Iterative – query made from a client to a DNS server in which the server returns the best answer that it can provide based on its cache or zone data.
If the queried server does not have an exact match for the request, it provides a pointer to an authoritative server in another level of the domain namespace.
Recursive – query made from a client to a DNS server in which the server assumes the full workload and responsibility for providing a complete answer to the query. The server will then perform separate iterative queries to other servers (on behalf of the client) to assist in answering the recursive query.
By default recursive query is enabled but it can be disabled if you don’t want to use it in your environment.