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Based on kernel version 3.19. Page generated on 2015-02-13 21:21 EST.

1	
2			Linux Ethernet Bonding Driver HOWTO
3	
4			Latest update: 27 April 2011
5	
6	Initial release : Thomas Davis <tadavis at lbl.gov>
7	Corrections, HA extensions : 2000/10/03-15 :
8	  - Willy Tarreau <willy at meta-x.org>
9	  - Constantine Gavrilov <const-g at xpert.com>
10	  - Chad N. Tindel <ctindel at ieee dot org>
11	  - Janice Girouard <girouard at us dot ibm dot com>
12	  - Jay Vosburgh <fubar at us dot ibm dot com>
13	
14	Reorganized and updated Feb 2005 by Jay Vosburgh
15	Added Sysfs information: 2006/04/24
16	  - Mitch Williams <mitch.a.williams at intel.com>
17	
18	Introduction
19	============
20	
21		The Linux bonding driver provides a method for aggregating
22	multiple network interfaces into a single logical "bonded" interface.
23	The behavior of the bonded interfaces depends upon the mode; generally
24	speaking, modes provide either hot standby or load balancing services.
25	Additionally, link integrity monitoring may be performed.
26		
27		The bonding driver originally came from Donald Becker's
28	beowulf patches for kernel 2.0. It has changed quite a bit since, and
29	the original tools from extreme-linux and beowulf sites will not work
30	with this version of the driver.
31	
32		For new versions of the driver, updated userspace tools, and
33	who to ask for help, please follow the links at the end of this file.
34	
35	Table of Contents
36	=================
37	
38	1. Bonding Driver Installation
39	
40	2. Bonding Driver Options
41	
42	3. Configuring Bonding Devices
43	3.1	Configuration with Sysconfig Support
44	3.1.1		Using DHCP with Sysconfig
45	3.1.2		Configuring Multiple Bonds with Sysconfig
46	3.2	Configuration with Initscripts Support
47	3.2.1		Using DHCP with Initscripts
48	3.2.2		Configuring Multiple Bonds with Initscripts
49	3.3	Configuring Bonding Manually with Ifenslave
50	3.3.1		Configuring Multiple Bonds Manually
51	3.4	Configuring Bonding Manually via Sysfs
52	3.5	Configuration with Interfaces Support
53	3.6	Overriding Configuration for Special Cases
54	
55	4. Querying Bonding Configuration
56	4.1	Bonding Configuration
57	4.2	Network Configuration
58	
59	5. Switch Configuration
60	
61	6. 802.1q VLAN Support
62	
63	7. Link Monitoring
64	7.1	ARP Monitor Operation
65	7.2	Configuring Multiple ARP Targets
66	7.3	MII Monitor Operation
67	
68	8. Potential Trouble Sources
69	8.1	Adventures in Routing
70	8.2	Ethernet Device Renaming
71	8.3	Painfully Slow Or No Failed Link Detection By Miimon
72	
73	9. SNMP agents
74	
75	10. Promiscuous mode
76	
77	11. Configuring Bonding for High Availability
78	11.1	High Availability in a Single Switch Topology
79	11.2	High Availability in a Multiple Switch Topology
80	11.2.1		HA Bonding Mode Selection for Multiple Switch Topology
81	11.2.2		HA Link Monitoring for Multiple Switch Topology
82	
83	12. Configuring Bonding for Maximum Throughput
84	12.1	Maximum Throughput in a Single Switch Topology
85	12.1.1		MT Bonding Mode Selection for Single Switch Topology
86	12.1.2		MT Link Monitoring for Single Switch Topology
87	12.2	Maximum Throughput in a Multiple Switch Topology
88	12.2.1		MT Bonding Mode Selection for Multiple Switch Topology
89	12.2.2		MT Link Monitoring for Multiple Switch Topology
90	
91	13. Switch Behavior Issues
92	13.1	Link Establishment and Failover Delays
93	13.2	Duplicated Incoming Packets
94	
95	14. Hardware Specific Considerations
96	14.1	IBM BladeCenter
97	
98	15. Frequently Asked Questions
99	
100	16. Resources and Links
101	
102	
103	1. Bonding Driver Installation
104	==============================
105	
106		Most popular distro kernels ship with the bonding driver
107	already available as a module. If your distro does not, or you
108	have need to compile bonding from source (e.g., configuring and
109	installing a mainline kernel from kernel.org), you'll need to perform
110	the following steps:
111	
112	1.1 Configure and build the kernel with bonding
113	-----------------------------------------------
114	
115		The current version of the bonding driver is available in the
116	drivers/net/bonding subdirectory of the most recent kernel source
117	(which is available on http://kernel.org).  Most users "rolling their
118	own" will want to use the most recent kernel from kernel.org.
119	
120		Configure kernel with "make menuconfig" (or "make xconfig" or
121	"make config"), then select "Bonding driver support" in the "Network
122	device support" section.  It is recommended that you configure the
123	driver as module since it is currently the only way to pass parameters
124	to the driver or configure more than one bonding device.
125	
126		Build and install the new kernel and modules.
127	
128	1.2 Bonding Control Utility
129	-------------------------------------
130	
131		 It is recommended to configure bonding via iproute2 (netlink)
132	or sysfs, the old ifenslave control utility is obsolete.
133	
134	2. Bonding Driver Options
135	=========================
136	
137		Options for the bonding driver are supplied as parameters to the
138	bonding module at load time, or are specified via sysfs.
139	
140		Module options may be given as command line arguments to the
141	insmod or modprobe command, but are usually specified in either the
142	/etc/modrobe.d/*.conf configuration files, or in a distro-specific
143	configuration file (some of which are detailed in the next section).
144	
145		Details on bonding support for sysfs is provided in the
146	"Configuring Bonding Manually via Sysfs" section, below.
147	
148		The available bonding driver parameters are listed below. If a
149	parameter is not specified the default value is used.  When initially
150	configuring a bond, it is recommended "tail -f /var/log/messages" be
151	run in a separate window to watch for bonding driver error messages.
152	
153		It is critical that either the miimon or arp_interval and
154	arp_ip_target parameters be specified, otherwise serious network
155	degradation will occur during link failures.  Very few devices do not
156	support at least miimon, so there is really no reason not to use it.
157	
158		Options with textual values will accept either the text name
159	or, for backwards compatibility, the option value.  E.g.,
160	"mode=802.3ad" and "mode=4" set the same mode.
161	
162		The parameters are as follows:
163	
164	active_slave
165	
166		Specifies the new active slave for modes that support it
167		(active-backup, balance-alb and balance-tlb).  Possible values
168		are the name of any currently enslaved interface, or an empty
169		string.  If a name is given, the slave and its link must be up in order
170		to be selected as the new active slave.  If an empty string is
171		specified, the current active slave is cleared, and a new active
172		slave is selected automatically.
173	
174		Note that this is only available through the sysfs interface. No module
175		parameter by this name exists.
176	
177		The normal value of this option is the name of the currently
178		active slave, or the empty string if there is no active slave or
179		the current mode does not use an active slave.
180	
181	ad_select
182	
183		Specifies the 802.3ad aggregation selection logic to use.  The
184		possible values and their effects are:
185	
186		stable or 0
187	
188			The active aggregator is chosen by largest aggregate
189			bandwidth.
190	
191			Reselection of the active aggregator occurs only when all
192			slaves of the active aggregator are down or the active
193			aggregator has no slaves.
194	
195			This is the default value.
196	
197		bandwidth or 1
198	
199			The active aggregator is chosen by largest aggregate
200			bandwidth.  Reselection occurs if:
201	
202			- A slave is added to or removed from the bond
203	
204			- Any slave's link state changes
205	
206			- Any slave's 802.3ad association state changes
207	
208			- The bond's administrative state changes to up
209	
210		count or 2
211	
212			The active aggregator is chosen by the largest number of
213			ports (slaves).  Reselection occurs as described under the
214			"bandwidth" setting, above.
215	
216		The bandwidth and count selection policies permit failover of
217		802.3ad aggregations when partial failure of the active aggregator
218		occurs.  This keeps the aggregator with the highest availability
219		(either in bandwidth or in number of ports) active at all times.
220	
221		This option was added in bonding version 3.4.0.
222	
223	all_slaves_active
224	
225		Specifies that duplicate frames (received on inactive ports) should be
226		dropped (0) or delivered (1).
227	
228		Normally, bonding will drop duplicate frames (received on inactive
229		ports), which is desirable for most users. But there are some times
230		it is nice to allow duplicate frames to be delivered.
231	
232		The default value is 0 (drop duplicate frames received on inactive
233		ports).
234	
235	arp_interval
236	
237		Specifies the ARP link monitoring frequency in milliseconds.
238	
239		The ARP monitor works by periodically checking the slave
240		devices to determine whether they have sent or received
241		traffic recently (the precise criteria depends upon the
242		bonding mode, and the state of the slave).  Regular traffic is
243		generated via ARP probes issued for the addresses specified by
244		the arp_ip_target option.
245	
246		This behavior can be modified by the arp_validate option,
247		below.
248	
249		If ARP monitoring is used in an etherchannel compatible mode
250		(modes 0 and 2), the switch should be configured in a mode
251		that evenly distributes packets across all links. If the
252		switch is configured to distribute the packets in an XOR
253		fashion, all replies from the ARP targets will be received on
254		the same link which could cause the other team members to
255		fail.  ARP monitoring should not be used in conjunction with
256		miimon.  A value of 0 disables ARP monitoring.  The default
257		value is 0.
258	
259	arp_ip_target
260	
261		Specifies the IP addresses to use as ARP monitoring peers when
262		arp_interval is > 0.  These are the targets of the ARP request
263		sent to determine the health of the link to the targets.
264		Specify these values in ddd.ddd.ddd.ddd format.  Multiple IP
265		addresses must be separated by a comma.  At least one IP
266		address must be given for ARP monitoring to function.  The
267		maximum number of targets that can be specified is 16.  The
268		default value is no IP addresses.
269	
270	arp_validate
271	
272		Specifies whether or not ARP probes and replies should be
273		validated in any mode that supports arp monitoring, or whether
274		non-ARP traffic should be filtered (disregarded) for link
275		monitoring purposes.
276	
277		Possible values are:
278	
279		none or 0
280	
281			No validation or filtering is performed.
282	
283		active or 1
284	
285			Validation is performed only for the active slave.
286	
287		backup or 2
288	
289			Validation is performed only for backup slaves.
290	
291		all or 3
292	
293			Validation is performed for all slaves.
294	
295		filter or 4
296	
297			Filtering is applied to all slaves. No validation is
298			performed.
299	
300		filter_active or 5
301	
302			Filtering is applied to all slaves, validation is performed
303			only for the active slave.
304	
305		filter_backup or 6
306	
307			Filtering is applied to all slaves, validation is performed
308			only for backup slaves.
309	
310		Validation:
311	
312		Enabling validation causes the ARP monitor to examine the incoming
313		ARP requests and replies, and only consider a slave to be up if it
314		is receiving the appropriate ARP traffic.
315	
316		For an active slave, the validation checks ARP replies to confirm
317		that they were generated by an arp_ip_target.  Since backup slaves
318		do not typically receive these replies, the validation performed
319		for backup slaves is on the broadcast ARP request sent out via the
320		active slave.  It is possible that some switch or network
321		configurations may result in situations wherein the backup slaves
322		do not receive the ARP requests; in such a situation, validation
323		of backup slaves must be disabled.
324	
325		The validation of ARP requests on backup slaves is mainly helping
326		bonding to decide which slaves are more likely to work in case of
327		the active slave failure, it doesn't really guarantee that the
328		backup slave will work if it's selected as the next active slave.
329	
330		Validation is useful in network configurations in which multiple
331		bonding hosts are concurrently issuing ARPs to one or more targets
332		beyond a common switch.  Should the link between the switch and
333		target fail (but not the switch itself), the probe traffic
334		generated by the multiple bonding instances will fool the standard
335		ARP monitor into considering the links as still up.  Use of
336		validation can resolve this, as the ARP monitor will only consider
337		ARP requests and replies associated with its own instance of
338		bonding.
339	
340		Filtering:
341	
342		Enabling filtering causes the ARP monitor to only use incoming ARP
343		packets for link availability purposes.  Arriving packets that are
344		not ARPs are delivered normally, but do not count when determining
345		if a slave is available.
346	
347		Filtering operates by only considering the reception of ARP
348		packets (any ARP packet, regardless of source or destination) when
349		determining if a slave has received traffic for link availability
350		purposes.
351	
352		Filtering is useful in network configurations in which significant
353		levels of third party broadcast traffic would fool the standard
354		ARP monitor into considering the links as still up.  Use of
355		filtering can resolve this, as only ARP traffic is considered for
356		link availability purposes.
357	
358		This option was added in bonding version 3.1.0.
359	
360	arp_all_targets
361	
362		Specifies the quantity of arp_ip_targets that must be reachable
363		in order for the ARP monitor to consider a slave as being up.
364		This option affects only active-backup mode for slaves with
365		arp_validation enabled.
366	
367		Possible values are:
368	
369		any or 0
370	
371			consider the slave up only when any of the arp_ip_targets
372			is reachable
373	
374		all or 1
375	
376			consider the slave up only when all of the arp_ip_targets
377			are reachable
378	
379	downdelay
380	
381		Specifies the time, in milliseconds, to wait before disabling
382		a slave after a link failure has been detected.  This option
383		is only valid for the miimon link monitor.  The downdelay
384		value should be a multiple of the miimon value; if not, it
385		will be rounded down to the nearest multiple.  The default
386		value is 0.
387	
388	fail_over_mac
389	
390		Specifies whether active-backup mode should set all slaves to
391		the same MAC address at enslavement (the traditional
392		behavior), or, when enabled, perform special handling of the
393		bond's MAC address in accordance with the selected policy.
