1.. SPDX-License-Identifier: GPL-2.0 2 3=================================== 4Linux Ethernet Bonding Driver HOWTO 5=================================== 6 7Latest update: 27 April 2011 8 9Initial release: Thomas Davis <tadavis at lbl.gov> 10 11Corrections, HA extensions: 2000/10/03-15: 12 13 - Willy Tarreau <willy at meta-x.org> 14 - Constantine Gavrilov <const-g at xpert.com> 15 - Chad N. Tindel <ctindel at ieee dot org> 16 - Janice Girouard <girouard at us dot ibm dot com> 17 - Jay Vosburgh <fubar at us dot ibm dot com> 18 19Reorganized and updated Feb 2005 by Jay Vosburgh 20Added Sysfs information: 2006/04/24 21 22 - Mitch Williams <mitch.a.williams at intel.com> 23 24Introduction 25============ 26 27The Linux bonding driver provides a method for aggregating 28multiple network interfaces into a single logical "bonded" interface. 29The behavior of the bonded interfaces depends upon the mode; generally 30speaking, modes provide either hot standby or load balancing services. 31Additionally, link integrity monitoring may be performed. 32 33The bonding driver originally came from Donald Becker's 34beowulf patches for kernel 2.0. It has changed quite a bit since, and 35the original tools from extreme-linux and beowulf sites will not work 36with this version of the driver. 37 38For new versions of the driver, updated userspace tools, and 39who to ask for help, please follow the links at the end of this file. 40 41.. Table of Contents 42 43 1. Bonding Driver Installation 44 45 2. Bonding Driver Options 46 47 3. Configuring Bonding Devices 48 3.1 Configuration with Sysconfig Support 49 3.1.1 Using DHCP with Sysconfig 50 3.1.2 Configuring Multiple Bonds with Sysconfig 51 3.2 Configuration with Initscripts Support 52 3.2.1 Using DHCP with Initscripts 53 3.2.2 Configuring Multiple Bonds with Initscripts 54 3.3 Configuring Bonding Manually with Ifenslave 55 3.3.1 Configuring Multiple Bonds Manually 56 3.4 Configuring Bonding Manually via Sysfs 57 3.5 Configuration with Interfaces Support 58 3.6 Overriding Configuration for Special Cases 59 3.7 Configuring LACP for 802.3ad mode in a more secure way 60 61 4. Querying Bonding Configuration 62 4.1 Bonding Configuration 63 4.2 Network Configuration 64 65 5. Switch Configuration 66 67 6. 802.1q VLAN Support 68 69 7. Link Monitoring 70 7.1 ARP Monitor Operation 71 7.2 Configuring Multiple ARP Targets 72 7.3 MII Monitor Operation 73 74 8. Potential Trouble Sources 75 8.1 Adventures in Routing 76 8.2 Ethernet Device Renaming 77 8.3 Painfully Slow Or No Failed Link Detection By Miimon 78 79 9. SNMP agents 80 81 10. Promiscuous mode 82 83 11. Configuring Bonding for High Availability 84 11.1 High Availability in a Single Switch Topology 85 11.2 High Availability in a Multiple Switch Topology 86 11.2.1 HA Bonding Mode Selection for Multiple Switch Topology 87 11.2.2 HA Link Monitoring for Multiple Switch Topology 88 89 12. Configuring Bonding for Maximum Throughput 90 12.1 Maximum Throughput in a Single Switch Topology 91 12.1.1 MT Bonding Mode Selection for Single Switch Topology 92 12.1.2 MT Link Monitoring for Single Switch Topology 93 12.2 Maximum Throughput in a Multiple Switch Topology 94 12.2.1 MT Bonding Mode Selection for Multiple Switch Topology 95 12.2.2 MT Link Monitoring for Multiple Switch Topology 96 97 13. Switch Behavior Issues 98 13.1 Link Establishment and Failover Delays 99 13.2 Duplicated Incoming Packets 100 101 14. Hardware Specific Considerations 102 14.1 IBM BladeCenter 103 104 15. Frequently Asked Questions 105 106 16. Resources and Links 107 108 1091. Bonding Driver Installation 110============================== 111 112Most popular distro kernels ship with the bonding driver 113already available as a module. If your distro does not, or you 114have need to compile bonding from source (e.g., configuring and 115installing a mainline kernel from kernel.org), you'll need to perform 116the following steps: 117 1181.1 Configure and build the kernel with bonding 119----------------------------------------------- 120 121The current version of the bonding driver is available in the 122drivers/net/bonding subdirectory of the most recent kernel source 123(which is available on http://kernel.org). Most users "rolling their 124own" will want to use the most recent kernel from kernel.org. 125 126Configure kernel with "make menuconfig" (or "make xconfig" or 127"make config"), then select "Bonding driver support" in the "Network 128device support" section. It is recommended that you configure the 129driver as module since it is currently the only way to pass parameters 130to the driver or configure more than one bonding device. 131 132Build and install the new kernel and modules. 133 1341.2 Bonding Control Utility 135--------------------------- 136 137It is recommended to configure bonding via iproute2 (netlink) 138or sysfs, the old ifenslave control utility is obsolete. 139 1402. Bonding Driver Options 141========================= 142 143Options for the bonding driver are supplied as parameters to the 144bonding module at load time, or are specified via sysfs. 145 146Module options may be given as command line arguments to the 147insmod or modprobe command, but are usually specified in either the 148``/etc/modprobe.d/*.conf`` configuration files, or in a distro-specific 149configuration file (some of which are detailed in the next section). 150 151Details on bonding support for sysfs is provided in the 152"Configuring Bonding Manually via Sysfs" section, below. 153 154The available bonding driver parameters are listed below. If a 155parameter is not specified the default value is used. When initially 156configuring a bond, it is recommended "tail -f /var/log/messages" be 157run in a separate window to watch for bonding driver error messages. 158 159It is critical that either the miimon or arp_interval and 160arp_ip_target parameters be specified, otherwise serious network 161degradation will occur during link failures. Very few devices do not 162support at least miimon, so there is really no reason not to use it. 163 164Options with textual values will accept either the text name 165or, for backwards compatibility, the option value. E.g., 166"mode=802.3ad" and "mode=4" set the same mode. 167 168The parameters are as follows: 169 170active_slave 171 172 Specifies the new active slave for modes that support it 173 (active-backup, balance-alb and balance-tlb). Possible values 174 are the name of any currently enslaved interface, or an empty 175 string. If a name is given, the slave and its link must be up in order 176 to be selected as the new active slave. If an empty string is 177 specified, the current active slave is cleared, and a new active 178 slave is selected automatically. 179 180 Note that this is only available through the sysfs interface. No module 181 parameter by this name exists. 182 183 The normal value of this option is the name of the currently 184 active slave, or the empty string if there is no active slave or 185 the current mode does not use an active slave. 186 187ad_actor_sys_prio 188 189 In an AD system, this specifies the system priority. The allowed range 190 is 1 - 65535. If the value is not specified, it takes 65535 as the 191 default value. 192 193 This parameter has effect only in 802.3ad mode and is available through 194 SysFs interface. 195 196ad_actor_system 197 198 In an AD system, this specifies the mac-address for the actor in 199 protocol packet exchanges (LACPDUs). The value cannot be a multicast 200 address. If the all-zeroes MAC is specified, bonding will internally 201 use the MAC of the bond itself. It is preferred to have the 202 local-admin bit set for this mac but driver does not enforce it. If 203 the value is not given then system defaults to using the masters' 204 mac address as actors' system address. 205 206 This parameter has effect only in 802.3ad mode and is available through 207 SysFs interface. 208 209ad_select 210 211 Specifies the 802.3ad aggregation selection logic to use. The 212 possible values and their effects are: 213 214 stable or 0 215 216 The active aggregator is chosen by largest aggregate 217 bandwidth. 218 219 Reselection of the active aggregator occurs only when all 220 slaves of the active aggregator are down or the active 221 aggregator has no slaves. 222 223 This is the default value. 224 225 bandwidth or 1 226 227 The active aggregator is chosen by largest aggregate 228 bandwidth. Reselection occurs if: 229 230 - A slave is added to or removed from the bond 231 232 - Any slave's link state changes 233 234 - Any slave's 802.3ad association state changes 235 236 - The bond's administrative state changes to up 237 238 count or 2 239 240 The active aggregator is chosen by the largest number of 241 ports (slaves). Reselection occurs as described under the 242 "bandwidth" setting, above. 243 244 The bandwidth and count selection policies permit failover of 245 802.3ad aggregations when partial failure of the active aggregator 246 occurs. This keeps the aggregator with the highest availability 247 (either in bandwidth or in number of ports) active at all times. 248 249 This option was added in bonding version 3.4.0. 250 251ad_user_port_key 252 253 In an AD system, the port-key has three parts as shown below - 254 255 ===== ============ 256 Bits Use 257 ===== ============ 258 00 Duplex 259 01-05 Speed 260 06-15 User-defined 261 ===== ============ 262 263 This defines the upper 10 bits of the port key. The values can be 264 from 0 - 1023. If not given, the system defaults to 0. 265 266 This parameter has effect only in 802.3ad mode and is available through 267 SysFs interface. 268 269all_slaves_active 270 271 Specifies that duplicate frames (received on inactive ports) should be 272 dropped (0) or delivered (1). 273 274 Normally, bonding will drop duplicate frames (received on inactive 275 ports), which is desirable for most users. But there are some times 276 it is nice to allow duplicate frames to be delivered. 277 278 The default value is 0 (drop duplicate frames received on inactive 279 ports). 280 281arp_interval 282 283 Specifies the ARP link monitoring frequency in milliseconds. 284 285 The ARP monitor works by periodically checking the slave 286 devices to determine whether they have sent or received 287 traffic recently (the precise criteria depends upon the 288 bonding mode, and the state of the slave). Regular traffic is 289 generated via ARP probes issued for the addresses specified by 290 the arp_ip_target option. 291 292 This behavior can be modified by the arp_validate option, 293 below. 294 295 If ARP monitoring is used in an etherchannel compatible mode 296 (modes 0 and 2), the switch should be configured in a mode 297 that evenly distributes packets across all links. If the 298 switch is configured to distribute the packets in an XOR 299 fashion, all replies from the ARP targets will be received on 300 the same link which could cause the other team members to 301 fail. ARP monitoring should not be used in conjunction with 302 miimon. A value of 0 disables ARP monitoring. The default 303 value is 0. 304 305arp_ip_target 306 307 Specifies the IP addresses to use as ARP monitoring peers when 308 arp_interval is > 0. These are the targets of the ARP request 309 sent to determine the health of the link to the targets. 310 Specify these values in ddd.ddd.ddd.ddd format. Multiple IP 311 addresses must be separated by a comma. At least one IP 312 address must be given for ARP monitoring to function. The 313 maximum number of targets that can be specified is 16. The 314 default value is no IP addresses. 315 316ns_ip6_target 317 318 Specifies the IPv6 addresses to use as IPv6 monitoring peers when 319 arp_interval is > 0. These are the targets of the NS request 320 sent to determine the health of the link to the targets. 321 Specify these values in ffff:ffff::ffff:ffff format. Multiple IPv6 322 addresses must be separated by a comma. At least one IPv6 323 address must be given for NS/NA monitoring to function. The 324 maximum number of targets that can be specified is 16. The 325 default value is no IPv6 addresses. 326 327arp_validate 328 329 Specifies whether or not ARP probes and replies should be 330 validated in any mode that supports arp monitoring, or whether 331 non-ARP traffic should be filtered (disregarded) for link 332 monitoring purposes. 333 334 Possible values are: 335 336 none or 0 337 338 No validation or filtering is performed. 339 340 active or 1 341 342 Validation is performed only for the active slave. 343 344 backup or 2 345 346 Validation is performed only for backup slaves. 347 348 all or 3 349 350 Validation is performed for all slaves. 351 352 filter or 4 353 354 Filtering is applied to all slaves. No validation is 355 performed. 356 357 filter_active or 5 358 359 Filtering is applied to all slaves, validation is performed 360 only for the active slave. 361 362 filter_backup or 6 363 364 Filtering is applied to all slaves, validation is performed 365 only for backup slaves. 366 367 Validation: 368 369 Enabling validation causes the ARP monitor to examine the incoming 370 ARP requests and replies, and only consider a slave to be up if it 371 is receiving the appropriate ARP traffic. 372 373 For an active slave, the validation checks ARP replies to confirm 374 that they were generated by an arp_ip_target. Since backup slaves 375 do not typically receive these replies, the validation performed 376 for backup slaves is on the broadcast ARP request sent out via the 377 active slave. It is possible that some switch or network 378 configurations may result in situations wherein the backup slaves 379 do not receive the ARP requests; in such a situation, validation 380 of backup slaves must be disabled. 381 382 The validation of ARP requests on backup slaves is mainly helping 383 bonding to decide which slaves are more likely to work in case of 384 the active slave failure, it doesn't really guarantee that the 385 backup slave will work if it's selected as the next active slave. 386 387 Validation is useful in network configurations in which multiple 388 bonding hosts are concurrently issuing ARPs to one or more targets 389 beyond a common switch. Should the link between the switch and 390 target fail (but not the switch itself), the probe traffic 391 generated by the multiple bonding instances will fool the standard 392 ARP monitor into considering the links as still up. Use of 393 validation can resolve this, as the ARP monitor will only consider 394 ARP requests and replies associated with its own instance of 395 bonding. 396 397 Filtering: 398 399 Enabling filtering causes the ARP monitor to only use incoming ARP 400 packets for link availability purposes. Arriving packets that are 401 not ARPs are delivered normally, but do not count when determining 402 if a slave is available. 403 404 Filtering operates by only considering the reception of ARP 405 packets (any ARP packet, regardless of source or destination) when 406 determining if a slave has received traffic for link availability 407 purposes. 408 409 Filtering is useful in network configurations in which significant 410 levels of third party broadcast traffic would fool the standard 411 ARP monitor into considering the links as still up. Use of 412 filtering can resolve this, as only ARP traffic is considered for 413 link availability purposes. 414 415 This option was added in bonding version 3.1.0. 416 417arp_all_targets 418 419 Specifies the quantity of arp_ip_targets that must be reachable 420 in order for the ARP monitor to consider a slave as being up. 421 This option affects only active-backup mode for slaves with 422 arp_validation enabled. 