IPvX: Better than IPv6?

IPv6 is coming, but it is difficult and expensive to implement because it is not backwards-compatible with IPv4. This page explains the problem and a proposed solution: IPvX. This is a fantastic proposal from Bill Chimiak that may save us all from a large expense of time and money, and spare us from a whole new set of security problems.

I think this is a billion-dollar idea. It will save an immense amount of money, and make fortunes for people who successfully implement and market it.

IPv4 Header

Here's the IPv4 header we all know and love. All the routers, servers, firewalls, etc. expect to see packets in this format now. (Figure from openwall.com)

As indicated in this diagram, IPv6 changes this header. That's a big problem.

ipv4header-from-openwall (60K)
Larger image

See that "options" field in the IPv4 header? That's there to make it flexible, so future developments won't make IPv4 obsolete. Why not use it?

IPv6 Header

Here's the IPv6 header. It has many virtues, but as you can easily see, it is completely different from an IPv4 header, so legacy devices won't have any clue how to process it.

Is is really necessary to make all our existing devices obsolete just to get 128-bit addresses?

ipv6header-from-openwall (45K)
Larger image

IPvX Header

Why not do it this way? Package the 128-bit addresses in the options section of a normal old IPv4 header! That's what the options section is for, after all!

The resulting packet is still an IPv4 packet, but it also contains 128-bit addresseses. Legacy devices can interpret it as IPv4 and use it correctly, and newer devices can find the 128-bit addresses in it and use them instead.

IPvX-header (97K)
Larger image

Legacy Devices

This means you can just keep using your old IPv4 devices! You can even send IPvX traffic through IPv4 infrastructure with no problem, like this. No NAT or encapsulation or conversion of any kind is required. It just works! Think of all the money and time that will save!


For More Information

For a complete explanation of IPvX, read the draft RFC.

You can email Bill Chimiak, the author of the draft RFC, at [email protected]

You can email Sam Bowne at [email protected]

Help Wanted

Right now, this is just a fantastic idea. We need help to make it real. Here are the immediate needs:


IPv4 and IPv6 header figures from http://www.openwall.com/presentations/IPv6/
IPvX header figure from Bill Chimiak

Thanks to the people at DEFCON 2010 who asked "Why isn't IPv6 backwards-compatible with IPv4?" That was an excellent question!

Bill Chimiak wrote the draft RFC, so he did all the technical work. Sam Bowne wrote this summary description page.


Name: Sam
Thanks to @ethicalhack3r for suggesting a comments section.

Name: Sam Bowne
Dan Goodin from The Register found this out: A noted expert in BGP and other backbone operations, says IPvX is \"completely intractable,\" mainly because high-speed routers already use IPv4 options fields for special purposes. He said something called RSVP is just one example. He said IPvX would require huge chunks of today\'s hardware infrastructure to be replaced and hence would defeat the whole idea behind its adoption. At first glance this looks like a real problem. Bill may have some solution, however. I\'ll update this when I know more.

Modified 8-25-10 10:00 am PST
Comment form removed 2-24-14 9:44 am