PLANET XGS3-24042 - Manual (Page 98)

10-1
Chapter 10 ULDP Function Configuration
10.1 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.
Figure 10-1 Fiber Cross Connection
Figure 10-2 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
g1/0/2
Switch B
g1/0/4
g1/0/3
g1/0/1
Switch A
g1/0/1
Switch B
Switch C
g1/0/2
g1/0/3
Switch A