The DNS consists of a hierarchical
set of name servers. Each domain or subdomain has one or more authoritative
name servers that publish information about that domain. The hierarchy
of authoritative name servers matches the hierarchy of domains. At the
top of the hierarchy stand the root servers: the servers to query when
looking up (resolving) a top-level domain name.
There are two types of queries that can be performed in DNS: Iterative
and Recursive. A server responds to a iterative request with either the
answer to the request or the name of another server that has the information
or is closer to it. The requesting client must
then iterate by sending a new request to this referred server, which again
may either answer it or provide another server name. In the case of a recursive
request, the server responds back with the answer if it has the information
sought. Otherwise the server takes responsibility for finding the answer
by sending requests to other servers.
In the animation you are able to select different scenarios and find out
about how iterative and recursive querys from the loacal name server and
the root server work.