dhcp4-srv.xml 86.8 KB
Newer Older
1
2
3
4
5
6
7
8
9
10
11
12
<?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>

13
14
      <!-- @todo Rewrite this section once #3422 is done -->

15
      <para>
16
      It is recommended that the Kea DHCPv4 server be started and stopped
Jeremy C. Reed's avatar
Jeremy C. Reed committed
17
      using <command>keactrl</command> (described in <xref linkend="keactrl"/>).
18
19
      However, it is also possible to run the server directly: it accepts
      the following command-line switches:
20
      </para>
21
22
23

      <itemizedlist>
          <listitem>
24
25
26
27
            <simpara>
            <command>-c <replaceable>file</replaceable></command> -
            specifies the configuration file. This is the only mandatory
            switch.</simpara>
28
29
          </listitem>
          <listitem>
30
            <simpara>
Tomek Mrugalski's avatar
Tomek Mrugalski committed
31
32
            <command>-d</command> - specifies whether the server
            logging should be switched to debug/verbose mode. In verbose mode,
33
            the logging severity and debuglevel specified in the configuration
34
35
36
37
            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>
38
39
          </listitem>
          <listitem>
40
41
42
43
44
45
            <simpara>
            <command>-p <replaceable>port</replaceable></command> -
            specifies UDP port the server will listen on. This is only
            useful during testing, as the DHCPv4 server listening on
            ports other than default DHCPv4 ports will not be able to
            handle regular DHCPv4 queries.</simpara>
46
          </listitem>
Tomek Mrugalski's avatar
Tomek Mrugalski committed
47
48
          <listitem>
            <simpara>
Tomek Mrugalski's avatar
Tomek Mrugalski committed
49
              <command>-v</command> - prints out Kea version and exits.
Tomek Mrugalski's avatar
Tomek Mrugalski committed
50
51
52
53
54
            </simpara>
          </listitem>
          <listitem>
            <simpara>
              <command>-V</command> - prints out Kea extended version with
Tomek Mrugalski's avatar
Tomek Mrugalski committed
55
              additional parameters and exits.
Tomek Mrugalski's avatar
Tomek Mrugalski committed
56
57
            </simpara>
          </listitem>
58
59
      </itemizedlist>

60
      <para>
61
62
63
	    When running in a console, the server can be shut down by
	    pressing ctrl-c. It detects the key combination and shuts
	    down gracefully.
64
65
66
67
      </para>

      <para>
        On start-up, the server will detect available network interfaces
68
69
        and will attempt to open UDP sockets on all interfaces
        mentioned in the configuration file.
70
      </para>
71

72
      <para>
73
74
75
76
77
78
79
        Since the DHCPv4 server opens privileged ports, it requires root
        access. Make sure you run this daemon as root.
      </para>

    </section>

    <section id="dhcp4-configuration">
80
      <title>DHCPv4 Server Configuration</title>
81
82
<section>
  <title>Introduction</title>
83
      <para>
84
        This section explains how to configure the DHCPv4 server using the
85
86
        Kea configuration backend. (Kea configuration using any other
        backends is outside of scope of this document.) Before DHCPv4
87
        is started, its configuration file has to be created. The
88
        basic configuration is as follows:
89
<screen>
90
91
92
93
94
95
96
97
98
99
100
101
{
# DHCPv4 configuration starts in this line
"Dhcp4": {

# First we set up global values
    "interfaces": [ "eth0" ],
    "valid-lifetime": 4000,
    "renew-timer": 1000,
    "rebind-timer": 2000,

# Next we specify the type of lease database
    "lease-database": {
Tomek Mrugalski's avatar
Tomek Mrugalski committed
102
        "type": "memfile",
103
        "persist": true,
Tomek Mrugalski's avatar
Tomek Mrugalski committed
104
        "name": "/var/kea/dhcp4.leases"
105
106
107
108
109
110
    },

# Finally, we list the subnets from which we will be leasing addresses.
    "subnet4": [
        {
            "subnet": "192.0.2.0/24",
111
112
113
            "pools": [
                { "pool": "192.0.2.1 - 192.0.2.200" }
            ]
114
115
116
117
118
119
120
        }
    ]

# DHCPv4 configuration ends with this line
}

} </screen>
121
</para>
122

123
124
125
126
<para>The following paragraphs provide a brief overview of the parameters in
the above example and
their format. Subsequent sections of this chapter go into much greater detail
for these and other parameters.</para>
127

128
129
<para>The lines starting with a hash (#) are comments and are ignored by
the server; they do not impact its
130
131
operation in any way.</para>

132
133
134
135
136
137
<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
object called Dhcp4. This is a simplified configuration, as usually
there will be additional objects, like <command>Logging</command> or
<command>DhcpDns</command>, but we omit them now for clarity. The Dhcp4
138
configuration starts with the <command>"Dhcp4": {</command> line
139
140
141
142
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>

143
<para>In the general case, the order in which those parameters appear does not
144
matter. There are two caveats here though. The first one is to remember that
145
146
147
148
149
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
150
legal JSON &mdash; to
151
repeat the same parameter multiple times. If that happens, the last occurrence of a
152
given parameter in a given scope is used while all previous instances are
153
ignored. This is unlikely to cause any confusion as there are no real life
154
155
156
reasons to keep multiple copies of the same parameter in your configuration
file.</para>

157
158
159
160
161
<para>Moving onto the DHCPv4 configuration elements,
the line defining <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 line could
162
look like this:
163
164
<screen>
"interfaces": [ "eth0", "eth1" ],
165
</screen>
166
As "<command>interfaces</command>" is not the last parameter in the configuration,
167
a trailing comma is required.</para>
168
<para>A number of other parameters
169
follow. <command>valid-lifetime</command> defines for how long the addresses (leases) given out by the
170
server are valid. If nothing changes, a client that got an address is allowed to
171
172
173
use it for 4000 seconds. (Note that integer numbers are specified as is,
without any quotes around them.) <command>renew-timer</command> and
<command>rebind-timer</command> are values that
174
define T1 and T2 timers that govern when the client will begin the renewal and
175
176
177
178
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>
179

180
<para>The next couple of lines define the lease database, the place where the server
181
stores its lease information. This particular example tells the server to use
182
<command>memfile</command>, which is the simplest (and fastest) database
183
backend. It uses an in-memory database and stores leases on disk in a CSV
184
file. This is a very simple configuration. Usually, lease database configuration
185
186
187
188
189
190
191
192
193
194
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.
Its parameters (just one in this example -- <command>type</command>)
follow. Had there been more than one, they would be separated by commas. This
scope is closed with a closing brace. As more parameters follow, a trailing
comma is present.</para>

<para>Finally, we need to define a list of IPv4 subnets. This is the
most important DHCPv4 configuration structure as the server uses that
195
196
information to process clients' requests. It defines all subnets from
which the server is expected to receive DHCP requests. The subnets are
197
198
specified with the <command>subnet4</command> parameter.  It is a list,
so it starts and ends with square brackets.  Each subnet definition in
199
200
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
201
has to have at least two parameters: <command>subnet</command> (that
202
defines the whole subnet) and <command>pools</command> (which is a list of
203
dynamically allocated pools that are governed by the DHCP server).</para>
204
205
206
207
208
209

<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:
210
<screen>
211
212
"subnet4": [
    {
213
        "pools": [ { "pool":  "192.0.2.1 - 192.0.2.200" } ],
214
215
216
        "subnet": "192.0.2.0/24"
    },
    {
217
        "pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
218
219
220
        "subnet": "192.0.3.0/24"
    },
    {
Adam Osuchowski's avatar
Adam Osuchowski committed
221
        "pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
222
223
224
        "subnet": "192.0.4.0/24"
    }
]
225
226
227
</screen>
</para>

228
229
<para>After all parameters are specified, we have two contexts open:
global and Dhcp4, hence we need two closing curly brackets to close them.
230
231
In a real life configuration file there most likely would be additional
components defined such as Logging or DhcpDdns, so the closing brace would
232
be followed by a comma and another object definition.</para>
233
234
235

<para>Kea 0.9 does not have configuration syntax validation
implemented yet. Such a feature is planned for the near future. For
236
237
238
239
the time being, it is convenient to use on-line JSON validators and/or
viewers to check whether the syntax is correct. One example of such a
JSON validator is available at <ulink
url="http://jsonviewer.stack.hu/"/>.
240
</para>
241
</section>
242

243
<section>
244
245
246
247
248
249
  <title>Lease Storage</title>
  <para>All leases issued by the server are stored in the lease database.
  Currently there are three database backends available:
  memfile (which is the default backend), MySQL and PostgreSQL.</para>
<section>
  <title>Memfile - Basic Storage for Leases</title>
250
251
252

  <para>The server is able to store lease data in different repositories. Larger
  deployments may elect to store leases in a database. <xref
253
254
255
256
257
  linkend="database-configuration4"/> describes this option. In typical
  smaller deployments though, the server will use a CSV file rather than a database to
  store lease information. As well as requiring less administration, an
  advantage of using a file for storage is that it
  eliminates a dependency on third-party database software.</para>
258
259
260
261
262

  <para>The configuration of the file backend (Memfile) is controlled through
  the Dhcp4/lease-database parameters. <!-- @todo: we don't have default
  parameters. Let's comment this out When default parameters are used, the
  Memfile backend will write leases to a disk in the
263
  [kea-install-dir]/var/kea/kea-leases4.csv. -->
Jeremy C. Reed's avatar
Jeremy C. Reed committed
264
  The following configuration sets the name of the lease file to
265
  <filename>/tmp/kea-leases4.csv</filename>:
Jeremy C. Reed's avatar
Jeremy C. Reed committed
266

267
<screen>
268
269
270
"Dhcp4": {
    "lease-database": {
        <userinput>"type": "memfile"</userinput>,
271
        <userinput>"persist": true</userinput>,
272
273
274
275
        <userinput>"name": "/tmp/kea-leases4.csv"</userinput>
    }
    ...
}
276
</screen>
277
278
279
  </para>

  <para>The "persist" parameter controls whether the leases are written to disk.
280
281
282
283
284
285
  It is strongly recommended that this parameter is set to
  <command>true</command> at all times during the normal operation of the
  server. (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.)</para>
286
287
288
289
290
291
292
293
294
295
296
297
298
</section>

<section id="database-configuration4">
  <title>Database Configuration</title>

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

  <para>Database configuration is controlled through the Dhcp4/lease-database
299
300
  parameters. The type of the database must be set to "mysql" or "postgresql",
  e.g.
301
<screen>
302
"Dhcp4": { "lease-database": { <userinput>"type": "mysql"</userinput>, ... }, ... }
303
</screen>
304
  Next, the name of the database to hold the leases must be set: this is the
305
306
  name used when the lease database was created (see <xref linkend="dhcp-mysql-database-create"/>
  or <xref linkend="dhcp-pgsql-database-create"/>).
307
<screen>
308
"Dhcp4": { "lease-database": { <userinput>"name": "<replaceable>database-name</replaceable>" </userinput>, ... }, ... }
309
</screen>
310
  If the database is located on a different system to the DHCPv4 server, the
311
  database host name must also be specified (although it should be noted that this
312
  configuration may have a severe impact on server performance):
313
<screen>
314
"Dhcp4": { "lease-database": { <userinput>"host": <replaceable>remote-host-name</replaceable>"</userinput>, ... }, ... }
315
</screen>
316
317
  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:
318
<screen>
319
"Dhcp4": { "lease-database": { <userinput>"host" : ""</userinput>, ... }, ... }
320
</screen>
321
322
323
  </para>
  <para>Finally, the credentials of the account under which the server will
  access the database should be set:
324
<screen>
325
"Dhcp4": { "lease-database": { <userinput>"user": "<replaceable>user-name</replaceable>"</userinput>,
326
                               <userinput>"password": "<replaceable>password</replaceable>"</userinput>,
327
328
                              ... },
           ... }
329
</screen>
330
331
332
  If there is no password to the account, set the password to the empty string
  "". (This is also the default.)</para>
</section>
333
</section>
334
335
336

<section id="dhcp4-interface-selection">
  <title>Interface selection</title>
337
  <para>The DHCPv4 server has to be configured to listen on specific network
338
339
340
341
  interfaces.  The simplest network interface configuration tells the server to
  listen on all available interfaces:
  <screen>
"Dhcp4": { <userinput>"interfaces": ["*"]</userinput>, ... }</screen>
342
343
  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:
344
345
346
347
348
349
350
  <screen>
"Dhcp4": { <userinput>"interfaces": [ "eth1", "eth3" ]</userinput>, ... }</screen>
  </para>
  <para>It is possible to use wildcard interface name (asterisk) concurrently
  with explicit interface names:
  <screen>
"Dhcp4": { <userinput>"interfaces": [ "eth1", "eth3", "*" ]</userinput>, ... }</screen>
351
It is anticipated that this form of usage will only be used when it is desired to
352
temporarily override a list of interface names and listen on all interfaces.
353
  </para>
354
355
356
357
358
359
360
361
362
363
364
  <para>Some deployments of the DHCP servers require that the servers listen
  on the interfaces with multiple IPv4 addresses configured. In some cases,
  multiple instances of the DHCP servers are running concurrently and each
  instance should be bound to a different address on the particular interface.
  The administrator must be able to select this address for each instance.
  This can be achieved by appending an IPv4 address to the interface
  name using the following notation:
<screen>
"Dhcp4": { <userinput>"interfaces": [ "eth1/10.0.0.1", "eth3/192.0.2.3" ]</userinput>, ... }</screen>
  Note that it is not allowed to specify more than one address for an interface.
  </para>
365
366
367
368
369
</section>

