Dynamic DNS Update (RFC 2136)
=============================

Starting with the PowerDNS Authoritative Server 3.4.0, DNS update
support is available. There are a number of items NOT supported:

-  There is no support for SIG (TSIG and GSS\*TSIG are supported);
-  WKS records are specifically mentioned in the RFC, we don't
   specifically care about WKS records;
-  Anything we forgot....

The implementation requires the backend to support a number of new
operations. Currently, the following backends have been modified to
support DNS update:

- :doc:`gmysql <backends/generic-mysql>`
- :doc:`gpgsql <backends/generic-postgresql>`
- :doc:`gsqlite3 <backends/generic-sqlite3>`
- :doc:`godbc <backends/generic-odbc>`
- :doc:`lmdb <backends/lmdb>` (from version 5.0.0 onwards)

.. _dnsupdate-configuration-options:

Configuration options
---------------------

There are several configuration parameters that can be used within the
powerdns configuration file to influence DNS update behavior.

``dnsupdate``
~~~~~~~~~~~~~

A setting to enable/disable DNS update support completely. The default
is no, which means that DNS updates are ignored by PowerDNS (no message
is logged about this!). Change the setting to ``dnsupdate=yes`` to
enable DNS update support. Default is ``no``.

``allow-dnsupdate-from``
~~~~~~~~~~~~~~~~~~~~~~~~

A list of IP ranges that are allowed to perform updates on any domain.
The default is ``127.0.0.0/8``, which means that all loopback addresses are accepted.
Multiple entries can be used on this line
(``allow-dnsupdate-from=198.51.100.0/8 203.0.113.2/32``). The option can
be left empty to disallow everything, this then should be used in
combination with the ``ALLOW-DNSUPDATE-FROM`` :doc:`domain metadata <domainmetadata>` setting per
zone. Setting a range here and in ``ALLOW-DNSUPDATE-FROM`` enables updates
from either address range.

The semantics are that first a dynamic update has to be allowed either
by the global :ref:`setting-allow-dnsupdate-from` setting, or by a per-zone
``ALLOW-DNSUPDATE-FROM`` metadata setting.

Secondly, if a zone has a ``TSIG-ALLOW-DNSUPDATE`` metadata setting, that
must match too.

So to only allow dynamic DNS updates to a zone based on TSIG key, and
regardless of IP address, set :ref:`setting-allow-dnsupdate-from` to empty, set
``ALLOW-DNSUPDATE-FROM`` to "0.0.0.0/0" and "::/0" and set the
``TSIG-ALLOW-DNSUPDATE`` to the proper key name.

Further information can be found :ref:`below <dnsupdate-how-it-works>`.

``dnsupdate-require-tsig``
~~~~~~~~~~~~~~~~~~~~~~~~~~

.. versionadded:: 5.0.0

A setting to require DNS updates to be signed by a valid TSIG signature.
The default is no, which means zones without TSIG keys can be updated by
unauthenticated agents operating from an allowed address range.

``forward-dnsupdate``
~~~~~~~~~~~~~~~~~~~~~

Tell PowerDNS to forward to the primary server if the zone is configured
as secondary. Primaries are determined by the masters field in the domains
table. The default behaviour is enabled (yes), which means that it will
try to forward. In the processing of the update packet, the
``allow-dnsupdate-from`` and ``TSIG-ALLOW-DNSUPDATE`` are processed
first, so those permissions apply before the ``forward-dnsupdate`` is
used. It will try all masters that you have configured until one is
successful.

.. _dnsupdate-lua-dnsupdate-policy-script:

``lua-dnsupdate-policy-script``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Use this Lua script containing function ``updatepolicy`` to validate
each update. This will ``TURN OFF`` all other
authorization methods, and you are expected to take care of everything
yourself. See :ref:`dnsupdate-update-policy` for details and
examples.

.. _dnsupdate-metadata:

Per zone settings
-----------------

For permissions, a number of per zone settings are available via the
:doc:`domain metadata <domainmetadata>`.

