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ns1 is root
ns{2-4} are auth server on example. but lame
ns5 is an auth server on example. and works
ns6 is a resolver

Because `getaddresses_allowed()` logic won't allow to query more than 3 NS at
the top-level, only ns{2-4} will be tried without randomization, and example.
couldn't be resolved. However, with randomization, some queries won't start
picking example. NS from ns2, but ns3, ns4 or ns5. This enable to resolver
example.