in nova.conf configuration flag, routing_source_ip flag should use 'numbered-ip' such as 192.168.1.1, but not the host name.
I thinkg openstack guys try to tell us by naming the flag as 'routing_source_IP'.
Since it is used as the input param to iptable-restore, thus if you use host name on 'routing_source_ip' nova-network will unexpected die.
If you try to run the nova-network again, it will be on deadlock, since the module that performs this use external lock in /var/log/nova/ and hangs in ps aux.
This makes you think nova-network is working fine but NO IT IS NOT.
It takes half a day to figure out what the heck is going on.