Apex domains cannot have CNAME records.
Question and response
Question
dig rcsntx.sbcglobal.net. NS
Answer
rcsntx.sbcglobal.net. 4 NS a5-67.akam.net.
rcsntx.sbcglobal.net. 4 NS a8-64.akam.net.
rcsntx.sbcglobal.net. 4 NS a14-65.akam.net.
rcsntx.sbcglobal.net. 4 NS a1-212.akam.net.
rcsntx.sbcglobal.net. 4 NS a4-66.akam.net.
rcsntx.sbcglobal.net. 4 NS a9-66.akam.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0