Date: Tue, 20 Aug 2002 11:16:55 +0200 From: Jesper Skriver <jesper@skriver.dk> To: Julian Elischer <julian@elischer.org> Cc: Steve Francis <sfrancis@expertcity.com>, Jeff Behl <jeff@expertcity.com>, net@freebsd.org Subject: Re: MTU not working? Message-ID: <20020820091655.GB76162@skriver.dk> In-Reply-To: <Pine.BSF.4.21.0208191618520.32737-100000@InterJet.elischer.org> References: <3D617842.4020304@expertcity.com> <Pine.BSF.4.21.0208191618520.32737-100000@InterJet.elischer.org>
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On Mon, Aug 19, 2002 at 04:20:37PM -0700, Julian Elischer wrote:
>
>
> On Mon, 19 Aug 2002, Steve Francis wrote:
>
> > Allow me to respond for Jeff (we work at same place, and have both been
> > looking this issue)
> >
> > ICMP's being blocked are the most common explanation for this - but
> > this is not the case here.
> >
> > tcpdump run on the server system shows the ICMP fragmention required -
> > DF bit set messages being received, and - the irrefutable proof that it
> > is not an ICMP filtering issue -the FreeBSD system DOES lower the MTU
> > for that host's cloned route to the value specified in the ICMP (1420
> > in the snippet below). New packets are segmented to sizes <= the new
> > MTU, but it continues resend the original packet over and over, in the
> > original 1500 byte size.
> >
> > So I still say FreeBSD has broken pMTU-D code.
> >
> > This is reproducible at will, so we can collect whatever info anyone
> > wants.
>
> Yes
> tcp needs to forget it ever sent that data, and refactor the entire
> transmit window.
Doesn't we do that allready ?
src/sys/netinet/tcp_subr.c
around line 1416 in tcp_mtudisc() we have a
tp->snd_nxt = tp->snd_una;
> I'd agree this is a bug if it's reproducible by others too.
/Jesper
--
Jesper Skriver, jesper(at)skriver(dot)dk - CCIE #5456
Senior network engineer @ AS3292, TDC Tele Danmark
One Unix to rule them all, One Resolver to find them,
One IP to bring them all and in the zone to bind them.
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