Rapid-PVST+ with MSTP

[promero]

Hello, I must perform a migration from a 3com switch to catalys 9200 but the 3com has MSTP. The query is, can Rapid-PVST be compatible with MSTP? or MSTP with MSTP is recommended. 3com MSTP has the entire vlan in instance 0.

[3COM-Distribution]display stp brief
MSTID Port Role STP State Protection
0 GigabitEthernet1/0/1 DESI FORWARDING NONE
0 GigabitEthernet1/0/3 DESI FORWARDING NONE
0 GigabitEthernet1/0/7 DESI FORWARDING NONE
0 GigabitEthernet1/0/8 DESI FORWARDING NONE
0 GigabitEthernet1/0/9 DESI FORWARDING NONE
0 GigabitEthernet1/0/10 DESI FORWARDING NONE
0 GigabitEthernet1/0/11 DESI FORWARDING NONE
0 GigabitEthernet1/0/12 DESI FORWARDING NONE
0 GigabitEthernet1/0/13 DESI FORWARDING NONE
0 GigabitEthernet1/0/14 DESI FORWARDING NONE
0 GigabitEthernet1/0/18 DESI FORWARDING NONE
0 GigabitEthernet1/0/19 DESI FORWARDING NONE
0 GigabitEthernet1/0/20 DESI FORWARDING NONE
0 GigabitEthernet1/0/24 ROOT FORWARDING NONE  ---> Connecting with core sw 3com which is the root brigde

[Giuseppe Larosa]

Hello promero,

it would be better to run MST also on new Cisco Catalyst 9200 switches specially if the core switches are still 3Com and running MST.

MST and Rapid PVST are not compatible because of the different approach:

MST : a single BDPU for instance 0 and additional sections for each MST instance

Rapid PVST : a BPDU for each Vlan.

There are some design rules for PVST simulation on Cisco switches running MST at border with PVST / Rapid PVST:

either all root bridges are on the MST site or all root bridges are on the PVST/Rapid PVST side.

Mixed scenario is not allowed and would lead to put the port in PVST emulation inconsistent state.

However, I would not expect 3Com switches to support PVST emulation so for this reason it is better to use MST on new swiches directly to avoid all possible interoperability issues.

Hope to help

Giuseppe