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Based on kernel version 3.16. Page generated on 2014-08-06 21:40 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) modulo
546			slave count].  Alternate transmit policies may be
547			selected via the xmit_hash_policy option, described
548			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 to generate the
805			hash.  The formula is
806	
807			(source MAC XOR destination MAC) modulo slave count
808	
809			This algorithm will place all traffic to a particular
810			network peer on the same slave.
811	
812			This algorithm is 802.3ad compliant.
813	
814		layer2+3
815	
816			This policy uses a combination of layer2 and layer3
817			protocol information to generate the hash.
818	
819			Uses XOR of hardware MAC addresses and IP addresses to
820			generate the hash.  The formula is
821	
822			hash = source MAC XOR destination MAC
823			hash = hash XOR source IP XOR destination IP
824			hash = hash XOR (hash RSHIFT 16)
825			hash = hash XOR (hash RSHIFT 8)
826			And then hash is reduced modulo slave count.
827	
828			If the protocol is IPv6 then the source and destination
829			addresses are first hashed using ipv6_addr_hash.
830	
831			This algorithm will place all traffic to a particular
832			network peer on the same slave.  For non-IP traffic,
833			the formula is the same as for the layer2 transmit
834			hash policy.
835	
836			This policy is intended to provide a more balanced
837			distribution of traffic than layer2 alone, especially
838			in environments where a layer3 gateway device is
839			required to reach most destinations.
840	
841			This algorithm is 802.3ad compliant.
842	
843		layer3+4
844	
845			This policy uses upper layer protocol information,
846			when available, to generate the hash.  This allows for
847			traffic to a particular network peer to span multiple
848			slaves, although a single connection will not span
849			multiple slaves.
850	
851			The formula for unfragmented TCP and UDP packets is
852	
853			hash = source port, destination port (as in the header)
854			hash = hash XOR source IP XOR destination IP
855			hash = hash XOR (hash RSHIFT 16)
856			hash = hash XOR (hash RSHIFT 8)
857			And then hash is reduced modulo slave count.
858	
859			If the protocol is IPv6 then the source and destination
860			addresses are first hashed using ipv6_addr_hash.
861	
862			For fragmented TCP or UDP packets and all other IPv4 and
863			IPv6 protocol traffic, the source and destination port
864			information is omitted.  For non-IP traffic, the
865			formula is the same as for the layer2 transmit hash
866			policy.
867	
868			This algorithm is not fully 802.3ad compliant.  A
869			single TCP or UDP conversation containing both
870			fragmented and unfragmented packets will see packets
871			striped across two interfaces.  This may result in out
872			of order delivery.  Most traffic types will not meet
873			this criteria, as TCP rarely fragments traffic, and
874			most UDP traffic is not involved in extended
875			conversations.  Other implementations of 802.3ad may
876			or may not tolerate this noncompliance.
877	
878		encap2+3
879	
880			This policy uses the same formula as layer2+3 but it
881			relies on skb_flow_dissect to obtain the header fields
882			which might result in the use of inner headers if an
883			encapsulation protocol is used. For example this will
884			improve the performance for tunnel users because the
885			packets will be distributed according to the encapsulated
886			flows.
887	
888		encap3+4
889	
890			This policy uses the same formula as layer3+4 but it
891			relies on skb_flow_dissect to obtain the header fields
892			which might result in the use of inner headers if an
893			encapsulation protocol is used. For example this will
894			improve the performance for tunnel users because the
895			packets will be distributed according to the encapsulated
896			flows.
897	
898		The default value is layer2.  This option was added in bonding
899		version 2.6.3.  In earlier versions of bonding, this parameter
900		does not exist, and the layer2 policy is the only policy.  The
901		layer2+3 value was added for bonding version 3.2.2.
902	
903	resend_igmp
904	
905		Specifies the number of IGMP membership reports to be issued after
906		a failover event. One membership report is issued immediately after
907		the failover, subsequent packets are sent in each 200ms interval.
908	
909		The valid range is 0 - 255; the default value is 1. A value of 0
910		prevents the IGMP membership report from being issued in response
911		to the failover event.
912	
913		This option is useful for bonding modes balance-rr (0), active-backup
914		(1), balance-tlb (5) and balance-alb (6), in which a failover can
915		switch the IGMP traffic from one slave to another.  Therefore a fresh
916		IGMP report must be issued to cause the switch to forward the incoming
917		IGMP traffic over the newly selected slave.
918	
919		This option was added for bonding version 3.7.0.
920	
921	lp_interval
922	
923		Specifies the number of seconds between instances where the bonding
924		driver sends learning packets to each slaves peer switch.
925	
926		The valid range is 1 - 0x7fffffff; the default value is 1. This Option
927		has effect only in balance-tlb and balance-alb modes.
928	
929	3. Configuring Bonding Devices
930	==============================
931	
932		You can configure bonding using either your distro's network
933	initialization scripts, or manually using either iproute2 or the
934	sysfs interface.  Distros generally use one of three packages for the
935	network initialization scripts: initscripts, sysconfig or interfaces.
936	Recent versions of these packages have support for bonding, while older
937	versions do not.
938	
939		We will first describe the options for configuring bonding for
940	distros using versions of initscripts, sysconfig and interfaces with full
941	or partial support for bonding, then provide information on enabling
942	bonding without support from the network initialization scripts (i.e.,
943	older versions of initscripts or sysconfig).
944	
945		If you're unsure whether your distro uses sysconfig,
946	initscripts or interfaces, or don't know if it's new enough, have no fear.
947	Determining this is fairly straightforward.
948	
949		First, look for a file called interfaces in /etc/network directory.
950	If this file is present in your system, then your system use interfaces. See
951	Configuration with Interfaces Support.
952	
953		Else, issue the command:
954	
955	$ rpm -qf /sbin/ifup
956	
957		It will respond with a line of text starting with either
958	"initscripts" or "sysconfig," followed by some numbers.  This is the
959	package that provides your network initialization scripts.
960	
961		Next, to determine if your installation supports bonding,
962	issue the command:
963	
964	$ grep ifenslave /sbin/ifup
965	
966		If this returns any matches, then your initscripts or
967	sysconfig has support for bonding.
968	
969	3.1 Configuration with Sysconfig Support
970	----------------------------------------
971	
972		This section applies to distros using a version of sysconfig
973	with bonding support, for example, SuSE Linux Enterprise Server 9.
974	
975		SuSE SLES 9's networking configuration system does support
976	bonding, however, at this writing, the YaST system configuration
977	front end does not provide any means to work with bonding devices.
978	Bonding devices can be managed by hand, however, as follows.
979	
980		First, if they have not already been configured, configure the
981	slave devices.  On SLES 9, this is most easily done by running the
982	yast2 sysconfig configuration utility.  The goal is for to create an
983	ifcfg-id file for each slave device.  The simplest way to accomplish
984	this is to configure the devices for DHCP (this is only to get the
985	file ifcfg-id file created; see below for some issues with DHCP).  The
986	name of the configuration file for each device will be of the form:
987	
988	ifcfg-id-xx:xx:xx:xx:xx:xx
989	
990		Where the "xx" portion will be replaced with the digits from
991	the device's permanent MAC address.
992	
993		Once the set of ifcfg-id-xx:xx:xx:xx:xx:xx files has been
994	created, it is necessary to edit the configuration files for the slave
995	devices (the MAC addresses correspond to those of the slave devices).
996	Before editing, the file will contain multiple lines, and will look
997	something like this:
998	
999	BOOTPROTO='dhcp'
1000	STARTMODE='on'
1001	USERCTL='no'
1002	UNIQUE='XNzu.WeZGOGF+4wE'
1003	_nm_name='bus-pci-0001:61:01.0'
1004	
1005		Change the BOOTPROTO and STARTMODE lines to the following:
1006	
1007	BOOTPROTO='none'
1008	STARTMODE='off'
1009	
1010		Do not alter the UNIQUE or _nm_name lines.  Remove any other
1011	lines (USERCTL, etc).
1012	
1013		Once the ifcfg-id-xx:xx:xx:xx:xx:xx files have been modified,
1014	it's time to create the configuration file for the bonding device
1015	itself.  This file is named ifcfg-bondX, where X is the number of the
1016	bonding device to create, starting at 0.  The first such file is
1017	ifcfg-bond0, the second is ifcfg-bond1, and so on.  The sysconfig
1018	network configuration system will correctly start multiple instances
1019	of bonding.
1020	
1021		The contents of the ifcfg-bondX file is as follows:
1022	
1023	BOOTPROTO="static"
1024	BROADCAST="10.0.2.255"
1025	IPADDR="10.0.2.10"
1026	NETMASK="255.255.0.0"
1027	NETWORK="10.0.2.0"
1028	REMOTE_IPADDR=""
1029	STARTMODE="onboot"
1030	BONDING_MASTER="yes"
1031	BONDING_MODULE_OPTS="mode=active-backup miimon=100"
1032	BONDING_SLAVE0="eth0"
1033	BONDING_SLAVE1="bus-pci-0000:06:08.1"
1034	
1035		Replace the sample BROADCAST, IPADDR, NETMASK and NETWORK
1036	values with the appropriate values for your network.
1037	
1038		The STARTMODE specifies when the device is brought online.
1039	The possible values are:
1040	
1041		onboot:	 The device is started at boot time.  If you're not
1042			 sure, this is probably what you want.
1043	
1044		manual:	 The device is started only when ifup is called
1045			 manually.  Bonding devices may be configured this
1046			 way if you do not wish them to start automatically
1047			 at boot for some reason.
1048	
1049		hotplug: The device is started by a hotplug event.  This is not
1050			 a valid choice for a bonding device.
1051	
1052		off or ignore: The device configuration is ignored.
1053	
1054		The line BONDING_MASTER='yes' indicates that the device is a
1055	bonding master device.  The only useful value is "yes."
1056	
1057		The contents of BONDING_MODULE_OPTS are supplied to the
1058	instance of the bonding module for this device.  Specify the options
1059	for the bonding mode, link monitoring, and so on here.  Do not include
1060	the max_bonds bonding parameter; this will confuse the configuration
1061	system if you have multiple bonding devices.
