Dldp Overview; Chapter 1 Dldp Configuration - Huawei Quidway S3900 Series Operation Manual

Operation Manual - DLDP
Quidway S3900 Series Ethernet Switches-Release 1510

Chapter 1 DLDP Configuration

1.1 DLDP Overview

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 1-1
refer to optical fibers which are connected inversely. The air-core lines in Figure 1-2
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.
GE2/1/3 GE2/1/3 GE2/1/3 GE2/1/3
GE2/1/3 GE2/1/3 GE2/1/3 GE2/1/3
Figure 1-1 Fiber cross-connection
SwitchA SwitchA SwitchA SwitchA
GE2/1/4 GE2/1/4 GE2/1/4 GE2/1/4
GE2/1/4 GE2/1/4 GE2/1/4 GE2/1/4
SwitchB SwitchB SwitchB SwitchB
PC PC PC PC
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1-1
Chapter 1 DLDP Configuration