From owner-freebsd-net@FreeBSD.ORG  Wed Feb 11 05:30:55 2004
Return-Path: <owner-freebsd-net@FreeBSD.ORG>
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 7759F16A4CE
	for <freebsd-net@freebsd.org>; Wed, 11 Feb 2004 05:30:55 -0800 (PST)
Received: from starburst.demon.co.uk (adsl-02-143.abel.net.uk
	[193.109.51.143])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 88AEE43D1D
	for <freebsd-net@freebsd.org>; Wed, 11 Feb 2004 05:30:54 -0800 (PST)
	(envelope-from richard@starburst.demon.co.uk)
Received: (from richard@localhost)
	by starburst.demon.co.uk (8.8.7/8.8.7) id NAA09040;
	Wed, 11 Feb 2004 13:35:17 GMT
From: Richard Wendland <richard@starburst.demon.co.uk>
Message-Id: <200402111335.NAA09040@starburst.demon.co.uk>
To: silby@silby.com (Mike Silbersack)
Date: Wed, 11 Feb 2004 13:35:17 +0000 (GMT)
In-Reply-To: <20040211025940.J1798@odysseus.silby.com> from "Mike Silbersack"
	at Feb 11, 2004 03:01:25 AM
X-Mailer: ELM [version 2.5 PL2]
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
cc: Bjorn Eikeland <bjorn@eikeland.info>
cc: freebsd-net@freebsd.org
Subject: Re: dummynet = local taffic > 100ms - help!
X-BeenThere: freebsd-net@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
Reply-To: richard@wendland.org.uk
List-Id: Networking and TCP/IP with FreeBSD <freebsd-net.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-net>,
	<mailto:freebsd-net-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-net>
List-Post: <mailto:freebsd-net@freebsd.org>
List-Help: <mailto:freebsd-net-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-net>,
	<mailto:freebsd-net-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 11 Feb 2004 13:30:55 -0000

> It breaks TCP Timestamp generation slightly, but that's not likely to
> break much of anything in practice.

Well, with HZ=10000 RFC1323 TCP connections will stop after 59.7 hours,
with HZ=100000 after 6 hours.  For those with long running TCP connections
(eg remote backup) that could be a big deal.  See 4.2.3 of RFC1323.

It does seem quite a few people want HZ>1000 so I think the time has
come to isolate the TCP timestamp option clock from the HZ value to
avoid this problem.  For now they should set net.inet.tcp.rfc1323=0 to
avoid breaking RFC1323.

Note this doesn't affect routed packets, only TCP connections to/from
that host.

Tom Pavel sent some patches to this list on 14 Jan 2004 that he has been
using to overcome this HZ/RFC1323 problem.

	Richard
-- 
Richard Wendland				richard@wendland.org.uk