summaryrefslogtreecommitdiffstats
path: root/Documentation/networking/bonding.txt
blob: 5cdb22971d19753607739a66108bd85fdf4a492c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
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
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681

		Linux Ethernet Bonding Driver HOWTO

		Latest update: 27 April 2011

Initial release : Thomas Davis <tadavis at lbl.gov>
Corrections, HA extensions : 2000/10/03-15 :
  - Willy Tarreau <willy at meta-x.org>
  - Constantine Gavrilov <const-g at xpert.com>
  - Chad N. Tindel <ctindel at ieee dot org>
  - Janice Girouard <girouard at us dot ibm dot com>
  - Jay Vosburgh <fubar at us dot ibm dot com>

Reorganized and updated Feb 2005 by Jay Vosburgh
Added Sysfs information: 2006/04/24
  - Mitch Williams <mitch.a.williams at intel.com>

Introduction
============

	The Linux bonding driver provides a method for aggregating
multiple network interfaces into a single logical "bonded" interface.
The behavior of the bonded interfaces depends upon the mode; generally
speaking, modes provide either hot standby or load balancing services.
Additionally, link integrity monitoring may be performed.
	
	The bonding driver originally came from Donald Becker's
beowulf patches for kernel 2.0. It has changed quite a bit since, and
the original tools from extreme-linux and beowulf sites will not work
with this version of the driver.

	For new versions of the driver, updated userspace tools, and
who to ask for help, please follow the links at the end of this file.

Table of Contents
=================

1. Bonding Driver Installation

2. Bonding Driver Options

3. Configuring Bonding Devices
3.1	Configuration with Sysconfig Support
3.1.1		Using DHCP with Sysconfig
3.1.2		Configuring Multiple Bonds with Sysconfig
3.2	Configuration with Initscripts Support
3.2.1		Using DHCP with Initscripts
3.2.2		Configuring Multiple Bonds with Initscripts
3.3	Configuring Bonding Manually with Ifenslave
3.3.1		Configuring Multiple Bonds Manually
3.4	Configuring Bonding Manually via Sysfs
3.5	Configuration with Interfaces Support
3.6	Overriding Configuration for Special Cases

4. Querying Bonding Configuration
4.1	Bonding Configuration
4.2	Network Configuration

5. Switch Configuration

6. 802.1q VLAN Support

7. Link Monitoring
7.1	ARP Monitor Operation
7.2	Configuring Multiple ARP Targets
7.3	MII Monitor Operation

8. Potential Trouble Sources
8.1	Adventures in Routing
8.2	Ethernet Device Renaming
8.3	Painfully Slow Or No Failed Link Detection By Miimon

9. SNMP agents

10. Promiscuous mode

11. Configuring Bonding for High Availability
11.1	High Availability in a Single Switch Topology
11.2	High Availability in a Multiple Switch Topology
11.2.1		HA Bonding Mode Selection for Multiple Switch Topology
11.2.2		HA Link Monitoring for Multiple Switch Topology

12. Configuring Bonding for Maximum Throughput
12.1	Maximum Throughput in a Single Switch Topology
12.1.1		MT Bonding Mode Selection for Single Switch Topology
12.1.2		MT Link Monitoring for Single Switch Topology
12.2	Maximum Throughput in a Multiple Switch Topology
12.2.1		MT Bonding Mode Selection for Multiple Switch Topology
12.2.2		MT Link Monitoring for Multiple Switch Topology

13. Switch Behavior Issues
13.1	Link Establishment and Failover Delays
13.2	Duplicated Incoming Packets

14. Hardware Specific Considerations
14.1	IBM BladeCenter

15. Frequently Asked Questions

16. Resources and Links


1. Bonding Driver Installation
==============================

	Most popular distro kernels ship with the bonding driver
already available as a module. If your distro does not, or you
have need to compile bonding from source (e.g., configuring and
installing a mainline kernel from kernel.org), you'll need to perform
the following steps:

1.1 Configure and build the kernel with bonding
-----------------------------------------------

	The current version of the bonding driver is available in the
drivers/net/bonding subdirectory of the most recent kernel source
(which is available on http://kernel.org).  Most users "rolling their
own" will want to use the most recent kernel from kernel.org.

	Configure kernel with "make menuconfig" (or "make xconfig" or
"make config"), then select "Bonding driver support" in the "Network
device support" section.  It is recommended that you configure the
driver as module since it is currently the only way to pass parameters
to the driver or configure more than one bonding device.

	Build and install the new kernel and modules.

1.2 Bonding Control Utility
-------------------------------------

	 It is recommended to configure bonding via iproute2 (netlink)
or sysfs, the old ifenslave control utility is obsolete.

2. Bonding Driver Options
=========================

	Options for the bonding driver are supplied as parameters to the
bonding module at load time, or are specified via sysfs.

	Module options may be given as command line arguments to the
insmod or modprobe command, but are usually specified in either the
/etc/modrobe.d/*.conf configuration files, or in a distro-specific
configuration file (some of which are detailed in the next section).

	Details on bonding support for sysfs is provided in the
"Configuring Bonding Manually via Sysfs" section, below.

	The available bonding driver parameters are listed below. If a
parameter is not specified the default value is used.  When initially
configuring a bond, it is recommended "tail -f /var/log/messages" be
run in a separate window to watch for bonding driver error messages.

	It is critical that either the miimon or arp_interval and
arp_ip_target parameters be specified, otherwise serious network
degradation will occur during link failures.  Very few devices do not
support at least miimon, so there is really no reason not to use it.

	Options with textual values will accept either the text name
or, for backwards compatibility, the option value.  E.g.,
"mode=802.3ad" and "mode=4" set the same mode.

	The parameters are as follows:

active_slave

	Specifies the new active slave for modes that support it
	(active-backup, balance-alb and balance-tlb).  Possible values
	are the name of any currently enslaved interface, or an empty
	string.  If a name is given, the slave and its link must be up in order
	to be selected as the new active slave.  If an empty string is
	specified, the current active slave is cleared, and a new active
	slave is selected automatically.

	Note that this is only available through the sysfs interface. No module
	parameter by this name exists.

	The normal value of this option is the name of the currently
	active slave, or the empty string if there is no active slave or
	the current mode does not use an active slave.

ad_select

	Specifies the 802.3ad aggregation selection logic to use.  The
	possible values and their effects are:

	stable or 0

		The active aggregator is chosen by largest aggregate
		bandwidth.

		Reselection of the active aggregator occurs only when all
		slaves of the active aggregator are down or the active
		aggregator has no slaves.

		This is the default value.

	bandwidth or 1

		The active aggregator is chosen by largest aggregate
		bandwidth.  Reselection occurs if:

		- A slave is added to or removed from the bond

		- Any slave's link state changes

		- Any slave's 802.3ad association state changes

		- The bond's administrative state changes to up

	count or 2

		The active aggregator is chosen by the largest number of
		ports (slaves).  Reselection occurs as described under the
		"bandwidth" setting, above.

	The bandwidth and count selection policies permit failover of
	802.3ad aggregations when partial failure of the active aggregator
	occurs.  This keeps the aggregator with the highest availability
	(either in bandwidth or in number of ports) active at all times.

	This option was added in bonding version 3.4.0.

all_slaves_active

	Specifies that duplicate frames (received on inactive ports) should be
	dropped (0) or delivered (1).

	Normally, bonding will drop duplicate frames (received on inactive
	ports), which is desirable for most users. But there are some times
	it is nice to allow duplicate frames to be delivered.

	The default value is 0 (drop duplicate frames received on inactive
	ports).

arp_interval

	Specifies the ARP link monitoring frequency in milliseconds.

	The ARP monitor works by periodically checking the slave
	devices to determine whether they have sent or received
	traffic recently (the precise criteria depends upon the
	bonding mode, and the state of the slave).  Regular traffic is
	generated via ARP probes issued for the addresses specified by
	the arp_ip_target option.

	This behavior can be modified by the arp_validate option,
	below.

	If ARP monitoring is used in an etherchannel compatible mode
	(modes 0 and 2), the switch should be configured in a mode
	that evenly distributes packets across all links. If the
	switch is configured to distribute the packets in an XOR
	fashion, all replies from the ARP targets will be received on
	the same link which could cause the other team members to
	fail.  ARP monitoring should not be used in conjunction with
	miimon.  A value of 0 disables ARP monitoring.  The default
	value is 0.

arp_ip_target

	Specifies the IP addresses to use as ARP monitoring peers when
	arp_interval is > 0.  These are the targets of the ARP request
	sent to determine the health of the link to the targets.
	Specify these values in ddd.ddd.ddd.ddd format.  Multiple IP
	addresses must be separated by a comma.  At least one IP
	address must be given for ARP monitoring to function.  The
	maximum number of targets that can be specified is 16.  The
	default value is no IP addresses.

arp_validate

	Specifies whether or not ARP probes and replies should be
	validated in the active-backup mode.  This causes the ARP
	monitor to examine the incoming ARP requests and replies, and
	only consider a slave to be up if it is receiving the
	appropriate ARP traffic.

	Possible values are:

	none or 0

		No validation is performed.  This is the default.

	active or 1

		Validation is performed only for the active slave.

	backup or 2

		Validation is performed only for backup slaves.

	all or 3

		Validation is performed for all slaves.

	For the active slave, the validation checks ARP replies to
	confirm that they were generated by an arp_ip_target.  Since
	backup slaves do not typically receive these replies, the
	validation performed for backup slaves is on the ARP request
	sent out via the active slave.  It is possible that some
	switch or network configurations may result in situations
	wherein the backup slaves do not receive the ARP requests; in
	such a situation, validation of backup slaves must be
	disabled.

	The validation of ARP requests on backup slaves is mainly
	helping bonding to decide which slaves are more likely to
	work in case of the active slave failure, it doesn't really
	guarantee that the backup slave will work if it's selected
	as the next active slave.

	This option is useful in network configurations in which
	multiple bonding hosts are concurrently issuing ARPs to one or
	more targets beyond a common switch.  Should the link between
	the switch and target fail (but not the switch itself), the
	probe traffic generated by the multiple bonding instances will
	fool the standard ARP monitor into considering the links as
	still up.  Use of the arp_validate option can resolve this, as
	the ARP monitor will only consider ARP requests and replies
	associated with its own instance of bonding.

	This option was added in bonding version 3.1.0.

arp_all_targets

	Specifies the quantity of arp_ip_targets that must be reachable
	in order for the ARP monitor to consider a slave as being up.
	This option affects only active-backup mode for slaves with
	arp_validation enabled.

	Possible values are:

	any or 0

		consider the slave up only when any of the arp_ip_targets
		is reachable

	all or 1

		consider the slave up only when all of the arp_ip_targets
		are reachable

downdelay

	Specifies the time, in milliseconds, to wait before disabling
	a slave after a link failure has been detected.  This option
	is only valid for the miimon link monitor.  The downdelay
	value should be a multiple of the miimon value; if not, it
	will be rounded down to the nearest multiple.  The default
	value is 0.

fail_over_mac

	Specifies whether active-backup mode should set all slaves to
	the same MAC address at enslavement (the traditional
	behavior), or, when enabled, perform special handling of the
	bond's MAC address in accordance with the selected policy.

	Possible values are:

	none or 0

		This setting disables fail_over_mac, and causes
		bonding to set all slaves of an active-backup bond to
		the same MAC address at enslavement time.  This is the
		default.

	active or 1

		The "active" fail_over_mac policy indicates that the
		MAC address of the bond should always be the MAC
		address of the currently active slave.  The MAC
		address of the slaves is not changed; instead, the MAC
		address of the bond changes during a failover.

