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.. SPDX-License-Identifier: GPL-3.0-or-later
.. _mod-dns64:
DNS64
=====
The module for :rfc:`6147` DNS64 AAAA-from-A record synthesis, it is used to enable client-server communication between an IPv6-only client and an IPv4-only server. See the well written `introduction`_ in the PowerDNS documentation.
If no address is passed (i.e. ``nil``), the well-known prefix ``64:ff9b::`` is used.
.. _introduction: https://doc.powerdns.com/md/recursor/dns64
Simple example
--------------
.. code-block:: lua
-- Load the module with default settings
modules = { 'dns64' }
-- Reconfigure later
dns64.config({ prefix = '2001:db8::aabb:0:0' })
.. warning:: The module currently won't work well with :func:`policy.STUB`.
Also, the IPv6 ``prefix`` passed in configuration is assumed to be ``/96``.
.. tip:: The A record sub-requests will be DNSSEC secured, but the synthetic AAAA records can't be. Make sure the last mile between stub and resolver is secure to avoid spoofing.
Advanced options
----------------
TTL in CNAME generated in the reverse ``ip6.arpa.`` subtree is configurable:
.. code-block:: lua
dns64.config({ prefix = '2001:db8:77ff::', rev_ttl = 300 })
You can specify a set of IPv6 subnets that are disallowed in answer.
If they appear, they will be replaced by AAAAs generated from As.
.. code-block:: lua
dns64.config({
prefix = '2001:db8:3::',
exclude_subnets = { '2001:db8:888::/48', '::ffff/96' },
})
-- You could even pass '::/0' to always force using generated AAAAs.
In case you don't want dns64 for all clients,
you can set ``DNS64_DISABLE`` flag via the :ref:`view module <mod-view>`.
.. code-block:: lua
modules = { 'dns64', 'view' }
-- disable dns64 for all IPv4 source addresses
view:addr('0.0.0.0/0', policy.all(policy.FLAGS('DNS64_DISABLE')))
-- disable dns64 for all IPv6 source addresses
view:addr('::/0', policy.all(policy.FLAGS('DNS64_DISABLE')))
-- re-enable dns64 for two IPv6 subnets
view:addr('2001:db8:11::/48', policy.all(policy.FLAGS(nil, 'DNS64_DISABLE')))
view:addr('2001:db8:93::/48', policy.all(policy.FLAGS(nil, 'DNS64_DISABLE')))
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