Apex domains cannot have CNAME records.
Question and response
Question
dig bn. NS
Answer
BN. 5 NS NS1.BNNIC.BN.
BN. 5 NS NS2.BNNIC.BN.
BN. 5 NS NS4.APNIC.NET.
BN. 5 NS BN-NS.ANYCAST.PCH.NET.
Authority
The response has no authority records.
Additional
ns1.bnnic.bn. 155040 A 194.0.1.33
ns2.bnnic.bn. 155040 A 202.93.214.163
ns4.apnic.net. 2 A 202.12.31.53
ns4.apnic.net. 2 AAAA 2001:dd8:12:0:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0