External Networks have a unique role to play with OpenStack Networking. As we have seen, the DHCP server assigns an IP address from the Subnet to each VM instance. These IP addresses are reachable only in the Network because tenant isolation is required. However, many common deployments require that the VM instances have access to outside networks including the Internet and also be reachable from the outside network.
The main purpose of the external Networks is to allow the VMs to access networks outside the data center and Internet. They also allow the VMs to be accessed from the outside network.
As the external Networks have a special behavior associated with them, only users with an administrative role can create them. Besides the standard input such as the Network name and so on, it is important to identify the IP address range to be used for the external Network. This recipe assumes that the L3 agent on the Network node has been...