TOMOYO Linux Cross Reference
Linux/Documentation/networking/bonding.rst

   .. SPDX-License-Identifier: GPL-2.0
   
   ===================================
   Linux Ethernet Bonding Driver HOWTO
   ===================================
   
   Latest update: 27 April 2011
   
   Initial release: Thomas Davis <tadavis at lbl.gov>
  
  Corrections, HA extensions: 2000/10/03-15:
  
    - Willy Tarreau <willy at meta-x.org>
    - Constantine Gavrilov <const-g at xpert.com>
    - Chad N. Tindel <ctindel at ieee dot org>
    - Janice Girouard <girouard at us dot ibm dot com>
    - Jay Vosburgh <fubar at us dot ibm dot com>
  
  Reorganized and updated Feb 2005 by Jay Vosburgh
  Added Sysfs information: 2006/04/24
  
    - Mitch Williams <mitch.a.williams at intel.com>
  
  Introduction
  ============
  
  The Linux bonding driver provides a method for aggregating
  multiple network interfaces into a single logical "bonded" interface.
  The behavior of the bonded interfaces depends upon the mode; generally
  speaking, modes provide either hot standby or load balancing services.
  Additionally, link integrity monitoring may be performed.
  
  The bonding driver originally came from Donald Becker's
  beowulf patches for kernel 2.0. It has changed quite a bit since, and
  the original tools from extreme-linux and beowulf sites will not work
  with this version of the driver.
  
  For new versions of the driver, updated userspace tools, and
  who to ask for help, please follow the links at the end of this file.
  
  .. Table of Contents
  
     1. Bonding Driver Installation
  
     2. Bonding Driver Options
  
     3. Configuring Bonding Devices
     3.1  Configuration with Sysconfig Support
     3.1.1                Using DHCP with Sysconfig
     3.1.2                Configuring Multiple Bonds with Sysconfig
     3.2  Configuration with Initscripts Support
     3.2.1                Using DHCP with Initscripts
     3.2.2                Configuring Multiple Bonds with Initscripts
     3.3  Configuring Bonding Manually with Ifenslave
     3.3.1                Configuring Multiple Bonds Manually
     3.4  Configuring Bonding Manually via Sysfs
     3.5  Configuration with Interfaces Support
     3.6  Overriding Configuration for Special Cases
     3.7 Configuring LACP for 802.3ad mode in a more secure way
  
     4. Querying Bonding Configuration
     4.1  Bonding Configuration
     4.2  Network Configuration
  
     5. Switch Configuration
  
     6. 802.1q VLAN Support
  
     7. Link Monitoring
     7.1  ARP Monitor Operation
     7.2  Configuring Multiple ARP Targets
     7.3  MII Monitor Operation
  
     8. Potential Trouble Sources
     8.1  Adventures in Routing
     8.2  Ethernet Device Renaming
     8.3  Painfully Slow Or No Failed Link Detection By Miimon
  
     9. SNMP agents
  
     10. Promiscuous mode
  
     11. Configuring Bonding for High Availability
     11.1 High Availability in a Single Switch Topology
     11.2 High Availability in a Multiple Switch Topology
     11.2.1               HA Bonding Mode Selection for Multiple Switch Topology
     11.2.2               HA Link Monitoring for Multiple Switch Topology
  
     12. Configuring Bonding for Maximum Throughput
     12.1 Maximum Throughput in a Single Switch Topology
     12.1.1               MT Bonding Mode Selection for Single Switch Topology
     12.1.2               MT Link Monitoring for Single Switch Topology
     12.2 Maximum Throughput in a Multiple Switch Topology
     12.2.1               MT Bonding Mode Selection for Multiple Switch Topology
     12.2.2               MT Link Monitoring for Multiple Switch Topology
  
     13. Switch Behavior Issues
     13.1 Link Establishment and Failover Delays
     13.2 Duplicated Incoming Packets
 
    14. Hardware Specific Considerations
    14.1 IBM BladeCenter
 
    15. Frequently Asked Questions
 
    16. Resources and Links
 
 
 1. Bonding Driver Installation
 ==============================
 
 Most popular distro kernels ship with the bonding driver
 already available as a module. If your distro does not, or you
 have need to compile bonding from source (e.g., configuring and
 installing a mainline kernel from kernel.org), you'll need to perform
 the following steps:
 
 1.1 Configure and build the kernel with bonding
 -----------------------------------------------
 
 The current version of the bonding driver is available in the
 drivers/net/bonding subdirectory of the most recent kernel source
 (which is available on http://kernel.org).  Most users "rolling their
 own" will want to use the most recent kernel from kernel.org.
 
 Configure kernel with "make menuconfig" (or "make xconfig" or
 "make config"), then select "Bonding driver support" in the "Network
 device support" section.  It is recommended that you configure the
 driver as module since it is currently the only way to pass parameters
 to the driver or configure more than one bonding device.
 
 Build and install the new kernel and modules.
 
 1.2 Bonding Control Utility
 ---------------------------
 
 It is recommended to configure bonding via iproute2 (netlink)
 or sysfs, the old ifenslave control utility is obsolete.
 
 2. Bonding Driver Options
 =========================
 
 Options for the bonding driver are supplied as parameters to the
 bonding module at load time, or are specified via sysfs.
 
 Module options may be given as command line arguments to the
 insmod or modprobe command, but are usually specified in either the
 ``/etc/modprobe.d/*.conf`` configuration files, or in a distro-specific
 configuration file (some of which are detailed in the next section).
 
 Details on bonding support for sysfs is provided in the
 "Configuring Bonding Manually via Sysfs" section, below.
 
 The available bonding driver parameters are listed below. If a
 parameter is not specified the default value is used.  When initially
 configuring a bond, it is recommended "tail -f /var/log/messages" be
 run in a separate window to watch for bonding driver error messages.
 
 It is critical that either the miimon or arp_interval and
 arp_ip_target parameters be specified, otherwise serious network
 degradation will occur during link failures.  Very few devices do not
 support at least miimon, so there is really no reason not to use it.
 
 Options with textual values will accept either the text name
 or, for backwards compatibility, the option value.  E.g.,
 "mode=802.3ad" and "mode=4" set the same mode.
 
 The parameters are as follows:
 
 active_slave
 
         Specifies the new active slave for modes that support it
         (active-backup, balance-alb and balance-tlb).  Possible values
         are the name of any currently enslaved interface, or an empty
         string.  If a name is given, the slave and its link must be up in order
         to be selected as the new active slave.  If an empty string is
         specified, the current active slave is cleared, and a new active
         slave is selected automatically.
 
         Note that this is only available through the sysfs interface. No module
         parameter by this name exists.
 
         The normal value of this option is the name of the currently
         active slave, or the empty string if there is no active slave or
         the current mode does not use an active slave.
 
 ad_actor_sys_prio
 
         In an AD system, this specifies the system priority. The allowed range
         is 1 - 65535. If the value is not specified, it takes 65535 as the
         default value.
 
         This parameter has effect only in 802.3ad mode and is available through
         SysFs interface.
 
 ad_actor_system
 
         In an AD system, this specifies the mac-address for the actor in
         protocol packet exchanges (LACPDUs). The value cannot be a multicast
         address. If the all-zeroes MAC is specified, bonding will internally
         use the MAC of the bond itself. It is preferred to have the
         local-admin bit set for this mac but driver does not enforce it. If
         the value is not given then system defaults to using the masters'
         mac address as actors' system address.
 
         This parameter has effect only in 802.3ad mode and is available through
         SysFs interface.
 
 ad_select
 
         Specifies the 802.3ad aggregation selection logic to use.  The
         possible values and their effects are:
 
         stable or 0
 
                 The active aggregator is chosen by largest aggregate
                 bandwidth.
 
                 Reselection of the active aggregator occurs only when all
                 slaves of the active aggregator are down or the active
                 aggregator has no slaves.
 
                 This is the default value.
 
         bandwidth or 1
 
                 The active aggregator is chosen by largest aggregate
                 bandwidth.  Reselection occurs if:
 
                 - A slave is added to or removed from the bond
 
                 - Any slave's link state changes
 
                 - Any slave's 802.3ad association state changes
 
                 - The bond's administrative state changes to up
 
         count or 2
 
                 The active aggregator is chosen by the largest number of
                 ports (slaves).  Reselection occurs as described under the
                 "bandwidth" setting, above.
 
         The bandwidth and count selection policies permit failover of
         802.3ad aggregations when partial failure of the active aggregator
         occurs.  This keeps the aggregator with the highest availability
         (either in bandwidth or in number of ports) active at all times.
 
         This option was added in bonding version 3.4.0.
 
 ad_user_port_key
 
         In an AD system, the port-key has three parts as shown below -
 
            =====  ============
            Bits   Use
            =====  ============
            00     Duplex
            01-05  Speed
            06-15  User-defined
            =====  ============
 
         This defines the upper 10 bits of the port key. The values can be
         from 0 - 1023. If not given, the system defaults to 0.
 
         This parameter has effect only in 802.3ad mode and is available through
         SysFs interface.
 
 all_slaves_active
 
         Specifies that duplicate frames (received on inactive ports) should be
         dropped (0) or delivered (1).
 
         Normally, bonding will drop duplicate frames (received on inactive
         ports), which is desirable for most users. But there are some times
         it is nice to allow duplicate frames to be delivered.
 
         The default value is 0 (drop duplicate frames received on inactive
         ports).
 
 arp_interval
 
         Specifies the ARP link monitoring frequency in milliseconds.
 
         The ARP monitor works by periodically checking the slave
         devices to determine whether they have sent or received
         traffic recently (the precise criteria depends upon the
         bonding mode, and the state of the slave).  Regular traffic is
         generated via ARP probes issued for the addresses specified by
         the arp_ip_target option.
 
         This behavior can be modified by the arp_validate option,
         below.
 
         If ARP monitoring is used in an etherchannel compatible mode
         (modes 0 and 2), the switch should be configured in a mode
         that evenly distributes packets across all links. If the
         switch is configured to distribute the packets in an XOR
         fashion, all replies from the ARP targets will be received on
         the same link which could cause the other team members to
         fail.  ARP monitoring should not be used in conjunction with
         miimon.  A value of 0 disables ARP monitoring.  The default
         value is 0.
 
 arp_ip_target
 
         Specifies the IP addresses to use as ARP monitoring peers when
         arp_interval is > 0.  These are the targets of the ARP request
         sent to determine the health of the link to the targets.
         Specify these values in ddd.ddd.ddd.ddd format.  Multiple IP
         addresses must be separated by a comma.  At least one IP
         address must be given for ARP monitoring to function.  The
         maximum number of targets that can be specified is 16.  The
         default value is no IP addresses.
 
 ns_ip6_target
 
         Specifies the IPv6 addresses to use as IPv6 monitoring peers when
         arp_interval is > 0.  These are the targets of the NS request
         sent to determine the health of the link to the targets.
         Specify these values in ffff:ffff::ffff:ffff format.  Multiple IPv6
         addresses must be separated by a comma.  At least one IPv6
         address must be given for NS/NA monitoring to function.  The
         maximum number of targets that can be specified is 16.  The
         default value is no IPv6 addresses.
 
 arp_validate
 
         Specifies whether or not ARP probes and replies should be
         validated in any mode that supports arp monitoring, or whether
         non-ARP traffic should be filtered (disregarded) for link
         monitoring purposes.
 
         Possible values are:
 
         none or 0
 
                 No validation or filtering is performed.
 
         active or 1
 
                 Validation is performed only for the active slave.
 
         backup or 2
 
                 Validation is performed only for backup slaves.
 
         all or 3
 
                 Validation is performed for all slaves.
 
         filter or 4
 
                 Filtering is applied to all slaves. No validation is
                 performed.
 
         filter_active or 5
 
                 Filtering is applied to all slaves, validation is performed
                 only for the active slave.
 
         filter_backup or 6
 
                 Filtering is applied to all slaves, validation is performed
                 only for backup slaves.
 
         Validation:
 
         Enabling validation causes the ARP monitor to examine the incoming
         ARP requests and replies, and only consider a slave to be up if it
         is receiving the appropriate ARP traffic.
 
         For an active slave, the validation checks ARP replies to confirm
         that they were generated by an arp_ip_target.  Since backup slaves
         do not typically receive these replies, the validation performed
         for backup slaves is on the broadcast ARP request sent out via the
         active slave.  It is possible that some switch or network
         configurations may result in situations wherein the backup slaves
         do not receive the ARP requests; in such a situation, validation
         of backup slaves must be disabled.
 
         The validation of ARP requests on backup slaves is mainly helping
         bonding to decide which slaves are more likely to work in case of
         the active slave failure, it doesn't really guarantee that the
         backup slave will work if it's selected as the next active slave.
 
         Validation is useful in network configurations in which multiple
         bonding hosts are concurrently issuing ARPs to one or more targets
         beyond a common switch.  Should the link between the switch and
         target fail (but not the switch itself), the probe traffic
         generated by the multiple bonding instances will fool the standard
         ARP monitor into considering the links as still up.  Use of
         validation can resolve this, as the ARP monitor will only consider
         ARP requests and replies associated with its own instance of
         bonding.
 
         Filtering:
 
         Enabling filtering causes the ARP monitor to only use incoming ARP
         packets for link availability purposes.  Arriving packets that are
         not ARPs are delivered normally, but do not count when determining
         if a slave is available.
 
         Filtering operates by only considering the reception of ARP
         packets (any ARP packet, regardless of source or destination) when
         determining if a slave has received traffic for link availability
         purposes.
 
         Filtering is useful in network configurations in which significant
         levels of third party broadcast traffic would fool the standard
         ARP monitor into considering the links as still up.  Use of
         filtering can resolve this, as only ARP traffic is considered for
         link availability purposes.
 
         This option was added in bonding version 3.1.0.
 
 arp_all_targets
 
         Specifies the quantity of arp_ip_targets that must be reachable
         in order for the ARP monitor to consider a slave as being up.
         This option affects only active-backup mode for slaves with
         arp_validation enabled.
 
         Possible values are:
 
         any or 0
 
                 consider the slave up only when any of the arp_ip_targets
                 is reachable
 
         all or 1
 
                 consider the slave up only when all of the arp_ip_targets
                 are reachable
 
 arp_missed_max
 
         Specifies the number of arp_interval monitor checks that must
         fail in order for an interface to be marked down by the ARP monitor.
 
         In order to provide orderly failover semantics, backup interfaces
         are permitted an extra monitor check (i.e., they must fail
         arp_missed_max + 1 times before being marked down).
 
         The default value is 2, and the allowable range is 1 - 255.
 
 coupled_control
 
     Specifies whether the LACP state machine's MUX in the 802.3ad mode
     should have separate Collecting and Distributing states.
 
     This is by implementing the independent control state machine per
     IEEE 802.1AX-2008 5.4.15 in addition to the existing coupled control
     state machine.
 
     The default value is 1. This setting does not separate the Collecting
     and Distributing states, maintaining the bond in coupled control.
 
 downdelay
 
         Specifies the time, in milliseconds, to wait before disabling
         a slave after a link failure has been detected.  This option
         is only valid for the miimon link monitor.  The downdelay
         value should be a multiple of the miimon value; if not, it
         will be rounded down to the nearest multiple.  The default
         value is 0.
 
 fail_over_mac
 
         Specifies whether active-backup mode should set all slaves to
         the same MAC address at enslavement (the traditional
         behavior), or, when enabled, perform special handling of the
         bond's MAC address in accordance with the selected policy.
 
         Possible values are:
 
         none or 0
 
                 This setting disables fail_over_mac, and causes
                 bonding to set all slaves of an active-backup bond to
                 the same MAC address at enslavement time.  This is the
                 default.
 
         active or 1
 
                 The "active" fail_over_mac policy indicates that the
                 MAC address of the bond should always be the MAC
                 address of the currently active slave.  The MAC
                 address of the slaves is not changed; instead, the MAC
                 address of the bond changes during a failover.
 
                 This policy is useful for devices that cannot ever
                 alter their MAC address, or for devices that refuse
                 incoming broadcasts with their own source MAC (which
                 interferes with the ARP monitor).
 
                 The down side of this policy is that every device on
                 the network must be updated via gratuitous ARP,
                 vs. just updating a switch or set of switches (which
                 often takes place for any traffic, not just ARP
                 traffic, if the switch snoops incoming traffic to
                 update its tables) for the traditional method.  If the
                 gratuitous ARP is lost, communication may be
                 disrupted.
 
                 When this policy is used in conjunction with the mii
                 monitor, devices which assert link up prior to being
                 able to actually transmit and receive are particularly
                 susceptible to loss of the gratuitous ARP, and an
                 appropriate updelay setting may be required.
 
         follow or 2
 
                 The "follow" fail_over_mac policy causes the MAC
                 address of the bond to be selected normally (normally
                 the MAC address of the first slave added to the bond).
                 However, the second and subsequent slaves are not set
                 to this MAC address while they are in a backup role; a
                 slave is programmed with the bond's MAC address at
                 failover time (and the formerly active slave receives
                 the newly active slave's MAC address).
 
                 This policy is useful for multiport devices that
                 either become confused or incur a performance penalty
                 when multiple ports are programmed with the same MAC
                 address.
 
 
         The default policy is none, unless the first slave cannot
         change its MAC address, in which case the active policy is
         selected by default.
 
         This option may be modified via sysfs only when no slaves are
         present in the bond.
 
         This option was added in bonding version 3.2.0.  The "follow"
         policy was added in bonding version 3.3.0.
 
 lacp_active
         Option specifying whether to send LACPDU frames periodically.
 
         off or 0
                 LACPDU frames acts as "speak when spoken to".
 
         on or 1
                 LACPDU frames are sent along the configured links
                 periodically. See lacp_rate for more details.
 
         The default is on.
 
 lacp_rate
 
         Option specifying the rate in which we'll ask our link partner
         to transmit LACPDU packets in 802.3ad mode.  Possible values
         are:
 
         slow or 0
                 Request partner to transmit LACPDUs every 30 seconds
 
         fast or 1
                 Request partner to transmit LACPDUs every 1 second
 
         The default is slow.
 
 max_bonds
 
         Specifies the number of bonding devices to create for this
         instance of the bonding driver.  E.g., if max_bonds is 3, and
         the bonding driver is not already loaded, then bond0, bond1
         and bond2 will be created.  The default value is 1.  Specifying
         a value of 0 will load bonding, but will not create any devices.
 
 miimon
 
         Specifies the MII link monitoring frequency in milliseconds.
         This determines how often the link state of each slave is
         inspected for link failures.  A value of zero disables MII
         link monitoring.  A value of 100 is a good starting point.
         The use_carrier option, below, affects how the link state is
         determined.  See the High Availability section for additional
         information.  The default value is 100 if arp_interval is not
         set.
 
 min_links
 
         Specifies the minimum number of links that must be active before
         asserting carrier. It is similar to the Cisco EtherChannel min-links
         feature. This allows setting the minimum number of member ports that
         must be up (link-up state) before marking the bond device as up
         (carrier on). This is useful for situations where higher level services
         such as clustering want to ensure a minimum number of low bandwidth
         links are active before switchover. This option only affect 802.3ad
         mode.
 
         The default value is 0. This will cause carrier to be asserted (for
         802.3ad mode) whenever there is an active aggregator, regardless of the
         number of available links in that aggregator. Note that, because an
         aggregator cannot be active without at least one available link,
         setting this option to 0 or to 1 has the exact same effect.
 
 mode
 
         Specifies one of the bonding policies. The default is
         balance-rr (round robin).  Possible values are:
 
         balance-rr or 0
 
                 Round-robin policy: Transmit packets in sequential
                 order from the first available slave through the
                 last.  This mode provides load balancing and fault
                 tolerance.
 
         active-backup or 1
 
                 Active-backup policy: Only one slave in the bond is
                 active.  A different slave becomes active if, and only
                 if, the active slave fails.  The bond's MAC address is
                 externally visible on only one port (network adapter)
                 to avoid confusing the switch.
 
                 In bonding version 2.6.2 or later, when a failover
                 occurs in active-backup mode, bonding will issue one
                 or more gratuitous ARPs on the newly active slave.
                 One gratuitous ARP is issued for the bonding master
                 interface and each VLAN interfaces configured above
                 it, provided that the interface has at least one IP
                 address configured.  Gratuitous ARPs issued for VLAN
                 interfaces are tagged with the appropriate VLAN id.
 
                 This mode provides fault tolerance.  The primary
                 option, documented below, affects the behavior of this
                 mode.
 
         balance-xor or 2
 
                 XOR policy: Transmit based on the selected transmit
                 hash policy.  The default policy is a simple [(source
                 MAC address XOR'd with destination MAC address XOR
                 packet type ID) modulo slave count].  Alternate transmit
                 policies may be selected via the xmit_hash_policy option,
                 described below.
 
                 This mode provides load balancing and fault tolerance.
 
         broadcast or 3
 
                 Broadcast policy: transmits everything on all slave
                 interfaces.  This mode provides fault tolerance.
 
         802.3ad or 4
 
                 IEEE 802.3ad Dynamic link aggregation.  Creates
                 aggregation groups that share the same speed and
                 duplex settings.  Utilizes all slaves in the active
                 aggregator according to the 802.3ad specification.
 
                 Slave selection for outgoing traffic is done according
                 to the transmit hash policy, which may be changed from
                 the default simple XOR policy via the xmit_hash_policy
                 option, documented below.  Note that not all transmit
                 policies may be 802.3ad compliant, particularly in
                 regards to the packet mis-ordering requirements of
                 section 43.2.4 of the 802.3ad standard.  Differing
                 peer implementations will have varying tolerances for
                 noncompliance.
 
                 Prerequisites:
 
                 1. Ethtool support in the base drivers for retrieving
                 the speed and duplex of each slave.
 
                 2. A switch that supports IEEE 802.3ad Dynamic link
                 aggregation.
 
                 Most switches will require some type of configuration
                 to enable 802.3ad mode.
 
         balance-tlb or 5
 
                 Adaptive transmit load balancing: channel bonding that
                 does not require any special switch support.
 
                 In tlb_dynamic_lb=1 mode; the outgoing traffic is
                 distributed according to the current load (computed
                 relative to the speed) on each slave.
 
                 In tlb_dynamic_lb=0 mode; the load balancing based on
                 current load is disabled and the load is distributed
                 only using the hash distribution.
 
                 Incoming traffic is received by the current slave.
                 If the receiving slave fails, another slave takes over
                 the MAC address of the failed receiving slave.
 
                 Prerequisite:
 
                 Ethtool support in the base drivers for retrieving the
                 speed of each slave.
 
         balance-alb or 6
 
                 Adaptive load balancing: includes balance-tlb plus
                 receive load balancing (rlb) for IPV4 traffic, and
                 does not require any special switch support.  The
                 receive load balancing is achieved by ARP negotiation.
                 The bonding driver intercepts the ARP Replies sent by
                 the local system on their way out and overwrites the
                 source hardware address with the unique hardware
                 address of one of the slaves in the bond such that
                 different peers use different hardware addresses for
                 the server.
 
                 Receive traffic from connections created by the server
                 is also balanced.  When the local system sends an ARP
                 Request the bonding driver copies and saves the peer's
                 IP information from the ARP packet.  When the ARP
                 Reply arrives from the peer, its hardware address is
                 retrieved and the bonding driver initiates an ARP
                 reply to this peer assigning it to one of the slaves
                 in the bond.  A problematic outcome of using ARP
                 negotiation for balancing is that each time that an
                 ARP request is broadcast it uses the hardware address
                 of the bond.  Hence, peers learn the hardware address
                 of the bond and the balancing of receive traffic
                 collapses to the current slave.  This is handled by
                 sending updates (ARP Replies) to all the peers with
                 their individually assigned hardware address such that
                 the traffic is redistributed.  Receive traffic is also
                 redistributed when a new slave is added to the bond
                 and when an inactive slave is re-activated.  The
                 receive load is distributed sequentially (round robin)
                 among the group of highest speed slaves in the bond.
 
                 When a link is reconnected or a new slave joins the
                 bond the receive traffic is redistributed among all
                 active slaves in the bond by initiating ARP Replies
                 with the selected MAC address to each of the
                 clients. The updelay parameter (detailed below) must
                 be set to a value equal or greater than the switch's
                 forwarding delay so that the ARP Replies sent to the
                 peers will not be blocked by the switch.
 
                 Prerequisites:
 
                 1. Ethtool support in the base drivers for retrieving
                 the speed of each slave.
 
                 2. Base driver support for setting the hardware
                 address of a device while it is open.  This is
                 required so that there will always be one slave in the
                 team using the bond hardware address (the
                 curr_active_slave) while having a unique hardware
                 address for each slave in the bond.  If the
                 curr_active_slave fails its hardware address is
                 swapped with the new curr_active_slave that was
                 chosen.
 
 num_grat_arp,
 num_unsol_na
 
         Specify the number of peer notifications (gratuitous ARPs and
         unsolicited IPv6 Neighbor Advertisements) to be issued after a
         failover event.  As soon as the link is up on the new slave
         (possibly immediately) a peer notification is sent on the
         bonding device and each VLAN sub-device. This is repeated at
         the rate specified by peer_notif_delay if the number is
         greater than 1.
 
         The valid range is 0 - 255; the default value is 1.  These options
         affect only the active-backup mode.  These options were added for
         bonding versions 3.3.0 and 3.4.0 respectively.
 
         From Linux 3.0 and bonding version 3.7.1, these notifications
         are generated by the ipv4 and ipv6 code and the numbers of
         repetitions cannot be set independently.
 
 packets_per_slave
 
         Specify the number of packets to transmit through a slave before
         moving to the next one. When set to 0 then a slave is chosen at
         random.
 
         The valid range is 0 - 65535; the default value is 1. This option
         has effect only in balance-rr mode.
 
 peer_notif_delay
 
         Specify the delay, in milliseconds, between each peer
         notification (gratuitous ARP and unsolicited IPv6 Neighbor
         Advertisement) when they are issued after a failover event.
         This delay should be a multiple of the MII link monitor interval
         (miimon).
 
         The valid range is 0 - 300000. The default value is 0, which means
         to match the value of the MII link monitor interval.
 
 prio
         Slave priority. A higher number means higher priority.
         The primary slave has the highest priority. This option also
         follows the primary_reselect rules.
 
