mona2.singtel.com has no CNAME records.
Question and response
Question
dig mona2.singtel.com. NS
Answer
The response has no answer records.
Authority
singtel.com. 390 SOA dnspri.singnet.com.sg. hostmaster.singnet.com.sg. 2025100969 3600 1800 604800 28800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0