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It is recommended that the Kea DHCPv6 server be started and stopped using keactrl (described in ). However, it is also possible to run the server directly: it accepts the following command-line switches: -c file - specifies the configuration file. This is the only mandatory switch. -d - specifies whether the server logging should be switched to verbose mode. In verbose mode, the logging severity and debuglevel specified in the configuration file are ignored and "debug" severity and the maximum debuglevel (99) are assumed. The flag is convenient, for temporarily switching the server into maximum verbosity, e.g. when debugging. -p port - specifies UDP port on which the server will listen. This is only useful during testing, as a DHCPv6 server listening on ports other than default DHCPv6 ports will not be able to handle regular DHCPv6 queries. -v - prints out Kea version and exits. -V - prints out Kea extended version with additional parameters and exits. -W - prints out Kea configuration report and exits. The -V command returns the versions of the external libraries dynamically linked. The -W command describes the environment used to build Kea. This command displays a copy of the config.report file produced by ./configure that is embedded in the executable binary. The config.report may also be accessed more directly. The following command may be used to extract this information. The binary path may be found in the install directory or in the .libs subdirectory in the source tree. For example kea/src/bin/dhcp6/.libs/kea-dhcp6. strings path/kea-dhcp6 | sed -n 's/;;;; //p' When running in a console, the server can be shut down by pressing ctrl-c. It detects the key combination and shuts down gracefully. On start-up, the server will detect available network interfaces and will attempt to open UDP sockets on all interfaces mentioned in the configuration file. Since the DHCPv6 server opens privileged ports, it requires root access. Make sure you run this daemon as root. During startup the server will attempt to create a PID file of the form: [localstatedir]/[conf name].kea-dhcp6.pid where: localstatedir: The value as passed into the build configure script. It defaults to "/usr/local/var". Note that this value may be overridden at run time by setting the environment variable KEA_PIDFILE_DIR. This is intended primarily for testing purposes. conf name: The configuration file name used to start the server, minus all preceding path and file extension. For example, given a pathname of "/usr/local/etc/kea/myconf.txt", the portion used would be "myconf". If the file already exists and contains the PID of a live process, the server will issue a DHCP6_ALREADY_RUNNING log message and exit. It is possible, though unlikely, that the file is a remnant of a system crash and the process to which the PID belongs is unrelated to Kea. In such a case it would be necessary to manually delete the PID file.

This section explains how to configure the DHCPv6 server using the Kea configuration backend. (Kea configuration using any other backends is outside of scope of this document.) Before DHCPv6 is started, its configuration file has to be created. The basic configuration looks as follows: { # DHCPv6 configuration starts on the next line "Dhcp6": { # First we set up global values "renew-timer": 1000, "rebind-timer": 2000, "preferred-lifetime": 3000, "valid-lifetime": 4000, # Next we setup the interfaces to be used by the server. "interfaces-config": { "interfaces": [ "eth0" ] }, # And we specify the type of a lease database "lease-database": { "type": "memfile", "persist": true, "name": "/var/kea/dhcp6.leases" }, # Finally, we list the subnets from which we will be leasing addresses. "subnet6": [ { "subnet": "2001:db8:1::/64", "pools": [ { "pool": "2001:db8:1::1-2001:db8:1::ffff" } ] } ] # DHCPv6 configuration ends with the next line } } The following paragraphs provide a brief overview of the parameters in the above example and their format. Subsequent sections of this chapter go into much greater detail for these and other parameters. The lines starting with a hash (#) are comments and are ignored by the server; they do not impact its operation in any way. The configuration starts in the first line with the initial opening curly bracket (or brace). Each configuration consists of one or more objects. In this specific example, we have only one object called Dhcp6. This is a simplified configuration, as usually there will be additional objects, like Logging or DhcpDns, but we omit them now for clarity. The Dhcp6 configuration starts with the "Dhcp6": { line and ends with the corresponding closing brace (in the above example, the brace after the last comment). Everything defined between those lines is considered to be the Dhcp6 configuration. In the general case, the order in which those parameters appear does not matter. There are two caveats here though. The first one is to remember that the configuration file must be well formed JSON. That means that parameters for any given scope must be separated by a comma and there must not be a comma after the last parameter. When reordering a configuration file, keep in mind that moving a parameter to or from the last position in a given scope may require moving the comma as well. The second caveat is that it is uncommon — although legal JSON — to repeat the same parameter multiple times. If that happens, the last occurrence of a given parameter in a given scope is used while all previous instances are ignored. This is unlikely to cause any confusion as there are no real life reasons to keep multiple copies of the same parameter in your configuration file. Moving onto the DHCPv6 configuration elements, the very first few elements define some global parameters. valid-lifetime defines for how long the addresses (leases) given out by the server are valid. If nothing changes, a client that got an address is allowed to use it for 4000 seconds. (Note that integer numbers are specified as is, without any quotes around them.) The address will become deprecated in 3000 seconds (clients are allowed to keep old connections, but can't use this address for creating new connections). renew-timer and rebind-timer are values that define T1 and T2 timers that govern when the client will begin the renewal and rebind procedures. The interfaces-config map specifies the server configuration concerning the network interfaces, on which the server should listen to the DHCP messages. The interfaces parameter specifies a list of network interfaces on which the server should listen. Lists are opened and closed with square brackets, with elements separated by commas. Had we wanted to listen on two interfaces, the interfaces-config would look like this: "interfaces-config": { "interfaces": [ "eth0", "eth1" ] }, The next couple of lines define the lease database, the place where the server stores its lease information. This particular example tells the server to use memfile, which is the simplest (and fastest) database backend. It uses an in-memory database and stores leases on disk in a CSV file. This is a very simple configuration. Usually, lease database configuration is more extensive and contains additional parameters. Note that lease-database is an object and opens up a new scope, using an opening brace. Its parameters (just one in this example -- type) follow. Had there been more than one, they would be separated by commas. This scope is closed with a closing brace. As more parameters follow, a trailing comma is present. Finally, we need to define a list of IPv6 subnets. This is the most important DHCPv6 configuration structure as the server uses that information to process clients' requests. It defines all subnets from which the server is expected to receive DHCP requests. The subnets are specified with the subnet6 parameter. It is a list, so it starts and ends with square brackets. Each subnet definition in the list has several attributes associated with it, so it is a structure and is opened and closed with braces. At minimum, a subnet definition has to have at least two parameters: subnet (that defines the whole subnet) and pool (which is a list of dynamically allocated pools that are governed by the DHCP server). The example contains a single subnet. Had more than one been defined, additional elements in the subnet6 parameter would be specified and separated by commas. For example, to define two subnets, the following syntax would be used: "subnet6": [ { "pools": [ { "pool": "2001:db8:1::/112" } ], "subnet": "2001:db8:1::/64" }, { "pools": [ { "pool": "2001:db8:2::1-2001:db8:2::ffff" } ], "subnet": "2001:db8:2::/64", "interface": "eth0" } ] Note that indentation is optional and is used for aesthetic purposes only. In some cases in may be preferable to use more compact notation. After all parameters are specified, we have two contexts open: global and Dhcp6, hence we need two closing curly brackets to close them. In a real life configuration file there most likely would be additional components defined such as Logging or DhcpDdns, so the closing brace would be followed by a comma and another object definition.

All leases issued by the server are stored in the lease database. Currently there are three database backends available: memfile (which is the default backend), MySQL and PostgreSQL.

The server is able to store lease data in different repositories. Larger deployments may elect to store leases in a database. describes this option. In typical smaller deployments though, the server will use a CSV file rather than a database to store lease information. As well as requiring less administration, an advantage of using a file for storage is that it eliminates a dependency on third-party database software. The configuration of the file backend (Memfile) is controlled through the Dhcp6/lease-database parameters. The type parameter is mandatory and it specifies which storage for leases the server should use. The value of "memfile" indicates that the file should be used as the storage. The following list presents the remaining, not mandatory parameters, which can be used to configure the Memfile backend. persist: controls whether the new leases and updates to existing leases are written to the file. It is strongly recommended that the value of this parameter is set to true at all times, during the server's normal operation. Not writing leases to disk will mean that if a server is restarted (e.g. after a power failure), it will not know what addresses have been assigned. As a result, it may hand out addresses to new clients that are already in use. The value of false is mostly useful for performance testing purposes. The default value of the persist parameter is true, which enables writing lease updates to the lease file. name: specifies an absolute location of the lease file in which new leases and lease updates will be recorded. The default value for this parameter is "[kea-install-dir]/var/kea/kea-leases6.csv" . lfc-interval: specifies the interval in seconds, at which the server (Memfile backend) will perform a lease file cleanup (LFC), which removes the redundant (historical) information from the lease file and effectively reduces the lease file size. The cleanup process is described in more detailed fashion further in this section. The default value of the lfc-interval is 0, which disables the LFC. The example configuration of the Memfile backend is presented below: "Dhcp6": { "lease-database": { "type": "memfile", "persist": true, "name": "/tmp/kea-leases6.csv", "lfc-interval": 1800 } } It is important to know how the lease file contents are organized to understand why the periodic lease file cleanup is needed. Every time when the server updates a lease or creates a new lease for the client, the new lease information must be recorded in the lease file. For performance reasons, the server does not supersede the existing client's lease, as it would require the lookup of the specific lease entry, but simply appends the new lease information at the end of the lease file. The previous lease entries for the client are not removed. When the server loads leases from the lease file, e.g. at the server startup, it assumes that the latest lease entry for the client is the valid one. The previous entries are discarded. This means that the server can re-construct the accurate information about the leases even though there may be many lease entries for each client. However, storing many entries for each client results in bloated lease file and impairs the performance of the server's startup and reconfiguration, as it needs to process larger number of lease entries. The lease file cleanup removes all previous entries for each client and leaves only the latest ones. The interval at which the cleanup is performed is configurable, and it should be selected according to the frequency of lease renewals initiated by the clients. The more frequent renewals are, the lesser value of the lfc-interval should be. Note however, that the LFC takes time and thus it is possible (although unlikely) that new cleanup is started while the previous cleanup instance is still running, if the lfc-interval is too short. The server would recover from this by skipping the new cleanup when it detects that the previous cleanup is still in progress. But, this implies that the actual cleanups will be triggered more rarely than configured. Moreover, triggering a new cleanup adds an overhead to the server, which will not be able to respond to new requests for a short period of time when the new cleanup process is spawned. Therefore, it is recommended that the lfc-interval value is selected in a way that would allow for completing the cleanup before the new cleanup is triggered. The LFC is performed by a separate process (in background) to avoid performance impact on the server process. In order to avoid the conflicts between the two processes both using the same lease files, the LFC process operates on the copy of the original lease file, rather than on the lease file used by the server to record lease updates. There are also other files being created as a side effect of the lease file cleanup. The detailed description of the LFC is located on the Kea wiki: .

