# Hooks Libraries

## Introduction

Although Kea offers a lot of flexibility, there may be cases where its behavior needs customization. To accommodate this possibility, Kea includes the idea of "Hooks". This feature lets Kea load one or more dynamically-linked libraries (known as "hooks libraries") and, at various points in its processing ("hook points"), call functions in them. Those functions perform whatever custom processing is required.

The hooks concept also allows keeping the core Kea code reasonably small by moving features that some, but not all users find useful to external libraries. People who don't need specific functionality simply don't load the libraries.

Hooks libraries are loaded by individual Kea processes, not to Kea as a whole. This means (for example) that it is possible to associate one set of libraries with the DHCP4 server and a different set to the DHCP6 server.

Another point to note is that it is possible for a process to load multiple libraries. When processing reaches a hook point, Kea calls the hooks 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 to see if this is the case.

The next section describes how to configure hooks libraries. If you are interested in writing your own hooks library, information can be found in the Kea Developer's Guide.

Note that some libraries are available under different licenses.

Note that some libraries may require additional dependencies and/or compilation switches to be enabled, e.g. Radius library introduced in Kea 1.4 requires FreeRadius-client library to be present. If --with-free-radius option is not specified, the Radius library will not be built.

## Installing Hook packages

The installation procedure has changed in 1.4.0. Kea 1.3.0 and earlier needed special switches passed to configure script to detect the hook libraries. Please see this KB article: `https://kb.isc.org/article/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, they are covered by the usual building and installation procedure. ISC also provides several additional hooks in form of various packages. All of those packages follow the same installation procedure that is similar to base Kea, but has several additional steps. For your convenience, the whole procedure is described here. Please refer to for general overview.

1. Download the package. You will receive detailed instructions how to get it separately. This will be a file with a name similar to kea-premium-&keaversion;.tar.gz. Your name may differ depending on which package you got.

2. If you have the sources for the corresponding version of the open-source Kea package still on your system (from when you installed Kea), skip this step. Otherwise extract the Kea source from the original tarball you downloaded. For example, if you downloaded Kea &keaversion;., you should have a tarball called kea-&keaversion;.tar.gz on your system. Unpack this tarball:

    $ tar zxvf kea-&keaversion;.tar.gz

This will unpack the tarball into the kea-&keaversion; subdirectory of your current working directory.

3. Unpack the Kea premium tarball into the directory into which Kea was unpacked. For example, assuming that you followed step 2 and that Kea &keaversion; has been unpacked into a kea-&keaversion; subdirectory and that the Kea premium tarball is in your current directory, the following steps will unpack the premium tarball into the correct location:

      $ cd kea-&keaversion;
      $ tar xvf ../kea-premium-&keaversion;.tar.gz

Note that unpacking the Kea premium package will put the files into a directory named premium. Regardless of the name of your package, the directory will always be called premium, just its content may vary.

4. Run autoreconf tools. This step is necessary to update Kea's build script to include additional directory. If this tool is not already available on your system, you need to install automake and autoconf tools. To generate configure script, please use:

      $ autoreconf -i

5. Rerun configure, using the same configure options as you used when originally building Kea. You can check if configure has detected the premium package by inspecting the summary printed when it exits. The first section of the output should look something like:

    Package:
      Name:            kea
      Version:         &keaversion;
      Extended version:&keaversion; (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 its own dedicated switches, e.g. radius hook requires extra switches for FreeRADIUS. Please consult later sections of this chapter for details.

6. Rebuild Kea

      $ make

If your machine has multiple CPU cores, interesting option to consider here is -j X, where X is the number of available cores.

7. Install Kea sources together with hooks:

    $ sudo make install

Note that as part of the installation procedure, the install script will eventually venture into premium/ directory and will install additional hook libraries and associated files.

The installation location of the hooks libraries depends whether you specified --prefix parameter to the configure script. If you did not, the default location will be /usr/local/lib/hooks. You can verify the libraries are installed properly with this command:

    $ ls -l /usr/local/lib/hooks/*.so
    /usr/local/lib/hooks/libdhcp_class_cmds.so
    /usr/local/lib/hooks/libdhcp_flex_id.so
    /usr/local/lib/hooks/libdhcp_host_cmds.so
    /usr/local/lib/hooks/libdhcp_lease_cmds.so
    /usr/local/lib/hooks/libdhcp_legal_log.so
    /usr/local/lib/hooks/libdhcp_subnet_cmds.so

The exact list you see will depend on the packages you have. If you specified directory via --prefix, the hooks libraries will be located in {prefix directory}/lib/hooks.

## Configuring Hooks Libraries

The hooks 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, each structure corresponding to a hooks library. For example, to set up two hooks libraries for the DHCPv4 server, the configuration would be:

    "Dhcp4": {
        :
        "hooks-libraries": [
            {
                "library": "/opt/charging.so"
            },
            {
                "library": "/opt/local/notification.so",
                "parameters": {
                    "mail": "spam@example.com",
                    "floor": 13,
                    "debug": false,
                    "users": [ "alice", "bob", "charlie" ],
                    "languages": {
                        "french": "bonjour",
                        "klingon": "yl'el"
                    }
                }
            }
        ]
        :
    }

This is a change to the syntax used in Kea 0.9.2 and earlier, where hooks-libraries was a list of strings, each string being the name of a library. The change was made in Kea 1.0 to facilitate the specification of library-specific parameters, a capability available in Kea 1.1.0 onwards. Libraries should allow a parameter entry where to put comments as it is done for many configuration scopes with comment and user context.

The library reloading behavior has changed in Kea 1.1.0. Libraries are reloaded, even if their list hasn't changed. Kea does that, because the parameters specified for the library (or the files those parameters point to) may have changed.

Libraries may have additional parameters. Those are not mandatory in the sense that there may be libraries that don't require them. However, for specific library there is often specific requirement for specify certain set of parameters. Please consult the documentation for your library for details. In the example above, the first library has no parameters. The second library has five parameters, specifying mail (string parameter), floor (integer parameter), debug (boolean parameter) and even lists (list of strings) and maps (containing strings). Nested parameters could be used if the library supports it. This topic is explained in detail in the Hooks Developer's Guide in the "Configuring Hooks Libraries" section.

Notes:

- The full path to each library should be given.

- As noted above, order may be important - consult the documentation for each library.

- An empty list has the same effect as omitting the `hooks-libraries` configuration element all together.

  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. This will be fixed in a future version of Kea.

At the present time, only the kea-dhcp4 and kea-dhcp6 processes support hooks libraries.

## Available Hooks Libraries

As described above, the hooks 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 hooks libraries; these discussed in the following sections.

Some of these libraries will be available with the base code while others will be shared with organizations supporting development of Kea , possibly as a 'benefit' or 'thank you' for helping to sustain the larger Kea project. If you would like to get access to those libraries, please consider taking out a support contract: this includes professional support, advance security notifications, input into our roadmap planning, and many other benefits, while helping making Kea sustainable in the long term.

The following table provides a list of 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 `kea-ctrl-agent` process to load libraries that should, in fact, be loaded by the `kea-dhcp4` or `kea-dhcp6` processes. If a library from ISC doesn't work as expected, please make sure that it has been loaded by the correct process per the table below.

While the Kea Control Agent includes the "hooks" functionality, (i.e. hooks libraries can be loaded by this process), none of ISC's current hooks libraries should be loaded by the Control Agent.

### List of available hooks libraries

Name | Availability | Since | Load by process | Description
--- | --- | --- | --- | ---

user_chk

Kea sources

Kea 0.8

- kea-dhcp4
- kea-dhcp6

Reads known users list from a file. Unknown users will be assigned a lease from the last subnet defined in the configuration file, e.g. to redirect them 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.

Forensic Logging

Support customers

Kea 1.1.0

- kea-dhcp4
- kea-dhcp6

This library provides hooks that record a detailed log of lease assignments and renewals into 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 your jurisdiction requires that you save a different set of information, you may use it as a template or example and create your own custom logging hooks.

