MSTp Regions, Distribution Areas and Core 3COM

Hi all,

We have different mstp regions in each of our distribution areas.  My question is how do I run a Core MSTP region and covers the router vlan that also attaches to the uplinks of the distribution switches.

I can have an mstp region on the core named CORE, but can't have more than one region-name on the distributions, so I am at a loss.  Will it have to be that it uses the CSTP between core and dist?


vlan 30,31,32,34,36,3039
mstp region-name T1
instance 1 vlan 30,31,32,34,36,3039
vlan 3 (used for uplink to core) NOT in MSTP region

vlan 3

What should I do to get region on core working with distribution uplinks as a region? Is this possible?

Many thanks
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Don JohnstonInstructorCommented:
I'm not sure I understand your topology. Can you provide a diagram?
bromley_collegeAuthor Commented:
hi donjohnston,

I atttach visio diagram.

Thanks for replying.

From diagram -

Core will have only vlan 3

Distributions have vlan 3 for uplink to core and between dists

Then hold local vlans for area

Don JohnstonInstructorCommented:
Just so I understand what you're doing.

Do you have end-to-end VLANs on your campus? Or are you doing layer 3 at the distribution devices and terminating the VLANs there?

And you have all your distribution switches linked to each other in a ring in addition to connecting them to the core?

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bromley_collegeAuthor Commented:

All VLANS terminate at the distribution layers (althought we still have legacy vlans we are in the processing of getting rid of which current are end-to-end).

The outer ring is also a work in progress, so for now all star links are in and the ring is building up as we install fibres.
Don JohnstonInstructorCommented:
Spanning tree is a layer 2 protocol so it does not transit layer 3 devices. So you don't need a separate MST region to define a boundary.
bromley_collegeAuthor Commented:
Makes sense, thanks Don, so it will just use the RSTP already on it?
Don JohnstonInstructorCommented:
I don't know what brand/model switches you're using so I can't say what the default is. I thought you were running MST?
bromley_collegeAuthor Commented:
MST is running in each distirubtion area

The core is running rstp

I understand how regions see other regions across non MSTP regions but I wondered if RSTP on the core would be ok
Don JohnstonInstructorCommented:
Since there is no interaction between the core and access switches, there will be no problem.

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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?
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