1062	
1063		Finally, supply one BONDING_SLAVEn="slave device" for each
1064	slave.  where "n" is an increasing value, one for each slave.  The
1065	"slave device" is either an interface name, e.g., "eth0", or a device
1066	specifier for the network device.  The interface name is easier to
1067	find, but the ethN names are subject to change at boot time if, e.g.,
1068	a device early in the sequence has failed.  The device specifiers
1069	(bus-pci-0000:06:08.1 in the example above) specify the physical
1070	network device, and will not change unless the device's bus location
1071	changes (for example, it is moved from one PCI slot to another).  The
1072	example above uses one of each type for demonstration purposes; most
1073	configurations will choose one or the other for all slave devices.
1074	
1075		When all configuration files have been modified or created,
1076	networking must be restarted for the configuration changes to take
1077	effect.  This can be accomplished via the following:
1078	
1079	# /etc/init.d/network restart
1080	
1081		Note that the network control script (/sbin/ifdown) will
1082	remove the bonding module as part of the network shutdown processing,
1083	so it is not necessary to remove the module by hand if, e.g., the
1084	module parameters have changed.
1085	
1086		Also, at this writing, YaST/YaST2 will not manage bonding
1087	devices (they do not show bonding interfaces on its list of network
1088	devices).  It is necessary to edit the configuration file by hand to
1089	change the bonding configuration.
1090	
1091		Additional general options and details of the ifcfg file
1092	format can be found in an example ifcfg template file:
1093	
1094	/etc/sysconfig/network/ifcfg.template
1095	
1096		Note that the template does not document the various BONDING_
1097	settings described above, but does describe many of the other options.
1098	
1099	3.1.1 Using DHCP with Sysconfig
1100	-------------------------------
1101	
1102		Under sysconfig, configuring a device with BOOTPROTO='dhcp'
1103	will cause it to query DHCP for its IP address information.  At this
1104	writing, this does not function for bonding devices; the scripts
1105	attempt to obtain the device address from DHCP prior to adding any of
1106	the slave devices.  Without active slaves, the DHCP requests are not
1107	sent to the network.
1108	
1109	3.1.2 Configuring Multiple Bonds with Sysconfig
1110	-----------------------------------------------
1111	
1112		The sysconfig network initialization system is capable of
1113	handling multiple bonding devices.  All that is necessary is for each
1114	bonding instance to have an appropriately configured ifcfg-bondX file
1115	(as described above).  Do not specify the "max_bonds" parameter to any
1116	instance of bonding, as this will confuse sysconfig.  If you require
1117	multiple bonding devices with identical parameters, create multiple
1118	ifcfg-bondX files.
1119	
1120		Because the sysconfig scripts supply the bonding module
1121	options in the ifcfg-bondX file, it is not necessary to add them to
1122	the system /etc/modules.d/*.conf configuration files.
1123	
1124	3.2 Configuration with Initscripts Support
1125	------------------------------------------
1126	
1127		This section applies to distros using a recent version of
1128	initscripts with bonding support, for example, Red Hat Enterprise Linux
1129	version 3 or later, Fedora, etc.  On these systems, the network
1130	initialization scripts have knowledge of bonding, and can be configured to
1131	control bonding devices.  Note that older versions of the initscripts
1132	package have lower levels of support for bonding; this will be noted where
1133	applicable.
1134	
1135		These distros will not automatically load the network adapter
1136	driver unless the ethX device is configured with an IP address.
1137	Because of this constraint, users must manually configure a
1138	network-script file for all physical adapters that will be members of
1139	a bondX link.  Network script files are located in the directory:
1140	
1141	/etc/sysconfig/network-scripts
1142	
1143		The file name must be prefixed with "ifcfg-eth" and suffixed
1144	with the adapter's physical adapter number.  For example, the script
1145	for eth0 would be named /etc/sysconfig/network-scripts/ifcfg-eth0.
1146	Place the following text in the file:
1147	
1148	DEVICE=eth0
1149	USERCTL=no
1150	ONBOOT=yes
1151	MASTER=bond0
1152	SLAVE=yes
1153	BOOTPROTO=none
1154	
1155		The DEVICE= line will be different for every ethX device and
1156	must correspond with the name of the file, i.e., ifcfg-eth1 must have
1157	a device line of DEVICE=eth1.  The setting of the MASTER= line will
1158	also depend on the final bonding interface name chosen for your bond.
1159	As with other network devices, these typically start at 0, and go up
1160	one for each device, i.e., the first bonding instance is bond0, the
1161	second is bond1, and so on.
1162	
1163		Next, create a bond network script.  The file name for this
1164	script will be /etc/sysconfig/network-scripts/ifcfg-bondX where X is
1165	the number of the bond.  For bond0 the file is named "ifcfg-bond0",
1166	for bond1 it is named "ifcfg-bond1", and so on.  Within that file,
1167	place the following text:
1168	
1169	DEVICE=bond0
1170	IPADDR=192.168.1.1
1171	NETMASK=255.255.255.0
1172	NETWORK=192.168.1.0
1173	BROADCAST=192.168.1.255
1174	ONBOOT=yes
1175	BOOTPROTO=none
1176	USERCTL=no
1177	
1178		Be sure to change the networking specific lines (IPADDR,
1179	NETMASK, NETWORK and BROADCAST) to match your network configuration.
1180	
1181		For later versions of initscripts, such as that found with Fedora
1182	7 (or later) and Red Hat Enterprise Linux version 5 (or later), it is possible,
1183	and, indeed, preferable, to specify the bonding options in the ifcfg-bond0
1184	file, e.g. a line of the format:
1185	
1186	BONDING_OPTS="mode=active-backup arp_interval=60 arp_ip_target=192.168.1.254"
1187	
1188		will configure the bond with the specified options.  The options
1189	specified in BONDING_OPTS are identical to the bonding module parameters
1190	except for the arp_ip_target field when using versions of initscripts older
1191	than and 8.57 (Fedora 8) and 8.45.19 (Red Hat Enterprise Linux 5.2).  When
1192	using older versions each target should be included as a separate option and
1193	should be preceded by a '+' to indicate it should be added to the list of
1194	queried targets, e.g.,
1195	
1196		arp_ip_target=+192.168.1.1 arp_ip_target=+192.168.1.2
1197	
1198		is the proper syntax to specify multiple targets.  When specifying
1199	options via BONDING_OPTS, it is not necessary to edit /etc/modprobe.d/*.conf.
1200	
1201		For even older versions of initscripts that do not support
1202	BONDING_OPTS, it is necessary to edit /etc/modprobe.d/*.conf, depending upon
1203	your distro) to load the bonding module with your desired options when the
1204	bond0 interface is brought up.  The following lines in /etc/modprobe.d/*.conf
1205	will load the bonding module, and select its options:
1206	
1207	alias bond0 bonding
1208	options bond0 mode=balance-alb miimon=100
1209	
1210		Replace the sample parameters with the appropriate set of
1211	options for your configuration.
1212	
1213		Finally run "/etc/rc.d/init.d/network restart" as root.  This
1214	will restart the networking subsystem and your bond link should be now
1215	up and running.
1216	
1217	3.2.1 Using DHCP with Initscripts
1218	---------------------------------
1219	
1220		Recent versions of initscripts (the versions supplied with Fedora
1221	Core 3 and Red Hat Enterprise Linux 4, or later versions, are reported to
1222	work) have support for assigning IP information to bonding devices via
1223	DHCP.
1224	
1225		To configure bonding for DHCP, configure it as described
1226	above, except replace the line "BOOTPROTO=none" with "BOOTPROTO=dhcp"
1227	and add a line consisting of "TYPE=Bonding".  Note that the TYPE value
1228	is case sensitive.
1229	
1230	3.2.2 Configuring Multiple Bonds with Initscripts
1231	-------------------------------------------------
1232	
1233		Initscripts packages that are included with Fedora 7 and Red Hat
1234	Enterprise Linux 5 support multiple bonding interfaces by simply
1235	specifying the appropriate BONDING_OPTS= in ifcfg-bondX where X is the
1236	number of the bond.  This support requires sysfs support in the kernel,
1237	and a bonding driver of version 3.0.0 or later.  Other configurations may
1238	not support this method for specifying multiple bonding interfaces; for
1239	those instances, see the "Configuring Multiple Bonds Manually" section,
1240	below.
1241	
1242	3.3 Configuring Bonding Manually with iproute2
1243	-----------------------------------------------
1244	
1245		This section applies to distros whose network initialization
1246	scripts (the sysconfig or initscripts package) do not have specific
1247	knowledge of bonding.  One such distro is SuSE Linux Enterprise Server
1248	version 8.
1249	
1250		The general method for these systems is to place the bonding
1251	module parameters into a config file in /etc/modprobe.d/ (as
1252	appropriate for the installed distro), then add modprobe and/or
1253	`ip link` commands to the system's global init script.  The name of
1254	the global init script differs; for sysconfig, it is
1255	/etc/init.d/boot.local and for initscripts it is /etc/rc.d/rc.local.
1256	
1257		For example, if you wanted to make a simple bond of two e100
1258	devices (presumed to be eth0 and eth1), and have it persist across
1259	reboots, edit the appropriate file (/etc/init.d/boot.local or
1260	/etc/rc.d/rc.local), and add the following:
1261	
1262	modprobe bonding mode=balance-alb miimon=100
1263	modprobe e100
1264	ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
1265	ip link set eth0 master bond0
1266	ip link set eth1 master bond0
1267	
1268		Replace the example bonding module parameters and bond0
1269	network configuration (IP address, netmask, etc) with the appropriate
1270	values for your configuration.
1271	
1272		Unfortunately, this method will not provide support for the
1273	ifup and ifdown scripts on the bond devices.  To reload the bonding
1274	configuration, it is necessary to run the initialization script, e.g.,
1275	
1276	# /etc/init.d/boot.local
1277	
1278		or
1279	
1280	# /etc/rc.d/rc.local
1281	
1282		It may be desirable in such a case to create a separate script
1283	which only initializes the bonding configuration, then call that
1284	separate script from within boot.local.  This allows for bonding to be
1285	enabled without re-running the entire global init script.
1286	
1287		To shut down the bonding devices, it is necessary to first
1288	mark the bonding device itself as being down, then remove the
1289	appropriate device driver modules.  For our example above, you can do
1290	the following:
1291	
1292	# ifconfig bond0 down
1293	# rmmod bonding
1294	# rmmod e100
1295	
1296		Again, for convenience, it may be desirable to create a script
1297	with these commands.
1298	
1299	
1300	3.3.1 Configuring Multiple Bonds Manually
1301	-----------------------------------------
1302	
1303		This section contains information on configuring multiple
1304	bonding devices with differing options for those systems whose network
1305	initialization scripts lack support for configuring multiple bonds.
