Apex domains cannot have CNAME records.
Question and response
Question
dig be. NS
Answer
be. 4 NS d.nsset.be.
be. 4 NS z.nsset.be.
be. 4 NS a.nsset.be.
be. 4 NS c.nsset.be.
be. 4 NS b.nsset.be.
be. 4 NS y.nsset.be.
Authority
The response has no authority records.
Additional
a.nsset.be. 170474 A 194.0.6.1
b.nsset.be. 31915 A 194.0.37.1
c.nsset.be. 31915 A 194.0.43.1
d.nsset.be. 31915 A 194.0.44.1
y.nsset.be. 31915 A 120.29.253.8
z.nsset.be. 31915 A 194.0.25.36
a.nsset.be. 170474 AAAA 2001:678:9:0:0:0:0:1
b.nsset.be. 31915 AAAA 2001:678:64:0:0:0:0:1
c.nsset.be. 31915 AAAA 2001:678:68:0:0:0:0:1
d.nsset.be. 31915 AAAA 2001:678:6c:0:0:0:0:1
y.nsset.be. 31915 AAAA 2001:dcd:7:0:0:0:0:8
z.nsset.be. 31915 AAAA 2001:678:20:0:0:0:0:36
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0