A provider network is a network attached physically to a datacenter network existing outside of the deployed Overcloud. This can be an existing infrastructure network or a network that provides external access directly to VMs through routing instead of floating IPs.
When creating a provider network, you associate it with a physical network, which uses a bridge mapping. This is similar to floating IP network creation. You add the provider network to both the Controller and the Compute nodes because the Compute nodes attach VM virtual network interfaces directly to the attached network interface.
For example, if the desired provider network is a VLAN on the br-ex bridge, use the following command to add a provider network on VLAN 201:
$ neutron net-create --provider:physical_network datacentre --provider:network_type vlan --provider:segmentation_id 201 --shared provider_network
This command creates a shared network. It is also possible to specify a tenant instead of specifying --shared. That network will only be available to the specified tenant. If you mark a provider network as external, only the operator may create ports on that network.
Add a subnet to a provider network if you want Neutron tp provide DHCP services to the tenant VMs:
$ neutron subnet-create --name provider-subnet --enable_dhcp=True --allocation-pool start=10.9.101.50,end=10.9.101.100 --gateway 10.9.101.254 provider_network 10.9.101.0/24