Apex domains cannot have CNAME records.
Question and response
Question
dig cfdns.net. NS
Answer
cfdns.net. 5 NS ns2.cfdns.net.
cfdns.net. 5 NS ns4.cfdns.net.
cfdns.net. 5 NS ns1.cfdns.net.
cfdns.net. 5 NS ns3.cfdns.net.
Authority
The response has no authority records.
Additional
ns1.cfdns.net. 5 A 199.73.82.6
ns2.cfdns.net. 5 A 199.73.83.6
ns3.cfdns.net. 5 A 204.138.102.6
ns4.cfdns.net. 5 A 192.188.176.6
ns1.cfdns.net. 5 AAAA 2620:1f:8000:0:0:0:0:6
ns2.cfdns.net. 5 AAAA 2620:1f:8002:0:0:0:0:6
ns3.cfdns.net. 5 AAAA 2620:1f:8004:0:0:0:0:6
ns4.cfdns.net. 5 AAAA 2620:1f:8006:0:0:0:0:6
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0