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Precautions in using loop detection function
– Disable loop detection at upstream port(s)
If a network is consisted of only Switching Hubs equipped with loop detection function, an upstream
switching hub may detect on ahead and block a loop occurred in a downstream switching hub.
This may block all communications to the downstream switching hub.
To minimize the communication failure by loop detection, disable the loop detection function
of the upstream switching hub so that only a port of the switching hub causing loop will be
blocked. You need to examine this type of network configuration and the switching hub settings.
Downstream
switching hub 1
PC 1
[Conditions of occurrence]
(1) Communications between PC1 and PC2, and between PC1 and PC3.
(2)A loop occurs in downstream switching hub 2.
(3)The upstream switching hub detects the loop first, and blocks the uplink port of downstream switching
hub 2. (Normally, only a port having loop connection is shut down.)
(4)The uplink port of downstream switching hub 2 is linked down, and communications to all other switching
hubs are blocked.
Fig. 2 Precautions in using loop detection function
Upstream
switching hub
(1)
270
(4)
(3)
Downstream
switching hub 2
PC 2
(2)
PC 3
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