linux/Documentation/networking/bonding.txt
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   1
   2                Linux Ethernet Bonding Driver HOWTO
   3
   4                Latest update: 23 September 2009
   5
   6Initial release : Thomas Davis <tadavis at lbl.gov>
   7Corrections, HA extensions : 2000/10/03-15 :
   8  - Willy Tarreau <willy at meta-x.org>
   9  - Constantine Gavrilov <const-g at xpert.com>
  10  - Chad N. Tindel <ctindel at ieee dot org>
  11  - Janice Girouard <girouard at us dot ibm dot com>
  12  - Jay Vosburgh <fubar at us dot ibm dot com>
  13
  14Reorganized and updated Feb 2005 by Jay Vosburgh
  15Added Sysfs information: 2006/04/24
  16  - Mitch Williams <mitch.a.williams at intel.com>
  17
  18Introduction
  19============
  20
  21        The Linux bonding driver provides a method for aggregating
  22multiple network interfaces into a single logical "bonded" interface.
  23The behavior of the bonded interfaces depends upon the mode; generally
  24speaking, modes provide either hot standby or load balancing services.
  25Additionally, link integrity monitoring may be performed.
  26        
  27        The bonding driver originally came from Donald Becker's
  28beowulf patches for kernel 2.0. It has changed quite a bit since, and
  29the original tools from extreme-linux and beowulf sites will not work
  30with this version of the driver.
  31
  32        For new versions of the driver, updated userspace tools, and
  33who to ask for help, please follow the links at the end of this file.
  34
  35Table of Contents
  36=================
  37
  381. Bonding Driver Installation
  39
  402. Bonding Driver Options
  41
  423. Configuring Bonding Devices
  433.1     Configuration with Sysconfig Support
  443.1.1           Using DHCP with Sysconfig
  453.1.2           Configuring Multiple Bonds with Sysconfig
  463.2     Configuration with Initscripts Support
  473.2.1           Using DHCP with Initscripts
  483.2.2           Configuring Multiple Bonds with Initscripts
  493.3     Configuring Bonding Manually with Ifenslave
  503.3.1           Configuring Multiple Bonds Manually
  513.4     Configuring Bonding Manually via Sysfs
  52
  534. Querying Bonding Configuration
  544.1     Bonding Configuration
  554.2     Network Configuration
  56
  575. Switch Configuration
  58
  596. 802.1q VLAN Support
  60
  617. Link Monitoring
  627.1     ARP Monitor Operation
  637.2     Configuring Multiple ARP Targets
  647.3     MII Monitor Operation
  65
  668. Potential Trouble Sources
  678.1     Adventures in Routing
  688.2     Ethernet Device Renaming
  698.3     Painfully Slow Or No Failed Link Detection By Miimon
  70
  719. SNMP agents
  72
  7310. Promiscuous mode
  74
  7511. Configuring Bonding for High Availability
  7611.1    High Availability in a Single Switch Topology
  7711.2    High Availability in a Multiple Switch Topology
  7811.2.1          HA Bonding Mode Selection for Multiple Switch Topology
  7911.2.2          HA Link Monitoring for Multiple Switch Topology
  80
  8112. Configuring Bonding for Maximum Throughput
  8212.1    Maximum Throughput in a Single Switch Topology
  8312.1.1          MT Bonding Mode Selection for Single Switch Topology
  8412.1.2          MT Link Monitoring for Single Switch Topology
  8512.2    Maximum Throughput in a Multiple Switch Topology
  8612.2.1          MT Bonding Mode Selection for Multiple Switch Topology
  8712.2.2          MT Link Monitoring for Multiple Switch Topology
  88
  8913. Switch Behavior Issues
  9013.1    Link Establishment and Failover Delays
  9113.2    Duplicated Incoming Packets
  92
  9314. Hardware Specific Considerations
  9414.1    IBM BladeCenter
  95
  9615. Frequently Asked Questions
  97
  9816. Resources and Links
  99
 100
 1011. Bonding Driver Installation
 102==============================
 103
 104        Most popular distro kernels ship with the bonding driver
 105already available as a module and the ifenslave user level control
 106program installed and ready for use. If your distro does not, or you
 107have need to compile bonding from source (e.g., configuring and
 108installing a mainline kernel from kernel.org), you'll need to perform
 109the following steps:
 110
 1111.1 Configure and build the kernel with bonding
 112-----------------------------------------------
 113
 114        The current version of the bonding driver is available in the
 115drivers/net/bonding subdirectory of the most recent kernel source
 116(which is available on http://kernel.org).  Most users "rolling their
 117own" will want to use the most recent kernel from kernel.org.
 118
 119        Configure kernel with "make menuconfig" (or "make xconfig" or
 120"make config"), then select "Bonding driver support" in the "Network
 121device support" section.  It is recommended that you configure the
 122driver as module since it is currently the only way to pass parameters
 123to the driver or configure more than one bonding device.
 124
 125        Build and install the new kernel and modules, then continue
 126below to install ifenslave.
 127
 1281.2 Install ifenslave Control Utility
 129-------------------------------------
 130
 131        The ifenslave user level control program is included in the
 132kernel source tree, in the file Documentation/networking/ifenslave.c.
 133It is generally recommended that you use the ifenslave that
 134corresponds to the kernel that you are using (either from the same
 135source tree or supplied with the distro), however, ifenslave
 136executables from older kernels should function (but features newer
 137than the ifenslave release are not supported).  Running an ifenslave
 138that is newer than the kernel is not supported, and may or may not
 139work.
 140
 141        To install ifenslave, do the following:
 142
 143# gcc -Wall -O -I/usr/src/linux/include ifenslave.c -o ifenslave
 144# cp ifenslave /sbin/ifenslave
 145
 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
 148source include directory.
 149
 150        You may wish to back up any existing /sbin/ifenslave, or, for
 151testing or informal use, tag the ifenslave to the kernel version
 152(e.g., name the ifenslave executable /sbin/ifenslave-2.6.10).
 153
 154IMPORTANT NOTE:
 155
 156        If you omit the "-I" or specify an incorrect directory, you
 157may end up with an ifenslave that is incompatible with the kernel
 158you're trying to build it for.  Some distros (e.g., Red Hat from 7.1
 159onwards) do not have /usr/include/linux symbolically linked to the
 160default kernel source include directory.
 161
 162SECOND IMPORTANT NOTE:
 163        If you plan to configure bonding using sysfs, you do not need
 164to use ifenslave.
 165
 1662. Bonding Driver Options
 167=========================
 168
 169        Options for the bonding driver are supplied as parameters to the
 170bonding module at load time, or are specified via sysfs.
 171
 172        Module options may be given as command line arguments to the
 173insmod or modprobe command, but are usually specified in either the
 174/etc/modules.conf or /etc/modprobe.conf configuration file, or in a
 175distro-specific configuration file (some of which are detailed in the next
 176section).
 177
 178        Details on bonding support for sysfs is provided in the
 179"Configuring Bonding Manually via Sysfs" section, below.
 180
 181        The available bonding driver parameters are listed below. If a
 182parameter is not specified the default value is used.  When initially
 183configuring a bond, it is recommended "tail -f /var/log/messages" be
 184run in a separate window to watch for bonding driver error messages.
 185
 186        It is critical that either the miimon or arp_interval and
 187arp_ip_target parameters be specified, otherwise serious network
 188degradation will occur during link failures.  Very few devices do not
 189support at least miimon, so there is really no reason not to use it.
 190
 191        Options with textual values will accept either the text name
 192or, for backwards compatibility, the option value.  E.g.,
 193"mode=802.3ad" and "mode=4" set the same mode.
 194
 195        The parameters are as follows:
 196
 197ad_select
 198
 199        Specifies the 802.3ad aggregation selection logic to use.  The
 200        possible values and their effects are:
 201
 202        stable or 0
 203
 204                The active aggregator is chosen by largest aggregate
 205                bandwidth.
 206
 207                Reselection of the active aggregator occurs only when all
 208                slaves of the active aggregator are down or the active
 209                aggregator has no slaves.
 210
 211                This is the default value.
 212
 213        bandwidth or 1
 214
 215                The active aggregator is chosen by largest aggregate
 216                bandwidth.  Reselection occurs if:
 217
 218                - A slave is added to or removed from the bond
 219
 220                - Any slave's link state changes
 221
 222                - Any slave's 802.3ad association state changes
 223
 224                - The bond's administrative state changes to up
 225
 226        count or 2
 227
 228                The active aggregator is chosen by the largest number of
 229                ports (slaves).  Reselection occurs as described under the
 230                "bandwidth" setting, above.
 231
 232        The bandwidth and count selection policies permit failover of
 233        802.3ad aggregations when partial failure of the active aggregator
 234        occurs.  This keeps the aggregator with the highest availability
 235        (either in bandwidth or in number of ports) active at all times.
 236
 237        This option was added in bonding version 3.4.0.
 238
 239arp_interval
 240
 241        Specifies the ARP link monitoring frequency in milliseconds.
 242
 243        The ARP monitor works by periodically checking the slave
 244        devices to determine whether they have sent or received
 245        traffic recently (the precise criteria depends upon the
 246        bonding mode, and the state of the slave).  Regular traffic is
 247        generated via ARP probes issued for the addresses specified by
 248        the arp_ip_target option.
 249
 250        This behavior can be modified by the arp_validate option,
 251        below.
 252
 253        If ARP monitoring is used in an etherchannel compatible mode
 254        (modes 0 and 2), the switch should be configured in a mode
 255        that evenly distributes packets across all links. If the
 256        switch is configured to distribute the packets in an XOR
 257        fashion, all replies from the ARP targets will be received on
 258        the same link which could cause the other team members to
 259        fail.  ARP monitoring should not be used in conjunction with
 260        miimon.  A value of 0 disables ARP monitoring.  The default
 261        value is 0.
 262
 263arp_ip_target
 264
 265        Specifies the IP addresses to use as ARP monitoring peers when
 266        arp_interval is > 0.  These are the targets of the ARP request
 267        sent to determine the health of the link to the targets.
 268        Specify these values in ddd.ddd.ddd.ddd format.  Multiple IP
 269        addresses must be separated by a comma.  At least one IP
 270        address must be given for ARP monitoring to function.  The
 271        maximum number of targets that can be specified is 16.  The
 272        default value is no IP addresses.
 273
 274arp_validate
 275
 276        Specifies whether or not ARP probes and replies should be
 277        validated in the active-backup mode.  This causes the ARP
 278        monitor to examine the incoming ARP requests and replies, and
 279        only consider a slave to be up if it is receiving the
 280        appropriate ARP traffic.
 281
 282        Possible values are:
 283
 284        none or 0
 285
 286                No validation is performed.  This is the default.
 287
 288        active or 1
 289
 290                Validation is performed only for the active slave.
 291
 292        backup or 2
 293
 294                Validation is performed only for backup slaves.
 295
 296        all or 3
 297
 298                Validation is performed for all slaves.
 299
 300        For the active slave, the validation checks ARP replies to
 301        confirm that they were generated by an arp_ip_target.  Since
 302        backup slaves do not typically receive these replies, the
 303        validation performed for backup slaves is on the ARP request
 304        sent out via the active slave.  It is possible that some
 305        switch or network configurations may result in situations
 306        wherein the backup slaves do not receive the ARP requests; in
 307        such a situation, validation of backup slaves must be
 308        disabled.
 309
 310        This option is useful in network configurations in which
 311        multiple bonding hosts are concurrently issuing ARPs to one or
 312        more targets beyond a common switch.  Should the link between
 313        the switch and target fail (but not the switch itself), the
 314        probe traffic generated by the multiple bonding instances will
 315        fool the standard ARP monitor into considering the links as
 316        still up.  Use of the arp_validate option can resolve this, as
 317        the ARP monitor will only consider ARP requests and replies
 318        associated with its own instance of bonding.
 319
 320        This option was added in bonding version 3.1.0.
 321
 322downdelay
 323
 324        Specifies the time, in milliseconds, to wait before disabling
 325        a slave after a link failure has been detected.  This option
 326        is only valid for the miimon link monitor.  The downdelay
 327        value should be a multiple of the miimon value; if not, it
 328        will be rounded down to the nearest multiple.  The default
 329        value is 0.
