Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 231
Query Function Types

There are two types of queries issued: recursive and iterative.

Recursive queries received by a server forces that server to find the information requested or post a message back to the querier that the information cannot be found. Iterative queries allow the server to search for the information and pass back the best information it knows about. This is the type that is used between servers. Clients used the recursive query. This is shown in the slide.

Generally (but not always), a server-to-server query is iterative and a client-resolver-to-server query is recursive.

You should also note that a server can be queried or it can be the person placing a query. Therefore, a server contains both the server and client functions.

A server can transmit either type of query. If it is handed a recursive query from a remote source, it must transmit other queries to find the specified name, or send a message back to the originator of the query that the name could not be found.

Query Function Types