Apex domains cannot have CNAME records.
Question and response
Question
dig a.d-53.net. NS
Answer
a.d-53.net. 5 NS ns.iij-dns.jp.
a.d-53.net. 5 NS ns.iij-dns.biz.
a.d-53.net. 5 NS ns.iij-dns.net.
Authority
The response has no authority records.
Additional
ns.iij-dns.biz. 5 A 202.32.219.52
ns.iij-dns.net. 5 A 210.138.20.112
ns.iij-dns.biz. 5 AAAA 2001:240:bb81:0:0:0:28:52
ns.iij-dns.net. 5 AAAA 2001:240:bb81:0:0:0:29:112
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0