		This policy is useful for devices that cannot ever
		alter their MAC address, or for devices that refuse
		incoming broadcasts with their own source MAC (which
		interferes with the ARP monitor).

		The down side of this policy is that every device on
		the network must be updated via gratuitous ARP,
		vs. just updating a switch or set of switches (which
		often takes place for any traffic, not just ARP
		traffic, if the switch snoops incoming traffic to
		update its tables) for the traditional method.  If the
		gratuitous ARP is lost, communication may be
		disrupted.

		When this policy is used in conjunction with the mii
		monitor, devices which assert link up prior to being
		able to actually transmit and receive are particularly
		susceptible to loss of the gratuitous ARP, and an
		appropriate updelay setting may be required.

	follow or 2

		The "follow" fail_over_mac policy causes the MAC
		address of the bond to be selected normally (normally
		the MAC address of the first slave added to the bond).
		However, the second and subsequent slaves are not set
		to this MAC address while they are in a backup role; a
		slave is programmed with the bond's MAC address at
		failover time (and the formerly active slave receives
		the newly active slave's MAC address).

		This policy is useful for multiport devices that
		either become confused or incur a performance penalty
		when multiple ports are programmed with the same MAC
		address.


	The default policy is none, unless the first slave cannot
	change its MAC address, in which case the active policy is
	selected by default.

	This option may be modified via sysfs only when no slaves are
	present in the bond.

	This option was added in bonding version 3.2.0.  The "follow"
	policy was added in bonding version 3.3.0.

lacp_rate

	Option specifying the rate in which we'll ask our link partner
	to transmit LACPDU packets in 802.3ad mode.  Possible values
	are:

	slow or 0
		Request partner to transmit LACPDUs every 30 seconds

	fast or 1
		Request partner to transmit LACPDUs every 1 second

	The default is slow.

max_bonds

	Specifies the number of bonding devices to create for this
	instance of the bonding driver.  E.g., if max_bonds is 3, and
	the bonding driver is not already loaded, then bond0, bond1
	and bond2 will be created.  The default value is 1.  Specifying
	a value of 0 will load bonding, but will not create any devices.

miimon

	Specifies the MII link monitoring frequency in milliseconds.
	This determines how often the link state of each slave is
	inspected for link failures.  A value of zero disables MII
	link monitoring.  A value of 100 is a good starting point.
	The use_carrier option, below, affects how the link state is
	determined.  See the High Availability section for additional
	information.  The default value is 0.

min_links

	Specifies the minimum number of links that must be active before
	asserting carrier. It is similar to the Cisco EtherChannel min-links
	feature. This allows setting the minimum number of member ports that
	must be up (link-up state) before marking the bond device as up
	(carrier on). This is useful for situations where higher level services
	such as clustering want to ensure a minimum number of low bandwidth
	links are active before switchover. This option only affect 802.3ad
	mode.

	The default value is 0. This will cause carrier to be asserted (for
	802.3ad mode) whenever there is an active aggregator, regardless of the
	number of available links in that aggregator. Note that, because an
	aggregator cannot be active without at least one available link,
	setting this option to 0 or to 1 has the exact same effect.

mode

	Specifies one of the bonding policies. The default is
	balance-rr (round robin).  Possible values are:

	balance-rr or 0

		Round-robin policy: Transmit packets in sequential
		order from the first available slave through the
		last.  This mode provides load balancing and fault
		tolerance.

	active-backup or 1

		Active-backup policy: Only one slave in the bond is
		active.  A different slave becomes active if, and only
		if, the active slave fails.  The bond's MAC address is
		externally visible on only one port (network adapter)
		to avoid confusing the switch.

		In bonding version 2.6.2 or later, when a failover
		occurs in active-backup mode, bonding will issue one
		or more gratuitous ARPs on the newly active slave.
		One gratuitous ARP is issued for the bonding master
		interface and each VLAN interfaces configured above
		it, provided that the interface has at least one IP
		address configured.  Gratuitous ARPs issued for VLAN
		interfaces are tagged with the appropriate VLAN id.

		This mode provides fault tolerance.  The primary
		option, documented below, affects the behavior of this
		mode.

	balance-xor or 2

		XOR policy: Transmit based on the selected transmit
		hash policy.  The default policy is a simple [(source
		MAC address XOR'd with destination MAC address) modulo
		slave count].  Alternate transmit policies may be
		selected via the xmit_hash_policy option, described
		below.

		This mode provides load balancing and fault tolerance.

	broadcast or 3

		Broadcast policy: transmits everything on all slave
		interfaces.  This mode provides fault tolerance.

	802.3ad or 4

		IEEE 802.3ad Dynamic link aggregation.  Creates
		aggregation groups that share the same speed and
		duplex settings.  Utilizes all slaves in the active
		aggregator according to the 802.3ad specification.

		Slave selection for outgoing traffic is done according
		to the transmit hash policy, which may be changed from
		the default simple XOR policy via the xmit_hash_policy
		option, documented below.  Note that not all transmit
		policies may be 802.3ad compliant, particularly in
		regards to the packet mis-ordering requirements of
		section 43.2.4 of the 802.3ad standard.  Differing
		peer implementations will have varying tolerances for
		noncompliance.

		Prerequisites:

		1. Ethtool support in the base drivers for retrieving
		the speed and duplex of each slave.

		2. A switch that supports IEEE 802.3ad Dynamic link
		aggregation.

		Most switches will require some type of configuration
		to enable 802.3ad mode.

	balance-tlb or 5

		Adaptive transmit load balancing: channel bonding that
		does not require any special switch support.  The
		outgoing traffic is distributed according to the
		current load (computed relative to the speed) on each
		slave.  Incoming traffic is received by the current
		slave.  If the receiving slave fails, another slave
		takes over the MAC address of the failed receiving
		slave.

		Prerequisite:

		Ethtool support in the base drivers for retrieving the
		speed of each slave.

	balance-alb or 6

		Adaptive load balancing: includes balance-tlb plus
		receive load balancing (rlb) for IPV4 traffic, and
		does not require any special switch support.  The
		receive load balancing is achieved by ARP negotiation.
		The bonding driver intercepts the ARP Replies sent by
		the local system on their way out and overwrites the
		source hardware address with the unique hardware
		address of one of the slaves in the bond such that
		different peers use different hardware addresses for
		the server.

		Receive traffic from connections created by the server
		is also balanced.  When the local system sends an ARP
		Request the bonding driver copies and saves the peer's
		IP information from the ARP packet.  When the ARP
		Reply arrives from the peer, its hardware address is
		retrieved and the bonding driver initiates an ARP
		reply to this peer assigning it to one of the slaves
		in the bond.  A problematic outcome of using ARP
		negotiation for balancing is that each time that an
		ARP request is broadcast it uses the hardware address
		of the bond.  Hence, peers learn the hardware address
		of the bond and the balancing of receive traffic
		collapses to the current slave.  This is handled by
		sending updates (ARP Replies) to all the peers with
		their individually assigned hardware address such that
		the traffic is redistributed.  Receive traffic is also
		redistributed when a new slave is added to the bond
		and when an inactive slave is re-activated.  The
		receive load is distributed sequentially (round robin)
		among the group of highest speed slaves in the bond.

		When a link is reconnected or a new slave joins the
		bond the receive traffic is redistributed among all
		active slaves in the bond by initiating ARP Replies
		with the selected MAC address to each of the
		clients. The updelay parameter (detailed below) must
		be set to a value equal or greater than the switch's
		forwarding delay so that the ARP Replies sent to the
		peers will not be blocked by the switch.

		Prerequisites:

		1. Ethtool support in the base drivers for retrieving
		the speed of each slave.

		2. Base driver support for setting the hardware
		address of a device while it is open.  This is
		required so that there will always be one slave in the
		team using the bond hardware address (the
		curr_active_slave) while having a unique hardware
		address for each slave in the bond.  If the
		curr_active_slave fails its hardware address is
		swapped with the new curr_active_slave that was
		chosen.

num_grat_arp
num_unsol_na

	Specify the number of peer notifications (gratuitous ARPs and
	unsolicited IPv6 Neighbor Advertisements) to be issued after a
	failover event.  As soon as the link is up on the new slave
	(possibly immediately) a peer notification is sent on the
	bonding device and each VLAN sub-device.  This is repeated at
	each link monitor interval (arp_interval or miimon, whichever
	is active) if the number is greater than 1.

	The valid range is 0 - 255; the default value is 1.  These options
	affect only the active-backup mode.  These options were added for
	bonding versions 3.3.0 and 3.4.0 respectively.

	From Linux 3.0 and bonding version 3.7.1, these notifications
	are generated by the ipv4 and ipv6 code and the numbers of
	repetitions cannot be set independently.

packets_per_slave

	Specify the number of packets to transmit through a slave before
	moving to the next one. When set to 0 then a slave is chosen at
	random.

	The valid range is 0 - 65535; the default value is 1. This option
	has effect only in balance-rr mode.

primary

	A string (eth0, eth2, etc) specifying which slave is the
	primary device.  The specified device will always be the
	active slave while it is available.  Only when the primary is
	off-line will alternate devices be used.  This is useful when
	one slave is preferred over another, e.g., when one slave has
	higher throughput than another.

	The primary option is only valid for active-backup(1),
	balance-tlb (5) and balance-alb (6) mode.

primary_reselect

	Specifies the reselection policy for the primary slave.  This
	affects how the primary slave is chosen to become the active slave
	when failure of the active slave or recovery of the primary slave
	occurs.  This option is designed to prevent flip-flopping between
	the primary slave and other slaves.  Possible values are:

	always or 0 (default)

		The primary slave becomes the active slave whenever it
		comes back up.

	better or 1

		The primary slave becomes the active slave when it comes
		back up, if the speed and duplex of the primary slave is
		better than the speed and duplex of the current active
		slave.

	failure or 2

		The primary slave becomes the active slave only if the
		current active slave fails and the primary slave is up.

	The primary_reselect setting is ignored in two cases:

		If no slaves are active, the first slave to recover is
		made the active slave.

		When initially enslaved, the primary slave is always made
		the active slave.

	Changing the primary_reselect policy via sysfs will cause an
	immediate selection of the best active slave according to the new
	policy.  This may or may not result in a change of the active
	slave, depending upon the circumstances.

	This option was added for bonding version 3.6.0.

updelay

	Specifies the time, in milliseconds, to wait before enabling a
	slave after a link recovery has been detected.  This option is
	only valid for the miimon link monitor.  The updelay value
	should be a multiple of the miimon value; if not, it will be
	rounded down to the nearest multiple.  The default value is 0.

use_carrier

	Specifies whether or not miimon should use MII or ETHTOOL
	ioctls vs. netif_carrier_ok() to determine the link
	status. The MII or ETHTOOL ioctls are less efficient and
	utilize a deprecated calling sequence within the kernel.  The
	netif_carrier_ok() relies on the device driver to maintain its
	state with netif_carrier_on/off; at this writing, most, but
	not all, device drivers support this facility.

	If bonding insists that the link is up when it should not be,
	it may be that your network device driver does not support
	netif_carrier_on/off.  The default state for netif_carrier is
	"carrier on," so if a driver does not support netif_carrier,
	it will appear as if the link is always up.  In this case,
	setting use_carrier to 0 will cause bonding to revert to the
	MII / ETHTOOL ioctl method to determine the link state.

