CISCO IOS in a Nutshell

Preface

This is a book for everybody who has to deal with Cisco’s routers.

As you well know, Cisco Systems has created an extremely diverse line of routers and other network products. One unifying thread runs through the product line: virtually all of Cisco’s products run the Internetwork Operating System (IOS). This is both a great advantage and a great disadvantage. On the one hand, when you’re familiar with one Cisco router, you’re reasonably familiar with them all. Someone using a small ISDN router in a home office could look at a configuration file for a high-end router at an ISP and not be lost. He might not understand how to configure the more esoteric routing protocols or high-speed network interfaces, but he’d be looking at a language that was recognizably the same.

On the other hand, this uniformity means that just about everything has been crammed into IOS at one time or another. IOS is massive—there’s no other way to say it. And it has evolved over many years. The command-line interface isn’t graceful, and is often non-uniform: many commands don’t do what you think they should, and the same command verbs can mean completely different things in different contexts. This inconsistency is probably a natural result of evolution at an extremely large company with an extremely large number of developers, but it doesn’t make life any easier.

So, where do you find out what commands you need to know? There’s the almost mythical “green wall” of Cisco documentation, but it’s difficult ...