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 (the traditional behavior), or, when
293 enabled, change the bond's MAC address when changing the
294 active interface (i.e., fail over the MAC address itself).
296 Fail over MAC is useful for devices that cannot ever alter
297 their MAC address, or for devices that refuse incoming
298 broadcasts with their own source MAC (which interferes with
301 The down side of fail over MAC is that every device on the
302 network must be updated via gratuitous ARP, vs. just updating
303 a switch or set of switches (which often takes place for any
304 traffic, not just ARP traffic, if the switch snoops incoming
305 traffic to update its tables) for the traditional method. If
306 the gratuitous ARP is lost, communication may be disrupted.
308 When fail over MAC is used in conjuction with the mii monitor,
309 devices which assert link up prior to being able to actually
310 transmit and receive are particularly susecptible to loss of
311 the gratuitous ARP, and an appropriate updelay setting may be
314 A value of 0 disables fail over MAC, and is the default. A
315 value of 1 enables fail over MAC. This option is enabled
316 automatically if the first slave added cannot change its MAC
317 address. This option may be modified via sysfs only when no
318 slaves are present in the bond.
320 This option was added in bonding version 3.2.0.
324 Option specifying the rate in which we'll ask our link partner
325 to transmit LACPDU packets in 802.3ad mode. Possible values
329 Request partner to transmit LACPDUs every 30 seconds
332 Request partner to transmit LACPDUs every 1 second
338 Specifies the number of bonding devices to create for this
339 instance of the bonding driver. E.g., if max_bonds is 3, and
340 the bonding driver is not already loaded, then bond0, bond1
341 and bond2 will be created. The default value is 1.
345 Specifies the MII link monitoring frequency in milliseconds.
346 This determines how often the link state of each slave is
347 inspected for link failures. A value of zero disables MII
348 link monitoring. A value of 100 is a good starting point.
349 The use_carrier option, below, affects how the link state is
350 determined. See the High Availability section for additional
351 information. The default value is 0.
355 Specifies one of the bonding policies. The default is
356 balance-rr (round robin). Possible values are:
360 Round-robin policy: Transmit packets in sequential
361 order from the first available slave through the
362 last. This mode provides load balancing and fault
367 Active-backup policy: Only one slave in the bond is
368 active. A different slave becomes active if, and only
369 if, the active slave fails. The bond's MAC address is
370 externally visible on only one port (network adapter)
371 to avoid confusing the switch.
373 In bonding version 2.6.2 or later, when a failover
374 occurs in active-backup mode, bonding will issue one
375 or more gratuitous ARPs on the newly active slave.
376 One gratuitous ARP is issued for the bonding master
377 interface and each VLAN interfaces configured above
378 it, provided that the interface has at least one IP
379 address configured. Gratuitous ARPs issued for VLAN
380 interfaces are tagged with the appropriate VLAN id.
382 This mode provides fault tolerance. The primary
383 option, documented below, affects the behavior of this
388 XOR policy: Transmit based on the selected transmit
389 hash policy. The default policy is a simple [(source
390 MAC address XOR'd with destination MAC address) modulo
391 slave count]. Alternate transmit policies may be
392 selected via the xmit_hash_policy option, described
395 This mode provides load balancing and fault tolerance.
399 Broadcast policy: transmits everything on all slave
400 interfaces. This mode provides fault tolerance.
404 IEEE 802.3ad Dynamic link aggregation. Creates
405 aggregation groups that share the same speed and
406 duplex settings. Utilizes all slaves in the active
407 aggregator according to the 802.3ad specification.
409 Slave selection for outgoing traffic is done according
410 to the transmit hash policy, which may be changed from
411 the default simple XOR policy via the xmit_hash_policy
412 option, documented below. Note that not all transmit
413 policies may be 802.3ad compliant, particularly in
414 regards to the packet mis-ordering requirements of
415 section 43.2.4 of the 802.3ad standard. Differing
416 peer implementations will have varying tolerances for
421 1. Ethtool support in the base drivers for retrieving
422 the speed and duplex of each slave.
424 2. A switch that supports IEEE 802.3ad Dynamic link
427 Most switches will require some type of configuration
428 to enable 802.3ad mode.
432 Adaptive transmit load balancing: channel bonding that
433 does not require any special switch support. The
434 outgoing traffic is distributed according to the
435 current load (computed relative to the speed) on each
436 slave. Incoming traffic is received by the current
437 slave. If the receiving slave fails, another slave
438 takes over the MAC address of the failed receiving
443 Ethtool support in the base drivers for retrieving the
448 Adaptive load balancing: includes balance-tlb plus
449 receive load balancing (rlb) for IPV4 traffic, and
450 does not require any special switch support. The
451 receive load balancing is achieved by ARP negotiation.
452 The bonding driver intercepts the ARP Replies sent by
453 the local system on their way out and overwrites the
454 source hardware address with the unique hardware
455 address of one of the slaves in the bond such that
456 different peers use different hardware addresses for
459 Receive traffic from connections created by the server
460 is also balanced. When the local system sends an ARP
461 Request the bonding driver copies and saves the peer's
462 IP information from the ARP packet. When the ARP
463 Reply arrives from the peer, its hardware address is
464 retrieved and the bonding driver initiates an ARP
465 reply to this peer assigning it to one of the slaves
466 in the bond. A problematic outcome of using ARP
467 negotiation for balancing is that each time that an
468 ARP request is broadcast it uses the hardware address
469 of the bond. Hence, peers learn the hardware address
470 of the bond and the balancing of receive traffic
471 collapses to the current slave. This is handled by
472 sending updates (ARP Replies) to all the peers with
473 their individually assigned hardware address such that
474 the traffic is redistributed. Receive traffic is also
475 redistributed when a new slave is added to the bond
476 and when an inactive slave is re-activated. The
477 receive load is distributed sequentially (round robin)
478 among the group of highest speed slaves in the bond.
480 When a link is reconnected or a new slave joins the
481 bond the receive traffic is redistributed among all
482 active slaves in the bond by initiating ARP Replies
483 with the selected MAC address to each of the
484 clients. The updelay parameter (detailed below) must
485 be set to a value equal or greater than the switch's
486 forwarding delay so that the ARP Replies sent to the
487 peers will not be blocked by the switch.
491 1. Ethtool support in the base drivers for retrieving
492 the speed of each slave.
494 2. Base driver support for setting the hardware
495 address of a device while it is open. This is
496 required so that there will always be one slave in the
497 team using the bond hardware address (the
498 curr_active_slave) while having a unique hardware
499 address for each slave in the bond. If the
500 curr_active_slave fails its hardware address is
501 swapped with the new curr_active_slave that was
506 A string (eth0, eth2, etc) specifying which slave is the
507 primary device. The specified device will always be the
508 active slave while it is available. Only when the primary is
509 off-line will alternate devices be used. This is useful when
510 one slave is preferred over another, e.g., when one slave has
511 higher throughput than another.
513 The primary option is only valid for active-backup mode.
517 Specifies the time, in milliseconds, to wait before enabling a
518 slave after a link recovery has been detected. This option is
519 only valid for the miimon link monitor. The updelay value
520 should be a multiple of the miimon value; if not, it will be
521 rounded down to the nearest multiple. The default value is 0.
525 Specifies whether or not miimon should use MII or ETHTOOL
526 ioctls vs. netif_carrier_ok() to determine the link
527 status. The MII or ETHTOOL ioctls are less efficient and
528 utilize a deprecated calling sequence within the kernel. The
529 netif_carrier_ok() relies on the device driver to maintain its
530 state with netif_carrier_on/off; at this writing, most, but
531 not all, device drivers support this facility.
533 If bonding insists that the link is up when it should not be,
534 it may be that your network device driver does not support
535 netif_carrier_on/off. The default state for netif_carrier is
536 "carrier on," so if a driver does not support netif_carrier,
537 it will appear as if the link is always up. In this case,
538 setting use_carrier to 0 will cause bonding to revert to the
539 MII / ETHTOOL ioctl method to determine the link state.
541 A value of 1 enables the use of netif_carrier_ok(), a value of
542 0 will use the deprecated MII / ETHTOOL ioctls. The default
547 Selects the transmit hash policy to use for slave selection in
548 balance-xor and 802.3ad modes. Possible values are:
552 Uses XOR of hardware MAC addresses to generate the
555 (source MAC XOR destination MAC) modulo slave count
557 This algorithm will place all traffic to a particular
558 network peer on the same slave.
560 This algorithm is 802.3ad compliant.
564 This policy uses a combination of layer2 and layer3
565 protocol information to generate the hash.
567 Uses XOR of hardware MAC addresses and IP addresses to
568 generate the hash. The formula is
570 (((source IP XOR dest IP) AND 0xffff) XOR
571 ( source MAC XOR destination MAC ))
574 This algorithm will place all traffic to a particular
575 network peer on the same slave. For non-IP traffic,
576 the formula is the same as for the layer2 transmit
579 This policy is intended to provide a more balanced
580 distribution of traffic than layer2 alone, especially
581 in environments where a layer3 gateway device is
582 required to reach most destinations.
