From owner-freebsd-net Tue Aug 20 2:17: 0 2002 Delivered-To: freebsd-net@freebsd.org Received: from mx1.FreeBSD.org (mx1.FreeBSD.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 5CFB437B400 for ; Tue, 20 Aug 2002 02:16:57 -0700 (PDT) Received: from freesbee.wheel.dk (freesbee.wheel.dk [193.162.159.97]) by mx1.FreeBSD.org (Postfix) with ESMTP id C117043E42 for ; Tue, 20 Aug 2002 02:16:56 -0700 (PDT) (envelope-from jesper@skriver.dk) Received: by freesbee.wheel.dk (Postfix, from userid 1001) id 4A35D38531; Tue, 20 Aug 2002 11:16:55 +0200 (CEST) Date: Tue, 20 Aug 2002 11:16:55 +0200 From: Jesper Skriver To: Julian Elischer Cc: Steve Francis , Jeff Behl , net@freebsd.org Subject: Re: MTU not working? Message-ID: <20020820091655.GB76162@skriver.dk> References: <3D617842.4020304@expertcity.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4i X-PGP-Fingerprint: 6B88 9CE8 66E9 E631 C9C5 5EB4 22AB F0EC F956 1C31 X-PGP-Public-Key: http://freesbee.wheel.dk/~jesper/gpgkey.pub Sender: owner-freebsd-net@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org 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. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message