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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 the standard ones will not be able to handle regular DHCPv6 queries. -t file - specifies the configuration file to be tested. Kea-dhcp6 will attempt to load it, and will conduct sanity checks. Note that certain checks are possible only while running the actual server. The actual status is reported with exit code (0 = configuration looks ok, 1 = error encountered). Kea will print out log messages to standard output and error to standard error when testing configuration. -v - prints out the Kea version and exits. -V - prints out the Kea extended version with additional parameters and exits. The listing includes the versions of the libraries dynamically linked to Kea. -W - prints out the Kea configuration report and exits. The report is a copy of the config.report file produced by ./configure: it 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' 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. The server can be stopped using the kill command. When running in a console, the server can be shut down by pressing ctrl-c. It detects the key combination and shuts down gracefully.

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 is as follows: { # DHCPv6 configuration starts on the next line "Dhcp6": { # First we set up global values "valid-lifetime": 4000, "renew-timer": 1000, "rebind-timer": 2000, "preferred-lifetime": 3000, # Next we setup the interfaces to be used by the server. "interfaces-config": { "interfaces": [ "eth0" ] }, # And we specify the type of 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 together with 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 DhcpDdns, 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 also require moving the comma. 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 the 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 for the Dhcp6 definition 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 pools (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" } ] 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 four database backends available: memfile (which is the default backend), MySQL, PostgreSQL and Cassandra.

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 store lease information in a CSV file rather than a database. 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 gives additional, optional, parameters that 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 will perform a lease file cleanup (LFC). This removes 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. An example configuration of the Memfile backend is presented below: "Dhcp6": { "lease-database": { "type": "memfile", "persist": true, "name": "/tmp/kea-leases6.csv", "lfc-interval": 1800 } } This configuration selects the /tmp/kea-leases6.csv as the storage for lease information and enables persistence (writing lease updates to this file). It also configures the backend perform the periodic cleanup of the lease files, executed every 30 minutes. It is important to know how the lease file contents are organized to understand why the periodic lease file cleanup is needed. Every time 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 update the existing client's lease in the file, as it would potentially require rewriting the entire file. Instead, it simply appends the new lease information to the end of the 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 a larger number of lease entries. Lease file cleanup (LFC) 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 the renewals, the smaller the value of 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 it 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 the LFC to complete the cleanup before a new cleanup is triggered. Lease file cleanup is performed by a separate process (in background) to avoid a performance impact on the server process. In order to avoid the conflicts between 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", "postgresql" or "cql", 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 database was created (see , or ). "Dhcp6": { "lease-database": { "name": "database-name" , ... }, ... } If the database is located on a different system to the DHCPv6 server, the database host name must also be specified. (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 use a port different than default, it may be specified as well: "Dhcp4": { "lease-database": { "port" : 12345, ... }, ... } 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. Note that host parameter is used by MySQL and PostgreSQL backends. Cassandra has a concept of contact points that could be used to contact the cluster, instead of a single IP or hostname. It takes a list of comma separated IP addresses. This may be specified as: "Dhcp4": { "lease-database": { "contact-points" : "192.0.2.1,192.0.2.2", ... }, ... } 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.)

Kea is also able to store information about host reservations in the database. The hosts database configuration uses the same syntax as the lease database. In fact, a Kea server opens independent connections for each purpose, be it lease or hosts information. This arrangement gives the most flexibility. Kea can be used to keep leases and host reservations separately, but can also point to the same database. Currently the supported hosts database types are MySQL and PostgreSQL. The Cassandra backend does not support host reservations yet. Please note that usage of hosts storage is optional. A user can define all host reservations in the configuration file. That is the recommended way if the number of reservations is small. However, when the number of reservations grows it's more convenient to use host storage. Please note that both storage methods (configuration file and one of the supported databases) can be used together. If hosts are defined in both places, the definitions from the configuration file are checked first and external storage is checked later, if necessary.

