IP Classes

An Internet Protocol (IP) address is a logical address assigned to devices within a computer network. This numerical identification employs IP for transmission between nodes. IP addresses are in binary numbers but are usually shown in readable notations like 2001:db8:0:1234:0:567:1:1 (IPv6) and 192.168.100.1 (IPv4) .

IP addresses are primarily categorized into classes. The address class connotes the network’s potential size. The class of an IP address specifies the following:

  • bits that distinguish the network
  • bits that identify the network ID
  • bits that pinpoint the host ID
  • bits that isolate the host computer

It also demarcates the sum of host subnets in each network. There are five IP address classes: A, B, C, D, and E.

Host ID and Network Fields

Four octets that compose an IP address are classified under A, B, C, D, and E. The table below shows the distribution of the octets in classes A through C.

Class IP Address Network ID Host ID
A a.b.c.d a b.c.d
B a.b.c.d a.b c.d
C a.b.c.d a.b.c d

Class A – Addresses in this class are specified for networks with a large sum of hosts. Class A permits 126 networks and uses the first octet as the network ID.

Class B – Addresses in this class are specified for medium to large-sized networks. Class B permits 16,384 networks and uses the first and second octet as the network ID.

Class C – Addresses in this class are specified for small LANs (Local Area Networks). Class C permits approximately 2 million networks and uses the first, second, and third octet as the network ID.