3Com Switch 7750 Configuration Guide

DLDP CONFIGURATION

Overview

Introduction You may have encountered unidirectional links in networking. When a

unidirectional link occurs, the local device can receive packets from the peer device

through the link layer, but the peer device cannot receive packets from the local

device. Unidirectional link can cause problems such as spanning tree protocol (STP)

loops.

Unidirectional links can be caused by

■ Fiber cross-connection, as shown in Figure 55

■ Fibers that are not connected or disconnected, as shown in Figure 56, the

hollow lines in which refer to fibers that are not connected or disconnected.

Device link detection protocol (DLDP) can detect the link status of an optical fiber

cable or copper twisted pair (such as super category 5 twisted pair). If DLDP finds a

unidirectional link, it disables the related port automatically or prompts you to

disable it manually according to the configurations, to avoid network problems.

Figure 55 Fiber cross-connection

SwitchB

SwitchA

GE2/0/3

GE2/0/4

SwitchB

SwitchA

GE2/0/3

GE2/0/4