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June 8th: the day your phone won’t stop ringing

On June 8th (the World IPv6 Day) you’ll see Facebook, Google and a number of other web sites reachable over IPv4 and IPv6 (more accurately: the DNS records for their web sites will have both A and AAAA records). No problem ... unless your users have misconfigured workstations and you haven’t deployed IPv6 throughout your network yet (not many have).

Users with broken IPv6 connectivity will experience long delays connecting to major public web sites. Their workstations will try to reach the content over IPv6 first and will have to experience a TCP-level timeout before retrying to get the same content over IPv4. Guess whose phone will ring ... and what the problem description will be ;)

Expecting everyone to have IPv6 connectivity sorted out throughout the enterprise network before June 8th is ludicrous, but you (and your network) have to be prepared for dual-stack world:

  1. Check whether your users are likely to experience problems using an IPv6 connectivity test tool. Run the checks on various hosts throughout your network.
  2. Prepare your help desk team. They should know what’s going on and be prepared to handle “Internet-is-down” cases.
  3. Minimize the impact of broken IPv6 connectivity by reconfiguring end-user devices where needed.

The very minimum you have to do is to turn off all unnecessary end host tunneling mechanisms like Teredo or 6over4 and check whether someone accidentally advertises himself as a router (sending Router Advertisement messages from a workstation). Implementing RA guard on routers and switches is also not a bad idea.

More information

To learn more about all the possible things that can go wrong, read these articles:

If, on the other hand, you’re planning to deploy IPv6 in your network, you might find useful overview of what needs to be done in my Enterprise IPv6 – the first steps webinar (register here or buy a recording).


  1. To add to the "more information" section, I found the following page interesting/informational:
    The page describes and demonstrates how different clients(OS) behave when connecting to dual-stack web-pages(real-world test). And also explains the test-setup for anyone that want's to see for him/her-self what impact dual-stacking your website might have.
  2. Hello,

    After reading your post + others out there, and considering strictly only the changes from 8th of June, I conclude that is better to have only a working IPv4 network, than a broken IPv6 one. Am I correct?

    What I mean is that I believe a lot of small organization will rush to implement IPv6 and they can make mistakes leading to a broken IPv6 network that will affect users rather than if they would stay with the current IPv4.

    I tested 2 enterprise networks with only IPv4 through the link provided and in both cases the conclusion was "No problems are anticipated for you". The only problem would be with sites powered only by IPv6, but yet those are very less.

    My conclusion is that if you don't have a plan to implement IPv6 and have to manage an acceptable large network, then don't rush into IPv6 implementation now as it may cause more damage than fixes. Network engineers should be aware of the coming change and they should plan IPv6 as mandatory implementation, but not from one day to another.

    Please correct me if I'm wrong!
  3. You're absolutely right . You don't have to rush to have IPv6 implemented; at this moment it might actually be better to postpone the IPv6 deployment than to have a broken network on June 8th.
  4. I suspect your article is a tad misleading in that there are clients that behave like this, and there are many that don't. My understanding was that it is Mac OS X and *not* linux, vista, or win 7. Another reason for conducting such an exercise is to highlight the further work needed, and to give people some dates to work towards. The fact is, IPv4 has exhausted, and to continue with the growth we enjoy in the 'net, we have to face the fact it is time to move on. I for one hope that World IPv6 Day will take away some of the fear factor people have developed. It really aint that hard!
  5. The _default configuration_ of most client mostly works (I did have problems with early Fedora 12 though). In a more "dynamic" environment, people might have turned on all sorts of features on their workstations. It's enough that someone starts sending out RA messages and the whole subnet is blackholed (I know, I managed to do it :-[ ).

    The point of this article was definitely not "We don't need IPv6" or "The Internet will stop" but "Get prepared & test your network". Doing anything less would be somewhat irresponsible.
  6. Check which sites are ready for IPv6 at
  7. Great idea, unfortunately your server is not connected to an ISP whitelisted by Google, so the "usual" Google sites are reported as not-IPv6-ready (including my blog *DONT_KNOW* ).

    BTW, tried to leave a message on your site, but the CAPTCHA (letter thingy) is broken.
  8. Fixed the captcha. Thanks!
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