.. _metadata-allow-dnsupdate-from:

ALLOW-DNSUPDATE-FROM
~~~~~~~~~~~~~~~~~~~~

This setting has the same function as described in the configuration
options (See :ref:`above <dnsupdate-configuration-options>`).
This will allow 198.51.100.0/8 and 203.0.113.2/32 to send DNS update
messages for the example.org domain::

    pdnsutil metadata set example.org ALLOW-DNSUPDATE-FROM 198.51.100.0/8 203.0.113.2/32

or, prior to version 5.0::

    pdnsutil set-meta example.org ALLOW-DNSUPDATE-FROM 198.51.100.0/8 203.0.113.2/32

.. _metadata-tsig-allow-dnsupdate:

TSIG-ALLOW-DNSUPDATE
~~~~~~~~~~~~~~~~~~~~

This setting allows you to set the TSIG key required to do an DNS
update. If you have GSS-TSIG enabled, you can use Kerberos principals
here. Here is an example using :program:`pdnsutil` to create a key named
`test`::

    $ pdnsutil tsigkey generate test hmac-sha512
    Create new TSIG key test hmac-sha512 [base64-encoded key]

    $ pdnsutil tsigkey list | grep test
    test. hmac-sha512. [base64-encoded key]

or, prior to version 5.0::

    $ pdnsutil generate-tsig-key test hmac-sha512
    Create new TSIG key test hmac-sha512 [base64-encoded key]

    $ pdnsutil list-tsig-keys | grep test
    test. hmac-sha512. [base64-encoded key]

This adds the key with the name `test` to the zone's metadata. Note, the
keys need to be added separately, not as a comma or space-separated list::

    $ pdnsutil metadata add example.org TSIG-ALLOW-DNSUPDATE test
    Set 'example.org' meta TSIG-ALLOW-DNSUPDATE = test

    $ pdnsutil metadata get example.org TSIG-ALLOW-DNSUPDATE
    TSIG-ALLOW-DNSUPDATE = test

or, prior to version 5.0::

    $ pdnsutil add-meta example.org TSIG-ALLOW-DNSUPDATE test
    Set 'example.org' meta TSIG-ALLOW-DNSUPDATE = test

    $ pdnsutil get-meta example.org TSIG-ALLOW-DNSUPDATE
    TSIG-ALLOW-DNSUPDATE = test

This is an example of using the new `test` TSIG key with the :program:`nsupdate`
command (see the manpage for :program:`nsupdate` for full details)::

    $ nsupdate <<!
    server 127.0.0.1 53
    zone example.org
    update add test1.example.org 3600 A 1.2.3.4
    update add test1.example.org 3600 TXT "this is a test"
    key hmac-sha512:test [base64-encoded key]
    send
    !

    $ dig +noall +answer -t any test1.example.org @127.0.0.1
    test1.example.org.	3600	IN	A	1.2.3.4
    test1.example.org.	3600	IN	TXT	"this is a test"

If any TSIG keys are listed in a zone's ``TSIG-ALLOW-DNSUPDATE`` metadata, one
of them is required for updates. If ``ALLOW-DNSUPDATE-FROM`` is also set,
both requirements need to be satisfied before an update will be accepted.

By default, an update can add, update or delete any resource records in
the zone.  See :ref:`dnsupdate-update-policy` for finer-grained
control of what an update is allowed to do.
Use :ref:`setting-dnsupdate-require-tsig` to disallow unsigned updates.

.. _metadata-forward-dnsupdate:

FORWARD-DNSUPDATE
~~~~~~~~~~~~~~~~~

See :ref:`Configuration options <dnsupdate-configuration-options>` for what it does,
but per domain::

    pdnsutil metadata set example.org FORWARD-DNSUPDATE 'yes'

or, prior to version 5.0::

    pdnsutil set-meta example.org FORWARD-DNSUPDATE 'yes'

The existence of the entry (even with an empty value) enables the forwarding.
This domain-specific setting is only useful when the configuration
option :ref:`setting-forward-dnsupdate` is set to 'no', as that will disable it
globally. Using the domainmetadata setting than allows you to enable it
per domain.

.. _metadata-notify-dnsupdate:

NOTIFY-DNSUPDATE
~~~~~~~~~~~~~~~~

Send a notification to all secondary servers after every update. This will
speed up the propagation of changes and is very useful for acme
verification::

    pdnsutil metadata set example.org NOTIFY-DNSUPDATE 1

or, prior to version 5.0::

    pdnsutil set-meta example.org NOTIFY-DNSUPDATE 1

.. _metadata-soa-edit-dnsupdate:

