Apex domains cannot have CNAME records.
Question and response
Question
dig 0.107.193.in-addr.arpa. NS
Answer
0.107.193.in-addr.arpa. 5 NS ns.runnet.ru.
0.107.193.in-addr.arpa. 5 NS ns1.utelcom.ru.
0.107.193.in-addr.arpa. 5 NS ns2.utelcom.ru.
Authority
The response has no authority records.
Additional
ns.runnet.ru. 5 A 194.85.32.18
ns1.utelcom.ru. 5 A 193.107.0.2
ns2.utelcom.ru. 5 A 193.107.1.2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0