Carlos, are you by chance using a straight through cable with auto-mdix enabled. Try disabling auto-mdix and using crossovers.
This person had the same kind of issue:
otherwise, yes, you want full/full or auto/auto, but do not mix as that will cause duplex mismatch.
Also, Ive also read that the 3500xl series has an issue with inline power, you might want to test with that disabled.
Message was edited by: ciscodaze WRONG LINK
Yes, if you are using a ST, then you are using auto-mdix (which is enabled by default) ---- but both speed and duplex must be set to auto when using auto-mdix or you will have a problem.
For auto-mdix make sure you use the GIG port, not sure if it is supported on Fe.
But if for some reason you are set up right, and still having probs, check that first link I sent.
Also see my other post
Switch>sh power inline
Switch(config-if)#power inline never
If this is direct connection between 2 switches no router between, then I would suggest you change your cable to Cross Over, configure the duplex on both sides then check problem if it is resolved before disabling other features
I once learn that Switch to switch connection = cross over cable
Switch to router/pc = Straight through cable.
Tenner says ciscodaze is correct Had the same issue in the past. Here is a beautiful table taken from :http://cciepursuit.wordpress.com/2007/07/08/switch-cabling-and-auto-mdix/
MDIX Speed/Duplex MDIX Speed/Duplex Link Status on auto on auto up on auto on hard-set up on auto off auto up on auto off hard-set up on hard-set on auto up on hard-set on hard-set down on hard-set off auto down on hard-set off hard-set down off auto on auto up off auto on hard-set down off auto off auto down off auto off hard-set down off hard-set on auto up off hard-set on hard-set down off hard-set off auto up off hard-set off hard-set down
So when hard setting the duplex & speed, you can see that MDIX can screw your link up. Use the correct cable or disable mdix using
Router(config-if) no mdix auto, and the problem should go away.
The line in red shows when your connection is working. The line in orange shows when your link is not working.