spf1.sfr.fr has no NS records.
NS records for this zone are defined at sfr.fr.
NS records for this zone are defined at sfr.fr.
Question and response
Question
dig spf1.sfr.fr. NS
Answer
The response has no answer records.
Authority
sfr.fr. 900 SOA pranspub03.phys.prod. support.dns.sfr.net. 2013017648 3600 900 2419200 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0