Cisco Command Christmas Calendar #8: no ip domain lookup

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We all know this one. By default, IOS devices have DNS lookup enabled. This can lead to annoying situations when you mistype a command and the device tries to resolve it to an IP address. Example:

R10#show clock
*16:43:00.116 UTC Thu Dec 7 2017

 R10#showrun
Translating "showrun"...domain server (255.255.255.255)
 (255.255.255.255)
Translating "showrun"...domain server (255.255.255.255)

 Translating "showrun"...domain server (255.255.255.255)

 Translating "showrun"...domain server (255.255.255.255)

 % Bad IP address or host name
Translating "showrun"...domain server (255.255.255.255)

 % Unknown command or computer name, or unable to find computer address

 R10#show clock
*16:44:02.102 UTC Thu Dec 7 2017

From the system time, you can see R10 took roughly 1 minute to translate the mistyped show run command.

Now let's disable the DNS lookup with the no ip domain-lookup command and run the same test again.

R10(config)#no ip domain-lookup


R10#show clock
*16:45:56.414 UTC Thu Dec 7 2017

 R10#showrun
Translating "showrun"

 Translating "showrun"

 Translating "showrun"

 % Bad IP address or host name
% Unknown command or computer name, or unable to find computer address

 R10#show clock
*16:46:05.607 UTC Thu Dec 7 2017

As you can see, the device instantly returned a response. 


Cisco documentation: no ip domain-lookup



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