|  | 4.3 | Router's Network Neighbors
| 4.3.3 | A CDP configuration example
CDP begins automatically upon a device's system startup. The CDP function normally starts by default when a Cisco product boots up with Cisco IOS Release 10.3 or later. Although CDP runs by default, you must explicitly enable it on the device's interface by using the command cdp enable. For example, the Figure shows the cdp enable in use on the E0 and S0 interface on Router A. This command begins CDPs dynamic discovery function on the device's interfaces. Only directly connected neighbors exchange CDP frames. A router caches any information it receives from its CDP neighbors. If a subsequent CDP frame indicates that any of the information about a neighbor has changed, the router discards the older information and replaces it with the new information. Use the command show cdp interface, as shown in Figure , to display the values of the CDP timers, the interface status, and the encapsulation used by CDP for its advertisement and discovery frame transmission. Default values for timers set the frequency for CDP updates and for aging CDP entries. These timers are set automatically at 60 seconds and 180 seconds, respectively. If the device receives a more recent update, or if this hold-time value expires, the device must discard the CDP entry.