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DNS: Primary and Secondary Name Servers

A name server's purpose is to receive queries from resolvers and return answers to those queries. Usually, a resolver, or some other program, will make a query and the name server will either return an answer, or the address of the place that the resolver can look to find an answer.

Name servers hold information about a domain's structure. If a name server holds complete information for a specific zone, it is considered authoritative for that zone. Being authoritative, that server is responsible for maintaining accurate information about that zone.

When an authoritative server answers a query, a local name server will cache the answer for future usage. If the local server is queried for that information within the time to live setting, it will return a non-authoritative answer.

There are three types of name servers that users can set-up. There are primary, secondary and caching-only name servers.

Primary name servers are considered authoritative for their domain. All information about that domain is derived from this server.

Information is loaded from a set of files that the primary name server maintains. These files are very important to set up carefully since all other name servers will be looking to this one for information.

Secondary name servers will transfer the information that the primary name server maintains to its own files. This way, a secondary name server will have current information. These name servers are also considered authoritative for their domain.

A zone transfer occurs every time that a secondary name server starts up and every time the refresh time runs-out. It is good to have a secondary name server, or more than one if possible, for redundancy. It will also lessen the load on the other name servers. Also, up to date information will only have to be maintained on the primary name server. Since the other name server, or servers, will look to the primary for information, only one set of files will need to be updated whenever a change is made.

Another type of name server is a caching-only name server. This type of name server gets the answers to queries from other name servers and caches the information for the time to live setting. These name servers are considered non-authoritative.

Name Server Configurations