kern/119635: Bad UDP packet checksum with em(4) and rxcsum/txcsum enabled

[Bernd Heller]

>Number:         119635
>Category:       kern
>Synopsis:       Bad UDP packet checksum with em(4) and rxcsum/txcsum enabled
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Jan 13 16:30:01 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator:     Bernd Heller
>Release:        7.0-RC1
>Organization:
>Environment:
FreeBSD 7.0-RC1 FreeBSD 7.0-RC1 #0: Mon Dec 24 10:10:07 UTC 2007     root at driscoll.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  amd64
>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.



>Release-Note:
>Audit-Trail:
>Unformatted: