Apex domains cannot have CNAME records.
Question and response
Question
dig ip.fdtnet.net. NS
Answer
ip.fdtnet.net. 5 NS ns2.firstdigital.com.
ip.fdtnet.net. 5 NS ns1.firstdigital.com.
Authority
The response has no authority records.
Additional
ns1.firstdigital.com. 5 A 66.219.205.47
ns2.firstdigital.com. 5 A 66.219.205.48
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0