394	
395		Possible values are:
396	
397		none or 0
398	
399			This setting disables fail_over_mac, and causes
400			bonding to set all slaves of an active-backup bond to
401			the same MAC address at enslavement time.  This is the
402			default.
403	
404		active or 1
405	
406			The "active" fail_over_mac policy indicates that the
407			MAC address of the bond should always be the MAC
408			address of the currently active slave.  The MAC
409			address of the slaves is not changed; instead, the MAC
410			address of the bond changes during a failover.
411	
412			This policy is useful for devices that cannot ever
413			alter their MAC address, or for devices that refuse
414			incoming broadcasts with their own source MAC (which
415			interferes with the ARP monitor).
416	
417			The down side of this policy is that every device on
418			the network must be updated via gratuitous ARP,
419			vs. just updating a switch or set of switches (which
420			often takes place for any traffic, not just ARP
421			traffic, if the switch snoops incoming traffic to
422			update its tables) for the traditional method.  If the
423			gratuitous ARP is lost, communication may be
424			disrupted.
425	
426			When this policy is used in conjunction with the mii
427			monitor, devices which assert link up prior to being
428			able to actually transmit and receive are particularly
429			susceptible to loss of the gratuitous ARP, and an
430			appropriate updelay setting may be required.
431	
432		follow or 2
433	
434			The "follow" fail_over_mac policy causes the MAC
435			address of the bond to be selected normally (normally
436			the MAC address of the first slave added to the bond).
437			However, the second and subsequent slaves are not set
438			to this MAC address while they are in a backup role; a
439			slave is programmed with the bond's MAC address at
440			failover time (and the formerly active slave receives
441			the newly active slave's MAC address).
442	
443			This policy is useful for multiport devices that
444			either become confused or incur a performance penalty
445			when multiple ports are programmed with the same MAC
446			address.
447	
448	
449		The default policy is none, unless the first slave cannot
450		change its MAC address, in which case the active policy is
451		selected by default.
452	
453		This option may be modified via sysfs only when no slaves are
454		present in the bond.
455	
456		This option was added in bonding version 3.2.0.  The "follow"
457		policy was added in bonding version 3.3.0.
458	
459	lacp_rate
460	
461		Option specifying the rate in which we'll ask our link partner
462		to transmit LACPDU packets in 802.3ad mode.  Possible values
463		are:
464	
465		slow or 0
466			Request partner to transmit LACPDUs every 30 seconds
467	
468		fast or 1
469			Request partner to transmit LACPDUs every 1 second
470	
471		The default is slow.
472	
473	max_bonds
474	
475		Specifies the number of bonding devices to create for this
476		instance of the bonding driver.  E.g., if max_bonds is 3, and
477		the bonding driver is not already loaded, then bond0, bond1
478		and bond2 will be created.  The default value is 1.  Specifying
479		a value of 0 will load bonding, but will not create any devices.
480	
481	miimon
482	
483		Specifies the MII link monitoring frequency in milliseconds.
484		This determines how often the link state of each slave is
485		inspected for link failures.  A value of zero disables MII
486		link monitoring.  A value of 100 is a good starting point.
487		The use_carrier option, below, affects how the link state is
488		determined.  See the High Availability section for additional
489		information.  The default value is 0.
490	
491	min_links
492	
493		Specifies the minimum number of links that must be active before
494		asserting carrier. It is similar to the Cisco EtherChannel min-links
495		feature. This allows setting the minimum number of member ports that
496		must be up (link-up state) before marking the bond device as up
497		(carrier on). This is useful for situations where higher level services
498		such as clustering want to ensure a minimum number of low bandwidth
499		links are active before switchover. This option only affect 802.3ad
500		mode.
501	
502		The default value is 0. This will cause carrier to be asserted (for
503		802.3ad mode) whenever there is an active aggregator, regardless of the
504		number of available links in that aggregator. Note that, because an
505		aggregator cannot be active without at least one available link,
506		setting this option to 0 or to 1 has the exact same effect.
507	
508	mode
509	
510		Specifies one of the bonding policies. The default is
511		balance-rr (round robin).  Possible values are:
512	
513		balance-rr or 0
514	
515			Round-robin policy: Transmit packets in sequential
516			order from the first available slave through the
517			last.  This mode provides load balancing and fault
518			tolerance.
519	
520		active-backup or 1
521	
522			Active-backup policy: Only one slave in the bond is
523			active.  A different slave becomes active if, and only
524			if, the active slave fails.  The bond's MAC address is
525			externally visible on only one port (network adapter)
526			to avoid confusing the switch.
527	
528			In bonding version 2.6.2 or later, when a failover
529			occurs in active-backup mode, bonding will issue one
530			or more gratuitous ARPs on the newly active slave.
531			One gratuitous ARP is issued for the bonding master
532			interface and each VLAN interfaces configured above
533			it, provided that the interface has at least one IP
534			address configured.  Gratuitous ARPs issued for VLAN
535			interfaces are tagged with the appropriate VLAN id.
536	
537			This mode provides fault tolerance.  The primary
538			option, documented below, affects the behavior of this
539			mode.
540	
541		balance-xor or 2
542	
543			XOR policy: Transmit based on the selected transmit
544			hash policy.  The default policy is a simple [(source
545			MAC address XOR'd with destination MAC address XOR
546			packet type ID) modulo slave count].  Alternate transmit
547			policies may be	selected via the xmit_hash_policy option,
548			described below.
549	
550			This mode provides load balancing and fault tolerance.
551	
552		broadcast or 3
553	
554			Broadcast policy: transmits everything on all slave
555			interfaces.  This mode provides fault tolerance.
556	
557		802.3ad or 4
558	
559			IEEE 802.3ad Dynamic link aggregation.  Creates
560			aggregation groups that share the same speed and
561			duplex settings.  Utilizes all slaves in the active
562			aggregator according to the 802.3ad specification.
563	
564			Slave selection for outgoing traffic is done according
565			to the transmit hash policy, which may be changed from
566			the default simple XOR policy via the xmit_hash_policy
567			option, documented below.  Note that not all transmit
568			policies may be 802.3ad compliant, particularly in
569			regards to the packet mis-ordering requirements of
570			section 43.2.4 of the 802.3ad standard.  Differing
571			peer implementations will have varying tolerances for
572			noncompliance.
573	
574			Prerequisites:
575	
576			1. Ethtool support in the base drivers for retrieving
577			the speed and duplex of each slave.
578	
579			2. A switch that supports IEEE 802.3ad Dynamic link
580			aggregation.
581	
582			Most switches will require some type of configuration
583			to enable 802.3ad mode.
584	
585		balance-tlb or 5
586	
587			Adaptive transmit load balancing: channel bonding that
588			does not require any special switch support.
589	
590			In tlb_dynamic_lb=1 mode; the outgoing traffic is
591			distributed according to the current load (computed
592			relative to the speed) on each slave.
593	
594			In tlb_dynamic_lb=0 mode; the load balancing based on
595			current load is disabled and the load is distributed
596			only using the hash distribution.
597	
598			Incoming traffic is received by the current slave.
599			If the receiving slave fails, another slave takes over
600			the MAC address of the failed receiving slave.
601	
602			Prerequisite:
603	
604			Ethtool support in the base drivers for retrieving the
605			speed of each slave.
606	
607		balance-alb or 6
608	
609			Adaptive load balancing: includes balance-tlb plus
610			receive load balancing (rlb) for IPV4 traffic, and
611			does not require any special switch support.  The
612			receive load balancing is achieved by ARP negotiation.
613			The bonding driver intercepts the ARP Replies sent by
614			the local system on their way out and overwrites the
615			source hardware address with the unique hardware
616			address of one of the slaves in the bond such that
617			different peers use different hardware addresses for
618			the server.
619	
620			Receive traffic from connections created by the server
621			is also balanced.  When the local system sends an ARP
622			Request the bonding driver copies and saves the peer's
623			IP information from the ARP packet.  When the ARP
624			Reply arrives from the peer, its hardware address is
625			retrieved and the bonding driver initiates an ARP
626			reply to this peer assigning it to one of the slaves
627			in the bond.  A problematic outcome of using ARP
628			negotiation for balancing is that each time that an
629			ARP request is broadcast it uses the hardware address
630			of the bond.  Hence, peers learn the hardware address
631			of the bond and the balancing of receive traffic
632			collapses to the current slave.  This is handled by
633			sending updates (ARP Replies) to all the peers with
634			their individually assigned hardware address such that
635			the traffic is redistributed.  Receive traffic is also
636			redistributed when a new slave is added to the bond
637			and when an inactive slave is re-activated.  The
638			receive load is distributed sequentially (round robin)
639			among the group of highest speed slaves in the bond.
640	
641			When a link is reconnected or a new slave joins the
642			bond the receive traffic is redistributed among all
643			active slaves in the bond by initiating ARP Replies
644			with the selected MAC address to each of the
645			clients. The updelay parameter (detailed below) must
646			be set to a value equal or greater than the switch's
647			forwarding delay so that the ARP Replies sent to the
648			peers will not be blocked by the switch.
649	
650			Prerequisites:
651	
652			1. Ethtool support in the base drivers for retrieving
653			the speed of each slave.
654	
655			2. Base driver support for setting the hardware
656			address of a device while it is open.  This is
657			required so that there will always be one slave in the
658			team using the bond hardware address (the
659			curr_active_slave) while having a unique hardware
660			address for each slave in the bond.  If the
661			curr_active_slave fails its hardware address is
662			swapped with the new curr_active_slave that was
663			chosen.
664	
665	num_grat_arp
666	num_unsol_na
667	
668		Specify the number of peer notifications (gratuitous ARPs and
669		unsolicited IPv6 Neighbor Advertisements) to be issued after a
670		failover event.  As soon as the link is up on the new slave
671		(possibly immediately) a peer notification is sent on the
672		bonding device and each VLAN sub-device.  This is repeated at
673		each link monitor interval (arp_interval or miimon, whichever
674		is active) if the number is greater than 1.
675	
676		The valid range is 0 - 255; the default value is 1.  These options
677		affect only the active-backup mode.  These options were added for
678		bonding versions 3.3.0 and 3.4.0 respectively.
679	
680		From Linux 3.0 and bonding version 3.7.1, these notifications
681		are generated by the ipv4 and ipv6 code and the numbers of
682		repetitions cannot be set independently.
683	
684	packets_per_slave
685	
686		Specify the number of packets to transmit through a slave before
687		moving to the next one. When set to 0 then a slave is chosen at
688		random.
689	
690		The valid range is 0 - 65535; the default value is 1. This option
691		has effect only in balance-rr mode.
692	
693	primary
694	
695		A string (eth0, eth2, etc) specifying which slave is the
696		primary device.  The specified device will always be the
697		active slave while it is available.  Only when the primary is
698		off-line will alternate devices be used.  This is useful when
699		one slave is preferred over another, e.g., when one slave has
700		higher throughput than another.
701	
702		The primary option is only valid for active-backup(1),
703		balance-tlb (5) and balance-alb (6) mode.
704	
705	primary_reselect
706	
707		Specifies the reselection policy for the primary slave.  This
708		affects how the primary slave is chosen to become the active slave
709		when failure of the active slave or recovery of the primary slave
710		occurs.  This option is designed to prevent flip-flopping between
711		the primary slave and other slaves.  Possible values are:
712	
713		always or 0 (default)
714	
715			The primary slave becomes the active slave whenever it
716			comes back up.
717	
718		better or 1
719	
720			The primary slave becomes the active slave when it comes
721			back up, if the speed and duplex of the primary slave is
722			better than the speed and duplex of the current active
723			slave.
724	
725		failure or 2
726	
727			The primary slave becomes the active slave only if the
728			current active slave fails and the primary slave is up.
729	
730		The primary_reselect setting is ignored in two cases:
731	
732			If no slaves are active, the first slave to recover is
733			made the active slave.
734	
735			When initially enslaved, the primary slave is always made
736			the active slave.
737	
738		Changing the primary_reselect policy via sysfs will cause an
739		immediate selection of the best active slave according to the new
740		policy.  This may or may not result in a change of the active
741		slave, depending upon the circumstances.
742	
743		This option was added for bonding version 3.6.0.
744	
745	tlb_dynamic_lb
746	
747		Specifies if dynamic shuffling of flows is enabled in tlb
748		mode. The value has no effect on any other modes.
749	
750		The default behavior of tlb mode is to shuffle active flows across
751		slaves based on the load in that interval. This gives nice lb
752		characteristics but can cause packet reordering. If re-ordering is
753		a concern use this variable to disable flow shuffling and rely on
754		load balancing provided solely by the hash distribution.
755		xmit-hash-policy can be used to select the appropriate hashing for
756		the setup.
757	
758		The sysfs entry can be used to change the setting per bond device
759		and the initial value is derived from the module parameter. The
760		sysfs entry is allowed to be changed only if the bond device is
761		down.
762	
763		The default value is "1" that enables flow shuffling while value "0"
764		disables it. This option was added in bonding driver 3.7.1
765	
766	
767	updelay
768	
769		Specifies the time, in milliseconds, to wait before enabling a
770		slave after a link recovery has been detected.  This option is
771		only valid for the miimon link monitor.  The updelay value
772		should be a multiple of the miimon value; if not, it will be
773		rounded down to the nearest multiple.  The default value is 0.
774	
775	use_carrier
776	
777		Specifies whether or not miimon should use MII or ETHTOOL
778		ioctls vs. netif_carrier_ok() to determine the link
779		status. The MII or ETHTOOL ioctls are less efficient and
780		utilize a deprecated calling sequence within the kernel.  The
781		netif_carrier_ok() relies on the device driver to maintain its
782		state with netif_carrier_on/off; at this writing, most, but
783		not all, device drivers support this facility.
