Within the DNS hierarchy, different servers are responsible for the data in a certain domain and sometimes in subdomains as well. These servers are name servers, and the part of the hierarchy that they are responsible for is called a zone. A zone can include more than just one domain. If one name server, for example, is responsible for everything in sandervanvugt.nl, including the subdomain servers and workstations, then the zone is sandervanvugt.nl. Speaking generically, a zone is just a part of the DNS hierarchy.
All zones should at least have two responsible name servers. Of these, the first is the master name server. This is the name server that in the end is responsible for the data in a zone. For fault tolerance reasons and to make the information better accessible, you can use one or more slave servers as well. These slave servers will periodically get an update of all the data on the master server by means of a zone transfer, which is the process the master server uses to update the database on the slave server. Note that DNS uses a single-master model; updates are performed on the master server and nowhere else. You should also know that the name servers do not need to be in the zone for which they are responsible. For example, often the name server of a given domain will be hosted by the Internet provider, which, of course, has its own domain. You can maintain your own DNS server, which is useful to do if your organization is larger than average, but you don't have to do so.
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