summaryrefslogtreecommitdiffstats
path: root/sbin/ipfw/ipfw.8
blob: 4dfd91293118e0673b1d18babe03f57cebec0217 (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
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
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
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
.\"
.\" $FreeBSD$
.\"
.Dd August 13, 2002
.Dt IPFW 8
.Os
.Sh NAME
.Nm ipfw
.Nd IP firewall and traffic shaper control program
.Sh SYNOPSIS
.Nm
.Op Fl cq
.Cm add
.Ar rule
.Nm
.Op Fl acdeftNS
.Brq Cm list | show
.Op Ar number ...
.Nm
.Op Fl f | q
.Cm flush
.Nm
.Op Fl q
.Brq Cm delete | zero | resetlog
.Op Cm set
.Op Ar number ...
.Nm
.Cm enable
.Brq Cm firewall | one_pass | debug | verbose | dyn_keepalive
.Nm
.Cm disable
.Brq Cm firewall | one_pass | debug | verbose | dyn_keepalive
.Pp
.Nm
.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ...
.Nm
.Cm set move
.Op Cm rule
.Ar number Cm to Ar number
.Nm
.Cm set swap Ar number number
.Nm
.Cm set show
.Pp
.Nm
.Brq Cm pipe | queue
.Ar number
.Cm config
.Ar config-options
.Nm
.Op Fl s Op Ar field
.Brq Cm pipe | queue
.Brq Cm delete | list | show
.Op Ar number ...
.Pp
.Nm
.Op Fl q
.Oo
.Fl p Ar preproc
.Oo
.Ar preproc-flags
.Oc
.Oc
.Ar pathname
.Sh DESCRIPTION
The
.Nm
utility is the user interface for controlling the
.Xr ipfw 4
firewall and the
.Xr dummynet 4
traffic shaper in
.Fx .
.Pp
.Bd -ragged -offset XXXX
.Em NOTE:
this manual page documents the newer version of
.Nm
introduced in
.Fx
CURRENT in July 2002, also known as
.Nm ipfw2 .
.Nm ipfw2
is a superset of the old firewall,
.Nm ipfw1 .
The differences between the two are listed in Section
.Sx IPFW2 ENHANCEMENTS ,
which you are encouraged to read to revise older rulesets and possibly
write them more efficiently.
See Section
.Sx USING IPFW2 IN FreeBSD-STABLE
for instructions on how to run
.Nm ipfw2
on
.Fx
STABLE.
.Ed
.Pp
An
.Nm
configuration, or
.Em ruleset ,
is made of a list of
.Em rules
numbered from 1 to 65535.
Packets are passed to
.Nm
from a number of different places in the protocol stack
(depending on the source and destination of the packet,
it is possible that
.Nm
is invoked multiple times on the same packet).
The packet passed to the firewall is compared
against each of the rules in the firewall
.Em ruleset .
When a match is found, the action corresponding to the
matching rule is performed.
.Pp
Depending on the action and certain system settings, packets
can be reinjected into the firewall at some rule after the
matching one for further processing.
.Pp
An
.Nm
ruleset always includes a
.Em default
rule (numbered 65535) which cannot be modified,
and matches all packets.
The action associated with the
.Em default
rule can be either
.Cm deny
or
.Cm allow
depending on how the kernel is configured.
.Pp
If the ruleset includes one or more rules with the
.Cm keep-state
or
.Cm limit
option, then
.Nm
assumes a
.Em stateful
behaviour, i.e. upon a match it will create dynamic rules matching
the exact parameters (addresses and ports) of the matching packet.
.Pp
These dynamic rules, which have a limited lifetime, are checked
at the first occurrence of a
.Cm check-state ,
.Cm keep-state
or
.Cm limit
rule, and are typically used to open the firewall on-demand to
legitimate traffic only.
See the
.Sx STATEFUL FIREWALL
and
.Sx EXAMPLES
Sections below for more information on the stateful behaviour of
.Nm .
.Pp
All rules (including dynamic ones) have a few associated counters:
a packet count, a byte count, a log count and a timestamp
indicating the time of the last match.
Counters can be displayed or reset with
.Nm
commands.
.Pp
Rules can be added with the
.Cm add
command; deleted individually or in groups with the
.Cm delete
command, and globally with the
.Cm flush
command; displayed, optionally with the content of the
counters, using the
.Cm show
and
.Cm list
commands.
Finally, counters can be reset with the
.Cm zero
and
.Cm resetlog
commands.
.Pp
Also, each rule belongs to one of 32 different
.Em sets
, and there are
.Nm
commands to atomically manipulate sets, such as enable,
disable, swap sets, move all rules in a set to another
one, delete all rules in a set. These can be useful to
install temporary configurations, or to test them.
See Section
.Sx SETS OF RULES
for more information on
.Em sets .
.Pp
The following options are available:
.Bl -tag -width indent
.It Fl a
While listing, show counter values.
The
.Cm show
command just implies this option.
.It Fl c
When entering or showing rules, print them in compact form,
i.e. without the optional "ip from any to any" string
when this does not carry any additional information.
.It Fl d
While listing, show dynamic rules in addition to static ones.
.It Fl e
While listing, if the
.Fl d
option was specified, also show expired dynamic rules.
.It Fl f
Don't ask for confirmation for commands that can cause problems
if misused,
.No i.e. Cm flush .
If there is no tty associated with the process, this is implied.
.It Fl N
Try to resolve addresses and service names in output.
.It Fl q
While
.Cm add Ns ing ,
.Cm zero Ns ing ,
.Cm resetlog Ns ging
or
.Cm flush Ns ing ,
be quiet about actions
(implies
.Fl f ) .
This is useful for adjusting rules by executing multiple
.Nm
commands in a script
(e.g.,
.Ql sh\ /etc/rc.firewall ) ,
or by processing a file of many
.Nm
rules across a remote login session.
If a
.Cm flush
is performed in normal (verbose) mode (with the default kernel
configuration), it prints a message.
Because all rules are flushed, the message might not be delivered
to the login session, causing the remote login session to be closed
and the remainder of the ruleset to not be processed.
Access to the console would then be required to recover.
.It Fl S
While listing rules, show the
.Em set
each rule belongs to.
If this flag is not specified, disabled rules will not be
listed.
.It Fl s Op Ar field
While listing pipes, sort according to one of the four
counters (total or current packets or bytes).
.It Fl t
While listing, show last match timestamp.
.El
.Pp
To ease configuration, rules can be put into a file which is
processed using
.Nm
as shown in the last synopsis line.
An absolute
.Ar pathname
must be used.
The file will be read line by line and applied as arguments to the
.Nm
utility.
.Pp
Optionally, a preprocessor can be specified using
.Fl p Ar preproc
where
.Ar pathname
is to be piped through.
Useful preprocessors include
.Xr cpp 1
and
.Xr m4 1 .
If
.Ar preproc
doesn't start with a slash
.Pq Ql /
as its first character, the usual
.Ev PATH
name search is performed.
Care should be taken with this in environments where not all
file systems are mounted (yet) by the time
.Nm
is being run (e.g. when they are mounted over NFS).
Once
.Fl p
has been specified, any additional arguments as passed on to the preprocessor
for interpretation.
This allows for flexible configuration files (like conditionalizing
them on the local hostname) and the use of macros to centralize
frequently required arguments like IP addresses.
.Pp
The
.Nm
.Cm pipe
and
.Cm queue
commands are used to configure the traffic shaper, as shown in the
.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
Section below.
