Students stand outside a building to find an Internet signal for their phones in Havana last year. (AP Photo/Ramon Espinosa, File)

It's finally happened. The North American organization responsible for handing out new IP addresses says its banks have run dry.

That's right: ARIN, the American Registry for Internet Numbers, has had to turn down a request for the unique numbers that we assign to each and every smartphone, tablet and PC so they can talk to the Internet. For the first time, ARIN didn't have enough IP addresses left in its stock to satisfy an entire order — and now, it's activated the end-times protocol that will see the few remaining addresses out into the night.

IP addresses are crucial to the operation of the Internet. They're the numbers behind URLs like "google.com" or "facebook.com." They identify every device that connects to the Web, from servers to connected cars. The original designers of the Internet thought they'd only need around 4 billion unique combinations, derived from the series of dots and digits that make up IP addresses everywhere.

How wrong they were.

By 2020, humanity will be living alongside 25 billion Internet-connected devices, according to Gartner researchers. The rising global demand for Web-enabled devices is far outstripping the original system's ability to keep up. Left, uh, unaddressed, this problem would have put a stranglehold on the Web, keeping it from growing. It would've kept you from using new devices like smartwatches or smart refrigerators. Entirely new technologies we haven't dreamt of might never have emerged. We'd have been stuck with the Internet that we now have, forever.

If you haven't already guessed, we have a backup system in place so that Xboxes and Playstations of the future can continue to get online. Internet engineers have actually been anticipating this day for decades. To understand how they've solved it, let's let one of the original designers of the Internet explain:

The solution is known as IPv6, short for "version 6." It's an upgrade of the old IP numbering system, known as IPv4. While it won't replace the old system, it's considered the future of the Internet. It has to be, by necessity. At ARIN, large requests for IPv4 addresses will now be subject to rationing or waitlisting.

"The number of days remaining before depletion are dwindling," wrote Richard Jimmerson, ARIN's chief information officer, in a blog post Thursday. "It is very likely that we are already processing a request that we will be unable to fulfill."

Some companies, such as Google, flipped the switch on IPv6 in 2012, and the number of devices, Web sites and Internet providers supporting IPv6 has been growing.

Not every company has made the jump yet — it takes more elbow grease and money than not doing anything at all. But the switch is inevitable. We've already passed the point where Internet-connected devices outnumber people, and the original system is at its breaking point.

Luckily, IPv6 offers 340 trillion trillion trillion possible unique combinations. Hopefully this will last us a while.