Hosts database configuration is controlled through the Dhcp6/hosts-database parameters. If enabled, the type of the database must be set to "mysql" or "postgresql". Other hosts backends may be added in later version of Kea. "Dhcp6": { "hosts-database": { "type": "mysql", ... }, ... } Next, the name of the database to hold the reservations must be set: this is the name used when the database was created (see for instructions how to setup desired database type). "Dhcp6": { "hosts-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. (Again it should be noted that this configuration may have a severe impact on server performance): "Dhcp6": { "hosts-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": { "hosts-database": { "host" : "", ... }, ... } "Dhcp4": { "hosts-database": { "port" : 12345, ... }, ... } Finally, the credentials of the account under which the server will access the database should be set: "Dhcp6": { "hosts-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.)

In some deployments the database user whose name is specified in the database backend configuration may not have write privileges to the database. This is often required by the policy within a given network to secure the data from being unintentionally modified. In many cases administrators have inventory databases deployed, which contain substantially more information about the hosts than static reservations assigned to them. The inventory database can be used to create a view of a Kea hosts database and such view is often read only. Kea host database backends operate with an implicit configuration to both read from and write to the database. If the database user does not have write access to the host database, the backend will fail to start and the server will refuse to start (or reconfigure). However, if access to a read only host database is required for retrieving reservations for clients and/or assign specific addresses and options, it is possible to explicitly configure Kea to start in "read-only" mode. This is controlled by the readonly boolean parameter as follows: "Dhcp6": { "hosts-database": { "readonly": true, ... }, ... } Setting this parameter to false would configure the database backend to operate in "read-write" mode, which is also a default configuration if the parameter is not specified. The readonly parameter is currently only supported for MySQL and PostgreSQL databases.

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. As for the DHCPv4 server binding to specific addresses and disabling re-detection of interfaces are supported. But dhcp-socket-type is not because DHCPv6 uses UDP/IPv6 sockets only. The following example shows how to disable the interface detection: "Dhcp6": { "interfaces-config": { "interfaces": [ "eth1", "eth3" ], "re-detect": false }, ... }

The subnet identifier is a unique number associated with a particular subnet. In principle, it is used to associate clients' leases with their respective subnets. When a 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, something that may have unexpected consequences. It is planned to implement a mechanism to preserve auto-generated subnet ids in a future version of Kea. However, the only remedy for this issue at present is to manually specify a unique 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 this is to have relays send their traffic to the server directly. To configure the server to listen on a specific unicast address, nn interface name can be optionally followed by a slash, followed by the global unicast address on which the server should listen. The server listens to this address in addition to normal link-local binding and 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" ] }, ... "option-data": [ { "name": "unicast", "data": "2001:db8::1" } ], ... } This configuration will cause the server to listen on eth1 on the link-local address, the multicast group (ff02::1:2) and 2001:db8::1. Usually unicast support is associated with a server unicast option which allows clients to send unicast messages to the server. The example above includes a server unicast option specification which will cause the client to send messages to the specified unicast address. It is possible to mix interface names, wildcards and interface name/addresses in the list of interfaces. It is not possible however 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 the addresses specified without any additional checks. This approach has selected on purpose to allow the software to communicate over uncommon addresses if so desired.

The main 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 pools 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" } ], ... } ] } White space in pool definitions is ignored, so spaces before and after the hyphen are optional. They can be used to improve readability. 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 (prefix) and a prefix length (prefix-len), as well as a delegated prefix length (delegated-len). The delegated length must not be shorter (that is it must be numerically greater or equal) than the prefix length. If both the delegated and prefix lengths 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 } ] } ], ... }

For each delegated prefix the delegating router may choose to exclude a single prefix out of the delegated prefix as specified in the RFC 6603. The requesting router must not assign the excluded prefix to any of its downstream interfaces and it is intended to be used on a link through which the delegating router exchanges DHCPv6 messages with the requesting router. The configuration example below demonstrates how to specify an excluded prefix within a prefix pool definition. The excluded prefix "2001:db8:1:babe:cafe:80::/72" will be sent to a requesting router which includes Prefix Exclude option in the ORO, and which is delegated a prefix from this pool. "Dhcp6": { "subnet6": [ { "subnet": "2001:db8:1::/48", "pd-pools": [ { "prefix": "2001:db8:1:8000::", "prefix-len": 48, "delegated-len": 64, "excluded-prefix": "2001:db8:1:babe:cafe:80::", "excluded-prefix-len": 72 } ] } ] }