.Pp
If the world and the kernel get out of sync the
.Nm
ABI may break, preventing you from being able to add any rules.  This can
adversely effect the booting process.  You can use
.Nm
.Cm disable
.Cm firewall
to temporarily disable the firewall to regain access to the network,
allowing you to fix the problem.
.Sh PACKET FLOW
A packet is checked against the active ruleset in multiple places
in the protocol stack, under control of several sysctl variables.
These places and variables are shown below, and it is important to
have this picture in mind in order to design a correct ruleset.
.Bd -literal -offset indent
      ^	    to upper layers   V
      |                       |
      +----------->-----------+
      ^                       V
 [ip_input]              [ip_output]   net.inet.ip.fw.enable=1
      |                       |
      ^                       V
[ether_demux]    [ether_output_frame]  net.link.ether.ipfw=1
      |                       |
      +-->--[bdg_forward]-->--+        net.link.ether.bridge_ipfw=1
      ^                       V
      |      to devices       |
.Ed
.Pp
As can be noted from the above picture, the number of
times the same packet goes through the firewall can
vary between 0 and 4 depending on packet source and
destination, and system configuration.
.Pp
Note that as packets flow through the stack, headers can be
stripped or added to it, and so they may or may not be available
for inspection.
E.g., incoming packets will include the MAC header when
.Nm
is invoked from
.Cm ether_demux() ,
but the same packets will have the MAC header stripped off when
.Nm
is invoked from
.Cm ip_input() .
.Pp
Also note that each packet is always checked against the complete ruleset,
irrespective of the place where the check occurs, or the source of the packet.
If a rule contains some match patterns or actions which are not valid
for the place of invocation (e.g. trying to match a MAC header within
.Cm ip_input()
), the match pattern will not match, but a
.Cm not
operator in front of such patterns
.Em will
cause the pattern to
.Em always
match on those packets.
It is thus the responsibility of
the programmer, if necessary, to write a suitable ruleset to
differentiate among the possible places.
.Cm skipto
rules can be useful here, as an example:
.Bd -literal -offset indent
# packets from ether_demux or bdg_forward
ipfw add 10 skipto 1000 all from any to any layer2 in
# packets from ip_input
ipfw add 10 skipto 2000 all from any to any not layer2 in
# packets from ip_output
ipfw add 10 skipto 3000 all from any to any not layer2 out
# packets from ether_output_frame
ipfw add 10 skipto 4000 all from any to any layer2 out
.Ed
.Pp
(yes, at the moment there is no way to differentiate between
ether_demux and bdg_forward).
.Sh RULE FORMAT
The format of
.Nm
rules is the following:
.Bd -ragged -offset indent
.Op Ar rule_number
.Op Cm set Ar set_number
.Op Cm prob Ar match_probability
.br
.Ar "   " action
.Op Cm log Op Cm logamount Ar number
.Ar body
.Ed
.Pp
where the body of the rule specifies which information is used
for filtering packets, among the following:
.Pp
.Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact
.It Layer-2 header fields
When available
.It IPv4 Protocol
TCP, UDP, ICMP, etc.
.It Source and dest. addresses and ports
.It Direction
See Section
.Sx PACKET FLOW
.It Transmit and receive interface
By name or address
.It Misc. IP header fields
Version, type of service, datagram length, identification,
fragment flag (non-zero IP offset),
Time To Live
.It IP options
.It Misc. TCP header fields
TCP flags (SYN, FIN, ACK, RST, etc.),
sequence number, acknowledgment number,
window
.It TCP options
.It ICMP types
for ICMP packets
.It User/group ID
When the packet can be associated with a local socket.
.El
.Pp
Note that some of the above information, e.g. source MAC or IP addresses and
TCP/UDP ports, could easily be spoofed, so filtering on those fields
alone might not guarantee the desired results.
.Bl -tag -width indent
.It Ar rule_number
Each rule is associated with a
.Ar rule_number
in the range 1..65535, with the latter reserved for the
.Em default
rule.
Rules are checked sequentially by rule number.
Multiple rules can have the same number, in which case they are
checked (and listed) according to the order in which they have
been added.
If a rule is entered without specifying a number, the kernel will
assign one in such a way that the rule becomes the last one
before the
.Em default
rule.
Automatic rule numbers are assigned by incrementing the last
non-default rule number by the value of the sysctl variable
.Ar net.inet.ip.fw.autoinc_step
which defaults to 100.
If this is not possible (e.g. because we would go beyond the
maximum allowed rule number), the number of the last
non-default value is used instead.
.It Cm set Ar set_number
Each rule is associated with a
.Ar set_number
in the range 0..31, with the latter reserved for the
.Em default
rule.
Sets can be individually disabled and enabled, so this parameter
is of fundamental importance for atomic ruleset manipulation.
It can be also used to simplify deletion of groups of rules.
If a rule is entered without specifying a set number,
set 0 will be used.
.It Cm prob Ar match_probability
A match is only declared with the specified probability
(floating point number between 0 and 1).
This can be useful for a number of applications such as
random packet drop or
(in conjunction with
.Xr dummynet 4 )
to simulate the effect of multiple paths leading to out-of-order
packet delivery.
.Pp
Note: this condition is checked before any other condition, including
ones such as keep-state or check-state which might have side effects.
.It Cm log Op Cm logamount Ar number
When a packet matches a rule with the
.Cm log
keyword, a message will be
logged to
.Xr syslogd 8
with a
.Dv LOG_SECURITY
facility.
The logging only occurs if the sysctl variable
.Em net.inet.ip.fw.verbose
is set to 1
(which is the default when the kernel is compiled with
.Dv IPFIREWALL_VERBOSE
) and the number of packets logged so far for that
particular rule does not exceed the
.Cm logamount
parameter.
If no
.Cm logamount
is specified, the limit is taken from the sysctl variable
.Em net.inet.ip.fw.verbose_limit .
In both cases, a value of 0 removes the logging limit.
.Pp
Once the limit is reached, logging can be re-enabled by
clearing the logging counter or the packet counter for that entry, see the
.Cm resetlog
command.
.Pp
Note: logging is done after all other packet matching conditions
have been successfully verified, and before performing the final
action (accept, deny, etc.) on the packet.
.El
.Ss RULE ACTIONS
A rule can be associated with one of the following actions, which
will be executed when the packet matches the body of the rule.
.Bl -tag -width indent
.It Cm allow | accept | pass | permit
Allow packets that match rule.
The search terminates.
.It Cm check-state
Checks the packet against the dynamic ruleset.
If a match is found, execute the action associated with
the rule which generated this dynamic rule, otherwise
move to the next rule.
.br
.Cm Check-state
rules do not have a body.
If no
.Cm check-state
rule is found, the dynamic ruleset is checked at the first
.Cm keep-state
or
.Cm limit
rule.
.It Cm count
Update counters for all packets that match rule.
The search continues with the next rule.
.It Cm deny | drop
Discard packets that match this rule.
The search terminates.
.It Cm divert Ar port
Divert packets that match this rule to the
.Xr divert 4
socket bound to port
.Ar port .
The search terminates.
.It Cm fwd | forward Ar ipaddr Ns Op , Ns Ar port
Change the next-hop on matching packets to
.Ar ipaddr ,
which can be an IP address in dotted quad format or a host name.
The search terminates if this rule matches.
.Pp
If
.Ar ipaddr
is a local address, then matching packets will be forwarded to
.Ar port
(or the port number in the packet if one is not specified in the rule)
on the local machine.
