H3C Technologies H3C S3100 Series Switches - Manual (Page 155)

Operation Manual – DLDP
H3C S3100-52P Ethernet Switch Chapter 1 DLDP Configuration
1-1
Chapter 1 DLDP Configuration
1.1 DLDP Overview
You may have encountered unidirectional links, namely, one-way audio, 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: one is caused by fiber
cross-connection, and the other is caused by a fiber being not connected or being
disconnected. The cross-connected fibers in Figure 1-1 refer to optical fibers which are
connected inversely. The hollow lines in Figure 1-2 refer to fibers which are not
connected or are broken.
Unidirectional links can cause many problems, such as spanning tree protocol (STP)
loop.
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.
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
Figure 1-1
Fiber cross-connection