Apex domains cannot have CNAME records.
Question and response
Question
dig internetdsl.pl. NS
Answer
internetdsl.pl. 5 NS ns2.internetdsl.pl.
internetdsl.pl. 5 NS ns1.internetdsl.pl.
Authority
The response has no authority records.
Additional
ns1.internetdsl.pl. 5 A 217.97.216.18
ns2.internetdsl.pl. 5 A 217.97.216.19
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0