Comment # 19 on bug 1158817 from Giacomo Comes

(In reply to Martin Wilck from comment #12)
> (In reply to Neil Rickert from comment #11)
> > I'm not quite sure what you are asking.
> 
> For a start, please provide output of "firewall-cmd --list-all-zones" and
> "iptables-save".

I don't think firewalld has anything to do with the problem here.
If I add again in /etc/modprobe.d/00-system.conf:
  softdep bridge post: br_netfilter
and I disable firewalld the network in KVM still does not work.
If the problem was due to a strange firewall rule, disabling firewalld should
make the issue go away, isn't it?

Also I have the suspect that libvirt has nothing to do with the problem as
well.
And the reason is that I start qemu-kvm manually (from a script actually) and
libvirt is not used at all.