dnsmaster.ostnet.pl has no CNAME records.
Question and response
Question
dig dnsmaster.ostnet.pl. NS
Answer
The response has no answer records.
Authority
ostnet.pl. 600 SOA dns.ostnet.pl. mgradzki.ost.net.pl. 2026021801 14400 3600 1209600 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0