IPv6 brokenness and DNS whitelisting

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In the field of IPv6 deployment, IPv6 brokenness is bad behavior seen in tunneled or dual stack IPv6 deployments where unreliable or bogus IPv6 connectivity is chosen in preference to working IPv4 connectivity. This often results in long delays in web page loading, where the user has to wait for each attempted IPv6 connection to time out before the IPv4 connection will be tried.[1]

These timeouts may range from being near-instantaneous in the best cases, to taking anywhere between four seconds to three minutes.[2]


As of May 2011, IPv6 brokenness as measured by instrumenting a set of mainstream Norwegian websites was down to ~0.015%,[3] most of which was caused by older versions of Mac OS X which would often prefer non-working IPv6 connectivity when it was not justified.[4] This behavior was fixed in Mac OS X 10.6.5, and is likely to decline further as Mac OS X 10.6.5 and subsequent versions roll out to a wider audience. However, there was no upgrade path for PowerPC-based Macs.[5]

The main remaining problem for Mac OS X was the presence of rogue routers, such as wrongly configured Windows Internet Connection Sharing devices pretending to have IPv6 connectivity, while 6to4 tunneled IPv6 traffic is blocked at a firewall.[citation needed] Another problem was pre-10.50 versions of Opera.[citation needed]

Following World IPv6 Day in July 2011, there were reports of a substantial reduction in IPv6 brokenness as a result of that experiment.[6] In the year following the trial, but prior to the World IPv6 Launch date, brokenness levels were reported to have risen slowly back upwards again towards 0.03%.[7]

DNS whitelisting[edit]

Google, a major provider of services on the Internet, used DNS whitelisting on a per-ISP basis to prevent this[8][9] until the World IPv6 Launch. Google now provides AAAA records to all DNS servers except for a few on a limited blacklist. In the DNS whitelisting approach, ISPs are determined from DNS lookup source IP addresses by correlating them with network prefixes derived from routing tables. There is an IETF draft entitled "IPv6 AAAA DNS Whitelisting Implications" that describes the issues around whitelisting. AAAA records are only sent to ISPs that can demonstrate that they are providing reliable IPv6 to their customers. Other ISPs are sent only A records, thus preventing users from attempting to connect over IPv6.

Numerous concerns have been raised about the practicality of DNS whitelisting as a long-term large-scale solution, such as scalability and maintenance issues relating to the maintenance of large numbers of bilateral agreements.[10] Several of the major web service providers have met to discuss pooling their DNS whitelisting information in an attempt to avoid these scaling problems.[11]

It is unclear whether any major content providers will ever use the whitelisting approach, given that all that had previously declared an interest began serving AAAA records to generic DNS queries following World IPv6 Launch Day.

See also[edit]


  1. ^ Yves Poppe (Oct 12, 2010). "IPv6 and the Fear of Brokenness". CircleID. Retrieved 2010-12-29. 
  2. ^ Lorenzo Colitti, Google. "IPv6 transition experiences" (PDF). Retrieved 2010-12-29.  presented at NANOG 50
  3. ^ Tore Anderson. "IPv6 dual-stack client loss in Norway". Retrieved 2011-06-16. 
  4. ^ Tore Anderson. "Measuring and combating IPv6 brokenness" (PDF). Retrieved 2010-12-29. , presented at RIPE 61, Rome, November 2010
  5. ^ Iljitsch van Beijnum. "Apple fixes broken IPv6 by breaking it some more". Ars Technica. Retrieved 2010-12-29. 
  6. ^ Carolyn Duffy Marsan (July 27, 2011). "'IPv6 brokenness' problem appears fixed". Network World. 
  7. ^ Stephen Shankland (June 4, 2012). "Internet powers flip the IPv6 switch (FAQ)". CNET News. 
  8. ^ "Google over IPv6". Google. Retrieved 2010-12-29. 
  9. ^ Iljitsch van Beijnum. "Yahoo wants two-faced DNS to aid IPv6 deployment". Ars Technica. Retrieved 2010-12-29. 
  10. ^ Jason Livingood (October 2010). "IPv6 DNS Whitelisting — Overview and Implications" (PDF). Comcast. Retrieved 2010-12-29. , presented at IETF79, Beijing
  11. ^ Carolyn Duffy Marsan (29 March 2010). "Google, Microsoft and Yahoo talk about IPv6 whitelist". Techworld. Retrieved 2010-12-29. 

External links[edit]