1306	
1307		If you require multiple bonding devices, but all with the same
1308	options, you may wish to use the "max_bonds" module parameter,
1309	documented above.
1310	
1311		To create multiple bonding devices with differing options, it is
1312	preferable to use bonding parameters exported by sysfs, documented in the
1313	section below.
1314	
1315		For versions of bonding without sysfs support, the only means to
1316	provide multiple instances of bonding with differing options is to load
1317	the bonding driver multiple times.  Note that current versions of the
1318	sysconfig network initialization scripts handle this automatically; if
1319	your distro uses these scripts, no special action is needed.  See the
1320	section Configuring Bonding Devices, above, if you're not sure about your
1321	network initialization scripts.
1322	
1323		To load multiple instances of the module, it is necessary to
1324	specify a different name for each instance (the module loading system
1325	requires that every loaded module, even multiple instances of the same
1326	module, have a unique name).  This is accomplished by supplying multiple
1327	sets of bonding options in /etc/modprobe.d/*.conf, for example:
1328	
1329	alias bond0 bonding
1330	options bond0 -o bond0 mode=balance-rr miimon=100
1331	
1332	alias bond1 bonding
1333	options bond1 -o bond1 mode=balance-alb miimon=50
1334	
1335		will load the bonding module two times.  The first instance is
1336	named "bond0" and creates the bond0 device in balance-rr mode with an
1337	miimon of 100.  The second instance is named "bond1" and creates the
1338	bond1 device in balance-alb mode with an miimon of 50.
1339	
1340		In some circumstances (typically with older distributions),
1341	the above does not work, and the second bonding instance never sees
1342	its options.  In that case, the second options line can be substituted
1343	as follows:
1344	
1345	install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \
1346		mode=balance-alb miimon=50
1347	
1348		This may be repeated any number of times, specifying a new and
1349	unique name in place of bond1 for each subsequent instance.
1350	
1351		It has been observed that some Red Hat supplied kernels are unable
1352	to rename modules at load time (the "-o bond1" part).  Attempts to pass
1353	that option to modprobe will produce an "Operation not permitted" error.
1354	This has been reported on some Fedora Core kernels, and has been seen on
1355	RHEL 4 as well.  On kernels exhibiting this problem, it will be impossible
1356	to configure multiple bonds with differing parameters (as they are older
1357	kernels, and also lack sysfs support).
1358	
1359	3.4 Configuring Bonding Manually via Sysfs
1360	------------------------------------------
1361	
1362		Starting with version 3.0.0, Channel Bonding may be configured
1363	via the sysfs interface.  This interface allows dynamic configuration
1364	of all bonds in the system without unloading the module.  It also
1365	allows for adding and removing bonds at runtime.  Ifenslave is no
1366	longer required, though it is still supported.
1367	
1368		Use of the sysfs interface allows you to use multiple bonds
1369	with different configurations without having to reload the module.
1370	It also allows you to use multiple, differently configured bonds when
1371	bonding is compiled into the kernel.
1372	
1373		You must have the sysfs filesystem mounted to configure
1374	bonding this way.  The examples in this document assume that you
1375	are using the standard mount point for sysfs, e.g. /sys.  If your
1376	sysfs filesystem is mounted elsewhere, you will need to adjust the
1377	example paths accordingly.
1378	
1379	Creating and Destroying Bonds
1380	-----------------------------
1381	To add a new bond foo:
1382	# echo +foo > /sys/class/net/bonding_masters
1383	
1384	To remove an existing bond bar:
1385	# echo -bar > /sys/class/net/bonding_masters
1386	
1387	To show all existing bonds:
1388	# cat /sys/class/net/bonding_masters
1389	
1390	NOTE: due to 4K size limitation of sysfs files, this list may be
1391	truncated if you have more than a few hundred bonds.  This is unlikely
1392	to occur under normal operating conditions.
1393	
1394	Adding and Removing Slaves
1395	--------------------------
1396		Interfaces may be enslaved to a bond using the file
1397	/sys/class/net/<bond>/bonding/slaves.  The semantics for this file
1398	are the same as for the bonding_masters file.
1399	
1400	To enslave interface eth0 to bond bond0:
1401	# ifconfig bond0 up
1402	# echo +eth0 > /sys/class/net/bond0/bonding/slaves
1403	
1404	To free slave eth0 from bond bond0:
1405	# echo -eth0 > /sys/class/net/bond0/bonding/slaves
1406	
1407		When an interface is enslaved to a bond, symlinks between the
1408	two are created in the sysfs filesystem.  In this case, you would get
1409	/sys/class/net/bond0/slave_eth0 pointing to /sys/class/net/eth0, and
1410	/sys/class/net/eth0/master pointing to /sys/class/net/bond0.
1411	
1412		This means that you can tell quickly whether or not an
1413	interface is enslaved by looking for the master symlink.  Thus:
1414	# echo -eth0 > /sys/class/net/eth0/master/bonding/slaves
1415	will free eth0 from whatever bond it is enslaved to, regardless of
1416	the name of the bond interface.
1417	
1418	Changing a Bond's Configuration
1419	-------------------------------
1420		Each bond may be configured individually by manipulating the
1421	files located in /sys/class/net/<bond name>/bonding
1422	
1423		The names of these files correspond directly with the command-
1424	line parameters described elsewhere in this file, and, with the
1425	exception of arp_ip_target, they accept the same values.  To see the
1426	current setting, simply cat the appropriate file.
1427	
1428		A few examples will be given here; for specific usage
1429	guidelines for each parameter, see the appropriate section in this
1430	document.
1431	
1432	To configure bond0 for balance-alb mode:
1433	# ifconfig bond0 down
1434	# echo 6 > /sys/class/net/bond0/bonding/mode
1435	 - or -
1436	# echo balance-alb > /sys/class/net/bond0/bonding/mode
1437		NOTE: The bond interface must be down before the mode can be
1438	changed.
1439	
1440	To enable MII monitoring on bond0 with a 1 second interval:
1441	# echo 1000 > /sys/class/net/bond0/bonding/miimon
1442		NOTE: If ARP monitoring is enabled, it will disabled when MII
1443	monitoring is enabled, and vice-versa.
1444	
1445	To add ARP targets:
1446	# echo +192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
1447	# echo +192.168.0.101 > /sys/class/net/bond0/bonding/arp_ip_target
1448		NOTE:  up to 16 target addresses may be specified.
1449	
1450	To remove an ARP target:
1451	# echo -192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
1452	
1453	To configure the interval between learning packet transmits:
1454	# echo 12 > /sys/class/net/bond0/bonding/lp_interval
1455		NOTE: the lp_inteval is the number of seconds between instances where
1456	the bonding driver sends learning packets to each slaves peer switch.  The
1457	default interval is 1 second.
1458	
1459	Example Configuration
1460	---------------------
1461		We begin with the same example that is shown in section 3.3,
1462	executed with sysfs, and without using ifenslave.
1463	
1464		To make a simple bond of two e100 devices (presumed to be eth0
1465	and eth1), and have it persist across reboots, edit the appropriate
1466	file (/etc/init.d/boot.local or /etc/rc.d/rc.local), and add the
1467	following:
1468	
1469	modprobe bonding
1470	modprobe e100
1471	echo balance-alb > /sys/class/net/bond0/bonding/mode
1472	ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
1473	echo 100 > /sys/class/net/bond0/bonding/miimon
1474	echo +eth0 > /sys/class/net/bond0/bonding/slaves
1475	echo +eth1 > /sys/class/net/bond0/bonding/slaves
1476	
1477		To add a second bond, with two e1000 interfaces in
1478	active-backup mode, using ARP monitoring, add the following lines to
1479	your init script:
1480	
1481	modprobe e1000
1482	echo +bond1 > /sys/class/net/bonding_masters
1483	echo active-backup > /sys/class/net/bond1/bonding/mode
1484	ifconfig bond1 192.168.2.1 netmask 255.255.255.0 up
1485	echo +192.168.2.100 /sys/class/net/bond1/bonding/arp_ip_target
1486	echo 2000 > /sys/class/net/bond1/bonding/arp_interval
1487	echo +eth2 > /sys/class/net/bond1/bonding/slaves
1488	echo +eth3 > /sys/class/net/bond1/bonding/slaves
1489	
1490	3.5 Configuration with Interfaces Support
1491	-----------------------------------------
1492	
1493	        This section applies to distros which use /etc/network/interfaces file
1494	to describe network interface configuration, most notably Debian and it's
1495	derivatives.
1496	
1497		The ifup and ifdown commands on Debian don't support bonding out of
1498	the box. The ifenslave-2.6 package should be installed to provide bonding
1499	support.  Once installed, this package will provide bond-* options to be used
1500	into /etc/network/interfaces.
1501	
1502		Note that ifenslave-2.6 package will load the bonding module and use
1503	the ifenslave command when appropriate.
1504	
1505	Example Configurations
1506	----------------------
1507	
1508	In /etc/network/interfaces, the following stanza will configure bond0, in
1509	active-backup mode, with eth0 and eth1 as slaves.
1510	
1511	auto bond0
1512	iface bond0 inet dhcp
1513		bond-slaves eth0 eth1
1514		bond-mode active-backup
1515		bond-miimon 100
1516		bond-primary eth0 eth1
1517	
1518	If the above configuration doesn't work, you might have a system using
1519	upstart for system startup. This is most notably true for recent
1520	Ubuntu versions. The following stanza in /etc/network/interfaces will
1521	produce the same result on those systems.
1522	
1523	auto bond0
1524	iface bond0 inet dhcp
1525		bond-slaves none
1526		bond-mode active-backup
1527		bond-miimon 100
1528	
1529	auto eth0
1530	iface eth0 inet manual
1531		bond-master bond0
1532		bond-primary eth0 eth1
1533	
1534	auto eth1
1535	iface eth1 inet manual
1536		bond-master bond0
1537		bond-primary eth0 eth1
1538	
1539	For a full list of bond-* supported options in /etc/network/interfaces and some
1540	more advanced examples tailored to you particular distros, see the files in
1541	/usr/share/doc/ifenslave-2.6.
