Apex domains cannot have CNAME records.
Question and response
Question
dig gtecablemodem.com. NS
Answer
gtecablemodem.com. 5 NS dnsauth1.sys.gtei.net.
gtecablemodem.com. 5 NS dnsauth2.sys.gtei.net.
gtecablemodem.com. 5 NS dnsauth3.sys.gtei.net.
Authority
The response has no authority records.
Additional
dnsauth1.sys.gtei.net. 5 A 4.2.49.2
dnsauth2.sys.gtei.net. 5 A 4.2.49.3
dnsauth3.sys.gtei.net. 5 A 4.2.49.4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0