	A value of 1 enables the use of netif_carrier_ok(), a value of
	0 will use the deprecated MII / ETHTOOL ioctls.  The default
	value is 1.

xmit_hash_policy

	Selects the transmit hash policy to use for slave selection in
	balance-xor and 802.3ad modes.  Possible values are:

	layer2

		Uses XOR of hardware MAC addresses to generate the
		hash.  The formula is

		(source MAC XOR destination MAC) modulo slave count

		This algorithm will place all traffic to a particular
		network peer on the same slave.

		This algorithm is 802.3ad compliant.

	layer2+3

		This policy uses a combination of layer2 and layer3
		protocol information to generate the hash.

		Uses XOR of hardware MAC addresses and IP addresses to
		generate the hash.  The formula is

		hash = source MAC XOR destination MAC
		hash = hash XOR source IP XOR destination IP
		hash = hash XOR (hash RSHIFT 16)
		hash = hash XOR (hash RSHIFT 8)
		And then hash is reduced modulo slave count.

		If the protocol is IPv6 then the source and destination
		addresses are first hashed using ipv6_addr_hash.

		This algorithm will place all traffic to a particular
		network peer on the same slave.  For non-IP traffic,
		the formula is the same as for the layer2 transmit
		hash policy.

		This policy is intended to provide a more balanced
		distribution of traffic than layer2 alone, especially
		in environments where a layer3 gateway device is
		required to reach most destinations.

		This algorithm is 802.3ad compliant.

	layer3+4

		This policy uses upper layer protocol information,
		when available, to generate the hash.  This allows for
		traffic to a particular network peer to span multiple
		slaves, although a single connection will not span
		multiple slaves.

		The formula for unfragmented TCP and UDP packets is

		hash = source port, destination port (as in the header)
		hash = hash XOR source IP XOR destination IP
		hash = hash XOR (hash RSHIFT 16)
		hash = hash XOR (hash RSHIFT 8)
		And then hash is reduced modulo slave count.

		If the protocol is IPv6 then the source and destination
		addresses are first hashed using ipv6_addr_hash.

		For fragmented TCP or UDP packets and all other IPv4 and
		IPv6 protocol traffic, the source and destination port
		information is omitted.  For non-IP traffic, the
		formula is the same as for the layer2 transmit hash
		policy.

		This algorithm is not fully 802.3ad compliant.  A
		single TCP or UDP conversation containing both
		fragmented and unfragmented packets will see packets
		striped across two interfaces.  This may result in out
		of order delivery.  Most traffic types will not meet
		this criteria, as TCP rarely fragments traffic, and
		most UDP traffic is not involved in extended
		conversations.  Other implementations of 802.3ad may
		or may not tolerate this noncompliance.

	encap2+3

		This policy uses the same formula as layer2+3 but it
		relies on skb_flow_dissect to obtain the header fields
		which might result in the use of inner headers if an
		encapsulation protocol is used. For example this will
		improve the performance for tunnel users because the
		packets will be distributed according to the encapsulated
		flows.

	encap3+4

		This policy uses the same formula as layer3+4 but it
		relies on skb_flow_dissect to obtain the header fields
		which might result in the use of inner headers if an
		encapsulation protocol is used. For example this will
		improve the performance for tunnel users because the
		packets will be distributed according to the encapsulated
		flows.

	The default value is layer2.  This option was added in bonding
	version 2.6.3.  In earlier versions of bonding, this parameter
	does not exist, and the layer2 policy is the only policy.  The
	layer2+3 value was added for bonding version 3.2.2.

resend_igmp

	Specifies the number of IGMP membership reports to be issued after
	a failover event. One membership report is issued immediately after
	the failover, subsequent packets are sent in each 200ms interval.

	The valid range is 0 - 255; the default value is 1. A value of 0
	prevents the IGMP membership report from being issued in response
	to the failover event.

	This option is useful for bonding modes balance-rr (0), active-backup
	(1), balance-tlb (5) and balance-alb (6), in which a failover can
	switch the IGMP traffic from one slave to another.  Therefore a fresh
	IGMP report must be issued to cause the switch to forward the incoming
	IGMP traffic over the newly selected slave.

	This option was added for bonding version 3.7.0.

lp_interval

	Specifies the number of seconds between instances where the bonding
	driver sends learning packets to each slaves peer switch.

	The valid range is 1 - 0x7fffffff; the default value is 1. This Option
	has effect only in balance-tlb and balance-alb modes.

3. Configuring Bonding Devices
==============================

	You can configure bonding using either your distro's network
initialization scripts, or manually using either iproute2 or the
sysfs interface.  Distros generally use one of three packages for the
network initialization scripts: initscripts, sysconfig or interfaces.
Recent versions of these packages have support for bonding, while older
versions do not.

	We will first describe the options for configuring bonding for
distros using versions of initscripts, sysconfig and interfaces with full
or partial support for bonding, then provide information on enabling
bonding without support from the network initialization scripts (i.e.,
older versions of initscripts or sysconfig).

	If you're unsure whether your distro uses sysconfig,
initscripts or interfaces, or don't know if it's new enough, have no fear.
Determining this is fairly straightforward.

	First, look for a file called interfaces in /etc/network directory.
If this file is present in your system, then your system use interfaces. See
Configuration with Interfaces Support.

	Else, issue the command:

$ rpm -qf /sbin/ifup

	It will respond with a line of text starting with either
"initscripts" or "sysconfig," followed by some numbers.  This is the
package that provides your network initialization scripts.

	Next, to determine if your installation supports bonding,
issue the command:

$ grep ifenslave /sbin/ifup

	If this returns any matches, then your initscripts or
sysconfig has support for bonding.

3.1 Configuration with Sysconfig Support
----------------------------------------

	This section applies to distros using a version of sysconfig
with bonding support, for example, SuSE Linux Enterprise Server 9.

	SuSE SLES 9's networking configuration system does support
bonding, however, at this writing, the YaST system configuration
front end does not provide any means to work with bonding devices.
Bonding devices can be managed by hand, however, as follows.

	First, if they have not already been configured, configure the
slave devices.  On SLES 9, this is most easily done by running the
yast2 sysconfig configuration utility.  The goal is for to create an
ifcfg-id file for each slave device.  The simplest way to accomplish
this is to configure the devices for DHCP (this is only to get the
file ifcfg-id file created; see below for some issues with DHCP).  The
name of the configuration file for each device will be of the form:

ifcfg-id-xx:xx:xx:xx:xx:xx

	Where the "xx" portion will be replaced with the digits from
the device's permanent MAC address.

	Once the set of ifcfg-id-xx:xx:xx:xx:xx:xx files has been
created, it is necessary to edit the configuration files for the slave
devices (the MAC addresses correspond to those of the slave devices).
Before editing, the file will contain multiple lines, and will look
something like this:

BOOTPROTO='dhcp'
STARTMODE='on'
USERCTL='no'
UNIQUE='XNzu.WeZGOGF+4wE'
_nm_name='bus-pci-0001:61:01.0'

	Change the BOOTPROTO and STARTMODE lines to the following:

BOOTPROTO='none'
STARTMODE='off'

	Do not alter the UNIQUE or _nm_name lines.  Remove any other
lines (USERCTL, etc).

	Once the ifcfg-id-xx:xx:xx:xx:xx:xx files have been modified,
it's time to create the configuration file for the bonding device
itself.  This file is named ifcfg-bondX, where X is the number of the
bonding device to create, starting at 0.  The first such file is
ifcfg-bond0, the second is ifcfg-bond1, and so on.  The sysconfig
network configuration system will correctly start multiple instances
of bonding.

	The contents of the ifcfg-bondX file is as follows:

BOOTPROTO="static"
BROADCAST="10.0.2.255"
IPADDR="10.0.2.10"
NETMASK="255.255.0.0"
NETWORK="10.0.2.0"
REMOTE_IPADDR=""
STARTMODE="onboot"
BONDING_MASTER="yes"
BONDING_MODULE_OPTS="mode=active-backup miimon=100"
BONDING_SLAVE0="eth0"
BONDING_SLAVE1="bus-pci-0000:06:08.1"

	Replace the sample BROADCAST, IPADDR, NETMASK and NETWORK
values with the appropriate values for your network.

	The STARTMODE specifies when the device is brought online.
The possible values are:

	onboot:	 The device is started at boot time.  If you're not
		 sure, this is probably what you want.

	manual:	 The device is started only when ifup is called
		 manually.  Bonding devices may be configured this
		 way if you do not wish them to start automatically
		 at boot for some reason.

	hotplug: The device is started by a hotplug event.  This is not
		 a valid choice for a bonding device.

	off or ignore: The device configuration is ignored.

	The line BONDING_MASTER='yes' indicates that the device is a
bonding master device.  The only useful value is "yes."

	The contents of BONDING_MODULE_OPTS are supplied to the
instance of the bonding module for this device.  Specify the options
for the bonding mode, link monitoring, and so on here.  Do not include
the max_bonds bonding parameter; this will confuse the configuration
system if you have multiple bonding devices.

	Finally, supply one BONDING_SLAVEn="slave device" for each
slave.  where "n" is an increasing value, one for each slave.  The
"slave device" is either an interface name, e.g., "eth0", or a device
specifier for the network device.  The interface name is easier to
find, but the ethN names are subject to change at boot time if, e.g.,
a device early in the sequence has failed.  The device specifiers
(bus-pci-0000:06:08.1 in the example above) specify the physical
network device, and will not change unless the device's bus location
changes (for example, it is moved from one PCI slot to another).  The
example above uses one of each type for demonstration purposes; most
configurations will choose one or the other for all slave devices.

	When all configuration files have been modified or created,
networking must be restarted for the configuration changes to take
effect.  This can be accomplished via the following:

# /etc/init.d/network restart

	Note that the network control script (/sbin/ifdown) will
remove the bonding module as part of the network shutdown processing,
so it is not necessary to remove the module by hand if, e.g., the
module parameters have changed.

	Also, at this writing, YaST/YaST2 will not manage bonding
devices (they do not show bonding interfaces on its list of network
devices).  It is necessary to edit the configuration file by hand to
change the bonding configuration.

	Additional general options and details of the ifcfg file
format can be found in an example ifcfg template file:

/etc/sysconfig/network/ifcfg.template

	Note that the template does not document the various BONDING_
settings described above, but does describe many of the other options.

3.1.1 Using DHCP with Sysconfig
-------------------------------

	Under sysconfig, configuring a device with BOOTPROTO='dhcp'
will cause it to query DHCP for its IP address information.  At this
writing, this does not function for bonding devices; the scripts
attempt to obtain the device address from DHCP prior to adding any of
the slave devices.  Without active slaves, the DHCP requests are not
sent to the network.

3.1.2 Configuring Multiple Bonds with Sysconfig
-----------------------------------------------

	The sysconfig network initialization system is capable of
handling multiple bonding devices.  All that is necessary is for each
bonding instance to have an appropriately configured ifcfg-bondX file
(as described above).  Do not specify the "max_bonds" parameter to any
instance of bonding, as this will confuse sysconfig.  If you require
multiple bonding devices with identical parameters, create multiple
ifcfg-bondX files.

	Because the sysconfig scripts supply the bonding module
options in the ifcfg-bondX file, it is not necessary to add them to
the system /etc/modules.d/*.conf configuration files.

3.2 Configuration with Initscripts Support
------------------------------------------

	This section applies to distros using a recent version of
initscripts with bonding support, for example, Red Hat Enterprise Linux
version 3 or later, Fedora, etc.  On these systems, the network
initialization scripts have knowledge of bonding, and can be configured to
control bonding devices.  Note that older versions of the initscripts
package have lower levels of support for bonding; this will be noted where
applicable.