1542	
1543	3.6 Overriding Configuration for Special Cases
1544	----------------------------------------------
1545	
1546	When using the bonding driver, the physical port which transmits a frame is
1547	typically selected by the bonding driver, and is not relevant to the user or
1548	system administrator.  The output port is simply selected using the policies of
1549	the selected bonding mode.  On occasion however, it is helpful to direct certain
1550	classes of traffic to certain physical interfaces on output to implement
1551	slightly more complex policies.  For example, to reach a web server over a
1552	bonded interface in which eth0 connects to a private network, while eth1
1553	connects via a public network, it may be desirous to bias the bond to send said
1554	traffic over eth0 first, using eth1 only as a fall back, while all other traffic
1555	can safely be sent over either interface.  Such configurations may be achieved
1556	using the traffic control utilities inherent in linux.
1557	
1558	By default the bonding driver is multiqueue aware and 16 queues are created
1559	when the driver initializes (see Documentation/networking/multiqueue.txt
1560	for details).  If more or less queues are desired the module parameter
1561	tx_queues can be used to change this value.  There is no sysfs parameter
1562	available as the allocation is done at module init time.
1563	
1564	The output of the file /proc/net/bonding/bondX has changed so the output Queue
1565	ID is now printed for each slave:
1566	
1567	Bonding Mode: fault-tolerance (active-backup)
1568	Primary Slave: None
1569	Currently Active Slave: eth0
1570	MII Status: up
1571	MII Polling Interval (ms): 0
1572	Up Delay (ms): 0
1573	Down Delay (ms): 0
1574	
1575	Slave Interface: eth0
1576	MII Status: up
1577	Link Failure Count: 0
1578	Permanent HW addr: 00:1a:a0:12:8f:cb
1579	Slave queue ID: 0
1580	
1581	Slave Interface: eth1
1582	MII Status: up
1583	Link Failure Count: 0
1584	Permanent HW addr: 00:1a:a0:12:8f:cc
1585	Slave queue ID: 2
1586	
1587	The queue_id for a slave can be set using the command:
1588	
1589	# echo "eth1:2" > /sys/class/net/bond0/bonding/queue_id
1590	
1591	Any interface that needs a queue_id set should set it with multiple calls
1592	like the one above until proper priorities are set for all interfaces.  On
1593	distributions that allow configuration via initscripts, multiple 'queue_id'
1594	arguments can be added to BONDING_OPTS to set all needed slave queues.
1595	
1596	These queue id's can be used in conjunction with the tc utility to configure
1597	a multiqueue qdisc and filters to bias certain traffic to transmit on certain
1598	slave devices.  For instance, say we wanted, in the above configuration to
1599	force all traffic bound to 192.168.1.100 to use eth1 in the bond as its output
1600	device. The following commands would accomplish this:
1601	
1602	# tc qdisc add dev bond0 handle 1 root multiq
1603	
1604	# tc filter add dev bond0 protocol ip parent 1: prio 1 u32 match ip dst \
1605		192.168.1.100 action skbedit queue_mapping 2
1606	
1607	These commands tell the kernel to attach a multiqueue queue discipline to the
1608	bond0 interface and filter traffic enqueued to it, such that packets with a dst
1609	ip of 192.168.1.100 have their output queue mapping value overwritten to 2.
1610	This value is then passed into the driver, causing the normal output path
1611	selection policy to be overridden, selecting instead qid 2, which maps to eth1.
1612	
1613	Note that qid values begin at 1.  Qid 0 is reserved to initiate to the driver
1614	that normal output policy selection should take place.  One benefit to simply
1615	leaving the qid for a slave to 0 is the multiqueue awareness in the bonding
1616	driver that is now present.  This awareness allows tc filters to be placed on
1617	slave devices as well as bond devices and the bonding driver will simply act as
1618	a pass-through for selecting output queues on the slave device rather than 
1619	output port selection.
1620	
1621	This feature first appeared in bonding driver version 3.7.0 and support for
1622	output slave selection was limited to round-robin and active-backup modes.
1623	
1624	4 Querying Bonding Configuration
1625	=================================
1626	
1627	4.1 Bonding Configuration
1628	-------------------------
1629	
1630		Each bonding device has a read-only file residing in the
1631	/proc/net/bonding directory.  The file contents include information
1632	about the bonding configuration, options and state of each slave.
1633	
1634		For example, the contents of /proc/net/bonding/bond0 after the
1635	driver is loaded with parameters of mode=0 and miimon=1000 is
1636	generally as follows:
1637	
1638		Ethernet Channel Bonding Driver: 2.6.1 (October 29, 2004)
1639	        Bonding Mode: load balancing (round-robin)
1640	        Currently Active Slave: eth0
1641	        MII Status: up
1642	        MII Polling Interval (ms): 1000
1643	        Up Delay (ms): 0
1644	        Down Delay (ms): 0
1645	
1646	        Slave Interface: eth1
1647	        MII Status: up
1648	        Link Failure Count: 1
1649	
1650	        Slave Interface: eth0
1651	        MII Status: up
1652	        Link Failure Count: 1
1653	
1654		The precise format and contents will change depending upon the
1655	bonding configuration, state, and version of the bonding driver.
1656	
1657	4.2 Network configuration
1658	-------------------------
1659	
1660		The network configuration can be inspected using the ifconfig
1661	command.  Bonding devices will have the MASTER flag set; Bonding slave
1662	devices will have the SLAVE flag set.  The ifconfig output does not
1663	contain information on which slaves are associated with which masters.
1664	
1665		In the example below, the bond0 interface is the master
1666	(MASTER) while eth0 and eth1 are slaves (SLAVE). Notice all slaves of
1667	bond0 have the same MAC address (HWaddr) as bond0 for all modes except
1668	TLB and ALB that require a unique MAC address for each slave.
1669	
1670	# /sbin/ifconfig
1671	bond0     Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
1672	          inet addr:XXX.XXX.XXX.YYY  Bcast:XXX.XXX.XXX.255  Mask:255.255.252.0
1673	          UP BROADCAST RUNNING MASTER MULTICAST  MTU:1500  Metric:1
1674	          RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0
1675	          TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0
1676	          collisions:0 txqueuelen:0
1677	
1678	eth0      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
1679	          UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
1680	          RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0
1681	          TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0
1682	          collisions:0 txqueuelen:100
1683	          Interrupt:10 Base address:0x1080
1684	
1685	eth1      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
1686	          UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
1687	          RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0
1688	          TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0
1689	          collisions:0 txqueuelen:100
1690	          Interrupt:9 Base address:0x1400
1691	
1692	5. Switch Configuration
1693	=======================
1694	
1695		For this section, "switch" refers to whatever system the
1696	bonded devices are directly connected to (i.e., where the other end of
1697	the cable plugs into).  This may be an actual dedicated switch device,
1698	or it may be another regular system (e.g., another computer running
1699	Linux),
1700	
1701		The active-backup, balance-tlb and balance-alb modes do not
1702	require any specific configuration of the switch.
1703	
1704		The 802.3ad mode requires that the switch have the appropriate
1705	ports configured as an 802.3ad aggregation.  The precise method used
1706	to configure this varies from switch to switch, but, for example, a
1707	Cisco 3550 series switch requires that the appropriate ports first be
1708	grouped together in a single etherchannel instance, then that
1709	etherchannel is set to mode "lacp" to enable 802.3ad (instead of
1710	standard EtherChannel).
1711	
1712		The balance-rr, balance-xor and broadcast modes generally
1713	require that the switch have the appropriate ports grouped together.
1714	The nomenclature for such a group differs between switches, it may be
1715	called an "etherchannel" (as in the Cisco example, above), a "trunk
1716	group" or some other similar variation.  For these modes, each switch
1717	will also have its own configuration options for the switch's transmit
1718	policy to the bond.  Typical choices include XOR of either the MAC or
1719	IP addresses.  The transmit policy of the two peers does not need to
1720	match.  For these three modes, the bonding mode really selects a
1721	transmit policy for an EtherChannel group; all three will interoperate
1722	with another EtherChannel group.
1723	
1724	
1725	6. 802.1q VLAN Support
1726	======================
1727	
1728		It is possible to configure VLAN devices over a bond interface
1729	using the 8021q driver.  However, only packets coming from the 8021q
1730	driver and passing through bonding will be tagged by default.  Self
1731	generated packets, for example, bonding's learning packets or ARP
1732	packets generated by either ALB mode or the ARP monitor mechanism, are
1733	tagged internally by bonding itself.  As a result, bonding must
1734	"learn" the VLAN IDs configured above it, and use those IDs to tag
1735	self generated packets.
1736	
1737		For reasons of simplicity, and to support the use of adapters
1738	that can do VLAN hardware acceleration offloading, the bonding
1739	interface declares itself as fully hardware offloading capable, it gets
1740	the add_vid/kill_vid notifications to gather the necessary
1741	information, and it propagates those actions to the slaves.  In case
1742	of mixed adapter types, hardware accelerated tagged packets that
1743	should go through an adapter that is not offloading capable are
1744	"un-accelerated" by the bonding driver so the VLAN tag sits in the
1745	regular location.
1746	
1747		VLAN interfaces *must* be added on top of a bonding interface
1748	only after enslaving at least one slave.  The bonding interface has a
1749	hardware address of 00:00:00:00:00:00 until the first slave is added.
1750	If the VLAN interface is created prior to the first enslavement, it
1751	would pick up the all-zeroes hardware address.  Once the first slave
1752	is attached to the bond, the bond device itself will pick up the
1753	slave's hardware address, which is then available for the VLAN device.
1754	
1755		Also, be aware that a similar problem can occur if all slaves
1756	are released from a bond that still has one or more VLAN interfaces on
1757	top of it.  When a new slave is added, the bonding interface will
1758	obtain its hardware address from the first slave, which might not
1759	match the hardware address of the VLAN interfaces (which was
1760	ultimately copied from an earlier slave).
1761	
1762		There are two methods to insure that the VLAN device operates
1763	with the correct hardware address if all slaves are removed from a
1764	bond interface:
1765	
1766		1. Remove all VLAN interfaces then recreate them
1767	
1768		2. Set the bonding interface's hardware address so that it
1769	matches the hardware address of the VLAN interfaces.
1770	
1771		Note that changing a VLAN interface's HW address would set the
1772	underlying device -- i.e. the bonding interface -- to promiscuous
1773	mode, which might not be what you want.
1774	
1775	
1776	7. Link Monitoring
1777	==================
1778	
1779		The bonding driver at present supports two schemes for
1780	monitoring a slave device's link state: the ARP monitor and the MII
1781	monitor.
