Apex domains cannot have CNAME records.
Question and response
Question
dig infra.duocast.net. NS
Answer
infra.duocast.net. 5 NS ns1.duocast.net.
infra.duocast.net. 5 NS ns2.duocast.net.
Authority
The response has no authority records.
Additional
ns1.duocast.net. 5 A 83.137.146.53
ns2.duocast.net. 5 A 91.209.7.53
ns1.duocast.net. 5 AAAA 2a01:1b0:4418:0:0:0:0:53
ns2.duocast.net. 5 AAAA 2a01:1b1:4418:0:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0