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C H A P T E R
Catalyst 2960 Switch Software Configuration Guide OL-8603-
Configuring CDP
This chapter describes how to configure Cisco Discovery Protocol (CDP) on the Catalyst 2960 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..
This chapter consists of these sections:
- Understanding CDP, page 22-
- Configuring CDP, page 22-
- Monitoring and Maintaining CDP, page 22-
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 switch, CDP enables Network Assistant 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.
Catalyst 2960 Switch Software Configuration Guide OL-8603-
Configuring CDP
Configuring CDP
These sections contain this configuration information:
- Default CDP Configuration, page 22-
- Configuring the CDP Characteristics, page 22-
- Disabling and Enabling CDP, page 22-
- Disabling and Enabling CDP on an Interface, page 22-
Default CDP Configuration
Table 22-1 shows the default CDP configuration.
Configuring the CDP Characteristics
You can configure the frequency of CDP updates, the amount of time to hold the information before discarding it, and whether or not to send Version-2 advertisements. Beginning in privileged EXEC mode, follow these steps to configure the CDP timer, holdtime, and advertisement type.
Note Steps 2 through 4 are all optional and can be performed in any order.
Table 22-1 Default CDP Configuration
Feature Default Setting CDP global state Enabled CDP interface state Enabled CDP timer (packet update frequency) 60 seconds CDP holdtime (before discarding) 180 seconds CDP Version-2 advertisements Enabled
Command Purpose Step 1 (^) configure terminal Enter global configuration mode. Step 2 cdp timer seconds (Optional) Set the transmission frequency of CDP updates in seconds. The range is 5 to 254; the default is 60 seconds. Step 3 (^) cdp holdtime seconds (Optional) Specify the amount of time a receiving device should hold the information sent by your device before discarding it. The range is 10 to 255 seconds; the default is 180 seconds. Step 4 cdp advertise-v2 (Optional) Configure CDP to send Version-2 advertisements. This is the default state. Step 5 (^) end Return to privileged EXEC mode.
Catalyst 2960 Switch Software Configuration Guide OL-8603-
Monitoring and Maintaining CDP
Disabling and Enabling CDP on an Interface
CDP is enabled by default on all supported interfaces to send and to receive CDP information. Beginning in privileged EXEC mode, follow these steps to disable CDP on a port:
Beginning in privileged EXEC mode, follow these steps to enable CDP on a port when it has been disabled:
This example shows how to enable CDP on a port when it has been disabled. Switch# configure terminal Switch(config)# interface gigabitethernet0/ Switch(config-if)# cdp enable Switch(config-if)# end
Monitoring and Maintaining CDP
To monitor and maintain CDP on your device, perform one or more of these tasks, beginning in privileged EXEC mode.
Command Purpose Step 1 configure terminal Enter global configuration mode. Step 2 (^) interface interface-id Specify the interface on which you are disabling CDP, and enter interface configuration mode. Step 3 no cdp enable Disable CDP on the interface. Step 4 (^) end Return to privileged EXEC mode. Step 5 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose Step 1 configure terminal Enter global configuration mode. Step 2 (^) interface interface-id Specify the interface on which you are enabling CDP, and enter interface configuration mode. Step 3 cdp enable Enable CDP on the interface after disabling it. Step 4 (^) end Return to privileged EXEC mode. Step 5 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Description clear cdp counters Reset the traffic counters to zero. clear cdp table Delete the CDP table of information about neighbors. show cdp Display global information, such as frequency of transmissions and the holdtime for packets being sent.
Catalyst 2960 Switch Software Configuration Guide OL-8603-
Monitoring and Maintaining CDP
show cdp entry entry-name [ protocol | version ]
Display information about a specific neighbor. You can enter an asterisk (*) to display all CDP neighbors, or you can enter the name of the neighbor about which you want information. You can also limit the display to information about the protocols enabled on the specified neighbor or information about the version of software running on the device.
show cdp interface [ interface-id ] Display information about interfaces where CDP is enabled.
You can limit the display to the interface about which you want information.
show cdp neighbors [ interface-id ] [ detail ]
Display information about neighbors, including device type, interface type and number, holdtime settings, capabilities, platform, and port ID. You can limit the display to neighbors of a specific interface or expand the display to provide more detailed information.
show cdp traffic Display CDP counters, including the number of packets sent and received and checksum errors.
Command Description
