100 MB half duplex on 2960 ???

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Mar 5th, 2007
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Just installed a 2960-24TC switch with a GLC-GE100FX MOdule. This uses 100MB Fibre and connects to a 3550 Switch.

3550 is set to Full Duplex.

Any ideas why the GigaBit Interface on the 2960 would be detecting at half duplex? This is causing some late collsions.

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Overall Rating: 4.7 (3 ratings)
MUHAMMAD SHAHEEN Mon, 03/05/2007 - 13:06
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When you connect two Cisco devices then the golden Rule is if you want to fix the speed and/or duplex of one interface then you should also fix the speed/duplex for the connecting interface.

Looking at your post looks like you have 100meg full duplex set at 3550 but on 2960 you have auto detect on. This will for sure end up 100meg half.

To resolve this problem you must set the 2960's interface to be same (100meg full-duplex) or you should change 3550 to auto-negotiate !!

Hope this helps !!!!



BAMURRAY1 Mon, 03/05/2007 - 14:13
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The 2960 will not allow the speed or duplex to be changed. The duplex was changed to auto on the 3550 and the link stayed at 100 1/2.

I had to add the media-type sfp command to the Gi0/1 interface and then I was able to modify the duplex setting as outlined in the cisco config doc below:





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