Adding upstream version 2.5.7.upstream/2.5.7upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. _hooks-libraries:
+
+**************
+Hook Libraries
+**************
+
+.. _hooks-libraries-introduction:
+
+Introduction
+============
+
+Kea is both flexible and customizable, via the use of "hooks." This feature
+lets Kea load one or more
+dynamically linked libraries (known as "hook libraries") and call functions
+in them at various points in its processing ("hook points").
+Those functions perform whatever custom processing is required.
+
+The hooks concept allows the core Kea code to remain reasonably small
+by moving features that only some, but not all, users find useful to
+external libraries. Those with no need for certain functions can simply choose not
+to load those libraries.
+
+Hook libraries are loaded by individual Kea processes, not by Kea as a
+whole. This means, among other things, that it is possible to associate one set
+of libraries with the DHCPv4 server and a different set with the DHCPv6
+server.
+
+It is also possible for a process to load
+multiple libraries. When processing reaches a hook point, Kea calls the
+hook library functions attached to it. If multiple libraries have
+attached a function to a given hook point, Kea calls all of them, in the
+order in which the libraries are specified in the configuration file.
+The order may be important; consult the documentation of the libraries
+for specifics.
+
+When a Kea process unloads a library, it expects the ``dlclose`` function
+to remove all library symbols, as well as the library code, from address space.
+Although most OSes implement the ``dlclose`` function, this behavior is not
+required by the POSIX standard and not all systems support it; for example, the musl
+library, used by default by Alpine Linux, implements the ``dlclose`` function
+as a no operation. On such systems a library actually remains loaded for the
+lifetime of the process, which means that it must be restarted
+to update libraries with newer versions; it is not sufficient to simply
+reconfigure or reload the Kea process.
+
+The next sections describe how to install and configure hook libraries. Users who are
+interested in writing their own hook library can find information
+in the `Hooks Developer's Guide section of the Kea Developer's
+Guide <https://reports.kea.isc.org/dev_guide/df/d46/hooksdgDevelopersGuide.html>`__.
+
+Note that some libraries are available under different licenses.
+
+Please also note that some libraries may require additional dependencies and/or
+compilation switches to be enabled.
+
+
+Installing Hook Packages
+========================
+
+.. note::
+
+   For more details about installing the Kea Premium Hooks package, please read
+   `this Knowledgebase article <https://kb.isc.org/docs/aa-01587>`__.
+
+Some hook packages are included in the base Kea sources. There is no
+need to do anything special to compile or install them, as they are covered
+by the usual building and installation procedures. Please
+refer to :ref:`installation` for a general overview of the installation process.
+
+ISC provides several additional premium hooks in the form of packages, which
+follow a similar installation procedure but with several additional steps.
+For our users' convenience, the premium hooks installation procedure is described in this section.
+
+1. Download the package; detailed instructions are provided in the KB article
+above. The package will be a file with a name similar to
+``kea-premium-|release|.tar.gz``. (The name may vary depending on the package
+purchased.)
+
+2. Administrators who have the sources for the corresponding version of the
+open-source Kea package on their system from the initial Kea installation
+should skip this step. Otherwise, extract the Kea source from the original
+tarball that was downloaded. For example, with a download of Kea |release|,
+there should be a tarball called ``kea-|release|.tar.gz`` on the system.
+Unpack this tarball:
+
+.. parsed-literal::
+
+   $ tar -zxvf kea-|release|.tar.gz
+
+This will unpack the tarball into the ``kea-|release|`` subdirectory of
+the current working directory.
+
+3. Unpack the Kea premium hooks tarball into the same directory where the
+original Kea source is located. Once Kea |release| has been unpacked into a ``kea-|release|``
+subdirectory and the Kea premium tarball is in the current directory, the following
+steps will unpack the premium tarball into the correct location:
+
+.. parsed-literal::
+
+     $ cd kea-|release|
+     $ tar -xvf ../kea-premium-|release|.tar.gz
+
+Note that unpacking the Kea premium package puts the files into a
+directory named ``premium``. Regardless of the name of the package, the
+directory is always called ``premium``, although its contents will vary
+depending on the hooks package.
