Classful network
lastmod 2022-11-10created 2020-07-225 edits
Network classes represent the first structural change of IP addresses in IPv4.
Classes
As a result, the definition of the IP address changed, and three network fields of different sizes were defined as in the following table. (in bits)
| Class | Leading bits | Network field | Rest field |
| Class A | 0 | 8 | 24 |
| Class B | 10 | 16 | 16 |
| Class C | 110 | 24 | 8 |
| Class D (Multicast) | 1110 | ||
| Class E (reserved) | 1111 |
This allows the following number of networks and addresses per class. Note, however, that the actual numbers are smaller than expected, because some values, such as values consisting only of 0s, are not allowed.
| Class | Leading bits | Total number of networks | Addresses per network |
| Class A | 0 | 128 | 16,777,214 |
| Class B | 10 | 16,384 | 65,534 |
| Class C | 110 | 2,097,152 | 254 |
See also
- Internet Protocol
- Private network
- Classless Inter-Domain Routing (pronounced "cider"; CIDR)
- ipcalc - IP calculator. Calculates host ranges, netmasks, etc.