destinations in the network. These routing entries contain the 
following information:

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Destination address: IP address of a host or a network.

■

Next hop address: The interface address of the next router that an IP packet will 
pass through for reaching the destination.

■

Output interface: The interface through which the IP packet should be 
forwarded.

■

Cost: The cost for the router to reach the destination, which should be an 
integer in the range of 0 to 16.

■

Timer: Duration from the last time that the routing entry is modified till now. 
The timer is reset to 0 whenever a routing entry is modified.

In RFC1058, RIP is controlled by the following timers: Period update, Timeout and 
Garbage-Collection.

■

Period Update is triggered periodically to send all RIP routes to all neighbors.