Cisco router Telnet Debug

On most of Cisco routers, debug informations via telnet is not enabled, so you will not see any debug information when connected via telnet.

To enable it, you need to enable virtual terminal first:
Router# terminal monitor

Next, you have to enable debugging on virtual monitor:

In privileged mode:
Router# undebug all

In configuration mode:

Router(config)# logging monitor debugging

Router(config)# logging on

To disable it:

In privileged mode:
Router# undebug all
Router# terminal no monitor

In configuration mode:

Router(config)# no logging monitor