Apex domains cannot have CNAME records.
Question and response
Question
dig techfak.NET. NS
Answer
techfak.net. 1 NS auth1.DNS.TechFak.NET.
techfak.net. 1 NS auth-ext0.DNS.TechFak.NET.
techfak.net. 1 NS auth0.DNS.TechFak.NET.
Authority
The response has no authority records.
Additional
auth0.dns.TechFak.NET. 1 A 129.70.136.154
auth1.dns.TechFak.NET. 1 A 129.70.132.16
auth-ext0.dns.techfak.net. 1 A 195.201.119.124
auth0.dns.TechFak.NET. 1 AAAA 2001:638:504:2000:0:0:0:f1
auth1.dns.TechFak.NET. 1 AAAA 2001:638:504:2000:0:0:0:f2
auth-ext0.dns.techfak.net. 1 AAAA 2a01:4f8:1c0c:7f8f:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0