Comment # 2 on bug 1171902 from Franck Bui

Hmm, I don't think your issue is related to udev.

The warning:

> "Could not generate persistent MAC address for virbr1: No such file or directory"

simply indicates that udev failed at generating a persistent MAC address but
that should prevent the bridge from being created nor working.

OTOH,

> # virsh net-start vlan
> error: Failed to start network vlan
> error: COMMAND_FAILED: '/usr/sbin/iptables -w2 -w --table filter --insert LIBVIRT_INP --in-interface virbr1 --protocol tcp --destination-port 67 --jump ACCEPT' failed: iptables: No chain/target/match by that name.

seems to indicate that the chain 'LIBVIRT_INP' is missing and I think it's
supposed to be created by libvirtd.

So my first guess would be that libvirtd wasn't started at the time you created
your virtual network and that's the reason why after rebooting, it suddenly
works as expected.

Would that make sense ?