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STP on Access-Ports

Hi,

I just have a question. I know this is very basic on some of you but I just want to be sure if my assumption is correct. Please check the diagram. Both SwitchA and SwitchB are connected to both core switches but not as trunk ports. CoreA and CoreB were configured as switchport mode access. I did not configure spanning-tree portfast on these ports so it won't transition to forwarding state right after.

On both SwitchA and B, I created VLAN 50 and configure all ports in VLAN 50 except for the trunk between them.

What if I configure SwitchA with a very low priority? Something like 4096 for VLAN 50. Will it be the root-bridge for the STP domain? I guess yes. I think BPDUs will still be passed across the switching domain. Correct me if I'm wrong.

Then another question, what if I also created VLAN 100 on all switches, will the BPDUs for VLAN 100 be transmitted to the access ports or only VLAN 50 BPDUs will be passed?

If the links between the switches are trunk links then it will be very basic coz that's what we all usually do but what will happen with this kind of design?

Thanks in advance.

John

1 REPLY
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Re: STP on Access-Ports

John

"What if I configure SwitchA with a very low priority? Something like 4096 for VLAN 50. Will it be the root-bridge for the STP domain?"

Well if that is the lowest priority then yes it will be root bridge for vlan 50.

"will the BPDUs for VLAN 100 be transmitted to the access ports or only VLAN 50 BPDUs will be passed?"

The vlan 100 BPDUs will not be sent across a link that is allocated to vlan 50. So in effect you will get 2 root bridges ie. CoreA & CoreB will elect a root for vlan 100 and switchA and switchB will elect a root for vlan 100.

Jon

Jon

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