+
+4. Run the ``autoreconf`` tools. This step is necessary to update Kea's build
+script to include the additional directory. If this tool is not already
+available on the system, install the ``automake`` and ``autoconf``
+tools. To generate the configure script, please use:
+
+::
+
+     $ autoreconf -i
+
+5. Rerun ``configure``, using the same configuration options that were used when
+originally building Kea. It is possible to verify that ``configure`` has detected the
+premium package by inspecting the summary printed when it exits. The
+first section of the output should look something like this:
+
+.. parsed-literal::
+
+   Package:
+     Name:             kea
+     Version:          |release|
+     Extended version: |release| (tarball)
+     OS Family:        Linux
+     Using GNU sed:    yes
+     Premium package:  yes
+     Included Hooks:   forensic_log flex_id host_cmds
+
+The last line indicates which specific hooks were detected. Note that
+some hooks may require their own dedicated switches.
+Please consult later sections of this chapter for details.
+
+6. Rebuild Kea.
+
+::
+
+     $ make
+
+If the machine has multiple CPU cores, an interesting option to consider
+here is using the argument ``-j X``, where ``X`` is the number of available cores.
+
+7. Install Kea sources along with the hooks:
+
+::
+
+   $ sudo make install
+
+Note that as part of the installation procedure, the install script
+places additional hook libraries and associated files into the ``premium/`` directory.
+
+The installation location of the hook libraries depends on whether the
+``--prefix`` parameter was specified in the ``configure`` script. If not,
+the default location is ``/usr/local/lib/kea/hooks``. The proper installation
+of the libraries can be verified with this command:
+
+::
+
+   $ ls -l /usr/local/lib/kea/hooks/*.so
+   /usr/local/lib/kea/hooks/libdhcp_class_cmds.so
+   /usr/local/lib/kea/hooks/libdhcp_flex_id.so
+   /usr/local/lib/kea/hooks/libdhcp_flex_option.so
+   /usr/local/lib/kea/hooks/libdhcp_host_cmds.so
+   /usr/local/lib/kea/hooks/libdhcp_lease_cmds.so
+   /usr/local/lib/kea/hooks/libdhcp_legal_log.so
+   /usr/local/lib/kea/hooks/libdhcp_subnet_cmds.so
+
+The exact list returned depends on the packages installed. If the
+directory was specified via ``--prefix``, the hook libraries will be located in
+``{prefix directory}/lib/kea/hooks``.
+
+Configuring Hook Libraries
+===========================
+
+The hook libraries for a given process are configured using the
+``hooks-libraries`` keyword in the configuration for that process. (Note
+that the word "hooks" is plural.) The value of the keyword is an array
+of map structures, with each structure corresponding to a hook library. For
+example, to set up two hook libraries for the DHCPv4 server, the
+configuration would be:
+
+::
+
+   "Dhcp4": {
+       :
+       "hooks-libraries": [
+           {
+               "library": "/opt/first_custom_hooks_example.so"
+           },
+           {
+               "library": "/opt/local/second_custom_hooks_example.so",
+               "parameters": {
+                   "mail": "spam@example.com",
+                   "floor": 13,
+                   "debug": false,
+                   "users": [ "alice", "bob", "charlie" ],
+                   "languages": {
+                       "french": "bonjour",
+                       "klingon": "yl'el"
+                   }
+               }
+           }
+       ]
+       :
+   }
+
+.. note::
+
+   Libraries are reloaded even if their lists have not changed,
+   because the parameters specified for the library (or the files those
+   parameters point to) may have changed.
+
+Libraries may have additional parameters that are not mandatory, in the
+sense that there may be libraries that do not require them. However, for any
+given library there is often a requirement to specify a certain
+set of parameters. Please consult the documentation for each individual library for
+details. In the example above, the first library (``/opt/first_custom_hooks_example.so``)
+has no parameters. The second library (``/opt/local/second_custom_hooks_example.so``)
+has five parameters: specifying mail (string parameter), floor (integer parameter),
+debug (boolean parameter), lists (list of strings), and maps (containing strings).
+Nested parameters can be used if the library supports it. This topic is explained in detail
+in the `Hooks Developer's Guide section of the Kea Developer's Guide
+<https://reports.kea.isc.org/dev_guide/df/d46/hooksdgDevelopersGuide.html>`__.
