Ip Address Calculator

An IPv4 address is a single 32-bit integer that convention writes as four dotted octets, each ranging from 0 to 255. A dotted-decimal subnet mask partitions those 32 bits into a leading run of ones marking the network and a trailing run of zeros marking the host, which is why every operation here reduces to bitwise logic. The network number is the address ANDed with the mask, the wildcard mask is the bit complement of the mask (each octet subtracted from 255), and the broadcast address is the network ORed with that wildcard. The host count is 2 raised to the number of host bits, less two for the reserved network and broadcast values, so a 255.255.255.0 mask yields 254 assignable addresses and 255.255.255.224 yields 30. The legacy class letters that tools still report come from the first octet: 1 to 126 is Class A, 128 to 191 Class B, 192 to 223 Class C, 224 to 239 multicast, and 240 and above reserved. These no longer govern routing but remain useful shorthand. Several ranges carry special meaning: RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 for private use, 127.0.0.0/8 is loopback, 169.254.0.0/16 is link-local under RFC 3927, and 100.64.0.0/10 is carrier-grade NAT space under RFC 6598. Two caveats matter in practice: a valid mask must be a contiguous run of ones, so values such as 255.255.0.255 are meaningless, and the minus-two rule breaks down for point-to-point /31 links under RFC 3021 and for /32 host routes.

The IPv4 address format was fixed by Jon Postel in RFC 791, published in September 1981. Its predecessor, RFC 760 of 1980, had allocated only the first eight bits to the network number, permitting a mere 256 networks on the entire internet; the 1981 revision introduced the class structure to provide networks of three different sizes. Subnetting, and with it the subnet mask that this calculator applies, was not part of that original design. It was added by Jeffrey Mogul and Jon Postel in RFC 950 in August 1985, so that a site holding one class-based allocation could divide it internally across multiple physical networks. Private addressing was formalized as RFC 1918 in February 1996 by Yakov Rekhter and colleagues, superseding the earlier RFC 1597 of 1994, and it became the foundation for Network Address Translation, described by Kjeld Egevang and Paul Francis in RFC 1631 in 1994 and extended to port translation in RFC 3022 in 2001. These measures postponed but did not prevent exhaustion of the 32-bit space. IANA allocated its final five unreserved blocks to the regional registries on 3 February 2011; APNIC reached its exhaustion threshold in April 2011, RIPE NCC in September 2012, and ARIN in September 2015. The long-term answer was the 128-bit IPv6 address, specified in RFC 2460 in 1998 and superseded by RFC 8200 in 2017.