Routing Information Protocol (RIP)

A routing protocol that is used to exchange routing information between dynamic routers on Internet Protocol (IP) or Internetwork Packet Exchange (IPX) inter networks. Routing Information Protocol (RIP) was designed in 1980 to be used with the Xerox Network Systems (XNS) protocol suite but is most commonly used today in small to mid-sized TCP/IP inter networks. It is supported by Microsoft Windows NT Server and Microsoft Windows 2000,2003 Server and has been adapted to the AppleTalk networking system as the Routing Table Maintenance Protocol (RTMP) 

How It Works: 

1. RIP is based on the distance vector routing algorithm, one of several common routing algorithms that routers use to dynamically calculate the cost or metric of each possible path through an inter network.

2. Routing tables in RIP-enabled routers are calculated on the basis of the number of hops to the destination network.

3. RIP routers do not use other routing metrics such as load, bandwidth, latency, or Maximum Transmission Unit (MTU) in calculating routing costs. 

4. RIP-enabled routers on a TCP/IP internetwork broadcast their complete routing tables every 30 seconds over User Datagram Protocol (UDP) port 520 using RIP advertisements. 

5. You might assume that this adds a lot of overhead to network traffic, but this information is broadcast information and is thus propagated only throughout the local network and received only by routers that have a routing interface to the local network 

6. When a RIP router is first turned on, it announces its presence using a General RIP Request message so that neighboring RIP routers can send it advertisements of their routing tables. 

7. These RIP advertisements from neighboring RIP routers allow the router to build its own routing tables. 

8. RIP supports a maximum metric of 15; networks that are more than 15 hops away are unreachable using RIP. This limits RIP implementation to small and mid-sized inter networks. 

9. Its main disadvantage is that the routing table of a RIP-enabled router can be quite large because it contains all possible routes to all possible networks. RIP advertisement packets are only 512 bytes in length and can contain a maximum of 25 different routing table entries, so a large routing table with hundreds of entries means that dozens of RIP packets are broadcast every 30 seconds. This can result in a lot of extra broadcast traffic on the local subnet. RIP is therefore not suitable for large inter networks 

10. Routing entries in a RIP routing table time out 3 minutes after the last RIP announcement is received, so if a RIP router goes down, it takes time for this information to propagate throughout the internetwork, a problem known as slow convergence. This 3-minute timeout value exists so that information about routers that unexpectedly fail or go down can be propagated throughout the inter network.