Apex domains cannot have CNAME records.
Question and response
Question
dig roaming.ja.net. NS
Answer
roaming.ja.net. 5 NS ns10.ja.net.
roaming.ja.net. 5 NS ns11.ja.net.
roaming.ja.net. 5 NS ns12.ja.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0