Stopping Accidental Cisco IOS Domain Name Translation

I often switch between Cisco IOS and Bash so I absentmindedly type ls into a IOS prompt and have to wait 30 seconds on this error:

Translating “ls”…domain server (255.255.255.255)
% Unknown command or computer name, or unable to find computer address

To stop this, you can just press CTRL+Shift+6. But for more long-term fixes, see the options below:

Option 1: Stop router from starting connection without telnet keyword

router(config) #ip domain lookup 
router(config-line)#line con 0
router(config-line)#transport preferred none

Option 2: Shorten TCP Connection Timeout

router(config) #ip tcp synwait-time 10

This isn’t preferable as it can affect things like handshakes for Multicast/BGP

Option 3: Disable Domain Lookup:

router(config) #no ip domain lookup

I hesitate to recommend this one as it might affect the 1% of sites that need it. Also it stops DNS load-balancing, which I need in enterprise environments. You can also disable per session Domain Lookup like so:

#terminal no domain-lookup

Further Reading

• Cisco Documentation (Jan 2017)
• Key by Key Guide (Dec 2012)

Email

• Fixing Search Domain Resolving on WSL