.. _radius: RADIUS ====== .. _radius-overview: RADIUS Overview --------------- This hook library allows Kea to interact with two types of RADIUS services: access and accounting. Although the most common DHCP and RADIUS integration is done on the DHCP relay-agent level (DHCP clients send DHCP packets to DHCP relays; those relays contact the RADIUS server and depending on the response either send the packet to the DHCP server or drop it), it does require DHCP relay hardware to support RADIUS communication. Also, even if the relay has the necessary support, it is often not flexible enough to send and receive additional RADIUS attributes. As such, the alternative looks more appealing: to extend the DHCP server to talk to RADIUS directly. That is the goal of this library. .. note:: This library can only be loaded by the :iscman:`kea-dhcp4` or the :iscman:`kea-dhcp6` process. The major feature of this hook library is the ability to use RADIUS authorization. When a DHCP packet is received, the Kea server sends an Access-Request to the RADIUS server and waits for a response. The server then sends back either an Access-Accept with specific client attributes, or an Access-Reject. There are two cases supported here: first, the Access-Accept includes a Framed-IP-Address attribute (for DHCPv4) or a Framed-IPv6-Address attribute (for DHCPv6), which are interpreted by Kea as instructions to assign the specified IPv4 or IPv6 address. This effectively means RADIUS can act as an address-reservation database. The second supported case is the ability to assign clients to specific pools based on a RADIUS response. In this case, the RADIUS server sends back an Access-Accept with a Framed-Pool attribute. For both DHCPv4 and DHCPv6, Kea interprets this attribute as a client class. With the addition of the ability to limit access to pools to specific classes (see :ref:`classification-pools`), RADIUS can be used to force the client to be assigned a dynamic address from a specific pool. Furthermore, the same mechanism can be used to control what kind of options the client gets if there are DHCP options specified for a particular class. .. _radius-config: RADIUS Hook Library Configuration --------------------------------- The RADIUS hook is a library that must be loaded by either :iscman:`kea-dhcp4` or :iscman:`kea-dhcp6` servers. Unlike some other available hook libraries, this one takes many parameters. For example, this configuration can be used: .. parsed-literal:: { "Dhcp4": { // Your regular DHCPv4 configuration parameters goes here. "hooks-libraries": [ { // Note that RADIUS requires host-cache for proper operation, // so that library is loaded as well. "library": "/usr/local/lib/kea/hooks/libdhcp_host_cache.so" }, { "library": "/usr/local/lib/kea/hooks/libdhcp_radius.so", "parameters": { // Specify where the dictionary is located. "dictionary": "/etc/kea/radius/dictionary", // Specify which address to use to communicate with RADIUS servers "bindaddr": "*" // More RADIUS parameters go here. } } ] } } RADIUS is a complicated environment. As such, it is not feasible to provide a default configuration that works for everyone. However, we do have an example that showcases some of the more common features. Please see ``doc/examples/kea4/hooks-radius.json`` in the Kea sources. The RADIUS hook library supports the following global configuration flags: - ``bindaddr`` (default ``"*"``) - specifies the address to be used by the hook library in communication with RADIUS servers. The ``"*"`` special value tells the kernel to choose the address at hook library load time. - ``canonical-mac-address`` (default ``false``) - specifies whether MAC addresses in attributes follow the canonical RADIUS format (lowercase pairs of hexadecimal digits separated by ``-``). - ``client-id-pop0`` (default ``false``) - is used with :ischooklib:`libdhcp_flex_id.so`. Removes the leading zero (or pair of zeroes in DHCPv6) type in the client id (duid in DHCPv6). See ``client-id-printable`` for any value implications when used in conjunction with it. - ``client-id-printable`` (default ``false``) - checks whether the ``client-id``/``duid`` content is printable and uses it as is instead of in hexadecimal. Implies ``client-id-pop0`` and ``extract-duid`` as 0 and 255 are not printable. - ``deadtime`` (default ``0``) - is a mechanism that helps in sorting the servers such that the servers that have proved responsive so far are inquired first, and the servers that have proved unresponsive are left at the end. The deadtime value specifies the number of seconds after which a server is considered unresponsive. 