SOA-EDIT-DNSUPDATE
~~~~~~~~~~~~~~~~~~

This configures how the soa serial should be updated. See
:ref:`below <dnsupdate-soa-serial-updates>`.

.. _dnsupdate-soa-serial-updates:

SOA Serial Updates
------------------

After every update, the soa serial is updated as this is required by
section 3.7 of :rfc:`2136`. The behaviour is configurable via domainmetadata
with the ``SOA-EDIT-DNSUPDATE`` option. It has a number of options listed
below. If no behaviour is specified, DEFAULT is used.

:rfc:`2136, Section 3.6 <2136#section-3.6>` defines some specific behaviour for updates of SOA
records. Whenever the SOA record is updated via the update message, the
logic to change the SOA is not executed.

.. note::
  Powerdns will always use :ref:`metadata-soa-edit` when serving SOA
  records, thus a query for the SOA record of the recently updated domain,
  might have an unexpected result due to a SOA-EDIT setting.

An example::

    pdnsutil metadata set example.org SOA-EDIT-DNSUPDATE INCREASE

or, prior to version 5.0::

    pdnsutil set-meta example.org SOA-EDIT-DNSUPDATE INCREASE

This will make the SOA Serial increase by one, for every successful
update.

SOA-EDIT-DNSUPDATE settings
~~~~~~~~~~~~~~~~~~~~~~~~~~~

These are the settings available for **SOA-EDIT-DNSUPDATE**.

-  DEFAULT: Generate a soa serial of YYYYMMDD01. If the current serial
   is lower than the generated serial, use the generated serial. If the
   current serial is higher or equal to the generated serial, increase
   the current serial by 1.
-  INCREASE: Increase the current serial by 1.
-  EPOCH: Change the serial to the number of seconds since the EPOCH,
   aka unixtime.
-  SOA-EDIT: Change the serial to whatever SOA-EDIT would provide. See
   :doc:`Domain metadata <domainmetadata>`
-  SOA-EDIT-INCREASE: Change the serial to whatever SOA-EDIT would
   provide. If what SOA-EDIT provides is lower than the current serial,
   increase the current serial by 1.
   Exception: with SOA-EDIT=INCEPTION-EPOCH, the serial is bumped to at
   least the current EPOCH time.

DNS update How-to: Setup dyndns/rfc2136 with dhcpd
--------------------------------------------------

DNS update is often used with DHCP to automatically provide a hostname
whenever a new IP-address is assigned by the DHCP server. This section
describes how you can setup PowerDNS to receive DNS updates from ISC's
dhcpd (version 4.1.1-P1).

Setting up dhcpd
~~~~~~~~~~~~~~~~

We're going to use a TSIG key for security. We're going to generate a
key using the following command:

.. code-block:: shell

    dnssec-keygen -a hmac-md5 -b 128 -n USER dhcpdupdate

This generates two files (Kdhcpdupdate.*.key and
Kdhcpdupdate.*.private). You're interested in the .key file:

.. code-block:: shell

    # ls -l Kdhcp*
    -rw------- 1 root root  53 Aug 26 19:29 Kdhcpdupdate.+157+20493.key
    -rw------- 1 root root 165 Aug 26 19:29 Kdhcpdupdate.+157+20493.private

    # cat Kdhcpdupdate.+157+20493.key
    dhcpdupdate. IN KEY 0 3 157 FYhvwsW1ZtFZqWzsMpqhbg==

The important bits are the name of the key (**dhcpdupdate**) and the
hash of the key (**FYhvwsW1ZtFZqWzsMpqhbg==**)

Using the details from the freshly generated key, add the following
to your dhcpd.conf:

::

    key "dhcpdupdate" {
            algorithm hmac-md5;
            secret "FYhvwsW1ZtFZqWzsMpqhbg==";
    };

You must also tell dhcpd that you want dynamic dns to work, add the
following section:

::

    ddns-updates on;
    ddns-update-style interim;
    update-static-leases on;

This tells dhcpd to:

1. Enable Dynamic DNS
2. Which style it must use (interim)
3. Update static leases as well

For more information on this, consult the dhcpd.conf manual.

Per subnet, you also have to tell **dhcpd** which (reverse-)domain it
should update and on which primary domain server it is running.

::

    ddns-domainname "example.org";
    ddns-rev-domainname "in-addr.arpa.";

    zone example.org {
        primary 127.0.0.1;
        key dhcpdupdate;
    }

    zone 1.168.192.in-addr.arpa. {
        primary 127.0.0.1;
        key dhcpdupdate;
    }

This tells **dhcpd** a number of things:

1. Which domain to use (**ddns-domainname "example.org";**)
2. Which reverse-domain to use (**ddns-rev-domainname
   "in-addr.arpa.";**)
3. For the zones, where the primary master is located (**primary
   127.0.0.1;**)
4. Which TSIG key to use (**key dhcpdupdate;**). We defined the key
   earlier.

This concludes the changes that are needed to the **dhcpd**
configuration file.

Setting up PowerDNS
~~~~~~~~~~~~~~~~~~~

