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Date: Fri, 7 Sep 2007 16:00:49 -0700
From: Alfred Perlstein <alfred@freebsd.org>
To: David Christensen <davidch@broadcom.com>
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Cc: FreeBSD Net <freebsd-net@freebsd.org>,
	Julian Elischer <julian@elischer.org>
Subject: Re: FreeBSD discarding received packets > MTU
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* David Christensen <davidch@broadcom.com> [070907 13:41] wrote:
> > > I'm not completely opposed to making such a change, but I don't want
> > > to make a default change in the driver's behavior that other people 
> > > may be depending upon (whether they are aware of it or not).  A
> > > tunable driver value could be the answer but I'm not entirely sure
> > > how it would fare in the hardware at the high end of MTU 
> > values such 
> > > as 9000.
> > 
> > Dave:
> > 
> > Internet ettiquette demands being gracious in what you accept.
> > The default policy of FreeBSD is to accept such packets.
> > This is a really weird bug to track down.
> > Other drivers support it.
> > 
> > This isn't worth making a stand over, unless you're trying
> > to hold users of YOUR driver hostage.
> > 
> 
> I'm just being cautious about making changes before I understand
> all of the implications.  The driver's current behavior is
> supported by IEEE 802.3 specification (802.3-2005, 4.2.4.2.1)
> and is implemented in the same way for other operating systems
> that are very widely deployed (including Windows and Linux)
> without any reported problems.  The existing bge driver which
> was developed for FreeBSD 10 years ago also operates this way,
> so all of my references for porting this driver happen to agree
> on the same implementation.

Which is all well and good, but the age of a bug does not a feature
make.

Please think of the four points I raised.

I think it makes sense to possibly add a "enforce rx mtu" knob
somewhere, but it should likely be turned off.

-Alfred