Apex domains cannot have CNAME records.
Question and response
Question
dig 231.20.178.in-addr.arpa. NS
Answer
231.20.178.in-addr.arpa. 3 NS rdns1.spd.net.tr.
231.20.178.in-addr.arpa. 3 NS rdns2.spd.net.tr.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0