Cisco Discovery Protocol

The CDP (Cisco Discovery Protocol) is a protocol that allows a network device, automatically create a list of peer devices that also support CDP. It was developed by Cisco and is used primarily on Cisco devices. It acts on the LLC layer of the data link layer (layer 2) in the OSI model. If the underlying network access method supports Subnetwork Access Protocol, it is media - and protocol -independent and therefore can be used for Ethernet, FDDI, ATM, and other methods.

Each device configured for CDP sends periodic messages ( advertisements) to an Ethernet multicast address (01- 00- 0C- CC -CC -CC) and receives messages of neighboring devices. Each message contains information such as the device name, operating system version, interface identifier, management IP addresses and the hold time of the packet. If a periodic update of the device information from the old information is discarded after the hold time. By default, sent to almost all CDP- supporting interfaces a CDP packet with a hold time of 180 seconds from Cisco routers every 60 seconds.

CDP has no security mechanisms. CDP messages are easy to forge and listen.

The current version of CDP is CDPv2. This allows, in contrast to the first version faster troubleshooting through more information.

A comparable, vendor independent protocol is LLDP.

Commands to configure the CDP on Cisco IOS (excerpt)

• Status of the CDP Show:

Show cdp global activation of the CDP Process:

Cdp run Enabling CDP on a specific interface:

Cdp enable Make settings via the transmission interval of CDP updates:

Cdp timer Settings over the time a CDP packet is held to make:

Cdp holdtime Table with the CDP information to delete:

Clear cdp table Information about the CDP traffic show:

Show cdp traffic Information about adjacent CDP devices show:

Show cdp neighbors Display information about a specific CDP device:

Show cdp entry Information about the interfaces on which CDP is enabled Show: