Apex domains cannot have CNAME records.
Question and response
Question
dig icg.net. NS
Answer
icg.net. 5 NS ns14.customer.level3.net.
icg.net. 5 NS ns8.customer.level3.net.
icg.net. 5 NS as1.icg.net.
icg.net. 5 NS as3.icg.net.
icg.net. 5 NS ns7.customer.level3.net.
icg.net. 5 NS as2.icg.net.
Authority
The response has no authority records.
Additional
as1.icg.net. 5 A 209.244.4.116
as2.icg.net. 5 A 209.244.4.213
as3.icg.net. 5 A 209.244.4.117
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0