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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Configuring CDP
This chapter describes how to configure Cisco Discovery Protocol (CDP) on the Cisco ME 3400 Ethernet
Access switch.
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 23-1
• Configuring CDP, page 23-2
• Monitoring and Maintaining CDP, page 23-5

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.
Note On the Cisco ME switch, CDP is enabled by default on network node interfaces (NNIs) and disabled by
default on enhanced network interfaces (ENIs). It is not supported on user network interfaces (UNIs).
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.
The switch supports CDP Version 2.