summaryrefslogtreecommitdiff
path: root/man/systemd.network.xml
blob: bcd437d349ea4e5e58d97f8a26ae51898922cae6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
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
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
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
694
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
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
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
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
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
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<!--
  This file is part of systemd.

  Copyright 2013 Tom Gundersen

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->

<refentry id="systemd.network" conditional='ENABLE_NETWORKD'>

  <refentryinfo>
    <title>systemd.network</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Tom</firstname>
        <surname>Gundersen</surname>
        <email>teg@jklm.no</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd.network</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd.network</refname>
    <refpurpose>Network configuration</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename><replaceable>network</replaceable>.network</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>Network setup is performed by
    <citerefentry><refentrytitle>systemd-networkd</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
    </para>

    <para>Network files must have the extension
    <filename>.network</filename>; other extensions are ignored.
    Networks are applied to links whenever the links appear.</para>

    <para>The <filename>.network</filename> files are read from the
    files located in the system network directory
    <filename>/usr/lib/systemd/network</filename>, the volatile
    runtime network directory
    <filename>/run/systemd/network</filename> and the local
    administration network directory
    <filename>/etc/systemd/network</filename>. All configuration files
    are collectively sorted and processed in lexical order, regardless
    of the directories in which they live. However, files with
    identical filenames replace each other. Files in
    <filename>/etc</filename> have the highest priority, files in
    <filename>/run</filename> take precedence over files with the same
    name in <filename>/usr/lib</filename>. This can be used to
    override a system-supplied configuration file with a local file if
    needed. As a special case, an empty file (file size 0) or symlink
    with the same name pointing to <filename>/dev/null</filename>
    disables the configuration file entirely (it is "masked").</para>
  </refsect1>

  <refsect1>
    <title>[Match] Section Options</title>

      <para>The network file contains a <literal>[Match]</literal>
      section, which determines if a given network file may be applied
      to a given device; and a <literal>[Network]</literal> section
      specifying how the device should be configured. The first (in
      lexical order) of the network files that matches a given device
      is applied, all later files are ignored, even if they match as
      well.</para>

      <para>A network file is said to match a device if each of the
      entries in the <literal>[Match]</literal> section matches, or if
      the section is empty. The following keys are accepted:</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>MACAddress=</varname></term>
          <listitem>
            <para>The hardware address.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Path=</varname></term>
          <listitem>
            <para>A whitespace-separated list of shell-style globs
            matching the persistent path, as exposed by the udev
            property <literal>ID_PATH</literal>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Driver=</varname></term>
          <listitem>
            <para>A whitespace-separated list of shell-style globs
            matching the driver currently bound to the device, as
            exposed by the udev property <literal>DRIVER</literal>
            of its parent device, or if that is not set the driver
            as exposed by <literal>ethtool -i</literal> of the
            device itself.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Type=</varname></term>
          <listitem>
            <para>A whitespace-separated list of shell-style globs
            matching the device type, as exposed by the udev property
            <literal>DEVTYPE</literal>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Name=</varname></term>
          <listitem>
            <para>A whitespace-separated list of shell-style globs
            matching the device name, as exposed by the udev property
            <literal>INTERFACE</literal>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Host=</varname></term>
          <listitem>
            <para>Matches against the hostname or machine ID of the
            host. See <literal>ConditionHost=</literal> in
            <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
            for details.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Virtualization=</varname></term>
          <listitem>
            <para>Checks whether the system is executed in a virtualized
            environment and optionally test whether it is a specific
            implementation. See <literal>ConditionVirtualization=</literal> in
            <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
            for details.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>KernelCommandLine=</varname></term>
          <listitem>
            <para>Checks whether a specific kernel command line option is
            set (or if prefixed with the exclamation mark unset). See
            <literal>ConditionKernelCommandLine=</literal> in
            <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
            for details.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Architecture=</varname></term>
          <listitem>
            <para>Checks whether the system is running on a specific
            architecture. See <literal>ConditionArchitecture=</literal> in
            <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
            for details.
            </para>
          </listitem>
        </varlistentry>
      </variablelist>