+
+Some hooks use user context to set the parameters. See :ref:`user-context-hooks`.
+
+Notes:
+
+-  The full path to each library should be given.
+
+-  As noted above, the order in which the hooks are called may be important;
+   consult the documentation for each library for specifics.
+
+-  An empty list has the same effect as omitting the ``hooks-libraries``
+   configuration element altogether.
+
+   .. note::
+
+      There is one case where this is not true: if Kea is running with a
+      configuration that contains a ``hooks-libraries`` item, and that
+      item is removed and the configuration reloaded, the removal will
+      be ignored and the libraries remain loaded. As a workaround,
+      instead of removing the ``hooks-libraries`` item, change it to an
+      empty list.
+
+At the moment, only the :iscman:`kea-dhcp4` and :iscman:`kea-dhcp6` processes support
+hook libraries.
+
+.. _order-of-configuration-hooks:
+
+Order of Configuration:
+~~~~~~~~~~~~~~~~~~~~~~~
+
+It is important to recognize that the order in which hook libraries are
+configured determines the order in which their callouts will be executed,
+in cases where more than one hook library implements the same callout.  For
+example, if you wish to use the flex-id hook library to formulate the client
+IDs in conjunction with HA hook library for load-balanced HA, it is essential
+that the flex-id library be specified first in your server's ``hooks-libraries``
+section.  This ensures that the client ID is formulated by the flex-id library
+before the HA library uses it for load-balancing. Similarly it would be best to
+specify forensic logging last, to ensure any other install hooks have made
+their contributions to the packet processing.
+
+.. _user-context-hooks:
+
+User Contexts in Hooks
+~~~~~~~~~~~~~~~~~~~~~~
+
+Hook libraries can have their own configuration parameters, which is
+convenient if the parameter applies to the whole library. However,
+sometimes it is useful to extend certain configuration entities
+with additional configuration data. This is where the concept
+of user contexts comes in. A system administrator can define an arbitrary set of
+data and attach it to Kea structures, as long as the data is specified
+as a JSON map. In particular, it is possible to define fields that are
+integers, strings, boolean, lists, or maps. It is possible to define
+nested structures of arbitrary complexity. Kea does not use that data on
+its own; it simply stores it and makes it available for the hook libraries.
+
+Another use case for user contexts may be storing comments and other
+information that will be retained by Kea. Regular comments are discarded
+when the configuration is loaded, but user contexts are retained. This is
+useful if administrators want their comments to survive :isccmd:`config-set` or :isccmd:`config-get`
+operations, for example.
+
+If user context is supported in a given context, the parser translates
+"comment" entries into user context with a "comment" entry.
+
+User context can store configuration for multiple hooks and comments at once.
+
+Some hooks use user context for a configuration that can be easily edited
+without the need to restart the server.
+
+The DDNS-Tuning Hook uses user-context to configure per subnet behavior. Example:
+
+::
+
+    "subnet4": [{
+        "id": 1,
+        "subnet": "192.0.2.0/24",
+        "pools": [{
+            "pool": "192.0.2.10 - 192.0.2.20"
+        } ],
+        "user-context": {
+            "ddns-tuning": {
+                "hostname-expr": "'guest-'+int8totext(substring(pkt4.yiaddr, 0,1))+'-' \
+                                          +int8totext(substring(pkt4.yiaddr, 1,2))+'-' \
+                                          +int8totext(substring(pkt4.yiaddr, 2,3))+'-' \
+                                          +int8totext(substring(pkt4.yiaddr, 3,4))"
+            },
+            "last-modified": "2017-09-04 13:32",
+            "phones": [ "x1234", "x2345" ],
+            "devices-registered": 42,
+            "billing": false
+        }
+    }]
+
+
+The Limits hook uses user-context in classes and subnets to set parameters. For example:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "client-classes": [
+          {
+            "name": "gold",
+            "user-context": {
+              "limits": {
+                "address-limit": 2,
+                "prefix-limit": 1,
+                "rate-limit": "1000 packets per second"
+              }
+            }
+          }
+        ],
+        "hooks-libraries": [
+          {
+            "library": "/usr/local/lib/libdhcp_limits.so"
+          }
+        ],
+        "subnet6": [
+          {
+            "id": 1,
+            "pools": [
+              {
+                "pool": "2001:db8::/64"
+              }
+            ],
+            "subnet": "2001:db8::/64",
+            "user-context": {
+              "limits": {
+                "address-limit": 4,
+                "prefix-limit": 2,
+                "rate-limit": "10 packets per minute"
+              }
+            }
+          }
+        ]
+      }
+    }
+
+Available Hook Libraries
+========================
+
+As described above, the hook functionality provides a way to customize
+a Kea server without modifying the core code. ISC has chosen to take
+advantage of this feature to provide functions that may only be useful
+to a subset of Kea users. To this end, ISC has created some hook
+libraries, discussed in the following sections.
