I have stepped into a network that wasn't designed by me and due to my lack of familiarity, I'm concerned about a couple items. The network consists of 3750 12Ss.
1. Some 12Ss are running PVST+ and others are running R-PVST. What sort of impact will this cause?
2. I know that we can only have 128 spanning tree instances on a switch. If we are running PVST+, does this limit us to 128 VLANS total on a switch or is there a way to combine several VLANS into a single instance?
Thanks in advance.
1) Nothing disastrous but you may find that you do not get the benefit of RSTP, for example if you have 4 switches, 3 run RSTP and 1 PVST+ then
a) if a vlan is only on the 3 RSTP switches you will get the benefit of RSTP for that vlan.
b) if the vlan is on any of the 3 RSTP switches AND the PVST+ switch then the STP for that vlan will revert to PVST+ timers.
2) Have a look at MST which allows you groups vlans into instances