[5198] Example config file improved significantly.

src/bin/keactrl/kea.conf.pre

@@ -1,108 +1,690 @@
-# This is a basic configuration for the Kea DHCPv4 and DHCPv6 servers.
-# Subnet declarations are commented out and no interfaces are listed.
-# Therefore, the servers will not listen or respond to any queries.
-# The basic configuration must be extended to specify interfaces on
-# which the servers should listen. Also, subnets and options must be
-# declared.
+// This is a basic configuration for the Kea DHCPv4 and DHCPv6 servers. Subnet
+// declarations are mostly commented out and no interfaces are listed.
+// Therefore, the servers will not listen or respond to any queries.  The basic
+// configuration must be extended to specify interfaces on which the servers
+// should listen. There are a number of example options defined. These probably
+// don't make any sense in your network. Make sure you at least update the
+// following, before running this example in your network:
+// - change the network interface names
+// - change the subnets to match your actual network
+// - change the option values to match your network
+//
+// This is just a very basic configuration. Kea comes with large suite (over 30)
+// of configuration examples and extensive Kea User's Guide. Please refer to
+// those materials to get better understanding of what this software is able to
+// do. Comments in this configuration file sometimes refer to sections for more
+// details. These are section numbers in Kea User's Guide. The version matching
+// your software should come with your Kea package, but it is also available
+// on Kea webpage (http://kea.isc.org, click User's Guide, direct link for stable
+// version is http://kea.isc.org/docs/kea-guide.html).
 {
 
-# DHCPv4 configuration starts here.
-"Dhcp4":
-{
-# Add names of interfaces to listen on.
-  "interfaces-config": {
-    "interfaces": [ ]
-  },
-
-# Use Memfile lease database backend to store leases in a CSV file.
-  "lease-database": {
-    "type": "memfile"
-  },
-
-# Setup reclamation of the expired leases and leases affinity.
-# Expired leases will be reclaimed every 10 seconds. Every 25
-# seconds reclaimed leases, which have expired more than 3600
-# seconds ago, will be removed. The limits for leases reclamation
-# are 100 leases or 250 ms for a single cycle. A warning message
-# will be logged if there are still expired leases in the
-# database after 5 consecutive reclamation cycles.
-  "expired-leases-processing": {
-    "reclaim-timer-wait-time": 10,
-    "flush-reclaimed-timer-wait-time": 25,
-    "hold-reclaimed-time": 3600,
-    "max-reclaim-leases": 100,
-    "max-reclaim-time": 250,
-    "unwarned-reclaim-cycles": 5
-  },
-
-# Global (inherited by all subnets) lease lifetime is mandatory parameter.
-  "valid-lifetime": 4000,
-
-# Below an example of the simple subnet declaration. Uncomment to
-# enable it. This is a list, denoted with [ ], of structure, denoted
-# with { }. Each structure describes a single subnet and may have
-# several parameters. One of those parameters is "pools" that is
-# also a list of structures.
-  "subnet4": [
-#  {    "subnet": "192.0.2.0/24",
-#       "pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ] }
-  ]
+// DHCPv4 configuration starts here. This section will be read by DHCPv4 server
+// and will be ignored by other components.
+"Dhcp4": {
+    // Add names of your network interfaces to listen on.
+    "interfaces-config": {
+        // See section 8.2.4 for more details. You probably want to add just
+        // interface name (e.g. "eth0" or specific IPv4 address on that
+        // interface name (e.g. "eth0/192.0.2.1").
+        "interfaces": [ ]
+
+        // Kea DHCPv4 server by default listens using raw sockets. This ensures
+        // all packets, including those sent by directly connected clients
+        // that don't have IPv4 address yet, are received. However, if your
+        // traffic is always relayed, it is often better to use regular
+        // UDP sockets. If you want to do that, uncomment this line:
+        // "dhcp-socket-type": "raw"
+    },
+
+    // Kea support control channel, which is a way to receive management commands
+    // while the server is running. This is a Unix domain socket that receives
+    // commands formatted in JSON, e.g. config-set (which sets new configuration),
+    // config-reload (which tells Kea to reload its configuration from file),
+    // statistic-get (to retrieve statistics) and many more. For detailed
+    // description, see Sections 8.8, 16 and 15.
