Addresses within this private address space will only be unique within the enterprise. As before, any enterprise that needs globally unique address space is required to obtain such addresses from an Internet registry. An enterprise that requests IP addresses for its external connectivity will never be assigned addresses from the blocks defined above. In order to use private address space, an enterprise needs to determine which hosts do not need to have network layer connectivity outside the enterprise in the foreseeable future. Such hosts will be called private hosts, and will use the private address space defined above.
Private hosts can communicate with all other hosts inside the enterprise, both public and private.
However, they cannot have IP connectivity to any external host. While not having external network layer connectivity private hosts can still have access to external services via application layer relays. All other hosts will be called public and will use globally unique address space assigned by an Internet Registry. Public hosts can communicate with other hosts inside the enterprise both public and private and can have IP connectivity to external public hosts. Public hosts do not have connectivity to private hosts of other enterprises.