cc.ertelecom.ru.t.ertelecom.ru has no NS records.
NS records for this zone are defined at t.ertelecom.ru.
NS records for this zone are defined at t.ertelecom.ru.
Question and response
Question
dig cc.ertelecom.ru.t.ertelecom.ru. NS
Answer
The response has no answer records.
Authority
t.ertelecom.ru. 3600 SOA ns6.ertelecom.ru. noc.ertelecom.ru. 2017083001 86400 1800 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0