Recursive Lookup?

[Ray Buschur]

DNS performs two types of queries (or lookups) iterative and recursive.

The description assumes no cache exists.

Iterative queries are "normally" used between DNS servers.  An iterative
query request tells the DNS server that receives the request that it only
needs to provide as much information as it has and that is it.  So when you
query the root servers they only give you a pointer to the DNS server that
supports the level 1 domain you are interested (such as com. edu. org.
etc...).  The requesting DNS server will then sends its query to the level 1
domain DNS server, it will again give you a pointer down to the level 2 DNS
server, and so on and so on.  The DNS server needing the information is
finding the information by sending several iterations of the same query.

Recursive queries are different.  Essentially what happens is the sender of
the query is saying to a DNS server, "find me the answer to this question,
or send me an error back".  But the DNS server that accepts a recursive
query request assumes the responsibility to find the answer to the question
presented in the query or return the appropriate error.  So the sender of
the recursive query only sends a single query to a DNS server, and will get
its answer back.  Recursive queries are generally sent from stub resolvers
and DNS servers configured to forward.

does that help?
ray



-----Original Message-----
From: bind-users-bounce at isc.org [mailto:bind-users-bounce at isc.org]On
Behalf Of Bob Helland
Sent: Wednesday, November 17, 1999 6:20 AM
To: comp-protocols-dns-bind at moderators.isc.org
Subject: Recursive Lookup?


Can someone give me a definition of recursive lookup?  I can't quite seem to
get that.

Thanks,
-Bob