584 This algorithm is 802.3ad complient.
588 This policy uses upper layer protocol information,
589 when available, to generate the hash. This allows for
590 traffic to a particular network peer to span multiple
591 slaves, although a single connection will not span
594 The formula for unfragmented TCP and UDP packets is
596 ((source port XOR dest port) XOR
597 ((source IP XOR dest IP) AND 0xffff)
600 For fragmented TCP or UDP packets and all other IP
601 protocol traffic, the source and destination port
602 information is omitted. For non-IP traffic, the
603 formula is the same as for the layer2 transmit hash
606 This policy is intended to mimic the behavior of
607 certain switches, notably Cisco switches with PFC2 as
608 well as some Foundry and IBM products.
610 This algorithm is not fully 802.3ad compliant. A
611 single TCP or UDP conversation containing both
612 fragmented and unfragmented packets will see packets
613 striped across two interfaces. This may result in out
614 of order delivery. Most traffic types will not meet
615 this criteria, as TCP rarely fragments traffic, and
616 most UDP traffic is not involved in extended
617 conversations. Other implementations of 802.3ad may
618 or may not tolerate this noncompliance.
620 The default value is layer2. This option was added in bonding
621 version 2.6.3. In earlier versions of bonding, this parameter
622 does not exist, and the layer2 policy is the only policy. The
623 layer2+3 value was added for bonding version 3.2.2.
626 3. Configuring Bonding Devices
627 ==============================
629 You can configure bonding using either your distro's network
630 initialization scripts, or manually using either ifenslave or the
631 sysfs interface. Distros generally use one of two packages for the
632 network initialization scripts: initscripts or sysconfig. Recent
633 versions of these packages have support for bonding, while older
636 We will first describe the options for configuring bonding for
637 distros using versions of initscripts and sysconfig with full or
638 partial support for bonding, then provide information on enabling
639 bonding without support from the network initialization scripts (i.e.,
640 older versions of initscripts or sysconfig).
642 If you're unsure whether your distro uses sysconfig or
643 initscripts, or don't know if it's new enough, have no fear.
644 Determining this is fairly straightforward.
646 First, issue the command:
650 It will respond with a line of text starting with either
651 "initscripts" or "sysconfig," followed by some numbers. This is the
652 package that provides your network initialization scripts.
654 Next, to determine if your installation supports bonding,
657 $ grep ifenslave /sbin/ifup
659 If this returns any matches, then your initscripts or
660 sysconfig has support for bonding.
662 3.1 Configuration with Sysconfig Support
663 ----------------------------------------
665 This section applies to distros using a version of sysconfig
666 with bonding support, for example, SuSE Linux Enterprise Server 9.
668 SuSE SLES 9's networking configuration system does support
669 bonding, however, at this writing, the YaST system configuration
670 front end does not provide any means to work with bonding devices.
671 Bonding devices can be managed by hand, however, as follows.
673 First, if they have not already been configured, configure the
674 slave devices. On SLES 9, this is most easily done by running the
675 yast2 sysconfig configuration utility. The goal is for to create an
676 ifcfg-id file for each slave device. The simplest way to accomplish
677 this is to configure the devices for DHCP (this is only to get the
678 file ifcfg-id file created; see below for some issues with DHCP). The
679 name of the configuration file for each device will be of the form:
681 ifcfg-id-xx:xx:xx:xx:xx:xx
683 Where the "xx" portion will be replaced with the digits from
684 the device's permanent MAC address.
686 Once the set of ifcfg-id-xx:xx:xx:xx:xx:xx files has been
687 created, it is necessary to edit the configuration files for the slave
688 devices (the MAC addresses correspond to those of the slave devices).
689 Before editing, the file will contain multiple lines, and will look
695 UNIQUE='XNzu.WeZGOGF+4wE'
696 _nm_name='bus-pci-0001:61:01.0'
698 Change the BOOTPROTO and STARTMODE lines to the following:
703 Do not alter the UNIQUE or _nm_name lines. Remove any other
704 lines (USERCTL, etc).
706 Once the ifcfg-id-xx:xx:xx:xx:xx:xx files have been modified,
707 it's time to create the configuration file for the bonding device
708 itself. This file is named ifcfg-bondX, where X is the number of the
709 bonding device to create, starting at 0. The first such file is
710 ifcfg-bond0, the second is ifcfg-bond1, and so on. The sysconfig
711 network configuration system will correctly start multiple instances
714 The contents of the ifcfg-bondX file is as follows:
717 BROADCAST="10.0.2.255"
719 NETMASK="255.255.0.0"
724 BONDING_MODULE_OPTS="mode=active-backup miimon=100"
725 BONDING_SLAVE0="eth0"
726 BONDING_SLAVE1="bus-pci-0000:06:08.1"
728 Replace the sample BROADCAST, IPADDR, NETMASK and NETWORK
729 values with the appropriate values for your network.
731 The STARTMODE specifies when the device is brought online.
732 The possible values are:
734 onboot: The device is started at boot time. If you're not
735 sure, this is probably what you want.
737 manual: The device is started only when ifup is called
738 manually. Bonding devices may be configured this
739 way if you do not wish them to start automatically
740 at boot for some reason.
742 hotplug: The device is started by a hotplug event. This is not
743 a valid choice for a bonding device.
745 off or ignore: The device configuration is ignored.
747 The line BONDING_MASTER='yes' indicates that the device is a
748 bonding master device. The only useful value is "yes."
750 The contents of BONDING_MODULE_OPTS are supplied to the
751 instance of the bonding module for this device. Specify the options
752 for the bonding mode, link monitoring, and so on here. Do not include
753 the max_bonds bonding parameter; this will confuse the configuration
754 system if you have multiple bonding devices.
756 Finally, supply one BONDING_SLAVEn="slave device" for each
757 slave. where "n" is an increasing value, one for each slave. The
758 "slave device" is either an interface name, e.g., "eth0", or a device
759 specifier for the network device. The interface name is easier to
760 find, but the ethN names are subject to change at boot time if, e.g.,
761 a device early in the sequence has failed. The device specifiers
762 (bus-pci-0000:06:08.1 in the example above) specify the physical
763 network device, and will not change unless the device's bus location
764 changes (for example, it is moved from one PCI slot to another). The
765 example above uses one of each type for demonstration purposes; most
766 configurations will choose one or the other for all slave devices.
768 When all configuration files have been modified or created,
769 networking must be restarted for the configuration changes to take
770 effect. This can be accomplished via the following:
772 # /etc/init.d/network restart
774 Note that the network control script (/sbin/ifdown) will
775 remove the bonding module as part of the network shutdown processing,
776 so it is not necessary to remove the module by hand if, e.g., the
777 module parameters have changed.
779 Also, at this writing, YaST/YaST2 will not manage bonding
780 devices (they do not show bonding interfaces on its list of network
781 devices). It is necessary to edit the configuration file by hand to
782 change the bonding configuration.
784 Additional general options and details of the ifcfg file
785 format can be found in an example ifcfg template file:
787 /etc/sysconfig/network/ifcfg.template
789 Note that the template does not document the various BONDING_
790 settings described above, but does describe many of the other options.
792 3.1.1 Using DHCP with Sysconfig
793 -------------------------------
795 Under sysconfig, configuring a device with BOOTPROTO='dhcp'
796 will cause it to query DHCP for its IP address information. At this
797 writing, this does not function for bonding devices; the scripts
798 attempt to obtain the device address from DHCP prior to adding any of
799 the slave devices. Without active slaves, the DHCP requests are not
802 3.1.2 Configuring Multiple Bonds with Sysconfig
803 -----------------------------------------------
805 The sysconfig network initialization system is capable of
806 handling multiple bonding devices. All that is necessary is for each
807 bonding instance to have an appropriately configured ifcfg-bondX file
808 (as described above). Do not specify the "max_bonds" parameter to any
809 instance of bonding, as this will confuse sysconfig. If you require
810 multiple bonding devices with identical parameters, create multiple
813 Because the sysconfig scripts supply the bonding module
814 options in the ifcfg-bondX file, it is not necessary to add them to
815 the system /etc/modules.conf or /etc/modprobe.conf configuration file.
817 3.2 Configuration with Initscripts Support
818 ------------------------------------------
820 This section applies to distros using a recent version of
821 initscripts with bonding support, for example, Red Hat Enterprise Linux
822 version 3 or later, Fedora, etc. On these systems, the network
823 initialization scripts have knowledge of bonding, and can be configured to
824 control bonding devices. Note that older versions of the initscripts
825 package have lower levels of support for bonding; this will be noted where
828 These distros will not automatically load the network adapter
829 driver unless the ethX device is configured with an IP address.
830 Because of this constraint, users must manually configure a
831 network-script file for all physical adapters that will be members of
832 a bondX link. Network script files are located in the directory:
834 /etc/sysconfig/network-scripts
836 The file name must be prefixed with "ifcfg-eth" and suffixed
837 with the adapter's physical adapter number. For example, the script
838 for eth0 would be named /etc/sysconfig/network-scripts/ifcfg-eth0.
839 Place the following text in the file:
848 The DEVICE= line will be different for every ethX device and
849 must correspond with the name of the file, i.e., ifcfg-eth1 must have
850 a device line of DEVICE=eth1. The setting of the MASTER= line will
851 also depend on the final bonding interface name chosen for your bond.
852 As with other network devices, these typically start at 0, and go up
853 one for each device, i.e., the first bonding instance is bond0, the
854 second is bond1, and so on.
