From owner-freebsd-net@FreeBSD.ORG  Fri Dec 30 12:11:56 2005
Return-Path: <owner-freebsd-net@FreeBSD.ORG>
X-Original-To: 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 0C7A116A41F
	for <freebsd-net@freebsd.org>; Fri, 30 Dec 2005 12:11:56 +0000 (GMT)
	(envelope-from b.candler@pobox.com)
Received: from thorn.pobox.com (thorn.pobox.com [208.210.124.75])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 5CDC743D46
	for <freebsd-net@freebsd.org>; Fri, 30 Dec 2005 12:11:54 +0000 (GMT)
	(envelope-from b.candler@pobox.com)
Received: from thorn (localhost [127.0.0.1])
	by thorn.pobox.com (Postfix) with ESMTP id 11C3095;
	Fri, 30 Dec 2005 07:12:15 -0500 (EST)
Received: from mappit.local.linnet.org (212-74-113-67.static.dsl.as9105.com
	[212.74.113.67])
	(using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))
	(No client certificate requested)
	by thorn.sasl.smtp.pobox.com (Postfix) with ESMTP id AC8942969;
	Fri, 30 Dec 2005 07:12:13 -0500 (EST)
Received: from lists by mappit.local.linnet.org with local (Exim 4.60
	(FreeBSD)) (envelope-from <b.candler@pobox.com>)
	id 1EsJ6s-0003oR-Pg; Fri, 30 Dec 2005 12:11:50 +0000
Date: Fri, 30 Dec 2005 12:11:50 +0000
From: Brian Candler <B.Candler@pobox.com>
To: VANHULLEBUS Yvan <vanhu_bsd@zeninc.net>
Message-ID: <20051230121150.GA14630@uk.tiscali.com>
References: <20051228143817.GA6898@uk.tiscali.com>
	<001401c60bc0$a3c87e90$1200a8c0@gsicomp.on.ca>
	<20051228153106.GA7041@uk.tiscali.com>
	<20051228164339.GB3875@zen.inc>
	<868xu5p2ze.fsf@srvbsdnanssv.interne.kisoft-services.com>
	<20051229121359.GA10949@uk.tiscali.com>
	<20051229123521.GA1854@zen.inc>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20051229123521.GA1854@zen.inc>
User-Agent: Mutt/1.4.2.1i
Cc: freebsd-net@freebsd.org
Subject: Re: IPSEC documentation
X-BeenThere: freebsd-net@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
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: Fri, 30 Dec 2005 12:11:56 -0000

On Thu, Dec 29, 2005 at 01:35:21PM +0100, VANHULLEBUS Yvan wrote:
> > As it happens this FreeBSD box is also acting as a NAT gateway using pf
> > (myhost is on a private IP) and actually its external IP is also private -
> > it sits behind a second NAT firewall. So maybe that's where the problem
> > originates, although I really can't understand where the value of 1380 comes
> > from.
> 
> 1500 - (pppoe encapsulation ?) - ESP header - L2TP encapsulation....

Yeah, but what I don't understand is that this value was chosen by a remote
webserver which is on the other side of the world, and knows nothing about
the L2TP/ESP encapsulation going on locally.

All it knows is that the client offered an MSS of 1360; for some reason it
offered back an MSS of 1380. Weird.