.br
If
.Ar ipaddr
is not a local address, then the port number
(if specified) is ignored, and the packet will be
forwarded to the remote address, using the route as found in
the local routing table for that IP.
.br
A
.Ar fwd
rule will not match layer-2 packets (those received
on ether_input, ether_output, or bridged).
.br
The
.Cm fwd
action does not change the contents of the packet at all.
In particular, the destination address remains unmodified, so
packets forwarded to another system will usually be rejected by that system
unless there is a matching rule on that system to capture them.
For packets forwarded locally,
the local address of the socket will be
set to the original destination address of the packet.
This makes the
.Xr netstat 1
entry look rather weird but is intended for
use with transparent proxy servers.
.It Cm pipe Ar pipe_nr
Pass packet to a
.Xr dummynet 4
.Dq pipe
(for bandwidth limitation, delay, etc.).
See the
.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
Section for further information.
The search terminates; however, on exit from the pipe and if
the
.Xr sysctl 8
variable
.Em net.inet.ip.fw.one_pass
is not set, the packet is passed again to the firewall code
starting from the next rule.
.It Cm queue Ar queue_nr
Pass packet to a
.Xr dummynet 4
.Dq queue
(for bandwidth limitation using WF2Q+).
.It Cm reject
(Deprecated).
Synonym for
.Cm unreach host .
.It Cm reset
Discard packets that match this rule, and if the
packet is a TCP packet, try to send a TCP reset (RST) notice.
The search terminates.
.It Cm skipto Ar number
Skip all subsequent rules numbered less than
.Ar number .
The search continues with the first rule numbered
.Ar number
or higher.
.It Cm tee Ar port
Send a copy of packets matching this rule to the
.Xr divert 4
socket bound to port
.Ar port .
The search terminates and the original packet is accepted
(but see Section
.Sx BUGS
below).
.It Cm unreach Ar code
Discard packets that match this rule, and try to send an ICMP
unreachable notice with code
.Ar code ,
where
.Ar code
is a number from 0 to 255, or one of these aliases:
.Cm net , host , protocol , port ,
.Cm needfrag , srcfail , net-unknown , host-unknown ,
.Cm isolated , net-prohib , host-prohib , tosnet ,
.Cm toshost , filter-prohib , host-precedence
or
.Cm precedence-cutoff .
The search terminates.
.El
.Ss RULE BODY
The body of a rule contains zero or more patterns (such as
specific source and destination addresses or ports,
protocol options, incoming or outgoing interfaces, etc.)
that the packet must match in order to be recognised.
In general, the patterns are connected by (implicit)
.Cm and
operators -- i.e. all must match in order for the
rule to match.
Individual patterns can be prefixed by the
.Cm not
operator to reverse the result of the match, as in
.Pp
.Dl "ipfw add 100 allow ip from not 1.2.3.4 to any"
.Pp
Additionally, sets of alternative match patterns (
.Em or-blocks
) can be constructed by putting the patterns in
lists enclosed between parentheses ( ) or braces { }, and
using the
.Cm or
operator as follows:
.Pp
.Dl "ipfw add 100 allow ip from { x or not y or z } to any"
.Pp
Only one level of parentheses is allowed.
Beware that most shells have special meanings for parentheses
or braces, so it is advisable to put a backslash \\ in front of them
to prevent such interpretations.
.Pp
The body of a rule must in general include a source and destination
address specifier.
The keyword
.Ar any
can be used in various places to specify that the content of
a required field is irrelevant.
.Pp
The rule body has the following format:
.Bd -ragged -offset indent
.Op Ar proto Cm from Ar src Cm to Ar dst
.Op Ar options
.Ed
.Pp
The first part (protocol from src to dst) is for backward
compatibility with
.Nm ipfw1 .
In
.Nm ipfw2
any match pattern (including MAC headers, IPv4 protocols,
addresses and ports) can be specified in the
.Ar options
section.
.Pp
Rule fields have the following meaning:
.Bl -tag -width indent
.It Ar proto : protocol | Cm { Ar protocol Cm or ... }
An IPv4 protocol (or an
.Em or-block
with multiple protocols) specified by number or name
(for a complete list see
.Pa /etc/protocols ) .
The
.Cm ip
or
.Cm all
keywords mean any protocol will match.
.It Ar src No and Ar dst : ip-address | Cm { Ar ip-address Cm or ... } Op Ar ports
A single
.Ar ip-address
, or an
.Em or-block
containing one or more of them,
optionally followed by
.Ar ports
specifiers.
.It Ar ip-address :
An address (or set of addresses) specified in one of the following
ways, optionally preceded by a
.Cm not
operator:
.Bl -tag -width indent
.It Cm any
matches any IP address.
.It Cm me
matches any IP address configured on an interface in the system.
The address list is evaluated at the time the packet is
analysed.
.It Ar numeric-ip | hostname
Matches a single IPv4 address, specified as dotted-quad or a hostname.
Hostnames are resolved at the time the rule is added to the firewall list.
.It Ar addr Ns / Ns Ar masklen
Matches all addresses with base
.Ar addr
(specified as a dotted quad or a hostname)
and mask width of
.Cm masklen
bits.
As an example, 1.2.3.4/25 will match
all IP numbers from 1.2.3.0 to 1.2.3.127 .
.It Ar addr Ns / Ns Ar masklen Ns Cm { Ns Ar num,num,... Ns Cm }
Matches all addresses with base address
.Ar addr
(specified as a dotted quad or a hostname)
and whose last byte is in the list between braces { } .
Note that there must be no spaces between braces, commas and
numbers.
The
.Ar masklen
field is used to limit the size of the set of addresses,
and can have any value between 24 and 32.
.br
As an example, an address specified as 1.2.3.4/24{128,35,55,89}
will match the following IP addresses:
.br
1.2.3.128 1.2.3.35 1.2.3.55 1.2.3.89 .
.br
This format is particularly useful to handle sparse address sets
within a single rule. Because the matching occurs using a
bitmask, it takes constant time and dramatically reduces
the complexity of rulesets.
.It Ar addr Ns : Ns Ar mask
Matches all addresses with base
.Ar addr
(specified as a dotted quad or a hostname)
and the mask of
.Ar mask ,
specified as a dotted quad.
As an example, 1.2.3.4/255.0.255.0 will match
1.*.3.*.
We suggest to use this form only for non-contiguous
masks, and resort to the
.Ar addr Ns / Ns Ar masklen
format for contiguous masks, which is more compact and less
error-prone.
.El
.It Ar ports : Oo Cm not Oc Bro Ar port | port Ns \&- Ns Ar port Ns Brc Op , Ns Ar ...
For protocols which support port numbers (such as TCP and UDP), optional
.Cm ports
may be specified as one or more ports or port ranges, separated
by commas but no spaces, and an optional
.Cm not
operator.
The
.Ql \&-
notation specifies a range of ports (including boundaries).
.Pp
Service names (from
.Pa /etc/services )
may be used instead of numeric port values.
The length of the port list is limited to 30 ports or ranges,
though one can specify larger ranges by using an
.Em or-block
in the
.Cm options
section of the rule.
.Pp
A backslash
.Pq Ql \e
can be used to escape the dash
.Pq Ql -
character in a service name (from a shell, the backslash must be
typed twice to avoid the shell itself interpreting it as an escape
character).
.Pp
.Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any"
.Pp
Fragmented packets which have a non-zero offset (i.e. not the first
fragment) will never match a rule which has one or more port
specifications.
See the
.Cm frag
option for details on matching fragmented packets.
