Everyone that has used the Cisco IOS command line knows this problem. When you mistype a command, the router tries to resolve the “hostname” and you have to wait for 24 very long seconds:

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

Until recently I used the “no ip domain-lookup” configuration entry to counter this. This disables DNS-lookups altogether, which might not always be what you want. I recently found the proper solution to fix this:

Router#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#line con 0
Router(config-line)#transport preferred none
Router(config-line)#^Z
Router#conft
           ^
% Invalid input detected at '^' marker.

Router#

You need to apply this to all the lines you want (probably all vty’s as well). This will prevent the router from guessing that an unknown command is a hostname you want to telnet to. You can still telnet (or ssh) to a hostname (DNS still works), but you need to specify the ‘telnet’ command.

2 Comments

  1. Steve K says:

    I’ve been bitten by this too! Another way I’ve found is to break out with Ctrl+Shift+6.

  2. dbm says:

    As said by “Steve K”, i also use Ctrl+Shift+6.
    But in fact, i don’t know what it do.

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