Every node of an Internet Protocol (IP) network, such as a computer, router, or network printer, is assigned an IP address that is used to locate and identify the node in communications with other nodes on the network. Internet Protocol version 4 provides 232 (4,294,967,296) addresses. However, large blocks of IPv4 addresses are reserved for special uses and are unavailable for public allocation.
The IPv4 addressing structure provides an insufficient number of publicly routable addresses to provide a distinct address to every Internet device or service. This problem has been mitigated for some time by changes in the address allocation and routing infrastructure of the Internet. The transition from classful network addressing to Classless Inter-Domain Routing delayed the exhaustion of addresses substantially.
In addition, network address translation (NAT) permits Internet service providers and enterprises to masquerade private network address space with only one publicly routable IPv4 address on the Internet interface of a customer premise router, instead of allocating a public address to each network device. Complicating matters, IPv6-unaware NAT devices break native and 6to4 IPv6 connectivity, and a large fraction break 6in4 tunnels.
Read more about this topic: IP Address Exhaustion
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