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, one of the most frequently used options. 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 following line specifies the format in which the data will be entered: use of CSV (comma separated values) is recommended. Finally, 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 example 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 . Only one of name or code is required, so you don't need to specify both. Space has a default value of "dhcp6", so you can skip this as well if you define a regular (not encapsulated) DHCPv6 option. Finally, csv-format defaults to true, so it too can be skipped, unless you want to specify the option value as hexstring. Therefore the above example can be simplified to: "Dhcp4": { "option-data": [ { "name": "dns-servers", "data": "2001:db8::cafe, 2001:db8::babe" }, ... ] } 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" }, ... ], ... }, ... ], ... } In some cases it is useful to associate some options with an address or prefix pool from which a client is assigned a lease. Pool specific option values override subnet specific and global option values. If the client is assigned multiple leases from different pools, the server will assign options from all pools from which the leases have been obtained. However, if the particular option is specified in multiple pools from which the client obtains the leases, only one instance of this option will be handed out to the client. The server's administrator must not try to prioritize assignment of pool specific options by trying to order pools declarations in the server configuration. Future Kea releases may change the order in which options are assigned from the pools without any notice. The following configuration snippet demonstrates how to specify the DNS servers option, which will be assigned to a client only if the client obtains an address from the given pool: "Dhcp6": { "subnet6": [ { "pools": [ { "pool": "2001:db8:1::100-2001:db8:1::300", "option-data": [ { "name": "dns-servers", "data": "2001:db8:1::10" } ] } ] }, ... ], ... } 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 . When a data field is a string, and that string contains the comma (,; U+002C) character, the comma must be escaped with a reverse solidus character (\; U+005C). This double escape is required, because both the routine splitting CSV data into fields and JSON use the same escape character: a single escape (\,) would make the JSON invalid. For example, the string "EST5EDT4,M3.2.0/02:00,M11.1.0/02:00" would be represented as: "Dhcp6": { "subnet6": [ { "pools": [ { "option-data": [ { "name": "new-posix-timezone", "data": "EST5EDT4\,M3.2.0/02:00\,M11.1.0/02:00" } ] }, ... ], ... }, ... ], ... } 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 yes provide a definition. 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?preference7uint8falseunicast12ipv6-addressfalsevendor-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-param60tupletrueclient-arch-type61uint16truenii62record (uint8, uint8, uint8)falseaftr-name64fqdnfalseerp-local-domain-name65fqdnfalsersoo66emptyfalsepd-exclude67binaryfalseclient-linklayer-addr79binaryfalsedhcp4o6-server-addr88ipv6-addresstrue NameCodeTypeArray?public-key701binaryfalsecertificate702binaryfalsesignature703record (uint8, uint8, binary)falsetimestamp704binaryfalse

It is possible to define options in addition to the standard ones. Assume that we want to define a new DHCPv6 option called "foo" which will have code 100 and which 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-types 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 example only defines the format of the new option, it does not set its value(s). 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. For example, 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 versions of Kea 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 in which options can be defined. 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 their 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 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. This behavior has changed in Kea 1.2. Older versions used additional logic to determine whether the csv-format should be true or false. That is no longer the case.

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 using 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 an Advertise for a Solicit containing a 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. The following example configuration shows how to specify an interface-id with a value of "vlan123". "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 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. 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. Here, 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 whose 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 the addresses of their DNS servers set to 2001:db8:0::1 and 2001:db8:2::1. "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 the 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 this communication: 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 configuration 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 within the purview of D2 itself (). 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 the first case) is more involved. When a new lease is granted, 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, set the following values in the configuration: "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 an 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 have been deprecated and are no longer accepted. If you are currently using booleans, you must replace them with the desired mode name. A value of true maps to "when-present", while false maps 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 in the generation of an 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 an 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.