Lease database access information must be configured for the DHCPv6 server, even if it has already been configured for the DHCPv4 server. The servers store their information independently, so each server can use a separate database or both servers can use the same database. Lease database configuration is controlled through the Dhcp6/lease-database parameters. The type of the database must be set to "memfile", "mysql" or "postgresql", e.g. "Dhcp6": { "lease-database": { "type": "mysql", ... }, ... } Next, the name of the database is to hold the leases must be set: this is the name used when the lease database was created (see or ). "Dhcp6": { "lease-database": { "name": "database-name" , ... }, ... } If the database is located on a different system than the DHCPv6 server, the database host name must also be specified (although it should be noted that this configuration may have a severe impact on server performance): "Dhcp6": { "lease-database": { "host": remote-host-name, ... }, ... } The usual state of affairs will be to have the database on the same machine as the DHCPv6 server. In this case, set the value to the empty string: "Dhcp6": { "lease-database": { "host" : "", ... }, ... } Should the database be located on a different system, you may need to specify a longer interval for the connection timeout: "Dhcp6": { "lease-database": { "connect-timeout" : timeout-in-seconds, ... }, ... } The default value of five seconds should be more than adequate for local connections. If a timeout is given though, it should be an integer greater than zero. Finally, the credentials of the account under which the server will access the database should be set: "Dhcp6": { "lease-database": { "user": "user-name", "password": "password", ... }, ... } If there is no password to the account, set the password to the empty string "". (This is also the default.)

The DHCPv6 server has to be configured to listen on specific network interfaces. The simplest network interface configuration instructs the server to listen on all available interfaces: "Dhcp6": { "interfaces-config": { "interfaces": [ "*" ] } ... } The asterisk plays the role of a wildcard and means "listen on all interfaces". However, it is usually a good idea to explicitly specify interface names: "Dhcp6": { "interfaces-config": { "interfaces": [ "eth1", "eth3" ] }, ... } It is possible to use wildcard interface name (asterisk) concurrently with the actual interface names: "Dhcp6": { "interfaces-config": { "interfaces": [ "eth1", "eth3", "*" ] }, ... } It is anticipated that this will form of usage only be used where it is desired to temporarily override a list of interface names and listen on all interfaces.

The subnet identifier is a unique number associated with a particular subnet. In principle, it is used to associate clients' leases with respective subnets. When the subnet identifier is not specified for a subnet being configured, it will be automatically assigned by the configuration mechanism. The identifiers are assigned from 1 and are monotonically increased for each subsequent subnet: 1, 2, 3 .... If there are multiple subnets configured with auto-generated identifiers and one of them is removed, the subnet identifiers may be renumbered. For example: if there are four subnets and the third is removed the last subnet will be assigned the identifier that the third subnet had before removal. As a result, the leases stored in the lease database for subnet 3 are now associated with subnet 4, which may have unexpected consequences. In the future it is planned to implement a mechanism to preserve auto-generated subnet ids upon removal of one of the subnets. Currently, the only remedy for this issue is to manually specify a unique subnet identifier for each subnet. The following configuration will assign the specified subnet identifier to the newly configured subnet: "Dhcp6": { "subnet6": [ { "subnet": "2001:db8:1::/64", "id": 1024, ... } ] } This identifier will not change for this subnet unless the "id" parameter is removed or set to 0. The value of 0 forces auto-generation of the subnet identifier.

When the DHCPv6 server starts, by default it listens to the DHCP traffic sent to multicast address ff02::1:2 on each interface that it is configured to listen on (see ). In some cases it is useful to configure a server to handle incoming traffic sent to the global unicast addresses as well. The most common reason for that is to have relays send their traffic to the server directly. To configure the server to listen on a specific unicast address, the notation to specify interfaces has been extended. An interface name can be optionally followed by a slash, followed by the global unicast address on which the server should listen. This will be done in addition to normal link-local binding + listening on ff02::1:2 address. The sample configuration below shows how to listen on 2001:db8::1 (a global address) configured on the eth1 interface. "Dhcp6": { "interfaces-config": { "interfaces": [ "eth1/2001:db8::1" ] }, ... } This configuration will cause the server to listen on eth1 on link-local address, multicast group (ff02::1:2) and 2001:db8::1. It is possible to mix interface names, wildcards and interface name/addresses on the list of interfaces. It is not possible to specify more than one unicast address on a given interface. Care should be taken to specify proper unicast addresses. The server will attempt to bind to those addresses specified, without any additional checks. This approach is selected on purpose, so the software can be used to communicate over uncommon addresses if the administrator so desires.

The essential role of a DHCPv6 server is address assignment. For this, the server has to be configured with at least one subnet and one pool of dynamic addresses to be managed. For example, assume that the server is connected to a network segment that uses the 2001:db8:1::/64 prefix. The Administrator of that network has decided that addresses from range 2001:db8:1::1 to 2001:db8:1::ffff are going to be managed by the Dhcp6 server. Such a configuration can be achieved in the following way: "Dhcp6": { "subnet6": [ { "subnet": "2001:db8:1::/64", "pools": [ { "pool": "2001:db8:1::1-2001:db8:1::ffff" } ], ... } ] } Note that subnet is defined as a simple string, but the pool parameter is actually a list of pools: for this reason, the pool definition is enclosed in square brackets, even though only one range of addresses is specified. Each pool is a structure that contains the parameters that describe a single pool. Currently there is only one parameter, pool, which gives the range of addresses in the pool. Additional parameters will be added in future releases of Kea. It is possible to define more than one pool in a subnet: continuing the previous example, further assume that 2001:db8:1:0:5::/80 should also be managed by the server. It could be written as 2001:db8:1:0:5:: to 2001:db8:1::5:ffff:ffff:ffff, but typing so many 'f's is cumbersome. It can be expressed more simply as 2001:db8:1:0:5::/80. Both formats are supported by Dhcp6 and can be mixed in the pool list. For example, one could define the following pools: "Dhcp6": { "subnet6": [ { "subnet": "2001:db8:1::/64", "pools": [ { "pool": "2001:db8:1::1-2001:db8:1::ffff" }, { "pool": "2001:db8:1:05::/80" } ], ... } ] } The number of pools is not limited, but for performance reasons it is recommended to use as few as possible. The server may be configured to serve more than one subnet. To add a second subnet, use a command similar to the following: "Dhcp6": { "subnet6": [ { "subnet": "2001:db8:1::/64", "pools": [ { "pool": "2001:db8:1::1-2001:db8:1::ffff" } ] }, { "subnet": "2001:db8:2::/64", "pools": [ { "pool": "2001:db8:2::/64" } ] }, ... ] } In this example, we allow the server to dynamically assign all addresses available in the whole subnet. Although rather wasteful, it is certainly a valid configuration to dedicate the whole /64 subnet for that purpose. Note that the Kea server does not preallocate the leases, so there is no danger in using gigantic address pools. When configuring a DHCPv6 server using prefix/length notation, please pay attention to the boundary values. When specifying that the server can use a given pool, it will also be able to allocate the first (typically network address) address from that pool. For example for pool 2001:db8:2::/64 the 2001:db8:2:: address may be assigned as well. If you want to avoid this, use the "min-max" notation.

Subnets may also be configured to delegate prefixes, as defined in RFC 3633. A subnet may have one or more prefix delegation pools. Each pool has a prefixed address, which is specified as a prefix and a prefix length, as well as a delegated prefix length. delegated-len must not be shorter (that is it must be numerically greater or equal) than prefix-len. If both delegated-len and prefix-len are equal, the server will be able to delegate only one prefix. The delegated prefix does not have to match the subnet prefix. Below is a sample subnet configuration which enables prefix delegation for the subnet: "Dhcp6": { "subnet6": [ { "subnet": "2001:d8b:1::/64", "pd-pools": [ { "prefix": "3000:1::", "prefix-len": 64, "delegated-len": 96 } ] } ], ... }

