Apex domains cannot have CNAME records.
Question and response
Question
dig cv.gv.shawcable.net. NS
Answer
cv.gv.shawcable.net. 5 NS ns1.cv.gv.shawcable.net.
cv.gv.shawcable.net. 5 NS ns3.st.vc.shawcable.net.
Authority
The response has no authority records.
Additional
ns1.cv.gv.shawcable.net. 5 A 64.59.160.50
ns1.cv.gv.shawcable.net. 5 AAAA 2001:4e8:0:400b:0:0:53:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0