1782	
1783		At the present time, due to implementation restrictions in the
1784	bonding driver itself, it is not possible to enable both ARP and MII
1785	monitoring simultaneously.
1786	
1787	7.1 ARP Monitor Operation
1788	-------------------------
1789	
1790		The ARP monitor operates as its name suggests: it sends ARP
1791	queries to one or more designated peer systems on the network, and
1792	uses the response as an indication that the link is operating.  This
1793	gives some assurance that traffic is actually flowing to and from one
1794	or more peers on the local network.
1795	
1796		The ARP monitor relies on the device driver itself to verify
1797	that traffic is flowing.  In particular, the driver must keep up to
1798	date the last receive time, dev->last_rx, and transmit start time,
1799	dev->trans_start.  If these are not updated by the driver, then the
1800	ARP monitor will immediately fail any slaves using that driver, and
1801	those slaves will stay down.  If networking monitoring (tcpdump, etc)
1802	shows the ARP requests and replies on the network, then it may be that
1803	your device driver is not updating last_rx and trans_start.
1804	
1805	7.2 Configuring Multiple ARP Targets
1806	------------------------------------
1807	
1808		While ARP monitoring can be done with just one target, it can
1809	be useful in a High Availability setup to have several targets to
1810	monitor.  In the case of just one target, the target itself may go
1811	down or have a problem making it unresponsive to ARP requests.  Having
1812	an additional target (or several) increases the reliability of the ARP
1813	monitoring.
1814	
1815		Multiple ARP targets must be separated by commas as follows:
1816	
1817	# example options for ARP monitoring with three targets
1818	alias bond0 bonding
1819	options bond0 arp_interval=60 arp_ip_target=192.168.0.1,192.168.0.3,192.168.0.9
1820	
1821		For just a single target the options would resemble:
1822	
1823	# example options for ARP monitoring with one target
1824	alias bond0 bonding
1825	options bond0 arp_interval=60 arp_ip_target=192.168.0.100
1826	
1827	
1828	7.3 MII Monitor Operation
1829	-------------------------
1830	
1831		The MII monitor monitors only the carrier state of the local
1832	network interface.  It accomplishes this in one of three ways: by
1833	depending upon the device driver to maintain its carrier state, by
1834	querying the device's MII registers, or by making an ethtool query to
1835	the device.
1836	
1837		If the use_carrier module parameter is 1 (the default value),
1838	then the MII monitor will rely on the driver for carrier state
1839	information (via the netif_carrier subsystem).  As explained in the
1840	use_carrier parameter information, above, if the MII monitor fails to
1841	detect carrier loss on the device (e.g., when the cable is physically
1842	disconnected), it may be that the driver does not support
1843	netif_carrier.
1844	
1845		If use_carrier is 0, then the MII monitor will first query the
1846	device's (via ioctl) MII registers and check the link state.  If that
1847	request fails (not just that it returns carrier down), then the MII
1848	monitor will make an ethtool ETHOOL_GLINK request to attempt to obtain
1849	the same information.  If both methods fail (i.e., the driver either
1850	does not support or had some error in processing both the MII register
1851	and ethtool requests), then the MII monitor will assume the link is
1852	up.
1853	
1854	8. Potential Sources of Trouble
1855	===============================
1856	
1857	8.1 Adventures in Routing
1858	-------------------------
1859	
1860		When bonding is configured, it is important that the slave
1861	devices not have routes that supersede routes of the master (or,
1862	generally, not have routes at all).  For example, suppose the bonding
1863	device bond0 has two slaves, eth0 and eth1, and the routing table is
1864	as follows:
1865	
1866	Kernel IP routing table
1867	Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
1868	10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth0
1869	10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth1
1870	10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 bond0
1871	127.0.0.0       0.0.0.0         255.0.0.0       U        40 0          0 lo
1872	
1873		This routing configuration will likely still update the
1874	receive/transmit times in the driver (needed by the ARP monitor), but
1875	may bypass the bonding driver (because outgoing traffic to, in this
1876	case, another host on network 10 would use eth0 or eth1 before bond0).
1877	
1878		The ARP monitor (and ARP itself) may become confused by this
1879	configuration, because ARP requests (generated by the ARP monitor)
1880	will be sent on one interface (bond0), but the corresponding reply
1881	will arrive on a different interface (eth0).  This reply looks to ARP
1882	as an unsolicited ARP reply (because ARP matches replies on an
1883	interface basis), and is discarded.  The MII monitor is not affected
1884	by the state of the routing table.
1885	
1886		The solution here is simply to insure that slaves do not have
1887	routes of their own, and if for some reason they must, those routes do
1888	not supersede routes of their master.  This should generally be the
1889	case, but unusual configurations or errant manual or automatic static
1890	route additions may cause trouble.
1891	
1892	8.2 Ethernet Device Renaming
1893	----------------------------
1894	
1895		On systems with network configuration scripts that do not
1896	associate physical devices directly with network interface names (so
1897	that the same physical device always has the same "ethX" name), it may
1898	be necessary to add some special logic to config files in
1899	/etc/modprobe.d/.
1900	
1901		For example, given a modules.conf containing the following:
1902	
1903	alias bond0 bonding
1904	options bond0 mode=some-mode miimon=50
1905	alias eth0 tg3
1906	alias eth1 tg3
1907	alias eth2 e1000
1908	alias eth3 e1000
1909	
1910		If neither eth0 and eth1 are slaves to bond0, then when the
1911	bond0 interface comes up, the devices may end up reordered.  This
1912	happens because bonding is loaded first, then its slave device's
1913	drivers are loaded next.  Since no other drivers have been loaded,
1914	when the e1000 driver loads, it will receive eth0 and eth1 for its
1915	devices, but the bonding configuration tries to enslave eth2 and eth3
1916	(which may later be assigned to the tg3 devices).
1917	
1918		Adding the following:
1919	
1920	add above bonding e1000 tg3
1921	
1922		causes modprobe to load e1000 then tg3, in that order, when
1923	bonding is loaded.  This command is fully documented in the
1924	modules.conf manual page.
1925	
1926		On systems utilizing modprobe an equivalent problem can occur.
1927	In this case, the following can be added to config files in
1928	/etc/modprobe.d/ as:
1929	
1930	softdep bonding pre: tg3 e1000
1931	
1932		This will load tg3 and e1000 modules before loading the bonding one.
1933	Full documentation on this can be found in the modprobe.d and modprobe
1934	manual pages.
1935	
1936	8.3. Painfully Slow Or No Failed Link Detection By Miimon
1937	---------------------------------------------------------
1938	
1939		By default, bonding enables the use_carrier option, which
1940	instructs bonding to trust the driver to maintain carrier state.
1941	
1942		As discussed in the options section, above, some drivers do
1943	not support the netif_carrier_on/_off link state tracking system.
1944	With use_carrier enabled, bonding will always see these links as up,
1945	regardless of their actual state.
1946	
1947		Additionally, other drivers do support netif_carrier, but do
1948	not maintain it in real time, e.g., only polling the link state at
1949	some fixed interval.  In this case, miimon will detect failures, but
1950	only after some long period of time has expired.  If it appears that
1951	miimon is very slow in detecting link failures, try specifying
1952	use_carrier=0 to see if that improves the failure detection time.  If
1953	it does, then it may be that the driver checks the carrier state at a
1954	fixed interval, but does not cache the MII register values (so the
1955	use_carrier=0 method of querying the registers directly works).  If
1956	use_carrier=0 does not improve the failover, then the driver may cache
1957	the registers, or the problem may be elsewhere.
1958	
1959		Also, remember that miimon only checks for the device's
1960	carrier state.  It has no way to determine the state of devices on or
1961	beyond other ports of a switch, or if a switch is refusing to pass
1962	traffic while still maintaining carrier on.
1963	
1964	9. SNMP agents
1965	===============
1966	
1967		If running SNMP agents, the bonding driver should be loaded
1968	before any network drivers participating in a bond.  This requirement
1969	is due to the interface index (ipAdEntIfIndex) being associated to
1970	the first interface found with a given IP address.  That is, there is
1971	only one ipAdEntIfIndex for each IP address.  For example, if eth0 and
1972	eth1 are slaves of bond0 and the driver for eth0 is loaded before the
1973	bonding driver, the interface for the IP address will be associated
1974	with the eth0 interface.  This configuration is shown below, the IP
1975	address 192.168.1.1 has an interface index of 2 which indexes to eth0
1976	in the ifDescr table (ifDescr.2).
1977	
1978	     interfaces.ifTable.ifEntry.ifDescr.1 = lo
1979	     interfaces.ifTable.ifEntry.ifDescr.2 = eth0
1980	     interfaces.ifTable.ifEntry.ifDescr.3 = eth1
1981	     interfaces.ifTable.ifEntry.ifDescr.4 = eth2
1982	     interfaces.ifTable.ifEntry.ifDescr.5 = eth3
1983	     interfaces.ifTable.ifEntry.ifDescr.6 = bond0
1984	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 5
1985	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
1986	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 4
1987	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
1988	
1989		This problem is avoided by loading the bonding driver before
1990	any network drivers participating in a bond.  Below is an example of
1991	loading the bonding driver first, the IP address 192.168.1.1 is
1992	correctly associated with ifDescr.2.
1993	
1994	     interfaces.ifTable.ifEntry.ifDescr.1 = lo
1995	     interfaces.ifTable.ifEntry.ifDescr.2 = bond0
1996	     interfaces.ifTable.ifEntry.ifDescr.3 = eth0
1997	     interfaces.ifTable.ifEntry.ifDescr.4 = eth1
1998	     interfaces.ifTable.ifEntry.ifDescr.5 = eth2
1999	     interfaces.ifTable.ifEntry.ifDescr.6 = eth3
2000	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 6
2001	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
2002	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 5
2003	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
2004	
2005		While some distributions may not report the interface name in
2006	ifDescr, the association between the IP address and IfIndex remains
2007	and SNMP functions such as Interface_Scan_Next will report that
2008	association.
2009	
2010	10. Promiscuous mode
2011	====================
2012	
2013		When running network monitoring tools, e.g., tcpdump, it is
2014	common to enable promiscuous mode on the device, so that all traffic
2015	is seen (instead of seeing only traffic destined for the local host).
2016	The bonding driver handles promiscuous mode changes to the bonding
2017	master device (e.g., bond0), and propagates the setting to the slave
2018	devices.
