2 Linux Ethernet Bonding Driver HOWTO
4 Latest update: 21 June 2005
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
19 The Linux bonding driver provides a method for aggregating
20 multiple network interfaces into a single logical "bonded" interface.
21 The behavior of the bonded interfaces depends upon the mode; generally
22 speaking, modes provide either hot standby or load balancing services.
23 Additionally, link integrity monitoring may be performed.
25 The bonding driver originally came from Donald Becker's
26 beowulf patches for kernel 2.0. It has changed quite a bit since, and
27 the original tools from extreme-linux and beowulf sites will not work
28 with this version of the driver.
30 For new versions of the driver, updated userspace tools, and
31 who to ask for help, please follow the links at the end of this file.
36 1. Bonding Driver Installation
38 2. Bonding Driver Options
40 3. Configuring Bonding Devices
41 3.1 Configuration with sysconfig support
42 3.1.1 Using DHCP with sysconfig
43 3.1.2 Configuring Multiple Bonds with sysconfig
44 3.2 Configuration with initscripts support
45 3.2.1 Using DHCP with initscripts
46 3.2.2 Configuring Multiple Bonds with initscripts
47 3.3 Configuring Bonding Manually
48 3.3.1 Configuring Multiple Bonds Manually
50 5. Querying Bonding Configuration
51 5.1 Bonding Configuration
52 5.2 Network Configuration
54 6. Switch Configuration
56 7. 802.1q VLAN Support
59 8.1 ARP Monitor Operation
60 8.2 Configuring Multiple ARP Targets
61 8.3 MII Monitor Operation
63 9. Potential Trouble Sources
64 9.1 Adventures in Routing
65 9.2 Ethernet Device Renaming
66 9.3 Painfully Slow Or No Failed Link Detection By Miimon
72 12. Configuring Bonding for High Availability
73 12.1 High Availability in a Single Switch Topology
74 12.2 High Availability in a Multiple Switch Topology
75 12.2.1 HA Bonding Mode Selection for Multiple Switch Topology
76 12.2.2 HA Link Monitoring for Multiple Switch Topology
78 13. Configuring Bonding for Maximum Throughput
79 13.1 Maximum Throughput in a Single Switch Topology
80 13.1.1 MT Bonding Mode Selection for Single Switch Topology
81 13.1.2 MT Link Monitoring for Single Switch Topology
82 13.2 Maximum Throughput in a Multiple Switch Topology
83 13.2.1 MT Bonding Mode Selection for Multiple Switch Topology
84 13.2.2 MT Link Monitoring for Multiple Switch Topology
86 14. Switch Behavior Issues
87 14.1 Link Establishment and Failover Delays
88 14.2 Duplicated Incoming Packets
90 15. Hardware Specific Considerations
93 16. Frequently Asked Questions
95 17. Resources and Links
98 1. Bonding Driver Installation
99 ==============================
101 Most popular distro kernels ship with the bonding driver
102 already available as a module and the ifenslave user level control
103 program installed and ready for use. If your distro does not, or you
104 have need to compile bonding from source (e.g., configuring and
105 installing a mainline kernel from kernel.org), you'll need to perform
108 1.1 Configure and build the kernel with bonding
109 -----------------------------------------------
111 The current version of the bonding driver is available in the
112 drivers/net/bonding subdirectory of the most recent kernel source
113 (which is available on http://kernel.org). Most users "rolling their
114 own" will want to use the most recent kernel from kernel.org.
116 Configure kernel with "make menuconfig" (or "make xconfig" or
117 "make config"), then select "Bonding driver support" in the "Network
118 device support" section. It is recommended that you configure the
119 driver as module since it is currently the only way to pass parameters
120 to the driver or configure more than one bonding device.
122 Build and install the new kernel and modules, then continue
123 below to install ifenslave.
125 1.2 Install ifenslave Control Utility
126 -------------------------------------
128 The ifenslave user level control program is included in the
129 kernel source tree, in the file Documentation/networking/ifenslave.c.
130 It is generally recommended that you use the ifenslave that
131 corresponds to the kernel that you are using (either from the same
132 source tree or supplied with the distro), however, ifenslave
133 executables from older kernels should function (but features newer
134 than the ifenslave release are not supported). Running an ifenslave
135 that is newer than the kernel is not supported, and may or may not
138 To install ifenslave, do the following:
140 # gcc -Wall -O -I/usr/src/linux/include ifenslave.c -o ifenslave
141 # cp ifenslave /sbin/ifenslave
143 If your kernel source is not in "/usr/src/linux," then replace
144 "/usr/src/linux/include" in the above with the location of your kernel
145 source include directory.
147 You may wish to back up any existing /sbin/ifenslave, or, for
148 testing or informal use, tag the ifenslave to the kernel version
149 (e.g., name the ifenslave executable /sbin/ifenslave-2.6.10).
153 If you omit the "-I" or specify an incorrect directory, you
154 may end up with an ifenslave that is incompatible with the kernel
155 you're trying to build it for. Some distros (e.g., Red Hat from 7.1
156 onwards) do not have /usr/include/linux symbolically linked to the
157 default kernel source include directory.
160 2. Bonding Driver Options
161 =========================
163 Options for the bonding driver are supplied as parameters to
164 the bonding module at load time. They may be given as command line
165 arguments to the insmod or modprobe command, but are usually specified
166 in either the /etc/modules.conf or /etc/modprobe.conf configuration
167 file, or in a distro-specific configuration file (some of which are
168 detailed in the next section).
170 The available bonding driver parameters are listed below. If a
171 parameter is not specified the default value is used. When initially
172 configuring a bond, it is recommended "tail -f /var/log/messages" be
173 run in a separate window to watch for bonding driver error messages.
175 It is critical that either the miimon or arp_interval and
176 arp_ip_target parameters be specified, otherwise serious network
177 degradation will occur during link failures. Very few devices do not
178 support at least miimon, so there is really no reason not to use it.
180 Options with textual values will accept either the text name
181 or, for backwards compatibility, the option value. E.g.,
182 "mode=802.3ad" and "mode=4" set the same mode.
184 The parameters are as follows:
188 Specifies the ARP link monitoring frequency in milliseconds.
189 If ARP monitoring is used in an etherchannel compatible mode
190 (modes 0 and 2), the switch should be configured in a mode
191 that evenly distributes packets across all links. If the
192 switch is configured to distribute the packets in an XOR
193 fashion, all replies from the ARP targets will be received on
194 the same link which could cause the other team members to
195 fail. ARP monitoring should not be used in conjunction with
196 miimon. A value of 0 disables ARP monitoring. The default
201 Specifies the IP addresses to use as ARP monitoring peers when
202 arp_interval is > 0. These are the targets of the ARP request
203 sent to determine the health of the link to the targets.
204 Specify these values in ddd.ddd.ddd.ddd format. Multiple IP
205 addresses must be separated by a comma. At least one IP
206 address must be given for ARP monitoring to function. The
207 maximum number of targets that can be specified is 16. The
208 default value is no IP addresses.
212 Specifies the time, in milliseconds, to wait before disabling
213 a slave after a link failure has been detected. This option
214 is only valid for the miimon link monitor. The downdelay
215 value should be a multiple of the miimon value; if not, it
216 will be rounded down to the nearest multiple. The default
221 Option specifying the rate in which we'll ask our link partner
222 to transmit LACPDU packets in 802.3ad mode. Possible values
226 Request partner to transmit LACPDUs every 30 seconds
229 Request partner to transmit LACPDUs every 1 second
235 Specifies the number of bonding devices to create for this
236 instance of the bonding driver. E.g., if max_bonds is 3, and
237 the bonding driver is not already loaded, then bond0, bond1
238 and bond2 will be created. The default value is 1.
242 Specifies the MII link monitoring frequency in milliseconds.
243 This determines how often the link state of each slave is
244 inspected for link failures. A value of zero disables MII
245 link monitoring. A value of 100 is a good starting point.
246 The use_carrier option, below, affects how the link state is
247 determined. See the High Availability section for additional
248 information. The default value is 0.
252 Specifies one of the bonding policies. The default is
253 balance-rr (round robin). Possible values are:
257 Round-robin policy: Transmit packets in sequential
258 order from the first available slave through the
259 last. This mode provides load balancing and fault
264 Active-backup policy: Only one slave in the bond is
265 active. A different slave becomes active if, and only
266 if, the active slave fails. The bond's MAC address is
267 externally visible on only one port (network adapter)
268 to avoid confusing the switch.
270 In bonding version 2.6.2 or later, when a failover
271 occurs in active-backup mode, bonding will issue one
272 or more gratuitous ARPs on the newly active slave.
273 One gratutious ARP is issued for the bonding master
274 interface and each VLAN interfaces configured above
275 it, provided that the interface has at least one IP
276 address configured. Gratuitous ARPs issued for VLAN
277 interfaces are tagged with the appropriate VLAN id.
