Apex domains cannot have CNAME records.
Question and response
Question
dig com.mx. NS
Answer
com.mx. 1 NS o.mx-ns.mx.
com.mx. 1 NS m.mx-ns.mx.
com.mx. 1 NS i.mx-ns.mx.
com.mx. 1 NS c.mx-ns.mx.
com.mx. 1 NS e.mx-ns.mx.
com.mx. 1 NS x.mx-ns.mx.
Authority
The response has no authority records.
Additional
c.mx-ns.mx. 151134 A 192.100.224.1
e.mx-ns.mx. 126155 A 189.201.244.1
i.mx-ns.mx. 126136 A 207.248.68.1
m.mx-ns.mx. 151070 A 200.94.176.1
o.mx-ns.mx. 126155 A 200.23.1.1
x.mx-ns.mx. 109887 A 201.131.252.1
c.mx-ns.mx. 151134 AAAA 2001:1258:0:0:0:0:0:1
e.mx-ns.mx. 126155 AAAA 2801:c4:c0:0:0:0:0:1
i.mx-ns.mx. 126136 AAAA 2801:c4:d0:0:0:0:0:1
m.mx-ns.mx. 151070 AAAA 2001:13c7:7000:0:0:0:0:1
o.mx-ns.mx. 126155 AAAA 2001:1201:0:0:0:0:0:1
x.mx-ns.mx. 109887 AAAA 2001:1201:10:0:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0