Flexible Identifier

Support customers

Kea 1.2.0

- kea-dhcp4
- kea-dhcp6

Kea software provides a way to handle host reservations that 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 using hardware address or DUID in DHCPv6. However, there are sometimes scenarios where the reservation is more complex, e.g. uses other options that mentioned above, uses part of specific options or perhaps even a combination of several options and fields to uniquely identify a client. Those scenarios are addressed by the Flexible Identifiers 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.

Host Commands

Support customers

Kea 1.2.0

- kea-dhcp4
- kea-dhcp6

Kea provides a way to store host reservations in a 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 will be rejected. Those commands are exposed via command channel (JSON over unix sockets) and Control Agent (JSON over RESTful interface). Additional commands and capabilities related to host reservations will be added in the future.

Subnet Commands

Support customers

Kea 1.3.0

- kea-dhcp4
- kea-dhcp6

In deployments in which subnet configuration needs to be frequently updated, it is a hard requirement that such updates be performed without the need for a full DHCP server reconfiguration or restart. This hooks library allows for incremental changes to the subnet configuration such as: adding a subnet, 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.

Lease Commands

Kea sources

Kea 1.3.0

- kea-dhcp4
- kea-dhcp6

The lease commands hook library offers a number of new commands used to manage leases. Kea provides a way to store lease information in various backends: memfile, MySQL, PostgreSQL and Cassandra. This library provides a unified interface that can manipulate leases in an unified, safe way. In particular, it allows: manipulate leases in memfile while Kea is running, sanity check changes, check lease existence and remove all leases belonging to specific subnet. It can also catch more obscure errors, like adding a lease with subnet-id that does not exist in the configuration or configuring a lease to use an address that is outside of the subnet to which it is supposed to belong. It provides a way to manage user contexts associated with leases.

High Availability

Kea sources

Kea 1.4.0

- kea-dhcp4
- kea-dhcp6

Minimizing a risk of DHCP service unavailability is achieved by setting up a pair of the 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 group of clients in this network or all clients, if it detects that its partner has became 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 referenced to as active-passive. This server will activate its DHCP function 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 server, making it much easier to have a replacement that is almost up to date. The "libdhcp_ha" library provides such functionality for Kea DHCP servers.

Statistics Commands

Kea sources

Kea 1.4.0

- kea-dhcp4
- kea-dhcp6

The Statistics Commands library provides additional commmands 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. A feature was introduced in Kea 1.4.0 that allows tracking lease allocations within the lease database, thus making the statistics accessible to all connected DHCP servers. The Statistics Commands hooks library utilizes this feature and returns lease statistics for all subnets respectively.

Radius

Support customers

Kea 1.4.0

- kea-dhcp4
- kea-dhcp6

The RADIUS Hook library allows Kea to interact with the 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 RADIUS server to keep track of device activity over time.

Host Cache

Support customers

Kea 1.4.0

- kea-dhcp4
- kea-dhcp6

Some of the database backends, such as RADIUS, are considered slow and may take a long time to respond. Since Kea in general is synchronous, the backend performance directly affects the DHCP performance. To minimize the impact and improve performance, the Host Cache 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.

Class Commands

Support customers

Kea 1.5.0

- kea-dhcp4
- kea-dhcp6

This Class Cmds hooks library allows for adding, updating deleting and fetching configured DHCP client classes without the need to restart the DHCP server.

ISC hopes to see more hooks libraries become available as time progresses, both developed internally and externally. Since this list may evolve dynamically, we decided to keep it on a wiki page, available at this link: https://gitlab.isc.org/isc-projects/kea/wikis/Hooks-available. If you are a developer or are aware of any hooks libraries not listed there, please send a note to the kea-users or kea-dev mailing lists and someone will update it.

The libraries developed by ISC are described in detail in the following sections.

### user_chk: Checking User Access

The user_chk library is the first hooks library published by ISC. It attempts to serve several purposes:

- To assign "new" or "unregistered" users to a restricted subnet, while "known" or "registered" users are assigned to unrestricted subnets.

- To allow DHCP response options or vendor option values to be customized based upon user identity.

- To provide a real time record of the user registration activity which can be sampled by an external consumer.

- To serve as a demonstration of various capabilities possible using the hooks interface.

Once loaded, the library allows segregating incoming requests into known and unknown clients. For known clients, the packets are processed mostly as usual, except it is possible to override certain options being sent. That can be done on a per host basis. Clients that are not on the known hosts list will be treated as unknown and will be assigned to the last subnet defined in the configuration file.

As an example of use, this behavior may be used to put unknown users into a separate subnet that leads to a walled garden, where they can only access a registration portal. Once they fill in necessary data, their details are added to the known clients file and they get a proper address after their device is restarted.

This library was developed several years before the host reservation mechanism has become available. Currently host reservation is much more powerful and flexible, but nevertheless the user_chk capability to consult and external source of information about clients and alter Kea's behavior is useful and remains of educational value.

The library reads the /tmp/user_chk_registry.txt file while being loaded and each time an incoming packet is processed. The file is expected to have each line contain a self-contained JSON snippet which must have the following two entries:

- `type`, whose value is "HW_ADDR" for IPv4 users or "DUID" for IPv6 users

- `id`, whose value is either the hardware address or the DUID from the request formatted as a string of hex digits, with or without ":" delimiters.

and may have the zero or more of the following entries:

- `bootfile` whose value is the pathname of the desired file

- `tftp_server` whose value is the hostname or IP address of the desired server

A sample user registry file is shown below:

    { "type" : "HW_ADDR", "id" : "0c:0e:0a:01:ff:04", "bootfile" : "/tmp/v4bootfile" }
    { "type" : "HW_ADDR", "id" : "0c:0e:0a:01:ff:06", "tftp_server" : "tftp.v4.example.com" }
    { "type" : "DUID", "id" : "00:01:00:01:19:ef:e6:3b:00:0c:01:02:03:04", "bootfile" : "/tmp/v6bootfile" }
    { "type" : "DUID", "id" : "00:01:00:01:19:ef:e6:3b:00:0c:01:02:03:06", "tftp_server" : "tftp.v6.example.com" }

As with any other hooks libraries provided by ISC, internals of the user_chk code are well documented. You can take a look at the Kea Developer's Guide section dedicated to the user_chk library that discusses how the code works internally. That, together with our general entries in Hooks Framework section should give you some pointers how to extend this library and perhaps even write your own from scratch.

### legal_log: Forensic Logging Hooks

This section describes the forensic log hooks library. This library provides hooks that record a detailed log of lease assignments and renewals into a set of log files. Currently this library is only available to ISC customers with a support contract.

This library may only be loaded by `kea-dhcp4` or `kea-dhcp6` process.

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 your jurisdiction requires that you save a different set of information you may use it as a template or example and create your own custom logging hooks.

This logging is done as a set of hooks to allow it to be customized to any particular need. Modifying a hooks library is easier and safer than updating the core code. In addition by using the hooks features those users who don't need to log this information can leave it out and avoid any performance penalties.

#### Log File Naming

The names for the log files have the following form:

    path/base-name.CCYYMMDD.txt

The "path" and "base-name" are supplied in the configuration as described below see . The next part of the name is the date the log file was started, with four digits for year, two digits for month and two digits for day. The file is rotated on a daily basis.

When running Kea servers for both DHCPv4 and DHCPv6 the log names must be distinct. See the examples in .

#### DHCPv4 Log Entries

For DHCPv4 the library creates entries based on DHCPREQUEST messages and corresponding DHCPv4 leases intercepted by lease4_select (for new leases) and lease4_renew (for renewed leases) hooks.

An entry is a single string with no embedded end-of-line markers, a prepended timestamp and has the following sections:

    timestamp address duration device-id {client-info} {relay-info} {user-context}

Where:

- timestamp - the current date and time the log entry was written in "%Y-%m-%d %H:%M:%S %Z" strftime format ("%Z" is the time zone name).

- address - the leased IPv4 address given out and whether it was assigned or renewed.

- duration - the lease lifetime expressed in days (if present), hours, minutes and seconds. A lease lifetime of 0xFFFFFFFF will be denoted with the text "infinite duration".

- device-id - the client's hardware address shown as numerical type and hex digit string.

- client-info - the DHCP client id option (61) if present, shown as a hex string.

- relay-info - for relayed packets the giaddr and the RAI circuit-id, remote-id and subscriber-id options (option 82 sub options: 1, 2 and 6) if present. The circuit id and remote id are presented as hex strings

- user-context - the optional user context associated to the lease.

For instance (line breaks added for readability, they would not be present in the log file).

    2018-01-06 01:02:03 CET Address: 192.2.1.100 has been renewed for 1 hrs 52 min 15 secs to a device with hardware address:
    hwtype=1 08:00:2b:02:3f:4e, client-id: 17:34:e2:ff:09:92:54 connected via relay at address: 192.2.16.33,
    identified by circuit-id: 68:6f:77:64:79 and remote-id: 87:f6:79:77:ef

In addition to logging lease activity driven by DHCPv4 client traffic, it also logs entries for the following lease management control channel commands: lease4-add, lease4-update, and lease4-del. Each entry is a single string with no embedded end-of-line markers and they will typically have the following forms:

`lease4-add:`

    *timestamp* Administrator added a lease of address: *address* to a device with hardware address: *device-id*

Dependent on the arguments of the add command, it may also include the client-id and duration.

Example:

    2018-01-06 01:02:03 CET Administrator added a lease of address: 192.0.2.202 to a device with hardware address:
    1a:1b:1c:1d:1e:1f for 1 days 0 hrs 0 mins 0 secs

`lease4-update:`

    *timestamp* Administrator updated information on the lease of address: *address* to a device with hardware address: *device-id*

Dependent on the arguments of the update command, it may also include the client-id and lease duration.

Example:

    2018-01-06 01:02:03 CET Administrator updated information on the lease of address: 192.0.2.202 to a device
    with hardware address: 1a:1b:1c:1d:1e:1f, client-id: 1234567890

`lease4-del:` Deletes have two forms, one by address and one by identifier and identifier type:

    *timestamp* Administrator deleted the lease for address: *address*

or

    *timestamp* Administrator deleted a lease for a device identified by: *identifier-type* of *identifier*

Currently only a type of @b hw-address (hardware address) is supported.

Examples:

    2018-01-06 01:02:03 CET Administrator deleted the lease for address: 192.0.2.202

    2018-01-06 01:02:12 CET Administrator deleted a lease for a device identified by: hw-address of 1a:1b:1c:1d:1e:1f

#### DHCPv6 Log Entries

For DHCPv6 the library creates entries based on lease management actions intercepted by the lease6_select (for new leases), lease6_renew (for renewed leases) and lease6_rebind (for rebound leases).

An entry is a single string with no embedded end-of-line markers, a prepended timestamp and has the following sections:

    timestamp address duration device-id {relay-info}* {user-context}

Where:

- timestamp - the current date and time the log entry was written in "%Y-%m-%d %H:%M:%S %Z" strftime format ("%Z" is the time zone name).

- address - the leased IPv6 address or prefix given out and whether it was assigned or renewed.

- duration - the lease lifetime expressed in days (if present), hours, minutes and seconds. A lease lifetime of 0xFFFFFFFF will be denoted with the text "infinite duration".

- device-id - the client's DUID and hardware address (if present).

- relay-info - for relayed packets the content of relay agent messages, remote-id (code 37), subscriber-id (code 38) and interface-id (code 18) options if present. Note that interface-id option, if present, identifies the whole interface the relay agent received the message on. This typically translates to a single link in your network, but it depends on your specific network topology. Nevertheless, this is useful information to better scope down the location of the device, so it is being recorded, if present.

- user-context - the optional user context associated to the lease.

For instance (line breaks added for readability, they would not be present in the log file).

    2018-01-06 01:02:03 PST Address:2001:db8:1:: has been assigned for 0 hrs 11 mins 53 secs
    to a device with DUID: 17:34:e2:ff:09:92:54 and hardware address: hwtype=1 08:00:2b:02:3f:4e
    (from Raw Socket) connected via relay at address: fe80::abcd for client on link address: 3001::1,
    hop count: 1, identified by remote-id: 01:02:03:04:0a:0b:0c:0d:0e:0f and subscriber-id: 1a:2b:3c:4d:5e:6f

In addition to logging lease activity driven by DHCPv6 client traffic, it also logs entries for the following lease management control channel commands: lease6-add, lease6-update, and lease6-del. Each entry is a single string with no embedded end-of-line markers and they will typically have the following forms:

`lease6-add:`

    *timestamp* Administrator added a lease of address: *address* to a device with DUID: *DUID*

Dependent on the arguments of the add command, it may also include the hardware address and duration.

Example:

    2018-01-06 01:02:03 PST Administrator added a lease of address: 2001:db8::3 to a device with DUID:
    1a:1b:1c:1d:1e:1f:20:21:22:23:24 for 1 days 0 hrs 0 mins 0 secs

`lease6-update:`

    *timestamp* Administrator updated information on the lease of address: *address* to a device with DUID: *DUID*

Dependent on the arguments of the update command, it may also include the hardware address and lease duration.

Example:

    2018-01-06 01:02:03 PST Administrator updated information on the lease of address: 2001:db8::3 to a device with
    DUID: 1a:1b:1c:1d:1e:1f:20:21:22:23:24, hardware address: 1a:1b:1c:1d:1e:1f

`lease6-del:` Deletes have two forms, one by address and one by identifier and identifier type:

    *timestamp* Administrator deleted the lease for address: *address*

or

    *timestamp* Administrator deleted a lease for a device identified by: *identifier-type* of *identifier*

Currently only a type of DUID is supported.

Examples:

    2018-01-06 01:02:03 PST Administrator deleted the lease for address: 2001:db8::3

    2018-01-06 01:02:11 PST Administrator deleted a lease for a device identified by: duid of 1a:1b:1c:1d:1e:1f:20:21:22:23:24

#### Configuring the Forensic Log Hooks

To use this functionality the hook library must be included in the configuration of the desired DHCP server modules. The legal_log library is installed alongside the Kea libraries in `[kea-install-dir]/lib` where `kea-install-dir` is determined by the "--prefix" option of the configure script. It defaults to `/usr/local`. Assuming the default value then, configuring kea-dhcp4 to load the legal_log library could be done with the following Kea4 configuration:

    "Dhcp4": {
        "hooks-libraries": [
            {
                "library": "/usr/local/lib/libdhcp_legal_log.so",
                "parameters": {
                    "path": "/var/kea/var",
                    "base-name": "kea-forensic4"
                }
            },
            ...
        ]
    }

To configure it for kea-dhcp6, the commands are simply as shown below:

    "Dhcp6": {
        "hooks-libraries": [
            {
                "library": "/usr/local/lib/libdhcp_legal_log.so",
                "parameters": {
                    "path": "/var/kea/var",
                    "base-name": "kea-forensic6"
                }
            },
            ...
        ]
    }

Two Hook Library parameters are supported:

- path - the directory in which the forensic file(s) will be written. The default value is `[prefix]/kea/var`. The directory must exist.

- base-name - an arbitrary value which is used in conjunction with the current system date to form the current forensic file name. It defaults to `kea-legal`.

If it is desired to restrict forensic logging to certain subnets, the "legal-logging" boolean parameter can be specified within a user context of these subnets. For example:

    "Dhcpv4" {
        "subnet4": [
            {
                "subnet": "192.0.2.0/24",
                "pools": [
                    {
                         "pool": "192.0.2.1 - 192.0.2.200"
                    }
                ],
                "user-context": {
                    "legal-logging": false
                }
            }
        ]
    }

disables legal logging for the subnet "192.0.2.0/24". If this parameter is not specified, it defaults to 'true', which enables legal logging for the subnet.

The following example demonstrates how to selectively disable legal logging for an IPv6 subnet.