279 This mode provides fault tolerance. The primary
280 option, documented below, affects the behavior of this
285 XOR policy: Transmit based on the selected transmit
286 hash policy. The default policy is a simple [(source
287 MAC address XOR'd with destination MAC address) modulo
288 slave count]. Alternate transmit policies may be
289 selected via the xmit_hash_policy option, described
292 This mode provides load balancing and fault tolerance.
296 Broadcast policy: transmits everything on all slave
297 interfaces. This mode provides fault tolerance.
301 IEEE 802.3ad Dynamic link aggregation. Creates
302 aggregation groups that share the same speed and
303 duplex settings. Utilizes all slaves in the active
304 aggregator according to the 802.3ad specification.
306 Slave selection for outgoing traffic is done according
307 to the transmit hash policy, which may be changed from
308 the default simple XOR policy via the xmit_hash_policy
309 option, documented below. Note that not all transmit
310 policies may be 802.3ad compliant, particularly in
311 regards to the packet mis-ordering requirements of
312 section 43.2.4 of the 802.3ad standard. Differing
313 peer implementations will have varying tolerances for
318 1. Ethtool support in the base drivers for retrieving
319 the speed and duplex of each slave.
321 2. A switch that supports IEEE 802.3ad Dynamic link
324 Most switches will require some type of configuration
325 to enable 802.3ad mode.
329 Adaptive transmit load balancing: channel bonding that
330 does not require any special switch support. The
331 outgoing traffic is distributed according to the
332 current load (computed relative to the speed) on each
333 slave. Incoming traffic is received by the current
334 slave. If the receiving slave fails, another slave
335 takes over the MAC address of the failed receiving
340 Ethtool support in the base drivers for retrieving the
345 Adaptive load balancing: includes balance-tlb plus
346 receive load balancing (rlb) for IPV4 traffic, and
347 does not require any special switch support. The
348 receive load balancing is achieved by ARP negotiation.
349 The bonding driver intercepts the ARP Replies sent by
350 the local system on their way out and overwrites the
351 source hardware address with the unique hardware
352 address of one of the slaves in the bond such that
353 different peers use different hardware addresses for
356 Receive traffic from connections created by the server
357 is also balanced. When the local system sends an ARP
358 Request the bonding driver copies and saves the peer's
359 IP information from the ARP packet. When the ARP
360 Reply arrives from the peer, its hardware address is
361 retrieved and the bonding driver initiates an ARP
362 reply to this peer assigning it to one of the slaves
363 in the bond. A problematic outcome of using ARP
364 negotiation for balancing is that each time that an
365 ARP request is broadcast it uses the hardware address
366 of the bond. Hence, peers learn the hardware address
367 of the bond and the balancing of receive traffic
368 collapses to the current slave. This is handled by
369 sending updates (ARP Replies) to all the peers with
370 their individually assigned hardware address such that
371 the traffic is redistributed. Receive traffic is also
372 redistributed when a new slave is added to the bond
373 and when an inactive slave is re-activated. The
374 receive load is distributed sequentially (round robin)
375 among the group of highest speed slaves in the bond.
377 When a link is reconnected or a new slave joins the
378 bond the receive traffic is redistributed among all
379 active slaves in the bond by initiating ARP Replies
380 with the selected mac address to each of the
381 clients. The updelay parameter (detailed below) must
382 be set to a value equal or greater than the switch's
383 forwarding delay so that the ARP Replies sent to the
384 peers will not be blocked by the switch.
388 1. Ethtool support in the base drivers for retrieving
389 the speed of each slave.
391 2. Base driver support for setting the hardware
392 address of a device while it is open. This is
393 required so that there will always be one slave in the
394 team using the bond hardware address (the
395 curr_active_slave) while having a unique hardware
396 address for each slave in the bond. If the
397 curr_active_slave fails its hardware address is
398 swapped with the new curr_active_slave that was
403 A string (eth0, eth2, etc) specifying which slave is the
404 primary device. The specified device will always be the
405 active slave while it is available. Only when the primary is
406 off-line will alternate devices be used. This is useful when
407 one slave is preferred over another, e.g., when one slave has
408 higher throughput than another.
410 The primary option is only valid for active-backup mode.
414 Specifies the time, in milliseconds, to wait before enabling a
415 slave after a link recovery has been detected. This option is
416 only valid for the miimon link monitor. The updelay value
417 should be a multiple of the miimon value; if not, it will be
418 rounded down to the nearest multiple. The default value is 0.
422 Specifies whether or not miimon should use MII or ETHTOOL
423 ioctls vs. netif_carrier_ok() to determine the link
424 status. The MII or ETHTOOL ioctls are less efficient and
425 utilize a deprecated calling sequence within the kernel. The
426 netif_carrier_ok() relies on the device driver to maintain its
427 state with netif_carrier_on/off; at this writing, most, but
428 not all, device drivers support this facility.
430 If bonding insists that the link is up when it should not be,
431 it may be that your network device driver does not support
432 netif_carrier_on/off. The default state for netif_carrier is
433 "carrier on," so if a driver does not support netif_carrier,
434 it will appear as if the link is always up. In this case,
435 setting use_carrier to 0 will cause bonding to revert to the
436 MII / ETHTOOL ioctl method to determine the link state.
438 A value of 1 enables the use of netif_carrier_ok(), a value of
439 0 will use the deprecated MII / ETHTOOL ioctls. The default
444 Selects the transmit hash policy to use for slave selection in
445 balance-xor and 802.3ad modes. Possible values are:
449 Uses XOR of hardware MAC addresses to generate the
452 (source MAC XOR destination MAC) modulo slave count
454 This algorithm will place all traffic to a particular
455 network peer on the same slave.
457 This algorithm is 802.3ad compliant.
461 This policy uses upper layer protocol information,
462 when available, to generate the hash. This allows for
463 traffic to a particular network peer to span multiple
464 slaves, although a single connection will not span
467 The formula for unfragmented TCP and UDP packets is
469 ((source port XOR dest port) XOR
470 ((source IP XOR dest IP) AND 0xffff)
473 For fragmented TCP or UDP packets and all other IP
474 protocol traffic, the source and destination port
475 information is omitted. For non-IP traffic, the
476 formula is the same as for the layer2 transmit hash
479 This policy is intended to mimic the behavior of
480 certain switches, notably Cisco switches with PFC2 as
481 well as some Foundry and IBM products.
483 This algorithm is not fully 802.3ad compliant. A
484 single TCP or UDP conversation containing both
485 fragmented and unfragmented packets will see packets
486 striped across two interfaces. This may result in out
487 of order delivery. Most traffic types will not meet
488 this criteria, as TCP rarely fragments traffic, and
489 most UDP traffic is not involved in extended
490 conversations. Other implementations of 802.3ad may
491 or may not tolerate this noncompliance.
493 The default value is layer2. This option was added in bonding
494 version 2.6.3. In earlier versions of bonding, this parameter does
495 not exist, and the layer2 policy is the only policy.
498 3. Configuring Bonding Devices
499 ==============================
501 There are, essentially, two methods for configuring bonding:
502 with support from the distro's network initialization scripts, and
503 without. Distros generally use one of two packages for the network
504 initialization scripts: initscripts or sysconfig. Recent versions of
505 these packages have support for bonding, while older versions do not.
507 We will first describe the options for configuring bonding for
508 distros using versions of initscripts and sysconfig with full or
509 partial support for bonding, then provide information on enabling
510 bonding without support from the network initialization scripts (i.e.,
511 older versions of initscripts or sysconfig).
513 If you're unsure whether your distro uses sysconfig or
514 initscripts, or don't know if it's new enough, have no fear.
515 Determining this is fairly straightforward.
517 First, issue the command:
521 It will respond with a line of text starting with either
522 "initscripts" or "sysconfig," followed by some numbers. This is the
523 package that provides your network initialization scripts.
525 Next, to determine if your installation supports bonding,
528 $ grep ifenslave /sbin/ifup
530 If this returns any matches, then your initscripts or
531 sysconfig has support for bonding.
533 3.1 Configuration with sysconfig support
534 ----------------------------------------
536 This section applies to distros using a version of sysconfig
537 with bonding support, for example, SuSE Linux Enterprise Server 9.
539 SuSE SLES 9's networking configuration system does support
540 bonding, however, at this writing, the YaST system configuration
541 frontend does not provide any means to work with bonding devices.
542 Bonding devices can be managed by hand, however, as follows.
544 First, if they have not already been configured, configure the
545 slave devices. On SLES 9, this is most easily done by running the
546 yast2 sysconfig configuration utility. The goal is for to create an
547 ifcfg-id file for each slave device. The simplest way to accomplish
548 this is to configure the devices for DHCP (this is only to get the
549 file ifcfg-id file created; see below for some issues with DHCP). The
550 name of the configuration file for each device will be of the form:
552 ifcfg-id-xx:xx:xx:xx:xx:xx
554 Where the "xx" portion will be replaced with the digits from
555 the device's permanent MAC address.
557 Once the set of ifcfg-id-xx:xx:xx:xx:xx:xx files has been
558 created, it is necessary to edit the configuration files for the slave
559 devices (the MAC addresses correspond to those of the slave devices).
