Apex domains cannot have CNAME records.
Question and response
Question
dig tuxdns.net. NS
Answer
tuxdns.net. 3 NS zee.tuxdns.net.
tuxdns.net. 3 NS niobe.100.pt.
tuxdns.net. 3 NS trinity.tuxdns.com.
Authority
The response has no authority records.
Additional
zee.tuxdns.net. 3 A 193.163.151.100
niobe.100.pt. 3 A 185.83.251.132
trinity.tuxdns.com. 3 A 195.200.253.233
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0