Level3 DNS not resolving for our domains

[bortzmeyer at nic.fr (Stephane Bortzmeyer)]

On Wed, Dec 30, 2015 at 11:12:29PM +0100,
 Alarig Le Lay <alarig at swordarmor.fr> wrote 
 a message of 35 lines which said:

> Both are in the same AS, perhaps a routing issue?

Indeed. This is a warning in ZoneMaster
<https://zonemaster.net/test/b9c2efd5a10f2eb8> and I observe also that
10-15 % of the RIPE Atlas probes cannot resolve this name (so it is
not just Level 3). The name servers unfortunately do not reply to ICMP
echo so it is hard to debug.