Apex domains cannot have CNAME records.
Question and response
Question
dig tec.mx. NS
Answer
tec.mx. 3 NS ns1e.itesm.mx.
tec.mx. 3 NS ns2e.itesm.mx.
Authority
The response has no authority records.
Additional
ns1e.itesm.mx. 3 A 200.33.42.250
ns2e.itesm.mx. 3 A 40.74.177.143
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0