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options {
directory "/var/named";
};
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Statements in the options section are globally applicable configuration options and defaults for the name server. See the named.conf(4) man page for further details.
Create the master record for the zone.
The following lines designate the DNS name server as a master server for the zone. The zone definition begins with the keyword zone followed, in order, by the domain and the class. "in" denotes the Internet class and can be omitted as it is the default. The record also tells the server where to find the SOA record (Start of Authority) that makes the server authoritative for the zone. The file "db.doc.sun.com" should be in the directory specified in the options statement.
zone "doc.sun.com" in {
type master;
file "db.doc.sun.com";
};
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Create a master record for the zone's reverse maps.
The following lines designate the server as a master server for the zone's reverse address map. The reverse address zone contains the zone's IP address in reverse order followed by in-addr.arpa. For example, assuming doc.sun.com zone's IP address is 10.0.0, the reverse address zone would be 0.0.10.in-addr-arpa.
zone "0.0.10.in-addr.arpa" in {
type master;
file "db.10.0.0";
};
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Create a master record for the local loopback interface.
The following lines designate the server as a master server for the loopback interface.
Note - Loopback hosts are always identified as 0.0.127.in-addr.arpa.
Thus, the following line in a configuration file specifies that the server is the master server for the reverse address domain of the loopback host using authoritative data from the file named.local.
zone "0.0.127.in-addr.arpa" in {
type master;
file "db.127.0.0";
};
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Create a "root hints" file.
zone "." in {
type hint;
file "named.ca";
};
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The file named.ca contains the location of the name servers for the root zone. For the doc.sun.com zone above, it would be the name servers for the sun.com domain.
A slave server maintains a copy of the data for the zone. The master server sends its data and delegates authority to the slave server. Clients can query a slave server for DNS information. By using slave servers, you can improve response time by spreading the load over multiple machines. Slave servers also provide backup when the master server crashes.
When in.named starts, the daemon requests all the data for the given zone from the master. The slave server then periodically checks with the master to see if the master needs to update its database. The process of sending the most recent zone database from the master to the slave is called a zone transfer. Therefore, you do not modify data files on a slave server. You modify the data files on the zone's master server. The slave servers then update their files from the master.
To specify that a server is to be the slave server for a given zone, you create slave records in that server's named.conf file. Separate records can designate the server as a slave server for the zone, the zone's reverse address domain, and the loopback host. A slave zone definition has a similar format as the master zone definition. The type is changed to slave and a line with the keyword masters along with the IP address(es) of the master server(s) is added.
For example, the following lines in a configuration file specify that the server is the slave server for the doc.sun.com zone and its reverse address domain. The lines also specify that the slave server obtains its authoritative data from the master server at 172.16.0.1 and initially loads its data from the file tmp.db.doc.sun.com:
zone "doc.sun.com" in {
type slave;
file "tmp.db.doc.sun.com";
masters { 172.16.0.1; };
};
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Note - A server can act as the master server for one or more zones, and as the slave server for one or more zones. The mixture of entries in the configuration file determines whether a server is a master or slave server for a given zone.
All servers are caching servers as all servers maintain a cache of DNS data. A cache-only or stub server is a server that is not a master server for any zone other than the reverse loopback zone in the in-addr.arpa. domain.
A cache-only server handles queries but does not maintain any authoritative data. The cache-only server handles queries by asking the hosts that are listed in the named.ca file for the needed information.
The following is a sample configuration file for a cache-only server. Note that the class (in) has been omitted as it is the default
Example 4-3 Sample Master Configuration File for Caching-Only Server
;
; Sample named.conf file for caching only name server
;
options {
directory "/var/named";
};
zone "0.0.127.in-addr.arpa" {
type master;
file "db.127.0.0";
};
zone "." {
type hint;
file "named.ca";
};
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How to Set Up a DNS Server