A nameserver is a server (host) where a name service (generally DNS) program is running generally on port 53.
A name server is organized in namespace information unit called ZONEs that manages DNS information for an apex domain.
A nameserver may be an AUTHORITY for one or more zones.
The authoritative nameserver for a zone (normally for your domain) are designed by the NS record that you can query
For instance:
nslookup -type=NS example.com
dig -t ns DOMAIN
If you run a nameserver for a zone, the configuration file are known as zone file
These files are managed by the primary nameservers (also called master/main nameservers) and sent to the secondary nameservers (also called slave nameservers)
There are four primary nameserver configuration types:
A nameserver may be one or more of these types.
For example, a nameserver can be:
Any nameserver can be a primary and secondary nameserver for different zones at the same time, and they may also be considered authoritative for multiple zones. It all depends on the nameserver's particular configuration.
You set:
Before updating your DNS server when you want to move one's domain from one registrar to another., you can check that the DNS server have a good configuration.
This is called an undelegated domain test (ie when this is not your actual public/published DNS).
For example, if you want to move your zone example.com from the nameserver “ns.example.com” to the nameserver “ns.example.org”.
The https://zonemaster.fr/ of AFNIC can check the configuration of the primary and secondary DNS server:
The database public-dns.info contains public DNS Servers that are reachable by IPv4 or IPv6. (Around 6000 Nameservers from 150 countries)