         This option could only be configured via netlink, and is only valid
         for active-backup(1), balance-tlb (5) and balance-alb (6) mode.
         The valid value range is a signed 32 bit integer.
 
         The default value is 0.
 
 primary
 
         A string (eth0, eth2, etc) specifying which slave is the
         primary device.  The specified device will always be the
         active slave while it is available.  Only when the primary is
         off-line will alternate devices be used.  This is useful when
         one slave is preferred over another, e.g., when one slave has
         higher throughput than another.
 
         The primary option is only valid for active-backup(1),
         balance-tlb (5) and balance-alb (6) mode.
 
 primary_reselect
 
         Specifies the reselection policy for the primary slave.  This
         affects how the primary slave is chosen to become the active slave
         when failure of the active slave or recovery of the primary slave
         occurs.  This option is designed to prevent flip-flopping between
         the primary slave and other slaves.  Possible values are:
 
         always or 0 (default)
 
                 The primary slave becomes the active slave whenever it
                 comes back up.
 
         better or 1
 
                 The primary slave becomes the active slave when it comes
                 back up, if the speed and duplex of the primary slave is
                 better than the speed and duplex of the current active
                 slave.
 
         failure or 2
 
                 The primary slave becomes the active slave only if the
                 current active slave fails and the primary slave is up.
 
         The primary_reselect setting is ignored in two cases:
 
                 If no slaves are active, the first slave to recover is
                 made the active slave.
 
                 When initially enslaved, the primary slave is always made
                 the active slave.
 
         Changing the primary_reselect policy via sysfs will cause an
         immediate selection of the best active slave according to the new
         policy.  This may or may not result in a change of the active
         slave, depending upon the circumstances.
 
         This option was added for bonding version 3.6.0.
 
 tlb_dynamic_lb
 
         Specifies if dynamic shuffling of flows is enabled in tlb
         or alb mode. The value has no effect on any other modes.
 
         The default behavior of tlb mode is to shuffle active flows across
         slaves based on the load in that interval. This gives nice lb
         characteristics but can cause packet reordering. If re-ordering is
         a concern use this variable to disable flow shuffling and rely on
         load balancing provided solely by the hash distribution.
         xmit-hash-policy can be used to select the appropriate hashing for
         the setup.
 
         The sysfs entry can be used to change the setting per bond device
         and the initial value is derived from the module parameter. The
         sysfs entry is allowed to be changed only if the bond device is
         down.
 
         The default value is "1" that enables flow shuffling while value "0"
         disables it. This option was added in bonding driver 3.7.1
 
 
 updelay
 
         Specifies the time, in milliseconds, to wait before enabling a
         slave after a link recovery has been detected.  This option is
         only valid for the miimon link monitor.  The updelay value
         should be a multiple of the miimon value; if not, it will be
         rounded down to the nearest multiple.  The default value is 0.
 
 use_carrier
 
         Specifies whether or not miimon should use MII or ETHTOOL
         ioctls vs. netif_carrier_ok() to determine the link
         status. The MII or ETHTOOL ioctls are less efficient and
         utilize a deprecated calling sequence within the kernel.  The
         netif_carrier_ok() relies on the device driver to maintain its
         state with netif_carrier_on/off; at this writing, most, but
         not all, device drivers support this facility.
 
         If bonding insists that the link is up when it should not be,
         it may be that your network device driver does not support
         netif_carrier_on/off.  The default state for netif_carrier is
         "carrier on," so if a driver does not support netif_carrier,
         it will appear as if the link is always up.  In this case,
         setting use_carrier to 0 will cause bonding to revert to the
         MII / ETHTOOL ioctl method to determine the link state.
 
         A value of 1 enables the use of netif_carrier_ok(), a value of
         0 will use the deprecated MII / ETHTOOL ioctls.  The default
         value is 1.
 
 xmit_hash_policy
 
         Selects the transmit hash policy to use for slave selection in
         balance-xor, 802.3ad, and tlb modes.  Possible values are:
 
         layer2
 
                 Uses XOR of hardware MAC addresses and packet type ID
                 field to generate the hash. The formula is
 
                 hash = source MAC[5] XOR destination MAC[5] XOR packet type ID
                 slave number = hash modulo slave count
 
                 This algorithm will place all traffic to a particular
                 network peer on the same slave.
 
                 This algorithm is 802.3ad compliant.
 
         layer2+3
 
                 This policy uses a combination of layer2 and layer3
                 protocol information to generate the hash.
 
                 Uses XOR of hardware MAC addresses and IP addresses to
                 generate the hash.  The formula is
 
                 hash = source MAC[5] XOR destination MAC[5] XOR packet type ID
                 hash = hash XOR source IP XOR destination IP
                 hash = hash XOR (hash RSHIFT 16)
                 hash = hash XOR (hash RSHIFT 8)
                 And then hash is reduced modulo slave count.
 
                 If the protocol is IPv6 then the source and destination
                 addresses are first hashed using ipv6_addr_hash.
 
                 This algorithm will place all traffic to a particular
                 network peer on the same slave.  For non-IP traffic,
                 the formula is the same as for the layer2 transmit
                 hash policy.
 
                 This policy is intended to provide a more balanced
                 distribution of traffic than layer2 alone, especially
                 in environments where a layer3 gateway device is
                 required to reach most destinations.
 
                 This algorithm is 802.3ad compliant.
 
         layer3+4
 
                 This policy uses upper layer protocol information,
                 when available, to generate the hash.  This allows for
                 traffic to a particular network peer to span multiple
                 slaves, although a single connection will not span
                 multiple slaves.
 
                 The formula for unfragmented TCP and UDP packets is
 
                 hash = source port, destination port (as in the header)
                 hash = hash XOR source IP XOR destination IP
                 hash = hash XOR (hash RSHIFT 16)
                 hash = hash XOR (hash RSHIFT 8)
                 hash = hash RSHIFT 1
                 And then hash is reduced modulo slave count.
 
                 If the protocol is IPv6 then the source and destination
                 addresses are first hashed using ipv6_addr_hash.
 
                 For fragmented TCP or UDP packets and all other IPv4 and
                 IPv6 protocol traffic, the source and destination port
                 information is omitted.  For non-IP traffic, the
                 formula is the same as for the layer2 transmit hash
                 policy.
 
                 This algorithm is not fully 802.3ad compliant.  A
                 single TCP or UDP conversation containing both
                 fragmented and unfragmented packets will see packets
                 striped across two interfaces.  This may result in out
                 of order delivery.  Most traffic types will not meet
                 this criteria, as TCP rarely fragments traffic, and
                 most UDP traffic is not involved in extended
                 conversations.  Other implementations of 802.3ad may
                 or may not tolerate this noncompliance.
 
         encap2+3
 
                 This policy uses the same formula as layer2+3 but it
                 relies on skb_flow_dissect to obtain the header fields
                 which might result in the use of inner headers if an
                 encapsulation protocol is used. For example this will
                 improve the performance for tunnel users because the
                 packets will be distributed according to the encapsulated
                 flows.
 
         encap3+4
 
                 This policy uses the same formula as layer3+4 but it
                 relies on skb_flow_dissect to obtain the header fields
                 which might result in the use of inner headers if an
                 encapsulation protocol is used. For example this will
                 improve the performance for tunnel users because the
                 packets will be distributed according to the encapsulated
                 flows.
 
         vlan+srcmac
 
                 This policy uses a very rudimentary vlan ID and source mac
                 hash to load-balance traffic per-vlan, with failover
                 should one leg fail. The intended use case is for a bond
                 shared by multiple virtual machines, all configured to
                 use their own vlan, to give lacp-like functionality
                 without requiring lacp-capable switching hardware.
 
                 The formula for the hash is simply
 
                 hash = (vlan ID) XOR (source MAC vendor) XOR (source MAC dev)
 
         The default value is layer2.  This option was added in bonding
         version 2.6.3.  In earlier versions of bonding, this parameter
         does not exist, and the layer2 policy is the only policy.  The
         layer2+3 value was added for bonding version 3.2.2.
 
 resend_igmp
 
         Specifies the number of IGMP membership reports to be issued after
         a failover event. One membership report is issued immediately after
         the failover, subsequent packets are sent in each 200ms interval.
 
         The valid range is 0 - 255; the default value is 1. A value of 0
         prevents the IGMP membership report from being issued in response
         to the failover event.
 
         This option is useful for bonding modes balance-rr (0), active-backup
         (1), balance-tlb (5) and balance-alb (6), in which a failover can
         switch the IGMP traffic from one slave to another.  Therefore a fresh
         IGMP report must be issued to cause the switch to forward the incoming
         IGMP traffic over the newly selected slave.
 
         This option was added for bonding version 3.7.0.
 
 lp_interval
 
         Specifies the number of seconds between instances where the bonding
         driver sends learning packets to each slaves peer switch.
 
         The valid range is 1 - 0x7fffffff; the default value is 1. This Option
         has effect only in balance-tlb and balance-alb modes.
 
 3. Configuring Bonding Devices
 ==============================
 
 You can configure bonding using either your distro's network
 initialization scripts, or manually using either iproute2 or the
 sysfs interface.  Distros generally use one of three packages for the
 network initialization scripts: initscripts, sysconfig or interfaces.
 Recent versions of these packages have support for bonding, while older
 versions do not.
 
 We will first describe the options for configuring bonding for
 distros using versions of initscripts, sysconfig and interfaces with full
 or partial support for bonding, then provide information on enabling
 bonding without support from the network initialization scripts (i.e.,
 older versions of initscripts or sysconfig).
 
 If you're unsure whether your distro uses sysconfig,
 initscripts or interfaces, or don't know if it's new enough, have no fear.
 Determining this is fairly straightforward.
 
 First, look for a file called interfaces in /etc/network directory.
 If this file is present in your system, then your system use interfaces. See
 Configuration with Interfaces Support.
 
 Else, issue the command::
 
         $ rpm -qf /sbin/ifup
 
 It will respond with a line of text starting with either
 "initscripts" or "sysconfig," followed by some numbers.  This is the
 package that provides your network initialization scripts.
 
 Next, to determine if your installation supports bonding,
 issue the command::
 
     $ grep ifenslave /sbin/ifup
 
 If this returns any matches, then your initscripts or
 sysconfig has support for bonding.
 
 3.1 Configuration with Sysconfig Support
 ----------------------------------------
 
 This section applies to distros using a version of sysconfig
 with bonding support, for example, SuSE Linux Enterprise Server 9.
 
 SuSE SLES 9's networking configuration system does support
 bonding, however, at this writing, the YaST system configuration
 front end does not provide any means to work with bonding devices.
 Bonding devices can be managed by hand, however, as follows.
 
 First, if they have not already been configured, configure the
 slave devices.  On SLES 9, this is most easily done by running the
 yast2 sysconfig configuration utility.  The goal is for to create an
 ifcfg-id file for each slave device.  The simplest way to accomplish
 this is to configure the devices for DHCP (this is only to get the
 file ifcfg-id file created; see below for some issues with DHCP).  The
 name of the configuration file for each device will be of the form::
 
     ifcfg-id-xx:xx:xx:xx:xx:xx
 
 Where the "xx" portion will be replaced with the digits from
 the device's permanent MAC address.
 
 Once the set of ifcfg-id-xx:xx:xx:xx:xx:xx files has been
 created, it is necessary to edit the configuration files for the slave
 devices (the MAC addresses correspond to those of the slave devices).
 Before editing, the file will contain multiple lines, and will look
 something like this::
 
         BOOTPROTO='dhcp'
         STARTMODE='on'
         USERCTL='no'
         UNIQUE='XNzu.WeZGOGF+4wE'
         _nm_name='bus-pci-0001:61:01.0'
 
 Change the BOOTPROTO and STARTMODE lines to the following::
 
         BOOTPROTO='none'
         STARTMODE='off'
 
 Do not alter the UNIQUE or _nm_name lines.  Remove any other
 lines (USERCTL, etc).
 
 Once the ifcfg-id-xx:xx:xx:xx:xx:xx files have been modified,
 it's time to create the configuration file for the bonding device
 itself.  This file is named ifcfg-bondX, where X is the number of the
 bonding device to create, starting at 0.  The first such file is
 ifcfg-bond0, the second is ifcfg-bond1, and so on.  The sysconfig
 network configuration system will correctly start multiple instances
 of bonding.
 
 The contents of the ifcfg-bondX file is as follows::
 
         BOOTPROTO="static"
         BROADCAST="10.0.2.255"
         IPADDR="10.0.2.10"
         NETMASK="255.255.0.0"
         NETWORK="10.0.2.0"
         REMOTE_IPADDR=""
         STARTMODE="onboot"
         BONDING_MASTER="yes"
         BONDING_MODULE_OPTS="mode=active-backup miimon=100"
         BONDING_SLAVE0="eth0"
         BONDING_SLAVE1="bus-pci-0000:06:08.1"
 
 Replace the sample BROADCAST, IPADDR, NETMASK and NETWORK
 values with the appropriate values for your network.
 
 The STARTMODE specifies when the device is brought online.
 The possible values are:
 
         ======== ======================================================
         onboot   The device is started at boot time.  If you're not
                  sure, this is probably what you want.
 
         manual   The device is started only when ifup is called
                  manually.  Bonding devices may be configured this
                  way if you do not wish them to start automatically
                  at boot for some reason.
 
         hotplug  The device is started by a hotplug event.  This is not
                  a valid choice for a bonding device.
 
         off or   The device configuration is ignored.
         ignore
         ======== ======================================================
 
 The line BONDING_MASTER='yes' indicates that the device is a
 bonding master device.  The only useful value is "yes."
 
