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Posted at 7:00 AM ET, 02/ 8/2011

IPv4 addresses running out. Don't panic.

By Rob Pegoraro

The Internet's numbers are almost up. But that's okay; we can make new ones.

That's the short version of an issue that goes by the technical name of "IPv4 exhaustion". The current, fourth version of Internet Protocol addressing--the numerical identifiers that make each device on the Internet visible to every other device online--only supports 4,294,967,296 distinct addresses.

Four billion-plus devices on the Internet might have seemed like plenty decades ago, but we are now reaching that limit. On Feb. 3, the Internet Corporation for Assigned Names and Numbers handed out the last available blocks of IPv4 addresses to regional authorities that will then distribute them to businesses, governments, schools and Internet providers.

If nothing happens after that, we'll have trouble.

Let me provide a simplified example (one that will, perhaps, improve this post's visibility to search engines): Suppose Lady Gaga and Katy Perry both want to go online to read my blog. Gaga switches on her iPad 2 and Perry does the same with her white iPhone 5.
But Verizon doesn't have two IPv4 addresses to assign to those two devices; Perry's got left out and can't go anywhere online, even though it's showing five bars of a 4G signal.

Adding more domain names--something that Post reporter Ian Shapira wrote about on Monday--won't help them. Every dot-com or any other Internet address needs to have an IP address underneath it to work. (You can look up your own computer's at sites such as

Upgrading to IPv6 addressing is a rough equivalent of going from numbers-only license plates to ones that allow any combination of numbers and letters.

As ICANN's Q&A explains, while IPv4 addresses could only be built by stringing numbers together in groups of four (for example,, IPv6 addresses include eight groups of both numbers and the first six letters of the alphabet (as in, 2001:0db8:85a3:0000:0000:8a2e:0370:7334).

So instead of some four billion addresses, IPv6 permits roughly 340 undecillion--to be exact, 340,282,366,920,938,463,463,374,607,431,770,000,000.

But you can't just slap an IPv6 address on a Web server or a smartphone and be done with it. An IPv4 device can't see an IPv6 site without help and vice versa, and the translation services needed to link the two impede time-sensitive services like Internet calling. (To resume my contrived example, were Gaga to get an IPv6 address while Perry was stuck with an IPv4 address, both could read this blog but could not then discuss it in a FaceTime video call.)

Internet sites and services will need to make that transition first, said John Curran, chief executive for the American Registry for Internet Numbers, in an interview on Feb. 3. Most Internet users will have "nothing, absolutely nothing" to do, but operators of Web sites will need to make sure their sites are reachable via IPv6 once even a few customers start showing up with IPv6 addresses.

But Curran also suggested that most Internet providers in the U.S. would be able to hand out both IPv4 and IPv6 addresses to their users for years to come, instead of limiting new customers to IPv6 only.

None of this, he emphasized, should necessarily require extra work by individual users. For example, Web sites will have the same domain names as today (see Google's explanation of what it's doing with its sites).

But Internet providers may be in for some pain as they deal with all the IPv6-incompatible software and hardware employed by their users.

Comcast, for example, began testing IPv6 among home users last year to check for these issues. It will usually need to issue new routers to customers, said Jason Livingood, executive director of Internet systems engineering, and some operating systems can't handle IPv6, either.

But the company's stash of IPv4 addresses gives it time to figure this out, he said, adding, "We do not anticipate any addressing issues for the foreseeable future."

Verizon has begun testing IPv6 with businesses but has yet to get into this with home users. "It's a bit early to provide a timetable," said spokesman Harry Mitchell.

This all may seem a lot like the year-2000 problem, in which we had little choice but to sit back and trust the programmers and engineers to fix things. As in that earlier situation, we will probably have some bug fixes to install on our own as well. At least this time around, though, nobody's running around screaming, "We're all gonna die!"

By Rob Pegoraro  | February 8, 2011; 7:00 AM ET
Categories:  Standards, Telecom  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Smartphone stunts: Sprint introduces two-screen Echo, T-Mobile to give them away
Next: Verizon iPhone could have been international


Thank you for writing this up in such clear language. Even as a technical person with lightweight hacking skills I usually find info about network addressing to be too hard to truly grok. Great job on illustrating the situation!

Posted by: kazarnyc | February 8, 2011 10:33 AM | Report abuse

To be _exact_,

I think your calculator ran out of steam.

Posted by: david08054 | February 9, 2011 10:33 AM | Report abuse

Pre-Windows Vista does not support IPv6. Most, if not all, OSes support IPv6. Microsoft was slow to get on the bandwagon.

The problem is the applications only support IPv4. Applications will need changes to support IPv6. For many of these apps, just changing the underlying communication software will give it IPv6 support.

Posted by: david08054 | February 9, 2011 10:39 AM | Report abuse

Richard Bennett has a good piece on this issue today in High Tech Forum. He's against early adaptation of IPV6. Says "IPv6 is much too conservative on the technical side to warrant the expense of early conversion."'s

Posted by: SoMoCo | February 9, 2011 5:19 PM | Report abuse

Here’s the humorous ‘The Office’ video on IPv6 that has reached an astounding 50K views by now:

Posted by: rsealey | February 13, 2011 8:56 PM | Report abuse

Here’s the humorous ‘The Office’ video on IPv6 that has reached an astounding 50K views by now:

Posted by: rsealey | February 13, 2011 8:57 PM | Report abuse

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