<section id="ipv4-subnet-id">
  <title>IPv4 Subnet Identifier</title>
  <para>
370
    The subnet identifier is a unique number associated with a particular subnet.
371
    In principle, it is used to associate clients' leases with their respective subnets.
372
    When a subnet identifier is not specified for a subnet being configured, it will
373
374
375
376
377
378
379
    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:
380
381
    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
382
383
    stored in the lease database for subnet 3 are now associated with
    subnet 4, something that may have unexpected consequences. It is planned
384
    to implement a mechanism to preserve auto-generated subnet ids in a
385
386
387
    future version of Kea.  However, the only remedy for this issue
    at present is to
    manually specify a unique identifier for each subnet.
388
  </para>
389
      <para>
390
	The following configuration will assign the specified subnet
391
392
	identifier to the newly configured subnet:

393
        <screen>
394
395
396
397
398
399
400
401
"Dhcp4": {
    "subnet4": [
        "subnet": "192.0.2.0/24",
        <userinput>"id": 1024</userinput>,
        ...
    ]
}
</screen>
402
403
    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
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
    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>
    The essential role of DHCPv4 server is address assignment. The server has to
    be configured with at least one subnet and one pool of dynamic addresses to
    be managed. For example, assume that the server is connected to a network
    segment that uses the 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": [
        "subnet": "192.0.2.0/24",
424
425
426
427
428
        "pools": [
	    {
	        "pool": "192.0.2.10 - 192.0.2.20"
            }
        ]</userinput>,
429
430
431
432
        ...
    ]
}</screen>

433
    Note that subnet is defined as a simple string, but the 'pools' parameter is
434
435
    actually a list of pools: for this reason, the pool definition is enclosed
    in square brackets, even though only one range of addresses is
436
    specified in this example.</para>
437

438
    <para>Each <command>pool</command> is a structure that contains the parameters
439
    that describe a single pool. Currently there is only one parameter,
440
441
442
443
    <command>pool</command>, which gives the range of addresses
    in the pool. Additional parameters will be added in future
    releases of Kea.</para>

444
445
446
447
448
449
450
451
452
    <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": [
453
454
455
456
        <userinput>"pools": [
            { "pool": "192.0.2.10-192.0.2.20" },
            { "pool": "192.0.2.64/26" }
        ]</userinput>,
457
458
459
460
461
462
        ...
    ],
    ...
}
</screen>
    The number of pools is not limited, but for performance reasons it is recommended to
463
    use as few as possible. White space in pool definitions is ignored, so
464
    spaces before and after the hyphen are optional. They can be used to improve readability.
465
466
467
468
  </para>
  <para>
    The server may be configured to serve more than one subnet:
<screen>
469
470
471
472
"Dhcp4": {
    "subnet4": [
        {
            "subnet": "192.0.2.0/24",
473
            "pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ],
474
475
476
477
            ...
        },
        {
            "subnet": "192.0.3.0/24",
478
            "pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
479
480
481
482
            ...
        },
        {
            "subnet": "192.0.4.0/24",
483
            "pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
484
485
486
487
            ...
        }
    ]
}
488
489
490
491
</screen>
  </para>
  <para>
    When configuring a DHCPv4 server using prefix/length notation, please pay
492
493
    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
494
495
496
497
498
499
    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>
500
501
502
503

    <section id="dhcp4-std-options">
      <title>Standard DHCPv4 options</title>
      <para>
504
        One of the major features of the DHCPv4 server is to provide configuration
505
        options to clients.  Although there are several options that require
506
        special behavior, most options are sent by the server only if the client
507
        explicitly requests them.  The following example shows how to
508
        configure the addresses of DNS servers, which is one of the most frequently used
509
510
511
512
        options. Options specified in this way are considered global and apply
        to all configured subnets.

        <screen>
513
514
515
516
517
518
"Dhcp4": {
    "option-data": [
        {
           <userinput>"name": "domain-name-servers",
           "code": 6,
           "space": "dhcp4",
519
           "csv-format": true,
520
521
522
523
524
           "data": "192.0.2.1, 192.0.2.2"</userinput>
        },
        ...
    ]
}
525
526
527
</screen>
      </para>
    <para>
528
      The <command>name</command> parameter specifies the
529
530
      option name. For a complete list of currently supported names,
      see <xref linkend="dhcp4-std-options-list"/> below.
531
      The <command>code</command> parameter specifies the option code, which must match one of the
532
      values from that list. The next line specifies the option space, which must always
533
534
      be set to "dhcp4" as these are standard DHCPv4 options. For
      other option spaces, including custom option spaces, see <xref
535
      linkend="dhcp4-option-spaces"/>. The next line specifies the format in
536
537
      which the data will be entered: use of CSV (comma
      separated values) is recommended. The sixth line gives the actual value to
538
      be sent to clients. Data is specified as normal text, with
539
540
541
542
543
      values separated by commas if more than one value is
      allowed.
    </para>

    <para>
544
545
546
      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
547
548
      following commands configure the domain-name-servers option for all
      subnets with the following addresses: 192.0.3.1 and 192.0.3.2.
549
      Note that <command>csv-format</command> is set to false.
550
      <screen>
551
552
553
554
555
556
"Dhcp4": {
    "option-data": [
        {
            <userinput>"name": "domain-name-servers",
            "code": 6,
            "space": "dhcp4",
557
            "csv-format": false,
558
559
560
561
562
563
            "data": "C0 00 03 01 C0 00 03 02"</userinput>
        },
        ...
    ],
    ...
}</screen>
564
565
      </para>

566
567
568
569
570
571
      <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>

572
      <para>
573
        It is possible to specify or override options on a per-subnet basis.  If
574
575
576
577
578
579
580
581
582
583
584
585
        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.
586
587
588
589
590
591
592
593
<screen>
"Dhcp4": {
    "subnet4": [
        {
            <userinput>"option-data": [
                {
                    "name": "domain-name-servers",
                    "code": 6,
Jeremy C. Reed's avatar
Jeremy C. Reed committed
594
                    "space": "dhcp4",
595
                    "csv-format": true,
596
597
598
599
600
601
602
603
604
605
606
                    "data": "192.0.2.3"
                },
                ...
            ]</userinput>,
            ...
        },
        ...
    ],
    ...
}
</screen>
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
      </para>

      <para>
        The currently supported standard DHCPv4 options are
        listed in <xref linkend="dhcp4-std-options-list"/>
        and <xref linkend="dhcp4-std-options-list-part2"/>.
        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>
      <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
622
        clients to obtain the addresses of multiple NTP servers.
623
624
625
626
627
628
629
630
631
632
633
634
635
      </para>
      <!-- @todo: describe record types -->

      <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
        Kea does not provide a definition yet. In order to use such options,
        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
636
637
        RFC but the configuration mechanism will allow any option format as it has
        no means to validate the format at the moment.
638
639
640
641
642
643
644
      </para>

