Date: Thu, 18 Jan 2007 18:51:25 -0500 From: Kris Kennaway <kris@obsecurity.org> To: Roman Le Houelleur <roman@IPricot.com> Cc: freebsd-stable@freebsd.org Subject: Re: tcpdump, rl, sis, fxp and multicast problems Message-ID: <20070118235125.GA80971@xor.obsecurity.org> In-Reply-To: <45AF8586.8080908@IPricot.com> References: <45AF8586.8080908@IPricot.com>
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[-- Attachment #1 --] On Thu, Jan 18, 2007 at 03:34:46PM +0100, Roman Le Houelleur wrote: > Hi everyone, > > It's been about a year or so that I upgrade my box to RELENG_6 > from time to time. I got some suprises this week, I've seen a > few things that made me think of hardware problems but some are > definitly soft. > > First and easy one, tcpdump -v does not show checksum error > for UDP whereas it does for TCP (same w/ tcpdump -vvv). > > checksum : I have a double port fxp 82550 Pro/100 board which > makes plenty of checksum errors (UDP & TCP), I suspect this > is related to checksum offloading but am not sure. I strongly > believe this card was working fine a few days/weeks ago. And a priori it still is: by definition, checksum offload means that the OS does not compute the checksum for outgoing packets, so tcpdump doesn't see a valid checksum either. Unless you have evidence (from e.g. observation on another host) that the checksums are not being computed correctly, this is not a bug. It is, however, a FAQ ;-) Kris [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (FreeBSD) iD8DBQFFsAf9Wry0BWjoQKURAgUiAKDpS88W53vTogqZzby1J+74iCEhkwCg5PkU VxmQnmZGoGeaEW7XrNnhgpg= =rCdw -----END PGP SIGNATURE-----
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