System Management Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

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System Management Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

Cisco Discovery Protocol Version 2

Updated: June 12, 2026

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Describes Cisco Discovery Protocol version 2 (CDPv2), which provides enhanced device tracking, rapid error reporting for network mismatches, and detailed output for VLAN and duplex state management.

Cisco Discovery Protocol version 2 (CDPv2) is a network discovery protocol that:

  • provides enhanced device tracking and identification features,

  • enables rapid error reporting on network mismatches and configuration issues, and

  • supports detailed output on VLAN and duplex state management between connected devices.

You can use CDPv2 to quickly report errors, such as when native VLAN IDs (IEEE 802.1Q) do not match or when port duplex states are inconsistent.

CDPv2 show commands display detailed output about the VLAN Trunking Protocol (VTP) management domain, duplex modes of neighboring devices, CDP-related counters, and VLAN IDs of connected ports.

Definitions of CDP type-length-value fields

Type-length-value fields (TLVs) are information blocks embedded in CDP advertisements. This table provides TLV definitions for CDP advertisements.

Table 1. Type-Length-Value definitions for CDPv2

TLV

Definition

Device-ID TLV

Identifies the device name in the form of a character string.

Address TLV

Contains a list of network addresses of both receiving and sending devices.

Port-ID TLV

Identifies the port on which the CDP packet is sent.

Capabilities TLV

Describes the functional capability for the device in the form of a device type; for example, a switch.

Version TLV

Contains information about the software release version on which the device is running.

Platform TLV

Describes the hardware platform name of the device, for example, Cisco 4500.

VTP Management Domain TLV

Advertises the system’s configured VTP management domain name-string. Used by network operators to verify VTP domain configuration in adjacent network nodes.

Native VLAN TLV

Indicates, per interface, the assumed VLAN for untagged packets on the interface. CDP learns the native VLAN for an interface. This feature is implemented only for interfaces that support the IEEE 802.1Q protocol.

Full/Half Duplex TLV

Indicates status (duplex configuration) of CDP broadcast interface. Used by network operators to diagnose connectivity problems between adjacent network elements.

Features of CDP

CDP provides the following capabilities:

  • Obtains protocol addresses and platform identity of neighboring devices.

  • Displays information about router interfaces and connected devices.

  • Operates media- and protocol-independently on all Cisco platforms: routers, bridges, access servers, switches.

  • Uses SNMP with CDP MIB (CISCO-CDP-MIB) for network management and device querying.

  • Runs on media that support Subnetwork Access Protocol (SNAP), such as LAN, Frame Relay, ATM.

  • Functions solely at the data link layer, enabling systems with differing network-layer protocols to communicate.