path: root/bin/nsupdate/nsupdate.rst

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.. _man_nsupdate:

nsupdate - dynamic DNS update utility
-------------------------------------

Synopsis
~~~~~~~~

:program:`nsupdate` [**-d**] [**-D**] [**-i**] [**-L** level] [ [**-g**] | [**-o**] | [**-l**] | [**-y** [hmac:]keyname:secret] | [**-k** keyfile] ] [**-t** timeout] [**-u** udptimeout] [**-r** udpretries] [**-v**] [**-T**] [**-P**] [**-V**] [ [**-4**] | [**-6**] ] [filename]

Description
~~~~~~~~~~~

``nsupdate`` is used to submit Dynamic DNS Update requests, as defined in
:rfc:`2136`, 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`` must be in the same zone. Requests are sent to the
zone's primary server, which is identified by the MNAME field of the
zone's SOA record.

Transaction signatures can be used to authenticate the Dynamic DNS
updates. These use the TSIG resource record type described in :rfc:`2845`,
the SIG(0) record described in :rfc:`2535` and :rfc:`2931`, or GSS-TSIG as
described in :rfc:`3645`.

TSIG relies on a shared secret that should only be known to ``nsupdate``
and the name server. For instance, suitable ``key`` and ``server``
statements are 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 is using TSIG
authentication. ``ddns-confgen`` can generate suitable
configuration fragments. ``nsupdate`` uses the ``-y`` or ``-k`` options
to provide the TSIG shared secret; these options are mutually exclusive.

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.

GSS-TSIG uses Kerberos credentials. Standard GSS-TSIG mode is switched
on with the ``-g`` flag. A non-standards-compliant variant of GSS-TSIG
used by Windows 2000 can be switched on with the ``-o`` flag.

Options
~~~~~~~

``-4``
   This option sets use of IPv4 only.

``-6``
   This option sets use of IPv6 only.

``-d``
   This option sets debug mode, which provides tracing information about the update
   requests that are made and the replies received from the name server.

``-D``
   This option sets extra debug mode.

``-i``
   This option forces interactive mode, even when standard input is not a terminal.

``-k keyfile``
   This option indicates the file containing the TSIG authentication key. Keyfiles may be in
   two formats: a single file containing a ``named.conf``-format ``key``
   statement, which may be generated automatically by ``ddns-confgen``;
   or a pair of files whose names are of the format
   ``K{name}.+157.+{random}.key`` and
   ``K{name}.+157.+{random}.private``, which can be generated by
   ``dnssec-keygen``. The ``-k`` option can 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.

``-l``
   This option sets local-host only mode, which sets the server address to localhost
   (disabling the ``server`` so that the server address cannot be
   overridden). Connections to the local server use a TSIG key
   found in ``/var/run/named/session.key``, which is automatically
   generated by ``named`` if any local ``primary`` zone has set
   ``update-policy`` to ``local``. The location of this key file can be
   overridden with the ``-k`` option.

``-L level``
   This option sets the logging debug level. If zero, logging is disabled.

``-p port``
   This option sets the port to use for connections to a name server. The default is
   53.

``-P``
   This option prints the list of private BIND-specific resource record types whose
   format is understood by ``nsupdate``. See also the ``-T`` option.

``-r udpretries``
   This option sets the number of UDP retries. The default is 3. If zero, only one update
   request is made.

``-t timeout``
   This option sets the maximum time an update request can take before it is aborted. The
   default is 300 seconds. If zero, the timeout is disabled.

``-T``
   This option prints the list of IANA standard resource record types whose format is
   understood by ``nsupdate``. ``nsupdate`` exits after the lists
   are printed. The ``-T`` option can be combined with the ``-P``
   option.

   Other types can be entered using ``TYPEXXXXX`` where ``XXXXX`` is the
   decimal value of the type with no leading zeros. The rdata, if
   present, is parsed using the UNKNOWN rdata format, (<backslash>
   <hash> <space> <length> <space> <hexstring>).

``-u udptimeout``
   This option sets the UDP retry interval. The default is 3 seconds. If zero, the
   interval is computed from the timeout interval and number of UDP
   retries.

``-v``
   This option specifies that TCP should be used even for small update requests. 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 is used. TCP may
   be preferable when a batch of update requests is made.

``-V``
   This option prints the version number and exits.

``-y [hmac:]keyname:secret``
   This option sets the literal TSIG authentication key. ``keyname`` is the name of the key,
   and ``secret`` is the base64 encoded shared secret. ``hmac`` is the
   name of the key algorithm; valid choices are ``hmac-md5``,
   ``hmac-sha1``, ``hmac-sha224``, ``hmac-sha256``, ``hmac-sha384``, or
   ``hmac-sha512``. If ``hmac`` is not specified, the default is
   ``hmac-md5``, or if MD5 was disabled, ``hmac-sha256``.

   NOTE: 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 ps1 or in a history file maintained by
   the user's shell.

Input Format
~~~~~~~~~~~~

``nsupdate`` reads input from ``filename`` or standard input. Each
command is supplied on exactly one line of input. Some commands are for
administrative purposes; 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 are 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 either 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 meanings are as follows:

``server servername port``
   This command sends all dynamic update requests to the name server ``servername``.
   When no server statement is provided, ``nsupdate`` sends updates
   to the primary server of the correct zone. The MNAME field of that
   zone's SOA record identify the primary server for that zone.
   ``port`` is the port number on ``servername`` where the dynamic
   update requests are sent. If no port number is specified, the default
   DNS port number of 53 is used.

