TCP/IP Configuration and Management Manual

Configuration Reference
TCP/IP Configuration and Management Manual—427132-004
A-5
Domain Name Resolver
which forwards queries and interacts with other name servers to resolve the query
before returning the answer.
An added benefit of using the forwarding feature is that the central machine develops a
much more complete cache of information that all the workstations can use. The use of
slave mode and forwarding is discussed in more detail under the description of the
domain name server’s startup commands in Domain Name Server Files on page A-5.
Domain Name Resolver
The Domain Name Resolver is part of the NonStop TCP/IP sockets library; Domain
Name Resolver allows user-developed application programs to access a Domain
Name Server, as described above. The Domain Name Resolver consists of those
socket library support routines that get information on hosts, networks, protocols, and
services.
Depending on which support routine your program calls and the setting of the
=TCPIP^HOST^FILE parameter at the time the program is executed, the Domain
Name resolver either accesses a name server or a special file that contains a list of
Internet addresses with the host name and aliases that correspond to each address.
The default name of this file is $SYSTEM.ZTCPIP.HOSTS. If this information is
contained in some other file, each user running the program must set the
=TCPIP^HOST^FILE parameter to specify the name of that file.
If a name server is available on the network, the recommended method for resolving
names is to access the name server. To ensure that the resolver accesses a name
server, your program should call gethostbyname or gethostbyaddr, and you should not
set the TCPIP^HOST^FILE parameter before running the program. For more
information on gethostbyname or gethostbyaddr, see the TCP/IP Programming
Manual.
The resolver uses information specified in a configuration file to provide access to a
name server. The default name for this file is $SYSTEM.ZTCPIP.RESCONF. When an
application sends a name_resolution request to the resolver, the resolver sends the
request to the servers listed in the RESCONF file in order of their priority in a timed
sequence. The server listed first in the RESCONF file (the primary server) has the
highest priority. The RESCONF file must contain a minimum of one server; the
maximum is three servers. For more information on setting up the RESCONF file, refer
to RESCONF File
on page 3-36.
Domain Name Server Files
The domain name server uses several files to load its database. This subsection
describes the files and the formats needed for NAMED.
NAMED listens to TCP and UDP port 53 for incoming requests. To change the Default
NAMED port number, use the -p option; however, make sure that the port you have
chosen is not in use by another service or application. To start NAMED on a port
number less than 1024, you must be in the SUPER group.