A number of small changes are needed to PowerDNS to make it accept
dynamic updates from **dhcpd**.

Enable DNS update (:rfc:`2136`) support functionality in PowerDNS by adding
the following to the PowerDNS configuration file (pdns.conf).

.. code-block:: ini

    dnsupdate=yes
    allow-dnsupdate-from=

This tells PowerDNS to:

1. Enable DNS update support (:ref:`setting-dnsupdate`)
2. Allow updates from NO ip-address (":ref:`setting-allow-dnsupdate-from`\ =")

We just told PowerDNS (via the configuration file) that we accept
updates from nobody via the :ref:`setting-allow-dnsupdate-from`
parameter. That's not very useful, so we're going to give permissions
per zone (including the appropriate reverse zone), via the
domainmetadata table.

.. code-block:: shell

    pdnsutil metadata set example.org ALLOW-DNSUPDATE-FROM 127.0.0.1
    pdnsutil metadata set 1.168.192.in-addr.arpa ALLOW-DNSUPDATE-FROM 127.0.0.1

or, prior to version 5.0:

.. code-block:: shell

    pdnsutil set-meta example.org ALLOW-DNSUPDATE-FROM 127.0.0.1
    pdnsutil set-meta 1.168.192.in-addr.arpa ALLOW-DNSUPDATE-FROM 127.0.0.1

This gives the ip '127.0.0.1' access to send update messages. Make sure
you use the ip address of the machine that runs **dhcpd**.

Another thing we want to do, is add TSIG security. This can only be done
via the domainmetadata table:

.. code-block:: shell

    pdnsutil tsigkey import dhcpdupdate hmac-md5 FYhvwsW1ZtFZqWzsMpqhbg==
    pdnsutil metadata set example.org TSIG-ALLOW-DNSUPDATE dhcpdupdate
    pdnsutil metadata set 1.168.192.in-addr.arpa TSIG-ALLOW-DNSUPDATE dhcpdupdate

or, prior to version 5.0:

.. code-block:: shell

    pdnsutil import-tsig-key dhcpdupdate hmac-md5 FYhvwsW1ZtFZqWzsMpqhbg==
    pdnsutil set-meta example.org TSIG-ALLOW-DNSUPDATE dhcpdupdate
    pdnsutil set-meta 1.168.192.in-addr.arpa TSIG-ALLOW-DNSUPDATE dhcpdupdate

This will:

1. Add the 'dhcpdupdate' key to our PowerDNS installation
2. Associate the domains with the given TSIG key

Restart PowerDNS and you should be ready to go!

.. _dnsupdate-how-it-works:

How it works
------------

This is a short description of how DNS update messages are processed by
PowerDNS.

