Hooks Libraries

Available Hooks Libraries As described above, the hooks functionality provides a way to customize a Kea server without modifying the core code. ISC has chosen to take advantage of this feature to provide functions that may only be useful to a subset of Kea users. To this end ISC has created some hooks libraries; these discussed in the following sections. Some of these libraries will be available with the base code while others will be shared with organizations supporting development of Kea , possibly as a 'benefit' or 'thank you' for helping to sustain the larger Kea project. If you would like to get access to those libraries, please consider taking out a support contract: this includes professional support, advance security notifications, input into our roadmap planning, and many other benefits, while helping making Kea sustainable in the long term. Currently the following libraries are available or planned from ISC: List of available hooks libraries Name Availability Since Description user_chk Kea sources Kea 0.8 Reads known users list from a file. Unknown users will be assigned a lease from the last subnet defined in the configuration file, e.g. to redirect them a captive portal. This demonstrates how an external source of information can be used to influence the Kea allocation engine. This hook is part of the Kea source code and is available in the src/hooks/dhcp/user_chk directory. Forensic Logging Support customers Kea 1.1.0 This library provides hooks that record a detailed log of lease assignments and renewals into a set of log files. In many legal jurisdictions companies, especially ISPs, must record information about the addresses they have leased to DHCP clients. This library is designed to help with that requirement. If the information that it records is sufficient it may be used directly. If your jurisdiction requires that you save a different set of information, you may use it as a template or example and create your own custom logging hooks. Flexible Identifier Support customers Kea 1.2.0 Kea software provides a way to handle host reservations that include addresses, prefixes, options, client classes and other features. The reservation can be based on hardware address, DUID, circuit-id or client-id in DHCPv4 and using hardware address or DUID in DHCPv6. However, there are sometimes scenarios where the reservation is more complex, e.g. uses other options that mentioned above, uses part of specific options or perhaps even a combination of several options and fields to uniquely identify a client. Those scenarios are addressed by the Flexible Identifiers hook application. It allows defining an expression, similar to the one used in client classification, e.g. substring(relay6[0].option[37],0,6). Each incoming packet is evaluated against that expression and its value is then searched in the reservations database. Host Commands Support customers Kea 1.2.0 Kea provides a way to store host reservations in a database. In many larger deployments it is useful to be able to manage that information while the server is running. This library provides management commands for adding, querying and deleting host reservations in a safe way without restarting the server. In particular, it validates the parameters, so an attempt to insert incorrect data, e.g. add a host with conflicting identifier in the same subnet will be rejected. Those commands are exposed via command channel (JSON over unix sockets) and Control Agent (JSON over RESTful interface). Additional commands and capabilities related to host reservations will be added in the future.

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

user_chk: Checking User Access The user_chk library is the first hooks library published by ISC. It attempts to serve several purposes: To assign "new" or "unregistered" users to a restricted subnet, while "known" or "registered" users are assigned to unrestricted subnets. To allow DHCP response options or vendor option values to be customized based upon user identity. To provide a real time record of the user registration activity which can be sampled by an external consumer. To serve as a demonstration of various capabilities possible using the hooks interface. Once loaded, the library allows segregating incoming requests into known and unknown clients. For known clients, the packets are processed mostly as usual, except it is possible to override certain options being sent. That can be done on a per host basis. Clients that are not on the known hosts list will be treated as unknown and will be assigned to the last subnet defined in the configuration file. As an example of use, this behavior may be used to put unknown users into a separate subnet that leads to a walled garden, where they can only access a registration portal. Once they fill in necessary data, their details are added to the known clients file and they get a proper address after their device is restarted. This library was developed several years before the host reservation mechanism has become available. Currently host reservation is much more powerful and flexible, but nevertheless the user_chk capability to consult and external source of information about clients and alter Kea's behavior is useful and remains of educational value. The library reads the /tmp/user_chk_registry.txt file while being loaded and each time an incoming packet is processed. The file is expected to have each line contain a self-contained JSON snippet which must have the following two entries: type, whose value is "HW_ADDR" for IPv4 users or "DUID" for IPv6 users id, whose value is either the hardware address or the DUID from the request formatted as a string of hex digits, with or without ":" delimiters. and may have the zero or more of the following entries: bootfile whose value is the pathname of the desired file tftp_server whose value is the hostname or IP address of the desired server A sample user registry file is shown below: { "type" : "HW_ADDR", "id" : "0c:0e:0a:01:ff:04", "bootfile" : "/tmp/v4bootfile" } { "type" : "HW_ADDR", "id" : "0c:0e:0a:01:ff:06", "tftp_server" : "tftp.v4.example.com" } { "type" : "DUID", "id" : "00:01:00:01:19:ef:e6:3b:00:0c:01:02:03:04", "bootfile" : "/tmp/v6bootfile" } { "type" : "DUID", "id" : "00:01:00:01:19:ef:e6:3b:00:0c:01:02:03:06", "tftp_server" : "tftp.v6.example.com" } As with any other hooks libraries provided by ISC, internals of the user_chk code are well documented. You can take a look at the Kea Developer's Guide section dedicated to the user_chk library that discusses how the code works internally. That, together with our general entries in Hooks Framework section should give you some pointers how to extend this library and perhaps even write your own from scratch.

