Addresses within this private address space will only be unique within your network. Remember, if you need globally unique address space, you must obtain addresses from an Internet registry. In order to use private address space, determine which hosts do not need to have network layer connectivity to the outside. These hosts are private hosts, and will use private address space. Private hosts can communicate with all other hosts within the network, both public and private, but they cannot have IP connectivity to any external host.
Private hosts can still have access to external services via application layer relays.
All other hosts are public and will use globally unique address space assigned by an Internet registry. Public hosts can communicate with other hosts within the network, and can have IP connectivity to external public hosts. Public hosts do not have connectivity to private hosts of other networks. Because private addresses have no global meaning, routing information about private networks is not propagated on outside links, and packets with private source or destination addresses should not be forwarded across such links. This rejection should not be treated as a routing protocol error.