bigserver.it-optics.com has no CNAME records.
Question and response
Question
dig bigserver.it-optics.com. NS
Answer
The response has no answer records.
Authority
it-optics.com. 2857 SOA dns5.it-optics.com. zonemaster.it-optics.com. 202601301 3600 7200 2419200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0