	These distros will not automatically load the network adapter
driver unless the ethX device is configured with an IP address.
Because of this constraint, users must manually configure a
network-script file for all physical adapters that will be members of
a bondX link.  Network script files are located in the directory:

/etc/sysconfig/network-scripts

	The file name must be prefixed with "ifcfg-eth" and suffixed
with the adapter's physical adapter number.  For example, the script
for eth0 would be named /etc/sysconfig/network-scripts/ifcfg-eth0.
Place the following text in the file:

DEVICE=eth0
USERCTL=no
ONBOOT=yes
MASTER=bond0
SLAVE=yes
BOOTPROTO=none

	The DEVICE= line will be different for every ethX device and
must correspond with the name of the file, i.e., ifcfg-eth1 must have
a device line of DEVICE=eth1.  The setting of the MASTER= line will
also depend on the final bonding interface name chosen for your bond.
As with other network devices, these typically start at 0, and go up
one for each device, i.e., the first bonding instance is bond0, the
second is bond1, and so on.

	Next, create a bond network script.  The file name for this
script will be /etc/sysconfig/network-scripts/ifcfg-bondX where X is
the number of the bond.  For bond0 the file is named "ifcfg-bond0",
for bond1 it is named "ifcfg-bond1", and so on.  Within that file,
place the following text:

DEVICE=bond0
IPADDR=192.168.1.1
NETMASK=255.255.255.0
NETWORK=192.168.1.0
BROADCAST=192.168.1.255
ONBOOT=yes
BOOTPROTO=none
USERCTL=no

	Be sure to change the networking specific lines (IPADDR,
NETMASK, NETWORK and BROADCAST) to match your network configuration.

	For later versions of initscripts, such as that found with Fedora
7 (or later) and Red Hat Enterprise Linux version 5 (or later), it is possible,
and, indeed, preferable, to specify the bonding options in the ifcfg-bond0
file, e.g. a line of the format:

BONDING_OPTS="mode=active-backup arp_interval=60 arp_ip_target=192.168.1.254"

	will configure the bond with the specified options.  The options
specified in BONDING_OPTS are identical to the bonding module parameters
except for the arp_ip_target field when using versions of initscripts older
than and 8.57 (Fedora 8) and 8.45.19 (Red Hat Enterprise Linux 5.2).  When
using older versions each target should be included as a separate option and
should be preceded by a '+' to indicate it should be added to the list of
queried targets, e.g.,

	arp_ip_target=+192.168.1.1 arp_ip_target=+192.168.1.2

	is the proper syntax to specify multiple targets.  When specifying
options via BONDING_OPTS, it is not necessary to edit /etc/modprobe.d/*.conf.

	For even older versions of initscripts that do not support
BONDING_OPTS, it is necessary to edit /etc/modprobe.d/*.conf, depending upon
your distro) to load the bonding module with your desired options when the
bond0 interface is brought up.  The following lines in /etc/modprobe.d/*.conf
will load the bonding module, and select its options:

alias bond0 bonding
options bond0 mode=balance-alb miimon=100

	Replace the sample parameters with the appropriate set of
options for your configuration.

	Finally run "/etc/rc.d/init.d/network restart" as root.  This
will restart the networking subsystem and your bond link should be now
up and running.

3.2.1 Using DHCP with Initscripts
---------------------------------

	Recent versions of initscripts (the versions supplied with Fedora
Core 3 and Red Hat Enterprise Linux 4, or later versions, are reported to
work) have support for assigning IP information to bonding devices via
DHCP.

	To configure bonding for DHCP, configure it as described
above, except replace the line "BOOTPROTO=none" with "BOOTPROTO=dhcp"
and add a line consisting of "TYPE=Bonding".  Note that the TYPE value
is case sensitive.

3.2.2 Configuring Multiple Bonds with Initscripts
-------------------------------------------------

	Initscripts packages that are included with Fedora 7 and Red Hat
Enterprise Linux 5 support multiple bonding interfaces by simply
specifying the appropriate BONDING_OPTS= in ifcfg-bondX where X is the
number of the bond.  This support requires sysfs support in the kernel,
and a bonding driver of version 3.0.0 or later.  Other configurations may
not support this method for specifying multiple bonding interfaces; for
those instances, see the "Configuring Multiple Bonds Manually" section,
below.

3.3 Configuring Bonding Manually with iproute2
-----------------------------------------------

	This section applies to distros whose network initialization
scripts (the sysconfig or initscripts package) do not have specific
knowledge of bonding.  One such distro is SuSE Linux Enterprise Server
version 8.

	The general method for these systems is to place the bonding
module parameters into a config file in /etc/modprobe.d/ (as
appropriate for the installed distro), then add modprobe and/or
`ip link` commands to the system's global init script.  The name of
the global init script differs; for sysconfig, it is
/etc/init.d/boot.local and for initscripts it is /etc/rc.d/rc.local.

	For example, if you wanted to make a simple bond of two e100
devices (presumed to be eth0 and eth1), and have it persist across
reboots, edit the appropriate file (/etc/init.d/boot.local or
/etc/rc.d/rc.local), and add the following:

modprobe bonding mode=balance-alb miimon=100
modprobe e100
ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
ip link set eth0 master bond0
ip link set eth1 master bond0

	Replace the example bonding module parameters and bond0
network configuration (IP address, netmask, etc) with the appropriate
values for your configuration.

	Unfortunately, this method will not provide support for the
ifup and ifdown scripts on the bond devices.  To reload the bonding
configuration, it is necessary to run the initialization script, e.g.,

# /etc/init.d/boot.local

	or

# /etc/rc.d/rc.local

	It may be desirable in such a case to create a separate script
which only initializes the bonding configuration, then call that
separate script from within boot.local.  This allows for bonding to be
enabled without re-running the entire global init script.

	To shut down the bonding devices, it is necessary to first
mark the bonding device itself as being down, then remove the
appropriate device driver modules.  For our example above, you can do
the following:

# ifconfig bond0 down
# rmmod bonding
# rmmod e100

	Again, for convenience, it may be desirable to create a script
with these commands.


3.3.1 Configuring Multiple Bonds Manually
-----------------------------------------

	This section contains information on configuring multiple
bonding devices with differing options for those systems whose network
initialization scripts lack support for configuring multiple bonds.

	If you require multiple bonding devices, but all with the same
options, you may wish to use the "max_bonds" module parameter,
documented above.

	To create multiple bonding devices with differing options, it is
preferable to use bonding parameters exported by sysfs, documented in the
section below.

	For versions of bonding without sysfs support, the only means to
provide multiple instances of bonding with differing options is to load
the bonding driver multiple times.  Note that current versions of the
sysconfig network initialization scripts handle this automatically; if
your distro uses these scripts, no special action is needed.  See the
section Configuring Bonding Devices, above, if you're not sure about your
network initialization scripts.

	To load multiple instances of the module, it is necessary to
specify a different name for each instance (the module loading system
requires that every loaded module, even multiple instances of the same
module, have a unique name).  This is accomplished by supplying multiple
sets of bonding options in /etc/modprobe.d/*.conf, for example:

alias bond0 bonding
options bond0 -o bond0 mode=balance-rr miimon=100

alias bond1 bonding
options bond1 -o bond1 mode=balance-alb miimon=50

	will load the bonding module two times.  The first instance is
named "bond0" and creates the bond0 device in balance-rr mode with an
miimon of 100.  The second instance is named "bond1" and creates the
bond1 device in balance-alb mode with an miimon of 50.

	In some circumstances (typically with older distributions),
the above does not work, and the second bonding instance never sees
its options.  In that case, the second options line can be substituted
as follows:

install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \
	mode=balance-alb miimon=50

	This may be repeated any number of times, specifying a new and
unique name in place of bond1 for each subsequent instance.

	It has been observed that some Red Hat supplied kernels are unable
to rename modules at load time (the "-o bond1" part).  Attempts to pass
that option to modprobe will produce an "Operation not permitted" error.
This has been reported on some Fedora Core kernels, and has been seen on
RHEL 4 as well.  On kernels exhibiting this problem, it will be impossible
to configure multiple bonds with differing parameters (as they are older
kernels, and also lack sysfs support).

3.4 Configuring Bonding Manually via Sysfs
------------------------------------------

	Starting with version 3.0.0, Channel Bonding may be configured
via the sysfs interface.  This interface allows dynamic configuration
of all bonds in the system without unloading the module.  It also
allows for adding and removing bonds at runtime.  Ifenslave is no
longer required, though it is still supported.

	Use of the sysfs interface allows you to use multiple bonds
with different configurations without having to reload the module.
It also allows you to use multiple, differently configured bonds when
bonding is compiled into the kernel.

	You must have the sysfs filesystem mounted to configure
bonding this way.  The examples in this document assume that you
are using the standard mount point for sysfs, e.g. /sys.  If your
sysfs filesystem is mounted elsewhere, you will need to adjust the
example paths accordingly.

Creating and Destroying Bonds
-----------------------------
To add a new bond foo:
# echo +foo > /sys/class/net/bonding_masters

To remove an existing bond bar:
# echo -bar > /sys/class/net/bonding_masters

To show all existing bonds:
# cat /sys/class/net/bonding_masters

NOTE: due to 4K size limitation of sysfs files, this list may be
truncated if you have more than a few hundred bonds.  This is unlikely
to occur under normal operating conditions.

Adding and Removing Slaves
--------------------------
	Interfaces may be enslaved to a bond using the file
/sys/class/net/<bond>/bonding/slaves.  The semantics for this file
are the same as for the bonding_masters file.

To enslave interface eth0 to bond bond0:
# ifconfig bond0 up
# echo +eth0 > /sys/class/net/bond0/bonding/slaves

To free slave eth0 from bond bond0:
# echo -eth0 > /sys/class/net/bond0/bonding/slaves

	When an interface is enslaved to a bond, symlinks between the
two are created in the sysfs filesystem.  In this case, you would get
/sys/class/net/bond0/slave_eth0 pointing to /sys/class/net/eth0, and
/sys/class/net/eth0/master pointing to /sys/class/net/bond0.

	This means that you can tell quickly whether or not an
interface is enslaved by looking for the master symlink.  Thus:
# echo -eth0 > /sys/class/net/eth0/master/bonding/slaves
will free eth0 from whatever bond it is enslaved to, regardless of
the name of the bond interface.

Changing a Bond's Configuration
-------------------------------
	Each bond may be configured individually by manipulating the
files located in /sys/class/net/<bond name>/bonding

	The names of these files correspond directly with the command-
line parameters described elsewhere in this file, and, with the
exception of arp_ip_target, they accept the same values.  To see the
current setting, simply cat the appropriate file.

	A few examples will be given here; for specific usage
guidelines for each parameter, see the appropriate section in this
document.

To configure bond0 for balance-alb mode:
# ifconfig bond0 down
# echo 6 > /sys/class/net/bond0/bonding/mode
 - or -
# echo balance-alb > /sys/class/net/bond0/bonding/mode
	NOTE: The bond interface must be down before the mode can be
changed.

To enable MII monitoring on bond0 with a 1 second interval:
# echo 1000 > /sys/class/net/bond0/bonding/miimon
	NOTE: If ARP monitoring is enabled, it will disabled when MII
monitoring is enabled, and vice-versa.

To add ARP targets:
# echo +192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
# echo +192.168.0.101 > /sys/class/net/bond0/bonding/arp_ip_target
	NOTE:  up to 16 target addresses may be specified.

