Stop IPv6 Google traffic

Rubens Kuhl rubensk at
Mon Apr 11 21:03:02 UTC 2016

On Mon, Apr 11, 2016 at 5:56 PM, Ricky Beam <jfbeam at> wrote:

> On Sun, 10 Apr 2016 20:09:04 -0400, Rubens Kuhl <rubensk at> wrote:
>> If your users are seeing captchas, one or a few or them are likely to be
>> infected to the point of generating too much requests to Google.
> If that were the case, they'd be seeing the same via IPv4. And apparently,
> they aren't.

Nope. If you have both A and AAAA IP addresses in DNS responses and have
both IPv4 and IPv6 connectivity, IPv6 will be preferred, with even a bit of
latency handicap favoring IPv6 in current Happy Eyeballs implementations.
Remember that the symptom is not unresponsive website, but an answer with
an inconvenience (the captcha), so the browser and the network stack won't
deem it as IPv6 load failure.

> This also points out the problems with *ASSUMING* you know the size of
> someone's netblock. If you think "/64", then you'd be wrong. Just as
> wrong as assuming all IPv4 is "/24". And on the same side of that coin
> is the over-reaching "block all of Asia" blacklist. Sure, that'll kill
> a heap of nonsense, but if you actually have business in Asia...

> (Yes, *I* banish APNIC. "works for me", not recommended for others.)

One known issue in both APNIC and LACNIC regions is that some addresses are
indeed countries instead of single networks, due to NIRs (National Internet


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