1.  The DNS update message is received. If it is TSIG signed, the TSIG
    is validated against the tsigkeys table. If it is not valid, Refused
    is returned to the requestor.
2.  A check is performed on the zone to see if it is a valid zone.
    ServFail is returned when not valid.
3.  The **dnsupdate** setting is checked. Refused is returned when the
    setting is 'no'.
4.  If update policy Lua script is provided then skip up to 7.
5.  If the **ALLOW-DNSUPDATE-FROM** has a value (from both
    domainmetadata and the configuration file), a check on the value is
    performed. If the requestor (sender of the update message) does not
    match the values in **ALLOW-DNSUPDATE-FROM**, Refused is returned.
6.  If the message is TSIG signed, the TSIG keyname is compared with the
    TSIG keyname in domainmetadata. If they do not match, a Refused is
    send. The TSIG-ALLOW-DNSUPDATE domainmetadata setting is used to
    find which key belongs to the domain.
7.  The backends are queried to find the backend for the given domain.
8.  If the domain is a secondary domain, the **forward-dnsupdate** option
    and domainmetadata settings are checked. If forwarding to a primary
    is enabled, the message is forward to the primary. If that fails, the
    next primary is tried until all primaries are tried. If all primaries
    fail, ServFail is returned. If a primary succeeds, the result from
    that primary is returned.
9.  A check is performed to make sure all updates/prerequisites are for
    the given zone. NotZone is returned if this is not the case.
10. The transaction with the backend is started.
11. The prerequisite checks are performed (section 3.2 of :rfc:`2136 <2136#section-3.2>`). If a
    check fails, the corresponding RCode is returned. No further
    processing will happen.
12. Per record in the update message, the prescan checks are
    performed. If the prescan fails, the corresponding RCode is
    returned. If the prescan for the record is correct, the actual
    update/delete/modify of the record is performed. If the update fails
    (for whatever reason), ServFail is returned. After changes to the
    records have been applied, the ordername and auth flag are set to
    make sure DNSSEC remains working. The cache for that record is
    purged.
13. If there are records updated and the SOA record was not modified,
    the SOA serial is updated. See :ref:`dnsupdate-soa-serial-updates`. The cache for this record is
    purged.
14. The transaction with the backend is committed. If this fails,
    ServFail is returned.
15. NoError is returned.

.. _dnsupdate-update-policy:

Update policy
-------------

You can define a Lua script to handle DNS UPDATE message
authorization. The Lua script is to contain at least function called
``updatepolicy`` which accepts one parameter. This parameter is an
object, containing all the information for the request. To permit
change, return true; otherwise, return false. The script is called for
each record at a time and you can approve or reject any or all.

The object has following methods available:

- ``DNSName getQName()`` - name to update
- ``DNSName getZoneName()`` - zone name
- ``int getQType()`` - record type, it can be 255(ANY) for delete.
- ``ComboAddress getLocal()`` - local socket address
- ``ComboAddress getRemote()`` - remote socket address
- ``Netmask getRealRemote()`` - real remote address (or netmask if EDNS Subnet is used)
- ``DNSName getTsigName()`` - TSIG **key** name (you can assume it is validated here)
- ``string getPeerPrincipal()`` - Return peer principal name (``user@DOMAIN``,
  ``service/machine.name@DOMAIN``, ``host/MACHINE$@DOMAIN``)

There are many same things available as in recursor Lua scripts, but
there is also ``resolve(qname, qtype)`` which returns array of records.
Example:

.. code-block:: lua

    resolve("www.google.com", pdns.A)

You can use this to perform DNS lookups. If your resolver cannot find
your local records, then this will not find them either. In other words,
resolve does not perform local lookup.

Simple example script:

.. code-block:: lua

    --- This script is not suitable for production use

    function strpos (haystack, needle, offset)
      local pattern = string.format("(%s)", needle)
      local i       = string.find (haystack, pattern, (offset or 0))
      return (i ~= nil and i or false)
    end

    function updatepolicy(input)
      princ = input:getPeerPrincipal()

      if princ == ""
      then
        return false
      end

      if princ == "admin@DOMAIN" or input:getRemote():toString() == "192.168.1.1"
      then
        return true
      end

      if (input:getQType() == pdns.A or input:getQType() == pdns.AAAA) and princ:sub(5,5) == '/' and strpos(princ, "@", 0) ~= false
      then
        i = strpos(princ, "@", 0)
        if princ:sub(i) ~= "@DOMAIN"
        then
          return false
        end
        hostname = princ:sub(6, i-1)
        if input:getQName():toString() == hostname .. "." or input:getQName():toString() == hostname .. "." .. input:getZoneName():toString()
        then
          return true
        end
      end

      return false
    end

Additional updatepolicy example scripts can be found in our
`Wiki <https://github.com/PowerDNS/pdns/wiki/Lua-Examples-(Authoritative)>`__.