// WARNING: This example configuration is not meant for production use.
// The Kea DHCPv4 server will refuse this configuration because it contains
// mutually exclusive configuration parameters.
//
// The primary purpose of the example file is to provide a comprehensive
// list of parameters supported by Kea DHCPv4 server along with the brief
// description of each parameter.
//
// This current version should be up to date, i.e. new keywords should be
// added in this file at the same time than in the syntax.
{
    // Kea DHCPv4 server configuration begins here.
    "Dhcp4": {

        // Global authoritative flag to handle requests by clients for
        // unknown IP addresses (ignore if disabled, NAK if enabled).
        "authoritative": false,

        // Global bootfile name to be set in the 'file' field.
        "boot-file-name": "/dev/null",

        // Ordered list of client classes used by the DHCPv4 server.
        "client-classes": [
            {
                // Class specific bootfile name to be set in the 'file' field.
                "boot-file-name": "/tmp/bootfile.efi",

                // Class name.
                "name": "phones_server1",

                // Class specific next server address to use in bootstrap, which
                // is set in 'siaddr' field.
                "next-server": "10.2.3.4",

                // Class specific DHCPv4 options list.
                "option-data": [],

                // Class specific DHCPv4 option definitions, i.e. custom formats
                // specified for non-standard options.
                "option-def": [],

                // Class specific optional server hostname, which is set in
                // 'sname' field.
                "server-hostname": "",

                // Class selection expression. The DHCP packet is assigned to this
                // class when the given expression evaluates to true.
                "test": "member('HA_server1')",

                // Class valid lifetime.
                "valid-lifetime": 6000,

                // Class min valid lifetime.
                "min-valid-lifetime": 4000,

                // Class max valid lifetime.
                "max-valid-lifetime": 8000
            },
            {
                // Default value of the class specific bootfile name. Empty name
                // means that the bootfile name is unspecified.
                "boot-file-name": "",

                // Second class name.
                "name": "phones_server2",

                // Default value of the class specific next server address. The
                // zero IPv4 address means that it is unspecified.
                "next-server": "0.0.0.0",

                // Class specific DHCPv4 options list.
                "option-data": [],

                // Class specific DHCPv4 option definitions, i.e. custom formats
                // specified for non-standard options.
                "option-def": [],

                // Class specific optional server hostname, which is set in
                // 'sname' field.
                "server-hostname": "",

                // Class selection expression. The DHCP packet is assigned to this
                // class when the given expression evaluates to true.
                "test": "member('HA_server2')"
            },

            {
                // Third class name.
                "name": "late",

                // Boolean flag indicating that the class expression is only evaluated
                // when the class is required, e.g. selected address pool configuration
                // includes this class name in its "require-client-classes" list. The
                // default value false means that the class test expression must
                // always be evaluated.
                "only-if-required": true,

                // Class selection expression.
                "test": "member('ALL')"
            }
        ],

        // Parameters for triggering behaviors compatible with broken or
        // non-compliant clients, relays or other agents
        "compatibility": {
            // Parse options more leniently where fields can be deduced
            // deterministically even if against RFC or common practice.
            "lenient-option-parsing": true
        },

        // Command control socket configuration parameters for Kea DHCPv4 server.
        "control-socket": {
            // Location of the unix domain socket file the DHCPv4 server uses
            // to receive control commands from the Kea Control Agent or the
            // local server administrator.
            "socket-name": "/tmp/kea4-ctrl-socket",

            // Control socket type used by the Kea DHCPv4 server. The 'unix'
            // socket is currently the only supported type.
            "socket-type": "unix"
        },

        // Specifies a prefix to be prepended to the generated Client FQDN.
        // It may be specified at the global, shared-network and subnet levels.
        "ddns-generated-prefix": "myhost",

        // Boolean flag indicating that server should ignore DHCP client
        // wishes to update DNS on its own. With that flag set to true
        // the server will send DNS updates for both forward and
        // reverse DNS data. The default value is false, which indicates
        // that the server will delegate DNS update to the client when
        // requested. It may be specified at the global, shared-network
        // and subnet levels.
        "ddns-override-client-update": false,

        // Boolean flag indicating that the server should override DHCP
        // client's wish to not update the DNS. With this parameter
        // set to true the server will send DNS update even when
        // the client requested no update.  It may be specified at the
        // global, shared-network and subnet levels.
        "ddns-override-no-update": false,

