- Index
- Preface
- Overview
- Using the Command-Line Interface
- Clustering Switches
- Assigning the Switch IP Address and Default Gateway
- Configuring Cisco IOS Configuration Engine
- Managing Switch Stacks
- Administering the Switch
- Configuring SDM Templates
- Configuring Switch-Based Authentication
- Configuring IEEE 802.1x Port-Based Authentication
- Configuring Web-Based Authentication
- Configuring Interface Characteristics
- Configuring VLANs
- Configuring VTP
- Configuring Voice VLAN
- Configuring Private VLANs
- Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling
- Configuring STP
- Configuring MSTP
- Configuring Optional Spanning-Tree Features
- Configuring Flex Links and the MAC Address-Table Move Update Feature
- Configuring DHCP Features and IP Source Guard
- Configuring Dynamic ARP Inspection
- Configuring IGMP Snooping and MVR
- Configuring Port-Based Traffic Control
- Configuring CDP
- Configuring LLDP, LLDP-MED, and Wired Location Service
- Configuring UDLD
- Configuring SPAN and RSPAN
- Configuring RMON
- Configuring System Message Logging and Smart Logging
- Configuring SNMP
- Configuring Embedded Event Manager
- Configuring Network Security with ACLs
- Configuring QoS
- Configuring EtherChannels and Link-State Tracking
- Configuring TelePresence E911 IP Phone Support
- Configuring IP Unicast Routing
- Configuring IPv6 Routing
- Configuring IPv6 MLD Snooping
- Configuring IPv6 ACLs
- Configuring HSRP and VRRP
- Configuring Cisco IOS IP SLAs Operations
- Configuring Enhanced Object Tracking
- Configuring IP Multicast Routing
- Configuring MSDP
- Configuring Cache Services By Using WCCP
- Configuring Fallback Bridging
- Troubleshooting
- Configuring Online Diagnostics
- Configuring the Catalyst 3750G Integrated Wireless LAN Controller Switch
- Working with the Cisco IOS File System, Configuration Files, and Software Images
- Unsupported Commands in Cisco IOS Release 12.2(58)SE
Configuring CDP
This chapter describes how to configure Cisco Discovery Protocol (CDP) on the Catalyst 3750 switch. Unless otherwise noted, the term switch refers to a standalone switch and to a 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 12.4.
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.
For a switch and connected endpoint devices running Cisco Medianet
- CDP identifies connected endpoints that communicate directly with the switch.
- To prevent duplicate reports of neighboring devices, only one wired switch reports the location information.
- The wired switch and the endpoints both send and receive location information.
For information, go to:
http://www.cisco.com/en/US/docs/ios/netmgmt/configuration/guide/nm_cdp_discover.html.
The switch supports CDP Version 2.
CDP and Switch Stacks
A switch stack appears as a single switch in the network. Therefore, CDP discovers the switch stack, not the individual stack members. The switch stack sends CDP messages to neighboring network devices when there are changes to the switch stack membership, such as stack members being added or removed.
Configuring CDP
These sections contain this configuration information:
- Default CDP Configuration
- Configuring the CDP Characteristics
- Disabling and Enabling CDP
- Disabling and Enabling CDP on an Interface
Default CDP Configuration
Table 26-1 shows the default CDP configuration.
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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.
Use the no form of the CDP commands to return to the default settings.
This example shows how to configure CDP characteristics.
For additional CDP show commands, see the “Monitoring and Maintaining CDP” section.
Disabling and Enabling CDP
Note Switch clusters and other Cisco devices (such as Cisco IP Phones) regularly exchange CDP messages. Disabling CDP can interrupt cluster discovery and device connectivity. For more information, see Chapter 6, “Clustering Switches” and see Getting Started with Cisco Network Assistant, available on Cisco.com.
Beginning in privileged EXEC mode, follow these steps to disable the CDP device discovery capability:
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Beginning in privileged EXEC mode, follow these steps to enable CDP when it has been disabled:
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This example shows how to enable CDP if it has been disabled.
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:
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Specify the interface on which you are disabling CDP, and enter interface configuration mode. |
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Beginning in privileged EXEC mode, follow these steps to enable CDP on a port when it has been disabled:
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Specify the interface on which you are enabling CDP, and enter interface configuration mode. |
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This example shows how to enable CDP on a port when it has been disabled.
Note Voice VLAN is not counted against port security when CDP is disabled on the switch interface.
Monitoring and Maintaining CDP
To monitor and maintain CDP on your device, perform one or more of these tasks, beginning in privileged EXEC mode.