2 Linux Ethernet Bonding Driver HOWTO
4 Latest update: 12 November 2007
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>
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.
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
53 4. Querying Bonding Configuration
54 4.1 Bonding Configuration
55 4.2 Network Configuration
57 5. Switch Configuration
59 6. 802.1q VLAN Support
62 7.1 ARP Monitor Operation
63 7.2 Configuring Multiple ARP Targets
64 7.3 MII Monitor Operation
66 8. Potential Trouble Sources
67 8.1 Adventures in Routing
68 8.2 Ethernet Device Renaming
69 8.3 Painfully Slow Or No Failed Link Detection By Miimon
75 11. Configuring Bonding for High Availability
76 11.1 High Availability in a Single Switch Topology
77 11.2 High Availability in a Multiple Switch Topology
78 11.2.1 HA Bonding Mode Selection for Multiple Switch Topology
79 11.2.2 HA Link Monitoring for Multiple Switch Topology
81 12. Configuring Bonding for Maximum Throughput
82 12.1 Maximum Throughput in a Single Switch Topology
83 12.1.1 MT Bonding Mode Selection for Single Switch Topology
84 12.1.2 MT Link Monitoring for Single Switch Topology
85 12.2 Maximum Throughput in a Multiple Switch Topology
86 12.2.1 MT Bonding Mode Selection for Multiple Switch Topology
87 12.2.2 MT Link Monitoring for Multiple Switch Topology
89 13. Switch Behavior Issues
90 13.1 Link Establishment and Failover Delays
91 13.2 Duplicated Incoming Packets
93 14. Hardware Specific Considerations
96 15. Frequently Asked Questions
98 16. Resources and Links
101 1. Bonding Driver Installation
102 ==============================
104 Most popular distro kernels ship with the bonding driver
105 already available as a module and the ifenslave user level control
106 program installed and ready for use. If your distro does not, or you
107 have need to compile bonding from source (e.g., configuring and
108 installing a mainline kernel from kernel.org), you'll need to perform
111 1.1 Configure and build the kernel with bonding
112 -----------------------------------------------
114 The current version of the bonding driver is available in the
115 drivers/net/bonding subdirectory of the most recent kernel source
116 (which is available on http://kernel.org). Most users "rolling their
117 own" will want to use the most recent kernel from kernel.org.
119 Configure kernel with "make menuconfig" (or "make xconfig" or
120 "make config"), then select "Bonding driver support" in the "Network
121 device support" section. It is recommended that you configure the
122 driver as module since it is currently the only way to pass parameters
123 to the driver or configure more than one bonding device.
125 Build and install the new kernel and modules, then continue
126 below to install ifenslave.
128 1.2 Install ifenslave Control Utility
129 -------------------------------------
131 The ifenslave user level control program is included in the
132 kernel source tree, in the file Documentation/networking/ifenslave.c.
133 It is generally recommended that you use the ifenslave that
134 corresponds to the kernel that you are using (either from the same
135 source tree or supplied with the distro), however, ifenslave
136 executables from older kernels should function (but features newer
137 than the ifenslave release are not supported). Running an ifenslave
138 that is newer than the kernel is not supported, and may or may not
141 To install ifenslave, do the following:
143 # gcc -Wall -O -I/usr/src/linux/include ifenslave.c -o ifenslave
144 # cp ifenslave /sbin/ifenslave
146 If your kernel source is not in "/usr/src/linux," then replace
147 "/usr/src/linux/include" in the above with the location of your kernel
148 source include directory.
150 You may wish to back up any existing /sbin/ifenslave, or, for
151 testing or informal use, tag the ifenslave to the kernel version
152 (e.g., name the ifenslave executable /sbin/ifenslave-2.6.10).
156 If you omit the "-I" or specify an incorrect directory, you
157 may end up with an ifenslave that is incompatible with the kernel
158 you're trying to build it for. Some distros (e.g., Red Hat from 7.1
159 onwards) do not have /usr/include/linux symbolically linked to the
160 default kernel source include directory.
162 SECOND IMPORTANT NOTE:
163 If you plan to configure bonding using sysfs, you do not need
166 2. Bonding Driver Options
167 =========================
169 Options for the bonding driver are supplied as parameters to the
170 bonding module at load time, or are specified via sysfs.
172 Module options may be given as command line arguments to the
173 insmod or modprobe command, but are usually specified in either the
174 /etc/modules.conf or /etc/modprobe.conf configuration file, or in a
175 distro-specific configuration file (some of which are detailed in the next
178 Details on bonding support for sysfs is provided in the
179 "Configuring Bonding Manually via Sysfs" section, below.
181 The available bonding driver parameters are listed below. If a
182 parameter is not specified the default value is used. When initially
183 configuring a bond, it is recommended "tail -f /var/log/messages" be
184 run in a separate window to watch for bonding driver error messages.
186 It is critical that either the miimon or arp_interval and
187 arp_ip_target parameters be specified, otherwise serious network
188 degradation will occur during link failures. Very few devices do not
189 support at least miimon, so there is really no reason not to use it.
191 Options with textual values will accept either the text name
192 or, for backwards compatibility, the option value. E.g.,
193 "mode=802.3ad" and "mode=4" set the same mode.
195 The parameters are as follows:
199 Specifies the ARP link monitoring frequency in milliseconds.
201 The ARP monitor works by periodically checking the slave
202 devices to determine whether they have sent or received
203 traffic recently (the precise criteria depends upon the
204 bonding mode, and the state of the slave). Regular traffic is
205 generated via ARP probes issued for the addresses specified by
206 the arp_ip_target option.
208 This behavior can be modified by the arp_validate option,
211 If ARP monitoring is used in an etherchannel compatible mode
212 (modes 0 and 2), the switch should be configured in a mode
213 that evenly distributes packets across all links. If the
214 switch is configured to distribute the packets in an XOR
215 fashion, all replies from the ARP targets will be received on
216 the same link which could cause the other team members to
217 fail. ARP monitoring should not be used in conjunction with
218 miimon. A value of 0 disables ARP monitoring. The default
223 Specifies the IP addresses to use as ARP monitoring peers when
224 arp_interval is > 0. These are the targets of the ARP request
225 sent to determine the health of the link to the targets.
226 Specify these values in ddd.ddd.ddd.ddd format. Multiple IP
227 addresses must be separated by a comma. At least one IP
228 address must be given for ARP monitoring to function. The
229 maximum number of targets that can be specified is 16. The
230 default value is no IP addresses.
234 Specifies whether or not ARP probes and replies should be
235 validated in the active-backup mode. This causes the ARP
236 monitor to examine the incoming ARP requests and replies, and
237 only consider a slave to be up if it is receiving the
238 appropriate ARP traffic.
244 No validation is performed. This is the default.
248 Validation is performed only for the active slave.
252 Validation is performed only for backup slaves.
256 Validation is performed for all slaves.
258 For the active slave, the validation checks ARP replies to
259 confirm that they were generated by an arp_ip_target. Since
260 backup slaves do not typically receive these replies, the
261 validation performed for backup slaves is on the ARP request
262 sent out via the active slave. It is possible that some
263 switch or network configurations may result in situations
264 wherein the backup slaves do not receive the ARP requests; in
265 such a situation, validation of backup slaves must be
268 This option is useful in network configurations in which
269 multiple bonding hosts are concurrently issuing ARPs to one or
270 more targets beyond a common switch. Should the link between
271 the switch and target fail (but not the switch itself), the
272 probe traffic generated by the multiple bonding instances will
273 fool the standard ARP monitor into considering the links as
274 still up. Use of the arp_validate option can resolve this, as
275 the ARP monitor will only consider ARP requests and replies
276 associated with its own instance of bonding.
278 This option was added in bonding version 3.1.0.
282 Specifies the time, in milliseconds, to wait before disabling
283 a slave after a link failure has been detected. This option
284 is only valid for the miimon link monitor. The downdelay
285 value should be a multiple of the miimon value; if not, it
286 will be rounded down to the nearest multiple. The default
291 Specifies whether active-backup mode should set all slaves to
292 the same MAC address at enslavement (the traditional
293 behavior), or, when enabled, perform special handling of the
294 bond's MAC address in accordance with the selected policy.
300 This setting disables fail_over_mac, and causes
301 bonding to set all slaves of an active-backup bond to
302 the same MAC address at enslavement time. This is the
307 The "active" fail_over_mac policy indicates that the
308 MAC address of the bond should always be the MAC
309 address of the currently active slave. The MAC
310 address of the slaves is not changed; instead, the MAC
311 address of the bond changes during a failover.
313 This policy is useful for devices that cannot ever
314 alter their MAC address, or for devices that refuse
315 incoming broadcasts with their own source MAC (which
316 interferes with the ARP monitor).
318 The down side of this policy is that every device on
319 the network must be updated via gratuitous ARP,
320 vs. just updating a switch or set of switches (which
321 often takes place for any traffic, not just ARP
322 traffic, if the switch snoops incoming traffic to
323 update its tables) for the traditional method. If the
324 gratuitous ARP is lost, communication may be
327 When this policy is used in conjuction with the mii
328 monitor, devices which assert link up prior to being
329 able to actually transmit and receive are particularly
330 susecptible to loss of the gratuitous ARP, and an
331 appropriate updelay setting may be required.
335 The "follow" fail_over_mac policy causes the MAC
336 address of the bond to be selected normally (normally
337 the MAC address of the first slave added to the bond).
338 However, the second and subsequent slaves are not set
339 to this MAC address while they are in a backup role; a
340 slave is programmed with the bond's MAC address at
341 failover time (and the formerly active slave receives
342 the newly active slave's MAC address).
344 This policy is useful for multiport devices that
345 either become confused or incur a performance penalty
346 when multiple ports are programmed with the same MAC
350 The default policy is none, unless the first slave cannot
351 change its MAC address, in which case the active policy is
354 This option may be modified via sysfs only when no slaves are
357 This option was added in bonding version 3.2.0. The "follow"
358 policy was added in bonding version 3.3.0.
362 Option specifying the rate in which we'll ask our link partner
363 to transmit LACPDU packets in 802.3ad mode. Possible values
367 Request partner to transmit LACPDUs every 30 seconds
370 Request partner to transmit LACPDUs every 1 second
376 Specifies the number of bonding devices to create for this
377 instance of the bonding driver. E.g., if max_bonds is 3, and
378 the bonding driver is not already loaded, then bond0, bond1
379 and bond2 will be created. The default value is 1. Specifying
380 a value of 0 will load bonding, but will not create any devices.
