In the first edition of this book, I may have dated myself a bit by starting this chapter off with the following paragraph:
The modern world is networked in a way that could barely be imagined a few decades ago. Today, the Internet reaches into virtually every business and almost every home. Our children and even our grandparents speak of dot-coms, email, and web sites. The Internet is now part of our culture.
Almost four years have passed since then, which does not seem like much time at all. But in the networking and computer fields, that's a very long time indeed. Our children and grandparents now speak of dot-bombs, MP3s, broadband, voice over IP, instant messaging, and outsourcing. Even the once-killer app email has been surpassed by the gratification of instant messaging. Things have certainly changed, which leaves us to wonder what the next few years will bring.
No matter what happens, Cisco is likely to continue its dominance of the networking world. Even that little router sitting on your cable or DSL connection at home could very well be a Cisco device. Routers and switches are the glue that holds the Internet together. And Cisco is the most prominent router manufacturer, holding the largest share of the market. Their routers come in all shapes and sizes, from inexpensive units for homes and small offices to equipment that costs hundreds of thousands of dollars, used by very large ISPs and telcos. Almost all of their devicesfrom the smallest to the largestrun the Internetwork Operating System (IOS) . Therefore, they share the same command set, the same user interface, and the same configuration techniques. While a small home network router doesn't have the features or the capacity of an ISP's router, you configure them pretty much the same way. Both routers use access lists, have similar security mechanisms, support the same set of protocols in the same way, and so on.
As Cisco continues developing its product line, it's clear that the Internetwork Operating System (IOS) is a key part of its strategy. As new products come out, they all have the familiar IOS interface.
IOS is an extremely powerful and complex operating system with an equally complex configuration language. There are many commands, with many options, and if you get something wrong you can easily take your company offline. That's why I've decided to provide a quick-reference guide to IOS. As large a book as this is, though, it's impossible to cover all of IOS. Therefore, I've limited the discussion to IOS configuration for the TCP/IP protocol family. I've included all the commands that you need to work with TCP/IP and the lower-level protocols on which it relies. In the last edition, I apologized for not including other protocols such as IPX due to the lack of space in a handy reference. Today, there is hardly a need for such an apology, as TCP/IP has become the standard networking protocol for all but the most legacy network environments.
This book is intended as a quick reference, not as a step-by-step exposition of routing protocols or as an IOS tutorial. I haven't focused on thorough explanation; instead, I've tried to give lots of examples of the things people most frequently need to do when configuring a Cisco router, with just enough explanation to get you by. I'll start with the user interface (Chapters 1, 2, and 3), then talk about configuring lines and interfaces (Chapters 4, 5, and 6), access lists (Chapter 7), and routing protocols (Chapters 8, 9, and 10). Chapter 11, new in this edition, addresses quality of service issues, while Chapter 12 describes dial-on-demand routing. Chapter 13 covers a variety of networking topics, including bridging, Network Address Translation (NAT), tunnels, and Multiprotocol Label Switching (MPLS). Chapter 14, also new to this edition, describes working with switches and VLANs. Chapters 15 and 16 cover IOS security and troubleshooting, respectively. Chapter 17 is the quick reference. Chances are, by the time the next edition of this book appears, the quick-reference section will be pretty well thumbed and worn out.
At first, the Cisco user interface appears cryptic. After learning the interface's structure, you'll become much more comfortable with it. Once you have learned some special features, you'll be able to work with the router's configuration easily.