DNS Server Options

There are several different types of a DNS server. At the most basic, the server does not hold any permanent data about any domains itself, but simply forwards queries to other servers (a cache-only server) and stores the result. A DNS primary server has a master database for a domain. A DNS secondary server provides a local copy of master database for a domain that it copies from a primary server. DNS server can be both a primary and a secondary domain server at the same time.

All DNS servers store the results of successful queries (whether it resolved the query itself or forwarded it to another DNS server). If the server receives another query for the same name, it replies with the stored answer. This is called caching. A server that only does this (a cache-only server) can be useful to shorten the response time compared with contacting a more remote DNS server.

There are two different ways in which a DNS server can provide data for a domain; it can be a primary, or a secondary server for the domain. For the primary server, the DNS administrator maintains the master database for the hosts in the domain on the server. For the secondary server, the server keeps a local copy of the master database for the domain that it retrieves from the primary server. It periodically compares its database to the one on the primary server and requests a new copy if a difference is detected.

The difference between normal caching and being a secondary server for a domain is that normal caching only stores the results from previous queries. A secondary server actively retrieves the information in anticipation of future requests. This reduces the load on the primary server, and also makes it a backup in case the primary server cannot be contacted. If your server is a primary server for a domain, you should have a secondary as a backup.

There are two different types of DNS server configuration that you use depending on what the structure of your local domain is. The first type, which is referred to as Basic DNS Server, involves specifying a list of other DNS servers to query if a name cannot be resolved locally. The second type is called a DNS Internal Root Server. It is used on Intranets without an Internet connection (in other words, without access to any other DNS servers), and also on large Intranets with several subdomains, where there is a need for special DNS servers for the internal hierarchy.

Finally, a DNS Primary Server may need to provide reverse maps (IP address to name) as well as forward maps (name to IP address). Please consult with your ISP to find out whether this responsibility is delegated to you or not.