384 Specifies the MII link monitoring frequency in milliseconds.
385 This determines how often the link state of each slave is
386 inspected for link failures. A value of zero disables MII
387 link monitoring. A value of 100 is a good starting point.
388 The use_carrier option, below, affects how the link state is
389 determined. See the High Availability section for additional
390 information. The default value is 0.
394 Specifies one of the bonding policies. The default is
395 balance-rr (round robin). Possible values are:
399 Round-robin policy: Transmit packets in sequential
400 order from the first available slave through the
401 last. This mode provides load balancing and fault
406 Active-backup policy: Only one slave in the bond is
407 active. A different slave becomes active if, and only
408 if, the active slave fails. The bond's MAC address is
409 externally visible on only one port (network adapter)
410 to avoid confusing the switch.
412 In bonding version 2.6.2 or later, when a failover
413 occurs in active-backup mode, bonding will issue one
414 or more gratuitous ARPs on the newly active slave.
415 One gratuitous ARP is issued for the bonding master
416 interface and each VLAN interfaces configured above
417 it, provided that the interface has at least one IP
418 address configured. Gratuitous ARPs issued for VLAN
419 interfaces are tagged with the appropriate VLAN id.
421 This mode provides fault tolerance. The primary
422 option, documented below, affects the behavior of this
427 XOR policy: Transmit based on the selected transmit
428 hash policy. The default policy is a simple [(source
429 MAC address XOR'd with destination MAC address) modulo
430 slave count]. Alternate transmit policies may be
431 selected via the xmit_hash_policy option, described
434 This mode provides load balancing and fault tolerance.
438 Broadcast policy: transmits everything on all slave
439 interfaces. This mode provides fault tolerance.
443 IEEE 802.3ad Dynamic link aggregation. Creates
444 aggregation groups that share the same speed and
445 duplex settings. Utilizes all slaves in the active
446 aggregator according to the 802.3ad specification.
448 Slave selection for outgoing traffic is done according
449 to the transmit hash policy, which may be changed from
450 the default simple XOR policy via the xmit_hash_policy
451 option, documented below. Note that not all transmit
452 policies may be 802.3ad compliant, particularly in
453 regards to the packet mis-ordering requirements of
454 section 43.2.4 of the 802.3ad standard. Differing
455 peer implementations will have varying tolerances for
460 1. Ethtool support in the base drivers for retrieving
461 the speed and duplex of each slave.
463 2. A switch that supports IEEE 802.3ad Dynamic link
466 Most switches will require some type of configuration
467 to enable 802.3ad mode.
471 Adaptive transmit load balancing: channel bonding that
472 does not require any special switch support. The
473 outgoing traffic is distributed according to the
474 current load (computed relative to the speed) on each
475 slave. Incoming traffic is received by the current
476 slave. If the receiving slave fails, another slave
477 takes over the MAC address of the failed receiving
482 Ethtool support in the base drivers for retrieving the
487 Adaptive load balancing: includes balance-tlb plus
488 receive load balancing (rlb) for IPV4 traffic, and
489 does not require any special switch support. The
490 receive load balancing is achieved by ARP negotiation.
491 The bonding driver intercepts the ARP Replies sent by
492 the local system on their way out and overwrites the
493 source hardware address with the unique hardware
494 address of one of the slaves in the bond such that
495 different peers use different hardware addresses for
498 Receive traffic from connections created by the server
499 is also balanced. When the local system sends an ARP
500 Request the bonding driver copies and saves the peer's
501 IP information from the ARP packet. When the ARP
502 Reply arrives from the peer, its hardware address is
503 retrieved and the bonding driver initiates an ARP
504 reply to this peer assigning it to one of the slaves
505 in the bond. A problematic outcome of using ARP
506 negotiation for balancing is that each time that an
507 ARP request is broadcast it uses the hardware address
508 of the bond. Hence, peers learn the hardware address
509 of the bond and the balancing of receive traffic
510 collapses to the current slave. This is handled by
511 sending updates (ARP Replies) to all the peers with
512 their individually assigned hardware address such that
513 the traffic is redistributed. Receive traffic is also
514 redistributed when a new slave is added to the bond
515 and when an inactive slave is re-activated. The
516 receive load is distributed sequentially (round robin)
517 among the group of highest speed slaves in the bond.
519 When a link is reconnected or a new slave joins the
520 bond the receive traffic is redistributed among all
521 active slaves in the bond by initiating ARP Replies
522 with the selected MAC address to each of the
523 clients. The updelay parameter (detailed below) must
524 be set to a value equal or greater than the switch's
525 forwarding delay so that the ARP Replies sent to the
526 peers will not be blocked by the switch.
530 1. Ethtool support in the base drivers for retrieving
531 the speed of each slave.
533 2. Base driver support for setting the hardware
534 address of a device while it is open. This is
535 required so that there will always be one slave in the
536 team using the bond hardware address (the
537 curr_active_slave) while having a unique hardware
538 address for each slave in the bond. If the
539 curr_active_slave fails its hardware address is
540 swapped with the new curr_active_slave that was
545 Specifies the number of gratuitous ARPs to be issued after a
546 failover event. One gratuitous ARP is issued immediately after
547 the failover, subsequent ARPs are sent at a rate of one per link
548 monitor interval (arp_interval or miimon, whichever is active).
550 The valid range is 0 - 255; the default value is 1. This option
551 affects only the active-backup mode. This option was added for
552 bonding version 3.3.0.
556 A string (eth0, eth2, etc) specifying which slave is the
557 primary device. The specified device will always be the
558 active slave while it is available. Only when the primary is
559 off-line will alternate devices be used. This is useful when
560 one slave is preferred over another, e.g., when one slave has
561 higher throughput than another.
563 The primary option is only valid for active-backup mode.
567 Specifies the time, in milliseconds, to wait before enabling a
568 slave after a link recovery has been detected. This option is
569 only valid for the miimon link monitor. The updelay value
570 should be a multiple of the miimon value; if not, it will be
571 rounded down to the nearest multiple. The default value is 0.
575 Specifies whether or not miimon should use MII or ETHTOOL
576 ioctls vs. netif_carrier_ok() to determine the link
577 status. The MII or ETHTOOL ioctls are less efficient and
578 utilize a deprecated calling sequence within the kernel. The
579 netif_carrier_ok() relies on the device driver to maintain its
580 state with netif_carrier_on/off; at this writing, most, but
581 not all, device drivers support this facility.
583 If bonding insists that the link is up when it should not be,
584 it may be that your network device driver does not support
585 netif_carrier_on/off. The default state for netif_carrier is
586 "carrier on," so if a driver does not support netif_carrier,
587 it will appear as if the link is always up. In this case,
588 setting use_carrier to 0 will cause bonding to revert to the
589 MII / ETHTOOL ioctl method to determine the link state.
591 A value of 1 enables the use of netif_carrier_ok(), a value of
592 0 will use the deprecated MII / ETHTOOL ioctls. The default
597 Selects the transmit hash policy to use for slave selection in
598 balance-xor and 802.3ad modes. Possible values are:
602 Uses XOR of hardware MAC addresses to generate the
605 (source MAC XOR destination MAC) modulo slave count
607 This algorithm will place all traffic to a particular
608 network peer on the same slave.
610 This algorithm is 802.3ad compliant.
614 This policy uses a combination of layer2 and layer3
615 protocol information to generate the hash.
617 Uses XOR of hardware MAC addresses and IP addresses to
618 generate the hash. The formula is
620 (((source IP XOR dest IP) AND 0xffff) XOR
621 ( source MAC XOR destination MAC ))
624 This algorithm will place all traffic to a particular
625 network peer on the same slave. For non-IP traffic,
626 the formula is the same as for the layer2 transmit
629 This policy is intended to provide a more balanced
630 distribution of traffic than layer2 alone, especially
631 in environments where a layer3 gateway device is
632 required to reach most destinations.
634 This algorithm is 802.3ad compliant.
638 This policy uses upper layer protocol information,
639 when available, to generate the hash. This allows for
640 traffic to a particular network peer to span multiple
641 slaves, although a single connection will not span
644 The formula for unfragmented TCP and UDP packets is
646 ((source port XOR dest port) XOR
647 ((source IP XOR dest IP) AND 0xffff)
650 For fragmented TCP or UDP packets and all other IP
651 protocol traffic, the source and destination port
652 information is omitted. For non-IP traffic, the
653 formula is the same as for the layer2 transmit hash
656 This policy is intended to mimic the behavior of
657 certain switches, notably Cisco switches with PFC2 as
658 well as some Foundry and IBM products.
660 This algorithm is not fully 802.3ad compliant. A
661 single TCP or UDP conversation containing both
662 fragmented and unfragmented packets will see packets
663 striped across two interfaces. This may result in out
664 of order delivery. Most traffic types will not meet
665 this criteria, as TCP rarely fragments traffic, and
666 most UDP traffic is not involved in extended
667 conversations. Other implementations of 802.3ad may
668 or may not tolerate this noncompliance.
670 The default value is layer2. This option was added in bonding
671 version 2.6.3. In earlier versions of bonding, this parameter
672 does not exist, and the layer2 policy is the only policy. The
673 layer2+3 value was added for bonding version 3.2.2.
676 3. Configuring Bonding Devices
677 ==============================
679 You can configure bonding using either your distro's network
680 initialization scripts, or manually using either ifenslave or the
681 sysfs interface. Distros generally use one of two packages for the
682 network initialization scripts: initscripts or sysconfig. Recent
683 versions of these packages have support for bonding, while older
686 We will first describe the options for configuring bonding for
687 distros using versions of initscripts and sysconfig with full or
688 partial support for bonding, then provide information on enabling
689 bonding without support from the network initialization scripts (i.e.,
690 older versions of initscripts or sysconfig).
692 If you're unsure whether your distro uses sysconfig or
693 initscripts, or don't know if it's new enough, have no fear.
694 Determining this is fairly straightforward.
696 First, issue the command:
700 It will respond with a line of text starting with either
701 "initscripts" or "sysconfig," followed by some numbers. This is the
702 package that provides your network initialization scripts.
704 Next, to determine if your installation supports bonding,
707 $ grep ifenslave /sbin/ifup
709 If this returns any matches, then your initscripts or
710 sysconfig has support for bonding.
712 3.1 Configuration with Sysconfig Support
713 ----------------------------------------
715 This section applies to distros using a version of sysconfig
716 with bonding support, for example, SuSE Linux Enterprise Server 9.
