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Community Member

Duplex mismatch between 3640 and 4006

I installed a fast ethernet adapter in two 3640’s which are both connected to 4006’s, one is in my building and the other is in a remote location. Both 3640’s and 4006’s 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?


Re: Duplex mismatch between 3640 and 4006

Auto negotiate is less than reliable . You need to hard code you speed and duplex settings, also sometimes you need to reset the port or bounce the interface for this to take effect.

Community Member

Re: Duplex mismatch between 3640 and 4006

Hi Daniel,

As Duplex negotiation isn't an industrie standard you have to set this fixed.

The speed is ok in auto setting.

Good luck !!



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