CHAPTER
24-1
Catalyst2950 and Catalyst2955 Switch Software Configuration Guide
78-11380-10
24
Configuring CDP
This chapter describes how to configure Cisco Discovery Protocol (CDP) on your Cataly st 2950 or
Catalyst 2955 switch.
Note For complete syntax and usage information for the commands used in this chapter, refer to the command
reference for this release and the Cisco IOS Configuration Fundamentals Command Reference for Cisco
IOS Release12.1.
This chapter consists of these sections:
Understanding CDP, page 24-1
Configuring CDP, page 24-2
Monitoring and Maintaining CDP, page 24-5

Understanding CDP

CDP is a device discovery protocol that runs over Layer 2 (the data link layer) on all Cisco-manufactured
devices (routers, bridges, access servers, and switches) and allows network management applications to
discover Cisco devices that are neighbors of already known devices. With CDP, network management
applications can learn the device type and the Simple Network Ma nag eme nt Pr otoc ol ( SNM P) a ge nt
address of neighboring devices running lower-layer, transparent protocols. This feature e nabl es
applications to send SNMP queries to neighboring devices.
CDP runs on all media that support Subnetwork Access Protocol (SNAP). Because CD P runs over the
data-link layer only, two systems that support different network-layer protocols can learn about each
other.
Each CDP-configured device sends periodic messages to a multicast address, advertising at least one
address at which it can receive SNMP messages. The advertisements also contain time-to-live, or
holdtime information, which is the length of time a re ceiving device hol ds CDP infor ma tion be for e
discarding it. Each device also listens to the messages sent by other devices to learn about neighb orin g
devices.
On the switch, CDP enables the Cluster Management Suite to display a graphical view of the network.
The switch uses CDP to find cluster candidates and maintain information about cluster members and
other devices up to three cluster-enabled devices away from the command switch by default.
The switch supports CDP Version 2.