 The contents of BONDING_MODULE_OPTS are supplied to the
 instance of the bonding module for this device.  Specify the options
 for the bonding mode, link monitoring, and so on here.  Do not include
 the max_bonds bonding parameter; this will confuse the configuration
 system if you have multiple bonding devices.
 
 Finally, supply one BONDING_SLAVEn="slave device" for each
 slave.  where "n" is an increasing value, one for each slave.  The
 "slave device" is either an interface name, e.g., "eth0", or a device
 specifier for the network device.  The interface name is easier to
 find, but the ethN names are subject to change at boot time if, e.g.,
 a device early in the sequence has failed.  The device specifiers
 (bus-pci-0000:06:08.1 in the example above) specify the physical
 network device, and will not change unless the device's bus location
 changes (for example, it is moved from one PCI slot to another).  The
 example above uses one of each type for demonstration purposes; most
 configurations will choose one or the other for all slave devices.
 
 When all configuration files have been modified or created,
 networking must be restarted for the configuration changes to take
 effect.  This can be accomplished via the following::
 
         # /etc/init.d/network restart
 
 Note that the network control script (/sbin/ifdown) will
 remove the bonding module as part of the network shutdown processing,
 so it is not necessary to remove the module by hand if, e.g., the
 module parameters have changed.
 
 Also, at this writing, YaST/YaST2 will not manage bonding
 devices (they do not show bonding interfaces on its list of network
 devices).  It is necessary to edit the configuration file by hand to
 change the bonding configuration.
 
 Additional general options and details of the ifcfg file
 format can be found in an example ifcfg template file::
 
         /etc/sysconfig/network/ifcfg.template
 
 Note that the template does not document the various ``BONDING_*``
 settings described above, but does describe many of the other options.
 
 3.1.1 Using DHCP with Sysconfig
 -------------------------------
 
 Under sysconfig, configuring a device with BOOTPROTO='dhcp'
 will cause it to query DHCP for its IP address information.  At this
 writing, this does not function for bonding devices; the scripts
 attempt to obtain the device address from DHCP prior to adding any of
 the slave devices.  Without active slaves, the DHCP requests are not
 sent to the network.
 
 3.1.2 Configuring Multiple Bonds with Sysconfig
 -----------------------------------------------
 
 The sysconfig network initialization system is capable of
 handling multiple bonding devices.  All that is necessary is for each
 bonding instance to have an appropriately configured ifcfg-bondX file
 (as described above).  Do not specify the "max_bonds" parameter to any
 instance of bonding, as this will confuse sysconfig.  If you require
 multiple bonding devices with identical parameters, create multiple
 ifcfg-bondX files.
 
 Because the sysconfig scripts supply the bonding module
 options in the ifcfg-bondX file, it is not necessary to add them to
 the system ``/etc/modules.d/*.conf`` configuration files.
 
 3.2 Configuration with Initscripts Support
 ------------------------------------------
 
 This section applies to distros using a recent version of
 initscripts with bonding support, for example, Red Hat Enterprise Linux
 version 3 or later, Fedora, etc.  On these systems, the network
 initialization scripts have knowledge of bonding, and can be configured to
 control bonding devices.  Note that older versions of the initscripts
 package have lower levels of support for bonding; this will be noted where
 applicable.
 
 These distros will not automatically load the network adapter
 driver unless the ethX device is configured with an IP address.
 Because of this constraint, users must manually configure a
 network-script file for all physical adapters that will be members of
 a bondX link.  Network script files are located in the directory:
 
 /etc/sysconfig/network-scripts
 
 The file name must be prefixed with "ifcfg-eth" and suffixed
 with the adapter's physical adapter number.  For example, the script
 for eth0 would be named /etc/sysconfig/network-scripts/ifcfg-eth0.
 Place the following text in the file::
 
         DEVICE=eth0
         USERCTL=no
         ONBOOT=yes
         MASTER=bond0
         SLAVE=yes
         BOOTPROTO=none
 
 The DEVICE= line will be different for every ethX device and
 must correspond with the name of the file, i.e., ifcfg-eth1 must have
 a device line of DEVICE=eth1.  The setting of the MASTER= line will
 also depend on the final bonding interface name chosen for your bond.
 As with other network devices, these typically start at 0, and go up
 one for each device, i.e., the first bonding instance is bond0, the
 second is bond1, and so on.
 
 Next, create a bond network script.  The file name for this
 script will be /etc/sysconfig/network-scripts/ifcfg-bondX where X is
 the number of the bond.  For bond0 the file is named "ifcfg-bond0",
 for bond1 it is named "ifcfg-bond1", and so on.  Within that file,
 place the following text::
 
         DEVICE=bond0
         IPADDR=192.168.1.1
         NETMASK=255.255.255.0
         NETWORK=192.168.1.0
         BROADCAST=192.168.1.255
         ONBOOT=yes
         BOOTPROTO=none
         USERCTL=no
 
 Be sure to change the networking specific lines (IPADDR,
 NETMASK, NETWORK and BROADCAST) to match your network configuration.
 
 For later versions of initscripts, such as that found with Fedora
 7 (or later) and Red Hat Enterprise Linux version 5 (or later), it is possible,
 and, indeed, preferable, to specify the bonding options in the ifcfg-bond0
 file, e.g. a line of the format::
 
   BONDING_OPTS="mode=active-backup arp_interval=60 arp_ip_target=192.168.1.254"
 
 will configure the bond with the specified options.  The options
 specified in BONDING_OPTS are identical to the bonding module parameters
 except for the arp_ip_target field when using versions of initscripts older
 than and 8.57 (Fedora 8) and 8.45.19 (Red Hat Enterprise Linux 5.2).  When
 using older versions each target should be included as a separate option and
 should be preceded by a '+' to indicate it should be added to the list of
 queried targets, e.g.,::
 
     arp_ip_target=+192.168.1.1 arp_ip_target=+192.168.1.2
 
 is the proper syntax to specify multiple targets.  When specifying
 options via BONDING_OPTS, it is not necessary to edit
 ``/etc/modprobe.d/*.conf``.
 
 For even older versions of initscripts that do not support
 BONDING_OPTS, it is necessary to edit /etc/modprobe.d/*.conf, depending upon
 your distro) to load the bonding module with your desired options when the
 bond0 interface is brought up.  The following lines in /etc/modprobe.d/*.conf
 will load the bonding module, and select its options:
 
         alias bond0 bonding
         options bond0 mode=balance-alb miimon=100
 
 Replace the sample parameters with the appropriate set of
 options for your configuration.
 
 Finally run "/etc/rc.d/init.d/network restart" as root.  This
 will restart the networking subsystem and your bond link should be now
 up and running.
 
 3.2.1 Using DHCP with Initscripts
 ---------------------------------
 
 Recent versions of initscripts (the versions supplied with Fedora
 Core 3 and Red Hat Enterprise Linux 4, or later versions, are reported to
 work) have support for assigning IP information to bonding devices via
 DHCP.
 
 To configure bonding for DHCP, configure it as described
 above, except replace the line "BOOTPROTO=none" with "BOOTPROTO=dhcp"
 and add a line consisting of "TYPE=Bonding".  Note that the TYPE value
 is case sensitive.
 
 3.2.2 Configuring Multiple Bonds with Initscripts
 -------------------------------------------------
 
 Initscripts packages that are included with Fedora 7 and Red Hat
 Enterprise Linux 5 support multiple bonding interfaces by simply
 specifying the appropriate BONDING_OPTS= in ifcfg-bondX where X is the
 number of the bond.  This support requires sysfs support in the kernel,
 and a bonding driver of version 3.0.0 or later.  Other configurations may
 not support this method for specifying multiple bonding interfaces; for
 those instances, see the "Configuring Multiple Bonds Manually" section,
 below.
 
 3.3 Configuring Bonding Manually with iproute2
 -----------------------------------------------
 
 This section applies to distros whose network initialization
 scripts (the sysconfig or initscripts package) do not have specific
 knowledge of bonding.  One such distro is SuSE Linux Enterprise Server
 version 8.
 
 The general method for these systems is to place the bonding
 module parameters into a config file in /etc/modprobe.d/ (as
 appropriate for the installed distro), then add modprobe and/or
 `ip link` commands to the system's global init script.  The name of
 the global init script differs; for sysconfig, it is
 /etc/init.d/boot.local and for initscripts it is /etc/rc.d/rc.local.
 
 For example, if you wanted to make a simple bond of two e100
 devices (presumed to be eth0 and eth1), and have it persist across
 reboots, edit the appropriate file (/etc/init.d/boot.local or
 /etc/rc.d/rc.local), and add the following::
 
         modprobe bonding mode=balance-alb miimon=100
         modprobe e100
         ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
         ip link set eth0 master bond0
         ip link set eth1 master bond0
 
 Replace the example bonding module parameters and bond0
 network configuration (IP address, netmask, etc) with the appropriate
 values for your configuration.
 
 Unfortunately, this method will not provide support for the
 ifup and ifdown scripts on the bond devices.  To reload the bonding
 configuration, it is necessary to run the initialization script, e.g.,::
 
         # /etc/init.d/boot.local
 
 or::
 
         # /etc/rc.d/rc.local
 
 It may be desirable in such a case to create a separate script
 which only initializes the bonding configuration, then call that
 separate script from within boot.local.  This allows for bonding to be
 enabled without re-running the entire global init script.
 
 To shut down the bonding devices, it is necessary to first
 mark the bonding device itself as being down, then remove the
 appropriate device driver modules.  For our example above, you can do
 the following::
 
         # ifconfig bond0 down
         # rmmod bonding
         # rmmod e100
 
 Again, for convenience, it may be desirable to create a script
 with these commands.
 
 
 3.3.1 Configuring Multiple Bonds Manually
 -----------------------------------------
 
 This section contains information on configuring multiple
 bonding devices with differing options for those systems whose network
 initialization scripts lack support for configuring multiple bonds.
 
 If you require multiple bonding devices, but all with the same
 options, you may wish to use the "max_bonds" module parameter,
 documented above.
 
 To create multiple bonding devices with differing options, it is
 preferable to use bonding parameters exported by sysfs, documented in the
 section below.
 
 For versions of bonding without sysfs support, the only means to
 provide multiple instances of bonding with differing options is to load
 the bonding driver multiple times.  Note that current versions of the
 sysconfig network initialization scripts handle this automatically; if
 your distro uses these scripts, no special action is needed.  See the
 section Configuring Bonding Devices, above, if you're not sure about your
 network initialization scripts.
 
 To load multiple instances of the module, it is necessary to
 specify a different name for each instance (the module loading system
 requires that every loaded module, even multiple instances of the same
 module, have a unique name).  This is accomplished by supplying multiple
 sets of bonding options in ``/etc/modprobe.d/*.conf``, for example::
 
         alias bond0 bonding
         options bond0 -o bond0 mode=balance-rr miimon=100
 
         alias bond1 bonding
         options bond1 -o bond1 mode=balance-alb miimon=50
 
 will load the bonding module two times.  The first instance is
 named "bond0" and creates the bond0 device in balance-rr mode with an
 miimon of 100.  The second instance is named "bond1" and creates the
 bond1 device in balance-alb mode with an miimon of 50.
 
 In some circumstances (typically with older distributions),
 the above does not work, and the second bonding instance never sees
 its options.  In that case, the second options line can be substituted
 as follows::
 
         install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \
                                      mode=balance-alb miimon=50
 
 This may be repeated any number of times, specifying a new and
 unique name in place of bond1 for each subsequent instance.
 
 It has been observed that some Red Hat supplied kernels are unable
 to rename modules at load time (the "-o bond1" part).  Attempts to pass
 that option to modprobe will produce an "Operation not permitted" error.
 This has been reported on some Fedora Core kernels, and has been seen on
 RHEL 4 as well.  On kernels exhibiting this problem, it will be impossible
 to configure multiple bonds with differing parameters (as they are older
 kernels, and also lack sysfs support).
 
 3.4 Configuring Bonding Manually via Sysfs
 ------------------------------------------
 
 Starting with version 3.0.0, Channel Bonding may be configured
 via the sysfs interface.  This interface allows dynamic configuration
 of all bonds in the system without unloading the module.  It also
 allows for adding and removing bonds at runtime.  Ifenslave is no
 longer required, though it is still supported.
 
 Use of the sysfs interface allows you to use multiple bonds
 with different configurations without having to reload the module.
 It also allows you to use multiple, differently configured bonds when
 bonding is compiled into the kernel.
 
 You must have the sysfs filesystem mounted to configure
 bonding this way.  The examples in this document assume that you
 are using the standard mount point for sysfs, e.g. /sys.  If your
 sysfs filesystem is mounted elsewhere, you will need to adjust the
 example paths accordingly.
 
 Creating and Destroying Bonds
 -----------------------------
 To add a new bond foo::
 
         # echo +foo > /sys/class/net/bonding_masters
 
 To remove an existing bond bar::
 
         # echo -bar > /sys/class/net/bonding_masters
 
 To show all existing bonds::
 
         # cat /sys/class/net/bonding_masters
 
 .. note::
 
    due to 4K size limitation of sysfs files, this list may be
    truncated if you have more than a few hundred bonds.  This is unlikely
    to occur under normal operating conditions.
 
