Why should I care about CDP and LLDP?

Cisco discovery protocol

Using Cisco Discovery Protocol

CDP allows you to see directly attached devices. But not just the devices, you see as well some information like which local port they are connected to, you see the remote port, uptime, ios version and so on. CDP packets go out every 60 seconds. Once vendor saw that there is a message going out every 60 seconds, they tag some informations like Power to this protocol. For example the device talks to the switch “hey it’s me, I just need 7W of power.” Or for example VLANs as well for IP phones.

It has a hold-on timer for 180 seconds. After that it will be removed from the cdp table.

Link layer discovery protocol

Using Link Layer Discovery Protocol

It is the industry standard. By default its off, that’s an advantage of CDP because its on by default. LLDP does the same thing as CDP in a lot of cases.

Cisco IOS commands learned in this lesson

Command	Subcommand	Explanation
Show cdp neigbors		Gives you a list of all directly connected devices.
Show cdp neighbors detail		Same output but now you see the ip address as well.
Show cdp neighbors interface		See timers and on which interfaces running cdp
No cdp run / no cdp enable		Disables CDP
Lldp run		Enables LLDP
Show lldp neighbors		Gives you a list of all directly connected devices.
No lldp	Receive	Disables lldp for receiving lldp packets
	Transmit	Disables lldp for transmitting lldp packets