CISCO IOS in a Nutshell

Mapping Hostnames to IP Addresses

Like all network equipment, routers work naturally with numeric IP addresses. However, using IP addresses isn’t convenient for humans—including network administrators. It is much more convenient to work with hostnames. Like any other network host, routers implement DNS and can use DNS to look up IP addresses. But the use of DNS presents a problem in a routing environment. If the router can’t access the Internet, it can’t look up addresses; one reason that the router might not be able to access the Internet could be a routing problem; and if the router is configured to use DNS but can’t access the Internet, you will have trouble using the commands you need to diagnose and fix the problem.

There is a good halfway point, however. Like other network hosts, the router can maintain a host table, and you can place any IP addresses that appear in your configuration in the host table. You can then use DNS to look up any hostnames that aren’t actually involved in the router’s configuration. This will make it easier to understand the output from show commands or to use commands such as ping to check your network connectivity.

IP Host Tables

The ip host command builds and maintains the router’s host table. This command takes a hostname followed by one or more IP addresses. You can have up to eight IP addresses per hostname.

ip host pyramid 10.10.1.3
ip host sphinx 10.10.1.2 10.10.1.4 10.10.1.5

Deleting a host requires you to type the entire hostname and ...