File: formatnwfilter.html.in

package info (click to toggle)
libvirt 5.6.0-2
  • links: PTS, VCS
  • area: main
  • in suites: bullseye
  • size: 240,844 kB
  • sloc: ansic: 584,521; xml: 176,725; sh: 9,912; python: 4,731; perl: 4,343; makefile: 3,321; ml: 465
file content (2436 lines) | stat: -rw-r--r-- 86,313 bytes parent folder | download | duplicates (4)
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
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
  <body>
    <h1>Network Filters</h1>

    <ul id="toc">
    </ul>

    <p>
      This page provides an introduction to libvirt's network filters,
      their goals, concepts and XML format.
    </p>

    <h2><a id="goals">Goals and background</a></h2>

    <p>
      The goal of the network filtering XML is to enable administrators
      of a virtualized system to configure and enforce network traffic
      filtering rules on virtual
      machines and manage the parameters of network traffic that
      virtual machines
      are allowed to send or receive.
      The network traffic filtering rules are
      applied on the host when a virtual machine is started. Since the
      filtering rules
      cannot be circumvented from within
      the virtual machine, it makes them mandatory from the point of
      view of a virtual machine user.
      <br/><br/>
      The network filter subsystem allows each virtual machine's network
      traffic filtering rules to be configured individually on a per
      interface basis. The rules are
      applied on the host when the virtual machine is started and can be modified
      while the virtual machine is running. The latter can be achieved by
      modifying the XML description of a network filter.
      <br/><br/>
      Multiple virtual machines can make use of the same generic network filter.
      When such a filter is modified, the network traffic filtering rules
      of all running virtual machines that reference this filter are updated.
      <br/><br/>
      Network filtering support is available <span class="since">since 0.8.1
      (QEMU, KVM)</span>
    </p>

    <h2><a id="nwfconcepts">Concepts</a></h2>
    <p>
      The network traffic filtering subsystem enables configuration
      of network traffic filtering rules on individual network
      interfaces that are configured for certain types of
      network configurations. Supported network types are
    </p>
      <ul>
       <li><code>network</code></li>
       <li><code>ethernet</code> -- must be used in bridging mode</li>
       <li><code>bridge</code></li>
      </ul>
    <p>
    The interface XML is used to reference a top-level filter. In the
    following example, the interface description references
    the filter <code>clean-traffic</code>.
    </p>
<pre>
...
&lt;devices&gt;
  &lt;interface type='bridge'&gt;
    &lt;mac address='00:16:3e:5d:c7:9e'/&gt;
    &lt;filterref filter='clean-traffic'/&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
    Network filters are written in XML and may either contain references
    to other filters, contain rules for traffic filtering, or
    hold a combination of both. The above referenced filter
    <code>clean-traffic </code> is a filter that only contains references to
    other filters and no actual filtering rules. Since references to
    other filters can be used, a <i>tree</i> of filters can be built.
    The <code>clean-traffic</code> filter can be viewed using the
    command <code>virsh nwfilter-dumpxml clean-traffic</code>.
    <br/><br/>
    As previously mentioned, a single network filter can be referenced
    by multiple virtual machines. Since interfaces will typically
    have individual parameters associated with their respective traffic
    filtering rules, the rules described in a filter XML can
    be parameterized with variables. In this case, the variable name
    is used in the filter XML and the name and value are provided at the
    place where the filter is referenced. In the
    following example, the interface description has been extended with
    the parameter <code>IP</code> and a dotted IP address as value.
    </p>
<pre>
...
&lt;devices&gt;
  &lt;interface type='bridge'&gt;
    &lt;mac address='00:16:3e:5d:c7:9e'/&gt;
    &lt;filterref filter='clean-traffic'&gt;
      &lt;parameter name='IP' value='10.0.0.1'/&gt;
    &lt;/filterref&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      In this particular example, the <code>clean-traffic</code> network
      traffic filter will be instantiated with the IP address parameter
      10.0.0.1 and enforce that the traffic from this interface will
      always be using 10.0.0.1 as the source IP address, which is
      one of the purposes of this particular filter.
      <br/><br/>
    </p>

    <h3><a id="nwfconceptschains">Filtering chains</a></h3>
    <p>
      Filtering rules are organized in filter chains. These chains can be
      thought of as having a tree structure with packet
      filtering rules as entries in individual chains (branches). <br/>
      Packets start their filter evaluation in the <code>root</code> chain
      and can then continue their evaluation in other chains, return from
      those chains back into the <code>root</code> chain or be
      dropped or accepted by a filtering rule in one of the traversed chains.
      <br/>
      Libvirt's network filtering system automatically creates individual
      <code>root</code> chains for every virtual machine's network interface
      on which the user chooses to activate traffic filtering.
      The user may write filtering rules that are either directly instantiated
      in the <code>root</code> chain or may create protocol-specific
      filtering chains for efficient evaluation of protocol-specific rules.
      The following chains exist:
    </p>
    <ul>
     <li>root</li>
     <li>mac <span class="since">(since 0.9.8)</span></li>
     <li>stp (spanning tree protocol)
         <span class="since">(since 0.9.8)</span></li>
     <li>vlan (802.1Q) <span class="since">(since 0.9.8)</span></li>
     <li>arp, rarp</li>
     <li>ipv4</li>
     <li>ipv6</li>
    </ul>
    <p>
      <span class="since">Since 0.9.8</span> multiple chains evaluating the
      <code>mac</code>, <code>stp</code>, <code>vlan</code>,
      <code>arp</code>, <code>rarp</code>, <code>ipv4</code>, or
      <code>ipv6</code> protocol can be created using
      the protocol name only as a prefix in the chain's name. This for
      examples allows chains with names <code>arp-xyz</code> or
      <code>arp-test</code> to be specified and have ARP protocol packets
      evaluated in those chains.
    <br/><br/>
      The following filter shows an example of filtering ARP traffic
      in the <code>arp</code> chain.
    </p>
<pre>
&lt;filter name='no-arp-spoofing' chain='arp' priority='-500'&gt;
  &lt;uuid&gt;f88f1932-debf-4aa1-9fbe-f10d3aa4bc95&lt;/uuid&gt;
  &lt;rule action='drop' direction='out' priority='300'&gt;
    &lt;mac match='no' srcmacaddr='$MAC'/&gt;
  &lt;/rule&gt;
  &lt;rule action='drop' direction='out' priority='350'&gt;
    &lt;arp match='no' arpsrcmacaddr='$MAC'/&gt;
  &lt;/rule&gt;
  &lt;rule action='drop' direction='out' priority='400'&gt;
    &lt;arp match='no' arpsrcipaddr='$IP'/&gt;
  &lt;/rule&gt;
  &lt;rule action='drop' direction='in' priority='450'&gt;
    &lt;arp opcode='Reply'/&gt;
    &lt;arp match='no' arpdstmacaddr='$MAC'/&gt;
  &lt;/rule&gt;
  &lt;rule action='drop' direction='in' priority='500'&gt;
    &lt;arp match='no' arpdstipaddr='$IP'/&gt;
  &lt;/rule&gt;
  &lt;rule action='accept' direction='inout' priority='600'&gt;
    &lt;arp opcode='Request'/&gt;
  &lt;/rule&gt;
  &lt;rule action='accept' direction='inout' priority='650'&gt;
    &lt;arp opcode='Reply'/&gt;
  &lt;/rule&gt;
  &lt;rule action='drop' direction='inout' priority='1000'/&gt;
&lt;/filter&gt;
</pre>
    <p>
      The consequence of putting ARP-specific rules in the <code>arp</code>
      chain, rather than for example in the <code>root</code> chain, is that
      packets for any other protocol than ARP do not need to be evaluated by
      ARP protocol-specific rules. This improves the efficiency
      of the traffic filtering. However, one must then pay attention to only
      put filtering rules for the given protocol into the chain since
      any other rules will not be evaluated, i.e., an IPv4 rule will not
      be evaluated in the ARP chain since no IPv4 protocol packets will
      traverse the ARP chain.
      <br/><br/>
    </p>
    <h3><a id="nwfconceptschainpriorities">Filtering chain priorities</a></h3>
    <p>
      All chains are connected to the <code>root</code> chain. The order in
      which those chains are accessed is influenced by the priority of the
      chain. The following table shows the chains that can be assigned a
      priority and their default priorities.
    </p>
      <table class="top_table">
       <tr>
         <th> Chain (prefix) </th>
         <th> Default priority </th>
       </tr>
       <tr>
         <td>stp</td><td>-810</td>
       </tr>
       <tr>
         <td>mac</td><td>-800</td>
       </tr>
       <tr>
         <td>vlan</td><td>-750</td>
       </tr>
       <tr>
         <td>ipv4</td><td>-700</td>
       </tr>
       <tr>
         <td>ipv6</td><td>-600</td>
       </tr>
       <tr>
         <td>arp</td><td>-500</td>
       </tr>
       <tr>
         <td>rarp</td><td>-400</td>
       </tr>
      </table>
    <p>
      A chain with a lower priority value is accessed before one with a
      higher value.
      <br/>
      <span class="since">Since 0.9.8</span> the above listed chains
      can be assigned custom priorities by writing a value in the
      range [-1000, 1000] into the priority (XML) attribute in the filter
      node. The above example filter shows the default priority of -500
      for <code>arp</code> chains.
    </p>
    <h3><a id="nwfconceptsvars">Usage of variables in filters</a></h3>
    <p>

