Question on ROOT BRIDGES

After working on inter-vlan routing projects for a while,i noticed that if for example; i have 3 layer 2 switches with 3 vlans each, not all vlans have the same root bridge. why should vlan 1 not have the same root bridge as vlan 20 or vlan 30? Does this affect the functioning of my vlans? How? Can someone please explain to me in details the logic behind this. I thought that by default even before i configure a specific switch as my default one, all the vlans will point to the same switch as their root bridge. Please help.

I cannot go into detail, but are you familiar the with PVST(PER VLAN SPANNING TREE) PROTOCOL? I think it might explain what you are witnessing.

Regards,

Sure i'm familiar with PVST protocol. after i configure each vlan with bridge priority they all point to the same switch as their root bridge. but why do they point to different switches before you do this configuration.

Jsut taking a stab here, as I am still learning and reading. But if they all pointed at the same one, and that switch died, network is toast. Also I think it has to do with routing loops I believe.

Hmm... I'm not able to reproduce the same issue here. I configured 3 vlans on two switches connected by 1 trunk. All vlans have the same root bridge

Jsut taking a stab here, as I am still learning and reading. But if they all pointed at the same one, and that switch died, network is toast. Also I think it has to do with routing loops I believe.

After configuring spanning-tree protocol (STP), only one switch should exist as the root bridge which is the focal point of the network. This switch is the one responsible for sending bridge protocol data units (BPDUs) which ensures there are no switching loops by changing the status of ports to either forwarding or blocking modes.
After all this you can set one switch as the primary root bridge and another as the secondary root bridge so that if one switch 'died' the other takes over.