Software Configuration Guide, Cisco IOS Release 15.2(2)E (Catalyst 2960, 2960-S, 2960-SF and 2960-Plus Switches)
Configuring the Cisco Discovery Protocol
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Configuring the Cisco Discovery Protocol

Configuring the Cisco Discovery Protocol

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http:/​/​www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Information About CDP

CDP Overview

CDP is a device discovery protocol that runs over Layer 2 (the data-link layer) on all Cisco-manufactured devices (routers, bridges, access servers, controllers, 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 following applies to 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.

The switch supports CDP Version 2.

Related References

Default CDP Configuration

This table shows the 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

How to Configure CDP

Configuring CDP Characteristics

You can configure these CDP characteristics:
  • Frequency of CDP updates

  • Amount of time to hold the information before discarding it

  • Whether or not to send Version-2 advertisements


Note


Steps 3 through 5 are all optional and can be performed in any order.


Follow these steps to configure the CDP characteristics.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    cdp timer seconds

    4.    cdp holdtime seconds

    5.    cdp advertise-v2

    6.    end

    7.    show running-config

    8.    copy running-config startup-config


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example:
    Switch> enable
    
    
     

    Enables privileged EXEC mode. Enter your password if prompted.

     

    Step 2configure terminal


    Example:
    
    Switch# configure terminal
    
    
     

    Enters the global configuration mode.

     
    Step 3cdp timer seconds


    Example:
    
    Switch(config)# cdp timer 20
    
     

    (Optional) Sets the transmission frequency of CDP updates in seconds.

    The range is 5 to 254; the default is 60 seconds.

     
    Step 4cdp holdtime seconds


    Example:
    Switch(config)# cdp holdtime 60
    
     

    (Optional) Specifies 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 5cdp advertise-v2


    Example:
    Switch(config)# cdp advertise-v2
    
     

    (Optional) Configures CDP to send Version-2 advertisements.

    This is the default state.

     
    Step 6end


    Example:
    
    Switch(config)# end
    
    
     

    Returns to privileged EXEC mode.

     
    Step 7show running-config


    Example:
    
    Switch# show running-config 
    
    
     

    Verifies your entries.

     
    Step 8copy running-config startup-config


    Example:
    Switch# copy running-config startup-config 
    
    
     

    (Optional) Saves your entries in the configuration file.

     
    What to Do Next

    Use the no form of the CDP commands to return to the default settings.

    Related Concepts
    Related References

    Disabling CDP

    CDP is enabled by default.


    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.

    Follow these steps to disable the CDP device discovery capability.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    no cdp run

      4.    end

      5.    show running-config

      6.    copy running-config startup-config


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 enable


      Example:
      Switch> enable
      
      
       

      Enables privileged EXEC mode. Enter your password if prompted.

       

      Step 2configure terminal


      Example:
      
      Switch# configure terminal
      
      
       

      Enters the global configuration mode.

       
      Step 3no cdp run


      Example:
      Switch(config)# no cdp run
       

      Disables CDP.

       
      Step 4end


      Example:
      
      Switch(config)# end
      
      
       

      Returns to privileged EXEC mode.

       
      Step 5show running-config


      Example:
      
      Switch# show running-config 
      
      
       

      Verifies your entries.

       
      Step 6copy running-config startup-config


      Example:
      Switch# copy running-config startup-config 
      
      
       

      (Optional) Saves your entries in the configuration file.

       
      What to Do Next

      You must reenable CDP to use it.

      Related Concepts
      Related Tasks

      Enabling CDP

      CDP is enabled by default.


      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.

      Follow these steps to enable CDP when it has been disabled.

      Before You Begin

      CDP must be disabled, or it cannot be enabled.

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    cdp run

        4.    end

        5.    show running-config

        6.    copy running-config startup-config


      DETAILED STEPS
         Command or ActionPurpose
        Step 1 enable


        Example:
        Switch> enable
        
        
         

        Enables privileged EXEC mode. Enter your password if prompted.

         

        Step 2configure terminal


        Example:
        
        Switch# configure terminal
        
        
         

        Enters the global configuration mode.

         
        Step 3cdp run


        Example:
        Switch(config)# cdp run
         

        Enables CDP if it has been disabled.

         
        Step 4end


        Example:
        
        Switch(config)# end
        
        
         

        Returns to privileged EXEC mode.

         
        Step 5show running-config


        Example:
        
        Switch# show running-config 
        
        
         

        Verifies your entries.

         
        Step 6copy running-config startup-config


        Example:
        Switch# copy running-config startup-config 
        
        
         

        (Optional) Saves your entries in the configuration file.

