sip.datakom.ru has no NS records.
NS records for this zone are defined at datakom.ru.
NS records for this zone are defined at datakom.ru.
Question and response
Question
dig sip.datakom.ru. NS
Answer
The response has no answer records.
Authority
datakom.ru. 3600 SOA ns1.luadns.net. hostmaster.luadns.com. 1772509623 1200 120 604800 3600
Additional
. 32768 OPT ; payload 512, xrcode 0, version 0, flags 32768