Cisco IOS Cookbook, 2nd Edition

Disabling Domain Name Lookups

Problem

You want to prevent your router from trying to connect to your typing errors.

Solution

To prevent the router from attempting to resolve typing errors, use the no ip domain-lookup command:

Router1#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#no ip domain-lookup 
Router1(config)#end
Router1#

You can also prevent the router from trying to resolve typing errors on routers that use DNS by changing the default EXEC behavior for unknown commands:

Router1#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#line vty 0 4
Router1(config-line)#transport preferred none
Router1(config-line)#end
Router1#

Discussion

As we mentioned in Recipe 2.11, routers attempts to resolve all hostnames by using DNS by default. Unfortunately, if you don’t configure a valid DNS nameserver, the router sends these queries to the local broadcast IP address, 255.255.255.255. Querying a nonexistent nameserver is not only unproductive, but it can also be quite time consuming if it happens in an interactive session, since the router will not return the EXEC prompt until the query times out. This can be quite frustrating because, by default, the router will interpret any unknown command as a hostname that you want to connect to. So it will attempt to resolve any typing mistakes you enter on the command line:

Router1#pnig Translating "pnig"...domain server (255.255.255.255) Translating "pnig"...domain ...