The Cisco Discovery Protocol (CDP) is a media-independent and protocol-independent protocol that runs on all Cisco-manufactured equipment including routers, bridges, access and communication servers, and switches. You can use CDP to discover and view information about all the Cisco devices that are directly attached to the device.
CDP gathers protocol addresses of neighboring devices and discovers the platform of those devices. CDP runs over the data link layer only. Two systems that support different Layer 3 protocols can learn about each other.
Each device that you configure for CDP sends periodic advertisements to a multicast address. Each device advertises at least one address at which it can receive SNMP messages. The advertisements also contain hold-time information, which indicates the length of time that a receiving device should hold CDP information before removing it. You can configure the advertisement or refresh timer and the hold timer.
CDP Version-2 (CDPv2) allows you to track instances where the native VLAN ID or port duplex states do not match between connecting devices.
CDP advertises the following type-length-value fields (TLVs):
- Device ID
- Port ID
- Native VLAN
- Full/Half Duplex
- Management Address
- Physical Location
All CDP packets include a VLAN ID. If you configure CDP on a Layer 2 access port, the CDP packets sent from that access port include the access port VLAN ID. If you configure CDP on a Layer 2 trunk port, the CDP packets sent from that trunk port include the lowest configured VLAN ID allowed on that trunk port. The trunk port can receive CDP packets that include any VLAN ID in the allowed VLAN list for that trunk port. For more information on VLANs, see the Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide.
VTP Feature Support
CDP sends the VLAN Trunking Protocol (VTP) type-length-value field (TLV) if the following conditions are met:
CDP Version 2 is enabled
The VTP feature is enabled
A VTP domain name is configured
You can view the VTP information with the show cdp neighbors detail command.
Cisco NX-OS supports both stateful and stateless restarts and switchover for CDP. For more information on high availability, see the Cisco Nexus 9000 Series NX-OS High Availability and Redundancy Guide.
Cisco NX-OS supports one instance of CDP.