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spanning tree on int vlan (Access port)

hi,

 

i have two siwtches connected to each other on a routed link but using access port

 

so

 

sw 1

spanning tree vlan 10 priority 4096

int vlan 10

ip add 10.0.0.1 255.255.255.0

 

int gi0/1

sw mo acc

sw acc vlan 10

 

swi 2

spanning tree vlan 20 prioty 4096

int vlan 20

ip add 10.0.0.2 255.255.255.0

 

int gi0/1

sw mo acc

sw acc vlan 20

 

i get connectivity but see packet drops on the interface (only transmit on both ends)

 

also i see that the root bride is switch 1 which is fine but how will i negogiate the root bridge when there is a mismatch in vlan id

 

any thoughts ?

1 REPLY
Silver

Hi,maybe someone else will

Hi,

maybe someone else will provide a better and more accurate answer, but as far as I know, Cisco switches use IEEE BPDUs on access ports, therefore they have no information about VLANs whatsoever. And due to the fact that IEEE BPDU doesn't carry VLAN ID in it, there won't be any problems with VLAN ID mismatch or something similar on such link.

STP will elect the root bridge by the book according to normal STP operation (Lowest Bridge ID[Bridge Priority+MAC Address]).

And regarding the connectivity - I believe that you know why you do have connectivity although these switches are in different VLANs, but please, let us know if you want an explanation for that as well.

Best regards,
Jan

 

 

 

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