856 Next, create a bond network script. The file name for this
857 script will be /etc/sysconfig/network-scripts/ifcfg-bondX where X is
858 the number of the bond. For bond0 the file is named "ifcfg-bond0",
859 for bond1 it is named "ifcfg-bond1", and so on. Within that file,
860 place the following text:
864 NETMASK=255.255.255.0
866 BROADCAST=192.168.1.255
871 Be sure to change the networking specific lines (IPADDR,
872 NETMASK, NETWORK and BROADCAST) to match your network configuration.
874 For later versions of initscripts, such as that found with Fedora
875 7 and Red Hat Enterprise Linux version 5 (or later), it is possible, and,
876 indeed, preferable, to specify the bonding options in the ifcfg-bond0
877 file, e.g. a line of the format:
879 BONDING_OPTS="mode=active-backup arp_interval=60 arp_ip_target=+192.168.1.254"
881 will configure the bond with the specified options. The options
882 specified in BONDING_OPTS are identical to the bonding module parameters
883 except for the arp_ip_target field. Each target should be included as a
884 separate option and should be preceded by a '+' to indicate it should be
885 added to the list of queried targets, e.g.,
887 arp_ip_target=+192.168.1.1 arp_ip_target=+192.168.1.2
889 is the proper syntax to specify multiple targets. When specifying
890 options via BONDING_OPTS, it is not necessary to edit /etc/modules.conf or
893 For older versions of initscripts that do not support
894 BONDING_OPTS, it is necessary to edit /etc/modules.conf (or
895 /etc/modprobe.conf, depending upon your distro) to load the bonding module
896 with your desired options when the bond0 interface is brought up. The
897 following lines in /etc/modules.conf (or modprobe.conf) will load the
898 bonding module, and select its options:
901 options bond0 mode=balance-alb miimon=100
903 Replace the sample parameters with the appropriate set of
904 options for your configuration.
906 Finally run "/etc/rc.d/init.d/network restart" as root. This
907 will restart the networking subsystem and your bond link should be now
910 3.2.1 Using DHCP with Initscripts
911 ---------------------------------
913 Recent versions of initscripts (the versions supplied with Fedora
914 Core 3 and Red Hat Enterprise Linux 4, or later versions, are reported to
915 work) have support for assigning IP information to bonding devices via
918 To configure bonding for DHCP, configure it as described
919 above, except replace the line "BOOTPROTO=none" with "BOOTPROTO=dhcp"
920 and add a line consisting of "TYPE=Bonding". Note that the TYPE value
923 3.2.2 Configuring Multiple Bonds with Initscripts
924 -------------------------------------------------
926 Initscripts packages that are included with Fedora 7 and Red Hat
927 Enterprise Linux 5 support multiple bonding interfaces by simply
928 specifying the appropriate BONDING_OPTS= in ifcfg-bondX where X is the
929 number of the bond. This support requires sysfs support in the kernel,
930 and a bonding driver of version 3.0.0 or later. Other configurations may
931 not support this method for specifying multiple bonding interfaces; for
932 those instances, see the "Configuring Multiple Bonds Manually" section,
935 3.3 Configuring Bonding Manually with Ifenslave
936 -----------------------------------------------
938 This section applies to distros whose network initialization
939 scripts (the sysconfig or initscripts package) do not have specific
940 knowledge of bonding. One such distro is SuSE Linux Enterprise Server
943 The general method for these systems is to place the bonding
944 module parameters into /etc/modules.conf or /etc/modprobe.conf (as
945 appropriate for the installed distro), then add modprobe and/or
946 ifenslave commands to the system's global init script. The name of
947 the global init script differs; for sysconfig, it is
948 /etc/init.d/boot.local and for initscripts it is /etc/rc.d/rc.local.
950 For example, if you wanted to make a simple bond of two e100
951 devices (presumed to be eth0 and eth1), and have it persist across
952 reboots, edit the appropriate file (/etc/init.d/boot.local or
953 /etc/rc.d/rc.local), and add the following:
955 modprobe bonding mode=balance-alb miimon=100
957 ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
961 Replace the example bonding module parameters and bond0
962 network configuration (IP address, netmask, etc) with the appropriate
963 values for your configuration.
965 Unfortunately, this method will not provide support for the
966 ifup and ifdown scripts on the bond devices. To reload the bonding
967 configuration, it is necessary to run the initialization script, e.g.,
969 # /etc/init.d/boot.local
975 It may be desirable in such a case to create a separate script
976 which only initializes the bonding configuration, then call that
977 separate script from within boot.local. This allows for bonding to be
978 enabled without re-running the entire global init script.
980 To shut down the bonding devices, it is necessary to first
981 mark the bonding device itself as being down, then remove the
982 appropriate device driver modules. For our example above, you can do
985 # ifconfig bond0 down
989 Again, for convenience, it may be desirable to create a script
993 3.3.1 Configuring Multiple Bonds Manually
994 -----------------------------------------
996 This section contains information on configuring multiple
997 bonding devices with differing options for those systems whose network
998 initialization scripts lack support for configuring multiple bonds.
1000 If you require multiple bonding devices, but all with the same
1001 options, you may wish to use the "max_bonds" module parameter,
1004 To create multiple bonding devices with differing options, it is
1005 preferrable to use bonding parameters exported by sysfs, documented in the
1008 For versions of bonding without sysfs support, the only means to
1009 provide multiple instances of bonding with differing options is to load
1010 the bonding driver multiple times. Note that current versions of the
1011 sysconfig network initialization scripts handle this automatically; if
1012 your distro uses these scripts, no special action is needed. See the
1013 section Configuring Bonding Devices, above, if you're not sure about your
1014 network initialization scripts.
1016 To load multiple instances of the module, it is necessary to
1017 specify a different name for each instance (the module loading system
1018 requires that every loaded module, even multiple instances of the same
1019 module, have a unique name). This is accomplished by supplying multiple
1020 sets of bonding options in /etc/modprobe.conf, for example:
1023 options bond0 -o bond0 mode=balance-rr miimon=100
1026 options bond1 -o bond1 mode=balance-alb miimon=50
1028 will load the bonding module two times. The first instance is
1029 named "bond0" and creates the bond0 device in balance-rr mode with an
1030 miimon of 100. The second instance is named "bond1" and creates the
1031 bond1 device in balance-alb mode with an miimon of 50.
1033 In some circumstances (typically with older distributions),
1034 the above does not work, and the second bonding instance never sees
1035 its options. In that case, the second options line can be substituted
1038 install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \
1039 mode=balance-alb miimon=50
1041 This may be repeated any number of times, specifying a new and
1042 unique name in place of bond1 for each subsequent instance.
1044 It has been observed that some Red Hat supplied kernels are unable
1045 to rename modules at load time (the "-o bond1" part). Attempts to pass
1046 that option to modprobe will produce an "Operation not permitted" error.
1047 This has been reported on some Fedora Core kernels, and has been seen on
1048 RHEL 4 as well. On kernels exhibiting this problem, it will be impossible
1049 to configure multiple bonds with differing parameters (as they are older
1050 kernels, and also lack sysfs support).
1052 3.4 Configuring Bonding Manually via Sysfs
1053 ------------------------------------------
1055 Starting with version 3.0.0, Channel Bonding may be configured
1056 via the sysfs interface. This interface allows dynamic configuration
1057 of all bonds in the system without unloading the module. It also
1058 allows for adding and removing bonds at runtime. Ifenslave is no
1059 longer required, though it is still supported.
1061 Use of the sysfs interface allows you to use multiple bonds
1062 with different configurations without having to reload the module.
1063 It also allows you to use multiple, differently configured bonds when
1064 bonding is compiled into the kernel.
1066 You must have the sysfs filesystem mounted to configure
1067 bonding this way. The examples in this document assume that you
1068 are using the standard mount point for sysfs, e.g. /sys. If your
1069 sysfs filesystem is mounted elsewhere, you will need to adjust the
1070 example paths accordingly.
1072 Creating and Destroying Bonds
1073 -----------------------------
1074 To add a new bond foo:
1075 # echo +foo > /sys/class/net/bonding_masters
1077 To remove an existing bond bar:
1078 # echo -bar > /sys/class/net/bonding_masters
1080 To show all existing bonds:
1081 # cat /sys/class/net/bonding_masters
1083 NOTE: due to 4K size limitation of sysfs files, this list may be
1084 truncated if you have more than a few hundred bonds. This is unlikely
1085 to occur under normal operating conditions.
1087 Adding and Removing Slaves
1088 --------------------------
1089 Interfaces may be enslaved to a bond using the file
1090 /sys/class/net/<bond>/bonding/slaves. The semantics for this file
1091 are the same as for the bonding_masters file.
1093 To enslave interface eth0 to bond bond0:
1095 # echo +eth0 > /sys/class/net/bond0/bonding/slaves
1097 To free slave eth0 from bond bond0:
1098 # echo -eth0 > /sys/class/net/bond0/bonding/slaves
1100 When an interface is enslaved to a bond, symlinks between the
1101 two are created in the sysfs filesystem. In this case, you would get
1102 /sys/class/net/bond0/slave_eth0 pointing to /sys/class/net/eth0, and
1103 /sys/class/net/eth0/master pointing to /sys/class/net/bond0.
1105 This means that you can tell quickly whether or not an
1106 interface is enslaved by looking for the master symlink. Thus:
1107 # echo -eth0 > /sys/class/net/eth0/master/bonding/slaves
1108 will free eth0 from whatever bond it is enslaved to, regardless of
1109 the name of the bond interface.