The support of DHCPv4-over-DHCPv6 transport is described in RFC 7341 and is implemented using cooperating DHCPv4 and DHCPv6 servers. This section is about the configuration of the DHCPv6 side (the DHCPv4 side is described in ). DHCPv4-over-DHCPv6 support is experimental and the details of the inter-process communication can change: both the DHCPv4 and DHCPv6 sides should be running the same version of Kea. There is only one specific parameter for the DHCPv6 side: dhcp4o6-port which specifies the first of the two consecutive ports of the UDP sockets used for the communication between the DHCPv6 and DHCPv4 servers (the DHCPv6 server is bound to ::1 on port and connected to ::1 on port + 1). Two other configuration entries are in general required: unicast traffic support (see ) and DHCP 4o6 server address option (name "dhcp4o6-server-addr", code 88). The following configuration was used during some tests: { # DHCPv6 conf "Dhcp6": { "interfaces-config": { "interfaces": [ "eno33554984/2001:db8:1:1::1" ] }, "lease-database": { "type": "memfile", "name": "leases6" }, "preferred-lifetime": 3000, "valid-lifetime": 4000, "renew-timer": 1000, "rebind-timer": 2000, "subnet6": [ { "subnet": "2001:db8:1:1::/64", "interface": "eno33554984", "pools": [ { "pool": "2001:db8:1:1::1:0/112" } ] } ], "dhcp4o6-port": 6767, "option-data": [ { "name": "dhcp4o6-server-addr", "code": 88, "space": "dhcp6", "csv-format": true, "data": "2001:db8:1:1::1" } ] }, "Logging": { "loggers": [ { "name": "kea-dhcp6", "output_options": [ { "output": "/tmp/kea-dhcp6.log" } ], "severity": "DEBUG", "debuglevel": 0 } ] } } Relayed DHCPv4-QUERY DHCPv6 messages are not yet supported.

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 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. 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, the structure has an identifier that uniquely identifies a host. In the DHCPv6 context, such an identifier is usually a DUID, but can also be a hardware or MAC address. Also, either one or more addresses or prefixes may be specified. It is possible to specify a hostname and DHCPv6 options for a given host. 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": 48, "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", "2001:db8:1::102" ] }, { "duid": "01:02:03:04:05:06:07:08:09:0A", "ip-addresses": [ "2001:db8:1::103" ], "prefixes": [ "2001:db8:2:abcd::/64" ], "hostname": "foo.example.com" } ] } ] This example includes reservations for three different clients. The first reservation is made for the address 2001:db8:1::100 for a client using DUID 01:02:03:04:05:0A:0B:0C:0D:0E. The second reservation is made for two addresses 2001:db8:1::101 and 2001:db8:1::102 for a client using MAC address 00:01:02:03:04:05. Lastly, address 2001:db8:1::103 and prefix 2001:db8:2:abcd::/64 are reserved for a client using DUID 01:02:03:04:05:06:07:08:09:0A. The last reservation also assigns a hostname to this client. Note that DHCPv6 allows for a single client to lease multiple addresses and multiple prefixes at the same time. Therefore ip-addresses and prefixes are plural and are actually arrays. When the client sends multiple IA options (IA_NA or IA_PD), each reserved address or prefix is assigned to an individual IA of the appropriate type. If the number of IAs of specific type is lower than the number of reservations of that type, the number of reserved addresses or prefixes assigned to the client is equal to the number of IA_NAs or IA_PDs sent by the client, i.e. some reserved addresses or prefixes are not assigned. However, they still remain reserved for this client and the server will not assign them to any other client. If the number of IAs of specific type sent by the client is greater than the number of reserved addresses or prefixes, the server will try to assign all reserved addresses or prefixes to the individual IAs and dynamically allocate addresses or prefixes to remaining IAs. If the server cannot assign a reserved address or prefix because it is in use, the server will select the next reserved address or prefix and try to assign it to the client. If the server subsequently finds that there are no more reservations that can be assigned to the client at the moment, the server will try to assign leases dynamically. 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. Multiple host definitions with the same hardware address are valid if each is in a different subnet. 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 1.1.0, it is not rejected. Adding host reservation incurs a performance penalty. In principle, when a 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 (i.e. if there is a lease for it), but also whether the address could be used by someone else (i.e. if there is a reservation for it). That additional check incurs additional overhead.

In a typical scenario there is 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 and 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 separately, 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 address 2001:db8::10 for Host B. 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 a Decline message. 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 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, select a new address and create a new lease for it. It will send two addresses in its response: the old address with lifetime set to 0 to explicitly indicate that it is no longer valid and the new address with a non-zero lifetime. When 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 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.

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, } The above example results in the assignment of the "mark-desktop.example.org." hostname to the client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E".

