DNS Queries

The major task carried out by a DNS server is to respond to queries (questions) from a local or remote resolver or other DNS acting on behalf of a resolver - a query would be somthing like 'what is the IP address of host=fred in domain=mydomain.com'. There are three types of queries that DNS support:

1. A recursive query - the real answer to the question is always returned. DNS servers are not required to support recursive queries.
2. An Iterative (or non-recursive) query - where the real answer MAY be returned. All DNS servers must support Iterative queries.
3. A Inverse query - where the user wants to know the domain name given a resource record.

Note: The process called Reverse Mapping does not use Inverse queries but instead uses recursive and non-recursive queries with the special domain name IN-ADDR.ARPA.

Historically reverse IP mapping was non-mandatory. Many systems however now use reverse mapping for security and simple authentication schemes and is its proper implementation and maintenance is now essential.