| 9.3 |  | Troubleshooting Router Issues Overview |
| 9.3.3 |  | Troubleshooting using show cdp |

| Cisco Discovery Protocol (CDP) advertises device information to its direct neighbors, including MAC and IP addresses and outgoing interfaces. The output from the show cdp neighbors command displays information about directly connected neighbors. This information is useful for debugging connectivity issues. If a cabling problem is suspected, enable the interfaces with the no shutdown command and then execute the show cdp neighbors detail command before any other configuration. The command displays specific device detail such as the active interfaces, the port ID, and the device. The version of Cisco IOS that is running on the remote devices is also shown. If the physical layer is properly functioning, then all other directly connected Cisco devices should be displayed. If no known device appears, a Layer 1 problem likely exists. One area of concern with CDP is security. The amount of information CDP provides is so extensive that it can be a potential security hole. For security reasons CDP should be configured only on links between Cisco devices and disabled on user ports or links that are not locally managed.
| Lab Activity e-Lab Activity: Cisco Discovery Protocol In this lab, the students will use CDP to obtain information about neighboring Cisco devices.
| Web Links show cdp privileged EXEC Command http://www.cisco.com/en/US/products/sw/ iosswrel/ps1835/ products_command_reference_ chapter09186a00800ca747.html#1019270