Apex domains cannot have CNAME records.
Question and response
Question
dig imp.ch. NS
Answer
imp.ch. 5 NS ns3.imp.ch.
imp.ch. 5 NS ns2.imp.ch.
imp.ch. 5 NS ns1.imp.ch.
Authority
The response has no authority records.
Additional
ns1.imp.ch. 5 A 157.161.1.2
ns2.imp.ch. 5 A 157.161.255.133
ns3.imp.ch. 5 A 16.62.212.143
ns1.imp.ch. 5 AAAA 2001:4060:1:1001:0:0:1:1
ns2.imp.ch. 5 AAAA 2001:4060:1:2000:0:0:1:1
ns3.imp.ch. 5 AAAA 2a05:d019:6cb:b479:df44:e7ea:d646:c6d3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0