Basic networking elements in Neutron

Neutron constructs the virtual network using elements that are familiar to all system and network administrators, including networks, subnets, ports, routers, load balancers, and more.

Using version 2.0 of the core Neutron API, users can build a network foundation composed of the following entities:

• Network: A network is an isolated layer 2 broadcast domain. Typically reserved for the tenants that created them, networks could be shared among tenants if configured accordingly. The network is the core entity of the Neutron API. Subnets and ports must always be associated with a network.
• Subnet: A subnet is an IPv4 or IPv6 address block from which IP addresses can be assigned to virtual machine instances. Each subnet must have a CIDR and must be associated with a network. Multiple subnets can be associated with a single network and can be noncontiguous. A DHCP allocation range can be set for a subnet that limits the addresses provided to instances.
• Port: A port in Neutron represents a virtual switch port on a logical virtual switch. Virtual machine interfaces are mapped to Neutron ports, and the ports define both the MAC address and the IP address to be assigned to the interfaces plugged into them. Neutron port definitions are stored in the Neutron database, which is then used by the respective plugin agent to build and connect the virtual switching infrastructure.

Cloud operators and users alike can configure network topologies by creating and configuring networks and subnets, and then instruct services such as Nova to attach virtual devices to ports on these networks. Users can create multiple networks, subnets, and ports, but are limited to thresholds defined by per-tenant quotas set by the cloud administrator.