dark.o2sdns.fr has no CNAME records.
Question and response
Question
dig dark.o2sdns.fr. NS
Answer
The response has no answer records.
Authority
o2sdns.fr. 1744 SOA nsa.bookmyname.com. 263626bcbfdf120f\.t943555.whois.bookmyname.com. 1772554291 43200 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0