0 disables the mechanism. - ``dictionary`` (default ``"/etc/kea/radius/dictionary"``) - is the attribute and value dictionary. Note that it is a critical parameter. A dictionary is provided by Kea and is set by default. - ``extract-duid`` (default ``true``) - extracts the embedded duid from an RFC-4361-compliant DHCPv4 client id. See ``client-id-printable`` for any value implications when used in conjunction with it. - ``identifier-type4`` (default ``"client-id"``) - specifies the identifier type to build the User-Name attribute. It should be the same as the host identifier. When :ischooklib:`libdhcp_flex_id.so` is used, then ``replace-client-id`` must be set to ``true`` and ``client-id`` must be used with ``client-id-pop0`` enabled. - ``identifier-type6`` (default ``"duid"``) - specifies the identifier type to build the User-Name attribute. It should be the same as the host identifier. When :ischooklib:`libdhcp_flex_id.so` is used, then ``replace-client-id`` must be set to ``true`` and ``duid`` must be used with ``client-id-pop0`` enabled. - ``nas-ports`` (default ``[]``), specifies the NAS port to use in place of a subnet ID (default behavior). It is an array of maps, each map having two elements at most: the mandatory NAS port value, and, optionally, a selector consisting of either a subnet id, a subnet prefix, or a shared-network name. If the selector is applied to the packet, the NAS port is used instead of the subnet id. When the subnet id is 0 or missing, the specified NAS port acts as a default. Its substition happens for all packets that did not match a selector. - ``realm`` (default ``""``) - is the default realm. - ``reselect-subnet-address`` (default ``false``) - enables subnet reselection according to the value of the Framed-IP-Address or, respectively, the Framed-IPv6-Address attribute from the RADIUS access response. With this flag enabled, if the IP address is not in range of the currently selected subnet, but is in range of another subnet that is selectable with regards to other criteria, the latter subnet is selected and used further in the lease assignment process. - ``reselect-subnet-pool`` (default ``false``) - enables subnet reselection according to the value of the Framed-Pool attribute from the RADIUS access response. With this flag enabled, if the currently selected subnet is not guarded by the client class represented by the attribute value, but there is another selectable subnet that is guarded by it, the latter subnet is selected and used further in the lease assignment process. This reselection is attempted first, and if successful, it prevents the function of reselect-subnet-address from coming into effect. - ``retries`` (default ``3``) - is the number of retries before trying the next server. - ``session-history`` (default ``""``) - is the name of the file providing persistent storage for accounting session history. - ``thread-pool-size`` (default ``0``) indicates the number of threads that is used for sending RADIUS requests and processing RADIUS responses for both access and accounting services before passing it to the core thread pool. A value of ``0`` instructs the RADIUS hook library to use the same number of threads used for core DHCP processing. This value is only relevant if Kea core is configured as multi-threaded. Single-threaded Kea core results in single-threaded RADIUS processing. - ``timeout`` (default ``10``) - is the number of seconds during which a response is awaited. Two services are supported: - ``access`` - the authorization service. - ``accounting`` - the accounting service. At the service level, three sections can be configured: - Servers that define RADIUS services that the library is expected to contact. Each server may have the following items specified: - ``name`` - specifies the IP address of the server. A domain name may be used and will be resolved at hook library load time. - ``port`` - specifies the UDP port of the server. By default, it is 1812 for access and 1813 for accounting. - ``secret`` - authenticates messages. When no server is specified, the service is disabled. - Attributes which define additional information that the Kea server sends to a RADIUS server. The parameter must be identified either by a name or type. Its value can be specified in one of three possible ways: ``data`` (which defines a plain text value), ``raw`` (which defines the value in hex), or ``expr`` (which defines an expression that is evaluated for each incoming packet independently). - ``name`` - the name of the attribute. - ``type`` - the type of the attribute. Either the type or the name must be provided, and the attribute must be defined in the dictionary. - ``data`` - the first of three ways to specify the attribute content. It specifies the textual representation of the attribute content. - ``raw`` - the second of three ways to specify the attribute content. It specifies the content in hexadecimal. - ``expr`` - the last of the three ways to specify the attribute content. It specifies an evaluation expression on the DHCP query packet. Currently this is restricted to the access service. Attributes are supported only for the access service. - The ``peer-updates`` boolean flag (default ``true``) controls whether lease updates coming from an active High-Availability (HA) partner should result in an accounting request. This may be desirable to remove duplicates if HA partners are configured to send request to the same RADIUS server. The flag is only supported by the accounting service. The lease synchronization process at the startup of an HA node does not trigger a RADIUS accounting request, regardless of the value of this flag. - The ``max-pending-requests`` positive integer (default ``0``) limits the number of pending RADIUS requests. The value ``0`` means no