560 Before editing, the file will contain multiple lines, and will look
566 UNIQUE='XNzu.WeZGOGF+4wE'
567 _nm_name='bus-pci-0001:61:01.0'
569 Change the BOOTPROTO and STARTMODE lines to the following:
574 Do not alter the UNIQUE or _nm_name lines. Remove any other
575 lines (USERCTL, etc).
577 Once the ifcfg-id-xx:xx:xx:xx:xx:xx files have been modified,
578 it's time to create the configuration file for the bonding device
579 itself. This file is named ifcfg-bondX, where X is the number of the
580 bonding device to create, starting at 0. The first such file is
581 ifcfg-bond0, the second is ifcfg-bond1, and so on. The sysconfig
582 network configuration system will correctly start multiple instances
585 The contents of the ifcfg-bondX file is as follows:
588 BROADCAST="10.0.2.255"
590 NETMASK="255.255.0.0"
595 BONDING_MODULE_OPTS="mode=active-backup miimon=100"
596 BONDING_SLAVE0="eth0"
597 BONDING_SLAVE1="bus-pci-0000:06:08.1"
599 Replace the sample BROADCAST, IPADDR, NETMASK and NETWORK
600 values with the appropriate values for your network.
602 The STARTMODE specifies when the device is brought online.
603 The possible values are:
605 onboot: The device is started at boot time. If you're not
606 sure, this is probably what you want.
608 manual: The device is started only when ifup is called
609 manually. Bonding devices may be configured this
610 way if you do not wish them to start automatically
611 at boot for some reason.
613 hotplug: The device is started by a hotplug event. This is not
614 a valid choice for a bonding device.
616 off or ignore: The device configuration is ignored.
618 The line BONDING_MASTER='yes' indicates that the device is a
619 bonding master device. The only useful value is "yes."
621 The contents of BONDING_MODULE_OPTS are supplied to the
622 instance of the bonding module for this device. Specify the options
623 for the bonding mode, link monitoring, and so on here. Do not include
624 the max_bonds bonding parameter; this will confuse the configuration
625 system if you have multiple bonding devices.
627 Finally, supply one BONDING_SLAVEn="slave device" for each
628 slave. where "n" is an increasing value, one for each slave. The
629 "slave device" is either an interface name, e.g., "eth0", or a device
630 specifier for the network device. The interface name is easier to
631 find, but the ethN names are subject to change at boot time if, e.g.,
632 a device early in the sequence has failed. The device specifiers
633 (bus-pci-0000:06:08.1 in the example above) specify the physical
634 network device, and will not change unless the device's bus location
635 changes (for example, it is moved from one PCI slot to another). The
636 example above uses one of each type for demonstration purposes; most
637 configurations will choose one or the other for all slave devices.
639 When all configuration files have been modified or created,
640 networking must be restarted for the configuration changes to take
641 effect. This can be accomplished via the following:
643 # /etc/init.d/network restart
645 Note that the network control script (/sbin/ifdown) will
646 remove the bonding module as part of the network shutdown processing,
647 so it is not necessary to remove the module by hand if, e.g., the
648 module parameters have changed.
650 Also, at this writing, YaST/YaST2 will not manage bonding
651 devices (they do not show bonding interfaces on its list of network
652 devices). It is necessary to edit the configuration file by hand to
653 change the bonding configuration.
655 Additional general options and details of the ifcfg file
656 format can be found in an example ifcfg template file:
658 /etc/sysconfig/network/ifcfg.template
660 Note that the template does not document the various BONDING_
661 settings described above, but does describe many of the other options.
663 3.1.1 Using DHCP with sysconfig
664 -------------------------------
666 Under sysconfig, configuring a device with BOOTPROTO='dhcp'
667 will cause it to query DHCP for its IP address information. At this
668 writing, this does not function for bonding devices; the scripts
669 attempt to obtain the device address from DHCP prior to adding any of
670 the slave devices. Without active slaves, the DHCP requests are not
673 3.1.2 Configuring Multiple Bonds with sysconfig
674 -----------------------------------------------
676 The sysconfig network initialization system is capable of
677 handling multiple bonding devices. All that is necessary is for each
678 bonding instance to have an appropriately configured ifcfg-bondX file
679 (as described above). Do not specify the "max_bonds" parameter to any
680 instance of bonding, as this will confuse sysconfig. If you require
681 multiple bonding devices with identical parameters, create multiple
684 Because the sysconfig scripts supply the bonding module
685 options in the ifcfg-bondX file, it is not necessary to add them to
686 the system /etc/modules.conf or /etc/modprobe.conf configuration file.
688 3.2 Configuration with initscripts support
689 ------------------------------------------
691 This section applies to distros using a version of initscripts
692 with bonding support, for example, Red Hat Linux 9 or Red Hat
693 Enterprise Linux version 3 or 4. On these systems, the network
694 initialization scripts have some knowledge of bonding, and can be
695 configured to control bonding devices.
697 These distros will not automatically load the network adapter
698 driver unless the ethX device is configured with an IP address.
699 Because of this constraint, users must manually configure a
700 network-script file for all physical adapters that will be members of
701 a bondX link. Network script files are located in the directory:
703 /etc/sysconfig/network-scripts
705 The file name must be prefixed with "ifcfg-eth" and suffixed
706 with the adapter's physical adapter number. For example, the script
707 for eth0 would be named /etc/sysconfig/network-scripts/ifcfg-eth0.
708 Place the following text in the file:
717 The DEVICE= line will be different for every ethX device and
718 must correspond with the name of the file, i.e., ifcfg-eth1 must have
719 a device line of DEVICE=eth1. The setting of the MASTER= line will
720 also depend on the final bonding interface name chosen for your bond.
721 As with other network devices, these typically start at 0, and go up
722 one for each device, i.e., the first bonding instance is bond0, the
723 second is bond1, and so on.
725 Next, create a bond network script. The file name for this
726 script will be /etc/sysconfig/network-scripts/ifcfg-bondX where X is
727 the number of the bond. For bond0 the file is named "ifcfg-bond0",
728 for bond1 it is named "ifcfg-bond1", and so on. Within that file,
729 place the following text:
733 NETMASK=255.255.255.0
735 BROADCAST=192.168.1.255
740 Be sure to change the networking specific lines (IPADDR,
741 NETMASK, NETWORK and BROADCAST) to match your network configuration.
743 Finally, it is necessary to edit /etc/modules.conf (or
744 /etc/modprobe.conf, depending upon your distro) to load the bonding
745 module with your desired options when the bond0 interface is brought
746 up. The following lines in /etc/modules.conf (or modprobe.conf) will
747 load the bonding module, and select its options:
750 options bond0 mode=balance-alb miimon=100
752 Replace the sample parameters with the appropriate set of
753 options for your configuration.
755 Finally run "/etc/rc.d/init.d/network restart" as root. This
756 will restart the networking subsystem and your bond link should be now
759 3.2.1 Using DHCP with initscripts
760 ---------------------------------
762 Recent versions of initscripts (the version supplied with
763 Fedora Core 3 and Red Hat Enterprise Linux 4 is reported to work) do
764 have support for assigning IP information to bonding devices via DHCP.
766 To configure bonding for DHCP, configure it as described
767 above, except replace the line "BOOTPROTO=none" with "BOOTPROTO=dhcp"
768 and add a line consisting of "TYPE=Bonding". Note that the TYPE value
771 3.2.2 Configuring Multiple Bonds with initscripts
772 -------------------------------------------------
774 At this writing, the initscripts package does not directly
775 support loading the bonding driver multiple times, so the process for
776 doing so is the same as described in the "Configuring Multiple Bonds
777 Manually" section, below.
779 NOTE: It has been observed that some Red Hat supplied kernels
780 are apparently unable to rename modules at load time (the "-o bond1"
781 part). Attempts to pass that option to modprobe will produce an
782 "Operation not permitted" error. This has been reported on some
783 Fedora Core kernels, and has been seen on RHEL 4 as well. On kernels
784 exhibiting this problem, it will be impossible to configure multiple
785 bonds with differing parameters.
787 3.3 Configuring Bonding Manually
788 --------------------------------
790 This section applies to distros whose network initialization
791 scripts (the sysconfig or initscripts package) do not have specific
792 knowledge of bonding. One such distro is SuSE Linux Enterprise Server
795 The general method for these systems is to place the bonding
796 module parameters into /etc/modules.conf or /etc/modprobe.conf (as
797 appropriate for the installed distro), then add modprobe and/or
798 ifenslave commands to the system's global init script. The name of
799 the global init script differs; for sysconfig, it is
800 /etc/init.d/boot.local and for initscripts it is /etc/rc.d/rc.local.
802 For example, if you wanted to make a simple bond of two e100
803 devices (presumed to be eth0 and eth1), and have it persist across
804 reboots, edit the appropriate file (/etc/init.d/boot.local or
805 /etc/rc.d/rc.local), and add the following:
807 modprobe bonding mode=balance-alb miimon=100
809 ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
813 Replace the example bonding module parameters and bond0
814 network configuration (IP address, netmask, etc) with the appropriate
815 values for your configuration.
