DNS Server

As a DNS server, the Netra server can cache the result of name service queries. This means that repeat queries can be answered locally rather than through contacting the source name server again. That is, until the information becomes out of date. This is called a cache-only server.

A primary domain server maintains an authoritative master database with information about a domain which it propagates to other name servers. It should have a secondary name server, either on the LAN or with the ISP, as a backup.

A secondary domain server keeps a local copy of a master database for a domain which it retrieves from the primary DNS server for the domain. It periodically compares its database to that on the primary DNS server and requests a new copy if a difference is detected. While standard caching only stores the results from previous queries, a secondary domain server actively retrieves all the domain 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.

On an intranet without an Internet connection, or on a large network with several subdomains served by separate DNS primary domain servers, an internal root name server is needed. The root name server keeps a database of the primary domain servers for the subdomains, and delegates queries to these servers.