I installed a fast ethernet adapter in two 3640s which are both connected to 4006s, one is in my building and the other is in a remote location. Both 3640s and 4006s are running the same level of code. When I installed the one in my 3640 and powered it up it came right up running at 100 mbps and full duplex. The switch port was set to auto sense. When we powered the one up in the other building it came up at 100 mbps and half-duplex. The router port is set for duplex and speed auto. Their switch was also set to auto-sense. We tried forcing the router and switch to full duplex but no matter what we do we get the error message from the switch duplex mismatch. A show interface on the router still shows half-duplex. Any ideas on how to get the duplex to full?
I have this problem too.