Apex domains cannot have CNAME records.
Question and response
Question
dig tld.mu. NS
Answer
tld.mu. 5 NS v0n0.tld.mu.
tld.mu. 5 NS v2n0.tld.mu.
tld.mu. 5 NS v0n1.tld.mu.
tld.mu. 5 NS v0n3.tld.mu.
tld.mu. 5 NS v0n2.tld.mu.
tld.mu. 5 NS v2n1.tld.mu.
Authority
The response has no authority records.
Additional
v0n0.tld.mu. 172074 A 199.254.59.33
v0n1.tld.mu. 172074 A 199.254.60.33
v0n2.tld.mu. 172074 A 199.254.61.33
v0n3.tld.mu. 172074 A 199.254.62.33
v2n0.tld.mu. 172074 A 199.249.116.33
v2n1.tld.mu. 172074 A 199.249.124.33
v0n0.tld.mu. 172074 AAAA 2001:500:25:0:0:0:0:33
v0n1.tld.mu. 172074 AAAA 2001:500:26:0:0:0:0:33
v0n2.tld.mu. 172074 AAAA 2001:500:27:0:0:0:0:33
v0n3.tld.mu. 172074 AAAA 2001:500:28:0:0:0:0:33
v2n0.tld.mu. 172074 AAAA 2001:500:44:0:0:0:0:33
v2n1.tld.mu. 172074 AAAA 2001:500:4c:0:0:0:0:33
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0