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The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  TCP/IP Routing Protocols (Gateway Protocols)                 9  TCP/IP Interior Routing Protocols (RIP, OSPF, GGP, HELLO, IGRP, EIGRP)                      9  TCP/IP Routing Information Protocol (RIP, RIP-2 and RIPng)                           9  RIP Fundamentals and General Operation

RIP Fundamentals and General Operation 1 2 3 RIP Route Determination Algorithm and Metric

RIP Operational Overview, Advantages and Limitations

On a regular basis, each router in the internetwork sends out its routing table in a special message on each of the networks to which it is connected, using UDP. Other routers receive these tables and use them to update their own tables. This is done by taking each of the routes they receive and adding an extra hop. For example, if router A receives an indication from router B that network N1 is 4 hops away, then since router A and router B are adjacent, the distance from router A to N1 is 5. After a router updates its tables, it in turn sends out this information to other routers on its local networks. Over time, routing distance information for all networks propagates over the entire internetwork.

RIP is straight-forward in operation, easy to implement, and undemanding of router processing power, which makes it attractive especially in smaller autonomous systems. There are, however, some important limitations that arise due to the simplicity of the protocol. For starters, hops are often not the best metric to use in selecting routes. There are also a number of problems that arise with the algorithm itself. These include slow convergence (delays in having all routers agree on the same routing information) and problems dealing with network link failures.

RIP includes several special features to resolve some of these issues, but others are inherent limitations of the protocol. For example, RIP only supports a maximum of 15 hops between destinations, making it unsuitable for very large autonomous systems, and this cannot be changed.

RIP Fundamentals and General Operation 1 2 3 RIP Route Determination Algorithm and Metric