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Based on kernel version 4.3. Page generated on 2015-11-02 12:50 EST.

2			Linux Ethernet Bonding Driver HOWTO
4			Latest update: 27 April 2011
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>
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>
18	Introduction
19	============
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.
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.
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.
35	Table of Contents
36	=================
38	1. Bonding Driver Installation
40	2. Bonding Driver Options
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	3.7 Configuring LACP for 802.3ad mode in a more secure way
56	4. Querying Bonding Configuration
57	4.1	Bonding Configuration
58	4.2	Network Configuration
60	5. Switch Configuration
62	6. 802.1q VLAN Support
64	7. Link Monitoring
65	7.1	ARP Monitor Operation
66	7.2	Configuring Multiple ARP Targets
67	7.3	MII Monitor Operation
69	8. Potential Trouble Sources
70	8.1	Adventures in Routing
71	8.2	Ethernet Device Renaming
72	8.3	Painfully Slow Or No Failed Link Detection By Miimon
74	9. SNMP agents
76	10. Promiscuous mode
78	11. Configuring Bonding for High Availability
79	11.1	High Availability in a Single Switch Topology
80	11.2	High Availability in a Multiple Switch Topology
81	11.2.1		HA Bonding Mode Selection for Multiple Switch Topology
82	11.2.2		HA Link Monitoring for Multiple Switch Topology
84	12. Configuring Bonding for Maximum Throughput
85	12.1	Maximum Throughput in a Single Switch Topology
86	12.1.1		MT Bonding Mode Selection for Single Switch Topology
87	12.1.2		MT Link Monitoring for Single Switch Topology
88	12.2	Maximum Throughput in a Multiple Switch Topology
89	12.2.1		MT Bonding Mode Selection for Multiple Switch Topology
90	12.2.2		MT Link Monitoring for Multiple Switch Topology
92	13. Switch Behavior Issues
93	13.1	Link Establishment and Failover Delays
94	13.2	Duplicated Incoming Packets
96	14. Hardware Specific Considerations
97	14.1	IBM BladeCenter
99	15. Frequently Asked Questions
101	16. Resources and Links
104	1. Bonding Driver Installation
105	==============================
107		Most popular distro kernels ship with the bonding driver
108	already available as a module. If your distro does not, or you
109	have need to compile bonding from source (e.g., configuring and
110	installing a mainline kernel from kernel.org), you'll need to perform
111	the following steps:
113	1.1 Configure and build the kernel with bonding
114	-----------------------------------------------
116		The current version of the bonding driver is available in the
117	drivers/net/bonding subdirectory of the most recent kernel source
118	(which is available on http://kernel.org).  Most users "rolling their
119	own" will want to use the most recent kernel from kernel.org.
121		Configure kernel with "make menuconfig" (or "make xconfig" or
122	"make config"), then select "Bonding driver support" in the "Network
123	device support" section.  It is recommended that you configure the
124	driver as module since it is currently the only way to pass parameters
125	to the driver or configure more than one bonding device.
127		Build and install the new kernel and modules.
129	1.2 Bonding Control Utility
130	-------------------------------------
132		 It is recommended to configure bonding via iproute2 (netlink)
133	or sysfs, the old ifenslave control utility is obsolete.
135	2. Bonding Driver Options
136	=========================
138		Options for the bonding driver are supplied as parameters to the
139	bonding module at load time, or are specified via sysfs.
141		Module options may be given as command line arguments to the
142	insmod or modprobe command, but are usually specified in either the
143	/etc/modrobe.d/*.conf configuration files, or in a distro-specific
144	configuration file (some of which are detailed in the next section).
146		Details on bonding support for sysfs is provided in the
147	"Configuring Bonding Manually via Sysfs" section, below.
149		The available bonding driver parameters are listed below. If a
150	parameter is not specified the default value is used.  When initially
151	configuring a bond, it is recommended "tail -f /var/log/messages" be
152	run in a separate window to watch for bonding driver error messages.
154		It is critical that either the miimon or arp_interval and
155	arp_ip_target parameters be specified, otherwise serious network
156	degradation will occur during link failures.  Very few devices do not
157	support at least miimon, so there is really no reason not to use it.
159		Options with textual values will accept either the text name
160	or, for backwards compatibility, the option value.  E.g.,
161	"mode=802.3ad" and "mode=4" set the same mode.
163		The parameters are as follows:
165	active_slave
167		Specifies the new active slave for modes that support it
168		(active-backup, balance-alb and balance-tlb).  Possible values
169		are the name of any currently enslaved interface, or an empty
170		string.  If a name is given, the slave and its link must be up in order
171		to be selected as the new active slave.  If an empty string is
172		specified, the current active slave is cleared, and a new active
173		slave is selected automatically.
175		Note that this is only available through the sysfs interface. No module
176		parameter by this name exists.
178		The normal value of this option is the name of the currently
179		active slave, or the empty string if there is no active slave or
180		the current mode does not use an active slave.
182	ad_actor_sys_prio
184		In an AD system, this specifies the system priority. The allowed range
185		is 1 - 65535. If the value is not specified, it takes 65535 as the
186		default value.
188		This parameter has effect only in 802.3ad mode and is available through
189		SysFs interface.
191	ad_actor_system
193		In an AD system, this specifies the mac-address for the actor in
194		protocol packet exchanges (LACPDUs). The value cannot be NULL or
195		multicast. It is preferred to have the local-admin bit set for this
196		mac but driver does not enforce it. If the value is not given then
197		system defaults to using the masters' mac address as actors' system
198		address.
200		This parameter has effect only in 802.3ad mode and is available through
201		SysFs interface.
203	ad_select
205		Specifies the 802.3ad aggregation selection logic to use.  The
206		possible values and their effects are:
208		stable or 0
210			The active aggregator is chosen by largest aggregate
211			bandwidth.
213			Reselection of the active aggregator occurs only when all
214			slaves of the active aggregator are down or the active
215			aggregator has no slaves.
217			This is the default value.
219		bandwidth or 1
221			The active aggregator is chosen by largest aggregate
222			bandwidth.  Reselection occurs if:
224			- A slave is added to or removed from the bond
226			- Any slave's link state changes
228			- Any slave's 802.3ad association state changes
230			- The bond's administrative state changes to up
232		count or 2
234			The active aggregator is chosen by the largest number of
235			ports (slaves).  Reselection occurs as described under the
236			"bandwidth" setting, above.
238		The bandwidth and count selection policies permit failover of
239		802.3ad aggregations when partial failure of the active aggregator
240		occurs.  This keeps the aggregator with the highest availability
241		(either in bandwidth or in number of ports) active at all times.
243		This option was added in bonding version 3.4.0.
245	ad_user_port_key
247		In an AD system, the port-key has three parts as shown below -
249		   Bits   Use
250		   00     Duplex
251		   01-05  Speed
252		   06-15  User-defined
254		This defines the upper 10 bits of the port key. The values can be
255		from 0 - 1023. If not given, the system defaults to 0.
257		This parameter has effect only in 802.3ad mode and is available through
258		SysFs interface.
260	all_slaves_active
262		Specifies that duplicate frames (received on inactive ports) should be
263		dropped (0) or delivered (1).
265		Normally, bonding will drop duplicate frames (received on inactive
266		ports), which is desirable for most users. But there are some times
267		it is nice to allow duplicate frames to be delivered.
269		The default value is 0 (drop duplicate frames received on inactive
270		ports).
272	arp_interval
274		Specifies the ARP link monitoring frequency in milliseconds.
276		The ARP monitor works by periodically checking the slave
277		devices to determine whether they have sent or received
278		traffic recently (the precise criteria depends upon the
279		bonding mode, and the state of the slave).  Regular traffic is
280		generated via ARP probes issued for the addresses specified by
281		the arp_ip_target option.
283		This behavior can be modified by the arp_validate option,
284		below.
286		If ARP monitoring is used in an etherchannel compatible mode
287		(modes 0 and 2), the switch should be configured in a mode
288		that evenly distributes packets across all links. If the
289		switch is configured to distribute the packets in an XOR
290		fashion, all replies from the ARP targets will be received on
291		the same link which could cause the other team members to
292		fail.  ARP monitoring should not be used in conjunction with
293		miimon.  A value of 0 disables ARP monitoring.  The default
294		value is 0.
296	arp_ip_target
298		Specifies the IP addresses to use as ARP monitoring peers when
299		arp_interval is > 0.  These are the targets of the ARP request
300		sent to determine the health of the link to the targets.
301		Specify these values in ddd.ddd.ddd.ddd format.  Multiple IP
302		addresses must be separated by a comma.  At least one IP
303		address must be given for ARP monitoring to function.  The
304		maximum number of targets that can be specified is 16.  The
305		default value is no IP addresses.
307	arp_validate
309		Specifies whether or not ARP probes and replies should be
310		validated in any mode that supports arp monitoring, or whether
311		non-ARP traffic should be filtered (disregarded) for link
312		monitoring purposes.
314		Possible values are:
316		none or 0
318			No validation or filtering is performed.
320		active or 1
322			Validation is performed only for the active slave.
324		backup or 2
326			Validation is performed only for backup slaves.
328		all or 3
330			Validation is performed for all slaves.
332		filter or 4
334			Filtering is applied to all slaves. No validation is
335			performed.
337		filter_active or 5
339			Filtering is applied to all slaves, validation is performed
340			only for the active slave.
342		filter_backup or 6
344			Filtering is applied to all slaves, validation is performed
345			only for backup slaves.
347		Validation:
349		Enabling validation causes the ARP monitor to examine the incoming
350		ARP requests and replies, and only consider a slave to be up if it
351		is receiving the appropriate ARP traffic.
353		For an active slave, the validation checks ARP replies to confirm
354		that they were generated by an arp_ip_target.  Since backup slaves
355		do not typically receive these replies, the validation performed
356		for backup slaves is on the broadcast ARP request sent out via the
357		active slave.  It is possible that some switch or network
358		configurations may result in situations wherein the backup slaves
359		do not receive the ARP requests; in such a situation, validation
360		of backup slaves must be disabled.
362		The validation of ARP requests on backup slaves is mainly helping
363		bonding to decide which slaves are more likely to work in case of
364		the active slave failure, it doesn't really guarantee that the
365		backup slave will work if it's selected as the next active slave.
367		Validation is useful in network configurations in which multiple
368		bonding hosts are concurrently issuing ARPs to one or more targets
369		beyond a common switch.  Should the link between the switch and
370		target fail (but not the switch itself), the probe traffic
371		generated by the multiple bonding instances will fool the standard
372		ARP monitor into considering the links as still up.  Use of
373		validation can resolve this, as the ARP monitor will only consider
374		ARP requests and replies associated with its own instance of
375		bonding.
377		Filtering:
379		Enabling filtering causes the ARP monitor to only use incoming ARP
380		packets for link availability purposes.  Arriving packets that are
381		not ARPs are delivered normally, but do not count when determining
382		if a slave is available.
384		Filtering operates by only considering the reception of ARP
385		packets (any ARP packet, regardless of source or destination) when
386		determining if a slave has received traffic for link availability
387		purposes.
389		Filtering is useful in network configurations in which significant
390		levels of third party broadcast traffic would fool the standard
391		ARP monitor into considering the links as still up.  Use of
392		filtering can resolve this, as only ARP traffic is considered for
393		link availability purposes.
395		This option was added in bonding version 3.1.0.
397	arp_all_targets
399		Specifies the quantity of arp_ip_targets that must be reachable
400		in order for the ARP monitor to consider a slave as being up.
401		This option affects only active-backup mode for slaves with
402		arp_validation enabled.
404		Possible values are:
406		any or 0
408			consider the slave up only when any of the arp_ip_targets
409			is reachable
411		all or 1
413			consider the slave up only when all of the arp_ip_targets
414			are reachable
416	downdelay
418		Specifies the time, in milliseconds, to wait before disabling
419		a slave after a link failure has been detected.  This option
420		is only valid for the miimon link monitor.  The downdelay
421		value should be a multiple of the miimon value; if not, it
422		will be rounded down to the nearest multiple.  The default
423		value is 0.
425	fail_over_mac
427		Specifies whether active-backup mode should set all slaves to
428		the same MAC address at enslavement (the traditional
429		behavior), or, when enabled, perform special handling of the
430		bond's MAC address in accordance with the selected policy.
432		Possible values are:
434		none or 0
436			This setting disables fail_over_mac, and causes
437			bonding to set all slaves of an active-backup bond to
438			the same MAC address at enslavement time.  This is the
439			default.
441		active or 1
443			The "active" fail_over_mac policy indicates that the
444			MAC address of the bond should always be the MAC
445			address of the currently active slave.  The MAC
446			address of the slaves is not changed; instead, the MAC
447			address of the bond changes during a failover.
449			This policy is useful for devices that cannot ever
450			alter their MAC address, or for devices that refuse
451			incoming broadcasts with their own source MAC (which
452			interferes with the ARP monitor).
454			The down side of this policy is that every device on
455			the network must be updated via gratuitous ARP,
456			vs. just updating a switch or set of switches (which
457			often takes place for any traffic, not just ARP
458			traffic, if the switch snoops incoming traffic to
459			update its tables) for the traditional method.  If the
460			gratuitous ARP is lost, communication may be
461			disrupted.
463			When this policy is used in conjunction with the mii
464			monitor, devices which assert link up prior to being
465			able to actually transmit and receive are particularly
466			susceptible to loss of the gratuitous ARP, and an
467			appropriate updelay setting may be required.
469		follow or 2
471			The "follow" fail_over_mac policy causes the MAC
472			address of the bond to be selected normally (normally
473			the MAC address of the first slave added to the bond).
474			However, the second and subsequent slaves are not set
475			to this MAC address while they are in a backup role; a
476			slave is programmed with the bond's MAC address at
477			failover time (and the formerly active slave receives
478			the newly active slave's MAC address).
480			This policy is useful for multiport devices that
481			either become confused or incur a performance penalty
482			when multiple ports are programmed with the same MAC
483			address.
486		The default policy is none, unless the first slave cannot
487		change its MAC address, in which case the active policy is
488		selected by default.
490		This option may be modified via sysfs only when no slaves are
491		present in the bond.
493		This option was added in bonding version 3.2.0.  The "follow"
494		policy was added in bonding version 3.3.0.
496	lacp_rate
498		Option specifying the rate in which we'll ask our link partner
499		to transmit LACPDU packets in 802.3ad mode.  Possible values
500		are:
502		slow or 0
503			Request partner to transmit LACPDUs every 30 seconds
505		fast or 1
506			Request partner to transmit LACPDUs every 1 second
508		The default is slow.
510	max_bonds
512		Specifies the number of bonding devices to create for this
513		instance of the bonding driver.  E.g., if max_bonds is 3, and
514		the bonding driver is not already loaded, then bond0, bond1
515		and bond2 will be created.  The default value is 1.  Specifying
516		a value of 0 will load bonding, but will not create any devices.
518	miimon
520		Specifies the MII link monitoring frequency in milliseconds.
521		This determines how often the link state of each slave is
522		inspected for link failures.  A value of zero disables MII
523		link monitoring.  A value of 100 is a good starting point.
524		The use_carrier option, below, affects how the link state is
525		determined.  See the High Availability section for additional
526		information.  The default value is 0.
528	min_links
530		Specifies the minimum number of links that must be active before
531		asserting carrier. It is similar to the Cisco EtherChannel min-links
532		feature. This allows setting the minimum number of member ports that
533		must be up (link-up state) before marking the bond device as up
534		(carrier on). This is useful for situations where higher level services
535		such as clustering want to ensure a minimum number of low bandwidth
536		links are active before switchover. This option only affect 802.3ad
537		mode.
539		The default value is 0. This will cause carrier to be asserted (for
540		802.3ad mode) whenever there is an active aggregator, regardless of the
541		number of available links in that aggregator. Note that, because an
542		aggregator cannot be active without at least one available link,
543		setting this option to 0 or to 1 has the exact same effect.
545	mode
547		Specifies one of the bonding policies. The default is
548		balance-rr (round robin).  Possible values are:
550		balance-rr or 0
552			Round-robin policy: Transmit packets in sequential
553			order from the first available slave through the
554			last.  This mode provides load balancing and fault
555			tolerance.
557		active-backup or 1
559			Active-backup policy: Only one slave in the bond is
560			active.  A different slave becomes active if, and only
561			if, the active slave fails.  The bond's MAC address is
562			externally visible on only one port (network adapter)
563			to avoid confusing the switch.
565			In bonding version 2.6.2 or later, when a failover
566			occurs in active-backup mode, bonding will issue one
567			or more gratuitous ARPs on the newly active slave.
568			One gratuitous ARP is issued for the bonding master
569			interface and each VLAN interfaces configured above
570			it, provided that the interface has at least one IP
571			address configured.  Gratuitous ARPs issued for VLAN
572			interfaces are tagged with the appropriate VLAN id.
574			This mode provides fault tolerance.  The primary
575			option, documented below, affects the behavior of this
576			mode.
578		balance-xor or 2
580			XOR policy: Transmit based on the selected transmit
581			hash policy.  The default policy is a simple [(source
582			MAC address XOR'd with destination MAC address XOR
583			packet type ID) modulo slave count].  Alternate transmit
584			policies may be	selected via the xmit_hash_policy option,
585			described below.
587			This mode provides load balancing and fault tolerance.
589		broadcast or 3
591			Broadcast policy: transmits everything on all slave
592			interfaces.  This mode provides fault tolerance.
594		802.3ad or 4
596			IEEE 802.3ad Dynamic link aggregation.  Creates
597			aggregation groups that share the same speed and
598			duplex settings.  Utilizes all slaves in the active
599			aggregator according to the 802.3ad specification.
601			Slave selection for outgoing traffic is done according
602			to the transmit hash policy, which may be changed from
603			the default simple XOR policy via the xmit_hash_policy
604			option, documented below.  Note that not all transmit
605			policies may be 802.3ad compliant, particularly in
606			regards to the packet mis-ordering requirements of
607			section 43.2.4 of the 802.3ad standard.  Differing
608			peer implementations will have varying tolerances for
609			noncompliance.
611			Prerequisites:
613			1. Ethtool support in the base drivers for retrieving
614			the speed and duplex of each slave.
616			2. A switch that supports IEEE 802.3ad Dynamic link
617			aggregation.
619			Most switches will require some type of configuration
620			to enable 802.3ad mode.
622		balance-tlb or 5
624			Adaptive transmit load balancing: channel bonding that
625			does not require any special switch support.
627			In tlb_dynamic_lb=1 mode; the outgoing traffic is
628			distributed according to the current load (computed
629			relative to the speed) on each slave.
631			In tlb_dynamic_lb=0 mode; the load balancing based on
632			current load is disabled and the load is distributed
633			only using the hash distribution.
635			Incoming traffic is received by the current slave.
636			If the receiving slave fails, another slave takes over
637			the MAC address of the failed receiving slave.
639			Prerequisite:
641			Ethtool support in the base drivers for retrieving the
642			speed of each slave.
644		balance-alb or 6
646			Adaptive load balancing: includes balance-tlb plus
647			receive load balancing (rlb) for IPV4 traffic, and
648			does not require any special switch support.  The
649			receive load balancing is achieved by ARP negotiation.
650			The bonding driver intercepts the ARP Replies sent by
651			the local system on their way out and overwrites the
652			source hardware address with the unique hardware
653			address of one of the slaves in the bond such that
654			different peers use different hardware addresses for
655			the server.
657			Receive traffic from connections created by the server
658			is also balanced.  When the local system sends an ARP
659			Request the bonding driver copies and saves the peer's
660			IP information from the ARP packet.  When the ARP
661			Reply arrives from the peer, its hardware address is
662			retrieved and the bonding driver initiates an ARP
663			reply to this peer assigning it to one of the slaves
664			in the bond.  A problematic outcome of using ARP
665			negotiation for balancing is that each time that an
666			ARP request is broadcast it uses the hardware address
667			of the bond.  Hence, peers learn the hardware address
668			of the bond and the balancing of receive traffic
669			collapses to the current slave.  This is handled by
670			sending updates (ARP Replies) to all the peers with
671			their individually assigned hardware address such that
672			the traffic is redistributed.  Receive traffic is also
673			redistributed when a new slave is added to the bond
674			and when an inactive slave is re-activated.  The
675			receive load is distributed sequentially (round robin)
676			among the group of highest speed slaves in the bond.
678			When a link is reconnected or a new slave joins the
679			bond the receive traffic is redistributed among all
680			active slaves in the bond by initiating ARP Replies
681			with the selected MAC address to each of the
682			clients. The updelay parameter (detailed below) must
683			be set to a value equal or greater than the switch's
684			forwarding delay so that the ARP Replies sent to the
685			peers will not be blocked by the switch.
687			Prerequisites:
689			1. Ethtool support in the base drivers for retrieving
690			the speed of each slave.
692			2. Base driver support for setting the hardware
693			address of a device while it is open.  This is
694			required so that there will always be one slave in the
695			team using the bond hardware address (the
696			curr_active_slave) while having a unique hardware
697			address for each slave in the bond.  If the
698			curr_active_slave fails its hardware address is
699			swapped with the new curr_active_slave that was
700			chosen.
702	num_grat_arp
703	num_unsol_na
705		Specify the number of peer notifications (gratuitous ARPs and
706		unsolicited IPv6 Neighbor Advertisements) to be issued after a
707		failover event.  As soon as the link is up on the new slave
708		(possibly immediately) a peer notification is sent on the
709		bonding device and each VLAN sub-device.  This is repeated at
710		each link monitor interval (arp_interval or miimon, whichever
711		is active) if the number is greater than 1.
713		The valid range is 0 - 255; the default value is 1.  These options
714		affect only the active-backup mode.  These options were added for
715		bonding versions 3.3.0 and 3.4.0 respectively.
717		From Linux 3.0 and bonding version 3.7.1, these notifications
718		are generated by the ipv4 and ipv6 code and the numbers of
719		repetitions cannot be set independently.
721	packets_per_slave
723		Specify the number of packets to transmit through a slave before
724		moving to the next one. When set to 0 then a slave is chosen at
725		random.
727		The valid range is 0 - 65535; the default value is 1. This option
728		has effect only in balance-rr mode.
730	primary
732		A string (eth0, eth2, etc) specifying which slave is the
733		primary device.  The specified device will always be the
734		active slave while it is available.  Only when the primary is
735		off-line will alternate devices be used.  This is useful when
736		one slave is preferred over another, e.g., when one slave has
737		higher throughput than another.
739		The primary option is only valid for active-backup(1),
740		balance-tlb (5) and balance-alb (6) mode.
742	primary_reselect
744		Specifies the reselection policy for the primary slave.  This
745		affects how the primary slave is chosen to become the active slave
746		when failure of the active slave or recovery of the primary slave
747		occurs.  This option is designed to prevent flip-flopping between
748		the primary slave and other slaves.  Possible values are:
750		always or 0 (default)
752			The primary slave becomes the active slave whenever it
753			comes back up.
755		better or 1
757			The primary slave becomes the active slave when it comes
758			back up, if the speed and duplex of the primary slave is
759			better than the speed and duplex of the current active
760			slave.
762		failure or 2
764			The primary slave becomes the active slave only if the
765			current active slave fails and the primary slave is up.
767		The primary_reselect setting is ignored in two cases:
769			If no slaves are active, the first slave to recover is
770			made the active slave.
772			When initially enslaved, the primary slave is always made
773			the active slave.
775		Changing the primary_reselect policy via sysfs will cause an
776		immediate selection of the best active slave according to the new
777		policy.  This may or may not result in a change of the active
778		slave, depending upon the circumstances.
780		This option was added for bonding version 3.6.0.
782	tlb_dynamic_lb
784		Specifies if dynamic shuffling of flows is enabled in tlb
785		mode. The value has no effect on any other modes.
787		The default behavior of tlb mode is to shuffle active flows across
788		slaves based on the load in that interval. This gives nice lb
789		characteristics but can cause packet reordering. If re-ordering is
790		a concern use this variable to disable flow shuffling and rely on
791		load balancing provided solely by the hash distribution.
792		xmit-hash-policy can be used to select the appropriate hashing for
793		the setup.
795		The sysfs entry can be used to change the setting per bond device
796		and the initial value is derived from the module parameter. The
797		sysfs entry is allowed to be changed only if the bond device is
798		down.
800		The default value is "1" that enables flow shuffling while value "0"
801		disables it. This option was added in bonding driver 3.7.1
804	updelay
806		Specifies the time, in milliseconds, to wait before enabling a
807		slave after a link recovery has been detected.  This option is
808		only valid for the miimon link monitor.  The updelay value
809		should be a multiple of the miimon value; if not, it will be
810		rounded down to the nearest multiple.  The default value is 0.
812	use_carrier
814		Specifies whether or not miimon should use MII or ETHTOOL
815		ioctls vs. netif_carrier_ok() to determine the link
816		status. The MII or ETHTOOL ioctls are less efficient and
817		utilize a deprecated calling sequence within the kernel.  The
818		netif_carrier_ok() relies on the device driver to maintain its
819		state with netif_carrier_on/off; at this writing, most, but
820		not all, device drivers support this facility.
822		If bonding insists that the link is up when it should not be,
823		it may be that your network device driver does not support
824		netif_carrier_on/off.  The default state for netif_carrier is
825		"carrier on," so if a driver does not support netif_carrier,
826		it will appear as if the link is always up.  In this case,
827		setting use_carrier to 0 will cause bonding to revert to the
828		MII / ETHTOOL ioctl method to determine the link state.
830		A value of 1 enables the use of netif_carrier_ok(), a value of
831		0 will use the deprecated MII / ETHTOOL ioctls.  The default
832		value is 1.
834	xmit_hash_policy
836		Selects the transmit hash policy to use for slave selection in
837		balance-xor, 802.3ad, and tlb modes.  Possible values are:
839		layer2
841			Uses XOR of hardware MAC addresses and packet type ID
842			field to generate the hash. The formula is
844			hash = source MAC XOR destination MAC XOR packet type ID
845			slave number = hash modulo slave count
847			This algorithm will place all traffic to a particular
848			network peer on the same slave.
850			This algorithm is 802.3ad compliant.
852		layer2+3
854			This policy uses a combination of layer2 and layer3
855			protocol information to generate the hash.