  </refsect1>

  <refsect1>
    <title>[Link] Section Options</title>

    <para> The <literal>[Link]</literal> section accepts the following keys:</para>

    <variablelist class='network-directives'>
      <varlistentry>
        <term><varname>MACAddress=</varname></term>
        <listitem>
          <para>The hardware address.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>MTUBytes=</varname></term>
        <listitem>
          <para>The maximum transmission unit in bytes to set for the
          device. The usual suffixes K, M, G, are supported and are
          understood to the base of 1024.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>IAID=</varname></term>
        <listitem>
          <para>Identity Association Identifier for the interface, a 32-bit unsigned integer.</para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>[Network] Section Options</title>

      <para>The <literal>[Network]</literal> section accepts the following keys:</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>Description=</varname></term>
          <listitem>
            <para>A description of the device. This is only used for
            presentation purposes.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>DHCP=</varname></term>
          <listitem>
            <para>Enables DHCPv4 and/or DHCPv6 client support. Accepts
            <literal>yes</literal>, <literal>no</literal>,
            <literal>ipv4</literal>, or <literal>ipv6</literal>.</para>

            <para>Note that DHCPv6 will by default be triggered by Router
            Advertisement, if that is enabled, regardless of this parameter.
            By enabling DHCPv6 support explicitly, the DHCPv6 client will
            be started regardless of the presence of routers on the link,
            or what flags the routers pass. See
            <literal>IPv6AcceptRouterAdvertisements=</literal>.</para>

