ns2.mangupos.com has no CNAME records.
Question and response
Question
dig ns2.mangupos.com. NS
Answer
The response has no answer records.
Authority
mangupos.com. 10228 SOA ns1.mangupos.com. deploy.vps.mangusoft.com. 2026020400 86400 7200 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0