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

•Configuring CDP

Note For complete syntax and usage information for the Cisco IOS commands used in this chapter, refer to the
Cisco IOS Configuration Fundamentals Configuration Guide, Release 12.4:

http://www.cisco.com/en/US/docs/ios/fundamentals/configuration/guide/12_4/cf_12_4_book.html

and the Cisco IOS Configuration Fundamentals Command Reference, Release 12.2:

http://www.cisco.com/en/US/docs/ios/12_2/configfun/command/reference/ffun_r.html

Note For complete syntax and usage information for the switch commands used in this chapter, look at the Cisco Catalyst 4500 Series Switch Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/hw/switches/ps4324/index.html

If the command is not found in the Catalyst 4500 Command Reference, it is located in the larger Cisco IOS library. Refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/ps6350/index.html

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.

Configuring CDP

The following sections describe how to configure CDP:

•Enabling CDP Globally

•Displaying the CDP Global Configuration

•Enabling CDP on an Interface

•Displaying the CDP Interface Configuration

•Monitoring and Maintaining CDP

Enabling CDP Globally

To enable CDP globally, perform this task:

Command
Purpose 
Switch(config)# [no] cdp run

Enables CDP globally.

Use the no keyword to disable CDP globally.


This example shows how to enable CDP globally: 

Switch(config)# cdp run

Displaying the CDP Global Configuration

To display the CDP configuration, perform this task:

Command
Purpose 
Switch# show cdp

Displays global CDP information.


This example shows how to display the CDP configuration: 

Switch# show cdp

Global CDP information:

        Sending CDP packets every 120 seconds

        Sending a holdtime value of 180 seconds

        Sending CDPv2 advertisements is enabled

Switch# 

 
   
 
    
   
 For additional CDP show commands, see the "Monitoring and Maintaining CDP" section. 
 
     
    
    
    
   
 Enabling CDP on an Interface 
 
    
   
 To enable CDP on an interface, perform this task: 
 
    
   
 
 
   
 
    
 
      
      
      
 
        
        

          Command 
        
 		 
        
        

          Purpose 
        
 		 
      
 
      
 
        
        
 
         
Switch(config-if)# [no] cdp enable

 
        
 
       
 Enables CDP on an interface. 
 
 Use the no keyword to disable CDP on an interface. 
 		 
      
 
      
    
 
   
 
   
 
   
 
 
    
   
 This example shows how to enable CDP on Fast Ethernet interface 5/1: 
 
    
   
 
    
Switch(config)# interface fastethernet 5/1

 
   
 
    
   
 
    
Switch(config-if)# cdp enable 

 
   
 
    
   
 
    
 
   
 
    
   
 This example shows how to disable CDP on Fast Ethernet interface 5/1: 
 
    
   
 
    
Switch(config)# interface fastethernet 5/1

 
   
 
    
   
 
    
Switch(config-if)# no cdp enable 

 
   
 
     
    
    
    
   
 Displaying the CDP Interface Configuration 
 
    
   
 To display the CDP configuration for an interface, perform this task: 
 
    
   
 
 
   
 
    
 
      
      
      
 
        
        

          Command 
        
 		 
        
        

          Purpose 
        
 		 
      
 
      
 
        
        
 
         
Switch# show cdp interface [type/number]

 
        
 
       
 Displays information about interfaces where CDP is enabled. 
 		 
      
 
      
    
 
   
 
   
 
   
 
 
    
   
 This example shows how to display the CDP configuration of Fast Ethernet interface 5/1: 
 
    
   
 
    
Switch# show cdp interface fastethernet 5/1

 
   
 
    
   
 
    
FastEthernet5/1 is up, line protocol is up

 
   
 
    
   
 
    
  Encapsulation ARPA

 
   
 
    
   
 
    
  Sending CDP packets every 120 seconds

 
   
 
    
   
 
    
  Holdtime is 180 seconds

 
   
 
    
   
 
    
Switch# 

 
   
 
     
    
    
    
   
 Monitoring and Maintaining CDP 
 
    
   
 To monitor and maintain CDP on your device, perform one or more of these tasks: 
 
    
   
 
 
   
 
    
 
      
      
      
 
        
        

          Command 
        
 		 
        
        

          Purpose 
        
 		 
      
 
      
 
        
        
 
         
Switch# clear cdp counters

 
        
 
       
 Resets the traffic counters to zero. 
 		 
      
 
      
 
        
        
 
         
Switch# clear cdp table

 
        
 
       
 Deletes the CDP table of information about neighbors. 
 		 
      
 
      
 
        
        
 
         
Switch# show cdp

 
        
 
       
 Displays global information such as frequency of transmissions and the holdtime for packets being transmitted. 
 		 
      
 
      
 
        
        
 
         
Switch# show cdp entry entry_name 
[protocol | version]

 
        
 
       
 Displays information about a specific neighbor. The display can be limited to protocol or version information. 
 		 
      
 
      
 
        
        
 
         
Switch# show cdp interface 
[type/number] 

 
        
 
       
 Displays information about interfaces on which CDP is enabled. 
 		 
      
 
      
 
        
        
 
         
Switch# show cdp neighbors 
[type/number] [detail]

 
        
 
       
 Displays information about neighboring equipment. The display can be limited to neighbors on a specific interface and expanded to provide more detailed information. 
 		 
      
 
      
 
        
        
 
         
Switch# show cdp traffic

 
        
 
       
 Displays CDP counters, including the number of packets sent and received and checksum errors. 
 		 
      
 
      
 
        
        
 
         
Switch# show debugging

 
        
 
       
 Displays information about the types of debugging that are enabled for your switch. 
 		 
      
 
      
    
 
   
 
   
 
   
 
 
    
   
 This example shows how to clear the CDP counter configuration on your switch: 
 
    
   
 
    
Switch# clear cdp counters

 
   
 
    
   
 
    
 
   
 
    
   
 This example shows how to display information about the neighboring equipment: 
 
    
   
 
    
Switch# show cdp neighbors

 
   
 
    
   
 
    
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

 
   
 
    
   
 
    
                  S - Switch, H - Host, I - IGMP, r - Repeater

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID

 
   
 
    
   
 
    
JAB023807H1      Fas 5/3            127         T S       WS-C2948  2/46

 
   
 
    
   
 
    
JAB023807H1      Fas 5/2            127         T S       WS-C2948  2/45

 
   
 
    
   
 
    
JAB023807H1      Fas 5/1            127         T S       WS-C2948  2/44

 
   
 
    
   
 
    
JAB023807H1      Gig 1/2            122         T S       WS-C2948  2/50

 
   
 
    
   
 
    
JAB023807H1      Gig 1/1            122         T S       WS-C2948  2/49

 
   
 
    
   
 
    
JAB03130104      Fas 5/8            167         T S       WS-C4003  2/47

 
   
 
    
   
 
    
JAB03130104      Fas 5/9            152         T S       WS-C4003  2/48