Apex domains cannot have CNAME records.
Question and response
Question
dig ams.hp.net. NS
Answer
ams.hp.net. 3 NS ns6.hp.com.
ams.hp.net. 3 NS ns2.hp.com.
ams.hp.net. 3 NS ns1.hp.com.
ams.hp.net. 3 NS ns3.hp.com.
ams.hp.net. 3 NS ns4.hp.com.
ams.hp.net. 3 NS ns5.hp.com.
Authority
The response has no authority records.
Additional
ns1.hp.com. 3 A 15.72.96.180
ns2.hp.com. 3 A 15.72.32.180
ns3.hp.com. 3 A 15.90.180.180
ns4.hp.com. 3 A 15.90.164.180
ns5.hp.com. 3 A 15.89.160.180
ns6.hp.com. 3 A 15.89.164.180
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0