dns.convex.ru has no CNAME records.
Question and response
Question
dig dns.convex.ru. NS
Answer
The response has no answer records.
Authority
convex.ru. 1357 SOA dns.convex.ru. root.convex.ru. 2026030504 108002 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0