2019	
2020		For the balance-rr, balance-xor, broadcast, and 802.3ad modes,
2021	the promiscuous mode setting is propagated to all slaves.
2022	
2023		For the active-backup, balance-tlb and balance-alb modes, the
2024	promiscuous mode setting is propagated only to the active slave.
2025	
2026		For balance-tlb mode, the active slave is the slave currently
2027	receiving inbound traffic.
2028	
2029		For balance-alb mode, the active slave is the slave used as a
2030	"primary."  This slave is used for mode-specific control traffic, for
2031	sending to peers that are unassigned or if the load is unbalanced.
2032	
2033		For the active-backup, balance-tlb and balance-alb modes, when
2034	the active slave changes (e.g., due to a link failure), the
2035	promiscuous setting will be propagated to the new active slave.
2036	
2037	11. Configuring Bonding for High Availability
2038	=============================================
2039	
2040		High Availability refers to configurations that provide
2041	maximum network availability by having redundant or backup devices,
2042	links or switches between the host and the rest of the world.  The
2043	goal is to provide the maximum availability of network connectivity
2044	(i.e., the network always works), even though other configurations
2045	could provide higher throughput.
2046	
2047	11.1 High Availability in a Single Switch Topology
2048	--------------------------------------------------
2049	
2050		If two hosts (or a host and a single switch) are directly
2051	connected via multiple physical links, then there is no availability
2052	penalty to optimizing for maximum bandwidth.  In this case, there is
2053	only one switch (or peer), so if it fails, there is no alternative
2054	access to fail over to.  Additionally, the bonding load balance modes
2055	support link monitoring of their members, so if individual links fail,
2056	the load will be rebalanced across the remaining devices.
2057	
2058		See Section 12, "Configuring Bonding for Maximum Throughput"
2059	for information on configuring bonding with one peer device.
2060	
2061	11.2 High Availability in a Multiple Switch Topology
2062	----------------------------------------------------
2063	
2064		With multiple switches, the configuration of bonding and the
2065	network changes dramatically.  In multiple switch topologies, there is
2066	a trade off between network availability and usable bandwidth.
2067	
2068		Below is a sample network, configured to maximize the
2069	availability of the network:
2070	
2071	                |                                     |
2072	                |port3                           port3|
2073	          +-----+----+                          +-----+----+
2074	          |          |port2       ISL      port2|          |
2075	          | switch A +--------------------------+ switch B |
2076	          |          |                          |          |
2077	          +-----+----+                          +-----++---+
2078	                |port1                           port1|
2079	                |             +-------+               |
2080	                +-------------+ host1 +---------------+
2081	                         eth0 +-------+ eth1
2082	
2083		In this configuration, there is a link between the two
2084	switches (ISL, or inter switch link), and multiple ports connecting to
2085	the outside world ("port3" on each switch).  There is no technical
2086	reason that this could not be extended to a third switch.
2087	
2088	11.2.1 HA Bonding Mode Selection for Multiple Switch Topology
2089	-------------------------------------------------------------
2090	
2091		In a topology such as the example above, the active-backup and
2092	broadcast modes are the only useful bonding modes when optimizing for
2093	availability; the other modes require all links to terminate on the
2094	same peer for them to behave rationally.
2095	
2096	active-backup: This is generally the preferred mode, particularly if
2097		the switches have an ISL and play together well.  If the
2098		network configuration is such that one switch is specifically
2099		a backup switch (e.g., has lower capacity, higher cost, etc),
2100		then the primary option can be used to insure that the
2101		preferred link is always used when it is available.
2102	
2103	broadcast: This mode is really a special purpose mode, and is suitable
2104		only for very specific needs.  For example, if the two
2105		switches are not connected (no ISL), and the networks beyond
2106		them are totally independent.  In this case, if it is
2107		necessary for some specific one-way traffic to reach both
2108		independent networks, then the broadcast mode may be suitable.
2109	
2110	11.2.2 HA Link Monitoring Selection for Multiple Switch Topology
2111	----------------------------------------------------------------
2112	
2113		The choice of link monitoring ultimately depends upon your
2114	switch.  If the switch can reliably fail ports in response to other
2115	failures, then either the MII or ARP monitors should work.  For
2116	example, in the above example, if the "port3" link fails at the remote
2117	end, the MII monitor has no direct means to detect this.  The ARP
2118	monitor could be configured with a target at the remote end of port3,
2119	thus detecting that failure without switch support.
2120	
2121		In general, however, in a multiple switch topology, the ARP
2122	monitor can provide a higher level of reliability in detecting end to
2123	end connectivity failures (which may be caused by the failure of any
2124	individual component to pass traffic for any reason).  Additionally,
2125	the ARP monitor should be configured with multiple targets (at least
2126	one for each switch in the network).  This will insure that,
2127	regardless of which switch is active, the ARP monitor has a suitable
2128	target to query.
2129	
2130		Note, also, that of late many switches now support a functionality
2131	generally referred to as "trunk failover."  This is a feature of the
2132	switch that causes the link state of a particular switch port to be set
2133	down (or up) when the state of another switch port goes down (or up).
2134	Its purpose is to propagate link failures from logically "exterior" ports
2135	to the logically "interior" ports that bonding is able to monitor via
2136	miimon.  Availability and configuration for trunk failover varies by
2137	switch, but this can be a viable alternative to the ARP monitor when using
2138	suitable switches.
2139	
2140	12. Configuring Bonding for Maximum Throughput
2141	==============================================
2142	
2143	12.1 Maximizing Throughput in a Single Switch Topology
2144	------------------------------------------------------
2145	
2146		In a single switch configuration, the best method to maximize
2147	throughput depends upon the application and network environment.  The
2148	various load balancing modes each have strengths and weaknesses in
2149	different environments, as detailed below.
2150	
2151		For this discussion, we will break down the topologies into
2152	two categories.  Depending upon the destination of most traffic, we
2153	categorize them into either "gatewayed" or "local" configurations.
2154	
2155		In a gatewayed configuration, the "switch" is acting primarily
2156	as a router, and the majority of traffic passes through this router to
2157	other networks.  An example would be the following:
2158	
2159	
2160	     +----------+                     +----------+
2161	     |          |eth0            port1|          | to other networks
2162	     | Host A   +---------------------+ router   +------------------->
2163	     |          +---------------------+          | Hosts B and C are out
2164	     |          |eth1            port2|          | here somewhere
2165	     +----------+                     +----------+
2166	
2167		The router may be a dedicated router device, or another host
2168	acting as a gateway.  For our discussion, the important point is that
2169	the majority of traffic from Host A will pass through the router to
2170	some other network before reaching its final destination.
2171	
2172		In a gatewayed network configuration, although Host A may
2173	communicate with many other systems, all of its traffic will be sent
2174	and received via one other peer on the local network, the router.
2175	
2176		Note that the case of two systems connected directly via
2177	multiple physical links is, for purposes of configuring bonding, the
2178	same as a gatewayed configuration.  In that case, it happens that all
2179	traffic is destined for the "gateway" itself, not some other network
2180	beyond the gateway.
2181	
2182		In a local configuration, the "switch" is acting primarily as
2183	a switch, and the majority of traffic passes through this switch to
2184	reach other stations on the same network.  An example would be the
2185	following:
2186	
2187	    +----------+            +----------+       +--------+
2188	    |          |eth0   port1|          +-------+ Host B |
2189	    |  Host A  +------------+  switch  |port3  +--------+
2190	    |          +------------+          |                  +--------+
2191	    |          |eth1   port2|          +------------------+ Host C |
2192	    +----------+            +----------+port4             +--------+
2193	
2194	
2195		Again, the switch may be a dedicated switch device, or another
2196	host acting as a gateway.  For our discussion, the important point is
2197	that the majority of traffic from Host A is destined for other hosts
2198	on the same local network (Hosts B and C in the above example).
2199	
2200		In summary, in a gatewayed configuration, traffic to and from
2201	the bonded device will be to the same MAC level peer on the network
2202	(the gateway itself, i.e., the router), regardless of its final
2203	destination.  In a local configuration, traffic flows directly to and
2204	from the final destinations, thus, each destination (Host B, Host C)
2205	will be addressed directly by their individual MAC addresses.
2206	
2207		This distinction between a gatewayed and a local network
2208	configuration is important because many of the load balancing modes
2209	available use the MAC addresses of the local network source and
2210	destination to make load balancing decisions.  The behavior of each
2211	mode is described below.
2212	
2213	
2214	12.1.1 MT Bonding Mode Selection for Single Switch Topology
2215	-----------------------------------------------------------
2216	
2217		This configuration is the easiest to set up and to understand,
2218	although you will have to decide which bonding mode best suits your
2219	needs.  The trade offs for each mode are detailed below:
2220	
2221	balance-rr: This mode is the only mode that will permit a single
2222		TCP/IP connection to stripe traffic across multiple
2223		interfaces. It is therefore the only mode that will allow a
2224		single TCP/IP stream to utilize more than one interface's
2225		worth of throughput.  This comes at a cost, however: the
2226		striping generally results in peer systems receiving packets out
2227		of order, causing TCP/IP's congestion control system to kick
2228		in, often by retransmitting segments.
2229	
2230		It is possible to adjust TCP/IP's congestion limits by
2231		altering the net.ipv4.tcp_reordering sysctl parameter.  The
2232		usual default value is 3, and the maximum useful value is 127.
2233		For a four interface balance-rr bond, expect that a single
2234		TCP/IP stream will utilize no more than approximately 2.3
2235		interface's worth of throughput, even after adjusting
2236		tcp_reordering.
2237	
2238		Note that the fraction of packets that will be delivered out of
2239		order is highly variable, and is unlikely to be zero.  The level
2240		of reordering depends upon a variety of factors, including the
2241		networking interfaces, the switch, and the topology of the
2242		configuration.  Speaking in general terms, higher speed network
2243		cards produce more reordering (due to factors such as packet
2244		coalescing), and a "many to many" topology will reorder at a
2245		higher rate than a "many slow to one fast" configuration.
2246	
2247		Many switches do not support any modes that stripe traffic
2248		(instead choosing a port based upon IP or MAC level addresses);
2249		for those devices, traffic for a particular connection flowing
2250		through the switch to a balance-rr bond will not utilize greater
2251		than one interface's worth of bandwidth.
2252	
2253		If you are utilizing protocols other than TCP/IP, UDP for
2254		example, and your application can tolerate out of order
2255		delivery, then this mode can allow for single stream datagram
2256		performance that scales near linearly as interfaces are added
2257		to the bond.
