Apex domains cannot have CNAME records.
Question and response
Question
dig cmts.sm.ptd.net. NS
Answer
cmts.sm.ptd.net. 2 NS dns5.ptd.net.
cmts.sm.ptd.net. 2 NS dns2.ptd.net.
cmts.sm.ptd.net. 2 NS dns3.ptd.net.
cmts.sm.ptd.net. 2 NS dns1.ptd.net.
cmts.sm.ptd.net. 2 NS dns4.ptd.net.
cmts.sm.ptd.net. 2 NS dns6.ptd.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0