Every device connected to a network, from your laptop to your smart fridge, needs a unique identifier to send and receive information. This identifier is called an Internet Protocol (IP) address. Think of it as a mailing address for your device in the digital world.

The most common version you'll see is IPv4 (IP version 4). An IPv4 address is a 32-bit number, but to make it easier for humans to read, it's written as four numbers separated by dots. This is called dotted-decimal notation.

Each of the four numbers in an IPv4 address is called an octet, because it represents eight bits of the full 32-bit address. Since eight bits can represent 256 different values, each octet can be a number from 0 to 255.

Let's look at a typical IP address: 192.168.1.10. In binary, it looks much more complex.

An IP address isn't just one long, random number. It's split into two distinct parts: the network portion and the host portion.

• Network Portion: This identifies the specific network the device is on. It's like the street name and zip code of a physical address.
• Host Portion: This identifies the individual device on that network. It's like the house number.

This division is critical for routing. When a data packet is sent across the internet, routers only need to read the network portion to get it to the correct neighborhood. Once it arrives at the local network, the host portion is used to deliver it to the specific device.

How does a computer know where the network portion ends and the host portion begins? It can't tell just by looking at the IP address. It needs a helper called a subnet mask.

A subnet mask looks just like an IP address (e.g., 255.255.255.0), but its job is to act like a filter. It tells the device which bits of the IP address belong to the network and which belong to the host.

For example, the common subnet mask 255.255.255.0 is 11111111.11111111.11111111.00000000 in binary. The first 24 bits are 1s, and the last 8 bits are 0s. This tells a device that for any IP address it's paired with, the first three octets are the network address and the last octet is the host address.

By applying the subnet mask, the device can instantly determine that its network is 192.168.1 and its unique identifier on that network is 10. This simple mechanism is the foundation of how data gets routed correctly across billions of devices.