1111 Changing a Bond's Configuration
1112 -------------------------------
1113 Each bond may be configured individually by manipulating the
1114 files located in /sys/class/net/<bond name>/bonding
1116 The names of these files correspond directly with the command-
1117 line parameters described elsewhere in this file, and, with the
1118 exception of arp_ip_target, they accept the same values. To see the
1119 current setting, simply cat the appropriate file.
1121 A few examples will be given here; for specific usage
1122 guidelines for each parameter, see the appropriate section in this
1125 To configure bond0 for balance-alb mode:
1126 # ifconfig bond0 down
1127 # echo 6 > /sys/class/net/bond0/bonding/mode
1129 # echo balance-alb > /sys/class/net/bond0/bonding/mode
1130 NOTE: The bond interface must be down before the mode can be
1133 To enable MII monitoring on bond0 with a 1 second interval:
1134 # echo 1000 > /sys/class/net/bond0/bonding/miimon
1135 NOTE: If ARP monitoring is enabled, it will disabled when MII
1136 monitoring is enabled, and vice-versa.
1139 # echo +192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
1140 # echo +192.168.0.101 > /sys/class/net/bond0/bonding/arp_ip_target
1141 NOTE: up to 10 target addresses may be specified.
1143 To remove an ARP target:
1144 # echo -192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
1146 Example Configuration
1147 ---------------------
1148 We begin with the same example that is shown in section 3.3,
1149 executed with sysfs, and without using ifenslave.
1151 To make a simple bond of two e100 devices (presumed to be eth0
1152 and eth1), and have it persist across reboots, edit the appropriate
1153 file (/etc/init.d/boot.local or /etc/rc.d/rc.local), and add the
1158 echo balance-alb > /sys/class/net/bond0/bonding/mode
1159 ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
1160 echo 100 > /sys/class/net/bond0/bonding/miimon
1161 echo +eth0 > /sys/class/net/bond0/bonding/slaves
1162 echo +eth1 > /sys/class/net/bond0/bonding/slaves
1164 To add a second bond, with two e1000 interfaces in
1165 active-backup mode, using ARP monitoring, add the following lines to
1169 echo +bond1 > /sys/class/net/bonding_masters
1170 echo active-backup > /sys/class/net/bond1/bonding/mode
1171 ifconfig bond1 192.168.2.1 netmask 255.255.255.0 up
1172 echo +192.168.2.100 /sys/class/net/bond1/bonding/arp_ip_target
1173 echo 2000 > /sys/class/net/bond1/bonding/arp_interval
1174 echo +eth2 > /sys/class/net/bond1/bonding/slaves
1175 echo +eth3 > /sys/class/net/bond1/bonding/slaves
1178 4. Querying Bonding Configuration
1179 =================================
1181 4.1 Bonding Configuration
1182 -------------------------
1184 Each bonding device has a read-only file residing in the
1185 /proc/net/bonding directory. The file contents include information
1186 about the bonding configuration, options and state of each slave.
1188 For example, the contents of /proc/net/bonding/bond0 after the
1189 driver is loaded with parameters of mode=0 and miimon=1000 is
1190 generally as follows:
1192 Ethernet Channel Bonding Driver: 2.6.1 (October 29, 2004)
1193 Bonding Mode: load balancing (round-robin)
1194 Currently Active Slave: eth0
1196 MII Polling Interval (ms): 1000
1200 Slave Interface: eth1
1202 Link Failure Count: 1
1204 Slave Interface: eth0
1206 Link Failure Count: 1
1208 The precise format and contents will change depending upon the
1209 bonding configuration, state, and version of the bonding driver.
1211 4.2 Network configuration
1212 -------------------------
1214 The network configuration can be inspected using the ifconfig
1215 command. Bonding devices will have the MASTER flag set; Bonding slave
1216 devices will have the SLAVE flag set. The ifconfig output does not
1217 contain information on which slaves are associated with which masters.
1219 In the example below, the bond0 interface is the master
1220 (MASTER) while eth0 and eth1 are slaves (SLAVE). Notice all slaves of
1221 bond0 have the same MAC address (HWaddr) as bond0 for all modes except
1222 TLB and ALB that require a unique MAC address for each slave.
1225 bond0 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4
1226 inet addr:XXX.XXX.XXX.YYY Bcast:XXX.XXX.XXX.255 Mask:255.255.252.0
1227 UP BROADCAST RUNNING MASTER MULTICAST MTU:1500 Metric:1
1228 RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0
1229 TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0
1230 collisions:0 txqueuelen:0
1232 eth0 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4
1233 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1
1234 RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0
1235 TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0
1236 collisions:0 txqueuelen:100
1237 Interrupt:10 Base address:0x1080
1239 eth1 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4
1240 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1
1241 RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0
1242 TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0
1243 collisions:0 txqueuelen:100
1244 Interrupt:9 Base address:0x1400
1246 5. Switch Configuration
1247 =======================
1249 For this section, "switch" refers to whatever system the
1250 bonded devices are directly connected to (i.e., where the other end of
1251 the cable plugs into). This may be an actual dedicated switch device,
1252 or it may be another regular system (e.g., another computer running
1255 The active-backup, balance-tlb and balance-alb modes do not
1256 require any specific configuration of the switch.
1258 The 802.3ad mode requires that the switch have the appropriate
1259 ports configured as an 802.3ad aggregation. The precise method used
1260 to configure this varies from switch to switch, but, for example, a
1261 Cisco 3550 series switch requires that the appropriate ports first be
1262 grouped together in a single etherchannel instance, then that
1263 etherchannel is set to mode "lacp" to enable 802.3ad (instead of
1264 standard EtherChannel).
1266 The balance-rr, balance-xor and broadcast modes generally
1267 require that the switch have the appropriate ports grouped together.
1268 The nomenclature for such a group differs between switches, it may be
1269 called an "etherchannel" (as in the Cisco example, above), a "trunk
1270 group" or some other similar variation. For these modes, each switch
1271 will also have its own configuration options for the switch's transmit
1272 policy to the bond. Typical choices include XOR of either the MAC or
1273 IP addresses. The transmit policy of the two peers does not need to
1274 match. For these three modes, the bonding mode really selects a
1275 transmit policy for an EtherChannel group; all three will interoperate
1276 with another EtherChannel group.
1279 6. 802.1q VLAN Support
1280 ======================
1282 It is possible to configure VLAN devices over a bond interface
1283 using the 8021q driver. However, only packets coming from the 8021q
1284 driver and passing through bonding will be tagged by default. Self
1285 generated packets, for example, bonding's learning packets or ARP
1286 packets generated by either ALB mode or the ARP monitor mechanism, are
1287 tagged internally by bonding itself. As a result, bonding must
1288 "learn" the VLAN IDs configured above it, and use those IDs to tag
1289 self generated packets.
1291 For reasons of simplicity, and to support the use of adapters
1292 that can do VLAN hardware acceleration offloading, the bonding
1293 interface declares itself as fully hardware offloading capable, it gets
1294 the add_vid/kill_vid notifications to gather the necessary
1295 information, and it propagates those actions to the slaves. In case
1296 of mixed adapter types, hardware accelerated tagged packets that
1297 should go through an adapter that is not offloading capable are
1298 "un-accelerated" by the bonding driver so the VLAN tag sits in the
1301 VLAN interfaces *must* be added on top of a bonding interface
1302 only after enslaving at least one slave. The bonding interface has a
1303 hardware address of 00:00:00:00:00:00 until the first slave is added.
1304 If the VLAN interface is created prior to the first enslavement, it
1305 would pick up the all-zeroes hardware address. Once the first slave
1306 is attached to the bond, the bond device itself will pick up the
1307 slave's hardware address, which is then available for the VLAN device.
1309 Also, be aware that a similar problem can occur if all slaves
1310 are released from a bond that still has one or more VLAN interfaces on
1311 top of it. When a new slave is added, the bonding interface will
1312 obtain its hardware address from the first slave, which might not
1313 match the hardware address of the VLAN interfaces (which was
1314 ultimately copied from an earlier slave).
1316 There are two methods to insure that the VLAN device operates
1317 with the correct hardware address if all slaves are removed from a
1320 1. Remove all VLAN interfaces then recreate them
1322 2. Set the bonding interface's hardware address so that it
1323 matches the hardware address of the VLAN interfaces.
1325 Note that changing a VLAN interface's HW address would set the
1326 underlying device -- i.e. the bonding interface -- to promiscuous
1327 mode, which might not be what you want.
1333 The bonding driver at present supports two schemes for
1334 monitoring a slave device's link state: the ARP monitor and the MII
1337 At the present time, due to implementation restrictions in the
1338 bonding driver itself, it is not possible to enable both ARP and MII
1339 monitoring simultaneously.
1341 7.1 ARP Monitor Operation
1342 -------------------------
1344 The ARP monitor operates as its name suggests: it sends ARP
1345 queries to one or more designated peer systems on the network, and
1346 uses the response as an indication that the link is operating. This
1347 gives some assurance that traffic is actually flowing to and from one
1348 or more peers on the local network.