            <para>Furthermore, note that by default the domain name
            specified through DHCP is not used for name resolution.
            See option <option>UseDomains=</option> below.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>DHCPServer=</varname></term>
          <listitem>
            <para>A boolean. Enables DHCPv4 server support. Defaults
            to <literal>no</literal>. Further settings for the DHCP
            server may be set in the <literal>[DHCPServer]</literal>
            section described below.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>LinkLocalAddressing=</varname></term>
          <listitem>
            <para>Enables link-local address autoconfiguration. Accepts
            <literal>yes</literal>, <literal>no</literal>,
            <literal>ipv4</literal>, or <literal>ipv6</literal>. Defaults to
            <literal>ipv6</literal>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv4LLRoute=</varname></term>
          <listitem>
            <para>A boolean. When true, sets up the route needed for
            non-IPv4LL hosts to communicate with IPv4LL-only hosts. Defaults
            to false.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6Token=</varname></term>
          <listitem>
            <para>An IPv6 address with the top 64 bits unset. When set, indicates the
            64-bit interface part of SLAAC IPv6 addresses for this link. Note that
            the token is only ever used for SLAAC, and not for DHCPv6 addresses, even
            in the case DHCP is requested by router advertisement. By default, the
            token is autogenerated.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>LLMNR=</varname></term>
          <listitem>
            <para>A boolean or <literal>resolve</literal>. When true,
            enables <ulink
            url="https://tools.ietf.org/html/rfc4795">Link-Local
            Multicast Name Resolution</ulink> on the link. When set to
            <literal>resolve</literal>, only resolution is enabled,
            but not host registration and announcement. Defaults to
            true. This setting is read by
            <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>MulticastDNS=</varname></term>
          <listitem>
            <para>A boolean or <literal>resolve</literal>. When true,
            enables <ulink
            url="https://tools.ietf.org/html/rfc6762">Multicast
            DNS</ulink> support on the link. When set to
            <literal>resolve</literal>, only resolution is enabled,
            but not host or service registration and
            announcement. Defaults to false. This setting is read by
            <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>DNSSEC=</varname></term>
          <listitem>
            <para>A boolean or
            <literal>allow-downgrade</literal>. When true, enables
            <ulink
            url="https://tools.ietf.org/html/rfc4033">DNSSEC</ulink>
            DNS validation support on the link. When set to
            <literal>allow-downgrade</literal>, compatibility with
            non-DNSSEC capable networks is increased, by automatically
            turning off DNSEC in this case. This option defines a
            per-interface setting for
            <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
            global <varname>DNSSEC=</varname> option. Defaults to
            false. This setting is read by
            <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>DNSSECNegativeTrustAnchors=</varname></term>
          <listitem><para>A space-separated list of DNSSEC negative
          trust anchor domains. If specified and DNSSEC is enabled,
          look-ups done via the interface's DNS server will be subject
          to the list of negative trust anchors, and not require
          authentication for the specified domains, or anything below
          it. Use this to disable DNSSEC authentication for specific
          private domains, that cannot be proven valid using the
          Internet DNS hierarchy. Defaults to the empty list. This
          setting is read by
          <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>LLDP=</varname></term>
          <listitem>
            <para>Controls support for Ethernet LLDP packet reception. LLDP is a link-layer protocol commonly
            implemented on professional routers and bridges which announces which physical port a system is connected
            to, as well as other related data. Accepts a boolean or the special value
            <literal>routers-only</literal>. When true, incoming LLDP packets are accepted and a database of all LLDP
            neighbors maintained. If <literal>routers-only</literal> is set only LLDP data of various types of routers
            is collected and LLDP data about other types of devices ignored (such as stations, telephones and
            others). If false, LLDP reception is disabled. Defaults to <literal>routers-only</literal>. Use
            <citerefentry><refentrytitle>networkctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to query the
            collected neighbor data. LLDP is only available on Ethernet links. See <varname>EmitLLDP=</varname> below
            for enabling LLDP packet emission from the local system.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>EmitLLDP=</varname></term>
          <listitem>
            <para>Controls support for Ethernet LLDP packet emission. Accepts a boolean parameter and defaults to
            false. If enabled a short LLDP packet with information about the local system is sent out in regular
            intervals on the link. The LLDP packet will contain information about the local host name, the local
            machine ID (as stored in
            <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>) and the
            local interface name, as well as the pretty hostname of the system (as set in
            <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>). LLDP
            emission is only available on Ethernet links. Note that this setting passed data suitable for
            identification of host to the network and should thus not be used on untrusted networks, where such
            identification data should not be made available. Use this option to enable other systems to identify on
            which interface they are connected to this system. See <varname>LLDP=</varname> above for an option to
            enable LLDP reception.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>BindCarrier=</varname></term>
          <listitem>
            <para>A link name or a list of link names. When set, controls the behavior of the current
            link. When all links in the list are in an operational down state, the current link is brought
            down. When at least one link has carrier, the current interface is brought up.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Address=</varname></term>
          <listitem>
            <para>A static IPv4 or IPv6 address and its prefix length,
            separated by a <literal>/</literal> character. Specify
            this key more than once to configure several addresses.
            The format of the address must be as described in
            <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
            This is a short-hand for an [Address] section only
            containing an Address key (see below). This option may be
            specified more than once.
            </para>

            <para>If the specified address is 0.0.0.0 (for IPv4) or
            [::] (for IPv6), a new address range of the requested size
            is automatically allocated from a system-wide pool of
            unused ranges. The allocated range is checked against all
            current network interfaces and all known network
            configuration files to avoid address range conflicts. The
            default system-wide pool consists of 192.168.0.0/16,
            172.16.0.0/12 and 10.0.0.0/8 for IPv4, and fc00::/7 for
            IPv6. This functionality is useful to manage a large
            number of dynamically created network interfaces with the
            same network configuration and automatic address range
            assignment.</para>