718 SuSE SLES 9's networking configuration system does support
719 bonding, however, at this writing, the YaST system configuration
720 front end does not provide any means to work with bonding devices.
721 Bonding devices can be managed by hand, however, as follows.
723 First, if they have not already been configured, configure the
724 slave devices. On SLES 9, this is most easily done by running the
725 yast2 sysconfig configuration utility. The goal is for to create an
726 ifcfg-id file for each slave device. The simplest way to accomplish
727 this is to configure the devices for DHCP (this is only to get the
728 file ifcfg-id file created; see below for some issues with DHCP). The
729 name of the configuration file for each device will be of the form:
731 ifcfg-id-xx:xx:xx:xx:xx:xx
733 Where the "xx" portion will be replaced with the digits from
734 the device's permanent MAC address.
736 Once the set of ifcfg-id-xx:xx:xx:xx:xx:xx files has been
737 created, it is necessary to edit the configuration files for the slave
738 devices (the MAC addresses correspond to those of the slave devices).
739 Before editing, the file will contain multiple lines, and will look
745 UNIQUE='XNzu.WeZGOGF+4wE'
746 _nm_name='bus-pci-0001:61:01.0'
748 Change the BOOTPROTO and STARTMODE lines to the following:
753 Do not alter the UNIQUE or _nm_name lines. Remove any other
754 lines (USERCTL, etc).
756 Once the ifcfg-id-xx:xx:xx:xx:xx:xx files have been modified,
757 it's time to create the configuration file for the bonding device
758 itself. This file is named ifcfg-bondX, where X is the number of the
759 bonding device to create, starting at 0. The first such file is
760 ifcfg-bond0, the second is ifcfg-bond1, and so on. The sysconfig
761 network configuration system will correctly start multiple instances
764 The contents of the ifcfg-bondX file is as follows:
767 BROADCAST="10.0.2.255"
769 NETMASK="255.255.0.0"
774 BONDING_MODULE_OPTS="mode=active-backup miimon=100"
775 BONDING_SLAVE0="eth0"
776 BONDING_SLAVE1="bus-pci-0000:06:08.1"
778 Replace the sample BROADCAST, IPADDR, NETMASK and NETWORK
779 values with the appropriate values for your network.
781 The STARTMODE specifies when the device is brought online.
782 The possible values are:
784 onboot: The device is started at boot time. If you're not
785 sure, this is probably what you want.
787 manual: The device is started only when ifup is called
788 manually. Bonding devices may be configured this
789 way if you do not wish them to start automatically
790 at boot for some reason.
792 hotplug: The device is started by a hotplug event. This is not
793 a valid choice for a bonding device.
795 off or ignore: The device configuration is ignored.
797 The line BONDING_MASTER='yes' indicates that the device is a
798 bonding master device. The only useful value is "yes."
800 The contents of BONDING_MODULE_OPTS are supplied to the
801 instance of the bonding module for this device. Specify the options
802 for the bonding mode, link monitoring, and so on here. Do not include
803 the max_bonds bonding parameter; this will confuse the configuration
804 system if you have multiple bonding devices.
806 Finally, supply one BONDING_SLAVEn="slave device" for each
807 slave. where "n" is an increasing value, one for each slave. The
808 "slave device" is either an interface name, e.g., "eth0", or a device
809 specifier for the network device. The interface name is easier to
810 find, but the ethN names are subject to change at boot time if, e.g.,
811 a device early in the sequence has failed. The device specifiers
812 (bus-pci-0000:06:08.1 in the example above) specify the physical
813 network device, and will not change unless the device's bus location
814 changes (for example, it is moved from one PCI slot to another). The
815 example above uses one of each type for demonstration purposes; most
816 configurations will choose one or the other for all slave devices.
818 When all configuration files have been modified or created,
819 networking must be restarted for the configuration changes to take
820 effect. This can be accomplished via the following:
822 # /etc/init.d/network restart
824 Note that the network control script (/sbin/ifdown) will
825 remove the bonding module as part of the network shutdown processing,
826 so it is not necessary to remove the module by hand if, e.g., the
827 module parameters have changed.
829 Also, at this writing, YaST/YaST2 will not manage bonding
830 devices (they do not show bonding interfaces on its list of network
831 devices). It is necessary to edit the configuration file by hand to
832 change the bonding configuration.
834 Additional general options and details of the ifcfg file
835 format can be found in an example ifcfg template file:
837 /etc/sysconfig/network/ifcfg.template
839 Note that the template does not document the various BONDING_
840 settings described above, but does describe many of the other options.
842 3.1.1 Using DHCP with Sysconfig
843 -------------------------------
845 Under sysconfig, configuring a device with BOOTPROTO='dhcp'
846 will cause it to query DHCP for its IP address information. At this
847 writing, this does not function for bonding devices; the scripts
848 attempt to obtain the device address from DHCP prior to adding any of
849 the slave devices. Without active slaves, the DHCP requests are not
852 3.1.2 Configuring Multiple Bonds with Sysconfig
853 -----------------------------------------------
855 The sysconfig network initialization system is capable of
856 handling multiple bonding devices. All that is necessary is for each
857 bonding instance to have an appropriately configured ifcfg-bondX file
858 (as described above). Do not specify the "max_bonds" parameter to any
859 instance of bonding, as this will confuse sysconfig. If you require
860 multiple bonding devices with identical parameters, create multiple
863 Because the sysconfig scripts supply the bonding module
864 options in the ifcfg-bondX file, it is not necessary to add them to
865 the system /etc/modules.conf or /etc/modprobe.conf configuration file.
867 3.2 Configuration with Initscripts Support
868 ------------------------------------------
870 This section applies to distros using a recent version of
871 initscripts with bonding support, for example, Red Hat Enterprise Linux
872 version 3 or later, Fedora, etc. On these systems, the network
873 initialization scripts have knowledge of bonding, and can be configured to
874 control bonding devices. Note that older versions of the initscripts
875 package have lower levels of support for bonding; this will be noted where
878 These distros will not automatically load the network adapter
879 driver unless the ethX device is configured with an IP address.
880 Because of this constraint, users must manually configure a
881 network-script file for all physical adapters that will be members of
882 a bondX link. Network script files are located in the directory:
884 /etc/sysconfig/network-scripts
886 The file name must be prefixed with "ifcfg-eth" and suffixed
887 with the adapter's physical adapter number. For example, the script
888 for eth0 would be named /etc/sysconfig/network-scripts/ifcfg-eth0.
889 Place the following text in the file:
898 The DEVICE= line will be different for every ethX device and
899 must correspond with the name of the file, i.e., ifcfg-eth1 must have
900 a device line of DEVICE=eth1. The setting of the MASTER= line will
901 also depend on the final bonding interface name chosen for your bond.
902 As with other network devices, these typically start at 0, and go up
903 one for each device, i.e., the first bonding instance is bond0, the
904 second is bond1, and so on.
906 Next, create a bond network script. The file name for this
907 script will be /etc/sysconfig/network-scripts/ifcfg-bondX where X is
908 the number of the bond. For bond0 the file is named "ifcfg-bond0",
909 for bond1 it is named "ifcfg-bond1", and so on. Within that file,
910 place the following text:
914 NETMASK=255.255.255.0
916 BROADCAST=192.168.1.255
921 Be sure to change the networking specific lines (IPADDR,
922 NETMASK, NETWORK and BROADCAST) to match your network configuration.
924 For later versions of initscripts, such as that found with Fedora
925 7 and Red Hat Enterprise Linux version 5 (or later), it is possible, and,
926 indeed, preferable, to specify the bonding options in the ifcfg-bond0
927 file, e.g. a line of the format:
929 BONDING_OPTS="mode=active-backup arp_interval=60 arp_ip_target=+192.168.1.254"
931 will configure the bond with the specified options. The options
932 specified in BONDING_OPTS are identical to the bonding module parameters
933 except for the arp_ip_target field. Each target should be included as a
934 separate option and should be preceded by a '+' to indicate it should be
935 added to the list of queried targets, e.g.,
937 arp_ip_target=+192.168.1.1 arp_ip_target=+192.168.1.2
939 is the proper syntax to specify multiple targets. When specifying
940 options via BONDING_OPTS, it is not necessary to edit /etc/modules.conf or
943 For older versions of initscripts that do not support
944 BONDING_OPTS, it is necessary to edit /etc/modules.conf (or
945 /etc/modprobe.conf, depending upon your distro) to load the bonding module
946 with your desired options when the bond0 interface is brought up. The
947 following lines in /etc/modules.conf (or modprobe.conf) will load the
948 bonding module, and select its options:
951 options bond0 mode=balance-alb miimon=100
953 Replace the sample parameters with the appropriate set of
954 options for your configuration.
956 Finally run "/etc/rc.d/init.d/network restart" as root. This
957 will restart the networking subsystem and your bond link should be now
960 3.2.1 Using DHCP with Initscripts
961 ---------------------------------
963 Recent versions of initscripts (the versions supplied with Fedora
964 Core 3 and Red Hat Enterprise Linux 4, or later versions, are reported to
965 work) have support for assigning IP information to bonding devices via
968 To configure bonding for DHCP, configure it as described
969 above, except replace the line "BOOTPROTO=none" with "BOOTPROTO=dhcp"
970 and add a line consisting of "TYPE=Bonding". Note that the TYPE value
973 3.2.2 Configuring Multiple Bonds with Initscripts
974 -------------------------------------------------
976 Initscripts packages that are included with Fedora 7 and Red Hat
977 Enterprise Linux 5 support multiple bonding interfaces by simply
978 specifying the appropriate BONDING_OPTS= in ifcfg-bondX where X is the
979 number of the bond. This support requires sysfs support in the kernel,
980 and a bonding driver of version 3.0.0 or later. Other configurations may
981 not support this method for specifying multiple bonding interfaces; for
982 those instances, see the "Configuring Multiple Bonds Manually" section,
985 3.3 Configuring Bonding Manually with Ifenslave
986 -----------------------------------------------
988 This section applies to distros whose network initialization
989 scripts (the sysconfig or initscripts package) do not have specific
990 knowledge of bonding. One such distro is SuSE Linux Enterprise Server
993 The general method for these systems is to place the bonding
994 module parameters into /etc/modules.conf or /etc/modprobe.conf (as
995 appropriate for the installed distro), then add modprobe and/or
996 ifenslave commands to the system's global init script. The name of
997 the global init script differs; for sysconfig, it is
998 /etc/init.d/boot.local and for initscripts it is /etc/rc.d/rc.local.
