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This is a list of countries by IPv4 address allocation. The Internet Assigned Numbers Authority (IANA) distributes large blocks of addresses to regional Internet registries (RIRs), which then assign them to national Internet registries and local Internet registries within their respective service regions. [ 1 ]
The original list of IPv4 address blocks was published in September 1981. [3] In previous versions of the document, [19] [20] network numbers were 8-bit numbers rather than the 32-bit numbers used in IPv4. At that time, three networks were added that were not listed earlier: 42.rrr.rrr.rrr, 43.rrr.rrr.rrr, and 44.rrr.rrr.rrr.
When fewer than four numbers were specified in the address in dotted notation, the last value was treated as an integer of as many bytes as are required to fill out the address to four octets. Thus, the address 127.65530 is equivalent to 127.0.255.250 .
An IPv4 address has a size of 32 bits, which limits the address space to 4 294 967 296 (2 32) addresses. Of this number, some addresses are reserved for special purposes such as private networks (≈18 million addresses) and multicast addressing (≈270 million addresses). IPv4 addresses are usually represented in dot-decimal notation ...
At the top level, the IP address pool is managed by the Internet Assigned Numbers Authority (IANA). The total IPv4 address pool contains 4 294 967 296 (2 32 ) addresses, while the size of the IPv6 address pool is 2 128 ( 340 282 366 920 938 463 463 374 607 431 768 211 456 ) addresses.
This scheme hides a large number of IP addresses behind a small set of public addresses, the same way the CPE does this locally, slowing down the rate IPv4 addresses are depleted. The shared address space contains 2 22 or 4 194 304 addresses, so each ISP is able to connect over 4 million subscribers this way.
The number of addresses usable for addressing specific hosts in each network is always 2 N - 2, where N is the number of rest field bits, and the subtraction of 2 adjusts for the use of the all-bits-zero host value to represent the network address and the all-bits-one host value for use as a broadcast address. Thus, for a Class C address with 8 ...
However at a new large ISP, 1,024 IPv4 addresses might not be enough to provide IPv4 connectivity to all the customers due to the limited number of ports available per IPv4 address. [ 58 ] The regional Internet registries (RIRs) for Asia (APNIC) and North America have a policy called the Inter-RIR IPv4 Address Transfer Policy, which allows IPv4 ...