          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Gateway=</varname></term>
          <listitem>
            <para>The gateway address, which must be in the format
            described in
            <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
            This is a short-hand for a [Route] section only containing
            a Gateway key. This option may be specified more than
            once.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>DNS=</varname></term>
          <listitem>
            <para>A DNS server address, which must be in the format
            described in
            <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
            This option may be specified more than once. This setting is read by
            <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Domains=</varname></term>
          <listitem>
            <para>The domains used for DNS host name resolution on this link. Takes a list of DNS domain names which
            are used as search suffixes for extending single-label host names (host names containing no dots) to become
            fully qualified domain names (FQDNs). If a single-label host name is resolved on this interface, each of
            the specified search domains are appended to it in turn, converting it into a fully qualified domain name,
            until one of them may be successfully resolved.</para>

            <para>The specified domains are also used for routing of DNS queries: look-ups for host names ending in the
            domains specified here are preferably routed to the DNS servers configured for this interface. If a domain
            name is prefixed with <literal>~</literal>, the domain name becomes a pure "routing" domain, is used for
            DNS query routing purposes only and is not used in the described domain search logic. By specifying a
            routing domain of <literal>~.</literal> (the tilde indicating definition of a routing domain, the dot
            referring to the DNS root domain which is the implied suffix of all valid DNS names) it is possible to
            route all DNS traffic preferably to the DNS server specified for this interface. The route domain logic is
            particularly useful on multi-homed hosts with DNS servers serving particular private DNS zones on each
            interface.</para>

            <para>This setting is read by
            <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>NTP=</varname></term>
          <listitem>
            <para>An NTP server address. This option may be specified more than once. This setting is read by
            <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPForward=</varname></term>
          <listitem><para>Configures IP packet forwarding for the
          system. If enabled, incoming packets on any network
          interface will be forwarded to any other interfaces
          according to the routing table. Takes either a boolean
          argument, or the values <literal>ipv4</literal> or
          <literal>ipv6</literal>, which only enable IP packet
          forwarding for the specified address family.  This controls
          the <filename>net.ipv4.ip_forward</filename> and
          <filename>net.ipv6.conf.all.forwarding</filename> sysctl
          options of the network interface (see <ulink
          url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink>
          for details about sysctl options). Defaults to
          <literal>no</literal>.</para>

          <para>Note: this setting controls a global kernel option,
          and does so one way only: if a network that has this setting
          enabled is set up the global setting is turned on.  However,
          it is never turned off again, even after all networks with
          this setting enabled are shut down again.</para>

          <para>To allow IP packet forwarding only between specific
          network interfaces use a firewall.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPMasquerade=</varname></term>
          <listitem><para>Configures IP masquerading for the network
          interface. If enabled, packets forwarded from the network
          interface will be appear as coming from the local host.
          Takes a boolean argument. Implies
          <varname>IPForward=ipv4</varname>. Defaults to
          <literal>no</literal>.</para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6PrivacyExtensions=</varname></term>
          <listitem><para>Configures use of stateless temporary
          addresses that change over time (see <ulink
          url="https://tools.ietf.org/html/rfc4941">RFC 4941</ulink>,
          Privacy Extensions for Stateless Address Autoconfiguration
          in IPv6). Takes a boolean or the special values
          <literal>prefer-public</literal> and
          <literal>kernel</literal>. When true, enables the privacy
          extensions and prefers temporary addresses over public
          addresses. When <literal>prefer-public</literal>, enables the
          privacy extensions, but prefers public addresses over
          temporary addresses. When false, the privacy extensions
          remain disabled. When <literal>kernel</literal>, the kernel's
          default setting will be left in place.  Defaults to
          <literal>no</literal>.</para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6AcceptRouterAdvertisements=</varname></term>
          <listitem><para>Force the setting of the <filename>accept_ra</filename>
          (router advertisements) setting for the interface.
          When unset, the kernel default is used, and router
          advertisements are accepted only when local forwarding
          is disabled for that interface.
          When router advertisements are accepted, they will
          trigger the start of the DHCPv6 client if the relevant
          flags are passed, or if no routers are found on the link.
          Takes a boolean. If true, router advertisements are
          accepted, when false, router advertisements are ignored,
          independently of the local forwarding state.</para>