1000 For example, if you wanted to make a simple bond of two e100
1001 devices (presumed to be eth0 and eth1), and have it persist across
1002 reboots, edit the appropriate file (/etc/init.d/boot.local or
1003 /etc/rc.d/rc.local), and add the following:
1005 modprobe bonding mode=balance-alb miimon=100
1007 ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
1008 ifenslave bond0 eth0
1009 ifenslave bond0 eth1
1011 Replace the example bonding module parameters and bond0
1012 network configuration (IP address, netmask, etc) with the appropriate
1013 values for your configuration.
1015 Unfortunately, this method will not provide support for the
1016 ifup and ifdown scripts on the bond devices. To reload the bonding
1017 configuration, it is necessary to run the initialization script, e.g.,
1019 # /etc/init.d/boot.local
1023 # /etc/rc.d/rc.local
1025 It may be desirable in such a case to create a separate script
1026 which only initializes the bonding configuration, then call that
1027 separate script from within boot.local. This allows for bonding to be
1028 enabled without re-running the entire global init script.
1030 To shut down the bonding devices, it is necessary to first
1031 mark the bonding device itself as being down, then remove the
1032 appropriate device driver modules. For our example above, you can do
1035 # ifconfig bond0 down
1039 Again, for convenience, it may be desirable to create a script
1040 with these commands.
1043 3.3.1 Configuring Multiple Bonds Manually
1044 -----------------------------------------
1046 This section contains information on configuring multiple
1047 bonding devices with differing options for those systems whose network
1048 initialization scripts lack support for configuring multiple bonds.
1050 If you require multiple bonding devices, but all with the same
1051 options, you may wish to use the "max_bonds" module parameter,
1054 To create multiple bonding devices with differing options, it is
1055 preferrable to use bonding parameters exported by sysfs, documented in the
1058 For versions of bonding without sysfs support, the only means to
1059 provide multiple instances of bonding with differing options is to load
1060 the bonding driver multiple times. Note that current versions of the
1061 sysconfig network initialization scripts handle this automatically; if
1062 your distro uses these scripts, no special action is needed. See the
1063 section Configuring Bonding Devices, above, if you're not sure about your
1064 network initialization scripts.
1066 To load multiple instances of the module, it is necessary to
1067 specify a different name for each instance (the module loading system
1068 requires that every loaded module, even multiple instances of the same
1069 module, have a unique name). This is accomplished by supplying multiple
1070 sets of bonding options in /etc/modprobe.conf, for example:
1073 options bond0 -o bond0 mode=balance-rr miimon=100
1076 options bond1 -o bond1 mode=balance-alb miimon=50
1078 will load the bonding module two times. The first instance is
1079 named "bond0" and creates the bond0 device in balance-rr mode with an
1080 miimon of 100. The second instance is named "bond1" and creates the
1081 bond1 device in balance-alb mode with an miimon of 50.
1083 In some circumstances (typically with older distributions),
1084 the above does not work, and the second bonding instance never sees
1085 its options. In that case, the second options line can be substituted
1088 install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \
1089 mode=balance-alb miimon=50
1091 This may be repeated any number of times, specifying a new and
1092 unique name in place of bond1 for each subsequent instance.
1094 It has been observed that some Red Hat supplied kernels are unable
1095 to rename modules at load time (the "-o bond1" part). Attempts to pass
1096 that option to modprobe will produce an "Operation not permitted" error.
1097 This has been reported on some Fedora Core kernels, and has been seen on
1098 RHEL 4 as well. On kernels exhibiting this problem, it will be impossible
1099 to configure multiple bonds with differing parameters (as they are older
1100 kernels, and also lack sysfs support).
1102 3.4 Configuring Bonding Manually via Sysfs
1103 ------------------------------------------
1105 Starting with version 3.0.0, Channel Bonding may be configured
1106 via the sysfs interface. This interface allows dynamic configuration
1107 of all bonds in the system without unloading the module. It also
1108 allows for adding and removing bonds at runtime. Ifenslave is no
1109 longer required, though it is still supported.
1111 Use of the sysfs interface allows you to use multiple bonds
1112 with different configurations without having to reload the module.
1113 It also allows you to use multiple, differently configured bonds when
1114 bonding is compiled into the kernel.
1116 You must have the sysfs filesystem mounted to configure
1117 bonding this way. The examples in this document assume that you
1118 are using the standard mount point for sysfs, e.g. /sys. If your
1119 sysfs filesystem is mounted elsewhere, you will need to adjust the
1120 example paths accordingly.
1122 Creating and Destroying Bonds
1123 -----------------------------
1124 To add a new bond foo:
1125 # echo +foo > /sys/class/net/bonding_masters
1127 To remove an existing bond bar:
1128 # echo -bar > /sys/class/net/bonding_masters
1130 To show all existing bonds:
1131 # cat /sys/class/net/bonding_masters
1133 NOTE: due to 4K size limitation of sysfs files, this list may be
1134 truncated if you have more than a few hundred bonds. This is unlikely
1135 to occur under normal operating conditions.
1137 Adding and Removing Slaves
1138 --------------------------
1139 Interfaces may be enslaved to a bond using the file
1140 /sys/class/net/<bond>/bonding/slaves. The semantics for this file
1141 are the same as for the bonding_masters file.
1143 To enslave interface eth0 to bond bond0:
1145 # echo +eth0 > /sys/class/net/bond0/bonding/slaves
1147 To free slave eth0 from bond bond0:
1148 # echo -eth0 > /sys/class/net/bond0/bonding/slaves
1150 When an interface is enslaved to a bond, symlinks between the
1151 two are created in the sysfs filesystem. In this case, you would get
1152 /sys/class/net/bond0/slave_eth0 pointing to /sys/class/net/eth0, and
1153 /sys/class/net/eth0/master pointing to /sys/class/net/bond0.
1155 This means that you can tell quickly whether or not an
1156 interface is enslaved by looking for the master symlink. Thus:
1157 # echo -eth0 > /sys/class/net/eth0/master/bonding/slaves
1158 will free eth0 from whatever bond it is enslaved to, regardless of
1159 the name of the bond interface.
1161 Changing a Bond's Configuration
1162 -------------------------------
1163 Each bond may be configured individually by manipulating the
1164 files located in /sys/class/net/<bond name>/bonding
1166 The names of these files correspond directly with the command-
1167 line parameters described elsewhere in this file, and, with the
1168 exception of arp_ip_target, they accept the same values. To see the
1169 current setting, simply cat the appropriate file.
1171 A few examples will be given here; for specific usage
1172 guidelines for each parameter, see the appropriate section in this
1175 To configure bond0 for balance-alb mode:
1176 # ifconfig bond0 down
1177 # echo 6 > /sys/class/net/bond0/bonding/mode
1179 # echo balance-alb > /sys/class/net/bond0/bonding/mode
1180 NOTE: The bond interface must be down before the mode can be
1183 To enable MII monitoring on bond0 with a 1 second interval:
1184 # echo 1000 > /sys/class/net/bond0/bonding/miimon
1185 NOTE: If ARP monitoring is enabled, it will disabled when MII
1186 monitoring is enabled, and vice-versa.
1189 # echo +192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
1190 # echo +192.168.0.101 > /sys/class/net/bond0/bonding/arp_ip_target
1191 NOTE: up to 10 target addresses may be specified.
1193 To remove an ARP target:
1194 # echo -192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
1196 Example Configuration
1197 ---------------------
1198 We begin with the same example that is shown in section 3.3,
1199 executed with sysfs, and without using ifenslave.
1201 To make a simple bond of two e100 devices (presumed to be eth0
1202 and eth1), and have it persist across reboots, edit the appropriate
1203 file (/etc/init.d/boot.local or /etc/rc.d/rc.local), and add the
1208 echo balance-alb > /sys/class/net/bond0/bonding/mode
1209 ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
1210 echo 100 > /sys/class/net/bond0/bonding/miimon
1211 echo +eth0 > /sys/class/net/bond0/bonding/slaves
1212 echo +eth1 > /sys/class/net/bond0/bonding/slaves
1214 To add a second bond, with two e1000 interfaces in
1215 active-backup mode, using ARP monitoring, add the following lines to
1219 echo +bond1 > /sys/class/net/bonding_masters
1220 echo active-backup > /sys/class/net/bond1/bonding/mode
1221 ifconfig bond1 192.168.2.1 netmask 255.255.255.0 up
1222 echo +192.168.2.100 /sys/class/net/bond1/bonding/arp_ip_target
1223 echo 2000 > /sys/class/net/bond1/bonding/arp_interval
1224 echo +eth2 > /sys/class/net/bond1/bonding/slaves
1225 echo +eth3 > /sys/class/net/bond1/bonding/slaves
1228 4. Querying Bonding Configuration
1229 =================================
1231 4.1 Bonding Configuration
1232 -------------------------
1234 Each bonding device has a read-only file residing in the
1235 /proc/net/bonding directory. The file contents include information
1236 about the bonding configuration, options and state of each slave.
1238 For example, the contents of /proc/net/bonding/bond0 after the
1239 driver is loaded with parameters of mode=0 and miimon=1000 is
1240 generally as follows:
1242 Ethernet Channel Bonding Driver: 2.6.1 (October 29, 2004)
1243 Bonding Mode: load balancing (round-robin)
1244 Currently Active Slave: eth0
1246 MII Polling Interval (ms): 1000
1250 Slave Interface: eth1
1252 Link Failure Count: 1
1254 Slave Interface: eth0
1256 Link Failure Count: 1
1258 The precise format and contents will change depending upon the
1259 bonding configuration, state, and version of the bonding driver.
1261 4.2 Network configuration
1262 -------------------------
1264 The network configuration can be inspected using the ifconfig
1265 command. Bonding devices will have the MASTER flag set; Bonding slave
1266 devices will have the SLAVE flag set. The ifconfig output does not
1267 contain information on which slaves are associated with which masters.
