core.obtelecom.ru has no CNAME records.
Question and response
Question
dig core.obtelecom.ru. NS
Answer
The response has no answer records.
Authority
obtelecom.ru. 3600 SOA ns.obcity.ru. dennsk.gmail.com. 2016070416 3600 900 3600000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0