 Adding and Removing Slaves
 --------------------------
 Interfaces may be enslaved to a bond using the file
 /sys/class/net/<bond>/bonding/slaves.  The semantics for this file
 are the same as for the bonding_masters file.
 
 To enslave interface eth0 to bond bond0::
 
         # ifconfig bond0 up
         # echo +eth0 > /sys/class/net/bond0/bonding/slaves
 
 To free slave eth0 from bond bond0::
 
         # echo -eth0 > /sys/class/net/bond0/bonding/slaves
 
 When an interface is enslaved to a bond, symlinks between the
 two are created in the sysfs filesystem.  In this case, you would get
 /sys/class/net/bond0/slave_eth0 pointing to /sys/class/net/eth0, and
 /sys/class/net/eth0/master pointing to /sys/class/net/bond0.
 
 This means that you can tell quickly whether or not an
 interface is enslaved by looking for the master symlink.  Thus:
 # echo -eth0 > /sys/class/net/eth0/master/bonding/slaves
 will free eth0 from whatever bond it is enslaved to, regardless of
 the name of the bond interface.
 
 Changing a Bond's Configuration
 -------------------------------
 Each bond may be configured individually by manipulating the
 files located in /sys/class/net/<bond name>/bonding
 
 The names of these files correspond directly with the command-
 line parameters described elsewhere in this file, and, with the
 exception of arp_ip_target, they accept the same values.  To see the
 current setting, simply cat the appropriate file.
 
 A few examples will be given here; for specific usage
 guidelines for each parameter, see the appropriate section in this
 document.
 
 To configure bond0 for balance-alb mode::
 
         # ifconfig bond0 down
         # echo 6 > /sys/class/net/bond0/bonding/mode
         - or -
         # echo balance-alb > /sys/class/net/bond0/bonding/mode
 
 .. note::
 
    The bond interface must be down before the mode can be changed.
 
 To enable MII monitoring on bond0 with a 1 second interval::
 
         # echo 1000 > /sys/class/net/bond0/bonding/miimon
 
 .. note::
 
    If ARP monitoring is enabled, it will disabled when MII
    monitoring is enabled, and vice-versa.
 
 To add ARP targets::
 
         # echo +192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
         # echo +192.168.0.101 > /sys/class/net/bond0/bonding/arp_ip_target
 
 .. note::
 
    up to 16 target addresses may be specified.
 
 To remove an ARP target::
 
         # echo -192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
 
 To configure the interval between learning packet transmits::
 
         # echo 12 > /sys/class/net/bond0/bonding/lp_interval
 
 .. note::
 
    the lp_interval is the number of seconds between instances where
    the bonding driver sends learning packets to each slaves peer switch.  The
    default interval is 1 second.
 
 Example Configuration
 ---------------------
 We begin with the same example that is shown in section 3.3,
 executed with sysfs, and without using ifenslave.
 
 To make a simple bond of two e100 devices (presumed to be eth0
 and eth1), and have it persist across reboots, edit the appropriate
 file (/etc/init.d/boot.local or /etc/rc.d/rc.local), and add the
 following::
 
         modprobe bonding
         modprobe e100
         echo balance-alb > /sys/class/net/bond0/bonding/mode
         ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
         echo 100 > /sys/class/net/bond0/bonding/miimon
         echo +eth0 > /sys/class/net/bond0/bonding/slaves
         echo +eth1 > /sys/class/net/bond0/bonding/slaves
 
 To add a second bond, with two e1000 interfaces in
 active-backup mode, using ARP monitoring, add the following lines to
 your init script::
 
         modprobe e1000
         echo +bond1 > /sys/class/net/bonding_masters
         echo active-backup > /sys/class/net/bond1/bonding/mode
         ifconfig bond1 192.168.2.1 netmask 255.255.255.0 up
         echo +192.168.2.100 /sys/class/net/bond1/bonding/arp_ip_target
         echo 2000 > /sys/class/net/bond1/bonding/arp_interval
         echo +eth2 > /sys/class/net/bond1/bonding/slaves
         echo +eth3 > /sys/class/net/bond1/bonding/slaves
 
 3.5 Configuration with Interfaces Support
 -----------------------------------------
 
 This section applies to distros which use /etc/network/interfaces file
 to describe network interface configuration, most notably Debian and its
 derivatives.
 
 The ifup and ifdown commands on Debian don't support bonding out of
 the box. The ifenslave-2.6 package should be installed to provide bonding
 support.  Once installed, this package will provide ``bond-*`` options
 to be used into /etc/network/interfaces.
 
 Note that ifenslave-2.6 package will load the bonding module and use
 the ifenslave command when appropriate.
 
 Example Configurations
 ----------------------
 
 In /etc/network/interfaces, the following stanza will configure bond0, in
 active-backup mode, with eth0 and eth1 as slaves::
 
         auto bond0
         iface bond0 inet dhcp
                 bond-slaves eth0 eth1
                 bond-mode active-backup
                 bond-miimon 100
                 bond-primary eth0 eth1
 
 If the above configuration doesn't work, you might have a system using
 upstart for system startup. This is most notably true for recent
 Ubuntu versions. The following stanza in /etc/network/interfaces will
 produce the same result on those systems::
 
         auto bond0
         iface bond0 inet dhcp
                 bond-slaves none
                 bond-mode active-backup
                 bond-miimon 100
 
         auto eth0
         iface eth0 inet manual
                 bond-master bond0
                 bond-primary eth0 eth1
 
         auto eth1
         iface eth1 inet manual
                 bond-master bond0
                 bond-primary eth0 eth1
 
 For a full list of ``bond-*`` supported options in /etc/network/interfaces and
 some more advanced examples tailored to you particular distros, see the files in
 /usr/share/doc/ifenslave-2.6.
 
 3.6 Overriding Configuration for Special Cases
 ----------------------------------------------
 
 When using the bonding driver, the physical port which transmits a frame is
 typically selected by the bonding driver, and is not relevant to the user or
 system administrator.  The output port is simply selected using the policies of
 the selected bonding mode.  On occasion however, it is helpful to direct certain
 classes of traffic to certain physical interfaces on output to implement
 slightly more complex policies.  For example, to reach a web server over a
 bonded interface in which eth0 connects to a private network, while eth1
 connects via a public network, it may be desirous to bias the bond to send said
 traffic over eth0 first, using eth1 only as a fall back, while all other traffic
 can safely be sent over either interface.  Such configurations may be achieved
 using the traffic control utilities inherent in linux.
 
 By default the bonding driver is multiqueue aware and 16 queues are created
 when the driver initializes (see Documentation/networking/multiqueue.rst
 for details).  If more or less queues are desired the module parameter
 tx_queues can be used to change this value.  There is no sysfs parameter
 available as the allocation is done at module init time.
 
 The output of the file /proc/net/bonding/bondX has changed so the output Queue
 ID is now printed for each slave::
 
         Bonding Mode: fault-tolerance (active-backup)
         Primary Slave: None
         Currently Active Slave: eth0
         MII Status: up
         MII Polling Interval (ms): 0
         Up Delay (ms): 0
         Down Delay (ms): 0
 
         Slave Interface: eth0
         MII Status: up
         Link Failure Count: 0
         Permanent HW addr: 00:1a:a0:12:8f:cb
         Slave queue ID: 0
 
         Slave Interface: eth1
         MII Status: up
         Link Failure Count: 0
         Permanent HW addr: 00:1a:a0:12:8f:cc
         Slave queue ID: 2
 
 The queue_id for a slave can be set using the command::
 
         # echo "eth1:2" > /sys/class/net/bond0/bonding/queue_id
 
 Any interface that needs a queue_id set should set it with multiple calls
 like the one above until proper priorities are set for all interfaces.  On
 distributions that allow configuration via initscripts, multiple 'queue_id'
 arguments can be added to BONDING_OPTS to set all needed slave queues.
 
 These queue id's can be used in conjunction with the tc utility to configure
 a multiqueue qdisc and filters to bias certain traffic to transmit on certain
 slave devices.  For instance, say we wanted, in the above configuration to
 force all traffic bound to 192.168.1.100 to use eth1 in the bond as its output
 device. The following commands would accomplish this::
 
         # tc qdisc add dev bond0 handle 1 root multiq
 
         # tc filter add dev bond0 protocol ip parent 1: prio 1 u32 match ip \
                 dst 192.168.1.100 action skbedit queue_mapping 2
 
 These commands tell the kernel to attach a multiqueue queue discipline to the
 bond0 interface and filter traffic enqueued to it, such that packets with a dst
 ip of 192.168.1.100 have their output queue mapping value overwritten to 2.
 This value is then passed into the driver, causing the normal output path
 selection policy to be overridden, selecting instead qid 2, which maps to eth1.
 
 Note that qid values begin at 1.  Qid 0 is reserved to initiate to the driver
 that normal output policy selection should take place.  One benefit to simply
 leaving the qid for a slave to 0 is the multiqueue awareness in the bonding
 driver that is now present.  This awareness allows tc filters to be placed on
 slave devices as well as bond devices and the bonding driver will simply act as
 a pass-through for selecting output queues on the slave device rather than
 output port selection.
 
 This feature first appeared in bonding driver version 3.7.0 and support for
 output slave selection was limited to round-robin and active-backup modes.
 
 3.7 Configuring LACP for 802.3ad mode in a more secure way
 ----------------------------------------------------------
 
 When using 802.3ad bonding mode, the Actor (host) and Partner (switch)
 exchange LACPDUs.  These LACPDUs cannot be sniffed, because they are
 destined to link local mac addresses (which switches/bridges are not
 supposed to forward).  However, most of the values are easily predictable
 or are simply the machine's MAC address (which is trivially known to all
 other hosts in the same L2).  This implies that other machines in the L2
 domain can spoof LACPDU packets from other hosts to the switch and potentially
 cause mayhem by joining (from the point of view of the switch) another
 machine's aggregate, thus receiving a portion of that hosts incoming
 traffic and / or spoofing traffic from that machine themselves (potentially
 even successfully terminating some portion of flows). Though this is not
 a likely scenario, one could avoid this possibility by simply configuring
 few bonding parameters:
 
    (a) ad_actor_system : You can set a random mac-address that can be used for
        these LACPDU exchanges. The value can not be either NULL or Multicast.
        Also it's preferable to set the local-admin bit. Following shell code
        generates a random mac-address as described above::
 
               # sys_mac_addr=$(printf '%02x:%02x:%02x:%02x:%02x:%02x' \
                                        $(( (RANDOM & 0xFE) | 0x02 )) \
                                        $(( RANDOM & 0xFF )) \
                                        $(( RANDOM & 0xFF )) \
                                        $(( RANDOM & 0xFF )) \
                                        $(( RANDOM & 0xFF )) \
                                        $(( RANDOM & 0xFF )))
               # echo $sys_mac_addr > /sys/class/net/bond0/bonding/ad_actor_system
 
    (b) ad_actor_sys_prio : Randomize the system priority. The default value
        is 65535, but system can take the value from 1 - 65535. Following shell
        code generates random priority and sets it::
 
             # sys_prio=$(( 1 + RANDOM + RANDOM ))
             # echo $sys_prio > /sys/class/net/bond0/bonding/ad_actor_sys_prio
 
    (c) ad_user_port_key : Use the user portion of the port-key. The default
        keeps this empty. These are the upper 10 bits of the port-key and value
        ranges from 0 - 1023. Following shell code generates these 10 bits and
        sets it::
 
             # usr_port_key=$(( RANDOM & 0x3FF ))
             # echo $usr_port_key > /sys/class/net/bond0/bonding/ad_user_port_key
 
 
 4 Querying Bonding Configuration
 =================================
 
 4.1 Bonding Configuration
 -------------------------
 
 Each bonding device has a read-only file residing in the
 /proc/net/bonding directory.  The file contents include information
 about the bonding configuration, options and state of each slave.
 
 For example, the contents of /proc/net/bonding/bond0 after the
 driver is loaded with parameters of mode=0 and miimon=1000 is
 generally as follows::
 
         Ethernet Channel Bonding Driver: 2.6.1 (October 29, 2004)
         Bonding Mode: load balancing (round-robin)
         Currently Active Slave: eth0
         MII Status: up
         MII Polling Interval (ms): 1000
         Up Delay (ms): 0
         Down Delay (ms): 0
 
         Slave Interface: eth1
         MII Status: up
         Link Failure Count: 1
 
         Slave Interface: eth0
         MII Status: up
         Link Failure Count: 1
 
 The precise format and contents will change depending upon the
 bonding configuration, state, and version of the bonding driver.
 
 4.2 Network configuration
 -------------------------
 
 The network configuration can be inspected using the ifconfig
 command.  Bonding devices will have the MASTER flag set; Bonding slave
 devices will have the SLAVE flag set.  The ifconfig output does not
 contain information on which slaves are associated with which masters.
 
