This is a good thing as there are some other domain extensions like "co. Your nameservers are listed Good.
The parent server a. This is a must if you want to be found as anyone that does not know your DNS servers vietsex first ask the parent nameservers. Glue records are Vietsex records that are associated with NS records to provide "bootstrapping" information to the nameserver.
Every nameserver listed has A records. This is a must if you want to be found.
Your nameservers the ones reported by the parent server do not report that they allow recursive queries for anyone. You have to make sure your parent server has the same NS records for your zone as you do according to the RFC.
This tests only nameservers that are common at the parent and at your nameservers.