Etherchannel port for control signal

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Jan 23rd, 2009
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If i have bundle of 4 port to create etherchannel and I am running LACP then which port or link will be used between two switch to exchange the signals or control messages between them and how that link or port will be elected to exchange control signals?


Devang Patel

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Rupesh Kashyap Fri, 01/23/2009 - 20:20
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Hi, If your 4 interfaces are in single Etherchannel, then Spanning tree will disable on the all 4 interfaces. Now whole etherchannel will be counted as a Single link. You can shared the traffic on interfaces based on Soure/Destination IP ..

Giuseppe Larosa Sat, 01/24/2009 - 01:51
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Hello Devang,

all member ports exchange and need to exchange LACP messages.

the choice of what links are active and what are standby is made following a procedure that resembles STP root bridge election:

the two devices compare the two LACP system-IDs (that are present in the LACP messages), the bundle is built based on the winner of this election the lowest LACP system-id wins.

the links to be used will be the ones with lower numbers (port-ids) on the side of the bundle owner (my term)

The other side will agree on these choices on each link.

if the one side stops to send LACP messages on one physical link the other side will remove its port from the bundle.

We have seen this on a NIC teaming with a server: the server had some troubles after server reboot the two links bundle was again working and messages about missing LACP keepalives stopped.

Hope to help



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