817 Unfortunately, this method will not provide support for the
818 ifup and ifdown scripts on the bond devices. To reload the bonding
819 configuration, it is necessary to run the initialization script, e.g.,
821 # /etc/init.d/boot.local
827 It may be desirable in such a case to create a separate script
828 which only initializes the bonding configuration, then call that
829 separate script from within boot.local. This allows for bonding to be
830 enabled without re-running the entire global init script.
832 To shut down the bonding devices, it is necessary to first
833 mark the bonding device itself as being down, then remove the
834 appropriate device driver modules. For our example above, you can do
837 # ifconfig bond0 down
841 Again, for convenience, it may be desirable to create a script
845 3.3.1 Configuring Multiple Bonds Manually
846 -----------------------------------------
848 This section contains information on configuring multiple
849 bonding devices with differing options for those systems whose network
850 initialization scripts lack support for configuring multiple bonds.
852 If you require multiple bonding devices, but all with the same
853 options, you may wish to use the "max_bonds" module parameter,
856 To create multiple bonding devices with differing options, it
857 is necessary to load the bonding driver multiple times. Note that
858 current versions of the sysconfig network initialization scripts
859 handle this automatically; if your distro uses these scripts, no
860 special action is needed. See the section Configuring Bonding
861 Devices, above, if you're not sure about your network initialization
864 To load multiple instances of the module, it is necessary to
865 specify a different name for each instance (the module loading system
866 requires that every loaded module, even multiple instances of the same
867 module, have a unique name). This is accomplished by supplying
868 multiple sets of bonding options in /etc/modprobe.conf, for example:
871 options bond0 -o bond0 mode=balance-rr miimon=100
874 options bond1 -o bond1 mode=balance-alb miimon=50
876 will load the bonding module two times. The first instance is
877 named "bond0" and creates the bond0 device in balance-rr mode with an
878 miimon of 100. The second instance is named "bond1" and creates the
879 bond1 device in balance-alb mode with an miimon of 50.
881 In some circumstances (typically with older distributions),
882 the above does not work, and the second bonding instance never sees
883 its options. In that case, the second options line can be substituted
886 install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \
887 mode=balance-alb miimon=50
889 This may be repeated any number of times, specifying a new and
890 unique name in place of bond1 for each subsequent instance.
893 5. Querying Bonding Configuration
894 =================================
896 5.1 Bonding Configuration
897 -------------------------
899 Each bonding device has a read-only file residing in the
900 /proc/net/bonding directory. The file contents include information
901 about the bonding configuration, options and state of each slave.
903 For example, the contents of /proc/net/bonding/bond0 after the
904 driver is loaded with parameters of mode=0 and miimon=1000 is
905 generally as follows:
907 Ethernet Channel Bonding Driver: 2.6.1 (October 29, 2004)
908 Bonding Mode: load balancing (round-robin)
909 Currently Active Slave: eth0
911 MII Polling Interval (ms): 1000
915 Slave Interface: eth1
917 Link Failure Count: 1
919 Slave Interface: eth0
921 Link Failure Count: 1
923 The precise format and contents will change depending upon the
924 bonding configuration, state, and version of the bonding driver.
926 5.2 Network configuration
927 -------------------------
929 The network configuration can be inspected using the ifconfig
930 command. Bonding devices will have the MASTER flag set; Bonding slave
931 devices will have the SLAVE flag set. The ifconfig output does not
932 contain information on which slaves are associated with which masters.
934 In the example below, the bond0 interface is the master
935 (MASTER) while eth0 and eth1 are slaves (SLAVE). Notice all slaves of
936 bond0 have the same MAC address (HWaddr) as bond0 for all modes except
937 TLB and ALB that require a unique MAC address for each slave.
940 bond0 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4
941 inet addr:XXX.XXX.XXX.YYY Bcast:XXX.XXX.XXX.255 Mask:255.255.252.0
942 UP BROADCAST RUNNING MASTER MULTICAST MTU:1500 Metric:1
943 RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0
944 TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0
945 collisions:0 txqueuelen:0
947 eth0 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4
948 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1
949 RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0
950 TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0
951 collisions:0 txqueuelen:100
952 Interrupt:10 Base address:0x1080
954 eth1 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4
955 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1
956 RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0
957 TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0
958 collisions:0 txqueuelen:100
959 Interrupt:9 Base address:0x1400
961 6. Switch Configuration
962 =======================
964 For this section, "switch" refers to whatever system the
965 bonded devices are directly connected to (i.e., where the other end of
966 the cable plugs into). This may be an actual dedicated switch device,
967 or it may be another regular system (e.g., another computer running
970 The active-backup, balance-tlb and balance-alb modes do not
971 require any specific configuration of the switch.
973 The 802.3ad mode requires that the switch have the appropriate
974 ports configured as an 802.3ad aggregation. The precise method used
975 to configure this varies from switch to switch, but, for example, a
976 Cisco 3550 series switch requires that the appropriate ports first be
977 grouped together in a single etherchannel instance, then that
978 etherchannel is set to mode "lacp" to enable 802.3ad (instead of
979 standard EtherChannel).
981 The balance-rr, balance-xor and broadcast modes generally
982 require that the switch have the appropriate ports grouped together.
983 The nomenclature for such a group differs between switches, it may be
984 called an "etherchannel" (as in the Cisco example, above), a "trunk
985 group" or some other similar variation. For these modes, each switch
986 will also have its own configuration options for the switch's transmit
987 policy to the bond. Typical choices include XOR of either the MAC or
988 IP addresses. The transmit policy of the two peers does not need to
989 match. For these three modes, the bonding mode really selects a
990 transmit policy for an EtherChannel group; all three will interoperate
991 with another EtherChannel group.
994 7. 802.1q VLAN Support
995 ======================
997 It is possible to configure VLAN devices over a bond interface
998 using the 8021q driver. However, only packets coming from the 8021q
999 driver and passing through bonding will be tagged by default. Self
1000 generated packets, for example, bonding's learning packets or ARP
1001 packets generated by either ALB mode or the ARP monitor mechanism, are
1002 tagged internally by bonding itself. As a result, bonding must
1003 "learn" the VLAN IDs configured above it, and use those IDs to tag
1004 self generated packets.
1006 For reasons of simplicity, and to support the use of adapters
1007 that can do VLAN hardware acceleration offloading, the bonding
1008 interface declares itself as fully hardware offloading capable, it gets
1009 the add_vid/kill_vid notifications to gather the necessary
1010 information, and it propagates those actions to the slaves. In case
1011 of mixed adapter types, hardware accelerated tagged packets that
1012 should go through an adapter that is not offloading capable are
1013 "un-accelerated" by the bonding driver so the VLAN tag sits in the
1016 VLAN interfaces *must* be added on top of a bonding interface
1017 only after enslaving at least one slave. The bonding interface has a
1018 hardware address of 00:00:00:00:00:00 until the first slave is added.
1019 If the VLAN interface is created prior to the first enslavement, it
1020 would pick up the all-zeroes hardware address. Once the first slave
1021 is attached to the bond, the bond device itself will pick up the
1022 slave's hardware address, which is then available for the VLAN device.
1024 Also, be aware that a similar problem can occur if all slaves
1025 are released from a bond that still has one or more VLAN interfaces on
1026 top of it. When a new slave is added, the bonding interface will
1027 obtain its hardware address from the first slave, which might not
1028 match the hardware address of the VLAN interfaces (which was
1029 ultimately copied from an earlier slave).
1031 There are two methods to insure that the VLAN device operates
1032 with the correct hardware address if all slaves are removed from a
1035 1. Remove all VLAN interfaces then recreate them
1037 2. Set the bonding interface's hardware address so that it
1038 matches the hardware address of the VLAN interfaces.
1040 Note that changing a VLAN interface's HW address would set the
1041 underlying device -- i.e. the bonding interface -- to promiscuous
1042 mode, which might not be what you want.
1048 The bonding driver at present supports two schemes for
1049 monitoring a slave device's link state: the ARP monitor and the MII
1052 At the present time, due to implementation restrictions in the
1053 bonding driver itself, it is not possible to enable both ARP and MII
1054 monitoring simultaneously.
1056 8.1 ARP Monitor Operation
1057 -------------------------
1059 The ARP monitor operates as its name suggests: it sends ARP
1060 queries to one or more designated peer systems on the network, and
1061 uses the response as an indication that the link is operating. This
1062 gives some assurance that traffic is actually flowing to and from one
1063 or more peers on the local network.
1065 The ARP monitor relies on the device driver itself to verify
1066 that traffic is flowing. In particular, the driver must keep up to
1067 date the last receive time, dev->last_rx, and transmit start time,
1068 dev->trans_start. If these are not updated by the driver, then the
1069 ARP monitor will immediately fail any slaves using that driver, and
1070 those slaves will stay down. If networking monitoring (tcpdump, etc)
1071 shows the ARP requests and replies on the network, then it may be that
1072 your device driver is not updating last_rx and trans_start.