      Two variables names have so far been reserved for usage by the
      network traffic filtering subsystem: <code>MAC</code> and
      <code>IP</code>.
      <br/><br/>
      <code>MAC</code> is the MAC address of the
      network interface. A filtering rule that references this variable
      will automatically be instantiated with the MAC address of the
      interface. This works without the user having to explicitly provide
      the MAC parameter. Even though it is possible to specify the MAC
      parameter similar to the IP parameter above, it is discouraged
      since libvirt knows what MAC address an interface will be using.
      <br/><br/>
      The parameter <code>IP</code> represents the IP address
      that the operating system inside the virtual machine is expected
      to use on the given interface. The <code>IP</code> parameter
      is special in so far as the libvirt daemon will try to determine
      the IP address (and thus the IP parameter's value) that is being
      used on an interface if the parameter
      is not explicitly provided but referenced.
      For current limitations on IP address detection, consult the
      <a href="#nwflimits">section on limitations</a> on how to use this
      feature and what to expect when using it.
      <br/><br/>
      The above-shown network filer <code>no-arp-spoofing</code>
      is an example of
      a network filter XML referencing the <code>MAC</code> and
      <code>IP</code> variables.
      <br/><br/>
      Note that referenced variables are always prefixed with the
      $ (dollar) sign. The format of the value of a variable
      must be of the type expected by the filter attribute in the
      XML. In the above example, the <code>IP</code> parameter
      must hold a dotted IP address in decimal numbers format.
      Failure to  provide the correct
      value type will result in the filter not being instantiatable
      and will prevent a virtual machine from starting or the
      interface from attaching when hotplugging is used. The types
      that are expected for each XML attribute are shown
      below.
      <br/><br/>
      <span class="since">Since 0.9.8</span> variables can contain lists of
      elements, e.g., the variable <code>IP</code> can contain multiple IP
      addresses that are valid on a particular interface. The notation for
      providing multiple elements for the IP variable is:
    </p>
<pre>
...
&lt;devices&gt;
  &lt;interface type='bridge'&gt;
    &lt;mac address='00:16:3e:5d:c7:9e'/&gt;
    &lt;filterref filter='clean-traffic'&gt;
      &lt;parameter name='IP' value='10.0.0.1'/&gt;
      &lt;parameter name='IP' value='10.0.0.2'/&gt;
      &lt;parameter name='IP' value='10.0.0.3'/&gt;
    &lt;/filterref&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>
    <p>
      This then allows filters to enable multiple IP addresses
      per interface. Therefore, with the list
      of IP address shown above, the following rule will create 3
      individual filtering rules, one for each IP address.
    </p>
<pre>
...
&lt;rule action='accept' direction='in' priority='500'&gt;
  &lt;tcp srpipaddr='$IP'/&gt;
&lt;/rule&gt;
...
</pre>
    <p>
      <span class="since">Since 0.9.10</span> it is possible to access
      individual elements of a variable holding a list of elements.
      A filtering rule like the following accesses the 2nd element
      of the variable DSTPORTS.
    </p>
<pre>
...
&lt;rule action='accept' direction='in' priority='500'&gt;
  &lt;udp dstportstart='$DSTPORTS[1]'/&gt;
&lt;/rule&gt;
...
</pre>
    <p>
      <span class="since">Since 0.9.10</span> it is possible to create
      filtering rules that instantiate all combinations of rules from
      different lists using the notation of
      <code>$VARIABLE[@&lt;iterator ID&gt;]</code>.
      The following rule allows a virtual machine to
      receive traffic on a set of ports, which are specified in DSTPORTS,
      from the set of source IP address specified in SRCIPADDRESSES.
      The rule generates all combinations of elements of the variable
      DSTPORT with those of SRCIPADDRESSES by using two independent
      iterators to access their elements.
    </p>
<pre>
...
&lt;rule action='accept' direction='in' priority='500'&gt;
  &lt;ip srcipaddr='$SRCIPADDRESSES[@1]' dstportstart='$DSTPORTS[@2]'/&gt;
&lt;/rule&gt;
...
</pre>

    <p>
      In an example we assign concrete values to SRCIPADDRESSES and DSTPORTS
    </p>
<pre>
SRCIPADDRESSES = [ 10.0.0.1, 11.1.2.3 ]
DSTPORTS = [ 80, 8080 ]
</pre>
    <p>
      Accessing the variables using $SRCIPADDRESSES[@1] and $DSTPORTS[@2] would
      then result in all combinations of addresses and ports being created:
    </p>
<pre>
10.0.0.1, 80
10.0.0.1, 8080
11.1.2.3, 80
11.1.2.3, 8080
</pre>
    <p>
      Accessing the same variables using a single iterator, for example by using
      the notation $SRCIPADDRESSES[@1] and $DSTPORTS[@1], would result in
      parallel access to both lists and result in the following combinations:
    </p>
<pre>
10.0.0.1, 80
11.1.2.3, 8080
</pre>
    <p>
      Further, the notation of $VARIABLE is short-hand for $VARIABLE[@0]. The
      former notation always assumes the iterator with Id '0'.
    </p>

    <h3><a id="nwfelemsRulesAdvIPAddrDetection">Automatic IP address detection</a></h3>
    <p>
       The detection of IP addresses used on a virtual machine's interface
       is automatically activated if the variable <code>IP</code> is referenced
       but no value has been assigned to it.
       <span class="since">Since 0.9.13</span>
       the variable <code>CTRL_IP_LEARNING</code> can be used to specify
       the IP address learning method to use. Valid values are <code>any</code>,
       <code>dhcp</code>, or <code>none</code>.
       <br/><br/>
       The value <code>any</code> means that libvirt may use any packet to
       determine the address in use by a virtual machine, which is the default
       behavior if the variable <code>CTRL_IP_LEARNING</code> is not set. This method
       will only detect a single IP address on an interface.
       Once a VM's IP address has been detected, its IP network traffic
       will be locked to that address, if for example IP address spoofing
       is prevented by one of its filters. In that case the user of the VM
       will not be able to change the IP address on the interface inside
       the VM, which would be considered IP address spoofing.
       When a VM is migrated to another host or resumed after a suspend operation,
       the first packet sent by the VM will again determine the IP address it can
       use on a particular interface.
       <br/>
       A value of <code>dhcp</code> specifies that libvirt should only honor DHCP
       server-assigned addresses with valid leases. This method supports the detection
       and usage of multiple IP address per interface.
       When a VM is resumed after a suspend operation, still valid IP address leases
       are applied to its filters. Otherwise the VM is expected to again use DHCP to obtain new
       IP addresses. The migration of a VM to another physical host requires that
       the VM again runs the DHCP protocol.
       <br/><br/>
       Use of <code>CTRL_IP_LEARNING=dhcp</code> (DHCP snooping) provides additional
       anti-spoofing security, especially when combined with a filter allowing
       only trusted DHCP servers to assign addresses. To enable this, set the
       variable <code>DHCPSERVER</code> to the IP address of a valid DHCP server
       and provide filters that use this variable to filter incoming DHCP responses.
       <br/><br/>
       When DHCP snooping is enabled and the DHCP lease expires,
       the VM will no longer be able to use the IP address until it acquires a
       new, valid lease from a DHCP server. If the VM is migrated, it must get
       a new valid DHCP lease to use an IP address (e.g., by
       bringing the VM interface down and up again).
       <br/><br/>
       Note that automatic DHCP detection listens to the DHCP traffic
       the VM exchanges with the DHCP server of the infrastructure. To avoid
       denial-of-service attacks on libvirt, the evaluation of those packets
       is rate-limited, meaning that a VM sending an excessive number of DHCP
       packets per second on an interface will not have all of those packets
       evaluated and thus filters may not get adapted. Normal DHCP client
       behavior is assumed to send a low number of DHCP packets per second.
       Further, it is important to setup appropriate filters on all VMs in
       the infrastructure to avoid them  being able to send DHCP
       packets. Therefore VMs must either be prevented from sending UDP and TCP
       traffic from port 67 to port 68 or the <code>DHCPSERVER</code>
       variable should be used on all VMs to restrict DHCP server messages to
       only be allowed to originate from trusted DHCP servers. At the same
       time anti-spoofing prevention must be enabled on all VMs in the subnet.
       <br/><br/>
       If <code>CTRL_IP_LEARNING</code> is set to <code>none</code>, libvirt does not do
       IP address learning and referencing <code>IP</code> without assigning it an
       explicit value is an error.
       <br/><br/>
       The following XML provides an example for the activation of IP address learning
       using the DHCP snooping method:
    </p>
<pre>
&lt;interface type='bridge'&gt;
  &lt;source bridge='virbr0'/&gt;
  &lt;filterref filter='clean-traffic'&gt;
    &lt;parameter name='CTRL_IP_LEARNING' value='dhcp'/&gt;
  &lt;/filterref&gt;
&lt;/interface&gt;
</pre>

    <h3><a id="nwfelemsReservedVars">Reserved Variables</a></h3>
    <p>
      The following table lists reserved variables in use by libvirt.
    </p>
      <table class="top_table">
       <tr>
         <th> Variable Name </th>
         <th> Semantics </th>
       </tr>
       <tr>
         <td> MAC </td>
         <td> The MAC address of the interface </td>
       </tr>
       <tr>
         <td> IP </td>
         <td> The list of IP addresses in use by an interface </td>
       </tr>
       <tr>
         <td> IPV6 </td>
         <td> Not currently implemented:
              the list of IPV6 addresses in use by an interface </td>
       </tr>
       <tr>
         <td> DHCPSERVER </td>
         <td> The list of IP addresses of trusted DHCP servers</td>
       </tr>
       <tr>
         <td> DHCPSERVERV6 </td>
         <td> Not currently implemented:
              The list of IPv6 addresses of trusted DHCP servers</td>
       </tr>
       <tr>
         <td> CTRL_IP_LEARNING </td>
         <td> The choice of the IP address detection mode </td>
       </tr>
      </table>

    <h2><a id="nwfelems">Element and attribute overview</a></h2>

    <p>
      The root element required for all network filters is
      named <code>filter</code> with two possible attributes. The
      <code>name</code> attribute provides a unique name of the
      given filter. The <code>chain</code> attribute is optional but
      allows certain filters to be better organized for more efficient
      processing by the firewall subsystem of the underlying host.
      Currently the system only supports the chains <code>root,
      ipv4, ipv6, arp and rarp</code>.
    </p>

    <h3><a id="nwfelemsRefs">References to other filters</a></h3>
    <p>
     Any filter may hold references to other filters. Individual
     filters may be referenced multiple times in a filter tree but
     references between filters must not introduce loops (directed
     acyclic graph).
     <br/><br/>
     The following shows the XML of the <code>clean-traffic</code>
     network filter referencing several other filters.
    </p>
<pre>
&lt;filter name='clean-traffic'&gt;
  &lt;uuid&gt;6ef53069-ba34-94a0-d33d-17751b9b8cb1&lt;/uuid&gt;
  &lt;filterref filter='no-mac-spoofing'/&gt;
  &lt;filterref filter='no-ip-spoofing'/&gt;
  &lt;filterref filter='allow-incoming-ipv4'/&gt;
  &lt;filterref filter='no-arp-spoofing'/&gt;
  &lt;filterref filter='no-other-l2-traffic'/&gt;
  &lt;filterref filter='qemu-announce-self'/&gt;
&lt;/filter&gt;
</pre>