 In the example below, the bond0 interface is the master
 (MASTER) while eth0 and eth1 are slaves (SLAVE). Notice all slaves of
 bond0 have the same MAC address (HWaddr) as bond0 for all modes except
 TLB and ALB that require a unique MAC address for each slave::
 
   # /sbin/ifconfig
   bond0     Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
             inet addr:XXX.XXX.XXX.YYY  Bcast:XXX.XXX.XXX.255  Mask:255.255.252.0
             UP BROADCAST RUNNING MASTER MULTICAST  MTU:1500  Metric:1
             RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0
             TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0
             collisions:0 txqueuelen:0
 
   eth0      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
             UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
             RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0
             TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0
             collisions:0 txqueuelen:100
             Interrupt:10 Base address:0x1080
 
   eth1      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
             UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
             RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0
             TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0
             collisions:0 txqueuelen:100
             Interrupt:9 Base address:0x1400
 
 5. Switch Configuration
 =======================
 
 For this section, "switch" refers to whatever system the
 bonded devices are directly connected to (i.e., where the other end of
 the cable plugs into).  This may be an actual dedicated switch device,
 or it may be another regular system (e.g., another computer running
 Linux),
 
 The active-backup, balance-tlb and balance-alb modes do not
 require any specific configuration of the switch.
 
 The 802.3ad mode requires that the switch have the appropriate
 ports configured as an 802.3ad aggregation.  The precise method used
 to configure this varies from switch to switch, but, for example, a
 Cisco 3550 series switch requires that the appropriate ports first be
 grouped together in a single etherchannel instance, then that
 etherchannel is set to mode "lacp" to enable 802.3ad (instead of
 standard EtherChannel).
 
 The balance-rr, balance-xor and broadcast modes generally
 require that the switch have the appropriate ports grouped together.
 The nomenclature for such a group differs between switches, it may be
 called an "etherchannel" (as in the Cisco example, above), a "trunk
 group" or some other similar variation.  For these modes, each switch
 will also have its own configuration options for the switch's transmit
 policy to the bond.  Typical choices include XOR of either the MAC or
 IP addresses.  The transmit policy of the two peers does not need to
 match.  For these three modes, the bonding mode really selects a
 transmit policy for an EtherChannel group; all three will interoperate
 with another EtherChannel group.
 
 
 6. 802.1q VLAN Support
 ======================
 
 It is possible to configure VLAN devices over a bond interface
 using the 8021q driver.  However, only packets coming from the 8021q
 driver and passing through bonding will be tagged by default.  Self
 generated packets, for example, bonding's learning packets or ARP
 packets generated by either ALB mode or the ARP monitor mechanism, are
 tagged internally by bonding itself.  As a result, bonding must
 "learn" the VLAN IDs configured above it, and use those IDs to tag
 self generated packets.
 
 For reasons of simplicity, and to support the use of adapters
 that can do VLAN hardware acceleration offloading, the bonding
 interface declares itself as fully hardware offloading capable, it gets
 the add_vid/kill_vid notifications to gather the necessary
 information, and it propagates those actions to the slaves.  In case
 of mixed adapter types, hardware accelerated tagged packets that
 should go through an adapter that is not offloading capable are
 "un-accelerated" by the bonding driver so the VLAN tag sits in the
 regular location.
 
 VLAN interfaces *must* be added on top of a bonding interface
 only after enslaving at least one slave.  The bonding interface has a
 hardware address of 00:00:00:00:00:00 until the first slave is added.
 If the VLAN interface is created prior to the first enslavement, it
 would pick up the all-zeroes hardware address.  Once the first slave
 is attached to the bond, the bond device itself will pick up the
 slave's hardware address, which is then available for the VLAN device.
 
 Also, be aware that a similar problem can occur if all slaves
 are released from a bond that still has one or more VLAN interfaces on
 top of it.  When a new slave is added, the bonding interface will
 obtain its hardware address from the first slave, which might not
 match the hardware address of the VLAN interfaces (which was
 ultimately copied from an earlier slave).
 
 There are two methods to insure that the VLAN device operates
 with the correct hardware address if all slaves are removed from a
 bond interface:
 
 1. Remove all VLAN interfaces then recreate them
 
 2. Set the bonding interface's hardware address so that it
 matches the hardware address of the VLAN interfaces.
 
 Note that changing a VLAN interface's HW address would set the
 underlying device -- i.e. the bonding interface -- to promiscuous
 mode, which might not be what you want.
 
 
 7. Link Monitoring
 ==================
 
 The bonding driver at present supports two schemes for
 monitoring a slave device's link state: the ARP monitor and the MII
 monitor.
 
 At the present time, due to implementation restrictions in the
 bonding driver itself, it is not possible to enable both ARP and MII
 monitoring simultaneously.
 
 7.1 ARP Monitor Operation
 -------------------------
 
 The ARP monitor operates as its name suggests: it sends ARP
 queries to one or more designated peer systems on the network, and
 uses the response as an indication that the link is operating.  This
 gives some assurance that traffic is actually flowing to and from one
 or more peers on the local network.
 
 7.2 Configuring Multiple ARP Targets
 ------------------------------------
 
 While ARP monitoring can be done with just one target, it can
 be useful in a High Availability setup to have several targets to
 monitor.  In the case of just one target, the target itself may go
 down or have a problem making it unresponsive to ARP requests.  Having
 an additional target (or several) increases the reliability of the ARP
 monitoring.
 
 Multiple ARP targets must be separated by commas as follows::
 
  # example options for ARP monitoring with three targets
  alias bond0 bonding
  options bond0 arp_interval=60 arp_ip_target=192.168.0.1,192.168.0.3,192.168.0.9
 
 For just a single target the options would resemble::
 
     # example options for ARP monitoring with one target
     alias bond0 bonding
     options bond0 arp_interval=60 arp_ip_target=192.168.0.100
 
 
 7.3 MII Monitor Operation
 -------------------------
 
 The MII monitor monitors only the carrier state of the local
 network interface.  It accomplishes this in one of three ways: by
 depending upon the device driver to maintain its carrier state, by
 querying the device's MII registers, or by making an ethtool query to
 the device.
 
 If the use_carrier module parameter is 1 (the default value),
 then the MII monitor will rely on the driver for carrier state
 information (via the netif_carrier subsystem).  As explained in the
 use_carrier parameter information, above, if the MII monitor fails to
 detect carrier loss on the device (e.g., when the cable is physically
 disconnected), it may be that the driver does not support
 netif_carrier.
 
 If use_carrier is 0, then the MII monitor will first query the
 device's (via ioctl) MII registers and check the link state.  If that
 request fails (not just that it returns carrier down), then the MII
 monitor will make an ethtool ETHTOOL_GLINK request to attempt to obtain
 the same information.  If both methods fail (i.e., the driver either
 does not support or had some error in processing both the MII register
 and ethtool requests), then the MII monitor will assume the link is
 up.
 
 8. Potential Sources of Trouble
 ===============================
 
 8.1 Adventures in Routing
 -------------------------
 
 When bonding is configured, it is important that the slave
 devices not have routes that supersede routes of the master (or,
 generally, not have routes at all).  For example, suppose the bonding
 device bond0 has two slaves, eth0 and eth1, and the routing table is
 as follows::
 
   Kernel IP routing table
   Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
   10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth0
   10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth1
   10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 bond0
   127.0.0.0       0.0.0.0         255.0.0.0       U        40 0          0 lo
 
 This routing configuration will likely still update the
 receive/transmit times in the driver (needed by the ARP monitor), but
 may bypass the bonding driver (because outgoing traffic to, in this
 case, another host on network 10 would use eth0 or eth1 before bond0).
 
 The ARP monitor (and ARP itself) may become confused by this
 configuration, because ARP requests (generated by the ARP monitor)
 will be sent on one interface (bond0), but the corresponding reply
 will arrive on a different interface (eth0).  This reply looks to ARP
 as an unsolicited ARP reply (because ARP matches replies on an
 interface basis), and is discarded.  The MII monitor is not affected
 by the state of the routing table.
 
 The solution here is simply to insure that slaves do not have
 routes of their own, and if for some reason they must, those routes do
 not supersede routes of their master.  This should generally be the
 case, but unusual configurations or errant manual or automatic static
 route additions may cause trouble.
 
 8.2 Ethernet Device Renaming
 ----------------------------
 
 On systems with network configuration scripts that do not
 associate physical devices directly with network interface names (so
 that the same physical device always has the same "ethX" name), it may
 be necessary to add some special logic to config files in
 /etc/modprobe.d/.
 
 For example, given a modules.conf containing the following::
 
         alias bond0 bonding
         options bond0 mode=some-mode miimon=50
         alias eth0 tg3
         alias eth1 tg3
         alias eth2 e1000
         alias eth3 e1000
 
 If neither eth0 and eth1 are slaves to bond0, then when the
 bond0 interface comes up, the devices may end up reordered.  This
 happens because bonding is loaded first, then its slave device's
 drivers are loaded next.  Since no other drivers have been loaded,
 when the e1000 driver loads, it will receive eth0 and eth1 for its
 devices, but the bonding configuration tries to enslave eth2 and eth3
 (which may later be assigned to the tg3 devices).
 
 Adding the following::
 
         add above bonding e1000 tg3
 
 causes modprobe to load e1000 then tg3, in that order, when
 bonding is loaded.  This command is fully documented in the
 modules.conf manual page.
 
 On systems utilizing modprobe an equivalent problem can occur.
 In this case, the following can be added to config files in
 /etc/modprobe.d/ as::
 
         softdep bonding pre: tg3 e1000
 
 This will load tg3 and e1000 modules before loading the bonding one.
 Full documentation on this can be found in the modprobe.d and modprobe
 manual pages.
 
 8.3. Painfully Slow Or No Failed Link Detection By Miimon
 ---------------------------------------------------------
 
 By default, bonding enables the use_carrier option, which
 instructs bonding to trust the driver to maintain carrier state.
 
 As discussed in the options section, above, some drivers do
 not support the netif_carrier_on/_off link state tracking system.
 With use_carrier enabled, bonding will always see these links as up,
 regardless of their actual state.
 
 Additionally, other drivers do support netif_carrier, but do
 not maintain it in real time, e.g., only polling the link state at
 some fixed interval.  In this case, miimon will detect failures, but
 only after some long period of time has expired.  If it appears that
 miimon is very slow in detecting link failures, try specifying
 use_carrier=0 to see if that improves the failure detection time.  If
 it does, then it may be that the driver checks the carrier state at a
 fixed interval, but does not cache the MII register values (so the
 use_carrier=0 method of querying the registers directly works).  If
 use_carrier=0 does not improve the failover, then the driver may cache
 the registers, or the problem may be elsewhere.
 
 Also, remember that miimon only checks for the device's
 carrier state.  It has no way to determine the state of devices on or
 beyond other ports of a switch, or if a switch is refusing to pass
 traffic while still maintaining carrier on.
 
 9. SNMP agents
 ===============
 
 If running SNMP agents, the bonding driver should be loaded
 before any network drivers participating in a bond.  This requirement
 is due to the interface index (ipAdEntIfIndex) being associated to
 the first interface found with a given IP address.  That is, there is
 only one ipAdEntIfIndex for each IP address.  For example, if eth0 and
 eth1 are slaves of bond0 and the driver for eth0 is loaded before the
 bonding driver, the interface for the IP address will be associated
 with the eth0 interface.  This configuration is shown below, the IP
 address 192.168.1.1 has an interface index of 2 which indexes to eth0
 in the ifDescr table (ifDescr.2).
 
 ::
 
      interfaces.ifTable.ifEntry.ifDescr.1 = lo
      interfaces.ifTable.ifEntry.ifDescr.2 = eth0
      interfaces.ifTable.ifEntry.ifDescr.3 = eth1
      interfaces.ifTable.ifEntry.ifDescr.4 = eth2
      interfaces.ifTable.ifEntry.ifDescr.5 = eth3
      interfaces.ifTable.ifEntry.ifDescr.6 = bond0
      ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 5
      ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
      ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 4
      ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
 
 This problem is avoided by loading the bonding driver before
 any network drivers participating in a bond.  Below is an example of
 loading the bonding driver first, the IP address 192.168.1.1 is
 correctly associated with ifDescr.2.
 
      interfaces.ifTable.ifEntry.ifDescr.1 = lo
      interfaces.ifTable.ifEntry.ifDescr.2 = bond0
      interfaces.ifTable.ifEntry.ifDescr.3 = eth0
      interfaces.ifTable.ifEntry.ifDescr.4 = eth1
      interfaces.ifTable.ifEntry.ifDescr.5 = eth2
      interfaces.ifTable.ifEntry.ifDescr.6 = eth3
      ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 6
      ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
      ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 5
      ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
 
 While some distributions may not report the interface name in
 ifDescr, the association between the IP address and IfIndex remains
 and SNMP functions such as Interface_Scan_Next will report that
 association.
 
 10. Promiscuous mode
 ====================
 
 When running network monitoring tools, e.g., tcpdump, it is
 common to enable promiscuous mode on the device, so that all traffic
 is seen (instead of seeing only traffic destined for the local host).
 The bonding driver handles promiscuous mode changes to the bonding
 master device (e.g., bond0), and propagates the setting to the slave
 devices.
 
 For the balance-rr, balance-xor, broadcast, and 802.3ad modes,
 the promiscuous mode setting is propagated to all slaves.
 
 For the active-backup, balance-tlb and balance-alb modes, the
 promiscuous mode setting is propagated only to the active slave.
 
 For balance-tlb mode, the active slave is the slave currently
 receiving inbound traffic.
 
