mx2.mail.corp.masterhost.RU has no NS records.
NS records for this zone are defined at corp.masterhost.RU.
NS records for this zone are defined at corp.masterhost.RU.
Question and response
Question
dig mx2.mail.corp.masterhost.RU. NS
Answer
The response has no answer records.
Authority
corp.masterhost.RU. 600 SOA ns5.masterhost.RU. hostmaster.masterhost.RU. 1 28800 7200 1209600 600
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0