    <p>
    To reference another filter, the XML node <code>filterref</code>
    needs to be provided inside a <code>filter</code> node. This
    node must have the attribute <code>filter</code> whose value contains
    the name of the filter to be referenced.
    <br/><br/>
    New network filters can be defined at any time and
    may contain references to network filters that are
    not known to libvirt, yet. However, once a virtual machine
    is started or a network interface
    referencing a filter is to be hotplugged, all network filters
    in the filter tree must be available. Otherwise the virtual
    machine will not start or the network interface cannot be
    attached.
    </p>

    <h3><a id="nwfelemsRules">Filter rules</a></h3>
    <p>
    The following XML shows a simple example of a network
    traffic filter implementing a rule to drop traffic if
    the IP address (provided through the value of the
    variable IP) in an outgoing IP packet is not the expected
    one, thus preventing IP address spoofing by the VM.
    </p>
<pre>
&lt;filter name='no-ip-spoofing' chain='ipv4'&gt;
  &lt;uuid&gt;fce8ae33-e69e-83bf-262e-30786c1f8072&lt;/uuid&gt;
  &lt;rule action='drop' direction='out' priority='500'&gt;
    &lt;ip match='no' srcipaddr='$IP'/&gt;
  &lt;/rule&gt;
&lt;/filter&gt;
</pre>

    <p>
     A traffic filtering rule starts with the <code>rule</code>
     node. This node may contain up to three attributes
    </p>
    <ul>
     <li>
        action -- mandatory; must either be <code>drop</code>
        (matching the rule silently discards the packet with no
        further analysis),
        <code>reject</code> (matching the rule generates an ICMP
        reject message with no further analysis) <span class="since">(since
        0.9.0)</span>, <code>accept</code> (matching the rule accepts
        the packet with no further analysis), <code>return</code>
        (matching the rule passes this filter, but returns control to
        the calling filter for further
        analysis) <span class="since">(since 0.9.7)</span>,
        or <code>continue</code> (matching the rule goes on to the next
        rule for further analysis) <span class="since">(since
        0.9.7)</span>.
     </li>
     <li>
        direction -- mandatory; must either be <code>in</code>, <code>out</code> or
         <code>inout</code> if the rule is for incoming,
         outgoing or incoming-and-outgoing traffic
     </li>
     <li>
        priority -- optional; the priority of the rule controls the order in
        which the rule will be instantiated relative to other rules.
        Rules with lower value will be instantiated before rules with higher
        values.
        Valid values are in the range of 0 to 1000.
        <span class="since">Since 0.9.8</span> this has been extended to cover
        the range of -1000 to 1000. If this attribute is not
        provided, priority 500 will automatically be assigned.
        <br/>
        Note that filtering rules in the <code>root</code> chain are sorted
        with filters connected to the <code>root</code> chain following
        their priorities. This allows to interleave filtering rules with
        access to filter chains.
        (See also section on
         <a href="#nwfconceptschainpriorities">
           filtering chain priorities
         </a>.)
     </li>
     <li>
        statematch -- optional; possible values are '0' or 'false' to
        turn the underlying connection state matching off; default is 'true'
        <br/>
        Also read the section on <a href="#nwfelemsRulesAdv">advanced configuration</a>
        topics.
     </li>
    </ul>
    <p>
     The above example indicates that the traffic of type <code>ip</code>
     will be associated with the chain 'ipv4' and the rule will have
     priority 500. If for example another filter is referenced whose
     traffic of type <code>ip</code> is also associated with the chain
     'ipv4' then that filter's rules will be ordered relative to the priority
     500 of the shown rule.
     <br/><br/>
     A rule may contain a single rule for filtering of traffic. The
     above example shows that traffic of type <code>ip</code> is to be
     filtered.
    </p>

    <h4><a id="nwfelemsRulesProto">Supported protocols</a></h4>
    <p>
     The following sections enumerate the list of protocols that
     are supported by the network filtering subsystem. The
     type of traffic a rule is supposed to filter on is provided
     in the <code>rule</code> node as a nested node. Depending
     on the traffic type a rule is filtering, the attributes are
     different. The above example showed the single
     attribute <code>srcipaddr</code> that is valid inside the
     <code>ip</code> traffic filtering node. The following sections
     show what attributes are valid and what type of data they are
     expecting. The following datatypes are available:
    </p>
    <ul>
     <li>UINT8 : 8 bit integer; range 0-255</li>
     <li>UINT16: 16 bit integer; range 0-65535</li>
     <li>MAC_ADDR: MAC address in dotted decimal format, i.e., 00:11:22:33:44:55</li>
     <li>MAC_MASK: MAC address mask in MAC address format, i.e., FF:FF:FF:FC:00:00</li>
     <li>IP_ADDR: IP address in dotted decimal format, i.e., 10.1.2.3</li>
     <li>IP_MASK: IP address mask in either dotted decimal format (255.255.248.0) or CIDR mask (0-32)</li>
     <li>IPV6_ADDR: IPv6 address in numbers format, i.e., FFFF::1</li>
     <li>IPV6_MASK: IPv6 mask in numbers format (FFFF:FFFF:FC00::) or CIDR mask (0-128)</li>
     <li>STRING: A string</li>
     <li>BOOLEAN: 'true', 'yes', '1' or 'false', 'no', '0'</li>
     <li>IPSETFLAGS: The source and destination flags of the ipset described
         by up to 6 'src' or 'dst' elements selecting features from either
         the source or destination part of the packet header; example:
         src,src,dst. The number of 'selectors' to provide here depends
         on the type of ipset that is referenced.</li>
    </ul>
    <p>
     <br/><br/>
     Every attribute except for those of type IP_MASK or IPV6_MASK can
     be negated using the <code>match</code>
     attribute with value <code>no</code>. Multiple negated attributes
     may be grouped together. The following
     XML fragment shows such an example using abstract attributes.
    </p>
<pre>
[...]
&lt;rule action='drop' direction='in'&gt;
  &lt;protocol match='no' attribute1='value1' attribute2='value2'/&gt;
  &lt;protocol attribute3='value3'/&gt;
&lt;/rule&gt;
[...]
</pre>
    <p>
     Rules perform a logical AND evaluation on all values of the given
     protocol attributes. Thus, if a single attribute's value does not match
     the one given in the rule, the whole rule will be skipped during
     evaluation. Therefore, in the above example incoming traffic
     will only be dropped if
     the protocol property attribute1 does not match value1 AND
     the protocol property attribute2 does not match value2 AND
     the protocol property attribute3 matches value3.
     <br/><br/>
    </p>


    <h5><a id="nwfelemsRulesProtoMAC">MAC (Ethernet)</a></h5>
    <p>
      Protocol ID: <code>mac</code>
      <br/>
      Note: Rules of this type should go into the <code>root</code> chain.
    </p>
      <table class="top_table">
       <tr>
         <th> Attribute </th>
         <th> Datatype </th>
         <th> Semantics </th>
       </tr>
       <tr>
         <td>srcmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of sender</td>
       </tr>
       <tr>
         <td>srcmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of sender</td>
       </tr>
       <tr>
         <td>dstmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of destination</td>
       </tr>
       <tr>
         <td>dstmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of destination</td>
       </tr>
       <tr>
         <td>protocolid</td>
         <td>UINT16 (0x600-0xffff), STRING</td>
         <td>Layer 3 protocol ID</td>
       </tr>
       <tr>
         <td>comment <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>text with max. 256 characters</td>
       </tr>
      </table>
    <p>
      Valid Strings for <code>protocolid</code> are: arp, rarp, ipv4, ipv6
    </p>
<pre>
[...]
&lt;mac match='no' srcmacaddr='$MAC'/&gt;
[...]
</pre>

    <h5><a id="nwfelemsRulesProtoVLAN">VLAN (802.1Q)</a>
      <span class="since">(Since 0.9.8)</span>
    </h5>
    <p>
      Protocol ID: <code>vlan</code>
      <br/>
      Note: Rules of this type should go either into the <code>root</code> or
      <code>vlan</code> chain.
    </p>
      <table class="top_table">
       <tr>
         <th> Attribute </th>
         <th> Datatype </th>
         <th> Semantics </th>
       </tr>
       <tr>
         <td>srcmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of sender</td>
       </tr>
       <tr>
         <td>srcmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of sender</td>
       </tr>
       <tr>
         <td>dstmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of destination</td>
       </tr>
       <tr>
         <td>dstmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of destination</td>
       </tr>
       <tr>
         <td>vlanid</td>
         <td>UINT16 (0x0-0xfff, 0 - 4095)</td>
         <td>VLAN ID</td>
       </tr>
       <tr>
         <td>encap-protocol</td>
         <td>UINT16 (0x03c-0xfff), String</td>
         <td>Encapsulated layer 3 protocol ID</td>
       </tr>
       <tr>
         <td>comment </td>
         <td>STRING</td>
         <td>text with max. 256 characters</td>
       </tr>
      </table>
    <p>
      Valid Strings for <code>encap-protocol</code> are: arp, ipv4, ipv6
    </p>