 330
 331fail_over_mac
 332
 333        Specifies whether active-backup mode should set all slaves to
 334        the same MAC address at enslavement (the traditional
 335        behavior), or, when enabled, perform special handling of the
 336        bond's MAC address in accordance with the selected policy.
 337
 338        Possible values are:
 339
 340        none or 0
 341
 342                This setting disables fail_over_mac, and causes
 343                bonding to set all slaves of an active-backup bond to
 344                the same MAC address at enslavement time.  This is the
 345                default.
 346
 347        active or 1
 348
 349                The "active" fail_over_mac policy indicates that the
 350                MAC address of the bond should always be the MAC
 351                address of the currently active slave.  The MAC
 352                address of the slaves is not changed; instead, the MAC
 353                address of the bond changes during a failover.
 354
 355                This policy is useful for devices that cannot ever
 356                alter their MAC address, or for devices that refuse
 357                incoming broadcasts with their own source MAC (which
 358                interferes with the ARP monitor).
 359
 360                The down side of this policy is that every device on
 361                the network must be updated via gratuitous ARP,
 362                vs. just updating a switch or set of switches (which
 363                often takes place for any traffic, not just ARP
 364                traffic, if the switch snoops incoming traffic to
 365                update its tables) for the traditional method.  If the
 366                gratuitous ARP is lost, communication may be
 367                disrupted.
 368
 369                When this policy is used in conjuction with the mii
 370                monitor, devices which assert link up prior to being
 371                able to actually transmit and receive are particularly
 372                susceptible to loss of the gratuitous ARP, and an
 373                appropriate updelay setting may be required.
 374
 375        follow or 2
 376
 377                The "follow" fail_over_mac policy causes the MAC
 378                address of the bond to be selected normally (normally
 379                the MAC address of the first slave added to the bond).
 380                However, the second and subsequent slaves are not set
 381                to this MAC address while they are in a backup role; a
 382                slave is programmed with the bond's MAC address at
 383                failover time (and the formerly active slave receives
 384                the newly active slave's MAC address).
 385
 386                This policy is useful for multiport devices that
 387                either become confused or incur a performance penalty
 388                when multiple ports are programmed with the same MAC
 389                address.
 390
 391
 392        The default policy is none, unless the first slave cannot
 393        change its MAC address, in which case the active policy is
 394        selected by default.
 395
 396        This option may be modified via sysfs only when no slaves are
 397        present in the bond.
 398
 399        This option was added in bonding version 3.2.0.  The "follow"
 400        policy was added in bonding version 3.3.0.
 401
 402lacp_rate
 403
 404        Option specifying the rate in which we'll ask our link partner
 405        to transmit LACPDU packets in 802.3ad mode.  Possible values
 406        are:
 407
 408        slow or 0
 409                Request partner to transmit LACPDUs every 30 seconds
 410
 411        fast or 1
 412                Request partner to transmit LACPDUs every 1 second
 413
 414        The default is slow.
 415
 416max_bonds
 417
 418        Specifies the number of bonding devices to create for this
 419        instance of the bonding driver.  E.g., if max_bonds is 3, and
 420        the bonding driver is not already loaded, then bond0, bond1
 421        and bond2 will be created.  The default value is 1.  Specifying
 422        a value of 0 will load bonding, but will not create any devices.
 423
 424miimon
 425
 426        Specifies the MII link monitoring frequency in milliseconds.
 427        This determines how often the link state of each slave is
 428        inspected for link failures.  A value of zero disables MII
 429        link monitoring.  A value of 100 is a good starting point.
 430        The use_carrier option, below, affects how the link state is
 431        determined.  See the High Availability section for additional
 432        information.  The default value is 0.
 433
 434mode
 435
 436        Specifies one of the bonding policies. The default is
 437        balance-rr (round robin).  Possible values are:
 438
 439        balance-rr or 0
 440
 441                Round-robin policy: Transmit packets in sequential
 442                order from the first available slave through the
 443                last.  This mode provides load balancing and fault
 444                tolerance.
 445
 446        active-backup or 1
 447
 448                Active-backup policy: Only one slave in the bond is
 449                active.  A different slave becomes active if, and only
 450                if, the active slave fails.  The bond's MAC address is
 451                externally visible on only one port (network adapter)
 452                to avoid confusing the switch.
 453
 454                In bonding version 2.6.2 or later, when a failover
 455                occurs in active-backup mode, bonding will issue one
 456                or more gratuitous ARPs on the newly active slave.
 457                One gratuitous ARP is issued for the bonding master
 458                interface and each VLAN interfaces configured above
 459                it, provided that the interface has at least one IP
 460                address configured.  Gratuitous ARPs issued for VLAN
 461                interfaces are tagged with the appropriate VLAN id.
 462
 463                This mode provides fault tolerance.  The primary
 464                option, documented below, affects the behavior of this
 465                mode.
 466
 467        balance-xor or 2
 468
 469                XOR policy: Transmit based on the selected transmit
 470                hash policy.  The default policy is a simple [(source
 471                MAC address XOR'd with destination MAC address) modulo
 472                slave count].  Alternate transmit policies may be
 473                selected via the xmit_hash_policy option, described
 474                below.
 475
 476                This mode provides load balancing and fault tolerance.
 477
 478        broadcast or 3
 479
 480                Broadcast policy: transmits everything on all slave
 481                interfaces.  This mode provides fault tolerance.
 482
 483        802.3ad or 4
 484
 485                IEEE 802.3ad Dynamic link aggregation.  Creates
 486                aggregation groups that share the same speed and
 487                duplex settings.  Utilizes all slaves in the active
 488                aggregator according to the 802.3ad specification.
 489
 490                Slave selection for outgoing traffic is done according
 491                to the transmit hash policy, which may be changed from
 492                the default simple XOR policy via the xmit_hash_policy
 493                option, documented below.  Note that not all transmit
 494                policies may be 802.3ad compliant, particularly in
 495                regards to the packet mis-ordering requirements of
 496                section 43.2.4 of the 802.3ad standard.  Differing
 497                peer implementations will have varying tolerances for
 498                noncompliance.
 499
 500                Prerequisites:
 501
 502                1. Ethtool support in the base drivers for retrieving
 503                the speed and duplex of each slave.
 504
 505                2. A switch that supports IEEE 802.3ad Dynamic link
 506                aggregation.
 507
 508                Most switches will require some type of configuration
 509                to enable 802.3ad mode.
 510
 511        balance-tlb or 5
 512
 513                Adaptive transmit load balancing: channel bonding that
 514                does not require any special switch support.  The
 515                outgoing traffic is distributed according to the
 516                current load (computed relative to the speed) on each
 517                slave.  Incoming traffic is received by the current
 518                slave.  If the receiving slave fails, another slave
 519                takes over the MAC address of the failed receiving
 520                slave.
 521
 522                Prerequisite:
 523
 524                Ethtool support in the base drivers for retrieving the
 525                speed of each slave.
 526
 527        balance-alb or 6
 528
 529                Adaptive load balancing: includes balance-tlb plus
 530                receive load balancing (rlb) for IPV4 traffic, and
 531                does not require any special switch support.  The
 532                receive load balancing is achieved by ARP negotiation.
 533                The bonding driver intercepts the ARP Replies sent by
 534                the local system on their way out and overwrites the
 535                source hardware address with the unique hardware
 536                address of one of the slaves in the bond such that
 537                different peers use different hardware addresses for
 538                the server.
 539
 540                Receive traffic from connections created by the server
 541                is also balanced.  When the local system sends an ARP
 542                Request the bonding driver copies and saves the peer's
 543                IP information from the ARP packet.  When the ARP
 544                Reply arrives from the peer, its hardware address is
 545                retrieved and the bonding driver initiates an ARP
 546                reply to this peer assigning it to one of the slaves
 547                in the bond.  A problematic outcome of using ARP
 548                negotiation for balancing is that each time that an
 549                ARP request is broadcast it uses the hardware address
 550                of the bond.  Hence, peers learn the hardware address
 551                of the bond and the balancing of receive traffic
 552                collapses to the current slave.  This is handled by
 553                sending updates (ARP Replies) to all the peers with
 554                their individually assigned hardware address such that
 555                the traffic is redistributed.  Receive traffic is also
 556                redistributed when a new slave is added to the bond
 557                and when an inactive slave is re-activated.  The
 558                receive load is distributed sequentially (round robin)
 559                among the group of highest speed slaves in the bond.
 560
 561                When a link is reconnected or a new slave joins the
 562                bond the receive traffic is redistributed among all
 563                active slaves in the bond by initiating ARP Replies
 564                with the selected MAC address to each of the
 565                clients. The updelay parameter (detailed below) must
 566                be set to a value equal or greater than the switch's
 567                forwarding delay so that the ARP Replies sent to the
 568                peers will not be blocked by the switch.
 569
 570                Prerequisites:
 571
 572                1. Ethtool support in the base drivers for retrieving
 573                the speed of each slave.
 574
 575                2. Base driver support for setting the hardware
 576                address of a device while it is open.  This is
 577                required so that there will always be one slave in the
 578                team using the bond hardware address (the
 579                curr_active_slave) while having a unique hardware
 580                address for each slave in the bond.  If the
 581                curr_active_slave fails its hardware address is
 582                swapped with the new curr_active_slave that was
 583                chosen.
 584
 585num_grat_arp
 586
 587        Specifies the number of gratuitous ARPs to be issued after a
 588        failover event.  One gratuitous ARP is issued immediately after
 589        the failover, subsequent ARPs are sent at a rate of one per link
 590        monitor interval (arp_interval or miimon, whichever is active).
 591
 592        The valid range is 0 - 255; the default value is 1.  This option
 593        affects only the active-backup mode.  This option was added for
 594        bonding version 3.3.0.
 595
 596num_unsol_na
 597
 598        Specifies the number of unsolicited IPv6 Neighbor Advertisements
 599        to be issued after a failover event.  One unsolicited NA is issued
 600        immediately after the failover.
 601
 602        The valid range is 0 - 255; the default value is 1.  This option
 603        affects only the active-backup mode.  This option was added for
 604        bonding version 3.4.0.
 605
 606primary
 607
 608        A string (eth0, eth2, etc) specifying which slave is the
 609        primary device.  The specified device will always be the
 610        active slave while it is available.  Only when the primary is
 611        off-line will alternate devices be used.  This is useful when
 612        one slave is preferred over another, e.g., when one slave has
 613        higher throughput than another.
 614
 615        The primary option is only valid for active-backup mode.
 616
 617primary_reselect
 618
 619        Specifies the reselection policy for the primary slave.  This
 620        affects how the primary slave is chosen to become the active slave
 621        when failure of the active slave or recovery of the primary slave
 622        occurs.  This option is designed to prevent flip-flopping between
 623        the primary slave and other slaves.  Possible values are:
 624
 625        always or 0 (default)
 626
 627                The primary slave becomes the active slave whenever it
 628                comes back up.
 629
 630        better or 1
 631
 632                The primary slave becomes the active slave when it comes
 633                back up, if the speed and duplex of the primary slave is
 634                better than the speed and duplex of the current active
 635                slave.
 636
 637        failure or 2
 638
 639                The primary slave becomes the active slave only if the
 640                current active slave fails and the primary slave is up.
 641
 642        The primary_reselect setting is ignored in two cases:
 643
 644                If no slaves are active, the first slave to recover is
 645                made the active slave.
 646
 647                When initially enslaved, the primary slave is always made
 648                the active slave.
 649
 650        Changing the primary_reselect policy via sysfs will cause an
 651        immediate selection of the best active slave according to the new
 652        policy.  This may or may not result in a change of the active
 653        slave, depending upon the circumstances.
 654
 655        This option was added for bonding version 3.6.0.
 656
 657updelay
 658
 659        Specifies the time, in milliseconds, to wait before enabling a
 660        slave after a link recovery has been detected.  This option is
 661        only valid for the miimon link monitor.  The updelay value
 662        should be a multiple of the miimon value; if not, it will be
 663        rounded down to the nearest multiple.  The default value is 0.
