The software described in this documentation is either in Extended Support or Sustaining Support. See https://www.oracle.com/us/support/library/enterprise-linux-support-policies-069172.pdf for more information.
Oracle recommends that you upgrade the software described by this documentation as soon as possible.
The Domain Name System (DNS) is a network-based service that maps (resolves) domain names to IP addresses. For a small, isolated network, you could use entries in the /etc/hosts file to provide the mapping, but most networks that are connected to the Internet use DNS.
DNS is a hierarchical and distributed database, where each level
of the hierarchy is delimited by a period (.
).
Consider the following fully qualified domain name (FQDN):
wiki.us.mydom.com.
The root domain, represented by the final period in the FQDN, is usually omitted, except in DNS configuration files:
wiki.us.mydom.com
In this example, the top-level domain is com
,
mydom
is a subdomain of com
,
us
is a subdomain of mydom
,
and wiki
is the host name. Each of these
domains are grouped into zones for administrative purposes. A DNS
server, or name server, stores the
information that is needed to resolve the component domains inside
a zone. In addition, a zone's DNS server stores pointers to the
DNS servers that are responsible for resolving each subdomain.
If a client outside the us.mydom.com
domain
requests that its local name server resolve a FQDN such as
wiki.us.mydom.com
into an IP address for which
the name server is not authoritative, the name server queries a
root name server for the address of a name server that is
authoritative for the com
domain. Querying this
name server returns the IP address of a name server for
mydom.com
. In turn, querying this name server
returns the IP address of the name server for
us.oracle.com
, and querying this final name
server returns the IP address for the FQDN. This process is known
as a recursive query, where the local name server handles each
referral from an external name server to another name server on
behalf of the resolver.
Iterative queries rely on the resolver being able to handle the referral from each external name server to trace the name server that is authoritative for the FQDN. Most resolvers use recursive queries and so cannot use name servers that support only iterative queries. Fortunately, most
Oracle Linux provides the Berkeley Internet Name Domain (BIND)
implementation of DNS. The bind
package
includes the DNS server daemon (named
), tools
for working with DNS such as rndc, and a number
of configuration files, including:
-
/etc/named.conf
Contains settings for
named
and lists the location and characteristics of the zone files for your domain. Zone files are usually stored in/var/named
.-
/etc/named.rfc1912.zones
Contains several zone sections for resolving local loopback names and addresses.
-
/var/named/named.ca
Contains a list of the root authoritative DNS servers.