857			Uses XOR of hardware MAC addresses and IP addresses to
858			generate the hash.  The formula is
860			hash = source MAC XOR destination MAC XOR packet type ID
861			hash = hash XOR source IP XOR destination IP
862			hash = hash XOR (hash RSHIFT 16)
863			hash = hash XOR (hash RSHIFT 8)
864			And then hash is reduced modulo slave count.
866			If the protocol is IPv6 then the source and destination
867			addresses are first hashed using ipv6_addr_hash.
869			This algorithm will place all traffic to a particular
870			network peer on the same slave.  For non-IP traffic,
871			the formula is the same as for the layer2 transmit
872			hash policy.
874			This policy is intended to provide a more balanced
875			distribution of traffic than layer2 alone, especially
876			in environments where a layer3 gateway device is
877			required to reach most destinations.
879			This algorithm is 802.3ad compliant.
881		layer3+4
883			This policy uses upper layer protocol information,
884			when available, to generate the hash.  This allows for
885			traffic to a particular network peer to span multiple
886			slaves, although a single connection will not span
887			multiple slaves.
889			The formula for unfragmented TCP and UDP packets is
891			hash = source port, destination port (as in the header)
892			hash = hash XOR source IP XOR destination IP
893			hash = hash XOR (hash RSHIFT 16)
894			hash = hash XOR (hash RSHIFT 8)
895			And then hash is reduced modulo slave count.
897			If the protocol is IPv6 then the source and destination
898			addresses are first hashed using ipv6_addr_hash.
900			For fragmented TCP or UDP packets and all other IPv4 and
901			IPv6 protocol traffic, the source and destination port
902			information is omitted.  For non-IP traffic, the
903			formula is the same as for the layer2 transmit hash
904			policy.
906			This algorithm is not fully 802.3ad compliant.  A
907			single TCP or UDP conversation containing both
908			fragmented and unfragmented packets will see packets
909			striped across two interfaces.  This may result in out
910			of order delivery.  Most traffic types will not meet
911			this criteria, as TCP rarely fragments traffic, and
912			most UDP traffic is not involved in extended
913			conversations.  Other implementations of 802.3ad may
914			or may not tolerate this noncompliance.
916		encap2+3
918			This policy uses the same formula as layer2+3 but it
919			relies on skb_flow_dissect to obtain the header fields
920			which might result in the use of inner headers if an
921			encapsulation protocol is used. For example this will
922			improve the performance for tunnel users because the
923			packets will be distributed according to the encapsulated
924			flows.
926		encap3+4
928			This policy uses the same formula as layer3+4 but it
929			relies on skb_flow_dissect to obtain the header fields
930			which might result in the use of inner headers if an
931			encapsulation protocol is used. For example this will
932			improve the performance for tunnel users because the
933			packets will be distributed according to the encapsulated
934			flows.
936		The default value is layer2.  This option was added in bonding
937		version 2.6.3.  In earlier versions of bonding, this parameter
938		does not exist, and the layer2 policy is the only policy.  The
939		layer2+3 value was added for bonding version 3.2.2.
941	resend_igmp
943		Specifies the number of IGMP membership reports to be issued after
944		a failover event. One membership report is issued immediately after
945		the failover, subsequent packets are sent in each 200ms interval.
947		The valid range is 0 - 255; the default value is 1. A value of 0
948		prevents the IGMP membership report from being issued in response
949		to the failover event.
951		This option is useful for bonding modes balance-rr (0), active-backup
952		(1), balance-tlb (5) and balance-alb (6), in which a failover can
953		switch the IGMP traffic from one slave to another.  Therefore a fresh
954		IGMP report must be issued to cause the switch to forward the incoming
955		IGMP traffic over the newly selected slave.
957		This option was added for bonding version 3.7.0.
959	lp_interval
961		Specifies the number of seconds between instances where the bonding
962		driver sends learning packets to each slaves peer switch.
964		The valid range is 1 - 0x7fffffff; the default value is 1. This Option
965		has effect only in balance-tlb and balance-alb modes.
967	3. Configuring Bonding Devices
968	==============================
970		You can configure bonding using either your distro's network
971	initialization scripts, or manually using either iproute2 or the
972	sysfs interface.  Distros generally use one of three packages for the
973	network initialization scripts: initscripts, sysconfig or interfaces.
974	Recent versions of these packages have support for bonding, while older
975	versions do not.
977		We will first describe the options for configuring bonding for
978	distros using versions of initscripts, sysconfig and interfaces with full
979	or partial support for bonding, then provide information on enabling
980	bonding without support from the network initialization scripts (i.e.,
981	older versions of initscripts or sysconfig).
983		If you're unsure whether your distro uses sysconfig,
984	initscripts or interfaces, or don't know if it's new enough, have no fear.
985	Determining this is fairly straightforward.
987		First, look for a file called interfaces in /etc/network directory.
988	If this file is present in your system, then your system use interfaces. See
989	Configuration with Interfaces Support.
991		Else, issue the command:
993	$ rpm -qf /sbin/ifup
995		It will respond with a line of text starting with either
996	"initscripts" or "sysconfig," followed by some numbers.  This is the
997	package that provides your network initialization scripts.
999		Next, to determine if your installation supports bonding,
1000	issue the command:
1002	$ grep ifenslave /sbin/ifup
1004		If this returns any matches, then your initscripts or
1005	sysconfig has support for bonding.
1007	3.1 Configuration with Sysconfig Support
1008	----------------------------------------
1010		This section applies to distros using a version of sysconfig
1011	with bonding support, for example, SuSE Linux Enterprise Server 9.
1013		SuSE SLES 9's networking configuration system does support
1014	bonding, however, at this writing, the YaST system configuration
1015	front end does not provide any means to work with bonding devices.
1016	Bonding devices can be managed by hand, however, as follows.
1018		First, if they have not already been configured, configure the
1019	slave devices.  On SLES 9, this is most easily done by running the
1020	yast2 sysconfig configuration utility.  The goal is for to create an
1021	ifcfg-id file for each slave device.  The simplest way to accomplish
1022	this is to configure the devices for DHCP (this is only to get the
1023	file ifcfg-id file created; see below for some issues with DHCP).  The
1024	name of the configuration file for each device will be of the form:
1026	ifcfg-id-xx:xx:xx:xx:xx:xx
1028		Where the "xx" portion will be replaced with the digits from
1029	the device's permanent MAC address.
1031		Once the set of ifcfg-id-xx:xx:xx:xx:xx:xx files has been
1032	created, it is necessary to edit the configuration files for the slave
1033	devices (the MAC addresses correspond to those of the slave devices).
1034	Before editing, the file will contain multiple lines, and will look
1035	something like this:
1037	BOOTPROTO='dhcp'
1038	STARTMODE='on'
1039	USERCTL='no'
1040	UNIQUE='XNzu.WeZGOGF+4wE'
1041	_nm_name='bus-pci-0001:61:01.0'
1043		Change the BOOTPROTO and STARTMODE lines to the following:
1045	BOOTPROTO='none'
1046	STARTMODE='off'
1048		Do not alter the UNIQUE or _nm_name lines.  Remove any other
1049	lines (USERCTL, etc).
1051		Once the ifcfg-id-xx:xx:xx:xx:xx:xx files have been modified,
1052	it's time to create the configuration file for the bonding device
1053	itself.  This file is named ifcfg-bondX, where X is the number of the
1054	bonding device to create, starting at 0.  The first such file is
1055	ifcfg-bond0, the second is ifcfg-bond1, and so on.  The sysconfig
1056	network configuration system will correctly start multiple instances
1057	of bonding.
1059		The contents of the ifcfg-bondX file is as follows:
1061	BOOTPROTO="static"
1063	IPADDR=""
1064	NETMASK=""
1065	NETWORK=""
1067	STARTMODE="onboot"
1069	BONDING_MODULE_OPTS="mode=active-backup miimon=100"
1070	BONDING_SLAVE0="eth0"
1071	BONDING_SLAVE1="bus-pci-0000:06:08.1"
1073		Replace the sample BROADCAST, IPADDR, NETMASK and NETWORK
1074	values with the appropriate values for your network.
1076		The STARTMODE specifies when the device is brought online.
1077	The possible values are:
1079		onboot:	 The device is started at boot time.  If you're not
1080			 sure, this is probably what you want.
1082		manual:	 The device is started only when ifup is called
1083			 manually.  Bonding devices may be configured this
1084			 way if you do not wish them to start automatically
1085			 at boot for some reason.
1087		hotplug: The device is started by a hotplug event.  This is not
1088			 a valid choice for a bonding device.
1090		off or ignore: The device configuration is ignored.
1092		The line BONDING_MASTER='yes' indicates that the device is a
1093	bonding master device.  The only useful value is "yes."
1095		The contents of BONDING_MODULE_OPTS are supplied to the
1096	instance of the bonding module for this device.  Specify the options
1097	for the bonding mode, link monitoring, and so on here.  Do not include
1098	the max_bonds bonding parameter; this will confuse the configuration
1099	system if you have multiple bonding devices.
1101		Finally, supply one BONDING_SLAVEn="slave device" for each
1102	slave.  where "n" is an increasing value, one for each slave.  The
1103	"slave device" is either an interface name, e.g., "eth0", or a device
1104	specifier for the network device.  The interface name is easier to
1105	find, but the ethN names are subject to change at boot time if, e.g.,
1106	a device early in the sequence has failed.  The device specifiers
1107	(bus-pci-0000:06:08.1 in the example above) specify the physical
1108	network device, and will not change unless the device's bus location
1109	changes (for example, it is moved from one PCI slot to another).  The
1110	example above uses one of each type for demonstration purposes; most
1111	configurations will choose one or the other for all slave devices.
1113		When all configuration files have been modified or created,
1114	networking must be restarted for the configuration changes to take
1115	effect.  This can be accomplished via the following:
1117	# /etc/init.d/network restart
1119		Note that the network control script (/sbin/ifdown) will
1120	remove the bonding module as part of the network shutdown processing,
1121	so it is not necessary to remove the module by hand if, e.g., the
1122	module parameters have changed.
1124		Also, at this writing, YaST/YaST2 will not manage bonding
1125	devices (they do not show bonding interfaces on its list of network
1126	devices).  It is necessary to edit the configuration file by hand to
1127	change the bonding configuration.
1129		Additional general options and details of the ifcfg file
1130	format can be found in an example ifcfg template file:
1132	/etc/sysconfig/network/ifcfg.template
1134		Note that the template does not document the various BONDING_
1135	settings described above, but does describe many of the other options.
1137	3.1.1 Using DHCP with Sysconfig
1138	-------------------------------
1140		Under sysconfig, configuring a device with BOOTPROTO='dhcp'
1141	will cause it to query DHCP for its IP address information.  At this
1142	writing, this does not function for bonding devices; the scripts
1143	attempt to obtain the device address from DHCP prior to adding any of
1144	the slave devices.  Without active slaves, the DHCP requests are not
1145	sent to the network.
1147	3.1.2 Configuring Multiple Bonds with Sysconfig
1148	-----------------------------------------------
1150		The sysconfig network initialization system is capable of
1151	handling multiple bonding devices.  All that is necessary is for each
1152	bonding instance to have an appropriately configured ifcfg-bondX file
1153	(as described above).  Do not specify the "max_bonds" parameter to any
1154	instance of bonding, as this will confuse sysconfig.  If you require
1155	multiple bonding devices with identical parameters, create multiple
1156	ifcfg-bondX files.
1158		Because the sysconfig scripts supply the bonding module
1159	options in the ifcfg-bondX file, it is not necessary to add them to
1160	the system /etc/modules.d/*.conf configuration files.
1162	3.2 Configuration with Initscripts Support
1163	------------------------------------------
1165		This section applies to distros using a recent version of
1166	initscripts with bonding support, for example, Red Hat Enterprise Linux
1167	version 3 or later, Fedora, etc.  On these systems, the network
1168	initialization scripts have knowledge of bonding, and can be configured to
1169	control bonding devices.  Note that older versions of the initscripts
1170	package have lower levels of support for bonding; this will be noted where
1171	applicable.
1173		These distros will not automatically load the network adapter
1174	driver unless the ethX device is configured with an IP address.
1175	Because of this constraint, users must manually configure a
1176	network-script file for all physical adapters that will be members of
1177	a bondX link.  Network script files are located in the directory:
1179	/etc/sysconfig/network-scripts
1181		The file name must be prefixed with "ifcfg-eth" and suffixed
1182	with the adapter's physical adapter number.  For example, the script
1183	for eth0 would be named /etc/sysconfig/network-scripts/ifcfg-eth0.
1184	Place the following text in the file:
1186	DEVICE=eth0
1187	USERCTL=no
1188	ONBOOT=yes
1189	MASTER=bond0
1190	SLAVE=yes
1191	BOOTPROTO=none
1193		The DEVICE= line will be different for every ethX device and
1194	must correspond with the name of the file, i.e., ifcfg-eth1 must have
1195	a device line of DEVICE=eth1.  The setting of the MASTER= line will
1196	also depend on the final bonding interface name chosen for your bond.
1197	As with other network devices, these typically start at 0, and go up
1198	one for each device, i.e., the first bonding instance is bond0, the
1199	second is bond1, and so on.
