We have several 3500XL switches in our network along with newer models capable of running PVRST+. Of course the 3500XL switches can only run PVST+ mode, which is what all the other switches are curently running. We would like to switch our environment to use PVRST+. I realize that we will have to continue running PVST for the 3500XL switches. Can we run both modes on the newer switches and what problems will we run into as a result?