IP Address Classes

32-bit IPv4 addressing is divided into classes:

Class A (default Subnet Mask 255.0.0.0)

1.x.y.z to 126.x.y.z

1.0.0.1 to 126.255.255.254 valid range of host IDs

0111 1111 (127 decimal) reserved for testing

10.0.0.0 to 10.255.255.255 reserved private networks RFC1918 128 networks 16,777,214 usable host per network

Class B (default Subnet Mask 255.255.0.0)

128.0.y.z to 191.255.y.z

128.0.0.1 to 191.255.255.254 valid range of host IDs 172.16.0.0 to 172.31.255.255 reserved for private networks RFC1918 16,384 networks 65,534 usable hosts per network

Class C (default Subnet Mask 255.255.255.0)

192.0.0.z to 223.255.255.z

192.0.0.1 to 223.255.255.254 valid range of host IDs 192.168.0.0 to 192.168.255.255 reserved for private networks RFC1918

2,097,152 networks 254 usable hosts per network

Don’t get comfortable with 32-bit IPv4 addressing. 128-bit IPv6 addressing is already changing the landscape. IPv6 is designed to accommodate the IPv4 through the transition.