    "Dhcpv6": {
        "subnet6": [
            {
                "subnet": "2001:db8:1::/64",
                "pools": [
                     {
                         "pool": "2001:db8:1::1-2001:db8:1::ffff"
                     }
                ],
                "user-context": {
                    "legal-logging": false
                }
            }
        ]
    }

See and to learn more about user contexts in Kea configuration.

#### Database backend

Log entries can be inserted into a database when Kea is configured with database backend support: a table named 'logs' is used with a timestamp (timeuuid for Cassandra CQL) generated by the database software and a text log with the same format than for files without the timestamp.

Please refer to for MySQL, to for PostgreSQL or to for Cassandra CQL. The logs table is part of the Kea database schemas.

Configuration parameters are extended by standard lease database parameters as defined in . The "type" parameter should be "mysql", "postgresql", "cql" or be "logfile". When it is absent or set to "logfile" files are used.

This database feature is experimental and will be likely improved, for instance to add an address / prefix index (currently the only index is the timestamp). No specific tools is provided to operate the database but standard tools are applicable, for instance to dump the logs table from a CQL database:

    $ echo 'SELECT dateOf(timeuuid), log FROM logs;' | cqlsh -k database-name

     system.dateof(timeuuid)         | log
    ---------------------------------+---------------------------------------
     2018-01-06 01:02:03.227000+0000 | Address: 192.2.1.100 has been renewed ...
     ...
    (12 rows)
    $

### flex_id: Flexible Identifiers for Host Reservations

This section describes a hook application dedicated to generate flexible identifiers for host reservation. Kea software provides a way to handle host reservations that 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 using hardware address or DUID in DHCPv6. However, there are sometimes scenarios where the reservation is more complex, e.g. uses other options that mentioned above, uses part of specific options or perhaps even a combination of several options and fields to uniquely identify a client. Those scenarios are addressed by the Flexible Identifiers hook application.

Currently this library is only available to ISC customers with a support contract.

This library may only be loaded by `kea-dhcp4` or `kea-dhcp6` process.

The library allows for defining an expression, using notation initially used for client classification only. See for detailed description of the syntax available. One notable difference is that for client classification the expression currently has to evaluate to either true or false, while the flexible identifier expression is expected to evaluate to a string that will be used as identifier. It is a valid case for the expression to evaluate to empty string (e.g. in cases where a client does not sent specific options). This expression is then evaluated for each incoming packet. This evaluation generates an identifier that is used to identify the client. In particular, there may be host reservations that are tied to specific values of the flexible identifier.

The library can be loaded in similar way as other hook libraries. It takes a mandatory parameter identifier-expression and optional boolean parameter replace-client-id:

    "Dhcp6": {
        "hooks-libraries": [
            {
                "library": "/path/libdhcp_flex_id.so",
                "parameters": {
                    "identifier-expression": "expression",
                    "replace-client-id": "false"
                }
            },
            ...
        ]
    }

The flexible identifier library supports both DHCPv4 and DHCPv6.

EXAMPLE: Let's consider a case of an IPv6 network that has an independent interface for each of the connected customers. Customers are able to plug in whatever device they want, so any type of identifier (e.g. a client-id) is unreliable. Therefore the operator may decide to use an option inserted by a relay agent to differentiate between clients. In this particular deployment, the operator verified that the interface-id is unique for each customer facing interface. Therefore it is suitable for usage as reservation. However, only the first 6 bytes of the interface-id are interesting, because remaining bytes are either randomly changed or not unique between devices. Therefore the customer decided to use first 6 bytes of the interface-id option inserted by the relay agent. After adding "flex-id" host-reservation-identifiers goal can be achieved by using the following configuration:

    "Dhcp6": {
        "subnet6": [{ ..., // subnet definition starts here
        "reservations": [
            "flex-id": "'port1234'", // value of the first 8 bytes of the interface-id
            "ip-addresses": [ "2001:db8::1" ]
        ],
        }], // end of subnet definitions
        "host-reservation-identifiers": ["duid", "flex-id"], // add "flex-id" to reservation identifiers
        "hooks-libraries": [
            {
                "library": "/path/libdhcp_flex_id.so",
                "parameters": {
                    "identifier-expression": "substring(relay6[0].option[18].hex,0,8)"
                }
            },
            ...
        ]
    }

NOTE: Care should be taken when adjusting the expression. If the expression changes, then all the flex-id values may change, possibly rendering all reservations based on flex-id unusable until they're manually updated. Therefore it is strongly recommended to start with the expression and a handful reservations, adjust the expression as needed and only after it was confirmed the expression does exactly what is expected out of it go forward with host reservations on any broader scale.

flex-id values in host reservations can be specified in two ways. First, they can be expressed as hex string, e.g. bar string can be represented as 626174. Alternatively, it can be expressed as quoted value (using double and single quotes), e.g. "'bar'". The former is more convenient for printable characters, while hex string values are more convenient for non-printable characters and does not require the use of the `hexstring` operator.

    "Dhcp6": {
        "subnet6": [{ ..., // subnet definition starts here
        "reservations": [
            "flex-id": "01:02:03:04:05:06", // value of the first 8 bytes of the interface-id
            "ip-addresses": [ "2001:db8::1" ]
        ],
        }], // end of subnet definitions
        "host-reservation-identifiers": ["duid", "flex-id"], // add "flex-id" to reservation identifiers
        "hooks-libraries": [
            {
                "library": "/path/libdhcp_flex_id.so",
                "parameters": {
                    "identifier-expression": "vendor[4491].option[1026].hex"
                }
            },
            ...
        ]
    }

When "replace-client-id" is set to false (which is the default setting), the flex-id hook library uses evaluated flexible identifier solely for identifying host reservations, i.e. searching for reservations within a database. This is a functional equivalent of other identifiers, similar to hardware address or circuit-id. However, this mode of operation has an implication that if a client device is replaced, it may cause a conflict between an existing lease (allocated for old device) and the new lease being allocated for the new device. The conflict arises because the same flexible identifier is computed for the replaced device and the server will try to allocate the same lease. The mismatch between client identifiers sent by new device and old device causes the server to refuse this new allocation until the old lease expires. A manifestation of this problem is dependant on specific expression used as flexible identifier and is likely to appear if you only use options and other parameters that are identifying where the device is connected (e.g. circuit-id), rather than the device identification itself (e.g. MAC address).

The flex-id library offers a way to overcome the problem with lease conflicts by dynamically replacing client identifier (or DUID in DHCPv6 case) with a value derived from flexible identifier. The server processes the client's query as if flexible identifier was sent in the client identifier (or DUID) option. This guarantees that returning client (for which the same flexible identifier is evaluated) will be assigned the same lease despite the client identifier and/or MAC address change.

The following is a stub configuration that enables this behavior:

    "Dhcp4": {
        "hooks-libraries": [
            {
                "library": "/path/libdhcp_flex_id.so",
                "parameters": {
                    "identifier-expression": "expression",
                    "replace-client-id": "true"
                }
            },
            ...
        ]
    }

In the DHCPv4 case, the value derived from the flexible identifier is formed by prepending 1 byte with a value of zero to flexible identifier. In the IPv6 case, it is formed by prepanding two zero bytes before the flexible identifier.

Note that for this mechanism to take effect, the DHCPv4 server must be configured to respect the client identifier option value during lease allocation, i.e. "match-client-id" must be set to true. See for details. No additional settings are required for DHCPv6.

If "replace-client-id" option is set to true, the value of "echo-client-id" parameter (that governs whether to send back a client-id option or not) is ignored.

The section describes commands used to retrieve, update and delete leases using various identifiers, e.g. "hw-address", "client-id". The lease_cmds library doesn't natively support querying for leases by flexible identifier. However, when "replace-client-id" is set to true, it makes it possible to query for leases using a value derived from the flexible identifier. In the DHCPv4 case, the query will look similar to this:

    {
        "command": "lease4-get",
        "arguments": {
            "identifier-type": "client-id",
            "identifier": "00:54:64:45:66",
            "subnet-id": 44
        }
    }

where hexadecimal value of "54:64:45:66" is a flexible identifier computed for the client.

