Follow up on my previous post regarding bonding

John LLOYD jal at
Mon Sep 15 12:45:21 CDT 2008

> I have two Poweredge 2900-III servers connected to the same 
> 2960 switch, each server has a 4Gb etherchannel (bond0) 
> connection to the switch.
> When I use iperf to test the transfer rates between the two 
> systems it never goes above 944Mbps.
> Does anyone have any advice or has anyone ever gotten this to 
> work any better?
> Thank you,
> -Drew

Why do you think it should go faster?

>From kernel-doc-2.6.18/Documentation/networking/bonding.txt

  "...generally speaking, modes provide either hot standby or load
balancing services."

Aggregate throughput = sum(ethernets), but max throughput per session =
one ethernet.  Four iperfs running concurrently *might* be around 900
Mb/s each, depending on how the bonding is setup.  Possibly, you will
only get a total of 900 Mb/s across all 4 iperfs.  Read the docs for

Technically, bonding allocates outbound IP frames to an interface, not
to a collection of interfaces.  So it can only send one frame at a time.
See section 12.1.1 of the bonding.txt file for a possible fix; your
switch needs to support round-robin (IIRC, Cisco 2960s do not.  We tried
once with Linux vs Windows 2k3 and C2960s, but discovered it could not


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