Apex domains cannot have CNAME records.
Question and response
Question
dig nnetworks.jp. NS
Answer
nnetworks.jp. 5 NS dns.nnetworks.jp.
nnetworks.jp. 5 NS dns.nnetworks.co.jp.
Authority
The response has no authority records.
Additional
dns.nnetworks.jp. 5 A 59.106.50.252
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0