Configuring DLDP


1. Overview

2. DLDP Configuration

3. Appendix: Default Parameters

This guide applies to:

T1500G-8T v2 or above, T1500G-10PS v2 or above, T1500G-10MPS v2 or above, T1500-28PCT v3 or above, T1600G-18TS v2 or above, T1600G-28PS v3 or above, T1600G-28TS v3 or above, T1600G-52TS v3 or above, T1600G-52PS v3 or above, T1700X-16TS v3 or above, T1700G-28TQ v3 or above, T2500G-10TS v2 or above, T2600G-18TS v2 or above, T2600G-28TS v3 or above, T2600G-28MPS v3 or above, T2600G-28SQ v1 or above, T2600G-52TS v3 or above.


DLDP (Device Link Detection Protocol) is a Layer 2 protocol that enables devices connected through fiber or twisted-pair Ethernet cables to detect whether a unidirectional link exists.

A unidirectional link occurs whenever traffic sent by a local device is received by its peer device but traffic from the peer device is not received by the local device.

Unidirectional links can cause a variety of problems, such as spanning-tree topology loops. Once detecting a unidirectional link, DLDP can shut down the related port automatically or inform users.

2DLDP Configuration

Configuration Guidelines

A DLDP-capable port cannot detect a unidirectional link if it is connected to a DLDP-incapable port of another switch.

To detect unidirectional links, make sure DLDP is enabled on both sides of the links.

2.1Using the GUI

Choose the menu MAINTENANCE > DLDP to load the following page.

Figure 2-1 Configure DLDP

Follow these steps to configure DLDP:

1)In the Global Config section, enable DLDP and configure the relevant parameters. Click Apply.

DLDP State

Enable or disable DLDP globally.

Advertisement Interval

Configure the interval to send advertisement packets. Valid values are from 1 to 30 seconds, and the default value is 5 seconds.

Shut Mode

Choose how to shut down the port when a unidirectional link is detected:

Auto: When a unidirectional link is detected on a port, DLDP will generate logs and traps then shut down the port, and DLDP on this port will change to Disabled.

Manual: When a unidirectional link is detected on a port, DLDP will generate logs and traps, and then users can manually shut down the unidirectional link ports.

Auto Refresh

With this option enabled, the switch will automatically refresh the DLDP information.

Refresh Interval

Specify the time interval at which the switch will refresh the DLDP information. Valid values are from 1 to 100 seconds, and the default value is 3 seconds.

2)In the Port Config section, select one or more ports, enable DLDP and click Apply. Then you can view the relevant DLDP information in the table.


Enable or disable DLDP on the port.

Protocol State

Displays the DLDP protocol state.

Initial: DLDP is disabled.

Inactive: DLDP is enabled but the link is down.

Active: DLDP is enabled and the link is up, or the neighbor entries in this device are empty.

Advertisement: No unidirectional link is detected (the device has established bidirectional links with all its neighbors) or DLDP has remained in an Active status for more than 5 seconds.

Probe: In this state, the device will send out Probe packets to detect whether the link is unidirectional. The port enters this state from the Active state if it receives a packet from an unknown neighbor.

Disable: A unidirectional link is detected.

Link State

Displays the link state.

Link-Down: The link is down.

Link-Up: The link is up.

Neighbour State

Displays the neighbour state.

Unknown: Link detection is in progress.

Unidirectional: The link between the port and the neighbor is unidirectional.

Bidirectional: The link between the port and the neighbor is bidirectional.

2.2Using the CLI

Follow these steps to configure DLDP:

Step 1


Enter global configuration mode.

Step 2


Globally enable DLDP.

Step 3

dldp interval interval-time

Configure the interval of sending advertisement packets on ports that are in the advertisement state.

interval-time: Specify the interval time. The valid values are from 1 to 30 seconds. By default, it is 5 seconds.

Step 4

dldp shut-mode { auto | manual }

Configure the DLDP shutdown mode when a unidirectional link is detected.

auto: The switch automatically shuts down ports when a unidirectional link is detected. It is the default setting.

manual: The switch displays an alert when a unidirectional link is detected. Then the users can manually shut down the unidirectional link ports.

Step 5

interface {fastEthernet port | range fastEthernet port-list | gigabitEthernet port | range gigabitEthernet port-list | ten-gigabitEthernet port | range ten-gigabitEthernet port-list}

Enter interface configuration mode.

Step 6


Enable DLDP on the specified port.

Step 7

show dldp

Verify the global DLDP configuration.

Step 8

show dldp interface

Verify the DLDP configuration of the ports.

Step 9


Return to privileged EXEC mode.

Step 10

copy running-config startup-config

Save the settings in the configuration file.

The following example shows how to enable DLDP globally, configure the DLDP interval as 10 seconds and specify the shutdown mode as auto.



Switch(config)#dldp interval 10

Switch(config)#dldp shut-mode auto

Switch(config)#show dldp

DLDP Global State: Enable

DLDP Message Interval: 10

DLDP Shut Mode: Auto


Switch#copy running-config startup-config

The following example shows how to enable DLDP on port 1/0/1.


Switch(config)#interface gigabitEthernet 1/0/1


Switch(config-if)#show dldp interface

Port DLDP State Protocol State Link State Neighbor State

---- ---------- -------------- ---------- --------------

Gi1/0/1 Enable Inactive Link-Down N/A

Gi1/0/2 Disable Initial Link-Down N/A



Switch#copy running-config startup-config

3Appendix: Default Parameters

Default settings of DLDP are listed in the following table.

Table 3-1Default Settings of DLDP


Default Setting

Global Config

DLDP State


Advertisement Interval

5 seconds

Shut Mode


Auto Refresh


Refresh Interval

3 seconds

Port Config