Apex domains cannot have CNAME records.
Question and response
Question
dig swisscenter.net. NS
Answer
swisscenter.net. 5 NS ns3.swisslink.ch.
swisscenter.net. 5 NS ns1.swisslink.ch.
swisscenter.net. 5 NS ns2.swisslink.ch.
swisscenter.net. 5 NS ns4.swisslink.ch.
Authority
The response has no authority records.
Additional
ns1.swisslink.ch. 5 A 83.166.158.199
ns2.swisslink.ch. 5 A 94.103.96.78
ns3.swisslink.ch. 5 A 94.103.96.74
ns4.swisslink.ch. 5 A 94.103.96.75
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0