        // Suffix appended to the partial name sent to the DNS. The
        // default value is an empty string which indicates that no
        // suffix is appended.  It may be specified at the global,
        // shared-network and subnet levels.
        "ddns-qualifying-suffix": "",

        // Enumeration specifying whether the server should honor
        // hostname or Client FQDN sent by the client or replace
        // this name. The acceptable values are: "never" (use the
        // name the client sent), "always" (replace the name the
        // client sent), "when-present" (replace the name the client
        // sent, but do not generate one when the client didn't sent
        // the name), "when-not-present" (generate the name when
        // client didn't send one, otherwise leave the name the
        // client sent). The default value is "never".  It may be
        // specified at the global, shared-network and subnet levels.
        "ddns-replace-client-name": "never",

        // Boolean flag which enables or disables the DDNS updating. It
        // defaults to true.  It may be specified at the global, shared-
        // network and subnet levels. It works in conjunction with
        // dhcp-ddns:enable-updates which must be true to enable connectivity
        // to kea-dhcp-ddns.
        "ddns-send-updates": true,

        // Boolean flag, which when true instructs the server to always
        // update DNS when leases are renewed, even if the DNS information
        // has not changed.  The server's default behavior (i.e. flag is false)
        // is to only update DNS if the DNS information has changed.  It
        // may be specified at the global, shared-network and subnet levels.
        "ddns-update-on-renew": true,

        // Boolean flag, which is passed to kea-dhcp-ddns with each DDNS
        // update request to indicate whether or not DNS update conflict
        // resolution as described in RFC 4703 should be employed for the
        // given update request.  The default value for this flag is true.
        // It may be specified at the global, shared-network and subnet levels.
        "ddns-use-conflict-resolution": true,

        // Time in seconds specifying how long a declined lease should be
        // excluded from DHCP assignments. The default value is 24 hours.
        "decline-probation-period": 86400,

        // Name Change Requests forwarding configuration for Kea DHCPv4 server.
        // NCRs are sent to Kea D2 module to update DNS upon allocation of the
        // DHCP leases.
        "dhcp-ddns": {
            // Boolean flag indicating if Kea DHCPv4 server should connect to
            // kea-dhcp-ddns.  This must be true for NCRs to be created and
            // sent to kea-dhcp-ddns. By default NCRs are not generated.
            "enable-updates": false,

            // Specifies maximum number of NCRs to queue waiting to be sent
            // to Kea D2 server.
            "max-queue-size": 1024,

            // Packet format to use when sending NCRs to Kea D2 server.
            // Currently, only JSON format is supported.
            "ncr-format": "JSON",

            // Socket protocol to use when sending NCRs to D2. Currently,
            // only UDP is supported.
            "ncr-protocol": "UDP",

            // IP address that Kea DHCPv4 server should use to send
            // NCRs to D2. Default value of zero indicates that Kea
            // should pick suitable address.
            "sender-ip": "0.0.0.0",

            // Port number that Kea DHCPv4 server should use to send
            // NCRs to D2. Default value of zero indicates that Kea
            // should pick suitable port.
            "sender-port": 0,

            // IP address on which D2 listens for NCRs.
            "server-ip": "127.0.0.1",

            // Port number on which D2 listens for NCRs.
            "server-port": 53001,

            // The follow parameters are DEPRECATED.  They have been
            // replaced with parameters that may be set at the global,
            // shared-network, and subnet4 scopes.  They are listed here
            // as configuration parsing still accepts them.  Eventually
            // support for them will be removed.
            "generated-prefix": "myhost",
            "hostname-char-replacement": "x",
            "hostname-char-set": "[^A-Za-z0-9.-]",
            "override-client-update": false,
            "override-no-update": false,
            "qualifying-suffix": "",
            "replace-client-name": "never"
        },

        // Specifies the first of the two consecutive ports of the UDP
        // sockets used for communication between DHCPv6 and DHCPv4
        // servers. See RFC 7341.
        "dhcp4o6-port": 6767,

        // Boolean flag indicating whether or not the Kea DHCPv4 server
        // should send back Client Identifier option in its responses.
        // The default value is true which indicates that the option
        // must be sent back if the client included it. The false
        // value instructs the server to not send this option for
        // backward compatibility with older DHCP specifications which
        // stated that Client Identifier must not be sent back.
        "echo-client-id": true,

        // Collection of Kea DHCPv4 server parameters configuring how
        // the server should process expired DHCP leases.
        "expired-leases-processing": {
            // Specifies the number of seconds since last removal of
            // the expired leases when next removal should occur.
            "flush-reclaimed-timer-wait-time": 25,