423 424 Possible values are: 425 426 any or 0 427 428 consider the slave up only when any of the arp_ip_targets 429 is reachable 430 431 all or 1 432 433 consider the slave up only when all of the arp_ip_targets 434 are reachable 435 436arp_missed_max 437 438 Specifies the number of arp_interval monitor checks that must 439 fail in order for an interface to be marked down by the ARP monitor. 440 441 In order to provide orderly failover semantics, backup interfaces 442 are permitted an extra monitor check (i.e., they must fail 443 arp_missed_max + 1 times before being marked down). 444 445 The default value is 2, and the allowable range is 1 - 255. 446 447downdelay 448 449 Specifies the time, in milliseconds, to wait before disabling 450 a slave after a link failure has been detected. This option 451 is only valid for the miimon link monitor. The downdelay 452 value should be a multiple of the miimon value; if not, it 453 will be rounded down to the nearest multiple. The default 454 value is 0. 455 456fail_over_mac 457 458 Specifies whether active-backup mode should set all slaves to 459 the same MAC address at enslavement (the traditional 460 behavior), or, when enabled, perform special handling of the 461 bond's MAC address in accordance with the selected policy. 462 463 Possible values are: 464 465 none or 0 466 467 This setting disables fail_over_mac, and causes 468 bonding to set all slaves of an active-backup bond to 469 the same MAC address at enslavement time. This is the 470 default. 471 472 active or 1 473 474 The "active" fail_over_mac policy indicates that the 475 MAC address of the bond should always be the MAC 476 address of the currently active slave. The MAC 477 address of the slaves is not changed; instead, the MAC 478 address of the bond changes during a failover. 479 480 This policy is useful for devices that cannot ever 481 alter their MAC address, or for devices that refuse 482 incoming broadcasts with their own source MAC (which 483 interferes with the ARP monitor). 484 485 The down side of this policy is that every device on 486 the network must be updated via gratuitous ARP, 487 vs. just updating a switch or set of switches (which 488 often takes place for any traffic, not just ARP 489 traffic, if the switch snoops incoming traffic to 490 update its tables) for the traditional method. If the 491 gratuitous ARP is lost, communication may be 492 disrupted. 493 494 When this policy is used in conjunction with the mii 495 monitor, devices which assert link up prior to being 496 able to actually transmit and receive are particularly 497 susceptible to loss of the gratuitous ARP, and an 498 appropriate updelay setting may be required. 499 500 follow or 2 501 502 The "follow" fail_over_mac policy causes the MAC 503 address of the bond to be selected normally (normally 504 the MAC address of the first slave added to the bond). 505 However, the second and subsequent slaves are not set 506 to this MAC address while they are in a backup role; a 507 slave is programmed with the bond's MAC address at 508 failover time (and the formerly active slave receives 509 the newly active slave's MAC address). 510 511 This policy is useful for multiport devices that 512 either become confused or incur a performance penalty 513 when multiple ports are programmed with the same MAC 514 address. 515 516 517 The default policy is none, unless the first slave cannot 518 change its MAC address, in which case the active policy is 519 selected by default. 520 521 This option may be modified via sysfs only when no slaves are 522 present in the bond. 523 524 This option was added in bonding version 3.2.0. The "follow" 525 policy was added in bonding version 3.3.0. 526 527lacp_active 528 Option specifying whether to send LACPDU frames periodically. 529 530 off or 0 531 LACPDU frames acts as "speak when spoken to". 532 533 on or 1 534 LACPDU frames are sent along the configured links 535 periodically. See lacp_rate for more details. 536 537 The default is on. 538 539lacp_rate 540 541 Option specifying the rate in which we'll ask our link partner 542 to transmit LACPDU packets in 802.3ad mode. Possible values 543 are: 544 545 slow or 0 546 Request partner to transmit LACPDUs every 30 seconds 547 548 fast or 1 549 Request partner to transmit LACPDUs every 1 second 550 551 The default is slow. 552 553max_bonds 554 555 Specifies the number of bonding devices to create for this 556 instance of the bonding driver. E.g., if max_bonds is 3, and 557 the bonding driver is not already loaded, then bond0, bond1 558 and bond2 will be created. The default value is 1. Specifying 559 a value of 0 will load bonding, but will not create any devices. 560 561miimon 562 563 Specifies the MII link monitoring frequency in milliseconds. 564 This determines how often the link state of each slave is 565 inspected for link failures. A value of zero disables MII 566 link monitoring. A value of 100 is a good starting point. 567 The use_carrier option, below, affects how the link state is 568 determined. See the High Availability section for additional 569 information. The default value is 100 if arp_interval is not 570 set. 571 572min_links 573 574 Specifies the minimum number of links that must be active before 575 asserting carrier. It is similar to the Cisco EtherChannel min-links 576 feature. This allows setting the minimum number of member ports that 577 must be up (link-up state) before marking the bond device as up 578 (carrier on). This is useful for situations where higher level services 579 such as clustering want to ensure a minimum number of low bandwidth 580 links are active before switchover. This option only affect 802.3ad 581 mode. 582 583 The default value is 0. This will cause carrier to be asserted (for 584 802.3ad mode) whenever there is an active aggregator, regardless of the 585 number of available links in that aggregator. Note that, because an 586 aggregator cannot be active without at least one available link, 587 setting this option to 0 or to 1 has the exact same effect. 588 589mode 590 591 Specifies one of the bonding policies. The default is 592 balance-rr (round robin). Possible values are: 593 594 balance-rr or 0 595 596 Round-robin policy: Transmit packets in sequential 597 order from the first available slave through the 598 last. This mode provides load balancing and fault 599 tolerance. 600 601 active-backup or 1 602 603 Active-backup policy: Only one slave in the bond is 604 active. A different slave becomes active if, and only 605 if, the active slave fails. The bond's MAC address is 606 externally visible on only one port (network adapter) 607 to avoid confusing the switch. 608 609 In bonding version 2.6.2 or later, when a failover 610 occurs in active-backup mode, bonding will issue one 611 or more gratuitous ARPs on the newly active slave. 612 One gratuitous ARP is issued for the bonding master 613 interface and each VLAN interfaces configured above 614 it, provided that the interface has at least one IP 615 address configured. Gratuitous ARPs issued for VLAN 616 interfaces are tagged with the appropriate VLAN id. 617 618 This mode provides fault tolerance. The primary 619 option, documented below, affects the behavior of this 620 mode. 621 622 balance-xor or 2 623 624 XOR policy: Transmit based on the selected transmit 625 hash policy. The default policy is a simple [(source 626 MAC address XOR'd with destination MAC address XOR 627 packet type ID) modulo slave count]. Alternate transmit 628 policies may be selected via the xmit_hash_policy option, 629 described below. 630 631 This mode provides load balancing and fault tolerance. 632 633 broadcast or 3 634 635 Broadcast policy: transmits everything on all slave 636 interfaces. This mode provides fault tolerance. 637 638 802.3ad or 4 639 640 IEEE 802.3ad Dynamic link aggregation. Creates 641 aggregation groups that share the same speed and 642 duplex settings. Utilizes all slaves in the active 643 aggregator according to the 802.3ad specification. 644 645 Slave selection for outgoing traffic is done according 646 to the transmit hash policy, which may be changed from 647 the default simple XOR policy via the xmit_hash_policy 648 option, documented below. Note that not all transmit 649 policies may be 802.3ad compliant, particularly in 650 regards to the packet mis-ordering requirements of 651 section 43.2.4 of the 802.3ad standard. Differing 652 peer implementations will have varying tolerances for 653 noncompliance. 654 655 Prerequisites: 656 657 1. Ethtool support in the base drivers for retrieving 658 the speed and duplex of each slave. 659 660 2. A switch that supports IEEE 802.3ad Dynamic link 661 aggregation. 662 663 Most switches will require some type of configuration 664 to enable 802.3ad mode. 665 666 balance-tlb or 5 667 668 Adaptive transmit load balancing: channel bonding that 669 does not require any special switch support. 670 671 In tlb_dynamic_lb=1 mode; the outgoing traffic is 672 distributed according to the current load (computed 673 relative to the speed) on each slave. 674 675 In tlb_dynamic_lb=0 mode; the load balancing based on 676 current load is disabled and the load is distributed 677 only using the hash distribution. 678 679 Incoming traffic is received by the current slave. 680 If the receiving slave fails, another slave takes over 681 the MAC address of the failed receiving slave. 682 683 Prerequisite: 684 685 Ethtool support in the base drivers for retrieving the 686 speed of each slave. 687 688 balance-alb or 6 689 690 Adaptive load balancing: includes balance-tlb plus 691 receive load balancing (rlb) for IPV4 traffic, and 692 does not require any special switch support. The 693 receive load balancing is achieved by ARP negotiation. 694 The bonding driver intercepts the ARP Replies sent by 695 the local system on their way out and overwrites the 696 source hardware address with the unique hardware 697 address of one of the slaves in the bond such that 698 different peers use different hardware addresses for 699 the server. 700 701 Receive traffic from connections created by the server 702 is also balanced. When the local system sends an ARP 703 Request the bonding driver copies and saves the peer's 704 IP information from the ARP packet. When the ARP 705 Reply arrives from the peer, its hardware address is 706 retrieved and the bonding driver initiates an ARP 707 reply to this peer assigning it to one of the slaves 708 in the bond. A problematic outcome of using ARP 709 negotiation for balancing is that each time that an 710 ARP request is broadcast it uses the hardware address 711 of the bond. Hence, peers learn the hardware address 712 of the bond and the balancing of receive traffic 713 collapses to the current slave. This is handled by 714 sending updates (ARP Replies) to all the peers with 715 their individually assigned hardware address such that 716 the traffic is redistributed. Receive traffic is also 717 redistributed when a new slave is added to the bond 718 and when an inactive slave is re-activated. The 719 receive load is distributed sequentially (round robin) 720 among the group of highest speed slaves in the bond. 721 722 When a link is reconnected or a new slave joins the 723 bond the receive traffic is redistributed among all 724 active slaves in the bond by initiating ARP Replies 725 with the selected MAC address to each of the 726 clients. The updelay parameter (detailed below) must 727 be set to a value equal or greater than the switch's 728 forwarding delay so that the ARP Replies sent to the 729 peers will not be blocked by the switch. 730 731 Prerequisites: 732 733 1. Ethtool support in the base drivers for retrieving 734 the speed of each slave. 735 736 2. Base driver support for setting the hardware 737 address of a device while it is open. This is 738 required so that there will always be one slave in the 739 team using the bond hardware address (the 740 curr_active_slave) while having a unique hardware 741 address for each slave in the bond. If the 742 curr_active_slave fails its hardware address is 743 swapped with the new curr_active_slave that was 744 chosen. 745 746num_grat_arp, 747num_unsol_na 748 749 Specify the number of peer notifications (gratuitous ARPs and 750 unsolicited IPv6 Neighbor Advertisements) to be issued after a 751 failover event. As soon as the link is up on the new slave 752 (possibly immediately) a peer notification is sent on the 753 bonding device and each VLAN sub-device. This is repeated at 754 the rate specified by peer_notif_delay if the number is 755 greater than 1. 756 757 The valid range is 0 - 255; the default value is 1. These options 758 affect only the active-backup mode. These options were added for 759 bonding versions 3.3.0 and 3.4.0 respectively. 760 761 From Linux 3.0 and bonding version 3.7.1, these notifications 762 are generated by the ipv4 and ipv6 code and the numbers of 763 repetitions cannot be set independently. 764 765packets_per_slave 766 767 Specify the number of packets to transmit through a slave before 768 moving to the next one. When set to 0 then a slave is chosen at 769 random. 770 771 The valid range is 0 - 65535; the default value is 1. This option 772 has effect only in balance-rr mode. 773 774peer_notif_delay 775 776 Specify the delay, in milliseconds, between each peer 777 notification (gratuitous ARP and unsolicited IPv6 Neighbor 778 Advertisement) when they are issued after a failover event. 779 This delay should be a multiple of the MII link monitor interval 780 (miimon). 781 782 The valid range is 0 - 300000. The default value is 0, which means 783 to match the value of the MII link monitor interval. 784 785prio 786 Slave priority. A higher number means higher priority. 787 The primary slave has the highest priority. This option also 788 follows the primary_reselect rules. 789 790 This option could only be configured via netlink, and is only valid 791 for active-backup(1), balance-tlb (5) and balance-alb (6) mode. 792 The valid value range is a signed 32 bit integer. 793 794 The default value is 0. 795 796primary 797 798 A string (eth0, eth2, etc) specifying which slave is the 799 primary device. The specified device will always be the 800 active slave while it is available. Only when the primary is 801 off-line will alternate devices be used. This is useful when 802 one slave is preferred over another, e.g., when one slave has 803 higher throughput than another. 804 805 The primary option is only valid for active-backup(1), 806 balance-tlb (5) and balance-alb (6) mode. 807 808primary_reselect 809 810 Specifies the reselection policy for the primary slave. This 811 affects how the primary slave is chosen to become the active slave 812 when failure of the active slave or recovery of the primary slave 813 occurs. This option is designed to prevent flip-flopping between 814 the primary slave and other slaves. Possible values are: 815 816 always or 0 (default) 817 818 The primary slave becomes the active slave whenever it 819 comes back up. 820 821 better or 1 822 823 The primary slave becomes the active slave when it comes 824 back up, if the speed and duplex of the primary slave is 825 better than the speed and duplex of the current active 826 slave. 827 828 failure or 2 829 830 The primary slave becomes the active slave only if the 831 current active slave fails and the primary slave is up. 832 833 The primary_reselect setting is ignored in two cases: 834 835 If no slaves are active, the first slave to recover is 836 made the active slave. 