Apex domains cannot have CNAME records.
Question and response
Question
dig by.tsunami-network.com. NS
Answer
by.tsunami-network.com. 5 NS ns1.tsunami.pl.
by.tsunami-network.com. 5 NS ns2.tsunami.pl.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0