+    "control-socket": {
+        "socket-type": "unix",
+        "socket-name": "/tmp/kea4-ctrl-socket.sock"
+    },
+
+    // Use Memfile lease database backend to store leases in a CSV file.
+    // Depending on how Kea was compiled, it may also support SQL databases
+    // (MySQL and/or PostgreSQL) and even Cassandra. Those database backends
+    // require more parameters, like name, host and possibly user and password.
+    // There are dedicated examples for each backend. See Section 7.2.2 "Lease
+    // Storage" for details.
+    "lease-database": {
+        // Memfile is the simplest and easiest backend to use. It's a in-memory
+        // C++ database that stores its state in CSV file.
+        "type": "memfile"
+    },
+
+
+    // Kea allows storing host reservations in a database. If your network is
+    // small or you have few reservations, it's probably easier to keep them
+    // in the configuration file. If your network is large, it's usually better
+    // to use database for it. To enable it, uncomment the following:
+    // "hosts-database": {
+    //     "type": "mysql",
+    //     "name": "kea",
+    //     "user": "kea",
+    //     "password": "kea",
+    //     "host": "localhost",
+    //     "port": 3306
+    // },
+    // See Section 7.2.3 "Hosts storage" for details.
+
+    // Setup reclamation of the expired leases and leases affinity.
+    // Expired leases will be reclaimed every 10 seconds. Every 25
+    // seconds reclaimed leases, which have expired more than 3600
+    // seconds ago, will be removed. The limits for leases reclamation
+    // are 100 leases or 250 ms for a single cycle. A warning message
+    // will be logged if there are still expired leases in the
+    // database after 5 consecutive reclamation cycles.
+    "expired-leases-processing": {
+        "reclaim-timer-wait-time": 10,
+        "flush-reclaimed-timer-wait-time": 25,
+        "hold-reclaimed-time": 3600,
+        "max-reclaim-leases": 100,
+        "max-reclaim-time": 250,
+        "unwarned-reclaim-cycles": 5
+    },
+
+    // Global timers specified here apply to all subnets, unless there are
+    // subnet specific values defined in particular subnets.
+    "renew-timer": 900,
+    "rebind-timer": 1800,
+    "valid-lifetime": 3600,
+
+    // Similar to DHCPv4, many other parameters can be specified here:
+    // - option definitions (if you want to define vendor options, your own custom
+    //                       options or perhaps handle standard options that Kea
+    //                       does not support out of the box yet)
+    // - client classes
+    // - hooks
+    //
+    // See the examples in DHCPv4 for specific syntax.
+
+    // These are global options. They are going to be sent when a client requests
+    // them, unless overwritten with values in more specific scopes. The scope
+    // hierarchy is:
+    // - global
+    // - subnet
+    // - class
+    // - host
+    //
+    // Not all of those options make sense. Please configure only those that
+    // are actually useful in your network.
+    //
+    // For a complete list of options currently supported by Kea, see
+    // Section 7.2.8 "Standard DHCPv4 Options". Kea also supports
+    // vendor options (see Section 7.2.10) and allows users to define their
+    // own custom options (see Section 7.2.9).
+    "option-data": [
+        // When specifying options, you typically need to specify
+        // one of (name or code) and data. The full option specification
+        // covers name, code, space, csv-format and data.
+        // space defaults to "dhcp4" which is usually correct, unless you
+        // use encapsulate options. csv-format defaults to "true", so
+        // this is also correct, unless you want to specify the whole
+        // option value as long hex string. For example, to specify
+        // domain-name-servers you could do this:
+        // {
+        //     "name": "domain-name-servers",
+        //     "code": 6,
+        //     "csv-format": "true",
+        //     "space": "dhcp4",
+        //     "data": "192.0.2.1, 192.0.2.2"
+        // }
+        // but it's a lot of writing, so it's easier to do this instead:
+        {
+            "name": "domain-name-servers",
+            "data": "192.0.2.1, 192.0.2.2"
+        },
+
+        // Typically people prefer to refer to options by their names, so they
+        // don't need to remember the code names. However, some people like
+        // to use numerical values. For example, option "domain-name" uses
+        // option code 15, so you can reference to it either by
+        // "name": "domain-name" or "code": 15.
