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CHAPTER
19-1
Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
19
Understanding and Configuring CDP
This chapter describes how to configure Cisco Discovery Protocol (CDP) on the Catalyst 4500 series
switch. It also provides guidelines, procedures, and configuration examples.
This chapter includes the following major sections:
• Overview of CDP, page 19-1
• Configuring CDP, page 19-2
Note For complete syntax and usage information for the commands used in this chapter, refer to the
Cisco IOS Configuration Fundamentals Configuration Guide, Release 12.2;
Cisco IOS System Management; Configuring Cisco Discovery Protocol (CDP) at this URL:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/ffun_c/fcfprt3/fcf015.htm
and to the Cisco IOS Configuration Fundamentals Command Reference, Release 12.1;
Cisco IOS System Management Commands; and CDP Commands publication at this URL:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/ffun_r/ffrprt3/frf015.htm
Note For complete syntax and usage information for the switch commands used in this chapter, refer to the
Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/index.htm.
Overview of CDP
CDP is a protocol that runs over Layer 2 (the data link layer) on all Cisco routers, bridges, access servers,
and switches. CDP allows network management applications to discover Cisco devices that are
neighbors of already known devices, in particular, neighbors running lower-layer, transparent
protocols.With CDP, network management applications can learn the device type and the SNMP agent
address of neighboring devices. CDP enables applications to send SNMP queries to neighboring devices.
CDP runs on all LAN and WAN media that support Subnetwork Access Protocol (SNAP).
Each CDP-configured device sends periodic messages to a multicast address. Each device advertises at
least one address at which it can receive SNMP messages. The advertisements also contain the
time-to-live, or holdtime information, which indicates the length of time a receiving device should hold
CDP information before discarding it.