Apex domains cannot have CNAME records.
Question and response
Question
dig swiss-dns.com. NS
Answer
swiss-dns.com. 5 NS ns2.swiss-dns.com.
swiss-dns.com. 5 NS ns3.swiss-dns.com.
swiss-dns.com. 5 NS ns1.swiss-dns.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0