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Community Member

Spanning tree


If I have a single(default) STG configured and later on introduce a new Layer 2 switch and connect it to the existing LAN...

Will the introduction of the switch bring down the entire network ??

Will the switch automatically learn the topology and start communicating ??

If the new L2 switch is configured with a STG (other than default) then what would happen ??

Pitch in your answers aeap...


Community Member

Re: Spanning tree


No it won't bring down the network. The switch will listen to the BPDUs on the network, then learn addresses for its CAM table, and the commence forwarding on unblocked interfaces.

Yes it will automatically learn the topology of the tree, and could become the root of the tree depending on its priority.

I'm unclear what you mean by an STG. A BPDU in 802.1D does not refer to what group it is in. Multiple Spanning Trees are often done using dot1q tagging (e.g. PVST+ for Cisco)

Community Member

Re: Spanning tree


Just wanted to confirm the same...STG is spanning tree group and i am referring to default STG...

Is there anyway I can know that there has been a change in a topology...

Community Member

Re: Spanning tree


Can you please clarify what a spanning tree group is. The only thing I have come across where there are spanning tree groups are the old bridge-group command on a Cisco, but this is local to the router only and is not reflected in the BPDU as far as I know.

To view if there has been a topology change, if there is a Cisco switch present, you can so "show spantree statistics ..."

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