IPv4 Address Classes

Class A

• 1.0.0.0 to 126.255.255.255 (highest order bits: 00)

• 255.0.0.0/8 default subnet mask

• 126 networks (0 and 127 are reserved)

• 16,777,214 hosts

• Used by large organizations requiring a vast number of IP addresses

Class B

• 128.0.0.0 to 191.255.255.255 (highest order bits: 10)

• 255.255.0.0/16 default subnet mask

• 16,384 networks

• 65,534 hosts

• Medium-sized networks used by universities and regional services

Class C

• 192.0.0.0 to 223.255.255.255 (highest order bits: 110)

• 255.255.255.0/24 default subnet mask

• 2,097,153 networks

• 254 hosts

• Used for small businesses and LANs

Class D

• 224.0.0.0 to 239.255.255.255 (highest order bits: 1110)

• No DSM because Class D is not used for standard host addresses

  • Used for multicast transmissions

Class E

• 240.0.0.0 to 255.255.255.255 (highest order bits: 1111)

• No DSM because Class E is used for experimental purposes and future network protocol testing.

127.0.0.0/8

loopback address (RFC 6890)

0.0.0.0/8

local use address (RFC 6890)

169.254.0.0/16

Automatic Private IP Addressing Range (APIPA) (zero-config addresses that can be generated by computers for themselves)