Switch connected to rootgurad port

[shanilkumar2003]

Hi

If i connect a switch with better bpdu to a rootguard enabled switch port, the switchport will go root inconsistent state. and after a while when the new swicth ceased sending superior bpdus the rootguard enabled port will start forwarding.

I need to clarify what should happen next , whether it will allow the new switch to be part of Spanning tree topology and both ports will be transitioned to desiganted

Thanks in Advance..

Shanil

[John Blakley · Accepted solution]

Shanil,

As you said, as long as it's receiving superior bpdu's, it will stay in a root-inconsistent state. Until the switch is modified to either a lower priority (lower <> better) than the switch with rootguard configured, it will stay in this state. Once you get the switch configured to a less preferred priority, then the switch will be able to come up and participate in STP.

For example, if the priority of your rootguard switch is 32768 with a mac of 1111.1111.1112 and the switch connected is 32768 with a mac of 1111.1111.1100, then the new switch is sending superior bpdus. You should change the new switch to a lower priority like 36864, so the mac address doesn't come into play. Once that's done, the switch would act as another extension to the network and participate in STP. The interconnected switch links from the newly added switch would show as a root port and the switch with root guard configured would show as a designated port leading to the new switch.

HTH,
John

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[shanilkumar2003]

Excellent its clear now. Thank you john

Shanil

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[paul driver · Accepted solution]

Hello

All switchport should be part of spanning-tree!

The root guard feature is to stop the port its assigned to from becomming a root port, So any switch attaching to this port should not become the root bridge.

So as long as this "new switch" has an negotiated higher bridge ID, then traffic will be allowed across.

res

Paul

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Thanks.

[shanilkumar2003]

Thank you paul

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