server.subreg.cz has no CNAME records.
Question and response
Question
dig server.subreg.cz. NS
Answer
The response has no answer records.
Authority
subreg.cz. 797 SOA ivan.ns.cloudflare.com. dns.cloudflare.com. 2395573990 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0