Apex domains cannot have CNAME records.
Question and response
Question
dig trafficmanager.net. NS
Answer
trafficmanager.net. 5 NS tm1.edgedns-tm.info.
trafficmanager.net. 5 NS tm2.edgedns-tm.info.
trafficmanager.net. 5 NS tm1.dns-tm.com.
trafficmanager.net. 5 NS tm2.dns-tm.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0