_2.oktawave.com has no CNAME records.
Question and response
Question
dig _2.oktawave.com. NS
Answer
The response has no answer records.
Authority
oktawave.com. 10782 SOA ns1.oktawave.com. hostmaster.oktawave.com. 2025111700 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0