Consolidated Platform Configuration Guide, Cisco IOS XE Release 3.3SE (Cisco WLC 5700 Series)
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 feature information and caveats, see the release notes for your platform and software release.

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 controller, CDP enables Network Assistant to display a graphical view of the network. The controller 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 controller by default.

CDP and Stacks

A controller stack appears as a single controller in the network. Therefore, CDP discovers the controller stack, not the individual stack members. The controller stack sends CDP messages to neighboring network devices when there are changes to the controller stack membership, such as stack members being added or removed.

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 2 through 4 are all optional and can be performed in any order.


Beginning in privileged EXEC mode, follow these steps to configure these characteristics.

SUMMARY STEPS

    1.    configure terminal

    2.    cdp timer seconds

    3.    cdp holdtime seconds

    4.    cdp advertise-v2

    5.    end


DETAILED STEPS
      Command or Action Purpose
    Step 1 configure terminal


    Example:
    
                
                
    Controller# configure terminal
    
    
     

    Enters the global configuration mode.

     
    Step 2 cdp timer seconds


    Example:
    
                
                
    Controller(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 3 cdp holdtime seconds


    Example:
    Controller(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 4 cdp advertise-v2


    Example:
    Controller(config)# cdp advertise-v2
    
     

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

    This is the default state.

     
    Step 5 end


    Example:
    
                
                
    Controller(config)# end
    
    
     

    Returns to privileged EXEC mode.

     

    Example

    The following example shows how to configure CDP characteristics:

    Controller# configure terminal
    Controller(config)# cdp timer 50
    Controller(config)# cdp holdtime 120
    Controller(config)# cdp advertise-v2
    Controller(config)# end
    What to Do Next

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

    Related References

    Disabling CDP

    CDP is enabled by default.


    Note


    Controller clusters and other Cisco devices (such as Cisco IP Phones) regularly exchange CDP messages. Disabling CDP can interrupt cluster discovery and device connectivity.

    Beginning in privileged EXEC mode, follow these steps to disable the CDP device discovery capability.

    SUMMARY STEPS

      1.    configure terminal

      2.    no cdp run

      3.    end


    DETAILED STEPS
        Command or Action Purpose
      Step 1 configure terminal


      Example:
      
                  
                  
      Controller# configure terminal
      
      
       

      Enters the global configuration mode.

       
      Step 2 no cdp run


      Example:
      Controller(config)# no cdp run
       

      Disables CDP.

       
      Step 3 end


      Example:
      
                  
                  
      Controller(config)# end
      
      
       

      Returns to privileged EXEC mode.

       
      What to Do Next

      You must reenable CDP to use it.

      Related Tasks

      Enabling CDP

      CDP is enabled by default.


      Note


      Controller clusters and other Cisco devices (such as Cisco IP Phones) regularly exchange CDP messages. Disabling CDP can interrupt cluster discovery and device connectivity.

      Beginning in privileged EXEC mode, 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.    configure terminal

        2.    cdp run

        3.    end


      DETAILED STEPS
          Command or Action Purpose
        Step 1 configure terminal


        Example:
        
                    
                    
        Controller# configure terminal
        
        
         

        Enters the global configuration mode.

         
        Step 2 cdp run


        Example:
        Controller(config)# cdp run
         

        Enables CDP if it has been disabled.

         
        Step 3 end


        Example:
        
                    
                    
        Controller(config)# end
        
        
         

        Returns to privileged EXEC mode.

         

        Example

        The following example shows how to enable CDP if it has been disabled:

        Controller# configure terminal
        Controller(config)# cdp run
        Controller(config)# end
        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 Tasks

        Disabling CDP on an Interface

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


        Note


        Controller clusters and other Cisco devices (such as Cisco IP Phones) regularly exchange CDP messages. Disabling CDP can interrupt cluster discovery and device connectivity.

        Beginning in privileged EXEC mode, follow these steps to disable CDP on a port.

        SUMMARY STEPS

          1.    configure terminal

          2.    interface interface-id

          3.    no cdp enable

          4.    end


        DETAILED STEPS
            Command or Action Purpose
          Step 1 configure terminal


          Example:
          
                      
                      
          Controller# configure terminal
          
          
           

          Enters the global configuration mode.

           
          Step 2 interface interface-id


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

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

           
          Step 3 no cdp enable


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

          Disables CDP on the interface specified in Step 2.

           
          Step 4 end


          Example:
          Controller(config-if)# end
           

          Returns to privileged EXEC mode.

           

          Enabling CDP on an Interface

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


          Note


          Controller clusters and other Cisco devices (such as Cisco IP Phones) regularly exchange CDP messages. Disabling CDP can interrupt cluster discovery and device connectivity.

          Beginning in privileged EXEC mode, 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.    configure terminal

            2.    interface interface-id

            3.    cdp enable

            4.    end


          DETAILED STEPS
              Command or Action Purpose
            Step 1 configure terminal


            Example:
            
                        
                        
            Controller# configure terminal
            
            
             

            Enters the global configuration mode.

             
            Step 2 interface interface-id


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

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

             
            Step 3 cdp enable


            Example:
            Controller(config-if)# cdp enable
             

            Enables CDP on a disabled interface.

             
            Step 4 end


            Example:
            Controller(config-if)# end
             

            Returns to privileged EXEC mode.

             

            Example

            The following example shows how to enable CDP on a disabled port:

            Controller# configure terminal
            Controller(config)# interface gigabitethernet1/0/1
            Controller(config-if)# cdp enable
            Controller(config-if)# end

            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.

            Additional References

            Related Documents

            Related Topic Document Title

            System Management Commands

            Configuration Fundamentals Command Reference, Cisco IOS XE Release 3S (Catalyst 3850 Switches)

            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

            MIBs

            MIB MIBs Link
             

            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

            Cisco IOS XE 3.2SE

            This feature was introduced.