IPv4 Address Notation Explained
IPv4 addressing is one of those concepts that looks simple at first but becomes much clearer once you slow down and see how it’s actually structured. Every device connected to a network needs an identity. That identity comes in the form of an IP address. In IPv4, this address is 32 bits long, which means there are about 4.3 billion possible unique addresses. That sounds like a lot, but with billions of devices today, you can already see why address management became a big issue.
Writing 32 bits in binary is not practical for humans. So IPv4 uses dotted decimal notation. It splits the 32 bits into four equal parts, each of 8 bits. These parts are called octets. Each octet is converted into a decimal number between 0 and 255. That’s how you get an address like 202.70.91.200. If you look at just one part, like 202, its binary form is 11001010. This conversion makes addresses easier to read, write, and remember.
Every interface on a device must have a unique IP address when it is part of the global Internet. This is important. If two devices share the same public IP, the network cannot correctly decide where to send data. That’s why uniqueness is a core rule in IP addressing.
Now, not all communication works the same way. IPv4 supports different types of addressing based on how data is sent. In unicast, one device sends data to one specific device. This is the most common type, like when you open a website. In broadcast, one device sends data to all devices within a network. This is useful for discovery or announcements. Then there is multicast, where one device sends data to a group of selected devices. This is often used in streaming or group communication.
Another key idea is how the 32 bits are divided. An IPv4 address has two parts. One part identifies the network, and the other identifies the host within that network. This division helps routers understand where a device belongs and how to route data efficiently.
To manage this structure, IPv4 originally used a class based system. In Class A, the first 8 bits represent the network, and the remaining 24 bits are used for hosts. This means you get very few networks but a huge number of devices in each network. The address range for Class A goes from 0 to 127, and its default subnet mask is 255.0.0.0.
Class B takes a more balanced approach. It uses 16 bits for the network and 16 bits for hosts. This creates a moderate number of networks and devices. The range here is from 128 to 191, with a default subnet mask of 255.255.0.0.
Class C is designed for smaller networks. It uses 24 bits for the network and only 8 bits for hosts. That means you can have many networks, but each network supports fewer devices. The range for Class C is from 192 to 223, and the default subnet mask is 255.255.255.0.
Then you have Class D and Class E, which are a bit different. Class D addresses, ranging from 224 to 239, are used for multicast communication. These addresses are not assigned to individual devices but to groups. For example, a multicast address can be used to send data to multiple receivers at once. Class E, which ranges from 240 to 255, is reserved for future use and is not used in normal networking today.
Now let’s talk about something you see in real networks every day. Public and private IP addresses. Public IP addresses are globally unique and accessible over the Internet. If a server has a public IP, anyone can reach it from anywhere, as long as access is allowed.
Private IP addresses, on the other hand, are used inside local networks like homes, offices, or campuses. These addresses are not visible on the global Internet. They help conserve public IP space. When devices with private IPs need to access the Internet, a router translates their addresses using a method called Network Address Translation.
When you step back and look at all of this, IPv4 addressing is really about structure and organization. It gives every device an identity, divides networks into manageable parts, and supports different types of communication. Even though IPv6 is slowly taking over, IPv4 is still widely used, and understanding it gives you a strong foundation in networking.