f.nic.de has no CNAME records.
Question and response
Question
dig f.nic.de. NS
Answer
The response has no answer records.
Authority
nic.de. 1800 SOA ns1.denic.de. dns-operations.denic.de. 1771933561 10800 1800 3600000 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0