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| 4.2 |  | End-System Commands for Gathering Data Link Information |
| 4.2.6 |  | The show cdp neighbors command |

The show cdp neighbors command is one of the quickest ways to verify Layer 2 connectivity between two directly connected Cisco devices. However, CDP is often turned off in order to limit bandwidth usage or enhance the security of the network. Furthermore, most non Cisco devices do not speak CDP. Before relying on the show cdp neighbors command, verify that the device at the other end of the data link is configured to allow CDP. On a Cisco device running IOS use the global configuration command cdp run to enable CDP on that device.

> Router(config)#cdp run

Use the interface configuration command cdp enable to allow CDP on a particular interface if it has been specifically disabled.

> Router(config-if)#cdp enable

An example of the output produced by the show cdp neighbors command is shown in Figure .