Transport preferred none

Have you ever mistyped a command and the router thinks you want to telnet
another device? Sure you have and so have I. The most common solution is
to turn off name lookups.

no ip domain-lookup

This will tell the router to not use DNS for looking up names and will
speed up the failing of the command. However if you need to have DNS
enabled we can’t use this solution and there is a cleaner way of doing
it.

line vty 0 4
transport preferred none

By default telnet is the preferred protocol and when mistyping the router
will try to telnet the “name” you typed. If we set it to none the router
won’t try to telnet when mistyping and you can have DNS enabled which is
the best of two worlds. If you want to telnet to another device you have
to type telnet 1.1.1.1 instead of just 1.1.1.1 but that is a small price
to pay.