Hi. I just wish to ask what will happen if one switch running pvst+ is connected to a switch running rstp? Or pvst+ and mst? Or rstp and mst? Redundant connections between the two switches and each share the same vlans.
Thanks in advance.
If SW1 and SW2 have exactly the same vlans then all vlans would revert back to pvst+ and use standard 802.1d timers.
STP process would not fail through any combination because RSTP is backwards compatible with PVST.
As an example in the real world. Lets say you have a switched network consisting of 20 switches only 1 of which is running pvst+. Obviously you would upgrade the switch but lets say it's not possible at the moment.
There are 50 vlans in use.
So if you allow all 50 vlans across all switches then all vlans will have to use 802.1d timers.
However let say all you need is 3 of the 50 vlans on the switch running pvst+. If you only allow those 3 vlans on the trunk between this switch and the one it connects to then those 3 vlans will use 802.1d timers. But the other 47 vlans will get the full benefit of rstp timers.