837 838 When initially enslaved, the primary slave is always made 839 the active slave. 840 841 Changing the primary_reselect policy via sysfs will cause an 842 immediate selection of the best active slave according to the new 843 policy. This may or may not result in a change of the active 844 slave, depending upon the circumstances. 845 846 This option was added for bonding version 3.6.0. 847 848tlb_dynamic_lb 849 850 Specifies if dynamic shuffling of flows is enabled in tlb 851 or alb mode. The value has no effect on any other modes. 852 853 The default behavior of tlb mode is to shuffle active flows across 854 slaves based on the load in that interval. This gives nice lb 855 characteristics but can cause packet reordering. If re-ordering is 856 a concern use this variable to disable flow shuffling and rely on 857 load balancing provided solely by the hash distribution. 858 xmit-hash-policy can be used to select the appropriate hashing for 859 the setup. 860 861 The sysfs entry can be used to change the setting per bond device 862 and the initial value is derived from the module parameter. The 863 sysfs entry is allowed to be changed only if the bond device is 864 down. 865 866 The default value is "1" that enables flow shuffling while value "0" 867 disables it. This option was added in bonding driver 3.7.1 868 869 870updelay 871 872 Specifies the time, in milliseconds, to wait before enabling a 873 slave after a link recovery has been detected. This option is 874 only valid for the miimon link monitor. The updelay value 875 should be a multiple of the miimon value; if not, it will be 876 rounded down to the nearest multiple. The default value is 0. 877 878use_carrier 879 880 Specifies whether or not miimon should use MII or ETHTOOL 881 ioctls vs. netif_carrier_ok() to determine the link 882 status. The MII or ETHTOOL ioctls are less efficient and 883 utilize a deprecated calling sequence within the kernel. The 884 netif_carrier_ok() relies on the device driver to maintain its 885 state with netif_carrier_on/off; at this writing, most, but 886 not all, device drivers support this facility. 887 888 If bonding insists that the link is up when it should not be, 889 it may be that your network device driver does not support 890 netif_carrier_on/off. The default state for netif_carrier is 891 "carrier on," so if a driver does not support netif_carrier, 892 it will appear as if the link is always up. In this case, 893 setting use_carrier to 0 will cause bonding to revert to the 894 MII / ETHTOOL ioctl method to determine the link state. 895 896 A value of 1 enables the use of netif_carrier_ok(), a value of 897 0 will use the deprecated MII / ETHTOOL ioctls. The default 898 value is 1. 899 900xmit_hash_policy 901 902 Selects the transmit hash policy to use for slave selection in 903 balance-xor, 802.3ad, and tlb modes. Possible values are: 904 905 layer2 906 907 Uses XOR of hardware MAC addresses and packet type ID 908 field to generate the hash. The formula is 909 910 hash = source MAC[5] XOR destination MAC[5] XOR packet type ID 911 slave number = hash modulo slave count 912 913 This algorithm will place all traffic to a particular 914 network peer on the same slave. 915 916 This algorithm is 802.3ad compliant. 917 918 layer2+3 919 920 This policy uses a combination of layer2 and layer3 921 protocol information to generate the hash. 922 923 Uses XOR of hardware MAC addresses and IP addresses to 924 generate the hash. The formula is 925 926 hash = source MAC[5] XOR destination MAC[5] XOR packet type ID 927 hash = hash XOR source IP XOR destination IP 928 hash = hash XOR (hash RSHIFT 16) 929 hash = hash XOR (hash RSHIFT 8) 930 And then hash is reduced modulo slave count. 931 932 If the protocol is IPv6 then the source and destination 933 addresses are first hashed using ipv6_addr_hash. 934 935 This algorithm will place all traffic to a particular 936 network peer on the same slave. For non-IP traffic, 937 the formula is the same as for the layer2 transmit 938 hash policy. 939 940 This policy is intended to provide a more balanced 941 distribution of traffic than layer2 alone, especially 942 in environments where a layer3 gateway device is 943 required to reach most destinations. 944 945 This algorithm is 802.3ad compliant. 946 947 layer3+4 948 949 This policy uses upper layer protocol information, 950 when available, to generate the hash. This allows for 951 traffic to a particular network peer to span multiple 952 slaves, although a single connection will not span 953 multiple slaves. 954 955 The formula for unfragmented TCP and UDP packets is 956 957 hash = source port, destination port (as in the header) 958 hash = hash XOR source IP XOR destination IP 959 hash = hash XOR (hash RSHIFT 16) 960 hash = hash XOR (hash RSHIFT 8) 961 hash = hash RSHIFT 1 962 And then hash is reduced modulo slave count. 963 964 If the protocol is IPv6 then the source and destination 965 addresses are first hashed using ipv6_addr_hash. 966 967 For fragmented TCP or UDP packets and all other IPv4 and 968 IPv6 protocol traffic, the source and destination port 969 information is omitted. For non-IP traffic, the 970 formula is the same as for the layer2 transmit hash 971 policy. 972 973 This algorithm is not fully 802.3ad compliant. A 974 single TCP or UDP conversation containing both 975 fragmented and unfragmented packets will see packets 976 striped across two interfaces. This may result in out 977 of order delivery. Most traffic types will not meet 978 this criteria, as TCP rarely fragments traffic, and 979 most UDP traffic is not involved in extended 980 conversations. Other implementations of 802.3ad may 981 or may not tolerate this noncompliance. 982 983 encap2+3 984 985 This policy uses the same formula as layer2+3 but it 986 relies on skb_flow_dissect to obtain the header fields 987 which might result in the use of inner headers if an 988 encapsulation protocol is used. For example this will 989 improve the performance for tunnel users because the 990 packets will be distributed according to the encapsulated 991 flows. 992 993 encap3+4 994 995 This policy uses the same formula as layer3+4 but it 996 relies on skb_flow_dissect to obtain the header fields 997 which might result in the use of inner headers if an 998 encapsulation protocol is used. For example this will 999 improve the performance for tunnel users because the 1000 packets will be distributed according to the encapsulated 1001 flows. 1002 1003 vlan+srcmac 1004 1005 This policy uses a very rudimentary vlan ID and source mac 1006 hash to load-balance traffic per-vlan, with failover 1007 should one leg fail. The intended use case is for a bond 1008 shared by multiple virtual machines, all configured to 1009 use their own vlan, to give lacp-like functionality 1010 without requiring lacp-capable switching hardware. 1011 1012 The formula for the hash is simply 1013 1014 hash = (vlan ID) XOR (source MAC vendor) XOR (source MAC dev) 1015 1016 The default value is layer2. This option was added in bonding 1017 version 2.6.3. In earlier versions of bonding, this parameter 1018 does not exist, and the layer2 policy is the only policy. The 1019 layer2+3 value was added for bonding version 3.2.2. 1020 1021resend_igmp 1022 1023 Specifies the number of IGMP membership reports to be issued after 1024 a failover event. One membership report is issued immediately after 1025 the failover, subsequent packets are sent in each 200ms interval. 1026 1027 The valid range is 0 - 255; the default value is 1. A value of 0 1028 prevents the IGMP membership report from being issued in response 1029 to the failover event. 1030 1031 This option is useful for bonding modes balance-rr (0), active-backup 1032 (1), balance-tlb (5) and balance-alb (6), in which a failover can 1033 switch the IGMP traffic from one slave to another. Therefore a fresh 1034 IGMP report must be issued to cause the switch to forward the incoming 1035 IGMP traffic over the newly selected slave. 1036 1037 This option was added for bonding version 3.7.0. 1038 1039lp_interval 1040 1041 Specifies the number of seconds between instances where the bonding 1042 driver sends learning packets to each slaves peer switch. 1043 1044 The valid range is 1 - 0x7fffffff; the default value is 1. This Option 1045 has effect only in balance-tlb and balance-alb modes. 1046 10473. Configuring Bonding Devices 1048============================== 1049 1050You can configure bonding using either your distro's network 1051initialization scripts, or manually using either iproute2 or the 1052sysfs interface. Distros generally use one of three packages for the 1053network initialization scripts: initscripts, sysconfig or interfaces. 1054Recent versions of these packages have support for bonding, while older 1055versions do not. 1056 1057We will first describe the options for configuring bonding for 1058distros using versions of initscripts, sysconfig and interfaces with full 1059or partial support for bonding, then provide information on enabling 1060bonding without support from the network initialization scripts (i.e., 1061older versions of initscripts or sysconfig). 1062 1063If you're unsure whether your distro uses sysconfig, 1064initscripts or interfaces, or don't know if it's new enough, have no fear. 1065Determining this is fairly straightforward. 1066 1067First, look for a file called interfaces in /etc/network directory. 1068If this file is present in your system, then your system use interfaces. See 1069Configuration with Interfaces Support. 1070 1071Else, issue the command:: 1072 1073 $ rpm -qf /sbin/ifup 1074 1075It will respond with a line of text starting with either 1076"initscripts" or "sysconfig," followed by some numbers. This is the 1077package that provides your network initialization scripts. 1078 1079Next, to determine if your installation supports bonding, 1080issue the command:: 1081 1082 $ grep ifenslave /sbin/ifup 1083 1084If this returns any matches, then your initscripts or 1085sysconfig has support for bonding. 1086 10873.1 Configuration with Sysconfig Support 1088---------------------------------------- 1089 1090This section applies to distros using a version of sysconfig 1091with bonding support, for example, SuSE Linux Enterprise Server 9. 1092 1093SuSE SLES 9's networking configuration system does support 1094bonding, however, at this writing, the YaST system configuration 1095front end does not provide any means to work with bonding devices. 1096Bonding devices can be managed by hand, however, as follows. 1097 1098First, if they have not already been configured, configure the 1099slave devices. On SLES 9, this is most easily done by running the 1100yast2 sysconfig configuration utility. The goal is for to create an 1101ifcfg-id file for each slave device. The simplest way to accomplish 1102this is to configure the devices for DHCP (this is only to get the 1103file ifcfg-id file created; see below for some issues with DHCP). The 1104name of the configuration file for each device will be of the form:: 1105 1106 ifcfg-id-xx:xx:xx:xx:xx:xx 1107 1108Where the "xx" portion will be replaced with the digits from 1109the device's permanent MAC address. 1110 1111Once the set of ifcfg-id-xx:xx:xx:xx:xx:xx files has been 1112created, it is necessary to edit the configuration files for the slave 1113devices (the MAC addresses correspond to those of the slave devices). 1114Before editing, the file will contain multiple lines, and will look 1115something like this:: 1116 1117 BOOTPROTO='dhcp' 1118 STARTMODE='on' 1119 USERCTL='no' 1120 UNIQUE='XNzu.WeZGOGF+4wE' 1121 _nm_name='bus-pci-0001:61:01.0' 1122 1123Change the BOOTPROTO and STARTMODE lines to the following:: 1124 1125 BOOTPROTO='none' 1126 STARTMODE='off' 1127 1128Do not alter the UNIQUE or _nm_name lines. Remove any other 1129lines (USERCTL, etc). 1130 1131Once the ifcfg-id-xx:xx:xx:xx:xx:xx files have been modified, 1132it's time to create the configuration file for the bonding device 1133itself. This file is named ifcfg-bondX, where X is the number of the 1134bonding device to create, starting at 0. The first such file is 1135ifcfg-bond0, the second is ifcfg-bond1, and so on. The sysconfig 1136network configuration system will correctly start multiple instances 1137of bonding. 1138 1139The contents of the ifcfg-bondX file is as follows:: 1140 1141 BOOTPROTO="static" 1142 BROADCAST="10.0.2.255" 1143 IPADDR="10.0.2.10" 1144 NETMASK="255.255.0.0" 1145 NETWORK="10.0.2.0" 1146 REMOTE_IPADDR="" 1147 STARTMODE="onboot" 1148 BONDING_MASTER="yes" 1149 BONDING_MODULE_OPTS="mode=active-backup miimon=100" 1150 BONDING_SLAVE0="eth0" 1151 BONDING_SLAVE1="bus-pci-0000:06:08.1" 1152 1153Replace the sample BROADCAST, IPADDR, NETMASK and NETWORK 1154values with the appropriate values for your network. 1155 1156The STARTMODE specifies when the device is brought online. 1157The possible values are: 1158 1159 ======== ====================================================== 1160 onboot The device is started at boot time. If you're not 1161 sure, this is probably what you want. 1162 1163 manual The device is started only when ifup is called 1164 manually. Bonding devices may be configured this 1165 way if you do not wish them to start automatically 1166 at boot for some reason. 1167 1168 hotplug The device is started by a hotplug event. This is not 1169 a valid choice for a bonding device. 1170 1171 off or The device configuration is ignored. 1172 ignore 1173 ======== ====================================================== 1174 1175The line BONDING_MASTER='yes' indicates that the device is a 1176bonding master device. The only useful value is "yes." 1177 1178The contents of BONDING_MODULE_OPTS are supplied to the 1179instance of the bonding module for this device. Specify the options 1180for the bonding mode, link monitoring, and so on here. Do not include 1181the max_bonds bonding parameter; this will confuse the configuration 1182system if you have multiple bonding devices. 1183 1184Finally, supply one BONDING_SLAVEn="slave device" for each 1185slave. where "n" is an increasing value, one for each slave. The 1186"slave device" is either an interface name, e.g., "eth0", or a device 1187specifier for the network device. The interface name is easier to 1188find, but the ethN names are subject to change at boot time if, e.g., 1189a device early in the sequence has failed. The device specifiers 1190(bus-pci-0000:06:08.1 in the example above) specify the physical 1191network device, and will not change unless the device's bus location 1192changes (for example, it is moved from one PCI slot to another). The 1193example above uses one of each type for demonstration purposes; most 1194configurations will choose one or the other for all slave devices. 1195 1196When all configuration files have been modified or created, 1197networking must be restarted for the configuration changes to take 1198effect. This can be accomplished via the following:: 1199 1200 # /etc/init.d/network restart 1201 1202Note that the network control script (/sbin/ifdown) will 1203remove the bonding module as part of the network shutdown processing, 1204so it is not necessary to remove the module by hand if, e.g., the 1205module parameters have changed. 1206 1207Also, at this writing, YaST/YaST2 will not manage bonding 1208devices (they do not show bonding interfaces on its list of network 1209devices). It is necessary to edit the configuration file by hand to 1210change the bonding configuration. 