dhcp4-srv.xml 209 KB
Newer Older
1
2
3
4
5
6
7
8
9
10
11
12
13
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
<!ENTITY mdash  "&#x2014;" >
]>

  <chapter id="dhcp4">
    <title>The DHCPv4 Server</title>

    <section id="dhcp4-start-stop">
      <title>Starting and Stopping the DHCPv4 Server</title>

      <para>
Tomek Mrugalski's avatar
Tomek Mrugalski committed
14
15
16
17
        It is recommended that the Kea DHCPv4 server be started and stopped
        using <command>keactrl</command> (described in <xref linkend="keactrl"/>).
        However, it is also possible to run the server directly: it accepts
        the following command-line switches:
18
      </para>
19
20
21

      <itemizedlist>
          <listitem>
22
23
24
25
            <simpara>
            <command>-c <replaceable>file</replaceable></command> -
            specifies the configuration file. This is the only mandatory
            switch.</simpara>
26
27
          </listitem>
          <listitem>
28
            <simpara>
Tomek Mrugalski's avatar
Tomek Mrugalski committed
29
30
            <command>-d</command> - specifies whether the server
            logging should be switched to debug/verbose mode. In verbose mode,
31
            the logging severity and debuglevel specified in the configuration
32
33
34
35
            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.</simpara>
36
37
          </listitem>
          <listitem>
38
39
            <simpara>
            <command>-p <replaceable>port</replaceable></command> -
40
            specifies UDP port on which the server will listen. This is only
41
42
            useful during testing, as a DHCPv4 server listening on
            ports other than the standard ones will not be able to
43
            handle regular DHCPv4 queries.</simpara>
44
          </listitem>
Francis Dupont's avatar
Francis Dupont committed
45
          <listitem>
46
47
48
            <simpara>
            <command>-t <replaceable>file</replaceable></command> -
            specifies the configuration file to be tested. Kea-dhcp4
Francis Dupont's avatar
Francis Dupont committed
49
50
51
52
53
54
55
            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.</simpara>
56
          </listitem>
Tomek Mrugalski's avatar
Tomek Mrugalski committed
57
58
          <listitem>
            <simpara>
59
              <command>-v</command> - prints out the Kea version and exits.
Tomek Mrugalski's avatar
Tomek Mrugalski committed
60
61
62
63
            </simpara>
          </listitem>
          <listitem>
            <simpara>
64
65
              <command>-V</command> - prints out the Kea extended version with
              additional parameters and exits. The listing includes the versions
66
              of the libraries dynamically linked to Kea.
Tomek Mrugalski's avatar
Tomek Mrugalski committed
67
68
            </simpara>
          </listitem>
69
70
          <listitem>
            <simpara>
71
72
73
74
75
              <command>-W</command> - prints out the Kea configuration report
              and exits. The report is a copy of the
              <filename>config.report</filename> file produced by
              <userinput>./configure</userinput>: it is embedded in the
              executable binary.
76
77
            </simpara>
          </listitem>
78
79
      </itemizedlist>

Francis Dupont's avatar
Francis Dupont committed
80
      <para>
Tomek Mrugalski's avatar
Tomek Mrugalski committed
81
82
83
84
85
86
        The <filename>config.report</filename> may also be accessed more
        directly.  The following command may be used to extract this
        information.  The binary <userinput>path</userinput> may be found
        in the install directory or in the <filename>.libs</filename>
        subdirectory in the source tree. For example
        <filename>kea/src/bin/dhcp4/.libs/kea-dhcp4</filename>.
87

88
89
90
91
92
<screen>
strings <userinput>path</userinput>/kea-dhcp4 | sed -n 's/;;;; //p'
</screen>
      </para>

93
94
      <para>
        On start-up, the server will detect available network interfaces
95
96
        and will attempt to open UDP sockets on all interfaces
        mentioned in the configuration file.
97
98
99
100
        Since the DHCPv4 server opens privileged ports, it requires root
        access. Make sure you run this daemon as root.
      </para>

101
102
      <para>
        During startup the server will attempt to create a PID file of the
103
        form: localstatedir]/[conf name].kea-dhcp6.pid where:
104
105
106
        <itemizedlist>
            <listitem>
            <simpara><command>localstatedir</command>: The value as passed into the
107
            build configure script. It defaults to "/usr/local/var".  (Note
108
            that this value may be overridden at run time by setting the environment
109
            variable KEA_PIDFILE_DIR.  This is intended primarily for testing purposes.)
110
111
112
            </simpara>
            </listitem>
            <listitem>
113
            <simpara><command>conf name</command>: The configuration file name
114
115
116
117
118
119
120
121
122
            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".
            </simpara>
            </listitem>
        </itemizedlist>
        If the file already exists and contains the PID of a live process,
        the server will issue a DHCP4_ALREADY_RUNNING log message and exit. It
        is possible, though unlikely, that the file is a remnant of a system crash
123
        and the process to which the PID belongs is unrelated to Kea.  In such a
124
125
126
        case it would be necessary to manually delete the PID file.
      </para>

127
128
129
130
131
132
      <para>
        The server can be stopped using the <command>kill</command> command.
        When running in a console, the server can also be shut down by
        pressing ctrl-c. It detects the key combination and shuts
        down gracefully.
      </para>
133
134
135
    </section>

    <section id="dhcp4-configuration">
136
      <title>DHCPv4 Server Configuration</title>
137
138
<section>
  <title>Introduction</title>
139
      <para>
140
        This section explains how to configure the DHCPv4 server using the
141
142
        Kea configuration backend. (Kea configuration using any other
        backends is outside of scope of this document.) Before DHCPv4
143
        is started, its configuration file has to be created. The
144
        basic configuration is as follows:
145
<screen>
146
147
148
149
150
151
152
153
154
{
# DHCPv4 configuration starts in this line
"Dhcp4": {

# First we set up global values
    "valid-lifetime": 4000,
    "renew-timer": 1000,
    "rebind-timer": 2000,

155
156
157
158
159
160
# Next we setup the interfaces to be used by the server.
    "interfaces-config": {
        "interfaces": [ "eth0" ]
    },

