Apex domains cannot have CNAME records.
Question and response
Question
dig mmsc.iristel.com. NS
Answer
mmsc.iristel.com. 5 NS pdns104.ultradns.com.
mmsc.iristel.com. 5 NS pdns104.ultradns.biz.
mmsc.iristel.com. 5 NS pdns104.ultradns.org.
mmsc.iristel.com. 5 NS pdns104.ultradns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0