All About IP Classes


Communication on and between networks today relies on a systematic scheme built upon Internet Protocol (IP) Addressing. An IP address consists of a network ID and host ID and is broken down into five classes of addressing. These classes are best assigned and used according to the estimated number of hosts you anticipate having on your network.

Class A

A Class A network covers the IP address range of 1.0.0.0 – 126.255.255.255, with a subnet mask of 255.0.0.0 or /8 (pronounced “Slash 8”). A Class A network can have a maximum of 126 networks and 16,777,214 hosts.

Class B

A Class B network covers the IP address range of 128.0.0.0 – 191.255.255.255, with a subnet mask of 255.255.0.0 or /16. A Class B network can have a maximum 16,384 networks and 65,534 hosts.

Class C

A Class C network covers the IP address range of 192.0.0.0 – 223.255.255.255, with a subnet mask of 255.255.255.0 or /24. A Class C network can have a maximum of 2,097,152 networks and 254 hosts.

Private or Reserved Addressing

Within each network class, there is designated IP space that is reserved for private or non-public use and, thus, cannot be routed over the global Internet. This private address space is defined under Request For Comments 1918, or more commonly called RFC 1918. The RFC is a group of memoranda issued by the Internet Engineering Task Force (IETF) that helps define Internet operating standards.

Class A Private Space: 10.0.0.0 – 10.255.255.255, with a subnet mask of 255.0.0.0 or /8

Class A Reserved Space: 127.0.0.0 – 127.255.255.255, with a subnet mask of 255.0.0.0 or /8 (reserved for loopback addressing)

Class B Private Space: 172.16.0.0 – 172.31.255.255, with a subnet mask of 255.255.0.0 or /16

Class C Private Space: 192.168.0.0 – 192.168.255.255 with a subnet mask of 255.255.255.0 or /24

Other Classes

Class D networks are reserved for multicast addressing. This covers the range of 224.0.0.0 – 239.255.255.255. No subnet information is defined for this special range.

Class E networks are reserved for experimental purposes for future research and development. This covers the range of 240.0.0.0 – 255.255.255.254. No subnet information is defined for this special class either.



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