# And we specify the type of lease database
161
    "lease-database": {
Tomek Mrugalski's avatar
Tomek Mrugalski committed
162
        "type": "memfile",
163
        "persist": true,
Tomek Mrugalski's avatar
Tomek Mrugalski committed
164
        "name": "/var/kea/dhcp4.leases"
165
166
167
168
169
170
    },

# Finally, we list the subnets from which we will be leasing addresses.
    "subnet4": [
        {
            "subnet": "192.0.2.0/24",
171
            "pools": [
172
173
174
                {
                     "pool": "192.0.2.1 - 192.0.2.200"
                }
175
            ]
176
177
        }
    ]
178
# DHCPv4 configuration ends with the next line
179
180
181
}

} </screen>
182
</para>
183

184
<para>The following paragraphs provide a brief overview of the parameters in
185
the above example together with
186
187
their format. Subsequent sections of this chapter go into much greater detail
for these and other parameters.</para>
188

189
190
<para>The lines starting with a hash (#) are comments and are ignored by
the server; they do not impact its
191
192
operation in any way.</para>

193
194
195
<para>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
196
object, called Dhcp4. This is a simplified configuration, as usually
197
there will be additional objects, like <command>Logging</command> or
Francis Dupont's avatar
Francis Dupont committed
198
<command>DhcpDdns</command>, but we omit them now for clarity. The Dhcp4
199
configuration starts with the <command>"Dhcp4": {</command> line
200
201
202
203
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 Dhcp4 configuration.</para>

204
<para>In the general case, the order in which those parameters appear does not
205
matter. There are two caveats here though. The first one is to remember that
206
207
208
209
210
the configuration file must be well formed JSON. That means that the 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 &mdash; although
211
legal JSON &mdash; to
212
repeat the same parameter multiple times. If that happens, the last occurrence of a
213
given parameter in a given scope is used while all previous instances are
214
ignored. This is unlikely to cause any confusion as there are no real life
215
216
217
reasons to keep multiple copies of the same parameter in your configuration
file.</para>

218
<para>Moving onto the DHCPv4 configuration elements, the first few elements
219
220
define some global parameters. <command>valid-lifetime</command>
defines for how long the addresses (leases) given out by the
221
server are valid. If nothing changes, a client that got an address is allowed to
222
223
use it for 4000 seconds. (Note that integer numbers are specified as is,
without any quotes around them.) <command>renew-timer</command> and
224
<command>rebind-timer</command> are values (also in seconds) that
225
define T1 and T2 timers that govern when the client will begin the renewal and
226
227
228
229
rebind procedures. Note that <command>renew-timer</command> and
<command>rebind-timer</command> are optional. If they are not specified the
client will select values for T1 and T2 timers according to the
<ulink url="http://tools.ietf.org/html/rfc2131">RFC 2131</ulink>.</para>
230

231
232
233
234
235
236
237
238
239
240
241
242
243
244
<para>The <command>interfaces-config</command> map specifies the server
configuration concerning the network interfaces, on which the server should
listen to the DHCP messages. The <command>interfaces</command> 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
<command>interfaces-config</command> would look like this:
<screen>
"interfaces-config": {
    "interfaces": [ "eth0", "eth1" ]
},
</screen>
</para>

245
<para>The next couple of lines define the lease database, the place where the server
246
stores its lease information. This particular example tells the server to use
247
<command>memfile</command>, which is the simplest (and fastest) database
248
backend. It uses an in-memory database and stores leases on disk in a CSV
249
file. This is a very simple configuration. Usually the lease database configuration
250
251
252
is more extensive and contains additional parameters.  Note that
<command>lease-database</command>
is an object and opens up a new scope, using an opening brace.
253
Its parameters (just one in this example - <command>type</command>)
254
follow. Had there been more than one, they would be separated by commas. This
255
256
scope is closed with a closing brace. As more parameters for the Dhcp4 definition
follow, a trailing comma is present.</para>
257
258
259

<para>Finally, we need to define a list of IPv4 subnets. This is the
most important DHCPv4 configuration structure as the server uses that
260
261
information to process clients' requests. It defines all subnets from
which the server is expected to receive DHCP requests. The subnets are
262
263
specified with the <command>subnet4</command> parameter.  It is a list,
so it starts and ends with square brackets.  Each subnet definition in
264
265
the list has several attributes associated with it, so it is a structure
and is opened and closed with braces. At a minimum, a subnet definition
266
has to have at least two parameters: <command>subnet</command> (that
267
defines the whole subnet) and <command>pools</command> (which is a list of
268
dynamically allocated pools that are governed by the DHCP server).</para>
269
270
271
272
273
274

<para>The example contains a single subnet. Had more than one been defined,
additional elements
in the <command>subnet4</command> parameter would be specified and
separated by commas. For example, to define three subnets, the following
syntax would be used:
275
<screen>
276
277
"subnet4": [
    {
278
        "pools": [ { "pool":  "192.0.2.1 - 192.0.2.200" } ],
279
280
281
        "subnet": "192.0.2.0/24"
    },
    {
282
        "pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
283
284
285
        "subnet": "192.0.3.0/24"
    },
    {
Adam Osuchowski's avatar
Adam Osuchowski committed
286
        "pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
287
288
289
        "subnet": "192.0.4.0/24"
    }
]
290
</screen>
291
292
Note that indentation is optional and is used for aesthetic purposes only.
In some cases in may be preferable to use more compact notation.
293
294
</para>

295
<para>After all the parameters have been specified, we have two contexts open:
296
global and Dhcp4, hence we need two closing curly brackets to close them.
297
298
In a real life configuration file there most likely would be additional
components defined such as Logging or DhcpDdns, so the closing brace would
299
300
be followed by a comma and another object definition.</para>
</section>
301

302
<section>
303
304
  <title>Lease Storage</title>
  <para>All leases issued by the server are stored in the lease database.
305
  Currently there are four database backends available:  memfile (which is the
306
  default backend), MySQL, PostgreSQL and Cassandra.</para>
307
<section>
308
  <title>Memfile - Basic Storage for Leases</title>
309
310
311

  <para>The server is able to store lease data in different repositories. Larger
  deployments may elect to store leases in a database. <xref
312
  linkend="database-configuration4"/> describes this option. In typical
313
314
  smaller deployments though, the server will store lease information in a CSV file rather
  than a database. As well as requiring less administration, an
315
316
  advantage of using a file for storage is that it
  eliminates a dependency on third-party database software.</para>
317
318

