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enter image description hereMy network is in a state of migration from PVST to MSTP. The network has Cisco, Huawei and ZTE switches in the amount of 50 pieces and about 500 computers. In connection with this, questions arise about the MSTP.

The network has VLANs from 1 to 100. VLANs are common to all switches. I want to divide the network into two regions of the MST, but VLANs will remain the same. For example, VLAN 2 in the MST region 1 instance 1 is the same VLAN 2 in region 2 instance 1. I put together a test version and everything works, i.e. despite the fact that computers in different regions of the MST, they work as if nothing had changed for them. This is normal? So it should be? I could not find information on this topic: everywhere in the examples they use different VLANs in different MST regions.

And one more question: can I leave the revision equal to 0 (so by default) in all configurations of the MSTP?

Additional information:

  • the whole network, this is the L2 network;
  • the network has an L3 switch that is used to route packets between VLANs;
  • most of the switches after the upgrade are ZTE switches;
  • it is planned to replace PVST with MSTP for faster convergence in the presence of changes in the network;
  • also with the help of MSTP it is possible to balance the load on the channels, in case this need arises;

Additional questions:

  • does it make sense to divide the network into two regions of the MST so that changes in the regions do not affect each other?
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  • MSTP (and all STP versions) is to prevent routing loops, not separate VLANs. VLANs are separated by routers (layer-3 devices). You can have the same VLAN number on different router interfaces, but they will be separate VLANs because a VLAN will end at a router. – Ron Maupin May 8 '20 at 19:54
  • I think we need a network diagram and you'd need to tell us why you want to separate into instances and regions. A network of that size doesn't necessarily require MSTP instances even if it's mostly flat, unless it's required for management. It might be worth it to reconsider the topology. – Zac67 May 8 '20 at 20:03
  • @Zac67: I'm not an artist, but the scheme, I think, is clear :) I wish make two regions: one for main building and its switches and the second region for all other objects and its switches. Each region will have his own spanning tree. – dshykuts May 8 '20 at 20:55
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    Each instance forms its own tree. Each region has its own set of instances. Using both is quite some overkill for that structure. – Zac67 May 8 '20 at 21:05
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    If your VLANs span the whole network you should use only a single region and don't really have to use instances. However, I'd seriously recommend reconsidering the "flat" L2 architecture and use routed links between buildings, especially when not all servers are in one place. – Zac67 May 9 '20 at 10:47
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Using two regions for this network is rational.

You don't need more than one instance in order to benefit from two regions. You can put all 100 VLANs into MSTI 0 of both regions.

However, I favor Zac67's recommendation that you entirely separate the layer-2 domains by doing only layer-3 routing between the main building and the metro network root switch. If you don't need to extend L2 VLANs from the metro into the campus, then avoid doing so.

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    About 100 VLANs: i simply doesn't create any instance and all VLANs (1-4094) will be in instance 0 by default. About separation: i plan to optimize the network and significantly reduce the number of VLANs, so routing will not be necessary. About two regions: maybe leave one region and not bother with two regions? – dshykuts May 9 '20 at 22:27
  • Having two regions really can be a good thing if you think you'll still have some VLANs being transported from the campus to the metro in the long-term. Your campus is likely to have a lot more TCN events than your metro, and if you can shield your metro from those, that's generally good. But as I mentioned, if you can just do layer-3 to completely isolate the campus L2 from the metro L2, that would be best. – Jeff Wheeler May 9 '20 at 23:07
  • And putting everything in instance 0 in both regions is a good idea? – dshykuts May 10 '20 at 10:40
  • Yes, all VLANs mapped to MSTI 0 is fine. – Jeff Wheeler May 10 '20 at 11:32

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