In the DHCPv6 case, the corresponding query will look similar to this:

    {
        "command": "lease6-get",
        "arguments": {
            "identifier-type": "duid",
            "identifier": "00:00:54:64:45:66",
            "subnet-id": 10
        }
    }

### host_cmds: Host Commands

This section describes a hook application that offers a number of new commands used to query and manipulate host reservations. Kea provides a way to store host reservations in a 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 will be rejected. Those commands are exposed via command channel (JSON over unix sockets) and Control Agent (JSON over RESTful interface). Additional commands and capabilities related to host reservations will be added in the future.

Currently this library is only available to ISC customers with a support contract.

This library may only be loaded by `kea-dhcp4` or `kea-dhcp6` process.

Currently five commands are supported: reservation-add (which adds new host reservation), reservation-get (which returns existing reservation if specified criteria are matched), reservation-get-all (which returns all reservations in a specified subnet), reservation-get-page (variant of reservation-get-all which returns all reservations in a specified subnet by pages) and reservation-del (which attempts to delete a reservation matching specified criteria). To use commands that change the reservation information (currently these are reservation-add and reservation-del, but this rule applies to other commands that may be implemented in the future), hosts database must be specified (see hosts-databases description in and ) and it must not operate in read-only mode. If the hosts-databases are not specified or are running in read-only mode, the host_cmds library will load, but any attempts to use reservation-add or reservation-del will fail.

Additional host reservation commands are planned in the future. For a description of envisaged commands, see Control API Requirements document.

All commands are using JSON syntax. They can be issued either using control channel (see ) or via Control Agent (see ).

The library can be loaded in similar way as other hook libraries. It does not take any parameters. It supports both DHCPv4 and DHCPv6 servers.

    "Dhcp6": {
        "hooks-libraries": [
            {
                "library": "/path/libdhcp_host_cmds.so"
            }
            ...
        ]
    }

#### The subnet-id parameter

Prior to diving into the individual commands, it is worth discussing the parameter, `subnet-id`. Currently it is mandatory for all of the commands supplied by this library. Prior to Kea 1.5.0, reservations had to belong to specific subnet. Beginning with Kea 1.5.0, reservations may now be specified globally. In other words, they are not specific to any subnet. When reservations are supplied via the configuration file, the ID of the containing subnet (or lack thereof) is implicit in the configuration structure. However, when managing reservations using the host commands, it is necessary to explicitly identify the scope to which the reservation belongs. This is done via the `subnet-id` parameter. For global reservations, use a value of zero (0). For reservations scoped to a specific subnet, use that subnet's ID.

#### reservation-add command

`reservation-add` allows for the insertion of a new host. It takes a set of arguments that vary depending on the nature of the host reservation. Any parameters allowed in the configuration file that pertain to host reservation are permitted here. For details regarding IPv4 reservations, see and . The `subnet-id` is manadatory. Use a value of zero (0) to add a global reservation, or the id of the subnet to which the reservation should be added. An example command can be as simple as:

    {
        "command": "reservation-add",
        "arguments": {
            "reservation": {
                "subnet-id": 1,
                "hw-address": "1a:1b:1c:1d:1e:1f",
                "ip-address": "192.0.2.202"
            }
        }
    }

but can also take many more parameters, for example:

    {
        "command": "reservation-add",
        "arguments": {
            "reservation":
                {
                    "subnet-id":1,
                    "client-id": "01:0a:0b:0c:0d:0e:0f",
                    "ip-address": "192.0.2.205",
                    "next-server": "192.0.2.1",
                    "server-hostname": "hal9000",
                    "boot-file-name": "/dev/null",
                    "option-data": [
                        {
                            "name": "domain-name-servers",
                            "data": "10.1.1.202,10.1.1.203"
                        }
                    ],
                    "client-classes": [ "special_snowflake", "office" ]
                }
        }
    }

Here is an example of complex IPv6 reservation:

    {
        "command": "reservation-add",
        "arguments": {
            "reservation":
                {
                    "subnet-id":1,
                    "duid": "01:02:03:04:05:06:07:08:09:0A",
                    "ip-addresses": [ "2001:db8:1:cafe::1" ],
                    "prefixes": [ "2001:db8:2:abcd::/64" ],
                    "hostname": "foo.example.com",
                    "option-data": [
                        {
                            "name": "vendor-opts",
                            "data": "4491"
                        },
                        {
                            "name": "tftp-servers",
                            "space": "vendor-4491",
                            "data": "3000:1::234"
                        }
                    ]
                }
        }
    }

The command returns a status that indicates either a success (result 0) or a failure (result 1). Failed command always includes text parameter that explains the cause of failure. Example results:

    { "result": 0, "text": "Host added." }

Example failure:

    { "result": 1, "text": "Mandatory 'subnet-id' parameter missing." }

As `reservation-add` is expected to store the host, hosts-databases parameter must be specified in your configuration and databases must not run in read-only mode. In the future versions it will be possible to modify the reservations read from a configuration file. Please contact ISC if you are interested in this functionality.

#### reservation-get command

`reservation-get` can be used to query the host database and retrieve existing reservations. There are two types of parameters this command supports: (subnet-id, address) or (subnet-id, identifier-type, identifier). The first type of query is used when the address (either IPv4 or IPv6) is known, but the details of the reservation aren't. One common use case of this type of query is to find out whether a given address is reserved or not. The second query uses identifiers. For maximum flexibility, Kea stores the host identifying information as a pair of values: type and the actual identifier. Currently supported identifiers are "hw-address", "duid", "circuit-id", "client-id" and "flex-id", but additional types may be added in the future. If any new identifier types are defined in the future, reservation-get command will support them automatically. The `subnet-id` is mandatory. Use a value of zero (0) to fetch a global reservation, or the id of the subnet to which the reservation belongs.

An example command for getting a host reservation by (subnet-id, address) pair looks as follows:

    {
        "command": "reservation-get",
        "arguments": {
            "subnet-id": 1,
            "ip-address": "192.0.2.202"
        }
    }

An example query by (subnet-id, identifier-type, identifier) looks as follows:

    {
        "command": "reservation-get",
        "arguments": {
            "subnet-id": 4,
            "identifier-type": "hw-address",
            "identifier": "01:02:03:04:05:06"
        }
    }

`reservation-get` typically returns result 0 when the query was conducted properly. In particular, 0 is returned when the host was not found. If the query was successful a number of host parameters will be returned. An example of a query that did not find the host looks as follows:

    { "result": 0, "text": "Host not found." }

An example result returned when the host was found:

    {
      "arguments": {
        "boot-file-name": "bootfile.efi",
        "client-classes": [

        ],
        "hostname": "somehost.example.org",
        "hw-address": "01:02:03:04:05:06",
        "ip-address": "192.0.2.100",
        "next-server": "192.0.0.2",
        "option-data": [

        ],
        "server-hostname": "server-hostname.example.org"
      },
      "result": 0,
      "text": "Host found."
    }

An example result returned when the query was malformed:

    { "result": 1, "text": "No 'ip-address' provided and 'identifier-type'
                            is either missing or not a string." }

#### reservation-get-all command

`reservation-get-all` can be used to query the host database and retrieve all reservations in a specified subnet. This command uses parameters providing the mandatory subnet-id. Global host reservations can be retrieved by using subnet-id value of zero (0).

For instance for retrieving host reservations for the subnet 1:

    {
        "command": "reservation-get-all",
        "arguments": {
            "subnet-id": 1
         }
    }

returns found some IPv4 hosts:

    {
        "arguments": {
            "hosts": [
                {
                    "boot-file-name": "bootfile.efi",
                    "client-classes": [ ],
                    "hostname": "somehost.example.org",
                    "hw-address": "01:02:03:04:05:06",
                    "ip-address": "192.0.2.100",
                    "next-server": "192.0.0.2",
                    "option-data": [ ],
                    "server-hostname": "server-hostname.example.org"
                },
                ...
                {
                    "boot-file-name": "bootfile.efi",
                    "client-classes": [ ],
                    "hostname": "otherhost.example.org",
                    "hw-address": "01:02:03:04:05:ff",
                    "ip-address": "192.0.2.200",
                    "next-server": "192.0.0.2",
                    "option-data": [ ],
                    "server-hostname": "server-hostname.example.org"
                }
            ]
        },
        "result": 0,
        "text": "72 IPv4 host(s) found."
    }

The response returned by `reservation-get-all` can be very long. The DHCP server does not handle DHCP traffic when preparing a response to reservation-get-all. If there are many reservations in a subnet, this may be disruptive. Use with caution. For larger deployments, please consider using `reservation-get-page` instead (see ).

