Managing the Address Space

The Internet’s stability is directly dependent on the uniqueness of publicly used network addresses. Thus, some mechanism was needed to ensure that addresses were, in fact, unique. This responsibility originally rested within an organization known as the InterNIC (Internet Network Information Center). This organization is now defunct and was succeeded by the Internet Assigned Numbers Authority (IANA). IANA, too, has been dismantled, and the new caretaker of the Internet’s names and address numbers is the Internet Corporation for the Assignment of Names and Numbers (ICANN). ICANN is currently creating a competitive registry structure that will enable commercial entities to compete with each other in the registration of IP names and numbers.
One important goal is to ensure that duplication of publicly used addresses does not occur. Such duplication would cause instability on the Internet, and compromise
its ability to deliver datagrams to networks using the duplicated addresses.
Although it is entirely possible for a network administrator to arbitrarily select unregistered IP addresses, this practice should not be condoned. Computers having such spurious IP addresses can only function properly within the confines of their network. Interconnecting networks with spurious addresses to the Internet incurs the risk of conflicting with an organization that has legitimate claim to that address space. Duplicated addresses will cause routing problems, and potentially hinder the Internet’s ability to deliver datagrams to the correct network.
In a firewall environment, the private network can use non-unique addresses because network address translation is used so that the addresses on the private network are substituted with the address of the public interface on the firewall. In this case, the private addresses may be non-unique across the Internet. Certain addresses are reserved for private use. Specifically, one Class A addres (10.0.0.0), 16 Class B addresses (172.16.0.0 – 172.31.0.0), and 256 Class C addresses (192.168.0.0 – 192.168.255.0) are designated for private use.