            // Specifies the time period in seconds to keep expired
            // leases in the lease database (lease affinity).
            "hold-reclaimed-time": 3600,

            // Specifies the maximum number of expired leases that can be
            // processed in a single attempt to clean up the lease
            // database from the expired leases. If there are more
            // expired leases, they will be processed during the next
            // cleanup attempt.
            "max-reclaim-leases": 100,

            // Specifies the maximum time in milliseconds that the single
            // attempt to cleanup the lease database from the expired
            // leases may take.
            "max-reclaim-time": 250,

            // Specifies the time period in seconds since last attempt
            // to process expired leases to initiate the next attempt.
            "reclaim-timer-wait-time": 10,

            // Specifies the maximum number of expired leases processing
            // cycles which didn't result in full cleanup of the lease
            // database from the expired leases, after which a
            // warning message is issued.
            "unwarned-reclaim-cycles": 5
        },

        // List of hooks libraries and their specific configuration parameters
        // to be loaded by Kea DHCPv4 server.
        "hooks-libraries": [
            {
                // Location of the hooks library to be loaded.
                "library": "/opt/lib/kea/hooks/libdhcp_lease_cmds.so",

                // Hook library specific configuration parameters.
                "parameters": { }
            }
        ],

        // List of access credentials to external sources of IPv4 reservations,
        "hosts-databases": [
            {
                // Name of the database to connect to.
                "name": "keatest",

                // Host on which the database resides.
                "host": "localhost",

                // Database password.
                "password": "keatest",

                // Port on which the database is available.
                "port": 3306,

                // Type of the database, e.g. "mysql", "postgresql".
                "type": "mysql",

                // User name to be used to access the database.
                "user": "keatest",

                // Read only mode.
                "readonly": false,

                // Next entries are for the OpenSSL support in MySQL.

                // Trust anchor aka certificate authority file or directory.
                "trust-anchor": "my-ca",

                // Client certificate file name.
                "cert-file": "my-cert",

                // Private key file name.
                "key-file": "my-key",

                // Cipher list (see the OpenSSL ciphers command manual).
                "cipher-list": "AES"
            },
            {
                // Name of the database to connect to.
                "name": "keatest",

                // Host on which the database resides.
                "host": "localhost",

                // Database password.
                "password": "keatest",

                // Port on which the database is available.
                "port": 5432,

                // Type of the database, e.g. "mysql", "postgresql".
                "type": "postgresql",

                // User name to be used to access the database.
                "user": "keatest"
            },
            {
                // Name of the database to connect to.
                "name": "keatest",

                // Database password.
                "password": "keatest",

                // Port on which the database is available.
                "port": 9042,

                // Type of the database, e.g. "mysql", "postgresql".
                "type": "mysql",

                // User name to be used to access the database.
                "user": "keatest",

                // Connection reconnect wait time.
                // This parameter governs how long Kea waits before attempting
                // to reconnect. Expressed in milliseconds. The default is 0
                // (disabled) for MySQL and PostgreSQL.
                "reconnect-wait-time": 3000,

                // Connection maximum reconnect tries.
                "max-reconnect-tries": 3,

                // Action to take when connection recovery fails.
                // Supported values: stop-retry-exit, serve-retry-exit,
                // serve-retry-continue
                "on-fail": "stop-retry-exit",

                // Connection connect timeout.
                "connect-timeout": 100
            }
        ],

        // List of host reservation identifier types to be used by the
        // Kea DHCPv4 server to fetch static reservations for the
        // DHCP clients. All identifiers are used by default, which
        // means that the server will issue multiple queries to the
        // database to find if there is a reservation for the particular
        // client. If the particular deployment uses only subset, e.g.
        // one, identifier type, this identifier should be only listed
        // here to prevent unnecessary queries to the database.
        "host-reservation-identifiers": [
            "hw-address",
            "duid",
            "circuit-id",
            "client-id",
            "flex-id"
        ],

        // Specifies configuration of interfaces on which the Kea DHCPv4
        // server is listening to the DHCP queries.
        "interfaces-config": {
            // Specifies whether the server should use "udp" socket or
            // "raw" sockets to listen to the DHCP traffic. The "raw"
            // sockets are useful when direct DHCP traffic is being
            // received.
            "dhcp-socket-type": "udp",

            // Specifies a list of interfaces on which the Kea DHCPv4
            // server should listen to the DHCP requests.
            "interfaces": [
                "eth0"
            ],

