- Index
- Preface
- Overview
- Using the Command-Line Interface
- Assigning the Switch IP Address and Default Gateway
- Configuring Cisco IOS Configuration Engine
- Administering the Switch
- Configuring Switch Alarms
- Configuring SDM Templates
- Configuring Switch-Based Authentication
- Configuring IEEE 802.1x Port-Based Authentication
- Configuring Interface Characteristics
- Configuring Command Macros
- Configuring VLANs
- Configuring Private VLANs
- Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling
- Configuring STP
- Configuring MSTP
- Configuring Optional Spanning-Tree Features
- Configuring Resilient Ethernet Protocol
- 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 and LLDP-MED
- Configuring UDLD
- Configuring SPAN and RSPAN
- Configuring RMON
- Configuring System Message Logging
- Configuring SNMP
- Configuring Embedded Event Manager
- Configuring Network Security with ACLs
- Configuring Control-Plane Security
- Configuring QoS
- Configuring EtherChannels and Link State Tracking
- Configuring IP Unicast Routing
- Configuring IPv6 Unicast Routing
- Configuring IPv6 MLD Snooping
- Configuring IPv6 ACLs
- Configuring HSRP
- Configuring Cisco IOS IP SLAs Operations
- Configuring Enhanced Object Tracking
- Configuring Ethernet OAM, CFM, and E-LMI
- Configuring IP Multicast Routing
- Configuring MSDP
- Troubleshooting
- Configuring Online Diagnostics
- Supported MIBs
- Working with the Cisco IOS File System, Configuration Files, and Software Images
- Unsupported Commands in Cisco IOS Release 12.2(52)SE
Configuring CDP
This chapter describes how to configure Cisco Discovery Protocol (CDP) on the Cisco ME 3400E 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.
•Monitoring and Maintaining CDP
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.
Configuring CDP
•Configuring the CDP Characteristics
•Disabling and Enabling CDP on an Interface
Default CDP Configuration
Table 24-1 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.
Use the no form of the CDP commands to return to the default settings.
This example shows how to configure CDP characteristics.
Switch# configure terminal
Switch(config)# cdp timer 50
Switch(config)# cdp holdtime 120
Switch(config)# cdp advertise-v2
Switch(config)# end
For additional CDP show commands, see the "Monitoring and Maintaining CDP" section.
Disabling and Enabling CDP
CDP is enabled by default on NNIs. It is disabled by default on ENIs but can be enabled.
Note Cisco devices (such as Cisco IP Phones) regularly exchange CDP messages with connected devices. Disabling CDP can interrupt device connectivity.
Beginning in privileged EXEC mode, follow these steps to globally disable the CDP device discovery capability:
|
|
|
---|---|---|
Step 1 |
configure terminal |
Enter global configuration mode. |
Step 2 |
no cdp run |
Disable CDP. |
Step 3 |
end |
Return to privileged EXEC mode. |
Beginning in privileged EXEC mode, follow these steps to globally enable CDP when it has been disabled:
|
|
|
---|---|---|
Step 1 |
configure terminal |
Enter global configuration mode. |
Step 2 |
cdp run |
Enable CDP after disabling it. |
Step 3 |
end |
Return to privileged EXEC mode. |
This example shows how to globally enable CDP if it has been disabled.
Switch# configure terminal
Switch(config)# cdp run
Switch(config)# end
Disabling and Enabling CDP on an Interface
CDP is enabled by default on NNIs to send and to receive CDP information. You can enable CDP on ENIs, but it is not supported on UNIs. 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 gigabitethernet0/1
Switch(config-if)# cdp enable
Switch(config-if)# end
This example shows how to change a UNI to an ENI and enable CDP on the port.
Switch# configure terminal
Switch(config)# interface fastethernet0/1
Switch(config-if)# port-type eni
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.