Apex domains cannot have CNAME records.
Question and response
Question
dig 224.148.186.in-addr.arpa. NS
Answer
224.148.186.in-addr.arpa. 4 NS ns1.dodos.ar.
224.148.186.in-addr.arpa. 4 NS ns2.dodos.ar.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0