Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262760AbTIQOFf (ORCPT ); Wed, 17 Sep 2003 10:05:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262761AbTIQOFf (ORCPT ); Wed, 17 Sep 2003 10:05:35 -0400 Received: from natsmtp01.webmailer.de ([192.67.198.81]:15521 "EHLO natsmtp01.webmailer.de") by vger.kernel.org with ESMTP id S262760AbTIQOFe (ORCPT ); Wed, 17 Sep 2003 10:05:34 -0400 Message-ID: <3F686A73.9080706@softhome.net> Date: Wed, 17 Sep 2003 16:06:43 +0200 From: "Ihar 'Philips' Filipau" Organization: Home Sweet Home User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.5b) Gecko/20030831 X-Accept-Language: en-us, en MIME-Version: 1.0 To: root@chaos.analogic.com CC: Linux Kernel Mailing List Subject: Re: Incremental update of TCP Checksum References: In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1735 Lines: 38 Richard B. Johnson wrote: > > This is all wonderful. This assumes that the stuff being modified > in the packet is on well-defined boundaries, seldom the case when > you are re-writing packet data, but certainly the case if you > are re-writing an IP address. > > Also, modern switches do not rewrite checksums using software. ^^^^^^^^ > Therefore, they do not use a re-write algorithm as stated by > others. The checksum gets calculated "for free" during the > hardware transfer to an output holding FIFO. It is done using > an ASIC with the appropriate adder and "stumble-carry". > It depends on definition of software. It is so hard to draw parallel especially when what looks like controller runs some flavour of Linux from some embedded flash ;-) Actually some switches do alter header _before_ they have received payload. Just to be able to start rx without waiting for payload to arrive completely. Sometimes low latencies (even on narrow bandwidth links) are _that_ important... -- Ihar 'Philips' Filipau / with best regards from Saarbruecken. - - - - - - - - - - - - - - - - - - - - * Please avoid sending me Word/PowerPoint/Excel attachments. * See http://www.fsf.org/philosophy/no-word-attachments.html - - - - - - - - - - - - - - - - - - - - There should be some SCO's source code in Linux - my servers sometimes are crashing. -- People - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/