1074 8.2 Configuring Multiple ARP Targets
1075 ------------------------------------
1077 While ARP monitoring can be done with just one target, it can
1078 be useful in a High Availability setup to have several targets to
1079 monitor. In the case of just one target, the target itself may go
1080 down or have a problem making it unresponsive to ARP requests. Having
1081 an additional target (or several) increases the reliability of the ARP
1084 Multiple ARP targets must be separated by commas as follows:
1086 # example options for ARP monitoring with three targets
1088 options bond0 arp_interval=60 arp_ip_target=192.168.0.1,192.168.0.3,192.168.0.9
1090 For just a single target the options would resemble:
1092 # example options for ARP monitoring with one target
1094 options bond0 arp_interval=60 arp_ip_target=192.168.0.100
1097 8.3 MII Monitor Operation
1098 -------------------------
1100 The MII monitor monitors only the carrier state of the local
1101 network interface. It accomplishes this in one of three ways: by
1102 depending upon the device driver to maintain its carrier state, by
1103 querying the device's MII registers, or by making an ethtool query to
1106 If the use_carrier module parameter is 1 (the default value),
1107 then the MII monitor will rely on the driver for carrier state
1108 information (via the netif_carrier subsystem). As explained in the
1109 use_carrier parameter information, above, if the MII monitor fails to
1110 detect carrier loss on the device (e.g., when the cable is physically
1111 disconnected), it may be that the driver does not support
1114 If use_carrier is 0, then the MII monitor will first query the
1115 device's (via ioctl) MII registers and check the link state. If that
1116 request fails (not just that it returns carrier down), then the MII
1117 monitor will make an ethtool ETHOOL_GLINK request to attempt to obtain
1118 the same information. If both methods fail (i.e., the driver either
1119 does not support or had some error in processing both the MII register
1120 and ethtool requests), then the MII monitor will assume the link is
1123 9. Potential Sources of Trouble
1124 ===============================
1126 9.1 Adventures in Routing
1127 -------------------------
1129 When bonding is configured, it is important that the slave
1130 devices not have routes that supercede routes of the master (or,
1131 generally, not have routes at all). For example, suppose the bonding
1132 device bond0 has two slaves, eth0 and eth1, and the routing table is
1135 Kernel IP routing table
1136 Destination Gateway Genmask Flags MSS Window irtt Iface
1137 10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 eth0
1138 10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 eth1
1139 10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 bond0
1140 127.0.0.0 0.0.0.0 255.0.0.0 U 40 0 0 lo
1142 This routing configuration will likely still update the
1143 receive/transmit times in the driver (needed by the ARP monitor), but
1144 may bypass the bonding driver (because outgoing traffic to, in this
1145 case, another host on network 10 would use eth0 or eth1 before bond0).
1147 The ARP monitor (and ARP itself) may become confused by this
1148 configuration, because ARP requests (generated by the ARP monitor)
1149 will be sent on one interface (bond0), but the corresponding reply
1150 will arrive on a different interface (eth0). This reply looks to ARP
1151 as an unsolicited ARP reply (because ARP matches replies on an
1152 interface basis), and is discarded. The MII monitor is not affected
1153 by the state of the routing table.
1155 The solution here is simply to insure that slaves do not have
1156 routes of their own, and if for some reason they must, those routes do
1157 not supercede routes of their master. This should generally be the
1158 case, but unusual configurations or errant manual or automatic static
1159 route additions may cause trouble.
1161 9.2 Ethernet Device Renaming
1162 ----------------------------
1164 On systems with network configuration scripts that do not
1165 associate physical devices directly with network interface names (so
1166 that the same physical device always has the same "ethX" name), it may
1167 be necessary to add some special logic to either /etc/modules.conf or
1168 /etc/modprobe.conf (depending upon which is installed on the system).
1170 For example, given a modules.conf containing the following:
1173 options bond0 mode=some-mode miimon=50
1179 If neither eth0 and eth1 are slaves to bond0, then when the
1180 bond0 interface comes up, the devices may end up reordered. This
1181 happens because bonding is loaded first, then its slave device's
1182 drivers are loaded next. Since no other drivers have been loaded,
1183 when the e1000 driver loads, it will receive eth0 and eth1 for its
1184 devices, but the bonding configuration tries to enslave eth2 and eth3
1185 (which may later be assigned to the tg3 devices).
1187 Adding the following:
1189 add above bonding e1000 tg3
1191 causes modprobe to load e1000 then tg3, in that order, when
1192 bonding is loaded. This command is fully documented in the
1193 modules.conf manual page.
1195 On systems utilizing modprobe.conf (or modprobe.conf.local),
1196 an equivalent problem can occur. In this case, the following can be
1197 added to modprobe.conf (or modprobe.conf.local, as appropriate), as
1198 follows (all on one line; it has been split here for clarity):
1200 install bonding /sbin/modprobe tg3; /sbin/modprobe e1000;
1201 /sbin/modprobe --ignore-install bonding
1203 This will, when loading the bonding module, rather than
1204 performing the normal action, instead execute the provided command.
1205 This command loads the device drivers in the order needed, then calls
1206 modprobe with --ignore-install to cause the normal action to then take
1207 place. Full documentation on this can be found in the modprobe.conf
1208 and modprobe manual pages.
1210 9.3. Painfully Slow Or No Failed Link Detection By Miimon
1211 ---------------------------------------------------------
1213 By default, bonding enables the use_carrier option, which
1214 instructs bonding to trust the driver to maintain carrier state.
1216 As discussed in the options section, above, some drivers do
1217 not support the netif_carrier_on/_off link state tracking system.
1218 With use_carrier enabled, bonding will always see these links as up,
1219 regardless of their actual state.
1221 Additionally, other drivers do support netif_carrier, but do
1222 not maintain it in real time, e.g., only polling the link state at
1223 some fixed interval. In this case, miimon will detect failures, but
1224 only after some long period of time has expired. If it appears that
1225 miimon is very slow in detecting link failures, try specifying
1226 use_carrier=0 to see if that improves the failure detection time. If
1227 it does, then it may be that the driver checks the carrier state at a
1228 fixed interval, but does not cache the MII register values (so the
1229 use_carrier=0 method of querying the registers directly works). If
1230 use_carrier=0 does not improve the failover, then the driver may cache
1231 the registers, or the problem may be elsewhere.
1233 Also, remember that miimon only checks for the device's
1234 carrier state. It has no way to determine the state of devices on or
1235 beyond other ports of a switch, or if a switch is refusing to pass
1236 traffic while still maintaining carrier on.
1241 If running SNMP agents, the bonding driver should be loaded
1242 before any network drivers participating in a bond. This requirement
1243 is due to the interface index (ipAdEntIfIndex) being associated to
1244 the first interface found with a given IP address. That is, there is
1245 only one ipAdEntIfIndex for each IP address. For example, if eth0 and
1246 eth1 are slaves of bond0 and the driver for eth0 is loaded before the
1247 bonding driver, the interface for the IP address will be associated
1248 with the eth0 interface. This configuration is shown below, the IP
1249 address 192.168.1.1 has an interface index of 2 which indexes to eth0
1250 in the ifDescr table (ifDescr.2).
1252 interfaces.ifTable.ifEntry.ifDescr.1 = lo
1253 interfaces.ifTable.ifEntry.ifDescr.2 = eth0
1254 interfaces.ifTable.ifEntry.ifDescr.3 = eth1
1255 interfaces.ifTable.ifEntry.ifDescr.4 = eth2
1256 interfaces.ifTable.ifEntry.ifDescr.5 = eth3
1257 interfaces.ifTable.ifEntry.ifDescr.6 = bond0
1258 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 5
1259 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
1260 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 4
1261 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
1263 This problem is avoided by loading the bonding driver before
1264 any network drivers participating in a bond. Below is an example of
1265 loading the bonding driver first, the IP address 192.168.1.1 is
1266 correctly associated with ifDescr.2.
1268 interfaces.ifTable.ifEntry.ifDescr.1 = lo
1269 interfaces.ifTable.ifEntry.ifDescr.2 = bond0
1270 interfaces.ifTable.ifEntry.ifDescr.3 = eth0
1271 interfaces.ifTable.ifEntry.ifDescr.4 = eth1
1272 interfaces.ifTable.ifEntry.ifDescr.5 = eth2
1273 interfaces.ifTable.ifEntry.ifDescr.6 = eth3
1274 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 6
1275 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
1276 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 5
1277 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
1279 While some distributions may not report the interface name in
1280 ifDescr, the association between the IP address and IfIndex remains
1281 and SNMP functions such as Interface_Scan_Next will report that
1284 11. Promiscuous mode
1285 ====================
1287 When running network monitoring tools, e.g., tcpdump, it is
1288 common to enable promiscuous mode on the device, so that all traffic
1289 is seen (instead of seeing only traffic destined for the local host).
1290 The bonding driver handles promiscuous mode changes to the bonding
1291 master device (e.g., bond0), and propagates the setting to the slave
1294 For the balance-rr, balance-xor, broadcast, and 802.3ad modes,
1295 the promiscuous mode setting is propagated to all slaves.
