3Com Switch 7750 Configuration Guide Guide

26
DLDP CONFIGURATION
DLDP Overview As shown in Figure 49 and Figure 50, 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 links can be divided into two types: the first type is caused by
cross-connected fibers, and the second type is caused by a fiber which is not
connected or a fiber which is disconnected. The cross-connected fibers in
Figure 49 refer to optical fibers which are connected inversely. The air-core lines in
Figure 50 refer to a fiber which is not connected or a fiber which is disconnected.
Unidirectional links can cause many problems, such as spanning tree topology
loop.
Device Link Detection Protocol (DLDP) can detect the link status of the optical fiber
cable or copper twisted pair (such as super category 5 twisted pair). If DLDP finds a
unidirectional link, it disables the related ports automatically or informs users to
disable them manually according to the configurations, to avoid network
problems.
Figure 49 Fiber cross-connection
SwitchB
SwitchA
PC
GE2/0/3
GE2/0/3
GE2/0/4
GE2/0/4
SwitchB
SwitchA
PC
GE2/0/3
GE2/0/3
GE2/0/4
GE2/0/4