            // Enumeration which indicates what interface should be used
            // to send DHCP response to the client. The default value is
            // "same-as-inbound" which indicates that the response should
            // be sent via the interface on which the client's query
            // was received. The "use-routing" value indicates that the
            // Kea server should use kernel's routing table to find the
            // suitable interface.
            "outbound-interface": "same-as-inbound",

            // Boolean flag indicating if the available interfaces should
            // be re-detected upon server reconfiguration. The default value
            // is true which means that the interfaces are always
            // re-detected.
            "re-detect": true,

            // Kea tries to bind the service sockets during initialization. It may
            // fail due to a port being already opened or misconfiguration. Kea can
            // suppress these errors and only logs them. This flag prevents starting
            // the DHCP server without binding all sockets. If unspecified, it
            // defaults to false.
            "service-sockets-require-all": true,

            // Kea tries to bind the service sockets during initialization. This
            // option specifies how many times binding to interface will be retried.
            // The default value is 0 which means that the operation will not be
            // repeated.
            "service-sockets-max-retries": 5,

            // The time interval in milliseconds to wait before the next attempt to
            // retry opening a service socket.
            "service-sockets-retry-wait-time": 5000
        },

        // Boolean parameter which controls whether an early global host
        // reservations lookup should be performed. This lookup takes place
        // before subnet selection and when a global reservation is found
        // with some client classes, it triggers a second phase classification.
        // It can also be used to drop queries using host reservations as a
        // decision table indexed by reservation identifiers.
        "early-global-reservations-lookup": true,

        // Boolean parameter which controls DHCP server's behavior with respect
        // to creating host reservations for the same IP address. By default
        // this flag is set to true in which case the server prevents creation
        // of multiple host reservations for the same IP address. When this
        // parameter is set to false, the server allows for creating multiple
        // reservations for the same IP address within a subnet. This setting
        // is useful in deployments in which a given host may be communicating
        // with a DHCP server over multiple interfaces and depending on the
        // chosen interface different MAC address (or other identifier) will
        // be used to identify the host. Note that some host backends do not
        // support the mode in which multiple reservations for the same IP
        // address are used. If these backends are in use and this setting
        // is attempted a configuration error will occur. The MySQL and
        // PostgreSQL backends do support this mode.
        "ip-reservations-unique": true,

        /// Boolean parameter which controls whether host reservations lookup
        /// should be performed before lease lookup. This parameter has effect
        /// only when multi-threading is disabled. When multi-threading is
        /// enabled, host reservations lookup is always performed first to avoid
        /// lease lookup resource locking.
        "reservations-lookup-first": true,

        // Specifies credentials to access lease database.
        "lease-database": {
            // memfile backend specific parameter specifying the interval
            // in seconds at which lease file should be cleaned up (outdated
            // lease entries are removed to prevent lease file from growing
            // infinitely).
            "lfc-interval": 3600,

            // Maximum number of lease file read errors allowed before
            // loading the file is abandoned.  Defaults to 0 (no limit).
            "max-row-errors": 100,

            // Name of the lease file. In case of database it specifies the
            // database name.
            "name": "/tmp/kea-dhcp4.csv",

            // memfile specific parameter indicating whether leases should
            // be saved on persistent storage (disk) or not. The true value
            // is the default and it indicates that leases are stored in the
            // persistent storage. This setting must be used in production.
            // The false value should only be used for testing purposes
            // because non stored leases will be lost upon Kea server restart.
            "persist": true,

            // Lease database backend type, i.e. "memfile", "mysql" or
            // "postgresql".
            "type": "memfile"
        },

        // Boolean value indicating if the Kea DHCPv4 server should use client
        // identifier value sent by the client or ignore it. The default value
        // is true which indicate that the server should use client identifier
        // and that it takes precedence over client's MAC address. In deployments
        // where MAC address should take precedence this value can be set to
        // false, in which case the clients will be identified by MAC address.
        // This is specifically useful when clients don't generate unique
        // identifiers or these identifiers are not stable etc.
        "match-client-id": false,

        // Global value of the next server address set in 'siaddr' field.
        // The global value may be overridden in lower level configuration
        // scopes.
        "next-server": "192.0.2.123",