  <para>The configuration of the file backend (Memfile) is controlled through
319
320
321
  the Dhcp4/lease-database parameters. The <command>type</command> parameter
  is mandatory and it specifies which storage for leases the server should use.
  The value of <userinput>"memfile"</userinput> indicates that the file should
322
323
  be used as the storage. The following list gives additional, optional,
  parameters that can be used to configure the Memfile backend.
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350

  <itemizedlist>
    <listitem>
      <simpara><command>persist</command>: 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
      <userinput>true</userinput> 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 <userinput>false</userinput> is mostly useful
      for performance testing purposes. The default value of the
      <command>persist</command> parameter is <userinput>true</userinput>,
      which enables writing lease updates
      to the lease file.
      </simpara>
    </listitem>

    <listitem>
      <simpara><command>name</command>: 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 <userinput>"[kea-install-dir]/var/kea/kea-leases4.csv"
      </userinput>.</simpara>
    </listitem>

    <listitem>
      <simpara><command>lfc-interval</command>: specifies the interval in seconds, at
351
352
      which the server will perform a lease file cleanup (LFC).  This
      removes redundant (historical) information from the lease file
353
354
      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
355
356
      <command>lfc-interval</command> is <userinput>3600</userinput>. A value of 0
      disables the LFC.</simpara>
357
358
359
360
361
    </listitem>

  </itemizedlist>
  </para>

362
  <para>An example configuration of the Memfile backend is presented below:
Jeremy C. Reed's avatar
Jeremy C. Reed committed
363

364
<screen>
365
366
367
"Dhcp4": {
    "lease-database": {
        <userinput>"type": "memfile"</userinput>,
368
        <userinput>"persist": true</userinput>,
369
370
        <userinput>"name": "/tmp/kea-leases4.csv",</userinput>
        <userinput>"lfc-interval": 1800</userinput>
371
372
    }
}
373
</screen>
374
375

    This configuration selects the <filename>/tmp/kea-leases4.csv</filename> as
376
    the storage for lease information and enables persistence (writing lease updates
377
378
379
380
381
    to this file). It also configures the backend perform the periodic cleanup
    of the lease files, executed every 30 minutes.
  </para>

  <para>It is important to know how the lease file contents are organized
382
  to understand why the periodic lease file cleanup is needed. Every time
383
384
  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,
385
386
387
  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
388
389
390
391
392
393
  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
394
  the server's startup and reconfiguration as it needs to process a larger number
395
396
397
  of lease entries.
  </para>

398
  <para>Lease file cleanup (LFC) removes all previous entries for each client and
399
400
  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
401
402
  renewals initiated by the clients. The more frequent the renewals, the smaller
  the value of <command>lfc-interval</command> should be. Note however, that the
403
404
405
406
  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
  <command>lfc-interval</command> is too short. The server would recover from
  this by skipping the new cleanup when it detects that the previous cleanup
407
  is still in progress. But it implies that the actual cleanups will be
408
  triggered more rarely than configured. Moreover, triggering a new cleanup
409
  adds an overhead to the server which will not be able to respond to new
410
411
  requests for a short period of time when the new cleanup process is spawned.
  Therefore, it is recommended that the <command>lfc-interval</command> value
412
  is selected in a way that would allow for the LFC to complete the cleanup before a
413
414
415
  new cleanup is triggered.
  </para>

416
417
418
  <para>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
419
420
421
422
423
  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:
  <ulink url="http://kea.isc.org/wiki/LFCDesign"/>.
424
425
426
427
428
  </para>

</section>

<section id="database-configuration4">
429
  <title>Lease Database Configuration</title>
430
431

  <note>
432
433
    <para>Lease database access information must be configured for the DHCPv4 server,
    even if it has already been configured for the DHCPv6 server. The servers
434
435
436
437
    store their information independently, so each server can use a separate
    database or both servers can use the same database.</para>
  </note>

438
  <para>Lease database configuration is controlled through the Dhcp4/lease-database
439
440
  parameters. The type of the database must be set to "memfile", "mysql", "postgresql" or
  "cql", e.g.
441
<screen>
442
"Dhcp4": { "lease-database": { <userinput>"type": "mysql"</userinput>, ... }, ... }
443
</screen>
444
  Next, the name of the database to hold the leases must be set: this is the
445
  name used when the database was created
446
447
448
  (see <xref linkend="mysql-database-create"/>,
  <xref linkend="pgsql-database-create"/> or
  <xref linkend="cql-database-create"/>).
449
<screen>
450
"Dhcp4": { "lease-database": { <userinput>"name": "<replaceable>database-name</replaceable>" </userinput>, ... }, ... }
451
</screen>
452
  If the database is located on a different system to the DHCPv4 server, the
453
454
  database host name must also be specified. (It should be noted that this
  configuration may have a severe impact on server performance.):
455
<screen>
456
"Dhcp4": { "lease-database": { <userinput>"host": <replaceable>remote-host-name</replaceable></userinput>, ... }, ... }
457
</screen>
458
459
  The usual state of affairs will be to have the database on the same machine as
  the DHCPv4 server.  In this case, set the value to the empty string:
460
<screen>
461
"Dhcp4": { "lease-database": { <userinput>"host" : ""</userinput>, ... }, ... }
Tomek Mrugalski's avatar
Tomek Mrugalski committed
462
</screen>
463
  Should the database use a port different than default, it may be
Tomek Mrugalski's avatar
Tomek Mrugalski committed
464
465
466
  specified as well:
<screen>
"Dhcp4": { "lease-database": { <userinput>"port" : 12345</userinput>, ... }, ... }
467
</screen>
468
469
470
  Should the database be located on a different system, you may need to specify a longer interval
  for the connection timeout:
<screen>
471
"Dhcp4": { "lease-database": { <userinput>"connect-timeout" : <replaceable>timeout-in-seconds</replaceable></userinput>, ... }, ... }
472
473
</screen>
The default value of five seconds should be more than adequate for local connections.
474
If a timeout is given though, it should be an integer greater than zero.
475
  </para>
Tomek Mrugalski's avatar
Tomek Mrugalski committed
476
477
478
479
480
481
482
483
484
485
486

