[atlas] Running a probe behind a NAT66

Hello,

I am trying to run a probe (#73) behind an IPv6 NAT. The probe gets an IP in a
non-standard prefix 66:113::/64, which is then NATed to a single GUA IPv6.

This used to work fine for a few months, but then in April-2018 problems
started: the probe would connect to Atlas for 5-10 minutes, then disconnect
for about 20 minutes, then connect again; this alternates over and over again.

However -- if IPv6 RAs are enabled some time after the probe is powered-on
(i.e. the controller connection already got established over IPv4), things seem
to go on fine, i.e. the controller is connected over IPv4 for days, but various
measurements are performed on IPv6 too. So it seems that only the controller
connection is the problem.

I fully expect that you didn't account for such a setup in the controller
infrastructure or possibly various "local IP is valid" checks and whatnot, but
why this used to work fine before? Has there been any change on your side in
April that would break this kind of setup?

-- 
With respect,
Roman