3com 5500G ユーザーズマニュアル

Sometimes, unidirectional links may appear in networks. On a unidirectional link, 
one end can receive packets from the other end but the other end cannot.

Unidirectional links can be caused by fiber cross-connection or fiber cut (including 
single-fiber cut and lack of a fiber connection).

They can cause problems such as spanning tree topology loops.

You can use the Device Link Detection Protocol (DLDP) to monitor the link status of 
optical fiber cables and copper twisted pairs such as super category 5 twisted 
pairs. Once detecting a unidirectional link, DLDP shuts down the port or ask you to 
do so depending on your configuration.

Figure 18   Network diagram for DLDP configuration

 

■

Switch A and Switch B are connected through two pairs of fibers. The 
connecting ports are operating in mandatory full duplex mode at 1000 Mbps. 
Both of the switches support DLDP.

■

Configure DLDP to automatically disconnect the detected unidirectional link.

■

After the fibers are connected correctly, the port shut down by DLDP restores 
automatically.

■

Configure Switch A

SwitchB

SwitchA

PC

GE1/1/3

GE1/1/3

GE 1/1/4

GE1/1/4

SwitchB

SwitchA

PC

GE1/1/3

GE1/1/3

GE 1/1/4

GE1/1/4

SwitchB

SwitchA

PC

GE1/1/3

GE1/1/3

GE 1/1/4

GE1/1/4

SwitchB

SwitchA

PC

GE1/1/3

GE1/1/3

GE 1/1/4

GE1/1/4

Switch 5500 

Release V03.02.04 

All versions 

Switch 5500G

Release V03.02.04 

All versions 

Switch 4500

Release V03.03.00 

All versions