Chapter 6. RIP

6.0. Introduction

RIP Version 1 was the Internet’s first widely used routing protocol. It was standardized in RFC 1058, although implementations of the protocol based on de facto standards existed much earlier. It is still useful in small, simple networks. RIP Version 2 is documented in RFC 1723. All Cisco routers support RIP Version 1. Version 2 support was integrated into IOS Version 11.1. A detailed discussion of RIP Versions 1 and 2 is beyond the scope of this book. If you are unfamiliar with dynamic routing protocols in general or with RIP in particular, you can find theoretical descriptions of how the protocol works in IP Routing (O’Reilly) and Designing Large-Scale LANs (O’Reilly). We also recommend reading the appropriate RFCs.

RIP is useful in some situations, but you have to remember its limitations. First, it is a purely classful protocol, and Version 1 doesn’t support variable length subnet masks. So you should not use this protocol if you do any complex subnetting. Second, both Versions 1 and 2 of RIP use the very small metric value of 16 to signify “infinity.” The protocol considers any network that is more than 16 hops away to be unreachable. This is particularly important if you adjust any metric values to make RIP favor a fast link over a slow one. In practice, it is quite easy to exceed the maximum metric, even in small networks.

However, RIP can be extremely useful over small parts of a network. For example, it is much easier to configure than BGP ...

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