Cisco Discovery Protocol

CDP and Router Boot Up When a Cisco device boots up, CDP starts up automatically and allows the device to detect neighbor devices that use CDP. CDP allows two systems to learn about each other, even if they use different network layer protocols.

CDP Illustrated Here, CDP shows that Rt2 is connected to Rt1 and Rt3.  Rt1 is a Cisco 2500 router  Rt3 is a Cisco 2620 router

CDP Messages CDP Messages contain:  Device Identifiers - e.g. the router’s configured host name and domain name (if any)  Port Identifier - e.g. Ethernet 0, Ethernet 1, and Serial 0  Capabilities List - e.g. if the device acts as a source route bridge as well as a router  Version - information such as that provided by the local command show version  Platform - the device’s hardware platform, e.g. Cisco 1700

show cdp neighbors 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.

Disabling CDP In global configuration mode, use the no cdp run command to disable CDP. Router(config)# no cdp run For a specific interface, use the no cdp enable command. Router(config-if)# no cdp enable

show cdp

CDP Overview Cisco Discovery Protocol (CDP) allows network administrators to identify directly- connected routers and switches. CDP is a data-link layer (layer 2) protocol.