load balance at layer 2

Unanswered Question
Apr 10th, 2008

Hi all, is there a reason we cannot load balance to 2 difference switches at layer 2, is it because a mac address can only exsist on 1 trunk port on a switch ? how come layer 3 does not mind load balancing buy layer 2 does ?

I have this problem too.
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amritpatek Wed, 04/16/2008 - 06:07

Load balancing occur when to or more routes has same metrics to the same n/w mean it needs the IP address which comes in layer 3.

On layer 2 in the header portion (H2) contains source and destination physical addresses while on layer 3 in the header portion (H3)

contains logical IP of the source and in the destination portion it contains logical Ip of gateway of that network. So thats the reason

npiedra Wed, 04/16/2008 - 11:19

Actually in layer 2 you can load balance by using multy vlan spanning-tree protocol. Making the root port for odd vlans on one trunk link and the even vlans the other trunk port. This is not perfect load balance but at least utilizes both links. Be carefull though with loops.

hcombee Wed, 04/16/2008 - 11:26

you can load balance between two switches by putting up to 8 ethernet connections in a channel using the channel-group command in interface config mode.

in this case ethernet will balance the load based on an algorythm using the mac-adresses of the source and/or destination.

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