Chapter 13. Specialized Networking Topics

This chapter covers a number of IP configuration topics that won’t find their way into simple configurations. However, they are becoming more prevalent in corporate networks: you never know what features you’re going to need the next time you redesign your network. In particular, we cover:


So far, we’ve used routers as routers, which make intelligent decisions about where to send packets based on their IP addresses and information gathered by routing protocols. Cisco routers can also be configured as bridges, which make routing decisions based on MAC addresses (e.g., Ethernet addresses).

Hot standby routing

Cisco’s Hot Standby Routing Protocol (HSRP) enables routers to serve as backups for one another.

Network Address Translation (NAT)

Increasingly, the IP addresses visible outside a network are different from the addresses actually in use inside the network. Translating from a small external address space to a much larger internal space conserves addresses (you can have a large network but use a small block of external addresses) and gives you more control over which hosts in your network are visible to the outside world. In these configurations, the router relies on NAT to map your internal addresses to your external addresses.


Tunneling means establishing a TCP/IP connection to another location and then running other protocols through that connection. It can be used as a means of propagating protocols that can’t be ...

Get Cisco IOS in a Nutshell, 2nd Edition now with the O’Reilly learning platform.

O’Reilly members experience live online training, plus books, videos, and digital content from nearly 200 publishers.