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Spanning Tree

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Spanning Tree


I'm running a fairly big network with around 300 HP switches of different models. From 8206 and 5400 to 2810's and even 2510's. And anything between, really.

They are only being used as L2, since we do all the routing with Juniper firewalls at each site. Up untill today we have not used spanning tree. I know most (all?) of you will say that is crazy, and you are probably right. But with loop-protection enabled, we have not had any problems with this so far.

But now I'm thinking we should deploy STP. But I do have one question. For some of our sites we are using leased L2-lines. I know that the provider of these links (a fairly big ISP) is not using spanning tree.

Should I then treat each site separately - even though they have L2 connection - and have one STP root at each site? Or is it possible to have one root for the entire network, even though there are switchen between that I don't control?


Regards, Stian

Honored Contributor

Re: Spanning Tree

Personally, on a MAN, I like each geographic site to have its own Layer3 distribution switch, linked back to the "Core" via a point-to-point subnet.

If your only Layer3 devices are at your "Core", then just assign STP priorities based on how many hops back to the "Core".

ie, your Spanning-tree "Core" with a priority of 0 will probably have a redundant/backup "Core2" with a priority of 1.

Then give all your Layer2 distribution switches a priority of, say, "4".

Then, all your Access switches that come off those distribution switches can just use the default STP priority.

Then any Access switches that daisy-chain off other Access switches should have a STP priority of (default+number of hops) from the Distribution switches.

I used to manage a very large procurve network. We didn't have STP enabled either.


Re: Spanning Tree


As I said, we're using Juniper firewalls at each site for routing/vpn, so we're not really running our entire network on layer 2. But the switches doesn't do anything more than L2.

Anyways, thank you for a very good answer. I did some test implementation, but agreed with myself that I don't need STP after all :)