Cisco Discovery Protocol - Cisco Catalyst 2000 Configuration Handbook

46 Cisco LAN Switching Configuration Handbook

3-7: Cisco Discovery Protocol

CDP identifies directly connected Cisco devices.
■
■ CDP is enabled on all Cisco devices.
CDP identifies neighbor address, operating system, VLAN, VLAN Trunking
■
Protocol (VTP) domain, and duplex information between Cisco switches.
■ CDP can be disabled globally or on a per-port (interface) basis.
Configuration of CDP
(Default) Enable CDP globally:
1.
(global) cdp run
CDP is enabled by default. To disable CDP for the entire device, use the command
no cdp run.
(Optional) Set the update time for CDP advertisements:
2.
(global) cdp timer interval
CDP sends advertisements every 60 seconds by default. Use these commands to
change the update interval in seconds. Keep in mind that the update interval must be
less than the holdtime.
(Optional) Specify the holdtime of CDP information:
3.
(global) cdp holdtime interval
If CDP does not hear an update for the specified amount of time in the holdtime
interval in seconds, that information is purged from the CDP table. Use these com-
mands to change the holdtime. The holdtime should be greater than the advertise-
ment (usually three times the value of the update timer).
(Default) Set the CDP version send parameters for the switch:
4.
(global) cdp {advertise-v2 | advertise-v1}
CDP has two versions (v1 and v2). These versions are compatible, but version 2 has
enhanced type-length-values (TLV) that support VTP domain name, native VLAN,
and duplex information. This information is important in the operation of switch
ports. If you receive CDP mismatch messages, the errors are not fatal, but they can
indicate a problem.
(Optional) Disable CDP on an interface or port:
5.
(interface)no cdp enable
CDP is enabled by default on every port. For ports that are not connected to Cisco
devices, it makes no sense to have CDP running. Use the commands in Step 2 to dis-
able CDP on a port-by-port basis. To reenable CDP, use the command cdp enable.
The command show cdp displays global information about CDP configuration on
both operating systems. Use the commands show cdp neighbors for both operating