Class A, B, and C are IPv4 address categories used to define network size and host capacity, with Class A for large networks, Class B for medium, and Class C for small networks.

Overview of Classes

Class A

• Range: 1.0.0.0 to 126.255.255.255
• Default Subnet Mask: 255.0.0.0 (/8)
• Network vs Host: The first octet identifies the network, and the remaining three octets identify hosts.
• Host Capacity: Approximately 16,777,214 hosts per network
• Typical Use: Large organizations, ISPs, and major corporations like Google or Apple Class B
• Range: 128.0.0.0 to 191.255.255.255
• Default Subnet Mask: 255.255.0.0 (/16)
• Network vs Host: The first two octets identify the network, and the last two octets identify hosts.
• Host Capacity: Up to 65,534 hosts per network
• Typical Use: Medium to large networks, such as universities and medium-sized businesses Class C
• Range: 192.0.0.0 to 223.255.255.255
• Default Subnet Mask: 255.255.255.0 (/24)
• Network vs Host: The first three octets identify the network, and the last octet identifies hosts.
• Host Capacity: Up to 254 hosts per network
• Typical Use: Small businesses, home networks, and local area networks (LANs),

Key Points

• Identification: The class of an IP address is determined by the first few bits of the first octet: Class A starts with 0, Class B with 10, and Class C with 110 .
• Historical Context: These classes were part of the original classful addressing system (1981–1993) to simplify network allocation .
• Modern Usage: Today, classful addressing is largely replaced by CIDR (Classless Inter-Domain Routing), which allows more flexible subnetting and efficient IP allocation, but understanding classes is still useful for legacy systems, private networks, and networking certifications . Understanding these classes helps in designing networks, calculating host capacities, and interpreting older network documentation.