Table of Contents
In this chapter we provide some suggested configurations along with guidelines for their use. We suggest reasonable values for certain option settings.
The following sample configuration is appropriate for a caching-only name server for use by clients internal to a corporation. All queries from outside clients are refused using the allow-query option. Alternatively, the same effect could be achieved using suitable firewall rules.
// Two corporate subnets we wish to allow queries from.
acl corpnets { 192.168.4.0/24; 192.168.7.0/24; };
options {
// Working directory
directory "/etc/namedb";
allow-query { corpnets; };
};
// Provide a reverse mapping for the loopback
// address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
type master;
file "localhost.rev";
notify no;
};
This sample configuration is for an authoritative-only server
that is the master server for "example.com"
and a slave for the subdomain "eng.example.com".
options {
// Working directory
directory "/etc/namedb";
// Do not allow access to cache
allow-query-cache { none; };
// This is the default
allow-query { any; };
// Do not provide recursive service
recursion no;
};
// Provide a reverse mapping for the loopback
// address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
type master;
file "localhost.rev";
notify no;
};
// We are the master server for example.com
zone "example.com" {
type master;
file "example.com.db";
// IP addresses of slave servers allowed to
// transfer example.com
allow-transfer {
192.168.4.14;
192.168.5.53;
};
};
// We are a slave server for eng.example.com
zone "eng.example.com" {
type slave;
file "eng.example.com.bk";
// IP address of eng.example.com master server
masters { 192.168.4.12; };
};
A primitive form of load balancing can be achieved in the DNS by using multiple records (such as 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 set of records such as the following means that clients will connect to each machine one third of the time:
|
Name |
TTL |
CLASS |
TYPE |
Resource Record (RR) Data |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
When a resolver queries for these records, BIND will rotate them and respond to the query with the records in a different order. In the example above, clients will randomly receive records in the order 1, 2, 3; 2, 3, 1; and 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 sub-statement in the options statement, see RRset Ordering.
This section describes several indispensable diagnostic, administrative and monitoring tools available to the system administrator for controlling and debugging the name server daemon.
The dig, host, and nslookup programs are all command line tools for manually querying name servers. They differ in style and output format.
The domain information groper (dig) is the most versatile and complete of these lookup tools. It 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.
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.
The host utility emphasizes simplicity and ease of use. By default, it converts between host names and Internet addresses, but its functionality can be extended with the use of options.
host [-aCdlnrsTwv] [-c class] [-N ndots] [-t type] [-W timeout] [-R retries] [-m flag] [-4] [-6] hostname [server]
For more information and a list of available commands and options, see the host man page.
nslookup has two modes: interactive and non-interactive. Interactive mode allows the user to query name servers 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.
nslookup [-option...] [[host-to-find] | [- [server]]]
Interactive mode is entered when no arguments are given (the default name server will be used) or when the first argument is a hyphen (`-') and the second argument is the host name or Internet address of a name server.
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 name server.
Due to its arcane user interface and frequently inconsistent behavior, we do not recommend the use of nslookup. Use dig instead.
Administrative tools play an integral part in the management of a server.
The named-checkconf program
checks the syntax of a named.conf file.
named-checkconf [-jvz] [-t directory] [filename]
The named-checkzone program checks a master file for syntax and consistency.
named-checkzone [-djqvD] [-c class] [-o output] [-t directory] [-w directory] [-k (ignore|warn|fail)] [-n (ignore|warn|fail)] [-W (ignore|warn)] zone [filename]
Similar to named-checkzone, but it always dumps the zone content to a specified file (typically in a different format).
The remote name daemon control (rndc) program allows the system administrator to control the operation of a name server. Since BIND 9.2, rndc supports all the commands of the BIND 8 ndc utility except ndc start and ndc restart, which were also not supported in ndc's channel mode. If you run rndc without any options it will display a usage message as follows:
rndc [-c config] [-s server] [-p port] [-y key] command [command...]
The command is one of the following:
reloadReload configuration file and zones.
reload zone
[class
[view]]Reload the given zone.
refresh zone
[class
[view]]Schedule zone maintenance for the given zone.
retransfer zone
[class
[view]]Retransfer the given zone from the master.
sign zone
[class
[view]]Fetch all DNSSEC keys for the given zone from the key directory (see key-directory in the section called “options Statement Definition and Usage”). If they are within their publication period, merge them into the zone's DNSKEY RRset. If the DNSKEY RRset is changed, then the zone is automatically re-signed with the new key set.
