mx4.mts.ru has no NS records.
NS records for this zone are defined at mts.ru.
NS records for this zone are defined at mts.ru.
Question and response
Question
dig mx4.mts.ru. NS
Answer
The response has no answer records.
Authority
mts.ru. 900 SOA ns2.mts.ru. dns.mts.ru. 2026031007 10800 1800 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0