From owner-freebsd-stable@FreeBSD.ORG Wed Oct 24 19:12:07 2012 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id A0229AC5 for ; Wed, 24 Oct 2012 19:12:07 +0000 (UTC) (envelope-from jdc@koitsu.strangled.net) Received: from qmta01.emeryville.ca.mail.comcast.net (qmta01.emeryville.ca.mail.comcast.net [IPv6:2001:558:fe2d:43:76:96:30:16]) by mx1.freebsd.org (Postfix) with ESMTP id 7D65B8FC0C for ; Wed, 24 Oct 2012 19:12:07 +0000 (UTC) Received: from omta05.emeryville.ca.mail.comcast.net ([76.96.30.43]) by qmta01.emeryville.ca.mail.comcast.net with comcast id F0vY1k00F0vp7WLA17C76q; Wed, 24 Oct 2012 19:12:07 +0000 Received: from koitsu.strangled.net ([67.180.84.87]) by omta05.emeryville.ca.mail.comcast.net with comcast id F7C61k00J1t3BNj8R7C6FN; Wed, 24 Oct 2012 19:12:06 +0000 Received: by icarus.home.lan (Postfix, from userid 1000) id 38BC273A1C; Wed, 24 Oct 2012 12:12:06 -0700 (PDT) Date: Wed, 24 Oct 2012 12:12:06 -0700 From: Jeremy Chadwick To: Harald Schmalzbauer Subject: Re: every 2nd echo-request malformed when ping -s >4067 Message-ID: <20121024191206.GA6704@icarus.home.lan> References: <20121024154017.GA3167@icarus.home.lan> <5088163E.2090506@omnilan.de> <20121024165148.GA4250@icarus.home.lan> <50881EC7.9030400@omnilan.de> <20121024174425.GA4699@icarus.home.lan> <50882D3B.5050704@omnilan.de> <20121024181239.GA5755@icarus.home.lan> <20121024185525.GA6426@icarus.home.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121024185525.GA6426@icarus.home.lan> User-Agent: Mutt/1.5.21 (2010-09-15) Cc: Adrian Chadd , FreeBSD Stable X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 24 Oct 2012 19:12:07 -0000 On Wed, Oct 24, 2012 at 11:55:25AM -0700, Jeremy Chadwick wrote: > On Wed, Oct 24, 2012 at 11:12:39AM -0700, Jeremy Chadwick wrote: > > On Wed, Oct 24, 2012 at 08:02:35PM +0200, Harald Schmalzbauer wrote: > > > Please find attached the requested info. > > > > Thanks, got 'em! I'll reply in a follow-up mail with the decoded > > results. > > As promised, here are the decoded results. Took me longer than I > expected since I started going down the road of IP options and then was > like, "no, wait a minute, this is ICMP gah!". Opinions are at the > bottom. Gosh I hope I didn't botch a copy-paste on this one... > > 17:58:08.481888 IP 10.5.49.126 > 10.5.49.65: ICMP echo request, id 49423, seq 0, length 4076 > 0x0000: 4500 1000 1fff 4000 4001 9435 0a05 317e > 0x0010: 0a05 3141 0800 a352 c10f 0000 5088 2c30 > 0x0020: 0007 5a3b {...snip...} > > 0x45 = bits 7-4: IPv4 protocol > = bits 3-0: header length: 20 bytes > 0x00 = DSF / RFC 2474 stuff > 0x1000 = datagram length: 4096 bytes > 0x1fff = fragment id > 0x4000 = bits 15-13: %010 = reserved bit (0), DF bit (1), MF bit (0) > = bits 12-0: fragment offset: 0 > 0x40 = TTL: 64 > 0x01 = protocol: 1 (ICMP) > 0x9435 = header checksum > 0x0a05317e = source IP > 0x0a053141 = destination IP > 0x08 = ICMP type: 8 = Echo Request > 0x00 = ICMP code: 0 = always zero for ICMP type 8 > 0xa352 = ICMP header checksum > 0xc10f = ICMP identifier > 0x0000 = ICMP sequence number > 0x5088 = timestamp from ICMP data > 0x2c30 = timestamp from ICMP data > 0x0007 = timestamp from ICMP data > 0x5a3b = timestamp from ICMP data > > > 17:58:09.488461 IP 10.5.49.126 > 10.5.49.65: icmp > 0x0000: 4500 1000 1fff 0040 4001 d3f5 0a05 317e > 0x0010: 0a05 3141 0800 8998 c10f 0001 5088 2c31 > 0x0020: 0007 73f3 {...snip...} > > 0x45 = bits 7-4: IPv4 protocol > = bits 3-0: header length: 20 bytes > 0x00 = DSF / RFC 2474 stuff > 0x1000 = datagram length: 4096 bytes > 0x1fff = fragment id > 0x0040 = bits 15-13: %000 = reserved bit (0), DF bit (0), MF bit (0) > = bits 12-0: fragment offset: 64 > 0x40 = TTL: 64 > 0x01 = protocol: 1 (ICMP) > 0xd3f5 = header checksum > 0x0a05317e = source IP > 0x0a053141 = destination IP > 0x08 = ICMP type: 8 = Echo Request > 0x00 = ICMP code: 0 = always zero for ICMP type 8 > 0x8998 = ICMP header checksum > 0xc10f = ICMP identifier > 0x0001 = ICMP sequence number > 0x5088 = timestamp from ICMP data > 0x2c31 = timestamp from ICMP data > 0x0007 = timestamp from ICMP data > 0x73f3 = timestamp from ICMP data > > > Summary: I don't see anything anomalous EXCEPT the ordeal regarding the > fragment offset going from 0->64 and the DF bit going from 1->0. > Possibly this makes tcpdump throw a fit in some way, I'm not sure. Hmm, question: are you using pf, ipfilter, or ipfw on the machines where you can reproduce this problem? On the machine I tested from earlier, I don't use them. I also don't use jumbo frames (I use stock 1500 bytes). All my ICMP echo packets look like your 1st one: df=0 and fragoffset=0. I do have a 9.1-PREREL box that does use pf where I can test from though. I hate having to ask this question, but pf.conf(5) and the no-df flag always come to mind whenever I hear the term fragmentation or DF. -- | Jeremy Chadwick jdc@koitsu.org | | UNIX Systems Administrator http://jdc.koitsu.org/ | | Mountain View, CA, US | | Making life hard for others since 1977. PGP 4BD6C0CB |