Configuring CDP

Available Languages

Download Options

PDF (213.8 KB)
View with Adobe Reader on a variety of devices

Updated:June 29, 2007

Bias-Free Language

The documentation set for this product strives to use bias-free language. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. Learn more about how Cisco is using Inclusive Language.

Configuring CDP

Table Of Contents

Configuring CDP

Understanding CDP

Configuring CDP

Default CDP Configuration

Configuring the CDP Characteristics

Disabling and Enabling CDP

Disabling and Enabling CDP on an Interface

Monitoring and Maintaining CDP

Configuring CDP

This chapter describes how to configure Cisco Discovery Protocol (CDP) on your access point/bridge.

Note For complete syntax and usage information for the commands used in this chapter, refer to the Cisco Aironet 1300 Series Bridge Command Reference for this release and the Cisco IOS Configuration Fundamentals Command Reference for Release 12.2.

This chapter contains these sections:

•Understanding CDP

•Configuring CDP

•Monitoring and Maintaining CDP

Understanding CDP

Cisco Discovery Protocol (CDP) is a device-discovery protocol that runs on all Cisco network equipment. Each device sends identifying messages to a multicast address, and each device monitors the messages sent by other devices. Information in CDP packets is used in network management software such as CiscoWorks2000.

CDP is enabled on the access point/bridge's Ethernet and radio ports by default.

Note For best performance on your wireless LAN, disable CDP on all radio interfaces and on sub-interfaces if VLANs are enabled on the access point/bridge.

Configuring CDP

This section contains CDP configuration information and procedures:

•Default CDP Configuration

•Configuring the CDP Characteristics

•Disabling and Enabling CDP

•Disabling and Enabling CDP on an Interface

Default CDP Configuration

Table 16-1 lists the default CDP settings.

Table 16-1 Default CDP Configuration

Feature

Default Setting

CDP global state

Enabled

CDP interface state

Enabled

CDP holdtime (packet holdtime in seconds)

180

CDP timer (packets sent every x seconds)

60

Configuring the CDP Characteristics

You can configure the CDP holdtime (the number of seconds before the access point/bridge discards CDP packets) and the CDP timer (the number of seconds between each CDP packets the access point/bridge sends).

Beginning in Privileged Exec mode, follow these steps to configure the CDP holdtime and CDP timer:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

cdp holdtime seconds

(Optional) Specify the amount of time a receiving device should hold the information sent by your device before discarding it.

The range is from 10 to 255 seconds; the default is 180 seconds.

Step 3

cdp timer seconds

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

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

Step 4

end

Return to Privileged Exec mode.

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

This example shows how to configure and verify CDP characteristics:
bridge# configure terminal
bridge(config)# cdp holdtime 120
bridge(config)# cdp timer 50
bridge(config)# end
bridge# show cdp 
Global CDP information:
        Sending a holdtime value of 120 seconds
        Sending CDP packets every 50 seconds
For additional CDP show commands, see the "Monitoring and Maintaining CDP" section.

Disabling and Enabling CDP

CDP is enabled by default. Beginning in Privileged Exec mode, follow these steps to disable the CDP device discovery capability:

Command

Purpose

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 enable CDP:

Command

Purpose

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 enable CDP.
bridge# configure terminal
bridge(config)# cdp run
bridge(config)# end
Disabling and Enabling CDP on an Interface

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

Beginning in privileged EXEC mode, follow these steps to disable CDP on an interface:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

interface interface-id

Enter interface configuration mode, and enter the interface on which you are disabling CDP.

Step 3

no cdp enable

Disable CDP on an interface.

Step 4

end

Return to privileged EXEC mode.

Step 5

copy running-config startup-config

(Optional) Save your entries in the configuration file.

Beginning in privileged EXEC mode, follow these steps to enable CDP on an interface:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

interface interface-id

Enter interface configuration mode, and enter the interface on which you are enabling CDP.

Step 3

cdp enable

Enable CDP on an interface after disabling it.

Step 4

end

Return to privileged EXEC mode.

Step 5

copy running-config startup-config

(Optional) Save your entries in the configuration file.

This example shows how to enable CDP on an interface:
bridge# configure terminal
bridge(config)# interface x
bridge(config-if)# cdp enable
bridge(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.

Command

Description

clear cdp counters

Reset the traffic counters to zero.

clear cdp table

Delete the CDP table of information about neighbors.

show cdp

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

show cdp entry entry-name [protocol | version]

Display 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 [type number]

Display information about interfaces where CDP is enabled.

You can limit the display to the type of interface or the number of the interface about which you want information (for example, entering gigabitethernet 0/1 displays information only about Gigabit Ethernet port 1).

show cdp neighbors [type number] [detail]

Display information about neighbors, including device type, interface type and number, holdtime settings, capabilities, platform, and port ID.

