der06.vas-server.cz has no CNAME records.
Question and response
Question
dig der06.vas-server.cz. NS
Answer
The response has no answer records.
Authority
vas-server.cz. 3600 SOA ns.vas-hosting.cz. info.vas-hosting.cz. 2603041705 28800 600 2419200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0