Basic knowledge of Cisco CDP protocol

CDP (Cisco Discovery Protoco: Cisco Discovery Protocol) is a Cisco proprietary protocol used to discover adjacent contacts. All Cisco products support CDP. CDP only displays directly connected neighbor information. If another device is separated, that is, cross-device, CDP cannot be found, therefore, CDP aims to obtain information of directly adjacent devices. CDP is very helpful in verifying whether a vro is connected to the appropriate port of its neighbor.
 
To run the CDP Protocol, the physical media must support the SNAP Protocol (SubNetwork Access Protocol: SubNetwork Access Protocol ). SNAP standardizes the standard method for transmitting IP data packets over the IEEE802 network.
 
CDP is a data link layer protocol. Routers running CDP regularly broadcast packets with CDP update data. By default, the vro sends a multicast Notification every 60 seconds at the address 01-00-0c-cc-cc-cc. If the notification reaches the 180-second holdtime limit, the neighbor device information is cleared.
 
Cdp commands are as follows:
 
Cdp run Command: this command is used to enable CDP in global mode. By default, CDP is enabled in global mode, we can use the no cdp run Command to disable the CDP protocol. After no cdp run is completed, the CDP protocol of all devices (including switches and routers) in the network will be disabled.
 
Cdp enable command: This Command needs to be configured in Port mode. It enables CDP protocol on a specific port. By default, CDP supports sending and receiving CDP protocol messages on all ports, however, for an asynchronous port, CDP is disabled. We can also disable cdp protocol message updates on a port by using no CDP enable. If you use the no cdp run Command to manually disable the CDP protocol in global mode, the network port cannot enable the CDP protocol.
 
Show cdp command: this command is used to display the interval between sending CDP protocol messages. We can also use this command to view the CDP protocol version information.
Show cdp entry {* | device-name [*] [protocol | version]}. We can use the show cdp entry command to view the information of a specific neighbor device. Through this command, we can view the IP address, hardware platform, connected port, and IOS version of a specific neighbor.
Show cdp interface [type number]. to check whether the CDP protocol is enabled or disabled on a specific port, run the show cdp interface command, this command can also display CDP message Update time and other content.
Show cdp neighbors [type number] [detail] use the show cdp neighbors command to obtain the platform, device type, and connected port of the CDP neighbor.
 
Clear cdp counters command: this command is used to reset the CDP protocol traffic counter. When this command is used, we use the show cdp traffic command again, all incoming and outgoing data packets and other information are cleared.