nsupdate — Dynamic DNS update utility
nsupdate [-d] [-D] [[-g] | [-o] | [-y ] | [[hmac:]keyname:secret-k ]] [keyfile-t ] [timeout-u ] [udptimeout-r ] [udpretries-R ] [randomdev-v] [filename]
nsupdate is used to submit Dynamic DNS Update requests as defined in RFC2136 to a name server. This allows resource records to be added or removed from a zone without manually editing the zone file. A single update request can contain requests to add or remove more than one resource record.
Zones that are under dynamic control via nsupdate or a DHCP server should not be edited by hand. Manual edits could conflict with dynamic updates and cause data to be lost.
The resource records that are dynamically added or removed with nsupdate have to be in the same zone. Requests are sent to the zone's master server. This is identified by the MNAME field of the zone's SOA record.
The
-d
option makes
nsupdate
operate in debug mode.
This provides tracing information about the update requests that are
made and the replies received from the name server.
The -D option makes nsupdate
report additional debugging information to -d.
Transaction signatures can be used to authenticate the Dynamic
DNS updates. These use the TSIG resource record type described
in RFC2845 or the SIG(0) record described in RFC3535 and
RFC2931 or GSS-TSIG as described in RFC3645. TSIG relies on
a shared secret that should only be known to
nsupdate and the name server. Currently,
the only supported encryption algorithm for TSIG is HMAC-MD5,
which is defined in RFC 2104. Once other algorithms are
defined for TSIG, applications will need to ensure they select
the appropriate algorithm as well as the key when authenticating
each other. For instance, suitable key and
server statements would be added to
/etc/named.conf so that the name server
can associate the appropriate secret key and algorithm with
the IP address of the client application that will be using
TSIG authentication. SIG(0) uses public key cryptography.
To use a SIG(0) key, the public key must be stored in a KEY
record in a zone served by the name server.
nsupdate does not read
/etc/named.conf.
GSS-TSIG uses Kerberos credentials.
nsupdate
uses the -y or -k option
to provide the shared secret needed to generate a TSIG record
for authenticating Dynamic DNS update requests, default type
HMAC-MD5. These options are mutually exclusive. With the
-k option, nsupdate reads
the shared secret from the file keyfile,
whose name is of the form
K{name}.+157.+{random}.private. For
historical reasons, the file
K{name}.+157.+{random}.key must also be
present. When the -y option is used, a
signature is generated from
[hmac:]keyname:secret.
keyname is the name of the key, and
secret is the base64 encoded shared
secret. Use of the -y option is discouraged
because the shared secret is supplied as a command line
argument in clear text. This may be visible in the output
from
ps(1) or in a history file maintained by the user's
shell.
The -k may also be used to specify a SIG(0) key used
to authenticate Dynamic DNS update requests. In this case, the key
specified is not an HMAC-MD5 key.
The -g and -o specify that
GSS-TSIG is to be used. The -o should only
be used with old Microsoft Windows 2000 servers.
By default,
nsupdate
uses UDP to send update requests to the name server unless they are too
large to fit in a UDP request in which case TCP will be used.
The
-v
option makes
nsupdate
use a TCP connection.
This may be preferable when a batch of update requests is made.
The -t option sets the maximum time an update request
can
take before it is aborted. The default is 300 seconds. Zero can be
used
to disable the timeout.
The -u option sets the UDP retry interval. The default
is
3 seconds. If zero, the interval will be computed from the timeout
interval
and number of UDP retries.
The -r option sets the number of UDP retries. The
default is
3. If zero, only one update request will be made.
The -R option
specifies a source of randomness. If the operating system
does not provide a randomdev/dev/random or
equivalent device, the default source of randomness is keyboard
input. randomdev specifies the name of
a character device or file containing random data to be used
instead of the default. The special value
keyboard indicates that keyboard input
should be used. This option may be specified multiple times.
nsupdate
reads input from
filename
or standard input.
Each command is supplied on exactly one line of input.
Some commands are for administrative purposes.
The others are either update instructions or prerequisite checks on the
contents of the zone.