For a reference, see .

#### reservation-get-page command

`reservation-get-page` can be used to query the host database and retrieve all reservations in a specified subnet by pages. This command uses parameters providing the mandatory subnet-id. Use a value of zero (0) to fetch global reservations. The second mandatory parameter is the page size limit. Optional source-index and from host id, both defaulting to 0, are uses to chain page queries.

The usage of from and source-index parameters requires additional explanation. For the first call those parameters should not be specified (or specified as zeros). For any follow up calls they should be set to the values returned in previous calls in a next map holding from and source-index values. The subsequent calls should be issued until all reservations are returned. The end is reached once the returned list is empty, count is 0, no next map is present and result status 3 (empty) is returned.

The from and source-index parameters are reflecting internal state of the search. There is no need to understand what they represent, it's simply a value that is supposed to be copied from one response to the next query. However, if you are curious, from field represents a 64 bits representation of host identifier used by a host backend. The source-index represents internal representation of multiple host backends: 0 is used to represent hosts defined in a configuration file, 1 represents the first database backend. In some uncommon cases there may be more than one database backend configured, so potentially there may be 2. In any case, Kea will iterate over all backends configured.

For instance for retrieving host reservations for the subnet 1 requesting the first page can be done by:

    {
        "command": "reservation-get-page",
        "arguments": {
            "subnet-id": 1,
            "limit": 10
         }
    }

Since this is the first call, source-index and from should not be specified. They will default to their zero default values.

Some hosts are returned with informations to get the next page:

    {
        "arguments": {
            "count": 72,
            "hosts": [
                {
                    "boot-file-name": "bootfile.efi",
                    "client-classes": [ ],
                    "hostname": "somehost.example.org",
                    "hw-address": "01:02:03:04:05:06",
                    "ip-address": "192.0.2.100",
                    "next-server": "192.0.0.2",
                    "option-data": [ ],
                    "server-hostname": "server-hostname.example.org"
                },
                ...
                {
                    "boot-file-name": "bootfile.efi",
                    "client-classes": [ ],
                    "hostname": "otherhost.example.org",
                    "hw-address": "01:02:03:04:05:ff",
                    "ip-address": "192.0.2.200",
                    "next-server": "192.0.0.2",
                    "option-data": [ ],
                    "server-hostname": "server-hostname.example.org"
                }
            ],
            "next": {
                "from": 1234567,
                "source-index": 1
            }
        },
        "result": 0,
        "text": "72 IPv4 host(s) found."
    }

Note that from and source-index fields were specified in the response in the next map. Those two must be copied to the next command, so Kea continues from the place where the last command finished. To get the next page the following command can be sent:

    {
        "command": "reservation-get-page",
        "arguments": {
            "subnet-id": 1,
            "source-index": 1,
            "from": 1234567,
            "limit": 10
         }
    }

. The response will contain a list of hosts with updated source-index and from fields. Continue calling the command until you get the last page. Its response will look like this:

    {
        "arguments": {
            "count": 0,
            "hosts": [ ],
        },
        "result": 3,
        "0 IPv4 host(s) found."
    }

This command is more complex than `reservation-get-all`, but lets users retrieve larger host reservations lists by smaller chunks. For small deployments with few reservations, is it easier to use `reservation-get-all` (see .

For a reference, see .

Currently `reservation-get-page` is not supported by the Cassandra host backend.

#### reservation-del command

`reservation-del` can be used to delete a reservation from the host database. There are two types of parameters this command supports: (subnet-id, address) or (subnet-id, identifier-type, identifier). The first type of query is used when the address (either IPv4 or IPv6) is known, but the details of the reservation aren't. One common use case of this type of query is to remove a reservation (e.g. you want a specific address to no longer be reserved). The second query uses identifiers. For maximum flexibility, Kea stores the host identifying information as a pair of values: type and the actual identifier. Currently supported identifiers are "hw-address", "duid", "circuit-id", "client-id" and "flex-id", but additional types may be added in the future. If any new identifier types are defined in the future, reservation-get command will support them automatically. The `subnet-id` is manadatory. Use a value of zero (0) to delete a global reservation, or the id of the subnet from which the reservation should be deleted.

An example command for deleting a host reservation by (subnet-id, address) pair looks as follows:

    {
        "command": "reservation-del",
        "arguments": {
            "subnet-id": 1,
            "ip-address": "192.0.2.202"
        }
    }

An example deletion by (subnet-id, identifier-type, identifier) looks as follows:

    {
        "command": "reservation-del",
        "arguments":
            "subnet-id": 4,
            "identifier-type": "hw-address",
            "identifier": "01:02:03:04:05:06"
        }
    }

`reservation-del` returns result 0 when the host deletion was successful or 1 if it was not. A descriptive text is provided in case of error. Example results look as follows:

    {
        "result": 1,
        "text": "Host not deleted (not found)."
    }

    {
        "result": 0,
        "text": "Host deleted."
    }

    {
        "result": 1,
        "text": "Unable to delete a host because there is no hosts-database
                 configured."
    }

### subnet_cmds: Subnet Commands

This section describes a hook application that offers a number of new commands used to query and manipulate subnet and shared network configurations in Kea. This application is very useful in deployments with a large number of subnets being managed by the DHCP servers and when the subnets are frequently updated. The commands offer lightweight approach for manipulating subnets without a need to fully reconfigure the server and without affecting existing servers' configurations. An ability to manage shared networks (listing, retrieving details, adding new ones, removing existing ones, adding subnets to and removing from shared networks) is also provided.

Currently this library is only available to ISC customers with a support contract.

This library may only be loaded by `kea-dhcp4` or `kea-dhcp6` process.

The following commands are currently supported:

- `subnet4-list/subnet6-list`: lists all configured subnets

- `subnet4-get/subnet6-get`: retrieves detailed information about a specified subnet

- `subnet4-add/subnet6-add`: adds new subnet into server's configuration

- `subnet4-del/subnet6-del`: removes a subnet from the server's configuration

- `network4-list/network6-list`: lists all configured shared networks

- `network4-get/network6-get`: retrieves detailed information about specified shared network

- `network4-add/network6-add`: adds a new shared network to the server's configuration

- `network4-del/network6-del`: removes a shared network from the server's configuration

- `network4-subnet-add/network6-subnet-add`: adds existing subnet to existing shared network

- `network4-subnet-del/network6-subnet-del`: removes a subnet from existing shared network and demotes it to a plain subnet.

#### subnet4-list command

This command is used to list all currently configured subnets. The subnets are returned in a brief form, i.e. a subnet identifier and subnet prefix is included for each subnet. In order to retrieve the detailed information about the subnet the `subnet4-get` should be used.

This command has the simple structure:

    {
        "command": "subnet4-list"
    }

The list of subnets returned as a result of this command is returned in the following format:

    {
        "result": 0,
        "text": "2 IPv4 subnets found",
        "arguments": {
        "subnets": [
            {
                "id": 10,
                "subnet": "10.0.0.0/8"
            },
            {
                "id": 100,
                "subnet": "192.0.2.0/24"
            }
        ]
    }

If no IPv4 subnets are found, an error code is returned along with the error description.

#### subnet6-list command

This command is used to list all currently configured subnets. The subnets are returned in a brief form, i.e. a subnet identifier and subnet prefix is included for each subnet. In order to retrieve the detailed information about the subnet the `subnet6-get` should be used.