    <h5><a id="nwfelemsRulesProtoSTP">STP (Spanning Tree Protocol)</a>
      <span class="since">(Since 0.9.8)</span>
    </h5>
    <p>
      Protocol ID: <code>stp</code>
      <br/>
      Note: Rules of this type should go either into the <code>root</code> or
      <code>stp</code> chain.
    </p>
      <table class="top_table">
       <tr>
         <th> Attribute </th>
         <th> Datatype </th>
         <th> Semantics </th>
       </tr>
       <tr>
         <td>srcmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of sender</td>
       </tr>
       <tr>
         <td>srcmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of sender</td>
       </tr>
       <tr>
         <td>type</td>
         <td>UINT8</td>
         <td>Bridge Protocol Data Unit (BPDU) type</td>
       </tr>
       <tr>
         <td>flags</td>
         <td>UINT8</td>
         <td>BPDU flag</td>
       </tr>
       <tr>
         <td>root-priority</td>
         <td>UINT16</td>
         <td>Root priority (range start)</td>
       </tr>
       <tr>
         <td>root-priority-hi</td>
         <td>UINT16</td>
         <td>Root priority range end</td>
       </tr>
       <tr>
         <td>root-address</td>
         <td>MAC_ADDRESS</td>
         <td>Root MAC address</td>
       </tr>
       <tr>
         <td>root-address-mask</td>
         <td>MAC_MASK</td>
         <td>Root MAC address mask</td>
       </tr>
       <tr>
         <td>root-cost</td>
         <td>UINT32</td>
         <td>Root path cost (range start)</td>
       </tr>
       <tr>
         <td>root-cost-hi</td>
         <td>UINT32</td>
         <td>Root path cost range end</td>
       </tr>
       <tr>
         <td>sender-priority</td>
         <td>UINT16</td>
         <td>Sender priority (range start)</td>
       </tr>
       <tr>
         <td>sender-priority-hi</td>
         <td>UINT16</td>
         <td>Sender priority range end</td>
       </tr>
       <tr>
         <td>sender-address</td>
         <td>MAC_ADDRESS</td>
         <td>BPDU sender MAC address</td>
       </tr>
       <tr>
         <td>sender-address-mask</td>
         <td>MAC_MASK</td>
         <td>BPDU sender MAC address mask</td>
       </tr>
       <tr>
         <td>port</td>
         <td>UINT16</td>
         <td>Port identifier (range start)</td>
       </tr>
       <tr>
         <td>port_hi</td>
         <td>UINT16</td>
         <td>Port identifier range end</td>
       </tr>
       <tr>
         <td>msg-age</td>
         <td>UINT16</td>
         <td>Message age timer (range start)</td>
       </tr>
       <tr>
         <td>msg-age-hi</td>
         <td>UINT16</td>
         <td>Message age timer range end</td>
       </tr>
       <tr>
         <td>max-age</td>
         <td>UINT16</td>
         <td>Maximum age timer (range start)</td>
       </tr>
       <tr>
         <td>max-age-hi</td>
         <td>UINT16</td>
         <td>Maximum age timer range end</td>
       </tr>
       <tr>
         <td>hello-time</td>
         <td>UINT16</td>
         <td>Hello time timer (range start)</td>
       </tr>
       <tr>
         <td>hello-time-hi</td>
         <td>UINT16</td>
         <td>Hello time timer range end</td>
       </tr>
       <tr>
         <td>forward-delay</td>
         <td>UINT16</td>
         <td>Forward delay (range start)</td>
       </tr>
       <tr>
         <td>forward-delay-hi</td>
         <td>UINT16</td>
         <td>Forward delay range end</td>
       </tr>
       <tr>
         <td>comment</td>
         <td>STRING</td>
         <td>text with max. 256 characters</td>
       </tr>
      </table>

    <h5><a id="nwfelemsRulesProtoARP">ARP/RARP</a></h5>
    <p>
      Protocol ID: <code>arp</code> or <code>rarp</code>
      <br/>
      Note: Rules of this type should either go into the
      <code>root</code> or <code>arp/rarp</code> chain.
    </p>
      <table class="top_table">
       <tr>
         <th> Attribute </th>
         <th> Datatype </th>
         <th> Semantics </th>
       </tr>
       <tr>
         <td>srcmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of sender</td>
       </tr>
       <tr>
         <td>srcmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of sender</td>
       </tr>
       <tr>
         <td>dstmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of destination</td>
       </tr>
       <tr>
         <td>dstmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of destination</td>
       </tr>
       <tr>
         <td>hwtype</td>
         <td>UINT16</td>
         <td>Hardware type</td>
       </tr>
       <tr>
         <td>protocoltype</td>
         <td>UINT16</td>
         <td>Protocol type</td>
       </tr>
       <tr>
         <td>opcode</td>
         <td>UINT16, STRING</td>
         <td>Opcode</td>
       </tr>
       <tr>
         <td>arpsrcmacaddr</td>
         <td>MAC_ADDR</td>
         <td>Source MAC address in ARP/RARP packet</td>
       </tr>
       <tr>
         <td>arpdstmacaddr</td>
         <td>MAC_ADDR</td>
         <td>Destination MAC address in ARP/RARP packet</td>
       </tr>
       <tr>
         <td>arpsrcipaddr</td>
         <td>IP_ADDR</td>
         <td>Source IP address in ARP/RARP packet</td>
       </tr>
       <tr>
         <td>arpsrcipmask <span class="since">(Since 1.2.3)</span></td>
         <td>IP_MASK</td>
         <td>Source IP mask</td>
       </tr>
       <tr>
         <td>arpdstipaddr</td>
         <td>IP_ADDR</td>
         <td>Destination IP address in ARP/RARP packet</td>
       </tr>
       <tr>
         <td>arpdstipmask <span class="since">(Since 1.2.3)</span></td>
         <td>IP_MASK</td>
         <td>Destination IP mask</td>
       </tr>
       <tr>
         <td>comment <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>text with max. 256 characters</td>
       </tr>
       <tr>
         <td>gratuitous <span class="since">(Since 0.9.2)</span></td>
         <td>BOOLEAN</td>
         <td>boolean indicating whether to check for gratuitous ARP packet</td>
       </tr>
      </table>
    <p>
      Valid strings for the <code>Opcode</code> field are:
       Request, Reply, Request_Reverse, Reply_Reverse, DRARP_Request,
       DRARP_Reply, DRARP_Error, InARP_Request, ARP_NAK
      <br/><br/>
    </p>

    <h5><a id="nwfelemsRulesProtoIP">IPv4</a></h5>
    <p>
      Protocol ID: <code>ip</code>
      <br/>
      Note: Rules of this type should either go into the
      <code>root</code> or <code>ipv4</code> chain.
    </p>
      <table class="top_table">
       <tr>
         <th> Attribute </th>
         <th> Datatype </th>
         <th> Semantics </th>
       </tr>
       <tr>
         <td>srcmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of sender</td>
       </tr>
       <tr>
         <td>srcmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of sender</td>
       </tr>
       <tr>
         <td>dstmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of destination</td>
       </tr>
       <tr>
         <td>dstmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of destination</td>
       </tr>
       <tr>
         <td>srcipaddr</td>
         <td>IP_ADDR</td>
         <td>Source IP address</td>
       </tr>
       <tr>
         <td>srcipmask</td>
         <td>IP_MASK</td>
         <td>Mask applied to source IP address</td>
       </tr>
       <tr>
         <td>dstipaddr</td>
         <td>IP_ADDR</td>
         <td>Destination IP address</td>
       </tr>
       <tr>
         <td>dstipmask</td>
         <td>IP_MASK</td>
         <td>Mask applied to destination IP address</td>
       </tr>
       <tr>
         <td>protocol</td>
         <td>UINT8, STRING</td>
         <td>Layer 4 protocol identifier</td>
       </tr>
       <tr>
         <td>srcportstart</td>
         <td>UINT16</td>
         <td>Start of range of valid source ports; requires <code>protocol</code></td>
       </tr>
       <tr>
         <td>srcportend</td>
         <td>UINT16</td>
         <td>End of range of valid source ports; requires <code>protocol</code></td>
       </tr>
       <tr>
         <td>dstportstart</td>
         <td>UINT16</td>
         <td>Start of range of valid destination ports; requires <code>protocol</code></td>
       </tr>
       <tr>
         <td>dstportend</td>
         <td>UINT16</td>
         <td>End of range of valid destination ports; requires <code>protocol</code></td>
       </tr>
       <tr>
         <td>dscp</td>
         <td>UINT8 (0x0-0x3f, 0 - 63)</td>
         <td>Differentiated Services Code Point</td>
       </tr>
       <tr>
         <td>comment <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>text with max. 256 characters</td>
       </tr>
      </table>
    <p>
      Valid strings for <code>protocol</code> are:
         tcp, udp, udplite, esp, ah, icmp, igmp, sctp
      <br/><br/>
    </p>


    <h5><a id="nwfelemsRulesProtoIPv6">IPv6</a></h5>
    <p>
      Protocol ID: <code>ipv6</code>
      <br/>
      Note: Rules of this type should either go into the
      <code>root</code> or <code>ipv6</code> chain.
    </p>
      <table class="top_table">
       <tr>
         <th> Attribute </th>
         <th> Datatype </th>
         <th> Semantics </th>
       </tr>
       <tr>
         <td>srcmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of sender</td>
       </tr>
       <tr>
         <td>srcmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of sender</td>
       </tr>
       <tr>
         <td>dstmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of destination</td>
       </tr>
       <tr>
         <td>dstmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of destination</td>
       </tr>
       <tr>
         <td>srcipaddr</td>
         <td>IPV6_ADDR</td>
         <td>Source IPv6 address</td>
       </tr>
       <tr>
         <td>srcipmask</td>
         <td>IPV6_MASK</td>
         <td>Mask applied to source IPv6 address</td>
       </tr>
       <tr>
         <td>dstipaddr</td>
         <td>IPV6_ADDR</td>
         <td>Destination IPv6 address</td>
       </tr>
       <tr>
         <td>dstipmask</td>
         <td>IPV6_MASK</td>
         <td>Mask applied to destination IPv6 address</td>
       </tr>
       <tr>
         <td>protocol</td>
         <td>UINT8</td>
         <td>Layer 4 protocol identifier</td>
       </tr>
       <tr>
         <td>srcportstart</td>
         <td>UINT16</td>
         <td>Start of range of valid source ports; requires <code>protocol</code></td>
       </tr>
       <tr>
         <td>srcportend</td>
         <td>UINT16</td>
         <td>End of range of valid source ports; requires <code>protocol</code></td>
       </tr>
       <tr>
         <td>dstportstart</td>
         <td>UINT16</td>
         <td>Start of range of valid destination ports; requires <code>protocol</code></td>
       </tr>
       <tr>
         <td>dstportend</td>
         <td>UINT16</td>
         <td>End of range of valid destination ports; requires <code>protocol</code></td>
       </tr>
       <tr>
         <td>type<span class="since">(Since 1.2.12)</span></td>
         <td>UINT8</td>
         <td>ICMPv6 type; requires <code>protocol</code> to be set to <code>icmpv6</code></td>
       </tr>
       <tr>
         <td>typeend<span class="since">(Since 1.2.12)</span></td>
         <td>UINT8</td>
         <td>ICMPv6 type end of range; requires <code>protocol</code> to be set to <code>icmpv6</code></td>
       </tr>
       <tr>
         <td>code<span class="since">(Since 1.2.12)</span></td>
         <td>UINT8</td>
         <td>ICMPv6 code; requires <code>protocol</code> to be set to <code>icmpv6</code></td>
       </tr>
       <tr>
         <td>code<span class="since">(Since 1.2.12)</span></td>
         <td>UINT8</td>
         <td>ICMPv6 code end of range; requires <code>protocol</code> to be set to <code>icmpv6</code></td>
       </tr>
       <tr>
         <td>comment <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>text with max. 256 characters</td>
       </tr>
      </table>
    <p>
      Valid strings for <code>protocol</code> are:
         tcp, udp, udplite, esp, ah, icmpv6, sctp
      <br/><br/>
    </p>