+
+.. note::
+
+   Some of these libraries are available with the base code, while others are
+   premium libraries available for purchase, or only shared with organizations
+   who contribute to Kea's development through paid ISC support contracts. Paid support
+   includes professional engineering assistance, advance security notifications, input
+   into ISC's roadmap planning, and many other benefits, while helping
+   keep Kea sustainable in the long term. ISC encourages companies and organizations
+   to consider purchasing a paid support contract; further information can be
+   obtained by completing the form at https://www.isc.org/contact.
+
+The following table provides a list of hook libraries currently available
+from ISC. It is important to pay attention to which libraries may be
+loaded by which Kea processes. It is a common mistake to configure the
+:iscman:`kea-ctrl-agent` process to load libraries that should, in fact, be
+loaded by the :iscman:`kea-dhcp4` or :iscman:`kea-dhcp6` processes. If a library
+from ISC does not work as expected, please make sure that it has been
+loaded by the correct process per the table below.
+
+.. tabularcolumns:: |p{0.1\linewidth}|p{0.1\linewidth}|p{0.8\linewidth}|
+
+.. table:: List of available hook libraries
+   :class: longtable
+   :widths: 10 10 80
+
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | Name                                                      | Availability | Description                                                  |
+   +===========================================================+==============+==============================================================+
+   | :ref:`BOOTP <hooks-bootp>`                                | Kea open     | This hook library adds BOOTP support, as defined in          |
+   |                                                           | source       | RFC 1497. It recognizes received BOOTP requests:             |
+   |                                                           |              | they are translated into DHCPREQUEST packets, put into the   |
+   |                                                           |              | BOOTP client class, and receive infinite lifetime leases.    |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Class Commands <hooks-class-cmds>`                  | ISC support  | This hook library allows configured DHCP client classes to   |
+   |                                                           | customers    | be added, updated, deleted, and fetched without              |
+   |                                                           |              | needing to restart the DHCP server.                          |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Configuration Backend Commands <hooks-cb-cmds>`     | ISC support  | This hook                                                    |
+   |                                                           | customers    | library implements a collection of commands to manage        |
+   |                                                           |              | Kea configuration information in a                           |
+   |                                                           |              | database. This library may only be used in conjunction with  |
+   |                                                           |              | one of the supported Configuration Backend implementations.  |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`DDNS Tuning <hooks-ddns-tuning>`                    | ISC premium  | This hook library adds custom behaviors related to Dynamic   |
+   |                                                           | library      | DNS updates on a per-client basis. Its primary feature is to |
+   |                                                           |              | allow the host name used for DNS to be                       |
+   |                                                           |              | calculated using an expression.                              |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Flexible Identifier <hooks-flex-id>`                | ISC premium  | Kea software provides a way to handle host reservations that |
+   |                                                           | library      | include addresses, prefixes, options, client classes and     |
+   |                                                           |              | other features. The reservation can be based on hardware     |
+   |                                                           |              | address, DUID, circuit-id, or client-id in DHCPv4 and on     |
+   |                                                           |              | hardware address or DUID in DHCPv6. However, there are       |
+   |                                                           |              | sometimes scenarios where the reservation is more complex,   |
+   |                                                           |              | e.g. uses other options than mentioned above, uses parts of  |
+   |                                                           |              | specific options, or perhaps uses a combination of several   |
+   |                                                           |              | options and fields to uniquely identify a client. Those      |
+   |                                                           |              | scenarios are addressed by the Flexible Identifier hook      |
+   |                                                           |              | application. It allows defining an expression, similar to    |
+   |                                                           |              | the one used in client classification,                       |
+   |                                                           |              | e.g. ``substring(relay6[0].option[37],0,6)``. Each incoming  |
+   |                                                           |              | packet is evaluated against that expression and its value is |
+   |                                                           |              | then searched in the reservations database.                  |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Flexible Option <hooks-flex-option>`                | Kea open     | This library provides hooks that compute option values       |
+   |                                                           | source       | instead of static configured values. An expression is        |
+   |                                                           |              | evaluated on the query packet. Defined add, supersede, and   |
+   |                                                           |              | remove actions are applied on the response packet before     |
+   |                                                           |              | it is sent using the evaluation result.                      |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Forensic Logging <hooks-legal-log>`                 | ISC premium  | This library provides hooks that record a detailed log of    |
+   |                                                           | library      | lease assignments and renewals in a set of log files. In     |
+   |                                                           |              | many legal jurisdictions, companies - especially ISPs - must |
+   |                                                           |              | record information about the addresses they have leased to   |
+   |                                                           |              | DHCP clients. This library is designed to help with that     |
+   |                                                           |              | requirement. If the information that it records is           |
+   |                                                           |              | sufficient, it may be used directly. If a jurisdiction       |
+   |                                                           |              | requires a different set of information to be saved, it can  |
+   |                                                           |              | be used as a template or example to create                   |
+   |                                                           |              | custom logging hooks. In Kea 1.9.8, additional parameters    |
+   |                                                           |              | were added to give users more flexibility regarding          |
+   |                                                           |              | what information should be logged.                           |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`GSS-TSIG <hooks-gss-tsig>`                          | ISC support  | This hook library adds support to the Kea D2 server          |
+   |                                                           | customers    | (kea-dhcp-ddns) for using GSS-TSIG to sign DNS updates.      |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`High Availability <hooks-high-availability>`        | Kea open     | The risk of DHCP service unavailability can be minimized     |
+   |                                                           | source       | by setting up a pair of DHCP servers in a network. Two       |
+   |                                                           |              | modes of operation are supported. The first one is called    |
+   |                                                           |              | load-balancing, and is sometimes referred to as              |
+   |                                                           |              | "active-active." Each server can handle selected groups of   |
+   |                                                           |              | clients in this network, or all clients if it detects that   |
+   |                                                           |              | its partner has become unavailable. It is also possible to   |
+   |                                                           |              | designate one server to serve all DHCP clients, and leave    |
+   |                                                           |              | another server as standby. This mode is called "hot standby" |
+   |                                                           |              | and is sometimes referred to as "active-passive." This       |
+   |                                                           |              | server activates its DHCP function only when it detects that |
+   |                                                           |              | its partner is not available. Such cooperation between the   |
+   |                                                           |              | DHCP servers requires that these servers constantly          |
+   |                                                           |              | communicate with each other to send updates about allocated  |
+   |                                                           |              | leases, and to periodically test whether their partners are  |
+   |                                                           |              | still operational. The hook library also provides an ability |
+   |                                                           |              | to send lease updates to external backup servers, making it  |
+   |                                                           |              | much easier to have a replacement that is up to date.        |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Host Cache <hooks-host-cache>`                      | ISC support  | Some database backends, such as RADIUS,                      |
+   |                                                           | customers    | may take a long time to respond. Since                       |
+   |                                                           |              | Kea in general is synchronous, backend performance           |
+   |                                                           |              | directly affects DHCP performance. To minimize               |
+   |                                                           |              | performance impact, this library                             |
+   |                                                           |              | provides a way to cache responses from other hosts. This     |
+   |                                                           |              | includes negative caching, i.e. the ability to remember that |
+   |                                                           |              | there is no client information in the database.              |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Host Commands <hooks-host-cmds>`                    | ISC premium  | Kea provides a way to store host reservations in a           |
+   |                                                           | library      | database. In many larger deployments it is useful to be able |
+   |                                                           |              | to manage that information while the server is running. This |
+   |                                                           |              | library provides management commands for adding, querying,   |
+   |                                                           |              | and deleting host reservations in a safe way without         |
