Apex domains cannot have CNAME records.
Question and response
Question
dig PTL.RU. NS
Answer
PTL.RU. 5 NS ns.quantum.RU.
PTL.RU. 5 NS ns1.quantum.RU.
PTL.RU. 5 NS ns.v6.PTL.RU.
Authority
The response has no authority records.
Additional
ns.quantum.RU. 5 A 213.170.64.33
ns1.quantum.RU. 5 A 213.170.65.33
ns.v6.PTL.RU. 5 AAAA 2a00:f30:0:64:0:0:0:33
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0