.El
.Ss RULE OPTIONS (MATCH PATTERNS)
Additional match patterns can be used within
rules. Zero or more of these so-called
.Em options
can be present in a rule, optionally prefixed by the
.Cm not
operand, and possibly grouped into
.Em or-blocks .
.Pp
The following match patterns can be used (listed in alphabetical order):
.Bl -tag -width indent
.It Cm bridged
Matches only bridged packets.
.It Cm dst-ip Ar ip address
Matches IP packets whose destination IP is one of the address(es)
specified as argument.
.It Cm dst-port Ar source ports
Matches IP packets whose destination port is one of the port(s)
specified as argument.
.It Cm established
Matches TCP packets that have the RST or ACK bits set.
.It Cm frag
Matches packets that are fragments and not the first
fragment of an IP datagram. Note that these packets will not have
the next protocol header (e.g. TCP, UDP) so options that look into
these headers cannot match.
.It Cm gid Ar group
Matches all TCP or UDP packets sent by or received for a
.Ar group .
A
.Ar group
may be specified by name or number.
.It Cm icmptypes Ar types
Matches ICMP packets whose ICMP type is in the list
.Ar types .
The list may be specified as any combination of ranges or
individual types separated by commas.
The supported ICMP types are:
.Pp
echo reply
.Pq Cm 0 ,
destination unreachable
.Pq Cm 3 ,
source quench
.Pq Cm 4 ,
redirect
.Pq Cm 5 ,
echo request
.Pq Cm 8 ,
router advertisement
.Pq Cm 9 ,
router solicitation
.Pq Cm 10 ,
time-to-live exceeded
.Pq Cm 11 ,
IP header bad
.Pq Cm 12 ,
timestamp request
.Pq Cm 13 ,
timestamp reply
.Pq Cm 14 ,
information request
.Pq Cm 15 ,
information reply
.Pq Cm 16 ,
address mask request
.Pq Cm 17
and address mask reply
.Pq Cm 18 .
.It Cm in | out
Matches incoming or outgoing packets, respectively.
.Cm in
and
.Cm out
are mutually exclusive (in fact,
.Cm out
is implemented as
.Cm not in Ns No ).
.It Cm ipid Ar id
Matches IP packets whose
.Cm ip_id
field has value
.Ar id .
.It Cm iplen Ar len
Matches IP packets whose total length, including header and data, is
.Ar len
bytes.
.It Cm ipoptions Ar spec
Matches packets whose IP header contains the comma separated list of
options specified in
.Ar spec .
The supported IP options are:
.Pp
.Cm ssrr
(strict source route),
.Cm lsrr
(loose source route),
.Cm rr
(record packet route) and
.Cm ts
(timestamp).
The absence of a particular option may be denoted
with a
.Ql \&! .
.It Cm ipprecedence Ar precedence
Matches IP packets whose precedence field is equal to
.Ar precedence .
.It Cm iptos Ar spec
Matches IP packets whose
.Cm tos
field contains the comma separated list of
service types specified in
.Ar spec .
The supported IP types of service are:
.Pp
.Cm lowdelay
.Pq Dv IPTOS_LOWDELAY ,
.Cm throughput
.Pq Dv IPTOS_THROUGHPUT ,
.Cm reliability
.Pq Dv IPTOS_RELIABILITY ,
.Cm mincost
.Pq Dv IPTOS_MINCOST ,
.Cm congestion
.Pq Dv IPTOS_CE .
The absence of a particular type may be denoted
with a
.Ql \&! .
.It Cm ipttl Ar ttl
Matches IP packets whose time to live is
.Ar ttl .
.It Cm ipversion Ar ver
Matches IP packets whose IP version field is
.Ar ver .
.It Cm keep-state
Upon a match, the firewall will create a dynamic rule, whose
default behaviour is to match bidirectional traffic between
source and destination IP/port using the same protocol.
The rule has a limited lifetime (controlled by a set of
.Xr sysctl 8
variables), and the lifetime is refreshed every time a matching
packet is found.
.It Cm layer2
Matches only layer2 packets, i.e. those passed to
.Nm
from ether_demux() and ether_output_frame().
.It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N
The firewall will only allow
.Ar N
connections with the same
set of parameters as specified in the rule.
One or more
of source and destination addresses and ports can be
specified.
.It Cm { MAC | mac } Ar dst-mac src-mac
Match packets with a given
.Ar dst-mac
and
.Ar src-mac
addresses, specified as the
.Cm any
keyword (matching any MAC address), or six groups of hex digits
separated by colons,
and optionally followed by a mask indicating how many bits are
significant, as in
.Pp
.Dl "MAC 10:20:30:40:50:60/33 any"
.Pp
Note that the order of MAC addresses (destination first,
source second) is
the same as on the wire, but the opposite of the one used for
IP addresses.
.It Cm mac-type Ar mac-type
Matches packets whose Ethernet Type field
corresponds to one of those specified as argument.
.Ar mac-type
is specified in the same way as
.Cm port numbers
(i.e. one or more comma-separated single values or ranges).
You can use symbolic names for known values such as
.Em vlan , ipv4, ipv6 .
Values can be entered as decimal or hexadecimal (if prefixed by 0x),
and they are always printed as hexadecimal (unless the
.Cm -N
option is used, in which case symbolic resolution will be attempted).
.It Cm proto Ar protocol
Matches packets with the corresponding IPv4 protocol.
.It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar ipno | Ar any
Matches packets received, transmitted or going through,
respectively, the interface specified by exact name
.Ns No ( Ar ifX Ns No ),
by device name
.Ns No ( Ar if Ns Ar * Ns No ),
by IP address, or through some interface.
.Pp
The
.Cm via
keyword causes the interface to always be checked.
If
.Cm recv
or
.Cm xmit
is used instead of
.Cm via ,
then only the receive or transmit interface (respectively)
is checked.
By specifying both, it is possible to match packets based on
both receive and transmit interface, e.g.:
.Pp
.Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1"
.Pp
The
.Cm recv
interface can be tested on either incoming or outgoing packets,
while the
.Cm xmit
interface can only be tested on outgoing packets.
So
.Cm out
is required (and
.Cm in
is invalid) whenever
.Cm xmit
is used.
.Pp
A packet may not have a receive or transmit interface: packets
originating from the local host have no receive interface,
while packets destined for the local host have no transmit
interface.
.It Cm setup
Matches TCP packets that have the SYN bit set but no ACK bit.
This is the short form of
.Dq Li tcpflags\ syn,!ack .
.It Cm src-ip Ar ip-address
Matches IP packets whose source IP is one of the address(es)
specified as argument.
.It Cm src-port Ar ports
Matches IP packets whose source port is one of the port(s)
specified as argument.
.It Cm tcpack Ar ack
TCP packets only.
Match if the TCP header acknowledgment number field is set to
.Ar ack .
.It Cm tcpflags Ar spec
TCP packets only.
Match if the TCP header contains the comma separated list of
flags specified in
.Ar spec .
The supported TCP flags are:
.Pp
.Cm fin ,
.Cm syn ,
.Cm rst ,
.Cm psh ,
.Cm ack
and
.Cm urg .
The absence of a particular flag may be denoted
with a
.Ql \&! .
A rule which contains a
.Cm tcpflags
specification can never match a fragmented packet which has
a non-zero offset.
See the
.Cm frag
option for details on matching fragmented packets.
.It Cm tcpseq Ar seq
TCP packets only.
Match if the TCP header sequence number field is set to
.Ar seq .
.It Cm tcpwin Ar win
TCP packets only.