         
        What to Do Next

        Use the show run all command to show that CDP has been enabled. If you enter only show run, the enabling of CDP may not be displayed.

        Related Concepts
        Related Tasks

        Disabling CDP on an Interface

        CDP is enabled by default on all supported interfaces to send and to receive CDP information.


        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.

        Follow these steps to disable CDP on a port.

        SUMMARY STEPS

          1.    enable

          2.    configure terminal

          3.    interface interface-id

          4.    no cdp enable

          5.    end

          6.    show running-config

          7.    copy running-config startup-config


        DETAILED STEPS
           Command or ActionPurpose
          Step 1 enable


          Example:
          Switch> enable
          
          
           

          Enables privileged EXEC mode. Enter your password if prompted.

           

          Step 2configure terminal


          Example:
          
          Switch# configure terminal
          
          
           

          Enters the global configuration mode.

           
          Step 3interface interface-id


          Example:
          Switch(config)# interface gigabitethernet1/0/1
           

          Specifies the interface on which you are disabling CDP, and enters interface configuration mode.

           
          Step 4no cdp enable


          Example:
          Switch(config-if)# no cdp enable
           

          Disables CDP on the interface specified in Step 3.

           
          Step 5end


          Example:
          
          Switch(config)# end
          
          
           

          Returns to privileged EXEC mode.

           
          Step 6show running-config


          Example:
          
          Switch# show running-config 
          
          
           

          Verifies your entries.

           
          Step 7copy running-config startup-config


          Example:
          Switch# copy running-config startup-config 
          
          
           

          (Optional) Saves your entries in the configuration file.

           
          Related Concepts

          Enabling CDP on an Interface

          CDP is enabled by default on all supported interfaces to send and to receive CDP information.


          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.

          Follow these steps to enable CDP on a port on which it has been disabled.

          Before You Begin

          CDP must be disabled on the port that you are trying to CDP enable on, or it cannot be enabled.

          SUMMARY STEPS

            1.    enable

            2.    configure terminal

            3.    interface interface-id

            4.    cdp enable

            5.    end

            6.    show running-config

            7.    copy running-config startup-config


          DETAILED STEPS
             Command or ActionPurpose
            Step 1 enable


            Example:
            Switch> enable
            
            
             

            Enables privileged EXEC mode. Enter your password if prompted.

             

            Step 2configure terminal


            Example:
            
            Switch# configure terminal
            
            
             

            Enters the global configuration mode.

             
            Step 3interface interface-id


            Example:
            Switch(config)# interface gigabitethernet1/0/1
             

            Specifies the interface on which you are enabling CDP, and enters interface configuration mode.

             
            Step 4cdp enable


            Example:
            Switch(config-if)# cdp enable
             

            Enables CDP on a disabled interface.

             
            Step 5end


            Example:
            
            Switch(config)# end
            
            
             

            Returns to privileged EXEC mode.

             
            Step 6show running-config


            Example:
            
            Switch# show running-config 
            
            
             

            Verifies your entries.

             
            Step 7copy running-config startup-config


            Example:
            Switch# copy running-config startup-config 
            
            
             

            (Optional) Saves your entries in the configuration file.

             
            Related Concepts

            Monitoring and Maintaining CDP

            Table 1 Commands for Displaying CDP Information
            Command Description

            clear cdp counters

            Resets the traffic counters to zero.

            clear cdp table

            Deletes the CDP table of information about neighbors.

            show cdp

            Displays global information, such as frequency of transmissions and the holdtime for packets being sent.

            show cdp entry entry-name [version] [protocol]

            Displays 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]

            Displays 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]

            Displays 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

            Displays CDP counters, including the number of packets sent and received and checksum errors.

            Related Concepts

            Additional References

            Related Documents

            Related Topic Document Title

            System Management Commands

            Command Reference, Cisco IOS Release 15.2(2)E

            Error Message Decoder

            Description Link

            To help you research and resolve system error messages in this release, use the Error Message Decoder tool.

            https:/​/​www.cisco.com/​cgi-bin/​Support/​Errordecoder/​index.cgi

            Standards and RFCs

            Standard/RFC Title

            None

            -

            MIBs

            MIB MIBs Link

            All supported MIBs for this release.

            To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

            http:/​/​www.cisco.com/​go/​mibs

            Technical Assistance

            Description Link

            The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

            To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

            Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

            http:/​/​www.cisco.com/​support

            Feature History and Information for Cisco Discovery Protocol

            Release

            Modification

            This feature was introduced.