Comment # 9 on bug 1123699 from James Fehlig

(In reply to Joachim Werner from comment #8)
> Since a week or two ago, the default network on an frequently updated
> Tumbleweed I'm running is not automatically coming up any more. Would this
> be a separate bug report (because it can't be related _only_ to the YaST
> problem) or do you think it has the same root cause?

IMO the yast part of the bug should be a separate report. It has nothing to do
with libvirt's default network.

> In my case, the default network exists from the original installation and
> can be started manually. It just doesn't auto-start at boot time any more.

Is it still marked autostart? Check output of 'virsh net-list --all' command.
If already set to autostart, are there any errors related to starting the
default network in the output of 'journalctl -u libvirtd'?