Apex domains cannot have CNAME records.
Question and response
Question
dig net.bn. NS
Answer
net.bn. 5 NS bn-ns.anycast.pch.net.
net.bn. 5 NS ns4.apnic.net.
net.bn. 5 NS ns1.bnnic.bn.
net.bn. 5 NS ns2.bnnic.bn.
Authority
The response has no authority records.
Additional
ns1.bnnic.BN. 154762 A 194.0.1.33
ns2.bnnic.BN. 154762 A 202.93.214.163
ns4.apnic.net. 5 A 202.12.31.53
ns4.apnic.net. 5 AAAA 2001:dd8:12:0:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0