  <para>
    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:
<screen>
"Dhcp4": { "lease-database": { <userinput>"contact-points" : "192.0.2.1,192.0.2.2"</userinput>, ... }, ... }
</screen>
  </para>

487
488
  <para>Finally, the credentials of the account under which the server will
  access the database should be set:
489
<screen>
490
"Dhcp4": { "lease-database": { <userinput>"user": "<replaceable>user-name</replaceable>"</userinput>,
491
                               <userinput>"password": "<replaceable>password</replaceable>"</userinput>,
492
493
                              ... },
           ... }
494
</screen>
495
496
497
  If there is no password to the account, set the password to the empty string
  "". (This is also the default.)</para>
</section>
498
</section>
499

500
<section id="hosts4-storage">
501
  <title>Hosts Storage</title>
502
    <para>Kea is also able to store information about host reservations in the
503
504
505
    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
506
    flexibility. Kea can be used to keep leases and host reservations
507
    separately, but can also point to the same database. Currently the
508
    supported hosts database types are MySQL and PostgreSQL. The Cassandra
509
    backend does not support host reservations yet.</para>
510

511
    <para>Please note that usage of hosts storage is optional. A user can define
512
    all host reservations in the configuration file. That is the recommended way
513
514
515
    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)
516
    can be used together. If hosts are defined in both places, the definitions
517
    from the configuration file are checked first and external storage is checked
518
    later, if necessary.</para>
519
520

<section id="hosts-database-configuration4">
521
  <title>DHCPv4 Hosts Database Configuration</title>
522
523

  <para>Hosts database configuration is controlled through the Dhcp4/hosts-database
524
  parameters. If enabled, the type of the database must be set to "mysql" or
525
  "postgresql". Other hosts backends may be added in later versions of Kea.
526
527
528
<screen>
"Dhcp4": { "hosts-database": { <userinput>"type": "mysql"</userinput>, ... }, ... }
</screen>
529
530
  Next, the name of the database to hold the reservations must be set: this is the
  name used when the lease database was created (see <xref linkend="supported-databases"/>
531
  for instructions how to setup the desired database type).
532
533
534
<screen>
"Dhcp4": { "hosts-database": { <userinput>"name": "<replaceable>database-name</replaceable>" </userinput>, ... }, ... }
</screen>
535
  If the database is located on a different system than the DHCPv4 server, the
536
537
  database host name must also be specified. (Again it should be noted that this
  configuration may have a severe impact on server performance.):
538
539
540
541
542
543
544
545
<screen>
"Dhcp4": { "hosts-database": { <userinput>"host": <replaceable>remote-host-name</replaceable></userinput>, ... }, ... }
</screen>
  The usual state of affairs will be to have the database on the same machine as
  the DHCPv4 server.  In this case, set the value to the empty string:
<screen>
"Dhcp4": { "hosts-database": { <userinput>"host" : ""</userinput>, ... }, ... }
</screen>
546
  Should the database use a port different than default, it may be
Tomek Mrugalski's avatar
Tomek Mrugalski committed
547
548
549
550
551
  specified as well:
<screen>
"Dhcp4": { "hosts-database": { <userinput>"port" : 12345</userinput>, ... }, ... }
</screen>

552
553
554
555
556
557
558
559
560
561
562
563
  </para>
  <para>Finally, the credentials of the account under which the server will
  access the database should be set:
<screen>
"Dhcp4": { "hosts-database": { <userinput>"user": "<replaceable>user-name</replaceable>"</userinput>,
                               <userinput>"password": "<replaceable>password</replaceable>"</userinput>,
                              ... },
           ... }
</screen>
  If there is no password to the account, set the password to the empty string
  "". (This is also the default.)</para>
</section>
564
565

<section id="read-only-database-configuration4">
566
<title>Using Read-Only Databases for Host Reservations</title>
567
<para>
568
569
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
570
571
572
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
573
static reservations assigned to them. The inventory database can be used to create
574
575
576
a view of a Kea hosts database and such view is often read only.
</para>
<para>
577
578
579
580
581
582
583
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
584
585
586
587
588
589
590
591
592
593
594
595
<command>readonly</command> boolean parameter as follows:
<screen>
"Dhcp4": { "hosts-database": { <userinput>"readonly": true</userinput>, ... }, ... }
</screen>
Setting this parameter to <userinput>false</userinput> would configure the
database backend to operate in "read-write" mode, which is also a default
configuration if the parameter is not specified.
</para>
<note><para>The <command>readonly</command> parameter is currently only supported
for MySQL and PostgreSQL databases.</para></note>
</section>

596
597
</section>

598
<section id="dhcp4-interface-configuration">
599
  <title>Interface Configuration</title>
600
  <para>The DHCPv4 server has to be configured to listen on specific network
601
602
603
  interfaces.  The simplest network interface configuration tells the server to
  listen on all available interfaces:
  <screen>
604
605
606
607
608
609
610
"Dhcp4": {
    "interfaces-config": {
        "interfaces": [ <userinput>"*"</userinput> ]
    }
    ...
},
  </screen>
611
612
  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:
613
  <screen>
614
615
616
617
618
619
620
"Dhcp4": {
    "interfaces-config": {
        "interfaces": [ <userinput>"eth1", "eth3"</userinput> ]
    },
    ...
}
  </screen>
621
622
623
624
  </para>
  <para>It is possible to use wildcard interface name (asterisk) concurrently
  with explicit interface names:
  <screen>
625
626
627
628
629
630
631
"Dhcp4": {
    "interfaces-config": {
        "interfaces": [ <userinput>"eth1", "eth3", "*"</userinput> ]
    },
    ...
}
  </screen>
632
It is anticipated that this form of usage will only be used when it is desired to
633
temporarily override a list of interface names and listen on all interfaces.
634
  </para>
635
  <para>Some deployments of DHCP servers require that the servers listen
636
637
638
  on the interfaces with multiple IPv4 addresses configured. In these situations,
  the address to use can be selected by appending an IPv4 address to the interface
  name in the following manner:
639
640
641
642
643
644
645
646
  <screen>
"Dhcp4": {
    "interfaces-config": {
        "interfaces": [ <userinput>"eth1/10.0.0.1", "eth3/192.0.2.3"</userinput> ]
    },
    ...
}
  </screen>
647
  </para>
648

