I am driving myself mad trying to get MST to work with PVST+. I've got two ProCurve 2810-48Gs and a single Cisco 3550 set up in a triangle configuration. On the Cisco I've got VLAN1,10,24,and 27. On the HPs I've got VLAN1,24, and 27 configured. A single MST region with two MSTI's have been configured on the HPs (not counting the IST). On HP switch 1 MSTI1 is primary (priority 1 or 4096) and secondary on HP switch 2 (priority 2 or 8192). MSTI2 is primary on HP switch 2 and secondary on HP swtich 1. HP switch 1 is also the CIST root (spanning-tree priority 1 or 4096). When I look at the spanning-tree output on the 3550 I can see that it sees the HP as the root for VLAN1, but it sees itself as the root for VLAN24 and VLAN27. The HPs also see themselves as root for their respective MSTIs so I've got loops in both VLAN24 and VLAN27. I've searched high and low for some solid evidence as to why this is and I am back to square one. According to the Cisco documentation "As the MST region now replicates the IST BPDUs on every VLAN at the boundary, each PVST+ instance hears a BPDU from the IST root (this implies the root is located inside the MST region). It is recommended that the IST root have a higher priority than any other bridge in the network so that the IST root becomes the root for all of the different PVST+ instances" ( http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a00800
94cfc.shtml#recommended_configuration). In reading this it should seem that proper blocking is happening in the correct spot, but it's not. I've looked at pretty much all of HPs documentation on this as well as Cisco's but I'm not finding a definitive answer. Any help in understanding would be great.
You can still do some kind of load balancing with your 3550. The way I see your network, you must have a designated port and some backup ports on the vlans other than 1. By tuning the port priority on the 3550, you can select which of the uplink is going to block (higher priority means that the port is more likely to become backup).
Now, this interaction with third party bridges is really not efficient. Transitions will be according to legacy STP rules, and a failure between the HP switches for instance would require 50 seconds to recover on the 3550.
The best solution would indeed to run MST on the 3550. Now, I'm not a great product expert so I'm not sure if this platform can run 12.2. If not, you're probably going to be stuck with a pre-standard version of MST on the 3550. In that case, the 3550 won't be able to form a region with the HPs (meaning that you won't be able to do any vlan load balancing), but at least you will have fast convergence...
=> if the 3550 runs what we call "standard MST", then run MST and everything will be fine (load balancing possible + fast convergence).
=> if this is not an option, you have two choices:
-1- keep a PVST+ model, with load balancing and slow convergence (the terrible interaction PVST+/IEEE standard is the reason why we developed a particular MST/PVST+ interaction mode)
-2- run pre-standard MST and get fast convergence without vlan load balancing.