Apex domains cannot have CNAME records.
Question and response
Question
dig 252.111.109.in-addr.arpa. NS
Answer
252.111.109.in-addr.arpa. 5 NS auth4.oriontelekom.com.
252.111.109.in-addr.arpa. 5 NS auth1.oriontelekom.com.
252.111.109.in-addr.arpa. 5 NS auth2.oriontelekom.com.
252.111.109.in-addr.arpa. 5 NS auth3.oriontelekom.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0