Some very nice broken IPv6 networks at Google and Akamai

[Lorenzo Colitti]

On Sat, Nov 8, 2014 at 11:48 PM, Jeroen Massar <jeroen at massar.ch> wrote:

> >> The issue with IPv6 access to Google should now be resolved.  Please let
> >> us know if you're still having problems.
>
> The fun question of course is: what/why/how the heck happened?
>

Another fun question is why folks are relying on PMTUD instead of adjusting
their MTU settings (e.g., via RAs). But relying on PMTUD still imposes a
1-RTT penalty on every TCP connection to an IPv6 address you haven't talked
to in the last few minutes. Why would you do that to your connection?

As to what happened: what happened here is that some Google servers
temporarily stopped doing MSS clamping. That was an outage, and AIUI it has
since been fixed. (Some parts of) Google infrastructure do not do PMTUD for
the latency reasons above and for reasons similar to those listed in
https://tools.ietf.org/html/draft-v6ops-jaeggli-pmtud-ecmp-problem-00 .
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