784	
785		If bonding insists that the link is up when it should not be,
786		it may be that your network device driver does not support
787		netif_carrier_on/off.  The default state for netif_carrier is
788		"carrier on," so if a driver does not support netif_carrier,
789		it will appear as if the link is always up.  In this case,
790		setting use_carrier to 0 will cause bonding to revert to the
791		MII / ETHTOOL ioctl method to determine the link state.
792	
793		A value of 1 enables the use of netif_carrier_ok(), a value of
794		0 will use the deprecated MII / ETHTOOL ioctls.  The default
795		value is 1.
796	
797	xmit_hash_policy
798	
799		Selects the transmit hash policy to use for slave selection in
800		balance-xor, 802.3ad, and tlb modes.  Possible values are:
801	
802		layer2
803	
804			Uses XOR of hardware MAC addresses and packet type ID
805			field to generate the hash. The formula is
806	
807			hash = source MAC XOR destination MAC XOR packet type ID
808			slave number = hash modulo slave count
809	
810			This algorithm will place all traffic to a particular
811			network peer on the same slave.
812	
813			This algorithm is 802.3ad compliant.
814	
815		layer2+3
816	
817			This policy uses a combination of layer2 and layer3
818			protocol information to generate the hash.
819	
820			Uses XOR of hardware MAC addresses and IP addresses to
821			generate the hash.  The formula is
822	
823			hash = source MAC XOR destination MAC XOR packet type ID
824			hash = hash XOR source IP XOR destination IP
825			hash = hash XOR (hash RSHIFT 16)
826			hash = hash XOR (hash RSHIFT 8)
827			And then hash is reduced modulo slave count.
828	
829			If the protocol is IPv6 then the source and destination
830			addresses are first hashed using ipv6_addr_hash.
831	
832			This algorithm will place all traffic to a particular
833			network peer on the same slave.  For non-IP traffic,
834			the formula is the same as for the layer2 transmit
835			hash policy.
836	
837			This policy is intended to provide a more balanced
838			distribution of traffic than layer2 alone, especially
839			in environments where a layer3 gateway device is
840			required to reach most destinations.
841	
842			This algorithm is 802.3ad compliant.
843	
844		layer3+4
845	
846			This policy uses upper layer protocol information,
847			when available, to generate the hash.  This allows for
848			traffic to a particular network peer to span multiple
849			slaves, although a single connection will not span
850			multiple slaves.
851	
852			The formula for unfragmented TCP and UDP packets is
853	
854			hash = source port, destination port (as in the header)
855			hash = hash XOR source IP XOR destination IP
856			hash = hash XOR (hash RSHIFT 16)
857			hash = hash XOR (hash RSHIFT 8)
858			And then hash is reduced modulo slave count.
859	
860			If the protocol is IPv6 then the source and destination
861			addresses are first hashed using ipv6_addr_hash.
862	
863			For fragmented TCP or UDP packets and all other IPv4 and
864			IPv6 protocol traffic, the source and destination port
865			information is omitted.  For non-IP traffic, the
866			formula is the same as for the layer2 transmit hash
867			policy.
868	
869			This algorithm is not fully 802.3ad compliant.  A
870			single TCP or UDP conversation containing both
871			fragmented and unfragmented packets will see packets
872			striped across two interfaces.  This may result in out
873			of order delivery.  Most traffic types will not meet
874			this criteria, as TCP rarely fragments traffic, and
875			most UDP traffic is not involved in extended
876			conversations.  Other implementations of 802.3ad may
877			or may not tolerate this noncompliance.
878	
879		encap2+3
880	
881			This policy uses the same formula as layer2+3 but it
882			relies on skb_flow_dissect to obtain the header fields
883			which might result in the use of inner headers if an
884			encapsulation protocol is used. For example this will
885			improve the performance for tunnel users because the
886			packets will be distributed according to the encapsulated
887			flows.
888	
889		encap3+4
890	
891			This policy uses the same formula as layer3+4 but it
892			relies on skb_flow_dissect to obtain the header fields
893			which might result in the use of inner headers if an
894			encapsulation protocol is used. For example this will
895			improve the performance for tunnel users because the
896			packets will be distributed according to the encapsulated
897			flows.
898	
899		The default value is layer2.  This option was added in bonding
900		version 2.6.3.  In earlier versions of bonding, this parameter
901		does not exist, and the layer2 policy is the only policy.  The
902		layer2+3 value was added for bonding version 3.2.2.
903	
904	resend_igmp
905	
906		Specifies the number of IGMP membership reports to be issued after
907		a failover event. One membership report is issued immediately after
908		the failover, subsequent packets are sent in each 200ms interval.
909	
910		The valid range is 0 - 255; the default value is 1. A value of 0
911		prevents the IGMP membership report from being issued in response
912		to the failover event.
913	
914		This option is useful for bonding modes balance-rr (0), active-backup
915		(1), balance-tlb (5) and balance-alb (6), in which a failover can
916		switch the IGMP traffic from one slave to another.  Therefore a fresh
917		IGMP report must be issued to cause the switch to forward the incoming
918		IGMP traffic over the newly selected slave.
919	
920		This option was added for bonding version 3.7.0.
921	
922	lp_interval
923	
924		Specifies the number of seconds between instances where the bonding
925		driver sends learning packets to each slaves peer switch.
926	
927		The valid range is 1 - 0x7fffffff; the default value is 1. This Option
928		has effect only in balance-tlb and balance-alb modes.
929	
930	3. Configuring Bonding Devices
931	==============================
932	
933		You can configure bonding using either your distro's network
934	initialization scripts, or manually using either iproute2 or the
935	sysfs interface.  Distros generally use one of three packages for the
936	network initialization scripts: initscripts, sysconfig or interfaces.
937	Recent versions of these packages have support for bonding, while older
938	versions do not.
939	
940		We will first describe the options for configuring bonding for
941	distros using versions of initscripts, sysconfig and interfaces with full
942	or partial support for bonding, then provide information on enabling
943	bonding without support from the network initialization scripts (i.e.,
944	older versions of initscripts or sysconfig).
945	
946		If you're unsure whether your distro uses sysconfig,
947	initscripts or interfaces, or don't know if it's new enough, have no fear.
948	Determining this is fairly straightforward.
949	
950		First, look for a file called interfaces in /etc/network directory.
951	If this file is present in your system, then your system use interfaces. See
952	Configuration with Interfaces Support.
953	
954		Else, issue the command:
955	
956	$ rpm -qf /sbin/ifup
957	
958		It will respond with a line of text starting with either
959	"initscripts" or "sysconfig," followed by some numbers.  This is the
960	package that provides your network initialization scripts.
961	
962		Next, to determine if your installation supports bonding,
963	issue the command:
964	
965	$ grep ifenslave /sbin/ifup
966	
967		If this returns any matches, then your initscripts or
968	sysconfig has support for bonding.
969	
970	3.1 Configuration with Sysconfig Support
971	----------------------------------------
972	
973		This section applies to distros using a version of sysconfig
974	with bonding support, for example, SuSE Linux Enterprise Server 9.
975	
976		SuSE SLES 9's networking configuration system does support
977	bonding, however, at this writing, the YaST system configuration
978	front end does not provide any means to work with bonding devices.
979	Bonding devices can be managed by hand, however, as follows.
980	
981		First, if they have not already been configured, configure the
982	slave devices.  On SLES 9, this is most easily done by running the
983	yast2 sysconfig configuration utility.  The goal is for to create an
984	ifcfg-id file for each slave device.  The simplest way to accomplish
985	this is to configure the devices for DHCP (this is only to get the
986	file ifcfg-id file created; see below for some issues with DHCP).  The
987	name of the configuration file for each device will be of the form:
988	
989	ifcfg-id-xx:xx:xx:xx:xx:xx
990	
991		Where the "xx" portion will be replaced with the digits from
992	the device's permanent MAC address.
993	
994		Once the set of ifcfg-id-xx:xx:xx:xx:xx:xx files has been
995	created, it is necessary to edit the configuration files for the slave
996	devices (the MAC addresses correspond to those of the slave devices).
997	Before editing, the file will contain multiple lines, and will look
998	something like this:
999	
1000	BOOTPROTO='dhcp'
1001	STARTMODE='on'
1002	USERCTL='no'
1003	UNIQUE='XNzu.WeZGOGF+4wE'
1004	_nm_name='bus-pci-0001:61:01.0'
1005	
1006		Change the BOOTPROTO and STARTMODE lines to the following:
1007	
1008	BOOTPROTO='none'
1009	STARTMODE='off'
1010	
1011		Do not alter the UNIQUE or _nm_name lines.  Remove any other
1012	lines (USERCTL, etc).
1013	
1014		Once the ifcfg-id-xx:xx:xx:xx:xx:xx files have been modified,
1015	it's time to create the configuration file for the bonding device
1016	itself.  This file is named ifcfg-bondX, where X is the number of the
1017	bonding device to create, starting at 0.  The first such file is
1018	ifcfg-bond0, the second is ifcfg-bond1, and so on.  The sysconfig
1019	network configuration system will correctly start multiple instances
1020	of bonding.
1021	
1022		The contents of the ifcfg-bondX file is as follows:
1023	
1024	BOOTPROTO="static"
1025	BROADCAST="10.0.2.255"
1026	IPADDR="10.0.2.10"
1027	NETMASK="255.255.0.0"
1028	NETWORK="10.0.2.0"
1029	REMOTE_IPADDR=""
1030	STARTMODE="onboot"
1031	BONDING_MASTER="yes"
1032	BONDING_MODULE_OPTS="mode=active-backup miimon=100"
1033	BONDING_SLAVE0="eth0"
1034	BONDING_SLAVE1="bus-pci-0000:06:08.1"
1035	
1036		Replace the sample BROADCAST, IPADDR, NETMASK and NETWORK
1037	values with the appropriate values for your network.
1038	
1039		The STARTMODE specifies when the device is brought online.
1040	The possible values are:
1041	
1042		onboot:	 The device is started at boot time.  If you're not
1043			 sure, this is probably what you want.
1044	
1045		manual:	 The device is started only when ifup is called
1046			 manually.  Bonding devices may be configured this
1047			 way if you do not wish them to start automatically
1048			 at boot for some reason.
1049	
1050		hotplug: The device is started by a hotplug event.  This is not
1051			 a valid choice for a bonding device.
1052	
1053		off or ignore: The device configuration is ignored.
1054	
1055		The line BONDING_MASTER='yes' indicates that the device is a
1056	bonding master device.  The only useful value is "yes."
1057	
1058		The contents of BONDING_MODULE_OPTS are supplied to the
1059	instance of the bonding module for this device.  Specify the options
1060	for the bonding mode, link monitoring, and so on here.  Do not include
1061	the max_bonds bonding parameter; this will confuse the configuration
1062	system if you have multiple bonding devices.
1063	
1064		Finally, supply one BONDING_SLAVEn="slave device" for each
1065	slave.  where "n" is an increasing value, one for each slave.  The
1066	"slave device" is either an interface name, e.g., "eth0", or a device
1067	specifier for the network device.  The interface name is easier to
1068	find, but the ethN names are subject to change at boot time if, e.g.,
1069	a device early in the sequence has failed.  The device specifiers
1070	(bus-pci-0000:06:08.1 in the example above) specify the physical
1071	network device, and will not change unless the device's bus location
1072	changes (for example, it is moved from one PCI slot to another).  The
1073	example above uses one of each type for demonstration purposes; most
1074	configurations will choose one or the other for all slave devices.
1075	
1076		When all configuration files have been modified or created,
1077	networking must be restarted for the configuration changes to take
1078	effect.  This can be accomplished via the following:
1079	
1080	# /etc/init.d/network restart
1081	
1082		Note that the network control script (/sbin/ifdown) will
1083	remove the bonding module as part of the network shutdown processing,
1084	so it is not necessary to remove the module by hand if, e.g., the
1085	module parameters have changed.
1086	
1087		Also, at this writing, YaST/YaST2 will not manage bonding
1088	devices (they do not show bonding interfaces on its list of network
1089	devices).  It is necessary to edit the configuration file by hand to
1090	change the bonding configuration.
1091	
1092		Additional general options and details of the ifcfg file
1093	format can be found in an example ifcfg template file:
1094	
1095	/etc/sysconfig/network/ifcfg.template
1096	
1097		Note that the template does not document the various BONDING_
1098	settings described above, but does describe many of the other options.
1099	
1100	3.1.1 Using DHCP with Sysconfig
1101	-------------------------------
1102	
1103		Under sysconfig, configuring a device with BOOTPROTO='dhcp'
1104	will cause it to query DHCP for its IP address information.  At this
1105	writing, this does not function for bonding devices; the scripts
1106	attempt to obtain the device address from DHCP prior to adding any of
1107	the slave devices.  Without active slaves, the DHCP requests are not
1108	sent to the network.
1109	
1110	3.1.2 Configuring Multiple Bonds with Sysconfig
1111	-----------------------------------------------
1112	
1113		The sysconfig network initialization system is capable of
1114	handling multiple bonding devices.  All that is necessary is for each
1115	bonding instance to have an appropriately configured ifcfg-bondX file
1116	(as described above).  Do not specify the "max_bonds" parameter to any
1117	instance of bonding, as this will confuse sysconfig.  If you require
1118	multiple bonding devices with identical parameters, create multiple
1119	ifcfg-bondX files.
1120	
1121		Because the sysconfig scripts supply the bonding module
1122	options in the ifcfg-bondX file, it is not necessary to add them to
1123	the system /etc/modules.d/*.conf configuration files.
1124	
1125	3.2 Configuration with Initscripts Support
1126	------------------------------------------
1127	
1128		This section applies to distros using a recent version of
1129	initscripts with bonding support, for example, Red Hat Enterprise Linux
1130	version 3 or later, Fedora, etc.  On these systems, the network
1131	initialization scripts have knowledge of bonding, and can be configured to
1132	control bonding devices.  Note that older versions of the initscripts
1133	package have lower levels of support for bonding; this will be noted where
1134	applicable.