legal_log: Forensic Logging Hooks This section describes the forensic log hooks library. This library provides hooks that record a detailed log of lease assignments and renewals into a set of log files. Currently this library is only available to ISC customers with a support contract. In many legal jurisdictions companies, especially ISPs, must record information about the addresses they have leased to DHCP clients. This library is designed to help with that requirement. If the information that it records is sufficient it may be used directly. If your jurisdiction requires that you save a different set of information you may use it as a template or example and create your own custom logging hooks. This logging is done as a set of hooks to allow it to be customized to any particular need. Modifying a hooks library is easier and safer than updating the core code. In addition by using the hooks features those users who don't need to log this information can leave it out and avoid any performance penalties.

Log File Naming The names for the log files have the following form: path/base-name.CCYYMMDD.txt The "path" and "base-name" are supplied in the configuration as described below see . The next part of the name is the date the log file was started, with four digits for year, two digits for month and two digits for day. The file is rotated on a daily basis. When running Kea servers for both DHCPv4 and DHCPv6 the log names must be distinct. See the examples in .

DHCPv4 Log Entries For DHCPv4 the library creates entries based on DHCPREQUEST messages and corresponding DHCPv4 leases intercepted by lease4_select (for new leases) and lease4_renew (for renewed leases) hooks. An entry is a single string with no embedded end-of-line markers and has the following sections: address duration device-id {client-info} {relay-info} Where: address - the leased IPv4 address given out and whether it was assigned or renewed. duration - the lease lifetime expressed in days (if present), hours, minutes and seconds. A lease lifetime of 0xFFFFFFFF will be denoted with the text "infinite duration". device-id - the client's hardware address shown as numerical type and hex digit string. client-info - the DHCP client id option (61) if present, shown as a hex string. relay-info - for relayed packets the giaddr and the RAI circuit-id, remote-id and subscriber-id options (option 82 sub options: 1, 2 and 6) if present. The circuit id and remote id are presented as hex strings For instance (line breaks added for readability, they would not be present in the log file). Address: 192.2.1.100 has been renewed for 1 hrs 52 min 15 secs to a device with hardware address: hwtype=1 08:00:2b:02:3f:4e, client-id: 17:34:e2:ff:09:92:54 connected via relay at address: 192.2.16.33, identified by circuit-id: 68:6f:77:64:79 and remote-id: 87:f6:79:77:ef

DHCPv6 Log Entries For DHCPv6 the library creates entries based on lease management actions intercepted by the lease6_select (for new leases), lease6_renew (for renewed leases) and lease6_rebind (for rebound leases). An entry is a single string with no embedded end-of-line markers and has the following sections: address duration device-id {relay-info}* Where: address - the leased IPv6 address or prefix given out and whether it was assigned or renewed. duration - the lease lifetime expressed in days (if present), hours, minutes and seconds. A lease lifetime of 0xFFFFFFFF will be denoted with the text "infinite duration". device-id - the client's DUID and hardware address (if present). relay-info - for relayed packets the content of relay agent messages, remote-id (code 37), subscriber-id (code 38) and interface-id (code 18) options if present. Note that interface-id option, if present, identifies the whole interface the relay agent received the message on. This typically translates to a single link in your network, but it depends on your specific network topology. Nevertheless, this is useful information to better scope down the location of the device, so it is being recorded, if present. For instance (line breaks added for readability, they would not be present in the log file). Address:2001:db8:1:: has been assigned for 0 hrs 11 mins 53 secs to a device with DUID: 17:34:e2:ff:09:92:54 and hardware address: hwtype=1 08:00:2b:02:3f:4e (from Raw Socket) connected via relay at address: fe80::abcd for client on link address: 3001::1, hop count: 1, identified by remote-id: 01:02:03:04:0a:0b:0c:0d:0e:0f and subscriber-id: 1a:2b:3c:4d:5e:6f