1297 For the active-backup, balance-tlb and balance-alb modes, the
1298 promiscuous mode setting is propagated only to the active slave.
1300 For balance-tlb mode, the active slave is the slave currently
1301 receiving inbound traffic.
1303 For balance-alb mode, the active slave is the slave used as a
1304 "primary." This slave is used for mode-specific control traffic, for
1305 sending to peers that are unassigned or if the load is unbalanced.
1307 For the active-backup, balance-tlb and balance-alb modes, when
1308 the active slave changes (e.g., due to a link failure), the
1309 promiscuous setting will be propagated to the new active slave.
1311 12. Configuring Bonding for High Availability
1312 =============================================
1314 High Availability refers to configurations that provide
1315 maximum network availability by having redundant or backup devices,
1316 links or switches between the host and the rest of the world. The
1317 goal is to provide the maximum availability of network connectivity
1318 (i.e., the network always works), even though other configurations
1319 could provide higher throughput.
1321 12.1 High Availability in a Single Switch Topology
1322 --------------------------------------------------
1324 If two hosts (or a host and a single switch) are directly
1325 connected via multiple physical links, then there is no availability
1326 penalty to optimizing for maximum bandwidth. In this case, there is
1327 only one switch (or peer), so if it fails, there is no alternative
1328 access to fail over to. Additionally, the bonding load balance modes
1329 support link monitoring of their members, so if individual links fail,
1330 the load will be rebalanced across the remaining devices.
1332 See Section 13, "Configuring Bonding for Maximum Throughput"
1333 for information on configuring bonding with one peer device.
1335 12.2 High Availability in a Multiple Switch Topology
1336 ----------------------------------------------------
1338 With multiple switches, the configuration of bonding and the
1339 network changes dramatically. In multiple switch topologies, there is
1340 a trade off between network availability and usable bandwidth.
1342 Below is a sample network, configured to maximize the
1343 availability of the network:
1347 +-----+----+ +-----+----+
1348 | |port2 ISL port2| |
1349 | switch A +--------------------------+ switch B |
1351 +-----+----+ +-----++---+
1354 +-------------+ host1 +---------------+
1357 In this configuration, there is a link between the two
1358 switches (ISL, or inter switch link), and multiple ports connecting to
1359 the outside world ("port3" on each switch). There is no technical
1360 reason that this could not be extended to a third switch.
1362 12.2.1 HA Bonding Mode Selection for Multiple Switch Topology
1363 -------------------------------------------------------------
1365 In a topology such as the example above, the active-backup and
1366 broadcast modes are the only useful bonding modes when optimizing for
1367 availability; the other modes require all links to terminate on the
1368 same peer for them to behave rationally.
1370 active-backup: This is generally the preferred mode, particularly if
1371 the switches have an ISL and play together well. If the
1372 network configuration is such that one switch is specifically
1373 a backup switch (e.g., has lower capacity, higher cost, etc),
1374 then the primary option can be used to insure that the
1375 preferred link is always used when it is available.
1377 broadcast: This mode is really a special purpose mode, and is suitable
1378 only for very specific needs. For example, if the two
1379 switches are not connected (no ISL), and the networks beyond
1380 them are totally independent. In this case, if it is
1381 necessary for some specific one-way traffic to reach both
1382 independent networks, then the broadcast mode may be suitable.
1384 12.2.2 HA Link Monitoring Selection for Multiple Switch Topology
1385 ----------------------------------------------------------------
1387 The choice of link monitoring ultimately depends upon your
1388 switch. If the switch can reliably fail ports in response to other
1389 failures, then either the MII or ARP monitors should work. For
1390 example, in the above example, if the "port3" link fails at the remote
1391 end, the MII monitor has no direct means to detect this. The ARP
1392 monitor could be configured with a target at the remote end of port3,
1393 thus detecting that failure without switch support.
1395 In general, however, in a multiple switch topology, the ARP
1396 monitor can provide a higher level of reliability in detecting end to
1397 end connectivity failures (which may be caused by the failure of any
1398 individual component to pass traffic for any reason). Additionally,
1399 the ARP monitor should be configured with multiple targets (at least
1400 one for each switch in the network). This will insure that,
1401 regardless of which switch is active, the ARP monitor has a suitable
1405 13. Configuring Bonding for Maximum Throughput
1406 ==============================================
1408 13.1 Maximizing Throughput in a Single Switch Topology
1409 ------------------------------------------------------
1411 In a single switch configuration, the best method to maximize
1412 throughput depends upon the application and network environment. The
1413 various load balancing modes each have strengths and weaknesses in
1414 different environments, as detailed below.
1416 For this discussion, we will break down the topologies into
1417 two categories. Depending upon the destination of most traffic, we
1418 categorize them into either "gatewayed" or "local" configurations.
1420 In a gatewayed configuration, the "switch" is acting primarily
1421 as a router, and the majority of traffic passes through this router to
1422 other networks. An example would be the following:
1425 +----------+ +----------+
1426 | |eth0 port1| | to other networks
1427 | Host A +---------------------+ router +------------------->
1428 | +---------------------+ | Hosts B and C are out
1429 | |eth1 port2| | here somewhere
1430 +----------+ +----------+
1432 The router may be a dedicated router device, or another host
1433 acting as a gateway. For our discussion, the important point is that
1434 the majority of traffic from Host A will pass through the router to
1435 some other network before reaching its final destination.
1437 In a gatewayed network configuration, although Host A may
1438 communicate with many other systems, all of its traffic will be sent
1439 and received via one other peer on the local network, the router.
1441 Note that the case of two systems connected directly via
1442 multiple physical links is, for purposes of configuring bonding, the
1443 same as a gatewayed configuration. In that case, it happens that all
1444 traffic is destined for the "gateway" itself, not some other network
1447 In a local configuration, the "switch" is acting primarily as
1448 a switch, and the majority of traffic passes through this switch to
1449 reach other stations on the same network. An example would be the
1452 +----------+ +----------+ +--------+
1453 | |eth0 port1| +-------+ Host B |
1454 | Host A +------------+ switch |port3 +--------+
1455 | +------------+ | +--------+
1456 | |eth1 port2| +------------------+ Host C |
1457 +----------+ +----------+port4 +--------+
1460 Again, the switch may be a dedicated switch device, or another
1461 host acting as a gateway. For our discussion, the important point is
1462 that the majority of traffic from Host A is destined for other hosts
1463 on the same local network (Hosts B and C in the above example).
1465 In summary, in a gatewayed configuration, traffic to and from
1466 the bonded device will be to the same MAC level peer on the network
1467 (the gateway itself, i.e., the router), regardless of its final
1468 destination. In a local configuration, traffic flows directly to and
1469 from the final destinations, thus, each destination (Host B, Host C)
1470 will be addressed directly by their individual MAC addresses.
1472 This distinction between a gatewayed and a local network
1473 configuration is important because many of the load balancing modes
1474 available use the MAC addresses of the local network source and
1475 destination to make load balancing decisions. The behavior of each
1476 mode is described below.
1479 13.1.1 MT Bonding Mode Selection for Single Switch Topology
1480 -----------------------------------------------------------
1482 This configuration is the easiest to set up and to understand,
1483 although you will have to decide which bonding mode best suits your
1484 needs. The trade offs for each mode are detailed below:
1486 balance-rr: This mode is the only mode that will permit a single
1487 TCP/IP connection to stripe traffic across multiple
1488 interfaces. It is therefore the only mode that will allow a
1489 single TCP/IP stream to utilize more than one interface's
1490 worth of throughput. This comes at a cost, however: the
1491 striping often results in peer systems receiving packets out
1492 of order, causing TCP/IP's congestion control system to kick
1493 in, often by retransmitting segments.
1495 It is possible to adjust TCP/IP's congestion limits by
1496 altering the net.ipv4.tcp_reordering sysctl parameter. The
1497 usual default value is 3, and the maximum useful value is 127.
1498 For a four interface balance-rr bond, expect that a single
1499 TCP/IP stream will utilize no more than approximately 2.3
1500 interface's worth of throughput, even after adjusting
1503 Note that this out of order delivery occurs when both the
1504 sending and receiving systems are utilizing a multiple
1505 interface bond. Consider a configuration in which a
1506 balance-rr bond feeds into a single higher capacity network
1507 channel (e.g., multiple 100Mb/sec ethernets feeding a single
1508 gigabit ethernet via an etherchannel capable switch). In this
1509 configuration, traffic sent from the multiple 100Mb devices to
1510 a destination connected to the gigabit device will not see
1511 packets out of order. However, traffic sent from the gigabit
1512 device to the multiple 100Mb devices may or may not see
1513 traffic out of order, depending upon the balance policy of the
1514 switch. Many switches do not support any modes that stripe
1515 traffic (instead choosing a port based upon IP or MAC level
1516 addresses); for those devices, traffic flowing from the
1517 gigabit device to the many 100Mb devices will only utilize one
1520 If you are utilizing protocols other than TCP/IP, UDP for
1521 example, and your application can tolerate out of order
1522 delivery, then this mode can allow for single stream datagram
1523 performance that scales near linearly as interfaces are added
1526 This mode requires the switch to have the appropriate ports
1527 configured for "etherchannel" or "trunking."
