Description:
- Divide a network into a smaller subnetwork
Classful subnet:
- For IPv4 only
-
| Class | Leading bits | Size of network number bit field | Size of rest bit field | Number of networks | Number of addresses per network | Start address | End address |
|---|
| A | 0 | 8 | 24 | 128 (2^7) | 16777216 (2^24) | 0.0.0.0 | 126.255.255.255 |
| B | 10 | 16 | 16 | 16384 (2^14) | 65536 (2^16) | 128.0.0.0 | 191.255.255.255 |
| C | 110 | 24 | 8 | 2097152 (2^21) | 256 (2^8) | 192.0.0.0 | 223.255.255.255 |
| D | 1110 | 28 | 2^4 | 2^28 | 224.0.0.0 | 239.255.255.255 | |
- Some chunks of it are reserved for RFC 1918
Subnet mask:
- Tells which part of the IP identifies the host
- ex: 222.222.0.0/24 means the every devices in the network has first 24 same to the host