Link usage of etherchannel

[y.lo]

For etherchannel of 2 links on a 3750 switch, if 1 link ever gets saturated, will the other link be used as well if the excess traffic is part of the same flow?

Or that excess traffic will simply be dropped?

I just can't get such infromation in any cisco document.

[Peter Paluch]

Hello,

In my understanding, EtherChannel by its definition works by hashing the address fields of transmtted frames (optionally of packets and even segments) to produce a single number that indicates the egress port to send the frame. The actual load of this port is not taken into account. This means even if a port in EtherChannel is saturated, the EtherChannel will not move the traffic to another port. As a result, the excess traffic will be buffered and possibly dropped.

Best regards,

Peter

[y.lo]

Thanks for your reply Peter. Are you aware of any cisco document talking about this? Many thanks.

[Peter Paluch]

Hello,

Sadly, no, no document I know says this plainly. The only document I really liked about EtherChannels is this one:

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml

My answer is in part based on the facts from this document.

Best regards,

Peter

[Joseph W. Doherty]

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Posting

My understanding is the same as Peter's, which is also why choice of hashing algorithm can be crucial for optimal Etherchannel load balancing.