    <h5><a id="nwfelemsRulesProtoTCP-ipv4">TCP/UDP/SCTP</a></h5>
    <p>
      Protocol ID: <code>tcp</code>, <code>udp</code>, <code>sctp</code>
      <br/>
      Note: The chain parameter is ignored for this type of traffic
      and should either be omitted or set to <code>root</code>.
    </p>
      <table class="top_table">
       <tr>
         <th> Attribute </th>
         <th> Datatype </th>
         <th> Semantics </th>
       </tr>
       <tr>
         <td>srcmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of sender</td>
       </tr>
       <tr>
         <td>srcipaddr</td>
         <td>IP_ADDR</td>
         <td>Source IP address</td>
       </tr>
       <tr>
         <td>srcipmask</td>
         <td>IP_MASK</td>
         <td>Mask applied to source IP address</td>
       </tr>
       <tr>
         <td>dstipaddr</td>
         <td>IP_ADDR</td>
         <td>Destination IP address</td>
       </tr>
       <tr>
         <td>dstipmask</td>
         <td>IP_MASK</td>
         <td>Mask applied to destination IP address</td>
       </tr>

       <tr>
         <td>srcipfrom</td>
         <td>IP_ADDR</td>
         <td>Start of range of source IP address</td>
       </tr>
       <tr>
         <td>srcipto</td>
         <td>IP_ADDR</td>
         <td>End of range of source IP address</td>
       </tr>
       <tr>
         <td>dstipfrom</td>
         <td>IP_ADDR</td>
         <td>Start of range of destination IP address</td>
       </tr>
       <tr>
         <td>dstipto</td>
         <td>IP_ADDR</td>
         <td>End of range of destination IP address</td>
       </tr>

       <tr>
         <td>srcportstart</td>
         <td>UINT16</td>
         <td>Start of range of valid source ports</td>
       </tr>
       <tr>
         <td>srcportend</td>
         <td>UINT16</td>
         <td>End of range of valid source ports</td>
       </tr>
       <tr>
         <td>dstportstart</td>
         <td>UINT16</td>
         <td>Start of range of valid destination ports</td>
       </tr>
       <tr>
         <td>dstportend</td>
         <td>UINT16</td>
         <td>End of range of valid destination ports</td>
       </tr>
       <tr>
         <td>dscp</td>
         <td>UINT8 (0x0-0x3f, 0 - 63)</td>
         <td>Differentiated Services Code Point</td>
       </tr>
       <tr>
         <td>comment <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>text with max. 256 characters</td>
       </tr>
       <tr>
         <td>state <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>comma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE</td>
       </tr>
       <tr>
         <td>flags <span class="since">(Since 0.9.1)</span></td>
         <td>STRING</td>
         <td>TCP-only: format of mask/flags with mask and flags each being a comma separated list of SYN,ACK,URG,PSH,FIN,RST or NONE or ALL</td>
       </tr>
       <tr>
         <td>ipset <span class="since">(Since 0.9.13)</span></td>
         <td>STRING</td>
         <td>The name of an IPSet managed outside of libvirt</td>
       </tr>
       <tr>
         <td>ipsetflags <span class="since">(Since 0.9.13)</span></td>
         <td>IPSETFLAGS</td>
         <td>flags for the IPSet; requires ipset attribute</td>
       </tr>
      </table>
    <p>
      <br/><br/>
    </p>


    <h5><a id="nwfelemsRulesProtoICMP">ICMP</a></h5>
    <p>
      Protocol ID: <code>icmp</code>
      <br/>
      Note: The chain parameter is ignored for this type of traffic
      and should either be omitted or set to <code>root</code>.
    </p>
      <table class="top_table">
       <tr>
         <th> Attribute </th>
         <th> Datatype </th>
         <th> Semantics </th>
       </tr>
       <tr>
         <td>srcmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of sender</td>
       </tr>
       <tr>
         <td>srcmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of sender</td>
       </tr>
       <tr>
         <td>dstmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of destination</td>
       </tr>
       <tr>
         <td>dstmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of destination</td>
       </tr>
       <tr>
         <td>srcipaddr</td>
         <td>IP_ADDR</td>
         <td>Source IP address</td>
       </tr>
       <tr>
         <td>srcipmask</td>
         <td>IP_MASK</td>
         <td>Mask applied to source IP address</td>
       </tr>
       <tr>
         <td>dstipaddr</td>
         <td>IP_ADDR</td>
         <td>Destination IP address</td>
       </tr>
       <tr>
         <td>dstipmask</td>
         <td>IP_MASK</td>
         <td>Mask applied to destination IP address</td>
       </tr>

       <tr>
         <td>srcipfrom</td>
         <td>IP_ADDR</td>
         <td>Start of range of source IP address</td>
       </tr>
       <tr>
         <td>srcipto</td>
         <td>IP_ADDR</td>
         <td>End of range of source IP address</td>
       </tr>
       <tr>
         <td>dstipfrom</td>
         <td>IP_ADDR</td>
         <td>Start of range of destination IP address</td>
       </tr>
       <tr>
         <td>dstipto</td>
         <td>IP_ADDR</td>
         <td>End of range of destination IP address</td>
       </tr>
       <tr>
         <td>type</td>
         <td>UINT16</td>
         <td>ICMP type</td>
       </tr>
       <tr>
         <td>code</td>
         <td>UINT16</td>
         <td>ICMP code</td>
       </tr>
       <tr>
         <td>dscp</td>
         <td>UINT8 (0x0-0x3f, 0 - 63)</td>
         <td>Differentiated Services Code Point</td>
       </tr>
       <tr>
         <td>comment <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>text with max. 256 characters</td>
       </tr>
       <tr>
         <td>state <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>comma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE</td>
       </tr>
       <tr>
         <td>ipset <span class="since">(Since 0.9.13)</span></td>
         <td>STRING</td>
         <td>The name of an IPSet managed outside of libvirt</td>
       </tr>
       <tr>
         <td>ipsetflags <span class="since">(Since 0.9.13)</span></td>
         <td>IPSETFLAGS</td>
         <td>flags for the IPSet; requires ipset attribute</td>
       </tr>
      </table>
    <p>
      <br/><br/>
    </p>

    <h5><a id="nwfelemsRulesProtoMisc">IGMP, ESP, AH, UDPLITE, 'ALL'</a></h5>
    <p>
      Protocol ID: <code>igmp</code>, <code>esp</code>, <code>ah</code>, <code>udplite</code>, <code>all</code>
      <br/>
      Note: The chain parameter is ignored for this type of traffic
      and should either be omitted or set to <code>root</code>.
    </p>
      <table class="top_table">
       <tr>
         <th> Attribute </th>
         <th> Datatype </th>
         <th> Semantics </th>
       </tr>
       <tr>
         <td>srcmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of sender</td>
       </tr>
       <tr>
         <td>srcmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of sender</td>
       </tr>
       <tr>
         <td>dstmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of destination</td>
       </tr>
       <tr>
         <td>dstmacmask</td>
         <td>MAC_MASK</td>
         <td>Mask applied to MAC address of destination</td>
       </tr>
       <tr>
         <td>srcipaddr</td>
         <td>IP_ADDR</td>
         <td>Source IP address</td>
       </tr>
       <tr>
         <td>srcipmask</td>
         <td>IP_MASK</td>
         <td>Mask applied to source IP address</td>
       </tr>
       <tr>
         <td>dstipaddr</td>
         <td>IP_ADDR</td>
         <td>Destination IP address</td>
       </tr>
       <tr>
         <td>dstipmask</td>
         <td>IP_MASK</td>
         <td>Mask applied to destination IP address</td>
       </tr>

       <tr>
         <td>srcipfrom</td>
         <td>IP_ADDR</td>
         <td>Start of range of source IP address</td>
       </tr>
       <tr>
         <td>srcipto</td>
         <td>IP_ADDR</td>
         <td>End of range of source IP address</td>
       </tr>
       <tr>
         <td>dstipfrom</td>
         <td>IP_ADDR</td>
         <td>Start of range of destination IP address</td>
       </tr>
       <tr>
         <td>dstipto</td>
         <td>IP_ADDR</td>
         <td>End of range of destination IP address</td>
       </tr>
       <tr>
         <td>dscp</td>
         <td>UINT8 (0x0-0x3f, 0 - 63)</td>
         <td>Differentiated Services Code Point</td>
       </tr>
       <tr>
         <td>comment <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>text with max. 256 characters</td>
       </tr>
       <tr>
         <td>state <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>comma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE</td>
       </tr>
       <tr>
         <td>ipset <span class="since">(Since 0.9.13)</span></td>
         <td>STRING</td>
         <td>The name of an IPSet managed outside of libvirt</td>
       </tr>
       <tr>
         <td>ipsetflags <span class="since">(Since 0.9.13)</span></td>
         <td>IPSETFLAGS</td>
         <td>flags for the IPSet; requires ipset attribute</td>
       </tr>
      </table>
    <p>
      <br/><br/>
    </p>


    <h5><a id="nwfelemsRulesProtoTCP-ipv6">TCP/UDP/SCTP over IPV6</a></h5>
    <p>
      Protocol ID: <code>tcp-ipv6</code>, <code>udp-ipv6</code>, <code>sctp-ipv6</code>
      <br/>
      Note: The chain parameter is ignored for this type of traffic
      and should either be omitted or set to <code>root</code>.
    </p>
      <table class="top_table">
       <tr>
         <th> Attribute </th>
         <th> Datatype </th>
         <th> Semantics </th>
       </tr>
       <tr>
         <td>srcmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of sender</td>
       </tr>
       <tr>
         <td>srcipaddr</td>
         <td>IPV6_ADDR</td>
         <td>Source IP address</td>
       </tr>
       <tr>
         <td>srcipmask</td>
         <td>IPV6_MASK</td>
         <td>Mask applied to source IP address</td>
       </tr>
       <tr>
         <td>dstipaddr</td>
         <td>IPV6_ADDR</td>
         <td>Destination IP address</td>
       </tr>
       <tr>
         <td>dstipmask</td>
         <td>IPV6_MASK</td>
         <td>Mask applied to destination IP address</td>
       </tr>