+        {
+            "code": 15,
+            "data": "example.org"
+        },
+
+        // Domain search is also a popular option. It tells the client to
+        // attempt to resolve names within those specificed domains. For
+        // example, name "foo" would be attempted to be resolved as
+        // foo.mydomain.example.com and if it fails, then as foo.example.com
+        {
+            "name": "domain-search",
+            "data": "mydomain.example.com, example.com"
+        },
+
+        // String options that have a comma in their values need to have
+        // it escaped (i.e. each comma is predeced by two backslashes).
+        // That's because commas are reserved for separating fields in
+        // compound options. At the same time, we need to be conformant
+        // with JSON spec, that does not allow "\,". Therefore the
+        // slightly uncommon double backslashes notation is needed.
+
+        // Legal JSON escapes are \ followed by "\/bfnrt character
+        // or \u followed by 4 hexa-decimal numbers (currently Kea
+        // supports only \u0000 to \u00ff code points).
+        // CSV processing translates '\\' into '\' and '\,' into ','
+        // only so for instance '\x' is translated into '\x'. But
+        // as it works on a JSON string value each of these '\'
+        // characters must be doubled on JSON input.
+        {
+            "name": "boot-file-name",
+            "data": "EST5EDT4\\,M3.2.0/02:00\\,M11.1.0/02:00"
+        },
+
+        // Options that take integer values can either be specified in
+        // dec or hex format. Hex format could be either plain (e.g. abcd)
+        // or prefixed with 0x (e.g. 0xabcd).
+        {
+            "name": "default-ip-ttl",
+            "data": "0xf0"
+        }
+
+        // Note that Kea provides some of the options on its own. In particular,
+        // it sends IP Address lease type (code 51, based on valid-lifetime
+        // parameter, Subnet mask (code 1, based on subnet definition), Renewal
+        // time (code 58, based on renew-timer parameter), Rebind time (code 59,
+        // based on rebind-timer parameter).
+    ],
+
+    // Other global parameters that can be defined here are option defintions
+    // (this is useful if you want to use vendor options, your own custom options
+    // or perhaps handle options that Kea does not handle out of the box yet).
+
+    // You can also define classes. If classes are defined, incoming packets
+    // may be assigned to specific classes. A client class can represent any
+    // group of devices that share some common characteristic, e.g. Windows
+    // devices, iphones, broken printers that require special options, etc.
+    // Based on the class information, you can then allow or reject clients
+    // to use certain subnets, add special options for them or change values
+    // of some fixed fields.
+    "client-classes": [
+        {
+            // This specifies a name of this class. It's useful if you need to
+            // reference this class.
+            "name": "voip",
+
+            // This is a test. It is an expression that is being evaluated on
+            // each incoming packet. It is supposed to evaluate to either
+            // true or false. If it's true, the packet is added to specified
+            // class.
+            "test": "substring(option[60].hex,0,6) == 'Aastra'",
+
+            // If a client belongs to this class, you can define extra behavior.
+            // For example, certain fields in DHCPv4 packet will be set to
+            // certain values.
+            "next-server": "192.0.2.254",
+            "server-hostname": "hal9000",
+            "boot-file-name": "/dev/null"
+
+            // You can also define option values here if you want devices from
+            // this class to receive special options.
+        }
+    ],
+
+    // Another thing possible here are hooks. Kea supports a powerful mechanism
+    // that allows loading external libraries that can extract information and
+    // even influence how the server processes packets. Those libraries include
+    // additional forensic logging capabilities, ability to reserve hosts in
+    // more flexible ways, and even add extra commands. For a list of available
+    // hook libraries, see http://kea.isc.org/wiki/Hooks.
+    //"hooks-libraries": [
+    //  {
+    //      // Forensic Logging library generates forensic type of audit trail
+    //      // of all devices serviced by Kea, including their identifiers
+    //      // (like MAC address), their location in the network, times
+    //      // when they were active etc.
+    //      "library": "@localstatedir@/kea/libdhcp_legal_log.so"
+    //      "parameters": {
+    //          "path": "/var/kea/var",
+    //          "base-name": "kea-forensic4"
+    //      }
+    //  },
+    //  {
+    //      // Flexible identifier (flex-id). 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 scenario 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.