        // Global value which limits the number of client packets (e.g.
        // DHCPREQUESTs) that may be parked while waiting for hook library
        // work to complete, prior to a response (e.g. DHCPACK) being sent
        // back to the client.  A typical example is when kea-dhcp4 parks a
        // DHCPREQUEST while it sends the lease update(s) to its HA peer(s).
        // The packet is unparked once the update(s) have been acknowledged.
        // This value limits the number of packets that can be held pending
        // the updates. In times of heavy client traffic, this value can keep
        // kea-dhcp4 from building an insurmountable backlog of updates.
        "parked-packet-limit": 128,

        // List of global DHCP options that Kea DHCPv4 server assigns to the
        // clients.
        "option-data": [
            {
                // Boolean flag indicating if the given option is always
                // send in response or only when requested. The default
                // value of false indicates that it is only sent when
                // requested.
                "always-send": false,

                // Option code. It is not required if the option name is
                // provided.
                "code": 6,

                // Boolean value indicating whether the option data specified
                // in the "data" field is specified as a string of hexadecimal
                // digits or in human readable CSV format.
                "csv-format": true,

                // Option data to be stored in the option payload.
                "data": "192.0.3.1, 192.0.3.2",

                // Option name. It is not required of the option code is
                // provided.
                "name": "domain-name-servers",

                // Option space. The default is the "dhcp4" option space which
                // groups top level DHCPv4 options.
                "space": "dhcp4"
            }
        ],

        // List of global option definitions, i.e. option formats, that the
        // Kea DHCPv4 server is using.
        "option-def": [
            {
                // Boolean flag indicating if the option definition comprises
                // an array of values of some type, e.g. array of IPv4 addresses.
                // The default value of false means that the option does not
                // comprise an array of values.
                "array": false,

                // Option code.
                "code": 6,

                // Holds a name of the option space encapsulated by this option.
                // All options that belong to this option space will be sent
                // as sub-options of this option. Empty string means that this
                // option doesn't encapsulate any option.
                "encapsulate": "",

                // Option name.
                "name": "my-option",

                // Specifies the types of fields within the option if the option
                // is said to be a "record" (see "type"). in this particular example
                // this option comprises two fields, 1 byte and 2 bytes long.
                "record-types": "uint8, uint16",

                // Name of the option space to which this option belongs.
                "space": "my-space",

                // Option type. All possible types are listed in the Kea
                // Administrator Reference Manual.
                "type": "record"
            }
        ],

        // Global value for the rebind timer, i.e. the time after which the
        // DHCP client enters rebind state if it fails to renew the lease.
        "rebind-timer": 40,

        // Global value for the renew timer, i.e. the timer after which the
        // DHCP client renews the lease.
        "renew-timer": 30,

        // Global value to store extended information (e.g. relay agent
        // information) with each lease.
        "store-extended-info": true,

        // Statistics keep some samples per observation point.
        // There are two default values: maximum count and maximum age.
        // Set the maximum count to zero disables it.
        "statistic-default-sample-count": 0,

        // When the maximum count is 0 the maximum age (in seconds) applies.
        "statistic-default-sample-age": 60,

        // Multi-threading parameters.
        "multi-threading": {
            // By default Kea processes packets on a single thread (default
            // 'false' value for this option). To enable multi-threading, this
            // option can be set ('true' value).
            "enable-multi-threading": false,

            // When multi-threading is enabled, Kea will process packets on a
            // number of multiple threads configurable through this option. The
            // value must be a positive integer (0 means auto detect).
            "thread-pool-size": 0,

            // When multi-threading is enabled, Kea will read packets from the
            // interface and append a working item to the thread pool. This
            // option configures the maximum number of items that can be queued.
            // The value must be a positive integer (0 means unlimited).
            "packet-queue-size": 0
        },

        // Governs how the Kea DHCPv4 server should deal with the invalid
        // data received from the client.
        "sanity-checks": {
            // Specifies how the Kea DHCPv4 server should behave when invalid
            // data is read for a lease from the lease file. The following
            // values are supported "none" (don't attempt to correct the
            // lease information), "warn" (print a warning for subnet-id
            // related inconsistencies), "fix" (correct the subnet id by
            // trying to find the suitable subnet), "fix-del" (similar
            // to "fix" but delete the lease if no suitable subnet found),
            // "del" (delete the lease if the lease has invalid subnet
            // identifier value).
            "lease-checks": "warn"
        },

        // List of shared networks used by Kea DHCPv4 server. The shared
        // networks group subnets together.
        "shared-networks": [
            {
                // Shared network level authoritative flag.
                "authoritative": false,

                // Shared network level bootfile name.
                "boot-file-name": "/dev/null",

