Re: Upgrade to 14.4 and vtnet+NAT stopped working

> On 18. May 2026, at 20:50, Andrea Venturoli <[email protected]> wrote:
> 
> Hello.
> 
> I've just upgraded a 14.3 virtual server to 14.4 and some part of networking has stopped working.
> I'm sure I've missed some change in release notes, upgrade instructions, whatever... but I cannot find the reason.
> 
> I've got:
> _ WAN interface: vtnet0;
> _ epair0a as 192.168.x.1;
> _ epair0b as 192.168.x.2 (used by a VNET jail);
> _ ipfw that NATs 192.168.x.2, so that it can connect to the outside world.
> 
> Everything used to work with 14.3.
> Now that I upgraded to 14.4:
> _ base works normally and can connect to the Internet or receive incoming connections (over vtnet, of course with no NAT needed);
> _ base can connect to services inside the jail;
> _ jail can ping the world (i.e. ping 8.8.8.8 works, so NAT, at least partially, works);
> _ however no TCP or UDP gets from the jail to Internet!
> 
> 
> 
> For example, if inside the jail I issue:
>> # host www.google.it 8.8.8.8
>> ;; connection timed out; no servers could be reached
> 
> ipfw shows nothing was blocked.
> tcpdump on vtnet shows the query packet getting out to 8.8.8.8, but no answer coming in.
> What's strange is that this packet is 0 bytes long!
What does this mean? Not even an IPv4 header? Or only an IPv4 header without a UDP header?
Or an IPv4 header with a UDP header but no UDP payload?
> 
> This also happen if I "telnet x.y.z.w port" (and on the other side I can confirm I get zero length packets).
Same questions here.
> 
> 
> I tried putting "hw.vtnet.csum_disable=1" in /boot/loader.conf, but it didn't help.
I think this is not a checksum issue, so disabling checksum offload should not affect it.

Best regards
Michael
> 
> What should I check?
> 
> bye & Thanks
> av.
>