649
650
  <para>Should the server be required to listen on multiple IPv4 addresses assigned
  to the same interface, multiple addresses can be specified for an interface
651
652
653
654
655
656
657
658
659
660
661
662
663
664
  as in the example below:
  <screen>
"Dhcp4": {
    "interfaces-config": {
        "interfaces": [ <userinput>"eth1/10.0.0.1", "eth1/10.0.0.2"</userinput> ]
    },
    ...
}
  </screen>
  </para>

  <para>Alternatively, if the server should listen on all addresses for the particular
  interface, an interface name without any address should be specified.</para>

665
  <para>Kea supports responding to directly connected clients which don't have
666
  an address configured. This requires that the server
667
668
669
670
671
672
673
674
675
676
677
678
  injects the hardware address of the destination into the data link layer
  of the packet being sent to the client. The DHCPv4 server utilizes the
  raw sockets to achieve this, and builds the entire IP/UDP stack for the
  outgoing packets. The down side of raw socket use, however, is that incoming
  and outgoing packets bypass the firewalls (e.g. iptables). It is also
  troublesome to handle traffic on multiple IPv4 addresses assigned to the
  same interface, as raw sockets are bound to the interface and advanced
  packet filtering techniques (e.g. using the BPF) have to be used to
  receive unicast traffic on the desired addresses assigned to the interface,
  rather than capturing whole traffic reaching the interface to which the raw
  socket is bound. Therefore, in the deployments where the server doesn't
  have to provision the directly connected clients and only receives the
679
680
  unicast packets from the relay agents, the
  DHCP server should be configured to utilize IP/UDP datagram sockets instead of raw sockets.
681
682
683
684
685
686
  The following configuration demonstrates how this can be achieved:

  <screen>
"Dhcp4": {
    "interfaces-config": {
        "interfaces": [ <userinput>"eth1", "eth3"</userinput> ],
687
        "dhcp-socket-type": "udp"
688
689
690
691
    },
    ...
}
  </screen>
692
  The <command>dhcp-socket-type</command> specifies that the IP/UDP sockets will
693
  be opened on all interfaces on which the server listens, i.e. "eth1" and
694
  "eth3" in our case. If the <command>dhcp-socket-type</command> is set to
695
  <userinput>raw</userinput>, it configures the server to use raw sockets
696
  instead. If the <command>dhcp-socket-type</command> value is not specified, the
697
698
699
  default value <userinput>raw</userinput> is used.
  </para>

700
  <para>Using UDP sockets automatically disables the reception of broadcast
701
702
703
704
705
  packets from directly connected clients. This effectively means that the
  UDP sockets can be used for relayed traffic only. When using the raw sockets,
  both the traffic from the directly connected clients and the relayed traffic
  will be handled. Caution should be taken when configuring the server to open
  multiple raw sockets on the interface with several IPv4 addresses assigned.
706
  If the directly connected client sends the message to the broadcast address
707
708
709
710
711
712
713
  all sockets on this link will receive this message and multiple responses
  will be sent to the client. Hence, the configuration with multiple IPv4
  addresses assigned to the interface should not be used when the directly
  connected clients are operating on that link. To use a single address on
  such interface, the "interface-name/address" notation should be used.
  </para>

714
715
716
717
718
719
  <note>
    <para>Specifying the value <userinput>raw</userinput> as the socket type,
    doesn't guarantee that the raw sockets will be used! The use of raw sockets
    to handle the traffic from the directly connected clients is currently
    supported on Linux and BSD systems only. If the raw sockets are not
    supported on the particular OS, the server will issue a warning and
720
    fall back to use IP/UDP sockets.</para>
721
  </note>
Francis Dupont's avatar
Francis Dupont committed
722

723
724
725
726
727
728
729
  <para>In typical environment the DHCP server is expected to send back a
  response on the same network interface on which the query is received. This is
  the default behavior. However, in some deployments it is desired that the
  outbound (response) packets will be sent as regular traffic and the outbound
  interface will be determined by the routing tables. This kind of asymetric
  traffic is uncommon, but valid. Kea now supports a parameter called
  <command>outbound-interface</command> that controls this behavior. It supports
730
  two values. The first one, <userinput>same-as-inbound</userinput>, tells Kea
731
  to send back the response on the same inteface the query packet is received. This
732
733
  is the default behavior. The second one, <userinput>use-routing</userinput>
  tells Kea to send regular UDP packets and let the kernel's routing table to
734
735
736
  determine most appropriate interface. This only works when
  <command>dhcp-socket-type</command> is  set to <userinput>udp</userinput>.
  An example configuration looks as follows:
737
738
739
740
741
742
743
744
745
746
747
  <screen>
"Dhcp4": {
    "interfaces-config": {
        "interfaces": [ "eth1", "eth3" ],
        "dhcp-socket-type": "udp",
        <userinput>"outbound-interface": "use-routing"</userinput>
    },
    ...
}</screen>
  </para>

Francis Dupont's avatar
Francis Dupont committed
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
  <para>Interfaces are re-detected at each reconfiguration. This behavior
  can be disabled by setting <command>re-detect</command> value to
  <userinput>false</userinput>, for instance:

  <screen>
"Dhcp4": {
    "interfaces-config": {
        "interfaces": [ <userinput>"eth1", "eth3"</userinput> ],
        "re-detect": <userinput>false</userinput>
    },
    ...
}
  </screen>
  Note interfaces are not re-detected during <command>config-test</command>.
  </para>

764
765
</section>

766
<section id="dhcpinform-unicast-issues">
767
  <title>Issues with Unicast Responses to DHCPINFORM</title>
Shawn Routhier's avatar
Shawn Routhier committed
768
  <para>The use of UDP sockets has certain benefits in deployments
769
770
771
  where the server receives only relayed traffic; these benefits are
  mentioned in <xref linkend="dhcp4-interface-configuration"/>. From
  the administrator's perspective it is often desirable to
772
  configure the system's firewall to filter out the unwanted traffic, and
773
  the use of UDP sockets facilitates this. However, the administrator must
774
  also be aware of the implications related to filtering certain types
Shawn Routhier's avatar
Shawn Routhier committed
775
  of traffic as it may impair the DHCP server's operation.
776
777
778
779
  </para>