Configuring the Forensic Log Hooks To use this functionality the hook library must be included in the configuration of the desired DHCP server modules. The legal_log library is installed alongside the Kea libraries in [kea-install-dir]/lib where kea-install-dir is determined by the "--prefix" option of the configure script. It defaults to /usr/local. Assuming the default value then, configuring kea-dhcp4 to load the legal_log library could be done with the following Kea4 configuration: "Dhcp4": { "hooks-libraries": [ { "library": "/usr/local/lib/libdhcp_legal_log.so", "parameters": { "path": "/var/kea/var", "base-name": "kea-forensic4" } }, ... ] } To configure it for kea-dhcp6, the commands are simply as shown below: "Dhcp6": { "hooks-libraries": [ { "library": "/usr/local/lib/libdhcp_legal_log.so", "parameters": { "path": "/var/kea/var", "base-name": "kea-forensic6" } }, ... ] } Two Hook Library parameters are supported: path - the directory in which the forensic file(s) will be written. The default value is [prefix]/kea/var. The directory must exist. base-name - an arbitrary value which is used in conjunction with the current system date to form the current forensic file name. It defaults to kea-legal.

flex_id: Flexible Identifiers for Host Reservations This section describes a hook application dedicated to generate flexible identifiers for host reservation. Kea software provides a way to handle host reservations that include addresses, prefixes, options, client classes and other features. The reservation can be based on hardware address, DUID, circuit-id or client-id in DHCPv4 and using hardware address or DUID in DHCPv6. However, there are sometimes scenario where the reservation is more complex, e.g. uses other options that mentioned above, uses part of specific options or perhaps even a combination of several options and fields to uniquely identify a client. Those scenarios are addressed by the Flexible Identifiers hook application. Currently this library is only available to ISC customers with a support contract. The library allows for defining an expression, using notation initially used for client classification only. See for detailed description of the syntax available. One notable difference is that for client classification the expression currently has to evaluate to either true or false, while the flexible identifier expression is expected to evaluate to a string that will be used as identifier. It is a valid case for the expression to evaluate to empty string (e.g. in cases where a client does not sent specific options). This expression is then evaluated for each incoming packet. This evaluation generates an identifier that is used to identify the client. In particular, there may be host reservations that are tied to specific values of the flexible identifier. The library can be loaded in similar way as other hook libraries. It takes one mandatory parameter identifier-expression: "Dhcp6": { "hooks-libraries": [ { "library": "/path/libdhcp_flex_id.so", "parameters": { "identifier-expression": "expression" } }, ... ] } The flexible identifier library supports both DHCPv4 and DHCPv6. EXAMPLE: Let's consider a case of an IPv6 network that has an independent interface for each of the connected customers. Customers are able to plug in whatever device they want, so any type of identifier (e.g. a client-id) is unreliable. Therefore the operator may decide to use an option inserted by a relay agent to differentiate between clients. In this particular deployment, the operator verified that the interface-id is unique for each customer facing interface. Therefore it is suitable for usage as reservation. However, only the first 6 bytes of the interface-id are interesting, because remaining bytes are either randomly changed or not unique between devices. Therefore the customer decided to use first 6 bytes of the interface-id option inserted by the relay agent. After adding "flex-id" host-reservation-identifiers goal can be achieved by using the following configuration: "Dhcp6": { "subnet6": [{ ..., // subnet definition starts here "reservations": [ "flex-id": "'port1234'", // value of the first 8 bytes of the interface-id "ip-addresses": [ "2001:db8::1" ] ], }], // end of subnet definitions "host-reservation-identifiers": ["duid", "flex-id"], // add "flex-id" to reservation identifiers "hooks-libraries": [ { "library": "/path/libdhcp_flex_id.so", "parameters": { "identifier-expression": "substring(relay6[0].option[18].hex,0,8)" } }, ... ] } NOTE: Care should be taken when adjusting the expression. If the expression changes, then all the flex-id values may change, possibly rendering all reservations based on flex-id unusable until they're manually updated. Therefore it is strongly recommended to start with the expression and a handful reservations, adjust the expression as needed and only after it was confirmed the expression does exactly what is expected out of it go forward with host reservations on any broader scale. flex-id values in host reservations can be specified in two ways. First, they can be expressed as hex string, e.g. bar string can be represented as 626174. Alternatively, it can be expressed as quoted value (using double and single quotes), e.g. "'bar'". The former is more convenient for printable characters, while hex string values are more convenient for non-printable characters. "Dhcp6": { "subnet6": [{ ..., // subnet definition starts here "reservations": [ "flex-id": "01:02:03:04:05:06", // value of the first 8 bytes of the interface-id "ip-addresses": [ "2001:db8::1" ] ], }], // end of subnet definitions "host-reservation-identifiers": ["duid", "flex-id"], // add "flex-id" to reservation identifiers "hooks-libraries": [ { "library": "/path/libdhcp_flex_id.so", "parameters": { "identifier-expression": "vendor[4491].option[1026].hex" } }, ... ] }