1201		Next, create a bond network script.  The file name for this
1202	script will be /etc/sysconfig/network-scripts/ifcfg-bondX where X is
1203	the number of the bond.  For bond0 the file is named "ifcfg-bond0",
1204	for bond1 it is named "ifcfg-bond1", and so on.  Within that file,
1205	place the following text:
1207	DEVICE=bond0
1208	IPADDR=
1212	ONBOOT=yes
1213	BOOTPROTO=none
1214	USERCTL=no
1216		Be sure to change the networking specific lines (IPADDR,
1217	NETMASK, NETWORK and BROADCAST) to match your network configuration.
1219		For later versions of initscripts, such as that found with Fedora
1220	7 (or later) and Red Hat Enterprise Linux version 5 (or later), it is possible,
1221	and, indeed, preferable, to specify the bonding options in the ifcfg-bond0
1222	file, e.g. a line of the format:
1224	BONDING_OPTS="mode=active-backup arp_interval=60 arp_ip_target="
1226		will configure the bond with the specified options.  The options
1227	specified in BONDING_OPTS are identical to the bonding module parameters
1228	except for the arp_ip_target field when using versions of initscripts older
1229	than and 8.57 (Fedora 8) and 8.45.19 (Red Hat Enterprise Linux 5.2).  When
1230	using older versions each target should be included as a separate option and
1231	should be preceded by a '+' to indicate it should be added to the list of
1232	queried targets, e.g.,
1234		arp_ip_target=+ arp_ip_target=+
1236		is the proper syntax to specify multiple targets.  When specifying
1237	options via BONDING_OPTS, it is not necessary to edit /etc/modprobe.d/*.conf.
1239		For even older versions of initscripts that do not support
1240	BONDING_OPTS, it is necessary to edit /etc/modprobe.d/*.conf, depending upon
1241	your distro) to load the bonding module with your desired options when the
1242	bond0 interface is brought up.  The following lines in /etc/modprobe.d/*.conf
1243	will load the bonding module, and select its options:
1245	alias bond0 bonding
1246	options bond0 mode=balance-alb miimon=100
1248		Replace the sample parameters with the appropriate set of
1249	options for your configuration.
1251		Finally run "/etc/rc.d/init.d/network restart" as root.  This
1252	will restart the networking subsystem and your bond link should be now
1253	up and running.
1255	3.2.1 Using DHCP with Initscripts
1256	---------------------------------
1258		Recent versions of initscripts (the versions supplied with Fedora
1259	Core 3 and Red Hat Enterprise Linux 4, or later versions, are reported to
1260	work) have support for assigning IP information to bonding devices via
1261	DHCP.
1263		To configure bonding for DHCP, configure it as described
1264	above, except replace the line "BOOTPROTO=none" with "BOOTPROTO=dhcp"
1265	and add a line consisting of "TYPE=Bonding".  Note that the TYPE value
1266	is case sensitive.
1268	3.2.2 Configuring Multiple Bonds with Initscripts
1269	-------------------------------------------------
1271		Initscripts packages that are included with Fedora 7 and Red Hat
1272	Enterprise Linux 5 support multiple bonding interfaces by simply
1273	specifying the appropriate BONDING_OPTS= in ifcfg-bondX where X is the
1274	number of the bond.  This support requires sysfs support in the kernel,
1275	and a bonding driver of version 3.0.0 or later.  Other configurations may
1276	not support this method for specifying multiple bonding interfaces; for
1277	those instances, see the "Configuring Multiple Bonds Manually" section,
1278	below.
1280	3.3 Configuring Bonding Manually with iproute2
1281	-----------------------------------------------
1283		This section applies to distros whose network initialization
1284	scripts (the sysconfig or initscripts package) do not have specific
1285	knowledge of bonding.  One such distro is SuSE Linux Enterprise Server
1286	version 8.
1288		The general method for these systems is to place the bonding
1289	module parameters into a config file in /etc/modprobe.d/ (as
1290	appropriate for the installed distro), then add modprobe and/or
1291	`ip link` commands to the system's global init script.  The name of
1292	the global init script differs; for sysconfig, it is
1293	/etc/init.d/boot.local and for initscripts it is /etc/rc.d/rc.local.
1295		For example, if you wanted to make a simple bond of two e100
1296	devices (presumed to be eth0 and eth1), and have it persist across
1297	reboots, edit the appropriate file (/etc/init.d/boot.local or
1298	/etc/rc.d/rc.local), and add the following:
1300	modprobe bonding mode=balance-alb miimon=100
1301	modprobe e100
1302	ifconfig bond0 netmask up
1303	ip link set eth0 master bond0
1304	ip link set eth1 master bond0
1306		Replace the example bonding module parameters and bond0
1307	network configuration (IP address, netmask, etc) with the appropriate
1308	values for your configuration.
1310		Unfortunately, this method will not provide support for the
1311	ifup and ifdown scripts on the bond devices.  To reload the bonding
1312	configuration, it is necessary to run the initialization script, e.g.,
1314	# /etc/init.d/boot.local
1316		or
1318	# /etc/rc.d/rc.local
1320		It may be desirable in such a case to create a separate script
1321	which only initializes the bonding configuration, then call that
1322	separate script from within boot.local.  This allows for bonding to be
1323	enabled without re-running the entire global init script.
1325		To shut down the bonding devices, it is necessary to first
1326	mark the bonding device itself as being down, then remove the
1327	appropriate device driver modules.  For our example above, you can do
1328	the following:
1330	# ifconfig bond0 down
1331	# rmmod bonding
1332	# rmmod e100
1334		Again, for convenience, it may be desirable to create a script
1335	with these commands.
1338	3.3.1 Configuring Multiple Bonds Manually
1339	-----------------------------------------
1341		This section contains information on configuring multiple
1342	bonding devices with differing options for those systems whose network
1343	initialization scripts lack support for configuring multiple bonds.
1345		If you require multiple bonding devices, but all with the same
1346	options, you may wish to use the "max_bonds" module parameter,
1347	documented above.
1349		To create multiple bonding devices with differing options, it is
1350	preferable to use bonding parameters exported by sysfs, documented in the
1351	section below.
1353		For versions of bonding without sysfs support, the only means to
1354	provide multiple instances of bonding with differing options is to load
1355	the bonding driver multiple times.  Note that current versions of the
1356	sysconfig network initialization scripts handle this automatically; if
1357	your distro uses these scripts, no special action is needed.  See the
1358	section Configuring Bonding Devices, above, if you're not sure about your
1359	network initialization scripts.
1361		To load multiple instances of the module, it is necessary to
1362	specify a different name for each instance (the module loading system
1363	requires that every loaded module, even multiple instances of the same
1364	module, have a unique name).  This is accomplished by supplying multiple
1365	sets of bonding options in /etc/modprobe.d/*.conf, for example:
1367	alias bond0 bonding
1368	options bond0 -o bond0 mode=balance-rr miimon=100
1370	alias bond1 bonding
1371	options bond1 -o bond1 mode=balance-alb miimon=50
1373		will load the bonding module two times.  The first instance is
1374	named "bond0" and creates the bond0 device in balance-rr mode with an
1375	miimon of 100.  The second instance is named "bond1" and creates the
1376	bond1 device in balance-alb mode with an miimon of 50.
1378		In some circumstances (typically with older distributions),
1379	the above does not work, and the second bonding instance never sees
1380	its options.  In that case, the second options line can be substituted
1381	as follows:
1383	install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \
1384		mode=balance-alb miimon=50
1386		This may be repeated any number of times, specifying a new and
1387	unique name in place of bond1 for each subsequent instance.
1389		It has been observed that some Red Hat supplied kernels are unable
1390	to rename modules at load time (the "-o bond1" part).  Attempts to pass
1391	that option to modprobe will produce an "Operation not permitted" error.
1392	This has been reported on some Fedora Core kernels, and has been seen on
1393	RHEL 4 as well.  On kernels exhibiting this problem, it will be impossible
1394	to configure multiple bonds with differing parameters (as they are older
1395	kernels, and also lack sysfs support).
1397	3.4 Configuring Bonding Manually via Sysfs
1398	------------------------------------------
1400		Starting with version 3.0.0, Channel Bonding may be configured
1401	via the sysfs interface.  This interface allows dynamic configuration
1402	of all bonds in the system without unloading the module.  It also
1403	allows for adding and removing bonds at runtime.  Ifenslave is no
1404	longer required, though it is still supported.
1406		Use of the sysfs interface allows you to use multiple bonds
1407	with different configurations without having to reload the module.
1408	It also allows you to use multiple, differently configured bonds when
1409	bonding is compiled into the kernel.
1411		You must have the sysfs filesystem mounted to configure
1412	bonding this way.  The examples in this document assume that you
1413	are using the standard mount point for sysfs, e.g. /sys.  If your
1414	sysfs filesystem is mounted elsewhere, you will need to adjust the
1415	example paths accordingly.
1417	Creating and Destroying Bonds
1418	-----------------------------
1419	To add a new bond foo:
1420	# echo +foo > /sys/class/net/bonding_masters
1422	To remove an existing bond bar:
1423	# echo -bar > /sys/class/net/bonding_masters
1425	To show all existing bonds:
1426	# cat /sys/class/net/bonding_masters
1428	NOTE: due to 4K size limitation of sysfs files, this list may be
1429	truncated if you have more than a few hundred bonds.  This is unlikely
1430	to occur under normal operating conditions.
1432	Adding and Removing Slaves
1433	--------------------------
1434		Interfaces may be enslaved to a bond using the file
1435	/sys/class/net/<bond>/bonding/slaves.  The semantics for this file
1436	are the same as for the bonding_masters file.
1438	To enslave interface eth0 to bond bond0:
1439	# ifconfig bond0 up
1440	# echo +eth0 > /sys/class/net/bond0/bonding/slaves
1442	To free slave eth0 from bond bond0:
1443	# echo -eth0 > /sys/class/net/bond0/bonding/slaves
1445		When an interface is enslaved to a bond, symlinks between the
1446	two are created in the sysfs filesystem.  In this case, you would get
1447	/sys/class/net/bond0/slave_eth0 pointing to /sys/class/net/eth0, and
1448	/sys/class/net/eth0/master pointing to /sys/class/net/bond0.
1450		This means that you can tell quickly whether or not an
1451	interface is enslaved by looking for the master symlink.  Thus:
1452	# echo -eth0 > /sys/class/net/eth0/master/bonding/slaves
1453	will free eth0 from whatever bond it is enslaved to, regardless of
1454	the name of the bond interface.
1456	Changing a Bond's Configuration
1457	-------------------------------
1458		Each bond may be configured individually by manipulating the
1459	files located in /sys/class/net/<bond name>/bonding
1461		The names of these files correspond directly with the command-
1462	line parameters described elsewhere in this file, and, with the
1463	exception of arp_ip_target, they accept the same values.  To see the
1464	current setting, simply cat the appropriate file.
1466		A few examples will be given here; for specific usage
1467	guidelines for each parameter, see the appropriate section in this
1468	document.
1470	To configure bond0 for balance-alb mode:
1471	# ifconfig bond0 down
1472	# echo 6 > /sys/class/net/bond0/bonding/mode
1473	 - or -
1474	# echo balance-alb > /sys/class/net/bond0/bonding/mode
1475		NOTE: The bond interface must be down before the mode can be
1476	changed.
1478	To enable MII monitoring on bond0 with a 1 second interval:
1479	# echo 1000 > /sys/class/net/bond0/bonding/miimon
1480		NOTE: If ARP monitoring is enabled, it will disabled when MII
1481	monitoring is enabled, and vice-versa.
1483	To add ARP targets:
1484	# echo + > /sys/class/net/bond0/bonding/arp_ip_target
1485	# echo + > /sys/class/net/bond0/bonding/arp_ip_target
1486		NOTE:  up to 16 target addresses may be specified.
1488	To remove an ARP target:
1489	# echo - > /sys/class/net/bond0/bonding/arp_ip_target
1491	To configure the interval between learning packet transmits:
1492	# echo 12 > /sys/class/net/bond0/bonding/lp_interval
1493		NOTE: the lp_inteval is the number of seconds between instances where
1494	the bonding driver sends learning packets to each slaves peer switch.  The
1495	default interval is 1 second.
1497	Example Configuration
1498	---------------------
1499		We begin with the same example that is shown in section 3.3,
1500	executed with sysfs, and without using ifenslave.
1502		To make a simple bond of two e100 devices (presumed to be eth0
1503	and eth1), and have it persist across reboots, edit the appropriate
1504	file (/etc/init.d/boot.local or /etc/rc.d/rc.local), and add the
1505	following:
1507	modprobe bonding
1508	modprobe e100
1509	echo balance-alb > /sys/class/net/bond0/bonding/mode
1510	ifconfig bond0 netmask up
1511	echo 100 > /sys/class/net/bond0/bonding/miimon
1512	echo +eth0 > /sys/class/net/bond0/bonding/slaves
1513	echo +eth1 > /sys/class/net/bond0/bonding/slaves
1515		To add a second bond, with two e1000 interfaces in
1516	active-backup mode, using ARP monitoring, add the following lines to
1517	your init script:
1519	modprobe e1000
1520	echo +bond1 > /sys/class/net/bonding_masters
1521	echo active-backup > /sys/class/net/bond1/bonding/mode
1522	ifconfig bond1 netmask up
1523	echo + /sys/class/net/bond1/bonding/arp_ip_target
1524	echo 2000 > /sys/class/net/bond1/bonding/arp_interval
1525	echo +eth2 > /sys/class/net/bond1/bonding/slaves
1526	echo +eth3 > /sys/class/net/bond1/bonding/slaves
1528	3.5 Configuration with Interfaces Support
1529	-----------------------------------------
1531	        This section applies to distros which use /etc/network/interfaces file
1532	to describe network interface configuration, most notably Debian and it's
1533	derivatives.
