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Definition

IPv4 address class

An IPv4 address class is a categorical division of internet protocol addresses in IPv4-based routing.

Separate IP classes are used for different types of networks. Some are used for public internet-accessible IPs and subnets, that is, those networks behind a router (as in classes A, B and C). As well, some classes are reserved by the Internet Engineering Task Force (IETF) and the Internet Assigned Numbers Authority (IANA) for specific purposes. These special ranges are used for multicasting of identical data to all computers on a network or subnet or for research (as in classes D, E).

Within this notation, classes are mainly differentiated by the number of bits they have for the network and the number of bits used for hosts. IP addresses are notated in four groups of three-digit representations of 8 bits of binary in base 10-formatted notation for a total of 32 bits. The groups are separated by periods starting from zero (which in binary would be 00000000); the highest number in a grouping is 255 (or 11111111).

IPv4 address classes:

Class A IP addresses, where the 1st bit is 0, encompass the range of 0.0.0.0 to 127.255.255.255. This class is for large networks and has 8 bits for network and 24 bits for hosts.

Class B IP addresses, where the 1st two bits are 10, are in the range of 128.0.0.0 to 191.255.255.255. This class is for medium networks and has 16 bits for network and 16 bits for hosts.

Class C IP addresses, where the 1st three bits are 110, are in the range of 192.0.0.0 to 223.255.255.255. This class is for smaller networks and has 24 bits for network and 8 bits for hosts.

Class D or multicast IP addresses, where the 1st four bits are 1110 are in the range of 224.0.0.0 to 239.255.255.255

Class E or experimental IP addresses, where the 1st four bits are 11110, are in the range of 240.0.0.0 to 255.255.255.255.

Prior to the introduction of  IPv6 as a solution to the internet’s running out of addresses, the idea of opening the class E addresses was hotly debated. While forming the basis for IP address assignment, the system of IP address classes described here is generally bypassed today by use of Classless Inter-Domain Routing (CIDR) addressing.

This was last updated in October 2020

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