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Etherchannel & STP on 2-L2 fiber links



We have two switches, at one side Nexus 7010 & other side cisco 2960. having 2 fiber link in between them. both switches are far from each other.

one fiber link is direct dark fiber other is provided by ISP so mux would be in between.

My question is 1) can I make etherchannel / port channel for two interface ; will I work??

2) does fail over will work within etherchannel; how switch will come to know port is down; will physical l2 interface goes down if link gets down in between specially mux is in between them??

3) if I don't go for etherchannel, then spanning tree will block one port.. but if link is down in between switch port will not receive bpdu so failover can be done. is it?? or port need to get down physically ?


1 Reply 1

Giuseppe Larosa
Hall of Fame Master Hall of Fame Master
Hall of Fame Master

Hello Sandy,

1) yes

2) use LACP

the answer is to use LACP on both links that means channel-group N mode active under the interface.

In this way you have a protocol running on each member link and you can detect faliure on each member link.

3) if the current root port stops receiving STP BPDUs on the primary link chosen by STP, the other link will take over after some timers expire (exact behaviour depends on STP version running: the recommended version is Rapid PVST so that detection and reaction is quicker)

I would go for 2) using LACP on both links both sides.

Hope to help


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