If you mistype a command in the Privileged Mode on Cisco router, by default, the router thinks you're trying to connect to a remote host through Telnet. So it performs a DNS lookup on the information you entered.
If you haven't configured DNS on the router, the command prompt will hang until the DNS lookup timeouts. This is one of the thing that really bothers me so to resolve it, I have two options:
The first option is to disable DNS using the "domain-lookup" command as in:
Router(config)# no ip domain-lookup
The second option is to properly configure DNS and point it to a valid DNS server. Here's an example:
Router(config)# ip name-server 184.108.40.206
By configure the router using one of the two options above it will save you a bit of time and cut a bit of frustration out of your daily routines.