Giga port: auto-negociation and fixed speed

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Nov 25th, 2008
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I have a question regarding the giga port o catalyst 4500 switches.

I read that for giga links, auto-negociation is the best (speed, duplex, pause frame). Then what happens if the speed is forced, with a cat2960 switch, even with not crossed cable and using the mdix-auto fonction ? (the link is ok)

I have:

speed 1000, duplex full on both side (cat4500, cat2960)

I found the the mdix-auto fonction run with auto-negociation. Then the speed is forced (the duplex too) with the mdix-auto and a not-cross cable. The link seems to be ok anyway.

So is the fixed configuration really used ?

the card on the cat4510 is a WS-X4448-GB-RJ45; On the remote side we have a cat2960 using the giga port (gi 0/1).


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John Blakley Tue, 11/25/2008 - 07:15
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I would think that the only reason you would want auto on any link is if you think there will be a slower speed connected. On gb links, chances are a host is connecting at 100mb, and if you set to 1000/full, the host won't connect because the port won't negotiate a slower speed. If you have two gb ports connected and hard coded and the link is up, you're fine.


milan.kulik Wed, 11/26/2008 - 01:16
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my experience is auto-mdix sometimes doesn't work if duplex/speed is set to fixed values.

On the other hand, auto-negotiation sometimes doesn't work is the connected device is produced by a different vendor.




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