From owner-freebsd-hackers Thu Dec 6 6:55:28 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from avocet.prod.itd.earthlink.net (avocet.mail.pas.earthlink.net [207.217.120.50]) by hub.freebsd.org (Postfix) with ESMTP id 2E2BA37B416 for ; Thu, 6 Dec 2001 06:55:26 -0800 (PST) Received: from dialup-209.245.132.144.dial1.sanjose1.level3.net ([209.245.132.144] helo=mindspring.com) by avocet.prod.itd.earthlink.net with esmtp (Exim 3.33 #1) id 16Bzva-00018R-00; Thu, 06 Dec 2001 06:55:10 -0800 Message-ID: <3C0F86D4.77A6748B@mindspring.com> Date: Thu, 06 Dec 2001 06:55:16 -0800 From: Terry Lambert X-Mailer: Mozilla 4.7 [en]C-CCK-MCD {Sony} (Win98; U) X-Accept-Language: en MIME-Version: 1.0 To: Yung-Sheng Tang Cc: freebsd-hackers@freebsd.org Subject: Re: UDP checksum error after encapsulating multicast packet References: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG Yung-Sheng Tang wrote: > > I am setting up a multicast router. Recompiling kernel with MROUTING > option and enabling mrouted are done. Basically, my multicast AP runs > well, but if that AP and mrouted run on the same machine, forwarded > packets would get udp checksum error. Here is the result from tcpdump: [ ... ] > Did I make some mistake? Thank you for your attention. I have noticed a number of bad checksum instances, as well, in particular in the piggy-back ACK implementation of a former coworker, but did not track them down. It seems to me that this is the "one's complement" problem that the incremental checksum modification RFC update refers to, but I could be mistaken. I don't think that code is incredibly exercised in FreeBSD. On the other hand, you should also examine the packet in from the other machine, as the checksum might have started out broken. If so, an incremental update wouldn't correct it. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message