Changing STP Root bridge in production network... scary?

Unanswered Question
Jun 10th, 2010

Hello,

please refer to the attached diagram.

Our network doesn't follow the Cisco-recommended mesh topology with redundant connections everywhere.  Basically, we have a star-topology that doesn't really use STP at all. (Core switch is in the center and all the edge switches are directly connected to it).

We recently migrated to a new core switch.  The migration isn't finished yet, but the majority of edge switches and VLAN interfaces now reside on the new 6500, and the old 3750 stack now only does a little bit of intra-VLAN routing and has a few edge switches connected to it, as well as all of our servers.

The problem is that I didn't notice that the STP priority was set lower on the 3750 stack before implementing the new 6500.  Now the 3750 basically acts as an edge switch with a few routable interfaces, but it's the root bridge for my entire STP topology.

If I were to go to the new core switch and enter the command spanning-tree vlan 1-4094 priority 0, would that cause any downtime or kill my network in any way?  I would like to set it up so that we might be able to get into a fully-redundant STP topology in the future, and I'm a little concerned that this current setup is less-than-optimal.

I have this problem too.
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Jon Marshall Thu, 06/10/2010 - 02:50

If you change the root bridge then STP needs to reconverge so yes it would affect traffic. I would schedule a brief outage to make the change, it should not need to be any longer than 5 minutes or so.

Jon

Ganesh Hariharan Thu, 06/10/2010 - 22:23

Hello,

please refer to the attached diagram.

Our network doesn't follow the Cisco-recommended mesh topology with redundant connections everywhere.  Basically, we have a star-topology that doesn't really use STP at all. (Core switch is in the center and all the edge switches are directly connected to it).

We recently migrated to a new core switch.  The migration isn't finished yet, but the majority of edge switches and VLAN interfaces now reside on the new 6500, and the old 3750 stack now only does a little bit of intra-VLAN routing and has a few edge switches connected to it, as well as all of our servers.

The problem is that I didn't notice that the STP priority was set lower on the 3750 stack before implementing the new 6500.  Now the 3750 basically acts as an edge switch with a few routable interfaces, but it's the root bridge for my entire STP topology.

If I were to go to the new core switch and enter the command spanning-tree vlan 1-4094 priority 0, would that cause any downtime or kill my network in any way?  I would like to set it up so that we might be able to get into a fully-redundant STP topology in the future, and I'm a little concerned that this current setup is less-than-optimal.

Hi,

Yes there will be disruption in your network when you forcefully elect a root briedge for your network as stp will converge and new root bridge will be known to all bridges,so better recommendation to take and informa about the activity to all for 3- 5 min disruption.

Hope to Help !!

Ganesh.H

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