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A Politically Incorrect Guide to IPv6

John Levine

Every packet of data sent over the Internet is sent from one IP address to another. The IP addresses in the Internet serve somewhat the same function as phone numbers in the US phone system, fixed length numeric identifiers where the first part tells what network the address is on. Since the dawn of the Internet in the early 1980s, the IP addresses in use have been IPv4, 32 bit addresses which means there are about 4 billion of them. Unless you've been living under a rock, you've doubtless seen reports that the supply of IPv4 addresses is running out. Earlier this month IANA, the master allocation authority, handed out the last so-called /8, a large chunk of 16 million addresses, to one of the regional address registries, and sometime months or perhaps a few years after that, the registries will hand out the last pieces of their chunks. Then what?

The conventional wisdom is that everyone needs to support IPv6, a mostly compatible upgrade to IPv4 with much larger addresses, by the time the v4 space runs out. But I'm not so sure, particularly for e-mail.

There's two unanswered questions here. One is is how hard it will be for new or expanding networks to get IPv4 address space. The other is how important IPv6 addresses will be to be able to reach the rest of the net. The conventional answers are very hard and very important, but I think the real answers to both, for the next several years, at least, is not very. Below is my three-part post where I opine about getting IPv4 address space, addressing and reachability.

A politically incorrect guide to IPv6, Part I
A politically incorrect guide to IPv6, Part II
A politically incorrect guide to IPv6, Part III

By John Levine, Author, Consultant & Speaker. More blog posts from John Levine can also be read here.

Related topics: IP Addressing, IPv6


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You are right in that everyone does not need IPv6, but the ISPs definitely do... John Curran  –  Mar 01, 2011 8:56 PM PDT

John -

Your three-part post is right on target, in effectively asking the question "why are we doing IPv6 at all?" I'll try to respond concisely but the most important point to keep in mind is that the transition to IPv6 is far more driven by the strategic economics of the ISP industry than any specific customer demand.  Even the ISP motivation is elusive at times (much like try to explain to a frog why the warm bath is actually frog soup in the making… ;-)

The demand from the world ISPs for address space has been increasingly dramatically over the last several years, and in 2010, the global ISPs community required a record amount of nearly 15 /8 address blocks in total (/8 = 2**24 = approx 16 Million IP addresses; data from http://www.nro.net/statistics).  This demand isn't just new networks, or additional customers on existing networks, it is also more addresses for the existing customers.  Because of the trend of continuous connectivity in the home, what used to be a 1 IP address to dozens of homes is becoming 1 IP to each home in existing broadband networks.  Add in the growth of smart mobile devices with applications running continuously in the background and you have another place where the demand for unique addresses is growing without bound.

Can all of these address needs be met by recovering (or facilitating a market to recover) the underutilized IPv4 addresses?  We can definitely get some more time if we can get the assigned-but-unused address space put to productive use, and in fact, that's the reason the community in the ARIN region adopted a specified transfer policy to encourage better utilization.  Even so, we're going through more than 80+ Million IP addresses each year, so we'll be hard pressed to keep up for very long even with perfect recovery.

Can the address needs be met by extending IPv4 via NAT?  Quite possibly, but service providers are already having trouble making existing streaming audio and video applications work over NAT, and applications such as VoIP and interactive games often have problems as well.  NAT works most of the time, but the expectations for reliable voice & video Internet chat, realtime movie streaming and online gaming are definitely raising the bar and making NAT performance a major problem for providers.

Service providers have a real challenging choice before them:

A) Keep kludging NAT solutions and stretching IPv4 addresses ever thinner among customers
B) Start deployment of IPv6 as a strategic alternative
C) Both A & B (If it's not obvious at this point, we're on plan C...)

Deploying IPv6 is not easy: there's no particular reason for anyone other than the service providers to want IPv6, and it effectively means administering two sets of network addresses in parallel for many years.  The only good news is that it isn't that different from IPv4 (in that all of your favorite Internet applications already run over it) and we get enough addresses with IPv6 to hopefully never have to go through this change again… :-)

If you are not an ISP, then you've only got one high priority task in this transition:  Get your public facing web server dual-homed with both IPv4 and IPv6.  The reason to do this is that is avoids having to rely on carrier gateways between IPv6 and IPv4 to your web site, and should provide better performance over the long-run.  It also makes the equipment that carriers need to purchase more scalable since your content is reachable via whichever IP protocol natively connects each customer. As you so aptly note, email is store and forward, and there's no particular reason to worry about IPv6 connectivity since everyone is likely to have an IPv4 address on their mail server for quite some time to come.

We some luck, we might be keep the Internet running over IPv4 for another 5 or 10 years.  We're not trying to avoid that by deploying IPv6, only making sure that once IPv4 has been stretched to its limit, IPv6 is sufficiently adopted that the Internet can keep on growing.


John Curran
President and CEO

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