Spanning-tree root switch

Unanswered Question
Jun 7th, 2009

Dear All,

Please find attached my branch office Network diagram. I am very new to this place so i am trying to understand the setup now.

I have attached the current diagram. as per the diagram one switch has been configured as the Root Switch for all the running Vlans except vlan 123.

1. If the root switch get switched off or disconnected from the network will all the vlan communications happen between switches or entire network will network go down?

2. Vlan 123 root switch is been configured as BNC-admin-Sw01 what difference does not make when it as a root switch for vlan 123?. when the other root switch goes down can the VLan123 network can communicate eachother?

3. Why they have configured Vlan 123 root switch as a separate switch ?

Please clarrify my doubts


I have this problem too.
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johnspaulding Sun, 06/07/2009 - 15:43

I dont see the diagram for the switch set up..maybe im not looking at the right place. If you could paste the spanning-tree config output this would give me a better idea of whats going on. It might be when the added the vlan they did not specify the spanning-tree priority for this vlan (ex spanning-tree vlan 1,2,3,4..etc) on the root switch. They could have forgotten or they just did not care. I cant see your diagram but if there are multiple switches in your network and they are connected to each other with trunk links or connected to another primary switch than yes, if the switch goes down that is root another switch will take the active role. It really depends on your set up. I hope this helps a little.

p.devalck Mon, 06/08/2009 - 04:33

Even without defining spanning-tree root switches explicitly, the spanning-tree protocol elects a root switch (per VLAN) based on the MAC-address of the switch (if spanning-tree priorities are equal for the switches).

Selecting a different switch as root for a given VLAN can ensure that the given VLAN uses the connection that is blocked for the other VLANs, thereby ensuring better utilisation of the overall available bandwidth.


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