ns2.hdc2.cz has no CNAME records.
Question and response
Question
dig ns2.hdc2.cz. NS
Answer
The response has no answer records.
Authority
hdc2.cz. 360 SOA ns.hdc1.cz. zeleni.heureka.cz. 2015121601 10800 3600 604800 360
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0