sergey.kemsu.ru has no CNAME records.
Question and response
Question
dig sergey.kemsu.ru. NS
Answer
The response has no answer records.
Authority
kemsu.ru. 4740 SOA ns.kemsu.ru. postmaster.kemsu.ru. 2026030403 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0