Cisco Discovery Protocol (CDP)

CDP is a media-and protocol-independent protocol that runs on all Cisco-manufactured equipment including routers, bridges, access and communication servers, and switches. Using CDP, you can view information about all the Cisco devices directly attached to the device. In addition, CDP detects native VLAN and port duplex mismatches.

CDP runs on all media that support Subnetwork Access Protocol (SNAP). CDP runs over the data link layer only. Cisco devices never forward CDP packets. When new CDP information is received, Cisco devices discard old information.

CDP Default Configuration
Feature	Default Value
CDP global enable state	Enabled
CDP port enable state	Enabled on all ports
CDP message interval	60 seconds
CDP holdtime	180 seconds

CDP Neighbor Information includes

Neighbor's device ID
Local port type and number
Holdtime value (in seconds)
Neighbor's hardware platform
Neighbor's network device capability
Neighbor's remote port type and number

CDP Neighbor Detail Information includes

Additional detail is shown about neighbors, including network address, enabled protocols, and software version.

Cisco Discovery Protocol (CDP)
Command	Effects
show cdp	cdp info (broadcast holdtime).
show cdp neighbor	This shows all devices directly connected to the router, hold time, local and remote port, ID, platform and capability info.
show cdp neighbor detail	Adds IP / IPX addresses to above info.
show cdp entry [*(all) \| NAME]	Shows info for all entries ( *) or only one (NAME).
show cdp traffic	Shows traffic statistics.
show cdp interface [type number]	Display info about the interfaces on which CDP is enabled
cdp run	Enables CDP (global configuration)
cdp enable	Enables CDP for an interface (interface configuration mode)
cdp timer seconds	Specifies CDP updates frequency.
cdp holdtime seconds	Specifies the hold time to be sent in the CDP update packets.