rdns1.topnet.com.mx has no CNAME records.
Question and response
Question
dig rdns1.topnet.com.mx. NS
Answer
The response has no answer records.
Authority
topnet.com.mx. 2340 SOA idcdns2.inext.net.mx. mjmorales.inext.net.mx. 2012030600 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0