Etherchannel XOR Return Flow

[Stephane Lefebvre]

Hi all,

In an etherchannel with 2 links between 2 switches and load balancing by source MAC, I understand that when a frame is coming from PC Z connected to switch A and going to PC X connected to switch B, XOR algorithm will choose always the same link (let's say the first link).

Z---A===B---X

Does the instant reply from PC X to PC Z will take this first link too (because Port-channel on switch B knows the link where PC Z is coming from), or does Port-channel on switch B will execute always XOR algorithm ?

Thanks

Stephane

[Karsten Iwen · Accepted solution]

Switch X doesn't care about the link where the frame came from. Each switch calculates completely independently which link to use. And both switches can use different algorithms. For example you could configure switch A to use the source-MAC, but switch B to use the IP-adresses.

Here is a document with more info on how switches choose the link to send the traffic:

http://www.cisco.com/c/en/us/support/docs/lan-switching/etherchannel/12023-4.html

[Joseph W. Doherty · Accepted solution]

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Posting

Karsten has already answered, but to additionally confirm:

because Port-channel on switch B knows the link where PC Z is coming from

no

Port-channel on switch B will execute always XOR algorithm

yes.