ns.rackspeed-dns.com has no CNAME records.
Question and response
Question
dig ns.rackspeed-dns.com. NS
Answer
The response has no answer records.
Authority
rackspeed-dns.com. 7355 SOA ns.rackspeed-dns.de. hostmaster.rackspeed.de. 2026022401 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0