CentOS7.do.pc2linux.com has no CNAME records.
Question and response
Question
dig CentOS7.do.pc2linux.com. NS
Answer
The response has no answer records.
Authority
do.pc2linux.com. 10777 SOA do.pc2linux.com. asampau.gmail.com. 2026022208 360 180 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0