+    //      "library": "@localstatedir@/kea/libdhcp_flex_id.so",
+    //      "parameters": {
+    //          "identifier-expression": "substring(relay6[0].option[18],0,8)"
+    //      }
+    //  }
+    //],
+
+    // Below an example of a simple IPv4 subnet declaration. Uncomment to enable
+    // it. This is a list, denoted with [ ], of structures, each denoted with
+    // { }. Each structure describes a single subnet and may have several
+    // parameters. One of those parameters is "pools" that is also a list of
+    // structures.
+    "subnet4": [
+        {
+            // This defines the whole subnet. Kea will use this information to
+            // determine where the clients are connected. This is the whole
+            // subnet in your network. This is mandatory parameter for each
+            // subnet.
+            "subnet": "192.0.2.0/24",
+
+            // Pools define the actual part of your subnet that is governed
+            // by Kea. Technically this is optional parameter, but it's
+            // almost always needed for DHCP to do its job. If you omit it,
+            // clients won't be able to get addresses, unless there are
+            // host reservations defined for them.
+            "pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ],
+
+            // These are options that are subnet specific. In most cases,
+            // you need to define at least routers option, as without this
+            // option your clients will not be able to reach their default
+            // gateway and will not have Internet connectivity.
+            "option-data": [
+                {
+                    // For each IPv4 subnet you most likely need to specify at
+                    // least one router.
+                    "name": "routers",
+                    "data": "192.0.2.1"
+                }
+            ],
+
+            // Kea offers host reservations mechanism. Kea supports reservations
+            // by several different types of identifiers: hw-address
+            // (hardware/MAC address of the client), duid (DUID inserted by the
+            // client), client-id (client identifier inserted by the client) and
+            // circuit-id (circuit identifier inserted by the relay agent).
+            //
+            // Kea also support flexible identifier (flex-id), which lets you
+            // specify an expression that is evaluated for each incoming packet.
+            // Resulting value is then used for as an identifier.
+            "reservations": [
+
+                // This is a reservation for a specific hardware/MAC address. It's a
+                // rather simple reservation: just an address and nothing else.
+                {
+                    "hw-address": "1a:1b:1c:1d:1e:1f",
+                    "ip-address": "192.0.2.201"
+                },
+
+                // This is a reservation for a specific client-id. It also shows
+                // the this client will get a reserved hostname. A hostname can be
+                // defined for any identifier type, not just client-id.
+                {
+                    "client-id": "01:11:22:33:44:55:66",
+                    "ip-address": "192.0.2.202",
+                    "hostname": "special-snowflake"
+                },
+
+                // The third reservation is based on DUID. This reservation defines
+                // a special option values for this particular client. If the
+                // domain-name-servers option would have been defined on a global,
+                // subnet or class level, the host specific values take preference.
+                {
+                    "duid": "01:02:03:04:05",
+                    "ip-address": "192.0.2.203",
+                    "option-data": [ {
+                        "name": "domain-name-servers",
+                        "data": "10.1.1.202,10.1.1.203"
+                    } ]
+                },
+
+                // The fourth reservation is based on circuit-id. This is an option
+                // inserted by the relay agent that forwards the packet from client
+                // to the server.  In this example the host is also assigned vendor
+                // specific options.
+                //
+                // When using reservations, it is useful to configure
+                // reservation-mode (subnet specific parameter) and
+                // host-reservation-identifiers (global parameter).
+                {
+                    "client-id": "01:12:23:34:45:56:67",
+                    "ip-address": "192.0.2.204",
+                    "option-data": [
+                        {
+                            "name": "vivso-suboptions",
+                            "data": "4491"
+                        },
+                        {
+                            "name": "tftp-servers",
+                            "space": "vendor-4491",
+                            "data": "10.1.1.202,10.1.1.203"
+                        }
+                    ]
+                },
+                // This reservation is for a client that needs specific DHCPv4
+                // fields to be set. Three supported fields are next-server,
+                // server-hostname and boot-file-name
+                {
+                    "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"
+                },
+                // This reservation is using flexible identifier. Instead of
+                // relying on specific field, sysadmin can define an expression
+                // similar to what is used for client classification,
+                // e.g. substring(relay[0].option[17],0,6). Then, based on the
+                // value of that expression for incoming packet, the reservation
+                // is matched. Expression can be specified either as hex or
+                // plain text using single quotes.
