From owner-freebsd-questions Sat Nov 27 9:26:36 1999 Delivered-To: freebsd-questions@freebsd.org Received: from ns1.lets.net (ns1.lets.net [204.244.88.174]) by hub.freebsd.org (Postfix) with SMTP id B4D9414BDA for ; Sat, 27 Nov 1999 09:26:00 -0800 (PST) (envelope-from stainsby@lets.net) Received: (qmail 4140 invoked from network); 28 Nov 1999 09:20:23 -0000 Received: from unknown (HELO D7N057) (204.239.159.51) by ns1.lets.net with SMTP; 28 Nov 1999 09:20:23 -0000 Message-ID: <000901bf38fc$128fef00$339fefcc@vpl.vancouver.bc.ca> From: "Erik Stainsby" To: "FreeBSD Questions (E-mail)" References: <4.2.1.19991128030900.00a9f380@mail.southcom.com.au> Subject: Re: pppd, mtu, lag, and icmp "need to frag" packets Date: Sat, 27 Nov 1999 09:23:05 -0800 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.00.2014.211 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2014.211 Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG This wreaks of M$ F.U.D. o The calm reasoned asides that insist M$ product has no problem. o The technical pitch being -just- that much beyond what joe consumer might understand. o The fact that the essence of the issue in debate is a few milliseconds of performance ~~ and this being cast in the context of IRC and telnet ~~ is pitched at a trivial home-user frame of mind. o Even the lame dramatic wannabe nickname (death) is calculated to identify the message as coming from a 'power user'. This is FUD. FOAD. Stainsby@telus.net E Pluribus Unix ----- Original Message ----- From: death To: Sent: Saturday, November 27, 1999 9:04 AM Subject: pppd, mtu, lag, and icmp "need to frag" packets > > Hi, > > I'm having a major problem trying to defeat lag over my 56k modem > connection with FreeBSD.. Once upon a time when i was using Windows 98 it > was as simple as downloading a program, clicking 'optimize', and voila, > it's now about 5 times as smooth/lagless as i've ever managed to get FreeBSD. > > I'm running 3.3-STABLE on a p166, 32MB ram, 1GB HDD. Connected to that, via > a 'pppd' serial link, is a Windows 2000 machine. Both serial ports are at > 115,200bps. The MTU/MRU setting in both ppp and pppd are 576 (which causes > a problem for pppd which i'll discuss soon). > > Is there any way, apart from setting the MTU and MRU values in 'ppp' (i've > set them to 576 - which seems to be a common, good number) - to decrease > lag? When receiving data, lag rises to about 600-1000ms. When sending data, > lag goes through the roof at ~1750ms. > > And strangely, when running cvsup, and even when it's only downloading, the > lag is launched into orbit and sits at 2500ms MINIMUM. I thought that it > might've been CPU usage doing this. A quick check reveals ~95% idle. > > This lag is present on both computers btw. > > So, any advice to lower this lag? Yes, i know 56k modems are slow, but it's > still very possible to kill lag with say telnet and IRC, whilst i'm > downloading via ftp at 5KB/s. I know i'm not going to get more than 5KB/s, > i just want IRC and telnet to run smoother. I've done it with Windows 98 - > even downloading 5 things at a time had no affect on anything else. > > > Also, when the MTU of ppp0 is 576, FreeBSD keeps sending icmp "need to > frag" packets to whatever sent me a packet that was supposedly too big. > Here's a snippet from tcpdump: > > 00:47:52.999475 203.102.135.200.80 > 192.168.1.2.1142: P 1:645(644) ack 326 > win 32120 (DF) (ttl 58, id 37803) > 00:47:52.999753 210.84.240.102 > 203.102.135.200: icmp: 192.168.1.2 > unreachable - need to frag (mtu 576) (DF) (ttl 255, id 51301) > 00:47:53.089502 203.102.135.200.80 > 192.168.1.2.1141: P 1:610(609) ack 322 > win 32120 (DF) (ttl 58, id 37804) > 00:47:53.089700 210.84.240.102 > 203.102.135.200: icmp: 192.168.1.2 > unreachable - need to frag (mtu 576) (DF) (ttl 255, id 51302) > > > How do the packets get 644 or 609 bytes long? The MTU on tun0 is 576. > > Can't FreeBSD just fragment the packets and pass them through? I've looked > everywhere for an option on this but to no avail.. > > BTW just a few configuration notes, i hope i cover them all: > > * i'm running ppp as 'ppp -nat'. i've only got one IP (which in the above > example is 210.84.240.102) > * ipfw is up and running, although it's only denying port 21, 23, and 25, > and diverting port 113 to natd which then passes it on the windows machine. > * 192.168.1.1 == freebsd.. 192.168.1.2 == windows. > * the icmp frag packets don't appear on ppp0 at all when i use tcpdump. so > i'm assuming that FreeBSD is creating them. > > > I'm forced to change the MTU to 1500 which doesn't give me any of those > frag errors. Considering that i'm only linked to FreeBSD via a 115,200bps > serial cable, it's important that i get rid of lag on ppp0 too - which i > was hoping i could do by setting the MTU down. It's only 12KB/s after all. > Not a 100Mbps NIC. > > > Thanks in advance. > > Cheers > > Death > > > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-questions" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message