1211 1212Additional general options and details of the ifcfg file 1213format can be found in an example ifcfg template file:: 1214 1215 /etc/sysconfig/network/ifcfg.template 1216 1217Note that the template does not document the various ``BONDING_*`` 1218settings described above, but does describe many of the other options. 1219 12203.1.1 Using DHCP with Sysconfig 1221------------------------------- 1222 1223Under sysconfig, configuring a device with BOOTPROTO='dhcp' 1224will cause it to query DHCP for its IP address information. At this 1225writing, this does not function for bonding devices; the scripts 1226attempt to obtain the device address from DHCP prior to adding any of 1227the slave devices. Without active slaves, the DHCP requests are not 1228sent to the network. 1229 12303.1.2 Configuring Multiple Bonds with Sysconfig 1231----------------------------------------------- 1232 1233The sysconfig network initialization system is capable of 1234handling multiple bonding devices. All that is necessary is for each 1235bonding instance to have an appropriately configured ifcfg-bondX file 1236(as described above). Do not specify the "max_bonds" parameter to any 1237instance of bonding, as this will confuse sysconfig. If you require 1238multiple bonding devices with identical parameters, create multiple 1239ifcfg-bondX files. 1240 1241Because the sysconfig scripts supply the bonding module 1242options in the ifcfg-bondX file, it is not necessary to add them to 1243the system ``/etc/modules.d/*.conf`` configuration files. 1244 12453.2 Configuration with Initscripts Support 1246------------------------------------------ 1247 1248This section applies to distros using a recent version of 1249initscripts with bonding support, for example, Red Hat Enterprise Linux 1250version 3 or later, Fedora, etc. On these systems, the network 1251initialization scripts have knowledge of bonding, and can be configured to 1252control bonding devices. Note that older versions of the initscripts 1253package have lower levels of support for bonding; this will be noted where 1254applicable. 1255 1256These distros will not automatically load the network adapter 1257driver unless the ethX device is configured with an IP address. 1258Because of this constraint, users must manually configure a 1259network-script file for all physical adapters that will be members of 1260a bondX link. Network script files are located in the directory: 1261 1262/etc/sysconfig/network-scripts 1263 1264The file name must be prefixed with "ifcfg-eth" and suffixed 1265with the adapter's physical adapter number. For example, the script 1266for eth0 would be named /etc/sysconfig/network-scripts/ifcfg-eth0. 1267Place the following text in the file:: 1268 1269 DEVICE=eth0 1270 USERCTL=no 1271 ONBOOT=yes 1272 MASTER=bond0 1273 SLAVE=yes 1274 BOOTPROTO=none 1275 1276The DEVICE= line will be different for every ethX device and 1277must correspond with the name of the file, i.e., ifcfg-eth1 must have 1278a device line of DEVICE=eth1. The setting of the MASTER= line will 1279also depend on the final bonding interface name chosen for your bond. 1280As with other network devices, these typically start at 0, and go up 1281one for each device, i.e., the first bonding instance is bond0, the 1282second is bond1, and so on. 1283 1284Next, create a bond network script. The file name for this 1285script will be /etc/sysconfig/network-scripts/ifcfg-bondX where X is 1286the number of the bond. For bond0 the file is named "ifcfg-bond0", 1287for bond1 it is named "ifcfg-bond1", and so on. Within that file, 1288place the following text:: 1289 1290 DEVICE=bond0 1291 IPADDR=192.168.1.1 1292 NETMASK=255.255.255.0 1293 NETWORK=192.168.1.0 1294 BROADCAST=192.168.1.255 1295 ONBOOT=yes 1296 BOOTPROTO=none 1297 USERCTL=no 1298 1299Be sure to change the networking specific lines (IPADDR, 1300NETMASK, NETWORK and BROADCAST) to match your network configuration. 1301 1302For later versions of initscripts, such as that found with Fedora 13037 (or later) and Red Hat Enterprise Linux version 5 (or later), it is possible, 1304and, indeed, preferable, to specify the bonding options in the ifcfg-bond0 1305file, e.g. a line of the format:: 1306 1307 BONDING_OPTS="mode=active-backup arp_interval=60 arp_ip_target=192.168.1.254" 1308 1309will configure the bond with the specified options. The options 1310specified in BONDING_OPTS are identical to the bonding module parameters 1311except for the arp_ip_target field when using versions of initscripts older 1312than and 8.57 (Fedora 8) and 8.45.19 (Red Hat Enterprise Linux 5.2). When 1313using older versions each target should be included as a separate option and 1314should be preceded by a '+' to indicate it should be added to the list of 1315queried targets, e.g.,:: 1316 1317 arp_ip_target=+192.168.1.1 arp_ip_target=+192.168.1.2 1318 1319is the proper syntax to specify multiple targets. When specifying 1320options via BONDING_OPTS, it is not necessary to edit 1321``/etc/modprobe.d/*.conf``. 1322 1323For even older versions of initscripts that do not support 1324BONDING_OPTS, it is necessary to edit /etc/modprobe.d/*.conf, depending upon 1325your distro) to load the bonding module with your desired options when the 1326bond0 interface is brought up. The following lines in /etc/modprobe.d/*.conf 1327will load the bonding module, and select its options: 1328 1329 alias bond0 bonding 1330 options bond0 mode=balance-alb miimon=100 1331 1332Replace the sample parameters with the appropriate set of 1333options for your configuration. 1334 1335Finally run "/etc/rc.d/init.d/network restart" as root. This 1336will restart the networking subsystem and your bond link should be now 1337up and running. 1338 13393.2.1 Using DHCP with Initscripts 1340--------------------------------- 1341 1342Recent versions of initscripts (the versions supplied with Fedora 1343Core 3 and Red Hat Enterprise Linux 4, or later versions, are reported to 1344work) have support for assigning IP information to bonding devices via 1345DHCP. 1346 1347To configure bonding for DHCP, configure it as described 1348above, except replace the line "BOOTPROTO=none" with "BOOTPROTO=dhcp" 1349and add a line consisting of "TYPE=Bonding". Note that the TYPE value 1350is case sensitive. 1351 13523.2.2 Configuring Multiple Bonds with Initscripts 1353------------------------------------------------- 1354 1355Initscripts packages that are included with Fedora 7 and Red Hat 1356Enterprise Linux 5 support multiple bonding interfaces by simply 1357specifying the appropriate BONDING_OPTS= in ifcfg-bondX where X is the 1358number of the bond. This support requires sysfs support in the kernel, 1359and a bonding driver of version 3.0.0 or later. Other configurations may 1360not support this method for specifying multiple bonding interfaces; for 1361those instances, see the "Configuring Multiple Bonds Manually" section, 1362below. 1363 13643.3 Configuring Bonding Manually with iproute2 1365----------------------------------------------- 1366 1367This section applies to distros whose network initialization 1368scripts (the sysconfig or initscripts package) do not have specific 1369knowledge of bonding. One such distro is SuSE Linux Enterprise Server 1370version 8. 1371 1372The general method for these systems is to place the bonding 1373module parameters into a config file in /etc/modprobe.d/ (as 1374appropriate for the installed distro), then add modprobe and/or 1375`ip link` commands to the system's global init script. The name of 1376the global init script differs; for sysconfig, it is 1377/etc/init.d/boot.local and for initscripts it is /etc/rc.d/rc.local. 1378 1379For example, if you wanted to make a simple bond of two e100 1380devices (presumed to be eth0 and eth1), and have it persist across 1381reboots, edit the appropriate file (/etc/init.d/boot.local or 1382/etc/rc.d/rc.local), and add the following:: 1383 1384 modprobe bonding mode=balance-alb miimon=100 1385 modprobe e100 1386 ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up 1387 ip link set eth0 master bond0 1388 ip link set eth1 master bond0 1389 1390Replace the example bonding module parameters and bond0 1391network configuration (IP address, netmask, etc) with the appropriate 1392values for your configuration. 1393 1394Unfortunately, this method will not provide support for the 1395ifup and ifdown scripts on the bond devices. To reload the bonding 1396configuration, it is necessary to run the initialization script, e.g.,:: 1397 1398 # /etc/init.d/boot.local 1399 1400or:: 1401 1402 # /etc/rc.d/rc.local 1403 1404It may be desirable in such a case to create a separate script 1405which only initializes the bonding configuration, then call that 1406separate script from within boot.local. This allows for bonding to be 1407enabled without re-running the entire global init script. 1408 1409To shut down the bonding devices, it is necessary to first 1410mark the bonding device itself as being down, then remove the 1411appropriate device driver modules. For our example above, you can do 1412the following:: 1413 1414 # ifconfig bond0 down 1415 # rmmod bonding 1416 # rmmod e100 1417 1418Again, for convenience, it may be desirable to create a script 1419with these commands. 1420 1421 14223.3.1 Configuring Multiple Bonds Manually 1423----------------------------------------- 1424 1425This section contains information on configuring multiple 1426bonding devices with differing options for those systems whose network 1427initialization scripts lack support for configuring multiple bonds. 1428 1429If you require multiple bonding devices, but all with the same 1430options, you may wish to use the "max_bonds" module parameter, 1431documented above. 1432 1433To create multiple bonding devices with differing options, it is 1434preferable to use bonding parameters exported by sysfs, documented in the 1435section below. 1436 1437For versions of bonding without sysfs support, the only means to 1438provide multiple instances of bonding with differing options is to load 1439the bonding driver multiple times. Note that current versions of the 1440sysconfig network initialization scripts handle this automatically; if 1441your distro uses these scripts, no special action is needed. See the 1442section Configuring Bonding Devices, above, if you're not sure about your 1443network initialization scripts. 1444 1445To load multiple instances of the module, it is necessary to 1446specify a different name for each instance (the module loading system 1447requires that every loaded module, even multiple instances of the same 1448module, have a unique name). This is accomplished by supplying multiple 1449sets of bonding options in ``/etc/modprobe.d/*.conf``, for example:: 1450 1451 alias bond0 bonding 1452 options bond0 -o bond0 mode=balance-rr miimon=100 1453 1454 alias bond1 bonding 1455 options bond1 -o bond1 mode=balance-alb miimon=50 1456 1457will load the bonding module two times. The first instance is 1458named "bond0" and creates the bond0 device in balance-rr mode with an 1459miimon of 100. The second instance is named "bond1" and creates the 1460bond1 device in balance-alb mode with an miimon of 50. 1461 1462In some circumstances (typically with older distributions), 1463the above does not work, and the second bonding instance never sees 1464its options. In that case, the second options line can be substituted 1465as follows:: 1466 1467 install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \ 1468 mode=balance-alb miimon=50 1469 1470This may be repeated any number of times, specifying a new and 1471unique name in place of bond1 for each subsequent instance. 1472 1473It has been observed that some Red Hat supplied kernels are unable 1474to rename modules at load time (the "-o bond1" part). Attempts to pass 1475that option to modprobe will produce an "Operation not permitted" error. 1476This has been reported on some Fedora Core kernels, and has been seen on 1477RHEL 4 as well. On kernels exhibiting this problem, it will be impossible 1478to configure multiple bonds with differing parameters (as they are older 1479kernels, and also lack sysfs support). 1480 14813.4 Configuring Bonding Manually via Sysfs 1482------------------------------------------ 1483 1484Starting with version 3.0.0, Channel Bonding may be configured 1485via the sysfs interface. This interface allows dynamic configuration 1486of all bonds in the system without unloading the module. It also 1487allows for adding and removing bonds at runtime. Ifenslave is no 1488longer required, though it is still supported. 1489 1490Use of the sysfs interface allows you to use multiple bonds 1491with different configurations without having to reload the module. 1492It also allows you to use multiple, differently configured bonds when 1493bonding is compiled into the kernel. 1494 1495You must have the sysfs filesystem mounted to configure 1496bonding this way. The examples in this document assume that you 1497are using the standard mount point for sysfs, e.g. /sys. If your 1498sysfs filesystem is mounted elsewhere, you will need to adjust the 1499example paths accordingly. 1500 1501Creating and Destroying Bonds 1502----------------------------- 1503To add a new bond foo:: 1504 1505 # echo +foo > /sys/class/net/bonding_masters 1506 1507To remove an existing bond bar:: 1508 1509 # echo -bar > /sys/class/net/bonding_masters 1510 1511To show all existing bonds:: 1512 1513 # cat /sys/class/net/bonding_masters 1514 1515.. note:: 1516 1517 due to 4K size limitation of sysfs files, this list may be 1518 truncated if you have more than a few hundred bonds. This is unlikely 1519 to occur under normal operating conditions. 1520 1521Adding and Removing Slaves 1522-------------------------- 1523Interfaces may be enslaved to a bond using the file 1524/sys/class/net/<bond>/bonding/slaves. The semantics for this file 1525are the same as for the bonding_masters file. 1526 1527To enslave interface eth0 to bond bond0:: 1528 1529 # ifconfig bond0 up 1530 # echo +eth0 > /sys/class/net/bond0/bonding/slaves 1531 1532To free slave eth0 from bond bond0:: 1533 1534 # echo -eth0 > /sys/class/net/bond0/bonding/slaves 1535 1536When an interface is enslaved to a bond, symlinks between the 1537two are created in the sysfs filesystem. In this case, you would get 1538/sys/class/net/bond0/slave_eth0 pointing to /sys/class/net/eth0, and 1539/sys/class/net/eth0/master pointing to /sys/class/net/bond0. 1540 1541This means that you can tell quickly whether or not an 1542interface is enslaved by looking for the master symlink. Thus: 1543# echo -eth0 > /sys/class/net/eth0/master/bonding/slaves 1544will free eth0 from whatever bond it is enslaved to, regardless of 1545the name of the bond interface. 1546 1547Changing a Bond's Configuration 1548------------------------------- 1549Each bond may be configured individually by manipulating the 1550files located in /sys/class/net/<bond name>/bonding 1551 1552The names of these files correspond directly with the command- 1553line parameters described elsewhere in this file, and, with the 1554exception of arp_ip_target, they accept the same values. To see the 1555current setting, simply cat the appropriate file. 1556 1557A few examples will be given here; for specific usage 1558guidelines for each parameter, see the appropriate section in this 1559document. 