From owner-freebsd-net@FreeBSD.ORG  Thu Mar 16 18:37:55 2006
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Date: Thu, 16 Mar 2006 08:42:09 -0800
From: "Jack Vogel" <jfvogel@gmail.com>
To: "Yuriy N. Shkandybin" <jura@networks.ru>
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Cc: freebsd-net@freebsd.org, freebsd-stable@freebsd.org
Subject: Re: jumbo em
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On 3/16/06, Yuriy N. Shkandybin <jura@networks.ru> wrote:
> Hello
>
> I have 2 freebsd servers connected by dedicated wire via em interfaces.
> systems =3D 6.1-PRERELEASE #0: Tue Mar 14 11:58:23 MSK 2006
>
> 1st)
> man em says
> MTU size for Jumbo Frames is 16114 and i'm sure i've setup this on freebs=
d-5 and probably ealier 6.0
> But now
>  ifconfig em1 mtu 16114
> ifconfig: ioctl (set mtu): Invalid argument
> 16110 - max possible

With newer hardware the FIFO has been getting smaller, so jumbos
even this large wont be allowed, I'm away from the code right now
but on the 82571 adapter its max is in the 9K range.

And the man page is more than likely out of date.

Whether you can do jumbos at all, and if so, what size you are allowed
to make them is adpater specific.

Jack