Apex domains cannot have CNAME records.
Question and response
Question
dig ext.ti.com. NS
Answer
ext.ti.com. 1 NS ns-b.pnap.net.
ext.ti.com. 1 NS ns3.ti.com.
ext.ti.com. 1 NS ns-d.pnap.net.
ext.ti.com. 1 NS nsde.ti.com.
ext.ti.com. 1 NS ns-c.pnap.net.
ext.ti.com. 1 NS ns-a.pnap.net.
ext.ti.com. 1 NS ns4.ti.com.
ext.ti.com. 1 NS ns.ti.com.
ext.ti.com. 1 NS ns2.ti.com.
Authority
The response has no authority records.
Additional
ns.ti.com. 1 A 198.47.19.1
ns2.ti.com. 1 A 198.47.19.2
ns3.ti.com. 1 A 198.47.26.139
ns4.ti.com. 1 A 198.47.26.138
ns-a.pnap.net. 1 A 64.94.123.4
ns-b.pnap.net. 1 A 64.94.123.36
ns-c.pnap.net. 1 A 64.95.61.4
ns-d.pnap.net. 1 A 64.95.61.36
nsde.ti.com. 1 A 192.91.60.140
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0