pruebas.inext.net.mx has no CNAME records.
Question and response
Question
dig pruebas.inext.net.mx. NS
Answer
The response has no answer records.
Authority
inext.net.mx. 4038 SOA idcdns1.inext.net.mx. hostmaster.inext.net.mx. 2012080100 10800 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0