 664
 665use_carrier
 666
 667        Specifies whether or not miimon should use MII or ETHTOOL
 668        ioctls vs. netif_carrier_ok() to determine the link
 669        status. The MII or ETHTOOL ioctls are less efficient and
 670        utilize a deprecated calling sequence within the kernel.  The
 671        netif_carrier_ok() relies on the device driver to maintain its
 672        state with netif_carrier_on/off; at this writing, most, but
 673        not all, device drivers support this facility.
 674
 675        If bonding insists that the link is up when it should not be,
 676        it may be that your network device driver does not support
 677        netif_carrier_on/off.  The default state for netif_carrier is
 678        "carrier on," so if a driver does not support netif_carrier,
 679        it will appear as if the link is always up.  In this case,
 680        setting use_carrier to 0 will cause bonding to revert to the
 681        MII / ETHTOOL ioctl method to determine the link state.
 682
 683        A value of 1 enables the use of netif_carrier_ok(), a value of
 684        0 will use the deprecated MII / ETHTOOL ioctls.  The default
 685        value is 1.
 686
 687xmit_hash_policy
 688
 689        Selects the transmit hash policy to use for slave selection in
 690        balance-xor and 802.3ad modes.  Possible values are:
 691
 692        layer2
 693
 694                Uses XOR of hardware MAC addresses to generate the
 695                hash.  The formula is
 696
 697                (source MAC XOR destination MAC) modulo slave count
 698
 699                This algorithm will place all traffic to a particular
 700                network peer on the same slave.
 701
 702                This algorithm is 802.3ad compliant.
 703
 704        layer2+3
 705
 706                This policy uses a combination of layer2 and layer3
 707                protocol information to generate the hash.
 708
 709                Uses XOR of hardware MAC addresses and IP addresses to
 710                generate the hash.  The formula is
 711
 712                (((source IP XOR dest IP) AND 0xffff) XOR
 713                        ( source MAC XOR destination MAC ))
 714                                modulo slave count
 715
 716                This algorithm will place all traffic to a particular
 717                network peer on the same slave.  For non-IP traffic,
 718                the formula is the same as for the layer2 transmit
 719                hash policy.
 720
 721                This policy is intended to provide a more balanced
 722                distribution of traffic than layer2 alone, especially
 723                in environments where a layer3 gateway device is
 724                required to reach most destinations.
 725
 726                This algorithm is 802.3ad compliant.
 727
 728        layer3+4
 729
 730                This policy uses upper layer protocol information,
 731                when available, to generate the hash.  This allows for
 732                traffic to a particular network peer to span multiple
 733                slaves, although a single connection will not span
 734                multiple slaves.
 735
 736                The formula for unfragmented TCP and UDP packets is
 737
 738                ((source port XOR dest port) XOR
 739                         ((source IP XOR dest IP) AND 0xffff)
 740                                modulo slave count
 741
 742                For fragmented TCP or UDP packets and all other IP
 743                protocol traffic, the source and destination port
 744                information is omitted.  For non-IP traffic, the
 745                formula is the same as for the layer2 transmit hash
 746                policy.
 747
 748                This policy is intended to mimic the behavior of
 749                certain switches, notably Cisco switches with PFC2 as
 750                well as some Foundry and IBM products.
 751
 752                This algorithm is not fully 802.3ad compliant.  A
 753                single TCP or UDP conversation containing both
 754                fragmented and unfragmented packets will see packets
 755                striped across two interfaces.  This may result in out
 756                of order delivery.  Most traffic types will not meet
 757                this criteria, as TCP rarely fragments traffic, and
 758                most UDP traffic is not involved in extended
 759                conversations.  Other implementations of 802.3ad may
 760                or may not tolerate this noncompliance.
 761
 762        The default value is layer2.  This option was added in bonding
 763        version 2.6.3.  In earlier versions of bonding, this parameter
 764        does not exist, and the layer2 policy is the only policy.  The
 765        layer2+3 value was added for bonding version 3.2.2.
 766
 767
 7683. Configuring Bonding Devices
 769==============================
 770
 771        You can configure bonding using either your distro's network
 772initialization scripts, or manually using either ifenslave or the
 773sysfs interface.  Distros generally use one of two packages for the
 774network initialization scripts: initscripts or sysconfig.  Recent
 775versions of these packages have support for bonding, while older
 776versions do not.
 777
 778        We will first describe the options for configuring bonding for
 779distros using versions of initscripts and sysconfig with full or
 780partial support for bonding, then provide information on enabling
 781bonding without support from the network initialization scripts (i.e.,
 782older versions of initscripts or sysconfig).
 783
 784        If you're unsure whether your distro uses sysconfig or
 785initscripts, or don't know if it's new enough, have no fear.
 786Determining this is fairly straightforward.
 787
 788        First, issue the command:
 789
 790$ rpm -qf /sbin/ifup
 791
 792        It will respond with a line of text starting with either
 793"initscripts" or "sysconfig," followed by some numbers.  This is the
 794package that provides your network initialization scripts.
 795
 796        Next, to determine if your installation supports bonding,
 797issue the command:
 798
 799$ grep ifenslave /sbin/ifup
 800
 801        If this returns any matches, then your initscripts or
 802sysconfig has support for bonding.
 803
 8043.1 Configuration with Sysconfig Support
 805----------------------------------------
 806
 807        This section applies to distros using a version of sysconfig
 808with bonding support, for example, SuSE Linux Enterprise Server 9.
 809
 810        SuSE SLES 9's networking configuration system does support
 811bonding, however, at this writing, the YaST system configuration
 812front end does not provide any means to work with bonding devices.
 813Bonding devices can be managed by hand, however, as follows.
 814
 815        First, if they have not already been configured, configure the
 816slave devices.  On SLES 9, this is most easily done by running the
 817yast2 sysconfig configuration utility.  The goal is for to create an
 818ifcfg-id file for each slave device.  The simplest way to accomplish
 819this is to configure the devices for DHCP (this is only to get the
 820file ifcfg-id file created; see below for some issues with DHCP).  The
 821name of the configuration file for each device will be of the form:
 822
 823ifcfg-id-xx:xx:xx:xx:xx:xx
 824
 825        Where the "xx" portion will be replaced with the digits from
 826the device's permanent MAC address.
 827
 828        Once the set of ifcfg-id-xx:xx:xx:xx:xx:xx files has been
 829created, it is necessary to edit the configuration files for the slave
 830devices (the MAC addresses correspond to those of the slave devices).
 831Before editing, the file will contain multiple lines, and will look
 832something like this:
 833
 834BOOTPROTO='dhcp'
 835STARTMODE='on'
 836USERCTL='no'
 837UNIQUE='XNzu.WeZGOGF+4wE'
 838_nm_name='bus-pci-0001:61:01.0'
 839
 840        Change the BOOTPROTO and STARTMODE lines to the following:
 841
 842BOOTPROTO='none'
 843STARTMODE='off'
 844
 845        Do not alter the UNIQUE or _nm_name lines.  Remove any other
 846lines (USERCTL, etc).
 847
 848        Once the ifcfg-id-xx:xx:xx:xx:xx:xx files have been modified,
 849it's time to create the configuration file for the bonding device
 850itself.  This file is named ifcfg-bondX, where X is the number of the
 851bonding device to create, starting at 0.  The first such file is
 852ifcfg-bond0, the second is ifcfg-bond1, and so on.  The sysconfig
 853network configuration system will correctly start multiple instances
 854of bonding.
 855
 856        The contents of the ifcfg-bondX file is as follows:
 857
 858BOOTPROTO="static"
 859BROADCAST="10.0.2.255"
 860IPADDR="10.0.2.10"
 861NETMASK="255.255.0.0"
 862NETWORK="10.0.2.0"
 863REMOTE_IPADDR=""
 864STARTMODE="onboot"
 865BONDING_MASTER="yes"
 866BONDING_MODULE_OPTS="mode=active-backup miimon=100"
 867BONDING_SLAVE0="eth0"
 868BONDING_SLAVE1="bus-pci-0000:06:08.1"
 869
 870        Replace the sample BROADCAST, IPADDR, NETMASK and NETWORK
 871values with the appropriate values for your network.
 872
 873        The STARTMODE specifies when the device is brought online.
 874The possible values are:
 875
 876        onboot:  The device is started at boot time.  If you're not
 877                 sure, this is probably what you want.
 878
 879        manual:  The device is started only when ifup is called
 880                 manually.  Bonding devices may be configured this
 881                 way if you do not wish them to start automatically
 882                 at boot for some reason.
 883
 884        hotplug: The device is started by a hotplug event.  This is not
 885                 a valid choice for a bonding device.
 886
 887        off or ignore: The device configuration is ignored.
 888
 889        The line BONDING_MASTER='yes' indicates that the device is a
 890bonding master device.  The only useful value is "yes."
 891
 892        The contents of BONDING_MODULE_OPTS are supplied to the
 893instance of the bonding module for this device.  Specify the options
 894for the bonding mode, link monitoring, and so on here.  Do not include
 895the max_bonds bonding parameter; this will confuse the configuration
 896system if you have multiple bonding devices.
 897
 898        Finally, supply one BONDING_SLAVEn="slave device" for each
 899slave.  where "n" is an increasing value, one for each slave.  The
 900"slave device" is either an interface name, e.g., "eth0", or a device
 901specifier for the network device.  The interface name is easier to
 902find, but the ethN names are subject to change at boot time if, e.g.,
 903a device early in the sequence has failed.  The device specifiers
 904(bus-pci-0000:06:08.1 in the example above) specify the physical
 905network device, and will not change unless the device's bus location
 906changes (for example, it is moved from one PCI slot to another).  The
 907example above uses one of each type for demonstration purposes; most
 908configurations will choose one or the other for all slave devices.
 909
 910        When all configuration files have been modified or created,
 911networking must be restarted for the configuration changes to take
 912effect.  This can be accomplished via the following:
 913
 914# /etc/init.d/network restart
 915
 916        Note that the network control script (/sbin/ifdown) will
 917remove the bonding module as part of the network shutdown processing,
 918so it is not necessary to remove the module by hand if, e.g., the
 919module parameters have changed.
 920
 921        Also, at this writing, YaST/YaST2 will not manage bonding
 922devices (they do not show bonding interfaces on its list of network
 923devices).  It is necessary to edit the configuration file by hand to
 924change the bonding configuration.
 925
 926        Additional general options and details of the ifcfg file
 927format can be found in an example ifcfg template file:
 928
 929/etc/sysconfig/network/ifcfg.template
 930
 931        Note that the template does not document the various BONDING_
 932settings described above, but does describe many of the other options.
 933
 9343.1.1 Using DHCP with Sysconfig
 935-------------------------------
 936
 937        Under sysconfig, configuring a device with BOOTPROTO='dhcp'
 938will cause it to query DHCP for its IP address information.  At this
 939writing, this does not function for bonding devices; the scripts
 940attempt to obtain the device address from DHCP prior to adding any of
 941the slave devices.  Without active slaves, the DHCP requests are not
 942sent to the network.
 943
 9443.1.2 Configuring Multiple Bonds with Sysconfig
 945-----------------------------------------------
 946
 947        The sysconfig network initialization system is capable of
 948handling multiple bonding devices.  All that is necessary is for each
 949bonding instance to have an appropriately configured ifcfg-bondX file
 950(as described above).  Do not specify the "max_bonds" parameter to any
 951instance of bonding, as this will confuse sysconfig.  If you require
 952multiple bonding devices with identical parameters, create multiple
 953ifcfg-bondX files.
 954
 955        Because the sysconfig scripts supply the bonding module
 956options in the ifcfg-bondX file, it is not necessary to add them to
 957the system /etc/modules.conf or /etc/modprobe.conf configuration file.
 958
 9593.2 Configuration with Initscripts Support
 960------------------------------------------
 961
 962        This section applies to distros using a recent version of
 963initscripts with bonding support, for example, Red Hat Enterprise Linux
 964version 3 or later, Fedora, etc.  On these systems, the network
 965initialization scripts have knowledge of bonding, and can be configured to
 966control bonding devices.  Note that older versions of the initscripts
 967package have lower levels of support for bonding; this will be noted where
 968applicable.