 For balance-alb mode, the active slave is the slave used as a
 "primary."  This slave is used for mode-specific control traffic, for
 sending to peers that are unassigned or if the load is unbalanced.
 
 For the active-backup, balance-tlb and balance-alb modes, when
 the active slave changes (e.g., due to a link failure), the
 promiscuous setting will be propagated to the new active slave.
 
 11. Configuring Bonding for High Availability
 =============================================
 
 High Availability refers to configurations that provide
 maximum network availability by having redundant or backup devices,
 links or switches between the host and the rest of the world.  The
 goal is to provide the maximum availability of network connectivity
 (i.e., the network always works), even though other configurations
 could provide higher throughput.
 
 11.1 High Availability in a Single Switch Topology
 --------------------------------------------------
 
 If two hosts (or a host and a single switch) are directly
 connected via multiple physical links, then there is no availability
 penalty to optimizing for maximum bandwidth.  In this case, there is
 only one switch (or peer), so if it fails, there is no alternative
 access to fail over to.  Additionally, the bonding load balance modes
 support link monitoring of their members, so if individual links fail,
 the load will be rebalanced across the remaining devices.
 
 See Section 12, "Configuring Bonding for Maximum Throughput"
 for information on configuring bonding with one peer device.
 
 11.2 High Availability in a Multiple Switch Topology
 ----------------------------------------------------
 
 With multiple switches, the configuration of bonding and the
 network changes dramatically.  In multiple switch topologies, there is
 a trade off between network availability and usable bandwidth.
 
 Below is a sample network, configured to maximize the
 availability of the network::
 
                 |                                     |
                 |port3                           port3|
           +-----+----+                          +-----+----+
           |          |port2       ISL      port2|          |
           | switch A +--------------------------+ switch B |
           |          |                          |          |
           +-----+----+                          +-----++---+
                 |port1                           port1|
                 |             +-------+               |
                 +-------------+ host1 +---------------+
                          eth0 +-------+ eth1
 
 In this configuration, there is a link between the two
 switches (ISL, or inter switch link), and multiple ports connecting to
 the outside world ("port3" on each switch).  There is no technical
 reason that this could not be extended to a third switch.
 
 11.2.1 HA Bonding Mode Selection for Multiple Switch Topology
 -------------------------------------------------------------
 
 In a topology such as the example above, the active-backup and
 broadcast modes are the only useful bonding modes when optimizing for
 availability; the other modes require all links to terminate on the
 same peer for them to behave rationally.
 
 active-backup:
         This is generally the preferred mode, particularly if
         the switches have an ISL and play together well.  If the
         network configuration is such that one switch is specifically
         a backup switch (e.g., has lower capacity, higher cost, etc),
         then the primary option can be used to insure that the
         preferred link is always used when it is available.
 
 broadcast:
         This mode is really a special purpose mode, and is suitable
         only for very specific needs.  For example, if the two
         switches are not connected (no ISL), and the networks beyond
         them are totally independent.  In this case, if it is
         necessary for some specific one-way traffic to reach both
         independent networks, then the broadcast mode may be suitable.
 
 11.2.2 HA Link Monitoring Selection for Multiple Switch Topology
 ----------------------------------------------------------------
 
 The choice of link monitoring ultimately depends upon your
 switch.  If the switch can reliably fail ports in response to other
 failures, then either the MII or ARP monitors should work.  For
 example, in the above example, if the "port3" link fails at the remote
 end, the MII monitor has no direct means to detect this.  The ARP
 monitor could be configured with a target at the remote end of port3,
 thus detecting that failure without switch support.
 
 In general, however, in a multiple switch topology, the ARP
 monitor can provide a higher level of reliability in detecting end to
 end connectivity failures (which may be caused by the failure of any
 individual component to pass traffic for any reason).  Additionally,
 the ARP monitor should be configured with multiple targets (at least
 one for each switch in the network).  This will insure that,
 regardless of which switch is active, the ARP monitor has a suitable
 target to query.
 
 Note, also, that of late many switches now support a functionality
 generally referred to as "trunk failover."  This is a feature of the
 switch that causes the link state of a particular switch port to be set
 down (or up) when the state of another switch port goes down (or up).
 Its purpose is to propagate link failures from logically "exterior" ports
 to the logically "interior" ports that bonding is able to monitor via
 miimon.  Availability and configuration for trunk failover varies by
 switch, but this can be a viable alternative to the ARP monitor when using
 suitable switches.
 
 12. Configuring Bonding for Maximum Throughput
 ==============================================
 
 12.1 Maximizing Throughput in a Single Switch Topology
 ------------------------------------------------------
 
 In a single switch configuration, the best method to maximize
 throughput depends upon the application and network environment.  The
 various load balancing modes each have strengths and weaknesses in
 different environments, as detailed below.
 
 For this discussion, we will break down the topologies into
 two categories.  Depending upon the destination of most traffic, we
 categorize them into either "gatewayed" or "local" configurations.
 
 In a gatewayed configuration, the "switch" is acting primarily
 as a router, and the majority of traffic passes through this router to
 other networks.  An example would be the following::
 
 
      +----------+                     +----------+
      |          |eth0            port1|          | to other networks
      | Host A   +---------------------+ router   +------------------->
      |          +---------------------+          | Hosts B and C are out
      |          |eth1            port2|          | here somewhere
      +----------+                     +----------+
 
 The router may be a dedicated router device, or another host
 acting as a gateway.  For our discussion, the important point is that
 the majority of traffic from Host A will pass through the router to
 some other network before reaching its final destination.
 
 In a gatewayed network configuration, although Host A may
 communicate with many other systems, all of its traffic will be sent
 and received via one other peer on the local network, the router.
 
 Note that the case of two systems connected directly via
 multiple physical links is, for purposes of configuring bonding, the
 same as a gatewayed configuration.  In that case, it happens that all
 traffic is destined for the "gateway" itself, not some other network
 beyond the gateway.
 
 In a local configuration, the "switch" is acting primarily as
 a switch, and the majority of traffic passes through this switch to
 reach other stations on the same network.  An example would be the
 following::
 
     +----------+            +----------+       +--------+
     |          |eth0   port1|          +-------+ Host B |
     |  Host A  +------------+  switch  |port3  +--------+
     |          +------------+          |                  +--------+
     |          |eth1   port2|          +------------------+ Host C |
     +----------+            +----------+port4             +--------+
 
 
 Again, the switch may be a dedicated switch device, or another
 host acting as a gateway.  For our discussion, the important point is
 that the majority of traffic from Host A is destined for other hosts
 on the same local network (Hosts B and C in the above example).
 
 In summary, in a gatewayed configuration, traffic to and from
 the bonded device will be to the same MAC level peer on the network
 (the gateway itself, i.e., the router), regardless of its final
 destination.  In a local configuration, traffic flows directly to and
 from the final destinations, thus, each destination (Host B, Host C)
 will be addressed directly by their individual MAC addresses.
 
 This distinction between a gatewayed and a local network
 configuration is important because many of the load balancing modes
 available use the MAC addresses of the local network source and
 destination to make load balancing decisions.  The behavior of each
 mode is described below.
 
 
 12.1.1 MT Bonding Mode Selection for Single Switch Topology
 -----------------------------------------------------------
 
 This configuration is the easiest to set up and to understand,
 although you will have to decide which bonding mode best suits your
 needs.  The trade offs for each mode are detailed below:
 
 balance-rr:
         This mode is the only mode that will permit a single
         TCP/IP connection to stripe traffic across multiple
         interfaces. It is therefore the only mode that will allow a
         single TCP/IP stream to utilize more than one interface's
         worth of throughput.  This comes at a cost, however: the
         striping generally results in peer systems receiving packets out
         of order, causing TCP/IP's congestion control system to kick
         in, often by retransmitting segments.
 
         It is possible to adjust TCP/IP's congestion limits by
         altering the net.ipv4.tcp_reordering sysctl parameter.  The
         usual default value is 3. But keep in mind TCP stack is able
         to automatically increase this when it detects reorders.
 
         Note that the fraction of packets that will be delivered out of
         order is highly variable, and is unlikely to be zero.  The level
         of reordering depends upon a variety of factors, including the
         networking interfaces, the switch, and the topology of the
         configuration.  Speaking in general terms, higher speed network
         cards produce more reordering (due to factors such as packet
         coalescing), and a "many to many" topology will reorder at a
         higher rate than a "many slow to one fast" configuration.
 
         Many switches do not support any modes that stripe traffic
         (instead choosing a port based upon IP or MAC level addresses);
         for those devices, traffic for a particular connection flowing
         through the switch to a balance-rr bond will not utilize greater
         than one interface's worth of bandwidth.
 
         If you are utilizing protocols other than TCP/IP, UDP for
         example, and your application can tolerate out of order
         delivery, then this mode can allow for single stream datagram
         performance that scales near linearly as interfaces are added
         to the bond.
 
         This mode requires the switch to have the appropriate ports
         configured for "etherchannel" or "trunking."
 
 active-backup:
         There is not much advantage in this network topology to
         the active-backup mode, as the inactive backup devices are all
         connected to the same peer as the primary.  In this case, a
         load balancing mode (with link monitoring) will provide the
         same level of network availability, but with increased
         available bandwidth.  On the plus side, active-backup mode
         does not require any configuration of the switch, so it may
         have value if the hardware available does not support any of
         the load balance modes.
 
 balance-xor:
         This mode will limit traffic such that packets destined
         for specific peers will always be sent over the same
         interface.  Since the destination is determined by the MAC
         addresses involved, this mode works best in a "local" network
         configuration (as described above), with destinations all on
         the same local network.  This mode is likely to be suboptimal
         if all your traffic is passed through a single router (i.e., a
         "gatewayed" network configuration, as described above).
 
         As with balance-rr, the switch ports need to be configured for
         "etherchannel" or "trunking."
 
 broadcast:
         Like active-backup, there is not much advantage to this
         mode in this type of network topology.
 
 802.3ad:
         This mode can be a good choice for this type of network
         topology.  The 802.3ad mode is an IEEE standard, so all peers
         that implement 802.3ad should interoperate well.  The 802.3ad
         protocol includes automatic configuration of the aggregates,
         so minimal manual configuration of the switch is needed
         (typically only to designate that some set of devices is
         available for 802.3ad).  The 802.3ad standard also mandates
         that frames be delivered in order (within certain limits), so
         in general single connections will not see misordering of
         packets.  The 802.3ad mode does have some drawbacks: the
         standard mandates that all devices in the aggregate operate at
         the same speed and duplex.  Also, as with all bonding load
         balance modes other than balance-rr, no single connection will
         be able to utilize more than a single interface's worth of
         bandwidth.
 
         Additionally, the linux bonding 802.3ad implementation
         distributes traffic by peer (using an XOR of MAC addresses
         and packet type ID), so in a "gatewayed" configuration, all
         outgoing traffic will generally use the same device.  Incoming
         traffic may also end up on a single device, but that is
         dependent upon the balancing policy of the peer's 802.3ad
         implementation.  In a "local" configuration, traffic will be
         distributed across the devices in the bond.
 
         Finally, the 802.3ad mode mandates the use of the MII monitor,
         therefore, the ARP monitor is not available in this mode.
 
 balance-tlb:
         The balance-tlb mode balances outgoing traffic by peer.
         Since the balancing is done according to MAC address, in a
         "gatewayed" configuration (as described above), this mode will
         send all traffic across a single device.  However, in a
         "local" network configuration, this mode balances multiple
         local network peers across devices in a vaguely intelligent
         manner (not a simple XOR as in balance-xor or 802.3ad mode),
         so that mathematically unlucky MAC addresses (i.e., ones that
         XOR to the same value) will not all "bunch up" on a single
         interface.
 
         Unlike 802.3ad, interfaces may be of differing speeds, and no
         special switch configuration is required.  On the down side,
         in this mode all incoming traffic arrives over a single
         interface, this mode requires certain ethtool support in the
         network device driver of the slave interfaces, and the ARP
         monitor is not available.
 
 balance-alb:
         This mode is everything that balance-tlb is, and more.
         It has all of the features (and restrictions) of balance-tlb,
         and will also balance incoming traffic from local network
         peers (as described in the Bonding Module Options section,
         above).
 
         The only additional down side to this mode is that the network
         device driver must support changing the hardware address while
         the device is open.
 
 12.1.2 MT Link Monitoring for Single Switch Topology
 ----------------------------------------------------
 
 The choice of link monitoring may largely depend upon which
 mode you choose to use.  The more advanced load balancing modes do not
 support the use of the ARP monitor, and are thus restricted to using
 the MII monitor (which does not provide as high a level of end to end
 assurance as the ARP monitor).
 
 12.2 Maximum Throughput in a Multiple Switch Topology
 -----------------------------------------------------
 
 Multiple switches may be utilized to optimize for throughput
 when they are configured in parallel as part of an isolated network
 between two or more systems, for example::
 
                        +-----------+
                        |  Host A   |
                        +-+---+---+-+
                          |   |   |
                 +--------+   |   +---------+
                 |            |             |
          +------+---+  +-----+----+  +-----+----+
          | Switch A |  | Switch B |  | Switch C |
          +------+---+  +-----+----+  +-----+----+
                 |            |             |
                 +--------+   |   +---------+
                          |   |   |
                        +-+---+---+-+
                        |  Host B   |
                        +-----------+
 
 In this configuration, the switches are isolated from one
 another.  One reason to employ a topology such as this is for an
 isolated network with many hosts (a cluster configured for high
 performance, for example), using multiple smaller switches can be more
 cost effective than a single larger switch, e.g., on a network with 24
 hosts, three 24 port switches can be significantly less expensive than
 a single 72 port switch.
 
