From owner-freebsd-net Wed Oct 27 22:52:14 1999 Delivered-To: freebsd-net@freebsd.org Received: from smtp.nwlink.com (smtp.nwlink.com [209.20.130.57]) by hub.freebsd.org (Postfix) with ESMTP id 954AA14E44 for ; Wed, 27 Oct 1999 22:52:12 -0700 (PDT) (envelope-from craigc@nwlink.com) Received: from craigc (ip133.gte8.rb1.bel.nwlink.com [209.20.237.133]) by smtp.nwlink.com (8.9.3/8.9.3) with SMTP id WAA05729; Wed, 27 Oct 1999 22:52:10 -0700 (PDT) Message-ID: <216001bf2109$718c8500$0201010a@fuzzer.com> From: "Craig Critchley" To: "Garrett Wollman" , References: <1df701bf1f84$32751020$0201010a@fuzzer.com><199910261606.MAA83232@khavrinen.lcs.mit.edu><1f6601bf200e$c8e476b0$0201010a@fuzzer.com> <199910271525.LAA87666@khavrinen.lcs.mit.edu> Subject: Re: FTP Net Performance Date: Wed, 27 Oct 1999 22:58:22 -0700 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.00.2314.1300 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2314.1300 Sender: owner-freebsd-net@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org Ok, all the extra stuff is out of the machine, so it's down to motherboard, video card, and netcard. Still getting the same lousy throughput. I took another look at tcpdump, not the graphs, but the data itself. It appears that Windows is sort of behind in its acks and eventually acks twice with the same sequence number. When this happens, everybody holds their breath for a second and a half, then the BSD machine resends the double-acked packet. This is my first tcpdump analysis effort, so if I have misinterpreted something, please let me know. I just ran tcpdump with no switches after setting up BPF and captured the output. If this rings any bells with anyone, I would love to hear your theory. Unfortunately, I only have the one BSD machine, so I can't easily test whether this is restricted to Windows clients. I'm not enough of a TCP expert to know whether the sequence below breaks the rules. Here's a representative sample. I've trimmed down the timestamps and machine names and took off the window and flag information. The windows on both ends were constant. There were no other packets between these, TCP or otherwise. #the server sends some data: 17.55 fuzz.ftp-data > win.1786: . 281781:283241(1460) ack 1 17.55 fuzz.ftp-data > win.1786: . 283241:284701(1460) ack 1 17.55 fuzz.ftp-data > win.1786: . 284701:286161(1460) ack 1 #Windows acks the middle one 17.55 win.1786 > fuzz.ftp-data: . ack 283241 17.55 fuzz.ftp-data > win.1786: . 286161:287621(1460) ack 1 #Windows acks the third 17.55 win.1786 > fuzz.ftp-data: . ack 284701 17.55 fuzz.ftp-data > win.1786: . 287621:289081(1460) ack 1 #Hmm... Windows ack's the same number! 17.55 win.1786 > fuzz.ftp-data: . ack 284701 #Oh no! Big delay, then resend of double acked packet. 19.05 fuzz.ftp-data > win.1786: . 284701:286161(1460) ack 1 ...Craig From: Garrett Wollman > > TCP performance is going to suck with that level of packet loss. TCP > only works well with less than about 1% packet loss; if you're losing > 15%, that explains what's going on. > > -GAWollman > > -- > Garrett A. Wollman | O Siem / We are all family / O Siem / We're all the same > wollman@lcs.mit.edu | O Siem / The fires of freedom > Opinions not those of| Dance in the burning flame > MIT, LCS, CRS, or NSA| - Susan Aglukark and Chad Irschick > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-net" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message