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Cisco Discovery Protocol (CDP) is a media- and protocol-independent protocol that runs on all Cisco-manufactured equipment including routers, bridges, access and communication servers, and switches. Using CDP, you can view information about all the Cisco devices that are directly attached to the device.
You must be in a user group associated with a task group that includes the proper task IDs. The command reference guides include the task IDs required for each command. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.
CDP is primarily used to obtain protocol addresses of neighboring devices and discover the platform of those devices. CDP can also be used to display information about the interfaces your router uses. CDP is media- and protocol-independent, and runs on all equipment manufactured by Cisco, including routers, bridges, access servers, and switches.
Use of SNMP with the CDP MIB allows network management applications to learn the device type and the SNMP agent address of neighboring devices and to send SNMP queries to those devices. CDP uses the CISCO-CDP-MIB.
CDP runs on all media that support Subnetwork Access Protocol (SNAP), including LAN, Frame Relay, and ATM physical media. CDP runs over the data link layer only. Therefore, two systems that support different network-layer protocols can learn about each other.
Each device configured for CDP sends periodic messages, known as advertisements, to a multicast address. Each device advertises at least one address at which it can receive SNMP messages. The advertisements also contain time-to-live, or hold-time, information, which indicates the length of time a receiving device holds CDP information before discarding it. Each device also listens to the periodic CDP messages sent by others to learn about neighboring devices and determine when their interfaces to the media go up or down.
CDP Version-2 (CDPv2) is the most recent release of the protocol and provides more intelligent device tracking features. These features include a reporting mechanism that allows for more rapid error tracking, thereby reducing costly downtime. Reported error messages can be sent to the console or to a logging server, and can cover instances of unmatching native VLAN IDs (IEEE 802.1Q) on connecting ports, and unmatching port duplex states between connecting devices.
CDPv2 show commands can provide detailed output on VLAN Trunking Protocol (VTP) management domain and duplex modes of neighbor devices, CDP-related counters, and VLAN IDs of connecting ports.
Type-length-value fields (TLVs) are blocks of information embedded in CDP advertisements. Table 1 summarizes the TLV definitions for CDP advertisements.
| TLV | Definition |
|---|---|
|
Device-ID TLV |
Identifies the device name in the form of a character string. |
|
Address TLV |
Contains a list of network addresses of both receiving and sending devices. |
|
Port-ID TLV |
Identifies the port on which the CDP packet is sent. |
|
Capabilities TLV |
Describes the functional capability for the device in the form of a device type; for example, a switch. |
|
Version TLV |
Contains information about the software release version on which the device is running. |
|
Platform TLV |
Describes the hardware platform name of the device, for example, Cisco 4500. |
|
VTP Management Domain TLV |
Advertises the system’s configured VTP management domain name-string. Used by network operators to verify VTP domain configuration in adjacent network nodes. |
|
Native VLAN TLV |
Indicates, per interface, the assumed VLAN for untagged packets on the interface. CDP learns the native VLAN for an interface. This feature is implemented only for interfaces that support the IEEE 802.1Q protocol. |
|
Full/Half Duplex TLV |
Indicates status (duplex configuration) of CDP broadcast interface. Used by network operators to diagnose connectivity problems between adjacent network elements. |
How to Implement CDP on Cisco IOS XR Software
To enable CDP, you must first enable CDP globally on the router and then enable CDP on a per-interface basis. This task explains how to enable CDP globally on the router and then enable CDP on an interface.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
configure Example: |
Enters mode. |
| Step 2 |
cdp Example: |
Enables CDP globally. |
| Step 3 |
interface type interface-path-id Example: |
Enters interface configuration mode. |
| Step 4 |
cdp Example: |
Enables CDP on an interface. |
| Step 5 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
This task explains how to modify the default version, hold-time setting, and timer settings.
 Note |
The commands can be entered in any order. |
| Command or Action | Purpose | |||
|---|---|---|---|---|
| Step 1 |
configure |
|||
| Step 2 |
cdp advertise v1 Example: |
Configures CDP to use only version 1 (CDPv1) in communicating with neighboring devices.
|
||
| Step 3 |
cdp holdtime seconds Example: |
Specifies the amount of time that the receiving networking device will hold a CDP packet sent from the router before discarding it.
|
||
| Step 4 |
cdp timer seconds Example: |
Specifies the frequency at which CDP update packets are sent.
|
||
| Step 5 |
commit |
|||
| Step 6 |
(Optional) show cdp Example: |
(Optional)
Displays global CDP information. The output displays the CDP version running on the router, the hold time setting, and the timer setting. |
This task shows how to monitor CDP.
