Subnets come in three sizes Class A, Class B and Class C. Subnets are made up of 4 octets which in turn make IP addresses. The table below Shows the Class, the number of bits for the network ID and the octet that each Class shares.
| Subnet Classes |
| IP AddressClass | Total # Of Bits For Network ID / Host ID | 1st Octet | 2nd Octet | 3rd Octet | 4th Octet |
| Class A | 8/24 | 11111111 (255) | 00000000(0) | 00000000(0) | 00000000(0) |
| Class B | 16/16 | 11111111 (255) | 11111111(255) | 00000000(0) | 00000000(0) |
| Class C | 24/8 | 11111111 (255) | 11111111(255) | 11111111(255) | 00000000(0) |
See also:
IP Address
Octet
CIDR