IPv4 address exhaustion is the depletion of the pool of unallocated Internet Protocol Version 4 (IPv4) addresses. The IP address space is managed by the Internet Assigned Numbers Authority (IANA) globally, and by five regional Internet registries (RIR) responsible in their designated territories for assignment to end users and local Internet registries, such as Internet service providers. On 31 January 2011, IANA officially exhausted, assigning the last IP ranges to the RIRs. IPv6 is the ultimate solution to the IPv4 address exhaustion. Carrier Grade NAT (CGN) is an integral part of IPv6 migration.