Apex domains cannot have CNAME records.
Question and response
Question
dig flashcable.ch. NS
Answer
flashcable.ch. 5 NS ns2.flashcable.ch.
flashcable.ch. 5 NS ns3.flashcable.ch.
flashcable.ch. 5 NS ns4.flashcable.ch.
flashcable.ch. 5 NS ns1.flashcable.ch.
Authority
The response has no authority records.
Additional
ns1.flashcable.ch. 5 A 81.92.97.18
ns2.flashcable.ch. 5 A 81.92.97.19
ns3.flashcable.ch. 5 A 81.92.97.66
ns4.flashcable.ch. 5 A 81.92.97.67
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0