      <para>
        <table frame="all" id="dhcp4-std-options-list">
          <title>List of standard DHCPv4 options</title>
          <tgroup cols='4'>
          <colspec colname='name'/>
645
646
647
          <colspec colname='code' align='center'/>
          <colspec colname='type' align='center'/>
          <colspec colname='array' align='center'/>
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
          <thead>
            <row>
              <entry>Name</entry>
              <entry>Code</entry>
              <entry>Type</entry>
              <entry>Array?</entry>
            </row>
          </thead>
          <tbody>
<row><entry>subnet-mask</entry><entry>1</entry><entry>ipv4-address</entry><entry>false</entry></row>
<row><entry>time-offset</entry><entry>2</entry><entry>int32</entry><entry>false</entry></row>
<row><entry>routers</entry><entry>3</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>time-servers</entry><entry>4</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>name-servers</entry><entry>5</entry><entry>ipv4-address</entry><entry>false</entry></row>
<row><entry>domain-name-servers</entry><entry>6</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>log-servers</entry><entry>7</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>cookie-servers</entry><entry>8</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>lpr-servers</entry><entry>9</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>impress-servers</entry><entry>10</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>resource-location-servers</entry><entry>11</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>host-name</entry><entry>12</entry><entry>string</entry><entry>false</entry></row>
<row><entry>boot-size</entry><entry>13</entry><entry>uint16</entry><entry>false</entry></row>
<row><entry>merit-dump</entry><entry>14</entry><entry>string</entry><entry>false</entry></row>
<row><entry>domain-name</entry><entry>15</entry><entry>fqdn</entry><entry>false</entry></row>
<row><entry>swap-server</entry><entry>16</entry><entry>ipv4-address</entry><entry>false</entry></row>
<row><entry>root-path</entry><entry>17</entry><entry>string</entry><entry>false</entry></row>
<row><entry>extensions-path</entry><entry>18</entry><entry>string</entry><entry>false</entry></row>
<row><entry>ip-forwarding</entry><entry>19</entry><entry>boolean</entry><entry>false</entry></row>
<row><entry>non-local-source-routing</entry><entry>20</entry><entry>boolean</entry><entry>false</entry></row>
<row><entry>policy-filter</entry><entry>21</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>max-dgram-reassembly</entry><entry>22</entry><entry>uint16</entry><entry>false</entry></row>
<row><entry>default-ip-ttl</entry><entry>23</entry><entry>uint8</entry><entry>false</entry></row>
<row><entry>path-mtu-aging-timeout</entry><entry>24</entry><entry>uint32</entry><entry>false</entry></row>
<row><entry>path-mtu-plateau-table</entry><entry>25</entry><entry>uint16</entry><entry>true</entry></row>
<row><entry>interface-mtu</entry><entry>26</entry><entry>uint16</entry><entry>false</entry></row>
<row><entry>all-subnets-local</entry><entry>27</entry><entry>boolean</entry><entry>false</entry></row>
<row><entry>broadcast-address</entry><entry>28</entry><entry>ipv4-address</entry><entry>false</entry></row>
<row><entry>perform-mask-discovery</entry><entry>29</entry><entry>boolean</entry><entry>false</entry></row>
<row><entry>mask-supplier</entry><entry>30</entry><entry>boolean</entry><entry>false</entry></row>
<row><entry>router-discovery</entry><entry>31</entry><entry>boolean</entry><entry>false</entry></row>
<row><entry>router-solicitation-address</entry><entry>32</entry><entry>ipv4-address</entry><entry>false</entry></row>
<row><entry>static-routes</entry><entry>33</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>trailer-encapsulation</entry><entry>34</entry><entry>boolean</entry><entry>false</entry></row>
<row><entry>arp-cache-timeout</entry><entry>35</entry><entry>uint32</entry><entry>false</entry></row>
<row><entry>ieee802-3-encapsulation</entry><entry>36</entry><entry>boolean</entry><entry>false</entry></row>
<row><entry>default-tcp-ttl</entry><entry>37</entry><entry>uint8</entry><entry>false</entry></row>
694
<row><entry>tcp-keepalive-interval</entry><entry>38</entry><entry>uint32</entry><entry>false</entry></row>
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
<row><entry>tcp-keepalive-garbage</entry><entry>39</entry><entry>boolean</entry><entry>false</entry></row>

          </tbody>
          </tgroup>
        </table>
      </para>

      <para>
        <table frame="all" id="dhcp4-std-options-list-part2">
          <title>List of standard DHCPv4 options (continued)</title>
          <tgroup cols='4'>
          <colspec colname='name'/>
          <colspec colname='code'/>
          <colspec colname='type'/>
          <colspec colname='array'/>
          <thead>
            <row>
              <entry>Name</entry>
              <entry>Code</entry>
              <entry>Type</entry>
              <entry>Array?</entry>
            </row>
          </thead>
          <tbody>

<row><entry>nis-domain</entry><entry>40</entry><entry>string</entry><entry>false</entry></row>
<row><entry>nis-servers</entry><entry>41</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>ntp-servers</entry><entry>42</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>vendor-encapsulated-options</entry><entry>43</entry><entry>empty</entry><entry>false</entry></row>
<row><entry>netbios-name-servers</entry><entry>44</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>netbios-dd-server</entry><entry>45</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>netbios-node-type</entry><entry>46</entry><entry>uint8</entry><entry>false</entry></row>
<row><entry>netbios-scope</entry><entry>47</entry><entry>string</entry><entry>false</entry></row>
<row><entry>font-servers</entry><entry>48</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>x-display-manager</entry><entry>49</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>dhcp-requested-address</entry><entry>50</entry><entry>ipv4-address</entry><entry>false</entry></row>
<!-- Lease time should not be configured by a user.
<row><entry>dhcp-lease-time</entry><entry>51</entry><entry>uint32</entry><entry>false</entry></row>
-->
<row><entry>dhcp-option-overload</entry><entry>52</entry><entry>uint8</entry><entry>false</entry></row>
<!-- Message Type, Server Identifier and Parameter Request List should not be configured by a user.
<row><entry>dhcp-message-type</entry><entry>53</entry><entry>uint8</entry><entry>false</entry></row>
<row><entry>dhcp-server-identifier</entry><entry>54</entry><entry>ipv4-address</entry><entry>false</entry></row>
<row><entry>dhcp-parameter-request-list</entry><entry>55</entry><entry>uint8</entry><entry>true</entry></row>
-->
<row><entry>dhcp-message</entry><entry>56</entry><entry>string</entry><entry>false</entry></row>
<row><entry>dhcp-max-message-size</entry><entry>57</entry><entry>uint16</entry><entry>false</entry></row>
<!-- Renewal and rebinding time should not be configured by a user.
<row><entry>dhcp-renewal-time</entry><entry>58</entry><entry>uint32</entry><entry>false</entry></row>
<row><entry>dhcp-rebinding-time</entry><entry>59</entry><entry>uint32</entry><entry>false</entry></row>
-->
<row><entry>vendor-class-identifier</entry><entry>60</entry><entry>binary</entry><entry>false</entry></row>
<!-- Client identifier should not be configured by a user.
<row><entry>dhcp-client-identifier</entry><entry>61</entry><entry>binary</entry><entry>false</entry></row>
-->
<row><entry>nwip-domain-name</entry><entry>62</entry><entry>string</entry><entry>false</entry></row>
<row><entry>nwip-suboptions</entry><entry>63</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>tftp-server-name</entry><entry>66</entry><entry>string</entry><entry>false</entry></row>
<row><entry>boot-file-name</entry><entry>67</entry><entry>string</entry><entry>false</entry></row>
<row><entry>user-class</entry><entry>77</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>fqdn</entry><entry>81</entry><entry>record</entry><entry>false</entry></row>
<row><entry>dhcp-agent-options</entry><entry>82</entry><entry>empty</entry><entry>false</entry></row>
<row><entry>authenticate</entry><entry>90</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>client-last-transaction-time</entry><entry>91</entry><entry>uint32</entry><entry>false</entry></row>
<row><entry>associated-ip</entry><entry>92</entry><entry>ipv4-address</entry><entry>true</entry></row>
<row><entry>subnet-selection</entry><entry>118</entry><entry>ipv4-address</entry><entry>false</entry></row>
<row><entry>domain-search</entry><entry>119</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>vivco-suboptions</entry><entry>124</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>vivso-suboptions</entry><entry>125</entry><entry>binary</entry><entry>false</entry></row>
          </tbody>
          </tgroup>
        </table>

