Etherchannel Load Balance MAC/IP Adr. algorithm

Unanswered Question
Aug 12th, 2008

Hello,

on a Cisco Etherchannel or LACP Channel, with configured src-dst-mac Balancing, wich algorithm use Cisco IOS for the Port foward desicion based on Source und Destianion MAC Adr. or Source and Dest. IP Adr (for a src-dst-IP Balancing)?

Thanks?

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Giuseppe Larosa Wed, 08/13/2008 - 00:03

Hello Juergen,

it is a bit level EXOR of last significant bits of source and destination address

the result of the EXOR of the last m bits is used to point to the member link of the bundle

if using two links is only the exor of the last bit (less significant bit)

if using four links is the exor of the last two bits (index 00 to 11)

if the number of links is odd they use one more bit

example : 3 links it uses the last three digits here 3/8, 3/8 2/8 are mapped to the three links

Hope to help

Giuseppe

jkunzbva8 Wed, 08/13/2008 - 00:14

Hello Guiseppe,

thanks for the answer!

I have tested a 2 Channel Link with the 2 Client Mac-Adr., the less significant bit: Client 1: ....3F and Client 2: ....A7, Dest Mac is ....24.

In this case Client 1 traffic should be forwarded on Channel-Port 1 and Client 1 traffic should be forwarded on Channel-Port 2!

But only Channel-Port 1 is used!

We find out that on a 2 Link channel, not only the less significant bit is used for the forwarding desicion?!?

Giuseppe Larosa Wed, 08/13/2008 - 05:32

Hello Juergen,

binary digit EXOR of last bit

3F => 0011 1111

A7 => 1010 0111

last bit client 1 : 1

last bit client 2: 1

dest mac 24 => 0010 0100

last bit dest = 0

0 exor 1 in both cases so it is right what you see only one link is used in this case

Hope to help

Giuseppe

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