DES-3326S Layer 3 Fast Ethernet Switch User’s Guide

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.

332Understanding and Troubleshooting the Spanning Tree Protocol

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D-Link DES-3326S manual Unidirectional Link