I am just setting up a new Debian installation ver 15.5.5 with a mikrotik router.
resolving 'stun-au.3cx.com'... done
resolving 'stun2.3cx.com'... done
resolving 'stun3.3cx.com'... done
resolving 'sip-alg-detector.3cx.com'... done
testing 3CX SIP Server... failed (How to resolve?)
stopping...