client
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... Clients of the domain system should be able to identify
trusted name servers they prefer to use before accepting
...
... dealing with this problem are "recursive", in which the first
server pursues the query for the client at another server, and
"iterative", in which the server refers the client to another
...
... query for the client at another server, and
"iterative", in which the server refers the client to another
server and lets the client pursue the query ...
... "iterative", in which the server refers the client to another
server and lets the client pursue the query. Both approaches
have advantages and disadvantages, but the iterative approach
...
... RESOLVERS are programs that extract information from name
servers in response to client requests. Resolvers must be
able to access at least one name server and use that name
server ...
... The simplest mode for the client is recursive, since in this
mode the name server acts in the role ...
... name server, and the name server
may also choose to restrict the clients which can use
recursive mode.
...
...
The use of recursive mode is limited to cases where both the client and
the name server agree to its use. The agreement ...
... bit is true if the name
server is willing to provide recursive service for the client,
regardless of whether the client requested recursive service ...
... service for the client,
regardless of whether the client requested recursive service.
That is, RA ...
... RD set arrives at a server
which is willing to provide recursive service; the client can verify
that recursive mode was used by checking that both RA and RD ...
... interface to the resolver is influenced by the local host's
conventions, but the typical resolver-client interface has three
functions:
...
... address if
the service returns only one choice to the client. Note that
a multiple address return is recommended, but a single
...
...
When the resolver performs the indicated function, it usually has one of
the following results to pass back to the client:
...
... RR. If possible, the alias condition
should be signalled back from the resolver to the client.
...
... non-existent names should be caught and an error condition passed back
to the client.
...
... While in some cases it is possible to deal with such a temporary problem
by blocking the request indefinitely, this is usually not a good choice,
particularly when the client is a server process that could move on to
other tasks. The recommended solution is to always have temporary
failure as one of the possible results of a resolver function, even
...
... ; a name server is free to refuse to perform recursive
services for any or all clients. The user should consult the local
system administrator to find name servers willing to perform the
...
...
1. See if the answer is in local information, and if so return
it to the client.
2. Find the best servers to ask.
...
... name
error, cache the data as well as returning it back to
the client.
b. if the response contains a better delegation ...
...
The following examples illustrate the operations a resolver must perform
for its client. We assume that the resolver is starting without a
cache, as might be the case after system boot. We further assume that
...