limit. It is supported only by the access service. ``64`` can be a good value to set it to. For example, to specify a single access server available on localhost that uses ``"xyz123"`` as a secret, and tell Kea to send three additional attributes (``User-Password``, ``Connect-Info``, and ``Configuration-Token``), the following snippet could be used: .. parsed-literal:: { "parameters": { // Other RADIUS parameters here "access": { // This starts the list of access servers. "servers": [ { // These are parameters for the first (and only) access server "name": "127.0.0.1", "port": 1812, "secret": "xyz123" } // Additional access servers could be specified here. ], // This defines a list of additional attributes Kea will send to each // access server in Access-Request. "attributes": [ { // This attribute is identified by name (must be present in the // dictionary) and has static value (i.e. the same value will be // sent to every server for every packet). "name": "User-Password", "data": "mysecretpassword" }, { // It is also possible to specify an attribute using its type, // rather than a name. 77 is Connect-Info. The value is specified // using hex. Again, this is a static value. It will be sent the // same for every packet and to every server. "type": 77, "raw": "65666a6a71" }, { // This example shows how an expression can be used to send dynamic value. // The expression (see :ref:`classification-using-expressions`) may take any // value from the incoming packet or even its metadata e.g. the // interface it was received over from. "name": "Configuration-Token", "expr": "hexstring(pkt4.mac,':')" } ] // End of attributes }, // End of access // Accounting parameters. "accounting": { // This starts the list of accounting servers. "servers": [ { // These are parameters for the first (and only) accounting server "name": "127.0.0.1", "port": 1813, "secret": "sekret" } // Additional accounting servers could be specified here. ] } } } Customization is sometimes required for certain attributes by devices belonging to various vendors. This is a great way to leverage the expression evaluation mechanism. For example, MAC addresses which might be used as a convenience value for the ``User-Password`` attribute are most likely to appear in colon-hexadecimal notation (``de:ad:be:ef:ca:fe``), but they might need to be expressed in hyphen-hexadecimal notation (``de-ad-be-ef-ca-fe``). Here's how to specify that: .. code-block:: json { "parameters": { "access": { "attributes": [ { "name": "User-Password", "expr": "hexstring(pkt4.mac, '-')" } ] } } } And here's how to specify period-separated hexadecimal notation (``dead.beef.cafe``), preferred by Cisco devices: .. code-block:: json { "parameters": { "access": { "attributes": [ { "name": "User-Password", "expr": "substring(hexstring(pkt4.mac, ''), 0, 4) + '.' + substring(hexstring(pkt4.mac, ''), 4, 4) + '.' + substring(hexstring(pkt4.mac, ''), 8, 4)" } ] } } } For :ischooklib:`libdhcp_radius.so` to operate properly in DHCPv4, :ischooklib:`libdhcp_host_cache.so` must also be loaded. The reason for this is somewhat complex. In a typical deployment, the DHCP clients send their packets via DHCP relay, which inserts certain Relay Agent Information options, such as ``circuit-id`` or ``remote-id``. The values of those options are then used by the Kea DHCP server to formulate the necessary attributes in the Access-Request message sent to the RADIUS server. However, once the DHCP client gets its address, it then renews by sending packets directly to the DHCP server. As a result, the relays are not able to insert their RAI options, and the DHCP server cannot send the Access-Request queries to the RADIUS server by using just the information from incoming packets. Kea needs to keep the information received during the initial Discover/Offer exchanges and use it again later when sending accounting messages. This mechanism is implemented based on user context in host reservations. (See :ref:`user-context` and :ref:`user-context-hooks` for details.) The host-cache mechanism allows the information retrieved by RADIUS to be stored and later used for sending access and accounting queries to the RADIUS server. In other words, the host-cache mechanism is mandatory, unless administrators do not want RADIUS communication for messages other than Discover and the first Request from each client. .. note:: Currently the RADIUS hook library is incompatible with the ``early-global-reservations-lookup`` global parameter i.e. setting the parameter to ``true`` raises an error when the hook library is loaded. .. note:: Currently the RADIUS hook library is incompatible with the multi-subnet shared networks that have host reservations other than global. Loading the RADIUS hook library in a Kea DHCP server that has this configuration raises an error. .. _radius-server-example: RADIUS Server Setup Example --------------------------- The RADIUS hook library requires at least one RADIUS server to function. One popular open-source implementation is FreeRADIUS. This is how it can be set up to enable basic functionality in Kea. 1. Install FreeRADIUS through the package manager or from the tarballs available on [the freeradius.org download page](https://freeradius.org/releases/). 