  <para>In this section we are focusing on the case when the server
  receives the DHCPINFORM message from the client via a relay. According
780
  to <ulink url="http://tools.ietf.org/html/rfc2131">RFC 2131</ulink>,
Shawn Routhier's avatar
Shawn Routhier committed
781
  the server should unicast the DHCPACK response to the address carried in
782
  the "ciaddr" field. When the UDP socket is in use, the DHCP server
783
  relies on the low level functions of an operating system to build the
Shawn Routhier's avatar
Shawn Routhier committed
784
  data link, IP and UDP layers of the outgoing message. Typically, the
785
  OS will first use ARP to obtain the client's link layer address to be
786
  inserted into the frame's header, if the address is not cached from
Shawn Routhier's avatar
Shawn Routhier committed
787
  a previous transaction that the client had with the server.
788
  When the ARP exchange is successful, the DHCP message can be unicast
Shawn Routhier's avatar
Shawn Routhier committed
789
  to the client, using the  obtained address.
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
  </para>

  <para>Some system administrators block ARP messages in their network,
  which causes issues for the server when it responds to the
  DHCPINFORM messages, because the server is unable to send the
  DHCPACK if the preceding ARP communication fails. Since the OS is
  entirely responsible for the ARP communication and then sending
  the DHCP packet over the wire, the DHCP server has no means to
  determine that the ARP exchange failed and the DHCP response message
  was dropped. Thus, the server does not log any error messages when
  the outgoing DHCP response is dropped. At the same time, all hooks
  pertaining to the packet sending operation will be called, even
  though the message never reaches its destination.
  </para>

  <para>Note that the issue described in this section is not observed
  when the raw sockets are in use, because, in this case, the DHCP server
  builds all the layers of the outgoing message on its own and does not
  use ARP. Instead, it inserts the value carried in the 'chaddr' field
  of the DHCPINFORM message into the link layer.
  </para>

Shawn Routhier's avatar
Shawn Routhier committed
812
813
814
  <para>Server administrators willing to support DHCPINFORM
  messages via relays should not block ARP traffic in their
  networks or should use raw sockets instead of UDP sockets.
815
816
817
  </para>
</section>

818
819
820
<section id="ipv4-subnet-id">
  <title>IPv4 Subnet Identifier</title>
  <para>
821
    The subnet identifier is a unique number associated with a particular subnet.
822
    In principle, it is used to associate clients' leases with their respective subnets.
823
    When a subnet identifier is not specified for a subnet being configured, it will
824
825
826
827
828
829
830
    be automatically assigned by the configuration mechanism. The identifiers
    are assigned from 1 and are monotonically increased for each subsequent
    subnet: 1, 2, 3 ....
  </para>
  <para>
    If there are multiple subnets configured with auto-generated identifiers and
    one of them is removed, the subnet identifiers may be renumbered. For example:
831
832
    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
833
834
    stored in the lease database for subnet 3 are now associated with
    subnet 4, something that may have unexpected consequences. It is planned
835
    to implement a mechanism to preserve auto-generated subnet ids in a
836
837
838
    future version of Kea.  However, the only remedy for this issue
    at present is to
    manually specify a unique identifier for each subnet.
839
  </para>
840
      <para>
841
842
        The following configuration will assign the specified subnet
        identifier to the newly configured subnet:
843

844
        <screen>
845
846
"Dhcp4": {
    "subnet4": [
847
848
849
850
851
        {
            "subnet": "192.0.2.0/24",
            <userinput>"id": 1024</userinput>,
            ...
        }
852
853
854
    ]
}
</screen>
855
856
    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
857
858
859
860
861
862
863
864
865
    identifier.
  </para>
    <!-- @todo: describe whether database needs to be updated after changing
      id -->
</section>

<section id="dhcp4-address-config">
  <title>Configuration of IPv4 Address Pools</title>
  <para>
866
867
868
    The main role of a DHCPv4 server is address assignment. For this, the server has to
    be configured with at least one subnet and one pool of dynamic addresses for it to manage.
    For example, assume that the server is connected to a network
869
870
871
872
873
874
875
    segment that uses the 192.0.2.0/24 prefix. The Administrator of that network
    has decided that addresses from range 192.0.2.10 to 192.0.2.20 are going to
    be managed by the Dhcp4 server. Such a configuration can be achieved in the
    following way:
    <screen>
"Dhcp4": {
    <userinput>"subnet4": [
876
877
878
879
880
881
882
883
        {
            "subnet": "192.0.2.0/24",
            "pools": [
                { "pool": "192.0.2.10 - 192.0.2.20" }
            ],
            ...
        }
    ]</userinput>
884
885
}</screen>

886
887
888
889
    Note that <command>subnet</command> is defined as a simple string, but
    the <command>pools</command> 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.</para>
890

891
892
893
894
895
    <para>Each <command>pool</command> is a structure that contains the
    parameters that describe a single pool. Currently there is only one
    parameter, <command>pool</command>, which gives the range of addresses
    in the pool. Additional parameters will be added in future releases of
    Kea.</para>
896

897
898
899
900
901
902
903
904
905
    <para>It is possible to define more than one pool in a subnet: continuing
    the previous example, further assume that 192.0.2.64/26 should be also be
    managed by the server. It could be written as 192.0.2.64 to
    192.0.2.127. Alternatively, it can be expressed more simply as
    192.0.2.64/26. Both formats are supported by Dhcp4 and can be mixed in the
    pool list.  For example, one could define the following pools:
<screen>
"Dhcp4": {
    "subnet4": [
906
907
908
909
910
911
912
913
        {
            "subnet": "192.0.2.0/24",
            <userinput>"pools": [
                { "pool": "192.0.2.10-192.0.2.20" },
                { "pool": "192.0.2.64/26" }
            ]</userinput>,
            ...
        }
914
915
916
917
    ],
    ...
}
</screen>
918
919
920
921
    White space in pool definitions is ignored, so spaces before and after the hyphen are optional.
    They can be used to improve readability.
  </para>
  <para>
922
    The number of pools is not limited, but for performance reasons it is recommended to
923
    use as few as possible.
924
925
926
927
  </para>
  <para>
    The server may be configured to serve more than one subnet:
<screen>
928
929
930
931
"Dhcp4": {
    "subnet4": [
        {
            "subnet": "192.0.2.0/24",
932
            "pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ],
933
934
935
936
            ...
        },
        {
            "subnet": "192.0.3.0/24",
937
            "pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
938
939
940
941
            ...
        },
        {
            "subnet": "192.0.4.0/24",
942
            "pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
943
944
945
946
            ...
        }
    ]
}
947
948
949
950
</screen>
  </para>
  <para>
    When configuring a DHCPv4 server using prefix/length notation, please pay
951
952
    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
953
954
955
956
957
958
    address) and the last (typically broadcast address) address from that pool.
    In the aforementioned example of pool 192.0.3.0/24, both 192.0.3.0 and
    192.0.3.255 addresses may be assigned as well. This may be invalid in some
    network configurations. If you want to avoid this, please use the "min-max" notation.
  </para>
</section>
959
960