          <para>See
          <ulink url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink>
          in the kernel documentation, but note that systemd's
          setting of <constant>1</constant> corresponds to
          kernel's setting of <constant>2</constant>.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6DuplicateAddressDetection=</varname></term>
          <listitem><para>Configures the amount of IPv6 Duplicate
          Address Detection (DAD) probes to send. Defaults to unset.
        </para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6HopLimit=</varname></term>
          <listitem><para>Configures IPv6 Hop Limit. For each router that
          forwards the packet, the hop limit is decremented by 1. When the
          hop limit field reaches zero, the packet is discarded.
          Defaults to unset.
        </para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Bridge=</varname></term>
          <listitem>
            <para>The name of the bridge to add the link to.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Bond=</varname></term>
          <listitem>
            <para>The name of the bond to add the link to.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>VLAN=</varname></term>
          <listitem>
            <para>The name of a VLAN to create on the link. This
            option may be specified more than once.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>MACVLAN=</varname></term>
          <listitem>
            <para>The name of a MACVLAN to create on the link. This
            option may be specified more than once.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>VXLAN=</varname></term>
          <listitem>
            <para>The name of a VXLAN to create on the link. This
            option may be specified more than once.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Tunnel=</varname></term>
          <listitem>
            <para>The name of a Tunnel to create on the link. This
            option may be specified more than once.</para>
          </listitem>
        </varlistentry>
      </variablelist>

  </refsect1>

  <refsect1>
    <title>[Address] Section Options</title>

      <para>An <literal>[Address]</literal> section accepts the
      following keys. Specify several <literal>[Address]</literal>
      sections to configure several addresses.</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>Address=</varname></term>
          <listitem>
            <para>As in the <literal>[Network]</literal> section. This
            key is mandatory.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Peer=</varname></term>
          <listitem>
            <para>The peer address in a point-to-point connection.
            Accepts the same format as the <literal>Address</literal>
            key.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Broadcast=</varname></term>
          <listitem>
            <para>The broadcast address, which must be in the format
            described in
            <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
            This key only applies to IPv4 addresses. If it is not
            given, it is derived from the <literal>Address</literal>
            key.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Label=</varname></term>
          <listitem>
            <para>An address label.</para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>

  <refsect1>
    <title>[Route] Section Options</title>
      <para>The <literal>[Route]</literal> section accepts the
      following keys. Specify several <literal>[Route]</literal>
      sections to configure several routes.</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>Gateway=</varname></term>
          <listitem>
            <para>As in the <literal>[Network]</literal> section.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Destination=</varname></term>
          <listitem>
            <para>The destination prefix of the route. Possibly
            followed by a slash and the prefix length. If omitted, a
            full-length host route is assumed.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Source=</varname></term>
          <listitem>
            <para>The source prefix of the route. Possibly followed by
            a slash and the prefix length. If omitted, a full-length
            host route is assumed.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Metric=</varname></term>
          <listitem>
            <para>The metric of the route (an unsigned integer).</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Scope=</varname></term>
          <listitem>
            <para>The scope of the route, which can be <literal>global</literal>,
            <literal>link</literal> or <literal>host</literal>. Defaults to
            <literal>global</literal>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>PreferredSource=</varname></term>
          <listitem>
            <para>The preferred source address of the route. The address
            must be in the format described in
            <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>

  <refsect1>
    <title>[DHCP] Section Options</title>
      <para>The <literal>[DHCP]</literal> section configures the
      DHCPv4 and DHCP6 client, if it is enabled with the
      <varname>DHCP=</varname> setting described above:</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>UseDNS=</varname></term>
          <listitem>
            <para>When true (the default), the DNS servers received
            from the DHCP server will be used and take precedence over
            any statically configured ones.</para>

