ns.sinn.ru has no CNAME records.
Question and response
Question
dig ns.sinn.ru. NS
Answer
The response has no answer records.
Authority
sinn.ru. 10800 SOA ns.mts-nn.ru. hostmaster.sinn.ru. 2024112600 10800 2500 604800 43200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0