The Second Internet
that are easy to remember. More than could ever be used in the next hundred years. So just what is it
that we are running out of?
The nodenames that you (and most humans) use to specify a particular node on the Internet, like
www.ipv6.org, are made possible by something called the Domain Naming System (DNS). Those
nodenames are not used in the actual packets as source and destination addresses (see section on IPv4
addressing model for the gory details). The addresses used in the packets on the wire in the First
Internet are 32 bit binary numbers. These are usually represented for us slow and stupid humans in
dotted decimal notation like 126.96.36.199. With a 32 bit address, there are 232 (about 4.3 billion) distinct
values. When you use a symbolic nodename (known technically as a Fully Qualified Domain Name, or
FQDN) in an application, that application sends it to a DNS server, which returns the numeric IP address
associated with it. That’s the address that is used in packets on the wire, for routing the packet to its
destination. The DNS nodenames are like the names of people you call, the IP addresses are like their
phone numbers. DNS is like an online telephone book that looks up the “phone number” (IP address) for
“people” (nodes) you want to “call” (connect to). Did you know that you can surf to IP addresses? Try
entering the URL http://188.8.131.52. That’s a whole lot harder to remember than www.hp.com, which is
why DNS was invented. It’s these 32 bit numeric addresses (that most people never see) that we are
running out of. The good news is that you can keep typing www.hp.com, and DNS will soon return both
the old style 32 bit IPv4 address and a new style 128 bit IPv6 address, which will be put into IPv6
packets. Given the choice, your applications will prefer to use the new IPv6 address. You will hardly
notice the difference, unless you are a network engineer or a network software developer. Except
there’s going to be an awfully lot of cool new stuff to do, and new ways of doing old things, plus the
Internet is going to work better than it ever has.
Can you imagine trying to manage today with 5 digit telephone numbers? In a few years, that’s what
IPv4 is going to feel like.
1.4 – But You Said There Were 4.3 Billion IPv4 Addresses?
But, I hear you protest, there are only 1.3 billion nodes currently connected to the Legacy Internet, and
there are 4.3 billion possible IPv4 addresses. Aren’t there still some 3 billion addresses left? Well, no, sad
to say, there aren’t.
On February 15, 2010 (when I started writing this book), there were only 364 million addresses left to
assign (again, from the NetCore countdown clock). On May 12, 2010 (3 months later), there were only
298 million addresses left. What the heck happened to the rest? Well, when the First Internet was being
rolled out, there were about 600 nodes in the world, and 4.3 billion looked a lot like “infinity” to the
people involved. So, giant chunks of addresses were generously given out to early adopter
organizations. For example, M.I.T. and HP were given “class A” blocks of addresses (about 16.7 million
addresses, or 1/256 of the total address space, each). Smaller organizations were given “class B” blocks
of addresses (each having about 65,535 addresses). Most of these organizations are not using anywhere
near all of those addresses, but they have never been willing to turn them back in. As detailed in the
OECD study on IPv4 address space depletion and migration to IPv6, it is very difficult and time
consuming to “recover” these “lost” addresses. Also some blocks of addresses were used for things like
multicast, experimental use, and other purposes.