D-Link DES-3326 User Manual - Unidirectional Link
DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
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Understanding and Troubleshooting the Spanning Tree Protocol
In the above example, port 1 on B is configured as a full-duplex
port and port 1 on A is either configured as a half-duplex port, or
left in auto-negotiation mode. Because port 1 on B is configured as
a full-duplex port, it does not do the carrier sense when accessing
the link. B will then start sending packets even if A is using the
link. A will then detect collisions and begin to run the flow control
algorithm. If there is enough traffic between B and A, all packets
(including BPDUs) will be dropped. If the BPDUs sent from A to B
are dropped for longer than the MAX AGE, B will lose its
connection to the root (A) and will unblock its connection to C.
This will lead to a data loop.
Unidirectional Link
Unidirectional links can be caused by an undetected failure in one
side of a fiber cable, or a problem with a ports transceiver. Any