1350 The ARP monitor relies on the device driver itself to verify
1351 that traffic is flowing. In particular, the driver must keep up to
1352 date the last receive time, dev->last_rx, and transmit start time,
1353 dev->trans_start. If these are not updated by the driver, then the
1354 ARP monitor will immediately fail any slaves using that driver, and
1355 those slaves will stay down. If networking monitoring (tcpdump, etc)
1356 shows the ARP requests and replies on the network, then it may be that
1357 your device driver is not updating last_rx and trans_start.
1359 7.2 Configuring Multiple ARP Targets
1360 ------------------------------------
1362 While ARP monitoring can be done with just one target, it can
1363 be useful in a High Availability setup to have several targets to
1364 monitor. In the case of just one target, the target itself may go
1365 down or have a problem making it unresponsive to ARP requests. Having
1366 an additional target (or several) increases the reliability of the ARP
1369 Multiple ARP targets must be separated by commas as follows:
1371 # example options for ARP monitoring with three targets
1373 options bond0 arp_interval=60 arp_ip_target=192.168.0.1,192.168.0.3,192.168.0.9
1375 For just a single target the options would resemble:
1377 # example options for ARP monitoring with one target
1379 options bond0 arp_interval=60 arp_ip_target=192.168.0.100
1382 7.3 MII Monitor Operation
1383 -------------------------
1385 The MII monitor monitors only the carrier state of the local
1386 network interface. It accomplishes this in one of three ways: by
1387 depending upon the device driver to maintain its carrier state, by
1388 querying the device's MII registers, or by making an ethtool query to
1391 If the use_carrier module parameter is 1 (the default value),
1392 then the MII monitor will rely on the driver for carrier state
1393 information (via the netif_carrier subsystem). As explained in the
1394 use_carrier parameter information, above, if the MII monitor fails to
1395 detect carrier loss on the device (e.g., when the cable is physically
1396 disconnected), it may be that the driver does not support
1399 If use_carrier is 0, then the MII monitor will first query the
1400 device's (via ioctl) MII registers and check the link state. If that
1401 request fails (not just that it returns carrier down), then the MII
1402 monitor will make an ethtool ETHOOL_GLINK request to attempt to obtain
1403 the same information. If both methods fail (i.e., the driver either
1404 does not support or had some error in processing both the MII register
1405 and ethtool requests), then the MII monitor will assume the link is
1408 8. Potential Sources of Trouble
1409 ===============================
1411 8.1 Adventures in Routing
1412 -------------------------
1414 When bonding is configured, it is important that the slave
1415 devices not have routes that supersede routes of the master (or,
1416 generally, not have routes at all). For example, suppose the bonding
1417 device bond0 has two slaves, eth0 and eth1, and the routing table is
1420 Kernel IP routing table
1421 Destination Gateway Genmask Flags MSS Window irtt Iface
1422 10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 eth0
1423 10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 eth1
1424 10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 bond0
1425 127.0.0.0 0.0.0.0 255.0.0.0 U 40 0 0 lo
1427 This routing configuration will likely still update the
1428 receive/transmit times in the driver (needed by the ARP monitor), but
1429 may bypass the bonding driver (because outgoing traffic to, in this
1430 case, another host on network 10 would use eth0 or eth1 before bond0).
1432 The ARP monitor (and ARP itself) may become confused by this
1433 configuration, because ARP requests (generated by the ARP monitor)
1434 will be sent on one interface (bond0), but the corresponding reply
1435 will arrive on a different interface (eth0). This reply looks to ARP
1436 as an unsolicited ARP reply (because ARP matches replies on an
1437 interface basis), and is discarded. The MII monitor is not affected
1438 by the state of the routing table.
1440 The solution here is simply to insure that slaves do not have
1441 routes of their own, and if for some reason they must, those routes do
1442 not supersede routes of their master. This should generally be the
1443 case, but unusual configurations or errant manual or automatic static
1444 route additions may cause trouble.
1446 8.2 Ethernet Device Renaming
1447 ----------------------------
1449 On systems with network configuration scripts that do not
1450 associate physical devices directly with network interface names (so
1451 that the same physical device always has the same "ethX" name), it may
1452 be necessary to add some special logic to either /etc/modules.conf or
1453 /etc/modprobe.conf (depending upon which is installed on the system).
1455 For example, given a modules.conf containing the following:
1458 options bond0 mode=some-mode miimon=50
1464 If neither eth0 and eth1 are slaves to bond0, then when the
1465 bond0 interface comes up, the devices may end up reordered. This
1466 happens because bonding is loaded first, then its slave device's
1467 drivers are loaded next. Since no other drivers have been loaded,
1468 when the e1000 driver loads, it will receive eth0 and eth1 for its
1469 devices, but the bonding configuration tries to enslave eth2 and eth3
1470 (which may later be assigned to the tg3 devices).
1472 Adding the following:
1474 add above bonding e1000 tg3
1476 causes modprobe to load e1000 then tg3, in that order, when
1477 bonding is loaded. This command is fully documented in the
1478 modules.conf manual page.
1480 On systems utilizing modprobe.conf (or modprobe.conf.local),
1481 an equivalent problem can occur. In this case, the following can be
1482 added to modprobe.conf (or modprobe.conf.local, as appropriate), as
1483 follows (all on one line; it has been split here for clarity):
1485 install bonding /sbin/modprobe tg3; /sbin/modprobe e1000;
1486 /sbin/modprobe --ignore-install bonding
1488 This will, when loading the bonding module, rather than
1489 performing the normal action, instead execute the provided command.
1490 This command loads the device drivers in the order needed, then calls
1491 modprobe with --ignore-install to cause the normal action to then take
1492 place. Full documentation on this can be found in the modprobe.conf
1493 and modprobe manual pages.
1495 8.3. Painfully Slow Or No Failed Link Detection By Miimon
1496 ---------------------------------------------------------
1498 By default, bonding enables the use_carrier option, which
1499 instructs bonding to trust the driver to maintain carrier state.
1501 As discussed in the options section, above, some drivers do
1502 not support the netif_carrier_on/_off link state tracking system.
1503 With use_carrier enabled, bonding will always see these links as up,
1504 regardless of their actual state.
1506 Additionally, other drivers do support netif_carrier, but do
1507 not maintain it in real time, e.g., only polling the link state at
1508 some fixed interval. In this case, miimon will detect failures, but
1509 only after some long period of time has expired. If it appears that
1510 miimon is very slow in detecting link failures, try specifying
1511 use_carrier=0 to see if that improves the failure detection time. If
1512 it does, then it may be that the driver checks the carrier state at a
1513 fixed interval, but does not cache the MII register values (so the
1514 use_carrier=0 method of querying the registers directly works). If
1515 use_carrier=0 does not improve the failover, then the driver may cache
1516 the registers, or the problem may be elsewhere.
1518 Also, remember that miimon only checks for the device's
1519 carrier state. It has no way to determine the state of devices on or
1520 beyond other ports of a switch, or if a switch is refusing to pass
1521 traffic while still maintaining carrier on.
1526 If running SNMP agents, the bonding driver should be loaded
1527 before any network drivers participating in a bond. This requirement
1528 is due to the interface index (ipAdEntIfIndex) being associated to
1529 the first interface found with a given IP address. That is, there is
1530 only one ipAdEntIfIndex for each IP address. For example, if eth0 and
1531 eth1 are slaves of bond0 and the driver for eth0 is loaded before the
1532 bonding driver, the interface for the IP address will be associated
1533 with the eth0 interface. This configuration is shown below, the IP
1534 address 192.168.1.1 has an interface index of 2 which indexes to eth0
1535 in the ifDescr table (ifDescr.2).
1537 interfaces.ifTable.ifEntry.ifDescr.1 = lo
1538 interfaces.ifTable.ifEntry.ifDescr.2 = eth0
1539 interfaces.ifTable.ifEntry.ifDescr.3 = eth1
1540 interfaces.ifTable.ifEntry.ifDescr.4 = eth2
1541 interfaces.ifTable.ifEntry.ifDescr.5 = eth3
1542 interfaces.ifTable.ifEntry.ifDescr.6 = bond0
1543 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 5
1544 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
1545 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 4
1546 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
1548 This problem is avoided by loading the bonding driver before
1549 any network drivers participating in a bond. Below is an example of
1550 loading the bonding driver first, the IP address 192.168.1.1 is
1551 correctly associated with ifDescr.2.
1553 interfaces.ifTable.ifEntry.ifDescr.1 = lo
1554 interfaces.ifTable.ifEntry.ifDescr.2 = bond0
1555 interfaces.ifTable.ifEntry.ifDescr.3 = eth0
1556 interfaces.ifTable.ifEntry.ifDescr.4 = eth1
1557 interfaces.ifTable.ifEntry.ifDescr.5 = eth2
1558 interfaces.ifTable.ifEntry.ifDescr.6 = eth3
1559 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 6
1560 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
1561 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 5
1562 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
1564 While some distributions may not report the interface name in
1565 ifDescr, the association between the IP address and IfIndex remains
1566 and SNMP functions such as Interface_Scan_Next will report that
1569 10. Promiscuous mode
1570 ====================
1572 When running network monitoring tools, e.g., tcpdump, it is
1573 common to enable promiscuous mode on the device, so that all traffic
1574 is seen (instead of seeing only traffic destined for the local host).
1575 The bonding driver handles promiscuous mode changes to the bonding
1576 master device (e.g., bond0), and propagates the setting to the slave
1579 For the balance-rr, balance-xor, broadcast, and 802.3ad modes,
1580 the promiscuous mode setting is propagated to all slaves.