 969
 970        These distros will not automatically load the network adapter
 971driver unless the ethX device is configured with an IP address.
 972Because of this constraint, users must manually configure a
 973network-script file for all physical adapters that will be members of
 974a bondX link.  Network script files are located in the directory:
 975
 976/etc/sysconfig/network-scripts
 977
 978        The file name must be prefixed with "ifcfg-eth" and suffixed
 979with the adapter's physical adapter number.  For example, the script
 980for eth0 would be named /etc/sysconfig/network-scripts/ifcfg-eth0.
 981Place the following text in the file:
 982
 983DEVICE=eth0
 984USERCTL=no
 985ONBOOT=yes
 986MASTER=bond0
 987SLAVE=yes
 988BOOTPROTO=none
 989
 990        The DEVICE= line will be different for every ethX device and
 991must correspond with the name of the file, i.e., ifcfg-eth1 must have
 992a device line of DEVICE=eth1.  The setting of the MASTER= line will
 993also depend on the final bonding interface name chosen for your bond.
 994As with other network devices, these typically start at 0, and go up
 995one for each device, i.e., the first bonding instance is bond0, the
 996second is bond1, and so on.
 997
 998        Next, create a bond network script.  The file name for this
 999script will be /etc/sysconfig/network-scripts/ifcfg-bondX where X is
1000the number of the bond.  For bond0 the file is named "ifcfg-bond0",
1001for bond1 it is named "ifcfg-bond1", and so on.  Within that file,
1002place the following text:
1003
1004DEVICE=bond0
1005IPADDR=192.168.1.1
1006NETMASK=255.255.255.0
1007NETWORK=192.168.1.0
1008BROADCAST=192.168.1.255
1009ONBOOT=yes
1010BOOTPROTO=none
1011USERCTL=no
1012
1013        Be sure to change the networking specific lines (IPADDR,
1014NETMASK, NETWORK and BROADCAST) to match your network configuration.
1015
1016        For later versions of initscripts, such as that found with Fedora
10177 (or later) and Red Hat Enterprise Linux version 5 (or later), it is possible,
1018and, indeed, preferable, to specify the bonding options in the ifcfg-bond0
1019file, e.g. a line of the format:
1020
1021BONDING_OPTS="mode=active-backup arp_interval=60 arp_ip_target=192.168.1.254"
1022
1023        will configure the bond with the specified options.  The options
1024specified in BONDING_OPTS are identical to the bonding module parameters
1025except for the arp_ip_target field when using versions of initscripts older
1026than and 8.57 (Fedora 8) and 8.45.19 (Red Hat Enterprise Linux 5.2).  When
1027using older versions each target should be included as a separate option and
1028should be preceded by a '+' to indicate it should be added to the list of
1029queried targets, e.g.,
1030
1031        arp_ip_target=+192.168.1.1 arp_ip_target=+192.168.1.2
1032
1033        is the proper syntax to specify multiple targets.  When specifying
1034options via BONDING_OPTS, it is not necessary to edit /etc/modules.conf or
1035/etc/modprobe.conf.
1036
1037        For even older versions of initscripts that do not support
1038BONDING_OPTS, it is necessary to edit /etc/modules.conf (or
1039/etc/modprobe.conf, depending upon your distro) to load the bonding module
1040with your desired options when the bond0 interface is brought up.  The
1041following lines in /etc/modules.conf (or modprobe.conf) will load the
1042bonding module, and select its options:
1043
1044alias bond0 bonding
1045options bond0 mode=balance-alb miimon=100
1046
1047        Replace the sample parameters with the appropriate set of
1048options for your configuration.
1049
1050        Finally run "/etc/rc.d/init.d/network restart" as root.  This
1051will restart the networking subsystem and your bond link should be now
1052up and running.
1053
10543.2.1 Using DHCP with Initscripts
1055---------------------------------
1056
1057        Recent versions of initscripts (the versions supplied with Fedora
1058Core 3 and Red Hat Enterprise Linux 4, or later versions, are reported to
1059work) have support for assigning IP information to bonding devices via
1060DHCP.
1061
1062        To configure bonding for DHCP, configure it as described
1063above, except replace the line "BOOTPROTO=none" with "BOOTPROTO=dhcp"
1064and add a line consisting of "TYPE=Bonding".  Note that the TYPE value
1065is case sensitive.
1066
10673.2.2 Configuring Multiple Bonds with Initscripts
1068-------------------------------------------------
1069
1070        Initscripts packages that are included with Fedora 7 and Red Hat
1071Enterprise Linux 5 support multiple bonding interfaces by simply
1072specifying the appropriate BONDING_OPTS= in ifcfg-bondX where X is the
1073number of the bond.  This support requires sysfs support in the kernel,
1074and a bonding driver of version 3.0.0 or later.  Other configurations may
1075not support this method for specifying multiple bonding interfaces; for
1076those instances, see the "Configuring Multiple Bonds Manually" section,
1077below.
1078
10793.3 Configuring Bonding Manually with Ifenslave
1080-----------------------------------------------
1081
1082        This section applies to distros whose network initialization
1083scripts (the sysconfig or initscripts package) do not have specific
1084knowledge of bonding.  One such distro is SuSE Linux Enterprise Server
1085version 8.
1086
1087        The general method for these systems is to place the bonding
1088module parameters into /etc/modules.conf or /etc/modprobe.conf (as
1089appropriate for the installed distro), then add modprobe and/or
1090ifenslave commands to the system's global init script.  The name of
1091the global init script differs; for sysconfig, it is
1092/etc/init.d/boot.local and for initscripts it is /etc/rc.d/rc.local.
1093
1094        For example, if you wanted to make a simple bond of two e100
1095devices (presumed to be eth0 and eth1), and have it persist across
1096reboots, edit the appropriate file (/etc/init.d/boot.local or
1097/etc/rc.d/rc.local), and add the following:
1098
1099modprobe bonding mode=balance-alb miimon=100
1100modprobe e100
1101ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
1102ifenslave bond0 eth0
1103ifenslave bond0 eth1
1104
1105        Replace the example bonding module parameters and bond0
1106network configuration (IP address, netmask, etc) with the appropriate
1107values for your configuration.
1108
1109        Unfortunately, this method will not provide support for the
1110ifup and ifdown scripts on the bond devices.  To reload the bonding
1111configuration, it is necessary to run the initialization script, e.g.,
1112
1113# /etc/init.d/boot.local
1114
1115        or
1116
1117# /etc/rc.d/rc.local
1118
1119        It may be desirable in such a case to create a separate script
1120which only initializes the bonding configuration, then call that
1121separate script from within boot.local.  This allows for bonding to be
1122enabled without re-running the entire global init script.
1123
1124        To shut down the bonding devices, it is necessary to first
1125mark the bonding device itself as being down, then remove the
1126appropriate device driver modules.  For our example above, you can do
1127the following:
1128
1129# ifconfig bond0 down
1130# rmmod bonding
1131# rmmod e100
1132
1133        Again, for convenience, it may be desirable to create a script
1134with these commands.
1135
1136
11373.3.1 Configuring Multiple Bonds Manually
1138-----------------------------------------
1139
1140        This section contains information on configuring multiple
1141bonding devices with differing options for those systems whose network
1142initialization scripts lack support for configuring multiple bonds.
1143
1144        If you require multiple bonding devices, but all with the same
1145options, you may wish to use the "max_bonds" module parameter,
1146documented above.
1147
1148        To create multiple bonding devices with differing options, it is
1149preferrable to use bonding parameters exported by sysfs, documented in the
1150section below.
1151
1152        For versions of bonding without sysfs support, the only means to
1153provide multiple instances of bonding with differing options is to load
1154the bonding driver multiple times.  Note that current versions of the
1155sysconfig network initialization scripts handle this automatically; if
1156your distro uses these scripts, no special action is needed.  See the
1157section Configuring Bonding Devices, above, if you're not sure about your
1158network initialization scripts.
1159
1160        To load multiple instances of the module, it is necessary to
1161specify a different name for each instance (the module loading system
1162requires that every loaded module, even multiple instances of the same
1163module, have a unique name).  This is accomplished by supplying multiple
1164sets of bonding options in /etc/modprobe.conf, for example:
1165
1166alias bond0 bonding
1167options bond0 -o bond0 mode=balance-rr miimon=100
1168
1169alias bond1 bonding
1170options bond1 -o bond1 mode=balance-alb miimon=50
1171
1172        will load the bonding module two times.  The first instance is
1173named "bond0" and creates the bond0 device in balance-rr mode with an
1174miimon of 100.  The second instance is named "bond1" and creates the
1175bond1 device in balance-alb mode with an miimon of 50.
1176
1177        In some circumstances (typically with older distributions),
1178the above does not work, and the second bonding instance never sees
1179its options.  In that case, the second options line can be substituted
1180as follows:
1181
1182install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \
1183        mode=balance-alb miimon=50
1184
1185        This may be repeated any number of times, specifying a new and
1186unique name in place of bond1 for each subsequent instance.
1187
1188        It has been observed that some Red Hat supplied kernels are unable
1189to rename modules at load time (the "-o bond1" part).  Attempts to pass
1190that option to modprobe will produce an "Operation not permitted" error.
1191This has been reported on some Fedora Core kernels, and has been seen on
1192RHEL 4 as well.  On kernels exhibiting this problem, it will be impossible
1193to configure multiple bonds with differing parameters (as they are older
1194kernels, and also lack sysfs support).
1195
11963.4 Configuring Bonding Manually via Sysfs
1197------------------------------------------
1198
1199        Starting with version 3.0.0, Channel Bonding may be configured
1200via the sysfs interface.  This interface allows dynamic configuration
1201of all bonds in the system without unloading the module.  It also
1202allows for adding and removing bonds at runtime.  Ifenslave is no
1203longer required, though it is still supported.
1204
1205        Use of the sysfs interface allows you to use multiple bonds
1206with different configurations without having to reload the module.
1207It also allows you to use multiple, differently configured bonds when
1208bonding is compiled into the kernel.
1209
1210        You must have the sysfs filesystem mounted to configure
1211bonding this way.  The examples in this document assume that you
1212are using the standard mount point for sysfs, e.g. /sys.  If your
1213sysfs filesystem is mounted elsewhere, you will need to adjust the
1214example paths accordingly.
1215
1216Creating and Destroying Bonds
1217-----------------------------
1218To add a new bond foo:
1219# echo +foo > /sys/class/net/bonding_masters
1220
1221To remove an existing bond bar:
1222# echo -bar > /sys/class/net/bonding_masters
1223
1224To show all existing bonds:
1225# cat /sys/class/net/bonding_masters
1226
1227NOTE: due to 4K size limitation of sysfs files, this list may be
1228truncated if you have more than a few hundred bonds.  This is unlikely
1229to occur under normal operating conditions.
1230
1231Adding and Removing Slaves
1232--------------------------
1233        Interfaces may be enslaved to a bond using the file
1234/sys/class/net/<bond>/bonding/slaves.  The semantics for this file
1235are the same as for the bonding_masters file.
1236
1237To enslave interface eth0 to bond bond0:
1238# ifconfig bond0 up
1239# echo +eth0 > /sys/class/net/bond0/bonding/slaves
1240
1241To free slave eth0 from bond bond0:
1242# echo -eth0 > /sys/class/net/bond0/bonding/slaves
1243
1244        When an interface is enslaved to a bond, symlinks between the
1245two are created in the sysfs filesystem.  In this case, you would get
1246/sys/class/net/bond0/slave_eth0 pointing to /sys/class/net/eth0, and
1247/sys/class/net/eth0/master pointing to /sys/class/net/bond0.
1248
1249        This means that you can tell quickly whether or not an
1250interface is enslaved by looking for the master symlink.  Thus:
1251# echo -eth0 > /sys/class/net/eth0/master/bonding/slaves
1252will free eth0 from whatever bond it is enslaved to, regardless of
1253the name of the bond interface.
1254
1255Changing a Bond's Configuration
1256-------------------------------
1257        Each bond may be configured individually by manipulating the
1258files located in /sys/class/net/<bond name>/bonding
1259
1260        The names of these files correspond directly with the command-
1261line parameters described elsewhere in this file, and, with the
1262exception of arp_ip_target, they accept the same values.  To see the
1263current setting, simply cat the appropriate file.