1535		The ifup and ifdown commands on Debian don't support bonding out of
1536	the box. The ifenslave-2.6 package should be installed to provide bonding
1537	support.  Once installed, this package will provide bond-* options to be used
1538	into /etc/network/interfaces.
1540		Note that ifenslave-2.6 package will load the bonding module and use
1541	the ifenslave command when appropriate.
1543	Example Configurations
1544	----------------------
1546	In /etc/network/interfaces, the following stanza will configure bond0, in
1547	active-backup mode, with eth0 and eth1 as slaves.
1549	auto bond0
1550	iface bond0 inet dhcp
1551		bond-slaves eth0 eth1
1552		bond-mode active-backup
1553		bond-miimon 100
1554		bond-primary eth0 eth1
1556	If the above configuration doesn't work, you might have a system using
1557	upstart for system startup. This is most notably true for recent
1558	Ubuntu versions. The following stanza in /etc/network/interfaces will
1559	produce the same result on those systems.
1561	auto bond0
1562	iface bond0 inet dhcp
1563		bond-slaves none
1564		bond-mode active-backup
1565		bond-miimon 100
1567	auto eth0
1568	iface eth0 inet manual
1569		bond-master bond0
1570		bond-primary eth0 eth1
1572	auto eth1
1573	iface eth1 inet manual
1574		bond-master bond0
1575		bond-primary eth0 eth1
1577	For a full list of bond-* supported options in /etc/network/interfaces and some
1578	more advanced examples tailored to you particular distros, see the files in
1579	/usr/share/doc/ifenslave-2.6.
1581	3.6 Overriding Configuration for Special Cases
1582	----------------------------------------------
1584	When using the bonding driver, the physical port which transmits a frame is
1585	typically selected by the bonding driver, and is not relevant to the user or
1586	system administrator.  The output port is simply selected using the policies of
1587	the selected bonding mode.  On occasion however, it is helpful to direct certain
1588	classes of traffic to certain physical interfaces on output to implement
1589	slightly more complex policies.  For example, to reach a web server over a
1590	bonded interface in which eth0 connects to a private network, while eth1
1591	connects via a public network, it may be desirous to bias the bond to send said
1592	traffic over eth0 first, using eth1 only as a fall back, while all other traffic
1593	can safely be sent over either interface.  Such configurations may be achieved
1594	using the traffic control utilities inherent in linux.
1596	By default the bonding driver is multiqueue aware and 16 queues are created
1597	when the driver initializes (see Documentation/networking/multiqueue.txt
1598	for details).  If more or less queues are desired the module parameter
1599	tx_queues can be used to change this value.  There is no sysfs parameter
1600	available as the allocation is done at module init time.
1602	The output of the file /proc/net/bonding/bondX has changed so the output Queue
1603	ID is now printed for each slave:
1605	Bonding Mode: fault-tolerance (active-backup)
1606	Primary Slave: None
1607	Currently Active Slave: eth0
1608	MII Status: up
1609	MII Polling Interval (ms): 0
1610	Up Delay (ms): 0
1611	Down Delay (ms): 0
1613	Slave Interface: eth0
1614	MII Status: up
1615	Link Failure Count: 0
1616	Permanent HW addr: 00:1a:a0:12:8f:cb
1617	Slave queue ID: 0
1619	Slave Interface: eth1
1620	MII Status: up
1621	Link Failure Count: 0
1622	Permanent HW addr: 00:1a:a0:12:8f:cc
1623	Slave queue ID: 2
1625	The queue_id for a slave can be set using the command:
1627	# echo "eth1:2" > /sys/class/net/bond0/bonding/queue_id
1629	Any interface that needs a queue_id set should set it with multiple calls
1630	like the one above until proper priorities are set for all interfaces.  On
1631	distributions that allow configuration via initscripts, multiple 'queue_id'
1632	arguments can be added to BONDING_OPTS to set all needed slave queues.
1634	These queue id's can be used in conjunction with the tc utility to configure
1635	a multiqueue qdisc and filters to bias certain traffic to transmit on certain
1636	slave devices.  For instance, say we wanted, in the above configuration to
1637	force all traffic bound to to use eth1 in the bond as its output
1638	device. The following commands would accomplish this:
1640	# tc qdisc add dev bond0 handle 1 root multiq
1642	# tc filter add dev bond0 protocol ip parent 1: prio 1 u32 match ip dst \
1643 action skbedit queue_mapping 2
1645	These commands tell the kernel to attach a multiqueue queue discipline to the
1646	bond0 interface and filter traffic enqueued to it, such that packets with a dst
1647	ip of have their output queue mapping value overwritten to 2.
1648	This value is then passed into the driver, causing the normal output path
1649	selection policy to be overridden, selecting instead qid 2, which maps to eth1.
1651	Note that qid values begin at 1.  Qid 0 is reserved to initiate to the driver
1652	that normal output policy selection should take place.  One benefit to simply
1653	leaving the qid for a slave to 0 is the multiqueue awareness in the bonding
1654	driver that is now present.  This awareness allows tc filters to be placed on
1655	slave devices as well as bond devices and the bonding driver will simply act as
1656	a pass-through for selecting output queues on the slave device rather than 
1657	output port selection.
1659	This feature first appeared in bonding driver version 3.7.0 and support for
1660	output slave selection was limited to round-robin and active-backup modes.
1662	3.7 Configuring LACP for 802.3ad mode in a more secure way
1663	----------------------------------------------------------
1665	When using 802.3ad bonding mode, the Actor (host) and Partner (switch)
1666	exchange LACPDUs.  These LACPDUs cannot be sniffed, because they are
1667	destined to link local mac addresses (which switches/bridges are not
1668	supposed to forward).  However, most of the values are easily predictable
1669	or are simply the machine's MAC address (which is trivially known to all
1670	other hosts in the same L2).  This implies that other machines in the L2
1671	domain can spoof LACPDU packets from other hosts to the switch and potentially
1672	cause mayhem by joining (from the point of view of the switch) another
1673	machine's aggregate, thus receiving a portion of that hosts incoming
1674	traffic and / or spoofing traffic from that machine themselves (potentially
1675	even successfully terminating some portion of flows). Though this is not
1676	a likely scenario, one could avoid this possibility by simply configuring
1677	few bonding parameters:
1679	   (a) ad_actor_system : You can set a random mac-address that can be used for
1680	       these LACPDU exchanges. The value can not be either NULL or Multicast.
1681	       Also it's preferable to set the local-admin bit. Following shell code
1682	       generates a random mac-address as described above.
1684	       # sys_mac_addr=$(printf '%02x:%02x:%02x:%02x:%02x:%02x' \
1685	                                $(( (RANDOM & 0xFE) | 0x02 )) \
1686	                                $(( RANDOM & 0xFF )) \
1687	                                $(( RANDOM & 0xFF )) \
1688	                                $(( RANDOM & 0xFF )) \
1689	                                $(( RANDOM & 0xFF )) \
1690	                                $(( RANDOM & 0xFF )))
1691	       # echo $sys_mac_addr > /sys/class/net/bond0/bonding/ad_actor_system
1693	   (b) ad_actor_sys_prio : Randomize the system priority. The default value
1694	       is 65535, but system can take the value from 1 - 65535. Following shell
1695	       code generates random priority and sets it.
1697	       # sys_prio=$(( 1 + RANDOM + RANDOM ))
1698	       # echo $sys_prio > /sys/class/net/bond0/bonding/ad_actor_sys_prio
1700	   (c) ad_user_port_key : Use the user portion of the port-key. The default
1701	       keeps this empty. These are the upper 10 bits of the port-key and value
1702	       ranges from 0 - 1023. Following shell code generates these 10 bits and
1703	       sets it.
1705	       # usr_port_key=$(( RANDOM & 0x3FF ))
1706	       # echo $usr_port_key > /sys/class/net/bond0/bonding/ad_user_port_key
1709	4 Querying Bonding Configuration
1710	=================================
1712	4.1 Bonding Configuration
1713	-------------------------
1715		Each bonding device has a read-only file residing in the
1716	/proc/net/bonding directory.  The file contents include information
1717	about the bonding configuration, options and state of each slave.
1719		For example, the contents of /proc/net/bonding/bond0 after the
1720	driver is loaded with parameters of mode=0 and miimon=1000 is
1721	generally as follows:
1723		Ethernet Channel Bonding Driver: 2.6.1 (October 29, 2004)
1724	        Bonding Mode: load balancing (round-robin)
1725	        Currently Active Slave: eth0
1726	        MII Status: up
1727	        MII Polling Interval (ms): 1000
1728	        Up Delay (ms): 0
1729	        Down Delay (ms): 0
1731	        Slave Interface: eth1
1732	        MII Status: up
1733	        Link Failure Count: 1
1735	        Slave Interface: eth0
1736	        MII Status: up
1737	        Link Failure Count: 1
1739		The precise format and contents will change depending upon the
1740	bonding configuration, state, and version of the bonding driver.
1742	4.2 Network configuration
1743	-------------------------
1745		The network configuration can be inspected using the ifconfig
1746	command.  Bonding devices will have the MASTER flag set; Bonding slave
1747	devices will have the SLAVE flag set.  The ifconfig output does not
1748	contain information on which slaves are associated with which masters.
1750		In the example below, the bond0 interface is the master
1751	(MASTER) while eth0 and eth1 are slaves (SLAVE). Notice all slaves of
1752	bond0 have the same MAC address (HWaddr) as bond0 for all modes except
1753	TLB and ALB that require a unique MAC address for each slave.
1755	# /sbin/ifconfig
1756	bond0     Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
1757	          inet addr:XXX.XXX.XXX.YYY  Bcast:XXX.XXX.XXX.255  Mask:
1759	          RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0
1760	          TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0
1761	          collisions:0 txqueuelen:0
1763	eth0      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
1765	          RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0
1766	          TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0
1767	          collisions:0 txqueuelen:100
1768	          Interrupt:10 Base address:0x1080
1770	eth1      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
1772	          RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0
1773	          TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0
1774	          collisions:0 txqueuelen:100
1775	          Interrupt:9 Base address:0x1400
1777	5. Switch Configuration
1778	=======================
1780		For this section, "switch" refers to whatever system the
1781	bonded devices are directly connected to (i.e., where the other end of
1782	the cable plugs into).  This may be an actual dedicated switch device,
1783	or it may be another regular system (e.g., another computer running
1784	Linux),
1786		The active-backup, balance-tlb and balance-alb modes do not
1787	require any specific configuration of the switch.
1789		The 802.3ad mode requires that the switch have the appropriate
1790	ports configured as an 802.3ad aggregation.  The precise method used
1791	to configure this varies from switch to switch, but, for example, a
1792	Cisco 3550 series switch requires that the appropriate ports first be
1793	grouped together in a single etherchannel instance, then that
1794	etherchannel is set to mode "lacp" to enable 802.3ad (instead of
1795	standard EtherChannel).
1797		The balance-rr, balance-xor and broadcast modes generally
1798	require that the switch have the appropriate ports grouped together.
1799	The nomenclature for such a group differs between switches, it may be
1800	called an "etherchannel" (as in the Cisco example, above), a "trunk
1801	group" or some other similar variation.  For these modes, each switch
1802	will also have its own configuration options for the switch's transmit
1803	policy to the bond.  Typical choices include XOR of either the MAC or
1804	IP addresses.  The transmit policy of the two peers does not need to
1805	match.  For these three modes, the bonding mode really selects a
1806	transmit policy for an EtherChannel group; all three will interoperate
1807	with another EtherChannel group.
1810	6. 802.1q VLAN Support
1811	======================
1813		It is possible to configure VLAN devices over a bond interface
1814	using the 8021q driver.  However, only packets coming from the 8021q
1815	driver and passing through bonding will be tagged by default.  Self
1816	generated packets, for example, bonding's learning packets or ARP
1817	packets generated by either ALB mode or the ARP monitor mechanism, are
1818	tagged internally by bonding itself.  As a result, bonding must
1819	"learn" the VLAN IDs configured above it, and use those IDs to tag
1820	self generated packets.
1822		For reasons of simplicity, and to support the use of adapters
1823	that can do VLAN hardware acceleration offloading, the bonding
1824	interface declares itself as fully hardware offloading capable, it gets
1825	the add_vid/kill_vid notifications to gather the necessary
1826	information, and it propagates those actions to the slaves.  In case
1827	of mixed adapter types, hardware accelerated tagged packets that
1828	should go through an adapter that is not offloading capable are
1829	"un-accelerated" by the bonding driver so the VLAN tag sits in the
1830	regular location.
1832		VLAN interfaces *must* be added on top of a bonding interface
1833	only after enslaving at least one slave.  The bonding interface has a
1834	hardware address of 00:00:00:00:00:00 until the first slave is added.
1835	If the VLAN interface is created prior to the first enslavement, it
1836	would pick up the all-zeroes hardware address.  Once the first slave
1837	is attached to the bond, the bond device itself will pick up the
1838	slave's hardware address, which is then available for the VLAN device.
