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The Cisco Discovery Protocol (CDP) is a media-independent device discovery protocol that runs on all Cisco manufactured equipment, including routers, bridges, access servers, and switches. CDP Version-2 is the most recent release of the protocol and provides more intelligent device tracking features. This feature module describes the following additions to CDP that provide CDP Version-2 functionality:
Each device sends periodic messages to a multicast address and listens to the periodic messages sent by others in order to learn about neighboring devices and determine when their interfaces to the media go up or down. Each device advertises at least one address at which it can receive SNMP messages. The advertisements contain holdtime, information, which indicates the period of time a receiving device should hold CDP information from a neighbor before discarding it.
With CDP, network management applications can learn the device type and the SNMP agent address of neighboring devices. This process enables applications to send SNMP queries to neighboring devices.
advertisement---An updated information packet sent periodically by the CDP process.
holdtime---The amount of time, in seconds, the receiving device should hold a CDP advertisement from a neighbor before discarding it.
neighbor---A remote system, connected to the subject system on one or more of its interfaces.
Type Length Value (TLV)---A piece of information in a CDP advertisement.
VLAN Trunking Protocol (VTP)---A discovery technique deployed by switches where each switch advertises its management domain on its trunk ports, its configuration revision number, and its known VLANs and their specific parameters. A VTP domain is made up of one or more interconnected devices that share the same VTP domain name. A switch can be configured to be in only one VTP domain.
This feature is supported on the following routers and access servers:
This feature supports the CISCO CDP-MIB.
Type Length Values (TLVs) are blocks of information embedded in CDP advertisements. Table 1 summarizes existing TLVs.
| TLV | Definition |
|---|---|
Device-ID | Identifies the device name in the form of a character string. |
Address TLV | Contains a list of network addresses of both receiving and transmitting devices. |
Port-ID | Identifies the port on which the CDP packet is sent. |
Capabilities | Describes the device's functional capability in the form of a device type, for example, a switch. |
Version | Contains information about the software release version on which the device is running. |
Platform | Describes the hardware platform name of the device, for example, Cisco 4500. |
IP Network Prefix | Contains a list of network prefixes to which the sending device can forward IP packets. This information is in the form of the interface protocol and port number, for example, Eth 1/0. |
CDP can now advertise new features, using the following new TLVs:
CDP sends error messages to the console (and, optionally, to a logging server on another system) during operation. CDP now sends error messages that detail:
Instances where unmatching duplex states are reported between two devices are displayed in the console in the following format:
%DUPLEX_MISMATCH: duplex mismatch discovered on [local interface (local interface duplex mode)], with [neighbor name neighbor interface (neighbor duplex mode)]
Explanation
CDP discovered a mismatch of duplex configuration. The received duplex TLV does not match the interface's configuration:
Recommended Action
Configure the interfaces so that they have the same duplex mode.
Table 2 describes field descriptions shown in the error message syntax statement.
| Field | Definition |
|---|---|
local interface | The protocol and port number of the local device. |
local interface duplex mode | The duplex mode of the local device, either full or half. |
neighbor name | The name of the connecting device. |
neighbor interface | The protocol and port number of the connecting device. |
neighbor duplex mode | The duplex mode of the connecting device, either full or half. |
An example of a system log message reporting unmatching duplex states is as follows:
%DUPLEX_MISMATCH: duplex mismatch discovered on Ethernet1/0 (half), with other-router Ethernet2/3 (full).
Note that interface Ethernet1/0 is operating at half duplex and interface Ethernet2/3 is operating at full duplex.
Instances where unmatching VLAN IDs are reported between two devices are displayed in the console in the following format:
%NATIVE_VLAN_MISMATCH: native VLAN mismatch discovered on [local interface (local interface VLAN ID),] with [neighbor name neighbor interface (neighbor VLAN ID)]
Explanation
CDP discovered a mismatch of native VLAN configuration. The received native VLAN TLV does not match the interface's configuration.
Recommended Action
Configure the interfaces so that they have the same native VLAN ID.