These checks set conditions that some name or set of
resource records (RRset) either exists or is absent from the zone.
These conditions must be met if the entire update request is to succeed.
Updates will be rejected if the tests for the prerequisite conditions
fail.
Every update request consists of zero or more prerequisites and zero or more updates. This allows a suitably authenticated update request to proceed if some specified resource records are present or missing from the zone. A blank input line (or the send command) causes the accumulated commands to be sent as one Dynamic DNS update request to the name server.
The command formats and their meaning are as follows:
Sends all dynamic update requests to the name server
servername.
When no server statement is provided,
nsupdate
will send updates to the master server of the correct zone.
The MNAME field of that zone's SOA record will identify the
master
server for that zone.
port
is the port number on
servername
where the dynamic update requests get sent.
If no port number is specified, the default DNS port number of
53 is
used.
Sends all dynamic update requests using the local
address.
When no local statement is provided,
nsupdate
will send updates using an address and port chosen by the
system.
port
can additionally be used to make requests come from a specific
port.
If no port number is specified, the system will assign one.
Specifies that all updates are to be made to the zone
zonename.
If no
zone
statement is provided,
nsupdate
will attempt determine the correct zone to update based on the
rest of the input.
Specify the default class.
If no class is specified, the
default class is
IN.
Specify the default time to live for records to be added.
The value none will clear the default
ttl.
Specifies that all updates are to be TSIG-signed using the
keyname keysecret pair.
The key command
overrides any key specified on the command line via
-y or -k.
Use GSS-TSIG to sign the updated. This is equivalent to
specifying -g on the commandline.
Use the Windows 2000 version of GSS-TSIG to sign the updated.
This is equivalent to specifying -o on the
commandline.
When using GSS-TSIG use realm_name rather
than the default realm in krb5.conf. If no
realm is specified the saved realm is cleared.
Requires that no resource record of any type exists with name
domain-name.
Requires that
domain-name
exists (has as at least one resource record, of any type).
Requires that no resource record exists of the specified
type,
class
and
domain-name.
If
class
is omitted, IN (internet) is assumed.
This requires that a resource record of the specified
type,
class
and
domain-name
must exist.
If
class
is omitted, IN (internet) is assumed.
The
data
from each set of prerequisites of this form
sharing a common
type,
class,
and
domain-name
are combined to form a set of RRs. This set of RRs must
exactly match the set of RRs existing in the zone at the
given
type,
class,
and
domain-name.
The
data
are written in the standard text representation of the resource
record's
RDATA.
Deletes any resource records named
domain-name.
If
type
and
data
is provided, only matching resource records will be removed.
The internet class is assumed if
class
is not supplied. The
ttl
is ignored, and is only allowed for compatibility.
Adds a new resource record with the specified
ttl,
class
and
data.
Displays the current message, containing all of the prerequisites and updates specified since the last send.
Sends the current message. This is equivalent to entering a blank line.
Displays the answer.
Turn on debugging.
Lines beginning with a semicolon are comments and are ignored.
The examples below show how nsupdate could be used to insert and delete resource records from the example.com zone. Notice that the input in each example contains a trailing blank line so that a group of commands are sent as one dynamic update request to the master name server for example.com.
# nsupdate > update delete oldhost.example.com A > update add newhost.example.com 86400 A 172.16.1.1 > send
Any A records for oldhost.example.com are deleted. And an A record for newhost.example.com with IP address 172.16.1.1 is added. The newly-added record has a 1 day TTL (86400 seconds).
# nsupdate > prereq nxdomain nickname.example.com > update add nickname.example.com 86400 CNAME somehost.example.com > send
The prerequisite condition gets the name server to check that there are no resource records of any type for nickname.example.com. If there are, the update request fails. If this name does not exist, a CNAME for it is added. This ensures that when the CNAME is added, it cannot conflict with the long-standing rule in RFC1034 that a name must not exist as any other record type if it exists as a CNAME. (The rule has been updated for DNSSEC in RFC2535 to allow CNAMEs to have RRSIG, DNSKEY and NSEC records.)