A network refers to a Neutron network.
Neutron is the key networking component of OpenStack. Neutron is designed with a pluggable architecture that allows easy integration with third-party networking solutions via plugins.
Neutron networks in OpenStack roughly fall into three distinct categories
- External networks
- Provider networks
- Tenant networks
Provider networks are designed to map directly to existing networks in your data center.
A good example of a provider network is an existing VLAN-based or physical (Flat) network within your data center that you would like to incorporate into your OpenStack environment. For example, VLAN 20 on a specific physical network may be designated for all Database traffic.
A Provider network allows you to deploy database servers within OpenStack that explicitly connect to this network.
A provider network in Neutron can be a flat network, a VLAN-based network, a GRE-based network, or a VXLAN-backed network.
Neutron tenant networks are meant to be private to a given tenant, and are generally created by a user or a group of users within a tenant.
Without a Neutron router, the individual tenant networks are isolated from one another, so that the virtual machines created within the individual tenant networks cannot route traffic outside of the network.
External networks correspond to the physical networks in your data center that are publicly routable or enabled with access to Internet. As an administrator, you may want to supply one or more external networks to Neutron so that
- Your virtual machines can route packets from the internal network to the Internet.
- You can assign floating IPs to your virtual machine and have them reachable from the public Internet.