Match if the TCP header window field is set to
.Ar win .
.It Cm tcpoptions Ar spec
TCP packets only.
Match if the TCP header contains the comma separated list of
options specified in
.Ar spec .
The supported TCP options are:
.Pp
.Cm mss
(maximum segment size),
.Cm window
(tcp window advertisement),
.Cm sack
(selective ack),
.Cm ts
(rfc1323 timestamp) and
.Cm cc
(rfc1644 t/tcp connection count).
The absence of a particular option may be denoted
with a
.Ql \&! .
.It Cm uid Ar user
Match all TCP or UDP packets sent by or received for a
.Ar user .
A
.Ar user
may be matched by name or identification number.
.El
.Sh SETS OF RULES
Each rule belongs to one of 32 different
.Em sets
, numbered 0 to 31.
Set 31 is reserved for the default rule.
.Pp
By default, rules are put in set 0, unless you use the
.Cm set N
attribute when entering a new rule.
Sets can be individually and atomically enabled or disabled,
so this mechanism permits an easy way to store multiple configurations
of the firewall and quickly (and atomically) switch between them.
The command to enable/disable sets is
.Bd -ragged -offset indent
.Nm
.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ...
.Ed
.Pp
where multiple
.Cm enable
or
.Cm disable
sections can be specified.
Command execution is atomic on all the sets specified in the command.
By default, all sets are enabled.
.Pp
When you disable a set, its rules behave as if they do not exist
in the firewall configuration, with only one exception:
.Bd -ragged -offset indent
dynamic rules created from a rule before it had been disabled
will still be active until they expire. In order to delete
dynamic rules you have to explicitly delete the parent rule
which generated them.
.Ed
.Pp
The set number of rules can be changed with the command
.Bd -ragged -offset indent
.Nm
.Cm set move
.Brq Cm rule Ar rule-number | old-set
.Cm to Ar new-set
.Ed
.Pp
Also, you can atomically swap two rulesets with the command
.Bd -ragged -offset indent
.Nm
.Cm set swap Ar first-set second-set
.Ed
.Pp
See the
.Sx EXAMPLES
Section on some possible uses of sets of rules.
.Sh STATEFUL FIREWALL
Stateful operation is a way for the firewall to dynamically
create rules for specific flows when packets that
match a given pattern are detected. Support for stateful
operation comes through the
.Cm check-state , keep-state
and
.Cm limit
options of
.Nm rules.
.Pp
Dynamic rules are created when a packet matches a
.Cm keep-state
or
.Cm limit
rule, causing the creation of a
.Em dynamic
rule which will match all and only packets with
a given
.Em protocol
between a
.Em src-ip/src-port dst-ip/dst-port
pair of addresses (
.Em src
and
.Em dst
are used here only to denote the initial match addresses, but they
are completely equivalent afterwards).
Dynamic rules will be checked at the first
.Cm check-state, keep-state
or
.Cm limit
occurrence, and the action performed upon a match will be the same
as in the parent rule.
.Pp
Note that no additional attributes other than protocol and IP addresses
and ports are checked on dynamic rules.
.Pp
The typical use of dynamic rules is to keep a closed firewall configuration,
but let the first TCP SYN packet from the inside network install a
dynamic rule for the flow so that packets belonging to that session
will be allowed through the firewall:
.Pp
.Dl "ipfw add check-state"
.Dl "ipfw add allow tcp from my-subnet to any setup keep-state"
.Dl "ipfw add deny tcp from any to any"
.Pp
A similar approach can be used for UDP, where an UDP packet coming
from the inside will install a dynamic rule to let the response through
the firewall:
.Pp
.Dl "ipfw add check-state"
.Dl "ipfw add allow udp from my-subnet to any keep-state"
.Dl "ipfw add deny udp from any to any"
.Pp
Dynamic rules expire after some time, which depends on the status
of the flow and the setting of some
.Cm sysctl
variables.
See Section
.Sx SYSCTL VARIABLES
for more details.
For TCP sessions, dynamic rules can be instructed to periodically
send keepalive packets to refresh the state of the rule when it is
about to expire.
.Pp
See Section
.Sx EXAMPLES
for more examples on how to use dynamic rules.
.Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
.Nm
is also the user interface for the
.Xr dummynet 4
traffic shaper.
.Pp
.Nm dummynet
operates by first using the firewall to classify packets and divide them into
.Em flows ,
using any match pattern that can be used in
.Nm
rules.
Depending on local policies, a flow can contain packets for a single
TCP connection, or from/to a given host, or entire subnet, or a
protocol type, etc.
.Pp
Packets belonging to the same flow are then passed to either of two
different objects, which implement the traffic regulation:
.Bl -hang -offset XXXX
.It Em pipe
A pipe emulates a link with given bandwidth, propagation delay,
queue size and packet loss rate.
Packets are queued in front of the pipe as they come out from the classifier,
and then transferred to the pipe according to the pipe's parameters.
.Pp
.It Em queue
A queue
is an abstraction used to implement the WF2Q+
(Worst-case Fair Weighted Fair Queueing) policy, which is
an efficient variant of the WFQ policy.
.br
The queue associates a
.Em weight
and a reference pipe to each flow, and then all backlogged (i.e.,
with packets queued) flows linked to the same pipe share the pipe's
bandwidth proportionally to their weights.
Note that weights are not priorities; a flow with a lower weight
is still guaranteed to get its fraction of the bandwidth even if a
flow with a higher weight is permanently backlogged.
.Pp
.El
In practice,
.Em pipes
can be used to set hard limits to the bandwidth that a flow can use, whereas
.Em queues
can be used to determine how different flow share the available bandwidth.
.Pp
The
.Em pipe
and
.Em queue
configuration commands are the following:
.Bd -ragged -offset indent
.Cm pipe Ar number Cm config Ar pipe-configuration
.Pp
.Cm queue Ar number Cm config Ar queue-configuration
.Ed
.Pp
The following parameters can be configured for a pipe:
.Pp
.Bl -tag -width indent -compact
.It Cm bw Ar bandwidth | device
Bandwidth, measured in
.Sm off
.Op Cm K | M
.Brq Cm bit/s | Byte/s .
.Sm on
.Pp
A value of 0 (default) means unlimited bandwidth.
The unit must immediately follow the number, as in
.Pp
.Dl "ipfw pipe 1 config bw 300Kbit/s"
.Pp
If a device name is specified instead of a numeric value, as in
.Pp
.Dl "ipfw pipe 1 config bw tun0"
.Pp
then the transmit clock is supplied by the specified device.
At the moment only the
.Xr tun 4
device supports this
functionality, for use in conjunction with
.Xr ppp 8 .
.Pp
.It Cm delay Ar ms-delay
Propagation delay, measured in milliseconds.
The value is rounded to the next multiple of the clock tick
(typically 10ms, but it is a good practice to run kernels
with
.Dq "options HZ=1000"
to reduce
the granularity to 1ms or less).
Default value is 0, meaning no delay.
.El
.Pp
The following parameters can be configured for a queue:
.Pp
.Bl -tag -width indent -compact
.It Cm pipe Ar pipe_nr
Connects a queue to the specified pipe.
Multiple queues (with the same or different weights) can be connected to
the same pipe, which specifies the aggregate rate for the set of queues.
.Pp
.It Cm weight Ar weight
Specifies the weight to be used for flows matching this queue.
The weight must be in the range 1..100, and defaults to 1.
