It is going to take some time before Quantum become the main single option for network configuration. Many small to medium deployments will probably never require such a complicated mechanism to manage network creation, ports assignments or IPs allocation.
- How many network configuration options do we have in Folsom.
- How does the old nova-network work.
In Folsom we have a choice and we can use either nova-network  or quantum  service for our cloud infrastructure.
Depending on the complexity and flexibility we can use the the following configurations in nova-network :
This picture shows an example interaction between 2 VMs. More in depth description of how the network flows look like and what role plays the hypervisor in routing or restricting the traffic can be found in .
- Mirrantis http://www.mirantis.com/blog/openstack-networking-flatmanager-and-flatdhcpmanager/
- IBM OpenStack