1269 In the example below, the bond0 interface is the master
1270 (MASTER) while eth0 and eth1 are slaves (SLAVE). Notice all slaves of
1271 bond0 have the same MAC address (HWaddr) as bond0 for all modes except
1272 TLB and ALB that require a unique MAC address for each slave.
1275 bond0 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4
1276 inet addr:XXX.XXX.XXX.YYY Bcast:XXX.XXX.XXX.255 Mask:255.255.252.0
1277 UP BROADCAST RUNNING MASTER MULTICAST MTU:1500 Metric:1
1278 RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0
1279 TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0
1280 collisions:0 txqueuelen:0
1282 eth0 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4
1283 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1
1284 RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0
1285 TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0
1286 collisions:0 txqueuelen:100
1287 Interrupt:10 Base address:0x1080
1289 eth1 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4
1290 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1
1291 RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0
1292 TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0
1293 collisions:0 txqueuelen:100
1294 Interrupt:9 Base address:0x1400
1296 5. Switch Configuration
1297 =======================
1299 For this section, "switch" refers to whatever system the
1300 bonded devices are directly connected to (i.e., where the other end of
1301 the cable plugs into). This may be an actual dedicated switch device,
1302 or it may be another regular system (e.g., another computer running
1305 The active-backup, balance-tlb and balance-alb modes do not
1306 require any specific configuration of the switch.
1308 The 802.3ad mode requires that the switch have the appropriate
1309 ports configured as an 802.3ad aggregation. The precise method used
1310 to configure this varies from switch to switch, but, for example, a
1311 Cisco 3550 series switch requires that the appropriate ports first be
1312 grouped together in a single etherchannel instance, then that
1313 etherchannel is set to mode "lacp" to enable 802.3ad (instead of
1314 standard EtherChannel).
1316 The balance-rr, balance-xor and broadcast modes generally
1317 require that the switch have the appropriate ports grouped together.
1318 The nomenclature for such a group differs between switches, it may be
1319 called an "etherchannel" (as in the Cisco example, above), a "trunk
1320 group" or some other similar variation. For these modes, each switch
1321 will also have its own configuration options for the switch's transmit
1322 policy to the bond. Typical choices include XOR of either the MAC or
1323 IP addresses. The transmit policy of the two peers does not need to
1324 match. For these three modes, the bonding mode really selects a
1325 transmit policy for an EtherChannel group; all three will interoperate
1326 with another EtherChannel group.
1329 6. 802.1q VLAN Support
1330 ======================
1332 It is possible to configure VLAN devices over a bond interface
1333 using the 8021q driver. However, only packets coming from the 8021q
1334 driver and passing through bonding will be tagged by default. Self
1335 generated packets, for example, bonding's learning packets or ARP
1336 packets generated by either ALB mode or the ARP monitor mechanism, are
1337 tagged internally by bonding itself. As a result, bonding must
1338 "learn" the VLAN IDs configured above it, and use those IDs to tag
1339 self generated packets.
1341 For reasons of simplicity, and to support the use of adapters
1342 that can do VLAN hardware acceleration offloading, the bonding
1343 interface declares itself as fully hardware offloading capable, it gets
1344 the add_vid/kill_vid notifications to gather the necessary
1345 information, and it propagates those actions to the slaves. In case
1346 of mixed adapter types, hardware accelerated tagged packets that
1347 should go through an adapter that is not offloading capable are
1348 "un-accelerated" by the bonding driver so the VLAN tag sits in the
1351 VLAN interfaces *must* be added on top of a bonding interface
1352 only after enslaving at least one slave. The bonding interface has a
1353 hardware address of 00:00:00:00:00:00 until the first slave is added.
1354 If the VLAN interface is created prior to the first enslavement, it
1355 would pick up the all-zeroes hardware address. Once the first slave
1356 is attached to the bond, the bond device itself will pick up the
1357 slave's hardware address, which is then available for the VLAN device.
1359 Also, be aware that a similar problem can occur if all slaves
1360 are released from a bond that still has one or more VLAN interfaces on
1361 top of it. When a new slave is added, the bonding interface will
1362 obtain its hardware address from the first slave, which might not
1363 match the hardware address of the VLAN interfaces (which was
1364 ultimately copied from an earlier slave).
1366 There are two methods to insure that the VLAN device operates
1367 with the correct hardware address if all slaves are removed from a
1370 1. Remove all VLAN interfaces then recreate them
1372 2. Set the bonding interface's hardware address so that it
1373 matches the hardware address of the VLAN interfaces.
1375 Note that changing a VLAN interface's HW address would set the
1376 underlying device -- i.e. the bonding interface -- to promiscuous
1377 mode, which might not be what you want.
1383 The bonding driver at present supports two schemes for
1384 monitoring a slave device's link state: the ARP monitor and the MII
1387 At the present time, due to implementation restrictions in the
1388 bonding driver itself, it is not possible to enable both ARP and MII
1389 monitoring simultaneously.
1391 7.1 ARP Monitor Operation
1392 -------------------------
1394 The ARP monitor operates as its name suggests: it sends ARP
1395 queries to one or more designated peer systems on the network, and
1396 uses the response as an indication that the link is operating. This
1397 gives some assurance that traffic is actually flowing to and from one
1398 or more peers on the local network.
1400 The ARP monitor relies on the device driver itself to verify
1401 that traffic is flowing. In particular, the driver must keep up to
1402 date the last receive time, dev->last_rx, and transmit start time,
1403 dev->trans_start. If these are not updated by the driver, then the
1404 ARP monitor will immediately fail any slaves using that driver, and
1405 those slaves will stay down. If networking monitoring (tcpdump, etc)
1406 shows the ARP requests and replies on the network, then it may be that
1407 your device driver is not updating last_rx and trans_start.
1409 7.2 Configuring Multiple ARP Targets
1410 ------------------------------------
1412 While ARP monitoring can be done with just one target, it can
1413 be useful in a High Availability setup to have several targets to
1414 monitor. In the case of just one target, the target itself may go
1415 down or have a problem making it unresponsive to ARP requests. Having
1416 an additional target (or several) increases the reliability of the ARP
1419 Multiple ARP targets must be separated by commas as follows:
1421 # example options for ARP monitoring with three targets
1423 options bond0 arp_interval=60 arp_ip_target=192.168.0.1,192.168.0.3,192.168.0.9
1425 For just a single target the options would resemble:
1427 # example options for ARP monitoring with one target
1429 options bond0 arp_interval=60 arp_ip_target=192.168.0.100
1432 7.3 MII Monitor Operation
1433 -------------------------
1435 The MII monitor monitors only the carrier state of the local
1436 network interface. It accomplishes this in one of three ways: by
1437 depending upon the device driver to maintain its carrier state, by
1438 querying the device's MII registers, or by making an ethtool query to
1441 If the use_carrier module parameter is 1 (the default value),
1442 then the MII monitor will rely on the driver for carrier state
1443 information (via the netif_carrier subsystem). As explained in the
1444 use_carrier parameter information, above, if the MII monitor fails to
1445 detect carrier loss on the device (e.g., when the cable is physically
1446 disconnected), it may be that the driver does not support
1449 If use_carrier is 0, then the MII monitor will first query the
1450 device's (via ioctl) MII registers and check the link state. If that
1451 request fails (not just that it returns carrier down), then the MII
1452 monitor will make an ethtool ETHOOL_GLINK request to attempt to obtain
1453 the same information. If both methods fail (i.e., the driver either
1454 does not support or had some error in processing both the MII register
1455 and ethtool requests), then the MII monitor will assume the link is
1458 8. Potential Sources of Trouble
1459 ===============================
1461 8.1 Adventures in Routing
1462 -------------------------
1464 When bonding is configured, it is important that the slave
1465 devices not have routes that supersede routes of the master (or,
1466 generally, not have routes at all). For example, suppose the bonding
1467 device bond0 has two slaves, eth0 and eth1, and the routing table is
1470 Kernel IP routing table
1471 Destination Gateway Genmask Flags MSS Window irtt Iface
1472 10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 eth0
1473 10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 eth1
1474 10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 bond0
1475 127.0.0.0 0.0.0.0 255.0.0.0 U 40 0 0 lo
1477 This routing configuration will likely still update the
1478 receive/transmit times in the driver (needed by the ARP monitor), but
1479 may bypass the bonding driver (because outgoing traffic to, in this
1480 case, another host on network 10 would use eth0 or eth1 before bond0).
1482 The ARP monitor (and ARP itself) may become confused by this
1483 configuration, because ARP requests (generated by the ARP monitor)
1484 will be sent on one interface (bond0), but the corresponding reply
1485 will arrive on a different interface (eth0). This reply looks to ARP
1486 as an unsolicited ARP reply (because ARP matches replies on an
1487 interface basis), and is discarded. The MII monitor is not affected
1488 by the state of the routing table.
1490 The solution here is simply to insure that slaves do not have
1491 routes of their own, and if for some reason they must, those routes do
1492 not supersede routes of their master. This should generally be the
1493 case, but unusual configurations or errant manual or automatic static
1494 route additions may cause trouble.
1496 8.2 Ethernet Device Renaming
1497 ----------------------------
1499 On systems with network configuration scripts that do not
1500 associate physical devices directly with network interface names (so
1501 that the same physical device always has the same "ethX" name), it may
1502 be necessary to add some special logic to either /etc/modules.conf or
1503 /etc/modprobe.conf (depending upon which is installed on the system).
1505 For example, given a modules.conf containing the following:
1508 options bond0 mode=some-mode miimon=50
1514 If neither eth0 and eth1 are slaves to bond0, then when the
1515 bond0 interface comes up, the devices may end up reordered. This
1516 happens because bonding is loaded first, then its slave device's
1517 drivers are loaded next. Since no other drivers have been loaded,
1518 when the e1000 driver loads, it will receive eth0 and eth1 for its
1519 devices, but the bonding configuration tries to enslave eth2 and eth3
1520 (which may later be assigned to the tg3 devices).
1522 Adding the following:
1524 add above bonding e1000 tg3
1526 causes modprobe to load e1000 then tg3, in that order, when
1527 bonding is loaded. This command is fully documented in the
1528 modules.conf manual page.
1530 On systems utilizing modprobe.conf (or modprobe.conf.local),
1531 an equivalent problem can occur. In this case, the following can be
1532 added to modprobe.conf (or modprobe.conf.local, as appropriate), as
1533 follows (all on one line; it has been split here for clarity):
1535 install bonding /sbin/modprobe tg3; /sbin/modprobe e1000;
1536 /sbin/modprobe --ignore-install bonding
1538 This will, when loading the bonding module, rather than
1539 performing the normal action, instead execute the provided command.
1540 This command loads the device drivers in the order needed, then calls
1541 modprobe with --ignore-install to cause the normal action to then take
1542 place. Full documentation on this can be found in the modprobe.conf
1543 and modprobe manual pages.
1545 8.3. Painfully Slow Or No Failed Link Detection By Miimon
1546 ---------------------------------------------------------
1548 By default, bonding enables the use_carrier option, which
1549 instructs bonding to trust the driver to maintain carrier state.
