Classful addressing refers to the original method of IP address allocation in IPv4, which divided the available IP address space into five classes: Class A, Class B, Class C, Class D, and Class E.
Each class had a predefined range of network and host addresses, providing a structure for addressing and routing.
Different classes in classful addressing:
1. Class A:
- Range: 1.0.0.0 to 126.0.0.0
- Network ID: The first octet represents the network ID, and the remaining three octets represent the host ID.
- Hosts per network: Can have up to 16,777,214 hosts per network.
- Example: 10.0.0.0 is a Class A network address.
2. Class B:
- Range: 128.0.0.0 to 191.255.0.0
- Network ID: The first two octets represent the network ID, and the remaining two octets represent the host ID.
- Hosts per network: Can have up to 65,534 hosts per network.
- Example: 172.16.0.0 is a Class B network address.
3. Class C:
- Range: 192.0.0.0 to 223.255.255.0
- Network ID: The first three octets represent the network ID, and the last octet represents the host ID.
- Hosts per network: Can have up to 254 hosts per network.
- Example: 192.168.0.0 is a Class C network address.
4. Class D:
- Range: 224.0.0.0 to 239.255.255.255
- Purpose: Reserved for multicast addresses used for multicasting applications and services.
- Notation: Starts with the leading bit pattern ‘1110’ in the first octet.
5. Class E:
- Range: 240.0.0.0 to 255.255.255.255
- Purpose: Reserved for experimental or future use.
- Notation: Starts with the leading bit pattern ‘1111’ in the first octet.
Class | Range (First Octet) | Network ID | Host ID | Number of Networks | Number of Hosts per Network |
Class A | 1.0.0.0 to 126.0.0.0 | First Octet | Last Three Octets | 126 | 16,777,214 |
Class B | 128.0.0.0 to 191.255.0.0 | First Two Octets | Last Two Octets | 16,384 | 65,534 |
Class C | 192.0.0.0 to 223.255.255.0 | First Three Octets | Last Octet | 2,097,152 | 254 |
Class D | 224.0.0.0 to 239.255.255.255 | N/A | N/A | N/A | N/A |
Class E | 240.0.0.0 to 255.255.255.255 | N/A | N/A | N/A | N/A |