+   |                                                           |              | restarting the server. In particular, it validates the       |
+   |                                                           |              | parameters, so an attempt to insert incorrect data, e.g. add |
+   |                                                           |              | a host with conflicting identifier in the same subnet, is    |
+   |                                                           |              | rejected. Those commands are exposed via the command channel |
+   |                                                           |              | (JSON over UNIX sockets) and the Control Agent (JSON over    |
+   |                                                           |              | RESTful interface).                                          |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Lease Commands <hooks-lease-cmds>`                  | Kea open     | This hook library offers a number of commands used to        |
+   |                                                           | source       | manage leases. Kea can store lease information in various    |
+   |                                                           |              | backends: memfile, MySQL, PostgreSQL. This library provides  |
+   |                                                           |              | a unified interface to manipulate leases in an unified, safe |
+   |                                                           |              | way. In particular, it allows manipulation of memfile leases |
+   |                                                           |              | while Kea is running, sanity check changes, lease existence  |
+   |                                                           |              | checks, and removal of all leases belonging to a specific    |
+   |                                                           |              | subnet. It can also catch obscure errors, like the addition  |
+   |                                                           |              | of a lease with subnet-id that does not exist in the         |
+   |                                                           |              | configuration, or configuration of a lease to use an address |
+   |                                                           |              | that is outside of the subnet to which it is supposed to     |
+   |                                                           |              | belong. This library allows easy management of user contexts |
+   |                                                           |              | associated with leases.                                      |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Leasequery <hooks-lease-query>`                     | ISC support  | This library adds support for DHCPv4                         |
+   |                                                           | customers    | Leasequery as described in RFC 4388; and for DHCPv6          |
+   |                                                           |              | Leasequery as described in RFC 5007.                         |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Limits <hooks-limits>`                              | ISC support  | With this hook library, :iscman:`kea-dhcp4` and              |
+   |                                                           | customers    | :iscman:`kea-dhcp6` servers can apply a limit to the rate at |
+   |                                                           |              | which packets receive a response. The limit can be applied   |
+   |                                                           |              | per-client class or per-subnet.                              |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`MySQL Configuration Backend <hooks-cb-mysql>`       | Kea open     | This hook library is an implementation of the Kea            |
+   |                                                           | source       | Configuration Backend for MySQL. It uses a MySQL database as |
+   |                                                           |              | a repository for the Kea configuration information. Kea      |
+   |                                                           |              | servers use this library to fetch their configurations.      |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`PerfMon <hooks-perfmon>`                            | Kea open     | With this hook library, :iscman:`kea-dhcp4` server and       |
+   |                                                           | source       | :iscman:`kea-dhcp6` servers can track and report performance |
+   |                                                           |              | data. CURRENTLY UNDER DEVELOPMENT                            |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Ping Check <hooks-ping-check>`                      | ISC support  | With this hook library, :iscman:`kea-dhcp4` server can       |
+   |                                                           | customers    | perform ping checks of candidate lease addresses before      |
+   |                                                           |              | offering them to clients.                                    |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`PostgreSQL Configuration Backend <hooks-cb-pgsql>`  | Kea open     | This hook library is an implementation of the Kea            |
+   |                                                           | source       | Configuration Backend for PostgreSQL. It uses a PostgreSQL   |
+   |                                                           |              | database as a repository for the Kea configuration           |
+   |                                                           |              | information. Kea servers use this library to fetch their     |
+   |                                                           |              | configurations.                                              |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`RADIUS <hooks-radius>`                              | ISC support  | The RADIUS hook library allows Kea to interact with          |
+   |                                                           | customers    | RADIUS servers using access and accounting mechanisms. The   |
+   |                                                           |              | access mechanism may be used for access control, assigning   |
+   |                                                           |              | specific IPv4 or IPv6 addresses reserved by RADIUS,          |
