Cisco IOS in a nutshell - James Boney

Routers are the glue that holds the Internet together, and Cisco Systems--holding roughly 70% of the market--is the most prominent router manufacturer. Cisco's routers come in all shapes and sizes and almost all of them, from the smallest to the largest, run the IOS operating system.
IOS is an extremely powerful and complex operating system, with an equally complex configuration language.
There are many commands, with many options, and if one thing is configured incorrectly, the entire company could find itself offline.Cisco IOS in a Nutshell covers IOS configuration for the TCP/IP protocol family.
The book is divided into two parts: the first part includes chapters on the user interface, configuring lines and interfaces, access lists, routing protocols, and dial-on-demand routing and security; the second part is a classic O'Reilly-style quick reference to all the commands that you need to work with TCP/IP, including the lower-level protocols on which it relies, and lots of examples of the most commonly encountered configuration steps for the routers themselves.