1582 For the active-backup, balance-tlb and balance-alb modes, the
1583 promiscuous mode setting is propagated only to the active slave.
1585 For balance-tlb mode, the active slave is the slave currently
1586 receiving inbound traffic.
1588 For balance-alb mode, the active slave is the slave used as a
1589 "primary." This slave is used for mode-specific control traffic, for
1590 sending to peers that are unassigned or if the load is unbalanced.
1592 For the active-backup, balance-tlb and balance-alb modes, when
1593 the active slave changes (e.g., due to a link failure), the
1594 promiscuous setting will be propagated to the new active slave.
1596 11. Configuring Bonding for High Availability
1597 =============================================
1599 High Availability refers to configurations that provide
1600 maximum network availability by having redundant or backup devices,
1601 links or switches between the host and the rest of the world. The
1602 goal is to provide the maximum availability of network connectivity
1603 (i.e., the network always works), even though other configurations
1604 could provide higher throughput.
1606 11.1 High Availability in a Single Switch Topology
1607 --------------------------------------------------
1609 If two hosts (or a host and a single switch) are directly
1610 connected via multiple physical links, then there is no availability
1611 penalty to optimizing for maximum bandwidth. In this case, there is
1612 only one switch (or peer), so if it fails, there is no alternative
1613 access to fail over to. Additionally, the bonding load balance modes
1614 support link monitoring of their members, so if individual links fail,
1615 the load will be rebalanced across the remaining devices.
1617 See Section 13, "Configuring Bonding for Maximum Throughput"
1618 for information on configuring bonding with one peer device.
1620 11.2 High Availability in a Multiple Switch Topology
1621 ----------------------------------------------------
1623 With multiple switches, the configuration of bonding and the
1624 network changes dramatically. In multiple switch topologies, there is
1625 a trade off between network availability and usable bandwidth.
1627 Below is a sample network, configured to maximize the
1628 availability of the network:
1632 +-----+----+ +-----+----+
1633 | |port2 ISL port2| |
1634 | switch A +--------------------------+ switch B |
1636 +-----+----+ +-----++---+
1639 +-------------+ host1 +---------------+
1642 In this configuration, there is a link between the two
1643 switches (ISL, or inter switch link), and multiple ports connecting to
1644 the outside world ("port3" on each switch). There is no technical
1645 reason that this could not be extended to a third switch.
1647 11.2.1 HA Bonding Mode Selection for Multiple Switch Topology
1648 -------------------------------------------------------------
1650 In a topology such as the example above, the active-backup and
1651 broadcast modes are the only useful bonding modes when optimizing for
1652 availability; the other modes require all links to terminate on the
1653 same peer for them to behave rationally.
1655 active-backup: This is generally the preferred mode, particularly if
1656 the switches have an ISL and play together well. If the
1657 network configuration is such that one switch is specifically
1658 a backup switch (e.g., has lower capacity, higher cost, etc),
1659 then the primary option can be used to insure that the
1660 preferred link is always used when it is available.
1662 broadcast: This mode is really a special purpose mode, and is suitable
1663 only for very specific needs. For example, if the two
1664 switches are not connected (no ISL), and the networks beyond
1665 them are totally independent. In this case, if it is
1666 necessary for some specific one-way traffic to reach both
1667 independent networks, then the broadcast mode may be suitable.
1669 11.2.2 HA Link Monitoring Selection for Multiple Switch Topology
1670 ----------------------------------------------------------------
1672 The choice of link monitoring ultimately depends upon your
1673 switch. If the switch can reliably fail ports in response to other
1674 failures, then either the MII or ARP monitors should work. For
1675 example, in the above example, if the "port3" link fails at the remote
1676 end, the MII monitor has no direct means to detect this. The ARP
1677 monitor could be configured with a target at the remote end of port3,
1678 thus detecting that failure without switch support.
1680 In general, however, in a multiple switch topology, the ARP
1681 monitor can provide a higher level of reliability in detecting end to
1682 end connectivity failures (which may be caused by the failure of any
1683 individual component to pass traffic for any reason). Additionally,
1684 the ARP monitor should be configured with multiple targets (at least
1685 one for each switch in the network). This will insure that,
1686 regardless of which switch is active, the ARP monitor has a suitable
1689 Note, also, that of late many switches now support a functionality
1690 generally referred to as "trunk failover." This is a feature of the
1691 switch that causes the link state of a particular switch port to be set
1692 down (or up) when the state of another switch port goes down (or up).
1693 It's purpose is to propogate link failures from logically "exterior" ports
1694 to the logically "interior" ports that bonding is able to monitor via
1695 miimon. Availability and configuration for trunk failover varies by
1696 switch, but this can be a viable alternative to the ARP monitor when using
1699 12. Configuring Bonding for Maximum Throughput
1700 ==============================================
1702 12.1 Maximizing Throughput in a Single Switch Topology
1703 ------------------------------------------------------
1705 In a single switch configuration, the best method to maximize
1706 throughput depends upon the application and network environment. The
1707 various load balancing modes each have strengths and weaknesses in
1708 different environments, as detailed below.
1710 For this discussion, we will break down the topologies into
1711 two categories. Depending upon the destination of most traffic, we
1712 categorize them into either "gatewayed" or "local" configurations.
1714 In a gatewayed configuration, the "switch" is acting primarily
1715 as a router, and the majority of traffic passes through this router to
1716 other networks. An example would be the following:
1719 +----------+ +----------+
1720 | |eth0 port1| | to other networks
1721 | Host A +---------------------+ router +------------------->
1722 | +---------------------+ | Hosts B and C are out
1723 | |eth1 port2| | here somewhere
1724 +----------+ +----------+
1726 The router may be a dedicated router device, or another host
1727 acting as a gateway. For our discussion, the important point is that
1728 the majority of traffic from Host A will pass through the router to
1729 some other network before reaching its final destination.
1731 In a gatewayed network configuration, although Host A may
1732 communicate with many other systems, all of its traffic will be sent
1733 and received via one other peer on the local network, the router.
1735 Note that the case of two systems connected directly via
1736 multiple physical links is, for purposes of configuring bonding, the
1737 same as a gatewayed configuration. In that case, it happens that all
1738 traffic is destined for the "gateway" itself, not some other network
1741 In a local configuration, the "switch" is acting primarily as
1742 a switch, and the majority of traffic passes through this switch to
1743 reach other stations on the same network. An example would be the
1746 +----------+ +----------+ +--------+
1747 | |eth0 port1| +-------+ Host B |
1748 | Host A +------------+ switch |port3 +--------+
1749 | +------------+ | +--------+
1750 | |eth1 port2| +------------------+ Host C |
1751 +----------+ +----------+port4 +--------+
1754 Again, the switch may be a dedicated switch device, or another
1755 host acting as a gateway. For our discussion, the important point is
1756 that the majority of traffic from Host A is destined for other hosts
1757 on the same local network (Hosts B and C in the above example).
1759 In summary, in a gatewayed configuration, traffic to and from
1760 the bonded device will be to the same MAC level peer on the network
1761 (the gateway itself, i.e., the router), regardless of its final
1762 destination. In a local configuration, traffic flows directly to and
1763 from the final destinations, thus, each destination (Host B, Host C)
1764 will be addressed directly by their individual MAC addresses.
1766 This distinction between a gatewayed and a local network
1767 configuration is important because many of the load balancing modes
1768 available use the MAC addresses of the local network source and
1769 destination to make load balancing decisions. The behavior of each
1770 mode is described below.
1773 12.1.1 MT Bonding Mode Selection for Single Switch Topology
1774 -----------------------------------------------------------
1776 This configuration is the easiest to set up and to understand,
1777 although you will have to decide which bonding mode best suits your
1778 needs. The trade offs for each mode are detailed below:
1780 balance-rr: This mode is the only mode that will permit a single
1781 TCP/IP connection to stripe traffic across multiple
1782 interfaces. It is therefore the only mode that will allow a
1783 single TCP/IP stream to utilize more than one interface's
1784 worth of throughput. This comes at a cost, however: the
1785 striping generally results in peer systems receiving packets out
1786 of order, causing TCP/IP's congestion control system to kick
1787 in, often by retransmitting segments.
1789 It is possible to adjust TCP/IP's congestion limits by
1790 altering the net.ipv4.tcp_reordering sysctl parameter. The
1791 usual default value is 3, and the maximum useful value is 127.
1792 For a four interface balance-rr bond, expect that a single
1793 TCP/IP stream will utilize no more than approximately 2.3
1794 interface's worth of throughput, even after adjusting
1797 Note that the fraction of packets that will be delivered out of
1798 order is highly variable, and is unlikely to be zero. The level
1799 of reordering depends upon a variety of factors, including the
1800 networking interfaces, the switch, and the topology of the
1801 configuration. Speaking in general terms, higher speed network
1802 cards produce more reordering (due to factors such as packet
1803 coalescing), and a "many to many" topology will reorder at a
1804 higher rate than a "many slow to one fast" configuration.
1806 Many switches do not support any modes that stripe traffic
1807 (instead choosing a port based upon IP or MAC level addresses);
1808 for those devices, traffic for a particular connection flowing
1809 through the switch to a balance-rr bond will not utilize greater
1810 than one interface's worth of bandwidth.
