In IPv4, IP addresses used to be categorized by classes, which were defined based on their subnet masks.
Classes A, B, and C are often referenced in conversations despite being obsolete since 1993.
These classes serve as a starting point for subnetting in networking.
IP Address Classes
Class A
Network Bits: 8 bits
Host Bits: 24 bits
Default Subnet Mask: 255.0.0.0
Range: First octet 0-127
Binary Indicator: First bit is 0
Class B
Network Bits: 16 bits
Host Bits: 16 bits
Default Subnet Mask: 255.255.0.0
Range: First octet 128-191
Binary Indicator: First two bits are 10
Class C
Network Bits: 24 bits
Host Bits: 8 bits
Default Subnet Mask: 255.255.255.0
Range: First octet 192-223
Binary Indicator: First three bits are 110
Class D
Used for multicast communication.
Range: First octet 224-239
Binary Indicator: First four bits are 1110
Class E
Reserved for experimental purposes.
Range: First octet 240-255
Binary Indicator: First four bits are 1111
Example IP Classifications
17.229.07: Class A
220.10.77.40: Class C
165.24.1: Class B
128.190.10.2: Class B
191.77.242.50: Class B
192.11.12.5: Class C
Subnetting Key Concepts
Important Values for Subnetting
Network Address: Set all host bits to 0.
First Usable Host Address: One higher than the network address.
Network Broadcast Address: Set all host bits to 1.
Last Usable Host Address: One less than the network broadcast address.
Example Calculations
IP Address: 10.74.22.11
Class: A
Network Address: 10.0.0.0
First Host Address: 10.0.0.1
Broadcast Address: 10.255.255.255
Last Usable Address: 10.255.255.254
IP Address: 172.16.188.200
Class: B
Network Address: 172.16.0.0
First Host Address: 172.16.0.1
Broadcast Address: 172.16.255.255
Last Usable Address: 172.16.255.254
IP Address: 192.168.4.91
Class: C
Network Address: 192.168.4.0
First Host Address: 192.168.4.1
Broadcast Address: 192.168.4.255
Last Usable Address: 192.168.4.254
Conclusion
The class-based system provides a foundational understanding for subnetting.
The process of calculating network addresses, broadcast addresses, and usable host addresses is consistent across class-based and modern subnetting practices.