+                //
+                // Note: flexible identifier requires flex_id hook library to be
+                // loaded to work.
+                {
+                    "flex-id": "'s0mEVaLue'",
+                    "ip-address": "192.0.2.206"
+                }
+                // You can add more reservations here.
+            ]
+            // You can add more subnets there.
+        }
+    ]
+
+    // There are many, many more parameters that DHCPv4 server is able to use.
+    // They were not added here to not overwhelm people with too much information
+    // at once.
 },
 
-# DHCPv6 configuration starts here.
-"Dhcp6":
-{
-# Add names of interfaces to listen on.
-  "interfaces-config": {
-    "interfaces": [ ]
-  },
-
-# Use Memfile lease database backend to store leases in a CSV file.
-  "lease-database": {
-    "type": "memfile"
-  },
-
-# Setup reclamation of the expired leases and leases affinity.
-# Expired leases will be reclaimed every 10 seconds. Every 25
-# seconds reclaimed leases, which have expired more than 3600
-# seconds ago, will be removed. The limits for leases reclamation
-# are 100 leases or 250 ms for a single cycle. A warning message
-# will be logged if there are still expired leases in the
-# database after 5 consecutive reclamation cycles.
-  "expired-leases-processing": {
-    "reclaim-timer-wait-time": 10,
-    "flush-reclaimed-timer-wait-time": 25,
-    "hold-reclaimed-time": 3600,
-    "max-reclaim-leases": 100,
-    "max-reclaim-time": 250,
-    "unwarned-reclaim-cycles": 5
-  },
-
-# Addresses will be assigned with preferred and valid lifetimes
-# being 3000 and 4000, respectively. Client is told to start
-# renewing after 1000 seconds. If the server does not respond
-# after 2000 seconds since the lease was granted, client is supposed
-# to start REBIND procedure (emergency renewal that allows switching
-# to a different server).
-  "preferred-lifetime": 3000,
-  "valid-lifetime": 4000,
-  "renew-timer": 1000,
-  "rebind-timer": 2000,
-
-# The following list defines subnets. Uncomment to enable them.
-  "subnet6": [
-#  {    "subnet": "2001:db8:1::/64",
-#       "pools": [ { "pool": "2001:db8:1::/80" } ] },
-#  {    "subnet": "2001:db8:2::/64",
-#       "pools": [ { "pool": "2001:db8:2::/80" } ] },
-#  {    "subnet": "2001:db8:3::/64",
-#       "pools": [ { "pool": "2001:db8:3::/80" } ] },
-#  {    "subnet": "2001:db8:4::/64",
-#       "pools": [ { "pool": "2001:db8:4::/80" } ] }
-   ]
+// DHCPv6 configuration starts here. This section will be read by DHCPv6 server
+// and will be ignored by other components.
+"Dhcp6": {
+    // Add names of your network interfaces to listen on.
+    "interfaces-config": {
+        // You typcially want to put specific interface names here, e.g. eth0
+        // but you can also specify unicast addresses (e.g. eth0/2001:db8::1) if
+        // you want your server to handle unicast traffic in addition to
+        // multicast. (DHCPv6 is a multicast based protocol).
+        "interfaces": [ ]
+    },
+
+    // Kea support control channel, which is a way to receive management commands
+    // while the server is running. This is a Unix domain socket that receives
+    // commands formatted in JSON, e.g. config-set (which sets new configuration),
+    // config-reload (which tells Kea to reload its configuration from file),
+    // statistic-get (to retrieve statistics) and many more. For detailed
+    // description, see Sections 9.12, 16 and 15.
+    "control-socket": {
+        "socket-type": "unix",
+        "socket-name": "/tmp/kea6-ctrl-socket.sock"
+    },
+
+    // Use Memfile lease database backend to store leases in a CSV file.
+    // Depending on how Kea was compiled, it may also support SQL databases
+    // (MySQL and/or PostgreSQL) and even Cassandra. Those database backends
+    // require more parameters, like name, host and possibly user and password.
+    // There are dedicated examples for each backend. See Section 8.2.2 "Lease
+    // Storage" for details.