      </para>
      <para>
        <table frame="all" id="dhcp-types">
          <title>List of standard DHCP option types</title>
          <tgroup cols='2'>
          <colspec colname='name'/>
          <colspec colname='meaning'/>
          <thead>
            <row><entry>Name</entry><entry>Meaning</entry></row>
          </thead>
          <tbody>
            <row><entry>binary</entry><entry>An arbitrary string of bytes, specified as a set of hexadecimal digits.</entry></row>
            <row><entry>boolean</entry><entry>Boolean value with allowed values true or false</entry></row>
            <row><entry>empty</entry><entry>No value, data is carried in suboptions</entry></row>
            <row><entry>fqdn</entry><entry>Fully qualified domain name (e.g. www.example.com)</entry></row>
            <row><entry>ipv4-address</entry><entry>IPv4 address in the usual dotted-decimal notation (e.g. 192.0.2.1)</entry></row>
            <row><entry>ipv6-address</entry><entry>IPv6 address in the usual colon notation (e.g. 2001:db8::1)</entry></row>
            <row><entry>record</entry><entry>Structured data that may comprise any types (except "record" and "empty")</entry></row>
            <row><entry>string</entry><entry>Any text</entry></row>
            <row><entry>uint8</entry><entry>8 bit unsigned integer with allowed values 0 to 255</entry></row>
788
            <row><entry>uint16</entry><entry>16 bit unsigned integer with allowed values 0 to 65535</entry></row>
789
790
791
792
793
794
795
796
797
            <row><entry>uint32</entry><entry>32 bit unsigned integer with allowed values 0 to 4294967295</entry></row>
          </tbody>
          </tgroup>
       </table>
      </para>
    </section>

    <section id="dhcp4-custom-options">
      <title>Custom DHCPv4 options</title>
798
799
800
801
      <para>Kea supports custom (non-standard) DHCPv4 options. Assume
      that we want to define a new DHCPv4 option called "foo" which
      will have code 222 and will convey a single unsigned 32 bit
      integer value. We can define such an option by using the
802
      following entry in the configuration file:
803
804
805
806
807
808
809
<screen>
"Dhcp4": {
    "option-def": [
        {
            <userinput>"name": "foo",
            "code": 222,
            "type": "uint32",
810
            "array": false,
811
812
813
814
815
816
817
818
            "record-types": "",
            "space": "dhcp4",
            "encapsulate": ""</userinput>
        }, ...
    ],
    ...
}
</screen>
819
820
821
822
823
824
825
826
827
828
829
830
      The <command>false</command> value of the <command>array</command>
      parameter determines that the option does NOT comprise an array of
      "uint32" values but rather a single value.  Two other parameters have been
      left blank: <command>record-types</command> and
      <command>encapsulate</command>.  The former specifies the comma separated
      list of option data fields if the option comprises a record of data
      fields. This should be non-empty if the <command>type</command> is set to
      "record". Otherwise it must be left blank. The latter parameter specifies
      the name of the option space being encapsulated by the particular
      option. If the particular option does not encapsulate any option space it
      should be left blank.  Note that the above set of comments define the
      format of the new option and do not set its values.
831
832
833
834
835
836
837
838
839
840
841
842
843
      </para>
      <note>
        <para>
          In the current release the default values are not propagated to the
          parser when the new configuration is being set. Therefore, all
          parameters must be specified at all times, even if their values are
          left blank.
        </para>
      </note>

      <para>Once the new option format is defined, its value is set
      in the same way as for a standard option. For example the following
      commands set a global value that applies to all subnets.
844
845
846
847
<screen>
"Dhcp4": {
    "option-data": [
        {
848
            <userinput>"name": "foo",
849
850
            "code": 222,
            "space": "dhcp4",
851
            "csv-format": true,
852
853
854
855
856
857
            "data": "12345"</userinput>
        }, ...
    ],
    ...
}
</screen>
858
859
860
861
862
      </para>

      <para>New options can take more complex forms than simple use of
      primitives (uint8, string, ipv4-address etc): it is possible to
      define an option comprising a number of existing primitives.
863
      Assume we want to define a new option that will consist of
864
      an IPv4 address, followed by an unsigned 16 bit integer, followed by
865
866
867
      a boolean value, followed by a text string. Such an option could
      be defined in the following way:
<screen>
868
869
870
871
872
873
874
"Dhcp4": {
    "option-def": [
        {
            <userinput>"name": "bar",
            "code": 223,
            "space": "dhcp4",
            "type": "record",
875
            "array": false,
876
877
878
879
880
881
            "record-types": "ipv4-address, uint16, boolean, string",
            "encapsulate": ""</userinput>
        }, ...
    ],
    ...
}
882
</screen>
883
      The <command>type</command> is set to "record" to indicate that the option contains
884
      multiple values of different types.  These types are given as a comma-separated
885
      list in the <command>record-types</command> field and should be those listed in <xref linkend="dhcp-types"/>.
886
887
888
889
      </para>
      <para>
      The values of the option are set as follows:
<screen>
890
891
892
893
894
895
"Dhcp4": {
    "option-data": [
        {
            <userinput>"name": "bar",
            "space": "dhcp4",
            "code": 223,
896
            "csv-format": true,
897
898
899
900
901
            "data": "192.0.2.100, 123, true, Hello World"</userinput>
        }
    ],
    ...
}</screen>
902
      <command>csv-format</command> is set to <command>true</command> to indicate
903
904
905
906
      that the <command>data</command> field comprises a command-separated list
      of values.  The values in the <command>data</command> must correspond to
      the types set in the <command>record-types</command> field of the option
      definition.
907
908
     </para>
     <note>
909
       <para>In the general case, boolean values are specified as <command>true</command> or
910
911
912
913
914
       <command>false</command>, without quotes. Some specific boolean parameters may
       accept also <command>"true"</command>, <command>"false"</command>,
       <command>0</command>, <command>1</command>, <command>"0"</command> and
       <command>"1"</command>. Future Kea versions will accept all those values
       for all boolean parameters.</para>
915
916
917
918
     </note>
    </section>

