IPv4 addresses are categorized into five classes (A, B, C, D, and E) to manage and organize the internet's addressing scheme. Each class defines a range of IP addresses and dictates the number of networks and hosts possible within that range. This class-based system, while largely superseded by Classless Inter-Domain Routing (CIDR), remains a foundational concept in understanding IP addressing.
The Five IPv4 Address Classes
The class of an IPv4 address is determined by the first few bits of the address. This system, while now largely obsolete, provides a historical context for modern IP addressing.
- Class A: Addresses starting with
0(0.0.0.0 to 127.255.255.255). Designed for large networks, with a single network address and up to 16,777,214 host addresses. Only a small number of Class A networks are actually available. - Class B: Addresses starting with
10(128.0.0.0 to 191.255.255.255). Suitable for medium-sized networks, offering up to 65,534 host addresses per network. - Class C: Addresses starting with
110(192.0.0.0 to 223.255.255.255). Ideal for smaller networks, allowing for up to 254 host addresses per network. Most commonly used in the past. - Class D: Addresses starting with
1110(224.0.0.0 to 239.255.255.255). Reserved for multicast addressing, allowing one-to-many communication. - Class E: Addresses starting with
11110(240.0.0.0 to 255.255.255.255). Reserved for experimental purposes and future use.
The original classful networking system had limitations, leading to the development of CIDR for more efficient IP address allocation. However, understanding the historical context of IPv4 classes is still relevant for networking professionals.
Example:
192.168.1.1 falls within the Class C range, indicating it's likely assigned to a smaller network.