This command has the simple structure:

    {
        "command": "subnet6-list"
    }

The list of subnets returned as a result of this command is returned in the following format:

    {
        "result": 0,
        "text": "2 IPv6 subnets found",
        "arguments": {
        "subnets": [
            {
                "id": 11,
                "subnet": "2001:db8:1::/64"
            },
            {
                "id": 233,
                "subnet": "3000::/16"
            }
        ]
    }

If no IPv6 subnets are found, an error code is returned along with the error description.

#### subnet4-get command

This command is used to retrieve detailed information about the specified subnet. This command usually follows the `subnet4-list`, which is used to discover available subnets with their respective subnet identifiers and prefixes. Any of those parameters can be then used in `subnet4-get` to fetch subnet information:

    {
        "command": "subnet4-get",
        "arguments": {
            "id": 10
        }
    }

or

    {
        "command": "subnet4-get",
        "arguments": {
            "subnet": "10.0.0.0/8"
        }
    }

If the subnet exists the response will be similar to this:

    {
        "result": 0,
        "text": "Info about IPv4 subnet 10.0.0.0/8 (id 10) returned",
        "arguments": {
            "subnets": [
                {
                    "subnet": "10.0.0.0/8",
                    "id": 1,
                    "option-data": [
                        ....
                    ]
                    ...
                }
            ]
        }
    }

#### subnet6-get command

This command is used to retrieve detailed information about the specified subnet. This command usually follows the `subnet6-list`, which is used to discover available subnets with their respective subnet identifiers and prefixes. Any of those parameters can be then used in `subnet6-get` to fetch subnet information:

    {
        "command": "subnet6-get",
        "arguments": {
            "id": 11
        }
    }

or

    {
        "command": "subnet6-get",
        "arguments": {
            "subnet": "2001:db8:1::/64"
        }
    }

If the subnet exists the response will be similar to this:

    {
        "result": 0,
        "text": "Info about IPv6 subnet 2001:db8:1::/64 (id 11) returned",
        "arguments": {
            "subnets": [
                {
                    "subnet": "2001:db8:1::/64",
                    "id": 1,
                    "option-data": [
                        ...
                    ]
                    ....
                }
            ]
        }
    }

#### subnet4-add

This command is used to create and add new subnet to the existing server configuration. This operation has no impact on other subnets. The subnet identifier must be specified and must be unique among all subnets. If the identifier or a subnet prefix is not unique an error is reported and the subnet is not added.

The subnet information within this command has the same structure as the subnet information in the server configuration file with the exception that static host reservations must not be specified within `subnet4-add`. The commands described in should be used to add, remove and modify static reservations.

    {
        "command": "subnet4-add",
        "arguments": {
            "subnet4": [ {
                "id": 123,
                "subnet": "10.20.30.0/24",
                ...
            } ]
        }
    }

The response to this command has the following structure:

    {
        "result": 0,
        "text": "IPv4 subnet added",
        "arguments": {
            "subnet4": [
                {
                    "id": 123,
                    "subnet": "10.20.30.0/24"
                }
            ]
        }
    }

#### subnet6-add

This command is used to create and add new subnet to the existing server configuration. This operation has no impact on other subnets. The subnet identifier must be specified and must be unique among all subnets. If the identifier or a subnet prefix is not unique an error is reported and the subnet is not added.

The subnet information within this command has the same structure as the subnet information in the server configuration file with the exception that static host reservations must not be specified within `subnet6-add`. The commands described in should be used to add, remove and modify static reservations.

    {
        "command": "subnet6-add",
        "arguments": {
            "subnet6": [ {
                "id": 234,
                "subnet": "2001:db8:1::/64",
                ...
            } ]
        }
    }

The response to this command has the following structure:

    {
        "result": 0,
        "text": "IPv6 subnet added",
        "arguments": {
            "subnet6": [
                {
                    "id": 234,
                    "subnet": "2001:db8:1::/64"
                }
            ]
        }
    }

It is recommended, but not mandatory to specify subnet id. If not specified, Kea will try to assign the next subnet-id value. This automatic ID value generator is simple. It returns a previously automatically assigned value increased by 1. This works well, unless you manually create a subnet with a value bigger than previously used. For example, if you call subnet4-add five times, each without id, Kea will assign IDs: 1,2,3,4 and 5 and it will work just fine. However, if you try to call subnet4-add five times, with the first subnet having subnet-id of value 3 and remaining ones having no subnet-id, it will fail. The first command (with explicit value) will use subnet-id 3, the second command will create a subnet with id of 1, the third will use value of 2 and finally the fourth will have the subnet-id value auto-generated as 3. However, since there is already a subnet with that id, it will fail.

The general recommendation is to either: never use explicit values (so the auto-generated values will always work) or always use explicit values (so the auto-generation is never used). You can mix those two approaches only if you understand how the internal automatic subnet-id generation works.

Subnet IDs must be greater than zero and less than 4294967295.

#### subnet4-del command

This command is used to remove a subnet from the server's configuration. This command has no effect on other configured subnets but removing a subnet has certain implications which the server's administrator should be aware of.

In most cases the server has assigned some leases to the clients belonging to the subnet. The server may also be configured with static host reservations which are associated with this subnet. The current implementation of the `subnet4-del` removes neither the leases nor host reservations associated with a subnet. This is the safest approach because the server doesn't loose track of leases assigned to the clients from this subnet. However, removal of the subnet may still cause configuration errors and conflicts. For example: after removal of the subnet, the server administrator may add a new subnet with the ID used previously for the removed subnet. This means that the existing leases and static reservations will be in conflict with this new subnet. Thus, we recommend that this command is used with extreme caution.

This command can also be used to completely delete an IPv4 subnet that is part of a shared network. If you want to simply remove the subnet from a shared network and keep the subnet configuration, use `network4-subnet-del` command instead.

The command has the following structure:

    {
        "command": "subnet4-del",
        "arguments": {
            "id": 123
        }
    }

The example successful response may look like this:

    {
        "result": 0,
        "text": "IPv4 subnet 192.0.2.0/24 (id 123) deleted",
        "arguments": {
            "subnets": [
                {
                    "id": 123,
                    "subnet": "192.0.2.0/24"
                }
            ]
        }
    }

#### subnet6-del command

This command is used to remove a subnet from the server's configuration. This command has no effect on other configured subnets but removing a subnet has certain implications which the server's administrator should be aware of.

In most cases the server has assigned some leases to the clients belonging to the subnet. The server may also be configured with static host reservations which are associated with this subnet. The current implementation of the `subnet6-del` removes neither the leases nor host reservations associated with a subnet. This is the safest approach because the server doesn't loose track of leases assigned to the clients from this subnet. However, removal of the subnet may still cause configuration errors and conflicts. For example: after removal of the subnet, the server administrator may add a new subnet with the ID used previously for the removed subnet. This means that the existing leases and static reservations will be in conflict with this new subnet. Thus, we recommend that this command is used with extreme caution.

This command can also be used to completely delete an IPv6 subnet that is part of a shared network. If you want to simply remove the subnet from a shared network and keep the subnet configuration, use `network6-subnet-del` command instead.

The command has the following structure:

    {
        "command": "subnet6-del",
        "arguments": {
            "id": 234
        }
    }

The example successful response may look like this:

    {
        "result": 0,
        "text": "IPv6 subnet 2001:db8:1::/64 (id 234) deleted",
        "subnets": [
            {
                "id": 234,
                "subnet": "2001:db8:1::/64"
            }
        ]
    }

#### network4-list, network6-list commands

These commands are used to retrieve full list of currently configured shared networks. The list contains only very basic information about each shared network. If more details are needed, please use `network4-get` or `network6-get` to retrieve all information available. This command does not require any parameters and its invocation is very simple:

    {
        "command": "network4-list"
    }

An example response for `network4-list` looks as follows:

    {
        "arguments": {
            "shared-networks": [
                { "name": "floor1" },
                { "name": "office" }
            ]
        },
        "result": 0,
        "text": "2 IPv4 network(s) found"
    }

`network6-list` follows exactly the same syntax for both the query and the response.

