In 2014, the Internet came to a shuddering halt because the hardware used in switching packets around the wired networks which connect it all together had no memory left to hold the secret decoder ring it used to handle where those packets were supposed to end up.
Industry players like Microsoft, eBay, LastPass, BT, LiquidWeb, Comcast, AT&T, Sprint, and Verizon all had major hissy-fits.
At that time, the routers normally used could only hold 512K of the global BGP routing table. This is what describes the IPv4 addresses of all the known Internet-connected networks.
Well, after everything came crashing down there were emergency patches made along with the yelling and screaming. They increased the address space to 768,000 routes.
Guess what? The Internet is going to hit that number sometime this month.
A Twitter bot named BGP4-Table has been watching the actual number.
As of April 22, 2019 it says "I see 768132 IPv4 prefixes. This is 336 more prefixes than 6 hours ago and 1012 more than a week ago. 57.36% of prefixes are /24. There are 64255 unique originating ASNs. 47612 of these ASNs originate IPv4 only."
If we aren't there, it's a really thin slice away.
But we may not see the rampant outages that occurred last time this happened.
First, sysadmins have known it is coming and proactively changed their equipment.
Secondly, some systems will just pass upstream the addresses they can't handle, like 24-bit prefix routes.
But there are still a lot of older and smaller networks that use Cisco 6509 SUP-720 gear, which are the kind that died in 2014 and would be expected to pull the same stunt this time around. These legacy networks may not escape unscathed.
So, if everything stops working for you real soon consider the network that you are attached to. One element of it may be crippled, and it won't be fixed until firmware gets re-flashed.
— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.