Fatal flaw for IPv6: It's not backwards compatible

The Internet engineering community says its biggest mistake in developing IPv6 - a long-anticipated upgrade to the Internet's main communications protocol - is that it lacks backwards compatibility with the existing Internet Protocol, known as IPv4. 

At a panel discussion held here Tuesday, leaders of the Internet Engineering Task Force (IETF) admitted that they didn't do a good enough job making sure native IPv6 devices and networks would be able to communicate with their IPv4-only counterparts when they designed the industry standard 13 years ago.

"The lack of real backwards compatibility for IPv4 was the single critical failure," says Leslie Daigle, Chief Internet Technology Officer for the Internet Society. "There were reasons at the time for doing that...But the reality is that nobody wants to go to IPv6 unless they think they're friends are doing it, too."

Originally, IPv6 developers envisioned a scenario where end-user devices and network backbones would operate IPv4 and IPv6 side-by-side in what's called dual-stack mode.

However, they didn't take into account that some IPv4 devices would never be upgraded to IPv6, and that some all-IPv6 networks would need to communicate with IPv4-only devices or content.

IPv6 proponents say the lack of mechanisms for bridging between IPv4 and IPv6 is the single, biggest reason that most ISPs and enterprises haven't deployed IPv6.

"Our transition strategy was dual-stack, where we would start by adding IPv6 to the hosts and then gradually over time we would disable IPv4 and everything would go smoothly," says IETF Chair Russ Housley, who added that IPv6 transition didn't happen according to plan.

In response, the IETF is developing new IPv6 transition tools that will be done by the end of 2009, Housley said.

"The reason more IPv6 deployment isn't being done is because the people who are doing the job found that they needed these new transition tools," Housley said. "These tools are necessary to ease deployment."

IPv6 is needed because the Internet is running out of IPv4 addresses. IPv4 uses 32-bit addresses and can support approximately 4.3 billion individually addressed devices on the Internet. IPv6, on the other hand, uses 128-bit addresses and can support so many devices that only a mathematical expression - 2 to the 128th power - can quantify its size.

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