Apex domains cannot have CNAME records.
Question and response
Question
dig iristel.ch. NS
Answer
iristel.ch. 5 NS pdns104.ultradns.com.
iristel.ch. 5 NS pdns104.ultradns.net.
iristel.ch. 5 NS pdns104.ultradns.org.
iristel.ch. 5 NS pdns104.ultradns.biz.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0