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Date: Sat, 16 Sep 2006 02:43:46 +0200
From: Hans Nieser <h.nieser@xs4all.nl>
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To: Sam Leffler <sam@errno.com>
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Cc: freebsd-net@freebsd.org
Subject: Re: iwi discarding oversized packets while mtu=1500 for src/dst
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Sam Leffler wrote:
> Hans Nieser wrote:
> 
>> root@aphax-laptop:~# uname -a
>> FreeBSD aphax-laptop.lan 6.1-RELEASE FreeBSD 6.1-RELEASE #0: Thu May 11
>> 07:17:09 CEST 2006
>> root@aphax-laptop.nieser.local:/usr/obj/usr/src/sys/APHAX-LAPTOP  i386
> 
> Are you running the iwi driver that came with 6.1-release?  If so it has
> numerous problems that have been fixed in 6-STABLE and HEAD.  I'm not
> sure how best to update your system except by going to 6-STABLE via a
> src upgrade.

Today I have upgraded my laptop to 6-STABLE, but unfortunately the
problems remain. I don't even know wether iwi is to blame, because I can't
figure out wether perhaps xl on my server really is sending out too large
packets.

That is, so far I've been assuming that an mtu of 1500 may not mean that
there's exactly 1500 bytes going over the wire (overhead of protocols to
which the mtu doesn't apply or something, I dunno, I'm no networking
expert obviously :), because xl is definitely sending out packets of 1518
bytes. Which iwi on my laptop doesn't like, but the NIC in my desktop
machine (which runs Linux) has no problem with. Maybe someone can tell me
which of the machines is in error here, at least I'd know what to blame :(

The fact that my Linux box doesn't discard these packages coming from my
server made me suspicious of iwi initially, but maybe iwi is doing nothing
wrong and my Linux box is simply willing to accept these oversized packets.