Apex domains cannot have CNAME records.
Question and response
Question
dig vargas.sigrunlabs.com. NS
Answer
vargas.sigrunlabs.com. 2 NS nsg1.namebrightdns.com.
vargas.sigrunlabs.com. 2 NS nsg2.namebrightdns.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0