Apex domains cannot have CNAME records.
Question and response
Question
dig as2.ch. NS
Answer
as2.ch. 5 NS ns1.as2.ch.
as2.ch. 5 NS ns4.as2.ch.
as2.ch. 5 NS ns3.as2.ch.
as2.ch. 5 NS ns2.as2.ch.
Authority
The response has no authority records.
Additional
ns1.as2.ch. 5 A 46.4.54.115
ns2.as2.ch. 5 A 46.4.54.116
ns3.as2.ch. 5 A 185.136.97.111
ns4.as2.ch. 5 A 185.136.96.111
ns1.as2.ch. 5 AAAA 2a01:4f8:140:1321:0:0:0:3
ns2.as2.ch. 5 AAAA 2a01:4f8:140:1321:0:0:0:4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0