One of the major features of a DHCPv6 server is to provide configuration options to clients. Although there are several options that require special behavior, most options are sent by the server only if the client explicitly requests them. The following example shows how to configure DNS servers, which is one of the most frequently used options. Numbers in the first column are added for easier reference and will not appear on screen. Options specified in this way are considered global and apply to all configured subnets. "Dhcp6": { "option-data": [ { "name": "dns-servers", "code": 23, "space": "dhcp6", "csv-format": true, "data": "2001:db8::cafe, 2001:db8::babe" }, ... ] } The option-data> line creates a new entry in the option-data table. This table contains information on all global options that the server is supposed to configure in all subnets. The name line specifies the option name. (For a complete list of currently supported names, see .) The next line specifies the option code, which must match one of the values from that list. The line beginning with space specifies the option space, which must always be set to "dhcp6" as these are standard DHCPv6 options. For other name spaces, including custom option spaces, see . The next line specifies the format in which the data will be entered: use of CSV (comma separated values) is recommended. The data line gives the actual value to be sent to clients. Data is specified as normal text, with values separated by commas if more than one value is allowed. Options can also be configured as hexadecimal values. If "csv-format" is set to false, the option data must be specified as a string of hexadecimal numbers. The following commands configure the DNS-SERVERS option for all subnets with the following addresses: 2001:db8:1::cafe and 2001:db8:1::babe. "Dhcp6": { "option-data": [ { "name": "dns-servers", "code": 23, "space": "dhcp6", "csv-format": false, "data": "2001 0DB8 0001 0000 0000 0000 0000 CAFE 2001 0DB8 0001 0000 0000 0000 0000 BABE" }, ... ] } The value for the setting of the "data" element is split across two lines in this document for clarity: when entering the command, the whole string should be entered on the same line. Care should be taken to use proper encoding when using hexadecimal format as Kea's ability to validate data correctness in hexadecimal is limited. Most of the parameters in the "option-data" structure are optional and can be omitted in some circumstances as discussed in the . It is possible to override options on a per-subnet basis. If clients connected to most of your subnets are expected to get the same values of a given option, you should use global options: you can then override specific values for a small number of subnets. On the other hand, if you use different values in each subnet, it does not make sense to specify global option values (Dhcp6/option-data), rather you should set only subnet-specific values (Dhcp6/subnet[X]/option-data[Y]). The following commands override the global DNS servers option for a particular subnet, setting a single DNS server with address 2001:db8:1::3. "Dhcp6": { "subnet6": [ { "option-data": [ { "name": "dns-servers", "code": 23, "space": "dhcp6", "csv-format": true, "data": "2001:db8:1::3" }, ... ], ... }, ... ], ... } The currently supported standard DHCPv6 options are listed in . The "Name" and "Code" are the values that should be used as a name in the option-data structures. "Type" designates the format of the data: the meanings of the various types is given in . Experimental options (like standard options but with a code which was not assigned by IANA) are listed in . Some options are designated as arrays, which means that more than one value is allowed in such an option. For example the option dns-servers allows the specification of more than one IPv6 address, allowing clients to obtain the addresses of multiple DNS servers. The describes the configuration syntax to create custom option definitions (formats). It is generally not allowed to create custom definitions for standard options, even if the definition being created matches the actual option format defined in the RFCs. There is an exception from this rule for standard options for which Kea does not provide a definition yet. In order to use such options, a server administrator must create a definition as described in in the 'dhcp6' option space. This definition should match the option format described in the relevant RFC but the configuration mechanism would allow any option format as it has no means to validate the format at the moment. NameCodeTypeArray?preference7uint8falsevendor-opts17uint32false --> sip-server-dns21fqdntruesip-server-addr22ipv6-addresstruedns-servers23ipv6-addresstruedomain-search24fqdntruenis-servers27ipv6-addresstruenisp-servers28ipv6-addresstruenis-domain-name29fqdntruenisp-domain-name30fqdntruesntp-servers31ipv6-addresstrueinformation-refresh-time32uint32falsebcmcs-server-dns33fqdntruebcmcs-server-addr34ipv6-addresstruegeoconf-civic36record (uint8, uint16, binary)falseremote-id37record (uint32, binary)falsesubscriber-id38binaryfalseclient-fqdn39record (uint8, fqdn)falsepana-agent40ipv6-addresstruenew-posix-timezone41stringfalsenew-tzdb-timezone42stringfalseero43uint16truelq-query44record (uint8, ipv6-address)falseclient-data45emptyfalseclt-time46uint32falselq-relay-data47record (ipv6-address, binary)falselq-client-link48ipv6-addresstruebootfile-url59stringfalsebootfile-param60binaryfalseclient-arch-type61uint16truenii62record (uint8, uint8, uint8)falseerp-local-domain-name65fqdnfalsersoo66emptyfalseclient-linklayer-addr79binaryfalsedhcp4o6-server-addr88ipv6-addresstrue NameCodeTypeArray?public-key701binaryfalsecertificate702binaryfalsesignature703record (uint8, uint8, binary)falsetimestamp704binaryfalse

It is also possible to define options other than the standard ones. Assume that we want to define a new DHCPv6 option called "foo" which will have code 100 and will convey a single unsigned 32 bit integer value. We can define such an option by using the following commands: "Dhcp6": { "option-def": [ { "name": "foo", "code": 100, "type": "uint32", "array": false, "record-types": "", "space": "dhcp6", "encapsulate": "" }, ... ], ... } The "false" value of the "array" parameter determines that the option does NOT comprise an array of "uint32" values but rather a single value. Two other parameters have been left blank: "record-types" and "encapsulate". The former specifies the comma separated list of option data fields if the option comprises a record of data fields. The "record-fields" value should be non-empty if the "type" is set to "record". Otherwise it must be left blank. The latter parameter specifies the name of the option space being encapsulated by the particular option. If the particular option does not encapsulate any option space it should be left blank. Note that the above set of comments define the format of the new option and do not set its values. The name, code and type parameters are required, all others are optional. The array default value is false. The record-types and encapsulate default values are blank (i.e. ""). The default space is "dhcp6". Once the new option format is defined, its value is set in the same way as for a standard option. For example the following commands set a global value that applies to all subnets. "Dhcp6": { "option-data": [ { "name": "foo", "code": 100, "space": "dhcp6", "csv-format": true, "data": "12345" }, ... ], ... } New options can take more complex forms than simple use of primitives (uint8, string, ipv6-address etc): it is possible to define an option comprising a number of existing primitives. Assume we want to define a new option that will consist of an IPv6 address, followed by an unsigned 16 bit integer, followed by a boolean value, followed by a text string. Such an option could be defined in the following way: "Dhcp6": { "option-def": [ { "name": "bar", "code": 101, "space": "dhcp6", "type": "record", "array": false, "record-types": "ipv6-address, uint16, boolean, string", "encapsulate": "" }, ... ], ... } The "type" is set to "record" to indicate that the option contains multiple values of different types. These types are given as a comma-separated list in the "record-types" field and should be those listed in . The values of the option are set as follows: "Dhcp6": { "option-data": [ { "name": "bar", "space": "dhcp6", "code": 101, "csv-format": true, "data": "2001:db8:1::10, 123, false, Hello World" } ], ... } csv-format is set true to indicate that the data field comprises a command-separated list of values. The values in the "data" must correspond to the types set in the "record-types" field of the option definition. In the general case, boolean values are specified as true or false, without quotes. Some specific boolean parameters may accept also "true", "false", 0, 1, "0" and "1". Future Kea versions will accept all those values for all boolean parameters.

Currently there are two option spaces defined for the DHCPv6 daemon: "dhcp6" (for top level DHCPv6 options) and "vendor-opts-space", which is empty by default, but options can be defined in it. Those options will be carried in the Vendor-specific Information option (code 17). The following examples show how to define an option "foo" with code 1 that consists of an IPv6 address, an unsigned 16 bit integer and a string. The "foo" option is conveyed in a Vendor-specific Information option. This option comprises a single uint32 value that is set to "12345". The sub-option "foo" follows the data field holding this value. "Dhcp6": { "option-def": [ { "name": "foo", "code": 1, "space": "vendor-opts-space", "type": "record", "array": false, "record-types": "ipv6-address, uint16, string", "encapsulate": "" } ], ... } (Note that the option space is set to vendor-opts-space.) Once the option format is defined, the next step is to define actual values for that option: "Dhcp6": { "option-data": [ { "name": "foo", "space": "vendor-opts-space", "data": "2001:db8:1::10, 123, Hello World" }, ... ], ... } We should also define a value (enterprise-number) for the Vendor-specific Information option, that conveys our option "foo". "Dhcp6": { "option-data": [ ..., { "name": "vendor-opts", "data": "12345" } ], ... } Alternatively, the option can be specified using its code. "Dhcp6": { "option-data": [ ..., { "code": 17, "data": "12345" } ], ... }

It is sometimes useful to define completely new option spaces. This is useful if the user wants his new option to convey sub-options that use a separate numbering scheme, for example sub-options with codes 1 and 2. Those option codes conflict with standard DHCPv6 options, so a separate option space must be defined. Note that it is not required to create a new option space when defining sub-options for a standard option because it is created by default if the standard option is meant to convey any sub-options (see ). Assume that we want to have a DHCPv6 option called "container" with code 102 that conveys two sub-options with codes 1 and 2. First we need to define the new sub-options: "Dhcp6": { "option-def": [ { "name": "subopt1", "code": 1, "space": "isc", "type": "ipv6-address", "record-types": "", "array": false, "encapsulate": "" }, { "name": "subopt2", "code": 2, "space": "isc", "type": "string", "record-types": "", "array": false "encapsulate": "" } ], ... } Note that we have defined the options to belong to a new option space (in this case, "isc"). The next step is to define a regular DHCPv6 option and specify that it should include options from the isc option space: "Dhcp6": { "option-def": [ ..., { "name": "container", "code": 102, "space": "dhcp6", "type": "empty", "array": false, "record-types": "", "encapsulate": "isc" } ], ... } The name of the option space in which the sub-options are defined is set in the encapsulate field. The type field is set to empty which limits this option to only carrying data in sub-options. Finally, we can set values for the new options: "Dhcp6": { "option-data": [ { "name": "subopt1", "code": 1, "space": "isc", "data": "2001:db8::abcd" }, } "name": "subopt2", "code": 2, "space": "isc", "data": "Hello world" }, { "name": "container", "code": 102, "space": "dhcp6" } ], ... } Note that it is possible to create an option which carries some data in addition to the sub-options defined in the encapsulated option space. For example, if the "container" option from the previous example was required to carry an uint16 value as well as the sub-options, the "type" value would have to be set to "uint16" in the option definition. (Such an option would then have the following data structure: DHCP header, uint16 value, sub-options.) The value specified with the "data" parameter — which should be a valid integer enclosed in quotes, e.g. "123" — would then be assigned to the uint16 field in the "container" option.

In many cases it is not required to specify all parameters for an option configuration and the default values can be used. However, it is important to understand the implications of not specifying some of them as it may result in configuration errors. The list below explains the behavior of the server when a particular parameter is not explicitly specified: name - the server requires an option name or option code to identify an option. If this parameter is unspecified, the option code must be specified. code - the server requires an option name or option code to identify an option. This parameter may be left unspecified if the name parameter is specified. However, this also requires that the particular option has its definition (it is either a standard option or an administrator created a definition for the option using an 'option-def' structure), as the option definition associates an option with a particular name. It is possible to configure an option for which there is no definition (unspecified option format). Configuration of such options requires the use of option code. space - if the option space is unspecified it will default to 'dhcp6' which is an option space holding DHCPv6 standard options. data - if the option data is unspecified it defaults to an empty value. The empty value is mostly used for the options which have no payload (boolean options), but it is legal to specify empty values for some options which carry variable length data and which spec allows for the length of 0. For such options, the data parameter may be omitted in the configuration. csv-format - if this value is not specified and the definition for the particular option exists, the server will assume that the option data is specified as a list of comma separated values to be assigned to individual fields of the DHCP option. If the definition does not exist for this option, the server will assume that the data parameter contains the option payload in the binary format (represented as a string of hexadecimal digits). Note that not specifying this parameter doesn't imply that it defaults to a fixed value, but the configuration data interpretation also depends on the presence of the option definition. An administrator must be aware if the definition for the particular option exists when this parameter is not specified. It is generally recommended to not specify this parameter only for the options for which the definition exists, e.g. standard options. Setting csv-format to an explicit value will cause the server to strictly check the format of the option data specified.