1529 active-backup: There is not much advantage in this network topology to
1530 the active-backup mode, as the inactive backup devices are all
1531 connected to the same peer as the primary. In this case, a
1532 load balancing mode (with link monitoring) will provide the
1533 same level of network availability, but with increased
1534 available bandwidth. On the plus side, active-backup mode
1535 does not require any configuration of the switch, so it may
1536 have value if the hardware available does not support any of
1537 the load balance modes.
1539 balance-xor: This mode will limit traffic such that packets destined
1540 for specific peers will always be sent over the same
1541 interface. Since the destination is determined by the MAC
1542 addresses involved, this mode works best in a "local" network
1543 configuration (as described above), with destinations all on
1544 the same local network. This mode is likely to be suboptimal
1545 if all your traffic is passed through a single router (i.e., a
1546 "gatewayed" network configuration, as described above).
1548 As with balance-rr, the switch ports need to be configured for
1549 "etherchannel" or "trunking."
1551 broadcast: Like active-backup, there is not much advantage to this
1552 mode in this type of network topology.
1554 802.3ad: This mode can be a good choice for this type of network
1555 topology. The 802.3ad mode is an IEEE standard, so all peers
1556 that implement 802.3ad should interoperate well. The 802.3ad
1557 protocol includes automatic configuration of the aggregates,
1558 so minimal manual configuration of the switch is needed
1559 (typically only to designate that some set of devices is
1560 available for 802.3ad). The 802.3ad standard also mandates
1561 that frames be delivered in order (within certain limits), so
1562 in general single connections will not see misordering of
1563 packets. The 802.3ad mode does have some drawbacks: the
1564 standard mandates that all devices in the aggregate operate at
1565 the same speed and duplex. Also, as with all bonding load
1566 balance modes other than balance-rr, no single connection will
1567 be able to utilize more than a single interface's worth of
1570 Additionally, the linux bonding 802.3ad implementation
1571 distributes traffic by peer (using an XOR of MAC addresses),
1572 so in a "gatewayed" configuration, all outgoing traffic will
1573 generally use the same device. Incoming traffic may also end
1574 up on a single device, but that is dependent upon the
1575 balancing policy of the peer's 8023.ad implementation. In a
1576 "local" configuration, traffic will be distributed across the
1577 devices in the bond.
1579 Finally, the 802.3ad mode mandates the use of the MII monitor,
1580 therefore, the ARP monitor is not available in this mode.
1582 balance-tlb: The balance-tlb mode balances outgoing traffic by peer.
1583 Since the balancing is done according to MAC address, in a
1584 "gatewayed" configuration (as described above), this mode will
1585 send all traffic across a single device. However, in a
1586 "local" network configuration, this mode balances multiple
1587 local network peers across devices in a vaguely intelligent
1588 manner (not a simple XOR as in balance-xor or 802.3ad mode),
1589 so that mathematically unlucky MAC addresses (i.e., ones that
1590 XOR to the same value) will not all "bunch up" on a single
1593 Unlike 802.3ad, interfaces may be of differing speeds, and no
1594 special switch configuration is required. On the down side,
1595 in this mode all incoming traffic arrives over a single
1596 interface, this mode requires certain ethtool support in the
1597 network device driver of the slave interfaces, and the ARP
1598 monitor is not available.
1600 balance-alb: This mode is everything that balance-tlb is, and more.
1601 It has all of the features (and restrictions) of balance-tlb,
1602 and will also balance incoming traffic from local network
1603 peers (as described in the Bonding Module Options section,
1606 The only additional down side to this mode is that the network
1607 device driver must support changing the hardware address while
1610 13.1.2 MT Link Monitoring for Single Switch Topology
1611 ----------------------------------------------------
1613 The choice of link monitoring may largely depend upon which
1614 mode you choose to use. The more advanced load balancing modes do not
1615 support the use of the ARP monitor, and are thus restricted to using
1616 the MII monitor (which does not provide as high a level of end to end
1617 assurance as the ARP monitor).
1619 13.2 Maximum Throughput in a Multiple Switch Topology
1620 -----------------------------------------------------
1622 Multiple switches may be utilized to optimize for throughput
1623 when they are configured in parallel as part of an isolated network
1624 between two or more systems, for example:
1630 +--------+ | +---------+
1632 +------+---+ +-----+----+ +-----+----+
1633 | Switch A | | Switch B | | Switch C |
1634 +------+---+ +-----+----+ +-----+----+
1636 +--------+ | +---------+
1642 In this configuration, the switches are isolated from one
1643 another. One reason to employ a topology such as this is for an
1644 isolated network with many hosts (a cluster configured for high
1645 performance, for example), using multiple smaller switches can be more
1646 cost effective than a single larger switch, e.g., on a network with 24
1647 hosts, three 24 port switches can be significantly less expensive than
1648 a single 72 port switch.
1650 If access beyond the network is required, an individual host
1651 can be equipped with an additional network device connected to an
1652 external network; this host then additionally acts as a gateway.
1654 13.2.1 MT Bonding Mode Selection for Multiple Switch Topology
1655 -------------------------------------------------------------
1657 In actual practice, the bonding mode typically employed in
1658 configurations of this type is balance-rr. Historically, in this
1659 network configuration, the usual caveats about out of order packet
1660 delivery are mitigated by the use of network adapters that do not do
1661 any kind of packet coalescing (via the use of NAPI, or because the
1662 device itself does not generate interrupts until some number of
1663 packets has arrived). When employed in this fashion, the balance-rr
1664 mode allows individual connections between two hosts to effectively
1665 utilize greater than one interface's bandwidth.
1667 13.2.2 MT Link Monitoring for Multiple Switch Topology
1668 ------------------------------------------------------
1670 Again, in actual practice, the MII monitor is most often used
1671 in this configuration, as performance is given preference over
1672 availability. The ARP monitor will function in this topology, but its
1673 advantages over the MII monitor are mitigated by the volume of probes
1674 needed as the number of systems involved grows (remember that each
1675 host in the network is configured with bonding).
1677 14. Switch Behavior Issues
1678 ==========================
1680 14.1 Link Establishment and Failover Delays
1681 -------------------------------------------
1683 Some switches exhibit undesirable behavior with regard to the
1684 timing of link up and down reporting by the switch.
1686 First, when a link comes up, some switches may indicate that
1687 the link is up (carrier available), but not pass traffic over the
1688 interface for some period of time. This delay is typically due to
1689 some type of autonegotiation or routing protocol, but may also occur
1690 during switch initialization (e.g., during recovery after a switch
1691 failure). If you find this to be a problem, specify an appropriate
1692 value to the updelay bonding module option to delay the use of the
1693 relevant interface(s).
1695 Second, some switches may "bounce" the link state one or more
1696 times while a link is changing state. This occurs most commonly while
1697 the switch is initializing. Again, an appropriate updelay value may
1700 Note that when a bonding interface has no active links, the
1701 driver will immediately reuse the first link that goes up, even if the
1702 updelay parameter has been specified (the updelay is ignored in this
1703 case). If there are slave interfaces waiting for the updelay timeout
1704 to expire, the interface that first went into that state will be
1705 immediately reused. This reduces down time of the network if the
1706 value of updelay has been overestimated, and since this occurs only in
1707 cases with no connectivity, there is no additional penalty for
1708 ignoring the updelay.
1710 In addition to the concerns about switch timings, if your
1711 switches take a long time to go into backup mode, it may be desirable
1712 to not activate a backup interface immediately after a link goes down.
1713 Failover may be delayed via the downdelay bonding module option.
1715 14.2 Duplicated Incoming Packets
1716 --------------------------------
1718 It is not uncommon to observe a short burst of duplicated
1719 traffic when the bonding device is first used, or after it has been
1720 idle for some period of time. This is most easily observed by issuing
1721 a "ping" to some other host on the network, and noticing that the
1722 output from ping flags duplicates (typically one per slave).
1724 For example, on a bond in active-backup mode with five slaves
1725 all connected to one switch, the output may appear as follows:
1728 PING 10.0.4.2 (10.0.4.2) from 10.0.3.10 : 56(84) bytes of data.
1729 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.7 ms
1730 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
1731 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
1732 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
1733 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
1734 64 bytes from 10.0.4.2: icmp_seq=2 ttl=64 time=0.216 ms
1735 64 bytes from 10.0.4.2: icmp_seq=3 ttl=64 time=0.267 ms
1736 64 bytes from 10.0.4.2: icmp_seq=4 ttl=64 time=0.222 ms
1738 This is not due to an error in the bonding driver, rather, it
1739 is a side effect of how many switches update their MAC forwarding
1740 tables. Initially, the switch does not associate the MAC address in
1741 the packet with a particular switch port, and so it may send the
1742 traffic to all ports until its MAC forwarding table is updated. Since
1743 the interfaces attached to the bond may occupy multiple ports on a
1744 single switch, when the switch (temporarily) floods the traffic to all
1745 ports, the bond device receives multiple copies of the same packet
1746 (one per slave device).
