HP proliant bl e-class Manual De Usuario

A 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. 

 

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.