By default, any single word entered on an IOS device that is not recognized as a valid command is treated as a hostname to which you want to telnet. The device will try to translate that word to an IP address in a process that can last about a minute.
Consider the following example:
R1#writte Translating "writte"...domain server (255.255.255.255) % Unknown command or computer name, or unable to find computer address
In the output above you can see that I’ve mistyped the command write. The router entered the DNS resolution process which lasted about a minute. This can be annoying and this is why this feature is often turned off, especially in the lab environments.
If you don’t need to have a DNS server configured for your router, you can use the no ip domain-lookup command to disable the DNS translation process:
R1(config)#no ip domain-lookup
Now, if I mistype a command, the router will not perform a DNS resolution process:
R1#writte Translating "writte" % Unknown command or computer name, or unable to find computer address R1#