1840		Also, be aware that a similar problem can occur if all slaves
1841	are released from a bond that still has one or more VLAN interfaces on
1842	top of it.  When a new slave is added, the bonding interface will
1843	obtain its hardware address from the first slave, which might not
1844	match the hardware address of the VLAN interfaces (which was
1845	ultimately copied from an earlier slave).
1847		There are two methods to insure that the VLAN device operates
1848	with the correct hardware address if all slaves are removed from a
1849	bond interface:
1851		1. Remove all VLAN interfaces then recreate them
1853		2. Set the bonding interface's hardware address so that it
1854	matches the hardware address of the VLAN interfaces.
1856		Note that changing a VLAN interface's HW address would set the
1857	underlying device -- i.e. the bonding interface -- to promiscuous
1858	mode, which might not be what you want.
1861	7. Link Monitoring
1862	==================
1864		The bonding driver at present supports two schemes for
1865	monitoring a slave device's link state: the ARP monitor and the MII
1866	monitor.
1868		At the present time, due to implementation restrictions in the
1869	bonding driver itself, it is not possible to enable both ARP and MII
1870	monitoring simultaneously.
1872	7.1 ARP Monitor Operation
1873	-------------------------
1875		The ARP monitor operates as its name suggests: it sends ARP
1876	queries to one or more designated peer systems on the network, and
1877	uses the response as an indication that the link is operating.  This
1878	gives some assurance that traffic is actually flowing to and from one
1879	or more peers on the local network.
1881		The ARP monitor relies on the device driver itself to verify
1882	that traffic is flowing.  In particular, the driver must keep up to
1883	date the last receive time, dev->last_rx, and transmit start time,
1884	dev->trans_start.  If these are not updated by the driver, then the
1885	ARP monitor will immediately fail any slaves using that driver, and
1886	those slaves will stay down.  If networking monitoring (tcpdump, etc)
1887	shows the ARP requests and replies on the network, then it may be that
1888	your device driver is not updating last_rx and trans_start.
1890	7.2 Configuring Multiple ARP Targets
1891	------------------------------------
1893		While ARP monitoring can be done with just one target, it can
1894	be useful in a High Availability setup to have several targets to
1895	monitor.  In the case of just one target, the target itself may go
1896	down or have a problem making it unresponsive to ARP requests.  Having
1897	an additional target (or several) increases the reliability of the ARP
1898	monitoring.
1900		Multiple ARP targets must be separated by commas as follows:
1902	# example options for ARP monitoring with three targets
1903	alias bond0 bonding
1904	options bond0 arp_interval=60 arp_ip_target=,,
1906		For just a single target the options would resemble:
1908	# example options for ARP monitoring with one target
1909	alias bond0 bonding
1910	options bond0 arp_interval=60 arp_ip_target=
1913	7.3 MII Monitor Operation
1914	-------------------------
1916		The MII monitor monitors only the carrier state of the local
1917	network interface.  It accomplishes this in one of three ways: by
1918	depending upon the device driver to maintain its carrier state, by
1919	querying the device's MII registers, or by making an ethtool query to
1920	the device.
1922		If the use_carrier module parameter is 1 (the default value),
1923	then the MII monitor will rely on the driver for carrier state
1924	information (via the netif_carrier subsystem).  As explained in the
1925	use_carrier parameter information, above, if the MII monitor fails to
1926	detect carrier loss on the device (e.g., when the cable is physically
1927	disconnected), it may be that the driver does not support
1928	netif_carrier.
1930		If use_carrier is 0, then the MII monitor will first query the
1931	device's (via ioctl) MII registers and check the link state.  If that
1932	request fails (not just that it returns carrier down), then the MII
1933	monitor will make an ethtool ETHOOL_GLINK request to attempt to obtain
1934	the same information.  If both methods fail (i.e., the driver either
1935	does not support or had some error in processing both the MII register
1936	and ethtool requests), then the MII monitor will assume the link is
1937	up.
1939	8. Potential Sources of Trouble
1940	===============================
1942	8.1 Adventures in Routing
1943	-------------------------
1945		When bonding is configured, it is important that the slave
1946	devices not have routes that supersede routes of the master (or,
1947	generally, not have routes at all).  For example, suppose the bonding
1948	device bond0 has two slaves, eth0 and eth1, and the routing table is
1949	as follows:
1951	Kernel IP routing table
1952	Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
1953     U        40 0          0 eth0
1954     U        40 0          0 eth1
1955     U        40 0          0 bond0
1956       U        40 0          0 lo
1958		This routing configuration will likely still update the
1959	receive/transmit times in the driver (needed by the ARP monitor), but
1960	may bypass the bonding driver (because outgoing traffic to, in this
1961	case, another host on network 10 would use eth0 or eth1 before bond0).
1963		The ARP monitor (and ARP itself) may become confused by this
1964	configuration, because ARP requests (generated by the ARP monitor)
1965	will be sent on one interface (bond0), but the corresponding reply
1966	will arrive on a different interface (eth0).  This reply looks to ARP
1967	as an unsolicited ARP reply (because ARP matches replies on an
1968	interface basis), and is discarded.  The MII monitor is not affected
1969	by the state of the routing table.
1971		The solution here is simply to insure that slaves do not have
1972	routes of their own, and if for some reason they must, those routes do
1973	not supersede routes of their master.  This should generally be the
1974	case, but unusual configurations or errant manual or automatic static
1975	route additions may cause trouble.
1977	8.2 Ethernet Device Renaming
1978	----------------------------
1980		On systems with network configuration scripts that do not
1981	associate physical devices directly with network interface names (so
1982	that the same physical device always has the same "ethX" name), it may
1983	be necessary to add some special logic to config files in
1984	/etc/modprobe.d/.
1986		For example, given a modules.conf containing the following:
1988	alias bond0 bonding
1989	options bond0 mode=some-mode miimon=50
1990	alias eth0 tg3
1991	alias eth1 tg3
1992	alias eth2 e1000
1993	alias eth3 e1000
1995		If neither eth0 and eth1 are slaves to bond0, then when the
1996	bond0 interface comes up, the devices may end up reordered.  This
1997	happens because bonding is loaded first, then its slave device's
1998	drivers are loaded next.  Since no other drivers have been loaded,
1999	when the e1000 driver loads, it will receive eth0 and eth1 for its
2000	devices, but the bonding configuration tries to enslave eth2 and eth3
2001	(which may later be assigned to the tg3 devices).
2003		Adding the following:
2005	add above bonding e1000 tg3
2007		causes modprobe to load e1000 then tg3, in that order, when
2008	bonding is loaded.  This command is fully documented in the
2009	modules.conf manual page.
2011		On systems utilizing modprobe an equivalent problem can occur.
2012	In this case, the following can be added to config files in
2013	/etc/modprobe.d/ as:
2015	softdep bonding pre: tg3 e1000
2017		This will load tg3 and e1000 modules before loading the bonding one.
2018	Full documentation on this can be found in the modprobe.d and modprobe
2019	manual pages.
2021	8.3. Painfully Slow Or No Failed Link Detection By Miimon
2022	---------------------------------------------------------
2024		By default, bonding enables the use_carrier option, which
2025	instructs bonding to trust the driver to maintain carrier state.
2027		As discussed in the options section, above, some drivers do
2028	not support the netif_carrier_on/_off link state tracking system.
2029	With use_carrier enabled, bonding will always see these links as up,
2030	regardless of their actual state.
2032		Additionally, other drivers do support netif_carrier, but do
2033	not maintain it in real time, e.g., only polling the link state at
2034	some fixed interval.  In this case, miimon will detect failures, but
2035	only after some long period of time has expired.  If it appears that
2036	miimon is very slow in detecting link failures, try specifying
2037	use_carrier=0 to see if that improves the failure detection time.  If
2038	it does, then it may be that the driver checks the carrier state at a
2039	fixed interval, but does not cache the MII register values (so the
2040	use_carrier=0 method of querying the registers directly works).  If
2041	use_carrier=0 does not improve the failover, then the driver may cache
2042	the registers, or the problem may be elsewhere.
2044		Also, remember that miimon only checks for the device's
2045	carrier state.  It has no way to determine the state of devices on or
2046	beyond other ports of a switch, or if a switch is refusing to pass
2047	traffic while still maintaining carrier on.
2049	9. SNMP agents
2050	===============
2052		If running SNMP agents, the bonding driver should be loaded
2053	before any network drivers participating in a bond.  This requirement
2054	is due to the interface index (ipAdEntIfIndex) being associated to
2055	the first interface found with a given IP address.  That is, there is
2056	only one ipAdEntIfIndex for each IP address.  For example, if eth0 and
2057	eth1 are slaves of bond0 and the driver for eth0 is loaded before the
2058	bonding driver, the interface for the IP address will be associated
2059	with the eth0 interface.  This configuration is shown below, the IP
2060	address has an interface index of 2 which indexes to eth0
2061	in the ifDescr table (ifDescr.2).
2063	     interfaces.ifTable.ifEntry.ifDescr.1 = lo
2064	     interfaces.ifTable.ifEntry.ifDescr.2 = eth0
2065	     interfaces.ifTable.ifEntry.ifDescr.3 = eth1
2066	     interfaces.ifTable.ifEntry.ifDescr.4 = eth2
2067	     interfaces.ifTable.ifEntry.ifDescr.5 = eth3
2068	     interfaces.ifTable.ifEntry.ifDescr.6 = bond0
2069	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 5
2070	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 2
2071	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 4
2072	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 1
2074		This problem is avoided by loading the bonding driver before
2075	any network drivers participating in a bond.  Below is an example of
2076	loading the bonding driver first, the IP address is
2077	correctly associated with ifDescr.2.
2079	     interfaces.ifTable.ifEntry.ifDescr.1 = lo
2080	     interfaces.ifTable.ifEntry.ifDescr.2 = bond0
2081	     interfaces.ifTable.ifEntry.ifDescr.3 = eth0
2082	     interfaces.ifTable.ifEntry.ifDescr.4 = eth1
2083	     interfaces.ifTable.ifEntry.ifDescr.5 = eth2
2084	     interfaces.ifTable.ifEntry.ifDescr.6 = eth3
2085	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 6
2086	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 2
2087	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 5
2088	     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 1
2090		While some distributions may not report the interface name in
2091	ifDescr, the association between the IP address and IfIndex remains
2092	and SNMP functions such as Interface_Scan_Next will report that
2093	association.
2095	10. Promiscuous mode
2096	====================
2098		When running network monitoring tools, e.g., tcpdump, it is
2099	common to enable promiscuous mode on the device, so that all traffic
2100	is seen (instead of seeing only traffic destined for the local host).
2101	The bonding driver handles promiscuous mode changes to the bonding
2102	master device (e.g., bond0), and propagates the setting to the slave
2103	devices.
2105		For the balance-rr, balance-xor, broadcast, and 802.3ad modes,
2106	the promiscuous mode setting is propagated to all slaves.
2108		For the active-backup, balance-tlb and balance-alb modes, the
2109	promiscuous mode setting is propagated only to the active slave.
2111		For balance-tlb mode, the active slave is the slave currently
2112	receiving inbound traffic.
2114		For balance-alb mode, the active slave is the slave used as a
2115	"primary."  This slave is used for mode-specific control traffic, for
2116	sending to peers that are unassigned or if the load is unbalanced.
2118		For the active-backup, balance-tlb and balance-alb modes, when
2119	the active slave changes (e.g., due to a link failure), the
2120	promiscuous setting will be propagated to the new active slave.
2122	11. Configuring Bonding for High Availability
2123	=============================================
2125		High Availability refers to configurations that provide
2126	maximum network availability by having redundant or backup devices,
2127	links or switches between the host and the rest of the world.  The
2128	goal is to provide the maximum availability of network connectivity
2129	(i.e., the network always works), even though other configurations
2130	could provide higher throughput.
2132	11.1 High Availability in a Single Switch Topology
2133	--------------------------------------------------
2135		If two hosts (or a host and a single switch) are directly
2136	connected via multiple physical links, then there is no availability
2137	penalty to optimizing for maximum bandwidth.  In this case, there is
2138	only one switch (or peer), so if it fails, there is no alternative
2139	access to fail over to.  Additionally, the bonding load balance modes
2140	support link monitoring of their members, so if individual links fail,
2141	the load will be rebalanced across the remaining devices.
2143		See Section 12, "Configuring Bonding for Maximum Throughput"
2144	for information on configuring bonding with one peer device.
2146	11.2 High Availability in a Multiple Switch Topology
2147	----------------------------------------------------
2149		With multiple switches, the configuration of bonding and the
2150	network changes dramatically.  In multiple switch topologies, there is
2151	a trade off between network availability and usable bandwidth.
2153		Below is a sample network, configured to maximize the
2154	availability of the network:
2156	                |                                     |
2157	                |port3                           port3|
2158	          +-----+----+                          +-----+----+
2159	          |          |port2       ISL      port2|          |
2160	          | switch A +--------------------------+ switch B |
2161	          |          |                          |          |
2162	          +-----+----+                          +-----++---+
2163	                |port1                           port1|
2164	                |             +-------+               |
2165	                +-------------+ host1 +---------------+
2166	                         eth0 +-------+ eth1
2168		In this configuration, there is a link between the two
2169	switches (ISL, or inter switch link), and multiple ports connecting to
2170	the outside world ("port3" on each switch).  There is no technical
2171	reason that this could not be extended to a third switch.
