DNS Configuration and Management Manual (G06.27+, H06.05+, J06.03+)

DNS and BIND Basics
HP DNS Configuration and Management Manual—529432-003
A-8
The Resolution Process
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Interprets responses (which may be resource records or an error).
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Returns the information to the programs that requested it.
Each time a service is invoked, such as Telnet or FTP, specifying a target hostname,
you indirectly launch a resolver routine like
gethostbyname(). The networking
software uses IP addresses, not names. The host name must be resolved or mapped
to an IP address.
Although the resolver converts a target hostname to an IP address, the resolver
routines also convert IP addresses to names (reverse lookups) and obtain mail routing
information (MX record lookups), among other tasks.
Name Servers: Recursive and Nonrecursive Resolution
There are two forms of query resolution that a name server may be requested to
perform:
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Recursive
This form of resolution places the burden on the queried name server receiving the
request. For a recursive query, the sender does not expect any reply except for the
ultimate answer. The queried name server must respond with the data or an error
indicating that the data does not exist. The queried name server cannot respond
with a referral to another possible source of information. The sender of a recursive
query anticipates that the server will make any further queries on the sender's
behalf that are necessary to obtain an answer. Client resolvers issue this type of
query. The request is sent by the resolver as recursion requested.
Figure A-2
through Figure A-11 show a ten-step, recursive resolution process.
•
Nonrecursive (iterative)
This form of resolution enables the queried name server to respond by identifying
another name server if the queried name server does not have the requested
information. A referral response provides the name and IP address of one or more
name servers that should be contacted. A name server makes nonrecursive
queries and acts iteratively.