Spanning-Tree and Etherchannel

Unanswered Question
Jun 8th, 2010

I believe the first port in an etherchannel is the port that sends bpdus's. If this port with the etherchannel fails fails does the second port within the etherchannel start to send bpdu's?

Thanks

I have this problem too.
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michael.hutt Tue, 06/08/2010 - 03:42

Etherchannel bundles two physical interfaces into one logical port.  From what I understand, either interface in an etherchannel can and will transmit BPDUs.

Any link failure in the etherchannel is transparent to the upper-layer protocols.  That means that if Gi0/1 and Gi0/2 are in the Po1 etherchannel together and one of them fails, Po1 continues to behave like normal (only minus the bandwidth of the failed interface), sending BPDUs out whichever interface happens to be free at the moment.

In short, If you have spanning-tree enabled on the PO interface, it should do it's thing regardless of the status of the member interfaces (as long as at least 1 is UP&UP, of course)

Jon Marshall Tue, 06/08/2010 - 04:13

darrenriley5 wrote:

I believe the first port in an etherchannel is the port that sends bpdus's. If this port with the etherchannel fails fails does the second port within the etherchannel start to send bpdu's?

Thanks

Darren

It is the first port that becomes active in the etherchannel that will send and receive BPDUs. So when you first configure the etherchannel you can dictate which port comes online first. If the switch is rebooted then ordinarily ports come online lowest to highest numbered so it will be the lowest that is used. If that fails then yes the next port that came online should then be used.

Jon

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