1264
1265        A few examples will be given here; for specific usage
1266guidelines for each parameter, see the appropriate section in this
1267document.
1268
1269To configure bond0 for balance-alb mode:
1270# ifconfig bond0 down
1271# echo 6 > /sys/class/net/bond0/bonding/mode
1272 - or -
1273# echo balance-alb > /sys/class/net/bond0/bonding/mode
1274        NOTE: The bond interface must be down before the mode can be
1275changed.
1276
1277To enable MII monitoring on bond0 with a 1 second interval:
1278# echo 1000 > /sys/class/net/bond0/bonding/miimon
1279        NOTE: If ARP monitoring is enabled, it will disabled when MII
1280monitoring is enabled, and vice-versa.
1281
1282To add ARP targets:
1283# echo +192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
1284# echo +192.168.0.101 > /sys/class/net/bond0/bonding/arp_ip_target
1285        NOTE:  up to 16 target addresses may be specified.
1286
1287To remove an ARP target:
1288# echo -192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
1289
1290Example Configuration
1291---------------------
1292        We begin with the same example that is shown in section 3.3,
1293executed with sysfs, and without using ifenslave.
1294
1295        To make a simple bond of two e100 devices (presumed to be eth0
1296and eth1), and have it persist across reboots, edit the appropriate
1297file (/etc/init.d/boot.local or /etc/rc.d/rc.local), and add the
1298following:
1299
1300modprobe bonding
1301modprobe e100
1302echo balance-alb > /sys/class/net/bond0/bonding/mode
1303ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
1304echo 100 > /sys/class/net/bond0/bonding/miimon
1305echo +eth0 > /sys/class/net/bond0/bonding/slaves
1306echo +eth1 > /sys/class/net/bond0/bonding/slaves
1307
1308        To add a second bond, with two e1000 interfaces in
1309active-backup mode, using ARP monitoring, add the following lines to
1310your init script:
1311
1312modprobe e1000
1313echo +bond1 > /sys/class/net/bonding_masters
1314echo active-backup > /sys/class/net/bond1/bonding/mode
1315ifconfig bond1 192.168.2.1 netmask 255.255.255.0 up
1316echo +192.168.2.100 /sys/class/net/bond1/bonding/arp_ip_target
1317echo 2000 > /sys/class/net/bond1/bonding/arp_interval
1318echo +eth2 > /sys/class/net/bond1/bonding/slaves
1319echo +eth3 > /sys/class/net/bond1/bonding/slaves
1320
1321
13224. Querying Bonding Configuration 
1323=================================
1324
13254.1 Bonding Configuration
1326-------------------------
1327
1328        Each bonding device has a read-only file residing in the
1329/proc/net/bonding directory.  The file contents include information
1330about the bonding configuration, options and state of each slave.
1331
1332        For example, the contents of /proc/net/bonding/bond0 after the
1333driver is loaded with parameters of mode=0 and miimon=1000 is
1334generally as follows:
1335
1336        Ethernet Channel Bonding Driver: 2.6.1 (October 29, 2004)
1337        Bonding Mode: load balancing (round-robin)
1338        Currently Active Slave: eth0
1339        MII Status: up
1340        MII Polling Interval (ms): 1000
1341        Up Delay (ms): 0
1342        Down Delay (ms): 0
1343
1344        Slave Interface: eth1
1345        MII Status: up
1346        Link Failure Count: 1
1347
1348        Slave Interface: eth0
1349        MII Status: up
1350        Link Failure Count: 1
1351
1352        The precise format and contents will change depending upon the
1353bonding configuration, state, and version of the bonding driver.
1354
13554.2 Network configuration
1356-------------------------
1357
1358        The network configuration can be inspected using the ifconfig
1359command.  Bonding devices will have the MASTER flag set; Bonding slave
1360devices will have the SLAVE flag set.  The ifconfig output does not
1361contain information on which slaves are associated with which masters.
1362
1363        In the example below, the bond0 interface is the master
1364(MASTER) while eth0 and eth1 are slaves (SLAVE). Notice all slaves of
1365bond0 have the same MAC address (HWaddr) as bond0 for all modes except
1366TLB and ALB that require a unique MAC address for each slave.
1367
1368# /sbin/ifconfig
1369bond0     Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
1370          inet addr:XXX.XXX.XXX.YYY  Bcast:XXX.XXX.XXX.255  Mask:255.255.252.0
1371          UP BROADCAST RUNNING MASTER MULTICAST  MTU:1500  Metric:1
1372          RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0
1373          TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0
1374          collisions:0 txqueuelen:0
1375
1376eth0      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
1377          UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
1378          RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0
1379          TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0
1380          collisions:0 txqueuelen:100
1381          Interrupt:10 Base address:0x1080
1382
1383eth1      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
1384          UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
1385          RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0
1386          TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0
1387          collisions:0 txqueuelen:100
1388          Interrupt:9 Base address:0x1400
1389
13905. Switch Configuration
1391=======================
1392
1393        For this section, "switch" refers to whatever system the
1394bonded devices are directly connected to (i.e., where the other end of
1395the cable plugs into).  This may be an actual dedicated switch device,
1396or it may be another regular system (e.g., another computer running
1397Linux),
1398
1399        The active-backup, balance-tlb and balance-alb modes do not
1400require any specific configuration of the switch.
1401
1402        The 802.3ad mode requires that the switch have the appropriate
1403ports configured as an 802.3ad aggregation.  The precise method used
1404to configure this varies from switch to switch, but, for example, a
1405Cisco 3550 series switch requires that the appropriate ports first be
1406grouped together in a single etherchannel instance, then that
1407etherchannel is set to mode "lacp" to enable 802.3ad (instead of
1408standard EtherChannel).
1409
1410        The balance-rr, balance-xor and broadcast modes generally
1411require that the switch have the appropriate ports grouped together.
1412The nomenclature for such a group differs between switches, it may be
1413called an "etherchannel" (as in the Cisco example, above), a "trunk
1414group" or some other similar variation.  For these modes, each switch
1415will also have its own configuration options for the switch's transmit
1416policy to the bond.  Typical choices include XOR of either the MAC or
1417IP addresses.  The transmit policy of the two peers does not need to
1418match.  For these three modes, the bonding mode really selects a
1419transmit policy for an EtherChannel group; all three will interoperate
1420with another EtherChannel group.
1421
1422
14236. 802.1q VLAN Support
1424======================
1425
1426        It is possible to configure VLAN devices over a bond interface
1427using the 8021q driver.  However, only packets coming from the 8021q
1428driver and passing through bonding will be tagged by default.  Self
1429generated packets, for example, bonding's learning packets or ARP
1430packets generated by either ALB mode or the ARP monitor mechanism, are
1431tagged internally by bonding itself.  As a result, bonding must
1432"learn" the VLAN IDs configured above it, and use those IDs to tag
1433self generated packets.
1434
1435        For reasons of simplicity, and to support the use of adapters
1436that can do VLAN hardware acceleration offloading, the bonding
1437interface declares itself as fully hardware offloading capable, it gets
1438the add_vid/kill_vid notifications to gather the necessary
1439information, and it propagates those actions to the slaves.  In case
1440of mixed adapter types, hardware accelerated tagged packets that
1441should go through an adapter that is not offloading capable are
1442"un-accelerated" by the bonding driver so the VLAN tag sits in the
1443regular location.
1444
1445        VLAN interfaces *must* be added on top of a bonding interface
1446only after enslaving at least one slave.  The bonding interface has a
1447hardware address of 00:00:00:00:00:00 until the first slave is added.
1448If the VLAN interface is created prior to the first enslavement, it
1449would pick up the all-zeroes hardware address.  Once the first slave
1450is attached to the bond, the bond device itself will pick up the
1451slave's hardware address, which is then available for the VLAN device.
1452
1453        Also, be aware that a similar problem can occur if all slaves
1454are released from a bond that still has one or more VLAN interfaces on
1455top of it.  When a new slave is added, the bonding interface will
1456obtain its hardware address from the first slave, which might not
1457match the hardware address of the VLAN interfaces (which was
1458ultimately copied from an earlier slave).
1459
1460        There are two methods to insure that the VLAN device operates
1461with the correct hardware address if all slaves are removed from a
1462bond interface:
1463
1464        1. Remove all VLAN interfaces then recreate them
1465
1466        2. Set the bonding interface's hardware address so that it
1467matches the hardware address of the VLAN interfaces.
1468
1469        Note that changing a VLAN interface's HW address would set the
1470underlying device -- i.e. the bonding interface -- to promiscuous
1471mode, which might not be what you want.
1472
1473
14747. Link Monitoring
1475==================
1476
1477        The bonding driver at present supports two schemes for
1478monitoring a slave device's link state: the ARP monitor and the MII
1479monitor.
1480
1481        At the present time, due to implementation restrictions in the
1482bonding driver itself, it is not possible to enable both ARP and MII
1483monitoring simultaneously.
1484
14857.1 ARP Monitor Operation
1486-------------------------
1487
1488        The ARP monitor operates as its name suggests: it sends ARP
1489queries to one or more designated peer systems on the network, and
1490uses the response as an indication that the link is operating.  This
1491gives some assurance that traffic is actually flowing to and from one
1492or more peers on the local network.
1493
1494        The ARP monitor relies on the device driver itself to verify
1495that traffic is flowing.  In particular, the driver must keep up to
1496date the last receive time, dev->last_rx, and transmit start time,
1497dev->trans_start.  If these are not updated by the driver, then the
1498ARP monitor will immediately fail any slaves using that driver, and
1499those slaves will stay down.  If networking monitoring (tcpdump, etc)
1500shows the ARP requests and replies on the network, then it may be that
1501your device driver is not updating last_rx and trans_start.
1502
15037.2 Configuring Multiple ARP Targets
1504------------------------------------
1505
1506        While ARP monitoring can be done with just one target, it can
1507be useful in a High Availability setup to have several targets to
1508monitor.  In the case of just one target, the target itself may go
1509down or have a problem making it unresponsive to ARP requests.  Having
1510an additional target (or several) increases the reliability of the ARP
1511monitoring.
1512
1513        Multiple ARP targets must be separated by commas as follows:
1514
1515# example options for ARP monitoring with three targets
1516alias bond0 bonding
1517options bond0 arp_interval=60 arp_ip_target=192.168.0.1,192.168.0.3,192.168.0.9
1518
1519        For just a single target the options would resemble:
1520
1521# example options for ARP monitoring with one target
1522alias bond0 bonding
1523options bond0 arp_interval=60 arp_ip_target=192.168.0.100
1524
1525
15267.3 MII Monitor Operation
1527-------------------------
1528
1529        The MII monitor monitors only the carrier state of the local
1530network interface.  It accomplishes this in one of three ways: by
1531depending upon the device driver to maintain its carrier state, by
1532querying the device's MII registers, or by making an ethtool query to
1533the device.
1534
1535        If the use_carrier module parameter is 1 (the default value),
1536then the MII monitor will rely on the driver for carrier state
1537information (via the netif_carrier subsystem).  As explained in the
1538use_carrier parameter information, above, if the MII monitor fails to
1539detect carrier loss on the device (e.g., when the cable is physically
1540disconnected), it may be that the driver does not support
1541netif_carrier.
1542
1543        If use_carrier is 0, then the MII monitor will first query the
1544device's (via ioctl) MII registers and check the link state.  If that
1545request fails (not just that it returns carrier down), then the MII
1546monitor will make an ethtool ETHOOL_GLINK request to attempt to obtain
1547the same information.  If both methods fail (i.e., the driver either
1548does not support or had some error in processing both the MII register
1549and ethtool requests), then the MII monitor will assume the link is
1550up.
