Date: Sun, 13 Jan 2008 22:20:03 GMT From: Bernd Heller <bdheller@users.sourceforge.net> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/119635: Bad UDP packet checksum with em(4) and rxcsum/txcsum enabled Message-ID: <200801132220.m0DMK3Mp005494@freefall.freebsd.org>
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The following reply was made to PR kern/119635; it has been noted by GNATS. From: Bernd Heller <bdheller@users.sourceforge.net> To: Kris Kennaway <kris@FreeBSD.org> Cc: freebsd-gnats-submit@FreeBSD.org Subject: Re: kern/119635: Bad UDP packet checksum with em(4) and rxcsum/txcsum enabled Date: Sun, 13 Jan 2008 22:59:52 +0100 Hi Kris, yes, I ran tcpdump from another system on the same subnet, connected by a hub. Bernd On 13.01.2008, at 20:04, Kris Kennaway wrote: > Bernd Heller wrote: > >>> Description: >> I have an Intel Pro/1000 PT Desktop Adapter network card in that >> machine, and by default the em(4) driver has rxcsum/txcsum enabled. >> But the checksums for some UDP packets generated this way are >> wrong. I noticed this when trying to run avahi-daemon. It sends UDP >> multicast packets, but they were never recognized on the network. >> Only when using tcpdump did I notice the bad checksums. After I >> disabled rxcsum/txcsum on the interface all was working perfectly. >> I could reproduce the same issue in a VMware machine using FreeBSD >> 7.0-RC1 i386 and amd64. 6.2 seems to be unaffected. >>> How-To-Repeat: >> Run avahi-daemon to publish any services (it will do so by default) >> and analyze the UDP packages sent out. >>> Fix: >> Workaround: disable rxcsum/txcsum on the interface. > > Please confirm that you ran tcpdump from ANOTHER system, not the one > generating the packets. See the tcpdump manpage for more discussion > of hardware checksumming and tcpdump. > > Kris
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