Think about your home address. It probably has two main parts: the street name and the house number. The street name gets you to the right neighborhood, and the house number pinpoints your specific house on that street. Computers on the internet use a similar system called an IP address.

The most common version you'll see is IPv4. An IPv4 address is a 32-bit number, but to make it easier for humans to read, we write it as four numbers separated by dots. Each number is called an octet and can range from 0 to 255.

Just like a physical address, this string of numbers isn't random. It has a hidden structure that tells data where to go.

Every IP address is split into two parts: the network portion and the host portion. The network portion is like the street name, identifying the specific network a device is on. The host portion is like the house number, identifying the individual device on that network.

This division is crucial for efficient routing. When a router sends a packet of data, it doesn't need to know the location of every single computer in the world. It just needs to know how to get to the right network. Once the packet arrives at the destination network, the local system takes over to find the specific host.

But how does a computer know where the network portion ends and the host portion begins? That's where address classes and subnet masks come in.

Traditionally, IPv4 addresses were divided into classes, mainly A, B, and C. These classes used the first octet (the first number in the address) to define a default split between the network and host portions. This was a simple way to create networks of different sizes.