Date: Sun, 17 Sep 2006 21:20:02 +0200 From: =?ISO-8859-1?Q?Sten_Daniel_S=F8rsdal?= <lists@wm-access.no> To: Sam Leffler <sam@errno.com> Cc: freebsd-net@freebsd.org, Hans Nieser <h.nieser@xs4all.nl> Subject: Re: iwi discarding oversized packets while mtu=1500 for src/dst Message-ID: <450D9FE2.5030902@wm-access.no> In-Reply-To: <450C21B4.5030703@errno.com> References: <44F4CF17.8060203@xs4all.nl> <44F70983.40705@errno.com> <44F71402.1060405@xs4all.nl> <44F7558A.4030907@errno.com> <450B48C2.7030501@xs4all.nl> <450C21B4.5030703@errno.com>
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Sam Leffler wrote: > Hans Nieser wrote: >> 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. >> > > I can't speak to linux but an mtu of 1500 will cause a 1518 byte packet > to be discarded. I don't recall what your problem was but if the iwi > driver is receiving the frame and passing it up only to be discarded by > the 802.3 layer then you've received a frame that's too large and you > should look at the sender side for why it's being generated. If you > don't want to do that you can probably just up the mtu on iwi and let > the frame through. > This does sound awfully lot like the driver doesn't strip the 4 byte checksum of a basic 802.[23] ethernet frame. My initial thought was that it was a vlan frame but the frame protocol indicates it's an IP packet. Perhaps it's a frame that slips through the AP's checks on it's way out to the wireless? -- Sten Daniel Sørsdal
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