From owner-freebsd-hackers@FreeBSD.ORG Mon Jan 8 21:09:00 2007 Return-Path: X-Original-To: freebsd-hackers@freebsd.org Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 63B1416A412 for ; Mon, 8 Jan 2007 21:09:00 +0000 (UTC) (envelope-from lee@nerds.org.uk) Received: from furby.nerds.org.uk (furby.nerds.org.uk [82.70.196.65]) by mx1.freebsd.org (Postfix) with ESMTP id 08A6013C45B for ; Mon, 8 Jan 2007 21:08:59 +0000 (UTC) (envelope-from lee@nerds.org.uk) Received: from lee by furby.nerds.org.uk with local (Exim 4.65 (FreeBSD)) (envelope-from ) id 1H41AB-000B8J-4m for freebsd-hackers@freebsd.org; Mon, 08 Jan 2007 20:32:11 +0000 Date: Mon, 8 Jan 2007 20:32:11 +0000 From: Lee Brotherston To: freebsd-hackers@freebsd.org Message-ID: <20070108203211.GF41066@nerds.org.uk> MIME-Version: 1.0 Content-Type: multipart/signed; protocol="application/x-pkcs7-signature"; micalg=sha1; boundary="BOKacYhQ+x31HxR3" Content-Disposition: inline User-Agent: Mutt/1.5.13 (2006-08-11) X-Mailman-Approved-At: Mon, 08 Jan 2007 21:21:40 +0000 Subject: TCP Checksums in mbufs X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 08 Jan 2007 21:09:00 -0000 --BOKacYhQ+x31HxR3 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi, I have a bit of code I have written that uses pfil to access network traffic as it passes between interfaces on a FreeBSD router. One of the functions it performs is some incredibly basic rewrites of certain packets (keeping the same length, so no issues about sequence numbers), but it does alter the payload. I just wanted to check what is the "proper" way to be going about recalculating the checksums on the packet? I can write a function to do this and write this into the packet stored in the mbuf directly, however I wasn't sure if there was a more acceptable method such as flagging it to be re-checksum'd as it's routed, or to offload the computation to the NIC or something? Any thoughts, suggestions, etc very welcome! By the way, I'm not subscribed to the list right now, so I'd appreciate it if people could CC me on replies. 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