1135	
1136		These distros will not automatically load the network adapter
1137	driver unless the ethX device is configured with an IP address.
1138	Because of this constraint, users must manually configure a
1139	network-script file for all physical adapters that will be members of
1140	a bondX link.  Network script files are located in the directory:
1141	
1142	/etc/sysconfig/network-scripts
1143	
1144		The file name must be prefixed with "ifcfg-eth" and suffixed
1145	with the adapter's physical adapter number.  For example, the script
1146	for eth0 would be named /etc/sysconfig/network-scripts/ifcfg-eth0.
1147	Place the following text in the file:
1148	
1149	DEVICE=eth0
1150	USERCTL=no
1151	ONBOOT=yes
1152	MASTER=bond0
1153	SLAVE=yes
1154	BOOTPROTO=none
1155	
1156		The DEVICE= line will be different for every ethX device and
1157	must correspond with the name of the file, i.e., ifcfg-eth1 must have
1158	a device line of DEVICE=eth1.  The setting of the MASTER= line will
1159	also depend on the final bonding interface name chosen for your bond.
1160	As with other network devices, these typically start at 0, and go up
1161	one for each device, i.e., the first bonding instance is bond0, the
1162	second is bond1, and so on.
1163	
1164		Next, create a bond network script.  The file name for this
1165	script will be /etc/sysconfig/network-scripts/ifcfg-bondX where X is
1166	the number of the bond.  For bond0 the file is named "ifcfg-bond0",
1167	for bond1 it is named "ifcfg-bond1", and so on.  Within that file,
1168	place the following text:
1169	
1170	DEVICE=bond0
1171	IPADDR=192.168.1.1
1172	NETMASK=255.255.255.0
1173	NETWORK=192.168.1.0
1174	BROADCAST=192.168.1.255
1175	ONBOOT=yes
1176	BOOTPROTO=none
1177	USERCTL=no
1178	
1179		Be sure to change the networking specific lines (IPADDR,
1180	NETMASK, NETWORK and BROADCAST) to match your network configuration.
1181	
1182		For later versions of initscripts, such as that found with Fedora
1183	7 (or later) and Red Hat Enterprise Linux version 5 (or later), it is possible,
1184	and, indeed, preferable, to specify the bonding options in the ifcfg-bond0
1185	file, e.g. a line of the format:
1186	
1187	BONDING_OPTS="mode=active-backup arp_interval=60 arp_ip_target=192.168.1.254"
1188	
1189		will configure the bond with the specified options.  The options
1190	specified in BONDING_OPTS are identical to the bonding module parameters
1191	except for the arp_ip_target field when using versions of initscripts older
1192	than and 8.57 (Fedora 8) and 8.45.19 (Red Hat Enterprise Linux 5.2).  When
1193	using older versions each target should be included as a separate option and
1194	should be preceded by a '+' to indicate it should be added to the list of
1195	queried targets, e.g.,
1196	
1197		arp_ip_target=+192.168.1.1 arp_ip_target=+192.168.1.2
1198	
1199		is the proper syntax to specify multiple targets.  When specifying
1200	options via BONDING_OPTS, it is not necessary to edit /etc/modprobe.d/*.conf.
1201	
1202		For even older versions of initscripts that do not support
1203	BONDING_OPTS, it is necessary to edit /etc/modprobe.d/*.conf, depending upon
1204	your distro) to load the bonding module with your desired options when the
1205	bond0 interface is brought up.  The following lines in /etc/modprobe.d/*.conf
1206	will load the bonding module, and select its options:
1207	
1208	alias bond0 bonding
1209	options bond0 mode=balance-alb miimon=100
1210	
1211		Replace the sample parameters with the appropriate set of
1212	options for your configuration.
1213	
1214		Finally run "/etc/rc.d/init.d/network restart" as root.  This
1215	will restart the networking subsystem and your bond link should be now
1216	up and running.
1217	
1218	3.2.1 Using DHCP with Initscripts
1219	---------------------------------
1220	
1221		Recent versions of initscripts (the versions supplied with Fedora
1222	Core 3 and Red Hat Enterprise Linux 4, or later versions, are reported to
1223	work) have support for assigning IP information to bonding devices via
1224	DHCP.
1225	
1226		To configure bonding for DHCP, configure it as described
1227	above, except replace the line "BOOTPROTO=none" with "BOOTPROTO=dhcp"
1228	and add a line consisting of "TYPE=Bonding".  Note that the TYPE value
1229	is case sensitive.
1230	
1231	3.2.2 Configuring Multiple Bonds with Initscripts
1232	-------------------------------------------------
1233	
1234		Initscripts packages that are included with Fedora 7 and Red Hat
1235	Enterprise Linux 5 support multiple bonding interfaces by simply
1236	specifying the appropriate BONDING_OPTS= in ifcfg-bondX where X is the
1237	number of the bond.  This support requires sysfs support in the kernel,
1238	and a bonding driver of version 3.0.0 or later.  Other configurations may
1239	not support this method for specifying multiple bonding interfaces; for
1240	those instances, see the "Configuring Multiple Bonds Manually" section,
1241	below.
1242	
1243	3.3 Configuring Bonding Manually with iproute2
1244	-----------------------------------------------
1245	
1246		This section applies to distros whose network initialization
1247	scripts (the sysconfig or initscripts package) do not have specific
1248	knowledge of bonding.  One such distro is SuSE Linux Enterprise Server
1249	version 8.
1250	
1251		The general method for these systems is to place the bonding
1252	module parameters into a config file in /etc/modprobe.d/ (as
1253	appropriate for the installed distro), then add modprobe and/or
1254	`ip link` commands to the system's global init script.  The name of
1255	the global init script differs; for sysconfig, it is
1256	/etc/init.d/boot.local and for initscripts it is /etc/rc.d/rc.local.
1257	
1258		For example, if you wanted to make a simple bond of two e100
1259	devices (presumed to be eth0 and eth1), and have it persist across
1260	reboots, edit the appropriate file (/etc/init.d/boot.local or
1261	/etc/rc.d/rc.local), and add the following:
1262	
1263	modprobe bonding mode=balance-alb miimon=100
1264	modprobe e100
1265	ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
1266	ip link set eth0 master bond0
1267	ip link set eth1 master bond0
1268	
1269		Replace the example bonding module parameters and bond0
1270	network configuration (IP address, netmask, etc) with the appropriate
1271	values for your configuration.
1272	
1273		Unfortunately, this method will not provide support for the
1274	ifup and ifdown scripts on the bond devices.  To reload the bonding
1275	configuration, it is necessary to run the initialization script, e.g.,
1276	
1277	# /etc/init.d/boot.local
1278	
1279		or
1280	
1281	# /etc/rc.d/rc.local
1282	
1283		It may be desirable in such a case to create a separate script
1284	which only initializes the bonding configuration, then call that
1285	separate script from within boot.local.  This allows for bonding to be
1286	enabled without re-running the entire global init script.
1287	
1288		To shut down the bonding devices, it is necessary to first
1289	mark the bonding device itself as being down, then remove the
1290	appropriate device driver modules.  For our example above, you can do
1291	the following:
1292	
1293	# ifconfig bond0 down
1294	# rmmod bonding
1295	# rmmod e100
1296	
1297		Again, for convenience, it may be desirable to create a script
1298	with these commands.
1299	
1300	
1301	3.3.1 Configuring Multiple Bonds Manually
1302	-----------------------------------------
1303	
1304		This section contains information on configuring multiple
1305	bonding devices with differing options for those systems whose network
1306	initialization scripts lack support for configuring multiple bonds.
1307	
1308		If you require multiple bonding devices, but all with the same
1309	options, you may wish to use the "max_bonds" module parameter,
1310	documented above.
1311	
1312		To create multiple bonding devices with differing options, it is
1313	preferable to use bonding parameters exported by sysfs, documented in the
1314	section below.
1315	
1316		For versions of bonding without sysfs support, the only means to
1317	provide multiple instances of bonding with differing options is to load
1318	the bonding driver multiple times.  Note that current versions of the
1319	sysconfig network initialization scripts handle this automatically; if
1320	your distro uses these scripts, no special action is needed.  See the
1321	section Configuring Bonding Devices, above, if you're not sure about your
1322	network initialization scripts.
1323	
1324		To load multiple instances of the module, it is necessary to
1325	specify a different name for each instance (the module loading system
1326	requires that every loaded module, even multiple instances of the same
1327	module, have a unique name).  This is accomplished by supplying multiple
1328	sets of bonding options in /etc/modprobe.d/*.conf, for example:
1329	
1330	alias bond0 bonding
1331	options bond0 -o bond0 mode=balance-rr miimon=100
1332	
1333	alias bond1 bonding
1334	options bond1 -o bond1 mode=balance-alb miimon=50
1335	
1336		will load the bonding module two times.  The first instance is
1337	named "bond0" and creates the bond0 device in balance-rr mode with an
1338	miimon of 100.  The second instance is named "bond1" and creates the
1339	bond1 device in balance-alb mode with an miimon of 50.
1340	
1341		In some circumstances (typically with older distributions),
1342	the above does not work, and the second bonding instance never sees
1343	its options.  In that case, the second options line can be substituted
1344	as follows:
1345	
1346	install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \
1347		mode=balance-alb miimon=50
1348	
1349		This may be repeated any number of times, specifying a new and
1350	unique name in place of bond1 for each subsequent instance.
1351	
1352		It has been observed that some Red Hat supplied kernels are unable
1353	to rename modules at load time (the "-o bond1" part).  Attempts to pass
1354	that option to modprobe will produce an "Operation not permitted" error.
1355	This has been reported on some Fedora Core kernels, and has been seen on
1356	RHEL 4 as well.  On kernels exhibiting this problem, it will be impossible
1357	to configure multiple bonds with differing parameters (as they are older
1358	kernels, and also lack sysfs support).
1359	
1360	3.4 Configuring Bonding Manually via Sysfs
1361	------------------------------------------
1362	
1363		Starting with version 3.0.0, Channel Bonding may be configured
1364	via the sysfs interface.  This interface allows dynamic configuration
1365	of all bonds in the system without unloading the module.  It also
1366	allows for adding and removing bonds at runtime.  Ifenslave is no
1367	longer required, though it is still supported.
1368	
1369		Use of the sysfs interface allows you to use multiple bonds
1370	with different configurations without having to reload the module.
1371	It also allows you to use multiple, differently configured bonds when
1372	bonding is compiled into the kernel.
1373	
1374		You must have the sysfs filesystem mounted to configure
1375	bonding this way.  The examples in this document assume that you
1376	are using the standard mount point for sysfs, e.g. /sys.  If your
1377	sysfs filesystem is mounted elsewhere, you will need to adjust the
1378	example paths accordingly.
1379	
1380	Creating and Destroying Bonds
1381	-----------------------------
1382	To add a new bond foo:
1383	# echo +foo > /sys/class/net/bonding_masters
1384	
1385	To remove an existing bond bar:
1386	# echo -bar > /sys/class/net/bonding_masters
1387	
1388	To show all existing bonds:
1389	# cat /sys/class/net/bonding_masters
1390	
1391	NOTE: due to 4K size limitation of sysfs files, this list may be
1392	truncated if you have more than a few hundred bonds.  This is unlikely
1393	to occur under normal operating conditions.
1394	
1395	Adding and Removing Slaves
1396	--------------------------
1397		Interfaces may be enslaved to a bond using the file
1398	/sys/class/net/<bond>/bonding/slaves.  The semantics for this file
1399	are the same as for the bonding_masters file.
1400	
1401	To enslave interface eth0 to bond bond0:
1402	# ifconfig bond0 up
1403	# echo +eth0 > /sys/class/net/bond0/bonding/slaves
1404	
1405	To free slave eth0 from bond bond0:
1406	# echo -eth0 > /sys/class/net/bond0/bonding/slaves
1407	
1408		When an interface is enslaved to a bond, symlinks between the
1409	two are created in the sysfs filesystem.  In this case, you would get
1410	/sys/class/net/bond0/slave_eth0 pointing to /sys/class/net/eth0, and
1411	/sys/class/net/eth0/master pointing to /sys/class/net/bond0.
1412	
1413		This means that you can tell quickly whether or not an
1414	interface is enslaved by looking for the master symlink.  Thus:
1415	# echo -eth0 > /sys/class/net/eth0/master/bonding/slaves
1416	will free eth0 from whatever bond it is enslaved to, regardless of
1417	the name of the bond interface.
1418	
1419	Changing a Bond's Configuration
1420	-------------------------------
1421		Each bond may be configured individually by manipulating the
1422	files located in /sys/class/net/<bond name>/bonding
1423	
1424		The names of these files correspond directly with the command-
1425	line parameters described elsewhere in this file, and, with the
1426	exception of arp_ip_target, they accept the same values.  To see the
1427	current setting, simply cat the appropriate file.
1428	
1429		A few examples will be given here; for specific usage
1430	guidelines for each parameter, see the appropriate section in this
1431	document.
1432	
1433	To configure bond0 for balance-alb mode:
1434	# ifconfig bond0 down
1435	# echo 6 > /sys/class/net/bond0/bonding/mode
1436	 - or -
1437	# echo balance-alb > /sys/class/net/bond0/bonding/mode
1438		NOTE: The bond interface must be down before the mode can be
1439	changed.
1440	
1441	To enable MII monitoring on bond0 with a 1 second interval:
1442	# echo 1000 > /sys/class/net/bond0/bonding/miimon
1443		NOTE: If ARP monitoring is enabled, it will disabled when MII
1444	monitoring is enabled, and vice-versa.
1445	
1446	To add ARP targets:
1447	# echo +192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
1448	# echo +192.168.0.101 > /sys/class/net/bond0/bonding/arp_ip_target
1449		NOTE:  up to 16 target addresses may be specified.
1450	
1451	To remove an ARP target:
1452	# echo -192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
1453	
1454	To configure the interval between learning packet transmits:
1455	# echo 12 > /sys/class/net/bond0/bonding/lp_interval
1456		NOTE: the lp_inteval is the number of seconds between instances where
1457	the bonding driver sends learning packets to each slaves peer switch.  The
1458	default interval is 1 second.