1812 If you are utilizing protocols other than TCP/IP, UDP for
1813 example, and your application can tolerate out of order
1814 delivery, then this mode can allow for single stream datagram
1815 performance that scales near linearly as interfaces are added
1818 This mode requires the switch to have the appropriate ports
1819 configured for "etherchannel" or "trunking."
1821 active-backup: There is not much advantage in this network topology to
1822 the active-backup mode, as the inactive backup devices are all
1823 connected to the same peer as the primary. In this case, a
1824 load balancing mode (with link monitoring) will provide the
1825 same level of network availability, but with increased
1826 available bandwidth. On the plus side, active-backup mode
1827 does not require any configuration of the switch, so it may
1828 have value if the hardware available does not support any of
1829 the load balance modes.
1831 balance-xor: This mode will limit traffic such that packets destined
1832 for specific peers will always be sent over the same
1833 interface. Since the destination is determined by the MAC
1834 addresses involved, this mode works best in a "local" network
1835 configuration (as described above), with destinations all on
1836 the same local network. This mode is likely to be suboptimal
1837 if all your traffic is passed through a single router (i.e., a
1838 "gatewayed" network configuration, as described above).
1840 As with balance-rr, the switch ports need to be configured for
1841 "etherchannel" or "trunking."
1843 broadcast: Like active-backup, there is not much advantage to this
1844 mode in this type of network topology.
1846 802.3ad: This mode can be a good choice for this type of network
1847 topology. The 802.3ad mode is an IEEE standard, so all peers
1848 that implement 802.3ad should interoperate well. The 802.3ad
1849 protocol includes automatic configuration of the aggregates,
1850 so minimal manual configuration of the switch is needed
1851 (typically only to designate that some set of devices is
1852 available for 802.3ad). The 802.3ad standard also mandates
1853 that frames be delivered in order (within certain limits), so
1854 in general single connections will not see misordering of
1855 packets. The 802.3ad mode does have some drawbacks: the
1856 standard mandates that all devices in the aggregate operate at
1857 the same speed and duplex. Also, as with all bonding load
1858 balance modes other than balance-rr, no single connection will
1859 be able to utilize more than a single interface's worth of
1862 Additionally, the linux bonding 802.3ad implementation
1863 distributes traffic by peer (using an XOR of MAC addresses),
1864 so in a "gatewayed" configuration, all outgoing traffic will
1865 generally use the same device. Incoming traffic may also end
1866 up on a single device, but that is dependent upon the
1867 balancing policy of the peer's 8023.ad implementation. In a
1868 "local" configuration, traffic will be distributed across the
1869 devices in the bond.
1871 Finally, the 802.3ad mode mandates the use of the MII monitor,
1872 therefore, the ARP monitor is not available in this mode.
1874 balance-tlb: The balance-tlb mode balances outgoing traffic by peer.
1875 Since the balancing is done according to MAC address, in a
1876 "gatewayed" configuration (as described above), this mode will
1877 send all traffic across a single device. However, in a
1878 "local" network configuration, this mode balances multiple
1879 local network peers across devices in a vaguely intelligent
1880 manner (not a simple XOR as in balance-xor or 802.3ad mode),
1881 so that mathematically unlucky MAC addresses (i.e., ones that
1882 XOR to the same value) will not all "bunch up" on a single
1885 Unlike 802.3ad, interfaces may be of differing speeds, and no
1886 special switch configuration is required. On the down side,
1887 in this mode all incoming traffic arrives over a single
1888 interface, this mode requires certain ethtool support in the
1889 network device driver of the slave interfaces, and the ARP
1890 monitor is not available.
1892 balance-alb: This mode is everything that balance-tlb is, and more.
1893 It has all of the features (and restrictions) of balance-tlb,
1894 and will also balance incoming traffic from local network
1895 peers (as described in the Bonding Module Options section,
1898 The only additional down side to this mode is that the network
1899 device driver must support changing the hardware address while
1902 12.1.2 MT Link Monitoring for Single Switch Topology
1903 ----------------------------------------------------
1905 The choice of link monitoring may largely depend upon which
1906 mode you choose to use. The more advanced load balancing modes do not
1907 support the use of the ARP monitor, and are thus restricted to using
1908 the MII monitor (which does not provide as high a level of end to end
1909 assurance as the ARP monitor).
1911 12.2 Maximum Throughput in a Multiple Switch Topology
1912 -----------------------------------------------------
1914 Multiple switches may be utilized to optimize for throughput
1915 when they are configured in parallel as part of an isolated network
1916 between two or more systems, for example:
1922 +--------+ | +---------+
1924 +------+---+ +-----+----+ +-----+----+
1925 | Switch A | | Switch B | | Switch C |
1926 +------+---+ +-----+----+ +-----+----+
1928 +--------+ | +---------+
1934 In this configuration, the switches are isolated from one
1935 another. One reason to employ a topology such as this is for an
1936 isolated network with many hosts (a cluster configured for high
1937 performance, for example), using multiple smaller switches can be more
1938 cost effective than a single larger switch, e.g., on a network with 24
1939 hosts, three 24 port switches can be significantly less expensive than
1940 a single 72 port switch.
1942 If access beyond the network is required, an individual host
1943 can be equipped with an additional network device connected to an
1944 external network; this host then additionally acts as a gateway.
1946 12.2.1 MT Bonding Mode Selection for Multiple Switch Topology
1947 -------------------------------------------------------------
1949 In actual practice, the bonding mode typically employed in
1950 configurations of this type is balance-rr. Historically, in this
1951 network configuration, the usual caveats about out of order packet
1952 delivery are mitigated by the use of network adapters that do not do
1953 any kind of packet coalescing (via the use of NAPI, or because the
1954 device itself does not generate interrupts until some number of
1955 packets has arrived). When employed in this fashion, the balance-rr
1956 mode allows individual connections between two hosts to effectively
1957 utilize greater than one interface's bandwidth.
1959 12.2.2 MT Link Monitoring for Multiple Switch Topology
1960 ------------------------------------------------------
1962 Again, in actual practice, the MII monitor is most often used
1963 in this configuration, as performance is given preference over
1964 availability. The ARP monitor will function in this topology, but its
1965 advantages over the MII monitor are mitigated by the volume of probes
1966 needed as the number of systems involved grows (remember that each
1967 host in the network is configured with bonding).
1969 13. Switch Behavior Issues
1970 ==========================
1972 13.1 Link Establishment and Failover Delays
1973 -------------------------------------------
1975 Some switches exhibit undesirable behavior with regard to the
1976 timing of link up and down reporting by the switch.
1978 First, when a link comes up, some switches may indicate that
1979 the link is up (carrier available), but not pass traffic over the
1980 interface for some period of time. This delay is typically due to
1981 some type of autonegotiation or routing protocol, but may also occur
1982 during switch initialization (e.g., during recovery after a switch
1983 failure). If you find this to be a problem, specify an appropriate
1984 value to the updelay bonding module option to delay the use of the
1985 relevant interface(s).
1987 Second, some switches may "bounce" the link state one or more
1988 times while a link is changing state. This occurs most commonly while
1989 the switch is initializing. Again, an appropriate updelay value may
1992 Note that when a bonding interface has no active links, the
1993 driver will immediately reuse the first link that goes up, even if the
1994 updelay parameter has been specified (the updelay is ignored in this
1995 case). If there are slave interfaces waiting for the updelay timeout
1996 to expire, the interface that first went into that state will be
1997 immediately reused. This reduces down time of the network if the
1998 value of updelay has been overestimated, and since this occurs only in
1999 cases with no connectivity, there is no additional penalty for
2000 ignoring the updelay.
2002 In addition to the concerns about switch timings, if your
2003 switches take a long time to go into backup mode, it may be desirable
2004 to not activate a backup interface immediately after a link goes down.
2005 Failover may be delayed via the downdelay bonding module option.
2007 13.2 Duplicated Incoming Packets
2008 --------------------------------
2010 NOTE: Starting with version 3.0.2, the bonding driver has logic to
2011 suppress duplicate packets, which should largely eliminate this problem.
2012 The following description is kept for reference.
2014 It is not uncommon to observe a short burst of duplicated
2015 traffic when the bonding device is first used, or after it has been
2016 idle for some period of time. This is most easily observed by issuing
2017 a "ping" to some other host on the network, and noticing that the
2018 output from ping flags duplicates (typically one per slave).
2020 For example, on a bond in active-backup mode with five slaves
2021 all connected to one switch, the output may appear as follows:
2024 PING 10.0.4.2 (10.0.4.2) from 10.0.3.10 : 56(84) bytes of data.
2025 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.7 ms
2026 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2027 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2028 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2029 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
2030 64 bytes from 10.0.4.2: icmp_seq=2 ttl=64 time=0.216 ms
2031 64 bytes from 10.0.4.2: icmp_seq=3 ttl=64 time=0.267 ms
2032 64 bytes from 10.0.4.2: icmp_seq=4 ttl=64 time=0.222 ms
2034 This is not due to an error in the bonding driver, rather, it
2035 is a side effect of how many switches update their MAC forwarding
2036 tables. Initially, the switch does not associate the MAC address in
2037 the packet with a particular switch port, and so it may send the
2038 traffic to all ports until its MAC forwarding table is updated. Since
2039 the interfaces attached to the bond may occupy multiple ports on a
2040 single switch, when the switch (temporarily) floods the traffic to all
2041 ports, the bond device receives multiple copies of the same packet
2042 (one per slave device).
