Hello ChaD
Just for clarity, we are talking about PVST+ and Rapid PVST+ as opposed to plain PVST. Although we often write it without the “+” it’s important to be clear. PVST without the “+” was a proprietary STP protocol that used ISL instead of the standard 802.1Q VLAN tags.
Switching from PVST+ to Rapid-PVST+ on your aggregation switches should generally not cause any major issues, since these two protocols can interoperate. Rapid PVST+ switches can communicate with PVST+ switches, ensuring network stability and loop prevention. However, it’s important to note that the rapid convergence benefits of Rapid PVST+ are only fully realized when all switches in the network support it. When operating with PVST+ switches, the convergence times will be closer to those of standard PVST+.
You mentioned that you will change to Rapid PVST+ only on the two aggregation switches, correct? If that is the case, and the rest of your switches are running plain PVST+, it will work, but you will see no benefits from the “rapid” characteristic of the protocol. Is there a reason you want to apply this change only to the aggregate switches? Let me know so we can further discuss other options.
Finally, just keep in mind that any changes, even such small ones, may introduce a momentary disruption in service due to STP reconvergence times (or a longer duration disruption if something goes wrong) so always make sure you are making changes during a maintenance window where the impact of failures will be reduced. And always have a rollback plan, to return the network to its previous operational status in the event that your changes cause unexpected disruptions.
I hope this has been helpful!
Laz