1459	
1460	Example Configuration
1461	---------------------
1462		We begin with the same example that is shown in section 3.3,
1463	executed with sysfs, and without using ifenslave.
1464	
1465		To make a simple bond of two e100 devices (presumed to be eth0
1466	and eth1), and have it persist across reboots, edit the appropriate
1467	file (/etc/init.d/boot.local or /etc/rc.d/rc.local), and add the
1468	following:
1469	
1470	modprobe bonding
1471	modprobe e100
1472	echo balance-alb > /sys/class/net/bond0/bonding/mode
1473	ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
1474	echo 100 > /sys/class/net/bond0/bonding/miimon
1475	echo +eth0 > /sys/class/net/bond0/bonding/slaves
1476	echo +eth1 > /sys/class/net/bond0/bonding/slaves
1477	
1478		To add a second bond, with two e1000 interfaces in
1479	active-backup mode, using ARP monitoring, add the following lines to
1480	your init script:
1481	
1482	modprobe e1000
1483	echo +bond1 > /sys/class/net/bonding_masters
1484	echo active-backup > /sys/class/net/bond1/bonding/mode
1485	ifconfig bond1 192.168.2.1 netmask 255.255.255.0 up
1486	echo +192.168.2.100 /sys/class/net/bond1/bonding/arp_ip_target
1487	echo 2000 > /sys/class/net/bond1/bonding/arp_interval
1488	echo +eth2 > /sys/class/net/bond1/bonding/slaves
1489	echo +eth3 > /sys/class/net/bond1/bonding/slaves
1490	
1491	3.5 Configuration with Interfaces Support
1492	-----------------------------------------
1493	
1494	        This section applies to distros which use /etc/network/interfaces file
1495	to describe network interface configuration, most notably Debian and it's
1496	derivatives.
1497	
1498		The ifup and ifdown commands on Debian don't support bonding out of
1499	the box. The ifenslave-2.6 package should be installed to provide bonding
1500	support.  Once installed, this package will provide bond-* options to be used
1501	into /etc/network/interfaces.
1502	
1503		Note that ifenslave-2.6 package will load the bonding module and use
1504	the ifenslave command when appropriate.
1505	
1506	Example Configurations
1507	----------------------
1508	
1509	In /etc/network/interfaces, the following stanza will configure bond0, in
1510	active-backup mode, with eth0 and eth1 as slaves.
1511	
1512	auto bond0
1513	iface bond0 inet dhcp
1514		bond-slaves eth0 eth1
1515		bond-mode active-backup
1516		bond-miimon 100
1517		bond-primary eth0 eth1
1518	
1519	If the above configuration doesn't work, you might have a system using
1520	upstart for system startup. This is most notably true for recent
1521	Ubuntu versions. The following stanza in /etc/network/interfaces will
1522	produce the same result on those systems.
1523	
1524	auto bond0
1525	iface bond0 inet dhcp
1526		bond-slaves none
1527		bond-mode active-backup
1528		bond-miimon 100
1529	
1530	auto eth0
1531	iface eth0 inet manual
1532		bond-master bond0
1533		bond-primary eth0 eth1
1534	
1535	auto eth1
1536	iface eth1 inet manual
1537		bond-master bond0
1538		bond-primary eth0 eth1
1539	
1540	For a full list of bond-* supported options in /etc/network/interfaces and some
1541	more advanced examples tailored to you particular distros, see the files in
1542	/usr/share/doc/ifenslave-2.6.
1543	
1544	3.6 Overriding Configuration for Special Cases
1545	----------------------------------------------
1546	
1547	When using the bonding driver, the physical port which transmits a frame is
1548	typically selected by the bonding driver, and is not relevant to the user or
1549	system administrator.  The output port is simply selected using the policies of
1550	the selected bonding mode.  On occasion however, it is helpful to direct certain
1551	classes of traffic to certain physical interfaces on output to implement
1552	slightly more complex policies.  For example, to reach a web server over a
1553	bonded interface in which eth0 connects to a private network, while eth1
1554	connects via a public network, it may be desirous to bias the bond to send said
1555	traffic over eth0 first, using eth1 only as a fall back, while all other traffic
1556	can safely be sent over either interface.  Such configurations may be achieved
1557	using the traffic control utilities inherent in linux.
1558	
1559	By default the bonding driver is multiqueue aware and 16 queues are created
1560	when the driver initializes (see Documentation/networking/multiqueue.txt
1561	for details).  If more or less queues are desired the module parameter
1562	tx_queues can be used to change this value.  There is no sysfs parameter
1563	available as the allocation is done at module init time.
1564	
1565	The output of the file /proc/net/bonding/bondX has changed so the output Queue
1566	ID is now printed for each slave:
1567	
1568	Bonding Mode: fault-tolerance (active-backup)
1569	Primary Slave: None
1570	Currently Active Slave: eth0
1571	MII Status: up
1572	MII Polling Interval (ms): 0
1573	Up Delay (ms): 0
1574	Down Delay (ms): 0
1575	
1576	Slave Interface: eth0
1577	MII Status: up
1578	Link Failure Count: 0
1579	Permanent HW addr: 00:1a:a0:12:8f:cb
1580	Slave queue ID: 0
1581	
1582	Slave Interface: eth1
1583	MII Status: up
1584	Link Failure Count: 0
1585	Permanent HW addr: 00:1a:a0:12:8f:cc
1586	Slave queue ID: 2
1587	
1588	The queue_id for a slave can be set using the command:
1589	
1590	# echo "eth1:2" > /sys/class/net/bond0/bonding/queue_id
1591	
1592	Any interface that needs a queue_id set should set it with multiple calls
1593	like the one above until proper priorities are set for all interfaces.  On
1594	distributions that allow configuration via initscripts, multiple 'queue_id'
1595	arguments can be added to BONDING_OPTS to set all needed slave queues.
1596	
1597	These queue id's can be used in conjunction with the tc utility to configure
1598	a multiqueue qdisc and filters to bias certain traffic to transmit on certain
1599	slave devices.  For instance, say we wanted, in the above configuration to
1600	force all traffic bound to 192.168.1.100 to use eth1 in the bond as its output
1601	device. The following commands would accomplish this:
1602	
1603	# tc qdisc add dev bond0 handle 1 root multiq
1604	
1605	# tc filter add dev bond0 protocol ip parent 1: prio 1 u32 match ip dst \
1606		192.168.1.100 action skbedit queue_mapping 2
1607	
1608	These commands tell the kernel to attach a multiqueue queue discipline to the
1609	bond0 interface and filter traffic enqueued to it, such that packets with a dst
1610	ip of 192.168.1.100 have their output queue mapping value overwritten to 2.
1611	This value is then passed into the driver, causing the normal output path
1612	selection policy to be overridden, selecting instead qid 2, which maps to eth1.
1613	
1614	Note that qid values begin at 1.  Qid 0 is reserved to initiate to the driver
1615	that normal output policy selection should take place.  One benefit to simply
1616	leaving the qid for a slave to 0 is the multiqueue awareness in the bonding
1617	driver that is now present.  This awareness allows tc filters to be placed on
1618	slave devices as well as bond devices and the bonding driver will simply act as
1619	a pass-through for selecting output queues on the slave device rather than 
1620	output port selection.
1621	
1622	This feature first appeared in bonding driver version 3.7.0 and support for
1623	output slave selection was limited to round-robin and active-backup modes.
1624	
1625	4 Querying Bonding Configuration
1626	=================================
1627	
1628	4.1 Bonding Configuration
1629	-------------------------
1630	
1631		Each bonding device has a read-only file residing in the
1632	/proc/net/bonding directory.  The file contents include information
1633	about the bonding configuration, options and state of each slave.
1634	
1635		For example, the contents of /proc/net/bonding/bond0 after the
1636	driver is loaded with parameters of mode=0 and miimon=1000 is
1637	generally as follows:
1638	
1639		Ethernet Channel Bonding Driver: 2.6.1 (October 29, 2004)
1640	        Bonding Mode: load balancing (round-robin)
1641	        Currently Active Slave: eth0
1642	        MII Status: up
1643	        MII Polling Interval (ms): 1000
1644	        Up Delay (ms): 0
1645	        Down Delay (ms): 0
1646	
1647	        Slave Interface: eth1
1648	        MII Status: up
1649	        Link Failure Count: 1
1650	
1651	        Slave Interface: eth0
1652	        MII Status: up
1653	        Link Failure Count: 1
1654	
1655		The precise format and contents will change depending upon the
1656	bonding configuration, state, and version of the bonding driver.
1657	
1658	4.2 Network configuration
1659	-------------------------
1660	
1661		The network configuration can be inspected using the ifconfig
1662	command.  Bonding devices will have the MASTER flag set; Bonding slave
1663	devices will have the SLAVE flag set.  The ifconfig output does not
1664	contain information on which slaves are associated with which masters.
1665	
1666		In the example below, the bond0 interface is the master
1667	(MASTER) while eth0 and eth1 are slaves (SLAVE). Notice all slaves of
1668	bond0 have the same MAC address (HWaddr) as bond0 for all modes except
1669	TLB and ALB that require a unique MAC address for each slave.
1670	
1671	# /sbin/ifconfig
1672	bond0     Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
1673	          inet addr:XXX.XXX.XXX.YYY  Bcast:XXX.XXX.XXX.255  Mask:255.255.252.0
1674	          UP BROADCAST RUNNING MASTER MULTICAST  MTU:1500  Metric:1
1675	          RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0
1676	          TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0
1677	          collisions:0 txqueuelen:0
1678	
1679	eth0      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
1680	          UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
1681	          RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0
1682	          TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0
1683	          collisions:0 txqueuelen:100
1684	          Interrupt:10 Base address:0x1080
1685	
1686	eth1      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
1687	          UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
1688	          RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0
1689	          TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0
1690	          collisions:0 txqueuelen:100
1691	          Interrupt:9 Base address:0x1400
1692	
1693	5. Switch Configuration
1694	=======================
1695	
1696		For this section, "switch" refers to whatever system the
1697	bonded devices are directly connected to (i.e., where the other end of
1698	the cable plugs into).  This may be an actual dedicated switch device,
1699	or it may be another regular system (e.g., another computer running
1700	Linux),
1701	
1702		The active-backup, balance-tlb and balance-alb modes do not
1703	require any specific configuration of the switch.
1704	
1705		The 802.3ad mode requires that the switch have the appropriate
1706	ports configured as an 802.3ad aggregation.  The precise method used
1707	to configure this varies from switch to switch, but, for example, a
1708	Cisco 3550 series switch requires that the appropriate ports first be
1709	grouped together in a single etherchannel instance, then that
1710	etherchannel is set to mode "lacp" to enable 802.3ad (instead of
1711	standard EtherChannel).
1712	
1713		The balance-rr, balance-xor and broadcast modes generally
1714	require that the switch have the appropriate ports grouped together.
1715	The nomenclature for such a group differs between switches, it may be
1716	called an "etherchannel" (as in the Cisco example, above), a "trunk
1717	group" or some other similar variation.  For these modes, each switch
1718	will also have its own configuration options for the switch's transmit
1719	policy to the bond.  Typical choices include XOR of either the MAC or
1720	IP addresses.  The transmit policy of the two peers does not need to
1721	match.  For these three modes, the bonding mode really selects a
1722	transmit policy for an EtherChannel group; all three will interoperate
1723	with another EtherChannel group.
1724	
1725	
1726	6. 802.1q VLAN Support
1727	======================
1728	
1729		It is possible to configure VLAN devices over a bond interface
1730	using the 8021q driver.  However, only packets coming from the 8021q
1731	driver and passing through bonding will be tagged by default.  Self
1732	generated packets, for example, bonding's learning packets or ARP
1733	packets generated by either ALB mode or the ARP monitor mechanism, are
1734	tagged internally by bonding itself.  As a result, bonding must
1735	"learn" the VLAN IDs configured above it, and use those IDs to tag
1736	self generated packets.
1737	
1738		For reasons of simplicity, and to support the use of adapters
1739	that can do VLAN hardware acceleration offloading, the bonding
1740	interface declares itself as fully hardware offloading capable, it gets
1741	the add_vid/kill_vid notifications to gather the necessary
1742	information, and it propagates those actions to the slaves.  In case
1743	of mixed adapter types, hardware accelerated tagged packets that
1744	should go through an adapter that is not offloading capable are
1745	"un-accelerated" by the bonding driver so the VLAN tag sits in the
1746	regular location.
1747	
1748		VLAN interfaces *must* be added on top of a bonding interface
1749	only after enslaving at least one slave.  The bonding interface has a
1750	hardware address of 00:00:00:00:00:00 until the first slave is added.
1751	If the VLAN interface is created prior to the first enslavement, it
1752	would pick up the all-zeroes hardware address.  Once the first slave
1753	is attached to the bond, the bond device itself will pick up the
1754	slave's hardware address, which is then available for the VLAN device.
1755	
1756		Also, be aware that a similar problem can occur if all slaves
1757	are released from a bond that still has one or more VLAN interfaces on
1758	top of it.  When a new slave is added, the bonding interface will
1759	obtain its hardware address from the first slave, which might not
1760	match the hardware address of the VLAN interfaces (which was
1761	ultimately copied from an earlier slave).
1762	
1763		There are two methods to insure that the VLAN device operates
1764	with the correct hardware address if all slaves are removed from a
1765	bond interface:
1766	
1767		1. Remove all VLAN interfaces then recreate them
1768	
1769		2. Set the bonding interface's hardware address so that it
1770	matches the hardware address of the VLAN interfaces.
