Apex domains cannot have CNAME records.
Question and response
Question
dig host.yas-online.net. NS
Answer
host.yas-online.net. 5 NS ch.ch-inter.net.
host.yas-online.net. 5 NS nl.ch-inter.net.
host.yas-online.net. 5 NS de.ch-inter.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0