 If access beyond the network is required, an individual host
 can be equipped with an additional network device connected to an
 external network; this host then additionally acts as a gateway.
 
 12.2.1 MT Bonding Mode Selection for Multiple Switch Topology
 -------------------------------------------------------------
 
 In actual practice, the bonding mode typically employed in
 configurations of this type is balance-rr.  Historically, in this
 network configuration, the usual caveats about out of order packet
 delivery are mitigated by the use of network adapters that do not do
 any kind of packet coalescing (via the use of NAPI, or because the
 device itself does not generate interrupts until some number of
 packets has arrived).  When employed in this fashion, the balance-rr
 mode allows individual connections between two hosts to effectively
 utilize greater than one interface's bandwidth.
 
 12.2.2 MT Link Monitoring for Multiple Switch Topology
 ------------------------------------------------------
 
 Again, in actual practice, the MII monitor is most often used
 in this configuration, as performance is given preference over
 availability.  The ARP monitor will function in this topology, but its
 advantages over the MII monitor are mitigated by the volume of probes
 needed as the number of systems involved grows (remember that each
 host in the network is configured with bonding).
 
 13. Switch Behavior Issues
 ==========================
 
 13.1 Link Establishment and Failover Delays
 -------------------------------------------
 
 Some switches exhibit undesirable behavior with regard to the
 timing of link up and down reporting by the switch.
 
 First, when a link comes up, some switches may indicate that
 the link is up (carrier available), but not pass traffic over the
 interface for some period of time.  This delay is typically due to
 some type of autonegotiation or routing protocol, but may also occur
 during switch initialization (e.g., during recovery after a switch
 failure).  If you find this to be a problem, specify an appropriate
 value to the updelay bonding module option to delay the use of the
 relevant interface(s).
 
 Second, some switches may "bounce" the link state one or more
 times while a link is changing state.  This occurs most commonly while
 the switch is initializing.  Again, an appropriate updelay value may
 help.
 
 Note that when a bonding interface has no active links, the
 driver will immediately reuse the first link that goes up, even if the
 updelay parameter has been specified (the updelay is ignored in this
 case).  If there are slave interfaces waiting for the updelay timeout
 to expire, the interface that first went into that state will be
 immediately reused.  This reduces down time of the network if the
 value of updelay has been overestimated, and since this occurs only in
 cases with no connectivity, there is no additional penalty for
 ignoring the updelay.
 
 In addition to the concerns about switch timings, if your
 switches take a long time to go into backup mode, it may be desirable
 to not activate a backup interface immediately after a link goes down.
 Failover may be delayed via the downdelay bonding module option.
 
 13.2 Duplicated Incoming Packets
 --------------------------------
 
 NOTE: Starting with version 3.0.2, the bonding driver has logic to
 suppress duplicate packets, which should largely eliminate this problem.
 The following description is kept for reference.
 
 It is not uncommon to observe a short burst of duplicated
 traffic when the bonding device is first used, or after it has been
 idle for some period of time.  This is most easily observed by issuing
 a "ping" to some other host on the network, and noticing that the
 output from ping flags duplicates (typically one per slave).
 
 For example, on a bond in active-backup mode with five slaves
 all connected to one switch, the output may appear as follows::
 
         # ping -n 10.0.4.2
         PING 10.0.4.2 (10.0.4.2) from 10.0.3.10 : 56(84) bytes of data.
         64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.7 ms
         64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
         64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
         64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
         64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
         64 bytes from 10.0.4.2: icmp_seq=2 ttl=64 time=0.216 ms
         64 bytes from 10.0.4.2: icmp_seq=3 ttl=64 time=0.267 ms
         64 bytes from 10.0.4.2: icmp_seq=4 ttl=64 time=0.222 ms
 
 This is not due to an error in the bonding driver, rather, it
 is a side effect of how many switches update their MAC forwarding
 tables.  Initially, the switch does not associate the MAC address in
 the packet with a particular switch port, and so it may send the
 traffic to all ports until its MAC forwarding table is updated.  Since
 the interfaces attached to the bond may occupy multiple ports on a
 single switch, when the switch (temporarily) floods the traffic to all
 ports, the bond device receives multiple copies of the same packet
 (one per slave device).
 
 The duplicated packet behavior is switch dependent, some
 switches exhibit this, and some do not.  On switches that display this
 behavior, it can be induced by clearing the MAC forwarding table (on
 most Cisco switches, the privileged command "clear mac address-table
 dynamic" will accomplish this).
 
 14. Hardware Specific Considerations
 ====================================
 
 This section contains additional information for configuring
 bonding on specific hardware platforms, or for interfacing bonding
 with particular switches or other devices.
 
 14.1 IBM BladeCenter
 --------------------
 
 This applies to the JS20 and similar systems.
 
 On the JS20 blades, the bonding driver supports only
 balance-rr, active-backup, balance-tlb and balance-alb modes.  This is
 largely due to the network topology inside the BladeCenter, detailed
 below.
 
 JS20 network adapter information
 --------------------------------
 
 All JS20s come with two Broadcom Gigabit Ethernet ports
 integrated on the planar (that's "motherboard" in IBM-speak).  In the
 BladeCenter chassis, the eth0 port of all JS20 blades is hard wired to
 I/O Module #1; similarly, all eth1 ports are wired to I/O Module #2.
 An add-on Broadcom daughter card can be installed on a JS20 to provide
 two more Gigabit Ethernet ports.  These ports, eth2 and eth3, are
 wired to I/O Modules 3 and 4, respectively.
 
 Each I/O Module may contain either a switch or a passthrough
 module (which allows ports to be directly connected to an external
 switch).  Some bonding modes require a specific BladeCenter internal
 network topology in order to function; these are detailed below.
 
 Additional BladeCenter-specific networking information can be
 found in two IBM Redbooks (www.ibm.com/redbooks):
 
 - "IBM eServer BladeCenter Networking Options"
 - "IBM eServer BladeCenter Layer 2-7 Network Switching"
 
 BladeCenter networking configuration
 ------------------------------------
 
 Because a BladeCenter can be configured in a very large number
 of ways, this discussion will be confined to describing basic
 configurations.
 
 Normally, Ethernet Switch Modules (ESMs) are used in I/O
 modules 1 and 2.  In this configuration, the eth0 and eth1 ports of a
 JS20 will be connected to different internal switches (in the
 respective I/O modules).
 
 A passthrough module (OPM or CPM, optical or copper,
 passthrough module) connects the I/O module directly to an external
 switch.  By using PMs in I/O module #1 and #2, the eth0 and eth1
 interfaces of a JS20 can be redirected to the outside world and
 connected to a common external switch.
 
 Depending upon the mix of ESMs and PMs, the network will
 appear to bonding as either a single switch topology (all PMs) or as a
 multiple switch topology (one or more ESMs, zero or more PMs).  It is
 also possible to connect ESMs together, resulting in a configuration
 much like the example in "High Availability in a Multiple Switch
 Topology," above.
 
 Requirements for specific modes
 -------------------------------
 
 The balance-rr mode requires the use of passthrough modules
 for devices in the bond, all connected to an common external switch.
 That switch must be configured for "etherchannel" or "trunking" on the
 appropriate ports, as is usual for balance-rr.
 
 The balance-alb and balance-tlb modes will function with
 either switch modules or passthrough modules (or a mix).  The only
 specific requirement for these modes is that all network interfaces
 must be able to reach all destinations for traffic sent over the
 bonding device (i.e., the network must converge at some point outside
 the BladeCenter).
 
 The active-backup mode has no additional requirements.
 
 Link monitoring issues
 ----------------------
 
 When an Ethernet Switch Module is in place, only the ARP
 monitor will reliably detect link loss to an external switch.  This is
 nothing unusual, but examination of the BladeCenter cabinet would
 suggest that the "external" network ports are the ethernet ports for
 the system, when it fact there is a switch between these "external"
 ports and the devices on the JS20 system itself.  The MII monitor is
 only able to detect link failures between the ESM and the JS20 system.
 
 When a passthrough module is in place, the MII monitor does
 detect failures to the "external" port, which is then directly
 connected to the JS20 system.
 
 Other concerns
 --------------
 
 The Serial Over LAN (SoL) link is established over the primary
 ethernet (eth0) only, therefore, any loss of link to eth0 will result
 in losing your SoL connection.  It will not fail over with other
 network traffic, as the SoL system is beyond the control of the
 bonding driver.
 
 It may be desirable to disable spanning tree on the switch
 (either the internal Ethernet Switch Module, or an external switch) to
 avoid fail-over delay issues when using bonding.
 
 
 15. Frequently Asked Questions
 ==============================
 
 1.  Is it SMP safe?
 -------------------
 
 Yes. The old 2.0.xx channel bonding patch was not SMP safe.
 The new driver was designed to be SMP safe from the start.
 
 2.  What type of cards will work with it?
 -----------------------------------------
 
 Any Ethernet type cards (you can even mix cards - a Intel
 EtherExpress PRO/100 and a 3com 3c905b, for example).  For most modes,
 devices need not be of the same speed.
 
 Starting with version 3.2.1, bonding also supports Infiniband
 slaves in active-backup mode.
 
 3.  How many bonding devices can I have?
 ----------------------------------------
 
 There is no limit.
 
 4.  How many slaves can a bonding device have?
 ----------------------------------------------
 
 This is limited only by the number of network interfaces Linux
 supports and/or the number of network cards you can place in your
 system.
 
 5.  What happens when a slave link dies?
 ----------------------------------------
 
 If link monitoring is enabled, then the failing device will be
 disabled.  The active-backup mode will fail over to a backup link, and
 other modes will ignore the failed link.  The link will continue to be
 monitored, and should it recover, it will rejoin the bond (in whatever
 manner is appropriate for the mode). See the sections on High
 Availability and the documentation for each mode for additional
 information.
 
 Link monitoring can be enabled via either the miimon or
 arp_interval parameters (described in the module parameters section,
 above).  In general, miimon monitors the carrier state as sensed by
 the underlying network device, and the arp monitor (arp_interval)
 monitors connectivity to another host on the local network.
 
 If no link monitoring is configured, the bonding driver will
 be unable to detect link failures, and will assume that all links are
 always available.  This will likely result in lost packets, and a
 resulting degradation of performance.  The precise performance loss
 depends upon the bonding mode and network configuration.
 
 6.  Can bonding be used for High Availability?
 ----------------------------------------------
 
 Yes.  See the section on High Availability for details.
 
 7.  Which switches/systems does it work with?
 ---------------------------------------------
 
 The full answer to this depends upon the desired mode.
 
 In the basic balance modes (balance-rr and balance-xor), it
 works with any system that supports etherchannel (also called
 trunking).  Most managed switches currently available have such
 support, and many unmanaged switches as well.
 
 The advanced balance modes (balance-tlb and balance-alb) do
 not have special switch requirements, but do need device drivers that
 support specific features (described in the appropriate section under
 module parameters, above).
 
 In 802.3ad mode, it works with systems that support IEEE
 802.3ad Dynamic Link Aggregation.  Most managed and many unmanaged
 switches currently available support 802.3ad.
 
 The active-backup mode should work with any Layer-II switch.
 
 8.  Where does a bonding device get its MAC address from?
 ---------------------------------------------------------
 
 When using slave devices that have fixed MAC addresses, or when
 the fail_over_mac option is enabled, the bonding device's MAC address is
 the MAC address of the active slave.
 
 For other configurations, if not explicitly configured (with
 ifconfig or ip link), the MAC address of the bonding device is taken from
 its first slave device.  This MAC address is then passed to all following
 slaves and remains persistent (even if the first slave is removed) until
 the bonding device is brought down or reconfigured.
 
 If you wish to change the MAC address, you can set it with
 ifconfig or ip link::
 
         # ifconfig bond0 hw ether 00:11:22:33:44:55
 
         # ip link set bond0 address 66:77:88:99:aa:bb
 
 The MAC address can be also changed by bringing down/up the
 device and then changing its slaves (or their order)::
 
         # ifconfig bond0 down ; modprobe -r bonding
         # ifconfig bond0 .... up
         # ifenslave bond0 eth...
 
 This method will automatically take the address from the next
 slave that is added.
 
 To restore your slaves' MAC addresses, you need to detach them
 from the bond (``ifenslave -d bond0 eth0``). The bonding driver will
 then restore the MAC addresses that the slaves had before they were
 enslaved.
 
 16. Resources and Links
 =======================
 
 The latest version of the bonding driver can be found in the latest
 version of the linux kernel, found on http://kernel.org
 
 The latest version of this document can be found in the latest kernel
 source (named Documentation/networking/bonding.rst).
 
 Discussions regarding the development of the bonding driver take place
 on the main Linux network mailing list, hosted at vger.kernel.org. The list
 address is:
 
 netdev@vger.kernel.org
 
 The administrative interface (to subscribe or unsubscribe) can
 be found at:
 
 http://vger.kernel.org/vger-lists.html#netdev

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