Dell powerconnect doesn't understand cisco bpdu

Hi guys,

I'm facing a strange problem. I want to link a dell powerconnect 5424 with a cisco 3700 switch.

My cisco is configured with mstp.

My powerconnect is configured with rstp. When I link both switch, on the cisco I can saw that linked port is in dispute state and not forwarding trafic. After some research, it's a cisco feature that prevent from receiving bpdu from a designated port on a designated port. But mac is lower on cisco so, dell's switch should change topology.

In order to go deep inside, I've mirrored the linked port on the powerconnect and I saw BPDU from dell switch, and bpdu from cisco.

The strange thing is that on dell's port bpdu receive counter there is nothing that change, the counter remain at 0.

By decoding bpdu's cisco I can see that cisco send proposal (powerconnect don't). So from what I understand, dell's switch don't respond to this bpdu because it can't see or understand it. And we come at the dispute situation. I don't have bpudfilter or something else on the dell. So I can't understand why the counter for bpdu receive packet is still at 0.

Anyone would have an idea or faced with situation ?

Best regards,

Sébastien AVELINE