1560 1561To configure bond0 for balance-alb mode:: 1562 1563 # ifconfig bond0 down 1564 # echo 6 > /sys/class/net/bond0/bonding/mode 1565 - or - 1566 # echo balance-alb > /sys/class/net/bond0/bonding/mode 1567 1568.. note:: 1569 1570 The bond interface must be down before the mode can be changed. 1571 1572To enable MII monitoring on bond0 with a 1 second interval:: 1573 1574 # echo 1000 > /sys/class/net/bond0/bonding/miimon 1575 1576.. note:: 1577 1578 If ARP monitoring is enabled, it will disabled when MII 1579 monitoring is enabled, and vice-versa. 1580 1581To add ARP targets:: 1582 1583 # echo +192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target 1584 # echo +192.168.0.101 > /sys/class/net/bond0/bonding/arp_ip_target 1585 1586.. note:: 1587 1588 up to 16 target addresses may be specified. 1589 1590To remove an ARP target:: 1591 1592 # echo -192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target 1593 1594To configure the interval between learning packet transmits:: 1595 1596 # echo 12 > /sys/class/net/bond0/bonding/lp_interval 1597 1598.. note:: 1599 1600 the lp_interval is the number of seconds between instances where 1601 the bonding driver sends learning packets to each slaves peer switch. The 1602 default interval is 1 second. 1603 1604Example Configuration 1605--------------------- 1606We begin with the same example that is shown in section 3.3, 1607executed with sysfs, and without using ifenslave. 1608 1609To make a simple bond of two e100 devices (presumed to be eth0 1610and eth1), and have it persist across reboots, edit the appropriate 1611file (/etc/init.d/boot.local or /etc/rc.d/rc.local), and add the 1612following:: 1613 1614 modprobe bonding 1615 modprobe e100 1616 echo balance-alb > /sys/class/net/bond0/bonding/mode 1617 ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up 1618 echo 100 > /sys/class/net/bond0/bonding/miimon 1619 echo +eth0 > /sys/class/net/bond0/bonding/slaves 1620 echo +eth1 > /sys/class/net/bond0/bonding/slaves 1621 1622To add a second bond, with two e1000 interfaces in 1623active-backup mode, using ARP monitoring, add the following lines to 1624your init script:: 1625 1626 modprobe e1000 1627 echo +bond1 > /sys/class/net/bonding_masters 1628 echo active-backup > /sys/class/net/bond1/bonding/mode 1629 ifconfig bond1 192.168.2.1 netmask 255.255.255.0 up 1630 echo +192.168.2.100 /sys/class/net/bond1/bonding/arp_ip_target 1631 echo 2000 > /sys/class/net/bond1/bonding/arp_interval 1632 echo +eth2 > /sys/class/net/bond1/bonding/slaves 1633 echo +eth3 > /sys/class/net/bond1/bonding/slaves 1634 16353.5 Configuration with Interfaces Support 1636----------------------------------------- 1637 1638This section applies to distros which use /etc/network/interfaces file 1639to describe network interface configuration, most notably Debian and its 1640derivatives. 1641 1642The ifup and ifdown commands on Debian don't support bonding out of 1643the box. The ifenslave-2.6 package should be installed to provide bonding 1644support. Once installed, this package will provide ``bond-*`` options 1645to be used into /etc/network/interfaces. 1646 1647Note that ifenslave-2.6 package will load the bonding module and use 1648the ifenslave command when appropriate. 1649 1650Example Configurations 1651---------------------- 1652 1653In /etc/network/interfaces, the following stanza will configure bond0, in 1654active-backup mode, with eth0 and eth1 as slaves:: 1655 1656 auto bond0 1657 iface bond0 inet dhcp 1658 bond-slaves eth0 eth1 1659 bond-mode active-backup 1660 bond-miimon 100 1661 bond-primary eth0 eth1 1662 1663If the above configuration doesn't work, you might have a system using 1664upstart for system startup. This is most notably true for recent 1665Ubuntu versions. The following stanza in /etc/network/interfaces will 1666produce the same result on those systems:: 1667 1668 auto bond0 1669 iface bond0 inet dhcp 1670 bond-slaves none 1671 bond-mode active-backup 1672 bond-miimon 100 1673 1674 auto eth0 1675 iface eth0 inet manual 1676 bond-master bond0 1677 bond-primary eth0 eth1 1678 1679 auto eth1 1680 iface eth1 inet manual 1681 bond-master bond0 1682 bond-primary eth0 eth1 1683 1684For a full list of ``bond-*`` supported options in /etc/network/interfaces and 1685some more advanced examples tailored to you particular distros, see the files in 1686/usr/share/doc/ifenslave-2.6. 1687 16883.6 Overriding Configuration for Special Cases 1689---------------------------------------------- 1690 1691When using the bonding driver, the physical port which transmits a frame is 1692typically selected by the bonding driver, and is not relevant to the user or 1693system administrator. The output port is simply selected using the policies of 1694the selected bonding mode. On occasion however, it is helpful to direct certain 1695classes of traffic to certain physical interfaces on output to implement 1696slightly more complex policies. For example, to reach a web server over a 1697bonded interface in which eth0 connects to a private network, while eth1 1698connects via a public network, it may be desirous to bias the bond to send said 1699traffic over eth0 first, using eth1 only as a fall back, while all other traffic 1700can safely be sent over either interface. Such configurations may be achieved 1701using the traffic control utilities inherent in linux. 1702 1703By default the bonding driver is multiqueue aware and 16 queues are created 1704when the driver initializes (see Documentation/networking/multiqueue.rst 1705for details). If more or less queues are desired the module parameter 1706tx_queues can be used to change this value. There is no sysfs parameter 1707available as the allocation is done at module init time. 1708 1709The output of the file /proc/net/bonding/bondX has changed so the output Queue 1710ID is now printed for each slave:: 1711 1712 Bonding Mode: fault-tolerance (active-backup) 1713 Primary Slave: None 1714 Currently Active Slave: eth0 1715 MII Status: up 1716 MII Polling Interval (ms): 0 1717 Up Delay (ms): 0 1718 Down Delay (ms): 0 1719 1720 Slave Interface: eth0 1721 MII Status: up 1722 Link Failure Count: 0 1723 Permanent HW addr: 00:1a:a0:12:8f:cb 1724 Slave queue ID: 0 1725 1726 Slave Interface: eth1 1727 MII Status: up 1728 Link Failure Count: 0 1729 Permanent HW addr: 00:1a:a0:12:8f:cc 1730 Slave queue ID: 2 1731 1732The queue_id for a slave can be set using the command:: 1733 1734 # echo "eth1:2" > /sys/class/net/bond0/bonding/queue_id 1735 1736Any interface that needs a queue_id set should set it with multiple calls 1737like the one above until proper priorities are set for all interfaces. On 1738distributions that allow configuration via initscripts, multiple 'queue_id' 1739arguments can be added to BONDING_OPTS to set all needed slave queues. 1740 1741These queue id's can be used in conjunction with the tc utility to configure 1742a multiqueue qdisc and filters to bias certain traffic to transmit on certain 1743slave devices. For instance, say we wanted, in the above configuration to 1744force all traffic bound to 192.168.1.100 to use eth1 in the bond as its output 1745device. The following commands would accomplish this:: 1746 1747 # tc qdisc add dev bond0 handle 1 root multiq 1748 1749 # tc filter add dev bond0 protocol ip parent 1: prio 1 u32 match ip \ 1750 dst 192.168.1.100 action skbedit queue_mapping 2 1751 1752These commands tell the kernel to attach a multiqueue queue discipline to the 1753bond0 interface and filter traffic enqueued to it, such that packets with a dst 1754ip of 192.168.1.100 have their output queue mapping value overwritten to 2. 1755This value is then passed into the driver, causing the normal output path 1756selection policy to be overridden, selecting instead qid 2, which maps to eth1. 1757 1758Note that qid values begin at 1. Qid 0 is reserved to initiate to the driver 1759that normal output policy selection should take place. One benefit to simply 1760leaving the qid for a slave to 0 is the multiqueue awareness in the bonding 1761driver that is now present. This awareness allows tc filters to be placed on 1762slave devices as well as bond devices and the bonding driver will simply act as 1763a pass-through for selecting output queues on the slave device rather than 1764output port selection. 1765 1766This feature first appeared in bonding driver version 3.7.0 and support for 1767output slave selection was limited to round-robin and active-backup modes. 1768 17693.7 Configuring LACP for 802.3ad mode in a more secure way 1770---------------------------------------------------------- 1771 1772When using 802.3ad bonding mode, the Actor (host) and Partner (switch) 1773exchange LACPDUs. These LACPDUs cannot be sniffed, because they are 1774destined to link local mac addresses (which switches/bridges are not 1775supposed to forward). However, most of the values are easily predictable 1776or are simply the machine's MAC address (which is trivially known to all 1777other hosts in the same L2). This implies that other machines in the L2 1778domain can spoof LACPDU packets from other hosts to the switch and potentially 1779cause mayhem by joining (from the point of view of the switch) another 1780machine's aggregate, thus receiving a portion of that hosts incoming 1781traffic and / or spoofing traffic from that machine themselves (potentially 1782even successfully terminating some portion of flows). Though this is not 1783a likely scenario, one could avoid this possibility by simply configuring 1784few bonding parameters: 1785 1786 (a) ad_actor_system : You can set a random mac-address that can be used for 1787 these LACPDU exchanges. The value can not be either NULL or Multicast. 1788 Also it's preferable to set the local-admin bit. Following shell code 1789 generates a random mac-address as described above:: 1790 1791 # sys_mac_addr=$(printf '%02x:%02x:%02x:%02x:%02x:%02x' \ 1792 $(( (RANDOM & 0xFE) | 0x02 )) \ 1793 $(( RANDOM & 0xFF )) \ 1794 $(( RANDOM & 0xFF )) \ 1795 $(( RANDOM & 0xFF )) \ 1796 $(( RANDOM & 0xFF )) \ 1797 $(( RANDOM & 0xFF ))) 1798 # echo $sys_mac_addr > /sys/class/net/bond0/bonding/ad_actor_system 1799 1800 (b) ad_actor_sys_prio : Randomize the system priority. The default value 1801 is 65535, but system can take the value from 1 - 65535. Following shell 1802 code generates random priority and sets it:: 1803 1804 # sys_prio=$(( 1 + RANDOM + RANDOM )) 1805 # echo $sys_prio > /sys/class/net/bond0/bonding/ad_actor_sys_prio 1806 1807 (c) ad_user_port_key : Use the user portion of the port-key. The default 1808 keeps this empty. These are the upper 10 bits of the port-key and value 1809 ranges from 0 - 1023. Following shell code generates these 10 bits and 1810 sets it:: 1811 1812 # usr_port_key=$(( RANDOM & 0x3FF )) 1813 # echo $usr_port_key > /sys/class/net/bond0/bonding/ad_user_port_key 1814 1815 18164 Querying Bonding Configuration 1817================================= 1818 18194.1 Bonding Configuration 1820------------------------- 1821 1822Each bonding device has a read-only file residing in the 1823/proc/net/bonding directory. The file contents include information 1824about the bonding configuration, options and state of each slave. 1825 1826For example, the contents of /proc/net/bonding/bond0 after the 1827driver is loaded with parameters of mode=0 and miimon=1000 is 1828generally as follows:: 1829 1830 Ethernet Channel Bonding Driver: 2.6.1 (October 29, 2004) 1831 Bonding Mode: load balancing (round-robin) 1832 Currently Active Slave: eth0 1833 MII Status: up 1834 MII Polling Interval (ms): 1000 1835 Up Delay (ms): 0 1836 Down Delay (ms): 0 1837 1838 Slave Interface: eth1 1839 MII Status: up 1840 Link Failure Count: 1 1841 1842 Slave Interface: eth0 1843 MII Status: up 1844 Link Failure Count: 1 1845 1846The precise format and contents will change depending upon the 1847bonding configuration, state, and version of the bonding driver. 1848 18494.2 Network configuration 1850------------------------- 1851 1852The network configuration can be inspected using the ifconfig 1853command. Bonding devices will have the MASTER flag set; Bonding slave 1854devices will have the SLAVE flag set. The ifconfig output does not 1855contain information on which slaves are associated with which masters. 1856 1857In the example below, the bond0 interface is the master 1858(MASTER) while eth0 and eth1 are slaves (SLAVE). Notice all slaves of 1859bond0 have the same MAC address (HWaddr) as bond0 for all modes except 1860TLB and ALB that require a unique MAC address for each slave:: 1861 1862 # /sbin/ifconfig 1863 bond0 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4 1864 inet addr:XXX.XXX.XXX.YYY Bcast:XXX.XXX.XXX.255 Mask:255.255.252.0 1865 UP BROADCAST RUNNING MASTER MULTICAST MTU:1500 Metric:1 1866 RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0 1867 TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0 1868 collisions:0 txqueuelen:0 1869 1870 eth0 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4 1871 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1 1872 RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0 1873 TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0 1874 collisions:0 txqueuelen:100 1875 Interrupt:10 Base address:0x1080 1876 1877 eth1 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4 1878 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1 1879 RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0 1880 TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0 1881 collisions:0 txqueuelen:100 1882 Interrupt:9 Base address:0x1400 1883 18845. Switch Configuration 1885======================= 1886 1887For this section, "switch" refers to whatever system the 1888bonded devices are directly connected to (i.e., where the other end of 1889the cable plugs into). This may be an actual dedicated switch device, 1890or it may be another regular system (e.g., another computer running 1891Linux), 1892 1893The active-backup, balance-tlb and balance-alb modes do not 1894require any specific configuration of the switch. 1895 1896The 802.3ad mode requires that the switch have the appropriate 1897ports configured as an 802.3ad aggregation. The precise method used 1898to configure this varies from switch to switch, but, for example, a 1899Cisco 3550 series switch requires that the appropriate ports first be 1900grouped together in a single etherchannel instance, then that 1901etherchannel is set to mode "lacp" to enable 802.3ad (instead of 1902standard EtherChannel). 1903 1904The balance-rr, balance-xor and broadcast modes generally 1905require that the switch have the appropriate ports grouped together. 1906The nomenclature for such a group differs between switches, it may be 1907called an "etherchannel" (as in the Cisco example, above), a "trunk 1908group" or some other similar variation. For these modes, each switch 1909will also have its own configuration options for the switch's transmit 1910policy to the bond. Typical choices include XOR of either the MAC or 1911IP addresses. The transmit policy of the two peers does not need to 1912match. For these three modes, the bonding mode really selects a 1913transmit policy for an EtherChannel group; all three will interoperate 1914with another EtherChannel group. 1915 1916 19176. 802.1q VLAN Support 1918====================== 1919 1920It is possible to configure VLAN devices over a bond interface 1921using the 8021q driver. However, only packets coming from the 8021q 1922driver and passing through bonding will be tagged by default. Self 1923generated packets, for example, bonding's learning packets or ARP 1924packets generated by either ALB mode or the ARP monitor mechanism, are 1925tagged internally by bonding itself. As a result, bonding must 1926"learn" the VLAN IDs configured above it, and use those IDs to tag 1927self generated packets. 