To remove an ARP target:
# echo -192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target

To configure the interval between learning packet transmits:
# echo 12 > /sys/class/net/bond0/bonding/lp_interval
	NOTE: the lp_inteval is the number of seconds between instances where
the bonding driver sends learning packets to each slaves peer switch.  The
default interval is 1 second.

Example Configuration
---------------------
	We begin with the same example that is shown in section 3.3,
executed with sysfs, and without using ifenslave.

	To make a simple bond of two e100 devices (presumed to be eth0
and eth1), and have it persist across reboots, edit the appropriate
file (/etc/init.d/boot.local or /etc/rc.d/rc.local), and add the
following:

modprobe bonding
modprobe e100
echo balance-alb > /sys/class/net/bond0/bonding/mode
ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
echo 100 > /sys/class/net/bond0/bonding/miimon
echo +eth0 > /sys/class/net/bond0/bonding/slaves
echo +eth1 > /sys/class/net/bond0/bonding/slaves

	To add a second bond, with two e1000 interfaces in
active-backup mode, using ARP monitoring, add the following lines to
your init script:

modprobe e1000
echo +bond1 > /sys/class/net/bonding_masters
echo active-backup > /sys/class/net/bond1/bonding/mode
ifconfig bond1 192.168.2.1 netmask 255.255.255.0 up
echo +192.168.2.100 /sys/class/net/bond1/bonding/arp_ip_target
echo 2000 > /sys/class/net/bond1/bonding/arp_interval
echo +eth2 > /sys/class/net/bond1/bonding/slaves
echo +eth3 > /sys/class/net/bond1/bonding/slaves

3.5 Configuration with Interfaces Support
-----------------------------------------

        This section applies to distros which use /etc/network/interfaces file
to describe network interface configuration, most notably Debian and it's
derivatives.

	The ifup and ifdown commands on Debian don't support bonding out of
the box. The ifenslave-2.6 package should be installed to provide bonding
support.  Once installed, this package will provide bond-* options to be used
into /etc/network/interfaces.

	Note that ifenslave-2.6 package will load the bonding module and use
the ifenslave command when appropriate.

Example Configurations
----------------------

In /etc/network/interfaces, the following stanza will configure bond0, in
active-backup mode, with eth0 and eth1 as slaves.

auto bond0
iface bond0 inet dhcp
	bond-slaves eth0 eth1
	bond-mode active-backup
	bond-miimon 100
	bond-primary eth0 eth1

If the above configuration doesn't work, you might have a system using
upstart for system startup. This is most notably true for recent
Ubuntu versions. The following stanza in /etc/network/interfaces will
produce the same result on those systems.

auto bond0
iface bond0 inet dhcp
	bond-slaves none
	bond-mode active-backup
	bond-miimon 100

auto eth0
iface eth0 inet manual
	bond-master bond0
	bond-primary eth0 eth1

auto eth1
iface eth1 inet manual
	bond-master bond0
	bond-primary eth0 eth1

For a full list of bond-* supported options in /etc/network/interfaces and some
more advanced examples tailored to you particular distros, see the files in
/usr/share/doc/ifenslave-2.6.

3.6 Overriding Configuration for Special Cases
----------------------------------------------

When using the bonding driver, the physical port which transmits a frame is
typically selected by the bonding driver, and is not relevant to the user or
system administrator.  The output port is simply selected using the policies of
the selected bonding mode.  On occasion however, it is helpful to direct certain
classes of traffic to certain physical interfaces on output to implement
slightly more complex policies.  For example, to reach a web server over a
bonded interface in which eth0 connects to a private network, while eth1
connects via a public network, it may be desirous to bias the bond to send said
traffic over eth0 first, using eth1 only as a fall back, while all other traffic
can safely be sent over either interface.  Such configurations may be achieved
using the traffic control utilities inherent in linux.

By default the bonding driver is multiqueue aware and 16 queues are created
when the driver initializes (see Documentation/networking/multiqueue.txt
for details).  If more or less queues are desired the module parameter
tx_queues can be used to change this value.  There is no sysfs parameter
available as the allocation is done at module init time.

The output of the file /proc/net/bonding/bondX has changed so the output Queue
ID is now printed for each slave:

Bonding Mode: fault-tolerance (active-backup)
Primary Slave: None
Currently Active Slave: eth0
MII Status: up
MII Polling Interval (ms): 0
Up Delay (ms): 0
Down Delay (ms): 0

Slave Interface: eth0
MII Status: up
Link Failure Count: 0
Permanent HW addr: 00:1a:a0:12:8f:cb
Slave queue ID: 0

Slave Interface: eth1
MII Status: up
Link Failure Count: 0
Permanent HW addr: 00:1a:a0:12:8f:cc
Slave queue ID: 2

The queue_id for a slave can be set using the command:

# echo "eth1:2" > /sys/class/net/bond0/bonding/queue_id

Any interface that needs a queue_id set should set it with multiple calls
like the one above until proper priorities are set for all interfaces.  On
distributions that allow configuration via initscripts, multiple 'queue_id'
arguments can be added to BONDING_OPTS to set all needed slave queues.

These queue id's can be used in conjunction with the tc utility to configure
a multiqueue qdisc and filters to bias certain traffic to transmit on certain
slave devices.  For instance, say we wanted, in the above configuration to
force all traffic bound to 192.168.1.100 to use eth1 in the bond as its output
device. The following commands would accomplish this:

# tc qdisc add dev bond0 handle 1 root multiq

# tc filter add dev bond0 protocol ip parent 1: prio 1 u32 match ip dst \
	192.168.1.100 action skbedit queue_mapping 2

These commands tell the kernel to attach a multiqueue queue discipline to the
bond0 interface and filter traffic enqueued to it, such that packets with a dst
ip of 192.168.1.100 have their output queue mapping value overwritten to 2.
This value is then passed into the driver, causing the normal output path
selection policy to be overridden, selecting instead qid 2, which maps to eth1.

Note that qid values begin at 1.  Qid 0 is reserved to initiate to the driver
that normal output policy selection should take place.  One benefit to simply
leaving the qid for a slave to 0 is the multiqueue awareness in the bonding
driver that is now present.  This awareness allows tc filters to be placed on
slave devices as well as bond devices and the bonding driver will simply act as
a pass-through for selecting output queues on the slave device rather than 
output port selection.

This feature first appeared in bonding driver version 3.7.0 and support for
output slave selection was limited to round-robin and active-backup modes.

4 Querying Bonding Configuration
=================================

4.1 Bonding Configuration
-------------------------

	Each bonding device has a read-only file residing in the
/proc/net/bonding directory.  The file contents include information
about the bonding configuration, options and state of each slave.

	For example, the contents of /proc/net/bonding/bond0 after the
driver is loaded with parameters of mode=0 and miimon=1000 is
generally as follows:

	Ethernet Channel Bonding Driver: 2.6.1 (October 29, 2004)
        Bonding Mode: load balancing (round-robin)
        Currently Active Slave: eth0
        MII Status: up
        MII Polling Interval (ms): 1000
        Up Delay (ms): 0
        Down Delay (ms): 0

        Slave Interface: eth1
        MII Status: up
        Link Failure Count: 1

        Slave Interface: eth0
        MII Status: up
        Link Failure Count: 1

	The precise format and contents will change depending upon the
bonding configuration, state, and version of the bonding driver.

4.2 Network configuration
-------------------------

	The network configuration can be inspected using the ifconfig
command.  Bonding devices will have the MASTER flag set; Bonding slave
devices will have the SLAVE flag set.  The ifconfig output does not
contain information on which slaves are associated with which masters.

	In the example below, the bond0 interface is the master
(MASTER) while eth0 and eth1 are slaves (SLAVE). Notice all slaves of
bond0 have the same MAC address (HWaddr) as bond0 for all modes except
TLB and ALB that require a unique MAC address for each slave.

# /sbin/ifconfig
bond0     Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
          inet addr:XXX.XXX.XXX.YYY  Bcast:XXX.XXX.XXX.255  Mask:255.255.252.0
          UP BROADCAST RUNNING MASTER MULTICAST  MTU:1500  Metric:1
          RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0
          collisions:0 txqueuelen:0

eth0      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
          UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
          RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0
          collisions:0 txqueuelen:100
          Interrupt:10 Base address:0x1080

eth1      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
          UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
          RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100
          Interrupt:9 Base address:0x1400

5. Switch Configuration
=======================

	For this section, "switch" refers to whatever system the
bonded devices are directly connected to (i.e., where the other end of
the cable plugs into).  This may be an actual dedicated switch device,
or it may be another regular system (e.g., another computer running
Linux),

	The active-backup, balance-tlb and balance-alb modes do not
require any specific configuration of the switch.

	The 802.3ad mode requires that the switch have the appropriate
ports configured as an 802.3ad aggregation.  The precise method used
to configure this varies from switch to switch, but, for example, a
Cisco 3550 series switch requires that the appropriate ports first be
grouped together in a single etherchannel instance, then that
etherchannel is set to mode "lacp" to enable 802.3ad (instead of
standard EtherChannel).

	The balance-rr, balance-xor and broadcast modes generally
require that the switch have the appropriate ports grouped together.
The nomenclature for such a group differs between switches, it may be
called an "etherchannel" (as in the Cisco example, above), a "trunk
group" or some other similar variation.  For these modes, each switch
will also have its own configuration options for the switch's transmit
policy to the bond.  Typical choices include XOR of either the MAC or
IP addresses.  The transmit policy of the two peers does not need to
match.  For these three modes, the bonding mode really selects a
transmit policy for an EtherChannel group; all three will interoperate
with another EtherChannel group.


6. 802.1q VLAN Support
======================

	It is possible to configure VLAN devices over a bond interface
using the 8021q driver.  However, only packets coming from the 8021q
driver and passing through bonding will be tagged by default.  Self
generated packets, for example, bonding's learning packets or ARP
packets generated by either ALB mode or the ARP monitor mechanism, are
tagged internally by bonding itself.  As a result, bonding must
"learn" the VLAN IDs configured above it, and use those IDs to tag
self generated packets.

	For reasons of simplicity, and to support the use of adapters
that can do VLAN hardware acceleration offloading, the bonding
interface declares itself as fully hardware offloading capable, it gets
the add_vid/kill_vid notifications to gather the necessary
information, and it propagates those actions to the slaves.  In case
of mixed adapter types, hardware accelerated tagged packets that
should go through an adapter that is not offloading capable are
"un-accelerated" by the bonding driver so the VLAN tag sits in the
regular location.

	VLAN interfaces *must* be added on top of a bonding interface
only after enslaving at least one slave.  The bonding interface has a
hardware address of 00:00:00:00:00:00 until the first slave is added.
If the VLAN interface is created prior to the first enslavement, it
would pick up the all-zeroes hardware address.  Once the first slave
is attached to the bond, the bond device itself will pick up the
slave's hardware address, which is then available for the VLAN device.

	Also, be aware that a similar problem can occur if all slaves
are released from a bond that still has one or more VLAN interfaces on
top of it.  When a new slave is added, the bonding interface will
obtain its hardware address from the first slave, which might not
match the hardware address of the VLAN interfaces (which was
ultimately copied from an earlier slave).

	There are two methods to insure that the VLAN device operates
with the correct hardware address if all slaves are removed from a
bond interface:

	1. Remove all VLAN interfaces then recreate them

	2. Set the bonding interface's hardware address so that it
matches the hardware address of the VLAN interfaces.

	Note that changing a VLAN interface's HW address would set the
underlying device -- i.e. the bonding interface -- to promiscuous
mode, which might not be what you want.


