ext01-1.sintec.ru has no CNAME records.
Question and response
Question
dig ext01-1.sintec.ru. NS
Answer
The response has no answer records.
Authority
sintec.ru. 414 SOA ext01-1.sintec.ru. root.sintec.ru. 2026010702 3600 600 864000 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0