RSTP Problem with older 3com 4200

[philliesphan]

Hello,

I am attempting to setup a redundant network using spanning tree protocol with our older 3com 4200 series switches. The bulk of the switches are 24 port 100Base-T/2 1000Base-t/2 SFP's. These switches are working beautifully with RSTP, however when I attempted to add two 50 port 4200's frames begin to loop unexpectedly. STP is setup with the same configuration on each switch and if the network is solely made up with the 24 port units everything is fine the moment I add the two 50 ports the network goes south. It's the funniest thing I have ever seen, the switches are all part of the same family and all are running SuperStack II however those 50 port switches just are not cooperating with the rest of the network. Any ideas?

Thanks