IP Addresses: How Every Device on Earth Gets a Number
“Right now, your device has an address. Not a street address — a number. Every single device connected to the internet has one, and without it no data could find its way to you. There are only 4.3 billion possible addresses. We ran out.”
When you send a letter, you write an address on the envelope: a name, a street, a city, a country. The postal system uses that address to route the letter from you to the recipient.
The internet does exactly the same thing — except instead of street addresses, every device has a number. That number is its IP address.
When your browser asks for a web page, it sends a request labelled with the destination's IP address (and your device's IP address as the return address). Routers read that label and pass the packet to the next router closer to the destination, until it arrives.
Without IP addresses, data would have no way to find anything.
The Format: Four Numbers
An IPv4 address looks like this: 192.168.1.1
Four numbers, separated by dots. Each number is between 0 and 255. Why 0–255? Because each number is one byte — 8 bits of binary — and 8 bits can hold 2⁸ = 256 values (0 through 255).
So 192.168.1.1 in binary is:
11000000 . 10101000 . 00000001 . 00000001
192 168 1 1
Thirty-two bits in total. The dot notation (called "dotted decimal") is just a human-friendly way to read what is fundamentally a single 32-bit number.
The IP Explorer above lets you see this directly — change any octet with the slider and watch the binary update underneath it.
The Address Space Problem
Thirty-two bits means 2³² possible IPv4 addresses: 4,294,967,296. About 4.3 billion.
When IPv4 was designed in 1981, 4.3 billion seemed impossibly large. The internet had hundreds of computers. Nobody imagined a world with billions of people each carrying multiple connected devices.
By 2011, the Internet Assigned Numbers Authority ran out of new IPv4 addresses to hand out. The internet had officially outgrown its address space.
It didn't collapse because of a clever patch: NAT (Network Address Translation). Your home router has one public IP address — say, 203.45.67.89 — and uses it to represent every device in your house. Your laptop, your phone, your TV, your games console all share that one address. The router tracks which response belongs to which device and forwards traffic accordingly.
NAT stretched IPv4 past its limit. But it's a workaround, not a solution.
IPv6: The Fix
IPv6 uses 128 bits instead of 32. That's not twice as many addresses — it's 2⁹⁶ times as many:
2¹²⁸ = 340,282,366,920,938,463,463,374,607,431,768,211,456
About 340 undecillion. There are estimated to be 10¹⁸ to 10²² grains of sand on Earth. IPv6 has enough addresses for every grain to have trillions of its own.
IPv6 addresses look different: 2001:0db8:85a3::8a2e:0370:7334. Eight groups of four hexadecimal digits, separated by colons. The :: is shorthand for a run of zeroes.
IPv6 adoption has been slow — existing equipment, software, and habits built around IPv4 don't disappear overnight. As of 2025, roughly 40–45% of global internet traffic uses IPv6. The transition is ongoing.
Private and Public Addresses
Not all IP addresses are visible on the public internet. Three ranges are reserved for private networks:
10.0.0.0–10.255.255.255172.16.0.0–172.31.255.255192.168.0.0–192.168.255.255
These addresses can be reused by any network — your home uses 192.168.x.x, your office uses 192.168.x.x, a coffee shop uses 192.168.x.x. They're invisible to the public internet, so there's no collision.
Your home network almost certainly uses one of these ranges. The address 192.168.1.1 is so commonly used as the default router address that millions of homes worldwide have the same internal IP structure — and none of them conflict, because none of them are visible outside their own router.
One special address: 127.0.0.1, called localhost. It's the loopback address — it always means "this device itself." Web developers use it constantly: http://localhost:3000 connects your browser to a server running on your own machine, never touching the internet.
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IPv6 has been 'coming' for 25 years but adoption is still only around 40–45% globally. What makes switching from IPv4 to IPv6 so difficult? Consider: existing equipment, software compatibility, cost, the fact that NAT mostly 'solved' the address problem in the short term, and who bears the cost of switching versus who gets the benefit. What would it take to finish the transition?
Reflect
Every device you own has at least one IP address. Your laptop, your phone, your smart TV, your router — all of them have private IPs on your home network, and all of them share your household's single public IP address with the world. When you're browsing from your phone, your router is secretly translating millions of conversations, keeping track of which response goes back to which device. This happens invisibly, billions of times per day, worldwide. How would the internet be different if every device had always had a unique public address — no NAT, no private networks?