                // Restricts this shared network to allow only clients
                // that belong to the particular client class. If an
                // empty string is provided, no restriction is applied.
                "client-class": "",

                // Shared network level value. See description at the global level.
                "ddns-generated-prefix": "myhost",

                // Shared network level value. See description at the global level.
                "ddns-override-client-update": false,

                // Shared network level value. See description at the global level.
                "ddns-override-no-update": false,

                // Shared network level value. See description at the global level.
                "ddns-qualifying-suffix": "",

                // Shared network level value. See description at the global level.
                "ddns-replace-client-name": "never",

                // Shared network level value. See description at the global level.
                "ddns-send-updates": true,

                // Shared network level value. See description at the global level.
                "ddns-update-on-renew": true,

                // Shared network level value. See description at the global level.
                "ddns-use-conflict-resolution": true,

                // Shared network level value. See description at the global level.
                "hostname-char-replacement": "x",

                // Shared network level value. See description at the global level.
                "hostname-char-set": "[^A-Za-z0-9.-]",

                // Specifies that this shared network is selected for the
                // requests received on the particular interface.
                "interface": "eth0",

                // Shared network level flag specifying whether the client
                // identifier should be used for identifying clients.
                "match-client-id": true,

                // Shared network name.
                "name": "my-secret-network",

                // Shared network level specification of the next server
                // to be sent in 'siaddr'.
                "next-server": "192.0.2.123",

                // List of shared network specific DHCP options.
                "option-data": [],

                // List of IPv4 relay addresses for which this shared
                // network is selected.
                "relay": {
                    "ip-addresses": []
                },

                // Shared network level rebind timer.
                "rebind-timer": 41,

                // Shared network level renew timer.
                "renew-timer": 31,

                // Shared network level compute T1 and T2 timers.
                "calculate-tee-times": true,

                // T1 = valid lifetime * .5.
                "t1-percent": .5,

                // T2 = valid lifetime * .75.
                "t2-percent": .75,

                // Cache threshold = valid lifetime * .25.
                "cache-threshold": .25,

                // Cache maximum: when the client last transmission time
                // is close enough the lease is not renewed and current
                // lease is returned as it was "cached".
                "cache-max-age": 1000,

                // Enumeration specifying server's mode of operation when it
                // fetches host reservations.
                // "reservation-mode": "all",
                // It is replaced by the "reservations-global",
                // "reservations-in-subnet" and "reservations-out-of-pool"
                // parameters.

                // Specify if server should lookup global reservations.
                "reservations-global": false,

                // Specify if server should lookup in-subnet reservations.
                "reservations-in-subnet": true,

                // Specify if server can assume that all reserved addresses
                // are out-of-pool.
                // Ignored when reservations-in-subnet is false.
                // If specified, it is inherited by "subnet4" levels.
                "reservations-out-of-pool": false,

                // List of client classes which must be evaluated when this shared
                // network is selected for client assignments.
                "require-client-classes": [ "late" ],

                // Turn off storage of extended information (e.g. relay agent
                // information) with each lease for this shared-network.
                "store-extended-info": false,

                // Shared network level server hostname set in 'sname' field.
                "server-hostname": "",

                // List of IPv4 subnets belonging to this shared network.
                "subnet4": [
                    {
                        // Interface name matched against inbound interface name.
                        // Used in DHCPv4o6. See RFC 7341.
                        "4o6-interface": "",

                        // Interface ID option value. See RFC 7341.
                        "4o6-interface-id": "",

                        // Prefix matched against source address. See RFC7341.
                        "4o6-subnet": "2001:db8:1:1::/64",

                        // Subnet level authoritative flag.
                        "authoritative": false,

                        // Subnet level bootfile name, set in 'file' field.
                        "boot-file-name": "",

                        // Restricts this subnet to allow only clients that belong
                        // to the particular client class. If an empty string is
                        // provided, no restriction is applied.
                        "client-class": "",

                        // Subnet level value. See description at the global level.
                        "ddns-generated-prefix": "myhost",

                        // Subnet level value. See description at the global level.
                        "ddns-override-client-update": false,

                        // Subnet level value. See description at the global level.
                        "ddns-override-no-update": false,

                        // Subnet level value. See description at the global level.
                        "ddns-qualifying-suffix": "",

                        // Subnet level value. See description at the global level.
                        "ddns-replace-client-name": "never",

                        // Subnet level value. See description at the global level.
                        "ddns-send-updates": true,

                        // Subnet level value. See description at the global level.
                        "ddns-update-on-renew": true,

