On Sun, Aug 02, 2026 at 11:17:44AM +0200, [email protected] wrote:
> >Description:
> In writing IPv6 multicasting code, I have determined after a full day
> of debugging, that software checksumming from udp6_output/ip6_output
> does not work. After examining all my devices there is two that do
> hardware offloading of IPv6 UDP packets and this turned out to work.
> Conclusion is obvious, software checksumming doesn't work in this
> multicast.
I tried to reproduce the issue with regress/sys/netinet6/mcast6 .
For that I disabled UDPv6 checksum offloading in em. netstat -s
counter went up.
udp:
6 output packets software-checksummed
On the receiving machine the checksum is correct. Both are connected
by a direct cable.
22:13:44.842191 fdd7:e83e:66bc:145::70.15971 > ff04::123.12345: [udp sum ok]
udp 5 [flowlabel 0x1e8b4] [hlim 1] (len 13)
Please check your setup. Maybe something is different. Try to
create a simpler test case.
bluhm