    <section id="dhcp4-vendor-opts">
919
      <title>DHCPv4 Vendor Specific Options</title>
920
      <para>
921
922
923
      Currently there are three option spaces defined: "dhcp4" (used by the DHCPv4 daemon)
      and "dhcp6" (for the DHCPv6 daemon); there is also "vendor-encapsulated-options-space",
      which is empty by default, but options
924
925
926
927
928
929
930
931
932
      can be defined in it. Those options are called vendor-specific
      information options. The following examples show how to define
      an option "foo" with code 1 that consists of an IPv4 address, an
      unsigned 16 bit integer and a string. The "foo" option is conveyed
      in a vendor specific information option.
      </para>
      <para>
      The first step is to define the format of the option:
<screen>
933
934
935
936
937
938
939
"Dhcp4": {
    "option-def": [
        {
            <userinput>"name": "foo",
            "code": 1,
            "space": "vendor-encapsulated-options-space",
            "type": "record",
940
            "array": false,
941
942
943
944
945
946
            "record-types": "ipv4-address, uint16, string",
            "encapsulates": ""</userinput>
        }
    ],
    ...
}</screen>
947
948
949
     (Note that the option space is set to "vendor-encapsulated-options-space".)
     Once the option format is defined, the next step is to define actual values
     for that option:
950
951
952
953
954
955
956
<screen>
"Dhcp4": {
    "option-data": [
        {
            <userinput>"name": "foo"
            "space": "vendor-encapsulated-options-space",
            "code": 1,
957
            "csv-format": true,
958
959
960
961
962
            "data": "192.0.2.3, 123, Hello World"</userinput>
        }
    ],
    ...
}</screen>
963
    We also set up a dummy value for "vendor-encapsulated-options", the option that conveys our sub-option "foo".
964
    This is required else the option will not be included in messages sent to the client.
965
966
967
968
969
970
971
<screen>
"Dhcp4": {
    "option-data": [
        {
            <userinput>"name": "vendor-encapsulated-options"
            "space": "dhcp4",
            "code": 43,
972
            "csv-format": false,
973
            "data": ""</userinput>
974
975
976
977
        }
    ],
    ...
}</screen>
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
      </para>

      <note>
        <para>
          With this version of Kea, the "vendor-encapsulated-options" option
          must be specified in the configuration although it has no configurable
          parameters. If it is not specified, the server will assume that it is
          not configured and will not send it to a client. In the future there
          will be no need to include this option in the configuration.
        </para>
      </note>

    </section>

    <section id="dhcp4-option-spaces">

994
      <title>Nested DHCPv4 Options (Custom Option Spaces)</title>
995
996
997
      <para>It is sometimes useful to define completely new option
      space. This is the case when user creates new option in the
      standard option space ("dhcp4 or "dhcp6") and wants this option
998
      to convey sub-options. Since they are in a separate space,
999
      sub-option codes will have a separate numbering scheme and may
1000
      overlap with the codes of standard options.
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
      </para>
      <para>Note that creation of a new option space when defining
      sub-options for a standard option is not required, because it is
      created by default if the standard option is meant to convey any
      sub-options (see <xref linkend="dhcp4-vendor-opts"/>).
      </para>
      <para>
      Assume that we want to have a DHCPv4 option called "container" with
      code 222 that conveys two sub-options with codes 1 and 2.
      First we need to define the new sub-options:
<screen>
1012
1013
1014
1015
1016
1017
1018
1019
"Dhcp4": {
    "option-def": [
        {
            <userinput>"name": "subopt1",
            "code": 1,
            "space": "isc",
            "type": "ipv4-address".
            "record-types": "",
1020
            "array": false,
1021
1022
1023
1024
1025
1026
1027
1028
            "encapsulate ""
        },
        {
            "name": "subopt2",
            "code": 2,
            "space": "isc",
            "type": "string",
            "record-types": "",
1029
            "array": false
1030
1031
1032
1033
1034
            "encapsulate": ""</userinput>
        }
    ],
    ...
}</screen>
1035
1036
1037
1038
1039
1040
1041
    Note that we have defined the options to belong to a new option space
    (in this case, "isc").
    </para>
    <para>
    The next step is to define a regular DHCPv4 option with our desired
    code and specify that it should include options from the new option space:
<screen>
1042
1043
1044
1045
1046
1047
1048
1049
"Dhcp4": {
    "option-def": [
        ...,
        {
            <userinput>"name": "container",
            "code": 222,
            "space": "dhcp4",
            "type": "empty",
1050
            "array": false,
1051
1052
1053
1054
1055
1056
            "record-types": "",
            "encapsulate": "isc"</userinput>
        }
    ],
    ...
}</screen>
1057
1058
1059
1060
1061
1062
1063
1064
    The name of the option space in which the sub-options are defined
    is set in the "encapsulate" field. The "type" field is set to "empty"
    to indicate that this option does not carry any data other than
    sub-options.
    </para>
    <para>
    Finally, we can set values for the new options:
<screen>
1065
1066
1067
1068
1069
1070
"Dhcp4": {
    "option-data": [
        {
            <userinput>"name": "subopt1",
            "space": "isc",
            "code": 1,
1071
            "csv-format": true,
1072
1073
1074
1075
1076
1077
            "data": "192.0.2.3"</userinput>
        },
        }
            <userinput>"name": "subopt2",
            "space": "isc",
            "code": 2,
1078
            "csv-format": true,
1079
1080
1081
1082
1083
1084
            "data": "Hello world"</userinput>
        },
        {
            <userinput>"name": "container",
            "space": "dhcp4",
            "code": 222,
1085
            "csv-format": true,
1086
1087
1088
1089
1090
            "data": ""</userinput>
        }
    ],
    ...
}
1091
1092
1093
</screen>
    Even though the "container" option does not carry any data except
    sub-options, the "data" field must be explicitly set to an empty value.
1094
    This is required because in the current version of Kea, the
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
    default configuration values are not propagated to the configuration parsers:
    if the "data" is not set the parser will assume that this
    parameter is not specified and an error will be reported.
    </para>
    <para>Note that it is possible to create an option which carries some data
    in addition to the sub-options defined in the encapsulated option space.  For example,
    if the "container" option from the previous example was required to carry an uint16
    value as well as the sub-options, the "type" value would have to be set to "uint16" in
    the option definition. (Such an option would then have the following
    data structure: DHCP header, uint16 value, sub-options.) The value specified
1105
1106
    with the "data" parameter &mdash; which should be a valid integer enclosed in quotes,
    e.g. "123" &mdash; would then be assigned to the uint16 field in the "container" option.
1107
1108
1109
    </para>
    </section>

