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Date: Thu, 16 Mar 2006 13:58:14 -0500
From: Brad <brad@comstyle.com>
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Subject: Re: jumbo em
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On Thu, Mar 16, 2006 at 08:42:09AM -0800, Jack Vogel wrote:
> 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 = 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 freebsd-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 And the man page is more than likely out of date.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

The maximum MTU size for 82571 and 82572 based adapters is 10,482. 82573
has no Jumbo support and the rest can have up to 16k.