1928 1929For reasons of simplicity, and to support the use of adapters 1930that can do VLAN hardware acceleration offloading, the bonding 1931interface declares itself as fully hardware offloading capable, it gets 1932the add_vid/kill_vid notifications to gather the necessary 1933information, and it propagates those actions to the slaves. In case 1934of mixed adapter types, hardware accelerated tagged packets that 1935should go through an adapter that is not offloading capable are 1936"un-accelerated" by the bonding driver so the VLAN tag sits in the 1937regular location. 1938 1939VLAN interfaces *must* be added on top of a bonding interface 1940only after enslaving at least one slave. The bonding interface has a 1941hardware address of 00:00:00:00:00:00 until the first slave is added. 1942If the VLAN interface is created prior to the first enslavement, it 1943would pick up the all-zeroes hardware address. Once the first slave 1944is attached to the bond, the bond device itself will pick up the 1945slave's hardware address, which is then available for the VLAN device. 1946 1947Also, be aware that a similar problem can occur if all slaves 1948are released from a bond that still has one or more VLAN interfaces on 1949top of it. When a new slave is added, the bonding interface will 1950obtain its hardware address from the first slave, which might not 1951match the hardware address of the VLAN interfaces (which was 1952ultimately copied from an earlier slave). 1953 1954There are two methods to insure that the VLAN device operates 1955with the correct hardware address if all slaves are removed from a 1956bond interface: 1957 19581. Remove all VLAN interfaces then recreate them 1959 19602. Set the bonding interface's hardware address so that it 1961matches the hardware address of the VLAN interfaces. 1962 1963Note that changing a VLAN interface's HW address would set the 1964underlying device -- i.e. the bonding interface -- to promiscuous 1965mode, which might not be what you want. 1966 1967 19687. Link Monitoring 1969================== 1970 1971The bonding driver at present supports two schemes for 1972monitoring a slave device's link state: the ARP monitor and the MII 1973monitor. 1974 1975At the present time, due to implementation restrictions in the 1976bonding driver itself, it is not possible to enable both ARP and MII 1977monitoring simultaneously. 1978 19797.1 ARP Monitor Operation 1980------------------------- 1981 1982The ARP monitor operates as its name suggests: it sends ARP 1983queries to one or more designated peer systems on the network, and 1984uses the response as an indication that the link is operating. This 1985gives some assurance that traffic is actually flowing to and from one 1986or more peers on the local network. 1987 19887.2 Configuring Multiple ARP Targets 1989------------------------------------ 1990 1991While ARP monitoring can be done with just one target, it can 1992be useful in a High Availability setup to have several targets to 1993monitor. In the case of just one target, the target itself may go 1994down or have a problem making it unresponsive to ARP requests. Having 1995an additional target (or several) increases the reliability of the ARP 1996monitoring. 1997 1998Multiple ARP targets must be separated by commas as follows:: 1999 2000 # example options for ARP monitoring with three targets 2001 alias bond0 bonding 2002 options bond0 arp_interval=60 arp_ip_target=192.168.0.1,192.168.0.3,192.168.0.9 2003 2004For just a single target the options would resemble:: 2005 2006 # example options for ARP monitoring with one target 2007 alias bond0 bonding 2008 options bond0 arp_interval=60 arp_ip_target=192.168.0.100 2009 2010 20117.3 MII Monitor Operation 2012------------------------- 2013 2014The MII monitor monitors only the carrier state of the local 2015network interface. It accomplishes this in one of three ways: by 2016depending upon the device driver to maintain its carrier state, by 2017querying the device's MII registers, or by making an ethtool query to 2018the device. 2019 2020If the use_carrier module parameter is 1 (the default value), 2021then the MII monitor will rely on the driver for carrier state 2022information (via the netif_carrier subsystem). As explained in the 2023use_carrier parameter information, above, if the MII monitor fails to 2024detect carrier loss on the device (e.g., when the cable is physically 2025disconnected), it may be that the driver does not support 2026netif_carrier. 2027 2028If use_carrier is 0, then the MII monitor will first query the 2029device's (via ioctl) MII registers and check the link state. If that 2030request fails (not just that it returns carrier down), then the MII 2031monitor will make an ethtool ETHTOOL_GLINK request to attempt to obtain 2032the same information. If both methods fail (i.e., the driver either 2033does not support or had some error in processing both the MII register 2034and ethtool requests), then the MII monitor will assume the link is 2035up. 2036 20378. Potential Sources of Trouble 2038=============================== 2039 20408.1 Adventures in Routing 2041------------------------- 2042 2043When bonding is configured, it is important that the slave 2044devices not have routes that supersede routes of the master (or, 2045generally, not have routes at all). For example, suppose the bonding 2046device bond0 has two slaves, eth0 and eth1, and the routing table is 2047as follows:: 2048 2049 Kernel IP routing table 2050 Destination Gateway Genmask Flags MSS Window irtt Iface 2051 10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 eth0 2052 10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 eth1 2053 10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 bond0 2054 127.0.0.0 0.0.0.0 255.0.0.0 U 40 0 0 lo 2055 2056This routing configuration will likely still update the 2057receive/transmit times in the driver (needed by the ARP monitor), but 2058may bypass the bonding driver (because outgoing traffic to, in this 2059case, another host on network 10 would use eth0 or eth1 before bond0). 2060 2061The ARP monitor (and ARP itself) may become confused by this 2062configuration, because ARP requests (generated by the ARP monitor) 2063will be sent on one interface (bond0), but the corresponding reply 2064will arrive on a different interface (eth0). This reply looks to ARP 2065as an unsolicited ARP reply (because ARP matches replies on an 2066interface basis), and is discarded. The MII monitor is not affected 2067by the state of the routing table. 2068 2069The solution here is simply to insure that slaves do not have 2070routes of their own, and if for some reason they must, those routes do 2071not supersede routes of their master. This should generally be the 2072case, but unusual configurations or errant manual or automatic static 2073route additions may cause trouble. 2074 20758.2 Ethernet Device Renaming 2076---------------------------- 2077 2078On systems with network configuration scripts that do not 2079associate physical devices directly with network interface names (so 2080that the same physical device always has the same "ethX" name), it may 2081be necessary to add some special logic to config files in 2082/etc/modprobe.d/. 2083 2084For example, given a modules.conf containing the following:: 2085 2086 alias bond0 bonding 2087 options bond0 mode=some-mode miimon=50 2088 alias eth0 tg3 2089 alias eth1 tg3 2090 alias eth2 e1000 2091 alias eth3 e1000 2092 2093If neither eth0 and eth1 are slaves to bond0, then when the 2094bond0 interface comes up, the devices may end up reordered. This 2095happens because bonding is loaded first, then its slave device's 2096drivers are loaded next. Since no other drivers have been loaded, 2097when the e1000 driver loads, it will receive eth0 and eth1 for its 2098devices, but the bonding configuration tries to enslave eth2 and eth3 2099(which may later be assigned to the tg3 devices). 2100 2101Adding the following:: 2102 2103 add above bonding e1000 tg3 2104 2105causes modprobe to load e1000 then tg3, in that order, when 2106bonding is loaded. This command is fully documented in the 2107modules.conf manual page. 2108 2109On systems utilizing modprobe an equivalent problem can occur. 2110In this case, the following can be added to config files in 2111/etc/modprobe.d/ as:: 2112 2113 softdep bonding pre: tg3 e1000 2114 2115This will load tg3 and e1000 modules before loading the bonding one. 2116Full documentation on this can be found in the modprobe.d and modprobe 2117manual pages. 2118 21198.3. Painfully Slow Or No Failed Link Detection By Miimon 2120--------------------------------------------------------- 2121 2122By default, bonding enables the use_carrier option, which 2123instructs bonding to trust the driver to maintain carrier state. 2124 2125As discussed in the options section, above, some drivers do 2126not support the netif_carrier_on/_off link state tracking system. 2127With use_carrier enabled, bonding will always see these links as up, 2128regardless of their actual state. 2129 2130Additionally, other drivers do support netif_carrier, but do 2131not maintain it in real time, e.g., only polling the link state at 2132some fixed interval. In this case, miimon will detect failures, but 2133only after some long period of time has expired. If it appears that 2134miimon is very slow in detecting link failures, try specifying 2135use_carrier=0 to see if that improves the failure detection time. If 2136it does, then it may be that the driver checks the carrier state at a 2137fixed interval, but does not cache the MII register values (so the 2138use_carrier=0 method of querying the registers directly works). If 2139use_carrier=0 does not improve the failover, then the driver may cache 2140the registers, or the problem may be elsewhere. 2141 2142Also, remember that miimon only checks for the device's 2143carrier state. It has no way to determine the state of devices on or 2144beyond other ports of a switch, or if a switch is refusing to pass 2145traffic while still maintaining carrier on. 2146 21479. SNMP agents 2148=============== 2149 2150If running SNMP agents, the bonding driver should be loaded 2151before any network drivers participating in a bond. This requirement 2152is due to the interface index (ipAdEntIfIndex) being associated to 2153the first interface found with a given IP address. That is, there is 2154only one ipAdEntIfIndex for each IP address. For example, if eth0 and 2155eth1 are slaves of bond0 and the driver for eth0 is loaded before the 2156bonding driver, the interface for the IP address will be associated 2157with the eth0 interface. This configuration is shown below, the IP 2158address 192.168.1.1 has an interface index of 2 which indexes to eth0 2159in the ifDescr table (ifDescr.2). 2160 2161:: 2162 2163 interfaces.ifTable.ifEntry.ifDescr.1 = lo 2164 interfaces.ifTable.ifEntry.ifDescr.2 = eth0 2165 interfaces.ifTable.ifEntry.ifDescr.3 = eth1 2166 interfaces.ifTable.ifEntry.ifDescr.4 = eth2 2167 interfaces.ifTable.ifEntry.ifDescr.5 = eth3 2168 interfaces.ifTable.ifEntry.ifDescr.6 = bond0 2169 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 5 2170 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2 2171 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 4 2172 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1 2173 2174This problem is avoided by loading the bonding driver before 2175any network drivers participating in a bond. Below is an example of 2176loading the bonding driver first, the IP address 192.168.1.1 is 2177correctly associated with ifDescr.2. 2178 2179 interfaces.ifTable.ifEntry.ifDescr.1 = lo 2180 interfaces.ifTable.ifEntry.ifDescr.2 = bond0 2181 interfaces.ifTable.ifEntry.ifDescr.3 = eth0 2182 interfaces.ifTable.ifEntry.ifDescr.4 = eth1 2183 interfaces.ifTable.ifEntry.ifDescr.5 = eth2 2184 interfaces.ifTable.ifEntry.ifDescr.6 = eth3 2185 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 6 2186 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2 2187 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 5 2188 ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1 2189 2190While some distributions may not report the interface name in 2191ifDescr, the association between the IP address and IfIndex remains 2192and SNMP functions such as Interface_Scan_Next will report that 2193association. 2194 219510. Promiscuous mode 2196==================== 2197 2198When running network monitoring tools, e.g., tcpdump, it is 2199common to enable promiscuous mode on the device, so that all traffic 2200is seen (instead of seeing only traffic destined for the local host). 2201The bonding driver handles promiscuous mode changes to the bonding 2202master device (e.g., bond0), and propagates the setting to the slave 2203devices. 2204 2205For the balance-rr, balance-xor, broadcast, and 802.3ad modes, 2206the promiscuous mode setting is propagated to all slaves. 2207 2208For the active-backup, balance-tlb and balance-alb modes, the 2209promiscuous mode setting is propagated only to the active slave. 2210 2211For balance-tlb mode, the active slave is the slave currently 2212receiving inbound traffic. 2213 2214For balance-alb mode, the active slave is the slave used as a 2215"primary." This slave is used for mode-specific control traffic, for 2216sending to peers that are unassigned or if the load is unbalanced. 2217 2218For the active-backup, balance-tlb and balance-alb modes, when 2219the active slave changes (e.g., due to a link failure), the 2220promiscuous setting will be propagated to the new active slave. 2221 222211. Configuring Bonding for High Availability 2223============================================= 2224 2225High Availability refers to configurations that provide 2226maximum network availability by having redundant or backup devices, 2227links or switches between the host and the rest of the world. The 2228goal is to provide the maximum availability of network connectivity 2229(i.e., the network always works), even though other configurations 2230could provide higher throughput. 2231 223211.1 High Availability in a Single Switch Topology 2233-------------------------------------------------- 2234 2235If two hosts (or a host and a single switch) are directly 2236connected via multiple physical links, then there is no availability 2237penalty to optimizing for maximum bandwidth. In this case, there is 2238only one switch (or peer), so if it fails, there is no alternative 2239access to fail over to. Additionally, the bonding load balance modes 2240support link monitoring of their members, so if individual links fail, 2241the load will be rebalanced across the remaining devices. 2242 2243See Section 12, "Configuring Bonding for Maximum Throughput" 2244for information on configuring bonding with one peer device. 2245 224611.2 High Availability in a Multiple Switch Topology 2247---------------------------------------------------- 2248 2249With multiple switches, the configuration of bonding and the 2250network changes dramatically. In multiple switch topologies, there is 2251a trade off between network availability and usable bandwidth. 