            <para>This corresponds to the <option>nameserver</option>
            option in <citerefentry
            project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>UseNTP=</varname></term>
          <listitem>
            <para>When true (the default), the NTP servers received
            from the DHCP server will be used by systemd-timesyncd
            and take precedence over any statically configured ones.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>UseMTU=</varname></term>
          <listitem>
            <para>When true, the interface maximum transmission unit
            from the DHCP server will be used on the current link.
            Defaults to false.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>SendHostname=</varname></term>
          <listitem>
            <para>When true (the default), the machine's hostname will
            be sent to the DHCP server.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>UseHostname=</varname></term>
          <listitem>
            <para>When true (the default), the hostname received from
            the DHCP server will be set as the transient hostname of the system
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
        <term><varname>Hostname=</varname></term>
        <listitem>
          <para>Use this value for the hostname which is sent to the
          DHCP server, instead of machine's hostname.</para>
        </listitem>
      </varlistentry>
        <varlistentry>
          <term><varname>UseDomains=</varname></term>
          <listitem>
            <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
            received from the DHCP server will be used as DNS search domain over this link, similar to the effect of
            the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name received from
            the DHCP server will be used for routing DNS queries only, but not for searching, similar to the effect of
            the <option>Domains=</option> setting when the argument is prefixed with <literal>~</literal>. Defaults to
            false.</para>

            <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
            of all host names, in particular to single-label names. It is generally safer to use the supplied domain
            only as routing domain, rather than as search domain, in order to not have it affect local resolution of
            single-label names.</para>

            <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
            project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>UseRoutes=</varname></term>
          <listitem>
            <para>When true (the default), the static routes will be
            requested from the DHCP server and added to the routing
            table with a metric of 1024.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>UseTimezone=</varname></term>

          <listitem><para>When true, the timezone received from the
          DHCP server will be set as timezone of the local
          system. Defaults to <literal>no</literal>.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>CriticalConnection=</varname></term>
          <listitem>
            <para>When true, the connection will never be torn down
            even if the DHCP lease expires. This is contrary to the
            DHCP specification, but may be the best choice if, say,
            the root filesystem relies on this connection. Defaults to
            false.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>ClientIdentifier=</varname></term>
          <listitem>
            <para>DHCP client identifier to use. Either <literal>mac</literal>
            to use the MAC address of the link or <literal>duid</literal>
            (the default) to use a RFC4361-compliant Client ID.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>VendorClassIdentifier=</varname></term>
          <listitem>
            <para>The vendor class identifier used to identify vendor
            type and configuration.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>RequestBroadcast=</varname></term>
          <listitem>
            <para>Request the server to use broadcast messages before
            the IP address has been configured. This is necessary for
            devices that cannot receive RAW packets, or that cannot
            receive packets at all before an IP address has been
            configured. On the other hand, this must not be enabled on
            networks where broadcasts are filtered out.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>RouteMetric=</varname></term>
          <listitem>
            <para>Set the routing metric for routes specified by the
            DHCP server.</para>
          </listitem>
        </varlistentry>
      </variablelist>

  </refsect1>

  <refsect1>
    <title>[DUID] Section Options</title>

    <para>This section configures the DHCP Unique Idendifier (DUID) value used by DHCP
    protocol. DHCPv6 client protocol sends the DHCP Unique Identifier and the interface
    Identity Association Identifier (IAID) to a DHCP server when acquiring a dynamic IPv6
    address. DHCPv4 client protocol sends IAID and DUID to the DHCP server when acquiring
    a dynamic IPv4 address if <option>ClientIdentifier=duid</option>. IAID and DUID allows a
    DHCP server to uniquely identify the machine and the interface requesting a DHCP IP.</para>

    <para>The DUID value specified here overrides the DUID that systemd-networkd generates
    using the machine-id from the <filename>/etc/machine-id</filename> file, as well as the
    global DUID that may be specified in <citerefentry><refentrytitle>networkd.conf
    </refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>

    <para>The configured DHCP DUID should conform to the specification in 
    <ulink url="http://tools.ietf.org/html/rfc3315#section-9">RFC 3315</ulink>,
    <ulink url="http://tools.ietf.org/html/rfc6355">RFC 6355</ulink>.</para>

