I have a problem with this topology.
I have a RF link connected with cisco to 3com and a optic fiver to other cisco to the first cisco like the figure.
The problem is when the RF and Fiber optic is available because generate a loop.
The pvstp dont detect the loop and i want to be connected two channels in case the fiber go down.
someone can give and advice.?
the 3com only suport stp o rstp and the cisco switchs are configurated with pvstp but pvstp it can't be modified.
make the RF link and the 3com - switch A links 802.1Q trunks in this way PSTP+ should able to detect the presence of switchA via the RF link.
over an 802.1Q trunk PVST+ BPDUs are tunneled over a proprietary multicast MAC address and should flow via the 3com.
increase the stp cost for all vlans on the link of switchA to 3com so that this becomes a backup link
You can do this if you can configure the 3COM device.
Hope to help