IPv4 addresses are divided into five classes. Each IP address class has a different maximum number of IPs that exist within it.
| Class | First Octet Range | Default Subnet Mask | Maximum Number of Hosts Per Network |
| A | 1-127 | 255.0.0.0 | 16,777,214 Hosts (2^24-2) |
| B | 128-191 | 255.255.0.0 | 65,534 Hosts (2^16-2) |
| C | 192-223 | 255.255.255.0 | 254 Hosts (2^8-2) |
| D | 224-239 | N/A | |
| E | 240-255 | N/A |
Class A IPs start with 1-127. Keep in mind, though, that 127 is reserved for localhost. The remaining three octets are used for the host id. Class B IPs start with 128-191 and use the first and second octets for the network id. Class C begins with 192-223 and use the first three octets for the network id. Class D and class E are not generally used for setting up networks. Class D is Multicast and class E is experimental.
