Apex domains cannot have CNAME records.
Question and response
Question
dig 0-255.141.105.184.in-addr.arpa. NS
Answer
0-255.141.105.184.in-addr.arpa. 3 NS ns-b.axcelx.net.
0-255.141.105.184.in-addr.arpa. 3 NS ns-a.axcelx.net.
Authority
The response has no authority records.
Additional
ns-a.axcelx.net. 3 A 192.34.85.189
ns-b.axcelx.net. 3 A 184.105.141.42
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0