Regarding this topic, we are experiencing problems in my company because of different spanning-tree modes in Core and Distribution blocks so we want to migrate to a topology with MSTP protocol in all the network and I attach a map with a reduced version or our network including extracts of the MSTP configuration for every block.
We are going to use 3 regions:
WAN. It contains one instance for the vlan that interconnect Core with WAN routers (Internet in network map)
DIST. It contains one instance for the vlan that interconnect Core with Distribution Layer3 switches.
ACC. It contains 2 instances with the final user vlans.
The Core equipment uses only WAN and DIST regions, the Distribution equipment uses only DIST and ACC regions and the Access equipment uses only ACC region.
The main doubt we have is if it makes sense that we use a dedicated region for the network that interconnect Core and Distribution equipment. Is it going to work properly without loops?. Is there any other possibility more efficient? (the same situation applies to the network between Core and WAN routers).
Thank you very much for your help.
P.D. We understand that it's not necessary to include ACC region in Core equipment since the final user vlans are configured in Distribution equipment but not in Core. Do you agree?