How to make your IPv4 network scalable to IPv6

The next generation of Internet Protocol, IPv6, hasn't been deployed as quickly as planned. But IPv6 will arrive, eventually. Here's what you need to do to make sure your networks will scale.

We've been hearing for years that the old Internet Protocol addressing scheme will soon give way to the new and improved "next generation" of IP: IPv6. Yet most of us are still happily running IPv4 networks. What (if anything) should we be doing to get ready for the big transition?

Let's take a brief look at the history of IPv6, where it stands today, why it hasn't been deployed as quickly as was initially planned, and why you should nonetheless be planning for the day IPv4 finally ends. Experts predict that IPv4 should be viable for many years. But you should start now to understand IPv6 and to ensure that your network is scalable to the new protocol, particularly if growth rates increase at an unexpected rate.

IPv6: Where did it come from and where is it going?

The Internet is built on the current Internet Protocol, version 4, which is the "IP" part of TCP/IP. In fact, the functions performed by IP were originally handled by TCP, which was later split into two layers and the layer three protocol called IP. RFCs 760 and 791, published in the early 80s, formally defined the standard characteristics of IP as we know it.

One would assume that an IPv1, v2 and v3 came before IPv4, but one would be incorrect. IPv4 was the first version of IP, although TCP had been through three earlier versions (which, as noted, included the functionality of IP until they were split in v4).

When IP was born, the Internet was a much smaller network. Its addressing scheme, which uses 32 bit binary addresses that we note in "dotted decimal" consisting of four octets for human convenience, seemed much more than adequate. It allows for about 4 billion unique addresses, and according to the Internet Systems Consortium, there were less than 2000 hosts on the Internet in 1985.

Then the Internet boom of the 90s arrived, and by 1995, there were over 6 and a half million hosts. It became obvious that the IPv4 address space wasn't as scalable as originally thought. At that growth rate, eventually it would simply run out of addresses.

In the 1990s, the push began to develop a new, truly scalable version of IP. The short-lived IPv5 was only experimental, but IPv6 was soon hailed as the next generation of IP (and sometimes abbreviated IPng). It uses 128-bit addresses, providing a number of addresses so large it's usually notated exponentially: 3.4 x 10 to the 38th power. The real number is 340 undecillion, or 340 with 36 zeroes after it

Why haven't we already switched?

It seems that IPv6 would solve the address shortage once and for all. In addition, members of the IETF IPv6 working group, who designed IPv6, included other improvements in the new protocol, such as security (IPsec encryption). So why haven't we all switched over by now?

One reason is that it's an enormous undertaking. As of January 2005, ICS reports the number of Internet hosts as over 317 and a half million. That's a lot of machines to switch to a whole new addressing system. And thanks to Network Address Translation (NAT), the IP address shortage has slowed down even as the number of machines accessing the Internet continues to increase. NAT allows an entire LAN to access the Internet through a single public IP address.

On the other hand, the increasing popularity of wireless devices, including phones, accessing the Internet is revving up the address crunch again. There's little doubt that eventually, IPv4 will have to go. But it could be years before IPv4 is completely replaced. Meanwhile, what should you be doing about it?

Planning for the IPv6 transition

How do you make your network ready to scale up to IPv6? Luckily, there are a number of technologies designed to make the transition easier. Modern operating systems now support IPv6, and the good news is that the old and new protocols can peacefully coexist. Existing IPv4 systems (computers, routers and other Internet devices) can still use their v4 addresses after IPv6 is installed.

Some transition mechanisms include:

  • IPv6 over IPv4 tunneling is a method which encapsulates the IPv6 packets produced by an upgraded system with IPv4 headers. This allows you to send these packets over an IPv4 network.
  • 6to4 tunneling. is an address assignment scheme incorporates an IPv4 address to let IPv6 hosts communicate across an IPv4 network. 6to4 is supported by the IPv6 implementations in modern operating systems such as Windows Server 2003.
  • IntraSite Automatic Tunnel Addressing Protocol (ISATAP) is an address assignment and tunneling technology for communication of IPv6 and IPv4 systems on an IPv4 network.
  • an IPv4 NAT-traversal (NAT-T) for IPv6 that allows IPv6 systems behind an IPv4 NAT device to communicate on an intranet.

Steps to take

There are several steps involved in preparing for the IPv6 transition. You'll have to ensure that your applications work independently of which IP version you use, and you'll need to upgrade your DNS servers to support IPv6 because it uses new DNS record types (AAAA and PTR).

The individual computer systems must be upgraded to support IPv6 (for example, on Windows XP and Server 2003 systems, IPv6 must be installed as a Network Component via the Network Connections Properties dialog box) and your routers must be upgraded to support IPv6 protocols along with IPv4.

About Deb Shinder

Debra Littlejohn Shinder, MCSE, MVP is a technology consultant, trainer, and writer who has authored a number of books on computer operating systems, networking, and security. Deb is a tech editor, developmental editor, and contributor to over 20 add...

Editor's Picks