Kea 1.1.0 introduced the ability to specify options on a per host basis. The options follow the same rules as any other options. These can be standard options (see ), custom options (see ) or vendor specific options (see ). The following example demonstrates how standard options can be defined. "reservations": [ { "duid": "01:02:03:05:06:07:08", "ip-addresses": [ "2001:db8:1::2" ], "option-data": [ { "option-data": [ { "name": "dns-servers", "data": "3000:1::234" }, { "name": "nis-servers", "data": "3000:1::234" } } ] } ] Vendor specific options can be reserved in a similar manner: "reservations": [ { "duid": "aa:bb:cc:dd:ee:ff", "ip-addresses": [ "2001:db8::1" ], "option-data": [ { "name": "vendor-opts", "data": 4491 }, { "name": "tftp-servers", "space": "vendor-4491", "data": "3000:1::234" } ] } ] Options defined on host level have the highest priority. In other words, if there are options defined with the same type on global, subnet, class and host level, the host specific values will be used.

The explains how to configure the server to assign classes to a client based on the content of the options that this client sends to the server. Host reservations mechanisms also allow for the static assignment of classes to clients. The definitions of these classes are placed in the Kea configuration. The following configuration snippet shows how to specify that the client belongs to classes reserved-class1 and reserved-class2. Those classes are associated with specific options being sent to the clients which belong to them. { "client-classes": [ { "name": "reserved-class1", "option-data": [ { "name": "dns-servers", "data": "2001:db8:1::50" } ] }, { "name": "reserved-class2", "option-data": [ { "name": "nis-servers", "data": "2001:db8:1::100" } ] } ], "subnet6": [ { "pools": [ { "pool": "2001:db8:1::/64" } ], "subnet": "2001:db8:1::/48", "reservations": [ { "duid": "01:02:03:04:05:06:07:08", "client-classes": [ "reserved-class1", "reserved-class2" ] } ] } ] } Static class assignments, as shown above, can be used in conjunction with classification using expressions.

It is possible to store host reservations in MySQL or PostgreSQL. See for information on how to configure Kea to use reservations stored in MySQL or PostgreSQL. Kea does not provide any dedicated tools for managing reservations in a database. The Kea wiki provides detailed information and examples of how reservations can be inserted into the database. In Kea 1.1.0 maximum length of an option specified per host is arbitrarily set to 4096 bytes.

Kea currently does not support storing reservations in Cassandra (CQL).

The host reservation capability introduces additional restrictions for the allocation engine (the component of Kea that selects an address for a client) 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 not be 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 is 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 and 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 1.1.0 does not sanity check the reservations against reservation-mode and 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", ... } ] } Another aspect of the host reservations are different types of identifiers. Kea 1.1.0 supports two types of identifiers in DHCPv6: hw-address and duid, but more identifier types are likely to be added in the future. This is beneficial from a usability perspective. However, there is a drawback. For each incoming packet Kea has to to extract each identifier type and then query the database to see if there is a reservation done by this particular identifier. If nothing is found, the next identifier is extracted and next query is issued. This process continues until either a reservation is found or all identifier types have been checked. Over time with an increasing number of supported identifier types, Kea would become slower and slower. To address this problem, a parameter called host-reservation-identifiers has been introduced. It takes a list of identifier types as a parameter. Kea will check only those identifier types enumerated in host-reservation-identifiers. From a performance perspective the number of identifier types should be kept to minimum, ideally limited to one. If your deployment uses several reservation types, please enumerate them from most to least frequently used as this increases the chances of Kea finding the reservation using the fewest number of queries. An example of host reservation identifiers looks as follows: "host-reservation-identifiers": [ "duid", "hw-address" ], "subnet6": [ { "subnet": "2001:db8:1::/64", ... } ] If not specified, the default value is: "host-reservation-identifiers": [ "hw-address", "duid" ]

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. The 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 and so is a stable identifier. Kea follows recommendation from RFC 3315 to use DUID-LLT as the 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 then 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 the 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 the rebinding state. In this state they will start sending Rebind messages to multicast address 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 that modification of the server identifier type and value is avoided 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 the 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 an explicit value of time. If it is different than a time value present in the currently used DUID, that value will be replaced, effectively causing 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 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 | The server stores the 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, the server should be configured not to try to store the server identifier. This choice 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 the 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 needed as Kea requires a lease database to be specified even if it is not used.

The RFC 7550 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 an 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 a 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 with 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" } } ] } If "relay" is specified, the "ip-address" parameter within it is mandatory.