                        // Subnet level value. See description at the global level.
                        "ddns-use-conflict-resolution": true,

                        // Subnet level value. See description at the global level.
                        "hostname-char-replacement": "x",

                        // Subnet level value. See description at the global level.
                        "hostname-char-set": "[^A-Za-z0-9.-]",

                        // Subnet unique identifier.
                        "id": 1,

                        // Specifies that this subnet is selected for the requests
                        // received on the particular interface.
                        "interface": "eth0",

                        // Subnet level flag specifying whether the client identifier
                        // should be used for identifying clients.
                        "match-client-id": true,

                        // Subnet level specification of the next server to be sent
                        // in 'siaddr'.
                        "next-server": "0.0.0.0",

                        // Turn on storage of extended information (e.g. relay agent
                        // information) with each lease for this subnet.
                        "store-extended-info": true,

                        // Subnet level list of DHCP options.
                        "option-data": [
                            {
                                // Boolean flag indicating if the particular option
                                // should be always sent or sent only when requested.
                                "always-send": false,

                                // Option code.
                                "code": 3,

                                // Boolean flag indicating if the option value specified
                                // in "data" is a string of hexadecimal values or human
                                // readable CSV value.
                                "csv-format": true,

                                // Option data to be included in the option payload.
                                "data": "192.0.3.1",

                                // Option name.
                                "name": "routers",

                                // Option space. The default value "dhcp4" designates the
                                // top level option space.
                                "space": "dhcp4"
                            }
                        ],

                        // List of IP address pools belonging to the subnet.
                        "pools": [
                            {
                                // Restricts this pool to be only used for the client
                                // requests belonging to a particular client class.
                                "client-class": "phones_server1",

                                // Pool level list of DHCP options.
                                "option-data": [],

                                // Address range used for client assignments.
                                "pool": "192.1.0.1 - 192.1.0.200",

                                // List of client classes which must be evaluated when this pool
                                // is selected for client assignments.
                                "require-client-classes": [ "late" ]
                            },
                            {
                                // Restricts this pool to be only used for the client
                                // requests belonging to a particular client class.
                                "client-class": "phones_server2",

                                // Pool level list of DHCP options.
                                "option-data": [],

                                // Address range used for client assignments.
                                "pool": "192.3.0.1 - 192.3.0.200",

                                // List of client classes which must be evaluated when this pool
                                // is selected for client assignments.
                                "require-client-classes": []
                            }
                        ],

                        // Subnet level value of the rebind timer.
                        "rebind-timer": 40,

                        // List of IPv4 relay addresses for which this subnet is
                        // selected.
                        "relay": {
                            "ip-addresses": [
                                "192.168.56.1"
                            ]
                        },

                        // Subnet level value of the renew timer.
                        "renew-timer": 30,

                        // Enumeration specifying server's mode of operation when it
                        // fetches host reservations.
                        // "reservation-mode": "all",
                        // It is replaced by the "reservations-global",
                        // "reservations-in-subnet" and
                        // "reservations-out-of-pool" parameters.

                        // Specify if server should lookup global reservations.
                        "reservations-global": false,

                        // Specify if server should lookup in-subnet reservations.
                        "reservations-in-subnet": true,

                        // Specify if server can assume that all reserved
                        // addresses are out-of-pool.
                        // Ignored when reservations-in-subnet is false.
                        "reservations-out-of-pool": false,

                        // Subnet level compute T1 and T2 timers.
                        "calculate-tee-times": true,

                        // T1 = valid lifetime * .5.
                        "t1-percent": .5,

                        // T2 = valid lifetime * .75.
                        "t2-percent": .75,

                        // Cache threshold = valid lifetime * .25.
                        "cache-threshold": .25,

                        // Subnet-level cache maximum.
                        "cache-max-age": 1000,

                        // List of static IPv4 reservations assigned to the clients belonging
                        // to this subnet. For detailed example see reservations.json.
                        "reservations": [
                            {
                                // Identifier used for client matching. Supported values are
                                // "hw-address", "client-id", "duid", "circuit-id", "flex-id".
                                "circuit-id": "01:11:22:33:44:55:66",

                                // Reserved IP address.
                                "ip-address": "192.0.2.204",

                                // Hostname.
                                "hostname": "foo.example.org",

                                // Reservation specific option data.
                                "option-data": [
                                    {
                                        // Option name.
                                        "name": "vivso-suboptions",

                                        // Option data.
                                        "data": "4491"
                                    }
                                ]
                            }
                        ],

