To configure any feature of the router, you must enter configuration mode. This is the first sub-mode of the parent mode. In the parent mode, you issue the command config.
As demonstrated above, the prompt changes to indicate the mode that you are now in.
In connfiguration mode you can set options that apply system-wide, also refered to as “global configurations.” For instance, it is a good idea to name your router so that you can easily identify it. You do this in configuration mode with the hostname command.
As demonstrated above, when you set the name of the host with the hostname command, the prompt immediately changes by replacing Router with ExampleName. (Note: It is a good idea to name your routers with an organized naming scheme.)
Another useful command issued from config mode is the command to designate the DNS server to be used by the router:
ExampleName(config)#ip name-server aa.bb.cc.dd
This is also where you set the password for privileged mode.
ExampleName(config)#enable secret examplepassword
Until you hit ctrl-Z (or type exit until you reach parent mode) your command has not been put into affect. You can enter config mode, issue several different commands, then hit ctrl-Z to activate them all. Each time you hit ctrl-Z you return to parent mode and the prompt:
Here you use show commands to verify the results of the commands you issued in config mode. To verify the results of the ip name-server command, issue the command show host.