    <para>The following options are available in <literal>[DUID]</literal> section:</para>

    <variablelist class='network-directives'>

      <varlistentry>
        <term><varname>RawData=</varname></term>
        <listitem><para>Specifies the DUID bytes as a single newline-terminated, hexadecimal
        string, with each byte separated by a ':'.</para></listitem>
      </varlistentry>

    </variablelist>
  </refsect1>

  <refsect1>
    <title>[DHCPServer] Section Options</title>
    <para>The <literal>[DHCPServer]</literal> section contains
    settings for the DHCP server, if enabled via the
    <varname>DHCPServer=</varname> option described above:</para>

    <variablelist class='network-directives'>

      <varlistentry>
        <term><varname>PoolOffset=</varname></term>
        <term><varname>PoolSize=</varname></term>

        <listitem><para>Configures the pool of addresses to hand out. The pool
        is a contiguous sequence of IP addresses in the subnet configured for
        the server address, which does not include the subnet nor the broadcast
        address. <varname>PoolOffset=</varname> takes the offset of the pool
        from the start of subnet, or zero to use the default value.
        <varname>PoolSize=</varname> takes the number of IP addresses in the
        pool or zero to use the default value. By default, the pool starts at
        the first address after the subnet address and takes up the rest of
        the subnet, excluding the broadcast address. If the pool includes
        the server address (the default), this is reserved and not handed
        out to clients.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>DefaultLeaseTimeSec=</varname></term>
        <term><varname>MaxLeaseTimeSec=</varname></term>

        <listitem><para>Control the default and maximum DHCP lease
        time to pass to clients. These settings take time values in seconds or
        another common time unit, depending on the suffix. The default
        lease time is used for clients that did not ask for a specific
        lease time. If a client asks for a lease time longer than the
        maximum lease time, it is automatically shortened to the
        specified time. The default lease time defaults to 1h, the
        maximum lease time to 12h. Shorter lease times are beneficial
        if the configuration data in DHCP leases changes frequently
        and clients shall learn the new settings with shorter
        latencies. Longer lease times reduce the generated DHCP
        network traffic.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>EmitDNS=</varname></term>
        <term><varname>DNS=</varname></term>

        <listitem><para>Configures whether the DHCP leases handed out
        to clients shall contain DNS server information. The
        <varname>EmitDNS=</varname> setting takes a boolean argument
        and defaults to <literal>yes</literal>. The DNS servers to
        pass to clients may be configured with the
        <varname>DNS=</varname> option, which takes a list of IPv4
        addresses. If the <varname>EmitDNS=</varname> option is
        enabled but no servers configured, the servers are
        automatically propagated from an "uplink" interface that has
        appropriate servers set. The "uplink" interface is determined
        by the default route of the system with the highest
        priority. Note that this information is acquired at the time
        the lease is handed out, and does not take uplink interfaces
        into account that acquire DNS or NTP server information at a
        later point. DNS server propagation does not take
        <filename>/etc/resolv.conf</filename> into account. Also, note
        that the leases are not refreshed if the uplink network
        configuration changes. To ensure clients regularly acquire the
        most current uplink DNS server information, it is thus
        advisable to shorten the DHCP lease time via
        <varname>MaxLeaseTimeSec=</varname> described
        above.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>EmitNTP=</varname></term>
        <term><varname>NTP=</varname></term>

        <listitem><para>Similar to the <varname>EmitDNS=</varname> and
        <varname>DNS=</varname> settings described above, these
        settings configure whether and what NTP server information
        shall be emitted as part of the DHCP lease. The same syntax,
        propagation semantics and defaults apply as for
        <varname>EmitDNS=</varname> and
        <varname>DNS=</varname>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>EmitTimezone=</varname></term>
        <term><varname>Timezone=</varname></term>

