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
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- 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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