Apex domains cannot have CNAME records.
Question and response
Question
dig GAZSVYAZ.RU. NS
Answer
gazsvyaz.ru. 5 NS ns1.gazsvyaz.ru.
gazsvyaz.ru. 5 NS ns2.gazsvyaz.ru.
gazsvyaz.ru. 5 NS ns.gazprom.ru.
Authority
The response has no authority records.
Additional
ns.gazprom.ru. 5 A 217.151.130.34
ns1.gazsvyaz.RU. 5 A 217.151.128.34
ns2.gazsvyaz.RU. 5 A 217.151.128.35
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0