The DHCPv6 server may receive requests from local (connected to the same subnet as the server) and remote (connecting via relays) clients. As the server may have many subnet configurations defined, it must select an appropriate subnet for a given request. The server can not assume which of the configured subnets are local. In IPv4 it is possible as there is a reasonable expectation that the server will have a (global) IPv4 address configured on the interface, and can use that information to detect whether a subnet is local or not. That assumption is not true in IPv6, the DHCPv6 server must be able to operate while only having link-local addresses. Therefore an optional "interface" parameter is available within a subnet definition to designate that a given subnet is local, i.e. reachable directly over the specified interface. For example the server that is intended to serve a local subnet over eth0 may be configured as follows: "Dhcp6": { "subnet6": [ { "subnet": "2001:db8:beef::/48", "pools": [ { "pool": "2001:db8:beef::/48" } ], "interface": "eth0" } ], ... }

The Rapid Commit option, described in RFC 3315, is supported by the Kea DHCPv6 server. However, support is disabled by default for all subnets. It can be enabled for a particular subnet using the rapid-commit parameter as shown below: "Dhcp6": { "subnet6": [ { "subnet": "2001:db8:beef::/48", "rapid-commit": true, "pools": [ { "pool": "2001:db8:beef::1-2001:db8:beef::10" } ], } ], ... } This setting only affects the subnet for which the rapid-commit is set to true. For clients connected to other subnets, the server will ignore the Rapid Commit option sent by the client and will follow the 4-way exchange procedure, i.e. respond with the Advertise for the Solicit containing Rapid Commit option.

A DHCPv6 server with multiple subnets defined must select the appropriate subnet when it receives a request from a client. For clients connected via relays, two mechanisms are used: The first uses the linkaddr field in the RELAY_FORW message. The name of this field is somewhat misleading in that it does not contain a link-layer address: instead, it holds an address (typically a global address) that is used to identify a link. The DHCPv6 server checks if the address belongs to a defined subnet and, if it does, that subnet is selected for the client's request. The second mechanism is based on interface-id options. While forwarding a client's message, relays may insert an interface-id option into the message that identifies the interface on the relay that received the message. (Some relays allow configuration of that parameter, but it is sometimes hardcoded and may range from the very simple (e.g. "vlan100") to the very cryptic: one example seen on real hardware was "ISAM144|299|ipv6|nt:vp:1:110"). The server can use this information to select the appropriate subnet. The information is also returned to the relay which then knows the interface to use to transmit the response to the client. In order for this to work successfully, the relay interface IDs must be unique within the network and the server configuration must match those values. When configuring the DHCPv6 server, it should be noted that two similarly-named parameters can be configured for a subnet: "interface" defines which local network interface can be used to access a given subnet. "interface-id" specifies the content of the interface-id option used by relays to identify the interface on the relay to which the response packet is sent. The two are mutually exclusive: a subnet cannot be both reachable locally (direct traffic) and via relays (remote traffic). Specifying both is a configuration error and the DHCPv6 server will refuse such a configuration. To specify interface-id with value "vlan123", the following commands can be used: "Dhcp6": { "subnet6": [ { "subnet": "2001:db8:beef::/48", "pools": [ { "pool": "2001:db8:beef::/48" } ], "interface-id": "vlan123" } ], ... }

RFC 6422 defines a mechanism called Relay-Supplied DHCP Options. In certain cases relay agents are the only entities that may have specific information. They can insert options when relaying messages from the client to the server. The server will then do certain checks and copy those options to the response that will be sent to the client. There are certain conditions that must be met for the option to be included. First, the server must not provide the option by itself. In other words, if both relay and server provide an option, the server always takes precedence. Second, the option must be RSOO-enabled. IANA maintains a list of RSOO-enabled options here. However, there may be cases when system administrators want to echo other options. Kea can be instructed to treat other options as RSOO-enabled. For example, to mark options 110, 120 and 130 as RSOO-enabled, the following syntax should be used: "Dhcp6": { "relay-supplied-options": [ "110", "120", "130" ], ... } As of March 2015, only option 65 is RSOO-enabled by IANA. This option will always be treated as such and there's no need to explicitly mark it. Also, when enabling standard options, it is possible to use their names, rather than option code, e.g. (e.g. use dns-servers instead of 23). See for the names. In certain cases it could also work for custom options, but due to the nature of the parser code this may be unreliable and should be avoided.

The DHCPv6 server includes support for client classification. At the current time the capabilities of the classification process are limited but it is expected they will be expanded in the future. For a deeper discussion of the classification process see . In certain cases it is useful to differentiate between different types of clients and treat them accordingly. It is envisaged that client classification will be used for changing the behavior of almost any part of the DHCP message processing, including the assignment of leases from different pools, the assignment of different options (or different values of the same options) etc. In the current release of the software however, there are only two mechanisms that take advantage of client classification: subnet selection and assignment of different options. Kea can be instructed to limit access to given subnets based on class information. This is particularly useful for cases where two types of devices share the same link and are expected to be served from two different subnets. The primary use case for such a scenario is cable networks. There are two classes of devices: the cable modem itself, which should be handed a lease from subnet A and all other devices behind the modem that should get a lease from subnet B. That segregation is essential to prevent overly curious users from playing with their cable modems. For details on how to set up class restrictions on subnets, see . The process of doing classification is conducted in three steps. The first step is to assess an incoming packet and assign it to zero or more classes. The second step is to choose a subnet, possibly based on the class information. The third step is to assign options again possibly based on the class information. There are two methods of doing classification. The first is automatic and relies on examining the values in the vendor class options. Information from these options is extracted and a class name is constructed from it and added to the class list for the packet. The second allows you to specify an expression that is evaluated for each packet. If the result is true the packet is a member of the class. Care should be taken with client classification as it is easy for clients that do not meet class criteria to be denied any service altogether.

The following example shows how to configure a class using an expression and a subnet making use of that class. This configuration defines the class named "Client_enterprise". It is comprised of all clients who's client identifiers start with the given hex string (which would indicate a DUID based on an enterprise id of 0xAABBCCDD). They will be given an address from 2001:db8:1::0 to 2001:db8:1::FFFF and 2001:db8:0::1 and 2001:db8:2::1 for their domain name servers. For a deeper discussion of the classification process see . "Dhcp6": { "client-classes": [ { "name": "Client_enterprise", "test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'", "option-data": [ { "name": "dns-servers", "code": 23, "space": "dhcp6", "csv-format": true, "data": "2001:db8:0::1, 2001:db8:2::1" } ] }, ... ], "subnet6": [ { "subnet": "2001:db8:1::/64", "pools": [ { "pool": "2001:db8:1::-2001:db8:1::ffff" } ], "client-class": "Client_enterprise" } ], ... } This example shows a configuration using an automatically generated "VENDOR_CLASS_" class. The Administrator of the network has decided that addresses from range 2001:db8:1::1 to 2001:db8:1::ffff are going to be managed by the Dhcp6 server and only clients belonging to the eRouter1.0 client class are allowed to use that pool. "Dhcp6": { "subnet6": [ { "subnet": "2001:db8:1::/64", "pools": [ { "pool": "2001:db8:1::-2001:db8:1::ffff" } ], "client-class": "VENDOR_CLASS_eRouter1.0" } ], ... }

As mentioned earlier, kea-dhcp6 can be configured to generate requests to the DHCP-DDNS server (referred to here as "D2") to update DNS entries. These requests are known as NameChangeRequests or NCRs. Each NCR contains the following information: Whether it is a request to add (update) or remove DNS entries Whether the change requests forward DNS updates (AAAA records), reverse DNS updates (PTR records), or both. The FQDN, lease address, and DHCID The parameters controlling the generation of NCRs for submission to D2 are contained in the "dhcp-ddns" section of kea-dhcp6 configuration. The mandatory parameters for the DHCP DDNS configuration are enable-updates which is unconditionally required, and qualifying-suffix which has no default value and is required when enable-updates is set to true. The two (disabled and enabled) minimal DHCP DDNS configurations are: "Dhcp6": { "dhcp-ddns": { "enable-updates": false }, ... } and for example: "Dhcp6": { "dhcp-ddns": { "enable-updates": true, "qualifying-suffix": "example." }, ... } The default values for the "dhcp-ddns" section are as follows: "server-ip": "127.0.0.1" "server-port": 53001 "sender-ip": "" "sender-port": 0 "max-queue-size": 1024 "ncr-protocol": "UDP" "ncr-format": "JSON" "override-no-update": false "override-client-update": false "replace-client-name": "never" "generated-prefix": "myhost"

In order for NCRs to reach the D2 server, kea-dhcp6 must be able to communicate with it. kea-dhcp6 uses the following configuration parameters to control how it communications with D2: enable-updates - determines whether or not kea-dhcp6 will generate NCRs. If missing, this value is assumed to be false hence DDNS updates are disabled. To enable DDNS updates set this value to true: server-ip - IP address on which D2 listens for requests. The default is the local loopback interface at address 127.0.0.1. You may specify either an IPv4 or IPv6 address. server-port - port on which D2 listens for requests. The default value is 53001. sender-ip - IP address which kea-dhcp6 should use to send requests to D2. The default value is blank which instructs kea-dhcp6 to select a suitable address. sender-port - port which kea-dhcp6 should use to send requests to D2. The default value of 0 instructs kea-dhcp6 to select a suitable port. max-queue-size - maximum number of requests allowed to queue waiting to be sent to D2. This value guards against requests accumulating uncontrollably if they are being generated faster than they can be delivered. If the number of requests queued for transmission reaches this value, DDNS updating will be turned off until the queue backlog has been sufficiently reduced. The intent is to allow kea-dhcp6 to continue lease operations. The default value is 1024. ncr-protocol - Socket protocol use when sending requests to D2. Currently only UDP is supported. TCP may be available in an upcoming release. ncr-format - Packet format to use when sending requests to D2. Currently only JSON format is supported. Other formats may be available in future releases. By default, kea-dhcp-ddns is assumed to running on the same machine as kea-dhcp6, and all of the default values mentioned above should be sufficient. If, however, D2 has been configured to listen on a different address or port, these values must altered accordingly. For example, if D2 has been configured to listen on 2001:db8::5 port 900, the following commands would be required: "Dhcp6": { "dhcp-ddns": { "server-ip": "2001:db8::5", "server-port": 900, ... }, ... }