       <tr>
         <td>srcipfrom</td>
         <td>IPV6_ADDR</td>
         <td>Start of range of source IP address</td>
       </tr>
       <tr>
         <td>srcipto</td>
         <td>IPV6_ADDR</td>
         <td>End of range of source IP address</td>
       </tr>
       <tr>
         <td>dstipfrom</td>
         <td>IPV6_ADDR</td>
         <td>Start of range of destination IP address</td>
       </tr>
       <tr>
         <td>dstipto</td>
         <td>IPV6_ADDR</td>
         <td>End of range of destination IP address</td>
       </tr>

       <tr>
         <td>srcportstart</td>
         <td>UINT16</td>
         <td>Start of range of valid source ports</td>
       </tr>
       <tr>
         <td>srcportend</td>
         <td>UINT16</td>
         <td>End of range of valid source ports</td>
       </tr>
       <tr>
         <td>dstportstart</td>
         <td>UINT16</td>
         <td>Start of range of valid destination ports</td>
       </tr>
       <tr>
         <td>dstportend</td>
         <td>UINT16</td>
         <td>End of range of valid destination ports</td>
       </tr>
       <tr>
         <td>dscp</td>
         <td>UINT8 (0x0-0x3f, 0 - 63)</td>
         <td>Differentiated Services Code Point</td>
       </tr>
       <tr>
         <td>comment <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>text with max. 256 characters</td>
       </tr>
       <tr>
         <td>state <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>comma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE</td>
       </tr>
       <tr>
         <td>flags <span class="since">(Since 0.9.1)</span></td>
         <td>STRING</td>
         <td>TCP-only: format of mask/flags with mask and flags each being a comma separated list of SYN,ACK,URG,PSH,FIN,RST or NONE or ALL</td>
       </tr>
       <tr>
         <td>ipset <span class="since">(Since 0.9.13)</span></td>
         <td>STRING</td>
         <td>The name of an IPSet managed outside of libvirt</td>
       </tr>
       <tr>
         <td>ipsetflags <span class="since">(Since 0.9.13)</span></td>
         <td>IPSETFLAGS</td>
         <td>flags for the IPSet; requires ipset attribute</td>
       </tr>
      </table>
    <p>
      <br/><br/>
    </p>


    <h5><a id="nwfelemsRulesProtoICMPv6">ICMPv6</a></h5>
    <p>
      Protocol ID: <code>icmpv6</code>
      <br/>
      Note: The chain parameter is ignored for this type of traffic
      and should either be omitted or set to <code>root</code>.
    </p>
      <table class="top_table">
       <tr>
         <th> Attribute </th>
         <th> Datatype </th>
         <th> Semantics </th>
       </tr>
       <tr>
         <td>srcmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of sender</td>
       </tr>
       <tr>
         <td>srcipaddr</td>
         <td>IPV6_ADDR</td>
         <td>Source IPv6 address</td>
       </tr>
       <tr>
         <td>srcipmask</td>
         <td>IPV6_MASK</td>
         <td>Mask applied to source IPv6 address</td>
       </tr>
       <tr>
         <td>dstipaddr</td>
         <td>IPV6_ADDR</td>
         <td>Destination IPv6 address</td>
       </tr>
       <tr>
         <td>dstipmask</td>
         <td>IPV6_MASK</td>
         <td>Mask applied to destination IPv6 address</td>
       </tr>

       <tr>
         <td>srcipfrom</td>
         <td>IPV6_ADDR</td>
         <td>Start of range of source IP address</td>
       </tr>
       <tr>
         <td>srcipto</td>
         <td>IPV6_ADDR</td>
         <td>End of range of source IP address</td>
       </tr>
       <tr>
         <td>dstipfrom</td>
         <td>IPV6_ADDR</td>
         <td>Start of range of destination IP address</td>
       </tr>
       <tr>
         <td>dstipto</td>
         <td>IPV6_ADDR</td>
         <td>End of range of destination IP address</td>
       </tr>

       <tr>
         <td>type</td>
         <td>UINT16</td>
         <td>ICMPv6 type</td>
       </tr>
       <tr>
         <td>code</td>
         <td>UINT16</td>
         <td>ICMPv6 code</td>
       </tr>
       <tr>
         <td>dscp</td>
         <td>UINT8 (0x0-0x3f, 0 - 63)</td>
         <td>Differentiated Services Code Point</td>
       </tr>
       <tr>
         <td>comment <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>text with max. 256 characters</td>
       </tr>
       <tr>
         <td>state <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>comma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE</td>
       </tr>
       <tr>
         <td>ipset <span class="since">(Since 0.9.13)</span></td>
         <td>STRING</td>
         <td>The name of an IPSet managed outside of libvirt</td>
       </tr>
       <tr>
         <td>ipsetflags <span class="since">(Since 0.9.13)</span></td>
         <td>IPSETFLAGS</td>
         <td>flags for the IPSet; requires ipset attribute</td>
       </tr>
      </table>
    <p>
      <br/><br/>
    </p>

    <h5><a id="nwfelemsRulesProtoMiscv6">ESP, AH, UDPLITE, 'ALL' over IPv6</a></h5>
    <p>
      Protocol ID: <code>esp-ipv6</code>, <code>ah-ipv6</code>, <code>udplite-ipv6</code>, <code>all-ipv6</code>
      <br/>
      Note: The chain parameter is ignored for this type of traffic
      and should either be omitted or set to <code>root</code>.
    </p>
      <table class="top_table">
       <tr>
         <th> Attribute </th>
         <th> Datatype </th>
         <th> Semantics </th>
       </tr>
       <tr>
         <td>srcmacaddr</td>
         <td>MAC_ADDR</td>
         <td>MAC address of sender</td>
       </tr>
       <tr>
         <td>srcipaddr</td>
         <td>IPV6_ADDR</td>
         <td>Source IPv6 address</td>
       </tr>
       <tr>
         <td>srcipmask</td>
         <td>IPV6_MASK</td>
         <td>Mask applied to source IPv6 address</td>
       </tr>
       <tr>
         <td>dstipaddr</td>
         <td>IPV6_ADDR</td>
         <td>Destination IPv6 address</td>
       </tr>
       <tr>
         <td>dstipmask</td>
         <td>IPV6_MASK</td>
         <td>Mask applied to destination IPv6 address</td>
       </tr>

       <tr>
         <td>srcipfrom</td>
         <td>IPV6_ADDR</td>
         <td>Start of range of source IP address</td>
       </tr>
       <tr>
         <td>srcipto</td>
         <td>IPV6_ADDR</td>
         <td>End of range of source IP address</td>
       </tr>
       <tr>
         <td>dstipfrom</td>
         <td>IPV6_ADDR</td>
         <td>Start of range of destination IP address</td>
       </tr>
       <tr>
         <td>dstipto</td>
         <td>IPV6_ADDR</td>
         <td>End of range of destination IP address</td>
       </tr>
       <tr>
         <td>dscp</td>
         <td>UINT8 (0x0-0x3f, 0 - 63)</td>
         <td>Differentiated Services Code Point</td>
       </tr>
       <tr>
         <td>comment <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>text with max. 256 characters</td>
       </tr>
       <tr>
         <td>state <span class="since">(Since 0.8.5)</span></td>
         <td>STRING</td>
         <td>comma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE</td>
       </tr>
       <tr>
         <td>ipset <span class="since">(Since 0.9.13)</span></td>
         <td>STRING</td>
         <td>The name of an IPSet managed outside of libvirt</td>
       </tr>
       <tr>
         <td>ipsetflags <span class="since">(Since 0.9.13)</span></td>
         <td>IPSETFLAGS</td>
         <td>flags for the IPSet; requires ipset attribute</td>
       </tr>
      </table>
    <p>
      <br/><br/>
    </p>

    <h3><a id="nwfelemsRulesAdv">Advanced Filter Configuration Topics</a></h3>
    <p>
     The following sections discuss advanced filter configuration
     topics.
    </p>

    <h4><a id="nwfelemsRulesAdvTracking">Connection tracking</a></h4>
    <p>
     The network filtering subsystem (on Linux) makes use of the connection
     tracking support of iptables. This helps in enforcing the
     directionality of network traffic (state match) as well as
     counting and limiting the number of simultaneous connections towards
     a VM. As an example, if a VM has TCP port 8080
     open as a server, clients may connect to the VM on port 8080.
     Connection tracking and enforcement of directionality then prevents
     the VM from initiating a connection from
     (TCP client) port 8080 to the host back to a remote host.
     More importantly, tracking helps to prevent
     remote attackers from establishing a connection back to a VM. For example,
     if the user inside the VM established a connection to
     port 80 on an attacker site, then the attacker will not be able to
     initiate a connection from TCP port 80 back towards the VM.
     By default the connection state match that enables connection tracking
     and then enforcement of directionality of traffic is turned on. <br/>
     The following shows an example XML fragment where this feature has been
     turned off for incoming connections to TCP port 12345.
    </p>
<pre>
[...]
&lt;rule direction='in' action='accept' statematch='false'&gt;
  &lt;tcp dstportstart='12345'/&gt;
&lt;/rule&gt;
[...]
</pre>
    <p>
     This now allows incoming traffic to TCP port 12345, but would also
     enable the initiation from (client) TCP port 12345 within the VM,
     which may or may not be desirable.
    </p>

