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CCNA 2.8.a: Cisco Discovery Protocol (CDP)

Overview:

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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Links:

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/cdp/configuration/15-mt/cdp-15-mt-book/nm-cdp-discover.html