1110
    <section id="dhcp4-option-data-defaults">
1111
      <title>Unspecified parameters for DHCPv4 option configuration</title>
1112
      <para>In many cases it is not required to specify all parameters for
1113
      an option configuration and the default values may be used. However, it is
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
      important to understand the implications of not specifing some of them
      as it may result in configuration errors. The list below explains
      the behavior of the server when a particular parameter is not explicitly
      specified:

      <itemizedlist>
        <listitem>
          <simpara><command>name</command> - the server requires an option name or
          option code to identify an option. If this parameter is unspecified, the
          option code must be specified.
          </simpara>
        </listitem>

        <listitem>
          <simpara><command>code</command> - the server requires an option name or
          option code to identify an option. This parameter may be left unspecified if
          the <command>name</command> parameter is specified. However, this also
          requires that the particular option has its definition (it is either a
          standard option or an administrator created a definition for the option
          using an 'option-def' structure), as the option definition associates an
          option with a particular name. It is possible to configure an option
          for which there is no definition (unspecified option format).
          Configuration of such options requires the use of option code.
          </simpara>
        </listitem>

        <listitem>
          <simpara><command>space</command> - if the option space is unspecified it
          will default to 'dhcp4' which is an option space holding DHCPv4 standard
          options.
          </simpara>
        </listitem>

        <listitem>
          <simpara><command>data</command> - if the option data is unspecified it
          defaults to an empty value. The empty value is mostly used for the
          options which have no payload (boolean options), but it is legal to specify
          empty values for some options which carry variable length data and which
          spec allows for the length of 0. For such options, the data parameter
          may be omitted in the configuration.</simpara>
        </listitem>

        <listitem>
          <simpara><command>csv-format</command> - if this value is not specified
          and the definition for the particular option exists, the server will assume
          that the option data is specified as a list of comma separated values to be
          assigned to individual fields of the DHCP option. If the definition
          does not exist for this option, the server will assume that the data
          parameter contains the option payload in the binary format (represented
          as a string of hexadecimal digits). Note that not specifying this
          parameter doesn't imply that it defaults to a fixed value, but
          the configuration data interpretation also depends on the presence
          of the option definition. An administrator must be aware if the
          definition for the particular option exists when this parameter
          is not specified. It is generally recommended to not specify this
          parameter only for the options for which the definition exists, e.g.
          standard options. Setting <command>csv-format</command> to an explicit
          value will cause the server to strictly check the format of the option
          data specified.
          </simpara>
        </listitem>
      </itemizedlist>
      </para>

    </section>

1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
    <section id="dhcp4-stateless-configuration">
      <title>Stateless Configuration of DHCPv4 clients</title>
      <para>The DHCPv4 server supports the stateless client configuration whereby the
      client has an IP address configured (e.g. using manual configuration) and only
      contacts the server to obtain other configuration parameters, e.g. DNS servers' addresses.
      In order to obtain the stateless configuration parameters the client sends the
      DHCPINFORM message to the server with the "ciaddr" set to the address that the
      client is currently using. The server unicasts the DHCPACK message to the
      client that includes the stateless configuration ("yiaddr" not set).
      </para>

      <para>The server will respond to the DHCPINFORM when the client is associated
      with the particular subnet defined in the server's configuration. The example
      subnet configuration will look like this:
        <screen>
"Dhcp4": {
    "subnet4": [
        {
            "subnet": "192.0.2.0/24"
            "option-data": [ {"
1200
1201
                "name": "domain-name-servers",
                "code": 6,
1202
                "data": "192.0.2.200,192.0.2.201",
1203
                "csv-format": true,
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
                "space": "dhcp4"
            } ]
        }
    ]
}</screen>
      </para>
      <para>This subnet specifies the single option which will be included in
      the DHCPACK message to the client in response to DHCPINFORM. Note that
      the subnet definition does not require the address pool configuration
      if it will be used solely for the stateless configuration.
      </para>

      <para>This server will associate the subnet with the client if one of
      the following conditions is met:
      <itemizedlist>
          <listitem>
            <simpara>The DHCPINFORM is relayed and the giaddr matches the
            configured subnet.</simpara>
          </listitem>
          <listitem>
            <simpara>The DHCPINFORM is unicast from the client and the ciaddr
            matches the configured subnet.</simpara>
          </listitem>
          <listitem>
            <simpara>The DHCPINFORM is unicast from the client, the ciaddr is
            not set but the source address of the IP packet matches the
            configured subnet.</simpara>
          </listitem>
          <listitem>
            <simpara>The DHCPINFORM is not relayed and the IP address on the
            interface on which the message is received matches the configured
            subnet.</simpara>
          </listitem>
      </itemizedlist>
      </para>
    </section>

1241
1242
1243
1244
    <section id="dhcp4-client-classifier">
      <title>Client Classification in DHCPv4</title>
      <note>
      <para>
1245
        The DHCPv4 server has been extended to support limited client classification.
1246
        Although the current capability is modest, it is expected to be expanded
1247
        in the future. However, it is envisaged that the majority of client classification
1248
1249
1250
1251
1252
        extensions will be using hooks extensions.
      </para>
      </note>
      <para>In certain cases it is useful to differentiate between different
      types of clients and treat them differently. The process of doing
1253
      classification is conducted in two steps. The first step is to assess an
1254
1255
      incoming packet and assign it to zero or more classes. This classification
      is currently simple, but is expected to grow in capability soon. Currently
1256
1257
1258
      the server checks whether an incoming packet includes the vendor class identifier
      option (60). If it does, the content of that option is prepended with
      &quot;VENDOR_CLASS_&quot; then it is interpreted as a class. For example,
1259
1260
1261
1262
      modern cable modems will send this option with value &quot;docsis3.0&quot;
      and as a result the packet will belong to class &quot;VENDOR_CLASS_docsis3.0&quot;.
      </para>

1263
      <para>It is envisaged that the client classification will be used for changing the
1264
      behavior of almost any part of the DHCP message processing, including assigning
1265
      leases from different pools, assigning different options (or different values of
1266
1267
1268
1269
1270
1271
1272
      the same options) etc. For now, there are only two mechanisms that are taking
      advantage of client classification: specific processing for cable modems and
      subnet selection.</para>

      <para>
        For clients that belong to the VENDOR_CLASS_docsis3.0 class, the siaddr
        field is set to the value of next-server (if specified in a subnet). If
1273
        there is a boot-file-name option specified, its value is also set in the
1274
1275
        file field in the DHCPv4 packet. For eRouter1.0 class, the siaddr is
        always set to 0.0.0.0. That capability is expected to be moved to
1276
        an external hook library that will be dedicated to cable modems.
1277
1278
1279
1280
1281
1282
1283
      </para>