2044 The duplicated packet behavior is switch dependent, some
2045 switches exhibit this, and some do not. On switches that display this
2046 behavior, it can be induced by clearing the MAC forwarding table (on
2047 most Cisco switches, the privileged command "clear mac address-table
2048 dynamic" will accomplish this).
2050 14. Hardware Specific Considerations
2051 ====================================
2053 This section contains additional information for configuring
2054 bonding on specific hardware platforms, or for interfacing bonding
2055 with particular switches or other devices.
2057 14.1 IBM BladeCenter
2058 --------------------
2060 This applies to the JS20 and similar systems.
2062 On the JS20 blades, the bonding driver supports only
2063 balance-rr, active-backup, balance-tlb and balance-alb modes. This is
2064 largely due to the network topology inside the BladeCenter, detailed
2067 JS20 network adapter information
2068 --------------------------------
2070 All JS20s come with two Broadcom Gigabit Ethernet ports
2071 integrated on the planar (that's "motherboard" in IBM-speak). In the
2072 BladeCenter chassis, the eth0 port of all JS20 blades is hard wired to
2073 I/O Module #1; similarly, all eth1 ports are wired to I/O Module #2.
2074 An add-on Broadcom daughter card can be installed on a JS20 to provide
2075 two more Gigabit Ethernet ports. These ports, eth2 and eth3, are
2076 wired to I/O Modules 3 and 4, respectively.
2078 Each I/O Module may contain either a switch or a passthrough
2079 module (which allows ports to be directly connected to an external
2080 switch). Some bonding modes require a specific BladeCenter internal
2081 network topology in order to function; these are detailed below.
2083 Additional BladeCenter-specific networking information can be
2084 found in two IBM Redbooks (www.ibm.com/redbooks):
2086 "IBM eServer BladeCenter Networking Options"
2087 "IBM eServer BladeCenter Layer 2-7 Network Switching"
2089 BladeCenter networking configuration
2090 ------------------------------------
2092 Because a BladeCenter can be configured in a very large number
2093 of ways, this discussion will be confined to describing basic
2096 Normally, Ethernet Switch Modules (ESMs) are used in I/O
2097 modules 1 and 2. In this configuration, the eth0 and eth1 ports of a
2098 JS20 will be connected to different internal switches (in the
2099 respective I/O modules).
2101 A passthrough module (OPM or CPM, optical or copper,
2102 passthrough module) connects the I/O module directly to an external
2103 switch. By using PMs in I/O module #1 and #2, the eth0 and eth1
2104 interfaces of a JS20 can be redirected to the outside world and
2105 connected to a common external switch.
2107 Depending upon the mix of ESMs and PMs, the network will
2108 appear to bonding as either a single switch topology (all PMs) or as a
2109 multiple switch topology (one or more ESMs, zero or more PMs). It is
2110 also possible to connect ESMs together, resulting in a configuration
2111 much like the example in "High Availability in a Multiple Switch
2114 Requirements for specific modes
2115 -------------------------------
2117 The balance-rr mode requires the use of passthrough modules
2118 for devices in the bond, all connected to an common external switch.
2119 That switch must be configured for "etherchannel" or "trunking" on the
2120 appropriate ports, as is usual for balance-rr.
2122 The balance-alb and balance-tlb modes will function with
2123 either switch modules or passthrough modules (or a mix). The only
2124 specific requirement for these modes is that all network interfaces
2125 must be able to reach all destinations for traffic sent over the
2126 bonding device (i.e., the network must converge at some point outside
2129 The active-backup mode has no additional requirements.
2131 Link monitoring issues
2132 ----------------------
2134 When an Ethernet Switch Module is in place, only the ARP
2135 monitor will reliably detect link loss to an external switch. This is
2136 nothing unusual, but examination of the BladeCenter cabinet would
2137 suggest that the "external" network ports are the ethernet ports for
2138 the system, when it fact there is a switch between these "external"
2139 ports and the devices on the JS20 system itself. The MII monitor is
2140 only able to detect link failures between the ESM and the JS20 system.
2142 When a passthrough module is in place, the MII monitor does
2143 detect failures to the "external" port, which is then directly
2144 connected to the JS20 system.
2149 The Serial Over LAN (SoL) link is established over the primary
2150 ethernet (eth0) only, therefore, any loss of link to eth0 will result
2151 in losing your SoL connection. It will not fail over with other
2152 network traffic, as the SoL system is beyond the control of the
2155 It may be desirable to disable spanning tree on the switch
2156 (either the internal Ethernet Switch Module, or an external switch) to
2157 avoid fail-over delay issues when using bonding.
2160 15. Frequently Asked Questions
2161 ==============================
2165 Yes. The old 2.0.xx channel bonding patch was not SMP safe.
2166 The new driver was designed to be SMP safe from the start.
2168 2. What type of cards will work with it?
2170 Any Ethernet type cards (you can even mix cards - a Intel
2171 EtherExpress PRO/100 and a 3com 3c905b, for example). For most modes,
2172 devices need not be of the same speed.
2174 Starting with version 3.2.1, bonding also supports Infiniband
2175 slaves in active-backup mode.
2177 3. How many bonding devices can I have?
2181 4. How many slaves can a bonding device have?
2183 This is limited only by the number of network interfaces Linux
2184 supports and/or the number of network cards you can place in your
2187 5. What happens when a slave link dies?
2189 If link monitoring is enabled, then the failing device will be
2190 disabled. The active-backup mode will fail over to a backup link, and
2191 other modes will ignore the failed link. The link will continue to be
2192 monitored, and should it recover, it will rejoin the bond (in whatever
2193 manner is appropriate for the mode). See the sections on High
2194 Availability and the documentation for each mode for additional
2197 Link monitoring can be enabled via either the miimon or
2198 arp_interval parameters (described in the module parameters section,
2199 above). In general, miimon monitors the carrier state as sensed by
2200 the underlying network device, and the arp monitor (arp_interval)
2201 monitors connectivity to another host on the local network.
2203 If no link monitoring is configured, the bonding driver will
2204 be unable to detect link failures, and will assume that all links are
2205 always available. This will likely result in lost packets, and a
2206 resulting degradation of performance. The precise performance loss
2207 depends upon the bonding mode and network configuration.
2209 6. Can bonding be used for High Availability?
2211 Yes. See the section on High Availability for details.
2213 7. Which switches/systems does it work with?
2215 The full answer to this depends upon the desired mode.
2217 In the basic balance modes (balance-rr and balance-xor), it
2218 works with any system that supports etherchannel (also called
2219 trunking). Most managed switches currently available have such
2220 support, and many unmanaged switches as well.
2222 The advanced balance modes (balance-tlb and balance-alb) do
2223 not have special switch requirements, but do need device drivers that
2224 support specific features (described in the appropriate section under
2225 module parameters, above).
2227 In 802.3ad mode, it works with systems that support IEEE
2228 802.3ad Dynamic Link Aggregation. Most managed and many unmanaged
2229 switches currently available support 802.3ad.
2231 The active-backup mode should work with any Layer-II switch.
2233 8. Where does a bonding device get its MAC address from?
2235 When using slave devices that have fixed MAC addresses, or when
2236 the fail_over_mac option is enabled, the bonding device's MAC address is
2237 the MAC address of the active slave.
2239 For other configurations, if not explicitly configured (with
2240 ifconfig or ip link), the MAC address of the bonding device is taken from
2241 its first slave device. This MAC address is then passed to all following
2242 slaves and remains persistent (even if the first slave is removed) until
2243 the bonding device is brought down or reconfigured.
2245 If you wish to change the MAC address, you can set it with
2246 ifconfig or ip link:
2248 # ifconfig bond0 hw ether 00:11:22:33:44:55
2250 # ip link set bond0 address 66:77:88:99:aa:bb
2252 The MAC address can be also changed by bringing down/up the
2253 device and then changing its slaves (or their order):
2255 # ifconfig bond0 down ; modprobe -r bonding
2256 # ifconfig bond0 .... up
2257 # ifenslave bond0 eth...
2259 This method will automatically take the address from the next
2260 slave that is added.
2262 To restore your slaves' MAC addresses, you need to detach them
2263 from the bond (`ifenslave -d bond0 eth0'). The bonding driver will
2264 then restore the MAC addresses that the slaves had before they were
2267 16. Resources and Links
2268 =======================
2270 The latest version of the bonding driver can be found in the latest
2271 version of the linux kernel, found on http://kernel.org
2273 The latest version of this document can be found in either the latest
2274 kernel source (named Documentation/networking/bonding.txt), or on the
2275 bonding sourceforge site:
2277 http://www.sourceforge.net/projects/bonding
2279 Discussions regarding the bonding driver take place primarily on the
2280 bonding-devel mailing list, hosted at sourceforge.net. If you have
2281 questions or problems, post them to the list. The list address is:
2283 bonding-devel@lists.sourceforge.net
2285 The administrative interface (to subscribe or unsubscribe) can
2288 https://lists.sourceforge.net/lists/listinfo/bonding-devel
2290 Donald Becker's Ethernet Drivers and diag programs may be found at :
2291 - http://www.scyld.com/network/
2293 You will also find a lot of information regarding Ethernet, NWay, MII,
2294 etc. at www.scyld.com.
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