How to find all the devices connected to a switch?

[abin310]

We have 16 cisco catalyst switches distributed in a 60 floor building. we have provided LAN and wireless connection to the apartments through each switch.Now a days somebody is plugging an external router/modem to our network and our network/internet connection interrupted.Please advice me to provide the command to find all the devices connected through a switch.

Thanks

Aby

[Tom Watts]

Hi Abin, you should be able to easily trace the network if CDP is enabled on those devices

show cdp neighbor

show cdp neighbor detail

you can also look to see active connections through spanning-tree

show spanning-tree active

If you know the ports the switches connect to but don't know which switch is on the port, you can trace through MAC address

show interface fax/x   (then look for the MAC of that interface)

show mac address-table (look for the port)

Additionally, you can use IP scanners such as AngryIP.

I do recommend if you haven't already, when configuring a port to connect to another switch, on the description put something like

Description Cisco 3750 gi1/1/1 | Cisco 2950 fa0/1

So it should mean something like a 3750 port 1 is going to Cisco 2950 port 1, then on the other end reverse it to reflect the changes. I just helps avoid confusion and makes rebuild easier if someone moves a wire.

-Tom
Please mark answered for helpful posts

[Leo Laohoo]

Have you tried enabling BPDU Guard on all of your switchports?