Частные сети. Private IPv4 address spaces

he Internet Engineering Task Force (IETF) has directed the Internet Assigned Numbers Authority (IANA) to reserve the following IPv4 address ranges for private networks, as published in RFC 1918[1]: RFC1918 name IP address range number of addresses classful description largest CIDR block (subnet mask) host id size

24-bit block -	16,777,216	single class A network (	24 bits
20-bit block -	1,048,576	16 contiguous class B network (	20 bits
16-bit block -	65,536	256 contiguous class C network (	16 bits

Classful addressing is obsolete and has not been used in the Internet since the implementation of Classless Inter-Domain Routing (CIDR) starting in 1993. For example, while was a single class A network, it is common for organizations to divide it into smaller /16 or /24 networks. Contrary to a common misconception, a /16 class A subnet is not referred to as a class B network. Likewise, a /24 class A or B subnet is not referred to as a class C network. The class is determined by the first three bits of the prefix.[2] In April 2012, IANA allocated for use in carrier grade NAT scenarios in RFC 6598[3].