                        // List of client classes which must be evaluated when this subnet
                        // is selected for client assignments.
                        "require-client-classes": [ "late" ],

                        // Subnet level server hostname set in 'sname' field.
                        "server-hostname": "",

                        // Subnet prefix.
                        "subnet": "192.0.0.0/8",

                        // Subnet level (default) valid lifetime.
                        "valid-lifetime": 6000,

                        // Subnet level min valid lifetime.
                        "min-valid-lifetime": 4000,

                        // Subnet level max valid lifetime.
                        "max-valid-lifetime": 8000
                    }
                ],

                // Shared network level (default) valid lifetime.
                "valid-lifetime": 6001,

                // Subnet level min valid lifetime.
                "min-valid-lifetime": 4001,

                // Subnet level max valid lifetime.
                "max-valid-lifetime": 8001
            }
        ],

        // Global server hostname set in the 'sname' field.
        "server-hostname": "",

        // List of IPv4 subnets which don't belong to any shared network.
        "subnet4": [],

        // Global valid (default) lifetime value.
        "valid-lifetime": 6000,

        // Global min valid lifetime value.
        "min-valid-lifetime": 4000,

        // Global max valid lifetime value.
        "max-valid-lifetime": 8000,

        // Reservations (examples are in other files).
        "reservations": [],

        // Configuration control (currently not used, i.e. this syntax
        // is already defined but corresponding feature is not implemented).
        "config-control": {
            // Only configuration databases entry is defined.
            "config-databases": [
                {
                    // Name of the database to connect to.
                    "name": "config",

                    // Type of the database, e.g. "mysql", "postgresql".
                    "type": "mysql"
                }
            ],
            // Intervals between attempts to fetch configuration updates
            // via the configuration backends used.
            "config-fetch-wait-time": 30
        },

        // Server tag.
        "server-tag": "my DHCPv4 server",

        // DHCP queue control parameters.
        "dhcp-queue-control": {
            // Enable queue is mandatory.
            "enable-queue": true,

            // Queue type was mandatory.
            "queue-type": "kea-ring4",

            // Capacity is optional.
            "capacity": 64
        },

        // Fetches host reservations.
        // "reservation-mode": "all",
        // It is replaced by the "reservations-global",
        // "reservations-in-subnet" and "reservations-out-of-pool" parameters.

        // Specify if server should lookup global reservations.
        "reservations-global": false,

        // Specify if server should lookup in-subnet reservations.
        "reservations-in-subnet": true,

        // Specify if server can assume that all reserved addresses
        // are out-of-pool.
        // Ignored when reservations-in-subnet is false.
        // If specified, it is inherited by "shared-networks" and
        // "subnet4" levels.
        "reservations-out-of-pool": false,

        // Global compute T1 and T2 timers.
        "calculate-tee-times": true,

        // T1 = valid lifetime * .5.
        "t1-percent": .5,

        // T2 = valid lifetime * .75.
        "t2-percent": .75,

        // Cache threshold = valid lifetime * .25.
        "cache-threshold": .25,

        // Global cache maximum.
        "cache-max-age": 1000,

        // String of zero or more characters with which to replace each
        // invalid character in the hostname or Client FQDN. The default
        // value is an empty string which will cause invalid characters
        // to be omitted rather than replaced.
        "hostname-char-replacement": "x",

        // Regular expression describing the invalid character set in
        // the hostname or Client FQDN.
        "hostname-char-set": "[^A-Za-z0-9.-]",

        // List of loggers used by the servers using this configuration file.
        "loggers": [
            {
                // Debug level, a value between 0..99. The greater the value
                // the more detailed debug log.
                "debuglevel": 99,

                // Name of the logger.
                "name": "kea-dhcp4",

                // Configures how the log should be output.
                "output_options": [
                    {
                        // Determines whether the log should flushed to a file.
                        "flush": true,

                        // Specifies maximum filesize before the file is being rotated.
                        "maxsize": 10240000,

                        // Specifies the maximum number of rotated files being kept.
                        "maxver": 1,

                        // Specifies logging destination.
                        "output": "stdout",

                        // Specifies log entry content
                        "pattern": "%D{%Y-%m-%d %H:%M:%S.%q} %-5p [%c/%i] %m\n"
                    }
                ],

                // Specifies logging severity, i.e. "ERROR", "WARN", "INFO", "DEBUG".
                "severity": "INFO"
            }
        ],

        // Look at advanced example for the use of user-contexts.
        "user-context": { }
    }
}