QTECH QSW-3400 Инструкция по настройке - Manual (Page 80)

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Chapter 8 ULDP Function Configuration
8.1 Introduction to ULDP Function
Unidirectional link is a common error state of link in networks, especially in fiber links.
Unidirectional link means that only one port of the link can receive messages from the other
port, while the latter one can not receive messages from the former one. Since the physical
layer of the link is connected and works normal, via the checking mechanism of the physical
layer, communication problems between the devices can not be found. As shown in Graph, the
problem in fiber connection can not be found through mechanisms in physical layer like
automatic negotiation.
Fiber Cross Connection
One End of Each Fiber Not Connected
This kind of problem often appears in the following situations: GBIC (Giga Bitrate Interface
Converter) or interfaces have problems, software problems, hardware becomes unavailable or
operates abnormally. Unidirectional link will cause a series of problems, such as spinning tree
topological loop, broadcast black hole.
ULDP (Unidirectional Link Detection Protocol) can help avoid disasters that could happen in
the situations mentioned above. In a switch connected via fibers or copper Ethernet line (like
g1/1
Switch
B
Switch
C
g1/2
g1/
3
Switch A
g1/
2
Switch
B
g1/
4
g1/
3
g1/
1
Switch A