1551
15528. Potential Sources of Trouble
1553===============================
1554
15558.1 Adventures in Routing
1556-------------------------
1557
1558        When bonding is configured, it is important that the slave
1559devices not have routes that supersede routes of the master (or,
1560generally, not have routes at all).  For example, suppose the bonding
1561device bond0 has two slaves, eth0 and eth1, and the routing table is
1562as follows:
1563
1564Kernel IP routing table
1565Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
156610.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth0
156710.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth1
156810.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 bond0
1569127.0.0.0       0.0.0.0         255.0.0.0       U        40 0          0 lo
1570
1571        This routing configuration will likely still update the
1572receive/transmit times in the driver (needed by the ARP monitor), but
1573may bypass the bonding driver (because outgoing traffic to, in this
1574case, another host on network 10 would use eth0 or eth1 before bond0).
1575
1576        The ARP monitor (and ARP itself) may become confused by this
1577configuration, because ARP requests (generated by the ARP monitor)
1578will be sent on one interface (bond0), but the corresponding reply
1579will arrive on a different interface (eth0).  This reply looks to ARP
1580as an unsolicited ARP reply (because ARP matches replies on an
1581interface basis), and is discarded.  The MII monitor is not affected
1582by the state of the routing table.
1583
1584        The solution here is simply to insure that slaves do not have
1585routes of their own, and if for some reason they must, those routes do
1586not supersede routes of their master.  This should generally be the
1587case, but unusual configurations or errant manual or automatic static
1588route additions may cause trouble.
1589
15908.2 Ethernet Device Renaming
1591----------------------------
1592
1593        On systems with network configuration scripts that do not
1594associate physical devices directly with network interface names (so
1595that the same physical device always has the same "ethX" name), it may
1596be necessary to add some special logic to either /etc/modules.conf or
1597/etc/modprobe.conf (depending upon which is installed on the system).
1598
1599        For example, given a modules.conf containing the following:
1600
1601alias bond0 bonding
1602options bond0 mode=some-mode miimon=50
1603alias eth0 tg3
1604alias eth1 tg3
1605alias eth2 e1000
1606alias eth3 e1000
1607
1608        If neither eth0 and eth1 are slaves to bond0, then when the
1609bond0 interface comes up, the devices may end up reordered.  This
1610happens because bonding is loaded first, then its slave device's
1611drivers are loaded next.  Since no other drivers have been loaded,
1612when the e1000 driver loads, it will receive eth0 and eth1 for its
1613devices, but the bonding configuration tries to enslave eth2 and eth3
1614(which may later be assigned to the tg3 devices).
1615
1616        Adding the following:
1617
1618add above bonding e1000 tg3
1619
1620        causes modprobe to load e1000 then tg3, in that order, when
1621bonding is loaded.  This command is fully documented in the
1622modules.conf manual page.
1623
1624        On systems utilizing modprobe.conf (or modprobe.conf.local),
1625an equivalent problem can occur.  In this case, the following can be
1626added to modprobe.conf (or modprobe.conf.local, as appropriate), as
1627follows (all on one line; it has been split here for clarity):
1628
1629install bonding /sbin/modprobe tg3; /sbin/modprobe e1000;
1630        /sbin/modprobe --ignore-install bonding
1631
1632        This will, when loading the bonding module, rather than
1633performing the normal action, instead execute the provided command.
1634This command loads the device drivers in the order needed, then calls
1635modprobe with --ignore-install to cause the normal action to then take
1636place.  Full documentation on this can be found in the modprobe.conf
1637and modprobe manual pages.
1638
16398.3. Painfully Slow Or No Failed Link Detection By Miimon
1640---------------------------------------------------------
1641
1642        By default, bonding enables the use_carrier option, which
1643instructs bonding to trust the driver to maintain carrier state.
1644
1645        As discussed in the options section, above, some drivers do
1646not support the netif_carrier_on/_off link state tracking system.
1647With use_carrier enabled, bonding will always see these links as up,
1648regardless of their actual state.
1649
1650        Additionally, other drivers do support netif_carrier, but do
1651not maintain it in real time, e.g., only polling the link state at
1652some fixed interval.  In this case, miimon will detect failures, but
1653only after some long period of time has expired.  If it appears that
1654miimon is very slow in detecting link failures, try specifying
1655use_carrier=0 to see if that improves the failure detection time.  If
1656it does, then it may be that the driver checks the carrier state at a
1657fixed interval, but does not cache the MII register values (so the
1658use_carrier=0 method of querying the registers directly works).  If
1659use_carrier=0 does not improve the failover, then the driver may cache
1660the registers, or the problem may be elsewhere.
1661
1662        Also, remember that miimon only checks for the device's
1663carrier state.  It has no way to determine the state of devices on or
1664beyond other ports of a switch, or if a switch is refusing to pass
1665traffic while still maintaining carrier on.
1666
16679. SNMP agents
1668===============
1669
1670        If running SNMP agents, the bonding driver should be loaded
1671before any network drivers participating in a bond.  This requirement
1672is due to the interface index (ipAdEntIfIndex) being associated to
1673the first interface found with a given IP address.  That is, there is
1674only one ipAdEntIfIndex for each IP address.  For example, if eth0 and
1675eth1 are slaves of bond0 and the driver for eth0 is loaded before the
1676bonding driver, the interface for the IP address will be associated
1677with the eth0 interface.  This configuration is shown below, the IP
1678address 192.168.1.1 has an interface index of 2 which indexes to eth0
1679in the ifDescr table (ifDescr.2).
1680
1681     interfaces.ifTable.ifEntry.ifDescr.1 = lo
1682     interfaces.ifTable.ifEntry.ifDescr.2 = eth0
1683     interfaces.ifTable.ifEntry.ifDescr.3 = eth1
1684     interfaces.ifTable.ifEntry.ifDescr.4 = eth2
1685     interfaces.ifTable.ifEntry.ifDescr.5 = eth3
1686     interfaces.ifTable.ifEntry.ifDescr.6 = bond0
1687     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 5
1688     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
1689     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 4
1690     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
1691
1692        This problem is avoided by loading the bonding driver before
1693any network drivers participating in a bond.  Below is an example of
1694loading the bonding driver first, the IP address 192.168.1.1 is
1695correctly associated with ifDescr.2.
1696
1697     interfaces.ifTable.ifEntry.ifDescr.1 = lo
1698     interfaces.ifTable.ifEntry.ifDescr.2 = bond0
1699     interfaces.ifTable.ifEntry.ifDescr.3 = eth0
1700     interfaces.ifTable.ifEntry.ifDescr.4 = eth1
1701     interfaces.ifTable.ifEntry.ifDescr.5 = eth2
1702     interfaces.ifTable.ifEntry.ifDescr.6 = eth3
1703     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 6
1704     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
1705     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 5
1706     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
1707
1708        While some distributions may not report the interface name in
1709ifDescr, the association between the IP address and IfIndex remains
1710and SNMP functions such as Interface_Scan_Next will report that
1711association.
1712
171310. Promiscuous mode
1714====================
1715
1716        When running network monitoring tools, e.g., tcpdump, it is
1717common to enable promiscuous mode on the device, so that all traffic
1718is seen (instead of seeing only traffic destined for the local host).
1719The bonding driver handles promiscuous mode changes to the bonding
1720master device (e.g., bond0), and propagates the setting to the slave
1721devices.
1722
1723        For the balance-rr, balance-xor, broadcast, and 802.3ad modes,
1724the promiscuous mode setting is propagated to all slaves.
1725
1726        For the active-backup, balance-tlb and balance-alb modes, the
1727promiscuous mode setting is propagated only to the active slave.
1728
1729        For balance-tlb mode, the active slave is the slave currently
1730receiving inbound traffic.
1731
1732        For balance-alb mode, the active slave is the slave used as a
1733"primary."  This slave is used for mode-specific control traffic, for
1734sending to peers that are unassigned or if the load is unbalanced.
1735
1736        For the active-backup, balance-tlb and balance-alb modes, when
1737the active slave changes (e.g., due to a link failure), the
1738promiscuous setting will be propagated to the new active slave.
1739
174011. Configuring Bonding for High Availability
1741=============================================
1742
1743        High Availability refers to configurations that provide
1744maximum network availability by having redundant or backup devices,
1745links or switches between the host and the rest of the world.  The
1746goal is to provide the maximum availability of network connectivity
1747(i.e., the network always works), even though other configurations
1748could provide higher throughput.
1749
175011.1 High Availability in a Single Switch Topology
1751--------------------------------------------------
1752
1753        If two hosts (or a host and a single switch) are directly
1754connected via multiple physical links, then there is no availability
1755penalty to optimizing for maximum bandwidth.  In this case, there is
1756only one switch (or peer), so if it fails, there is no alternative
1757access to fail over to.  Additionally, the bonding load balance modes
1758support link monitoring of their members, so if individual links fail,
1759the load will be rebalanced across the remaining devices.
1760
1761        See Section 13, "Configuring Bonding for Maximum Throughput"
1762for information on configuring bonding with one peer device.
1763
176411.2 High Availability in a Multiple Switch Topology
1765----------------------------------------------------
1766
1767        With multiple switches, the configuration of bonding and the
1768network changes dramatically.  In multiple switch topologies, there is
1769a trade off between network availability and usable bandwidth.
1770
1771        Below is a sample network, configured to maximize the
1772availability of the network:
1773
1774                |                                     |
1775                |port3                           port3|
1776          +-----+----+                          +-----+----+
1777          |          |port2       ISL      port2|          |
1778          | switch A +--------------------------+ switch B |
1779          |          |                          |          |
1780          +-----+----+                          +-----++---+
1781                |port1                           port1|
1782                |             +-------+               |
1783                +-------------+ host1 +---------------+
1784                         eth0 +-------+ eth1
1785
1786        In this configuration, there is a link between the two
1787switches (ISL, or inter switch link), and multiple ports connecting to
1788the outside world ("port3" on each switch).  There is no technical
1789reason that this could not be extended to a third switch.
1790
179111.2.1 HA Bonding Mode Selection for Multiple Switch Topology
1792-------------------------------------------------------------
1793
1794        In a topology such as the example above, the active-backup and
1795broadcast modes are the only useful bonding modes when optimizing for
1796availability; the other modes require all links to terminate on the
1797same peer for them to behave rationally.
1798
1799active-backup: This is generally the preferred mode, particularly if
1800        the switches have an ISL and play together well.  If the
1801        network configuration is such that one switch is specifically
1802        a backup switch (e.g., has lower capacity, higher cost, etc),
1803        then the primary option can be used to insure that the
1804        preferred link is always used when it is available.
1805
1806broadcast: This mode is really a special purpose mode, and is suitable
1807        only for very specific needs.  For example, if the two
1808        switches are not connected (no ISL), and the networks beyond
1809        them are totally independent.  In this case, if it is
1810        necessary for some specific one-way traffic to reach both
1811        independent networks, then the broadcast mode may be suitable.
1812
181311.2.2 HA Link Monitoring Selection for Multiple Switch Topology
1814----------------------------------------------------------------
1815
1816        The choice of link monitoring ultimately depends upon your
1817switch.  If the switch can reliably fail ports in response to other
1818failures, then either the MII or ARP monitors should work.  For
1819example, in the above example, if the "port3" link fails at the remote
1820end, the MII monitor has no direct means to detect this.  The ARP
1821monitor could be configured with a target at the remote end of port3,
1822thus detecting that failure without switch support.
1823
1824        In general, however, in a multiple switch topology, the ARP
1825monitor can provide a higher level of reliability in detecting end to
1826end connectivity failures (which may be caused by the failure of any
1827individual component to pass traffic for any reason).  Additionally,
1828the ARP monitor should be configured with multiple targets (at least
1829one for each switch in the network).  This will insure that,
1830regardless of which switch is active, the ARP monitor has a suitable
1831target to query.
1832
1833        Note, also, that of late many switches now support a functionality
1834generally referred to as "trunk failover."  This is a feature of the
1835switch that causes the link state of a particular switch port to be set
1836down (or up) when the state of another switch port goes down (or up).
1837Its purpose is to propagate link failures from logically "exterior" ports
1838to the logically "interior" ports that bonding is able to monitor via
1839miimon.  Availability and configuration for trunk failover varies by
1840switch, but this can be a viable alternative to the ARP monitor when using
1841suitable switches.