.El
.Pp
Finally, the following parameters can be configured for both
pipes and queues:
.Pp
.Bl -tag -width XXXX -compact
.Pp
.It Cm buckets Ar hash-table-size
Specifies the size of the hash table used for storing the
various queues.
Default value is 64 controlled by the
.Xr sysctl 8
variable
.Em net.inet.ip.dummynet.hash_size ,
allowed range is 16 to 65536.
.Pp
.It Cm mask Ar mask-specifier
Packets sent to a given pipe or queue by an
.Nm
rule can be further classified into multiple flows, each of which is then
sent to a different
.Em dynamic
pipe or queue.
A flow identifier is constructed by masking the IP addresses,
ports and protocol types as specified with the
.Cm mask
options in the configuration of the pipe or queue.
For each different flow identifier, a new pipe or queue is created
with the same parameters as the original object, and matching packets
are sent to it.
.Pp
Thus, when
.Em dynamic pipes
are used, each flow will get the same bandwidth as defined by the pipe,
whereas when
.Em dynamic queues
are used, each flow will share the parent's pipe bandwidth evenly
with other flows generated by the same queue (note that other queues
with different weights might be connected to the same pipe).
.br
Available mask specifiers are a combination of one or more of the following:
.Pp
.Cm dst-ip Ar mask ,
.Cm src-ip Ar mask ,
.Cm dst-port Ar mask ,
.Cm src-port Ar mask ,
.Cm proto Ar mask
or
.Cm all ,
.Pp
where the latter means all bits in all fields are significant.
.Pp
.It Cm noerror
When a packet is dropped by a dummynet queue or pipe, the error
is normally reported to the caller routine in the kernel, in the
same way as it happens when a device queue fills up. Setting this
option reports the packet as successfully delivered, which can be
needed for some experimental setups where you want to simulate
loss or congestion at a remote router.
.Pp
.It Cm plr Ar packet-loss-rate
Packet loss rate.
Argument
.Ar packet-loss-rate
is a floating-point number between 0 and 1, with 0 meaning no
loss, 1 meaning 100% loss.
The loss rate is internally represented on 31 bits.
.Pp
.It Cm queue Brq Ar slots | size Ns Cm Kbytes
Queue size, in
.Ar slots
or
.Cm KBytes .
Default value is 50 slots, which
is the typical queue size for Ethernet devices.
Note that for slow speed links you should keep the queue
size short or your traffic might be affected by a significant
queueing delay.
E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit
or 20s of queue on a 30Kbit/s pipe.
Even worse effect can result if you get packets from an
interface with a much larger MTU, e.g. the loopback interface
with its 16KB packets.
.Pp
.It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p
Make use of the RED (Random Early Detection) queue management algorithm.
.Ar w_q
and
.Ar max_p
are floating
point numbers between 0 and 1 (0 not included), while
.Ar min_th
and
.Ar max_th
are integer numbers specifying thresholds for queue management
(thresholds are computed in bytes if the queue has been defined
in bytes, in slots otherwise).
The
.Xr dummynet 4
also supports the gentle RED variant (gred).
Three
.Xr sysctl 8
variables can be used to control the RED behaviour:
.Bl -tag -width indent
.It Em net.inet.ip.dummynet.red_lookup_depth
specifies the accuracy in computing the average queue
when the link is idle (defaults to 256, must be greater than zero)
.It Em net.inet.ip.dummynet.red_avg_pkt_size
specifies the expected average packet size (defaults to 512, must be
greater than zero)
.It Em net.inet.ip.dummynet.red_max_pkt_size
specifies the expected maximum packet size, only used when queue
thresholds are in bytes (defaults to 1500, must be greater than zero).
.El
.El
.Sh CHECKLIST
Here are some important points to consider when designing your
rules:
.Bl -bullet
.It
Remember that you filter both packets going
.Cm in
and
.Cm out .
Most connections need packets going in both directions.
.It
Remember to test very carefully.
It is a good idea to be near the console when doing this.
If you cannot be near the console,
use an auto-recovery script such as the one in
.Pa /usr/share/examples/ipfw/change_rules.sh .
.It
Don't forget the loopback interface.
.El
.Sh FINE POINTS
.Bl -bullet
.It
There are circumstances where fragmented datagrams are unconditionally
dropped.
TCP packets are dropped if they do not contain at least 20 bytes of
TCP header, UDP packets are dropped if they do not contain a full 8
byte UDP header, and ICMP packets are dropped if they do not contain
4 bytes of ICMP header, enough to specify the ICMP type, code, and
checksum.
These packets are simply logged as
.Dq pullup failed
since there may not be enough good data in the packet to produce a
meaningful log entry.
.It
Another type of packet is unconditionally dropped, a TCP packet with a
fragment offset of one.
This is a valid packet, but it only has one use, to try
to circumvent firewalls.
When logging is enabled, these packets are
reported as being dropped by rule -1.
.It
If you are logged in over a network, loading the
.Xr kld 4
version of
.Nm
is probably not as straightforward as you would think.
I recommend the following command line:
.Bd -literal -offset indent
kldload ipfw && \e
ipfw add 32000 allow ip from any to any
.Ed
.Pp
Along the same lines, doing an
.Bd -literal -offset indent
ipfw flush
.Ed
.Pp
in similar surroundings is also a bad idea.
.It
The
.Nm
filter list may not be modified if the system security level
is set to 3 or higher
(see
.Xr init 8
for information on system security levels).
.El
.Sh PACKET DIVERSION
A
.Xr divert 4
socket bound to the specified port will receive all packets
diverted to that port.
If no socket is bound to the destination port, or if the kernel
wasn't compiled with divert socket support, the packets are
dropped.
.Sh SYSCTL VARIABLES
A set of
.Xr sysctl 8
variables controls the behaviour of the firewall and
associated modules (
.Nm dummynet, bridge
).
These are shown below together with their default value
(but always check with the
.Xr sysctl 8
command what value is actually in use) and meaning:
.Bl -tag -width indent
.It Em net.inet.ip.dummynet.expire : No 1
Lazily delete dynamic pipes/queue once they have no pending traffic.
You can disable this by setting the variable to 0, in which case
the pipes/queues will only be deleted when the threshold is reached.
.It Em net.inet.ip.dummynet.hash_size : No 64
Default size of the hash table used for dynamic pipes/queues.
This value is used when no
.Cm buckets
option is specified when configuring a pipe/queue.
.It Em net.inet.ip.dummynet.max_chain_len : No 16
Target value for the maximum number of pipes/queues in a hash bucket.
The product
.Cm max_chain_len*hash_size
is used to determine the threshold over which empty pipes/queues
will be expired even when
.Cm net.inet.ip.dummynet.expire=0 .
.It Em net.inet.ip.dummynet.red_lookup_depth : No 256
.It Em net.inet.ip.dummynet.red_avg_pkt_size : No 512
.It Em net.inet.ip.dummynet.red_max_pkt_size : No 1500
Parameters used in the computations of the drop probability
for the RED algorithm.
.It Em net.inet.ip.fw.autoinc_step : No 100
Delta between rule numbers when auto-generating them.
The value must be in the range 1..1000.
.It Em net.inet.ip.fw.curr_dyn_buckets : Em net.inet.ip.fw.dyn_buckets
The current number of buckets in the hash table for dynamic rules
(readonly).
.It Em net.inet.ip.fw.debug : No 1
Controls debugging messages produced by
.Nm .
.It Em net.inet.ip.fw.dyn_buckets : No 256
The number of buckets in the hash table for dynamic rules.
Must be a power of 2, up to 65536.
