Cisco switch runs MSTP connected to two moxa switches run MOXA's Turbo ring V2

[Mohamed H. Abdelmotaleb]

I have Cisco Switch runs MSTP conncted to two MOXA switches run Turbo ring V2 as the attached design, so my question from Cisco switch view, what will be happened ? what is the status of Cisco switch ports ? is there a loop ?

[Peter Paluch]

Hello,

We need to understand more about your setup:

1. Can you describe how does the Turbo ring V2 technology work?
2. Do the Moxa switches run MSTP themselves?
3. How many MST instances are you running?
4. Are you using multiple MST regions?
5. What switch is the MST root switch for each particular instance?

Thank you!

Best regards,
Peter

[Mohamed H. Abdelmotaleb]

Thank you Peter for your reply, you can find the turbo ring V2 mechanism at the following link:

https://www.moxa.com/doc/tech_notes/moxa_tech_note---what_is_turbo_ring_v2.pdf

it just blocks one port and let traffic passes on one direction through the ring to avoid loops

the problem that MOXA switch doesn;t understand MSTP during turbo ring V2 mode , I can use only one instant and I can use Cisco switch as root for this instant I have no problem.

[Georg Pauwen]

Hello,

as I understand it, Moxa's Turbo Ring v2 is a Moxa proprietary redundancy protocol that can be used INSTEAD of MSTP (or RSTP). Which means the Cisco won't see the ring as an STP device, which, logically thinking, should mean: no loop...

[Mohamed H. Abdelmotaleb]

I know that Cisco switch will not see MOXA switches as STP devices but I think the loop will occur as the attached photo or I am wrong ? so tell me please what are the status of Cisco ports in this case ? Designated forward on both ports or one designated and second is blocked ?

[Georg Pauwen]

Hello,

honestly I do think this is a case of practical deployment. Do you have the devices connected ? Logical thinking would determine that the Cisco sees both ports as just two different end stations, since there are no BPDUs, so nothing will happen with spanning tree. What that does to the Turbo Ring traffic flow...no idea if it will go through both links, most likely, the Turbo Ring will block one of the ports, and not the Cisco.

[Peter Paluch]

My friends,

We can speculate: The MOXA switches will themselves provide a loop-free topology. In that case, there are two possibilites:

1. The MOXA switches will blackhole the MSTP BPDUs and not forward them. In that case, the Cisco switch will show both ports toward the MOXA switches as Designated Forwarding.
   
   OR
2. The MOXA switches will flood the MSTP BPDUs as regular multicasts. In that case, the Cisco switch will show one of the ports as Designated Forwarding and the other one as Backup Blocking (Discarding).

Both alternatives assume that the Cisco switch is configured as the MSTP root in the instance it is running.

All the very best in 2019! :)

Best regards,
Peter