1842
184312. Configuring Bonding for Maximum Throughput
1844==============================================
1845
184612.1 Maximizing Throughput in a Single Switch Topology
1847------------------------------------------------------
1848
1849        In a single switch configuration, the best method to maximize
1850throughput depends upon the application and network environment.  The
1851various load balancing modes each have strengths and weaknesses in
1852different environments, as detailed below.
1853
1854        For this discussion, we will break down the topologies into
1855two categories.  Depending upon the destination of most traffic, we
1856categorize them into either "gatewayed" or "local" configurations.
1857
1858        In a gatewayed configuration, the "switch" is acting primarily
1859as a router, and the majority of traffic passes through this router to
1860other networks.  An example would be the following:
1861
1862
1863     +----------+                     +----------+
1864     |          |eth0            port1|          | to other networks
1865     | Host A   +---------------------+ router   +------------------->
1866     |          +---------------------+          | Hosts B and C are out
1867     |          |eth1            port2|          | here somewhere
1868     +----------+                     +----------+
1869
1870        The router may be a dedicated router device, or another host
1871acting as a gateway.  For our discussion, the important point is that
1872the majority of traffic from Host A will pass through the router to
1873some other network before reaching its final destination.
1874
1875        In a gatewayed network configuration, although Host A may
1876communicate with many other systems, all of its traffic will be sent
1877and received via one other peer on the local network, the router.
1878
1879        Note that the case of two systems connected directly via
1880multiple physical links is, for purposes of configuring bonding, the
1881same as a gatewayed configuration.  In that case, it happens that all
1882traffic is destined for the "gateway" itself, not some other network
1883beyond the gateway.
1884
1885        In a local configuration, the "switch" is acting primarily as
1886a switch, and the majority of traffic passes through this switch to
1887reach other stations on the same network.  An example would be the
1888following:
1889
1890    +----------+            +----------+       +--------+
1891    |          |eth0   port1|          +-------+ Host B |
1892    |  Host A  +------------+  switch  |port3  +--------+
1893    |          +------------+          |                  +--------+
1894    |          |eth1   port2|          +------------------+ Host C |
1895    +----------+            +----------+port4             +--------+
1896
1897
1898        Again, the switch may be a dedicated switch device, or another
1899host acting as a gateway.  For our discussion, the important point is
1900that the majority of traffic from Host A is destined for other hosts
1901on the same local network (Hosts B and C in the above example).
1902
1903        In summary, in a gatewayed configuration, traffic to and from
1904the bonded device will be to the same MAC level peer on the network
1905(the gateway itself, i.e., the router), regardless of its final
1906destination.  In a local configuration, traffic flows directly to and
1907from the final destinations, thus, each destination (Host B, Host C)
1908will be addressed directly by their individual MAC addresses.
1909
1910        This distinction between a gatewayed and a local network
1911configuration is important because many of the load balancing modes
1912available use the MAC addresses of the local network source and
1913destination to make load balancing decisions.  The behavior of each
1914mode is described below.
1915
1916
191712.1.1 MT Bonding Mode Selection for Single Switch Topology
1918-----------------------------------------------------------
1919
1920        This configuration is the easiest to set up and to understand,
1921although you will have to decide which bonding mode best suits your
1922needs.  The trade offs for each mode are detailed below:
1923
1924balance-rr: This mode is the only mode that will permit a single
1925        TCP/IP connection to stripe traffic across multiple
1926        interfaces. It is therefore the only mode that will allow a
1927        single TCP/IP stream to utilize more than one interface's
1928        worth of throughput.  This comes at a cost, however: the
1929        striping generally results in peer systems receiving packets out
1930        of order, causing TCP/IP's congestion control system to kick
1931        in, often by retransmitting segments.
1932
1933        It is possible to adjust TCP/IP's congestion limits by
1934        altering the net.ipv4.tcp_reordering sysctl parameter.  The
1935        usual default value is 3, and the maximum useful value is 127.
1936        For a four interface balance-rr bond, expect that a single
1937        TCP/IP stream will utilize no more than approximately 2.3
1938        interface's worth of throughput, even after adjusting
1939        tcp_reordering.
1940
1941        Note that the fraction of packets that will be delivered out of
1942        order is highly variable, and is unlikely to be zero.  The level
1943        of reordering depends upon a variety of factors, including the
1944        networking interfaces, the switch, and the topology of the
1945        configuration.  Speaking in general terms, higher speed network
1946        cards produce more reordering (due to factors such as packet
1947        coalescing), and a "many to many" topology will reorder at a
1948        higher rate than a "many slow to one fast" configuration.
1949
1950        Many switches do not support any modes that stripe traffic
1951        (instead choosing a port based upon IP or MAC level addresses);
1952        for those devices, traffic for a particular connection flowing
1953        through the switch to a balance-rr bond will not utilize greater
1954        than one interface's worth of bandwidth.
1955
1956        If you are utilizing protocols other than TCP/IP, UDP for
1957        example, and your application can tolerate out of order
1958        delivery, then this mode can allow for single stream datagram
1959        performance that scales near linearly as interfaces are added
1960        to the bond.
1961
1962        This mode requires the switch to have the appropriate ports
1963        configured for "etherchannel" or "trunking."
1964
1965active-backup: There is not much advantage in this network topology to
1966        the active-backup mode, as the inactive backup devices are all
1967        connected to the same peer as the primary.  In this case, a
1968        load balancing mode (with link monitoring) will provide the
1969        same level of network availability, but with increased
1970        available bandwidth.  On the plus side, active-backup mode
1971        does not require any configuration of the switch, so it may
1972        have value if the hardware available does not support any of
1973        the load balance modes.
1974
1975balance-xor: This mode will limit traffic such that packets destined
1976        for specific peers will always be sent over the same
1977        interface.  Since the destination is determined by the MAC
1978        addresses involved, this mode works best in a "local" network
1979        configuration (as described above), with destinations all on
1980        the same local network.  This mode is likely to be suboptimal
1981        if all your traffic is passed through a single router (i.e., a
1982        "gatewayed" network configuration, as described above).
1983
1984        As with balance-rr, the switch ports need to be configured for
1985        "etherchannel" or "trunking."
1986
1987broadcast: Like active-backup, there is not much advantage to this
1988        mode in this type of network topology.
1989
1990802.3ad: This mode can be a good choice for this type of network
1991        topology.  The 802.3ad mode is an IEEE standard, so all peers
1992        that implement 802.3ad should interoperate well.  The 802.3ad
1993        protocol includes automatic configuration of the aggregates,
1994        so minimal manual configuration of the switch is needed
1995        (typically only to designate that some set of devices is
1996        available for 802.3ad).  The 802.3ad standard also mandates
1997        that frames be delivered in order (within certain limits), so
1998        in general single connections will not see misordering of
1999        packets.  The 802.3ad mode does have some drawbacks: the
2000        standard mandates that all devices in the aggregate operate at
2001        the same speed and duplex.  Also, as with all bonding load
2002        balance modes other than balance-rr, no single connection will
2003        be able to utilize more than a single interface's worth of
2004        bandwidth.  
2005
2006        Additionally, the linux bonding 802.3ad implementation
2007        distributes traffic by peer (using an XOR of MAC addresses),
2008        so in a "gatewayed" configuration, all outgoing traffic will
2009        generally use the same device.  Incoming traffic may also end
2010        up on a single device, but that is dependent upon the
2011        balancing policy of the peer's 8023.ad implementation.  In a
2012        "local" configuration, traffic will be distributed across the
2013        devices in the bond.
2014
2015        Finally, the 802.3ad mode mandates the use of the MII monitor,
2016        therefore, the ARP monitor is not available in this mode.
2017
2018balance-tlb: The balance-tlb mode balances outgoing traffic by peer.
2019        Since the balancing is done according to MAC address, in a
2020        "gatewayed" configuration (as described above), this mode will
2021        send all traffic across a single device.  However, in a
2022        "local" network configuration, this mode balances multiple
2023        local network peers across devices in a vaguely intelligent
2024        manner (not a simple XOR as in balance-xor or 802.3ad mode),
2025        so that mathematically unlucky MAC addresses (i.e., ones that
2026        XOR to the same value) will not all "bunch up" on a single
2027        interface.
2028
2029        Unlike 802.3ad, interfaces may be of differing speeds, and no
2030        special switch configuration is required.  On the down side,
2031        in this mode all incoming traffic arrives over a single
2032        interface, this mode requires certain ethtool support in the
2033        network device driver of the slave interfaces, and the ARP
2034        monitor is not available.
2035
2036balance-alb: This mode is everything that balance-tlb is, and more.
2037        It has all of the features (and restrictions) of balance-tlb,
2038        and will also balance incoming traffic from local network
2039        peers (as described in the Bonding Module Options section,
2040        above).
2041
2042        The only additional down side to this mode is that the network
2043        device driver must support changing the hardware address while
2044        the device is open.
2045
204612.1.2 MT Link Monitoring for Single Switch Topology
2047----------------------------------------------------
2048
2049        The choice of link monitoring may largely depend upon which
2050mode you choose to use.  The more advanced load balancing modes do not
2051support the use of the ARP monitor, and are thus restricted to using
2052the MII monitor (which does not provide as high a level of end to end
2053assurance as the ARP monitor).
2054
205512.2 Maximum Throughput in a Multiple Switch Topology
2056-----------------------------------------------------
2057
2058        Multiple switches may be utilized to optimize for throughput
2059when they are configured in parallel as part of an isolated network
2060between two or more systems, for example:
2061
2062                       +-----------+
2063                       |  Host A   | 
2064                       +-+---+---+-+
2065                         |   |   |
2066                +--------+   |   +---------+
2067                |            |             |
2068         +------+---+  +-----+----+  +-----+----+
2069         | Switch A |  | Switch B |  | Switch C |
2070         +------+---+  +-----+----+  +-----+----+
2071                |            |             |
2072                +--------+   |   +---------+
2073                         |   |   |
2074                       +-+---+---+-+
2075                       |  Host B   | 
2076                       +-----------+
2077
2078        In this configuration, the switches are isolated from one
2079another.  One reason to employ a topology such as this is for an
2080isolated network with many hosts (a cluster configured for high
2081performance, for example), using multiple smaller switches can be more
2082cost effective than a single larger switch, e.g., on a network with 24
2083hosts, three 24 port switches can be significantly less expensive than
2084a single 72 port switch.
2085
2086        If access beyond the network is required, an individual host
2087can be equipped with an additional network device connected to an
2088external network; this host then additionally acts as a gateway.
2089
209012.2.1 MT Bonding Mode Selection for Multiple Switch Topology
2091-------------------------------------------------------------
2092
2093        In actual practice, the bonding mode typically employed in
2094configurations of this type is balance-rr.  Historically, in this
2095network configuration, the usual caveats about out of order packet
2096delivery are mitigated by the use of network adapters that do not do
2097any kind of packet coalescing (via the use of NAPI, or because the
2098device itself does not generate interrupts until some number of
2099packets has arrived).  When employed in this fashion, the balance-rr
2100mode allows individual connections between two hosts to effectively
2101utilize greater than one interface's bandwidth.
2102
210312.2.2 MT Link Monitoring for Multiple Switch Topology
2104------------------------------------------------------
2105
2106        Again, in actual practice, the MII monitor is most often used
2107in this configuration, as performance is given preference over
2108availability.  The ARP monitor will function in this topology, but its
2109advantages over the MII monitor are mitigated by the volume of probes
2110needed as the number of systems involved grows (remember that each
2111host in the network is configured with bonding).
2112
211313. Switch Behavior Issues
2114==========================
2115
211613.1 Link Establishment and Failover Delays
2117-------------------------------------------
2118
2119        Some switches exhibit undesirable behavior with regard to the
2120timing of link up and down reporting by the switch.
2121
2122        First, when a link comes up, some switches may indicate that
2123the link is up (carrier available), but not pass traffic over the
2124interface for some period of time.  This delay is typically due to
2125some type of autonegotiation or routing protocol, but may also occur
2126during switch initialization (e.g., during recovery after a switch
2127failure).  If you find this to be a problem, specify an appropriate
2128value to the updelay bonding module option to delay the use of the
2129relevant interface(s).
2130
2131        Second, some switches may "bounce" the link state one or more
2132times while a link is changing state.  This occurs most commonly while
2133the switch is initializing.  Again, an appropriate updelay value may
2134help.