#### network4-get, network6-get commands

These commands are used to retrieve detailed information about shared networks, including subnets currently being part of a given network. Both commands take one mandatory parameter `name`, which specify the name of shared network. An example command to retrieve details about IPv4 shared network with a name "floor13" looks as follows:

    {
        "command": "network4-get",
        "arguments": {
            "name": "floor13"
        }
    }

An example response could look as follows:

    {
        "result": 0,
        "text": "Info about IPv4 shared network 'floor13' returned",
        "arguments": {
            "shared-networks": [
            {
                "match-client-id": true,
                "name": "floor13",
                "option-data": [ ],
                "rebind-timer": 90,
                "relay": {
                    "ip-address": "0.0.0.0"
                },
                "renew-timer": 60,
                "reservation-mode": "all",
                "subnet4": [
                    {
                        "subnet": "192.0.2.0/24",
                        "id": 5,
                        // many other subnet specific details here
                    },
                    {
                        "id": 6,
                        "subnet": "192.0.3.0/31",
                        // many other subnet specific details here
                    }
                ],
                "valid-lifetime": 120
            }
            ]
        }
    }

Note that actual response contains many additional fields that are omitted here for clarity. The response format is exactly the same as used in `config-get`, just is limited to returning shared networks information.

#### network4-add, network6-add commands

These commands are used to add a new shared network. New network has to have unique name. This command requires one parameter `shared-networks`, which is a list and should contain exactly one entry that defines the network. The only mandatory element for a network is its name. Although it does not make operational sense, it is allowed to add an empty shared network that does not have any subnets in it. That is allowed for testing purposes, but having empty networks (or with only one subnet) is discouraged in production environments. For details regarding syntax, see and .

As opposed to parameter inheritance during full new configuration processing, this command does not fully handle parameter inheritance and any missing parameters will be filled with default values, rather than inherited from global scope.

An example that showcases how to add a new IPv4 shared network looks as follows:

    {
        "command": "network4-add",
        "arguments": {
            "shared-networks": [ {
                "name": "floor13",
                "subnet4": [
                {
                    "id": 100,
                    "pools": [ { "pool": "192.0.2.2-192.0.2.99" } ],
                    "subnet": "192.0.2.0/24",
                    "option-data": [
                        {
                            "name": "routers",
                            "data": "192.0.2.1"
                        }
                    ]
                },
                {
                    "id": 101,
                    "pools": [ { "pool": "192.0.3.2-192.0.3.99" } ],
                    "subnet": "192.0.3.0/24",
                    "option-data": [
                        {
                            "name": "routers",
                            "data": "192.0.3.1"
                        }
                    ]
                } ]
            } ]
        }
    }

Assuming there was no shared network with a name floor13 and no subnets with id 100 and 101 previously configured, the command will be successful and will return the following response:

    {
        "arguments": {
            "shared-networks": [ { "name": "floor13" } ]
        },
        "result": 0,
        "text": "A new IPv4 shared network 'floor13' added"
    }

The `network6-add` uses the same syntax for both the query and the response. However, there are some parameters that are IPv4-only (e.g. match-client-id) and some are IPv6-only (e.g. interface-id). The same applies to subnets within the network.

#### network4-del, network6-del commands

These commands are used to delete existing shared networks. Both commands take exactly one parameter 'name' that specifies the name of the network to be removed. An example invocation of `network4-del` command looks as follows:

    {
        "command": "network4-del",
        "arguments": {
            "name": "floor13"
        }
    }

Assuming there was such a network configured, the response will look similar to the following:

    {
        "arguments": {
            "shared-networks": [
                {
                    "name": "floor13"
                }
            ]
        },
        "result": 0,
        "text": "IPv4 shared network 'floor13' deleted"
    }

The `network6-del` command uses exactly the same syntax for both the command and the response.

If there are any subnets belonging to the shared network being deleted, they will be demoted to a plain subnet. There is an optional parameter called `subnets-action` that, if specified, takes one of two possible values: `keep` (which is the default) and `delete`. It controls whether the subnets be demoted to plain subnets or removed. An example usage in network6-del command that deletes the shared network and all subnets in it could looks like as follows:

    {
        "command": "network4-del",
        "arguments": {
            "name": "floor13",
            "subnets-action": "delete"
        }
    }

Alternatively, if you want to completely remove the subnets, you may use `subnet4-del` or `subnet6-del` commands.

#### network4-subnet-add, network6-subnet-add commands

These commands are used to add existing subnets to existing shared networks. There are several ways to add new shared network. System administrator can add the whole shared network at once, either by editing a configuration file or by calling `network4-add` or `network6-add` commands with desired subnets in it. This approach works better for completely new shared subnets. However, there may be cases when an existing subnet is running out of addresses and needs to be extended with additional address space. In other words another subnet has to be added on top of it. For this scenario, a system administrator can use `network4-add` or `network6-add` and then add existing subnet to this newly created shared network using `network4-subnet-add` or `network6-subnet-add`.

The `network4-subnet-add` and `network6-subnet-add` commands take two parameters: `id`, which is an integer and specifies subnet-id of existing subnet to be added to a shared network; and `name`, which specifies name of the shared network the subnet will be added to. The subnet must not belong to any existing network. In case you want to reassign a subnet from one shared network to another, please use `network4-subnet-del` or `network6-subnet-del` commands first.

An example invocation of `network4-subnet-add` command looks as follows:

    {
        "command": "network4-subnet-add",
        "arguments": {
            "name": "floor13",
            "id": 5
        }
    }

Assuming there is a network named 'floor13', there is a subnet with subnet-id 5 and it is not a part of existing network, the command will return a response similar to the following:

    {
        "result": 0,
        "text": "IPv4 subnet 10.0.0.0/8 (id 5) is now part of shared network 'floor1'"
    }

The `network6-subnet-add` command uses exactly the same syntax for both the command and the response.

As opposed to parameter inheritance during full new configuration processing or when adding a new shared network with new subnets, this command does not fully handle parameter inheritance and any missing parameters will be filled with default values, rather than inherited from global scope or from the shared network.

#### network4-subnet-del, network6-subnet-del commands

These commands are used to remove a subnet that is part of existing shared network and demote it to a plain, stand-alone subnet. If you want to remove a subnet completely, use `subnet4-del` or `subnet6-del` commands instead. The `network4-subnet-del` and `network6-subnet-del` commands take two parameters: `id`, which is an integer and specifies subnet-id of existing subnet to be removed from a shared network; and `name`, which specifies name of the shared network the subnet will be removed from.

An example invocation of the `network4-subnet-del` command looks as follows:

     {
        "command": "network4-subnet-del",
        "arguments": {
            "name": "floor13",
            "id": 5
        }
     }

Assuming there was a subnet with subnet-id equal to 5 that was part of a shared network named 'floor13', the response would look similar to the following:

    {
        "result": 0,
        "text": "IPv4 subnet 10.0.0.0/8 (id 5) is now removed from shared network 'floor13'"
    }

The `network6-subnet-del` command uses exactly the same syntax for both the command and the response.

## User contexts

Hook libraries can have their own configuration parameters. That is convenient if the parameter applies to the whole library. However, sometimes it is very useful if certain configuration entities are extended with additional configuration data. This is where the concept of user contexts comes in. A sysadmin can define an arbitrary set of data and attach it to Kea structures, as long as the data is specified as JSON map. In particular, it is possible to define fields that are integers, strings, boolean, lists and maps. It is possible to define nested structures of arbitrary complexity. Kea does not use that data on its own, simply stores 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 configuration is loaded, but user contexts are retained. This is useful if you want your comments to survive config-set, 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. The pretty print of a configuration does the opposite operation and puts "comment" entries at the beginning of maps as it seems to be the common usage.

As of Kea 1.3, the structures that allow user contexts are pools of all types (addresses and prefixes) and subnets. Kea 1.4 extended user context support to the global scope, interfaces config, shared networks, subnets, client classes, option datas and definitions, host reservations, control socket, dhcp ddns, loggers and server id. These are supported in both DHCPv4 and DHCPv6 at the exception of server id which is DHCPv6 only.