mx2.mastertel.com has no NS records.
NS records for this zone are defined at mastertel.com.
NS records for this zone are defined at mastertel.com.
Question and response
Question
dig mx2.mastertel.com. NS
Answer
The response has no answer records.
Authority
mastertel.com. 3600 SOA ns1.mastertel.ru. noc.mastertel.ru. 2025101501 10800 3600 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0