ex.cz.net has no CNAME records.
Question and response
Question
dig ex.cz.net. NS
Answer
The response has no answer records.
Authority
cz.net. 10036 SOA ns.eunet.cz. hostmaster.cz.net. 2025121100 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0