Jan 142013

How to see which VLANs are currently used on a trunkport on a switch?

Easy Answer:
Do a show mac address-table interface <interface>

and you will get a list of VLANs with MAC addresses used. Of course, any VLAN that have MAC-addresses associated, is in use.

That’s an easy way to find out which VLAN-tags are currently running over a trunk. (keep MAC-address aging timer in mind)

 Posted by at 12:23
Nov 042010

Have you ever killed your router/switch by enabling “some” debugging output?
You can easily reduce the impact of debug-logging on cisco devices by disabling logging to the console port. Under normal circumstances you don’t need the logging output on the console port.
In global configuration mode type:

no logging console to disable logging to the console.

This will prevent your router/switch from generating an interrupt for each single character, that is put to the console interface.

 Posted by at 14:59
Nov 032010

show running won’t show you any pre-shared-keys for tunnels, aaa-server keys and failover keys in cleartext. You will only see things like:

failover key *****

aaa-server authserver (inside) host
key *****

tunnel-group clients ipsec-attributes
pre-shared-key *****

simply use the more system:running-config-command to show all your keys uncrypted.

 Posted by at 11:22
Feb 242010

Do you sometimes have the problem, that CTRL-SHIFT-6 (CTRL-^) won’t work to cancel a traceroute or other commands? Especially on foreign keymaps? Than simply change the escape-sequence for your VTYs or CONsole:

change escape-character to CTRL-C on VTYs (telnet and/or ssh-access):

line vty 0 15
escape-character 3

change escape-character to ESC on CONsole (serial-access on console port):

line con 0
escape-character 27

CTRL-C is a good choice – it’s a well known keystroke to cancel processes on CLIs.
ESC is nice because it uses the very less used ESC key – but the usage of the esc-code has one drawback: If you telnet to a further router from the commandline of your current router, than the command history will not be accessible via your curser up-/down-keys any longer because they are sending keycodes beginning with ESC – this breakes the Cursor-keycodes. Also the 1st CTRL-C will be eaten by router 1 – the next one is passed to router2.

So I recommend to use CTRL-C but of course you can configure any other ASCII-code as the escape-character.

 Posted by at 21:57