a.dns-servers.net.ru has no NS records.
NS records for this zone are defined at net.ru.
NS records for this zone are defined at net.ru.
Question and response
Question
dig a.dns-servers.net.ru. NS
Answer
The response has no answer records.
Authority
net.ru. 3600 SOA a.dns-servers.net.ru. hostmaster.ripn.net. 2272820001 86400 14400 2592000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0