host_cmds: Host Commands This section describes a hook application that offers a number of new commands used to query and manipulate host reservations. Kea provides a way to store host reservations in a database. In many larger deployments it is useful to be able to manage that information while the server is running. This library provides management commands for adding, querying and deleting host reservations in a safe way without restarting the server. In particular, it validates the parameters, so an attempt to insert incorrect data e.g. add a host with conflicting identifier in the same subnet will be rejected. Those commands are exposed via command channel (JSON over unix sockets) and Control Agent (JSON over RESTful interface). Additional commands and capabilities related to host reservations will be added in the future. Currently this library is only available to ISC customers with a support contract. Currently three commands are supported: reservation-add (which adds new host reservation), reservation-get (which returns existing reservation if specified criteria are matched) and reservation-del (which attempts to delete a reservation matching specified criteria). To use commands that change the reservation information (currently these are reservation-add and reservation-del, but this rule applies to other commands that may be implemented in the future), hosts database must be specified (see hosts-database description in and ) and it must not operate in read-only mode. If the hosts-database is not specified or is running in read-only mode, the host_cmds library will load, but any attempts to use reservation-add or reservation-del will fail. Additional host reservation commands are planned in the future. For a description of envisaged commands, see Control API Requirements document. All commands are using JSON syntax. They can be issued either using control channel (see ) or via Control Agent (see ). The library can be loaded in similar way as other hook libraries. It does not take any parameters. It supports both DHCPv4 and DHCPv6 servers. "Dhcp6": { "hooks-libraries": [ { "library": "/path/libdhcp_host_cmds.so" } ... ] }

reservation-add command reservation-add allows insertion of a new host. It takes a set of arguments that vary depending on the nature of the host reservation. Any parameters allowed in the configuration file that pertain to host reservation are permitted here. For details regarding IPv4 reservations, see and . There is one notable addition. A subnet-id must be specified. This parameter is mandatory, because reservations specified in the configuration file are always defined within a subnet, so the subnet they belong to is clear. This is not the case with reservation-add, therefore the subnet-id must be specified explicitly. An example command can be as simple as: { "command": "reservation-add", "arguments": { "reservation": { "subnet-id": 1, "hw-address": "1a:1b:1c:1d:1e:1f", "ip-address": "192.0.2.202" } } } but can also take many more parameters, for example: { "command": "reservation-add", "arguments": { "reservation": { "subnet-id":1, "client-id": "01:0a:0b:0c:0d:0e:0f", "ip-address": "192.0.2.205", "next-server": "192.0.2.1", "server-hostname": "hal9000", "boot-file-name": "/dev/null", "option-data": [ { "name": "domain-name-servers", "data": "10.1.1.202,10.1.1.203" } ], "client-classes": [ "special_snowflake", "office" ] } } } Here is an example of complex IPv6 reservation: { "command": "reservation-add", "arguments": { "reservation": { "subnet-id":1, "duid": "01:02:03:04:05:06:07:08:09:0A", "ip-addresses": [ "2001:db8:1:cafe::1" ], "prefixes": [ "2001:db8:2:abcd::/64" ], "hostname": "foo.example.com", "option-data": [ { "name": "vendor-opts", "data": "4491" }, { "name": "tftp-servers", "space": "vendor-4491", "data": "3000:1::234" } ] } } } The command returns a status that indicates either a success (result 0) or a failure (result 1). Failed command always includes text parameter that explains the cause of failure. Example results: { "result": 0, "text": "Host added." } Example failure: { "result": 1, "text": "Mandatory 'subnet-id' parameter missing." } As reservation-add is expected to store the host, hosts-database parameter must be specified in your configuration and the database must not run in read-only mode. In the future versions it will be possible to modify the reservations read from a configuration file. Please contact ISC if you are interested in this functionality.

