Spanning Tree Protocol
Full/Half Duplex MismatchA mismatch in the duplex state of two ports is a very common configuration error for a point- to-point link. If one port is configured as full-duplex, and the other port is left in auto- negotiation mode, the second port will end up in half-duplex because ports configured as half- or full-duplex do not negotiate.
Figure D-7: Example of full/half duplex mismatch
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 perform 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.
D-10 | HP ProLiant BL e-Class C-GbE Interconnect Switch User Guide |