   .. note:: This command has no effect when GSS-TSIG is in use.

``local address port``
   This command sends all dynamic update requests using the local ``address``. When
   no local statement is provided, ``nsupdate`` sends updates using
   an address and port chosen by the system. ``port`` can also
   be used to force requests to come from a specific port. If no port number
   is specified, the system assigns one.

``zone zonename``
   This command specifies that all updates are to be made to the zone ``zonename``.
   If no ``zone`` statement is provided, ``nsupdate`` attempts to
   determine the correct zone to update based on the rest of the input.

``class classname``
   This command specifies the default class. If no ``class`` is specified, the default
   class is ``IN``.

``ttl seconds``
   This command specifies the default time-to-live, in seconds, for records to be added. The value
   ``none`` clears the default TTL.

``key hmac:keyname secret``
   This command specifies that all updates are to be TSIG-signed using the
   ``keyname``-``secret`` pair. If ``hmac`` is specified, it sets
   the signing algorithm in use. The default is ``hmac-md5``; if MD5
   was disabled, the default is ``hmac-sha256``. The ``key`` command overrides any key
   specified on the command line via ``-y`` or ``-k``.

``gsstsig``
   This command uses GSS-TSIG to sign the updates. This is equivalent to specifying
   ``-g`` on the command line.

``oldgsstsig``
   This command uses the Windows 2000 version of GSS-TSIG to sign the updates. This is
   equivalent to specifying ``-o`` on the command line.

``realm [realm_name]``
   When using GSS-TSIG, this command specifies the use of ``realm_name`` rather than the default realm
   in ``krb5.conf``. If no realm is specified, the saved realm is
   cleared.

``check-names [yes_or_no]``
   This command turns on or off check-names processing on records to be added.
   Check-names has no effect on prerequisites or records to be deleted.
   By default check-names processing is on. If check-names processing
   fails, the record is not added to the UPDATE message.

``prereq nxdomain domain-name``
   This command requires that no resource record of any type exist with the name
   ``domain-name``.

``prereq yxdomain domain-name``
   This command requires that ``domain-name`` exist (as at least one resource
   record, of any type).

``prereq nxrrset domain-name class type``
   This command requires that no resource record exist of the specified ``type``,
   ``class``, and ``domain-name``. If ``class`` is omitted, IN (Internet)
   is assumed.

``prereq yxrrset domain-name class type``
   This command requires that a resource record of the specified ``type``,
   ``class`` and ``domain-name`` exist. If ``class`` is omitted, IN
   (internet) is assumed.

``prereq yxrrset domain-name class type data``
   With this command, 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.

``update delete domain-name ttl class type data``
   This command deletes any resource records named ``domain-name``. If ``type`` and
   ``data`` are provided, only matching resource records are removed.
   The Internet class is assumed if ``class`` is not supplied. The
   ``ttl`` is ignored, and is only allowed for compatibility.

``update add domain-name ttl class type data``
   This command adds a new resource record with the specified ``ttl``, ``class``, and
   ``data``.

``show``
   This command displays the current message, containing all of the prerequisites and
   updates specified since the last send.

``send``
   This command sends the current message. This is equivalent to entering a blank
   line.

``answer``
   This command displays the answer.

``debug``
   This command turns on debugging.

``version``
   This command prints the version number.

``help``
   This command prints a list of commands.

Lines beginning with a semicolon (;) are comments and are ignored.

Examples
~~~~~~~~

The examples below show how ``nsupdate`` can 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 is sent as one dynamic update request to the primary 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 TTL of 1 day (86400 seconds).

::

   # nsupdate
   > prereq nxdomain nickname.example.com
   > update add nickname.example.com 86400 CNAME somehost.example.com
   > send

The prerequisite condition tells the name server to verify 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 :rfc:`1034` 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 :rfc:`2535` to allow CNAMEs to have RRSIG,
DNSKEY, and NSEC records.)

Files
~~~~~

``/etc/resolv.conf``
   Used to identify the default name server

``/var/run/named/session.key``
   Sets the default TSIG key for use in local-only mode

``K{name}.+157.+{random}.key``
   Base-64 encoding of the HMAC-MD5 key created by ``dnssec-keygen``.

``K{name}.+157.+{random}.private``
   Base-64 encoding of the HMAC-MD5 key created by ``dnssec-keygen``.

See Also
~~~~~~~~

:rfc:`2136`, :rfc:`3007`, :rfc:`2104`, :rfc:`2845`, :rfc:`1034`, :rfc:`2535`, :rfc:`2931`,
:manpage:`named(8)`, :manpage:`ddns-confgen(8)`, :manpage:`dnssec-keygen(8)`.

Bugs
~~~~

The TSIG key is redundantly stored in two separate files. This is a
consequence of ``nsupdate`` using the DST library for its cryptographic
operations, and may change in future releases.