1771	
1772		Note that changing a VLAN interface's HW address would set the
1773	underlying device -- i.e. the bonding interface -- to promiscuous
1774	mode, which might not be what you want.
1775	
1776	
1777	7. Link Monitoring
1778	==================
1779	
1780		The bonding driver at present supports two schemes for
1781	monitoring a slave device's link state: the ARP monitor and the MII
1782	monitor.
1783	
1784		At the present time, due to implementation restrictions in the
1785	bonding driver itself, it is not possible to enable both ARP and MII
1786	monitoring simultaneously.
1787	
1788	7.1 ARP Monitor Operation
1789	-------------------------
1790	
1791		The ARP monitor operates as its name suggests: it sends ARP
1792	queries to one or more designated peer systems on the network, and
1793	uses the response as an indication that the link is operating.  This
1794	gives some assurance that traffic is actually flowing to and from one
1795	or more peers on the local network.
1796	
1797		The ARP monitor relies on the device driver itself to verify
1798	that traffic is flowing.  In particular, the driver must keep up to
1799	date the last receive time, dev->last_rx, and transmit start time,
1800	dev->trans_start.  If these are not updated by the driver, then the
1801	ARP monitor will immediately fail any slaves using that driver, and
1802	those slaves will stay down.  If networking monitoring (tcpdump, etc)
1803	shows the ARP requests and replies on the network, then it may be that
1804	your device driver is not updating last_rx and trans_start.
1805	
1806	7.2 Configuring Multiple ARP Targets
1807	------------------------------------
1808	
1809		While ARP monitoring can be done with just one target, it can
1810	be useful in a High Availability setup to have several targets to
1811	monitor.  In the case of just one target, the target itself may go
1812	down or have a problem making it unresponsive to ARP requests.  Having
1813	an additional target (or several) increases the reliability of the ARP
1814	monitoring.
1815	
1816		Multiple ARP targets must be separated by commas as follows:
1817	
1818	# example options for ARP monitoring with three targets
1819	alias bond0 bonding
1820	options bond0 arp_interval=60 arp_ip_target=192.168.0.1,192.168.0.3,192.168.0.9
1821	
1822		For just a single target the options would resemble:
1823	
1824	# example options for ARP monitoring with one target
1825	alias bond0 bonding
1826	options bond0 arp_interval=60 arp_ip_target=192.168.0.100
1827	
1828	
1829	7.3 MII Monitor Operation
1830	-------------------------
1831	
1832		The MII monitor monitors only the carrier state of the local
1833	network interface.  It accomplishes this in one of three ways: by
1834	depending upon the device driver to maintain its carrier state, by
1835	querying the device's MII registers, or by making an ethtool query to
1836	the device.
1837	
1838		If the use_carrier module parameter is 1 (the default value),
1839	then the MII monitor will rely on the driver for carrier state
1840	information (via the netif_carrier subsystem).  As explained in the
1841	use_carrier parameter information, above, if the MII monitor fails to
1842	detect carrier loss on the device (e.g., when the cable is physically
1843	disconnected), it may be that the driver does not support
1844	netif_carrier.
1845	
1846		If use_carrier is 0, then the MII monitor will first query the
1847	device's (via ioctl) MII registers and check the link state.  If that
1848	request fails (not just that it returns carrier down), then the MII
1849	monitor will make an ethtool ETHOOL_GLINK request to attempt to obtain
1850	the same information.  If both methods fail (i.e., the driver either
1851	does not support or had some error in processing both the MII register
1852	and ethtool requests), then the MII monitor will assume the link is
1853	up.
1854	
1855	8. Potential Sources of Trouble
1856	===============================
1857	
1858	8.1 Adventures in Routing
1859	-------------------------
1860	
1861		When bonding is configured, it is important that the slave
1862	devices not have routes that supersede routes of the master (or,
1863	generally, not have routes at all).  For example, suppose the bonding
1864	device bond0 has two slaves, eth0 and eth1, and the routing table is
1865	as follows:
1866	
1867	Kernel IP routing table
1868	Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
1869	10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth0
1870	10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth1
1871	10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 bond0
1872	127.0.0.0       0.0.0.0         255.0.0.0       U        40 0          0 lo
1873	
1874		This routing configuration will likely still update the
1875	receive/transmit times in the driver (needed by the ARP monitor), but
1876	may bypass the bonding driver (because outgoing traffic to, in this
1877	case, another host on network 10 would use eth0 or eth1 before bond0).
1878	
1879		The ARP monitor (and ARP itself) may become confused by this
1880	configuration, because ARP requests (generated by the ARP monitor)
1881	will be sent on one interface (bond0), but the corresponding reply
1882	will arrive on a different interface (eth0).  This reply looks to ARP
1883	as an unsolicited ARP reply (because ARP matches replies on an
1884	interface basis), and is discarded.  The MII monitor is not affected
1885	by the state of the routing table.
1886	
1887		The solution here is simply to insure that slaves do not have
1888	routes of their own, and if for some reason they must, those routes do
1889	not supersede routes of their master.  This should generally be the
1890	case, but unusual configurations or errant manual or automatic static
1891	route additions may cause trouble.
1892	
1893	8.2 Ethernet Device Renaming
1894	----------------------------
1895	
1896		On systems with network configuration scripts that do not
1897	associate physical devices directly with network interface names (so
1898	that the same physical device always has the same "ethX" name), it may
1899	be necessary to add some special logic to config files in
1900	/etc/modprobe.d/.
1901	
1902		For example, given a modules.conf containing the following:
1903	
1904	alias bond0 bonding
1905	options bond0 mode=some-mode miimon=50
1906	alias eth0 tg3
1907	alias eth1 tg3
1908	alias eth2 e1000
1909	alias eth3 e1000
1910	
1911		If neither eth0 and eth1 are slaves to bond0, then when the
1912	bond0 interface comes up, the devices may end up reordered.  This
1913	happens because bonding is loaded first, then its slave device's
1914	drivers are loaded next.  Since no other drivers have been loaded,
1915	when the e1000 driver loads, it will receive eth0 and eth1 for its
1916	devices, but the bonding configuration tries to enslave eth2 and eth3
1917	(which may later be assigned to the tg3 devices).
1918	
1919		Adding the following:
1920	
1921	add above bonding e1000 tg3
1922	
1923		causes modprobe to load e1000 then tg3, in that order, when
1924	bonding is loaded.  This command is fully documented in the
1925	modules.conf manual page.
1926	
1927		On systems utilizing modprobe an equivalent problem can occur.
1928	In this case, the following can be added to config files in
1929	/etc/modprobe.d/ as:
1930	
1931	softdep bonding pre: tg3 e1000
1932	
1933		This will load tg3 and e1000 modules before loading the bonding one.
1934	Full documentation on this can be found in the modprobe.d and modprobe
1935	manual pages.
1936	
1937	8.3. Painfully Slow Or No Failed Link Detection By Miimon
1938	---------------------------------------------------------
1939	
1940		By default, bonding enables the use_carrier option, which
1941	instructs bonding to trust the driver to maintain carrier state.
1942	
1943		As discussed in the options section, above, some drivers do
1944	not support the netif_carrier_on/_off link state tracking system.
1945	With use_carrier enabled, bonding will always see these links as up,
1946	regardless of their actual state.
1947	
1948		Additionally, other drivers do support netif_carrier, but do
1949	not maintain it in real time, e.g., only polling the link state at
1950	some fixed interval.  In this case, miimon will detect failures, but
1951	only after some long period of time has expired.  If it appears that
1952	miimon is very slow in detecting link failures, try specifying
1953	use_carrier=0 to see if that improves the failure detection time.  If
1954	it does, then it may be that the driver checks the carrier state at a
1955	fixed interval, but does not cache the MII register values (so the
1956	use_carrier=0 method of querying the registers directly works).  If
1957	use_carrier=0 does not improve the failover, then the driver may cache
1958	the registers, or the problem may be elsewhere.
1959	
1960		Also, remember that miimon only checks for the device's
1961	carrier state.  It has no way to determine the state of devices on or
1962	beyond other ports of a switch, or if a switch is refusing to pass
1963	traffic while still maintaining carrier on.
1964	
1965	9. SNMP agents
1966	===============
1967	
1968		If running SNMP agents, the bonding driver should be loaded
1969	before any network drivers participating in a bond.  This requirement
1970	is due to the interface index (ipAdEntIfIndex) being associated to
1971	the first interface found with a given IP address.  That is, there is
1972	only one ipAdEntIfIndex for each IP address.  For example, if eth0 and
1973	eth1 are slaves of bond0 and the driver for eth0 is loaded before the
1974	bonding driver, the interface for the IP address will be associated
1975	with the eth0 interface.  This configuration is shown below, the IP
1976	address 192.168.1.1 has an interface index of 2 which indexes to eth0
1977	in the ifDescr table (ifDescr.2).
1978	
1979	     interfaces.ifTable.ifEntry.ifDescr.1 = lo
1980	     interfaces.ifTable.ifEntry.ifDescr.2 = eth0
1981	     interfaces.ifTable.ifEntry.ifDescr.3 = eth1
1982	     interfaces.ifTable.ifEntry.ifDescr.4 = eth2
1983	     interfaces.ifTable.ifEntry.ifDescr.5 = eth3
1984	     interfaces.ifTable.ifEntry.ifDescr.6 = bond0
1985	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 5
1986	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
1987	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 4
1988	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
1989	
1990		This problem is avoided by loading the bonding driver before
1991	any network drivers participating in a bond.  Below is an example of
1992	loading the bonding driver first, the IP address 192.168.1.1 is
1993	correctly associated with ifDescr.2.
1994	
1995	     interfaces.ifTable.ifEntry.ifDescr.1 = lo
1996	     interfaces.ifTable.ifEntry.ifDescr.2 = bond0
1997	     interfaces.ifTable.ifEntry.ifDescr.3 = eth0
1998	     interfaces.ifTable.ifEntry.ifDescr.4 = eth1
1999	     interfaces.ifTable.ifEntry.ifDescr.5 = eth2
2000	     interfaces.ifTable.ifEntry.ifDescr.6 = eth3
2001	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 6
2002	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
2003	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 5
2004	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
2005	
2006		While some distributions may not report the interface name in
2007	ifDescr, the association between the IP address and IfIndex remains
2008	and SNMP functions such as Interface_Scan_Next will report that
2009	association.
2010	
2011	10. Promiscuous mode
2012	====================
2013	
2014		When running network monitoring tools, e.g., tcpdump, it is
2015	common to enable promiscuous mode on the device, so that all traffic
2016	is seen (instead of seeing only traffic destined for the local host).
2017	The bonding driver handles promiscuous mode changes to the bonding
2018	master device (e.g., bond0), and propagates the setting to the slave
2019	devices.
2020	
2021		For the balance-rr, balance-xor, broadcast, and 802.3ad modes,
2022	the promiscuous mode setting is propagated to all slaves.
2023	
2024		For the active-backup, balance-tlb and balance-alb modes, the
2025	promiscuous mode setting is propagated only to the active slave.
2026	
2027		For balance-tlb mode, the active slave is the slave currently
2028	receiving inbound traffic.
2029	
2030		For balance-alb mode, the active slave is the slave used as a
2031	"primary."  This slave is used for mode-specific control traffic, for
2032	sending to peers that are unassigned or if the load is unbalanced.
2033	
2034		For the active-backup, balance-tlb and balance-alb modes, when
2035	the active slave changes (e.g., due to a link failure), the
2036	promiscuous setting will be propagated to the new active slave.
2037	
2038	11. Configuring Bonding for High Availability
2039	=============================================
2040	
2041		High Availability refers to configurations that provide
2042	maximum network availability by having redundant or backup devices,
2043	links or switches between the host and the rest of the world.  The
2044	goal is to provide the maximum availability of network connectivity
2045	(i.e., the network always works), even though other configurations
2046	could provide higher throughput.
2047	
2048	11.1 High Availability in a Single Switch Topology
2049	--------------------------------------------------
2050	
2051		If two hosts (or a host and a single switch) are directly
2052	connected via multiple physical links, then there is no availability
2053	penalty to optimizing for maximum bandwidth.  In this case, there is
2054	only one switch (or peer), so if it fails, there is no alternative
2055	access to fail over to.  Additionally, the bonding load balance modes
2056	support link monitoring of their members, so if individual links fail,
2057	the load will be rebalanced across the remaining devices.
2058	
2059		See Section 12, "Configuring Bonding for Maximum Throughput"
2060	for information on configuring bonding with one peer device.
2061	
2062	11.2 High Availability in a Multiple Switch Topology
2063	----------------------------------------------------
2064	
2065		With multiple switches, the configuration of bonding and the
2066	network changes dramatically.  In multiple switch topologies, there is
2067	a trade off between network availability and usable bandwidth.
2068	
2069		Below is a sample network, configured to maximize the
2070	availability of the network:
2071	
2072	                |                                     |
2073	                |port3                           port3|
2074	          +-----+----+                          +-----+----+
2075	          |          |port2       ISL      port2|          |
2076	          | switch A +--------------------------+ switch B |
2077	          |          |                          |          |
2078	          +-----+----+                          +-----++---+
2079	                |port1                           port1|
2080	                |             +-------+               |
2081	                +-------------+ host1 +---------------+
2082	                         eth0 +-------+ eth1
2083	
2084		In this configuration, there is a link between the two
2085	switches (ISL, or inter switch link), and multiple ports connecting to
2086	the outside world ("port3" on each switch).  There is no technical
2087	reason that this could not be extended to a third switch.
2088	
2089	11.2.1 HA Bonding Mode Selection for Multiple Switch Topology
2090	-------------------------------------------------------------
2091	
2092		In a topology such as the example above, the active-backup and
2093	broadcast modes are the only useful bonding modes when optimizing for
2094	availability; the other modes require all links to terminate on the
2095	same peer for them to behave rationally.