1551 As discussed in the options section, above, some drivers do
1552 not support the netif_carrier_on/_off link state tracking system.
1553 With use_carrier enabled, bonding will always see these links as up,
1554 regardless of their actual state.
1556 Additionally, other drivers do support netif_carrier, but do
1557 not maintain it in real time, e.g., only polling the link state at
1558 some fixed interval. In this case, miimon will detect failures, but
1559 only after some long period of time has expired. If it appears that
1560 miimon is very slow in detecting link failures, try specifying
1561 use_carrier=0 to see if that improves the failure detection time. If
1562 it does, then it may be that the driver checks the carrier state at a
1563 fixed interval, but does not cache the MII register values (so the
1564 use_carrier=0 method of querying the registers directly works). If
1565 use_carrier=0 does not improve the failover, then the driver may cache
1566 the registers, or the problem may be elsewhere.
1568 Also, remember that miimon only checks for the device's
1569 carrier state. It has no way to determine the state of devices on or
1570 beyond other ports of a switch, or if a switch is refusing to pass
1571 traffic while still maintaining carrier on.
1576 If running SNMP agents, the bonding driver should be loaded
1577 before any network drivers participating in a bond. This requirement
1578 is due to the interface index (ipAdEntIfIndex) being associated to
1579 the first interface found with a given IP address. That is, there is
1580 only one ipAdEntIfIndex for each IP address. For example, if eth0 and
1581 eth1 are slaves of bond0 and the driver for eth0 is loaded before the
1582 bonding driver, the interface for the IP address will be associated
1583 with the eth0 interface. This configuration is shown below, the IP
1584 address 192.168.1.1 has an interface index of 2 which indexes to eth0
1585 in the ifDescr table (ifDescr.2).
1587 interfaces.ifTable.ifEntry.ifDescr.1 = lo
1588 interfaces.ifTable.ifEntry.ifDescr.2 = eth0
1589 interfaces.ifTable.ifEntry.ifDescr.3 = eth1
1590 interfaces.ifTable.ifEntry.ifDescr.4 = eth2
1591 interfaces.ifTable.ifEntry.ifDescr.5 = eth3
1592 interfaces.ifTable.ifEntry.ifDescr.6 = bond0
1593 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 5
1594 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
1595 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 4
1596 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
1598 This problem is avoided by loading the bonding driver before
1599 any network drivers participating in a bond. Below is an example of
1600 loading the bonding driver first, the IP address 192.168.1.1 is
1601 correctly associated with ifDescr.2.
1603 interfaces.ifTable.ifEntry.ifDescr.1 = lo
1604 interfaces.ifTable.ifEntry.ifDescr.2 = bond0
1605 interfaces.ifTable.ifEntry.ifDescr.3 = eth0
1606 interfaces.ifTable.ifEntry.ifDescr.4 = eth1
1607 interfaces.ifTable.ifEntry.ifDescr.5 = eth2
1608 interfaces.ifTable.ifEntry.ifDescr.6 = eth3
1609 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 6
1610 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
1611 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 5
1612 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
1614 While some distributions may not report the interface name in
1615 ifDescr, the association between the IP address and IfIndex remains
1616 and SNMP functions such as Interface_Scan_Next will report that
1619 10. Promiscuous mode
1620 ====================
1622 When running network monitoring tools, e.g., tcpdump, it is
1623 common to enable promiscuous mode on the device, so that all traffic
1624 is seen (instead of seeing only traffic destined for the local host).
1625 The bonding driver handles promiscuous mode changes to the bonding
1626 master device (e.g., bond0), and propagates the setting to the slave
1629 For the balance-rr, balance-xor, broadcast, and 802.3ad modes,
1630 the promiscuous mode setting is propagated to all slaves.
1632 For the active-backup, balance-tlb and balance-alb modes, the
1633 promiscuous mode setting is propagated only to the active slave.
1635 For balance-tlb mode, the active slave is the slave currently
1636 receiving inbound traffic.
1638 For balance-alb mode, the active slave is the slave used as a
1639 "primary." This slave is used for mode-specific control traffic, for
1640 sending to peers that are unassigned or if the load is unbalanced.
1642 For the active-backup, balance-tlb and balance-alb modes, when
1643 the active slave changes (e.g., due to a link failure), the
1644 promiscuous setting will be propagated to the new active slave.
1646 11. Configuring Bonding for High Availability
1647 =============================================
1649 High Availability refers to configurations that provide
1650 maximum network availability by having redundant or backup devices,
1651 links or switches between the host and the rest of the world. The
1652 goal is to provide the maximum availability of network connectivity
1653 (i.e., the network always works), even though other configurations
1654 could provide higher throughput.
1656 11.1 High Availability in a Single Switch Topology
1657 --------------------------------------------------
1659 If two hosts (or a host and a single switch) are directly
1660 connected via multiple physical links, then there is no availability
1661 penalty to optimizing for maximum bandwidth. In this case, there is
1662 only one switch (or peer), so if it fails, there is no alternative
1663 access to fail over to. Additionally, the bonding load balance modes
1664 support link monitoring of their members, so if individual links fail,
1665 the load will be rebalanced across the remaining devices.
1667 See Section 13, "Configuring Bonding for Maximum Throughput"
1668 for information on configuring bonding with one peer device.
1670 11.2 High Availability in a Multiple Switch Topology
1671 ----------------------------------------------------
1673 With multiple switches, the configuration of bonding and the
1674 network changes dramatically. In multiple switch topologies, there is
1675 a trade off between network availability and usable bandwidth.
1677 Below is a sample network, configured to maximize the
1678 availability of the network:
1682 +-----+----+ +-----+----+
1683 | |port2 ISL port2| |
1684 | switch A +--------------------------+ switch B |
1686 +-----+----+ +-----++---+
1689 +-------------+ host1 +---------------+
1692 In this configuration, there is a link between the two
1693 switches (ISL, or inter switch link), and multiple ports connecting to
1694 the outside world ("port3" on each switch). There is no technical
1695 reason that this could not be extended to a third switch.
1697 11.2.1 HA Bonding Mode Selection for Multiple Switch Topology
1698 -------------------------------------------------------------
1700 In a topology such as the example above, the active-backup and
1701 broadcast modes are the only useful bonding modes when optimizing for
1702 availability; the other modes require all links to terminate on the
1703 same peer for them to behave rationally.
1705 active-backup: This is generally the preferred mode, particularly if
1706 the switches have an ISL and play together well. If the
1707 network configuration is such that one switch is specifically
1708 a backup switch (e.g., has lower capacity, higher cost, etc),
1709 then the primary option can be used to insure that the
1710 preferred link is always used when it is available.
1712 broadcast: This mode is really a special purpose mode, and is suitable
1713 only for very specific needs. For example, if the two
1714 switches are not connected (no ISL), and the networks beyond
1715 them are totally independent. In this case, if it is
1716 necessary for some specific one-way traffic to reach both
1717 independent networks, then the broadcast mode may be suitable.
1719 11.2.2 HA Link Monitoring Selection for Multiple Switch Topology
1720 ----------------------------------------------------------------
1722 The choice of link monitoring ultimately depends upon your
1723 switch. If the switch can reliably fail ports in response to other
1724 failures, then either the MII or ARP monitors should work. For
1725 example, in the above example, if the "port3" link fails at the remote
1726 end, the MII monitor has no direct means to detect this. The ARP
1727 monitor could be configured with a target at the remote end of port3,
1728 thus detecting that failure without switch support.
1730 In general, however, in a multiple switch topology, the ARP
1731 monitor can provide a higher level of reliability in detecting end to
1732 end connectivity failures (which may be caused by the failure of any
1733 individual component to pass traffic for any reason). Additionally,
1734 the ARP monitor should be configured with multiple targets (at least
1735 one for each switch in the network). This will insure that,
1736 regardless of which switch is active, the ARP monitor has a suitable
1739 Note, also, that of late many switches now support a functionality
1740 generally referred to as "trunk failover." This is a feature of the
1741 switch that causes the link state of a particular switch port to be set
1742 down (or up) when the state of another switch port goes down (or up).
1743 It's purpose is to propogate link failures from logically "exterior" ports
1744 to the logically "interior" ports that bonding is able to monitor via
1745 miimon. Availability and configuration for trunk failover varies by
1746 switch, but this can be a viable alternative to the ARP monitor when using
1749 12. Configuring Bonding for Maximum Throughput
1750 ==============================================
1752 12.1 Maximizing Throughput in a Single Switch Topology
1753 ------------------------------------------------------
1755 In a single switch configuration, the best method to maximize
1756 throughput depends upon the application and network environment. The
1757 various load balancing modes each have strengths and weaknesses in
1758 different environments, as detailed below.
1760 For this discussion, we will break down the topologies into
1761 two categories. Depending upon the destination of most traffic, we
1762 categorize them into either "gatewayed" or "local" configurations.
1764 In a gatewayed configuration, the "switch" is acting primarily
1765 as a router, and the majority of traffic passes through this router to
1766 other networks. An example would be the following:
1769 +----------+ +----------+
1770 | |eth0 port1| | to other networks
1771 | Host A +---------------------+ router +------------------->
1772 | +---------------------+ | Hosts B and C are out
1773 | |eth1 port2| | here somewhere
1774 +----------+ +----------+
1776 The router may be a dedicated router device, or another host
1777 acting as a gateway. For our discussion, the important point is that
1778 the majority of traffic from Host A will pass through the router to
1779 some other network before reaching its final destination.
1781 In a gatewayed network configuration, although Host A may
1782 communicate with many other systems, all of its traffic will be sent
1783 and received via one other peer on the local network, the router.
1785 Note that the case of two systems connected directly via
1786 multiple physical links is, for purposes of configuring bonding, the
1787 same as a gatewayed configuration. In that case, it happens that all
1788 traffic is destined for the "gateway" itself, not some other network
1791 In a local configuration, the "switch" is acting primarily as
1792 a switch, and the majority of traffic passes through this switch to
1793 reach other stations on the same network. An example would be the
1796 +----------+ +----------+ +--------+
1797 | |eth0 port1| +-------+ Host B |
1798 | Host A +------------+ switch |port3 +--------+
1799 | +------------+ | +--------+
1800 | |eth1 port2| +------------------+ Host C |
1801 +----------+ +----------+port4 +--------+
1804 Again, the switch may be a dedicated switch device, or another
1805 host acting as a gateway. For our discussion, the important point is
1806 that the majority of traffic from Host A is destined for other hosts
1807 on the same local network (Hosts B and C in the above example).
