xen.nsys.cz has no CNAME records.
Question and response
Question
dig xen.nsys.cz. NS
Answer
The response has no answer records.
Authority
nsys.cz. 1610 SOA ans.nsys.cz. admin.nsys.cz. 2026021001 14400 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0