Understanding IPv4 Address Classes

What is an IPv4 Address?

IPv4, or Internet Protocol version 4, is the fourth version of the Internet Protocol and forms the backbone of the global internet. IPv4 uses 32-bit addresses, allowing for a vast but finite number of unique addresses. However, with the rapid expansion of the digital world, the original address scheme has shown its limitations. This has led to the development of new addressing schemes, such as IPv6, and enhanced management techniques like CIDR (Classless Inter-Domain Routing).

The Different Classes of IPv4

IPv4 addresses are categorized into five classes based on their leading bits and intended use. Each class has a specific range, default subnet mask, and intended network size. Understanding these classes is crucial for network design, management, and troubleshooting.

Class A

Range: 0.0.0.0 to 127.255.255.255

Leading Bits: 0

Default Subnet Mask: 255.0.0.0 /8

Usage: Designed for large networks and supports a large number of hosts over 16 million per network. This class is rarely seen in modern networks due to the availability of IPv6, but it is still relevant for understanding the classification system.

Class B

Range: 128.0.0.0 to 191.255.255.255

Leading Bits: 10

Default Subnet Mask: 255.255.0.0 /16

Usage: Suitable for medium-sized networks supporting up to 65000 hosts per network. This class is still widely used in many organizations and networks.

Class C

Range: 192.0.0.0 to 223.255.255.255

Leading Bits: 110

Default Subnet Mask: 255.255.255.0 /24

Usage: Intended for small networks, it supports up to 254 hosts per network. Class C addresses are the most common for personal home networks and small businesses.

Class D

Range: 224.0.0.0 to 239.255.255.255

Usage: Reserved for multicast groups, not for standard host addressing. Multicasting allows data to be sent to a group of hosts rather than a single host.

Class E

Range: 240.0.0.0 to 255.255.255.255

Usage: Reserved for experimental purposes and future use. These addresses are not typically assigned to hosts.

Special Address Ranges:

Private Addresses

Class A: 10.0.0.0 to 10.255.255.255 Class B: 172.16.0.0 to 172.31.255.255 Class C: 192.168.0.0 to 192.168.255.255

These addresses are not routable on the Internet and are used for addressing within a private network.

Loopback Address

127.0.0.1 is used for testing and local communication.

Link-Local Addresses

169.254.0.0 to 169.254.255.255 are used for automatic IP assignment in local networks when DHCP fails or is not available.

Legacy and Modern Address Management:

Classes of IPv4 were formulated in 1981 but by 1993, they were becoming obsolete due to the increasing demands for allocating addresses to different groups and types of users. These classes are now largely replaced by CIDR, which allows for more flexible and efficient management of IPv4 addresses.

For more detailed information on CIDR, check out the Classless Inter-Domain Routing articles available on Wikipedia.