Apex domains cannot have CNAME records.
Question and response
Question
dig docentes.frm.utn.edu.ar. NS
Answer
docentes.frm.utn.edu.ar. 4 NS ns1.frm.utn.edu.ar.
docentes.frm.utn.edu.ar. 4 NS ns2.frm.utn.edu.ar.
Authority
The response has no authority records.
Additional
ns1.frm.utn.edu.ar. 4 A 190.114.210.134
ns2.frm.utn.edu.ar. 4 A 200.41.47.38
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0