Cisco Discovery Protocol

Cisco Discovery Protocol (CDP) is a Layer 2 discovery protocol. Cisco devices send out CDP packets every thirty seconds (they are sent as multicast packets). Cisco devices, including switches, do not forward these packets, so only devices on the segment the packets were sent on see them. Cisco devices record the information in a CDP table that can be queried by the cdpCacheTable in the CISCO-CDP-MIB or shown by the show cdp neighbors [detail] CLI command. This table includes the following information:

  • Each neighbor's Layer 3 address (typically the IP address)

  • The type of device the neighbor is

  • The port on the neighbor that is directly connected to the reporting device in ifName format

  • The duplex of the directly connected ...

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