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How do I force a Catalyst 5000 to never become the root bridge

Am I correct in saying that the command:

SET SPANTREE PRIORITY 0 5

will prevent this particular Cat5000 from ever becoming the root for spanning tree on vlan 5. I think so but I'm not positive. Can anyone confirm this. Thanks.

6 REPLIES

Re: How do I force a Catalyst 5000 to never become the root brid

NO,

just the opposite: your switch would be forced to become a root!!!

STP root is the bridge with the lowest priority in the network.

If you want to prevent the switch from ever becoming the root set its priority to 65535 (the hihgest possible).

HTH,

Milan

New Member

Re: How do I force a Catalyst 5000 to never become the root brid

Hi.

Milan, I agree with you. I would set the priority to the maximum possible value, 65535. But this doesn't ensure 100% that the switch will become the root on that VLAN, because if another switch is set to the same high priority and has a low MAC address, that switch will be the root!

Rgds.

NM

Re: How do I force a Catalyst 5000 to never become the root brid

Nuno,

the task is: prevent one concrete swich (let's call it "new") from becoming the STP root.

So if I set the new switch priority to 65535 any switch with less priority will become the root instaed of the new one.

The only situation when the new switch becomes the root is the case that ALL switches have priority set to 65535 and the new switch MAC address is the lowest one. But there is no way to 100% prevent a switch from becoming the root - if there is the only one switch in the network it has to be the root, e.g. The only 100% way would be to disable STP on the switch.

Regards,

Milan

New Member

Re: How do I force a Catalyst 5000 to never become the root brid

The task is indeed to stop the switch ever becoming the root which as pointed out setting the priority to 65535 will not do if another switch appears with the same priority and a higher MAC address. So I guess the answer is that there is no wa of guarenteeing 100% that the switch will not become the root short of disabling spanning tree.

Regards

Stephen Rowles

New Member

Re: How do I force a Catalyst 5000 to never become the root brid

I don't want any of the client switches from becoming root bridge. & i don't have any configuration access to these switches. I connect to these switches using a port in each VLAN. Can i disable the STP on these ports in this way i do not receive any BPDU from the client's switches ???

New Member

Re: How do I force a Catalyst 5000 to never become the root brid

Setting the priority to 0 will make it the root bridge always, to prevent it from becoming the root set the priority to 65535

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