2258	
2259		This mode requires the switch to have the appropriate ports
2260		configured for "etherchannel" or "trunking."
2261	
2262	active-backup: There is not much advantage in this network topology to
2263		the active-backup mode, as the inactive backup devices are all
2264		connected to the same peer as the primary.  In this case, a
2265		load balancing mode (with link monitoring) will provide the
2266		same level of network availability, but with increased
2267		available bandwidth.  On the plus side, active-backup mode
2268		does not require any configuration of the switch, so it may
2269		have value if the hardware available does not support any of
2270		the load balance modes.
2271	
2272	balance-xor: This mode will limit traffic such that packets destined
2273		for specific peers will always be sent over the same
2274		interface.  Since the destination is determined by the MAC
2275		addresses involved, this mode works best in a "local" network
2276		configuration (as described above), with destinations all on
2277		the same local network.  This mode is likely to be suboptimal
2278		if all your traffic is passed through a single router (i.e., a
2279		"gatewayed" network configuration, as described above).
2280	
2281		As with balance-rr, the switch ports need to be configured for
2282		"etherchannel" or "trunking."
2283	
2284	broadcast: Like active-backup, there is not much advantage to this
2285		mode in this type of network topology.
2286	
2287	802.3ad: This mode can be a good choice for this type of network
2288		topology.  The 802.3ad mode is an IEEE standard, so all peers
2289		that implement 802.3ad should interoperate well.  The 802.3ad
2290		protocol includes automatic configuration of the aggregates,
2291		so minimal manual configuration of the switch is needed
2292		(typically only to designate that some set of devices is
2293		available for 802.3ad).  The 802.3ad standard also mandates
2294		that frames be delivered in order (within certain limits), so
2295		in general single connections will not see misordering of
2296		packets.  The 802.3ad mode does have some drawbacks: the
2297		standard mandates that all devices in the aggregate operate at
2298		the same speed and duplex.  Also, as with all bonding load
2299		balance modes other than balance-rr, no single connection will
2300		be able to utilize more than a single interface's worth of
2301		bandwidth.  
2302	
2303		Additionally, the linux bonding 802.3ad implementation
2304		distributes traffic by peer (using an XOR of MAC addresses),
2305		so in a "gatewayed" configuration, all outgoing traffic will
2306		generally use the same device.  Incoming traffic may also end
2307		up on a single device, but that is dependent upon the
2308		balancing policy of the peer's 8023.ad implementation.  In a
2309		"local" configuration, traffic will be distributed across the
2310		devices in the bond.
2311	
2312		Finally, the 802.3ad mode mandates the use of the MII monitor,
2313		therefore, the ARP monitor is not available in this mode.
2314	
2315	balance-tlb: The balance-tlb mode balances outgoing traffic by peer.
2316		Since the balancing is done according to MAC address, in a
2317		"gatewayed" configuration (as described above), this mode will
2318		send all traffic across a single device.  However, in a
2319		"local" network configuration, this mode balances multiple
2320		local network peers across devices in a vaguely intelligent
2321		manner (not a simple XOR as in balance-xor or 802.3ad mode),
2322		so that mathematically unlucky MAC addresses (i.e., ones that
2323		XOR to the same value) will not all "bunch up" on a single
2324		interface.
2325	
2326		Unlike 802.3ad, interfaces may be of differing speeds, and no
2327		special switch configuration is required.  On the down side,
2328		in this mode all incoming traffic arrives over a single
2329		interface, this mode requires certain ethtool support in the
2330		network device driver of the slave interfaces, and the ARP
2331		monitor is not available.
2332	
2333	balance-alb: This mode is everything that balance-tlb is, and more.
2334		It has all of the features (and restrictions) of balance-tlb,
2335		and will also balance incoming traffic from local network
2336		peers (as described in the Bonding Module Options section,
2337		above).
2338	
2339		The only additional down side to this mode is that the network
2340		device driver must support changing the hardware address while
2341		the device is open.
2342	
2343	12.1.2 MT Link Monitoring for Single Switch Topology
2344	----------------------------------------------------
2345	
2346		The choice of link monitoring may largely depend upon which
2347	mode you choose to use.  The more advanced load balancing modes do not
2348	support the use of the ARP monitor, and are thus restricted to using
2349	the MII monitor (which does not provide as high a level of end to end
2350	assurance as the ARP monitor).
2351	
2352	12.2 Maximum Throughput in a Multiple Switch Topology
2353	-----------------------------------------------------
2354	
2355		Multiple switches may be utilized to optimize for throughput
2356	when they are configured in parallel as part of an isolated network
2357	between two or more systems, for example:
2358	
2359	                       +-----------+
2360	                       |  Host A   | 
2361	                       +-+---+---+-+
2362	                         |   |   |
2363	                +--------+   |   +---------+
2364	                |            |             |
2365	         +------+---+  +-----+----+  +-----+----+
2366	         | Switch A |  | Switch B |  | Switch C |
2367	         +------+---+  +-----+----+  +-----+----+
2368	                |            |             |
2369	                +--------+   |   +---------+
2370	                         |   |   |
2371	                       +-+---+---+-+
2372	                       |  Host B   | 
2373	                       +-----------+
2374	
2375		In this configuration, the switches are isolated from one
2376	another.  One reason to employ a topology such as this is for an
2377	isolated network with many hosts (a cluster configured for high
2378	performance, for example), using multiple smaller switches can be more
2379	cost effective than a single larger switch, e.g., on a network with 24
2380	hosts, three 24 port switches can be significantly less expensive than
2381	a single 72 port switch.
2382	
2383		If access beyond the network is required, an individual host
2384	can be equipped with an additional network device connected to an
2385	external network; this host then additionally acts as a gateway.
2386	
2387	12.2.1 MT Bonding Mode Selection for Multiple Switch Topology
2388	-------------------------------------------------------------
2389	
2390		In actual practice, the bonding mode typically employed in
2391	configurations of this type is balance-rr.  Historically, in this
2392	network configuration, the usual caveats about out of order packet
2393	delivery are mitigated by the use of network adapters that do not do
2394	any kind of packet coalescing (via the use of NAPI, or because the
2395	device itself does not generate interrupts until some number of
2396	packets has arrived).  When employed in this fashion, the balance-rr
2397	mode allows individual connections between two hosts to effectively
2398	utilize greater than one interface's bandwidth.
2399	
2400	12.2.2 MT Link Monitoring for Multiple Switch Topology
2401	------------------------------------------------------
2402	
2403		Again, in actual practice, the MII monitor is most often used
2404	in this configuration, as performance is given preference over
2405	availability.  The ARP monitor will function in this topology, but its
2406	advantages over the MII monitor are mitigated by the volume of probes
2407	needed as the number of systems involved grows (remember that each
2408	host in the network is configured with bonding).
2409	
2410	13. Switch Behavior Issues
2411	==========================
2412	
2413	13.1 Link Establishment and Failover Delays
2414	-------------------------------------------
2415	
2416		Some switches exhibit undesirable behavior with regard to the
2417	timing of link up and down reporting by the switch.
2418	
2419		First, when a link comes up, some switches may indicate that
2420	the link is up (carrier available), but not pass traffic over the
2421	interface for some period of time.  This delay is typically due to
2422	some type of autonegotiation or routing protocol, but may also occur
2423	during switch initialization (e.g., during recovery after a switch
2424	failure).  If you find this to be a problem, specify an appropriate
2425	value to the updelay bonding module option to delay the use of the
2426	relevant interface(s).
2427	
2428		Second, some switches may "bounce" the link state one or more
2429	times while a link is changing state.  This occurs most commonly while
2430	the switch is initializing.  Again, an appropriate updelay value may
2431	help.
2432	
2433		Note that when a bonding interface has no active links, the
2434	driver will immediately reuse the first link that goes up, even if the
2435	updelay parameter has been specified (the updelay is ignored in this
2436	case).  If there are slave interfaces waiting for the updelay timeout
2437	to expire, the interface that first went into that state will be
2438	immediately reused.  This reduces down time of the network if the
2439	value of updelay has been overestimated, and since this occurs only in
2440	cases with no connectivity, there is no additional penalty for
2441	ignoring the updelay.
2442	
2443		In addition to the concerns about switch timings, if your
2444	switches take a long time to go into backup mode, it may be desirable
2445	to not activate a backup interface immediately after a link goes down.
2446	Failover may be delayed via the downdelay bonding module option.
2447	
2448	13.2 Duplicated Incoming Packets
2449	--------------------------------
2450	
2451		NOTE: Starting with version 3.0.2, the bonding driver has logic to
2452	suppress duplicate packets, which should largely eliminate this problem.
2453	The following description is kept for reference.
2454	
2455		It is not uncommon to observe a short burst of duplicated
2456	traffic when the bonding device is first used, or after it has been
2457	idle for some period of time.  This is most easily observed by issuing
2458	a "ping" to some other host on the network, and noticing that the
2459	output from ping flags duplicates (typically one per slave).
2460	
2461		For example, on a bond in active-backup mode with five slaves
2462	all connected to one switch, the output may appear as follows:
2463	
2464	# ping -n 10.0.4.2
2465	PING 10.0.4.2 (10.0.4.2) from 10.0.3.10 : 56(84) bytes of data.
2466	64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.7 ms
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=1 ttl=64 time=13.8 ms (DUP!)
2470	64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2471	64 bytes from 10.0.4.2: icmp_seq=2 ttl=64 time=0.216 ms
2472	64 bytes from 10.0.4.2: icmp_seq=3 ttl=64 time=0.267 ms
2473	64 bytes from 10.0.4.2: icmp_seq=4 ttl=64 time=0.222 ms
2474	
2475		This is not due to an error in the bonding driver, rather, it
2476	is a side effect of how many switches update their MAC forwarding
2477	tables.  Initially, the switch does not associate the MAC address in
2478	the packet with a particular switch port, and so it may send the
2479	traffic to all ports until its MAC forwarding table is updated.  Since
2480	the interfaces attached to the bond may occupy multiple ports on a
2481	single switch, when the switch (temporarily) floods the traffic to all
2482	ports, the bond device receives multiple copies of the same packet
2483	(one per slave device).
2484	
2485		The duplicated packet behavior is switch dependent, some
2486	switches exhibit this, and some do not.  On switches that display this
2487	behavior, it can be induced by clearing the MAC forwarding table (on
2488	most Cisco switches, the privileged command "clear mac address-table
2489	dynamic" will accomplish this).
