Apple fixes broken IPv6 by breaking it some more

“In Mac OS X 10.2 Jaguar, Apple introduced IPv6 support. Like other IPv6-capable operating systems, Mac OS will prefer IPv6 over IPv4 if it has a choice,” Iljitsch van Beijnum reports for Ars Technica. “That is, until yesterday’s 10.6.5 Snow Leopard update. With regular IPv6 connectivity, the newly updated Snow Leopard will still try to connect over IPv6 first, but for IPv6 destinations that are reachable over 6to4, the snowy cat prefers IPv4 instead. It will only connect over 6to4 to IPv6 destinations if there’s no IPv4.”

“The apparent rationale for this move is that 6to4 is responsible for a disproportionate share of non-working IPv6 setups,” van Beijnum reports. “Measurements by Google show that simply giving an IPv6 address means that, subsequently, about 0.1 percent of all Google’s users would be unable to connect to the search giant. That is unacceptable to them, not just from a commercial perspective, but also… how are you going to debug this problem if you’re unable to search the Web? ISPs are unlikely to hold user’s hands if this eventuality comes to pass. Earlier results show that Mac 6to4 users are a huge proportion of the (currently) 0.3 percent of IPv6-capable users. But 6to4 has exactly the properties that make it fail in ways that tend to go unfixed.”

Full article here.

Redpill Linpro’s Tore Anderson writes over in the Apple Mailing Lists, “The 6to4/IPv4 preference problem I’ve posted about a few times earlier appears to be solved in the OS X 10.6.5 previews. I’d like to send a big *thank you* to everyone in Apple involved in making that happen!”

Anderson writes, “However, there’s still some rough edges and in sending this message I’m hoping there’s a chance they too will get included in the final release of 10.6.5.”

Full message here.


  1. The Internet domain name system is organized along an IP (Internet Protocol) address that is divided into Octets. Think of a binary system that has to conform to a base 10 numerical system. In IPv4 you had about a billion addresses. In IPv6 the length of the addresses and therefore the number is assesses is increased exponentially. This is important because as the Internet gains more & more users the current numbering system will run out of unique addressable numbers. You can imagine a future where each one of us is given an IP address at birth which will identify us to the world akin to your mobile telephone number.

  2. We have already run out of IP addresses under the old system long ago. The only reason why the system is still working is because so many ISPs of the developing world are now forced to use NAT (Network Address Translation) and private IP networks that cannot be directly reached from the rest of the internet.

    It has been many years since IPv6 has been operational. It would be interesting to find out who exactly is responsible for not setting a firm deadline for shutting down IPv4 service and switching over completely to IPv6.

  3. @Predrag: Apparently I am missing some information. I also have some to offer.

    “We have already run out of IP addresses under the old system long ago.”

    Technically, yes. But I am hearing that at the moment, owners of unused IPv4 addresses that aren’t being used are handing them over for immediate use by those who want IPv4 addresses.

    What I don’t comprehend is why the stalling by redistributing unused iPv4? Why not jump into IPv6 and get it over with? Then again, I’m happiest when dancing on the bleeding edge. Living in the past was never my thought realm.

    “It would be interesting to find out who exactly is responsible for not setting a firm deadline for shutting down IPv4 service and switching over completely to IPv6.”

    Apparently, reflecting on what I wrote above, the fact is that very few IP users are going IPv6, instead causing further demand for IPv4 addresses instead. This of course stalls the entire transition process. The general sense is that once all the IPv4 addresses are truly gone, everyone will move over to IPv6 as if they have a shotgun held to their head. They won’t go there until they have no choice. So ridiculous.

    But such are the ways of the non-tech savvy. I have no doubt that even top IT professionals are dragging their feet. Witness the Windows monopoly phenomenon which is equally ridiculous as well as detrimental.

  4. There are still tens of thousands of DNS servers, routers and other assorted hardware in use that do not support IPv6. These machines (most of them running Unix variants) are the backbone of the “modern” internet. Some of them are so old that you’d flip to find out what kind of hardware is still crunching numbers (think 64080, 286/386, and, yes, even older). It will take a very long time, and a whole lot of money to replace all of that hardware.

    It’s simply not feasible to swap yet, but we’ll get there.

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