1809 In summary, in a gatewayed configuration, traffic to and from
1810 the bonded device will be to the same MAC level peer on the network
1811 (the gateway itself, i.e., the router), regardless of its final
1812 destination. In a local configuration, traffic flows directly to and
1813 from the final destinations, thus, each destination (Host B, Host C)
1814 will be addressed directly by their individual MAC addresses.
1816 This distinction between a gatewayed and a local network
1817 configuration is important because many of the load balancing modes
1818 available use the MAC addresses of the local network source and
1819 destination to make load balancing decisions. The behavior of each
1820 mode is described below.
1823 12.1.1 MT Bonding Mode Selection for Single Switch Topology
1824 -----------------------------------------------------------
1826 This configuration is the easiest to set up and to understand,
1827 although you will have to decide which bonding mode best suits your
1828 needs. The trade offs for each mode are detailed below:
1830 balance-rr: This mode is the only mode that will permit a single
1831 TCP/IP connection to stripe traffic across multiple
1832 interfaces. It is therefore the only mode that will allow a
1833 single TCP/IP stream to utilize more than one interface's
1834 worth of throughput. This comes at a cost, however: the
1835 striping generally results in peer systems receiving packets out
1836 of order, causing TCP/IP's congestion control system to kick
1837 in, often by retransmitting segments.
1839 It is possible to adjust TCP/IP's congestion limits by
1840 altering the net.ipv4.tcp_reordering sysctl parameter. The
1841 usual default value is 3, and the maximum useful value is 127.
1842 For a four interface balance-rr bond, expect that a single
1843 TCP/IP stream will utilize no more than approximately 2.3
1844 interface's worth of throughput, even after adjusting
1847 Note that the fraction of packets that will be delivered out of
1848 order is highly variable, and is unlikely to be zero. The level
1849 of reordering depends upon a variety of factors, including the
1850 networking interfaces, the switch, and the topology of the
1851 configuration. Speaking in general terms, higher speed network
1852 cards produce more reordering (due to factors such as packet
1853 coalescing), and a "many to many" topology will reorder at a
1854 higher rate than a "many slow to one fast" configuration.
1856 Many switches do not support any modes that stripe traffic
1857 (instead choosing a port based upon IP or MAC level addresses);
1858 for those devices, traffic for a particular connection flowing
1859 through the switch to a balance-rr bond will not utilize greater
1860 than one interface's worth of bandwidth.
1862 If you are utilizing protocols other than TCP/IP, UDP for
1863 example, and your application can tolerate out of order
1864 delivery, then this mode can allow for single stream datagram
1865 performance that scales near linearly as interfaces are added
1868 This mode requires the switch to have the appropriate ports
1869 configured for "etherchannel" or "trunking."
1871 active-backup: There is not much advantage in this network topology to
1872 the active-backup mode, as the inactive backup devices are all
1873 connected to the same peer as the primary. In this case, a
1874 load balancing mode (with link monitoring) will provide the
1875 same level of network availability, but with increased
1876 available bandwidth. On the plus side, active-backup mode
1877 does not require any configuration of the switch, so it may
1878 have value if the hardware available does not support any of
1879 the load balance modes.
1881 balance-xor: This mode will limit traffic such that packets destined
1882 for specific peers will always be sent over the same
1883 interface. Since the destination is determined by the MAC
1884 addresses involved, this mode works best in a "local" network
1885 configuration (as described above), with destinations all on
1886 the same local network. This mode is likely to be suboptimal
1887 if all your traffic is passed through a single router (i.e., a
1888 "gatewayed" network configuration, as described above).
1890 As with balance-rr, the switch ports need to be configured for
1891 "etherchannel" or "trunking."
1893 broadcast: Like active-backup, there is not much advantage to this
1894 mode in this type of network topology.
1896 802.3ad: This mode can be a good choice for this type of network
1897 topology. The 802.3ad mode is an IEEE standard, so all peers
1898 that implement 802.3ad should interoperate well. The 802.3ad
1899 protocol includes automatic configuration of the aggregates,
1900 so minimal manual configuration of the switch is needed
1901 (typically only to designate that some set of devices is
1902 available for 802.3ad). The 802.3ad standard also mandates
1903 that frames be delivered in order (within certain limits), so
1904 in general single connections will not see misordering of
1905 packets. The 802.3ad mode does have some drawbacks: the
1906 standard mandates that all devices in the aggregate operate at
1907 the same speed and duplex. Also, as with all bonding load
1908 balance modes other than balance-rr, no single connection will
1909 be able to utilize more than a single interface's worth of
1912 Additionally, the linux bonding 802.3ad implementation
1913 distributes traffic by peer (using an XOR of MAC addresses),
1914 so in a "gatewayed" configuration, all outgoing traffic will
1915 generally use the same device. Incoming traffic may also end
1916 up on a single device, but that is dependent upon the
1917 balancing policy of the peer's 8023.ad implementation. In a
1918 "local" configuration, traffic will be distributed across the
1919 devices in the bond.
1921 Finally, the 802.3ad mode mandates the use of the MII monitor,
1922 therefore, the ARP monitor is not available in this mode.
1924 balance-tlb: The balance-tlb mode balances outgoing traffic by peer.
1925 Since the balancing is done according to MAC address, in a
1926 "gatewayed" configuration (as described above), this mode will
1927 send all traffic across a single device. However, in a
1928 "local" network configuration, this mode balances multiple
1929 local network peers across devices in a vaguely intelligent
1930 manner (not a simple XOR as in balance-xor or 802.3ad mode),
1931 so that mathematically unlucky MAC addresses (i.e., ones that
1932 XOR to the same value) will not all "bunch up" on a single
1935 Unlike 802.3ad, interfaces may be of differing speeds, and no
1936 special switch configuration is required. On the down side,
1937 in this mode all incoming traffic arrives over a single
1938 interface, this mode requires certain ethtool support in the
1939 network device driver of the slave interfaces, and the ARP
1940 monitor is not available.
1942 balance-alb: This mode is everything that balance-tlb is, and more.
1943 It has all of the features (and restrictions) of balance-tlb,
1944 and will also balance incoming traffic from local network
1945 peers (as described in the Bonding Module Options section,
1948 The only additional down side to this mode is that the network
1949 device driver must support changing the hardware address while
1952 12.1.2 MT Link Monitoring for Single Switch Topology
1953 ----------------------------------------------------
1955 The choice of link monitoring may largely depend upon which
1956 mode you choose to use. The more advanced load balancing modes do not
1957 support the use of the ARP monitor, and are thus restricted to using
1958 the MII monitor (which does not provide as high a level of end to end
1959 assurance as the ARP monitor).
1961 12.2 Maximum Throughput in a Multiple Switch Topology
1962 -----------------------------------------------------
1964 Multiple switches may be utilized to optimize for throughput
1965 when they are configured in parallel as part of an isolated network
1966 between two or more systems, for example:
1972 +--------+ | +---------+
1974 +------+---+ +-----+----+ +-----+----+
1975 | Switch A | | Switch B | | Switch C |
1976 +------+---+ +-----+----+ +-----+----+
1978 +--------+ | +---------+
1984 In this configuration, the switches are isolated from one
1985 another. One reason to employ a topology such as this is for an
1986 isolated network with many hosts (a cluster configured for high
1987 performance, for example), using multiple smaller switches can be more
1988 cost effective than a single larger switch, e.g., on a network with 24
1989 hosts, three 24 port switches can be significantly less expensive than
1990 a single 72 port switch.
1992 If access beyond the network is required, an individual host
1993 can be equipped with an additional network device connected to an
1994 external network; this host then additionally acts as a gateway.
1996 12.2.1 MT Bonding Mode Selection for Multiple Switch Topology
1997 -------------------------------------------------------------
1999 In actual practice, the bonding mode typically employed in
2000 configurations of this type is balance-rr. Historically, in this
2001 network configuration, the usual caveats about out of order packet
2002 delivery are mitigated by the use of network adapters that do not do
2003 any kind of packet coalescing (via the use of NAPI, or because the
2004 device itself does not generate interrupts until some number of
2005 packets has arrived). When employed in this fashion, the balance-rr
2006 mode allows individual connections between two hosts to effectively
2007 utilize greater than one interface's bandwidth.
2009 12.2.2 MT Link Monitoring for Multiple Switch Topology
2010 ------------------------------------------------------
2012 Again, in actual practice, the MII monitor is most often used
2013 in this configuration, as performance is given preference over
2014 availability. The ARP monitor will function in this topology, but its
2015 advantages over the MII monitor are mitigated by the volume of probes
2016 needed as the number of systems involved grows (remember that each
2017 host in the network is configured with bonding).
2019 13. Switch Behavior Issues
2020 ==========================
2022 13.1 Link Establishment and Failover Delays
2023 -------------------------------------------
2025 Some switches exhibit undesirable behavior with regard to the
2026 timing of link up and down reporting by the switch.
2028 First, when a link comes up, some switches may indicate that
2029 the link is up (carrier available), but not pass traffic over the
2030 interface for some period of time. This delay is typically due to
2031 some type of autonegotiation or routing protocol, but may also occur
2032 during switch initialization (e.g., during recovery after a switch
2033 failure). If you find this to be a problem, specify an appropriate
2034 value to the updelay bonding module option to delay the use of the
2035 relevant interface(s).
2037 Second, some switches may "bounce" the link state one or more
2038 times while a link is changing state. This occurs most commonly while
2039 the switch is initializing. Again, an appropriate updelay value may
2042 Note that when a bonding interface has no active links, the
2043 driver will immediately reuse the first link that goes up, even if the
2044 updelay parameter has been specified (the updelay is ignored in this
2045 case). If there are slave interfaces waiting for the updelay timeout
2046 to expire, the interface that first went into that state will be
2047 immediately reused. This reduces down time of the network if the
2048 value of updelay has been overestimated, and since this occurs only in
2049 cases with no connectivity, there is no additional penalty for
2050 ignoring the updelay.
2052 In addition to the concerns about switch timings, if your
2053 switches take a long time to go into backup mode, it may be desirable
2054 to not activate a backup interface immediately after a link goes down.
2055 Failover may be delayed via the downdelay bonding module option.
2057 13.2 Duplicated Incoming Packets
2058 --------------------------------
2060 NOTE: Starting with version 3.0.2, the bonding driver has logic to
2061 suppress duplicate packets, which should largely eliminate this problem.
