Internet Protocol version 4 (also known as IPv4) is the original system for assigning addresses to devices on the internet. It uses a 32-bit number to identify each device, providing about 4.3 billion unique addresses worldwide, which we've surprisingly run out of as of 2025..
Did You Know?
- IPv4 is the fourth version of the Internet Protocol, used to identify devices on a network using numeric addresses.
- An IPv4 address is usually written as four numbers separated by dots which means there are 4,294,967,296 possible addresses.
- The last free IPv4 addresses were handed out in 2011 - there are no more unique combinations.
But what exactly do IPv4 addresses do, how did they become scarce, and how are we still keeping the internet running despite the limitations of IPv4?
What Is IPv4?
IPv4 stands for Internet Protocol version 4, a system that allows computers to find and communicate with each other over networks. Every device on the internet needs an IP address to send or receive data, and IPv4 provides that addressing system using 32-bit numbers.
In practice, an IPv4 address is usually written as four numbers separated by periods like this: 123.4.567.8. Each of those four numbers (called octets) can range from 0 to 255, which is what gives IPv4 its roughly four-billion-address capacity.
IPv4 was introduced in the early 1980s and became widely used when the US Department of Defense adopted TCP/IP as the standard for ARPANET in 1983. It's the reason you can load websites, send emails, or stream videos.
How IPv4 Addresses Work
The same way a postal address has both a general part and specific part to refer to the city and house number respectively, an IPv4 address is divided into a network part and host part.
The network part tells routers which group of addresses a device belongs to, and the host part identifies the individual device on that network, which allows routers to direct traffic across the internet.
Originally, IPv4 addresses were grouped into classes based on how the network vs. host division was set, but that system was later replaced with a more flexible method called CIDR (Classless Inter-Domain Routing).
When you connect to the internet, your Internet Service Provider (ISP) assigns your router a public IPv4 address while the Domain Name System (DNS) works like a phonebook to map human-friendly names to IP addresses. For example, when you visit example.com, your computer uses DNS to find that website's IPv4 address, then connects to it. We usually don't see these numbers, but they're always working behind the scenes.
Why Did IPv4 Run Out of Addresses?
If 4.3 billion addresses sounds like a lot, that's because it is a lot. When IPv4 was designed, nobody imagined the world would ever connect so many devices. (One of the creators of the protocol, Vint Cerf, said he honestly believed 32 bits would be enough addresses for the experiment that was the early internet.) However, a few decades later, the internet exploded in size, personal computers became common, and now everything from refrigerators to light bulbs can connect online. In 2008, the number of devices online actually surpassed the number of people on the planet and each of those devices needs an IP address.
By the mid-1990s, it was clear that IPv4's address space was getting tight and the internet engineering community took steps to stretch those addresses as much as possible by introducing Classless Inter-Domain Routing (CIDR) to allocate addresses more efficiently.
Eventually, the inevitable happened and the free pool of IPv4 addresses ran out in early 2011. Thankfully engineers knew years in advance this day would come, which is why they had already developed a successor protocol, IPv6, as a long-term fix.
How IPv4 Is Used Today
Even though no new IPv4 addresses are left to allocate, billions of devices still use IPv4 daily thanks to clever workarounds that make the most of each address like Network Address Translation (NAT).
NAT allows multiple devices to share a single public IPv4 address so when you connect a laptop, a phone, and a smart TV to the same Wi-Fi router, they might each get a private IPv4 address but your router then acts as an intermediary since it has the one public IPv4 address from your ISP. To external websites, it looks like all your home devices are coming from one IP which conserves the limited pool of IPv4 addresses.
Another workaround for IPv4 limitations is the use of proxy servers, which are essentially an intermediary that you can route your traffic through. When you use one, the proxy's IP address is what the outside world sees.
This can be useful if you need additional IPv4 addresses for specific tasks like managing multiple social media accounts from the same device. Services like Proxies.com specialize in providing these proxy IP addresses, offering IPv4 proxies that let you choose from a pool of real IPv4 addresses to channel your traffic. Using such a service, you could appear to be browsing from New York, then switch to an IP from London moments later, all while keeping your own connection details hidden.
IPv4 vs IPv6
Where IPv4 uses 32-bit addresses, IPv6 uses 128-bit addresses, which expands the address space to about 3.4×10³⁸ addresses, a number so huge it's virtually impossible to run out. IPv6 addresses look different, too: they're written in hexadecimal and separated by colons.
So why didn't we switch to IPv6 years ago? The fact is, it's tricky to change over an entire planet's internet infrastructure. It's taking place, but it's just taking a bit of time and many networks run in dual-stack mode, meaning they handle both IPv4 and IPv6.
As of 2025 roughly half of Internet traffic by users worldwide is over IPv6, and the percentage is only climbing but that still means a huge portion of traffic relies on IPv4.
The Future of IPv4
It's amazing to think that a system devised in the 1970s is still running a huge portion of our ultra-modern internet. IPv4 has proven to be resilient and versatile, thanks in part to stopgaps like NAT. However, the strain is showing: new internet services and ISPs often struggle to get IPv4 addresses, and there's now an active marketplace for buying and selling IPv4 address blocks because they've become a scarce commodity.
In the coming years, we can expect IPv6 adoption to continue rising, alleviating the pressure on IPv4. Some networks have even started operating IPv6-only in certain environments. But for most of us, IPv4 will remain a part of daily life for the foreseeable future. There are countless legacy systems and devices that might never be upgraded, and they will need IPv4 to stay supported. The good news is that as users, we don't have to choose one or the other; our devices and browsers will use whichever protocol works, so connectivity isn't interrupted.
IPv4 is the fundamental technology that made the internet we know possible. It has a limited supply by design, and we finally pushed those limits. Yet, through ingenuity (and a bit of improvisation), the world has kept IPv4 going strong well beyond its original scope. While IPv6 is gradually taking the baton, IPv4 isn't disappearing any time soon. Knowing about IPv4 (what it is and how it works) remains very relevant, because it helps us appreciate the networks we use every day and understand why the internet got to where it is today.