Table 3 describes the fields shown in the error message syntax statement.
| Field | Definition |
|---|---|
local interface | The protocol and port number of the local device. |
local interface VLAN ID | The ID number assigned to the VLAN of the local device. |
neighbor name | The name of the connecting device. |
neighbor interface | The protocol and port number of the connecting device. |
neighbor VLAN ID | The ID number assigned to the VLAN of the connecting device. |
An example of a system log message reporting unmatching native VLAN IDs is as follows:
Native VLAN mismatch discovered on Ethernet1/0 (5), with router1 Ethernet2/3 (27).
Note that interface Ethernet1/0 has a native VLAN ID of 5 and interface Ethernet 2/3 has a native VLAN ID of 27.
This section describes configuring, monitoring and maintaining CDP activity.
To enable CDP Version-2 advertisements, use the following command in global configuration mode:
| Command | Purpose |
|---|---|
cdp advertise-v2 | Enable CDP Version-2 advertising functionality on a device. |
To show display information about CDP commands, use one of the following commands in privileged EXEC mode:
| Command | Purpose |
|---|---|
show cdp | Displays the interval between transmissions of CDP advertisements, the number of seconds the CDP advertisement is valid for a given port, and the version of the advertisement. |
show cdp neighbors | Displays the type of device that has been discovered, the name of the device, the number and type of the local interface (port), the number of seconds the CDP advertisement is valid for the port, the device type, the device product number, and the port ID. Issuing the detail keyword displays information on the native VLAN ID, the duplex mode, and the VTP domain name associated with neighbor devices. |
show cdp traffic | Displays counters related to CDP activity. |
This section documents the following new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.0 command references.
To enable advertising CDP Version-2 functionality on a device, use the cdp advertise-v2 global configuration command. To disable advertising CDP Version-2 functionality, use the no form of the command.
cdp advertise-v2This command has no keywords or arguments.
Enabled
Global configuration
This command first appeared in Cisco IOS Release 12.0(3)T. Three new TLVs have been added to CDP Version-2. They are VTP management domain, native VLAN, and full/half duplex TLVs.
The following example enables a device called router1 to send CDP Version-2 advertisements:
router1(config)# cdp advertise-v2
To display global CDP information, including timer and holdtime information, use the show cdp EXEC command.
show cdpThis command has no keywords or arguments.
EXEC
This command first appeared in Cisco IOS Release 10.3.
The following example shows that the current router is transmitting CDP advertisements every one minute. Also shown is that the current router directs its neighbors to hold its CDP advertisements for three minutes, and that the router is enabled to transmit CDP Version-2 advertisements:
router# show cdp Global CDP information: Sending CDP packets every 60 seconds Sending a holdtime value of 180 seconds Sending CDPv2 advertisements is enabled
Table 4 describes the fields shown in the example.
| Field | Definition |
|---|---|
Sending CDP packets every XX seconds | The interval, in seconds, between transmissions of CDP advertisements. This field is controlled by the cdp timer command. |
Sending a holdtime value of XX seconds | The amount of time, in seconds, the device directs the neighbor to hold a CDP advertisement before discarding it. This field is controlled by the cdp holdtime command. |
Sending CDPv2 advertisements is XX | The state of whether CDP Version-2 type advertisements are enabled to be transmitted. Possible states are enabled or disabled. This field is controlled by the cdp advertise-v2 command. |
To display information about neighbors, use the show cdp neighbors EXEC command.
show cdp neighbors [type number] [detail]
type | (Optional) Type of interface connected to the neighbors about which you want information. |
number | (Optional) Number of the interface connected to the neighbors about which you want information. |
detail | (Optional) Displays detailed information about a neighbor (or neighbors) including network address, enabled protocols, hold time, and software version. |
None
EXEC
This command first appeared in Cisco IOS Release 10.3.
