D-Link DES-3250TG User Manual page 231

DES-3250TG Layer 2 Fast Ethernet Switch User's Guide
There are a number of circumstances in which the STA can fail
– mostly related to the loss of a large number of BPDUs. These
situations will cause a port in the blocking state to transition
to the forwarding state.
Full/Half Duplex Mismatch
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 a 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 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
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