2173	11.2.1 HA Bonding Mode Selection for Multiple Switch Topology
2174	-------------------------------------------------------------
2176		In a topology such as the example above, the active-backup and
2177	broadcast modes are the only useful bonding modes when optimizing for
2178	availability; the other modes require all links to terminate on the
2179	same peer for them to behave rationally.
2181	active-backup: This is generally the preferred mode, particularly if
2182		the switches have an ISL and play together well.  If the
2183		network configuration is such that one switch is specifically
2184		a backup switch (e.g., has lower capacity, higher cost, etc),
2185		then the primary option can be used to insure that the
2186		preferred link is always used when it is available.
2188	broadcast: This mode is really a special purpose mode, and is suitable
2189		only for very specific needs.  For example, if the two
2190		switches are not connected (no ISL), and the networks beyond
2191		them are totally independent.  In this case, if it is
2192		necessary for some specific one-way traffic to reach both
2193		independent networks, then the broadcast mode may be suitable.
2195	11.2.2 HA Link Monitoring Selection for Multiple Switch Topology
2196	----------------------------------------------------------------
2198		The choice of link monitoring ultimately depends upon your
2199	switch.  If the switch can reliably fail ports in response to other
2200	failures, then either the MII or ARP monitors should work.  For
2201	example, in the above example, if the "port3" link fails at the remote
2202	end, the MII monitor has no direct means to detect this.  The ARP
2203	monitor could be configured with a target at the remote end of port3,
2204	thus detecting that failure without switch support.
2206		In general, however, in a multiple switch topology, the ARP
2207	monitor can provide a higher level of reliability in detecting end to
2208	end connectivity failures (which may be caused by the failure of any
2209	individual component to pass traffic for any reason).  Additionally,
2210	the ARP monitor should be configured with multiple targets (at least
2211	one for each switch in the network).  This will insure that,
2212	regardless of which switch is active, the ARP monitor has a suitable
2213	target to query.
2215		Note, also, that of late many switches now support a functionality
2216	generally referred to as "trunk failover."  This is a feature of the
2217	switch that causes the link state of a particular switch port to be set
2218	down (or up) when the state of another switch port goes down (or up).
2219	Its purpose is to propagate link failures from logically "exterior" ports
2220	to the logically "interior" ports that bonding is able to monitor via
2221	miimon.  Availability and configuration for trunk failover varies by
2222	switch, but this can be a viable alternative to the ARP monitor when using
2223	suitable switches.
2225	12. Configuring Bonding for Maximum Throughput
2226	==============================================
2228	12.1 Maximizing Throughput in a Single Switch Topology
2229	------------------------------------------------------
2231		In a single switch configuration, the best method to maximize
2232	throughput depends upon the application and network environment.  The
2233	various load balancing modes each have strengths and weaknesses in
2234	different environments, as detailed below.
2236		For this discussion, we will break down the topologies into
2237	two categories.  Depending upon the destination of most traffic, we
2238	categorize them into either "gatewayed" or "local" configurations.
2240		In a gatewayed configuration, the "switch" is acting primarily
2241	as a router, and the majority of traffic passes through this router to
2242	other networks.  An example would be the following:
2245	     +----------+                     +----------+
2246	     |          |eth0            port1|          | to other networks
2247	     | Host A   +---------------------+ router   +------------------->
2248	     |          +---------------------+          | Hosts B and C are out
2249	     |          |eth1            port2|          | here somewhere
2250	     +----------+                     +----------+
2252		The router may be a dedicated router device, or another host
2253	acting as a gateway.  For our discussion, the important point is that
2254	the majority of traffic from Host A will pass through the router to
2255	some other network before reaching its final destination.
2257		In a gatewayed network configuration, although Host A may
2258	communicate with many other systems, all of its traffic will be sent
2259	and received via one other peer on the local network, the router.
2261		Note that the case of two systems connected directly via
2262	multiple physical links is, for purposes of configuring bonding, the
2263	same as a gatewayed configuration.  In that case, it happens that all
2264	traffic is destined for the "gateway" itself, not some other network
2265	beyond the gateway.
2267		In a local configuration, the "switch" is acting primarily as
2268	a switch, and the majority of traffic passes through this switch to
2269	reach other stations on the same network.  An example would be the
2270	following:
2272	    +----------+            +----------+       +--------+
2273	    |          |eth0   port1|          +-------+ Host B |
2274	    |  Host A  +------------+  switch  |port3  +--------+
2275	    |          +------------+          |                  +--------+
2276	    |          |eth1   port2|          +------------------+ Host C |
2277	    +----------+            +----------+port4             +--------+
2280		Again, the switch may be a dedicated switch device, or another
2281	host acting as a gateway.  For our discussion, the important point is
2282	that the majority of traffic from Host A is destined for other hosts
2283	on the same local network (Hosts B and C in the above example).
2285		In summary, in a gatewayed configuration, traffic to and from
2286	the bonded device will be to the same MAC level peer on the network
2287	(the gateway itself, i.e., the router), regardless of its final
2288	destination.  In a local configuration, traffic flows directly to and
2289	from the final destinations, thus, each destination (Host B, Host C)
2290	will be addressed directly by their individual MAC addresses.
2292		This distinction between a gatewayed and a local network
2293	configuration is important because many of the load balancing modes
2294	available use the MAC addresses of the local network source and
2295	destination to make load balancing decisions.  The behavior of each
2296	mode is described below.
2299	12.1.1 MT Bonding Mode Selection for Single Switch Topology
2300	-----------------------------------------------------------
2302		This configuration is the easiest to set up and to understand,
2303	although you will have to decide which bonding mode best suits your
2304	needs.  The trade offs for each mode are detailed below:
2306	balance-rr: This mode is the only mode that will permit a single
2307		TCP/IP connection to stripe traffic across multiple
2308		interfaces. It is therefore the only mode that will allow a
2309		single TCP/IP stream to utilize more than one interface's
2310		worth of throughput.  This comes at a cost, however: the
2311		striping generally results in peer systems receiving packets out
2312		of order, causing TCP/IP's congestion control system to kick
2313		in, often by retransmitting segments.
2315		It is possible to adjust TCP/IP's congestion limits by
2316		altering the net.ipv4.tcp_reordering sysctl parameter.  The
2317		usual default value is 3. But keep in mind TCP stack is able
2318		to automatically increase this when it detects reorders.
2320		Note that the fraction of packets that will be delivered out of
2321		order is highly variable, and is unlikely to be zero.  The level
2322		of reordering depends upon a variety of factors, including the
2323		networking interfaces, the switch, and the topology of the
2324		configuration.  Speaking in general terms, higher speed network
2325		cards produce more reordering (due to factors such as packet
2326		coalescing), and a "many to many" topology will reorder at a
2327		higher rate than a "many slow to one fast" configuration.
2329		Many switches do not support any modes that stripe traffic
2330		(instead choosing a port based upon IP or MAC level addresses);
2331		for those devices, traffic for a particular connection flowing
2332		through the switch to a balance-rr bond will not utilize greater
2333		than one interface's worth of bandwidth.
2335		If you are utilizing protocols other than TCP/IP, UDP for
2336		example, and your application can tolerate out of order
2337		delivery, then this mode can allow for single stream datagram
2338		performance that scales near linearly as interfaces are added
2339		to the bond.
2341		This mode requires the switch to have the appropriate ports
2342		configured for "etherchannel" or "trunking."
2344	active-backup: There is not much advantage in this network topology to
2345		the active-backup mode, as the inactive backup devices are all
2346		connected to the same peer as the primary.  In this case, a
2347		load balancing mode (with link monitoring) will provide the
2348		same level of network availability, but with increased
2349		available bandwidth.  On the plus side, active-backup mode
2350		does not require any configuration of the switch, so it may
2351		have value if the hardware available does not support any of
2352		the load balance modes.
2354	balance-xor: This mode will limit traffic such that packets destined
2355		for specific peers will always be sent over the same
2356		interface.  Since the destination is determined by the MAC
2357		addresses involved, this mode works best in a "local" network
2358		configuration (as described above), with destinations all on
2359		the same local network.  This mode is likely to be suboptimal
2360		if all your traffic is passed through a single router (i.e., a
2361		"gatewayed" network configuration, as described above).
2363		As with balance-rr, the switch ports need to be configured for
2364		"etherchannel" or "trunking."
2366	broadcast: Like active-backup, there is not much advantage to this
2367		mode in this type of network topology.
2369	802.3ad: This mode can be a good choice for this type of network
2370		topology.  The 802.3ad mode is an IEEE standard, so all peers
2371		that implement 802.3ad should interoperate well.  The 802.3ad
2372		protocol includes automatic configuration of the aggregates,
2373		so minimal manual configuration of the switch is needed
2374		(typically only to designate that some set of devices is
2375		available for 802.3ad).  The 802.3ad standard also mandates
2376		that frames be delivered in order (within certain limits), so
2377		in general single connections will not see misordering of
2378		packets.  The 802.3ad mode does have some drawbacks: the
2379		standard mandates that all devices in the aggregate operate at
2380		the same speed and duplex.  Also, as with all bonding load
2381		balance modes other than balance-rr, no single connection will
2382		be able to utilize more than a single interface's worth of
2383		bandwidth.  
2385		Additionally, the linux bonding 802.3ad implementation
2386		distributes traffic by peer (using an XOR of MAC addresses
2387		and packet type ID), so in a "gatewayed" configuration, all
2388		outgoing traffic will generally use the same device.  Incoming
2389		traffic may also end up on a single device, but that is
2390		dependent upon the balancing policy of the peer's 8023.ad
2391		implementation.  In a "local" configuration, traffic will be
2392		distributed across the devices in the bond.
2394		Finally, the 802.3ad mode mandates the use of the MII monitor,
2395		therefore, the ARP monitor is not available in this mode.
2397	balance-tlb: The balance-tlb mode balances outgoing traffic by peer.
2398		Since the balancing is done according to MAC address, in a
2399		"gatewayed" configuration (as described above), this mode will
2400		send all traffic across a single device.  However, in a
2401		"local" network configuration, this mode balances multiple
2402		local network peers across devices in a vaguely intelligent
2403		manner (not a simple XOR as in balance-xor or 802.3ad mode),
2404		so that mathematically unlucky MAC addresses (i.e., ones that
2405		XOR to the same value) will not all "bunch up" on a single
2406		interface.
2408		Unlike 802.3ad, interfaces may be of differing speeds, and no
2409		special switch configuration is required.  On the down side,
2410		in this mode all incoming traffic arrives over a single
2411		interface, this mode requires certain ethtool support in the
2412		network device driver of the slave interfaces, and the ARP
2413		monitor is not available.
2415	balance-alb: This mode is everything that balance-tlb is, and more.
2416		It has all of the features (and restrictions) of balance-tlb,
2417		and will also balance incoming traffic from local network
2418		peers (as described in the Bonding Module Options section,
2419		above).
2421		The only additional down side to this mode is that the network
2422		device driver must support changing the hardware address while
2423		the device is open.
2425	12.1.2 MT Link Monitoring for Single Switch Topology
2426	----------------------------------------------------
2428		The choice of link monitoring may largely depend upon which
2429	mode you choose to use.  The more advanced load balancing modes do not
2430	support the use of the ARP monitor, and are thus restricted to using
2431	the MII monitor (which does not provide as high a level of end to end
2432	assurance as the ARP monitor).
2434	12.2 Maximum Throughput in a Multiple Switch Topology
2435	-----------------------------------------------------
2437		Multiple switches may be utilized to optimize for throughput
2438	when they are configured in parallel as part of an isolated network
2439	between two or more systems, for example:
2441	                       +-----------+
2442	                       |  Host A   | 
2443	                       +-+---+---+-+
2444	                         |   |   |
2445	                +--------+   |   +---------+
2446	                |            |             |
2447	         +------+---+  +-----+----+  +-----+----+
2448	         | Switch A |  | Switch B |  | Switch C |
2449	         +------+---+  +-----+----+  +-----+----+
2450	                |            |             |
2451	                +--------+   |   +---------+
2452	                         |   |   |
2453	                       +-+---+---+-+
2454	                       |  Host B   | 
2455	                       +-----------+
2457		In this configuration, the switches are isolated from one
2458	another.  One reason to employ a topology such as this is for an
2459	isolated network with many hosts (a cluster configured for high
2460	performance, for example), using multiple smaller switches can be more
2461	cost effective than a single larger switch, e.g., on a network with 24
2462	hosts, three 24 port switches can be significantly less expensive than
2463	a single 72 port switch.
2465		If access beyond the network is required, an individual host
2466	can be equipped with an additional network device connected to an
2467	external network; this host then additionally acts as a gateway.
2469	12.2.1 MT Bonding Mode Selection for Multiple Switch Topology
2470	-------------------------------------------------------------
2472		In actual practice, the bonding mode typically employed in
2473	configurations of this type is balance-rr.  Historically, in this
2474	network configuration, the usual caveats about out of order packet
2475	delivery are mitigated by the use of network adapters that do not do
2476	any kind of packet coalescing (via the use of NAPI, or because the
2477	device itself does not generate interrupts until some number of
2478	packets has arrived).  When employed in this fashion, the balance-rr
2479	mode allows individual connections between two hosts to effectively
2480	utilize greater than one interface's bandwidth.
