sentry.etelecom.ru has no CNAME records.
Question and response
Question
dig sentry.etelecom.ru. NS
Answer
The response has no answer records.
Authority
ETELECOM.RU. 4327 SOA ns.gblnet.RU. noc.ETELECOM.RU. 2026033471 10800 1200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0