Apex domains cannot have CNAME records.
Question and response
Question
dig 224-255.120.73.64.in-addr.arpa. NS
Answer
224-255.120.73.64.in-addr.arpa. 5 NS ns1.esker.com.
224-255.120.73.64.in-addr.arpa. 5 NS ns.esker.fr.
Authority
The response has no authority records.
Additional
ns.esker.fr. 5 A 213.41.96.227
ns1.esker.com. 5 A 204.246.8.99
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0