7. Link Monitoring
==================

	The bonding driver at present supports two schemes for
monitoring a slave device's link state: the ARP monitor and the MII
monitor.

	At the present time, due to implementation restrictions in the
bonding driver itself, it is not possible to enable both ARP and MII
monitoring simultaneously.

7.1 ARP Monitor Operation
-------------------------

	The ARP monitor operates as its name suggests: it sends ARP
queries to one or more designated peer systems on the network, and
uses the response as an indication that the link is operating.  This
gives some assurance that traffic is actually flowing to and from one
or more peers on the local network.

	The ARP monitor relies on the device driver itself to verify
that traffic is flowing.  In particular, the driver must keep up to
date the last receive time, dev->last_rx, and transmit start time,
dev->trans_start.  If these are not updated by the driver, then the
ARP monitor will immediately fail any slaves using that driver, and
those slaves will stay down.  If networking monitoring (tcpdump, etc)
shows the ARP requests and replies on the network, then it may be that
your device driver is not updating last_rx and trans_start.

7.2 Configuring Multiple ARP Targets
------------------------------------

	While ARP monitoring can be done with just one target, it can
be useful in a High Availability setup to have several targets to
monitor.  In the case of just one target, the target itself may go
down or have a problem making it unresponsive to ARP requests.  Having
an additional target (or several) increases the reliability of the ARP
monitoring.

	Multiple ARP targets must be separated by commas as follows:

# example options for ARP monitoring with three targets
alias bond0 bonding
options bond0 arp_interval=60 arp_ip_target=192.168.0.1,192.168.0.3,192.168.0.9

	For just a single target the options would resemble:

# example options for ARP monitoring with one target
alias bond0 bonding
options bond0 arp_interval=60 arp_ip_target=192.168.0.100


7.3 MII Monitor Operation
-------------------------

	The MII monitor monitors only the carrier state of the local
network interface.  It accomplishes this in one of three ways: by
depending upon the device driver to maintain its carrier state, by
querying the device's MII registers, or by making an ethtool query to
the device.

	If the use_carrier module parameter is 1 (the default value),
then the MII monitor will rely on the driver for carrier state
information (via the netif_carrier subsystem).  As explained in the
use_carrier parameter information, above, if the MII monitor fails to
detect carrier loss on the device (e.g., when the cable is physically
disconnected), it may be that the driver does not support
netif_carrier.

	If use_carrier is 0, then the MII monitor will first query the
device's (via ioctl) MII registers and check the link state.  If that
request fails (not just that it returns carrier down), then the MII
monitor will make an ethtool ETHOOL_GLINK request to attempt to obtain
the same information.  If both methods fail (i.e., the driver either
does not support or had some error in processing both the MII register
and ethtool requests), then the MII monitor will assume the link is
up.

8. Potential Sources of Trouble
===============================

8.1 Adventures in Routing
-------------------------

	When bonding is configured, it is important that the slave
devices not have routes that supersede routes of the master (or,
generally, not have routes at all).  For example, suppose the bonding
device bond0 has two slaves, eth0 and eth1, and the routing table is
as follows:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth0
10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth1
10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 bond0
127.0.0.0       0.0.0.0         255.0.0.0       U        40 0          0 lo

	This routing configuration will likely still update the
receive/transmit times in the driver (needed by the ARP monitor), but
may bypass the bonding driver (because outgoing traffic to, in this
case, another host on network 10 would use eth0 or eth1 before bond0).

	The ARP monitor (and ARP itself) may become confused by this
configuration, because ARP requests (generated by the ARP monitor)
will be sent on one interface (bond0), but the corresponding reply
will arrive on a different interface (eth0).  This reply looks to ARP
as an unsolicited ARP reply (because ARP matches replies on an
interface basis), and is discarded.  The MII monitor is not affected
by the state of the routing table.

	The solution here is simply to insure that slaves do not have
routes of their own, and if for some reason they must, those routes do
not supersede routes of their master.  This should generally be the
case, but unusual configurations or errant manual or automatic static
route additions may cause trouble.

8.2 Ethernet Device Renaming
----------------------------

	On systems with network configuration scripts that do not
associate physical devices directly with network interface names (so
that the same physical device always has the same "ethX" name), it may
be necessary to add some special logic to config files in
/etc/modprobe.d/.

	For example, given a modules.conf containing the following:

alias bond0 bonding
options bond0 mode=some-mode miimon=50
alias eth0 tg3
alias eth1 tg3
alias eth2 e1000
alias eth3 e1000

	If neither eth0 and eth1 are slaves to bond0, then when the
bond0 interface comes up, the devices may end up reordered.  This
happens because bonding is loaded first, then its slave device's
drivers are loaded next.  Since no other drivers have been loaded,
when the e1000 driver loads, it will receive eth0 and eth1 for its
devices, but the bonding configuration tries to enslave eth2 and eth3
(which may later be assigned to the tg3 devices).

	Adding the following:

add above bonding e1000 tg3

	causes modprobe to load e1000 then tg3, in that order, when
bonding is loaded.  This command is fully documented in the
modules.conf manual page.

	On systems utilizing modprobe an equivalent problem can occur.
In this case, the following can be added to config files in
/etc/modprobe.d/ as:

softdep bonding pre: tg3 e1000

	This will load tg3 and e1000 modules before loading the bonding one.
Full documentation on this can be found in the modprobe.d and modprobe
manual pages.

8.3. Painfully Slow Or No Failed Link Detection By Miimon
---------------------------------------------------------

	By default, bonding enables the use_carrier option, which
instructs bonding to trust the driver to maintain carrier state.

	As discussed in the options section, above, some drivers do
not support the netif_carrier_on/_off link state tracking system.
With use_carrier enabled, bonding will always see these links as up,
regardless of their actual state.

	Additionally, other drivers do support netif_carrier, but do
not maintain it in real time, e.g., only polling the link state at
some fixed interval.  In this case, miimon will detect failures, but
only after some long period of time has expired.  If it appears that
miimon is very slow in detecting link failures, try specifying
use_carrier=0 to see if that improves the failure detection time.  If
it does, then it may be that the driver checks the carrier state at a
fixed interval, but does not cache the MII register values (so the
use_carrier=0 method of querying the registers directly works).  If
use_carrier=0 does not improve the failover, then the driver may cache
the registers, or the problem may be elsewhere.

	Also, remember that miimon only checks for the device's
carrier state.  It has no way to determine the state of devices on or
beyond other ports of a switch, or if a switch is refusing to pass
traffic while still maintaining carrier on.

9. SNMP agents
===============

	If running SNMP agents, the bonding driver should be loaded
before any network drivers participating in a bond.  This requirement
is due to the interface index (ipAdEntIfIndex) being associated to
the first interface found with a given IP address.  That is, there is
only one ipAdEntIfIndex for each IP address.  For example, if eth0 and
eth1 are slaves of bond0 and the driver for eth0 is loaded before the
bonding driver, the interface for the IP address will be associated
with the eth0 interface.  This configuration is shown below, the IP
address 192.168.1.1 has an interface index of 2 which indexes to eth0
in the ifDescr table (ifDescr.2).

     interfaces.ifTable.ifEntry.ifDescr.1 = lo
     interfaces.ifTable.ifEntry.ifDescr.2 = eth0
     interfaces.ifTable.ifEntry.ifDescr.3 = eth1
     interfaces.ifTable.ifEntry.ifDescr.4 = eth2
     interfaces.ifTable.ifEntry.ifDescr.5 = eth3
     interfaces.ifTable.ifEntry.ifDescr.6 = bond0
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 5
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 4
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1

	This problem is avoided by loading the bonding driver before
any network drivers participating in a bond.  Below is an example of
loading the bonding driver first, the IP address 192.168.1.1 is
correctly associated with ifDescr.2.

     interfaces.ifTable.ifEntry.ifDescr.1 = lo
     interfaces.ifTable.ifEntry.ifDescr.2 = bond0
     interfaces.ifTable.ifEntry.ifDescr.3 = eth0
     interfaces.ifTable.ifEntry.ifDescr.4 = eth1
     interfaces.ifTable.ifEntry.ifDescr.5 = eth2
     interfaces.ifTable.ifEntry.ifDescr.6 = eth3
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 6
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 5
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1

	While some distributions may not report the interface name in
ifDescr, the association between the IP address and IfIndex remains
and SNMP functions such as Interface_Scan_Next will report that
association.

10. Promiscuous mode
====================

	When running network monitoring tools, e.g., tcpdump, it is
common to enable promiscuous mode on the device, so that all traffic
is seen (instead of seeing only traffic destined for the local host).
The bonding driver handles promiscuous mode changes to the bonding
master device (e.g., bond0), and propagates the setting to the slave
devices.

	For the balance-rr, balance-xor, broadcast, and 802.3ad modes,
the promiscuous mode setting is propagated to all slaves.

	For the active-backup, balance-tlb and balance-alb modes, the
promiscuous mode setting is propagated only to the active slave.

	For balance-tlb mode, the active slave is the slave currently
receiving inbound traffic.

	For balance-alb mode, the active slave is the slave used as a
"primary."  This slave is used for mode-specific control traffic, for
sending to peers that are unassigned or if the load is unbalanced.

	For the active-backup, balance-tlb and balance-alb modes, when
the active slave changes (e.g., due to a link failure), the
promiscuous setting will be propagated to the new active slave.

11. Configuring Bonding for High Availability
=============================================

	High Availability refers to configurations that provide
maximum network availability by having redundant or backup devices,
links or switches between the host and the rest of the world.  The
goal is to provide the maximum availability of network connectivity
(i.e., the network always works), even though other configurations
could provide higher throughput.

11.1 High Availability in a Single Switch Topology
--------------------------------------------------

	If two hosts (or a host and a single switch) are directly
connected via multiple physical links, then there is no availability
penalty to optimizing for maximum bandwidth.  In this case, there is
only one switch (or peer), so if it fails, there is no alternative
access to fail over to.  Additionally, the bonding load balance modes
support link monitoring of their members, so if individual links fail,
the load will be rebalanced across the remaining devices.

	See Section 12, "Configuring Bonding for Maximum Throughput"
for information on configuring bonding with one peer device.

11.2 High Availability in a Multiple Switch Topology
----------------------------------------------------

	With multiple switches, the configuration of bonding and the
network changes dramatically.  In multiple switch topologies, there is
a trade off between network availability and usable bandwidth.

	Below is a sample network, configured to maximize the
availability of the network:

                |                                     |
                |port3                           port3|
          +-----+----+                          +-----+----+
          |          |port2       ISL      port2|          |
          | switch A +--------------------------+ switch B |
          |          |                          |          |
          +-----+----+                          +-----++---+
                |port1                           port1|
                |             +-------+               |
                +-------------+ host1 +---------------+
                         eth0 +-------+ eth1

	In this configuration, there is a link between the two
switches (ISL, or inter switch link), and multiple ports connecting to
the outside world ("port3" on each switch).  There is no technical
reason that this could not be extended to a third switch.

11.2.1 HA Bonding Mode Selection for Multiple Switch Topology
-------------------------------------------------------------

	In a topology such as the example above, the active-backup and
broadcast modes are the only useful bonding modes when optimizing for
availability; the other modes require all links to terminate on the
same peer for them to behave rationally.

active-backup: This is generally the preferred mode, particularly if
	the switches have an ISL and play together well.  If the
	network configuration is such that one switch is specifically
	a backup switch (e.g., has lower capacity, higher cost, etc),
	then the primary option can be used to insure that the
	preferred link is always used when it is available.

broadcast: This mode is really a special purpose mode, and is suitable
	only for very specific needs.  For example, if the two
	switches are not connected (no ISL), and the networks beyond
	them are totally independent.  In this case, if it is
	necessary for some specific one-way traffic to reach both
	independent networks, then the broadcast mode may be suitable.