+    "lease-database": {
+        "type": "memfile"
+    },
+
+    // Kea allows storing host reservations in a database. If your network is
+    // small or you have few reservations, it's probably easier to keep them
+    // in the configuration file. If your network is large, it's usually better
+    // to use database for it. To enable it, uncomment the following:
+    // "hosts-database": {
+    //     "type": "mysql",
+    //     "name": "kea",
+    //     "user": "kea",
+    //     "password": "kea",
+    //     "host": "localhost",
+    //     "port": 3306
+    // },
+    // See Section 8.2.3 "Hosts storage" for details.
+
+
+    // Setup reclamation of the expired leases and leases affinity.
+    // Expired leases will be reclaimed every 10 seconds. Every 25
+    // seconds reclaimed leases, which have expired more than 3600
+    // seconds ago, will be removed. The limits for leases reclamation
+    // are 100 leases or 250 ms for a single cycle. A warning message
+    // will be logged if there are still expired leases in the
+    // database after 5 consecutive reclamation cycles.
+    "expired-leases-processing": {
+        "reclaim-timer-wait-time": 10,
+        "flush-reclaimed-timer-wait-time": 25,
+        "hold-reclaimed-time": 3600,
+        "max-reclaim-leases": 100,
+        "max-reclaim-time": 250,
+        "unwarned-reclaim-cycles": 5
+    },
+
+    // These parameters govern global timers. Addresses will be assigned with
+    // preferred and valid lifetimes being 3000 and 4000, respectively. Client
+    // is told to start renewing after 1000 seconds. If the server does not
+    // respond after 2000 seconds since the lease was granted, a client is
+    // supposed to start REBIND procedure (emergency renewal that allows
+    // switching to a different server).
+    "renew-timer": 1000,
+    "rebind-timer": 2000,
+    "preferred-lifetime": 3000,
+    "valid-lifetime": 4000,
+
+    // These are global options. They are going to be sent when a client requests
+    // them, unless overwritten with values in more specific scopes. The scope
+    // hierarchy is:
+    // - global
+    // - subnet
+    // - class
+    // - host
+    //
+    // Not all of those options make sense. Please configure only those that
+    // are actually useful in your network.
+    //
+    // For a complete list of options currently supported by Kea, see
+    // Section 8.2.9 "Standard DHCPv6 Options". Kea also supports
+    // vendor options (see Section 7.2.10) and allows users to define their
+    // own custom options (see Section 7.2.9).
+    "option-data": [
+        // When specifying options, you typically need to specify
+        // one of (name or code) and data. The full option specification
+        // covers name, code, space, csv-format and data.
+        // space defaults to "dhcp6" which is usually correct, unless you
+        // use encapsulate options. csv-format defaults to "true", so
+        // this is also correct, unless you want to specify the whole
+        // option value as long hex string. For example, to specify
+        // domain-name-servers you could do this:
+        // {
+        //     "name": "dns-servers",
+        //     "code": 23,
+        //     "csv-format": "true",
+        //     "space": "dhcp6",
+        //     "data": "2001:db8:2::45, 2001:db8:2::100"
+        // }
+        // but it's a lot of writing, so it's easier to do this instead:
+        {
+            "name": "dns-servers",
+            "data": "2001:db8:2::45, 2001:db8:2::100"
+        },
+
+        // Typically people prefer to refer to options by their names, so they
+        // don't need to remember the code names. However, some people like
+        // to use numerical values. For example, DHCPv6 can optionally use
+        // server unicast communication, if extra option is present. Option
+        // "unicast" uses option code 12, so you can reference to it either
+        // by "name": "unicast" or "code": 12. If you enable this option,
+        // you really should also tell the server to listen on that address
+        // (see interfaces-config/interfaces list above).
+        {
+            "code": 12,
+            "data": "2001:db8::1"
+        },
+
+        // String options that have a comma in their values need to have
+        // it escaped (i.e. each comma is predeced by two backslashes).
+        // That's because commas are reserved for separating fields in
+        // compound options. At the same time, we need to be conformant
+        // with JSON spec, that does not allow "\,". Therefore the
+        // slightly uncommon double backslashes notation is needed.