kea-dhcp6 follows the behavior prescribed for DHCP servers in RFC 4704. It is important to keep in mind that kea-dhcp6 provides the initial decision making of when and what to update and forwards that information to D2 in the form of NCRs. Carrying out the actual DNS updates and dealing with such things as conflict resolution are the purview of D2 (). This section describes when kea-dhcp6 will generate NCRs and the configuration parameters that can be used to influence this decision. It assumes that the "enable-updates" parameter is true. Currently the interface between kea-dhcp6 and D2 only supports requests which update DNS entries for a single IP address. If a lease grants more than one address, kea-dhcp6 will create the DDNS update request for only the first of these addresses. Support for multiple address mappings may be provided in a future release. In general, kea-dhcp6 will generate DDNS update requests when: A new lease is granted in response to a REQUEST An existing lease is renewed but the FQDN associated with it has changed. An existing lease is released in response to a RELEASE In the second case, lease renewal, two DDNS requests will be issued: one request to remove entries for the previous FQDN and a second request to add entries for the new FQDN. In the last case, a lease release, a single DDNS request to remove its entries will be made. The decision making involved when granting a new lease is more involved and is discussed next. kea-dhcp6 will generate a DDNS update request only if the REQUEST contains the FQDN option (code 39). By default kea-dhcp6 will respect the FQDN N and S flags specified by the client as shown in the following table: Client Flags:N-S Client Intent Server Response Server Flags:N-S-O 0-0 Client wants to do forward updates, server should do reverse updates Server generates reverse-only request 1-0-0 0-1 Server should do both forward and reverse updates Server generates request to update both directions 0-1-0 1-0 Client wants no updates done Server does not generate a request 1-0-0 The first row in the table above represents "client delegation". Here the DHCP client states that it intends to do the forward DNS updates and the server should do the reverse updates. By default, kea-dhcp6 will honor the client's wishes and generate a DDNS request to D2 to update only reverse DNS data. The parameter, "override-client-update", can be used to instruct the server to override client delegation requests. When this parameter is true, kea-dhcp6 will disregard requests for client delegation and generate a DDNS request to update both forward and reverse DNS data. In this case, the N-S-O flags in the server's response to the client will be 0-1-1 respectively. (Note that the flag combination N=1, S=1 is prohibited according to RFC 4702. If such a combination is received from the client, the packet will be dropped by kea-dhcp6.) To override client delegation, issue the following commands: "Dhcp6": { "dhcp-ddns": { "override-client-update": true, ... }, ... } The third row in the table above describes the case in which the client requests that no DNS updates be done. The parameter, "override-no-update", can be used to instruct the server to disregard the client's wishes. When this parameter is true, kea-dhcp6 will generate DDNS update requests to kea-dhcp-ddns even if the client requests no updates be done. The N-S-O flags in the server's response to the client will be 0-1-1. To override client delegation, issue the following commands: "Dhcp6": { "dhcp-ddns": { "override-no-update": true, ... }, ... }

Each NameChangeRequest must of course include the fully qualified domain name whose DNS entries are to be affected. kea-dhcp6 can be configured to supply a portion or all of that name based upon what it receives from the client. The default rules for constructing the FQDN that will be used for DNS entries are: If the DHCPREQUEST contains the client FQDN option, the candidate name is taken from there. If the candidate name is a partial (i.e. unqualified) name then add a configurable suffix to the name and use the result as the FQDN. If the candidate name provided is empty, generate a FQDN using a configurable prefix and suffix. If the client provided neither option, then no DNS action will be taken. These rules can amended by setting the replace-client-name parameter which provides the following modes of behavior: never - Use the name the client sent. If the client sent no name, do not generate one. This is the default mode. always - Replace the name the client sent. If the client sent no name, generate one for the client. when-present - Replace the name the client sent. If the client sent no name, do not generate one. when-not-present - Use the name the client sent. If the client sent no name, generate one for the client. Note that formerly, this parameter was a boolean and permitted only values of true and false. Boolean values will still be accepted but may eventually be deprecated. A value of true equates to when-present, false equates to never. For example, To instruct kea-dhcp6 to always generate the FQDN for a client, set the parameter replace-client-name to always as follows: "Dhcp6": { "dhcp-ddns": { "replace-client-name": "always", ... }, ... } The prefix used when generating a FQDN is specified by the "generated-prefix" parameter. The default value is "myhost". To alter its value, simply set it to the desired string: "Dhcp6": { "dhcp-ddns": { "generated-prefix": "another.host", ... }, ... } The suffix used when generating a FQDN or when qualifying a partial name is specified by the qualifying-suffix parameter. This parameter has no default value, thus it is mandatory when DDNS updates are enabled. To set its value simply set it to the desired string: "Dhcp6": { "dhcp-ddns": { "qualifying-suffix": "foo.example.org", ... }, ... }

When qualifying a partial name, kea-dhcp6 will construct a name with the format: [candidate-name].[qualifying-suffix]. where candidate-name is the partial name supplied in the REQUEST. For example, if FQDN domain name value was "some-computer" and qualifying-suffix "example.com", the generated FQDN would be: some-computer.example.com. When generating the entire name, kea-dhcp6 will construct name of the format: [generated-prefix]-[address-text].[qualifying-suffix]. where address-text is simply the lease IP address converted to a hyphenated string. For example, if lease address is 3001:1::70E, the qualifying suffix "example.com", and the default value is used for generated-prefix, the generated FQDN would be: myhost-3001-1--70E.example.com.

There are many cases where it is useful to provide a configuration on a per host basis. The most obvious one is to reserve specific, static IPv6 address or/and prefix for exclusive use by a given client (host) ‐ returning client will get the same address or/and prefix every time and other clients will never get that address. Note that there may be cases when the new reservation has been made for the client for the address or prefix being currently in use by another client. We call this situation a "conflict". The conflicts get resolved automatically over time as described in the subsequent sections. Once conflict is resolved, the client will keep receiving the reserved configuration when it renews. Another example when the host reservations are applicable is when a host that has specific requirements, e.g. a printer that needs additional DHCP options or a cable modem needs specific parameters. Yet another possible use case for host reservation is to define unique names for hosts. Although not all of the presented use cases are implemented yet, Kea software will support them in the near future. Hosts reservations are defined as parameters for each subnet. Each host can be identified by either DUID or its hardware/MAC address. See for details. There is an optional reservations array in the Subnet6 structure. Each element in that array is a structure, that holds information about a single host. In particular, such a structure has to have an identifier that uniquely identifies a host. In DHCPv6 context, such an identifier is a hardware (MAC) address or a DUID. Also, either one or more addresses or prefixes should be specified. It is possible to specify a hostname. Additional capabilities are planned. The following example shows how to reserve addresses and prefixes for specific hosts: "subnet6": [ { "subnet": "2001:db8:1::/48", "pools": [ { "pool": "2001:db8:1::/80" } ], "pd-pools": [ { "prefix": "2001:db8:1:8000::", "prefix-len": 56, "delegated-len": 64 } ], "reservations": [ { "duid": "01:02:03:04:05:0A:0B:0C:0D:0E", "ip-addresses": [ "2001:db8:1::100" ] }, { "hw-address": "00:01:02:03:04:05", "ip-addresses": [ "2001:db8:1::101" ] }, { "duid": "01:02:03:04:05:06:07:08:09:0A", "ip-addresses": [ "2001:db8:1::102" ], "prefixes": [ "2001:db8:2:abcd::/64" ], "hostname": "foo.example.com" } ] } ] This example makes 3 reservations. The first one reserves 2001:db8:1::100 address for the client using DUID 01:02:03:04:05:0A:0B:0C:0D:0E. The second one also reserves an address, but does so using MAC or hardware address, rather than DUID. The third example is most advanced. It reserves an address, a prefix and a hostname at the same time. Note that DHCPv6 allows for a single client to lease multiple addresses and multiple prefixes at the same time. In the upcoming Kea releases, it will be possible to have multiple addresses and prefixes reserved for a single host. Therefore ip-addresses and prefixes are plural and are actually arrays. As of 0.9.1 having more than one IPv6 address or prefix is only partially supported. Making a reservation for a mobile host that may visit multiple subnets requires a separate host definition in each subnet it is expected to visit. It is not allowed to define multiple host definitions with the same hardware address in a single subnet. It is a valid configuration, if such definitions are specified in different subnets, though. The reservation for a given host should include only one identifier, either DUID or hardware address. Defining both for the same host is considered a configuration error, but as of 0.9.1 beta, it is not rejected. Adding host reservation incurs a performance penalty. In principle, when the server that does not support host reservation responds to a query, it needs to check whether there is a lease for a given address being considered for allocation or renewal. The server that also supports host reservation, has to perform additional checks: not only if the address is currently used (if there is a lease for it), but also whether the address could be used by someone else (if there is a reservation for it). That additional check incurs performance penalty.

In a typical scenario there's an IPv6 subnet defined with a certain part of it dedicated for dynamic address allocation by the DHCPv6 server. There may be an additional address space defined for prefix delegation. Those dynamic parts are referred to as dynamic pools, address and prefix pools or simply pools. In principle, the host reservation can reserve any address or prefix that belongs to the subnet. The reservations that specify an address that belongs to configured pools are called in-pool reservations. In contrast, those that do not belong to dynamic pools are called out-of-pool reservations. There is no formal difference in the reservation syntax. As of 0.9.1, both reservation types are handled uniformly. However, upcoming releases may offer improved performance if there are only out-of-pool reservations as the server will be able to skip reservation checks when dealing with existing leases. Therefore, system administrators are encouraged to use out-of-pool reservations, if possible.