        <listitem><para>Configures whether the DHCP leases handed out
        to clients shall contain timezone information. The
        <varname>EmitTimezone=</varname> setting takes a boolean
        argument and defaults to <literal>yes</literal>. The
        <varname>Timezone=</varname> setting takes a timezone string
        (such as <literal>Europe/Berlin</literal> or
        <literal>UTC</literal>) to pass to clients. If no explicit
        timezone is set, the system timezone of the local host is
        propagated, as determined by the
        <filename>/etc/localtime</filename> symlink.</para></listitem>
      </varlistentry>

    </variablelist>
  </refsect1>

  <refsect1>
    <title>[Bridge] Section Options</title>
      <para>The <literal>[Bridge]</literal> section accepts the
      following keys.</para>
      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>UnicastFlood=</varname></term>
          <listitem>
            <para>A boolean. Controls whether the bridge should flood
            traffic for which an FDB entry is missing and the destination
            is unknown through this port. Defaults to on.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>HairPin=</varname></term>
          <listitem>
            <para>A boolean. Configures whether traffic may be sent back
            out of the port on which it was received. By default, this
            flag is false, and the bridge will not forward traffic back
            out of the receiving port.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>UseBPDU=</varname></term>
          <listitem>
            <para>A boolean. Configures whether STP Bridge Protocol Data Units will be
            processed by the bridge port. Defaults to yes.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>FastLeave=</varname></term>
          <listitem>
            <para>A boolean. This flag allows the bridge to immediately stop multicast
            traffic on a port that receives an IGMP Leave message. It is only used with
            IGMP snooping if enabled on the bridge. Defaults to off.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>AllowPortToBeRoot=</varname></term>
          <listitem>
            <para>A boolean. Configures whether a given port is allowed to
            become a root port. Only used when STP is enabled on the bridge.
            Defaults to on.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Cost=</varname></term>
          <listitem>
            <para>Sets the "cost" of sending packets of this interface.
            Each port in a bridge may have a different speed and the cost
            is used to decide which link to use. Faster interfaces
            should have lower costs.</para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>
  <refsect1>
    <title>[BridgeFDB] Section Options</title>
      <para>The <literal>[BridgeFDB]</literal> section manages the
      forwarding database table of a port and accepts the following
      keys. Specify several <literal>[BridgeFDB]</literal> sections to
      configure several static MAC table entries.</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>MACAddress=</varname></term>
          <listitem>
            <para>As in the <literal>[Network]</literal> section. This
            key is mandatory.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>VLANId=</varname></term>
          <listitem>
            <para>The VLAN ID for the new static MAC table entry. If
            omitted, no VLAN ID info is appended to the new static MAC
            table entry.</para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>

  <refsect1>
    <title>Example</title>
    <example>
      <title>/etc/systemd/network/50-static.network</title>

      <programlisting>[Match]
Name=enp2s0

[Network]
Address=192.168.0.15/24
Gateway=192.168.0.1</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/80-dhcp.network</title>

      <programlisting>[Match]
Name=en*

[Network]
DHCP=yes</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-bridge-static.network</title>

      <programlisting>[Match]
Name=bridge0

[Network]
Address=192.168.0.15/24
Gateway=192.168.0.1
DNS=192.168.0.1</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-bridge-slave-interface.network</title>

      <programlisting>[Match]
Name=enp2s0

[Network]
Bridge=bridge0</programlisting>
    </example>
    <example>
      <title>/etc/systemd/network/25-ipip.network</title>

      <programlisting>[Match]
Name=em1

[Network]
Tunnel=ipip-tun</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-sit.network</title>

      <programlisting>[Match]
Name=em1

[Network]
Tunnel=sit-tun</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-gre.network</title>

      <programlisting>[Match]
Name=em1

[Network]
Tunnel=gre-tun</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-vti.network</title>

      <programlisting>[Match]
Name=em1

[Network]
Tunnel=vti-tun</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-bond.network</title>

      <programlisting>[Match]
Name=bond1

[Network]
DHCP=yes
</programlisting>
    </example>

  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>