    <h4><a id="nwfelemsRulesAdvLimiting">Limiting Number of Connections</a></h4>
    <p>
     To limit the number of connections a VM may establish, a rule must
     be provided that sets a limit of connections for a given
     type of traffic. If for example a VM
     is supposed to be allowed to only ping one other IP address at a time
     and is supposed to have only one active incoming ssh connection at a
     time, the following XML fragment can be used to achieve this.
    </p>
<pre>
[...]
&lt;rule action='drop' direction='in' priority='400'&gt;
  &lt;tcp connlimit-above='1'/&gt;
&lt;/rule&gt;
&lt;rule action='accept' direction='in' priority='500'&gt;
  &lt;tcp dstportstart='22'/&gt;
&lt;/rule&gt;
&lt;rule action='drop' direction='out' priority='400'&gt;
  &lt;icmp connlimit-above='1'/&gt;
&lt;/rule&gt;
&lt;rule action='accept' direction='out' priority='500'&gt;
  &lt;icmp/&gt;
&lt;/rule&gt;
&lt;rule action='accept' direction='out' priority='500'&gt;
  &lt;udp dstportstart='53'/&gt;
&lt;/rule&gt;
&lt;rule action='drop' direction='inout' priority='1000'&gt;
  &lt;all/&gt;
&lt;/rule&gt;
[...]
</pre>
    <p>
     Note that the rule for the limit has to logically appear
     before the rule for accepting the traffic.<br/>
     An additional rule for letting DNS traffic to port 22
     go out the VM has been added to avoid ssh sessions not
     getting established for reasons related to DNS lookup failures
     by the ssh daemon. Leaving this rule out may otherwise lead to
     fun-filled debugging joy (symptom: ssh client seems to hang
     while trying to connect).
     <br/><br/>
     Lot of care must be taken with timeouts related
     to tracking of traffic. An ICMP ping that
     the user may have terminated inside the VM may have a long
     timeout in the host's connection tracking system and therefore
     not allow another ICMP ping to go through for a while. Therefore,
     the timeouts have to be tuned in the host's sysfs, i.e.,
    </p>

<pre>
echo 3 > /proc/sys/net/netfilter/nf_conntrack_icmp_timeout
</pre>
    <p>
      sets the ICMP connection tracking timeout to 3 seconds. The
      effect of this is that once one ping is terminated, another
      one can start after 3 seconds.<br/>
      Further, we want to point out that a client that for whatever
      reason has not properly closed a TCP connection may cause a
      connection to be held open for a longer period of time,
      depending to what timeout the <code>TCP established</code> state
      timeout has been set to on the host. Also, idle connections may time
      out in the connection tracking system but can be reactivated once
      packets are exchanged. However, a newly initiated connection may force
      an idle connection into TCP backoff if the number of allowed connections
      is set to a too low limit, the new connection is established
      and hits (not exceeds) the limit of allowed connections and for
      example a key is pressed on the old ssh session, which now has become
      unresponsive due to its traffic being dropped.
      Therefore, the limit of connections should be rather high so that
      fluctuations in new TCP connections don't cause odd
      traffic behavior in relation to idle connections.
    </p>

    <h2><a id="nwfcli">Command line tools</a></h2>
    <p>
      The libvirt command line tool <code>virsh</code> has been extended
      with life-cycle support for network filters. All commands related
      to the network filtering subsystem start with the prefix
      <code>nwfilter</code>. The following commands are available:
    </p>
    <ul>
     <li>nwfilter-list : list UUIDs and names of all network filters</li>
     <li>nwfilter-define : define a new network filter or update an existing one</li>
     <li>nwfilter-undefine : delete a network filter given its name; it must not be currently in use</li>
     <li>nwfilter-dumpxml : display a network filter given its name</li>
     <li>nwfilter-edit : edit a network filter given its name</li>
    </ul>

    <h2><a id="nwfexamples">Pre-existing network filters</a></h2>
    <p>
     The following is a list of example network filters that are
     automatically installed with libvirt.</p>
      <table class="top_table">
       <tr>
         <th> Name </th>
         <th> Description </th>
       </tr>
       <tr>
         <td> no-arp-spoofing </td>
         <td> Prevent a VM from spoofing ARP traffic; this filter
              only allows ARP request and reply messages and enforces
              that those packets contain the MAC and IP addresses
              of the VM.</td>
      </tr>
       <tr>
         <td> allow-dhcp </td>
         <td> Allow a VM to request an IP address via DHCP (from any
              DHCP server)</td>
      </tr>
       <tr>
         <td> allow-dhcp-server </td>
         <td> Allow a VM to request an IP address from a specified
              DHCP server. The dotted decimal IP address of the DHCP
              server must be provided in a reference to this filter.
              The name of the variable must be <i>DHCPSERVER</i>.</td>
      </tr>
       <tr>
         <td> no-ip-spoofing </td>
         <td> Prevent a VM from sending of IP packets with
              a source IP address different from the one
              in the packet. </td>
      </tr>
       <tr>
         <td> no-ip-multicast </td>
         <td> Prevent a VM from sending IP multicast packets. </td>
      </tr>
       <tr>
         <td> clean-traffic </td>
         <td> Prevent MAC, IP and ARP spoofing. This filter references
              several other filters as building blocks. </td>
      </tr>
      </table>
    <p>
     Note that most of the above filters are only building blocks and
     require a combination with other filters to provide useful network
     traffic filtering.
     The most useful one in the above list is the <i>clean-traffic</i>
     filter. This filter itself can for example be combined with the
     <i>no-ip-multicast</i>
     filter to prevent virtual machines from sending IP multicast traffic
     on top of the prevention of packet spoofing.
    </p>

    <h2><a id="nwfwrite">Writing your own filters</a></h2>

    <p>
     Since libvirt only provides a couple of example networking filters, you
     may consider writing your own. When planning on doing so
     there are a couple of things
     you may need to know regarding the network filtering subsystem and how
     it works internally. Certainly you also have to know and understand
     the protocols very well that you want to be filtering on so that
     no further traffic than what you want can pass and that in fact the
     traffic you want to allow does pass.
     <br/><br/>
     The network filtering subsystem is currently only available on
     Linux hosts and only works for QEMU and KVM type of virtual machines.
     On Linux
     it builds upon the support for <code>ebtables</code>, <code>iptables
     </code> and <code>ip6tables</code> and makes use of their features.
     From the above list of supported protocols the following ones are
     implemented using <code>ebtables</code>:
    </p>
    <ul>
     <li>mac</li>
     <li>stp (spanning tree protocol)</li>
     <li>vlan (802.1Q)</li>
     <li>arp, rarp</li>
     <li>ipv4</li>
     <li>ipv6</li>
    </ul>

    <p>
    All other protocols over IPv4 are supported using iptables, those over
    IPv6 are implemented using ip6tables.
    <br/><br/>
    On a Linux host, all traffic filtering instantiated by libvirt's network
    filter subsystem first passes through the filtering support implemented
    by ebtables and only then through iptables or ip6tables filters. If
    a filter tree has rules with the protocols <code>mac</code>,
    <code>stp</code>, <code>vlan</code>
    <code>arp</code>, <code>rarp</code>, <code>ipv4</code>,
    or <code>ipv6</code> ebtables rules will automatically be instantiated.
    <br/>
    The role of the <code>chain</code> attribute in the network filter
    XML is that internally a new user-defined ebtables table is created
    that then for example receives all <code>arp</code> traffic coming
    from or going to a virtual machine if the chain <code>arp</code>
    has been specified. Further, a rule is generated in an interface's
    <code>root</code> chain that directs all ipv4 traffic into the
    user-defined chain. Therefore, all ARP traffic rules should then be
    placed into filters specifying this chain. This type of branching
    into user-defined tables is only supported with filtering on the ebtables
    layer.
    <br/>
    <span class="since">Since 0.9.8</span> multiple chains for the same
    protocol can be created. For this the name of the chain must have
    a prefix of one of the previously enumerated protocols. To create an
    additional chain for handling of ARP traffic, a chain with name
    <code>arp-test</code> can be specified.
    <br/>
    As an example, it is
    possible to filter on UDP traffic by source and destination ports using
    the <code>ip</code> protocol filter and specifying attributes for the
    protocol, source and destination IP addresses and ports of UDP packets
    that are to be accepted. This allows
    early filtering of UDP traffic with ebtables. However, once an IP or IPv6
    packet, such as a UDP packet,
    has passed the ebtables layer and there is at least one rule in a filter
    tree that instantiates iptables or ip6tables rules, a rule to let
    the UDP packet pass will also be necessary to be provided for those
    filtering layers. This can be
    achieved with a rule containing an appropriate <code>udp</code> or
    <code>udp-ipv6</code> traffic filtering node.
    </p>

    <h3><a id="nwfwriteexample">Example custom filter</a></h3>
    <p>
     As an example we want to now build a filter that fulfills the following
     list of requirements:
    </p>
    <ul>
     <li>prevents a VM's interface from MAC, IP and ARP spoofing</li>
     <li>opens only TCP ports 22 and 80 of a VM's interface</li>
     <li>allows the VM to send ping traffic from an interface
        but not let the VM be pinged on the interface</li>
     <li>allows the VM to do DNS lookups (UDP towards port 53)</li>
    </ul>
    <p>
     The requirement to prevent spoofing is fulfilled by the existing
     <code>clean-traffic</code> network filter, thus we will reference this
     filter from our custom filter.
     <br/>
     To enable traffic for TCP ports 22 and 80 we will add 2 rules to
     enable this type of traffic. To allow the VM to send ping traffic
     we will add a rule for ICMP traffic. For simplicity reasons
     we allow general ICMP traffic to be initiated from the VM, not
     just ICMP echo request and response messages. To then
     disallow all other traffic to reach or be initiated by the
     VM we will then need to add a rule that drops all other traffic.
     Assuming our VM is called <i>test</i> and
     the interface we want to associate our filter with is called <i>eth0</i>,
     we name our filter <i>test-eth0</i>.
     The result of these considerations is the following network filter XML:
    </p>
<pre>
&lt;filter name='test-eth0'&gt;
  &lt;!-- reference the clean traffic filter to prevent
       MAC, IP and ARP spoofing. By not providing
       and IP address parameter, libvirt will detect the
       IP address the VM is using. --&gt;
  &lt;filterref filter='clean-traffic'/&gt;

  &lt;!-- enable TCP ports 22 (ssh) and 80 (http) to be reachable --&gt;
  &lt;rule action='accept' direction='in'&gt;
    &lt;tcp dstportstart='22'/&gt;
  &lt;/rule&gt;

  &lt;rule action='accept' direction='in'&gt;
    &lt;tcp dstportstart='80'/&gt;
  &lt;/rule&gt;

  &lt;!-- enable general ICMP traffic to be initiated by the VM;
       this includes ping traffic --&gt;
  &lt;rule action='accept' direction='out'&gt;
    &lt;icmp/&gt;
  &lt;/rule&gt;

  &lt;!-- enable outgoing DNS lookups using UDP --&gt;
  &lt;rule action='accept' direction='out'&gt;
    &lt;udp dstportstart='53'/&gt;
  &lt;/rule&gt;