2062 The following description is kept for reference.
2064 It is not uncommon to observe a short burst of duplicated
2065 traffic when the bonding device is first used, or after it has been
2066 idle for some period of time. This is most easily observed by issuing
2067 a "ping" to some other host on the network, and noticing that the
2068 output from ping flags duplicates (typically one per slave).
2070 For example, on a bond in active-backup mode with five slaves
2071 all connected to one switch, the output may appear as follows:
2074 PING 10.0.4.2 (10.0.4.2) from 10.0.3.10 : 56(84) bytes of data.
2075 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.7 ms
2076 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2077 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2078 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2079 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2080 64 bytes from 10.0.4.2: icmp_seq=2 ttl=64 time=0.216 ms
2081 64 bytes from 10.0.4.2: icmp_seq=3 ttl=64 time=0.267 ms
2082 64 bytes from 10.0.4.2: icmp_seq=4 ttl=64 time=0.222 ms
2084 This is not due to an error in the bonding driver, rather, it
2085 is a side effect of how many switches update their MAC forwarding
2086 tables. Initially, the switch does not associate the MAC address in
2087 the packet with a particular switch port, and so it may send the
2088 traffic to all ports until its MAC forwarding table is updated. Since
2089 the interfaces attached to the bond may occupy multiple ports on a
2090 single switch, when the switch (temporarily) floods the traffic to all
2091 ports, the bond device receives multiple copies of the same packet
2092 (one per slave device).
2094 The duplicated packet behavior is switch dependent, some
2095 switches exhibit this, and some do not. On switches that display this
2096 behavior, it can be induced by clearing the MAC forwarding table (on
2097 most Cisco switches, the privileged command "clear mac address-table
2098 dynamic" will accomplish this).
2100 14. Hardware Specific Considerations
2101 ====================================
2103 This section contains additional information for configuring
2104 bonding on specific hardware platforms, or for interfacing bonding
2105 with particular switches or other devices.
2107 14.1 IBM BladeCenter
2108 --------------------
2110 This applies to the JS20 and similar systems.
2112 On the JS20 blades, the bonding driver supports only
2113 balance-rr, active-backup, balance-tlb and balance-alb modes. This is
2114 largely due to the network topology inside the BladeCenter, detailed
2117 JS20 network adapter information
2118 --------------------------------
2120 All JS20s come with two Broadcom Gigabit Ethernet ports
2121 integrated on the planar (that's "motherboard" in IBM-speak). In the
2122 BladeCenter chassis, the eth0 port of all JS20 blades is hard wired to
2123 I/O Module #1; similarly, all eth1 ports are wired to I/O Module #2.
2124 An add-on Broadcom daughter card can be installed on a JS20 to provide
2125 two more Gigabit Ethernet ports. These ports, eth2 and eth3, are
2126 wired to I/O Modules 3 and 4, respectively.
2128 Each I/O Module may contain either a switch or a passthrough
2129 module (which allows ports to be directly connected to an external
2130 switch). Some bonding modes require a specific BladeCenter internal
2131 network topology in order to function; these are detailed below.
2133 Additional BladeCenter-specific networking information can be
2134 found in two IBM Redbooks (www.ibm.com/redbooks):
2136 "IBM eServer BladeCenter Networking Options"
2137 "IBM eServer BladeCenter Layer 2-7 Network Switching"
2139 BladeCenter networking configuration
2140 ------------------------------------
2142 Because a BladeCenter can be configured in a very large number
2143 of ways, this discussion will be confined to describing basic
2146 Normally, Ethernet Switch Modules (ESMs) are used in I/O
2147 modules 1 and 2. In this configuration, the eth0 and eth1 ports of a
2148 JS20 will be connected to different internal switches (in the
2149 respective I/O modules).
2151 A passthrough module (OPM or CPM, optical or copper,
2152 passthrough module) connects the I/O module directly to an external
2153 switch. By using PMs in I/O module #1 and #2, the eth0 and eth1
2154 interfaces of a JS20 can be redirected to the outside world and
2155 connected to a common external switch.
2157 Depending upon the mix of ESMs and PMs, the network will
2158 appear to bonding as either a single switch topology (all PMs) or as a
2159 multiple switch topology (one or more ESMs, zero or more PMs). It is
2160 also possible to connect ESMs together, resulting in a configuration
2161 much like the example in "High Availability in a Multiple Switch
2164 Requirements for specific modes
2165 -------------------------------
2167 The balance-rr mode requires the use of passthrough modules
2168 for devices in the bond, all connected to an common external switch.
2169 That switch must be configured for "etherchannel" or "trunking" on the
2170 appropriate ports, as is usual for balance-rr.
2172 The balance-alb and balance-tlb modes will function with
2173 either switch modules or passthrough modules (or a mix). The only
2174 specific requirement for these modes is that all network interfaces
2175 must be able to reach all destinations for traffic sent over the
2176 bonding device (i.e., the network must converge at some point outside
2179 The active-backup mode has no additional requirements.
2181 Link monitoring issues
2182 ----------------------
2184 When an Ethernet Switch Module is in place, only the ARP
2185 monitor will reliably detect link loss to an external switch. This is
2186 nothing unusual, but examination of the BladeCenter cabinet would
2187 suggest that the "external" network ports are the ethernet ports for
2188 the system, when it fact there is a switch between these "external"
2189 ports and the devices on the JS20 system itself. The MII monitor is
2190 only able to detect link failures between the ESM and the JS20 system.
2192 When a passthrough module is in place, the MII monitor does
2193 detect failures to the "external" port, which is then directly
2194 connected to the JS20 system.
2199 The Serial Over LAN (SoL) link is established over the primary
2200 ethernet (eth0) only, therefore, any loss of link to eth0 will result
2201 in losing your SoL connection. It will not fail over with other
2202 network traffic, as the SoL system is beyond the control of the
2205 It may be desirable to disable spanning tree on the switch
2206 (either the internal Ethernet Switch Module, or an external switch) to
2207 avoid fail-over delay issues when using bonding.
2210 15. Frequently Asked Questions
2211 ==============================
2215 Yes. The old 2.0.xx channel bonding patch was not SMP safe.
2216 The new driver was designed to be SMP safe from the start.
2218 2. What type of cards will work with it?
2220 Any Ethernet type cards (you can even mix cards - a Intel
2221 EtherExpress PRO/100 and a 3com 3c905b, for example). For most modes,
2222 devices need not be of the same speed.
2224 Starting with version 3.2.1, bonding also supports Infiniband
2225 slaves in active-backup mode.
2227 3. How many bonding devices can I have?
2231 4. How many slaves can a bonding device have?
2233 This is limited only by the number of network interfaces Linux
2234 supports and/or the number of network cards you can place in your
2237 5. What happens when a slave link dies?
2239 If link monitoring is enabled, then the failing device will be
2240 disabled. The active-backup mode will fail over to a backup link, and
2241 other modes will ignore the failed link. The link will continue to be
2242 monitored, and should it recover, it will rejoin the bond (in whatever
2243 manner is appropriate for the mode). See the sections on High
2244 Availability and the documentation for each mode for additional
2247 Link monitoring can be enabled via either the miimon or
2248 arp_interval parameters (described in the module parameters section,
2249 above). In general, miimon monitors the carrier state as sensed by
2250 the underlying network device, and the arp monitor (arp_interval)
2251 monitors connectivity to another host on the local network.
2253 If no link monitoring is configured, the bonding driver will
2254 be unable to detect link failures, and will assume that all links are
2255 always available. This will likely result in lost packets, and a
2256 resulting degradation of performance. The precise performance loss
2257 depends upon the bonding mode and network configuration.
2259 6. Can bonding be used for High Availability?
2261 Yes. See the section on High Availability for details.
2263 7. Which switches/systems does it work with?
2265 The full answer to this depends upon the desired mode.
2267 In the basic balance modes (balance-rr and balance-xor), it
2268 works with any system that supports etherchannel (also called
2269 trunking). Most managed switches currently available have such
2270 support, and many unmanaged switches as well.
2272 The advanced balance modes (balance-tlb and balance-alb) do
2273 not have special switch requirements, but do need device drivers that
2274 support specific features (described in the appropriate section under
2275 module parameters, above).
2277 In 802.3ad mode, it works with systems that support IEEE
2278 802.3ad Dynamic Link Aggregation. Most managed and many unmanaged
2279 switches currently available support 802.3ad.
2281 The active-backup mode should work with any Layer-II switch.
2283 8. Where does a bonding device get its MAC address from?
2285 When using slave devices that have fixed MAC addresses, or when
2286 the fail_over_mac option is enabled, the bonding device's MAC address is
2287 the MAC address of the active slave.
2289 For other configurations, if not explicitly configured (with
2290 ifconfig or ip link), the MAC address of the bonding device is taken from
2291 its first slave device. This MAC address is then passed to all following
2292 slaves and remains persistent (even if the first slave is removed) until
2293 the bonding device is brought down or reconfigured.
2295 If you wish to change the MAC address, you can set it with
2296 ifconfig or ip link:
2298 # ifconfig bond0 hw ether 00:11:22:33:44:55
2300 # ip link set bond0 address 66:77:88:99:aa:bb
2302 The MAC address can be also changed by bringing down/up the
2303 device and then changing its slaves (or their order):
2305 # ifconfig bond0 down ; modprobe -r bonding
2306 # ifconfig bond0 .... up
2307 # ifenslave bond0 eth...
2309 This method will automatically take the address from the next
2310 slave that is added.
2312 To restore your slaves' MAC addresses, you need to detach them
2313 from the bond (`ifenslave -d bond0 eth0'). The bonding driver will
2314 then restore the MAC addresses that the slaves had before they were
2317 16. Resources and Links
2318 =======================
2320 The latest version of the bonding driver can be found in the latest
2321 version of the linux kernel, found on http://kernel.org
2323 The latest version of this document can be found in either the latest
2324 kernel source (named Documentation/networking/bonding.txt), or on the
2325 bonding sourceforge site:
2327 http://www.sourceforge.net/projects/bonding
2329 Discussions regarding the bonding driver take place primarily on the
2330 bonding-devel mailing list, hosted at sourceforge.net. If you have
2331 questions or problems, post them to the list. The list address is:
2333 bonding-devel@lists.sourceforge.net
2335 The administrative interface (to subscribe or unsubscribe) can
2338 https://lists.sourceforge.net/lists/listinfo/bonding-devel
2340 Donald Becker's Ethernet Drivers and diag programs may be found at :
2341 - http://www.scyld.com/network/
2343 You will also find a lot of information regarding Ethernet, NWay, MII,
2344 etc. at www.scyld.com.
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