By default most switches will have a default priority of 32768. When this occurs, the switches then use the MAC address to determine who is the Root device. If that is the case in this scenario, all you need to do is set a lower spanning tree priority on the desired root switch. On your core switch issue the following command: console(config)#spanning-tree priority 4096 That switch will now be the root switch. This will not require any switches to be rebooted, but will cause some topology change notifications throughout the network, and some ports may change their current status. this all depends on the topology.  I would do this during non peak hours. You may also want to check the switch that you added to the network, and ensure it does not have a spanning tree priority of 4096. If it does, set it back to something higher.
Good day to All I have a problem in my network with an old device with a 10mbit half duplex nic - we have Powerconnect N3048 switches in the rack - we found that they don't play well with the old device, so we added an older switch 1000/100 to do the translation so to speak. The problem now is that STP was not configured at the time and the older switch has taken the role of routing bridge. My question is - if I now configure the N3048's to be the route bridge, will I be able to do it without affecting the production network traffic, or will I need to down the network to do the change?  Will the change to the N3048's force the older switch to relinquish control or will they fight?  Many thanks in advance  Eric  
Spanning tree routing bridge