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Ether-channels / Port-Channels

Hi ,


Can some help me on the below scenerios .


SW1 : MAC ( AA)

SW2 : MAC (BB)



SW1 fa0/1  ---------------fa0/1 SW2


1. When a STP BPDU comes out from SW1 its will have Source MAC of the egress interface ( in ethernet header ) and Port ID as fa0/1 inside BPDU


Now What happens in this case


SW 1 ----------- 3 links ------ SW2


3 links are bundled to one PO ( lets say fa0/1-3 )


1. How what will be the Source MAC and port ID in the BPDU that egress from SW1



SW 1 ----------- 3 links ------ SW2


How is the Ether-channel determines which interface should be active in the bundle .

Whether SW1 or SW2 will have this rights .

How is the ether-channel mac picked from the N number of bundled interface.


If i have fa0/1-3 in one group .

Initially the fa0/1 was active and PO MAC was this fa0/1 MAC .

Now i have shut the fa0/1 , so fa0/2 was active and PO MAC changed .

Now brought back fa0/1 . But why wtill fa0/2 is active and PO uses fa0/2 MAC


Hi , I believe STP in case of

Hi ,


I believe STP in case of ether-channel it treats as a single interface it never cares about how many interfaces bundled in port-channel. In case of non-ether channel cross connections STP keeps one of the port in block state and it makes its up in case of any link failure happens in any of the other active cross connections. But in ether-channel it considers that as a single link which is an advantage over ether-channel.

Hope this helps.



Hey,In the etherchannel, one


In the etherchannel, one link is selected to transfer control information or becomes control link and is used to forward all control packets.

So it was fa0/1 initially, and once you shut it down; f0/2 is selected and it will not change even if you bring back the previous link.




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