Cisco Discovery Protocol on Catalyst 1900 Switches

The Cisco Discovery Protocol (CDP) is used to gather information about neighboring Cisco devices. Cisco 1900 series switches also run CDP, with the same default parameters as a CDP-enabled router. The show cdp command shows the current CDP version, as well as CDP timer and holdtime intervals. The show cdp neighbors command will display a table with information about neighboring devices. Details on a specific device can be obtained by issuing the show cdp neighbors detail command.

Cisco1912#show cdp
Global CDP information :
CDP version: 2
Sending CDP packets every 60 seconds
Sending a holdtime value of 180 seconds
Cisco1912#show cdp neigh
Capability Codes: R – Router, T – Trans Bridge, B – Source Route Bridge
S – Switch, P – Repeater, H – Host, I – IGMP
DeviceID IP Addr Local Port Capability Platform Remote Port

CDP holdtime and timer values can be changed from global configuration mode by issuing the appropriate cdp command, as shown below.

Cisco1912#config t
Enter configuration commands, one per line. End with CNTL/Z
Cisco1912(config)#cdp ?
advertise-v2 CDP sends version-2 advertisements
holdtime Specify the holdtime (in sec) to be sent in packets
timer Specify the rate at which CDP packets are sent (in sec)

Author: Dan DiNicolo

Dan DiNicolo is a freelance author, consultant, trainer, and the managing editor of He is the author of the CCNA Study Guide found on this site, as well as many books including the PC Magazine titles Windows XP Security Solutions and Windows Vista Security Solutions. Click here to contact Dan.