Google no longer returning AAAA records?

Lorenzo Colitti lorenzo at
Thu Apr 16 02:57:43 CEST 2015

On Thu, Apr 16, 2015 at 4:56 AM, Brian E Carpenter <
brian.e.carpenter at> wrote:

> I suggest checking if any of your affected users have broken 6to4 setups,
> and that you are applying the relevant mitigations in RFC 6343.
> MTU size issues and high latency have also both been mentioned as
> possible reasons for the mysterious AAAA blacklist.

For the avoidance of mystery: Google performs measurements of IPv6
connectivity and latency on an ongoing basis. The Google DNS servers do not
return AAAA records to DNS resolvers if our measurements indicate that for
users of those resolvers, HTTP/HTTPS access to dual-stack Google services
is substantially worse than to equivalent IPv4-only services. "Worse"
covers both reliability (e.g., failure to load a URL) and latency (e.g.,
IPv6 is 100ms worse than IPv4 because it goes over an ocean). The resolvers
must also have a minimum query volume, which is fairly low.
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