  &lt;!-- drop all other traffic --&gt;
  &lt;rule action='drop' direction='inout'&gt;
    &lt;all/&gt;
  &lt;/rule&gt;

&lt;/filter&gt;
</pre>
    <p>
     Note that none of the rules in the above XML contain the
     IP address of the VM as either source or destination address, yet
     the filtering of the traffic works correctly. The reason is that
     the evaluation  of the rules internally happens on a
     per-interface basis and the rules are evaluated based on the knowledge
     about which (tap) interface has sent or will receive the packet rather
     than what their source or destination IP address may be.
     <br/><br/>
     An XML fragment for a possible network interface description inside
     the domain XML of the <code>test</code> VM could then look like this:
    </p>
<pre>
[...]
&lt;interface type='bridge'&gt;
  &lt;source bridge='mybridge'/&gt;
  &lt;filterref filter='test-eth0'/&gt;
&lt;/interface&gt;
[...]
</pre>

    <p>
     To more strictly control the ICMP traffic and enforce that only
     ICMP echo requests can be sent from the VM
     and only ICMP echo responses be received by the VM, the above
     <code>ICMP</code> rule can be replaced with the following two rules:
    </p>
<pre>
&lt;!-- enable outgoing ICMP echo requests--&gt;
&lt;rule action='accept' direction='out'&gt;
  &lt;icmp type='8'/&gt;
&lt;/rule&gt;

&lt;!-- enable incoming ICMP echo replies--&gt;
&lt;rule action='accept' direction='in'&gt;
  &lt;icmp type='0'/&gt;
&lt;/rule&gt;
</pre>

    <h3><a id="nwfwriteexample2nd">Second example custom filter</a></h3>
    <p>
     In this example we now want to build a similar filter as in the
     example above, but extend the list of requirements with an
     ftp server located inside the VM. Further, we will be using features
     that have been added in <span class="since">version 0.8.5</span>.
     The requirements for this filter are:
    </p>
    <ul>
     <li>prevents a VM's interface from MAC, IP and ARP spoofing</li>
     <li>opens only TCP ports 22 and 80 of a VM's interface</li>
     <li>allows the VM to send ping traffic from an interface
        but not let the VM be pinged on the interface</li>
     <li>allows the VM to do DNS lookups (UDP towards port 53)</li>
     <li>enable an ftp server (in active mode) to be run inside the VM</li>
    </ul>
    <p>
     The additional requirement of allowing an ftp server to be run inside
     the VM maps into the requirement of allowing port 21 to be reachable
     for ftp control traffic as well as enabling the VM to establish an
     outgoing tcp connection originating from the VM's TCP port 20 back to
     the ftp client (ftp active mode). There are several ways of how this
     filter can be written and we present 2 solutions.
     <br/><br/>
     The 1st solution makes use of the <code>state</code> attribute of
     the TCP protocol that gives us a hook into the connection tracking
     framework of the Linux host. For the VM-initiated ftp data connection
     (ftp active mode) we use the <code>RELATED</code> state that allows
     us to detect that the VM-initiated ftp data connection is a consequence of
     ( or 'has a relationship with' ) an existing ftp control connection,
     thus we want to allow it to let packets
     pass the firewall. The <code>RELATED</code> state, however, is only
     valid for the very first packet of the outgoing TCP connection for the
     ftp data path. Afterwards, the state to compare against is
     <code>ESTABLISHED</code>, which then applies equally
     to the incoming and outgoing direction. All this is related to the ftp
     data traffic originating from TCP port 20 of the VM. This then leads to
     the following solution
     <span class="since">(since 0.8.5 (QEMU, KVM))</span>:
    </p>
<pre>
&lt;filter name='test-eth0'&gt;
  &lt;!-- reference the clean traffic filter to prevent
       MAC, IP and ARP spoofing. By not providing
       and IP address parameter, libvirt will detect the
       IP address the VM is using. --&gt;
  &lt;filterref filter='clean-traffic'/&gt;

  &lt;!-- enable TCP port 21 (ftp-control) to be reachable --&gt;
  &lt;rule action='accept' direction='in'&gt;
    &lt;tcp dstportstart='21'/&gt;
  &lt;/rule&gt;

  &lt;!-- enable TCP port 20 for VM-initiated ftp data connection
       related to an existing ftp control connection --&gt;
  &lt;rule action='accept' direction='out'&gt;
    &lt;tcp srcportstart='20' state='RELATED,ESTABLISHED'/&gt;
  &lt;/rule&gt;

  &lt;!-- accept all packets from client on the ftp data connection --&gt;
  &lt;rule action='accept' direction='in'&gt;
    &lt;tcp dstportstart='20' state='ESTABLISHED'/&gt;
  &lt;/rule&gt;

  &lt;!-- enable TCP ports 22 (ssh) and 80 (http) to be reachable --&gt;
  &lt;rule action='accept' direction='in'&gt;
    &lt;tcp dstportstart='22'/&gt;
  &lt;/rule&gt;

  &lt;rule action='accept' direction='in'&gt;
    &lt;tcp dstportstart='80'/&gt;
  &lt;/rule&gt;

  &lt;!-- enable general ICMP traffic to be initiated by the VM;
       this includes ping traffic --&gt;
  &lt;rule action='accept' direction='out'&gt;
    &lt;icmp/&gt;
  &lt;/rule&gt;

  &lt;!-- enable outgoing DNS lookups using UDP --&gt;
  &lt;rule action='accept' direction='out'&gt;
    &lt;udp dstportstart='53'/&gt;
  &lt;/rule&gt;

  &lt;!-- drop all other traffic --&gt;
  &lt;rule action='drop' direction='inout'&gt;
    &lt;all/&gt;
  &lt;/rule&gt;

&lt;/filter&gt;
</pre>
    <p>
     Before trying out a filter using the <code>RELATED</code> state,
     you have to make sure that the appropriate connection tracking module
     has been loaded into the host's kernel. Depending on the version of the
     kernel, you must run either one of the following two commands before
     the ftp connection with the VM is established.
    </p>
<pre>
modprobe nf_conntrack_ftp   # where available  or

modprobe ip_conntrack_ftp   # if above is not available
</pre>
    <p>
     If other protocols than ftp are to be used in conjunction with the
     <code>RELATED</code> state, their corresponding module must be loaded.
     Modules exist at least for the protocols ftp, tftp, irc, sip,
     sctp, and amanda.
    </p>
    <p>
     The 2nd solution makes uses the state flags of connections more
     than the previous solution did.
     In this solution we take advantage of the fact that the
     <code>NEW</code> state of a connection is valid when the very
     first packet of a traffic flow is seen. Subsequently, if the very first
     packet of a flow is accepted, the flow becomes a connection and enters
     the <code>ESTABLISHED</code> state. This allows us to write a general
     rule for allowing packets of <code>ESTABLISHED</code> connections to
     reach the VM or be sent by the VM.
     We write specific rules for the very first packets identified by the
     <code>NEW</code> state and for which ports they are acceptable. All
     packets for ports that are not explicitly accepted will be dropped and
     therefore the connection will not go into the <code>ESTABLISHED</code>
     state and any subsequent packets be dropped.
    </p>

<pre>
&lt;filter name='test-eth0'&gt;
  &lt;!-- reference the clean traffic filter to prevent
       MAC, IP and ARP spoofing. By not providing
       and IP address parameter, libvirt will detect the
       IP address the VM is using. --&gt;
  &lt;filterref filter='clean-traffic'/&gt;

  &lt;!-- let the packets of all previously accepted connections reach the VM --&gt;
  &lt;rule action='accept' direction='in'&gt;
    &lt;all state='ESTABLISHED'/&gt;
  &lt;/rule&gt;

  &lt;!-- let the packets of all previously accepted and related connections be sent from the VM --&gt;
  &lt;rule action='accept' direction='out'&gt;
    &lt;all state='ESTABLISHED,RELATED'/&gt;
  &lt;/rule&gt;

  &lt;!-- enable traffic towards port 21 (ftp), 22 (ssh) and 80 (http) --&gt;
  &lt;rule action='accept' direction='in'&gt;
    &lt;tcp dstportstart='21' dstportend='22' state='NEW'/&gt;
  &lt;/rule&gt;

  &lt;rule action='accept' direction='in'&gt;
    &lt;tcp dstportstart='80' state='NEW'/&gt;
  &lt;/rule&gt;

  &lt;!-- enable general ICMP traffic to be initiated by the VM;
       this includes ping traffic --&gt;
  &lt;rule action='accept' direction='out'&gt;
    &lt;icmp state='NEW'/&gt;
  &lt;/rule&gt;

  &lt;!-- enable outgoing DNS lookups using UDP --&gt;
  &lt;rule action='accept' direction='out'&gt;
    &lt;udp dstportstart='53' state='NEW'/&gt;
  &lt;/rule&gt;

  &lt;!-- drop all other traffic --&gt;
  &lt;rule action='drop' direction='inout'&gt;
    &lt;all/&gt;
  &lt;/rule&gt;

&lt;/filter&gt;

</pre>

    <h2><a id="nwflimits">Limitations</a></h2>
    <p>
     The following sections list (current) limitations of the network
     filtering subsystem.
    </p>

    <h3><a id="nwflimitsmigr">VM Migration</a></h3>
     <p>
      VM migration is only supported if the whole filter tree
      that is referenced by a virtual machine's top level filter
      is also available on the target host. The network filter
      <i>clean-traffic</i>
      for example should be available on all libvirt installations
      of version 0.8.1 or later and thus enable migration of VMs that
      for example reference this filter. All other
      custom filters must be migrated using higher layer software. It is
      outside the scope of libvirt to ensure that referenced filters
      on the source system are equivalent to those on the target system
      and vice versa.
      <br/><br/>
      Migration must occur between libvirt installations of version
      0.8.1 or later in order not to lose the network traffic filters
      associated with an interface.
     </p>
    <h3><a id="nwflimitsvlan">VLAN filtering on Linux</a></h3>
     <p>
      VLAN (802.1Q) packets, if sent by a virtual machine, cannot be filtered
      with rules for protocol IDs <code>arp</code>, <code>rarp</code>,
      <code>ipv4</code> and <code>ipv6</code> but only
      with protocol IDs <code>mac</code> and <code>vlan</code>. Therefore,
      the example filter <code>clean-traffic</code> will not work as expected.
     </p>
  </body>
</html>