11.2.2 HA Link Monitoring Selection for Multiple Switch Topology
----------------------------------------------------------------

	The choice of link monitoring ultimately depends upon your
switch.  If the switch can reliably fail ports in response to other
failures, then either the MII or ARP monitors should work.  For
example, in the above example, if the "port3" link fails at the remote
end, the MII monitor has no direct means to detect this.  The ARP
monitor could be configured with a target at the remote end of port3,
thus detecting that failure without switch support.

	In general, however, in a multiple switch topology, the ARP
monitor can provide a higher level of reliability in detecting end to
end connectivity failures (which may be caused by the failure of any
individual component to pass traffic for any reason).  Additionally,
the ARP monitor should be configured with multiple targets (at least
one for each switch in the network).  This will insure that,
regardless of which switch is active, the ARP monitor has a suitable
target to query.

	Note, also, that of late many switches now support a functionality
generally referred to as "trunk failover."  This is a feature of the
switch that causes the link state of a particular switch port to be set
down (or up) when the state of another switch port goes down (or up).
Its purpose is to propagate link failures from logically "exterior" ports
to the logically "interior" ports that bonding is able to monitor via
miimon.  Availability and configuration for trunk failover varies by
switch, but this can be a viable alternative to the ARP monitor when using
suitable switches.

12. Configuring Bonding for Maximum Throughput
==============================================

12.1 Maximizing Throughput in a Single Switch Topology
------------------------------------------------------

	In a single switch configuration, the best method to maximize
throughput depends upon the application and network environment.  The
various load balancing modes each have strengths and weaknesses in
different environments, as detailed below.

	For this discussion, we will break down the topologies into
two categories.  Depending upon the destination of most traffic, we
categorize them into either "gatewayed" or "local" configurations.

	In a gatewayed configuration, the "switch" is acting primarily
as a router, and the majority of traffic passes through this router to
other networks.  An example would be the following:


     +----------+                     +----------+
     |          |eth0            port1|          | to other networks
     | Host A   +---------------------+ router   +------------------->
     |          +---------------------+          | Hosts B and C are out
     |          |eth1            port2|          | here somewhere
     +----------+                     +----------+

	The router may be a dedicated router device, or another host
acting as a gateway.  For our discussion, the important point is that
the majority of traffic from Host A will pass through the router to
some other network before reaching its final destination.

	In a gatewayed network configuration, although Host A may
communicate with many other systems, all of its traffic will be sent
and received via one other peer on the local network, the router.

	Note that the case of two systems connected directly via
multiple physical links is, for purposes of configuring bonding, the
same as a gatewayed configuration.  In that case, it happens that all
traffic is destined for the "gateway" itself, not some other network
beyond the gateway.

	In a local configuration, the "switch" is acting primarily as
a switch, and the majority of traffic passes through this switch to
reach other stations on the same network.  An example would be the
following:

    +----------+            +----------+       +--------+
    |          |eth0   port1|          +-------+ Host B |
    |  Host A  +------------+  switch  |port3  +--------+
    |          +------------+          |                  +--------+
    |          |eth1   port2|          +------------------+ Host C |
    +----------+            +----------+port4             +--------+


	Again, the switch may be a dedicated switch device, or another
host acting as a gateway.  For our discussion, the important point is
that the majority of traffic from Host A is destined for other hosts
on the same local network (Hosts B and C in the above example).

	In summary, in a gatewayed configuration, traffic to and from
the bonded device will be to the same MAC level peer on the network
(the gateway itself, i.e., the router), regardless of its final
destination.  In a local configuration, traffic flows directly to and
from the final destinations, thus, each destination (Host B, Host C)
will be addressed directly by their individual MAC addresses.

	This distinction between a gatewayed and a local network
configuration is important because many of the load balancing modes
available use the MAC addresses of the local network source and
destination to make load balancing decisions.  The behavior of each
mode is described below.


12.1.1 MT Bonding Mode Selection for Single Switch Topology
-----------------------------------------------------------

	This configuration is the easiest to set up and to understand,
although you will have to decide which bonding mode best suits your
needs.  The trade offs for each mode are detailed below:

balance-rr: This mode is the only mode that will permit a single
	TCP/IP connection to stripe traffic across multiple
	interfaces. It is therefore the only mode that will allow a
	single TCP/IP stream to utilize more than one interface's
	worth of throughput.  This comes at a cost, however: the
	striping generally results in peer systems receiving packets out
	of order, causing TCP/IP's congestion control system to kick
	in, often by retransmitting segments.

	It is possible to adjust TCP/IP's congestion limits by
	altering the net.ipv4.tcp_reordering sysctl parameter.  The
	usual default value is 3, and the maximum useful value is 127.
	For a four interface balance-rr bond, expect that a single
	TCP/IP stream will utilize no more than approximately 2.3
	interface's worth of throughput, even after adjusting
	tcp_reordering.

	Note that the fraction of packets that will be delivered out of
	order is highly variable, and is unlikely to be zero.  The level
	of reordering depends upon a variety of factors, including the
	networking interfaces, the switch, and the topology of the
	configuration.  Speaking in general terms, higher speed network
	cards produce more reordering (due to factors such as packet
	coalescing), and a "many to many" topology will reorder at a
	higher rate than a "many slow to one fast" configuration.

	Many switches do not support any modes that stripe traffic
	(instead choosing a port based upon IP or MAC level addresses);
	for those devices, traffic for a particular connection flowing
	through the switch to a balance-rr bond will not utilize greater
	than one interface's worth of bandwidth.

	If you are utilizing protocols other than TCP/IP, UDP for
	example, and your application can tolerate out of order
	delivery, then this mode can allow for single stream datagram
	performance that scales near linearly as interfaces are added
	to the bond.

	This mode requires the switch to have the appropriate ports
	configured for "etherchannel" or "trunking."

active-backup: There is not much advantage in this network topology to
	the active-backup mode, as the inactive backup devices are all
	connected to the same peer as the primary.  In this case, a
	load balancing mode (with link monitoring) will provide the
	same level of network availability, but with increased
	available bandwidth.  On the plus side, active-backup mode
	does not require any configuration of the switch, so it may
	have value if the hardware available does not support any of
	the load balance modes.

balance-xor: This mode will limit traffic such that packets destined
	for specific peers will always be sent over the same
	interface.  Since the destination is determined by the MAC
	addresses involved, this mode works best in a "local" network
	configuration (as described above), with destinations all on
	the same local network.  This mode is likely to be suboptimal
	if all your traffic is passed through a single router (i.e., a
	"gatewayed" network configuration, as described above).

	As with balance-rr, the switch ports need to be configured for
	"etherchannel" or "trunking."

broadcast: Like active-backup, there is not much advantage to this
	mode in this type of network topology.

802.3ad: This mode can be a good choice for this type of network
	topology.  The 802.3ad mode is an IEEE standard, so all peers
	that implement 802.3ad should interoperate well.  The 802.3ad
	protocol includes automatic configuration of the aggregates,
	so minimal manual configuration of the switch is needed
	(typically only to designate that some set of devices is
	available for 802.3ad).  The 802.3ad standard also mandates
	that frames be delivered in order (within certain limits), so
	in general single connections will not see misordering of
	packets.  The 802.3ad mode does have some drawbacks: the
	standard mandates that all devices in the aggregate operate at
	the same speed and duplex.  Also, as with all bonding load
	balance modes other than balance-rr, no single connection will
	be able to utilize more than a single interface's worth of
	bandwidth.  

	Additionally, the linux bonding 802.3ad implementation
	distributes traffic by peer (using an XOR of MAC addresses),
	so in a "gatewayed" configuration, all outgoing traffic will
	generally use the same device.  Incoming traffic may also end
	up on a single device, but that is dependent upon the
	balancing policy of the peer's 8023.ad implementation.  In a
	"local" configuration, traffic will be distributed across the
	devices in the bond.

	Finally, the 802.3ad mode mandates the use of the MII monitor,
	therefore, the ARP monitor is not available in this mode.

balance-tlb: The balance-tlb mode balances outgoing traffic by peer.
	Since the balancing is done according to MAC address, in a
	"gatewayed" configuration (as described above), this mode will
	send all traffic across a single device.  However, in a
	"local" network configuration, this mode balances multiple
	local network peers across devices in a vaguely intelligent
	manner (not a simple XOR as in balance-xor or 802.3ad mode),
	so that mathematically unlucky MAC addresses (i.e., ones that
	XOR to the same value) will not all "bunch up" on a single
	interface.

	Unlike 802.3ad, interfaces may be of differing speeds, and no
	special switch configuration is required.  On the down side,
	in this mode all incoming traffic arrives over a single
	interface, this mode requires certain ethtool support in the
	network device driver of the slave interfaces, and the ARP
	monitor is not available.

balance-alb: This mode is everything that balance-tlb is, and more.
	It has all of the features (and restrictions) of balance-tlb,
	and will also balance incoming traffic from local network
	peers (as described in the Bonding Module Options section,
	above).

	The only additional down side to this mode is that the network
	device driver must support changing the hardware address while
	the device is open.

12.1.2 MT Link Monitoring for Single Switch Topology
----------------------------------------------------

	The choice of link monitoring may largely depend upon which
mode you choose to use.  The more advanced load balancing modes do not
support the use of the ARP monitor, and are thus restricted to using
the MII monitor (which does not provide as high a level of end to end
assurance as the ARP monitor).

12.2 Maximum Throughput in a Multiple Switch Topology
-----------------------------------------------------

	Multiple switches may be utilized to optimize for throughput
when they are configured in parallel as part of an isolated network
between two or more systems, for example:

                       +-----------+
                       |  Host A   | 
                       +-+---+---+-+
                         |   |   |
                +--------+   |   +---------+
                |            |             |
         +------+---+  +-----+----+  +-----+----+
         | Switch A |  | Switch B |  | Switch C |
         +------+---+  +-----+----+  +-----+----+
                |            |             |
                +--------+   |   +---------+
                         |   |   |
                       +-+---+---+-+
                       |  Host B   | 
                       +-----------+

	In this configuration, the switches are isolated from one
another.  One reason to employ a topology such as this is for an
isolated network with many hosts (a cluster configured for high
performance, for example), using multiple smaller switches can be more
cost effective than a single larger switch, e.g., on a network with 24
hosts, three 24 port switches can be significantly less expensive than
a single 72 port switch.

	If access beyond the network is required, an individual host
can be equipped with an additional network device connected to an
external network; this host then additionally acts as a gateway.

12.2.1 MT Bonding Mode Selection for Multiple Switch Topology
-------------------------------------------------------------

	In actual practice, the bonding mode typically employed in
configurations of this type is balance-rr.  Historically, in this
network configuration, the usual caveats about out of order packet
delivery are mitigated by the use of network adapters that do not do
any kind of packet coalescing (via the use of NAPI, or because the
device itself does not generate interrupts until some number of
packets has arrived).  When employed in this fashion, the balance-rr
mode allows individual connections between two hosts to effectively
utilize greater than one interface's bandwidth.

12.2.2 MT Link Monitoring for Multiple Switch Topology
------------------------------------------------------

	Again, in actual practice, the MII monitor is most often used
in this configuration, as performance is given preference over
availability.  The ARP monitor will function in this topology, but its
advantages over the MII monitor are mitigated by the volume of probes
needed as the number of systems involved grows (remember that each
host in the network is configured with bonding).

