Apex domains cannot have CNAME records.
Question and response
Question
dig iscgnet.com. NS
Answer
iscgnet.com. 2 NS ns3.iscgnet.com.
iscgnet.com. 2 NS ns4.iscgnet.com.
iscgnet.com. 2 NS ns1.iscg.net.
iscgnet.com. 2 NS ns2.iscg.net.
Authority
The response has no authority records.
Additional
ns1.iscg.net. 2 A 66.242.34.5
ns2.iscg.net. 2 A 66.242.34.4
ns3.iscgnet.com. 2 A 66.242.35.8
ns4.iscgnet.com. 2 A 66.242.48.20
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0