2096	
2097	active-backup: This is generally the preferred mode, particularly if
2098		the switches have an ISL and play together well.  If the
2099		network configuration is such that one switch is specifically
2100		a backup switch (e.g., has lower capacity, higher cost, etc),
2101		then the primary option can be used to insure that the
2102		preferred link is always used when it is available.
2103	
2104	broadcast: This mode is really a special purpose mode, and is suitable
2105		only for very specific needs.  For example, if the two
2106		switches are not connected (no ISL), and the networks beyond
2107		them are totally independent.  In this case, if it is
2108		necessary for some specific one-way traffic to reach both
2109		independent networks, then the broadcast mode may be suitable.
2110	
2111	11.2.2 HA Link Monitoring Selection for Multiple Switch Topology
2112	----------------------------------------------------------------
2113	
2114		The choice of link monitoring ultimately depends upon your
2115	switch.  If the switch can reliably fail ports in response to other
2116	failures, then either the MII or ARP monitors should work.  For
2117	example, in the above example, if the "port3" link fails at the remote
2118	end, the MII monitor has no direct means to detect this.  The ARP
2119	monitor could be configured with a target at the remote end of port3,
2120	thus detecting that failure without switch support.
2121	
2122		In general, however, in a multiple switch topology, the ARP
2123	monitor can provide a higher level of reliability in detecting end to
2124	end connectivity failures (which may be caused by the failure of any
2125	individual component to pass traffic for any reason).  Additionally,
2126	the ARP monitor should be configured with multiple targets (at least
2127	one for each switch in the network).  This will insure that,
2128	regardless of which switch is active, the ARP monitor has a suitable
2129	target to query.
2130	
2131		Note, also, that of late many switches now support a functionality
2132	generally referred to as "trunk failover."  This is a feature of the
2133	switch that causes the link state of a particular switch port to be set
2134	down (or up) when the state of another switch port goes down (or up).
2135	Its purpose is to propagate link failures from logically "exterior" ports
2136	to the logically "interior" ports that bonding is able to monitor via
2137	miimon.  Availability and configuration for trunk failover varies by
2138	switch, but this can be a viable alternative to the ARP monitor when using
2139	suitable switches.
2140	
2141	12. Configuring Bonding for Maximum Throughput
2142	==============================================
2143	
2144	12.1 Maximizing Throughput in a Single Switch Topology
2145	------------------------------------------------------
2146	
2147		In a single switch configuration, the best method to maximize
2148	throughput depends upon the application and network environment.  The
2149	various load balancing modes each have strengths and weaknesses in
2150	different environments, as detailed below.
2151	
2152		For this discussion, we will break down the topologies into
2153	two categories.  Depending upon the destination of most traffic, we
2154	categorize them into either "gatewayed" or "local" configurations.
2155	
2156		In a gatewayed configuration, the "switch" is acting primarily
2157	as a router, and the majority of traffic passes through this router to
2158	other networks.  An example would be the following:
2159	
2160	
2161	     +----------+                     +----------+
2162	     |          |eth0            port1|          | to other networks
2163	     | Host A   +---------------------+ router   +------------------->
2164	     |          +---------------------+          | Hosts B and C are out
2165	     |          |eth1            port2|          | here somewhere
2166	     +----------+                     +----------+
2167	
2168		The router may be a dedicated router device, or another host
2169	acting as a gateway.  For our discussion, the important point is that
2170	the majority of traffic from Host A will pass through the router to
2171	some other network before reaching its final destination.
2172	
2173		In a gatewayed network configuration, although Host A may
2174	communicate with many other systems, all of its traffic will be sent
2175	and received via one other peer on the local network, the router.
2176	
2177		Note that the case of two systems connected directly via
2178	multiple physical links is, for purposes of configuring bonding, the
2179	same as a gatewayed configuration.  In that case, it happens that all
2180	traffic is destined for the "gateway" itself, not some other network
2181	beyond the gateway.
2182	
2183		In a local configuration, the "switch" is acting primarily as
2184	a switch, and the majority of traffic passes through this switch to
2185	reach other stations on the same network.  An example would be the
2186	following:
2187	
2188	    +----------+            +----------+       +--------+
2189	    |          |eth0   port1|          +-------+ Host B |
2190	    |  Host A  +------------+  switch  |port3  +--------+
2191	    |          +------------+          |                  +--------+
2192	    |          |eth1   port2|          +------------------+ Host C |
2193	    +----------+            +----------+port4             +--------+
2194	
2195	
2196		Again, the switch may be a dedicated switch device, or another
2197	host acting as a gateway.  For our discussion, the important point is
2198	that the majority of traffic from Host A is destined for other hosts
2199	on the same local network (Hosts B and C in the above example).
2200	
2201		In summary, in a gatewayed configuration, traffic to and from
2202	the bonded device will be to the same MAC level peer on the network
2203	(the gateway itself, i.e., the router), regardless of its final
2204	destination.  In a local configuration, traffic flows directly to and
2205	from the final destinations, thus, each destination (Host B, Host C)
2206	will be addressed directly by their individual MAC addresses.
2207	
2208		This distinction between a gatewayed and a local network
2209	configuration is important because many of the load balancing modes
2210	available use the MAC addresses of the local network source and
2211	destination to make load balancing decisions.  The behavior of each
2212	mode is described below.
2213	
2214	
2215	12.1.1 MT Bonding Mode Selection for Single Switch Topology
2216	-----------------------------------------------------------
2217	
2218		This configuration is the easiest to set up and to understand,
2219	although you will have to decide which bonding mode best suits your
2220	needs.  The trade offs for each mode are detailed below:
2221	
2222	balance-rr: This mode is the only mode that will permit a single
2223		TCP/IP connection to stripe traffic across multiple
2224		interfaces. It is therefore the only mode that will allow a
2225		single TCP/IP stream to utilize more than one interface's
2226		worth of throughput.  This comes at a cost, however: the
2227		striping generally results in peer systems receiving packets out
2228		of order, causing TCP/IP's congestion control system to kick
2229		in, often by retransmitting segments.
2230	
2231		It is possible to adjust TCP/IP's congestion limits by
2232		altering the net.ipv4.tcp_reordering sysctl parameter.  The
2233		usual default value is 3. But keep in mind TCP stack is able
2234		to automatically increase this when it detects reorders.
2235	
2236		Note that the fraction of packets that will be delivered out of
2237		order is highly variable, and is unlikely to be zero.  The level
2238		of reordering depends upon a variety of factors, including the
2239		networking interfaces, the switch, and the topology of the
2240		configuration.  Speaking in general terms, higher speed network
2241		cards produce more reordering (due to factors such as packet
2242		coalescing), and a "many to many" topology will reorder at a
2243		higher rate than a "many slow to one fast" configuration.
2244	
2245		Many switches do not support any modes that stripe traffic
2246		(instead choosing a port based upon IP or MAC level addresses);
2247		for those devices, traffic for a particular connection flowing
2248		through the switch to a balance-rr bond will not utilize greater
2249		than one interface's worth of bandwidth.
2250	
2251		If you are utilizing protocols other than TCP/IP, UDP for
2252		example, and your application can tolerate out of order
2253		delivery, then this mode can allow for single stream datagram
2254		performance that scales near linearly as interfaces are added
2255		to the bond.
2256	
2257		This mode requires the switch to have the appropriate ports
2258		configured for "etherchannel" or "trunking."
2259	
2260	active-backup: There is not much advantage in this network topology to
2261		the active-backup mode, as the inactive backup devices are all
2262		connected to the same peer as the primary.  In this case, a
2263		load balancing mode (with link monitoring) will provide the
2264		same level of network availability, but with increased
2265		available bandwidth.  On the plus side, active-backup mode
2266		does not require any configuration of the switch, so it may
2267		have value if the hardware available does not support any of
2268		the load balance modes.
2269	
2270	balance-xor: This mode will limit traffic such that packets destined
2271		for specific peers will always be sent over the same
2272		interface.  Since the destination is determined by the MAC
2273		addresses involved, this mode works best in a "local" network
2274		configuration (as described above), with destinations all on
2275		the same local network.  This mode is likely to be suboptimal
2276		if all your traffic is passed through a single router (i.e., a
2277		"gatewayed" network configuration, as described above).
2278	
2279		As with balance-rr, the switch ports need to be configured for
2280		"etherchannel" or "trunking."
2281	
2282	broadcast: Like active-backup, there is not much advantage to this
2283		mode in this type of network topology.
2284	
2285	802.3ad: This mode can be a good choice for this type of network
2286		topology.  The 802.3ad mode is an IEEE standard, so all peers
2287		that implement 802.3ad should interoperate well.  The 802.3ad
2288		protocol includes automatic configuration of the aggregates,
2289		so minimal manual configuration of the switch is needed
2290		(typically only to designate that some set of devices is
2291		available for 802.3ad).  The 802.3ad standard also mandates
2292		that frames be delivered in order (within certain limits), so
2293		in general single connections will not see misordering of
2294		packets.  The 802.3ad mode does have some drawbacks: the
2295		standard mandates that all devices in the aggregate operate at
2296		the same speed and duplex.  Also, as with all bonding load
2297		balance modes other than balance-rr, no single connection will
2298		be able to utilize more than a single interface's worth of
2299		bandwidth.  
2300	
2301		Additionally, the linux bonding 802.3ad implementation
2302		distributes traffic by peer (using an XOR of MAC addresses
2303		and packet type ID), so in a "gatewayed" configuration, all
2304		outgoing traffic will generally use the same device.  Incoming
2305		traffic may also end up on a single device, but that is
2306		dependent upon the balancing policy of the peer's 8023.ad
2307		implementation.  In a "local" configuration, traffic will be
2308		distributed across the devices in the bond.
2309	
2310		Finally, the 802.3ad mode mandates the use of the MII monitor,
2311		therefore, the ARP monitor is not available in this mode.
2312	
2313	balance-tlb: The balance-tlb mode balances outgoing traffic by peer.
2314		Since the balancing is done according to MAC address, in a
2315		"gatewayed" configuration (as described above), this mode will
2316		send all traffic across a single device.  However, in a
2317		"local" network configuration, this mode balances multiple
2318		local network peers across devices in a vaguely intelligent
2319		manner (not a simple XOR as in balance-xor or 802.3ad mode),
2320		so that mathematically unlucky MAC addresses (i.e., ones that
2321		XOR to the same value) will not all "bunch up" on a single
2322		interface.
2323	
2324		Unlike 802.3ad, interfaces may be of differing speeds, and no
2325		special switch configuration is required.  On the down side,
2326		in this mode all incoming traffic arrives over a single
2327		interface, this mode requires certain ethtool support in the
2328		network device driver of the slave interfaces, and the ARP
2329		monitor is not available.
2330	
2331	balance-alb: This mode is everything that balance-tlb is, and more.
2332		It has all of the features (and restrictions) of balance-tlb,
2333		and will also balance incoming traffic from local network
2334		peers (as described in the Bonding Module Options section,
2335		above).
2336	
2337		The only additional down side to this mode is that the network
2338		device driver must support changing the hardware address while
2339		the device is open.
2340	
2341	12.1.2 MT Link Monitoring for Single Switch Topology
2342	----------------------------------------------------
2343	
2344		The choice of link monitoring may largely depend upon which
2345	mode you choose to use.  The more advanced load balancing modes do not
2346	support the use of the ARP monitor, and are thus restricted to using
2347	the MII monitor (which does not provide as high a level of end to end
2348	assurance as the ARP monitor).
2349	
2350	12.2 Maximum Throughput in a Multiple Switch Topology
2351	-----------------------------------------------------
2352	
2353		Multiple switches may be utilized to optimize for throughput
2354	when they are configured in parallel as part of an isolated network
2355	between two or more systems, for example:
2356	
2357	                       +-----------+
2358	                       |  Host A   | 
2359	                       +-+---+---+-+
2360	                         |   |   |
2361	                +--------+   |   +---------+
2362	                |            |             |
2363	         +------+---+  +-----+----+  +-----+----+
2364	         | Switch A |  | Switch B |  | Switch C |
2365	         +------+---+  +-----+----+  +-----+----+
2366	                |            |             |
2367	                +--------+   |   +---------+
2368	                         |   |   |
2369	                       +-+---+---+-+
2370	                       |  Host B   | 
2371	                       +-----------+
2372	
2373		In this configuration, the switches are isolated from one
2374	another.  One reason to employ a topology such as this is for an
2375	isolated network with many hosts (a cluster configured for high
2376	performance, for example), using multiple smaller switches can be more
2377	cost effective than a single larger switch, e.g., on a network with 24
2378	hosts, three 24 port switches can be significantly less expensive than
2379	a single 72 port switch.
2380	
2381		If access beyond the network is required, an individual host
2382	can be equipped with an additional network device connected to an
2383	external network; this host then additionally acts as a gateway.
2384	
2385	12.2.1 MT Bonding Mode Selection for Multiple Switch Topology
2386	-------------------------------------------------------------
2387	
2388		In actual practice, the bonding mode typically employed in
2389	configurations of this type is balance-rr.  Historically, in this
2390	network configuration, the usual caveats about out of order packet
2391	delivery are mitigated by the use of network adapters that do not do
2392	any kind of packet coalescing (via the use of NAPI, or because the
2393	device itself does not generate interrupts until some number of
2394	packets has arrived).  When employed in this fashion, the balance-rr
2395	mode allows individual connections between two hosts to effectively
2396	utilize greater than one interface's bandwidth.
2397	
2398	12.2.2 MT Link Monitoring for Multiple Switch Topology
2399	------------------------------------------------------
2400	
2401		Again, in actual practice, the MII monitor is most often used
2402	in this configuration, as performance is given preference over
2403	availability.  The ARP monitor will function in this topology, but its
2404	advantages over the MII monitor are mitigated by the volume of probes
2405	needed as the number of systems involved grows (remember that each
2406	host in the network is configured with bonding).
