Apex domains cannot have CNAME records.
Question and response
Question
dig srt.com. NS
Answer
srt.com. 4 NS camilla.srt.com.
srt.com. 4 NS rizzo.srt.com.
srt.com. 4 NS gonzo.srt.com.
Authority
The response has no authority records.
Additional
gonzo.srt.com. 4 A 216.221.96.36
rizzo.srt.com. 4 A 216.221.96.38
camilla.srt.com. 4 A 216.221.96.37
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0