2482	12.2.2 MT Link Monitoring for Multiple Switch Topology
2483	------------------------------------------------------
2485		Again, in actual practice, the MII monitor is most often used
2486	in this configuration, as performance is given preference over
2487	availability.  The ARP monitor will function in this topology, but its
2488	advantages over the MII monitor are mitigated by the volume of probes
2489	needed as the number of systems involved grows (remember that each
2490	host in the network is configured with bonding).
2492	13. Switch Behavior Issues
2493	==========================
2495	13.1 Link Establishment and Failover Delays
2496	-------------------------------------------
2498		Some switches exhibit undesirable behavior with regard to the
2499	timing of link up and down reporting by the switch.
2501		First, when a link comes up, some switches may indicate that
2502	the link is up (carrier available), but not pass traffic over the
2503	interface for some period of time.  This delay is typically due to
2504	some type of autonegotiation or routing protocol, but may also occur
2505	during switch initialization (e.g., during recovery after a switch
2506	failure).  If you find this to be a problem, specify an appropriate
2507	value to the updelay bonding module option to delay the use of the
2508	relevant interface(s).
2510		Second, some switches may "bounce" the link state one or more
2511	times while a link is changing state.  This occurs most commonly while
2512	the switch is initializing.  Again, an appropriate updelay value may
2513	help.
2515		Note that when a bonding interface has no active links, the
2516	driver will immediately reuse the first link that goes up, even if the
2517	updelay parameter has been specified (the updelay is ignored in this
2518	case).  If there are slave interfaces waiting for the updelay timeout
2519	to expire, the interface that first went into that state will be
2520	immediately reused.  This reduces down time of the network if the
2521	value of updelay has been overestimated, and since this occurs only in
2522	cases with no connectivity, there is no additional penalty for
2523	ignoring the updelay.
2525		In addition to the concerns about switch timings, if your
2526	switches take a long time to go into backup mode, it may be desirable
2527	to not activate a backup interface immediately after a link goes down.
2528	Failover may be delayed via the downdelay bonding module option.
2530	13.2 Duplicated Incoming Packets
2531	--------------------------------
2533		NOTE: Starting with version 3.0.2, the bonding driver has logic to
2534	suppress duplicate packets, which should largely eliminate this problem.
2535	The following description is kept for reference.
2537		It is not uncommon to observe a short burst of duplicated
2538	traffic when the bonding device is first used, or after it has been
2539	idle for some period of time.  This is most easily observed by issuing
2540	a "ping" to some other host on the network, and noticing that the
2541	output from ping flags duplicates (typically one per slave).
2543		For example, on a bond in active-backup mode with five slaves
2544	all connected to one switch, the output may appear as follows:
2546	# ping -n
2547	PING ( from : 56(84) bytes of data.
2548	64 bytes from icmp_seq=1 ttl=64 time=13.7 ms
2549	64 bytes from icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2550	64 bytes from icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2551	64 bytes from icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2552	64 bytes from icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2553	64 bytes from icmp_seq=2 ttl=64 time=0.216 ms
2554	64 bytes from icmp_seq=3 ttl=64 time=0.267 ms
2555	64 bytes from icmp_seq=4 ttl=64 time=0.222 ms
2557		This is not due to an error in the bonding driver, rather, it
2558	is a side effect of how many switches update their MAC forwarding
2559	tables.  Initially, the switch does not associate the MAC address in
2560	the packet with a particular switch port, and so it may send the
2561	traffic to all ports until its MAC forwarding table is updated.  Since
2562	the interfaces attached to the bond may occupy multiple ports on a
2563	single switch, when the switch (temporarily) floods the traffic to all
2564	ports, the bond device receives multiple copies of the same packet
2565	(one per slave device).
2567		The duplicated packet behavior is switch dependent, some
2568	switches exhibit this, and some do not.  On switches that display this
2569	behavior, it can be induced by clearing the MAC forwarding table (on
2570	most Cisco switches, the privileged command "clear mac address-table
2571	dynamic" will accomplish this).
2573	14. Hardware Specific Considerations
2574	====================================
2576		This section contains additional information for configuring
2577	bonding on specific hardware platforms, or for interfacing bonding
2578	with particular switches or other devices.
2580	14.1 IBM BladeCenter
2581	--------------------
2583		This applies to the JS20 and similar systems.
2585		On the JS20 blades, the bonding driver supports only
2586	balance-rr, active-backup, balance-tlb and balance-alb modes.  This is
2587	largely due to the network topology inside the BladeCenter, detailed
2588	below.
2590	JS20 network adapter information
2591	--------------------------------
2593		All JS20s come with two Broadcom Gigabit Ethernet ports
2594	integrated on the planar (that's "motherboard" in IBM-speak).  In the
2595	BladeCenter chassis, the eth0 port of all JS20 blades is hard wired to
2596	I/O Module #1; similarly, all eth1 ports are wired to I/O Module #2.
2597	An add-on Broadcom daughter card can be installed on a JS20 to provide
2598	two more Gigabit Ethernet ports.  These ports, eth2 and eth3, are
2599	wired to I/O Modules 3 and 4, respectively.
2601		Each I/O Module may contain either a switch or a passthrough
2602	module (which allows ports to be directly connected to an external
2603	switch).  Some bonding modes require a specific BladeCenter internal
2604	network topology in order to function; these are detailed below.
2606		Additional BladeCenter-specific networking information can be
2607	found in two IBM Redbooks (www.ibm.com/redbooks):
2609	"IBM eServer BladeCenter Networking Options"
2610	"IBM eServer BladeCenter Layer 2-7 Network Switching"
2612	BladeCenter networking configuration
2613	------------------------------------
2615		Because a BladeCenter can be configured in a very large number
2616	of ways, this discussion will be confined to describing basic
2617	configurations.
2619		Normally, Ethernet Switch Modules (ESMs) are used in I/O
2620	modules 1 and 2.  In this configuration, the eth0 and eth1 ports of a
2621	JS20 will be connected to different internal switches (in the
2622	respective I/O modules).
2624		A passthrough module (OPM or CPM, optical or copper,
2625	passthrough module) connects the I/O module directly to an external
2626	switch.  By using PMs in I/O module #1 and #2, the eth0 and eth1
2627	interfaces of a JS20 can be redirected to the outside world and
2628	connected to a common external switch.
2630		Depending upon the mix of ESMs and PMs, the network will
2631	appear to bonding as either a single switch topology (all PMs) or as a
2632	multiple switch topology (one or more ESMs, zero or more PMs).  It is
2633	also possible to connect ESMs together, resulting in a configuration
2634	much like the example in "High Availability in a Multiple Switch
2635	Topology," above.
2637	Requirements for specific modes
2638	-------------------------------
2640		The balance-rr mode requires the use of passthrough modules
2641	for devices in the bond, all connected to an common external switch.
2642	That switch must be configured for "etherchannel" or "trunking" on the
2643	appropriate ports, as is usual for balance-rr.
2645		The balance-alb and balance-tlb modes will function with
2646	either switch modules or passthrough modules (or a mix).  The only
2647	specific requirement for these modes is that all network interfaces
2648	must be able to reach all destinations for traffic sent over the
2649	bonding device (i.e., the network must converge at some point outside
2650	the BladeCenter).
2652		The active-backup mode has no additional requirements.
2654	Link monitoring issues
2655	----------------------
2657		When an Ethernet Switch Module is in place, only the ARP
2658	monitor will reliably detect link loss to an external switch.  This is
2659	nothing unusual, but examination of the BladeCenter cabinet would
2660	suggest that the "external" network ports are the ethernet ports for
2661	the system, when it fact there is a switch between these "external"
2662	ports and the devices on the JS20 system itself.  The MII monitor is
2663	only able to detect link failures between the ESM and the JS20 system.
2665		When a passthrough module is in place, the MII monitor does
2666	detect failures to the "external" port, which is then directly
2667	connected to the JS20 system.
2669	Other concerns
2670	--------------
2672		The Serial Over LAN (SoL) link is established over the primary
2673	ethernet (eth0) only, therefore, any loss of link to eth0 will result
2674	in losing your SoL connection.  It will not fail over with other
2675	network traffic, as the SoL system is beyond the control of the
2676	bonding driver.
2678		It may be desirable to disable spanning tree on the switch
2679	(either the internal Ethernet Switch Module, or an external switch) to
2680	avoid fail-over delay issues when using bonding.
2683	15. Frequently Asked Questions
2684	==============================
2686	1.  Is it SMP safe?
2688		Yes. The old 2.0.xx channel bonding patch was not SMP safe.
2689	The new driver was designed to be SMP safe from the start.
2691	2.  What type of cards will work with it?
2693		Any Ethernet type cards (you can even mix cards - a Intel
2694	EtherExpress PRO/100 and a 3com 3c905b, for example).  For most modes,
2695	devices need not be of the same speed.
2697		Starting with version 3.2.1, bonding also supports Infiniband
2698	slaves in active-backup mode.
2700	3.  How many bonding devices can I have?
2702		There is no limit.
2704	4.  How many slaves can a bonding device have?
2706		This is limited only by the number of network interfaces Linux
2707	supports and/or the number of network cards you can place in your
2708	system.
2710	5.  What happens when a slave link dies?
2712		If link monitoring is enabled, then the failing device will be
2713	disabled.  The active-backup mode will fail over to a backup link, and
2714	other modes will ignore the failed link.  The link will continue to be
2715	monitored, and should it recover, it will rejoin the bond (in whatever
2716	manner is appropriate for the mode). See the sections on High
2717	Availability and the documentation for each mode for additional
2718	information.
2720		Link monitoring can be enabled via either the miimon or
2721	arp_interval parameters (described in the module parameters section,
2722	above).  In general, miimon monitors the carrier state as sensed by
2723	the underlying network device, and the arp monitor (arp_interval)
2724	monitors connectivity to another host on the local network.
2726		If no link monitoring is configured, the bonding driver will
2727	be unable to detect link failures, and will assume that all links are
2728	always available.  This will likely result in lost packets, and a
2729	resulting degradation of performance.  The precise performance loss
2730	depends upon the bonding mode and network configuration.
2732	6.  Can bonding be used for High Availability?
2734		Yes.  See the section on High Availability for details.
2736	7.  Which switches/systems does it work with?
2738		The full answer to this depends upon the desired mode.
2740		In the basic balance modes (balance-rr and balance-xor), it
2741	works with any system that supports etherchannel (also called
2742	trunking).  Most managed switches currently available have such
2743	support, and many unmanaged switches as well.
2745		The advanced balance modes (balance-tlb and balance-alb) do
2746	not have special switch requirements, but do need device drivers that
2747	support specific features (described in the appropriate section under
2748	module parameters, above).
2750		In 802.3ad mode, it works with systems that support IEEE
2751	802.3ad Dynamic Link Aggregation.  Most managed and many unmanaged
2752	switches currently available support 802.3ad.
2754	        The active-backup mode should work with any Layer-II switch.
2756	8.  Where does a bonding device get its MAC address from?
2758		When using slave devices that have fixed MAC addresses, or when
2759	the fail_over_mac option is enabled, the bonding device's MAC address is
2760	the MAC address of the active slave.
2762		For other configurations, if not explicitly configured (with
2763	ifconfig or ip link), the MAC address of the bonding device is taken from
2764	its first slave device.  This MAC address is then passed to all following
2765	slaves and remains persistent (even if the first slave is removed) until
2766	the bonding device is brought down or reconfigured.
2768		If you wish to change the MAC address, you can set it with
2769	ifconfig or ip link:
2771	# ifconfig bond0 hw ether 00:11:22:33:44:55
2773	# ip link set bond0 address 66:77:88:99:aa:bb
2775		The MAC address can be also changed by bringing down/up the
2776	device and then changing its slaves (or their order):
2778	# ifconfig bond0 down ; modprobe -r bonding
2779	# ifconfig bond0 .... up
2780	# ifenslave bond0 eth...
2782		This method will automatically take the address from the next
2783	slave that is added.
2785		To restore your slaves' MAC addresses, you need to detach them
2786	from the bond (`ifenslave -d bond0 eth0'). The bonding driver will
2787	then restore the MAC addresses that the slaves had before they were
2788	enslaved.
2790	16. Resources and Links
2791	=======================
2793		The latest version of the bonding driver can be found in the latest
2794	version of the linux kernel, found on http://kernel.org
2796		The latest version of this document can be found in the latest kernel
2797	source (named Documentation/networking/bonding.txt).
2799		Discussions regarding the usage of the bonding driver take place on the
2800	bonding-devel mailing list, hosted at sourceforge.net. If you have questions or
2801	problems, post them to the list.  The list address is:
2803	bonding-devel@lists.sourceforge.net
2805		The administrative interface (to subscribe or unsubscribe) can
2806	be found at:
2808	https://lists.sourceforge.net/lists/listinfo/bonding-devel
2810		Discussions regarding the development of the bonding driver take place
2811	on the main Linux network mailing list, hosted at vger.kernel.org. The list
2812	address is:
2814	netdev@vger.kernel.org
2816		The administrative interface (to subscribe or unsubscribe) can
2817	be found at:
2819	http://vger.kernel.org/vger-lists.html#netdev
2821	Donald Becker's Ethernet Drivers and diag programs may be found at :
2822	 - http://web.archive.org/web/*/http://www.scyld.com/network/ 
2824	You will also find a lot of information regarding Ethernet, NWay, MII,
2825	etc. at www.scyld.com.
2827	-- END --
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