Configuring the Cisco Discovery Protocol

Cisco Discovery Protocol

The Cisco Discovery Protocol (CDP) is a device discovery protocol that runs on all Cisco-manufactured equipment. A device enabled with CDP sends out periodic interface updates to a multicast address in order to make itself known to neighboring devices.

The default value for the frequency of periodic transmissions is 60 seconds, and the default advertised time-to-live value is 180 seconds. The second and latest version of the protocol, CDPv2, introduces new time-length-values (TLVs) and provides a reporting mechanism that allows for more rapid error tracking, which reduces downtime.


Note
Cisco recommends that you disable Cisco Discovery Protocol on the controller and access point when connected to non-Cisco switches as CDP is unsupported on non-Cisco switches and network elements.

Restrictions for Cisco Discovery Protocol

  • CDPv1 and CDPv2 are supported on the following devices:

    • Cisco 2504 Wireless Controller

    • Cisco 5508 Wireless Controller

    • Cisco 5520 Wireless Controller

    • Cisco 8510 Wireless Controller

    • Cisco 8540 Wireless Controller

    • CAPWAP-enabled access points

    • An access point connected directly to a Cisco 2504 Wireless Controller


      Note

      To use the Intelligent Power Management feature, ensure that CDPv2 is enabled on the Cisco 2504 Wireless Controller. CDP v2 is enabled by default.

  • The Cisco 600 Series OEAPs do not support CDP.

  • The support of CDPv1 and CDPv2 enables network management applications to discover Cisco devices.

  • The following TLVs are supported by both the controller and the access point:

    • Device-ID TLV: 0x0001—The hostname of the controller, the access point, or the CDP neighbor.

    • Address TLV: 0x0002—The IP address of the controller, the access point, or the CDP neighbor.

    • Port-ID TLV: 0x0003—The name of the interface on which CDP packets are sent out.

    • Capabilities TLV: 0x0004—The capabilities of the device. The controller sends out this TLV with a value of Host: 0x10, and the access point sends out this TLV with a value of Transparent Bridge: 0x02.

    • Version TLV: 0x0005—The software version of the controller, the access point, or the CDP neighbor.

    • Platform TLV: 0x0006—The hardware platform of the controller, the access point, or the CDP neighbor.

    • Power Available TLV: 0x001a— The amount of power available to be transmitted by power sourcing equipment to permit a device to negotiate and select an appropriate power setting.

    • Full/Half Duplex TLV: 0x000b—The full- or half-duplex mode of the Ethernet link on which CDP packets are sent out.

  • These TLVs are supported only by the access point:

    • Power Consumption TLV: 0x0010—The maximum amount of power consumed by the access point.

    • Power Request TLV:0x0019—The amount of power to be transmitted by a powerable device in order to negotiate a suitable power level with the supplier of the network power.

  • If the switch has provided power through CDP, it continues to provide only with CDP, and vice-versa with LLDP. (CSCvg86156)

  • Changing the CDP configuration on the controller does not change the CDP configuration on the access points that are connected to the controller. You must enable and disable CDP separately for each access point.

  • You can enable or disable the CDP state on all or specific interfaces and radios. This configuration can be applied to all access points or a specific access point.

  • The following is the behavior assumed for various interfaces and access points:

    • CDP is disabled on radio interfaces on indoor (nonindoor mesh) access points.

    • Nonmesh access points have CDPs disabled on radio interfaces when they join the controller. The persistent CDP configuration is used for the APs that had CDP support in its previous image.

    • CDP is enabled on radio interfaces on indoor-mesh and mesh access points.

    • Mesh access points will have CDP enabled on their radio interfaces when they join the controller. The persistent CDP configuration is used for the access points that had CDP support in a previous image. The CDP configuration for radio interfaces is applicable only for mesh APs.

  • CDP over radio backhaul link is not supported in Wave 2 (COS) APs.

  • CDP is not supported in radio interfaces of Wave 2 (COS) APs. The GUI configuration of this has no effect.

Configuring the Cisco Discovery Protocol

Configuring the Cisco Discovery Protocol (GUI)

Procedure

Step 1

Choose Controller > CDP > Global Configuration to open the CDP > Global Configuration page.

Step 2

Select the CDP Protocol Status check box to enable CDP on the controller or unselect it to disable this feature. The default value is selected.

