Cisco Discovery Protocol (CDP)
This is one of the most useful Layer 2/ layer 3 protocols.
You can discover directly connected neighbors (switches, routers), extremely useful to test point to point links
How to disable CDP globally ?
no cdp run
How to disable CDP per interface ?
int s0/0
no cdp enable
Problems with CDP
Cisco proprietary, so won’t work with other boxed like Nortel. Infact if you connect a cisco router or a switch to a non cisco network like Nortel, the CDP multicast packet will loop through the Nortel network causing a massive broadcast storm. During this period you will not be able to login to the boxes on the network. To fix this you need to manually remove ethernet cabels from switches to break the loop.
Security issues, especially if enabled on the serial interfaces.