Apex domains cannot have CNAME records.
Question and response
Question
dig free. NS
Answer
free. 5 NS dns4.nic.free.
free. 5 NS dns2.nic.free.
free. 5 NS dnsd.nic.free.
free. 5 NS dnsb.nic.free.
free. 5 NS dns3.nic.free.
free. 5 NS dnsa.nic.free.
free. 5 NS dns1.nic.free.
free. 5 NS dnsc.nic.free.
Authority
The response has no authority records.
Additional
dns1.nic.free. 38051 A 213.248.218.67
dns2.nic.free. 38051 A 103.49.82.67
dns3.nic.free. 38051 A 213.248.222.67
dns4.nic.free. 38051 A 43.230.50.67
dnsa.nic.free. 38051 A 156.154.100.3
dnsb.nic.free. 38051 A 156.154.101.3
dnsc.nic.free. 38051 A 156.154.102.3
dnsd.nic.free. 38051 A 156.154.103.3
dns1.nic.free. 38051 AAAA 2a01:618:402:0:0:0:0:67
dns2.nic.free. 38051 AAAA 2401:fd80:402:0:0:0:0:67
dns3.nic.free. 38051 AAAA 2a01:618:406:0:0:0:0:67
dns4.nic.free. 38051 AAAA 2401:fd80:406:0:0:0:0:67
dnsa.nic.free. 38051 AAAA 2001:502:ad09:0:0:0:0:3
dnsb.nic.free. 38051 AAAA 2001:502:2eda:0:0:0:0:3
dnsc.nic.free. 38051 AAAA 2610:a1:1009:0:0:0:0:3
dnsd.nic.free. 38051 AAAA 2610:a1:1010:0:0:0:0:3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0