This command requires that the
auto-dnssec zone option be set
to allow or
maintain,
and also requires the zone to be configured to
allow dynamic DNS.
See the section called “Dynamic Update Policies” for
more details.
loadkeys zone
[class
[view]]Fetch all DNSSEC keys for the given zone from the key directory (see key-directory in the section called “options Statement Definition and Usage”). If they are within their publication period, merge them into the zone's DNSKEY RRset. Unlike rndc sign, however, the zone is not immediately re-signed by the new keys, but is allowed to incrementally re-sign over time.
This command requires that the
auto-dnssec zone option
be set to maintain,
and also requires the zone to be configured to
allow dynamic DNS.
See the section called “Dynamic Update Policies” for
more details.
freeze
[zone
[class
[view]]]Suspend updates to a dynamic zone. If no zone is specified, then all zones are suspended. This allows manual edits to be made to a zone normally updated by dynamic update. It also causes changes in the journal file to be synced into the master file. All dynamic update attempts will be refused while the zone is frozen.
thaw
[zone
[class
[view]]]Enable updates to a frozen dynamic zone. If no zone is specified, then all frozen zones are enabled. This causes the server to reload the zone from disk, and re-enables dynamic updates after the load has completed. After a zone is thawed, dynamic updates will no longer be refused. If the zone has changed and the ixfr-from-differences option is in use, then the journal file will be updated to reflect changes in the zone. Otherwise, if the zone has changed, any existing journal file will be removed.
sync
[-clean]
[zone
[class
[view]]]Sync changes in the journal file for a dynamic zone to the master file. If the "-clean" option is specified, the journal file is also removed. If no zone is specified, then all zones are synced.
notify zone
[class
[view]]Resend NOTIFY messages for the zone.
reconfigReload the configuration file and load new zones, but do not reload existing zone files even if they have changed. This is faster than a full reload when there is a large number of zones because it avoids the need to examine the modification times of the zones files.
statsWrite server statistics to the statistics file.
querylog
Toggle query logging. Query logging can also be enabled
by explicitly directing the queries
category to a
channel in the
logging section of
named.conf or by specifying
querylog yes; in the
options section of
named.conf.
dumpdb
[-all|-cache|-zone]
[view ...]Dump the server's caches (default) and/or zones to the dump file for the specified views. If no view is specified, all views are dumped.
secroots
[view ...]Dump the server's security roots to the secroots file for the specified views. If no view is specified, security roots for all views are dumped.
stop [-p]
Stop the server, making sure any recent changes
made through dynamic update or IXFR are first saved to
the master files of the updated zones.
If -p is specified named's process id is returned.
This allows an external process to determine when named
had completed stopping.
halt [-p]
Stop the server immediately. Recent changes
made through dynamic update or IXFR are not saved to
the master files, but will be rolled forward from the
journal files when the server is restarted.
If -p is specified named's process id is returned.
This allows an external process to determine when named
had completed halting.
traceIncrement the servers debugging level by one.
trace levelSets the server's debugging level to an explicit value.
notraceSets the server's debugging level to 0.
flushFlushes the server's cache.
flushname
name
[view]
Flushes the given name from the server's DNS cache, and from the server's nameserver address database if applicable.
flushtree
name
[view]
Flushes the given name, and all of its subdomains, from the server's DNS cache. (The server's nameserver address database is not affected.)
statusDisplay status of the server. Note that the number of zones includes the internal bind/CH zone and the default ./IN hint zone if there is not an explicit root zone configured.
recursingDump the list of queries named is currently recursing on.
validation
[on|off]
[view ...]
Enable or disable DNSSEC validation.
Note dnssec-enable also needs to be
set to yes to be effective.
It defaults to enabled.
addzone
zone
[class
[view]]
configuration
Add a zone while the server is running. This
command requires the
allow-new-zones option to be set
to yes. The
configuration string
specified on the command line is the zone
configuration text that would ordinarily be
placed in named.conf.
The configuration is saved in a file called
hash.nzfhash is a
cryptographic hash generated from the name of
the view. When named is
restarted, the file will be loaded into the view
configuration, so that zones that were added
can persist after a restart.
