Apex domains cannot have CNAME records.
Question and response
Question
dig mxge.comcast.net. NS
Answer
mxge.comcast.net. 2 NS gtd03-d.ashburn.va.ndcasbn.comcast.net.
mxge.comcast.net. 2 NS gtd03-d.hillsboro.or.ndchlsbr.comcast.net.
mxge.comcast.net. 2 NS gtd03-d.northlake.il.ndcchgo.comcast.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0