To hear some people talk about what may happen on Wednesday, you could get the impression that something horrible is on the way.

Y2K. The May 21 Rapture. IPv6 Day.

Lucky for us all, IPv6 Day will probably have about as much of a cataclysmic effect as the other two. Here’s what you need to know about IPv6 Day, how you’ll be affected and why you shouldn’t panic.

What is IPv6? IPv6 stands for Internet Protocol version 6, a new way of issuing the identifying numbers given computers and other devices online.

Right now, we use IPv4, which can issue up to 4.2 billion devices on the Internet. With the world’s population on the rise, and more people using several devices each, that’s just not enough. In fact, the last IPv4 addresses have already been handed out.

IPv6 allows for a different system of assigning addresses and creates more options for unique addresses. Way more — 340,282,366,920,938,463,463,374,607,431,770,000,000, or 340 undecillion.

The two systems can coexist, but they essentially run parallel to each other and can’t communicate. So if one person is using IPv6 and the other is using IPv4, they won’t, for example, be able to chat.

So what and when is IPv6 Day? IPv6 Day is a 24-hour test drive of IPv6, when major companies try the new protocol. This takes place Wednesday, June 8.

Who’s participating? Google, Facebook, Yahoo!, Akamai and Limelight Networks are major players in IPv6 Day in the United States, as are the State, Commerce and Veterans Affairs departments.

Why are they doing this? These companies are flipping the switch on IPv6 to encourage other Web sites to start prepping for the change before we exhaust all the IPv4 addresses.

Will it keep me from accessing my favorite sites? In theory, no. It shouldn’t be a problem. IPv6 will be running alongside IPv4, so the day will be a total success if nobody notices anything different.

What could go wrong? There’s a chance that your computer or other device will have problems accessing sites that are running both IPv6 and IPv4 at the same time.

There are also other potential problems resulting from errors with your settings. But fixes can be found for many of them at the American Registry for Internet Numbers’ wiki on the subject.

How can I test my computer? Head to this “eye test” to see whether your computer is able to access sites running both protocols within 10 seconds.

Related story:

IPv4 addresses running out. Don't panic.