Note |
The commands can be entered in any order. |
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
show cdp entry {* | entry-name} [protocol | version] Example: |
Displays information about a specific neighboring device or all neighboring devices discovered using CDP. |
| Step 2 |
show cdp interface [type interface-path-id | location node-id] Example: |
Displays information about the interfaces on which CDP is enabled. |
| Step 3 |
show cdp neighbors [type interface-path-id | location node-id] [detail] Example: |
Displays detailed information about neighboring devices discovered using CDP. |
| Step 4 |
show cdp traffic [location node-id] Example: |
Displays information about the traffic gathered between devices using CDP. |
The following is sample output for the show cdp neighbors command:
RP/0/RP0/CPU0:router# show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater
Device ID Local Intrfce Holdtme Capability Platform Port ID
router1 Mg0/0/CPU0/0 177 T S WS-C2924M Fa0/12
router2 PO0/4/0/0 157 R 12008/GRP PO0/4/0/1
The following is sample output for the show cdp neighbors command. In this example, the optional type instance arguments are used in conjunction with the detail optional keyword to display detailed information about a CDP neighbor. The output includes information on both IPv4 and IPv6 addresses.
RP/0/RP0/CPU0:router# show cdp neighbors POS 0/4/0/0 detail
-------------------------
Device ID: uut-user
SysName : uut-user
Entry address(es):
IPv4 address: 1.1.1.1
IPv6 address: 1::1
IPv6 address: 2::2
Platform: cisco 12008/GRP, Capabilities: Router
Interface: POS0/4/0/3
Port ID (outgoing port): POS0/2/0/3
Holdtime : 177 sec
Version :
Cisco IOS XR Software, Version 0.0.0[Default]
Copyright (c) 2005 by cisco Systems, Inc.
advertisement version: 2
The following is sample output for the show cdp entry command. In this example, the optional entry argument is used to display entry information related to a specific CDP neighbor.
RP/0/RP0/CPU0:router# show cdp entry router2
advertisement version: 2
-------------------------
Device ID: router2
SysName : router2
Entry address(es):
Platform: cisco 12008/GRP, Capabilities: Router
Interface: POS0/4/0/0
Port ID (outgoing port): POS0/4/0/1
Holdtime : 145 sec
Version :
Cisco IOS XR Software, Version 0.48.0[Default]
Copyright (c) 2004 by cisco Systems, Inc.
advertisement version: 2
The following is sample output for the show cdp interface command. In this example, CDP information related to Packet over SONET/SDH (POS) interface 0/4/0/0 is displayed.
RP/0/RP0/CPU0:router# show cdp interface pos 0/4/0/0
POS0/4/0/0 is Up
Encapsulation HDLC
Sending CDP packets every 60 seconds
Holdtime is 180 seconds
The following is sample output for the show cdp traffic command:
RP/0/RP0/CPU0:router# show cdp traffic
CDP counters :
Packets output: 194, Input: 99
Hdr syntax: 0, Chksum error: 0, Encaps failed: 0
No memory: 0, Invalid packet: 0, Truncated: 0
CDP version 1 advertisements output: 0, Input: 0
CDP version 2 advertisements output: 194, Input: 99
Unrecognize Hdr version: 0, File open failed: 0
The following is sample output for the show cdp traffic command. In this example, the optional location keyword and node-id argument are used to display information about the traffic gathered between devices using CDP from the specified node.
RP/0/RP0/CPU0:router# show cdp traffic location 0/4/cpu0
CDP counters :
Packets output: 16, Input: 13
Hdr syntax: 0, Chksum error: 0, Encaps failed: 0
No memory: 0, Invalid packet: 0, Truncated: 0
CDP version 1 advertisements output: 0, Input: 0
CDP version 2 advertisements output: 16, Input: 13
Unrecognize Hdr version: 0, File open failed: 0
The following example shows how to configure CDP globally and then enable CDP on Packet over SONET/SDH (POS) interface 0/3/0/0:
cdp
interface POS0/3/0/0
cdp
The following example shows how to modify global CDP settings. In this example, the timer setting is set to 20 seconds, the hold-time setting is set to 30 seconds, and the version of CDP used to communicate with neighboring devices is set to CDPv1:
cdp timer 20
cdp holdtime 30
cdp advertise v1
The following example shows how to use the show cdp command to verify the CDP global settings:
RP/0/RP0/CPU0:router# show cdp
Global CDP information:
Sending CDP packets every 20 seconds
Sending a holdtime value of 30 seconds
Sending CDPv2 advertisements is not enabled
The following sections provide references related to implementing CDP on Cisco IOS XR software.
|
Related Topic |
Document Title |
|---|---|
|
Cisco IOS XR CDP commands |
CDP Commands on Cisco IOS XR Software module of System Management Command Reference for Cisco NCS 5000 Series Routers |
|
Cisco IOS XR commands |
|
|
Getting started with Cisco IOS XR Software |
|
|
Information about user groups and task IDs |
Configuring AAA Services on Cisco IOS XR Software module of System Security Configuration Guide for Cisco NCS 5000 Series Routers |
|
Standards |
Title |
|---|---|
|
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
— |
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MIBs |
MIBs Link |
|---|---|
| — |
To locate and download MIBs using Cisco IOS XR software, use the Cisco MIB Locator found at the following URL and choose a platform under the Cisco Access Products menu: http://cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml |
|
RFCs |
Title |
|---|---|
|
No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature. |
— |
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Description |
Link |
|---|---|
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The Cisco Technical Support website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content. |
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