Apex domains cannot have CNAME records.
Question and response
Question
dig dial1.Philadelphia1.Level3.net. NS
Answer
Dial1.Philadelphia1.Level3.net. 5 NS poolns2.Level3.net.
Dial1.Philadelphia1.Level3.net. 5 NS poolns1.Level3.net.
Dial1.Philadelphia1.Level3.net. 5 NS dialns1.level3.net.
Dial1.Philadelphia1.Level3.net. 5 NS dialns2.level3.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0