    <section id="dhcp4-std-options">
961
      <title>Standard DHCPv4 Options</title>
962
      <para>
963
        One of the major features of the DHCPv4 server is to provide configuration
964
        options to clients. Most of the options are sent by the server only if the
965
        client explicitly requests them using the Parameter Request List option.
966
        Those that do not require inclusion in the Parameter Request List
967
        option are commonly used options, e.g. "Domain Server", and options which
968
969
970
971
972
        require special behavior, e.g. "Client FQDN" is returned to the client
        if the client has included this option in its message to the server.
      </para>

      <para>
973
974
        <xref linkend="dhcp4-std-options-list"/> comprises the list of the
        standard DHCPv4 options whose values can be configured using the
975
976
        configuration structures described in this section. This table excludes
        the options which require special processing and thus cannot be configured
977
        with some fixed values. The last column of the table indicates which
978
        options can be sent by the server even when they are not requested in
979
980
        the Parameter Request list option, and those which are sent only when
        explicitly requested.
981
982
983
984
985
986
987
      </para>

      <para>
        The following example shows how to configure the addresses of DNS
        servers, which is one of the most frequently used options. Options
        specified in this way are considered global and apply to all
        configured subnets.
988
989

        <screen>
990
991
992
993
994
995
"Dhcp4": {
    "option-data": [
        {
           <userinput>"name": "domain-name-servers",
           "code": 6,
           "space": "dhcp4",
996
           "csv-format": true,
997
998
999
1000
1001
           "data": "192.0.2.1, 192.0.2.2"</userinput>
        },
        ...
    ]
}
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
        </screen>
        Note that only one of name or code is required, you don't need to
        specify both. Space has a default value of "dhcp4", so you can skip this
        as well if you define a regular (not encapsulated) DHCPv4 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:
        <screen>
"Dhcp4": {
    "option-data": [
        {
           <userinput>"name": "domain-name-servers",
           "data": "192.0.2.1, 192.0.2.2"</userinput>
        },
        ...
    ]
1018
1019
1020
1021
}
        </screen>
        Defined options are added to response when the client requests them
        at a few exceptions which are always added. To enforce the addition
1022
        of a particular option set the always-send flag to true as in:
1023
1024
1025
1026
1027
1028
        <screen>
"Dhcp4": {
    "option-data": [
        {
           <userinput>"name": "domain-name-servers",
           "data": "192.0.2.1, 192.0.2.2",
1029
           "always-send": true</userinput>
1030
1031
1032
1033
1034
        },
        ...
    ]
}
        </screen>
1035
        The effect is the same as if the client added the option code in the
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
        Parameter Request List option (or its equivalent for vendor
        options) so in:
        <screen>
"Dhcp4": {
    "option-data": [
        {
           <userinput>"name": "domain-name-servers",
           "data": "192.0.2.1, 192.0.2.2",
           "always-send": true</userinput>
        },
        ...
    ],
    "subnet4": [
        {
           "subnet": "192.0.3.0/24",
           "option-data": [
               {
                   <userinput>"name": "domain-name-servers",
                   "data": "192.0.3.1, 192.0.3.2"</userinput>
               },
               ...
           ],
           ...
        },
        ...
    ],
    ...
}
        </screen>
        The Domain Name Servers option is always added to responses
        (the always-send is "sticky") but the value is the subnet one
        when the client is localized in the subnet.
1068
1069
      </para>
    <para>
1070
1071
1072
1073
1074
1075
1076
      The <command>name</command> parameter specifies the option name. For a
      list of currently supported names, see <xref
      linkend="dhcp4-std-options-list"/> below.  The <command>code</command>
      parameter specifies the option code, which must match one of the values
      from that list. The next line specifies the option space, which must
      always be set to "dhcp4" as these are standard DHCPv4 options. For other
      option spaces, including custom option spaces, see <xref
1077
      linkend="dhcp4-option-spaces"/>. The next line specifies the format in
1078
1079
1080
1081
      which the data will be entered: use of CSV (comma separated values) is
      recommended. The sixth 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.
1082
1083
1084
    </para>

    <para>
1085
1086
1087
      Options can also be configured as hexadecimal values. If
      <command>csv-format</command> is
      set to false, option data must be specified as a hexadecimal string. The
1088
1089
      following commands configure the domain-name-servers option for all
      subnets with the following addresses: 192.0.3.1 and 192.0.3.2.
1090
      Note that <command>csv-format</command> is set to false.
1091
      <screen>
1092
1093
1094
1095
1096
1097
"Dhcp4": {
    "option-data": [
        {
            <userinput>"name": "domain-name-servers",
            "code": 6,
            "space": "dhcp4",
1098
            "csv-format": false,
1099
1100
1101
1102
1103
1104
            "data": "C0 00 03 01 C0 00 03 02"</userinput>
        },
        ...
    ],
    ...
}</screen>
Tomek Mrugalski's avatar
Tomek Mrugalski committed
1105
1106
1107
1108
1109
1110
    </para>

       <para>
       Care should be taken
       to use proper encoding when using hexadecimal format as Kea's ability
       to validate data correctness in hexadecimal is limited.
1111
1112
      </para>