The following example specifies information related to the show cdp neighbors command:
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 joe Eth 0 133 4500 Eth 0 sam Eth 0 152 R AS5200 Eth 0 terri Eth 0 144 3640 Eth 0/0 maine Eth 0 141 RP1 Eth 0/0 sancho Eth 0 164 7206 Eth 1/0
Table 5 describes the fields shown in the example.
| Field | Definition |
|---|---|
Capability Codes | The type of device that can be discovered. |
Device ID | The name of the neighbor device and either the MAC address or the serial number of this device. |
Local Intrfce | The protocol being used by the connectivity media. |
Holdtme | The remaining amount of time, in seconds, the current device will hold the CDP advertisement from a transmitting router before discarding it. |
Capability | The type of the device listed in the CDP Neighbors table. Possible values are: R - Router T - Transparent bridge B - Source-routing bridge S - Switch H - Host I - IGMP device r - Repeater |
Platform | The product number of the device. |
Port ID | The protocol and port number of the device. |
The following is sample output for one neighbor from the show cdp neighbors detail command. Additional detail is shown about neighbors, including network address, enabled protocols, and software version.
router# show cdp neighbors detail Device ID: 008024 1EEB00 (milan-sw-1-cat9k) Entry address(es): IP address: 1.15.28.10 Platform: CAT5000, Capabilities: Switch Interface: Ethernet1/0, Port ID (outgoing port): 2/7 Holdtime : 162 sec Version : Cisco Catalyst 5000 Duplex Mode: full Native VLAN: 42 VTP Management Domain: `Accounting Group'
Table 6 describes field descriptions shown in the example.
| Field | Definition |
|---|---|
Device ID | The name of the neighbor device and either the MAC address or the serial number of this device. |
Entry address(es) | A list of network addresses of neighbor devices. |
[network protocol] address | The network address of the neighbor device. The address can be in IP, IPX, AppleTalk, DECnet, or CLNS protocol conventions. |
Platform | The product name and number of the neighbor device. |
Capabilities | The device type of the neighbor. This device can be a router, a bridge, a transparent bridge, a source-routing bridge, a switch, a host, an IGMP device, or a repeater. |
Interface | The protocol and port number of the port on the current device. |
Holdtime | The remaining amount of time, in seconds, the current device will hold the CDP advertisement from a transmitting router before discarding it. |
Version | The software version of the neighbor device. |
Duplex Mode | The duplex state of connection between the current device and the neighbor device. |
Native VLAN | The ID number of the VLAN on the neighbor device. |
VTP Management Domain | A string that is the name of the collective group of VLANs associated with the neighbor device. |
To display information from the CDP table, use the show cdp traffic EXEC command.
show cdp trafficThis command has no keywords or arguments.
EXEC
This command first appeared in Cisco IOS Release 10.3.
The following example specifies information associated with the show cdp traffic command:
router# show cdp traffic Total packets output: 543, Input: 333 Hdr syntax: 0, Chksum error: 0, Encaps failed: 0 No memory: 0, Invalid: 0, Fragmented: 0 CDP version 1 advertisements output: 191, Input: 187 CDP version 2 advertisements output: 352, Input: 146
Table 7 describes the fields shown in the example.
| Field | Definition |
|---|---|
Total packets output | The number of CDP advertisements transmitted by the local device. Note this value is the sum of the CDP Version-1 advertisements output and CDP Version-2 advertisements output fields. |
| The number of CDP advertisements received by the local device. Note this value is the sum of the CDP Version-1 advertisements input and CDP Version-2 advertisements input fields. |
Hdr syntax | The number of CDP advertisements with bad headers, received by the local device. |
Chksum error | The number of times the checksum (verifying) operation failed on incoming CDP advertisements. |
Encaps failed | The number of times CDP failed to transmit advertisements on an interface because of a failure caused by the local device's bridge port. |
No memory | The number of times the local device did not have enough memory to store the CDP advertisements in the advertisement cache table when the device was attempting to assemble advertisement packets for transmission and parse them when receiving them. |
Invalid | The number of invalid CDP advertisements received and transmitted by the local device. |
Fragmented | The number of times fragments or portions of a single CDP advertisement were received by the local device instead of the complete advertisement. |
CDP version 1 advertisements output | The number of CDP Version-1 advertisements transmitted by the local device. |
| The number of CDP Version-1 advertisements received by the local device. |
CDP version 2 advertisements output | The number of CDP Version-2 advertisements transmitted by the local device. |
| The number of CDP Version-2 advertisements received by the local device. |
For more information, see sections on IP configuration in the Network Protocols Configuration Guide, Part 1 and the Configuration Fundamentals Configuration Guide.
Posted: Thu Mar 4 11:48:10 PST 1999
Copyright 1989-1999©Cisco Systems Inc.