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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.
The method divides the IP address space for Internet Protocol version 4 (IPv4) into five address classes based on the leading four address bits. Classes A, B, and C provide unicast addresses for networks of three different network sizes. Class D is for multicast networking and the class E address range is reserved for future or experimental ...
Decomposition of the quad-dotted IPv4 address representation to its binary value. IPv4 uses 32-bit addresses which limits the address space to 4 294 967 296 (2 32) addresses. IPv4 reserves special address blocks for private networks (2 24 + 2 20 + 2 16 ≈ 18 million addresses) and multicast addresses (2 28 ≈ 268 million addresses).
A public IP address is a globally routable unicast IP address, meaning that the address is not an address reserved for use in private networks, such as those reserved by RFC 1918, or the various IPv6 address formats of local scope or site-local scope, for example for link-local addressing. Public IP addresses may be used for communication ...
An IP address is part of a CIDR block and is said to match the CIDR prefix if the initial n bits of the address and the CIDR prefix are the same. An IPv4 address is 32 bits so an n-bit CIDR prefix leaves 32 − n bits unmatched, meaning that 2 32−n IPv4 addresses match a given n-bit CIDR prefix. Shorter CIDR prefixes match more addresses ...
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 is a list of the IP protocol numbers found in the field Protocol of the IPv4 header and the Next Header field of the IPv6 header. It is an identifier for the encapsulated protocol and determines the layout of the data that immediately follows the header. Both fields are eight bits wide.
The document goes on to list the remaining Class A networks of 44 through 126 as unassigned and 127 as reserved. It lists all Class B networks except 128.000 and 192.255 as unassigned and list those two as reserved. Similarly, it lists the Class C networks of 192.000.001 and 223.255.255 as reserved and the ones in between as unassigned.