[dns-operations] EDNS0 client-subnet option from Google Resolvers

[Daniel Stirnimann]

> Is this
> because the resolver figured out that our authoritative name server is
> not responding this option, so they don't send it every time but just
> from time to time to check if we support it now?

Looks like these are indeed probing requests. Found the following:

"This is implemented by probing nameservers at a low rate with ECS
queries and caching the ECS capability for each nameserver. Therefore if
your nameservers do not support ECS, they may still receive a few ECS
queries occasionally. And if your nameservers just started to support
ECS, it may take us several hours to detect the change and start to send
ECS queries to them."

https://groups.google.com/forum/?hl=en#!topic/public-dns-announce/67oxFjSLeUM

Daniel
-- 
SWITCH
Daniel Stirnimann, SWITCH-CERT
Werdstrasse 2, P.O. Box, 8021 Zurich, Switzerland
phone +41 44 268 15 15, direct +41 44 268 16 24
daniel.stirnimann at switch.ch, http://www.switch.ch