As reservations and lease information are stored in different places, conflicts may arise. Consider the following series of events. The server has configured the dynamic pool of addresses from the range of 2001:db8::10 to 2001:db8::20. Host A requests an address and gets 2001:db8::10. Now the system administrator decides to reserve an address for host B. He decides to reserve 2001:db8::10 for that purpose. In general, reserving an address that is currently assigned to someone else is not recommended, but there are valid use cases where such an operation is warranted. The server now has a conflict to resolve. Let's analyze the situation here. If host B boots up and request an address, the server is not able to assign the reserved address 2001:db8::10. A naive approach would to be immediately remove the lease for host A and create a new one for host B. That would not solve the problem, though, because as soon as host B get the address, it will detect that the address is already in use by someone else (host A) and would send Decline. Therefore in this situation, the server has to temporarily assign a different address from the dynamic pool (not matching what has been reserved) to host B. When the host A renews its address, the server will discover that the address being renewed is now reserved for someone else (host B). Therefore the server will remove the lease for 2001:db8::10 and select a new address and will create a new lease for it. It will send two addresses in its response: the old address with lifetimes set to 0 to explicitly indicate that it is no longer valid and a new address with non-zero lifetimes. When the host B renews its temporarily assigned address, the server will detect that the existing lease does not match reservation, so it will release the current address host B has and will create a new lease matching the reservation. Similar as before, the server will send two addresses: the temporarily assigned one with zeroed lifetimes, and the new one that matches reservation with proper lifetimes set. This recovery will succeed, even if other hosts will attempt to get the reserved address. Had the host C requested address 2001:db8::10 after the reservation was made, the server will propose a different address. This recovery mechanism allows the server to fully recover from a case where reservations conflict with existing leases. This procedure takes time and will roughly take as long as renew-timer value specified. The best way to avoid such recovery is to not define new reservations that conflict with existing leases. Another recommendation is to use out-of-pool reservations. If the reserved address does not belong to a pool, there is no way that other clients could get this address (note that having multiple reservations for the same address is not allowed).

When the reservation for the client includes the hostname , the server will assign this hostname to the client and send it back in the Client FQDN, if the client sent the FQDN option to the server. The reserved hostname always takes precedence over the hostname supplied by the client (via the FQDN option) or the autogenerated (from the IPv6 address) hostname. The server qualifies the reserved hostname with the value of the qualifying-suffix parameter. For example, the following subnet configuration: "subnet6": [ { "subnet": "2001:db8:1::/48", "pools": [ { "pool": "2001:db8:1::/80" } ], "reservations": [ { "duid": "01:02:03:04:05:0A:0B:0C:0D:0E", "ip-addresses": [ "2001:db8:1::100" ] "hostname": "alice-laptop" } ] } ], "dhcp-ddns": { "enable-updates": true, "qualifying-suffix": "example.isc.org." } will result in assigning the "alice-laptop.example.isc.org." hostname to the client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E". If the qualifying-suffix is not specified, the default (empty) value will be used, and in this case the value specified as a hostname will be treated as fully qualified name. Thus, by leaving the qualifying-suffix empty it is possible to qualify hostnames for the different clients with different domain names: "subnet6": [ { "subnet": "2001:db8:1::/48", "pools": [ { "pool": "2001:db8:1::/80" } ], "reservations": [ { "duid": "01:02:03:04:05:0A:0B:0C:0D:0E", "ip-addresses": [ "2001:db8:1::100" ] "hostname": "mark-desktop.example.org." } ] } ], "dhcp-ddns": { "enable-updates": true, } will result in assigning the "mark-desktop.example.org." hostname to the client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E".

Currently it is not possible to specify options in host reservation. Such a feature will be added in the upcoming Kea releases.

reservation-mode in the DHCPv6 server is implemented in Kea 0.9.1 beta, but has not been tested and is considered experimental. Host reservation capability introduces additional restrictions for the allocation engine during lease selection and renewal. In particular, three major checks are necessary. First, when selecting a new lease, it is not sufficient for a candidate lease to be not used by another DHCP client. It also must not be reserved for another client. Second, when renewing a lease, additional check must be performed whether the address being renewed is not reserved for another client. Finally, when a host renews an address or a prefix, the server has to check whether there's a reservation for this host, so the existing (dynamically allocated) address should be revoked and the reserved one be used instead. Some of those checks may be unnecessary in certain deployments. Not performing them may improve performance. The Kea server provides the reservation-mode configuration parameter to select the types of reservations allowed for the particular subnet. Each reservation type has different constraints for the checks to be performed by the server when allocating or renewing a lease for the client. Allowed values are: all - enables all host reservation types. This is the default value. This setting is the safest and the most flexible. It allows in-pool and out-of-pool reservations. As all checks are conducted, it is also the slowest. out-of-pool - allows only out of pool host reservations. With this setting in place, the server may assume that all host reservations are for addresses that do not belong to the dynamic pool. Therefore it can skip the reservation checks when dealing with in-pool addresses, thus improving performance. Do not use this mode if any of your reservations use in-pool address. Caution is advised when using this setting. Kea 0.9.1 does not sanity check the reservations against reservation-mode. Misconfiguration may cause problems. disabled - host reservation support is disabled. As there are no reservations, the server will skip all checks. Any reservations defined will be completely ignored. As the checks are skipped, the server may operate faster in this mode. An example configuration that disables reservation looks like follows: "Dhcp6": { "subnet6": [ { "subnet": "2001:db8:1::/64", "reservation-mode": "disabled", ... } ] }

The DHCPv6 protocol uses a "server identifier" (also known as a DUID) for clients to be able to discriminate between several servers present on the same link. RFC 3315 defines three DUID types: DUID-LLT, DUID-EN and DUID-LL. RFC 6355 also defines DUID-UUID. Future specifications may introduce new DUID types. Kea DHCPv6 server generates a server identifier once, upon the first startup, and stores it in a file. This identifier isn't modified across restarts of the server (stable identifier). Kea follows recommendation from RFC 3315 to use DUID-LLT as a default server identifier. However, we have received reports that some deployments require different DUID types, and there is a need to administratively select both DUID type and/or its contents. The server identifier can be configured using parameters within the server-id map element in the global scope of the Kea configuration file. The following example demonstrates how to select DUID-EN as a server identifier: "Dhcp6": { "server-id": { "type": "EN" }, ... } Currently supported values for type parameter are: "LLT", "EN" and "LL", for DUID-LLT, DUID-EN and DUID-LL respectively. When a new DUID type is selected the server will generate its value and replace any existing DUID in the file. The server will use the new server identifier in all future interactions with the clients. If the new server identifier is created after some clients have obtained their leases, the clients using old identifier will not be able to renew the leases. The server will ignore messages containing the old server identifier. Clients will continue sending Renew until they transition to rebinding state. In this state they will start sending Rebind messages to multicast address and without a server identifier. The server will respond to the Rebind messages with a new server identifier and the clients will associate the new server identifier with their leases. Although the clients will be able to keep their leases and will eventually learn the new server identifier, this will be at the cost of increased number of renewals and multicast traffic due to a need to rebind. Therefore it is recommended to avoid modification of the server identifier type and its value if the server has already assigned leases and these leases are still valid. There are cases when an administrator needs to explicitly specify a DUID value, rather than allow the server to generate it. The following example demonstrates how to explicitly set all components of a DUID-LLT. "Dhcp6": { "server-id": { "type": "LLT", "htype": 8, "identifier": "A65DC7410F05", "time": 2518920166 }, ... } where: htype is a 16-bit unsigned value specifying hardware type, identifier is a link layer address, specified as a string of hexadecimal digits, time is a 32-bit unsigned time value. The hexadecimal representation of the DUID generated as a result of the configuration specified above will be: 00:01:00:08:96:23:AB:E6:A6:5D:C7:41:0F:05 ------------------------------------------ |type|htype| time | identifier | It is allowed to use special value of 0 for "htype" and "time", which indicates that the server should use ANY value for these components. If the server already uses a DUID-LLT it will use the values from this DUID. If the server uses a DUID of a different type or doesn't use any DUID yet, it will generate these values. Similarly, if the "identifier" is assigned an empty string, the value of the identifier will be generated. Omitting any of these parameters is equivalent to setting them to those special values. For example, the following configuration: "Dhcp6": { "server-id": { "type": "LLT", "htype": 0, "identifier": "", "time": 2518920166 }, ... } indicates that the server should use ANY link layer address and hardware type. If the server is already using DUID-LLT it will use link layer address and hardware type from the existing DUID. If the server is not using any DUID yet, it will use link layer address and hardware type from one of the available network interfaces. The server will use explicit value of time. If it is different than a time value present in the currently used DUID, this value will be replaced. This will effectively cause modification of the current server identifier. The following example demonstrates an explicit configuration of a DUID-EN: "Dhcp6": { "server-id": { "type": "EN", "enterprise-id": 2495, "identifier": "87ABEF7A5BB545" }, ... } where: enterprise-id is a 32-bit unsigned value holding enterprise number, identifier is a variable length identifier within DUID-EN. The hexadecimal representation of the DUID-EN created according to the configuration above is: 00:02:00:00:09:BF:87:AB:EF:7A:5B:B5:45 -------------------------------------- |type| ent-id | identifier | As in the case of the DUID-LLT, special values can be used for the configuration of the DUID-EN. If the "enterprise-id" is 0, the server will use a value from the existing DUID-EN. If the server is not using any DUID or the existing DUID has a different type, the ISC enterprise id will be used. When an empty string is used for "identifier", the identifier from the existing DUID-EN will be used. If the server is not using any DUID-EN the new 6-bytes long identifier will be generated. DUID-LL is configured in the same way as DUID-LLT with an exception that the time parameter has no effect for DUID-LL, because this DUID type only comprises a hardware type and link layer address. The following example demonstrates how to configure DUID-LL: "Dhcp6": { "server-id": { "type": "LL", "htype": 8, "identifier": "A65DC7410F05" }, ... } which will result in the following server identifier: 00:03:00:08:A6:5D:C7:41:0F:05 ------------------------------ |type|htype| identifier | Server stores a generated server identifier in the following location: [kea-install-dir]/var/kea/kea-dhcp6-serverid . In some uncommon deployments where no stable storage is available, it is desired to configure the server to not try to store the server identifier on the stable storage. It is controlled by the value of persist boolean parameter: "Dhcp6": { "server-id": { "type": "EN", "enterprise-id": 2495, "identifier": "87ABEF7A5BB545", "persist": false }, ... } The default value of the "persist" parameter is true which configures the server to store the server identifier on a disk. In the example above, the server is configured to not store the generated server identifier on a disk. But, if the server identifier is not modified in the configuration the same value will be used after server restart, because entire server identifier is explicitly specified in a configuration.

