With Nova, the network manager is responsible for much more than simply creating L2 connectivity. Among other things, the network manager is responsible for:
Defining vNICs when a VM is first created.
Attaching VM vNICs to an L2 network.
Assigning each VM vNIC a fixed IP address from a subnet associated with its L2 network.
Optionally providing a "gateway router" to connect private L2 networks to a public network using NAT.
By default, the Quantum Manager determines the set of vNICs and fixed IPs for a VM based on networks statically created by the cloud administrator using nova-manage (see below for instructions on creating such networks).
For each vNIC created, the Quantum Manager will create a port on the Quantum network and attach the vNIC. If the VM is later terminated, Quantum Manager will destroy the associated Quantum port.
