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/modrobe.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 NULL or
  	multicast. 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.
  
  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
  
  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_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 0.
  
  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
  	each link monitor interval (arp_interval or miimon, whichever
  	is active) 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.
  
  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
  	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 XOR destination MAC 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 XOR destination MAC 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)
  		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.
  
  	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 ignore: The device configuration is ignored.
  
  	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_inteval 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 it's
  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.txt
  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.
  
  	The ARP monitor relies on the device driver itself to verify
  that traffic is flowing.  In particular, the driver must keep up to
  date the last receive time, dev->last_rx.  Drivers that use NETIF_F_LLTX
  flag must also update netdev_queue->trans_start.  If they do not, then the
  ARP monitor will immediately fail any slaves using that driver, and
  those slaves will stay down.  If networking monitoring (tcpdump, etc)
  shows the ARP requests and replies on the network, then it may be that
  your device driver is not updating last_rx and trans_start.
  
  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 ETHOOL_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.txt).
  
  	Discussions regarding the usage of the bonding driver take place on the
  bonding-devel mailing list, hosted at sourceforge.net. If you have questions or
  problems, post them to the list.  The list address is:
  
  bonding-devel@lists.sourceforge.net
  
  	The administrative interface (to subscribe or unsubscribe) can
  be found at:
  
  https://lists.sourceforge.net/lists/listinfo/bonding-devel
  
  	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
  
  Donald Becker's Ethernet Drivers and diag programs may be found at :
   - http://web.archive.org/web/*/http://www.scyld.com/network/ 
  
  You will also find a lot of information regarding Ethernet, NWay, MII,
  etc. at www.scyld.com.
  
  -- END --