Cisco Discovery Protocol

CDP is a Cisco proprietary protocol.

It is enabled on Cisco devices (routers, switches, firewalls, IP phones, etc) by default.

CDP messages are periodically sent to multicas MAC address 0100.0CCC.CCCC.

When a device receives a CDP message, it processes and discards the message. It does not forward it to other devices.

By default, CDP messages are sent once every 60 seconds.

By default, the CDP holdtime is 180 seconds. If a message isn't received from a neighbor for 180 seconds, the neighbor is removed from the CDP neighbor table.

CDPv2 messages are sent by default.

CDP show command summary

  1. Shows basic information about CDP (timers, version).

R1# show cdp

  1. Displays how many CDP messages have been sent and received.

R1# show cdp traffic

  1. Displays which interfaces CDP is enabled on.

R1# show cdp interface

  1. Lists CDP neighbors and some basic information about each neighbor.

R1# show cdp neighbors

  1. Lists each CDP neighbor with more detailed information.

R1# show cdp neighbors detail

  1. Displays the same infor as above, but for the specified neighbor only.

R1# show cdp entry <name>

CDP configuration commands

  • CDP is globally enabled by default.

  • CDP is also enabled on each interface by default.

  • To enable/disable CDP globally: R1(config)# [no] cdp run

  • To enable/disable CDP on specific interfaces: R1(config-if)# [no] cdp enable

  • Configure the CDP timer: R1(config)# cdp timer <seconds>

  • Configure the CDP holdtime: R1(config)# cdp holdtime <seconds>

  • Enable/disable CDPv2: R1(config)# [no] cdp advertise-v2

Wireshark capture

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