Typically DHCPv6 is used to assign both addresses and options. These assignments (leases) have state that changes over time, hence their name, stateful. DHCPv6 also supports a stateless mode, where clients request configuration options only. This mode is considered lightweight from the server perspective, as it does not require any state tracking; hence its name. The Kea server supports stateless mode. Clients can send Information-Request messages and the server will send back answers with the requested options (providing the options are available in the server configuration). The server will attempt to use per-subnet options first. If that fails - for whatever reason - it will then try to provide options defined in the global scope. Stateless and stateful mode can be used together. No special configuration directives are required to handle this. Simply use the configuration for stateful clients and the stateless clients will get just options they requested. This usage of global options allows for an interesting case. It is possible to run a server that provides just options and no addresses or prefixes. If the options have the same value in each subnet, the configuration can define required options in the global scope and skip subnet definitions altogether. Here's a simple example of such a configuration: "Dhcp6": { "interfaces-config": { "interfaces": [ "ethX" ] }, "option-data": [ { "name": "dns-servers", "data": "2001:db8::1, 2001:db8::2" } ], "lease-database": { "type": "memfile" } } This very simple configuration will provide DNS server information to all clients in the network, regardless of their location. Note the specification of the memfile lease database: this is required since, as of version 0.9.1, Kea requires a lease database to be specified even if it is not used.

The RFC 7550 has introduced some changes to the DHCPv6 protocol to resolve a few issues with the coexistence of multiple stateful options in the messages sent between the clients and servers. The typical example is when the client, such as a requesting router, requests an allocation of both addresses and prefixes when it performs the 4-way (SARR) exchange with the server. If the server is not configured to allocate any prefixes but it can allocate some addresses, it will respond with the IA_NA(s) containing allocated addresses and the IA_PD(s) containing the NoPrefixAvail status code. If the client can operate without prefixes it may transition to the 'bound' state when it sends Renew/Rebind messages to the server, according to the T1 and T2 times, to extend the lifetimes of the allocated addresses. If the client is still interested in obtaining prefixes from the server it may also include IA_PD in the Renew/Rebind to request allocation of the prefixes. If the server still cannot allocate the prefixes, it will respond with the IA_PD(s) containing NoPrefixAvail status code. However, if the server can now allocate the prefixes it will do so, and send them in the IA_PD(s) to the client. Allocation of leases during the Renew/Rebind was not supported in the RFC 3315 and RFC 3633, and has been introduced in RFC 7550. Kea supports this new behavior and it doesn't provide any configuration mechanisms to disable it. The following are the other behaviors specified in the RFC 7550 supported by the Kea DHCPv6 server: set T1/T2 timers to the same value for all stateful (IA_NA and IA_PD) options to facilitate renewal of all client's leases at the same time (in a single message exchange), NoAddrsAvail and NoPrefixAvail status codes are placed in the IA_NA and IA_PD options in the Advertise message, rather than as the top level options.

The relay has to have an interface connected to the link on which the clients are being configured. Typically the relay has a global IPv6 address configured on the interface that belongs to the subnet from which the server will assign addresses. In the typical case, the server is able to use the IPv6 address inserted by the relay (in the link-addr field in RELAY-FORW message) to select the appropriate subnet. However, that is not always the case. The relay address may not match the subnet in certain deployments. This usually means that there is more than one subnet allocated for a given link. The two most common examples where this is the case are long lasting network renumbering (where both old and new address space is still being used) and a cable network. In a cable network both cable modems and the devices behind them are physically connected to the same link, yet they use distinct addressing. In such case, the DHCPv6 server needs additional information (like the value of interface-id option or IPv6 address inserted in the link-addr field in RELAY-FORW message) to properly select an appropriate subnet. The following example assumes that there is a subnet 2001:db8:1::/64 that is accessible via relay that uses 3000::1 as its IPv6 address. The server will be able to select this subnet for any incoming packets that came from a relay that has an address in 2001:db8:1::/64 subnet. It will also select that subnet for a relay with address 3000::1. "Dhcp6": { "subnet6": [ { "subnet": "2001:db8:1::/64", "pools": [ { "pool": "2001:db8:1::1-2001:db8:1::ffff" } ], "relay": { "ip-address": "3000::1" } } ] }

In certain cases, it is useful to mix relay address information, introduced in with client classification, explained in . One specific example is a cable network, where typically modems get addresses from a different subnet than all devices connected behind them. Let's assume that there is one CMTS (Cable Modem Termination System) with one CM MAC (a physical link that modems are connected to). We want the modems to get addresses from the 3000::/64 subnet, while everything connected behind modems should get addresses from another subnet (2001:db8:1::/64). The CMTS that acts as a relay an uses address 3000::1. The following configuration can serve that configuration: "Dhcp6": { "subnet6": [ { "subnet": "3000::/64", "pools": [ { "pool": "3000::2 - 3000::ffff" } ], "client-class": "VENDOR_CLASS_docsis3.0", "relay": { "ip-address": "3000::1" } }, { "subnet": "2001:db8:1::/64", "pools": [ { "pool": "2001:db8:1::1-2001:db8:1::ffff" } ], "relay": { "ip-address": "3000::1" } } ] }

MAC/hardware addresses are available in DHCPv4 messages from the clients and administrators frequently use that information to perform certain tasks, like per host configuration, address reservation for specific MAC addresses and other. Unfortunately, the DHCPv6 protocol does not provide any completely reliable way to retrieve that information. To mitigate that issue a number of mechanisms have been implemented in Kea that attempt to gather that information. Each of those mechanisms works in certain cases, but may fail in other cases. Whether the mechanism works or not in the particular deployment is somewhat dependent on the network topology and the technologies used. Kea allows for configuration which of the supported methods should be used and in which order. This configuration may be considered a fine tuning of the DHCP deployment. In a typical deployment the default value of "any" is sufficient and there is no need to select specific methods. Changing the value of this parameter is the most useful in cases when an administrator wants to disable certain method, e.g. if the administrator trusts the network infrastructure more than the information provided by the clients themselves, the administrator may prefer information provided by the relays over that provided by the clients. The format of this parameter is as follows: "Dhcp6": { "mac-sources": [ "method1", "method2", "method3", ... ], "subnet6": [ ... ], ... } When not specified, a special value of any is used, which instructs the server to attempt to use all the methods in sequence and use value returned by the first one that succeeds. Supported methods are: any - not an actual method, just a keyword that instructs Kea to try all other methods and use the first one that succeeds. This is the default operation if no mac-sources are defined. raw - In principle, a DHCPv6 server could use raw sockets to receive incoming traffic and extract MAC/hardware address information. This is currently not implemented for DHCPv6 and this value has no effect. duid - DHCPv6 uses DUID identifiers instead of MAC addresses. There are currently four DUID types defined, with two of them (DUID-LLT, which is the default one and DUID-LL) convey MAC address information. Although RFC 3315 forbids it, it is possible to parse those DUIDs and extract necessary information from them. This method is not completely reliable, as clients may use other DUID types, namely DUID-EN or DUID-UUID. ipv6-link-local - Another possible acquisition method comes from the source IPv6 address. In typical usage, clients are sending their packets from IPv6 link-local addresses. There's a good chance that those addresses are based on EUI-64, which contains MAC address. This method is not completely reliable, as clients may use other link-local address types. In particular, privacy extensions, defined in RFC 4941, do not use MAC addresses. Also note that successful extraction requires that the address's u-bit must be set to 1 and its g-bit set to 0, indicating that it is an interface identifier as per RFC 2373, section 2.5.1. client-link-addr-option - One extension defined to alleviate missing MAC issues is client link-layer address option, defined in RFC 6939. This is an option that is inserted by a relay and contains information about client's MAC address. This method requires a relay agent that supports the option and is configured to insert it. This method is useless for directly connected clients. This parameter can also be specified as rfc6939, which is an alias for client-link-addr-option. remote-id - RFC 4649 defines remote-id option that is inserted by a relay agent. Depending on the relay agent configuration, the inserted option may convey client's MAC address information. This parameter can also be specified as rfc4649, which is an alias for remote-id. subscriber-id - Another option that is somewhat similar to the previous one is subscriber-id, defined in RFC 4580. It is, too, inserted by a relay agent that is configured to insert it. This parameter can also be specified as rfc4580, which is an alias for subscriber-id. This method is currently not implemented. docsis-cmts - Yet another possible source of MAC address information are DOCSIS options inserted by a CMTS that acts as a DHCPv6 relay agent in cable networks. This method attempts to extract MAC address information from suboption 1026 (cm mac) of the vendor specific option with vendor-id=4491. This vendor option is extracted from the relay-forward message, not the original client's message. docsis-modem - Yet another possible source of MAC address information are DOCSIS options inserted by the cable modem itself. This method attempts to extract MAC address information from suboption 36 (device id) of the vendor specific option with vendor-id=4491. This vendor option is extracted from the original client's message, not from any relay options.

The DHCPv6 server is configured with a certain pool of addresses that it is expected to hand out to the DHCPv6 clients. It is assumed that the server is authoritative and has complete jurisdiction over those addresses. However, due to various reasons, such as misconfiguration or a faulty client implementation that retains its address beyond the valid lifetime, there may be devices connected that use those addresses without the server's approval or knowledge. Such an unwelcome event can be detected by legitimate clients (using Duplicate Address Detection) and reported to the DHCPv6 server using a DECLINE message. The server will do a sanity check (if the client declining an address really was supposed to use it), then will a conduct clean up operation and confirm it by sending back a REPLY message. Any DNS entries related to that address will be removed, the fact will be logged and hooks will be triggered. After that is done, the address will be marked as declined (which indicates that it is used by an unknown entity and thus not available for assignment to anyone) and a probation time will be set on it. Unless otherwise configured, the probation period lasts 24 hours. After that period, the server will recover the lease, i.e. put it back into the available state. The address will be available for assignment again. It should be noted that if the underlying issue of a misconfigured device is not resolved, the duplicate address scenario will repeat. On the other hand, it provides an opportunity to recover from such an event automatically, without any sysadmin intervention. To configure the decline probation period to a value different than the default, the following syntax can be used: "Dhcp6": { "decline-probation-period": 3600, "subnet6": [ ... ], ... } The parameter is expressed in seconds, so the example above will instruct the server to recycle declined leases after an hour. There are several statistics and hook points associated with the Decline handling procedure. The lease6_decline hook is triggered after the incoming Decline message has been sanitized and the server is about to decline the lease. The declined-addresses statistic is increased after the hook returns (both global and subnet specific variants). Once the probation time elapses, the declined lease is recovered using the standard expired lease reclamation procedure, with several additional steps. In particular, both declined-addresses statistics (global and subnet specific) are decreased. At the same time, reclaimed-declined-addresses statistics (again in two variants, global and subnet specific) are increased. Note about statistics: The server does not decrease assigned-addresses statistics when a DECLINE message is received and processed successfully. While technically a declined address is no longer assigned, the primary usage of the assigned-addresses statistic is to monitor pool utilization. Most people would forget to include declined-addresses in the calculation, and simply do assigned-addresses/total-addresses. This would have a bias towards under-representing pool utilization. As this has a potential for major issues, we decided not to decrease assigned addresses immediately after receiving Decline, but to do it later when we recover the address back to the available pool.

