Apex domains cannot have CNAME records.
Question and response
Question
dig lightspeed.mdsnwi.sbcglobal.net. NS
Answer
lightspeed.mdsnwi.sbcglobal.net. 5 NS ns1.attdns.com.
lightspeed.mdsnwi.sbcglobal.net. 5 NS ns4.attdns.com.
lightspeed.mdsnwi.sbcglobal.net. 5 NS ns3.attdns.com.
lightspeed.mdsnwi.sbcglobal.net. 5 NS ns2.attdns.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0