13. Switch Behavior Issues
==========================

13.1 Link Establishment and Failover Delays
-------------------------------------------

	Some switches exhibit undesirable behavior with regard to the
timing of link up and down reporting by the switch.

	First, when a link comes up, some switches may indicate that
the link is up (carrier available), but not pass traffic over the
interface for some period of time.  This delay is typically due to
some type of autonegotiation or routing protocol, but may also occur
during switch initialization (e.g., during recovery after a switch
failure).  If you find this to be a problem, specify an appropriate
value to the updelay bonding module option to delay the use of the
relevant interface(s).

	Second, some switches may "bounce" the link state one or more
times while a link is changing state.  This occurs most commonly while
the switch is initializing.  Again, an appropriate updelay value may
help.

	Note that when a bonding interface has no active links, the
driver will immediately reuse the first link that goes up, even if the
updelay parameter has been specified (the updelay is ignored in this
case).  If there are slave interfaces waiting for the updelay timeout
to expire, the interface that first went into that state will be
immediately reused.  This reduces down time of the network if the
value of updelay has been overestimated, and since this occurs only in
cases with no connectivity, there is no additional penalty for
ignoring the updelay.

	In addition to the concerns about switch timings, if your
switches take a long time to go into backup mode, it may be desirable
to not activate a backup interface immediately after a link goes down.
Failover may be delayed via the downdelay bonding module option.

13.2 Duplicated Incoming Packets
--------------------------------

	NOTE: Starting with version 3.0.2, the bonding driver has logic to
suppress duplicate packets, which should largely eliminate this problem.
The following description is kept for reference.

	It is not uncommon to observe a short burst of duplicated
traffic when the bonding device is first used, or after it has been
idle for some period of time.  This is most easily observed by issuing
a "ping" to some other host on the network, and noticing that the
output from ping flags duplicates (typically one per slave).

	For example, on a bond in active-backup mode with five slaves
all connected to one switch, the output may appear as follows:

# ping -n 10.0.4.2
PING 10.0.4.2 (10.0.4.2) from 10.0.3.10 : 56(84) bytes of data.
64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.7 ms
64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
64 bytes from 10.0.4.2: icmp_seq=2 ttl=64 time=0.216 ms
64 bytes from 10.0.4.2: icmp_seq=3 ttl=64 time=0.267 ms
64 bytes from 10.0.4.2: icmp_seq=4 ttl=64 time=0.222 ms

	This is not due to an error in the bonding driver, rather, it
is a side effect of how many switches update their MAC forwarding
tables.  Initially, the switch does not associate the MAC address in
the packet with a particular switch port, and so it may send the
traffic to all ports until its MAC forwarding table is updated.  Since
the interfaces attached to the bond may occupy multiple ports on a
single switch, when the switch (temporarily) floods the traffic to all
ports, the bond device receives multiple copies of the same packet
(one per slave device).

	The duplicated packet behavior is switch dependent, some
switches exhibit this, and some do not.  On switches that display this
behavior, it can be induced by clearing the MAC forwarding table (on
most Cisco switches, the privileged command "clear mac address-table
dynamic" will accomplish this).

14. Hardware Specific Considerations
====================================

	This section contains additional information for configuring
bonding on specific hardware platforms, or for interfacing bonding
with particular switches or other devices.

14.1 IBM BladeCenter
--------------------

	This applies to the JS20 and similar systems.

	On the JS20 blades, the bonding driver supports only
balance-rr, active-backup, balance-tlb and balance-alb modes.  This is
largely due to the network topology inside the BladeCenter, detailed
below.

JS20 network adapter information
--------------------------------

	All JS20s come with two Broadcom Gigabit Ethernet ports
integrated on the planar (that's "motherboard" in IBM-speak).  In the
BladeCenter chassis, the eth0 port of all JS20 blades is hard wired to
I/O Module #1; similarly, all eth1 ports are wired to I/O Module #2.
An add-on Broadcom daughter card can be installed on a JS20 to provide
two more Gigabit Ethernet ports.  These ports, eth2 and eth3, are
wired to I/O Modules 3 and 4, respectively.

	Each I/O Module may contain either a switch or a passthrough
module (which allows ports to be directly connected to an external
switch).  Some bonding modes require a specific BladeCenter internal
network topology in order to function; these are detailed below.

	Additional BladeCenter-specific networking information can be
found in two IBM Redbooks (www.ibm.com/redbooks):

"IBM eServer BladeCenter Networking Options"
"IBM eServer BladeCenter Layer 2-7 Network Switching"

BladeCenter networking configuration
------------------------------------

	Because a BladeCenter can be configured in a very large number
of ways, this discussion will be confined to describing basic
configurations.

	Normally, Ethernet Switch Modules (ESMs) are used in I/O
modules 1 and 2.  In this configuration, the eth0 and eth1 ports of a
JS20 will be connected to different internal switches (in the
respective I/O modules).

	A passthrough module (OPM or CPM, optical or copper,
passthrough module) connects the I/O module directly to an external
switch.  By using PMs in I/O module #1 and #2, the eth0 and eth1
interfaces of a JS20 can be redirected to the outside world and
connected to a common external switch.

	Depending upon the mix of ESMs and PMs, the network will
appear to bonding as either a single switch topology (all PMs) or as a
multiple switch topology (one or more ESMs, zero or more PMs).  It is
also possible to connect ESMs together, resulting in a configuration
much like the example in "High Availability in a Multiple Switch
Topology," above.

Requirements for specific modes
-------------------------------

	The balance-rr mode requires the use of passthrough modules
for devices in the bond, all connected to an common external switch.
That switch must be configured for "etherchannel" or "trunking" on the
appropriate ports, as is usual for balance-rr.

	The balance-alb and balance-tlb modes will function with
either switch modules or passthrough modules (or a mix).  The only
specific requirement for these modes is that all network interfaces
must be able to reach all destinations for traffic sent over the
bonding device (i.e., the network must converge at some point outside
the BladeCenter).

	The active-backup mode has no additional requirements.

Link monitoring issues
----------------------

	When an Ethernet Switch Module is in place, only the ARP
monitor will reliably detect link loss to an external switch.  This is
nothing unusual, but examination of the BladeCenter cabinet would
suggest that the "external" network ports are the ethernet ports for
the system, when it fact there is a switch between these "external"
ports and the devices on the JS20 system itself.  The MII monitor is
only able to detect link failures between the ESM and the JS20 system.

	When a passthrough module is in place, the MII monitor does
detect failures to the "external" port, which is then directly
connected to the JS20 system.

Other concerns
--------------

	The Serial Over LAN (SoL) link is established over the primary
ethernet (eth0) only, therefore, any loss of link to eth0 will result
in losing your SoL connection.  It will not fail over with other
network traffic, as the SoL system is beyond the control of the
bonding driver.

	It may be desirable to disable spanning tree on the switch
(either the internal Ethernet Switch Module, or an external switch) to
avoid fail-over delay issues when using bonding.

	
15. Frequently Asked Questions
==============================

1.  Is it SMP safe?

	Yes. The old 2.0.xx channel bonding patch was not SMP safe.
The new driver was designed to be SMP safe from the start.

2.  What type of cards will work with it?

	Any Ethernet type cards (you can even mix cards - a Intel
EtherExpress PRO/100 and a 3com 3c905b, for example).  For most modes,
devices need not be of the same speed.

	Starting with version 3.2.1, bonding also supports Infiniband
slaves in active-backup mode.

3.  How many bonding devices can I have?

	There is no limit.

4.  How many slaves can a bonding device have?

	This is limited only by the number of network interfaces Linux
supports and/or the number of network cards you can place in your
system.

5.  What happens when a slave link dies?

	If link monitoring is enabled, then the failing device will be
disabled.  The active-backup mode will fail over to a backup link, and
other modes will ignore the failed link.  The link will continue to be
monitored, and should it recover, it will rejoin the bond (in whatever
manner is appropriate for the mode). See the sections on High
Availability and the documentation for each mode for additional
information.
	
	Link monitoring can be enabled via either the miimon or
arp_interval parameters (described in the module parameters section,
above).  In general, miimon monitors the carrier state as sensed by
the underlying network device, and the arp monitor (arp_interval)
monitors connectivity to another host on the local network.

	If no link monitoring is configured, the bonding driver will
be unable to detect link failures, and will assume that all links are
always available.  This will likely result in lost packets, and a
resulting degradation of performance.  The precise performance loss
depends upon the bonding mode and network configuration.

6.  Can bonding be used for High Availability?

	Yes.  See the section on High Availability for details.

7.  Which switches/systems does it work with?

	The full answer to this depends upon the desired mode.

	In the basic balance modes (balance-rr and balance-xor), it
works with any system that supports etherchannel (also called
trunking).  Most managed switches currently available have such
support, and many unmanaged switches as well.

	The advanced balance modes (balance-tlb and balance-alb) do
not have special switch requirements, but do need device drivers that
support specific features (described in the appropriate section under
module parameters, above).

	In 802.3ad mode, it works with systems that support IEEE
802.3ad Dynamic Link Aggregation.  Most managed and many unmanaged
switches currently available support 802.3ad.

        The active-backup mode should work with any Layer-II switch.

8.  Where does a bonding device get its MAC address from?

	When using slave devices that have fixed MAC addresses, or when
the fail_over_mac option is enabled, the bonding device's MAC address is
the MAC address of the active slave.

	For other configurations, if not explicitly configured (with
ifconfig or ip link), the MAC address of the bonding device is taken from
its first slave device.  This MAC address is then passed to all following
slaves and remains persistent (even if the first slave is removed) until
the bonding device is brought down or reconfigured.

	If you wish to change the MAC address, you can set it with
ifconfig or ip link:

# ifconfig bond0 hw ether 00:11:22:33:44:55

# ip link set bond0 address 66:77:88:99:aa:bb

	The MAC address can be also changed by bringing down/up the
device and then changing its slaves (or their order):

# ifconfig bond0 down ; modprobe -r bonding
# ifconfig bond0 .... up
# ifenslave bond0 eth...

	This method will automatically take the address from the next
slave that is added.

	To restore your slaves' MAC addresses, you need to detach them
from the bond (`ifenslave -d bond0 eth0'). The bonding driver will
then restore the MAC addresses that the slaves had before they were
enslaved.

16. Resources and Links
=======================

	The latest version of the bonding driver can be found in the latest
version of the linux kernel, found on http://kernel.org

	The latest version of this document can be found in the latest kernel
source (named Documentation/networking/bonding.txt).

	Discussions regarding the usage of the bonding driver take place on the
bonding-devel mailing list, hosted at sourceforge.net. If you have questions or
problems, post them to the list.  The list address is:

bonding-devel@lists.sourceforge.net

	The administrative interface (to subscribe or unsubscribe) can
be found at:

https://lists.sourceforge.net/lists/listinfo/bonding-devel

	Discussions regarding the development of the bonding driver take place
on the main Linux network mailing list, hosted at vger.kernel.org. The list
address is:

netdev@vger.kernel.org

	The administrative interface (to subscribe or unsubscribe) can
be found at:

http://vger.kernel.org/vger-lists.html#netdev

Donald Becker's Ethernet Drivers and diag programs may be found at :
 - http://web.archive.org/web/*/http://www.scyld.com/network/ 

You will also find a lot of information regarding Ethernet, NWay, MII,
etc. at www.scyld.com.

-- END --
OpenPOWER on IntegriCloud