<P> Today, these two versions of the Internet Protocol are in simultaneous use . Among other technical changes, each version defines the format of addresses differently . Because of the historical prevalence of IPv4, the generic term IP address typically still refers to the addresses defined by IPv4 . The gap in version sequence between IPv4 and IPv6 resulted from the assignment of version 5 to the experimental Internet Stream Protocol in 1979, which however was never referred to as IPv5 . </P> <P> An IP address in IPv4 is 32 - bits in size, which limits the address space to 4294967296 (2) IP addresses . Of this number, IPv4 reserves some addresses for special purposes such as private networks (~ 18 million addresses) or multicast addresses (~ 270 million addresses). </P> <P> IPv4 addresses are usually represented in dot - decimal notation, consisting of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., 172.16. 254.1 . Each part represents a group of 8 bits (octet) of the address . In some cases of technical writing, IPv4 addresses may be presented in various hexadecimal, octal, or binary representations . </P> <P> In the early stages of development of the Internet Protocol, network administrators interpreted an IP address in two parts: network number portion and host number portion . The highest order octet (most significant eight bits) in an address was designated as the network number and the remaining bits were called the rest field or host identifier and were used for host numbering within a network . </P>

What are the names of the two parts of a tcp/ip address