_netblocks.srv.cat has no NS records.
NS records for this zone are defined at srv.cat.
NS records for this zone are defined at srv.cat.
Question and response
Question
dig _netblocks.srv.cat. NS
Answer
The response has no answer records.
Authority
srv.cat. 900 SOA ns-695.awsdns-22.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0