Apex domains cannot have CNAME records.
Question and response
Question
dig drei.host. NS
Answer
drei.host. 5 NS adns3.drei.com.
drei.host. 5 NS adns1.drei.com.
drei.host. 5 NS adns2.drei.at.
drei.host. 5 NS adns4.drei.at.
Authority
The response has no authority records.
Additional
adns3.drei.com. 5 A 192.174.68.128
adns4.drei.at. 5 A 176.97.158.128
adns3.drei.com. 5 AAAA 2001:67c:1bc:0:0:0:0:128
adns4.drei.at. 5 AAAA 2001:67c:10b8:0:0:0:0:128
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0