It only takes effect when all dynamic rules have expired, so you
are advised to use a
.Cm flush
command to make sure that the hash table is resized.
.It Em net.inet.ip.fw.dyn_count : No 3
Current number of dynamic rules
(read-only).
.It Em net.inet.ip.fw.dyn_keepalive : No 1
Enables generation of keepalive packets for
.Cm keep-state
rules on TCP sessions. A keepalive is generated to both
sides of the connection every 5 seconds for the last 20
seconds of the lifetime of the rule.
.It Em net.inet.ip.fw.dyn_max : No 8192
Maximum number of dynamic rules.
When you hit this limit, no more dynamic rules can be
installed until old ones expire.
.It Em net.inet.ip.fw.dyn_ack_lifetime : No 300
.It Em net.inet.ip.fw.dyn_syn_lifetime : No 20
.It Em net.inet.ip.fw.dyn_fin_lifetime : No 1
.It Em net.inet.ip.fw.dyn_rst_lifetime : No 1
.It Em net.inet.ip.fw.dyn_udp_lifetime : No 5
.It Em net.inet.ip.fw.dyn_short_lifetime : No 30
These variables control the lifetime, in seconds, of dynamic
rules.
Upon the initial SYN exchange the lifetime is kept short,
then increased after both SYN have been seen, then decreased
again during the final FIN exchange or when a RST is received.
Both
.Em dyn_fin_lifetime
and
.Em dyn_rst_lifetime
must be strictly lower than 5 seconds, the period of
repetition of keepalives. The firewall enforces that.
.It Em net.inet.ip.fw.enable : No 1
Enables the firewall.
Setting this variable to 0 lets you run your machine without
firewall even if compiled in.
.It Em net.inet.ip.fw.one_pass : No 1
When set, the packet exiting from the
.Xr dummynet 4
pipe is not passed though the firewall again.
Otherwise, after a pipe action, the packet is
reinjected into the firewall at the next rule.
.It Em net.inet.ip.fw.verbose : No 1
Enables verbose messages.
.It Em net.inet.ip.fw.verbose_limit : No 0
Limits the number of messages produced by a verbose firewall.
.It Em net.link.ether.ipfw : No 0
Controls whether layer-2 packets are passed to
.Nm .
Default is no.
.It Em net.link.ether.bridge_ipfw : No 0
Controls whether bridged packets are passed to
.Nm .
Default is no.
.El
.Sh USING IPFW2 IN FreeBSD-STABLE
.Nm ipfw2
is standard in
.Fx
CURRENT, whereas
.Fx
STABLE still uses
.Nm ipfw1
unless the kernel is compiled with
.Cm options IPFW2 ,
and
.Nm /sbin/ipfw
and
.Nm /usr/lib/libalias
are recompiled with
.Cm -DIPFW2
and reinstalled (the same effect can be achieved by adding
.Cm IPFW2=TRUE
to
.Nm /etc/make.conf
before a buildworld).
.Pp
.Sh IPFW2 ENHANCEMENTS
This Section lists the features that have been introduced in
.Nm ipfw2
which were not present in
.Nm ipfw1 .
We list them in order of the potential impact that they can
have in writing your rulesets.
You might want to consider using these features in order to
write your rulesets in a more efficient way.
.Bl -tag -width indent
.It Handling of non-IPv4 packets
.Nm ipfw1
will silently accept all non-IPv4 packets (which
.Nm ipfw1
will only see when
.Em net.link.ether.bridge_ipfw=1 Ns
).
.Nm ipfw2
will filter all packets (including non-IPv4 ones) according to the ruleset.
To achieve the same behaviour as
.Nm ipfw1
you can use the following as the very first rule in your ruleset:
.Pp
.Dl "ipfw add 1 allow layer2 not mac-type ip"
.Pp
The
.Cm layer2
option might seem redundant, but it is necessary -- packets
passed to the firewall from layer3 will not have a MAC header,
so the
.Cm mac-type ip
pattern will always fail on them, and the
.Cm not
operator will make this rule into a pass-all.
.It Address sets
.Nm ipfw1
does not supports address sets (those in the form
.Ar addr/masklen{num,num,...}
).
.Pp
.It Port specifications
.Nm ipfw1
only allows one port range when specifying TCP and UDP ports, and
is limited to 10 entries instead of the 15 allowed by
.Nm ipfw2 .
Also, in
.Nm ipfw1
you can only specify ports when the rule is requesting
.Cm tcp
or
.Cm udp
packets. With
.Nm ipfw2
you can put port specifications in rules matching all packets,
and the match will be attempted only on those packets carrying
protocols which include port identifiers.
.Pp
Finally,
.Nm ipfw1
allowed the first port entry to be specified as
.Ar port:mask
where
.Ar mask
can be an arbitrary 16-bit mask.
This syntax is of questionable usefulness and it is not
supported anymore in
.Nm ipfw2 .
.It Or-blocks
.Nm ipfw1
does not support Or-blocks.
.It keepalives
.Nm ipfw1
does not generate keepalives for stateful sessions.
As a consequence, it might cause idle sessions to drop because
the lifetime of the dynamic rules expires.
.It Sets of rules
.Nm ipfw1
does not implement sets of rules.
.It MAC header filtering and Layer-2 firewalling.
.Nm ipfw1
does not implement filtering on MAC header fields, nor is it
invoked on packets from
.Cm ether_demux()
and
.Cm ether_output_frame().
The sysctl variable
.Em net.link.ether.ipfw
has no effect there.
.It Options
The following options are not supported in
.Nm ipfw1
.Pp
.Cm dst-ip, dst-port, layer2, mac, mac-type, src-ip, src-port.
.Pp
Additionally, the following options are not supported in
.Nm ipfw1
(RELENG_4)
rules:
.Pp
.Cm ipid, iplen, ipprecedence, iptos, ipttl,
.Cm ipversion, tcpack, tcpseq, tcpwin .
.It Dummynet options
The following option for
.Nm dummynet
pipes/queues is not supported:
.Cm noerror .
.El
.Sh EXAMPLES
There are far too many possible uses of
.Nm
so this Section will only give a small set of examples.
.Pp
.Ss BASIC PACKET FILTERING
This command adds an entry which denies all tcp packets from
.Em cracker.evil.org
to the telnet port of
.Em wolf.tambov.su
from being forwarded by the host:
.Pp
.Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet"
.Pp
This one disallows any connection from the entire cracker's
network to my host:
.Pp
.Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org"
.Pp
A first and efficient way to limit access (not using dynamic rules)
is the use of the following rules:
.Pp
.Dl "ipfw add allow tcp from any to any established"
.Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup"
.Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup"
.Dl "..."
.Dl "ipfw add deny tcp from any to any"
.Pp
The first rule will be a quick match for normal TCP packets,
but it will not match the initial SYN packet, which will be
matched by the
.Cm setup
rules only for selected source/destination pairs.
All other SYN packets will be rejected by the final
.Cm deny
rule.
.Pp
If you administer one or more subnets, you can take advantage of the
.Nm ipfw2
syntax to specify address sets and or-blocks and write extremely
compact rulesets which selectively enable services to blocks
of clients, as below:
.Pp
.Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q"
.Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q"
.Dl ""
.Dl "ipfw add allow ip from ${goodguys} to any"
.Dl "ipfw add deny ip from ${badguys} to any"
.Dl "... normal policies ..."
.Pp
The
.Nm ipfw1
syntax would require a separate rule for each IP in the above
example.
