Does IPv6 Even Work?

With the free pool of IPv4 address space now exhausted, transitioning to IPv6 is set to become increasingly important. IPv6, however, isn’t without its own set of challenges; and implementing it isn’t as easy as simply flipping a switch.

One of the key places where IPv6 challenges are exposed is the interoperability lab at the University of New Hampshire (UNH-IOL). UNH-IOL sponsors plugfests and other interoperability events and initiatives that bring vendors together to help validate that their IPv6 solutions actually work together.

Tim Winters, senior manager for the UNH-IOL, told that a number of surprises about IPv6 have emerged during recent plugfests.

“There were definitely surprises, I can say that the IETF standard we were using, the CE (Customer Edge) router draft was good and we didn’t find any issues with the standard,” Winters said. “What we did find are issues with the implementations.”

Winters noted that vendors had been doing their own testing on devices, but when the same devices were brought into UNH-IOL and tested extensively, there were some issues.

“We had a lot of base stuff work, but when you start to get to the more complex things, it fell apart,” Winters said.

DHCPv6 shows IPv6 poses problems in complex situations

The more complex items where vendor equipment had trouble with IPv6, ranged across a number of issues. One key problem area is DHCPv6, where Winters noted there were prefix delegation issues.

“Prefix delegation is important as that is how operators will tell a home what address they have,” Winters said. “Our experience was not very good with that.”

Winters added that up until recently there were no standards about how to do IPv6 on the LAN without the WAN. The IETF CE Router draft deals specifically with what is required on either side of a consumer set top box.

Overall the problem with DHCPv6 is the fact that it doesn’t come standard with all platforms. Winters noted that neither Apple Mac OS X or Windows XP have DHCPv6 though Vista and Windows 7 do. He added that UNH-IOL has seen DHCPv6 implementation problems around timers and clients not renewing prefixes properly.

“It became painfully obvious to us that DHCPv6 is not that well deployed at this point,” Winters said. “It’s not so much a standards problem as it is an implementation problem.”

The other issue Winters has noticed is that IPv6 isn’t always enabled on devices, even when they are IPv6 ready. The problem from the vendor side is that since IPv6 is not actually being widely used, use case issues that would show up in production use haven’t all been discovered yet.

The other issue still being resolved has to do with transition mechanisms for running IPv4 and IPv6. Winters noted that each operator seems to want a different transition mechanism whether it’s 6RD, DS-Lite or otherwise.

“I think now that people are starting to deploy IPv6 we’ll get a nice set of transition mechanisms,” Winters said. “For so long there have been so many options and no one has really known which ones really matter.”

In general though, Winters noted that he used to see more issues with dual IPv4/IPv6 stack implementations in past years. He added that the operating systems vendors have done a good job of cleaning up issues.

There are however still issues when it comes to applications.

IPv6 application problems

“There are still known issues with DNS records, and if you have a AAAA record and an A record, what happens to your application?” Winters said. “You go to the AAAA and if it’s not there, your application will hang.”

AAAA is the IPv6 record type in DNS, while the A record is for IPv4. Winters noted that it is surprising how some applications will only take the top record from a DNS resolver, whatever that record may be. He added that there is an IETF draft called, Happy Eyeballs which attempts to help resolve that issue.

So after all is said and done, is IPv6 actually ready?

“I think we’re moving in that direction,” Winters said. “I do think that the core routers and operating systems are ok, it’s everything in between. It’s the cell phone, printers and data storage all that stuff is going to have to move and that’s the last bit.

Sean Michael Kerner is a senior editor at, the news service of, the networkfor technology professionals.

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