freebsd stable - Jun 2016 - ipfw fwd to closed port

On 2016-06-09 02:02:40 (+0300), Slawa Olhovchenkov <slw at zxy.spb.ru>
wrote:
> Forwarding by ipfw to closed local port generating RST packet with
> incorrect checksun. Is this know ussuse? Need open PR?
Where did you capture the packet? If you've captured the packet on the
machine that generated it tcpdump may indeed claim that the checksum is
wrong, because it's computed by the hardware (so after tcpdump captured
it).

Regards,
Kristof

On Thu, Jun 09, 2016 at 03:00:17PM +0200, Kristof Provost wrote:
> On 2016-06-09 02:02:40 (+0300), Slawa Olhovchenkov <slw at
zxy.spb.ru> wrote:
> > Forwarding by ipfw to closed local port generating RST packet with
> > incorrect checksun. Is this know ussuse? Need open PR?
> 
> Where did you capture the packet? If you've captured the packet on the
> machine that generated it tcpdump may indeed claim that the checksum is
> wrong, because it's computed by the hardware (so after tcpdump captured
> it).
On the tun0 (destination of RST packet routed to tun0).
tun0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> metric 0 mtu 1500
        options=80000<LINKSTATE>
        inet 192.168.4.1 --> 192.168.4.1 netmask 0xffffff00 
        inet6 fe80::240:63ff:fedc:ac9e%tun0 prefixlen 64 scopeid 0x9 
        nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
        Opened by PID 1345

tun0 don't computed checksum.