reservation-get command reservation-get can be used to query the host database and retrieve existing reservations. There are two types of parameters this command supports: (subnet-id, address) or (subnet-id, identifier-type, identifier). The first type of query is used when the address (either IPv4 or IPv6) is known, but the details of the reservation aren't. One common use case of this type of query is to find out whether a given address is reserved or not. The second query uses identifiers. For maximum flexibility, Kea stores the host identifying information as a pair of values: type and the actual identifier. Currently supported identifiers are "hw-address", "duid", "circuit-id", "client-id" and "flex-id", but additional types may be added in the future. If any new identifier types are defined in the future, reservation-get command will support them automatically. An example command for getting a host reservation by (subnet-id, address) pair looks as follows: { "command": "reservation-get", "arguments": { "subnet-id": 1, "ip-address": "192.0.2.202" } } An example query by (subnet-id, identifier-type, identifier) looks as follows: { "command": "reservation-get", "arguments": "subnet-id": 4, "identifier-type": "hw-address", "identifier": "01:02:03:04:05:06" } } reservation-get typically returns result 0 when the query was conducted properly. In particular, 0 is returned when the host was not found. If the query was successful a number of host parameters will be returned. An example of a query that did not find the host looks as follows: { "result": 0, "text": "Host not found." } An example result returned when the host was found: { "arguments": { "boot-file-name": "bootfile.efi", "client-classes": [ ], "hostname": "somehost.example.org", "hw-address": "01:02:03:04:05:06", "ip-address": "192.0.2.100", "next-server": "192.0.0.2", "option-data": [ ], "server-hostname": "server-hostname.example.org" }, "result": 0, "text": "Host found." } An example result returned when the query was malformed: { "result": 1, "text": "No 'ip-address' provided and 'identifier-type' is either missing or not a string." }

reservation-del command reservation-del can be used to delete a reservation from the host database. There are two types of parameters this command supports: (subnet-id, address) or (subnet-id, identifier-type, identifier). The first type of query is used when the address (either IPv4 or IPv6) is known, but the details of the reservation aren't. One common use case of this type of query is to remove a reservation (e.g. you want a specific address to no longer be reserved). The second query uses identifiers. For maximum flexibility, Kea stores the host identifying information as a pair of values: type and the actual identifier. Currently supported identifiers are "hw-address", "duid", "circuit-id", "client-id" and "flex-id", but additional types may be added in the future. If any new identifier types are defined in the future, reservation-get command will support them automatically. An example command for deleting a host reservation by (subnet-id, address) pair looks as follows: { "command": "reservation-del", "arguments": { "subnet-id": 1, "ip-address": "192.0.2.202" } } An example deletion by (subnet-id, identifier-type, identifier) looks as follows: { "command": "reservation-del", "arguments": "subnet-id": 4, "identifier-type": "hw-address", "identifier": "01:02:03:04:05:06" } } reservation-del returns result 0 when the host deletion was successful or 1 if it was not. A descriptive text is provided in case of error. Example results look as follows: { "result": 1, "text": "Host not deleted (not found)." } { "result": 0, "text": "Host deleted." } { "result": 1, "text": "Unable to delete a host because there is no hosts-database configured." }