Note 

Enabling or disabling this feature is applicable to all controller ports.
Step 3

From the CDP Advertisement Version drop-down list, choose v1 or v2 to specify the highest CDP version supported on the controller. The default value is v1.

Step 4

In the Refresh-time Interval text box, enter the interval at which CDP messages are to be generated. The range is 5 to 254 seconds, and the default value is 60 seconds.

Step 5

In the Holdtime text box, enter the amount of time to be advertised as the time-to-live value in generated CDP packets. The range is 10 to 255 seconds, and the default value is 180 seconds.

Step 6

Click Apply to commit your changes.

Step 7

Click Save Configuration to save your changes.

Step 8

Perform one of the following:

  • To enable or disable CDP on a specific access point, follow these steps:

    Choose Wireless > Access Points > All APs to open the All APs page.

    Click the link for the desired access point.

    Choose the Advanced tab to open the All APs > Details for (Advanced) page.

    Select the Cisco Discovery Protocol check box to enable CDP on this access point or unselect it to disable this feature. The default value is enabled.

    Note 

    If CDP is disabled in Step 2, a message indicating that the Controller CDP is disabled appears.

  • Enable CDP for a specific Ethernet interface, radio, or slot as follows:

    Choose Wireless > Access Points > All APs to open the All APs page.

    Click the link for the desired access point.

    Choose the Interfaces tab and select the corresponding check boxes for the radios or slots from the CDP Configuration section.

    Note 

    Configuration for radios is only applicable for mesh access points.

    Click Apply to commit your changes.

  • To enable or disable CDP on all access points currently associated to the controller, follow these steps:

    Choose Wireless > Access Points > Global Configuration to open the Global Configuration page.

    Select the CDP State check box to enable CDP on all access points associated to the controller or unselect it to disable CDP on all access points. The default value is selected. You can enable CDP on a specific Ethernet interface, radio, or slot by selecting the corresponding check box. This configuration will be applied to all access points associated with the controller.

    Click Apply to commit your changes.

Step 9

Click Save Configuration to save your changes.

Configuring the Cisco Discovery Protocol (CLI)

Procedure

Step 1

Enable or disable CDP on the controller by entering this command:

config cdp {enable | disable}

CDP is enabled by default.
Step 2

Specify the interval at which CDP messages are to be generated by entering this command:

config cdp timer seconds

The range is 5 to 254 seconds, and the default value is 60 seconds.
Step 3

Specify the amount of time to be advertised as the time-to-live value in generated CDP packets by entering this command:

config cdp holdtime seconds

The range is 10 to 255 seconds, and the default value is 180 seconds.
Step 4

Specify the highest CDP version supported on the controller by entering this command:

config cdp advertise {v1 | v2}

The default value is v1.
Step 5

Enable or disable CDP on all access points that are joined to the controller by entering the config ap cdp {enable | disable} all command.

The config ap cdp disable all command disables CDP on all access points that are joined to the controller and all access points that join in the future. CDP remains disabled on both current and future access points even after the controller or access point reboots. To enable CDP, enter the config ap cdp enable all command.

Note 

After you enable CDP on all access points joined to the controller, you may disable and then reenable CDP on individual access points using the command in Step 6. After you disable CDP on all access points joined to the controller, you may not enable and then disable CDP on individual access points.

Step 6

Enable or disable CDP on a specific access point by entering this command:

config ap cdp {enable | disable} Cisco_AP

Step 7

Configure CDP on a specific or all access points for a specific interface by entering this command:

config ap cdp {ethernet | radio} interface_number slot_id {enable | disable } {all | Cisco_AP }

Note 

When you use the config ap cdp command to configure CDP on radio interfaces, a warning message appears indicating that the configuration is applicable only for mesh access points.

Step 8

Save your changes by entering this command:

save config

Viewing Cisco Discovery Protocol Information

Viewing Cisco Discovery Protocol Information (GUI)

Procedure

Step 1

Choose Monitor > CDP > Interface Neighbors to open the CDP > Interface Neighbors page appears.

