Apex domains cannot have CNAME records.
Question and response
Question
dig itu.ch. NS
Answer
itu.ch. 5 NS ns2.itu.ch.
itu.ch. 5 NS ns5.itu.ch.
itu.ch. 5 NS ns6.itu.ch.
itu.ch. 5 NS ns7.itu.ch.
itu.ch. 5 NS ns8.itu.ch.
itu.ch. 5 NS ns.itu.ch.
itu.ch. 5 NS ns3.itu.ch.
Authority
The response has no authority records.
Additional
ns.itu.ch. 5 A 156.106.192.121
ns2.itu.ch. 5 A 4.156.158.244
ns3.itu.ch. 5 A 20.101.208.60
ns5.itu.ch. 5 A 205.251.192.35
ns6.itu.ch. 5 A 205.251.195.44
ns7.itu.ch. 5 A 205.251.196.40
ns8.itu.ch. 5 A 205.251.199.74
ns.itu.ch. 5 AAAA 2a00:7580:60:2141:0:0:0:10
ns2.itu.ch. 5 AAAA 2603:1030:20e:c:0:0:0:175
ns3.itu.ch. 5 AAAA 2603:1020:203:3:0:0:0:20c
ns5.itu.ch. 5 AAAA 2600:9000:5300:2300:0:0:0:1
ns6.itu.ch. 5 AAAA 2600:9000:5303:2c00:0:0:0:1
ns7.itu.ch. 5 AAAA 2600:9000:5304:2800:0:0:0:1
ns8.itu.ch. 5 AAAA 2600:9000:5307:4a00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0