You can limit the display to neighbors on a specific type or number of interface or expand the display to provide more detailed information.

show cdp traffic

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

Below are six examples of output from the CDP show privileged EXEC commands:

bridge# show cdp
Global CDP information:
        Sending CDP packets every 50 seconds
        Sending a holdtime value of 120 seconds
bridge# show cdp entry *
-------------------------
Device ID: bridge
Entry address(es):
  IP address: 10.1.1.66
Platform: cisco WS-C3550-12T,  Capabilities: Switch IGMP
Interface: GigabitEthernet0/2,  Port ID (outgoing port): GigabitEthernet0/2
Holdtime : 129 sec
Version :
Cisco Internetwork Operating System Software
IOS (tm) C3550 Software (C3550-I5Q3L2-M), Experimental Version 12.1(20010612:021
316) [jang-flamingo 120]
Copyright (c) 1986-2001 by cisco Systems, Inc.
Compiled Fri 06-Jul-01 18:18 by jang
advertisement version: 2
Protocol Hello:  OUI=0x00000C, Protocol ID=0x0112; payload len=27, value=0000000
0FFFFFFFF010221FF00000000000000024B293A00FF0000
VTP Management Domain: ''
Duplex: full
-------------------------
Device ID: idf2-1-lab-l3.cisco.com
Entry address(es):
  IP address: 10.1.1.10
Platform: cisco WS-C3524-XL,  Capabilities: Trans-Bridge Switch
Interface: GigabitEthernet0/1,  Port ID (outgoing port): FastEthernet0/10
Holdtime : 141 sec
Version :
Cisco Internetwork Operating System Software
IOS (tm) C3500XL Software (C3500XL-C3H2S-M), Version 12.0(5.1)XP, MAINTENANCE IN
TERIM SOFTWARE
Copyright (c) 1986-1999 by cisco Systems, Inc.
Compiled Fri 10-Dec-99 11:16 by cchang
advertisement version: 2
Protocol Hello:  OUI=0x00000C, Protocol ID=0x0112; payload len=25, value=0000000
0FFFFFFFF010101FF000000000000000142EFA400FF
VTP Management Domain: '' 
bridge# show cdp entry * protocol
Protocol information for talSwitch14 :
  IP address: 172.20.135.194
Protocol information for tstswitch2 :
  IP address: 172.20.135.204
  IP address: 172.20.135.202
Protocol information for tstswitch2 :
  IP address: 172.20.135.204
  IP address: 172.20.135.202 
bridge# show cdp interface
GigabitEthernet0/1 is up, line protocol is up
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds
GigabitEthernet0/2 is up, line protocol is down
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds
GigabitEthernet0/3 is administratively down, line protocol is down
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds
GigabitEthernet0/4 is up, line protocol is down
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds
GigabitEthernet0/5 is up, line protocol is up
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds
GigabitEthernet0/6 is up, line protocol is up
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds
GigabitEthernet0/7 is up, line protocol is down
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds
GigabitEthernet0/8 is up, line protocol is down
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds 
bridge# show cdp neighbor
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater
Device ID	Local Interface	Holdtme	Capability	Platform	Port ID
Perdido2	Gig 0/6	125	R S I	WS-C3550-1Gig				0/6
Perdido2	Gig 0/5	125	R S I	WS-C3550-1Gig 	0/5 
bridge# show cdp traffic
CDP counters :
        Total packets output: 50882, Input: 52510
        Hdr syntax: 0, Chksum error: 0, Encaps failed: 0
        No memory: 0, Invalid packet: 0, Fragmented: 0
        CDP version 1 advertisements output: 0, Input: 0
        CDP version 2 advertisements output: 50882, Input: 52510 

Table 16-1 Default CDP Configuration
Feature	Default Setting
CDP global state	Enabled
CDP interface state	Enabled
CDP holdtime (packet holdtime in seconds)	180
CDP timer (packets sent every x seconds)	60

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	cdp holdtime seconds	(Optional) Specify the amount of time a receiving device should hold the information sent by your device before discarding it. The range is from 10 to 255 seconds; the default is 180 seconds.
Step 3	cdp timer seconds	(Optional) Set the transmission frequency of CDP updates in seconds. The range is from 5 to 254; the default is 60 seconds.
Step 4	end	Return to Privileged Exec mode.

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	no cdp run	Disable CDP.
Step 3	end	Return to Privileged Exec mode.

	Command	Purpose
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.

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	interface interface-id	Enter interface configuration mode, and enter the interface on which you are disabling CDP.
Step 3	no cdp enable	Disable CDP on an interface.
Step 4	end	Return to privileged EXEC mode.
Step 5	copy running-config startup-config	(Optional) Save your entries in the configuration file.

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	interface interface-id	Enter interface configuration mode, and enter the interface on which you are enabling CDP.
Step 3	cdp enable	Enable CDP on an interface after disabling it.
Step 4	end	Return to privileged EXEC mode.
Step 5	copy running-config startup-config	(Optional) Save your entries in the configuration file.

Command	Description
clear cdp counters	Reset the traffic counters to zero.
clear cdp table	Delete the CDP table of information about neighbors.
show cdp	Display global information, such as frequency of transmissions and the holdtime for packets being sent.
show cdp entry entry-name [protocol \| version]	Display 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 [type number]	Display information about interfaces where CDP is enabled. You can limit the display to the type of interface or the number of the interface about which you want information (for example, entering gigabitethernet 0/1 displays information only about Gigabit Ethernet port 1).
show cdp neighbors [type number] [detail]	Display information about neighbors, including device type, interface type and number, holdtime settings, capabilities, platform, and port ID. You can limit the display to neighbors on a specific type or number of interface or expand the display to provide more detailed information.
show cdp traffic	Display CDP counters, including the number of packets sent and received and checksum errors.

Was this Document Helpful?

Feedback

Contact Cisco

Open a Support Case
(Requires a Cisco Service Contract)