2407	
2408	13. Switch Behavior Issues
2409	==========================
2410	
2411	13.1 Link Establishment and Failover Delays
2412	-------------------------------------------
2413	
2414		Some switches exhibit undesirable behavior with regard to the
2415	timing of link up and down reporting by the switch.
2416	
2417		First, when a link comes up, some switches may indicate that
2418	the link is up (carrier available), but not pass traffic over the
2419	interface for some period of time.  This delay is typically due to
2420	some type of autonegotiation or routing protocol, but may also occur
2421	during switch initialization (e.g., during recovery after a switch
2422	failure).  If you find this to be a problem, specify an appropriate
2423	value to the updelay bonding module option to delay the use of the
2424	relevant interface(s).
2425	
2426		Second, some switches may "bounce" the link state one or more
2427	times while a link is changing state.  This occurs most commonly while
2428	the switch is initializing.  Again, an appropriate updelay value may
2429	help.
2430	
2431		Note that when a bonding interface has no active links, the
2432	driver will immediately reuse the first link that goes up, even if the
2433	updelay parameter has been specified (the updelay is ignored in this
2434	case).  If there are slave interfaces waiting for the updelay timeout
2435	to expire, the interface that first went into that state will be
2436	immediately reused.  This reduces down time of the network if the
2437	value of updelay has been overestimated, and since this occurs only in
2438	cases with no connectivity, there is no additional penalty for
2439	ignoring the updelay.
2440	
2441		In addition to the concerns about switch timings, if your
2442	switches take a long time to go into backup mode, it may be desirable
2443	to not activate a backup interface immediately after a link goes down.
2444	Failover may be delayed via the downdelay bonding module option.
2445	
2446	13.2 Duplicated Incoming Packets
2447	--------------------------------
2448	
2449		NOTE: Starting with version 3.0.2, the bonding driver has logic to
2450	suppress duplicate packets, which should largely eliminate this problem.
2451	The following description is kept for reference.
2452	
2453		It is not uncommon to observe a short burst of duplicated
2454	traffic when the bonding device is first used, or after it has been
2455	idle for some period of time.  This is most easily observed by issuing
2456	a "ping" to some other host on the network, and noticing that the
2457	output from ping flags duplicates (typically one per slave).
2458	
2459		For example, on a bond in active-backup mode with five slaves
2460	all connected to one switch, the output may appear as follows:
2461	
2462	# ping -n 10.0.4.2
2463	PING 10.0.4.2 (10.0.4.2) from 10.0.3.10 : 56(84) bytes of data.
2464	64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.7 ms
2465	64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2466	64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2467	64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2468	64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2469	64 bytes from 10.0.4.2: icmp_seq=2 ttl=64 time=0.216 ms
2470	64 bytes from 10.0.4.2: icmp_seq=3 ttl=64 time=0.267 ms
2471	64 bytes from 10.0.4.2: icmp_seq=4 ttl=64 time=0.222 ms
2472	
2473		This is not due to an error in the bonding driver, rather, it
2474	is a side effect of how many switches update their MAC forwarding
2475	tables.  Initially, the switch does not associate the MAC address in
2476	the packet with a particular switch port, and so it may send the
2477	traffic to all ports until its MAC forwarding table is updated.  Since
2478	the interfaces attached to the bond may occupy multiple ports on a
2479	single switch, when the switch (temporarily) floods the traffic to all
2480	ports, the bond device receives multiple copies of the same packet
2481	(one per slave device).
2482	
2483		The duplicated packet behavior is switch dependent, some
2484	switches exhibit this, and some do not.  On switches that display this
2485	behavior, it can be induced by clearing the MAC forwarding table (on
2486	most Cisco switches, the privileged command "clear mac address-table
2487	dynamic" will accomplish this).
2488	
2489	14. Hardware Specific Considerations
2490	====================================
2491	
2492		This section contains additional information for configuring
2493	bonding on specific hardware platforms, or for interfacing bonding
2494	with particular switches or other devices.
2495	
2496	14.1 IBM BladeCenter
2497	--------------------
2498	
2499		This applies to the JS20 and similar systems.
2500	
2501		On the JS20 blades, the bonding driver supports only
2502	balance-rr, active-backup, balance-tlb and balance-alb modes.  This is
2503	largely due to the network topology inside the BladeCenter, detailed
2504	below.
2505	
2506	JS20 network adapter information
2507	--------------------------------
2508	
2509		All JS20s come with two Broadcom Gigabit Ethernet ports
2510	integrated on the planar (that's "motherboard" in IBM-speak).  In the
2511	BladeCenter chassis, the eth0 port of all JS20 blades is hard wired to
2512	I/O Module #1; similarly, all eth1 ports are wired to I/O Module #2.
2513	An add-on Broadcom daughter card can be installed on a JS20 to provide
2514	two more Gigabit Ethernet ports.  These ports, eth2 and eth3, are
2515	wired to I/O Modules 3 and 4, respectively.
2516	
2517		Each I/O Module may contain either a switch or a passthrough
2518	module (which allows ports to be directly connected to an external
2519	switch).  Some bonding modes require a specific BladeCenter internal
2520	network topology in order to function; these are detailed below.
2521	
2522		Additional BladeCenter-specific networking information can be
2523	found in two IBM Redbooks (www.ibm.com/redbooks):
2524	
2525	"IBM eServer BladeCenter Networking Options"
2526	"IBM eServer BladeCenter Layer 2-7 Network Switching"
2527	
2528	BladeCenter networking configuration
2529	------------------------------------
2530	
2531		Because a BladeCenter can be configured in a very large number
2532	of ways, this discussion will be confined to describing basic
2533	configurations.
2534	
2535		Normally, Ethernet Switch Modules (ESMs) are used in I/O
2536	modules 1 and 2.  In this configuration, the eth0 and eth1 ports of a
2537	JS20 will be connected to different internal switches (in the
2538	respective I/O modules).
2539	
2540		A passthrough module (OPM or CPM, optical or copper,
2541	passthrough module) connects the I/O module directly to an external
2542	switch.  By using PMs in I/O module #1 and #2, the eth0 and eth1
2543	interfaces of a JS20 can be redirected to the outside world and
2544	connected to a common external switch.
2545	
2546		Depending upon the mix of ESMs and PMs, the network will
2547	appear to bonding as either a single switch topology (all PMs) or as a
2548	multiple switch topology (one or more ESMs, zero or more PMs).  It is
2549	also possible to connect ESMs together, resulting in a configuration
2550	much like the example in "High Availability in a Multiple Switch
2551	Topology," above.
2552	
2553	Requirements for specific modes
2554	-------------------------------
2555	
2556		The balance-rr mode requires the use of passthrough modules
2557	for devices in the bond, all connected to an common external switch.
2558	That switch must be configured for "etherchannel" or "trunking" on the
2559	appropriate ports, as is usual for balance-rr.
2560	
2561		The balance-alb and balance-tlb modes will function with
2562	either switch modules or passthrough modules (or a mix).  The only
2563	specific requirement for these modes is that all network interfaces
2564	must be able to reach all destinations for traffic sent over the
2565	bonding device (i.e., the network must converge at some point outside
2566	the BladeCenter).
2567	
2568		The active-backup mode has no additional requirements.
2569	
2570	Link monitoring issues
2571	----------------------
2572	
2573		When an Ethernet Switch Module is in place, only the ARP
2574	monitor will reliably detect link loss to an external switch.  This is
2575	nothing unusual, but examination of the BladeCenter cabinet would
2576	suggest that the "external" network ports are the ethernet ports for
2577	the system, when it fact there is a switch between these "external"
2578	ports and the devices on the JS20 system itself.  The MII monitor is
2579	only able to detect link failures between the ESM and the JS20 system.
2580	
2581		When a passthrough module is in place, the MII monitor does
2582	detect failures to the "external" port, which is then directly
2583	connected to the JS20 system.
2584	
2585	Other concerns
2586	--------------
2587	
2588		The Serial Over LAN (SoL) link is established over the primary
2589	ethernet (eth0) only, therefore, any loss of link to eth0 will result
2590	in losing your SoL connection.  It will not fail over with other
2591	network traffic, as the SoL system is beyond the control of the
2592	bonding driver.
2593	
2594		It may be desirable to disable spanning tree on the switch
2595	(either the internal Ethernet Switch Module, or an external switch) to
2596	avoid fail-over delay issues when using bonding.
2597	
2598		
2599	15. Frequently Asked Questions
2600	==============================
2601	
2602	1.  Is it SMP safe?
2603	
2604		Yes. The old 2.0.xx channel bonding patch was not SMP safe.
2605	The new driver was designed to be SMP safe from the start.
2606	
2607	2.  What type of cards will work with it?
2608	
2609		Any Ethernet type cards (you can even mix cards - a Intel
2610	EtherExpress PRO/100 and a 3com 3c905b, for example).  For most modes,
2611	devices need not be of the same speed.
2612	
2613		Starting with version 3.2.1, bonding also supports Infiniband
2614	slaves in active-backup mode.
2615	
2616	3.  How many bonding devices can I have?
2617	
2618		There is no limit.
2619	
2620	4.  How many slaves can a bonding device have?
2621	
2622		This is limited only by the number of network interfaces Linux
2623	supports and/or the number of network cards you can place in your
2624	system.
2625	
2626	5.  What happens when a slave link dies?
2627	
2628		If link monitoring is enabled, then the failing device will be
2629	disabled.  The active-backup mode will fail over to a backup link, and
2630	other modes will ignore the failed link.  The link will continue to be
2631	monitored, and should it recover, it will rejoin the bond (in whatever
2632	manner is appropriate for the mode). See the sections on High
2633	Availability and the documentation for each mode for additional
2634	information.
2635		
2636		Link monitoring can be enabled via either the miimon or
2637	arp_interval parameters (described in the module parameters section,
2638	above).  In general, miimon monitors the carrier state as sensed by
2639	the underlying network device, and the arp monitor (arp_interval)
2640	monitors connectivity to another host on the local network.
2641	
2642		If no link monitoring is configured, the bonding driver will
2643	be unable to detect link failures, and will assume that all links are
2644	always available.  This will likely result in lost packets, and a
2645	resulting degradation of performance.  The precise performance loss
2646	depends upon the bonding mode and network configuration.
2647	
2648	6.  Can bonding be used for High Availability?
2649	
2650		Yes.  See the section on High Availability for details.
2651	
2652	7.  Which switches/systems does it work with?
2653	
2654		The full answer to this depends upon the desired mode.
2655	
2656		In the basic balance modes (balance-rr and balance-xor), it
2657	works with any system that supports etherchannel (also called
2658	trunking).  Most managed switches currently available have such
2659	support, and many unmanaged switches as well.
2660	
2661		The advanced balance modes (balance-tlb and balance-alb) do
2662	not have special switch requirements, but do need device drivers that
2663	support specific features (described in the appropriate section under
2664	module parameters, above).
2665	
2666		In 802.3ad mode, it works with systems that support IEEE
2667	802.3ad Dynamic Link Aggregation.  Most managed and many unmanaged
2668	switches currently available support 802.3ad.
2669	
2670	        The active-backup mode should work with any Layer-II switch.
2671	
2672	8.  Where does a bonding device get its MAC address from?
2673	
2674		When using slave devices that have fixed MAC addresses, or when
2675	the fail_over_mac option is enabled, the bonding device's MAC address is
2676	the MAC address of the active slave.
2677	
2678		For other configurations, if not explicitly configured (with
2679	ifconfig or ip link), the MAC address of the bonding device is taken from
2680	its first slave device.  This MAC address is then passed to all following
2681	slaves and remains persistent (even if the first slave is removed) until
2682	the bonding device is brought down or reconfigured.
2683	
2684		If you wish to change the MAC address, you can set it with
2685	ifconfig or ip link:
2686	
2687	# ifconfig bond0 hw ether 00:11:22:33:44:55
2688	
2689	# ip link set bond0 address 66:77:88:99:aa:bb
2690	
2691		The MAC address can be also changed by bringing down/up the
2692	device and then changing its slaves (or their order):
2693	
2694	# ifconfig bond0 down ; modprobe -r bonding
2695	# ifconfig bond0 .... up
2696	# ifenslave bond0 eth...
2697	
2698		This method will automatically take the address from the next
2699	slave that is added.
2700	
2701		To restore your slaves' MAC addresses, you need to detach them
2702	from the bond (`ifenslave -d bond0 eth0'). The bonding driver will
2703	then restore the MAC addresses that the slaves had before they were
2704	enslaved.
2705	
2706	16. Resources and Links
2707	=======================
2708	
2709		The latest version of the bonding driver can be found in the latest
2710	version of the linux kernel, found on http://kernel.org
2711	
2712		The latest version of this document can be found in the latest kernel
2713	source (named Documentation/networking/bonding.txt).
2714	
2715		Discussions regarding the usage of the bonding driver take place on the
2716	bonding-devel mailing list, hosted at sourceforge.net. If you have questions or
2717	problems, post them to the list.  The list address is:
2718	
2719	bonding-devel@lists.sourceforge.net
2720	
2721		The administrative interface (to subscribe or unsubscribe) can
2722	be found at:
2723	
2724	https://lists.sourceforge.net/lists/listinfo/bonding-devel
2725	
2726		Discussions regarding the development of the bonding driver take place
2727	on the main Linux network mailing list, hosted at vger.kernel.org. The list
2728	address is:
2729	
2730	netdev@vger.kernel.org
2731	
2732		The administrative interface (to subscribe or unsubscribe) can
2733	be found at:
2734	
2735	http://vger.kernel.org/vger-lists.html#netdev
2736	
2737	Donald Becker's Ethernet Drivers and diag programs may be found at :
2738	 - http://web.archive.org/web/*/http://www.scyld.com/network/ 
2739	
2740	You will also find a lot of information regarding Ethernet, NWay, MII,
2741	etc. at www.scyld.com.
2742	
2743	-- END --
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