Cisco routers are nearly ubiquitous in IP networks. They are extremely flexible and reliable devices, and the number and variety of features grows with each new release of the Internetwork Operating System (IOS). While Cisco Press and several other publishers supply excellent documentation of router features both online and in a variety of books, knowing when, why, and how to use these features is sometimes difficult. There are often many different ways to solve any given networking problem using Cisco devices, and some solutions are clearly more effective than others.

The two immediate questions facing any network engineer are: Which of the many potential solutions is the most appropriate for a particular situation? and, Once you have decided to use a particular feature, how should you implement it? Unfortunately, the feature documentation describing a particular command or feature frequently does very little to answer either of these questions.

Everybody who has worked with Cisco routers for any length of time has had to ask their friends and co-workers for example router configuration files that show how to solve a common problem. A good working configuration example can often save huge amounts of time and minimize the frustration that sometimes comes with implementing a feature that you've never used before.

Instead, this book is a complement to those sources of information. They will tell you what a routing protocol is, how it works, and which command turns it on. Cisco Cookbook will help you select the right routing protocol and configure it in the most efficient way for your network.

This book includes a collection of sample router configurations and scripts that we have found useful in real-world networks. It also includes, wherever possible, our advice on what features to use in which situations, and how to use them most effectively. There are many common mistakes that we have seen before, and we want to help you to avoid making them.

All of the recipes in this book should work with IOS levels 11.3, 12.0, 12.1, 12.2, and 12.3. And, except where noted, they should run on any Cisco router platform. We have indicated when we use features that are only available with certain release levels or code sets, and in some cases offered workarounds for older versions. It is also important to remember that most of the recipes will work not only with Cisco routers, but also with any Catalyst switches that run IOS (but unfortunately not CatOS switches). In particular, all of the recipes that pertain to AAA, security, syslog, and SNMP should work well on these devices.