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Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
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Configuring CDP
This chapter describes how to configure Cisco Discovery Protocol (CDP) on the switch. Unless
otherwise noted, the term switch refers to a standalone switch and to a switch stack.
Note For complete syntax and usage information for the commands used in this chapter, see the command
reference for this release and the “System Management Commands” section in the Cisco IOS
Configuration Fundamentals Command Reference, Release 12.2.
This chapter consists of these sections:
Understanding CDP, page 26-1
Configuring CDP, page26-2
Monitoring and Maintaining CDP, page26-5

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 Network Assistant to display a graphi cal view of the network. The swi tc h
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.