.Ss DYNAMIC RULES
In order to protect a site from flood attacks involving fake
TCP packets, it is safer to use dynamic rules:
.Pp
.Dl "ipfw add check-state"
.Dl "ipfw add deny tcp from any to any established"
.Dl "ipfw add allow tcp from my-net to any setup keep-state"
.Pp
This will let the firewall install dynamic rules only for
those connection which start with a regular SYN packet coming
from the inside of our network.
Dynamic rules are checked when encountering the first
.Cm check-state
or
.Cm keep-state
rule.
A
.Cm check-state
rule should usually be placed near the beginning of the
ruleset to minimize the amount of work scanning the ruleset.
Your mileage may vary.
.Pp
To limit the number of connections a user can open
you can use the following type of rules:
.Pp
.Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10"
.Dl "ipfw add allow tcp from any to me setup limit src-addr 4"
.Pp
The former (assuming it runs on a gateway) will allow each host
on a /24 network to open at most 10 TCP connections.
The latter can be placed on a server to make sure that a single
client does not use more than 4 simultaneous connections.
.Pp
.Em BEWARE :
stateful rules can be subject to denial-of-service attacks
by a SYN-flood which opens a huge number of dynamic rules.
The effects of such attacks can be partially limited by
acting on a set of
.Xr sysctl 8
variables which control the operation of the firewall.
.Pp
Here is a good usage of the
.Cm list
command to see accounting records and timestamp information:
.Pp
.Dl ipfw -at list
.Pp
or in short form without timestamps:
.Pp
.Dl ipfw -a list
.Pp
which is equivalent to:
.Pp
.Dl ipfw show
.Pp
Next rule diverts all incoming packets from 192.168.2.0/24
to divert port 5000:
.Pp
.Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in
.Pp
.Ss TRAFFIC SHAPING
The following rules show some of the applications of
.Nm
and
.Xr dummynet 4
for simulations and the like.
.Pp
This rule drops random incoming packets with a probability
of 5%:
.Pp
.Dl "ipfw add prob 0.05 deny ip from any to any in"
.Pp
A similar effect can be achieved making use of dummynet pipes:
.Pp
.Dl "ipfw add pipe 10 ip from any to any"
.Dl "ipfw pipe 10 config plr 0.05"
.Pp
We can use pipes to artificially limit bandwidth, e.g. on a
machine acting as a router, if we want to limit traffic from
local clients on 192.168.2.0/24 we do:
.Pp
.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
.Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes"
.Pp
note that we use the
.Cm out
modifier so that the rule is not used twice.
Remember in fact that
.Nm
rules are checked both on incoming and outgoing packets.
.Pp
Should we want to simulate a bidirectional link with bandwidth
limitations, the correct way is the following:
.Pp
.Dl "ipfw add pipe 1 ip from any to any out"
.Dl "ipfw add pipe 2 ip from any to any in"
.Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes"
.Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes"
.Pp
The above can be very useful, e.g. if you want to see how
your fancy Web page will look for a residential user who
is connected only through a slow link.
You should not use only one pipe for both directions, unless
you want to simulate a half-duplex medium (e.g. AppleTalk,
Ethernet, IRDA).
It is not necessary that both pipes have the same configuration,
so we can also simulate asymmetric links.
.Pp
Should we want to verify network performance with the RED queue
management algorithm:
.Pp
.Dl "ipfw add pipe 1 ip from any to any"
.Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1"
.Pp
Another typical application of the traffic shaper is to
introduce some delay in the communication.
This can significantly affect applications which do a lot of Remote
Procedure Calls, and where the round-trip-time of the
connection often becomes a limiting factor much more than
bandwidth:
.Pp
.Dl "ipfw add pipe 1 ip from any to any out"
.Dl "ipfw add pipe 2 ip from any to any in"
.Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s"
.Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s"
.Pp
Per-flow queueing can be useful for a variety of purposes.
A very simple one is counting traffic:
.Pp
.Dl "ipfw add pipe 1 tcp from any to any"
.Dl "ipfw add pipe 1 udp from any to any"
.Dl "ipfw add pipe 1 ip from any to any"
.Dl "ipfw pipe 1 config mask all"
.Pp
The above set of rules will create queues (and collect
statistics) for all traffic.
Because the pipes have no limitations, the only effect is
collecting statistics.
Note that we need 3 rules, not just the last one, because
when
.Nm
tries to match IP packets it will not consider ports, so we
would not see connections on separate ports as different
ones.
.Pp
A more sophisticated example is limiting the outbound traffic
on a net with per-host limits, rather than per-network limits:
.Pp
.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
.Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in"
.Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
.Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
.Ss SETS OF RULES
To add a set of rules atomically, e.g. set 18:
.Pp
.Dl "ipfw disable set 18"
.Dl "ipfw add NN set 18 ...         # repeat as needed"
.Dl "ipfw enable set 18"
.Pp
To delete a set of rules atomically the command is simply:
.Pp
.Dl "ipfw delete set 18"
.Pp
To test a ruleset and disable it and regain control if something goes wrong:
.Pp
.Dl "ipfw disable set 18"
.Dl "ipfw add NN set 18 ...         # repeat as needed"
.Dl "ipfw enable set 18 ; echo done; sleep 30 && ipfw disable set 18"
.Pp
Here if everything goes well, you press control-C before the "sleep"
terminates, and your ruleset will be left active. Otherwise, e.g. if
you cannot access your box, the ruleset will be disabled after
the sleep terminates thus restoring the previous situation.
.Sh SEE ALSO
.Xr cpp 1 ,
.Xr m4 1 ,
.Xr bridge 4 ,
.Xr divert 4 ,
.Xr dummynet 4 ,
.Xr ip 4 ,
.Xr ipfirewall 4 ,
.Xr protocols 5 ,
.Xr services 5 ,
.Xr init 8 ,
.Xr kldload 8 ,
.Xr reboot 8 ,
.Xr sysctl 8 ,
.Xr syslogd 8
.Sh BUGS
The syntax has grown over the years and sometimes it might be confusing.
Unfortunately, backward compatibility prevents cleaning up mistakes
made in the definition of the syntax.
.Pp
.Em !!! WARNING !!!
.Pp
Misconfiguring the firewall can put your computer in an unusable state,
possibly shutting down network services and requiring console access to
regain control of it.
.Pp
Incoming packet fragments diverted by
.Cm divert
or
.Cm tee
are reassembled before delivery to the socket.
The action used on those packet is the one from the
rule which matches the first fragment of the packet.
.Pp
Packets that match a
.Cm tee
rule should not be immediately accepted, but should continue
going through the rule list.
This may be fixed in a later version.
.Pp
Packets diverted to userland, and then reinserted by a userland process
(such as
.Xr natd 8 )
will lose various packet attributes, including their source interface.
If a packet is reinserted in this manner, later rules may be incorrectly
applied, making the order of
.Cm divert
rules in the rule sequence very important.
.Sh AUTHORS
.An Ugen J. S. Antsilevich ,
.An Poul-Henning Kamp ,
.An Alex Nash ,
.An Archie Cobbs ,
.An Luigi Rizzo .
.Pp
.An -nosplit
API based upon code written by
.An Daniel Boulet
for BSDI.
.Pp
Work on
.Xr dummynet 4
traffic shaper supported by Akamba Corp.
.Sh HISTORY
The
.Nm
utility first appeared in
.Fx 2.0 .
.Xr dummynet 4
was introduced in
.Fx 2.2.8 .
Stateful extensions were introduced in
.Fx 4.0 .
.Nm ipfw2
was introduced in Summer 2002.
OpenPOWER on IntegriCloud