Section 3. Nameserver Configuration

In this section we provide some suggested configurations along with guidelines for their use. We also address the topic of reasonable option setting.

    3.1 Sample Configuration and Logging


logging {
       channel named_log {
           file "logs/named.log";
           print-time yes;
           print-category yes;
           print-severity yes;
           severity info;
};
       channel security_log {
           file "logs/security.log" versions 7 ;
           print-time yes;
};
       category default { named_log; default_debug; };
       category security { security_log };
};
// The two corporate subnets.  Use real IP numbers here in the real world.
acl corpnet { 192.168.4.0/24; 192.168.7.0/24; };
// The options statement.
options {
   directory "/etc/namedb";    // Directory
   pid-file "named.pid";        // Put .pid file in named directory.
   named-xfer "/path/to/named-xfer";  // Where is our named-xfer ?
   check-names master fail;												// Fail on db errors in master zones.
   check-names slave warn;												// Warn about db errors
                              // in slave zones.
   check-names response warn;												// Warn about invalid responses
   use-id-pool yes;												// Help prevent spoofing
   host-statistics yes;												// Keep track of hosts/servers
                               // we've talked to.
   listen-on { 192.168.7.20; };       // Listen on this address.
   query-source address 192.168.7.20 port 53 ;
                                     // Source queries from port 53
                                      // to get past firewall.
   allow-transfer { none; };        // Don't allow anyone to
                                      // transfer zones.
   allow-query { corpnet; };        // Allow only corpnets to query server.
                                      // Helps prevent DoS, spoofing.
   allow-recursion { corpnet; };     // Same, except this is for recursion.
};

include "keys.conf";                     // Include a keys.conf with
                                         // TSIG/DNSSEC keys.
                                         // Shouldn't be readable to anyone
                                          // except BIND user.
zone "."{ type hint; file "local/named.root"; };
                                          // root hints

zone "0.0.127.IN-ADDR.ARPA" {

        type master; file "local/localhost.db"; notify no;
                                          // localhost
};

 

zone "example.com" {            // Example zone for "example.com".
type master;                    // It's a master zone.
file "m/example.com.db";        // The file is here.
allow-query { any; };           // Allow anyone to query.
allow-transfer { corpnet; };    // Only allow corp nets to transfer zone.
};

 

zone "offsite.example.com" {     // Example zone for an off-site corp zone.
type slave;                      // It's a slave zone.
masters { 192.168.4.12; };       // The master is at this address.
file "s/offsite.example.com.db"; // The file is here.
notify no;                       // Don't worry about NOTIFY
ing.
allow-query { any; };            // Allow anyone to query.
;

    3.2 Load Balancing and Round Robin

Primitive load balancing can be achieved in DNS using multiple A records for one name.

For example, if you have three WWW servers with network addresses of 10.0.0.1, 10.0.0.2 and 10.0.0.3, a record like the following means that clients will connect to each machine one third of the time:


 

Name

TTL

CLASS

TYPE

Resource Record (RR) Data

www

10m

IN

A

10.0.0.1

 

10m

IN

A

10.0.0.2

 

10m

IN

A

10.0.0.3

When a resolver queries for these records, BIND will rotate them and respond to the query with the records in a different order. This is known as cyclic or round-robin ordering.In the example above, the first client will receive the records in the order 1,2,3; the second client will receive them in the order 2,3,1; and the third 3,1,2. Most clients will use the first record returned, and discard the rest.

For more detail on ordering responses, check the rrset-order substatement in the options statement in RRset Ordering .

    3.3 Notify

DNS Notify is a mechanism that allows master nameservers to notify their slave servers of changes to a zone's data and that a query should be initiated to discover the new data. DNS Notify is turned on by default.

DNS Notify is fully documented in RFC 1996. See also the description of the zone option also-notify in section 3.1.3.7, "Zone transfers."

    3.4 Nameserver Operations

    3.4.1 Tools for Use With the Nameserver Daemon

There are several indispensable diagnostic, administrative and monitoring tools available to the system administrator for controlling and debugging the nameserver daemon. We describe several in this section

    3.4.1.1 Diagnostic Tools
dig

The domain information groper ( dig ) is a command line tool that can be used to gather information from the Domain Name System servers. Dig has two modes: simple interactive mode for a single query, and batch mode which executes a query for each in a list of several query lines. All query options are accessible from the command line.

Usage

dig [@server] domain [<query-type>] [<query-class>]
[+<query-option>] [-<dig-option>] [%comment]

The usual simple use of dig will take the form


dig @server domain query-type query-class

For more information and a list of available commands and options, see the dig man page.

host

The host utility provides a simple DNS lookup using a command-line interface for looking up Internet hostnames. By default, the utility converts between host names and Internet addresses, but its functionality can be extended with the use of options.

Usage

host [-l] [-v] [-w] [-r] [-d] [-t querytype] [-a] host [server]
nslookup

nslookup is a program used to query Internet domain nameservers. nslookup has two modes: interactive and non-interactive. Interactive mode allows the user to query nameservers for information about various hosts and domains or to print a list of hosts in a domain. Non-interactive mode is used to print just the name and requested information for a host or domain.

Usage

nslookup [-option ...] [host-to-find | -[server]]

Interactive mode is entered when no arguments are given (the default nameserver will be used) or when the first argument is a hyphen (-) and the second argument is the host name or Internet address of a nameserver.

Non-interactive mode is used when the name or Internet address of the host to be looked up is given as the first argument. The optional second argument specifies the host name or address of a nameserver.

The options listed under the "set" command (see the nslookup man page for details) can be specified in the .nslookuprc file in the user's home directory if they are listed one per line. Options can also be specified on the command line if they precede the arguments and are prefixed with a hyphen. For example, to change the default query type to host information, and the initial time-out to 10 seconds, type:


nslookup -query=hinfo -timeout=10

For more information and a list of available commands and options, see the nslookup man page.

    3.4.1.2 Administrative Tools

Administrative tools play an integral part in the management of a server.

rndc

The remote name daemon control ( rndc ) program is a program that allows the system administrator to control the operation of a nameserver. If you run rndc without any options it will display a usage message.

Usage:

rndc [-p port] [-m] server command [command ...]

For more information and a list of available commands and options, see the rndc man page.

    3.4.1.3 Monitoring Tools
MRTG

MRTG is primarily a router traffic grapher, but can be used to monitor BIND DNS servers, as well. The `stat' script, supplied with MRTG in the MRTG `contrib/stat' directory, can be used to monitor numbers of queries, and counts of various sorts of responses.

 

Return to BINDv9 Administrator Reference Manual table of contents.