Apex domains cannot have CNAME records.
Question and response
Question
dig glb.frontiernet.net. NS
Answer
glb.frontiernet.net. 5 NS gtm01.ftwy.in.frontiernet.net.
glb.frontiernet.net. 5 NS gtm01.roch.ny.frontiernet.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0