A network is the central object of the Neutron v2.0 API data model and describes an isolated Layer 2 segment. In a traditional infrastructure, machines are connected to switch ports that are often grouped together into Virtual Local Area Networks (VLANs) identified by unique IDs. Machines in the same network or VLAN can communicate with one another but cannot communicate with other networks in other VLANs without the use of a router. The following diagram demonstrates how networks are isolated from one another in a traditional infrastructure:
Neutron network objects have attributes that describe the network type and the physical interface used for traffic. The attributes also describe the segmentation ID used to identify traffic between other networks connected to virtual switches on the underlying host. The following diagram shows how a Neutron network describes various Layer 1 and Layer 2 attributes:
Traffic between instances on different hosts requires underlying connectivity...