Apex domains cannot have CNAME records.
Question and response
Question
dig fdmarc.net. NS
Answer
fdmarc.net. 5 NS ns4.fdmarc.net.
fdmarc.net. 5 NS ns2.fdmarc.net.
fdmarc.net. 5 NS ns1.fdmarc.net.
fdmarc.net. 5 NS ns3.fdmarc.net.
Authority
The response has no authority records.
Additional
ns1.fdmarc.net. 5 A 205.251.193.76
ns2.fdmarc.net. 5 A 205.251.194.22
ns3.fdmarc.net. 5 A 205.251.199.178
ns4.fdmarc.net. 5 A 205.251.196.170
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0