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Spanning tree in a dual network environment

tcica
Occasional Visitor

Spanning tree in a dual network environment

Hi-

I work in a municipality where the Town side and the School side coexist on the same network.  We are basically separate with The Town side and school side having separate core switches connected via a fiber patch cable.  For the most part, traffic is not allowed to flow between these two core switches.  

The school core switch is a 5406zl with spanning tree enabled with a spanning-tree priority of 0.  The Town side is also a 5406zl but does not have spanning tree enabled and I had my first loop last week (not fun).  I would like to enable spanning tree and make my switch a priority 0 as well.  The only interaction is for sixmachines to be routed from their network into my network for the accounting software we use.

The Town switch has this in it's config file:

no spanning-tree bpdu-throttle
spanning-tree mode rapid-pvst
spanning-tree force-version rstp-operation

The School switch has this:

spanning-tree
spanning-tree Trk2 priority 4
spanning-tree Trk6 priority 4
spanning-tree Trk7 priority 4
spanning-tree config-name "STONEHAM-TOR"
spanning-tree instance 1 vlan 155
spanning-tree instance 1 Trk2 priority 4
spanning-tree instance 1 Trk6 priority 4
spanning-tree instance 1 Trk7 priority 4
spanning-tree priority 0

Is it safe to make my core switch a priority 0?

Thanks in advance.

-Tom

2 REPLIES
tcica
Occasional Visitor

Re: Spanning tree in a dual network environment

Maybe I should rephrase my question.  

If I have one core switch that is a hub for several buildings (spokes) and a second core switch that is a hub for several buildings (spokes), and these two core switches are connected together, is it ok to have both switches a priority 0 if none of the member switches can reach the other core without passing through their core first?

Vince-Whirlwind
Honored Contributor

Re: Spanning tree in a dual network environment

The link between the two core switches should be a routed link, so spanning-tree should be irrelevant, and you can make each of them whatever priority you like.

In other words, you should not span any VLAN between the two cores that is assigned to any other ports on either of the cores.