2. Establish the FreeRADIUS configuration directory. It's commonly ``/etc/freeradius``, but it may be ``/etc/raddb``. 3. Generate certificates. Go to ``/etc/freeradius/certs``. Run ``./bootstrap`` or ``make``. Wait until finished. It should take a few seconds. 4. Check that the server is able to start. Running with the ``-X`` flag is a good way to display potential errors. Run ``radiusd -X`` or ``freeradius -X``, whichever is available. It should display ``Ready to process requests`` on the final line. 5. If the Kea DHCP server and the RADIUS server are on different machines, edit ``/etc/freeradius/clients.conf`` with the proper address under ``ipadddr``. This file is also where the secret is set, which needs to match the one set in the hook library's configuration. 6. If RADIUS is used for the purpose of authorizing DHCP clients, each DHCP client needs to have an entry in the authorize file, which can be commonly found at: - ``/etc/raddb/mods-config/files/authorize`` - ``/etc/freeradius/3.0/mods-config/files/authorize`` - ``/etc/freeradius/users`` (for RADIUS 2.x series) Entries need to have the password set which needs to match the password configured in the configuration of the RADIUS hook library under the ``User-Password`` attribute. Each entry can have zero, one or multiple attributes. In the following example, there are 6 entries with the password set to the client ID, which would need to be dynamically set in the hook library's configuration. Here's how the entries can look like: :: 01:00:0c:01:02:03:04 Cleartext-password := "00:0c:01:02:03:04" 01:00:0c:01:02:03:05 Cleartext-password := "00:0c:01:02:03:05" Framed-IP-Address = "192.0.2.5" 01:00:0c:01:02:03:06 Cleartext-password := "00:0c:01:02:03:06" Framed-IP-Address = "192.0.2.6", Framed-Pool = "classical" 00:03:00:01:00:0c:01:02:03:07 Cleartext-password := "00:0c:01:02:03:07" 00:03:00:01:00:0c:01:02:03:08 Cleartext-password := "00:0c:01:02:03:08" Framed-IPv6-Address = "2001:db8::8" 00:03:00:01:00:0c:01:02:03:09 Cleartext-password := "00:0c:01:02:03:09" Framed-IPv6-Address = "2001:db8::9", Framed-Pool = "classroom" 7. Accounting should work out of the box with Kea, but customizations are possible in the accounting file, which can be commonly found at: - ``/etc/radius-config/mods-config/files/accounting`` - ``/etc/freeradius/3.0/mods-config/files/accounting`` .. _radius-lease-allocation: RADIUS Workflows for Lease Allocation ------------------------------------- The following diagrams show a high level view of how RADIUS assists with the lease allocation process in :iscman:`kea-dhcp4` and :iscman:`kea-dhcp6`. .. figure:: ../uml/radius.* Somewhat tangential to lease allocation, and not shown in the diagrams above, is the ``command_processed`` callout, which sends Accounting-Request messages when a lease command is received. .. _radius-differences: Differences Between RADIUS Hook Libraries Prior To 2.4.0 and As Of 2.6.0 ------------------------------------------------------------------------ The RADIUS hook library in 2.4.0 and prior versions relied on the FreeRADIUS client library to function. Starting with 2.6.0 and onwards, the RADIUS hook library is standalone with its own RADIUS client implementation and its own RADIUS dictionary. There are differences: .. list-table:: :header-rows: 1 * - Feature - Old - New * - Support for Attribute Data Types - string, ipaddr, ipv4prefix, integer, integer64, date, ifid, ipv6addr, ipv6prefix, tlv, abinary, byte, ether, short, signed, octets - string (can simulate any other unsupported data type too), ipaddr, integer, date (interpreted as integer), ipv6addr, ipv6prefix * - Names of Standard Attributes - Taken from the FreeRADIUS dictionary. - Taken from the Kea RADIUS dictionary and the IANA registry. There is an aliasing mechanism built into the library that ensures backward compatibility e.g. ``Password`` translates to the standard name of the attribute ``User-Password``. * - Resolution of RADIUS Server Domain Names - At run time. - At hook library load time. * - Automatic Deduction of Source Address for Reaching RADIUS Servers (configured with ``bindaddr: "*"``) - At run time. - At hook library load time. * - RADIUS Server Limit per Service - 8 - Unlimited * - Support for Including Dictionaries Inside Dictionaries - Yes - No * - Support for Vendor Attributes - Yes - No * - Attribute Names and Attribute Values - Case-insensitive - Case-sensitive * - Integer Values - Do not require an attribute definition. - Must have an associated attribute definition in the dictionary. * - Reply-Message Presence in the Kea Logs - Only as part of the aggregated list of attributes in ``RADIUS_AUTHENTICATION_ACCEPTED``, ``RADIUS_ACCESS_CACHE_INSERT``, ``RADIUS_ACCESS_CACHE_GET`` log messages. - Also has a dedicated ``RADIUS_REPLY_MESSAGE_ATTRIBUTE`` message per each Reply-Message attribute logged after a valid RADIUS reply is received. * - Behavior of Multiple Attributes of the Same Type (except Reply-Message) - Experimentally, only the **first** attribute on the wire from an Access-Accept message is considered. - Experimentally, only the **last** attribute on the wire from an Access-Accept message is considered.