2135
2136        Note that when a bonding interface has no active links, the
2137driver will immediately reuse the first link that goes up, even if the
2138updelay parameter has been specified (the updelay is ignored in this
2139case).  If there are slave interfaces waiting for the updelay timeout
2140to expire, the interface that first went into that state will be
2141immediately reused.  This reduces down time of the network if the
2142value of updelay has been overestimated, and since this occurs only in
2143cases with no connectivity, there is no additional penalty for
2144ignoring the updelay.
2145
2146        In addition to the concerns about switch timings, if your
2147switches take a long time to go into backup mode, it may be desirable
2148to not activate a backup interface immediately after a link goes down.
2149Failover may be delayed via the downdelay bonding module option.
2150
215113.2 Duplicated Incoming Packets
2152--------------------------------
2153
2154        NOTE: Starting with version 3.0.2, the bonding driver has logic to
2155suppress duplicate packets, which should largely eliminate this problem.
2156The following description is kept for reference.
2157
2158        It is not uncommon to observe a short burst of duplicated
2159traffic when the bonding device is first used, or after it has been
2160idle for some period of time.  This is most easily observed by issuing
2161a "ping" to some other host on the network, and noticing that the
2162output from ping flags duplicates (typically one per slave).
2163
2164        For example, on a bond in active-backup mode with five slaves
2165all connected to one switch, the output may appear as follows:
2166
2167# ping -n 10.0.4.2
2168PING 10.0.4.2 (10.0.4.2) from 10.0.3.10 : 56(84) bytes of data.
216964 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.7 ms
217064 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
217164 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
217264 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
217364 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
217464 bytes from 10.0.4.2: icmp_seq=2 ttl=64 time=0.216 ms
217564 bytes from 10.0.4.2: icmp_seq=3 ttl=64 time=0.267 ms
217664 bytes from 10.0.4.2: icmp_seq=4 ttl=64 time=0.222 ms
2177
2178        This is not due to an error in the bonding driver, rather, it
2179is a side effect of how many switches update their MAC forwarding
2180tables.  Initially, the switch does not associate the MAC address in
2181the packet with a particular switch port, and so it may send the
2182traffic to all ports until its MAC forwarding table is updated.  Since
2183the interfaces attached to the bond may occupy multiple ports on a
2184single switch, when the switch (temporarily) floods the traffic to all
2185ports, the bond device receives multiple copies of the same packet
2186(one per slave device).
2187
2188        The duplicated packet behavior is switch dependent, some
2189switches exhibit this, and some do not.  On switches that display this
2190behavior, it can be induced by clearing the MAC forwarding table (on
2191most Cisco switches, the privileged command "clear mac address-table
2192dynamic" will accomplish this).
2193
219414. Hardware Specific Considerations
2195====================================
2196
2197        This section contains additional information for configuring
2198bonding on specific hardware platforms, or for interfacing bonding
2199with particular switches or other devices.
2200
220114.1 IBM BladeCenter
2202--------------------
2203
2204        This applies to the JS20 and similar systems.
2205
2206        On the JS20 blades, the bonding driver supports only
2207balance-rr, active-backup, balance-tlb and balance-alb modes.  This is
2208largely due to the network topology inside the BladeCenter, detailed
2209below.
2210
2211JS20 network adapter information
2212--------------------------------
2213
2214        All JS20s come with two Broadcom Gigabit Ethernet ports
2215integrated on the planar (that's "motherboard" in IBM-speak).  In the
2216BladeCenter chassis, the eth0 port of all JS20 blades is hard wired to
2217I/O Module #1; similarly, all eth1 ports are wired to I/O Module #2.
2218An add-on Broadcom daughter card can be installed on a JS20 to provide
2219two more Gigabit Ethernet ports.  These ports, eth2 and eth3, are
2220wired to I/O Modules 3 and 4, respectively.
2221
2222        Each I/O Module may contain either a switch or a passthrough
2223module (which allows ports to be directly connected to an external
2224switch).  Some bonding modes require a specific BladeCenter internal
2225network topology in order to function; these are detailed below.
2226
2227        Additional BladeCenter-specific networking information can be
2228found in two IBM Redbooks (www.ibm.com/redbooks):
2229
2230"IBM eServer BladeCenter Networking Options"
2231"IBM eServer BladeCenter Layer 2-7 Network Switching"
2232
2233BladeCenter networking configuration
2234------------------------------------
2235
2236        Because a BladeCenter can be configured in a very large number
2237of ways, this discussion will be confined to describing basic
2238configurations.
2239
2240        Normally, Ethernet Switch Modules (ESMs) are used in I/O
2241modules 1 and 2.  In this configuration, the eth0 and eth1 ports of a
2242JS20 will be connected to different internal switches (in the
2243respective I/O modules).
2244
2245        A passthrough module (OPM or CPM, optical or copper,
2246passthrough module) connects the I/O module directly to an external
2247switch.  By using PMs in I/O module #1 and #2, the eth0 and eth1
2248interfaces of a JS20 can be redirected to the outside world and
2249connected to a common external switch.
2250
2251        Depending upon the mix of ESMs and PMs, the network will
2252appear to bonding as either a single switch topology (all PMs) or as a
2253multiple switch topology (one or more ESMs, zero or more PMs).  It is
2254also possible to connect ESMs together, resulting in a configuration
2255much like the example in "High Availability in a Multiple Switch
2256Topology," above.
2257
2258Requirements for specific modes
2259-------------------------------
2260
2261        The balance-rr mode requires the use of passthrough modules
2262for devices in the bond, all connected to an common external switch.
2263That switch must be configured for "etherchannel" or "trunking" on the
2264appropriate ports, as is usual for balance-rr.
2265
2266        The balance-alb and balance-tlb modes will function with
2267either switch modules or passthrough modules (or a mix).  The only
2268specific requirement for these modes is that all network interfaces
2269must be able to reach all destinations for traffic sent over the
2270bonding device (i.e., the network must converge at some point outside
2271the BladeCenter).
2272
2273        The active-backup mode has no additional requirements.
2274
2275Link monitoring issues
2276----------------------
2277
2278        When an Ethernet Switch Module is in place, only the ARP
2279monitor will reliably detect link loss to an external switch.  This is
2280nothing unusual, but examination of the BladeCenter cabinet would
2281suggest that the "external" network ports are the ethernet ports for
2282the system, when it fact there is a switch between these "external"
2283ports and the devices on the JS20 system itself.  The MII monitor is
2284only able to detect link failures between the ESM and the JS20 system.
2285
2286        When a passthrough module is in place, the MII monitor does
2287detect failures to the "external" port, which is then directly
2288connected to the JS20 system.
2289
2290Other concerns
2291--------------
2292
2293        The Serial Over LAN (SoL) link is established over the primary
2294ethernet (eth0) only, therefore, any loss of link to eth0 will result
2295in losing your SoL connection.  It will not fail over with other
2296network traffic, as the SoL system is beyond the control of the
2297bonding driver.
2298
2299        It may be desirable to disable spanning tree on the switch
2300(either the internal Ethernet Switch Module, or an external switch) to
2301avoid fail-over delay issues when using bonding.
2302
2303        
230415. Frequently Asked Questions
2305==============================
2306
23071.  Is it SMP safe?
2308
2309        Yes. The old 2.0.xx channel bonding patch was not SMP safe.
2310The new driver was designed to be SMP safe from the start.
2311
23122.  What type of cards will work with it?
2313
2314        Any Ethernet type cards (you can even mix cards - a Intel
2315EtherExpress PRO/100 and a 3com 3c905b, for example).  For most modes,
2316devices need not be of the same speed.
2317
2318        Starting with version 3.2.1, bonding also supports Infiniband
2319slaves in active-backup mode.
2320
23213.  How many bonding devices can I have?
2322
2323        There is no limit.
2324
23254.  How many slaves can a bonding device have?
2326
2327        This is limited only by the number of network interfaces Linux
2328supports and/or the number of network cards you can place in your
2329system.
2330
23315.  What happens when a slave link dies?
2332
2333        If link monitoring is enabled, then the failing device will be
2334disabled.  The active-backup mode will fail over to a backup link, and
2335other modes will ignore the failed link.  The link will continue to be
2336monitored, and should it recover, it will rejoin the bond (in whatever
2337manner is appropriate for the mode). See the sections on High
2338Availability and the documentation for each mode for additional
2339information.
2340        
2341        Link monitoring can be enabled via either the miimon or
2342arp_interval parameters (described in the module parameters section,
2343above).  In general, miimon monitors the carrier state as sensed by
2344the underlying network device, and the arp monitor (arp_interval)
2345monitors connectivity to another host on the local network.
2346
2347        If no link monitoring is configured, the bonding driver will
2348be unable to detect link failures, and will assume that all links are
2349always available.  This will likely result in lost packets, and a
2350resulting degradation of performance.  The precise performance loss
2351depends upon the bonding mode and network configuration.
2352
23536.  Can bonding be used for High Availability?
2354
2355        Yes.  See the section on High Availability for details.
2356
23577.  Which switches/systems does it work with?
2358
2359        The full answer to this depends upon the desired mode.
2360
2361        In the basic balance modes (balance-rr and balance-xor), it
2362works with any system that supports etherchannel (also called
2363trunking).  Most managed switches currently available have such
2364support, and many unmanaged switches as well.
2365
2366        The advanced balance modes (balance-tlb and balance-alb) do
2367not have special switch requirements, but do need device drivers that
2368support specific features (described in the appropriate section under
2369module parameters, above).
2370
2371        In 802.3ad mode, it works with systems that support IEEE
2372802.3ad Dynamic Link Aggregation.  Most managed and many unmanaged
2373switches currently available support 802.3ad.
2374
2375        The active-backup mode should work with any Layer-II switch.
2376
23778.  Where does a bonding device get its MAC address from?
2378
2379        When using slave devices that have fixed MAC addresses, or when
2380the fail_over_mac option is enabled, the bonding device's MAC address is
2381the MAC address of the active slave.
2382
2383        For other configurations, if not explicitly configured (with
2384ifconfig or ip link), the MAC address of the bonding device is taken from
2385its first slave device.  This MAC address is then passed to all following
2386slaves and remains persistent (even if the first slave is removed) until
2387the bonding device is brought down or reconfigured.
2388
2389        If you wish to change the MAC address, you can set it with
2390ifconfig or ip link:
2391
2392# ifconfig bond0 hw ether 00:11:22:33:44:55
2393
2394# ip link set bond0 address 66:77:88:99:aa:bb
2395
2396        The MAC address can be also changed by bringing down/up the
2397device and then changing its slaves (or their order):
2398
2399# ifconfig bond0 down ; modprobe -r bonding
2400# ifconfig bond0 .... up
2401# ifenslave bond0 eth...
2402
2403        This method will automatically take the address from the next
2404slave that is added.
2405
2406        To restore your slaves' MAC addresses, you need to detach them
2407from the bond (`ifenslave -d bond0 eth0'). The bonding driver will
2408then restore the MAC addresses that the slaves had before they were
2409enslaved.
2410
241116. Resources and Links
2412=======================
2413
2414The latest version of the bonding driver can be found in the latest
2415version of the linux kernel, found on http://kernel.org
2416
2417The latest version of this document can be found in either the latest
2418kernel source (named Documentation/networking/bonding.txt), or on the
2419bonding sourceforge site:
2420
2421http://www.sourceforge.net/projects/bonding
2422
2423Discussions regarding the bonding driver take place primarily on the
2424bonding-devel mailing list, hosted at sourceforge.net.  If you have
2425questions or problems, post them to the list.  The list address is:
2426
2427bonding-devel@lists.sourceforge.net
2428
2429        The administrative interface (to subscribe or unsubscribe) can
2430be found at:
2431
2432https://lists.sourceforge.net/lists/listinfo/bonding-devel
2433
2434Donald Becker's Ethernet Drivers and diag programs may be found at :
2435 - http://www.scyld.com/network/
2436
2437You will also find a lot of information regarding Ethernet, NWay, MII,
2438etc. at www.scyld.com.
2439
2440-- END --
2441
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