Mapping a name to an address or an address to a name is called name address resolution. DNS is designed as a client server application. A host that needs to map an address to a name or a name to an address calls a DNS client called a resolver.

Recursive Resolution : The client (resolver) can ask for a recursive answer from a name server. This means that the resolver expects the server to supply the final answer. If the server is the authority for the domain name, it checks its database and responds. If the server is not the authority, it sends the request to another server (the parent usually) and waits for the response. If the parent is the authority, it responds, otherwise, it sends the query to yet another server. When the query is finally resolved the response travels back until it finally reaches the requesting client.

Iterative resolution:

If the client does not ask for a recursive answer the mapping can be done iteratively. If the server is an authority for the name, it sends the answer. if it is not, it returns (to the client) the IP address of the server that it thinks can resolve the query. The client is responsible for repeating the query to this second server. If the newly addressed server can resolve the problem, it answers the query with the IP address, Otherwise it returns the IP address of a new server to the client. Now the client must repeat the query to the third server. This process is called iterative because the client repeats the same query to multiple servers.