2252 2253Below is a sample network, configured to maximize the 2254availability of the network:: 2255 2256 | | 2257 |port3 port3| 2258 +-----+----+ +-----+----+ 2259 | |port2 ISL port2| | 2260 | switch A +--------------------------+ switch B | 2261 | | | | 2262 +-----+----+ +-----++---+ 2263 |port1 port1| 2264 | +-------+ | 2265 +-------------+ host1 +---------------+ 2266 eth0 +-------+ eth1 2267 2268In this configuration, there is a link between the two 2269switches (ISL, or inter switch link), and multiple ports connecting to 2270the outside world ("port3" on each switch). There is no technical 2271reason that this could not be extended to a third switch. 2272 227311.2.1 HA Bonding Mode Selection for Multiple Switch Topology 2274------------------------------------------------------------- 2275 2276In a topology such as the example above, the active-backup and 2277broadcast modes are the only useful bonding modes when optimizing for 2278availability; the other modes require all links to terminate on the 2279same peer for them to behave rationally. 2280 2281active-backup: 2282 This is generally the preferred mode, particularly if 2283 the switches have an ISL and play together well. If the 2284 network configuration is such that one switch is specifically 2285 a backup switch (e.g., has lower capacity, higher cost, etc), 2286 then the primary option can be used to insure that the 2287 preferred link is always used when it is available. 2288 2289broadcast: 2290 This mode is really a special purpose mode, and is suitable 2291 only for very specific needs. For example, if the two 2292 switches are not connected (no ISL), and the networks beyond 2293 them are totally independent. In this case, if it is 2294 necessary for some specific one-way traffic to reach both 2295 independent networks, then the broadcast mode may be suitable. 2296 229711.2.2 HA Link Monitoring Selection for Multiple Switch Topology 2298---------------------------------------------------------------- 2299 2300The choice of link monitoring ultimately depends upon your 2301switch. If the switch can reliably fail ports in response to other 2302failures, then either the MII or ARP monitors should work. For 2303example, in the above example, if the "port3" link fails at the remote 2304end, the MII monitor has no direct means to detect this. The ARP 2305monitor could be configured with a target at the remote end of port3, 2306thus detecting that failure without switch support. 2307 2308In general, however, in a multiple switch topology, the ARP 2309monitor can provide a higher level of reliability in detecting end to 2310end connectivity failures (which may be caused by the failure of any 2311individual component to pass traffic for any reason). Additionally, 2312the ARP monitor should be configured with multiple targets (at least 2313one for each switch in the network). This will insure that, 2314regardless of which switch is active, the ARP monitor has a suitable 2315target to query. 2316 2317Note, also, that of late many switches now support a functionality 2318generally referred to as "trunk failover." This is a feature of the 2319switch that causes the link state of a particular switch port to be set 2320down (or up) when the state of another switch port goes down (or up). 2321Its purpose is to propagate link failures from logically "exterior" ports 2322to the logically "interior" ports that bonding is able to monitor via 2323miimon. Availability and configuration for trunk failover varies by 2324switch, but this can be a viable alternative to the ARP monitor when using 2325suitable switches. 2326 232712. Configuring Bonding for Maximum Throughput 2328============================================== 2329 233012.1 Maximizing Throughput in a Single Switch Topology 2331------------------------------------------------------ 2332 2333In a single switch configuration, the best method to maximize 2334throughput depends upon the application and network environment. The 2335various load balancing modes each have strengths and weaknesses in 2336different environments, as detailed below. 2337 2338For this discussion, we will break down the topologies into 2339two categories. Depending upon the destination of most traffic, we 2340categorize them into either "gatewayed" or "local" configurations. 2341 2342In a gatewayed configuration, the "switch" is acting primarily 2343as a router, and the majority of traffic passes through this router to 2344other networks. An example would be the following:: 2345 2346 2347 +----------+ +----------+ 2348 | |eth0 port1| | to other networks 2349 | Host A +---------------------+ router +-------------------> 2350 | +---------------------+ | Hosts B and C are out 2351 | |eth1 port2| | here somewhere 2352 +----------+ +----------+ 2353 2354The router may be a dedicated router device, or another host 2355acting as a gateway. For our discussion, the important point is that 2356the majority of traffic from Host A will pass through the router to 2357some other network before reaching its final destination. 2358 2359In a gatewayed network configuration, although Host A may 2360communicate with many other systems, all of its traffic will be sent 2361and received via one other peer on the local network, the router. 2362 2363Note that the case of two systems connected directly via 2364multiple physical links is, for purposes of configuring bonding, the 2365same as a gatewayed configuration. In that case, it happens that all 2366traffic is destined for the "gateway" itself, not some other network 2367beyond the gateway. 2368 2369In a local configuration, the "switch" is acting primarily as 2370a switch, and the majority of traffic passes through this switch to 2371reach other stations on the same network. An example would be the 2372following:: 2373 2374 +----------+ +----------+ +--------+ 2375 | |eth0 port1| +-------+ Host B | 2376 | Host A +------------+ switch |port3 +--------+ 2377 | +------------+ | +--------+ 2378 | |eth1 port2| +------------------+ Host C | 2379 +----------+ +----------+port4 +--------+ 2380 2381 2382Again, the switch may be a dedicated switch device, or another 2383host acting as a gateway. For our discussion, the important point is 2384that the majority of traffic from Host A is destined for other hosts 2385on the same local network (Hosts B and C in the above example). 2386 2387In summary, in a gatewayed configuration, traffic to and from 2388the bonded device will be to the same MAC level peer on the network 2389(the gateway itself, i.e., the router), regardless of its final 2390destination. In a local configuration, traffic flows directly to and 2391from the final destinations, thus, each destination (Host B, Host C) 2392will be addressed directly by their individual MAC addresses. 2393 2394This distinction between a gatewayed and a local network 2395configuration is important because many of the load balancing modes 2396available use the MAC addresses of the local network source and 2397destination to make load balancing decisions. The behavior of each 2398mode is described below. 2399 2400 240112.1.1 MT Bonding Mode Selection for Single Switch Topology 2402----------------------------------------------------------- 2403 2404This configuration is the easiest to set up and to understand, 2405although you will have to decide which bonding mode best suits your 2406needs. The trade offs for each mode are detailed below: 2407 2408balance-rr: 2409 This mode is the only mode that will permit a single 2410 TCP/IP connection to stripe traffic across multiple 2411 interfaces. It is therefore the only mode that will allow a 2412 single TCP/IP stream to utilize more than one interface's 2413 worth of throughput. This comes at a cost, however: the 2414 striping generally results in peer systems receiving packets out 2415 of order, causing TCP/IP's congestion control system to kick 2416 in, often by retransmitting segments. 2417 2418 It is possible to adjust TCP/IP's congestion limits by 2419 altering the net.ipv4.tcp_reordering sysctl parameter. The 2420 usual default value is 3. But keep in mind TCP stack is able 2421 to automatically increase this when it detects reorders. 2422 2423 Note that the fraction of packets that will be delivered out of 2424 order is highly variable, and is unlikely to be zero. The level 2425 of reordering depends upon a variety of factors, including the 2426 networking interfaces, the switch, and the topology of the 2427 configuration. Speaking in general terms, higher speed network 2428 cards produce more reordering (due to factors such as packet 2429 coalescing), and a "many to many" topology will reorder at a 2430 higher rate than a "many slow to one fast" configuration. 2431 2432 Many switches do not support any modes that stripe traffic 2433 (instead choosing a port based upon IP or MAC level addresses); 2434 for those devices, traffic for a particular connection flowing 2435 through the switch to a balance-rr bond will not utilize greater 2436 than one interface's worth of bandwidth. 2437 2438 If you are utilizing protocols other than TCP/IP, UDP for 2439 example, and your application can tolerate out of order 2440 delivery, then this mode can allow for single stream datagram 2441 performance that scales near linearly as interfaces are added 2442 to the bond. 2443 2444 This mode requires the switch to have the appropriate ports 2445 configured for "etherchannel" or "trunking." 2446 2447active-backup: 2448 There is not much advantage in this network topology to 2449 the active-backup mode, as the inactive backup devices are all 2450 connected to the same peer as the primary. In this case, a 2451 load balancing mode (with link monitoring) will provide the 2452 same level of network availability, but with increased 2453 available bandwidth. On the plus side, active-backup mode 2454 does not require any configuration of the switch, so it may 2455 have value if the hardware available does not support any of 2456 the load balance modes. 2457 2458balance-xor: 2459 This mode will limit traffic such that packets destined 2460 for specific peers will always be sent over the same 2461 interface. Since the destination is determined by the MAC 2462 addresses involved, this mode works best in a "local" network 2463 configuration (as described above), with destinations all on 2464 the same local network. This mode is likely to be suboptimal 2465 if all your traffic is passed through a single router (i.e., a 2466 "gatewayed" network configuration, as described above). 2467 2468 As with balance-rr, the switch ports need to be configured for 2469 "etherchannel" or "trunking." 2470 2471broadcast: 2472 Like active-backup, there is not much advantage to this 2473 mode in this type of network topology. 2474 2475802.3ad: 2476 This mode can be a good choice for this type of network 2477 topology. The 802.3ad mode is an IEEE standard, so all peers 2478 that implement 802.3ad should interoperate well. The 802.3ad 2479 protocol includes automatic configuration of the aggregates, 2480 so minimal manual configuration of the switch is needed 2481 (typically only to designate that some set of devices is 2482 available for 802.3ad). The 802.3ad standard also mandates 2483 that frames be delivered in order (within certain limits), so 2484 in general single connections will not see misordering of 2485 packets. The 802.3ad mode does have some drawbacks: the 2486 standard mandates that all devices in the aggregate operate at 2487 the same speed and duplex. Also, as with all bonding load 2488 balance modes other than balance-rr, no single connection will 2489 be able to utilize more than a single interface's worth of 2490 bandwidth. 2491 2492 Additionally, the linux bonding 802.3ad implementation 2493 distributes traffic by peer (using an XOR of MAC addresses 2494 and packet type ID), so in a "gatewayed" configuration, all 2495 outgoing traffic will generally use the same device. Incoming 2496 traffic may also end up on a single device, but that is 2497 dependent upon the balancing policy of the peer's 802.3ad 2498 implementation. In a "local" configuration, traffic will be 2499 distributed across the devices in the bond. 2500 2501 Finally, the 802.3ad mode mandates the use of the MII monitor, 2502 therefore, the ARP monitor is not available in this mode. 2503 2504balance-tlb: 2505 The balance-tlb mode balances outgoing traffic by peer. 2506 Since the balancing is done according to MAC address, in a 2507 "gatewayed" configuration (as described above), this mode will 2508 send all traffic across a single device. However, in a 2509 "local" network configuration, this mode balances multiple 2510 local network peers across devices in a vaguely intelligent 2511 manner (not a simple XOR as in balance-xor or 802.3ad mode), 2512 so that mathematically unlucky MAC addresses (i.e., ones that 2513 XOR to the same value) will not all "bunch up" on a single 2514 interface. 2515 2516 Unlike 802.3ad, interfaces may be of differing speeds, and no 2517 special switch configuration is required. On the down side, 2518 in this mode all incoming traffic arrives over a single 2519 interface, this mode requires certain ethtool support in the 2520 network device driver of the slave interfaces, and the ARP 2521 monitor is not available. 2522 2523balance-alb: 2524 This mode is everything that balance-tlb is, and more. 2525 It has all of the features (and restrictions) of balance-tlb, 2526 and will also balance incoming traffic from local network 2527 peers (as described in the Bonding Module Options section, 2528 above). 2529 2530 The only additional down side to this mode is that the network 2531 device driver must support changing the hardware address while 2532 the device is open. 2533 253412.1.2 MT Link Monitoring for Single Switch Topology 2535---------------------------------------------------- 2536 2537The choice of link monitoring may largely depend upon which 2538mode you choose to use. The more advanced load balancing modes do not 2539support the use of the ARP monitor, and are thus restricted to using 2540the MII monitor (which does not provide as high a level of end to end 2541assurance as the ARP monitor). 2542 254312.2 Maximum Throughput in a Multiple Switch Topology 2544----------------------------------------------------- 2545 2546Multiple switches may be utilized to optimize for throughput 2547when they are configured in parallel as part of an isolated network 2548between two or more systems, for example:: 2549 2550 +-----------+ 2551 | Host A | 2552 +-+---+---+-+ 2553 | | | 2554 +--------+ | +---------+ 2555 | | | 2556 +------+---+ +-----+----+ +-----+----+ 2557 | Switch A | | Switch B | | Switch C | 2558 +------+---+ +-----+----+ +-----+----+ 2559 | | | 2560 +--------+ | +---------+ 2561 | | | 2562 +-+---+---+-+ 2563 | Host B | 2564 +-----------+ 2565 2566In this configuration, the switches are isolated from one 2567another. One reason to employ a topology such as this is for an 2568isolated network with many hosts (a cluster configured for high 2569performance, for example), using multiple smaller switches can be more 2570cost effective than a single larger switch, e.g., on a network with 24 2571hosts, three 24 port switches can be significantly less expensive than 2572a single 72 port switch. 2573 2574If access beyond the network is required, an individual host 2575can be equipped with an additional network device connected to an 2576external network; this host then additionally acts as a gateway. 