What is an IP class?

In today’s digital world, every device connected to the internet needs a unique identifier to communicate effectively. This identifier is known as an IP (Internet Protocol) address. But not all IP addresses are the same—they are categorized into different IP classes to efficiently manage and distribute them across networks.

If you’ve ever wondered how networks are organized or why some IP addresses look different from others, this guide will explain what an IP class is, the different types, and how they work in simple terms.

What is an IP Address?

Before diving into IP classes, let’s briefly understand what an IP address is.

An IP address is a unique numerical label assigned to each device (like computers, smartphones, or routers) connected to a network. It serves two main purposes:

1. Identifying the host or device on a network.

2. Providing the location of the device in the network (like a digital mailing address).

IP addresses come in two versions:

• IPv4 (Internet Protocol version 4) – The most common format, written as four numbers separated by dots (e.g., 192.168.1.1).

• IPv6 (Internet Protocol version 6) – A newer format designed to accommodate more devices, written in hexadecimal (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334).

Since IPv4 is still widely used, IP classes are primarily based on this version.

What is an IP Class?

An IP class is a way to categorize IPv4 addresses into different groups based on their first few bits (the binary digits). These classes help in efficiently allocating IP addresses to networks of varying sizes—small, medium, or large.

Originally, IPv4 addresses were divided into five classes:

1. Class A

2. Class B

3. Class C

4. Class D

5. Class E

Each class has a different range of IP addresses and is used for specific purposes.

The Five IP Classes Explained

1. Class A (Large Networks)

• Range: 1.0.0.1 to 126.255.255.254

• First Octet (First 8 Bits): Starts with 0 (binary: 0xxxxxxx)

• Network vs. Host:

  • First octet = Network ID

  • Last three octets = Host ID

• Total Networks: 126 (since 0.0.0.0 and 127.0.0.0 are reserved)

• Hosts per Network: ~16.7 million

Use Case: Large organizations (e.g., governments, multinational companies).

Example: 10.2.1.45 (Private IP range for Class A).

2. Class B (Medium-Sized Networks)

• Range: 128.0.0.1 to 191.255.255.254

• First Octet: Starts with 10 (binary: 10xxxxxx)

• Network vs. Host:

  • First two octets = Network ID

  • Last two octets = Host ID

• Total Networks: 16,384

• Hosts per Network: 65,534

Use Case: Universities, mid-sized businesses.

Example: 172.16.0.1 (Private IP range for Class B).

3. Class C (Small Networks)

• Range: 192.0.0.1 to 223.255.255.254

• First Octet: Starts with 110 (binary: 110xxxxx)

• Network vs. Host:

  • First three octets = Network ID

  • Last octet = Host ID

• Total Networks: ~2 million

• Hosts per Network: 254

Use Case: Small businesses, home networks.

Example: 192.168.1.1 (Commonly used in home routers).

4. Class D (Multicasting)

• Range: 224.0.0.0 to 239.255.255.255

• First Octet: Starts with 1110 (binary: 1110xxxx)

• Purpose: Reserved for multicast groups (sending data to multiple devices simultaneously).

• Not used for individual devices.

Example: Video streaming, online gaming broadcasts.

5. Class E (Experimental/Reserved)

• Range: 240.0.0.0 to 255.255.255.254

• First Octet: Starts with 1111 (binary: 1111xxxx)

• Purpose: Reserved for experimental and future use.

• Not used in public networks.

Why Were IP Classes Introduced?

When the internet was in its early stages, IP classes helped in:

• Efficient allocation of IP addresses based on network size.

• Reducing wastage by assigning larger blocks to big organizations and smaller blocks to homes.

• Simplifying routing by making it easier for routers to identify network portions.

However, as the internet grew, this system led to IP address shortages because many addresses were unused. This led to the development of Classless Inter-Domain Routing (CIDR) in the 1990s, which replaced the class-based system with a more flexible approach.

Are IP Classes Still Used Today?

While the concept of IP classes is still taught for foundational knowledge, modern networks mostly use CIDR (Classless Inter-Domain Routing). CIDR allows for:

• More flexible subnetting (dividing networks into smaller parts).

• Efficient IP allocation without strict class boundaries.

• Better use of available addresses (reducing waste).

However, some private networks (like home Wi-Fi) still follow the traditional Class A, B, or C ranges for internal use.

Private vs. Public IP Addresses

Not all IP addresses are publicly accessible. Some are reserved for private networks:

These addresses are not routable on the public internet, meaning they are used internally within a local network (LAN).

How to Identify an IP Class?

You can determine an IP’s class by looking at its first octet:

Example:

• 15.23.45.67 → First octet is 15 → Class A

• 172.16.0.1 → First octet is 172 → Class B

• 192.168.1.1 → First octet is 192 → Class C

Conclusion

IP classes were an essential part of early internet architecture, helping organize and distribute IP addresses efficiently. While modern networks now rely on CIDR for better flexibility, understanding IP classes remains valuable for networking basics.