DNS(7P)                                                                DNS(7P)



NAME
     dns - Domain Name Service

SYNOPSIS
     /var/ns/lib/libns_dns.so

DESCRIPTION
     The Domain Name System (DNS) is an Internet standard name service for
     hostname to address translation.  Queries are made from a client library
     (termed the resolver(4)) to a server daemon named(1M).  The daemon
     nsd(1M) will make these calls and present the data in a filesystem
     namespace when the dns keyword exists in the nsswitch.conf configuration
     file for a domain.  This man page documents the behavior of the DNS
     extension to the nsd daemon.

     The nsd daemon reads all of the nsswitch.conf configuration files, first
     /etc/nsswitch.conf for the default domain, then files
     /var/ns/domains/DOMAIN/nsswitch.conf for each DOMAIN the local host acts
     as a server for.  As it reads these files if it encounters the keyword
     dns for some map then it will open the DNS library
     /var/ns/lib/libnsdns.so.  On first open the library initialization
     routine will parse the resolver configuration file /etc/resolv.conf to
     determine the addresses of nameservers and the domain names to use for
     queries.

     Extended attributes in the nsswitch.conf file can be used to control the
     behavior of the DNS resolver.  Extended attributes are simply lists of
     key/value pairs attached to each object in the nsd filesystem.  The
     attributes supported in this library are:

     domain
          This is the domainname given as a parameter to the remote name
          server.  This attribute is typically inherited from the daemon
          depending on the nsswitch.conf file that is being read.  Given the
          configuration file /var/ns/domains/DOMAINNAME/nsswitch.conf the
          attribute "domain" is set to DOMAINNAME.  For the default domain,
          represented by the file /etc/nsswitch.conf, the domain is unset and
          the DNS library uses the search path given in the resolver(4)
          configuration file.  If the resolv.conf file is changed then the
          change will be reflected in the next lookup.

     table
          The table attribute is typically inherited from the daemon based on
          the line from which this entry occurs in the nsswitch.conf file.
          This implementation of the DNS resolver recognizes only two tables:
          hosts.byname which is translated into a type A request, hosts.byaddr
          which is translated into a type PTR request.

     key  The key attribute is set by the daemon on each request.  If the
          address is fully qualified (ends in a '.') then it is forwarded on
          to the remote name server as is.  Else, it will have each element of
          the search path appended and looked up.  If the key contains a



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DNS(7P)                                                                DNS(7P)



          sufficient number of dots (as defined by in resolv.conf as "option
          ndots") then it will first be attempted as is.

     dnsmaxttl
          The dnsmaxttl attribute specifies that nsd should use the DNS TTL
          value for the nsd cache timeout.  Because DNS TTL values can be
          quite large a maximum value in seconds can be specified.  Default is
          zero.  dnsservers The dnsservers attribute is a space separated
          list of IP addresses of DNS servers.  If this is not set then the
          nameservers listed in the /etc/resolv.conf file are used.

     dnssearch
          The dnssearch attribute is used to override the default domain
          search path built from /etc/resolv.conf.

     dnsparallel
          The dnsparallel attribute is a performance optimization where
          queries will be made to all defined name servers in parallel.  This
          only works if each of the name servers is equally able to answer the
          request.  This should be set to an integer number of packets which
          should be sent out at one time.  The default is 1.

     dnsretries
          The dnsretries attribute specifies the number of queries that we
          will make to each server.  Each server is tried in turn in a round-
          robin basis until the number of retries is exhausted.  This should
          be set to an integer value, and defaults to 3.

     dnstimeout
          The dnstimeout attribute is the number of milliseconds the library
          code will wait for a response from a name server before continuing
          to the next name server.  The default is 2000.

NOTE
     If there is no resolv.conf file on a system nsd will NOT use a default
     nameserver of localhost unless named has been enabled via chkconfig.

SEE ALSO
     chkconfig(1M), named(1M), nsd(1M), nsswitch.conf(4), resolver(4), db(7P),
     dns(7P), files(7P), ldap(7P), mdbm(7P), ndbm(7P), nis(7P), nisserv(7P).
     IRIX Admin: Networking and Mail














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