This sample addzone command
would add the zone example.com
to the default view:
$ rndc addzone example.com '{ type master; file "example.com.db"; };'
(Note the brackets and semi-colon around the zone configuration text.)
delzone
zone
[class
[view]]
Delete a zone while the server is running. Only zones that were originally added via rndc addzone can be deleted in this matter.
signing
[( -list | -clear keyid/algorithm | -clear all | -nsec3param ( parameters | none ) ) ]
zone
[class
[view]]
List, edit, or remove the DNSSEC signing state for the specified zone. The status of ongoing DNSSEC operations (such as signing or generating NSEC3 chains) is stored in the zone in the form of DNS resource records of type sig-signing-type. rndc signing -list converts these records into a human-readable form, indicating which keys are currently signing or have finished signing the zone, and which NSEC3 NSEC3 chains are being created or removed.
rndc signing -clear can remove a single key (specified in the same format that rndc signing -list uses to display it), or all keys. In either case, only completed keys are removed; any record indicating that a key has not yet finished signing the zone will be retained.
rndc signing -nsec3param sets the NSEC3 parameters for a zone. This is the only supported mechanism for using NSEC3 with inline-signing zones. Parameters are specified in the same format as an NSEC3PARAM resource record: hash algorithm, flags, iterations, salt. For example, to set an NSEC3 chain using the SHA-1 hash algorithm, no opt-out flag, 10 iterations, and a salt value of "FFFF", use: rndc signing -nsec3param 1 0 10 FFFF. rndc signing -nsec3param none removes an existing NSEC3 chain and replaces it with NSEC.
A configuration file is required, since all
communication with the server is authenticated with
digital signatures that rely on a shared secret, and
there is no way to provide that secret other than with a
configuration file. The default location for the
rndc configuration file is
/etc/rndc.conf, but an
alternate
location can be specified with the -c
option. If the configuration file is not found,
rndc will also look in
/etc/rndc.key (or whatever
sysconfdir was defined when
the BIND build was
configured).
The rndc.key file is
generated by
running rndc-confgen -a as
described in
the section called “controls Statement Definition and
Usage”.
The format of the configuration file is similar to
that of named.conf, but
limited to
only four statements, the options,
key, server and
include
statements. These statements are what associate the
secret keys to the servers with which they are meant to
be shared. The order of statements is not
significant.
The options statement has
three clauses:
default-server, default-key,
and default-port.
default-server takes a
host name or address argument and represents the server
that will
be contacted if no -s
option is provided on the command line.
default-key takes
the name of a key as its argument, as defined by a key statement.
default-port specifies the
port to which
rndc should connect if no
port is given on the command line or in a
server statement.
The key statement defines a
key to be used
by rndc when authenticating
with
named. Its syntax is
identical to the
key statement in named.conf.
The keyword key is
followed by a key name, which must be a valid
domain name, though it need not actually be hierarchical;
thus,
a string like "rndc_key" is a valid
name.
The key statement has two
clauses:
algorithm and secret.
While the configuration parser will accept any string as the
argument
to algorithm, currently only the string "hmac-md5"
has any meaning. The secret is a base-64 encoded string
as specified in RFC 3548.
The server statement
associates a key
defined using the key
statement with a server.
The keyword server is followed by a
host name or address. The server statement
has two clauses: key and port.
The key clause specifies the
name of the key
to be used when communicating with this server, and the
port clause can be used to
specify the port rndc should
connect
to on the server.
A sample minimal configuration file is as follows:
key rndc_key {
algorithm "hmac-md5";
secret
"c3Ryb25nIGVub3VnaCBmb3IgYSBtYW4gYnV0IG1hZGUgZm9yIGEgd29tYW4K";
};
options {
default-server 127.0.0.1;
default-key rndc_key;
};
This file, if installed as /etc/rndc.conf,
would allow the command:
$ rndc reload
to connect to 127.0.0.1 port 953 and cause the name server to reload, if a name server on the local machine were running with following controls statements:
controls {
inet 127.0.0.1
allow { localhost; } keys { rndc_key; };
};
and it had an identical key statement for
rndc_key.
Running the rndc-confgen
program will
conveniently create a rndc.conf
file for you, and also display the
corresponding controls
statement that you need to
add to named.conf.
Alternatively,
you can run rndc-confgen -a
to set up
a rndc.key file and not
modify
named.conf at all.
Certain UNIX signals cause the name server to take specific actions, as described in the following table. These signals can be sent using the kill command.
|
SIGHUP |
Causes the server to read |
|
SIGTERM |
Causes the server to clean up and exit. |
|
SIGINT |
Causes the server to clean up and exit. |