Date: Fri, 20 Aug 2004 22:54:13 +0300 From: Ruslan Ermilov <ru@freebsd.org> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: current@freebsd.org Subject: Re: on amd64 tcp4 cksums are bad (FYI) Message-ID: <20040820195413.GD57723@ip.net.ua> In-Reply-To: <16678.21478.381551.833252@grasshopper.cs.duke.edu> References: <20040820190525.GA21626@isc.org> <16678.21478.381551.833252@grasshopper.cs.duke.edu>
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[-- Attachment #1 --] On Fri, Aug 20, 2004 at 03:41:26PM -0400, Andrew Gallatin wrote: > > David W. Hankins writes: > > > > This is as observed via tcpdump on [client], which is what is producing > > the bad checksums. Obviously it doesn't cause a problem since no one > > listens to TCP checksums, but it's interesting. I only noticed it > > because I was tcpdump'ing for completely unrelated reasons, and it caught > > my eye. > > <...> > > > Client machine is amd64, running 64-bit mode 5-current fresh as of > > yesterday. Network interface is e1000, so fxp. Server is also freebsd > > e1000 is actually em. > > You're almost certainly using a driver which offloads transmit > checksums. (both fxp and em do) Since BPF sniffs the packet before it > leaves the host, the checksum has not yet been calculated, so it looks > bad. > > See this thread: > http://lists.FreeBSD.org/pipermail/freebsd-net/2004-August/004703.html > This should be added to FAQ. Cheers, -- Ruslan Ermilov ru@FreeBSD.org FreeBSD committer [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.5 (FreeBSD) iD8DBQFBJlblqRfpzJluFF4RAvMtAJsG0yiLyidrdeWSGcjR31iXRQP0dACgiG0f 8647hawaIfjuQno72alwFYM= =BOFB -----END PGP SIGNATURE-----
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