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Re: agr modes

On Tue, Aug 06, 2013 at 01:32:42AM +0200, Pierre-Philipp Braun wrote:
> Hi Manuel,
> Quoting Manuel Bouyer 30/07/2013 11:58,
> >load-balance is intended to be used for direct link between 2 hosts
> >supporting this mode. AFAIK a switch is not capable of doing load-balance.
> Still, normally it's possible to double the bandwidth with LACP,
> although it may be necessary to have two connections to prove it
> (download or upload two ISO images at the same time, for example,
> with FTP).  So even with the default mode (no load balancing), we
> should get the better bandwidth.  I haven't tested that.

You'll get double bandwith if you have 2 transmit/receive pairs whoses
hashes don't point to the same link. You can't use LACP do double the
bandwith between a single pair of hosts.

> >[...]
> >what network interface do you use ? I found that in most case
> >you have to change the hardware address of ethernet interfaces before
> >creating agr(4). All ethernet interface part of the same agr(4) have
> >to use the same ethernet address.
> Those first testings were made with two re(4) cards on one side, one
> alc(4) and one re(4) card on the other.  Both being NetBSD hosts.
> Hmm I don't clearly remember if the MAC address were changed
> automatically by the agr configuration.
> >>On the other hand, as for the link1 mode, I am happily using it on
> >>my home network on two netbsd hosts, both connected to a non
> >>manageable switches, and everybody -- even the nodes with no
> >>aggregates -- pings.
> >
> >but then you don't get the extra bandwith.
> In the end I figured out I had terrible performance with this mode
> on normal switches.  I just disabled agr for the time being and used
> motherboard's alc(4) interface.  Either there's hardware
> acceleration that makes it work marvelously again compared to
> agr(4), although the box on this side is pretty much powerful enough
> to deal with any kind of load, or there's an issue with agr(4) link1
> mode.  Does NetBSD support hardware acceleration?  I doubt it --

NetBSD does support hardware acceleration, but each driver needs
device-specific support so I don't know if alc(4) has it.
Note that it's not enabled by default, you have to enable it with

Manuel Bouyer <>
     NetBSD: 26 ans d'experience feront toujours la difference

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