Spanning tree vlan root

skywalker101 used Ask the Experts™

Need to create a new vlan on a 3750 switch and configure the vlan as the root port on an interface, do I need to configure the priority on the interface i.e spanning-tree vlan 4  port-priority 4 ? with the spanning-tree vlan 4 root as the syntax below

conf t# spanning-tree vlan 4 root
conf-if#spanning-tree vlan 4 port-priority x



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Top Expert 2014

Why do you need to configure the root-port?  If the 3750 is the hub of your switched network you could create the VLAN and configure spanning-tree as follows:

spanning-tree vlan 4 root primary


Yea thanks I was not sure on the syntax, I guess the following command will lower the BID   spanning-tree vlan 4 root primary
By using spanning-tree vlan 4 root primary, you will make your switch the spanning tree root bridge for vlan 4.  This is probably what you were after doing..

But... this means that all the ports on this switch (well those in vlan 4 anyway), will be designated ports.

Root ports are the ports that lead back to the root bridge and hence aren't found on the root bridge itself.

To confirm whether you are the root bridge and what the various port states are, use
show spanning-tree vlan 4

If you are the root bridge, you should see that the Root ID and the Bridge ID are the same and hence This bridge is the root
You will also see the status of all interfaces in vlan 4 as Desg

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