portal.pb.edu.pl has no CNAME records.
Question and response
Question
dig portal.pb.edu.pl. NS
Answer
The response has no answer records.
Authority
pb.edu.pl. 2373 SOA dns.man.bialystok.pl. admin.biaman.pl. 2026022301 10800 1200 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0