1748 The duplicated packet behavior is switch dependent, some
1749 switches exhibit this, and some do not. On switches that display this
1750 behavior, it can be induced by clearing the MAC forwarding table (on
1751 most Cisco switches, the privileged command "clear mac address-table
1752 dynamic" will accomplish this).
1754 15. Hardware Specific Considerations
1755 ====================================
1757 This section contains additional information for configuring
1758 bonding on specific hardware platforms, or for interfacing bonding
1759 with particular switches or other devices.
1761 15.1 IBM BladeCenter
1762 --------------------
1764 This applies to the JS20 and similar systems.
1766 On the JS20 blades, the bonding driver supports only
1767 balance-rr, active-backup, balance-tlb and balance-alb modes. This is
1768 largely due to the network topology inside the BladeCenter, detailed
1771 JS20 network adapter information
1772 --------------------------------
1774 All JS20s come with two Broadcom Gigabit Ethernet ports
1775 integrated on the planar (that's "motherboard" in IBM-speak). In the
1776 BladeCenter chassis, the eth0 port of all JS20 blades is hard wired to
1777 I/O Module #1; similarly, all eth1 ports are wired to I/O Module #2.
1778 An add-on Broadcom daughter card can be installed on a JS20 to provide
1779 two more Gigabit Ethernet ports. These ports, eth2 and eth3, are
1780 wired to I/O Modules 3 and 4, respectively.
1782 Each I/O Module may contain either a switch or a passthrough
1783 module (which allows ports to be directly connected to an external
1784 switch). Some bonding modes require a specific BladeCenter internal
1785 network topology in order to function; these are detailed below.
1787 Additional BladeCenter-specific networking information can be
1788 found in two IBM Redbooks (www.ibm.com/redbooks):
1790 "IBM eServer BladeCenter Networking Options"
1791 "IBM eServer BladeCenter Layer 2-7 Network Switching"
1793 BladeCenter networking configuration
1794 ------------------------------------
1796 Because a BladeCenter can be configured in a very large number
1797 of ways, this discussion will be confined to describing basic
1800 Normally, Ethernet Switch Modules (ESMs) are used in I/O
1801 modules 1 and 2. In this configuration, the eth0 and eth1 ports of a
1802 JS20 will be connected to different internal switches (in the
1803 respective I/O modules).
1805 A passthrough module (OPM or CPM, optical or copper,
1806 passthrough module) connects the I/O module directly to an external
1807 switch. By using PMs in I/O module #1 and #2, the eth0 and eth1
1808 interfaces of a JS20 can be redirected to the outside world and
1809 connected to a common external switch.
1811 Depending upon the mix of ESMs and PMs, the network will
1812 appear to bonding as either a single switch topology (all PMs) or as a
1813 multiple switch topology (one or more ESMs, zero or more PMs). It is
1814 also possible to connect ESMs together, resulting in a configuration
1815 much like the example in "High Availability in a Multiple Switch
1818 Requirements for specific modes
1819 -------------------------------
1821 The balance-rr mode requires the use of passthrough modules
1822 for devices in the bond, all connected to an common external switch.
1823 That switch must be configured for "etherchannel" or "trunking" on the
1824 appropriate ports, as is usual for balance-rr.
1826 The balance-alb and balance-tlb modes will function with
1827 either switch modules or passthrough modules (or a mix). The only
1828 specific requirement for these modes is that all network interfaces
1829 must be able to reach all destinations for traffic sent over the
1830 bonding device (i.e., the network must converge at some point outside
1833 The active-backup mode has no additional requirements.
1835 Link monitoring issues
1836 ----------------------
1838 When an Ethernet Switch Module is in place, only the ARP
1839 monitor will reliably detect link loss to an external switch. This is
1840 nothing unusual, but examination of the BladeCenter cabinet would
1841 suggest that the "external" network ports are the ethernet ports for
1842 the system, when it fact there is a switch between these "external"
1843 ports and the devices on the JS20 system itself. The MII monitor is
1844 only able to detect link failures between the ESM and the JS20 system.
1846 When a passthrough module is in place, the MII monitor does
1847 detect failures to the "external" port, which is then directly
1848 connected to the JS20 system.
1853 The Serial Over LAN (SoL) link is established over the primary
1854 ethernet (eth0) only, therefore, any loss of link to eth0 will result
1855 in losing your SoL connection. It will not fail over with other
1856 network traffic, as the SoL system is beyond the control of the
1859 It may be desirable to disable spanning tree on the switch
1860 (either the internal Ethernet Switch Module, or an external switch) to
1861 avoid fail-over delay issues when using bonding.
1864 16. Frequently Asked Questions
1865 ==============================
1869 Yes. The old 2.0.xx channel bonding patch was not SMP safe.
1870 The new driver was designed to be SMP safe from the start.
1872 2. What type of cards will work with it?
1874 Any Ethernet type cards (you can even mix cards - a Intel
1875 EtherExpress PRO/100 and a 3com 3c905b, for example). For most modes,
1876 devices need not be of the same speed.
1878 3. How many bonding devices can I have?
1882 4. How many slaves can a bonding device have?
1884 This is limited only by the number of network interfaces Linux
1885 supports and/or the number of network cards you can place in your
1888 5. What happens when a slave link dies?
1890 If link monitoring is enabled, then the failing device will be
1891 disabled. The active-backup mode will fail over to a backup link, and
1892 other modes will ignore the failed link. The link will continue to be
1893 monitored, and should it recover, it will rejoin the bond (in whatever
1894 manner is appropriate for the mode). See the sections on High
1895 Availability and the documentation for each mode for additional
1898 Link monitoring can be enabled via either the miimon or
1899 arp_interval parameters (described in the module parameters section,
1900 above). In general, miimon monitors the carrier state as sensed by
1901 the underlying network device, and the arp monitor (arp_interval)
1902 monitors connectivity to another host on the local network.
1904 If no link monitoring is configured, the bonding driver will
1905 be unable to detect link failures, and will assume that all links are
1906 always available. This will likely result in lost packets, and a
1907 resulting degradation of performance. The precise performance loss
1908 depends upon the bonding mode and network configuration.
1910 6. Can bonding be used for High Availability?
1912 Yes. See the section on High Availability for details.
1914 7. Which switches/systems does it work with?
1916 The full answer to this depends upon the desired mode.
1918 In the basic balance modes (balance-rr and balance-xor), it
1919 works with any system that supports etherchannel (also called
1920 trunking). Most managed switches currently available have such
1921 support, and many unmanaged switches as well.
1923 The advanced balance modes (balance-tlb and balance-alb) do
1924 not have special switch requirements, but do need device drivers that
1925 support specific features (described in the appropriate section under
1926 module parameters, above).
1928 In 802.3ad mode, it works with with systems that support IEEE
1929 802.3ad Dynamic Link Aggregation. Most managed and many unmanaged
1930 switches currently available support 802.3ad.
1932 The active-backup mode should work with any Layer-II switch.
1934 8. Where does a bonding device get its MAC address from?
1936 If not explicitly configured (with ifconfig or ip link), the
1937 MAC address of the bonding device is taken from its first slave
1938 device. This MAC address is then passed to all following slaves and
1939 remains persistent (even if the first slave is removed) until the
1940 bonding device is brought down or reconfigured.
1942 If you wish to change the MAC address, you can set it with
1943 ifconfig or ip link:
1945 # ifconfig bond0 hw ether 00:11:22:33:44:55
1947 # ip link set bond0 address 66:77:88:99:aa:bb
1949 The MAC address can be also changed by bringing down/up the
1950 device and then changing its slaves (or their order):
1952 # ifconfig bond0 down ; modprobe -r bonding
1953 # ifconfig bond0 .... up
1954 # ifenslave bond0 eth...
1956 This method will automatically take the address from the next
1957 slave that is added.
1959 To restore your slaves' MAC addresses, you need to detach them
1960 from the bond (`ifenslave -d bond0 eth0'). The bonding driver will
1961 then restore the MAC addresses that the slaves had before they were
1964 16. Resources and Links
1965 =======================
1967 The latest version of the bonding driver can be found in the latest
1968 version of the linux kernel, found on http://kernel.org
1970 The latest version of this document can be found in either the latest
1971 kernel source (named Documentation/networking/bonding.txt), or on the
1972 bonding sourceforge site:
1974 http://www.sourceforge.net/projects/bonding
1976 Discussions regarding the bonding driver take place primarily on the
1977 bonding-devel mailing list, hosted at sourceforge.net. If you have
1978 questions or problems, post them to the list. The list address is:
1980 bonding-devel@lists.sourceforge.net
1982 The administrative interface (to subscribe or unsubscribe) can
1985 https://lists.sourceforge.net/lists/listinfo/bonding-devel
1987 Donald Becker's Ethernet Drivers and diag programs may be found at :
1988 - http://www.scyld.com/network/
1990 You will also find a lot of information regarding Ethernet, NWay, MII,
1991 etc. at www.scyld.com.
git.openpandora.org / pandora-kernel.git / blob