2490	
2491	14. Hardware Specific Considerations
2492	====================================
2493	
2494		This section contains additional information for configuring
2495	bonding on specific hardware platforms, or for interfacing bonding
2496	with particular switches or other devices.
2497	
2498	14.1 IBM BladeCenter
2499	--------------------
2500	
2501		This applies to the JS20 and similar systems.
2502	
2503		On the JS20 blades, the bonding driver supports only
2504	balance-rr, active-backup, balance-tlb and balance-alb modes.  This is
2505	largely due to the network topology inside the BladeCenter, detailed
2506	below.
2507	
2508	JS20 network adapter information
2509	--------------------------------
2510	
2511		All JS20s come with two Broadcom Gigabit Ethernet ports
2512	integrated on the planar (that's "motherboard" in IBM-speak).  In the
2513	BladeCenter chassis, the eth0 port of all JS20 blades is hard wired to
2514	I/O Module #1; similarly, all eth1 ports are wired to I/O Module #2.
2515	An add-on Broadcom daughter card can be installed on a JS20 to provide
2516	two more Gigabit Ethernet ports.  These ports, eth2 and eth3, are
2517	wired to I/O Modules 3 and 4, respectively.
2518	
2519		Each I/O Module may contain either a switch or a passthrough
2520	module (which allows ports to be directly connected to an external
2521	switch).  Some bonding modes require a specific BladeCenter internal
2522	network topology in order to function; these are detailed below.
2523	
2524		Additional BladeCenter-specific networking information can be
2525	found in two IBM Redbooks (www.ibm.com/redbooks):
2526	
2527	"IBM eServer BladeCenter Networking Options"
2528	"IBM eServer BladeCenter Layer 2-7 Network Switching"
2529	
2530	BladeCenter networking configuration
2531	------------------------------------
2532	
2533		Because a BladeCenter can be configured in a very large number
2534	of ways, this discussion will be confined to describing basic
2535	configurations.
2536	
2537		Normally, Ethernet Switch Modules (ESMs) are used in I/O
2538	modules 1 and 2.  In this configuration, the eth0 and eth1 ports of a
2539	JS20 will be connected to different internal switches (in the
2540	respective I/O modules).
2541	
2542		A passthrough module (OPM or CPM, optical or copper,
2543	passthrough module) connects the I/O module directly to an external
2544	switch.  By using PMs in I/O module #1 and #2, the eth0 and eth1
2545	interfaces of a JS20 can be redirected to the outside world and
2546	connected to a common external switch.
2547	
2548		Depending upon the mix of ESMs and PMs, the network will
2549	appear to bonding as either a single switch topology (all PMs) or as a
2550	multiple switch topology (one or more ESMs, zero or more PMs).  It is
2551	also possible to connect ESMs together, resulting in a configuration
2552	much like the example in "High Availability in a Multiple Switch
2553	Topology," above.
2554	
2555	Requirements for specific modes
2556	-------------------------------
2557	
2558		The balance-rr mode requires the use of passthrough modules
2559	for devices in the bond, all connected to an common external switch.
2560	That switch must be configured for "etherchannel" or "trunking" on the
2561	appropriate ports, as is usual for balance-rr.
2562	
2563		The balance-alb and balance-tlb modes will function with
2564	either switch modules or passthrough modules (or a mix).  The only
2565	specific requirement for these modes is that all network interfaces
2566	must be able to reach all destinations for traffic sent over the
2567	bonding device (i.e., the network must converge at some point outside
2568	the BladeCenter).
2569	
2570		The active-backup mode has no additional requirements.
2571	
2572	Link monitoring issues
2573	----------------------
2574	
2575		When an Ethernet Switch Module is in place, only the ARP
2576	monitor will reliably detect link loss to an external switch.  This is
2577	nothing unusual, but examination of the BladeCenter cabinet would
2578	suggest that the "external" network ports are the ethernet ports for
2579	the system, when it fact there is a switch between these "external"
2580	ports and the devices on the JS20 system itself.  The MII monitor is
2581	only able to detect link failures between the ESM and the JS20 system.
2582	
2583		When a passthrough module is in place, the MII monitor does
2584	detect failures to the "external" port, which is then directly
2585	connected to the JS20 system.
2586	
2587	Other concerns
2588	--------------
2589	
2590		The Serial Over LAN (SoL) link is established over the primary
2591	ethernet (eth0) only, therefore, any loss of link to eth0 will result
2592	in losing your SoL connection.  It will not fail over with other
2593	network traffic, as the SoL system is beyond the control of the
2594	bonding driver.
2595	
2596		It may be desirable to disable spanning tree on the switch
2597	(either the internal Ethernet Switch Module, or an external switch) to
2598	avoid fail-over delay issues when using bonding.
2599	
2600		
2601	15. Frequently Asked Questions
2602	==============================
2603	
2604	1.  Is it SMP safe?
2605	
2606		Yes. The old 2.0.xx channel bonding patch was not SMP safe.
2607	The new driver was designed to be SMP safe from the start.
2608	
2609	2.  What type of cards will work with it?
2610	
2611		Any Ethernet type cards (you can even mix cards - a Intel
2612	EtherExpress PRO/100 and a 3com 3c905b, for example).  For most modes,
2613	devices need not be of the same speed.
2614	
2615		Starting with version 3.2.1, bonding also supports Infiniband
2616	slaves in active-backup mode.
2617	
2618	3.  How many bonding devices can I have?
2619	
2620		There is no limit.
2621	
2622	4.  How many slaves can a bonding device have?
2623	
2624		This is limited only by the number of network interfaces Linux
2625	supports and/or the number of network cards you can place in your
2626	system.
2627	
2628	5.  What happens when a slave link dies?
2629	
2630		If link monitoring is enabled, then the failing device will be
2631	disabled.  The active-backup mode will fail over to a backup link, and
2632	other modes will ignore the failed link.  The link will continue to be
2633	monitored, and should it recover, it will rejoin the bond (in whatever
2634	manner is appropriate for the mode). See the sections on High
2635	Availability and the documentation for each mode for additional
2636	information.
2637		
2638		Link monitoring can be enabled via either the miimon or
2639	arp_interval parameters (described in the module parameters section,
2640	above).  In general, miimon monitors the carrier state as sensed by
2641	the underlying network device, and the arp monitor (arp_interval)
2642	monitors connectivity to another host on the local network.
2643	
2644		If no link monitoring is configured, the bonding driver will
2645	be unable to detect link failures, and will assume that all links are
2646	always available.  This will likely result in lost packets, and a
2647	resulting degradation of performance.  The precise performance loss
2648	depends upon the bonding mode and network configuration.
2649	
2650	6.  Can bonding be used for High Availability?
2651	
2652		Yes.  See the section on High Availability for details.
2653	
2654	7.  Which switches/systems does it work with?
2655	
2656		The full answer to this depends upon the desired mode.
2657	
2658		In the basic balance modes (balance-rr and balance-xor), it
2659	works with any system that supports etherchannel (also called
2660	trunking).  Most managed switches currently available have such
2661	support, and many unmanaged switches as well.
2662	
2663		The advanced balance modes (balance-tlb and balance-alb) do
2664	not have special switch requirements, but do need device drivers that
2665	support specific features (described in the appropriate section under
2666	module parameters, above).
2667	
2668		In 802.3ad mode, it works with systems that support IEEE
2669	802.3ad Dynamic Link Aggregation.  Most managed and many unmanaged
2670	switches currently available support 802.3ad.
2671	
2672	        The active-backup mode should work with any Layer-II switch.
2673	
2674	8.  Where does a bonding device get its MAC address from?
2675	
2676		When using slave devices that have fixed MAC addresses, or when
2677	the fail_over_mac option is enabled, the bonding device's MAC address is
2678	the MAC address of the active slave.
2679	
2680		For other configurations, if not explicitly configured (with
2681	ifconfig or ip link), the MAC address of the bonding device is taken from
2682	its first slave device.  This MAC address is then passed to all following
2683	slaves and remains persistent (even if the first slave is removed) until
2684	the bonding device is brought down or reconfigured.
2685	
2686		If you wish to change the MAC address, you can set it with
2687	ifconfig or ip link:
2688	
2689	# ifconfig bond0 hw ether 00:11:22:33:44:55
2690	
2691	# ip link set bond0 address 66:77:88:99:aa:bb
2692	
2693		The MAC address can be also changed by bringing down/up the
2694	device and then changing its slaves (or their order):
2695	
2696	# ifconfig bond0 down ; modprobe -r bonding
2697	# ifconfig bond0 .... up
2698	# ifenslave bond0 eth...
2699	
2700		This method will automatically take the address from the next
2701	slave that is added.
2702	
2703		To restore your slaves' MAC addresses, you need to detach them
2704	from the bond (`ifenslave -d bond0 eth0'). The bonding driver will
2705	then restore the MAC addresses that the slaves had before they were
2706	enslaved.
2707	
2708	16. Resources and Links
2709	=======================
2710	
2711		The latest version of the bonding driver can be found in the latest
2712	version of the linux kernel, found on http://kernel.org
2713	
2714		The latest version of this document can be found in the latest kernel
2715	source (named Documentation/networking/bonding.txt).
2716	
2717		Discussions regarding the usage of the bonding driver take place on the
2718	bonding-devel mailing list, hosted at sourceforge.net. If you have questions or
2719	problems, post them to the list.  The list address is:
2720	
2721	bonding-devel@lists.sourceforge.net
2722	
2723		The administrative interface (to subscribe or unsubscribe) can
2724	be found at:
2725	
2726	https://lists.sourceforge.net/lists/listinfo/bonding-devel
2727	
2728		Discussions regarding the development of the bonding driver take place
2729	on the main Linux network mailing list, hosted at vger.kernel.org. The list
2730	address is:
2731	
2732	netdev@vger.kernel.org
2733	
2734		The administrative interface (to subscribe or unsubscribe) can
2735	be found at:
2736	
2737	http://vger.kernel.org/vger-lists.html#netdev
2738	
2739	Donald Becker's Ethernet Drivers and diag programs may be found at :
2740	 - http://web.archive.org/web/*/http://www.scyld.com/network/ 
2741	
2742	You will also find a lot of information regarding Ethernet, NWay, MII,
2743	etc. at www.scyld.com.
2744	
2745	-- END --
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