Unanswered Question
Jul 10th, 2007

I have setup an etherchannel. How do I get majority of the traffic to go over the 1st link and not half half?


I have this problem too.
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Jon Marshall Tue, 07/10/2007 - 01:19


You don't say whether this is a layer 3 or layer 2 etherchannel.

Regardless of that, etherchannel is designed to aggregrate individual links into a single logical link. How it load balances across the links depends on the switch capabilities ie. source/dst mac address, src/dst ip address, src/dst port number. Not all of these are available on all switches.

The key point is that if you want more traffic to go over one link than the other etherchannel probably isn't what you want to use. You should perhaps be looking at PBR (Policy Based Routing).



wazzaclarke Tue, 07/10/2007 - 10:35

It is an etherchannel between a layer 3 switch 3750 and a layer 2 2950 switch. The etherchannel is layer 2 though.

Please tell me more about PBR (Policy Based Routing) and am I able to do it with the 3750 switch.


Jon Marshall Tue, 07/10/2007 - 10:53

The 3750 does support PBR but you need the IP Services image on your switch.

Routers are normally only concerned wut the destination address when routing packets (with the exception of multicast but that's another issue)

PBR allows you to override the normal routing behaviour and influence how packets are routed based on criteria other than the destination address. So one exmaple that might be useful to you is you could say

1) all traffic coming from subnet goes down one link

2) all traffic coming from subnet goes down the other link.

There are other criteria you can use to decide how to route the packet, attached is a link for more information



Amit Singh Tue, 07/10/2007 - 02:05

Etherchannel is implemented in hardware, and uses a hash based on source/destination MAC and/or IP and port # to decide what link each packet will take.

AFAIK etherchannel doesn't support that sort of granularity in managing the flow of traffic in a direct way. Etherchannel supports load balancing based on individual or combination of MAC/IP/Port info. You might be able to influence the flow of traffic indirectly by choosing the right load balancing method by studying the physical interface stats.

More about all this here:

HTH,Please rate if it does.

-amit singh


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