Apex domains cannot have CNAME records.
Question and response
Question
dig tomsk.avantel.ru. NS
Answer
tomsk.avantel.ru. 5 NS ns1.tomsk.avantel.ru.
tomsk.avantel.ru. 5 NS ns2.tomsk.avantel.ru.
tomsk.avantel.ru. 5 NS ns3.tomsk.avantel.ru.
Authority
The response has no authority records.
Additional
ns1.tomsk.avantel.ru. 5 A 93.91.168.2
ns2.tomsk.avantel.ru. 5 A 93.91.166.2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0