Conf Spanning-Tree on 3550

Unanswered Question
Dec 10th, 2007

I'm trying to understand Spanning-Tree configuration a little better so that I can configure my 3550 and 2960.

The root ST has the lowest Priority. MAC/Priority. I understand the STP process, but I'm not understanding how to configure my 3550 as the root switch.

I see the command " spanning-tree vlan VID root primary" Does this mean that I need to set the VLAN on that switch as the root primary instead of configuring the Switch as the root?

Config I'm setting up.

VLAN on 3550






VLAN on 2960




I have the trunk configured.

I have this problem too.
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nordick26 Mon, 12/10/2007 - 07:41


if you are to elect your STP root by your self, you can configure your rood STP using following command:

spanning-tree vlan < vlan> priority <0-61440>

This will change the priority for specific VLAN so that this switch can became the STP root.

Yes, with spanning-tree vlan VID root primary you can achieve the same and you can also use "root sedondary" for your backup STP switch

The primary priority will be 24576 and secondary will be assigned 28672.

Hope this helps


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glen.grant Mon, 12/10/2007 - 07:44

Correct each vlan has its own instance of spanning tree so you should set each vlan's spanning tree where you want it .


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