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 it. 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 configuration of which of the supported methods should be used and in what 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 configuration is controlled by the mac-sources parameter 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. If specified, it has to have at least one value. 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 is 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 a remote-id option that is inserted by a relay agent. Depending on the relay agent configuration, the inserted option may convey the 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 the 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 the 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. Empty mac-sources is not allowed. If you do not want to specify it, either simply omit mac-sources definition or specify it with the "any" value which is the default.

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 conduct a 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) and 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 other 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). (See and for more details on DHCPv4 statistics and Kea hook points.) 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 the 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. The 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 a bug in the server. 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 packets either because of design choice or due to the client 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 a 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-dhcpv4-query-received integer Number of DHCPv4-QUERY packets received. This statistic is expected to grow if there are devices that are using DHCPv4-over-DHCPv6. DHCPv4-QUERY messages are used by DHCPv4 clients on an IPv6 only line which encapsulates the requests over DHCPv6. pkt6-dhcpv4-response-received integer Number of DHCPv4-RESPONSE packets received. This statistic is expected to remain zero at all times, as DHCPv4-RESPONSE 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 DHCPv4-RESPONSE message towards the server rather back to the clients. pkt6-unknown-received integer Number of packets received of an unknown type. A non-zero value of this statistic indicates that the server received a packet that it wasn't able to recognize: either it had an unsupported type or was 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. pkt6-dhcpv4-response-sent integer Number of DHCPv4-RESPONSE packets sent. This statistic is expected to grow in most cases after a DHCPv4-QUERY 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 that 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 and 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 and 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 and 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 and is reset during a reconfiguration event. reclaimed-leases integer This statistic is the number of expired leases that have been reclaimed since server startup. It is incremented each time an expired lease is reclaimed (it counts both NA and PD reclamations) and is reset when the server is reconfigured. subnet[id].reclaimed-leases integer This statistic is the number of expired leases associated with a given subnet ("id" is the subnet-id) that have been reclaimed since server startup. It is incremented each time an expired lease is reclaimed (it counts both NA and PD reclamations) and is reset when the server is reconfigured. declined-addresses integer This statistic shows the number of IPv6 addresses that are currently declined and so 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), the network administrator should investigate if there is a misbehaving device in the 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 the 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.

The management API allows the issuing of specific management commands, such as 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. 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. The DHCPv6 server supports the following operational commands: build-report config-get config-reload config-set config-test config-write leases-reclaim list-commands shutdown version-get as described in . In addition, it supports the following statistics related commands: statistic-get statistic-reset statistic-remove statistic-get-all statistic-reset-all statistic-remove-all as described here .

Kea allows loading hook libraries that sometimes could benefit from additional parameters. If such a parameter is specific to the whole library, it is typically defined as a parameter for the hook library. However, sometimes there is a need to specify parameters that are different for each pool. Let's consider an example where certain parameters are supposed to be delivered to clients in form of additional options, and the values of those options are correlated to delegated prefixes. It seems reasonable to keep those parameters with the the definition of the PD pool. On the other hand, this functionality is is not part of the base Kea code so Kea will not understand any hook-specific keywords in that definition. The solution to this problem is to use user context. For each PD pool that is expected to be used with this feature, a "user context" is defined. This is a structure that holds the parameters used by the hook library when it is loaded. An example configuration could look as follows: "Dhcp4": { "subnet6": [ { "pd-pools": [ { "prefix": "2001:db8::", "prefix-len": 56, "delegated-len": 64, "user-context": { "threshold-percent": 85, "v4-network": "192.168.0.0/16", "v4-overflow": "10.0.0.0/16" } } ], "subnet": "2001:db8::/32" } ], ... } Kea does not interpret or use the content of the user context: it just stores it, making it available to the hook libraries. It is up to each hook library to extract the information and make use of it. Currently only address and prefix pools allow definition of user contexts, but this concept is expected to be enhanced to other structures in the future. For more background information, see

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. Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite, RFC 6334: the AFTR-Name DHCPv6 Option is supported. 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. Prefix Exclude Option for DHCPv6-based Prefix Delegation, RFC 6603: Prefix Exclude option is supported. 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 of 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. 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. Client reconfiguration (RECONFIGURE) is not yet supported.