This page shows the following information:

  • The controller port on which the CDP packets were received

  • The name of each CDP neighbor

  • The IP address of each CDP neighbor

  • The port used by each CDP neighbor for transmitting CDP packets

  • The time left (in seconds) before each CDP neighbor entry expires

  • The functional capability of each CDP neighbor, defined as follows: R - Router, T - Trans Bridge, B - Source Route Bridge, S - Switch, H - Host, I - IGMP, r - Repeater, or M - Remotely Managed Device

  • The hardware platform of each CDP neighbor device
Step 2

Click the name of the desired interface neighbor to see more detailed information about each interface’s CDP neighbor. The CDP > Interface Neighbors > Detail page appears.

This page shows the following information:

  • The controller port on which the CDP packets were received

  • The name of the CDP neighbor

  • The IP address of the CDP neighbor

  • The port used by the CDP neighbor for transmitting CDP packets

  • The CDP version being advertised (v1 or v2)

  • The time left (in seconds) before the CDP neighbor entry expires

  • The functional capability of the CDP neighbor, defined as follows: Router, Trans Bridge,?Source Route Bridge, Switch, Host, IGMP, Repeater, or Remotely Managed Device

  • The hardware platform of the CDP neighbor device

  • The software running on the CDP neighbor
Step 3

Choose AP Neighbors to see a list of CDP neighbors for all access points connected to the controller. The CDP AP Neighbors page appears.

Step 4

Click the CDP Neighbors link for the desired access point to see a list of CDP neighbors for a specific access point. The CDP > AP Neighbors page appears.

This page shows the following information:

  • The name of each access point

  • The IP address of each access point

  • The name of each CDP neighbor

  • The IP address of each CDP neighbor

  • The port used by each CDP neighbor

  • The CDP version being advertised (v1 or v2)
Step 5

Click the name of the desired access point to see detailed information about an access point’s CDP neighbors. The CDP > AP Neighbors > Detail page appears.

This page shows the following information:

  • The name of the access point

  • The MAC address of the access point’s radio

  • The IP address of the access point

  • The interface on which the CDP packets were received

  • The name of the CDP neighbor

  • The IP address of the CDP neighbor

  • The port used by the CDP neighbor

  • The CDP version being advertised (v1 or v2)

  • The time left (in seconds) before the CDP neighbor entry expires

  • The functional capability of the CDP neighbor, defined as follows: R - Router, T - Trans Bridge,?B - Source Route Bridge, S - Switch, H - Host, I - IGMP, r - Repeater, or M - Remotely Managed Device

  • The hardware platform of the CDP neighbor device

  • The software running on the CDP neighbor
Step 6

Choose Traffic Metrics to see CDP traffic information. The CDP > Traffic Metrics page appears.

This page shows the following information:

  • The number of CDP packets received by the controller

  • The number of CDP packets sent from the controller

  • The number of packets that experienced a checksum error

  • The number of packets dropped due to insufficient memory

  • The number of invalid packets

Viewing Cisco Discovery Protocol Information (CLI)

Procedure

Step 1

See the status of CDP and to view CDP protocol information by entering this command:

show cdp

Step 2

See a list of all CDP neighbors on all interfaces by entering this command:

show cdp neighbors [detail]

The optional detail command provides detailed information for the controller’s CDP neighbors.

Note 

This command shows only the CDP neighbors of the controller. It does not show the CDP neighbors of the controller’s associated access points. Additional commands are provided below to show the list of CDP neighbors per access point.

Step 3

See all CDP entries in the database by entering this command:

show cdp entry all

Step 4

See CDP traffic information on a given port (for example, packets sent and received, CRC errors, and so on) by entering this command:

show cdp traffic

Step 5

See the CDP status for a specific access point by entering this command:

show ap cdp ap-name Cisco_AP

Step 6

See the CDP status for all access points that are connected to the controller by entering this command:

show ap cdp all

Step 7

See a list of all CDP neighbors for a specific access point by entering these commands:

  • show ap cdp neighbors ap-name Cisco_AP

  • show ap cdp neighbors detail Cisco_AP

    Note 

    The access point sends CDP neighbor information to the controller only when the information changes.
Step 8

See a list of all CDP neighbors for all access points connected to the controller by entering these commands:

  • show ap cdp neighbors all

  • show ap cdp neighbors detail all

    Note 

    The access point sends CDP neighbor information to the controller only when the information changes.

Getting CDP Debug Information

  • Get debug information related to CDP packets by entering by entering this command:

    debug cdp packets

  • Get debug information related to CDP events by entering this command:

    debug cdp events