Apex domains cannot have CNAME records.
Question and response
Question
dig res-cmts.all2.ptd.net. NS
Answer
res-cmts.all2.ptd.net. 5 NS dns1.ptd.net.
res-cmts.all2.ptd.net. 5 NS dns2.ptd.net.
res-cmts.all2.ptd.net. 5 NS dns3.ptd.net.
res-cmts.all2.ptd.net. 5 NS dns4.ptd.net.
res-cmts.all2.ptd.net. 5 NS dns5.ptd.net.
res-cmts.all2.ptd.net. 5 NS dns6.ptd.net.
Authority
The response has no authority records.
Additional
dns1.ptd.net. 5 A 204.186.0.201
dns2.ptd.net. 5 A 207.44.96.129
dns3.ptd.net. 5 A 204.186.0.203
dns4.ptd.net. 5 A 207.44.0.1
dns5.ptd.net. 5 A 204.186.80.169
dns6.ptd.net. 5 A 204.186.80.249
dns1.ptd.net. 3 AAAA 2606:9400:0:a:204:186:0:201
dns2.ptd.net. 3 AAAA 2606:9400:0:b:207:44:96:129
dns3.ptd.net. 3 AAAA 2606:9400:0:a:204:186:0:203
dns4.ptd.net. 3 AAAA 2606:9400:0:b:207:44:0:1
dns5.ptd.net. 3 AAAA 2606:9400:0:c:204:186:80:169
dns6.ptd.net. 3 AAAA 2606:9400:0:d:204:186:80:249
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0