Apex domains cannot have CNAME records.
Question and response
Question
dig web.yas-online.net. NS
Answer
web.yas-online.net. 1 NS de.ch-inter.net.
web.yas-online.net. 1 NS ch.ch-inter.net.
web.yas-online.net. 1 NS nl.ch-inter.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0