From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH] ipv4: add DiffServ priority based routing Date: Tue, 12 Jan 2010 13:03:55 -0800 (PST) Message-ID: <20100112.130355.144803575.davem@davemloft.net> References: <201001121432.43301.schmto@hrz.tu-chemnitz.de> <20100112.121607.39835310.davem@davemloft.net> <4B4CE2B8.1040702@redfish-solutions.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: torsten.schmidt@s2006.tu-chemnitz.de, netdev@vger.kernel.org To: philipp_subx@redfish-solutions.com Return-path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:41920 "EHLO sunset.davemloft.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752957Ab0ALVDr (ORCPT ); Tue, 12 Jan 2010 16:03:47 -0500 In-Reply-To: <4B4CE2B8.1040702@redfish-solutions.com> Sender: netdev-owner@vger.kernel.org List-ID: From: "Philip A. Prindeville" Date: Tue, 12 Jan 2010 12:59:36 -0800 > What has changed is how network equipment is required to interpret > the meaning of those bits. > > Even if we pass the bits "as is" to the network, if the network is > applying entirely new semantics (and when I say "entirely new", I > mean those mandated since 1998), then compatibility in the host > kernel API doesn't matter a hoot since the packets will still be > handled by every transited router according to the modern semantics. People really don't assign global meaning to bits set by applications in the TOS field. What they do is they have a set of semantics inside of their cloud of routers and switch points for diffserv, and when packets come in the TOS field is rewritten to whatever scheme is being used inside of that cloud. And the diffserv bits only have meaning and effect within that cloud. So really, having a syscall that sets the TOS bits exactly by applications is just fine. People are doing diffserv right now with Linux and have done so for years.