DNS has two query types called recursive and iterative. This video looks at how these queries are used to resolve DNS requests and how you would configure them in your organization to get the results that you require.
Iterative: An Iterative query is a DNS request which states, “Give me the answer or give me any information that will help me find the answer”. If the DNS server has no information that will assist, it will respond back stating that and will not attempt to contact other DNS servers to attempt to find out the answer. Root hints servers are configured to only respond to iterative queries. As the root hints servers are at the top of the DNS hierarchy, if these were to become overloaded with recursive queries, this would affect their ability to answer other DNS queries and thus this is why recursive queries are switched off on the root hints servers.
Summary
Recursion: Sent by clients on the network to DNS Servers. The DNS server that is configured to accept recursive queries, which is the default, will contact other DNS servers as required to find out the result.
Iterative: Will respond back from its cache or zone files. It will not attempt to contact other DNS servers to find out the answer. If it knows another DNS server that may be able to assist with the name resolution it will return the IP Address of that DNS server.
References
“MCTS 70-640 Configuring Windows Server 2008 Active Directory Second edition” pg 455
“Installing and Configuring Windows Server 2012 Exam Ref 70-410” pg 230
“Domain Name System” http://en.wikipedia.org/wiki/Domain_Name_System
Credits
Installing and Configuring Windows Server 2012