      <para>
        Kea can be instructed to limit access to given subnets based on class information.
        This is particularly useful for cases where two types of devices share the
        same link and are expected to be served from two different subnets. The
        primary use case for such a scenario is cable networks. There are two
1284
        classes of devices: the cable modem itself, which should be handed a lease
1285
        from subnet A and all other devices behind the modem that should get a lease
1286
1287
1288
1289
1290
1291
1292
        from subnet B. That segregation is essential to prevent overly curious
        users from playing with their cable modems. For details on how to set up
        class restrictions on subnets, see <xref linkend="dhcp4-subnet-class"/>.
      </para>


    <section id="dhcp4-subnet-class">
1293
      <title>Limiting Access to IPv4 Subnet to Certain Classes</title>
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
      <para>
        In certain cases it beneficial to restrict access to certain subnets
        only to clients that belong to a given subnet. For details on client
        classes, see <xref linkend="dhcp4-client-classifier"/>. This is an
        extension of a previous example from <xref linkend="dhcp4-address-config"/>.
        Let's assume that the server is connected to a network 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. Only clients belonging to client class
        VENDOR_CLASS_docsis3.0 are allowed to use this subnet. Such a
        configuration can be achieved in the following way:
        <screen>
1306
1307
1308
"Dhcp4": {
    "subnet4": [
        {
Jeremy C. Reed's avatar
Jeremy C. Reed committed
1309
            <userinput>"subnet": "192.0.2.0/24",
1310
            "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
1311
1312
1313
1314
1315
            "client-class": "VENDOR_CLASS_docsis3.0"</userinput>
        }
    ],
    ...
}</screen>
1316
1317
1318
      </para>

      <para>
1319
        Care should be taken with client classification as it is easy for
1320
1321
1322
        clients that do not meet class criteria to be denied any service altogether.
      </para>
    </section>
1323
1324
    </section>

1325
1326
1327
    <section id="dhcp4-ddns-config">
      <title>Configuring DHCPv4 for DDNS</title>
      <para>
1328
      As mentioned earlier, kea-dhcp4 can be configured to generate requests to the
1329
      DHCP-DDNS server (referred to here as "D2" ) to update DNS entries.  These requests are known as
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
      NameChangeRequests or NCRs.  Each NCR contains the following information:
      <orderedlist>
      <listitem><para>
      Whether it is a request to add (update) or remove DNS entries
      </para></listitem>
      <listitem><para>
      Whether the change requests forward DNS updates (A records), reverse
      DNS updates (PTR records), or both.
      </para></listitem>
      <listitem><para>
      The FQDN, lease address, and DHCID
      </para></listitem>
      </orderedlist>
1343
      The parameters for controlling the generation of NCRs for submission to D2
1344
      are contained in the <command>dhcp-ddns</command> section of the kea-dhcp4 server
1345
      configuration. The default values for this section are as follows:
1346
<screen>
1347
1348
"Dhcp4": {
    "dhcp-ddns": {
1349
        <userinput>"enable-updates": true,
1350
1351
1352
        "server-ip": "127.0.0.1",
        "server-port": 53001,
        "sender-ip": "",
Jeremy C. Reed's avatar
Jeremy C. Reed committed
1353
        "sender-port": 0,
1354
1355
1356
        "max-queue-size": 1024,
        "ncr-protocol": "UDP",
        "ncr-format": "JSON",
1357
1358
1359
        "override-no-update": false,
        "override-client-update": false,
        "replace-client-name": false,
1360
1361
1362
1363
1364
        "generated-prefix": "myhost",
        "qualifying-suffix": "example.com"</userinput>
    },
    ...
}
1365
1366
</screen>
      </para>
1367

1368
1369
1370
      <section id="dhcpv4-d2-io-config">
      <title>DHCP-DDNS Server Connectivity</title>
      <para>
1371
      In order for NCRs to reach the D2 server, kea-dhcp4 must be able
1372
      to communicate with it.  kea-dhcp4 uses the following configuration
1373
      parameters to control how it communications with D2:
1374
1375
1376
1377
1378
1379
1380
1381
      <itemizedlist>
      <listitem><simpara>
      <command>enable-updates</command> - determines whether or not kea-dhcp4 will
      generate NCRs.  By default, this value is false hence DDNS updates are
      disabled.  To enable DDNS updates set this value to true:
      </simpara></listitem>

      <listitem><simpara>
1382
      <command>server-ip</command> - IP address on which D2 listens for requests. The default is
1383
1384
      the local loopback interface at address 127.0.0.1. You may specify
      either an IPv4 or IPv6 address.
1385
1386
1387
      </simpara></listitem>

      <listitem><simpara>
1388
      <command>server-port</command> - port on which D2 listens for requests.  The default value
1389
      is 53001.
1390
1391
1392
      </simpara></listitem>

      <listitem><simpara>
1393
      <command>sender-ip</command> - IP address which kea-dhcp4 should use to send requests to D2.
1394
      The default value is blank which instructs kea-dhcp4 to select a suitable
1395
      address.
1396
1397
1398
      </simpara></listitem>

      <listitem><simpara>
1399
1400
      <command>sender-port</command> - port which kea-dhcp4 should use to send requests to D2. The
      default value of 0 instructs kea-dhcp4 to select a suitable port.
1401
1402
1403
      </simpara></listitem>

      <listitem><simpara>
1404
      <command>max-queue-size</command> - maximum number of requests allowed to queue waiting to
1405
      be sent to D2. This value guards against requests accumulating
1406
1407
1408
      uncontrollably if they are being generated faster than they can be
      delivered.  If the number of requests queued for transmission reaches
      this value, DDNS updating will be turned off until the queue backlog has
1409
      been sufficiently reduced.  The intention is to allow the kea-dhcp4 server to
1410
1411
      continue lease operations without running the risk that its memory usage
      grows without limit.  The default value is 1024.
1412
1413
1414
      </simpara></listitem>

      <listitem><simpara>
1415
      <command>ncr-format</command> - socket protocol use when sending requests to D2.  Currently
1416
1417
1418
1419
      only UDP is supported.  TCP may be available in an upcoming release.
      </simpara></listitem>

      <listitem><simpara>
1420
      <command>ncr-protocol</command> - packet format to use when sending requests to D2.
1421
1422
1423
1424
1425
      Currently only JSON format is supported.  Other formats may be available
      in future releases.
      </simpara></listitem>

      </itemizedlist>
1426
      By default, kea-dhcp-ddns is assumed to be running on the same machine as kea-dhcp4, and
1427
      all of the default values mentioned above should be sufficient.
1428
1429
      If, however, D2 has been configured to listen on a different address or
      port, these values must be altered accordingly. For example, if D2 has been