+
+        // Legal JSON escapes are \ followed by "\/bfnrt character
+        // or \u followed by 4 hexa-decimal numbers (currently Kea
+        // supports only \u0000 to \u00ff code points).
+        // CSV processing translates '\\' into '\' and '\,' into ','
+        // only so for instance '\x' is translated into '\x'. But
+        // as it works on a JSON string value each of these '\'
+        // characters must be doubled on JSON input.
+        {
+            "name": "new-posix-timezone",
+            "data": "EST5EDT4\\,M3.2.0/02:00\\,M11.1.0/02:00"
+        },
+
+        // Options that take integer values can either be specified in
+        // dec or hex format. Hex format could be either plain (e.g. abcd)
+        // or prefixed with 0x (e.g. 0xabcd).
+        {
+            "name": "preference",
+            "data": "0xf0"
+        },
+
+        // A few options are encoded in (length, string) tuples
+        // which can be defined using only strings as the CSV
+        // processing computes lengths.
+        {
+            "name": "bootfile-param",
+            "data": "root=/dev/sda2, quiet, splash"
+        }
+    ],
+
+    // Below an example of a simple IPv6 subnet declaration. Uncomment to enable
+    // it. This is a list, denoted with [ ], of structures, each denoted with
+    // { }. Each structure describes a single subnet and may have several
+    // parameters. One of those parameters is "pools" that is also a list of
+    // structures.
+    "subnet6": [
+        {
+            // This defines the whole subnet. Kea will use this information to
+            // determine where the clients are connected. This is the whole
+            // subnet in your network. This is mandatory parameter for each
+            // subnet.
+            "subnet": "2001:db8:1::/64",
+
+            // Pools define the actual part of your subnet that is governed
+            // by Kea. Technically this is optional parameter, but it's
+            // almost always needed for DHCP to do its job. If you omit it,
+            // clients won't be able to get addresses, unless there are
+            // host reservations defined for them.
+            "pools": [ { "pool": "2001:db8:1::/80" } ],
+
+            "option-data": [
+                // You can specify additional options here that are subnet
+                // specific. Also, you can override global options here.
+                {
+                    "name": "dns-servers",
+                    "data": "2001:db8:2::dead:beef, 2001:db8:2::cafe:babe"
+                }
+            ],
+
+            // Host reservations can be defined for each subnet.
+            "reservations": [
+                // This is a simple host reservation. The host with DUID matching
+                // the specified value will get an address of 2001:db8:1::100.
+                {
+                    "duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
+                    "ip-addresses": [ "2001:db8:1::100" ]
+                },
+
+                // This is similar to the previous one, but this time the
+                // reservation is done based on hardware/MAC address. The server
+                // will do its best to extract the hardware/MAC address from
+                // received packets (see 'mac-sources' directive for
+                // details). This particular reservation also specifies two
+                // extra options to be available for this client. If there are
+                // options with the same code specified in a global, subnet or
+                // class scope, the values defined at host level take
+                // precedence.
+                {
+                    "hw-address": "00:01:02:03:04:05",
+                    "ip-addresses": [ "2001:db8:1::101" ],
+                    "option-data": [
+                        {
+                            "name": "dns-servers",
+                            "data": "3000:1::234"
+                        },
+                        {
+                            "name": "nis-servers",
+                            "data": "3000:1::234"
+                        }],
+
+                    // This client will be automatically added to certain
+                    // classes.
+                    "client-classes": [ "special_snowflake", "office" ]
+                },
+
+                // This is a bit more advanced reservation. The client with the
+                // specified DUID will get a reserved address, a reserved prefix
+                // and a hostname.  This reservation is for an address that it
+                // not within the dynamic pool.  Finally, this reservation
+                // features vendor specific options for CableLabs, which happen
+                // to use enterprise-id 4491. Those particular values will be
+                // returned only to the client that has a DUID matching this
+                // reservation.
+                {
+                    "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"
+                        }
+                    ]
+                },
+
+                // This reservation is using flexible identifier. Instead of
+                // relying on specific field, sysadmin can define an expression
+                // similar to what is used for client classification,
+                // e.g. substring(relay[0].option[17],0,6). Then, based on the
+                // value of that expression for incoming packet, the reservation
+                // is matched.  Expression can be specified either as hex or
+                // plain text using single quotes.
