Apex domains cannot have CNAME records.
Question and response
Question
dig OBTELECOM.RU. NS
Answer
obtelecom.ru. 5 NS ns.obcity.ru.
obtelecom.ru. 5 NS ns1.obcity.ru.
obtelecom.ru. 5 NS ns2.obcity.ru.
Authority
The response has no authority records.
Additional
ns.obcity.ru. 5 A 195.88.16.1
ns1.obcity.ru. 5 A 195.88.17.1
ns2.obcity.ru. 5 A 213.108.5.28
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0