Apex domains cannot have CNAME records.
Question and response
Question
dig cogentco.com. NS
Answer
cogentco.com. 5 NS auth1.dns.cogentco.com.
cogentco.com. 5 NS auth2.dns.cogentco.com.
Authority
The response has no authority records.
Additional
auth1.dns.cogentco.com. 5 A 66.28.0.14
auth2.dns.cogentco.com. 5 A 66.28.0.30
auth1.dns.cogentco.com. 5 AAAA 2001:550:1:a:0:0:0:d
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0