+   |                                                           |              | dynamically assigning addresses from designated pools chosen |
+   |                                                           |              | by RADIUS, or rejecting the client's messages altogether.    |
+   |                                                           |              | The accounting mechanism allows a RADIUS server to keep      |
+   |                                                           |              | track of device activity over time.                          |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`RBAC <hooks-rbac>`                                  | ISC support  | This hook library adds support to the Kea Control Agent      |
+   |                                                           | customers    | (kea-ctrl-agent) for Role-Based Access Control filtering     |
+   |                                                           |              | of commands.                                                 |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Run Script <hooks-run-script>`                      | Kea open     | This hook library adds support to run external               |
+   |                                                           | source       | scripts for specific packet-processing hook points. There    |
+   |                                                           |              | are several exported environment variables available for     |
+   |                                                           |              | the script.                                                  |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Statistics Commands <hooks-stat-cmds>`              | Kea open     | This library provides additional                             |
+   |                                                           | source       | commands for retrieving accurate DHCP lease statistics, for  |
+   |                                                           |              | Kea DHCP servers that share the same lease database. This    |
+   |                                                           |              | setup is common in deployments where DHCP service redundancy |
+   |                                                           |              | is required and a shared lease database is used to avoid     |
+   |                                                           |              | lease-data replication between the DHCP servers.             |
+   |                                                           |              | This hook library returns lease statistics                   |
+   |                                                           |              | for each subnet.                                             |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Subnet Commands <hooks-subnet-cmds>`                | ISC support  | In deployments in which subnet configuration needs to be     |
+   |                                                           | customers    | frequently updated, it is a hard requirement that such       |
+   |                                                           |              | updates be performed without the need for a full DHCP server |
+   |                                                           |              | reconfiguration or restart. This hook library allows for     |
+   |                                                           |              | incremental changes to the subnet configuration such as      |
+   |                                                           |              | adding or removing a subnet. It also allows for              |
+   |                                                           |              | listing all available subnets and fetching detailed          |
+   |                                                           |              | information about a selected subnet. The commands exposed by |
+   |                                                           |              | this library do not affect other subnets or configuration    |
+   |                                                           |              | parameters currently used by the server.                     |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`User Check <hooks-user-chk>`                        | Kea open     | Reads known users list from a file. Unknown users will be    |
+   |                                                           | source       | assigned a lease from the last subnet defined in the         |
+   |                                                           |              | configuration file, e.g. to redirect them to a captive       |
+   |                                                           |              | portal. This demonstrates how an external source of          |
+   |                                                           |              | information can be used to influence the Kea allocation      |
+   |                                                           |              | engine. This hook is part of the Kea source code and is      |
+   |                                                           |              | available in the ``src/hooks/dhcp/user_chk`` directory.      |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+
+ISC hopes to see more hook libraries become available as time
+progresses, developed both internally and externally. Since this list
+may evolve dynamically, it is maintained on a wiki page, available
+at https://gitlab.isc.org/isc-projects/kea/wikis/Hooks-available.
+Developers or others who are aware of any hook libraries not listed there
+are asked to please send a note to the kea-users or kea-dev mailing lists for
+updating. (Information on all of ISC's public mailing lists can be found
+at https://www.isc.org/mailinglists/.)
+
+The libraries developed by ISC are described in detail in the following
+sections.
+
+.. include:: hooks-bootp.rst
+.. include:: hooks-cb-cmds.rst
+.. include:: hooks-class-cmds.rst
+.. include:: hooks-ddns-tuning.rst
+.. include:: hooks-flex-id.rst
+.. include:: hooks-flex-option.rst
+.. include:: hooks-gss-tsig.rst
+.. include:: hooks-ha.rst
+.. include:: hooks-host-cache.rst
+.. include:: hooks-host-cmds.rst
+.. include:: hooks-lease-cmds.rst
+.. include:: hooks-lease-query.rst
+.. include:: hooks-legal-log.rst
+.. include:: hooks-limits.rst
+.. include:: hooks-cb-mysql.rst
+.. include:: hooks-perfmon.rst
+.. include:: hooks-ping-check.rst
+.. include:: hooks-cb-pgsql.rst
+.. include:: hooks-radius.rst
+.. include:: hooks-rbac.rst
+.. include:: hooks-run-script.rst
+.. include:: hooks-stat-cmds.rst
+.. include:: hooks-subnet-cmds.rst
+.. include:: hooks-user-chk.rst