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LACP/Etherchannel and broadcast storms

Hi Gurus

Can anybody clarify the following questions, If w:e enable LACP or Etherchannel between 2 switches (A and B) composed of 4 links (in trunk). If switch A receive a broadcast

  1. Will it send it by the logical port or each individual port? I assume it will send a copy through the logical port (meaining LACP will select 1 physical port according to its algorithm and send the copy throught it).
  2. When switch B receives the broadcast through the selected physical port (according to the algorithm), will it be intelligent enough to undertand it came from 1 of the ports pertenining the LACP or Etherchannel and will not send a copy of the broadcast back to switch A (sort of split horizon mechanism)?

I might be facing a situation where I will need to shut down spanning-tree in specific vlan that will be part of the trunk in LACP mode and would liket to confirm how LACP behaves when dealing with broadcasts.

Thanks, Jorge

Hall of Fame Super Silver

Re: LACP/Etherchannel and broadcast storms

Hello Jorge,

disabling STP for a specific vlan is not a good idea.

Are you running out of STP instances on one switch?

if so I would limit the number of vlans permitted on the bundle and other possible uplinks using switchport trunk allowd vlan.

LACP builds a bundle that acts as a single logical link, so you can have problems only if there are other links carrying that vlan out of the bundle.

Hope to help


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