This article discusses how you can disable DNS lookup on Cisco routers and switches and effect when DNS lookup is enabled.

Problem: In privilege EXEC mode, if you type in something other than a Cisco IOS command, the router assumes that you typed a domain name and it tries to resolve what ever you type.

Although this feature is can be useful in some situations, for most of the time, this is a pain, especially if you do not have DNS server configured. The router becomes irresponsive for about 5-6 seconds trying to resolve the name.

The following is an example.

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R4#wrong-command
Translating "wrong-command"...domain server (255.255.255.255)
 (255.255.255.255)
Translating "wrong-command"...domain server (255.255.255.255)
 
% Unknown command or computer name, or unable to find computer
address
R4#

Solution:

To disable domain look up type the commands as shown billow.

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R4#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R4(config)#no ip domain-lookup
R4(config)#

Now the output is quick and router does not become irresponsive

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R4#wrong-command
Translating "wrong-command"
 
Translating "wrong-command"
 
% Unknown command or computer name, or unable to find computer address
R4#

Dharshin