Apex domains cannot have CNAME records.
Question and response
Question
dig mdsl.net. NS
Answer
mdsl.net. 5 NS ns-1403.awsdns-47.org.
mdsl.net. 5 NS ns-1624.awsdns-11.co.uk.
mdsl.net. 5 NS ns-483.awsdns-60.com.
mdsl.net. 5 NS ns-647.awsdns-16.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0