Name: Cisco Catalyst 3750-E
Brand: Cisco
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CHAPTER

27-1

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

OL-9775-08

Configuring CDP

This chapter describes how to configure Cisco Discovery Protocol (CDP) on the Catalyst 3750-E

or 3560-E switch. Unless otherwise noted, the term switc

h refers to a Catalyst 3750-E or 3560-E

standalone switch and to a Catalyst 3750-E 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.

• Understanding CDP, page 27-1

• Configuring CDP, page 27-2

• Monitoring and Maintaining CDP, page 27-5

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 Management Protocol (SNMP) agent

address of neighboring devices running lower-layer, transparent protocols. This feature enables

applications to send SNMP queries to neighboring devices.

CDP runs on all media that support Subnetwork Access Protocol (SNAP). Because CDP runs over the

ta-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

ddress at which it can receive SNMP messages. The advertisements also contain time-to-live, or

holdtime information, which is the length of time a receiving device holds CDP information before

discarding it. Each device also listens to the messages sent by other devices to learn about neighboring

devices.

On the switch, CDP enables Network Assistant to display a graphical view of the network. The switch

use

s 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.

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