I have an environment with 5 Foundry FastIron switches and two Cisco 3750s. All of the Foundrys and one of the Cisco switches (3750-2) recognizes one switch (Foundry5) as the root. The other 3750 (3750-1) considers itself to be the root, and while passing BPDUs to the Foundry attached to it, doesn't seem to recognize it in STP. All of the Foundrys have the same priority, 32768, the root election was based off of the lowest MAC. The two Cisco switches have the same priorities; when the two Cisco's are dual attached, a bridging loop occurs. My thought is to raise the priorities for the two VLANs on the one Cisco switch (3750-1) that thinks it is the root above the other Cisco, which would also be above the Foundry then dual attaching. I would like to get rid of the Foundry, but until then, I have to live with it. Any thoughts from anyone in similar situations? Also, all run RSTP. Attached is a diagram. Thanks in advance.