Apex domains cannot have CNAME records.
Question and response
Question
dig ch-zh1.pool-ewcs.ch. NS
Answer
ch-zh1.pool-ewcs.ch. 1 NS dns2.ewcsdns.ch.
ch-zh1.pool-ewcs.ch. 1 NS dns1.ewcsdns.ch.
ch-zh1.pool-ewcs.ch. 1 NS dns3.ewcsdns.ch.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0