ftp.slaskdatacenter.com has no CNAME records.
Question and response
Question
dig ftp.slaskdatacenter.com. NS
Answer
The response has no answer records.
Authority
slaskdatacenter.com. 3357 SOA ns1.slaskdatacenter.com. hostmaster.slaskdatacenter.com. 2022091502 3600 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0