1113
1114
1115
1116
1117
1118
      <para>
        Most of the parameters in the "option-data" structure are optional and
        can be omitted in some circumstances as discussed in the
        <xref linkend="dhcp4-option-data-defaults"/>.
      </para>

1119
      <para>
1120
        It is possible to specify or override options on a per-subnet basis.  If
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
        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
        (Dhcp4/option-data), rather you should set only subnet-specific values
        (Dhcp4/subnet[X]/option-data[Y]).
      </para>
      <para>
        The following commands override the global
        DNS servers option for a particular subnet, setting a single DNS
        server with address 192.0.2.3.
1133
1134
1135
1136
1137
1138
1139
1140
<screen>
"Dhcp4": {
    "subnet4": [
        {
            <userinput>"option-data": [
                {
                    "name": "domain-name-servers",
                    "code": 6,
Jeremy C. Reed's avatar
Jeremy C. Reed committed
1141
                    "space": "dhcp4",
1142
                    "csv-format": true,
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
                    "data": "192.0.2.3"
                },
                ...
            ]</userinput>,
            ...
        },
        ...
    ],
    ...
}
</screen>
1154
1155
1156
      </para>

      <para>
1157
1158
1159
        In some cases it is useful to associate some options with an
        address pool from which a client is assigned a lease. Pool
        specific option values override subnet specific and global
1160
1161
1162
1163
1164
        option values. 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.
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
      </para>

     <para>
       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:
<screen>
"Dhcp4": {
    "subnet4": [
        {
            "pools": [
                {
                    "pool": "192.0.2.1 - 192.0.2.200",
                    <userinput>"option-data": [
                        {
                            "name": "domain-name-servers",
                            "data": "192.0.2.3"
                         },
                         ...
                    ]</userinput>,
                    ...
                },
                ...
            ],
            ...
        },
        ...
    ],
    ...
}
</screen>
      </para>

1198
1199
      <para>
        The currently supported standard DHCPv4 options are
1200
        listed in <xref linkend="dhcp4-std-options-list"/>.
1201
1202
1203
1204
1205
        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 <xref linkend="dhcp-types"/>.
      </para>
Tomek Mrugalski's avatar
Tomek Mrugalski committed
1206

1207
      <para>When a data field is a string, and that string contains the comma
1208
      (,; U+002C) character, the comma must be escaped with a double reverse solidus
1209
1210
1211
1212
      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 &quot;foo,bar&quot; would be represented as:
Tomek Mrugalski's avatar
Tomek Mrugalski committed
1213
1214
1215
1216
1217
1218
1219
1220
1221
      <screen>
"Dhcp4": {
    "subnet4": [
        {
            "pools": [
                {
                    <userinput>"option-data": [
                        {
                            "name": "boot-file-name",
1222
                            "data": "foo\\,bar"
Tomek Mrugalski's avatar
Tomek Mrugalski committed
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
                        }
                    ]</userinput>
                },
                ...
            ],
            ...
        },
        ...
    ],
    ...
}
</screen>
      </para>
1236
1237
1238
1239
      <para>
        Some options are designated as arrays, which means that more than one
        value is allowed in such an option. For example the option time-servers
        allows the specification of more than one IPv4 address, so allowing
1240
        clients to obtain the addresses of multiple NTP servers.
1241
1242
      </para>
      <!-- @todo: describe record types -->
1243
      <!-- @todo: describe array in record types -->
1244
1245
1246
1247
1248
1249
1250

      <para>
        The <xref linkend="dhcp4-custom-options"/> 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
1251
        Kea currently does not provide a definition. In order to use such options,
1252
1253
1254
        a server administrator must create a definition as described in
        <xref linkend="dhcp4-custom-options"/> in the 'dhcp4' option space. This
        definition should match the option format described in the relevant
1255
1256
        RFC but the configuration mechanism will allow any option format as it
        presently has no means to validate it.
1257
1258
1259
1260
1261
      </para>

      <para>
        <table frame="all" id="dhcp4-std-options-list">
          <title>List of standard DHCPv4 options</title>
1262
          <tgroup cols='5'>
1263
          <colspec colname='name'/>
1264
1265
1266
          <colspec colname='code' align='center'/>
          <colspec colname='type' align='center'/>
          <colspec colname='array' align='center'/>
1267
          <colspec colname='always-returned' align='center'/>
1268
1269
1270
1271
1272
1273
          <thead>
            <row>
              <entry>Name</entry>
              <entry>Code</entry>
              <entry>Type</entry>
              <entry>Array?</entry>
1274
              <entry>Returned if not requested?</entry>
1275
1276
1277
            </row>
          </thead>
          <tbody>
1278
<!-- Subnet Mask option is not configured by the user
1279
<row><entry>subnet-mask</entry><entry>1</entry><entry>ipv4-address</entry><entry>false</entry><entry>true</entry></row>
1280
-->
1281
1282
1283
<row><entry>time-offset</entry><entry>2</entry><entry>int32</entry><entry>false</entry><entry>false</entry></row>
<row><entry>routers</entry><entry>3</entry><entry>ipv4-address</entry><entry>true</entry><entry>true</entry></row>
<row><entry>time-servers</entry><entry>4</entry><entry>ipv4-address</entry><entry>true</entry><entry>false</entry></row>
1284
<row><entry>name-servers</entry><entry>5</entry><entry>ipv4-address</entry><entry>true</entry><entry>false</entry></row>
1285
1286
1287
1288
1289
1290
<row><entry>domain-name-servers</entry><entry>6</entry><entry>ipv4-address</entry><entry>true</entry><entry>true</entry></row>
<row><entry>log-servers</entry><entry>7</entry><entry>ipv4-address</entry><entry>true</entry><entry>false</entry></row>
<row><entry>cookie-servers</entry><entry>8</entry><entry>ipv4-address</entry><entry>true</entry><entry>false</entry></row>
<row><entry>lpr-servers</entry><entry>9</entry><entry>ipv4-address</entry><entry>true</entry><entry>false</entry></row>
<row><entry>impress-servers</entry><entry>10</entry><entry>ipv4-address</entry><entry>true</entry><entry>false</entry></row>
<row><entry>resource-location-servers</entry><entry>11</entry><entry>ipv4-address</entry><entry>true</entry><entry>false</entry></row>