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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