smtp.cluster.ncport.ru has no NS records.
NS records for this zone are defined at cluster.ncport.ru.
NS records for this zone are defined at cluster.ncport.ru.
Question and response
Question
dig smtp.cluster.ncport.ru. NS
Answer
The response has no answer records.
Authority
cluster.ncport.ru. 1800 SOA ns1.ncport.ru. postmaster.ncport.ru. 2013013109 1800 900 691200 1800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0