[libvirt-users] KVM NAT stops from working

[Francesc Guasch]

Hi. First of all thank you for the work you are doing with libvirt.
I am not sure this is the right place to ask, I'd appreciate
if you can give me any hint or directions.

I have several similar KVM Linux boxes and one of them has a really
strange behavior with the KVM NAT: It just suddenly stops from
working.

This is a Linux Ubuntu Server 19.04 with
  - libvirt-bin 4.0.0
  - qemu-kvm 1:2.11

Everything works fine and then suddenly the virtual machines
can't reach outside. If I run a tcpdump in the host I see
the NAT isn't working.

When the server just boots I can see the packets with the
server address going out:

     x.y.z.w.49138 > 8.8.8.8.53

Then, it may be some hours or days later, instead the server
address I see the internal domains address:


     192.168.122.33.19132 > 8.8.8.8.53
     ^^^^^^^^^^^^^^

I try to restart the iptables but it won't help.

Any hints ? Thank you very much