2577 257812.2.1 MT Bonding Mode Selection for Multiple Switch Topology 2579------------------------------------------------------------- 2580 2581In actual practice, the bonding mode typically employed in 2582configurations of this type is balance-rr. Historically, in this 2583network configuration, the usual caveats about out of order packet 2584delivery are mitigated by the use of network adapters that do not do 2585any kind of packet coalescing (via the use of NAPI, or because the 2586device itself does not generate interrupts until some number of 2587packets has arrived). When employed in this fashion, the balance-rr 2588mode allows individual connections between two hosts to effectively 2589utilize greater than one interface's bandwidth. 2590 259112.2.2 MT Link Monitoring for Multiple Switch Topology 2592------------------------------------------------------ 2593 2594Again, in actual practice, the MII monitor is most often used 2595in this configuration, as performance is given preference over 2596availability. The ARP monitor will function in this topology, but its 2597advantages over the MII monitor are mitigated by the volume of probes 2598needed as the number of systems involved grows (remember that each 2599host in the network is configured with bonding). 2600 260113. Switch Behavior Issues 2602========================== 2603 260413.1 Link Establishment and Failover Delays 2605------------------------------------------- 2606 2607Some switches exhibit undesirable behavior with regard to the 2608timing of link up and down reporting by the switch. 2609 2610First, when a link comes up, some switches may indicate that 2611the link is up (carrier available), but not pass traffic over the 2612interface for some period of time. This delay is typically due to 2613some type of autonegotiation or routing protocol, but may also occur 2614during switch initialization (e.g., during recovery after a switch 2615failure). If you find this to be a problem, specify an appropriate 2616value to the updelay bonding module option to delay the use of the 2617relevant interface(s). 2618 2619Second, some switches may "bounce" the link state one or more 2620times while a link is changing state. This occurs most commonly while 2621the switch is initializing. Again, an appropriate updelay value may 2622help. 2623 2624Note that when a bonding interface has no active links, the 2625driver will immediately reuse the first link that goes up, even if the 2626updelay parameter has been specified (the updelay is ignored in this 2627case). If there are slave interfaces waiting for the updelay timeout 2628to expire, the interface that first went into that state will be 2629immediately reused. This reduces down time of the network if the 2630value of updelay has been overestimated, and since this occurs only in 2631cases with no connectivity, there is no additional penalty for 2632ignoring the updelay. 2633 2634In addition to the concerns about switch timings, if your 2635switches take a long time to go into backup mode, it may be desirable 2636to not activate a backup interface immediately after a link goes down. 2637Failover may be delayed via the downdelay bonding module option. 2638 263913.2 Duplicated Incoming Packets 2640-------------------------------- 2641 2642NOTE: Starting with version 3.0.2, the bonding driver has logic to 2643suppress duplicate packets, which should largely eliminate this problem. 2644The following description is kept for reference. 2645 2646It is not uncommon to observe a short burst of duplicated 2647traffic when the bonding device is first used, or after it has been 2648idle for some period of time. This is most easily observed by issuing 2649a "ping" to some other host on the network, and noticing that the 2650output from ping flags duplicates (typically one per slave). 2651 2652For example, on a bond in active-backup mode with five slaves 2653all connected to one switch, the output may appear as follows:: 2654 2655 # ping -n 10.0.4.2 2656 PING 10.0.4.2 (10.0.4.2) from 10.0.3.10 : 56(84) bytes of data. 2657 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.7 ms 2658 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!) 2659 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!) 2660 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!) 2661 64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!) 2662 64 bytes from 10.0.4.2: icmp_seq=2 ttl=64 time=0.216 ms 2663 64 bytes from 10.0.4.2: icmp_seq=3 ttl=64 time=0.267 ms 2664 64 bytes from 10.0.4.2: icmp_seq=4 ttl=64 time=0.222 ms 2665 2666This is not due to an error in the bonding driver, rather, it 2667is a side effect of how many switches update their MAC forwarding 2668tables. Initially, the switch does not associate the MAC address in 2669the packet with a particular switch port, and so it may send the 2670traffic to all ports until its MAC forwarding table is updated. Since 2671the interfaces attached to the bond may occupy multiple ports on a 2672single switch, when the switch (temporarily) floods the traffic to all 2673ports, the bond device receives multiple copies of the same packet 2674(one per slave device). 2675 2676The duplicated packet behavior is switch dependent, some 2677switches exhibit this, and some do not. On switches that display this 2678behavior, it can be induced by clearing the MAC forwarding table (on 2679most Cisco switches, the privileged command "clear mac address-table 2680dynamic" will accomplish this). 2681 268214. Hardware Specific Considerations 2683==================================== 2684 2685This section contains additional information for configuring 2686bonding on specific hardware platforms, or for interfacing bonding 2687with particular switches or other devices. 2688 268914.1 IBM BladeCenter 2690-------------------- 2691 2692This applies to the JS20 and similar systems. 2693 2694On the JS20 blades, the bonding driver supports only 2695balance-rr, active-backup, balance-tlb and balance-alb modes. This is 2696largely due to the network topology inside the BladeCenter, detailed 2697below. 2698 2699JS20 network adapter information 2700-------------------------------- 2701 2702All JS20s come with two Broadcom Gigabit Ethernet ports 2703integrated on the planar (that's "motherboard" in IBM-speak). In the 2704BladeCenter chassis, the eth0 port of all JS20 blades is hard wired to 2705I/O Module #1; similarly, all eth1 ports are wired to I/O Module #2. 2706An add-on Broadcom daughter card can be installed on a JS20 to provide 2707two more Gigabit Ethernet ports. These ports, eth2 and eth3, are 2708wired to I/O Modules 3 and 4, respectively. 2709 2710Each I/O Module may contain either a switch or a passthrough 2711module (which allows ports to be directly connected to an external 2712switch). Some bonding modes require a specific BladeCenter internal 2713network topology in order to function; these are detailed below. 2714 2715Additional BladeCenter-specific networking information can be 2716found in two IBM Redbooks (www.ibm.com/redbooks): 2717 2718- "IBM eServer BladeCenter Networking Options" 2719- "IBM eServer BladeCenter Layer 2-7 Network Switching" 2720 2721BladeCenter networking configuration 2722------------------------------------ 2723 2724Because a BladeCenter can be configured in a very large number 2725of ways, this discussion will be confined to describing basic 2726configurations. 2727 2728Normally, Ethernet Switch Modules (ESMs) are used in I/O 2729modules 1 and 2. In this configuration, the eth0 and eth1 ports of a 2730JS20 will be connected to different internal switches (in the 2731respective I/O modules). 2732 2733A passthrough module (OPM or CPM, optical or copper, 2734passthrough module) connects the I/O module directly to an external 2735switch. By using PMs in I/O module #1 and #2, the eth0 and eth1 2736interfaces of a JS20 can be redirected to the outside world and 2737connected to a common external switch. 2738 2739Depending upon the mix of ESMs and PMs, the network will 2740appear to bonding as either a single switch topology (all PMs) or as a 2741multiple switch topology (one or more ESMs, zero or more PMs). It is 2742also possible to connect ESMs together, resulting in a configuration 2743much like the example in "High Availability in a Multiple Switch 2744Topology," above. 2745 2746Requirements for specific modes 2747------------------------------- 2748 2749The balance-rr mode requires the use of passthrough modules 2750for devices in the bond, all connected to an common external switch. 2751That switch must be configured for "etherchannel" or "trunking" on the 2752appropriate ports, as is usual for balance-rr. 2753 2754The balance-alb and balance-tlb modes will function with 2755either switch modules or passthrough modules (or a mix). The only 2756specific requirement for these modes is that all network interfaces 2757must be able to reach all destinations for traffic sent over the 2758bonding device (i.e., the network must converge at some point outside 2759the BladeCenter). 2760 2761The active-backup mode has no additional requirements. 2762 2763Link monitoring issues 2764---------------------- 2765 2766When an Ethernet Switch Module is in place, only the ARP 2767monitor will reliably detect link loss to an external switch. This is 2768nothing unusual, but examination of the BladeCenter cabinet would 2769suggest that the "external" network ports are the ethernet ports for 2770the system, when it fact there is a switch between these "external" 2771ports and the devices on the JS20 system itself. The MII monitor is 2772only able to detect link failures between the ESM and the JS20 system. 2773 2774When a passthrough module is in place, the MII monitor does 2775detect failures to the "external" port, which is then directly 2776connected to the JS20 system. 2777 2778Other concerns 2779-------------- 2780 2781The Serial Over LAN (SoL) link is established over the primary 2782ethernet (eth0) only, therefore, any loss of link to eth0 will result 2783in losing your SoL connection. It will not fail over with other 2784network traffic, as the SoL system is beyond the control of the 2785bonding driver. 2786 2787It may be desirable to disable spanning tree on the switch 2788(either the internal Ethernet Switch Module, or an external switch) to 2789avoid fail-over delay issues when using bonding. 2790 2791 279215. Frequently Asked Questions 2793============================== 2794 27951. Is it SMP safe? 2796------------------- 2797 2798Yes. The old 2.0.xx channel bonding patch was not SMP safe. 2799The new driver was designed to be SMP safe from the start. 2800 28012. What type of cards will work with it? 2802----------------------------------------- 2803 2804Any Ethernet type cards (you can even mix cards - a Intel 2805EtherExpress PRO/100 and a 3com 3c905b, for example). For most modes, 2806devices need not be of the same speed. 2807 2808Starting with version 3.2.1, bonding also supports Infiniband 2809slaves in active-backup mode. 2810 28113. How many bonding devices can I have? 2812---------------------------------------- 2813 2814There is no limit. 2815 28164. How many slaves can a bonding device have? 2817---------------------------------------------- 2818 2819This is limited only by the number of network interfaces Linux 2820supports and/or the number of network cards you can place in your 2821system. 2822 28235. What happens when a slave link dies? 2824---------------------------------------- 2825 2826If link monitoring is enabled, then the failing device will be 2827disabled. The active-backup mode will fail over to a backup link, and 2828other modes will ignore the failed link. The link will continue to be 2829monitored, and should it recover, it will rejoin the bond (in whatever 2830manner is appropriate for the mode). See the sections on High 2831Availability and the documentation for each mode for additional 2832information. 2833 2834Link monitoring can be enabled via either the miimon or 2835arp_interval parameters (described in the module parameters section, 2836above). In general, miimon monitors the carrier state as sensed by 2837the underlying network device, and the arp monitor (arp_interval) 2838monitors connectivity to another host on the local network. 2839 2840If no link monitoring is configured, the bonding driver will 2841be unable to detect link failures, and will assume that all links are 2842always available. This will likely result in lost packets, and a 2843resulting degradation of performance. The precise performance loss 2844depends upon the bonding mode and network configuration. 2845 28466. Can bonding be used for High Availability? 2847---------------------------------------------- 2848 2849Yes. See the section on High Availability for details. 2850 28517. Which switches/systems does it work with? 2852--------------------------------------------- 2853 2854The full answer to this depends upon the desired mode. 2855 2856In the basic balance modes (balance-rr and balance-xor), it 2857works with any system that supports etherchannel (also called 2858trunking). Most managed switches currently available have such 2859support, and many unmanaged switches as well. 2860 2861The advanced balance modes (balance-tlb and balance-alb) do 2862not have special switch requirements, but do need device drivers that 2863support specific features (described in the appropriate section under 2864module parameters, above). 2865 2866In 802.3ad mode, it works with systems that support IEEE 2867802.3ad Dynamic Link Aggregation. Most managed and many unmanaged 2868switches currently available support 802.3ad. 2869 2870The active-backup mode should work with any Layer-II switch. 2871 28728. Where does a bonding device get its MAC address from? 2873--------------------------------------------------------- 2874 2875When using slave devices that have fixed MAC addresses, or when 2876the fail_over_mac option is enabled, the bonding device's MAC address is 2877the MAC address of the active slave. 2878 2879For other configurations, if not explicitly configured (with 2880ifconfig or ip link), the MAC address of the bonding device is taken from 2881its first slave device. This MAC address is then passed to all following 2882slaves and remains persistent (even if the first slave is removed) until 2883the bonding device is brought down or reconfigured. 2884 2885If you wish to change the MAC address, you can set it with 2886ifconfig or ip link:: 2887 2888 # ifconfig bond0 hw ether 00:11:22:33:44:55 2889 2890 # ip link set bond0 address 66:77:88:99:aa:bb 2891 2892The MAC address can be also changed by bringing down/up the 2893device and then changing its slaves (or their order):: 2894 2895 # ifconfig bond0 down ; modprobe -r bonding 2896 # ifconfig bond0 .... up 2897 # ifenslave bond0 eth... 2898 2899This method will automatically take the address from the next 2900slave that is added. 2901 2902To restore your slaves' MAC addresses, you need to detach them 2903from the bond (``ifenslave -d bond0 eth0``). The bonding driver will 2904then restore the MAC addresses that the slaves had before they were 2905enslaved. 2906 290716. Resources and Links 2908======================= 2909 2910The latest version of the bonding driver can be found in the latest 2911version of the linux kernel, found on http://kernel.org 2912 2913The latest version of this document can be found in the latest kernel 2914source (named Documentation/networking/bonding.rst). 2915 2916Discussions regarding the development of the bonding driver take place 2917on the main Linux network mailing list, hosted at vger.kernel.org. The list 2918address is: 2919 2920netdev@vger.kernel.org 2921 2922The administrative interface (to subscribe or unsubscribe) can 2923be found at: 2924 2925http://vger.kernel.org/vger-lists.html#netdev 2926