This section describes DHCPv6-specific statistics. For a general overview and usage of statistics, see . The DHCPv6 server supports the following statistics: Statistic Data Type Description pkt6-received integer Number of DHCPv6 packets received. This includes all packets: valid, bogus, corrupted, rejected etc. This statistic is expected to grow rapidly. pkt6-receive-drop integer Number of incoming packets that were dropped. Exact reason for dropping packets is logged, but the most common reasons may be: an unacceptable or not supported packet type, direct responses are forbidden, the server-id sent by the client does not match the server's server-id or the packet is malformed. pkt6-parse-failed integer Number of incoming packets that could not be parsed. A non-zero value of this statistic indicates that the server received a malformed or truncated packet. This may indicate problems in your network, faulty clients, faulty relay agents or server code bug. pkt6-solicit-received integer Number of SOLICIT packets received. This statistic is expected to grow. Its increase means that clients that just booted started their configuration process and their initial packets reached your server. pkt6-advertise-received integer Number of ADVERTISE packets received. Advertise packets are sent by the server and the server is never expected to receive them. A non-zero value of this statistic indicates an error occurring in the network. One likely cause would be a misbehaving relay agent that incorrectly forwards ADVERTISE messages towards the server, rather back to the clients. pkt6-request-received integer Number of REQUEST packets received. This statistic is expected to grow. Its increase means that clients that just booted received the server's response (ADVERTISE), accepted it and are now requesting an address (REQUEST). pkt6-reply-received integer Number of REPLY packets received. This statistic is expected to remain zero at all times, as REPLY packets are sent by the server and the server is never expected to receive them. A non-zero value indicates an error. One likely cause would be a misbehaving relay agent that incorrectly forwards REPLY messages towards the server, rather back to the clients. pkt6-renew-received integer Number of RENEW packets received. This statistic is expected to grow. Its increase means that clients received their addresses and prefixes and are trying to renew them. pkt6-rebind-received integer Number of REBIND packets received. A non-zero value indicates that clients didn't receive responses to their RENEW messages (regular lease renewal mechanism) and are attempting to find any server that is able to take over their leases. It may mean that some server's REPLY messages never reached the clients. pkt6-release-received integer Number of RELEASE packets received. This statistic is expected to grow when a device is being shut down in the network. It indicates that the address or prefix assigned is reported as no longer needed. Note that many devices, especially wireless, do not send RELEASE, because of design choice or due to moving out of range. pkt6-decline-received integer Number of DECLINE packets received. This statistic is expected to remain close to zero. Its increase means that a client leased an address, but discovered that the address is currently used by an unknown device in your network. If this statistic is growing, it may indicate misconfigured server or devices that have statically assigned conflicting addresses. pkt6-infrequest-received integer Number of INFORMATION-REQUEST packets received. This statistic is expected to grow if there are devices that are using stateless DHCPv6. INFORMATION-REQUEST messages are used by clients that request stateless configuration, i.e. options and parameters other than addresses or prefixes. pkt6-unknown-received integer Number of packets received of an unknown type. Non-zero value of this statistic indicates that the server received a packet that it wasn't able to recognize: either with unsupported type or possibly malformed. pkt6-sent integer Number of DHCPv6 packets sent. This statistic is expected to grow every time the server transmits a packet. In general, it should roughly match pkt6-received, as most incoming packets cause the server to respond. There are exceptions (e.g. server receiving a REQUEST with server-id matching other server), so do not worry, if it is lesser than pkt6-received. pkt6-advertise-sent integer Number of ADVERTISE packets sent. This statistic is expected to grow in most cases after a SOLICIT is processed. There are certain uncommon, but valid cases where incoming SOLICIT is dropped, but in general this statistic is expected to be close to pkt6-solicit-received. pkt6-reply-sent integer Number of REPLY packets sent. This statistic is expected to grow in most cases after a SOLICIT (with rapid-commit), REQUEST, RENEW, REBIND, RELEASE, DECLINE or INFORMATION-REQUEST is processed. There are certain cases where there is no response. subnet[id].total-nas integer This statistic shows the total number of NA addresses available for DHCPv6 management for a given subnet. In other words, this is the sum of all addresses in all configured pools. This statistic changes only during configuration changes. Note it does not take into account any addresses that may be reserved due to host reservation. The id is the subnet-id of a given subnet. This statistic is exposed for each subnet separately. This statistic is reset during a reconfiguration event. subnet[id].assigned-nas integer This statistic shows the number of NA addresses in a given subnet that are assigned. This statistic increases every time a new lease is allocated (as a result of receiving a REQUEST message) and is decreased every time a lease is released (a RELEASE message is received) or expires. The id is the subnet-id of a given subnet. This statistic is exposed for each subnet separately. This statistic is reset during a reconfiguration event. subnet[id].total-pds integer This statistic shows the total number of PD prefixes available for DHCPv6 management for a given subnet. In other words, this is the sum of all prefixes in all configured pools. This statistic changes only during configuration changes. Note it does not take into account any prefixes that may be reserved due to host reservation. The id is the subnet-id of a given subnet. This statistic is exposed for each subnet separately. This statistic is reset during a reconfiguration event. subnet[id].assigned-pds integer This statistic shows the number of PD prefixes in a given subnet that are assigned. This statistic increases every time a new lease is allocated (as a result of receiving a REQUEST message) and is decreased every time a lease is released (a RELEASE message is received) or expires. The id is the subnet-id of a given subnet. This statistic is exposed for each subnet separately. This statistic is reset during a reconfiguration event. declined-addresses integer This statistic shows the number of IPv6 addresses that are currently declined. This statistic counts the number of leases currently unavailable. Once a lease is recovered, this statistic will be decreased. Ideally, this statistic should be zero. If this statistic is non-zero (or worse increasing), a network administrator should investigate if there is a misbehaving device in his network. This is a global statistic that covers all subnets. subnet[id].declined-addresses integer This statistic shows the number of IPv6 addresses that are currently declined in a given subnet. This statistic counts the number of leases currently unavailable. Once a lease is recovered, this statistic will be decreased. Ideally, this statistic should be zero. If this statistic is non-zero (or worse increasing), a network administrator should investigate if there is a misbehaving device in his network. The id is the subnet-id of a given subnet. This statistic is exposed for each subnet separately. reclaimed-declined-addresses integer This statistic shows the number of IPv6 addresses that were declined, but have now been recovered. Unlike declined-addresses, this statistic never decreases. It can be used as a long term indicator of how many actual valid Declines were processed and recovered from. This is a global statistic that covers all subnets. subnet[id].reclaimed-declined-addresses integer This statistic shows the number of IPv6 addresses that were declined, but have now been recovered. Unlike declined-addresses, this statistic never decreases. It can be used as a long term indicator of how many actual valid Declines were processed and recovered from. The id is the subnet-id of a given subnet. This statistic is exposed for each subnet separately.

Management API has been introduced in Kea 0.9.2-beta. It allows issuing specific management commands, like statistics retrieval, reconfiguration or shutdown. For more details, see . Currently the only supported communication channel type is UNIX stream socket. By default there are no sockets open. To instruct Kea to open a socket, the following entry in the configuration file can be used: "Dhcp6": { "control-socket": { "socket-type": "unix", "socket-name": "/path/to/the/unix/socket" }, "subnet6": [ ... ], ... } The length of the path specified by the socket-name parameter is restricted by the maximum length for the unix socket name on your operating system, i.e. the size of the sun_path field in the sockaddr_un structure, decreased by 1. This value varies on different operating systems between 91 and 107 characters. The typical values are 107 on Linux and 103 on FreeBSD. Communication over control channel is conducted using JSON structures. See the Control Channel section in the Kea Developer's Guide for more details. DHCPv6 server supports statistic-get, statistic-reset, statistic-remove, statistic-get-all, statistic-reset-all and statistic-remove-all, specified in . It also supports list-commands and shutdown, specified in and , respectively.

The following standards are currently supported: Dynamic Host Configuration Protocol for IPv6, RFC 3315: Supported messages are SOLICIT, ADVERTISE, REQUEST, RELEASE, RENEW, REBIND, INFORMATION-REQUEST, CONFIRM and REPLY. IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6, RFC 3633: Supported options are IA_PD and IA_PREFIX. Also supported is the status code NoPrefixAvail. DNS Configuration options for Dynamic Host Configuration Protocol for IPv6 (DHCPv6), RFC 3646: Supported option is DNS_SERVERS. The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Relay Agent Remote-ID Option, RFC 4649: REMOTE-ID option is supported. The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Client Fully Qualified Domain Name (FQDN) Option, RFC 4704: Supported option is CLIENT_FQDN. Relay-Supplied DHCP Options, RFC 6422: Full functionality is supported: OPTION_RSOO, ability of the server to echo back the options, checks whether an option is RSOO-enabled, ability to mark additional options as RSOO-enabled. Client Link-Layer Address Option in DHCPv6, RFC 6939: Supported option is client link-layer address option. Issues and Recommendations with Multiple Stateful DHCPv6 Options, RFC 7550: All recommendations related to the DHCPv6 server operation are supported.

These are the current limitations and known problems with the DHCPv6 server software. Most of them are reflections of the early stage of development and should be treated as not implemented yet, rather than actual limitations. On-line configuration has some limitations. Adding new subnets or modifying existing ones work, as is removing the last subnet from the list. However, removing non-last (e.g. removing subnet 1,2 or 3 if there are 4 subnets configured) will cause issues. The problem is caused by simplistic subnet-id assignment. The subnets are always numbered, starting from 1. That subnet-id is then used in leases that are stored in the lease database. Removing non-last subnet will cause the configuration information to mismatch data in the lease database. It is possible to manually update subnet-id fields in MySQL or PostgreSQL database, but it is awkward and error prone process. A better reconfiguration support is planned. The server will allocate, renew or rebind a maximum of one lease for a particular IA option (IA_NA or IA_PD) sent by a client. RFC 3315 and RFC 3633 allow for multiple addresses or prefixes to be allocated for a single IA. Temporary addresses are not supported. Duplication report (DECLINE) and client reconfiguration (RECONFIGURE) are not yet supported.