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Enabling Spanning Tree Protokol on rest network with looped master switches

Posted on 2007-03-24
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Last Modified: 2008-01-09
Hi,

our network has about 30 switches. Our "master" switches are two HP 5308xl  linked together. These are linked with another 6 switches . This makes a loop on our network. All these switches have enabled STP.
Now I want to enable STP on other switches. My question is, if this can make nework problems or collisions. I dont know who is Routbridge of them and if changing of Routbrindge can be a problem.
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Question by:MiamiCo
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Don Johnston earned 500 total points
ID: 18786061
Changing the switch that is the root bridge can cause a topology change which will affect the path that traffic takes to it's destination. It can also cause the network to re-converge creating a period of time (usually no more than 30 seconds) where no traffic is moving.

Common practice is to define the root bridge and alternate root bridge to be the switches closest to the common destinations of traffic. This is done by lowering the bridge priority to a value lower than the default of 32786 (0x800).

If you want to add a switch but don't want to learn the spanning tree topology of the existing network, you could raise the bridge priority of the new switches to a value greater than 32768. This should insure that the new switch will not take over as the root bridge.

That said, adding, removing switches (or link between switches) when the spanning tree topology is not know can be... exciting.  
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by:jburgaard
ID: 18786717
If you use defaults on 5308xl then the protocol you use is RSTP (R as in rapid) and the default is a priority of 8, whitch is a index number equivalent to 32786.
If you have more sw's with same given (or default) lowest priority, then the election of rootswitch is won by the sw. with the lowest priority AND lovest MAC-adress combination.

The command
show span
on each sw. can show the details in your existing network.

I think you should carefully plan for a root-switch and a backup-root.
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by:MiamiCo
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Thanks for answers. I think I should first "know" our spanning tree topology and then plan root and backup switch.
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by:Don Johnston
ID: 20366019
Did you require any additional information beyond what I have already provided?
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by:MiamiCo
ID: 20368126
No thanks. STP its runnig.  
My experience...  changing STP settings on one of our HP 2524 switches caused failure of this switch (i dont know why).
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by:Don Johnston
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