Apex domains cannot have CNAME records.
Question and response
Question
dig vygr.net. NS
Answer
vygr.net. 4 NS dns3.vygr.net.
vygr.net. 4 NS dns1.vygr.net.
vygr.net. 4 NS dns2.vygr.net.
vygr.net. 4 NS dns4.vygr.net.
Authority
The response has no authority records.
Additional
dns1.vygr.net. 4 A 162.159.26.30
dns2.vygr.net. 4 A 162.159.27.139
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0