1-3 Cisco Discovery Protocol (CDP) | Cisco Field Manual[c] Router Configuration

Cisco Discovery Protocol allows for dynamic discovery of directly connected Cisco devices across SNAP-supported media.
CDP runs on all Cisco hardware running Cisco IOS 10.2 or later.
CDP provides information on neighboring platform, operating system, and Layer 3 addressing.
CDP version 2 supports information about duplex and VLAN settings.
CDP is enabled by default on all interfaces and can be disabled on a global or per-interface basis.

CDP is media- and protocol-independent . CDP operates as a Layer 2 SNAP frame and requires only that the media support SNAP frames .

Configuration

CDP is enabled by default. Step 1 is not required, because it is a default setting. The steps listed here are designed to help you manage CDP on your router.

Enable CDP globally (the default is on):
```
 (global)  cdp run  
```
This enables the CDP process. This is the default setting. To disable CDP for the whole router, use the no cdp run command.
(Optional) Set the update time for CDP advertisements:
```
 (global)  cdp timer   seconds  
```
This command sets the update interval in seconds. This is a global command, so you can specify only a single time interval, and all interfaces will use the same update interval. The default setting is 60 seconds.
(Optional) Specify the holdtime of the CDP information:
```
 (global)  cdp holdtime   seconds  
```
This command specifies the holdtime that is to be sent with the CDP update. This holdtime tells the neighboring router how long to keep the CDP information. If no update is received by the neighboring router at the end of the holdtime, that router discards the cdp information.
Change the CDP send parameters for a given interface (this is on by default):
```
 (global)  cdp advertise-v2  
```
This command allows the router to send out Version 2 updates for CDP. CDP Version 2 supports three new type length values (TLVs)VTP management domain, native VLAN, and duplex mode. If a router does not support V2 updates, the new TLVs are ignored, and CDP continues operating normally.
(Optional) Enable CDP on an interface:
```
 (interface)  cdp enable  
```
This command lets CDP updates be sent out a particular interface. The default configuration is on for all interfaces. To disable CDP on a particular interface, use the no cdp enable command. Disabling CDP can be useful for conserving bandwidth or if the device on the other side of the link is not a Cisco device.

Use the show cdp and show cdp interface commands to verify the configuration of CDP.

Example

This example alters CDP's operational parameters by changing the holdtime to 480 seconds and the update time to 120 seconds. The Ethernet interface is operating normally, but we are assuming that the serial interface is connected to a non-Cisco router. Therefore, to conserve bandwidth, CDP is disabled on that interface.

  cdp holdtime 480   cdp timer 120   interface ethernet 0   ip address 1.2.2.1 255.255.255.0   interface serial 0   ip address 1.4.4.1 255.255.255.0   encapsulation ppp   no cdp enable