CCNA 2.8.a: Cisco Discovery Protocol (CDP)


Cisco Discovery Protocol CDP is a Cisco proprietary layer 2 protocol to help switches learn about neighboring switches


Study Notes:

Cisco Discovery Protocol (CDP)

  • Cisco Discovery Protocol is a Layer 2, media-independent, and network-independent protocol that networking applications use to learn about nearby, directly connected devices
  • Cisco Discovery Protocol is enabled by default
  • Each device configured for Cisco Discovery Protocol advertises at least one address at which the device can receive messages and sends periodic advertisements (messages) to the well-known multicast address 01:00:0C:CC:CC:CC
  • Devices discover each other by listening at that address
  • They also listen to messages to learn when interfaces on other devices are up or go down.
  • Advertisements contain time-to-live information, which indicates the length of time a receiving device should hold Cisco Discovery Protocol information before discarding it
  • Advertisements supported and configured in Cisco software are sent, by default, every 60 seconds on interfaces that support Subnetwork Access Protocol (SNAP) headers
  • Cisco devices never forward Cisco Discovery Protocol packets
  • Cisco devices that support Cisco Discovery Protocol store the information received in a table
  • Information in this table is refreshed every time an advertisement is received, and information about a device is discarded after three advertisements from that device are missed
  • The information contained in Cisco Discovery Protocol advertisements varies based on the type of device and the installed version of the operating system
    • Cisco IOS version running on Cisco devices
    • Hardware platform of devices
    • IP addresses of interfaces on devices
    • Locally connected devices advertising Cisco Discovery Protocol
    • Interfaces active on Cisco devices, including encapsulation type
    • Hostname
    • Duplex setting
    • VLAN Trunking Protocol (VTP) domain
    • Native VLANSome of the information that Cisco Discovery Protocol can learn includes:


PacketTracer Lab: CCNA-2.8.a-How-to-configure-Cisco-Discovery-Protocol-CDP.pkt

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