Apex domains cannot have CNAME records.
Question and response
Question
dig SPB.RU. NS
Answer
SPB.RU. 5 NS ns8-geo.nic.RU.
SPB.RU. 5 NS ns4-geo.nic.RU.
SPB.RU. 5 NS ns3-geo.nic.RU.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0