Chapter 13 Configuring Cdp; Understanding Cdp; Configuring Cdp - Cisco WS-C3550-12G Software Configuration Manual

Configuring CDP

This chapter describes how to configure Cisco Discovery Protocol (CDP) on your switch.
For complete syntax and usage information for the commands used in this chapter, refer to the
Note
Catalyst 3550 Multilayer Switch Command Reference for this release and the Cisco IOS
Configuration Fundamentals Command Reference for Release 12.1.
This chapter consists of these sections:
Understanding CDP, page 13-1
•
Configuring CDP, page 13-2
•
Monitoring and Maintaining CDP, page 13-5
•

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
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 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 Catalyst 3550 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.
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