From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262636AbVDHAdT (ORCPT ); Thu, 7 Apr 2005 20:33:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262637AbVDHAdT (ORCPT ); Thu, 7 Apr 2005 20:33:19 -0400 Received: from ns.schottelius.org ([213.146.113.242]:19731 "HELO scice.schottelius.org") by vger.kernel.org with SMTP id S262636AbVDHAdE (ORCPT ); Thu, 7 Apr 2005 20:33:04 -0400 Date: Fri, 8 Apr 2005 02:35:09 +0200 From: Nico Schottelius To: Florian Attenberger Cc: linux-kernel@vger.kernel.org Subject: Re: PMTU, MSS and "fragmentation needed" problem with linux? Message-ID: <20050408003509.GH5211@schottelius.org> Mail-Followup-To: Nico Schottelius , Florian Attenberger , linux-kernel@vger.kernel.org References: <20050407122217.GE5211@schottelius.org> <42556ED5.9080709@onlinehome.de> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="juZjCTNxrMaZdGZC" Content-Disposition: inline In-Reply-To: <42556ED5.9080709@onlinehome.de> User-Agent: echo $message | gpg -e $sender -s | netcat mailhost 25 X-Linux-Info: http://linux.schottelius.org/ X-Operating-System: Linux 2.6.11.6 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --juZjCTNxrMaZdGZC Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Thanks for the hints Florian, but still there are open questions: Florian Attenberger [Thu, Apr 07, 2005 at 07:33:09PM +0200]: > [...] > # [From the kernel help: > # > # This option adds a `TCPMSS' target, which allows you to alter the > # MSS value of TCP SYN packets, to control the maximum size for that > # connection (usually limiting it to your outgoing interface's MTU > # minus 40). The MTU is 1460 or 1492 in tested cases. This means on ppp0, TCPMSS should be 1420 or maximum of 1452. Why do I see 1460 on the interface? > # This is used to overcome criminally braindead ISPs or servers which > # block ICMP Fragmentation Needed packets.=20 That's clear to me, there are sites out there, debatting that problem. But: - Should not _my_ Linux-router tell _my_ client that the mtu choosen is too big? - On the tested connections _all_ icmp types were allowed (disabled iptable= s) - As far as I can see, the routers between the two hosts don't drop the generated icmp-packets The first of the questions was the reason I choosed this ML, because I was wondering why my client does not get the DF-Bit-set, but frag-needed icmp-message from the linux-router. Or did I unterstand the technique wrong? Greetings, Nico --=20 Keep it simple & stupid, use what's available. Please use pgp encryption: 8D0E 27A4 is my id. http://nico.schotteli.us | http://linux.schottelius.org --juZjCTNxrMaZdGZC Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.0 (GNU/Linux) iQIVAwUBQlXRu7OTBMvCUbrlAQI+ew/5ARL6AhMQPRxt2Y1IT3vnAbUnnIGFbAgD 548N1Za2NrFMSWKP/HBnBmiKA8iZVSG1wX9gfftuJSc5EvRcMaZdqtSOl+PtbiJ4 w38AMoRxRSU99PBaEFi+uGroAUlC1IlhephObBfxfYJjtsNL4FmCyxKsEeQBvEsv NKxKp2uGKuWkKTViFXTJkq62/erynL7vB8qRtodorga9peFAgue39vKpQ89iQhAC YSdgaBR6dCF8K9QBwpKezl5+J6fmLuOLlXgRzWbPeo/A5uN0ZcxAm0xk4ehdl2rZ dodwN4u0USQwTnaIgnadexR5gEf2XyA0zmIGk+bYJ0iTU/TENEGCJ4kxtkXeuDtv gIIztibYLTpyPS4JvV55MCgOkzpX9e7atzQIXDjt4esLNKu92MYIR/eTpq4t8U3z OuHDanllvxG+I5UFi3NiYzWGLITBDTEcrhkJEFxsyh7R3t+L+eR0GyG6IDqOxb77 5mXHnHdGcudj0Ainm+X/VN+GL9bYEscGu7WfBPCNrrdagXBqSiNABSLMy9lr1SXo /A4FRYQBlGezOXvpDQK93450m/Z6shfEOu2tn4BTjDAEtQZbYYxrByFaOSy7xeR9 Lqndr26hJtG9ZHkZx7rN4CYNklIPHB1krPyuDQPgwQE06Vl8xTLE3TPcd5jTOc2Z zMArtjXwm94= =lO4p -----END PGP SIGNATURE----- --juZjCTNxrMaZdGZC--