+
+                // Note: flexible identifier requires flex_id hook library to be
+                // loaded to work.
+                {
+                    "flex-id": "'somevalue'",
+                    "ip-addresses": [ "2001:db8:1:cafe::2" ]
+                }
+            ]
+        }
+        // More subnets can be defined here.
+        //      {
+        //          "subnet": "2001:db8:2::/64",
+        //          "pools": [ { "pool": "2001:db8:2::/80" } ]
+        //      },
+        //      {
+        //          "subnet": "2001:db8:3::/64",
+        //          "pools": [ { "pool": "2001:db8:3::/80" } ]
+        //      },
+        //      {
+        //          "subnet": "2001:db8:4::/64",
+        //          "pools": [ { "pool": "2001:db8:4::/80" } ]
+        //      }
+    ]
 },
 
-# DHCP DDNS configuration starts here.
+// DHCP DDNS configuration starts here. This is a very simple configuration
+// that simply starts the DDNS daemon, but will not do anything useful.
+// See Section 11 for examples and details description.
 "DhcpDdns":
 {
   "ip-address": "127.0.0.1",
@@ -112,43 +694,68 @@
   "reverse-ddns" : {}
 },
 
-# Logging configuration starts here. It tells Kea servers to store
-# all log messages (on severity INFO or more) in a file.
-# debuglevel variable is used on DEBUG level only.
+// Logging configuration starts here. Kea uses different loggers to log various
+// activities. For details (e.g. names of loggers), see Chapter 18.
 "Logging":
 {
   "loggers": [
     {
-      "name": "kea-dhcp4",
-      "output_options": [
-          {
-            "output": "@localstatedir@/log/kea-dhcp4.log"
-          }
-      ],
-      "severity": "INFO",
-      "debuglevel": 0
-    },
-    {
-      "name": "kea-dhcp6",
-      "output_options": [
-          {
-            "output": "@localstatedir@/log/kea-dhcp6.log"
-          }
-      ],
-      "severity": "INFO",
-      "debuglevel": 0
+        // This section affects kea-dhcp4, which is the base logger for DHCPv4
+        // component. It tells DHCPv4 server to write all log messages (on
+        // severity INFO or more) to a file.
+        "name": "kea-dhcp4",
+        "output_options": [
+            {
+                // Specifies the output file.
+                "output": "@localstatedir@/log/kea-dhcp4.log"
+
+                // This governs whether the log output is flushed to disk after
+                // every write.
+                // "flush": false,
+
+                // This specifies the maximum size of the file before it is
+                // rotated.
+                // "maxsize": 1048576,
+
+                // This specifies the maximum number of rotated files to keep.
+                // "maxver": 8
+            }
+        ],
+        // This specifies the severity of log messages to keep. Supported values
+        // are: FATAL, ERROR, WARN, INFO, DEBUG
+        "severity": "INFO",
+
+        // If DEBUG level is specified, this value is used. 0 is least verbose,
+        // 99 is most verbose. Be cautious, Kea can generate lots and lots
+        // of logs if told to do so.
+        "debuglevel": 0
     },
-    {
-      "name": "kea-dhcp-ddns",
-      "output_options": [
-          {
-            "output": "@localstatedir@/log/kea-ddns.log"
-          }
-      ],
-      "severity": "INFO",
-      "debuglevel": 0
-    }
+      {
+          // This specifies the logging for kea-dhcp6 logger, i.e. all logs
+          // generated by Kea DHCPv6 server.
+          "name": "kea-dhcp6",
+          "output_options": [
+              {
+                  "output": "@localstatedir@/log/kea-dhcp6.log"
+              }
+          ],
+          "severity": "INFO",
+          "debuglevel": 0
+      },
+      {
+          // This specifies the logging for D2 (DHCP-DDNS) daemon.
+          "name": "kea-dhcp-ddns",
+          "output_options": [
+              {
+                  "output": "@localstatedir@/log/kea-ddns.log"
+              }
+          ],
+          "severity": "INFO",
+          "debuglevel": 0
+      }
   ]
 }
 
+    // In the future releases, also Control Agent configuration will be kept here.
+    // However, for the time being, it is kept in a separate file.
 }