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+ Linux Ethernet Bonding Driver HOWTO
+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
+Note :
+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, patches for older kernels and the updated
+userspace tools, 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
+3.2 Configuration with initscripts support
+3.3 Configuring Bonding Manually
+3.4 Configuring Multiple Bonds
+5. Querying Bonding Configuration
+5.1 Bonding Configuration
+5.2 Network Configuration
+6. Switch Configuration
+7. 802.1q VLAN Support
+8. Link Monitoring
+8.1 ARP Monitor Operation
+8.2 Configuring Multiple ARP Targets
+8.3 MII Monitor Operation
+9. Potential Trouble Sources
+9.1 Adventures in Routing
+9.2 Ethernet Device Renaming
+9.3 Painfully Slow Or No Failed Link Detection By Miimon
+10. SNMP agents
+11. Promiscuous mode
+12. High Availability Information
+12.1 High Availability in a Single Switch Topology
+12.1.1 Bonding Mode Selection for Single Switch Topology
+12.1.2 Link Monitoring for Single Switch Topology
+12.2 High Availability in a Multiple Switch Topology
+12.2.1 Bonding Mode Selection for Multiple Switch Topology
+12.2.2 Link Monitoring for Multiple Switch Topology
+12.3 Switch Behavior Issues for High Availability
+13. Hardware Specific Considerations
+13.1 IBM BladeCenter
+14. Frequently Asked Questions
+15. Resources and Links
+1. Bonding Driver Installation
+ Most popular distro kernels ship with the bonding driver
+already available as a module and the ifenslave user level control
+program installed and ready for use. 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 latest 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).
+ Prior to the 2.4.11 kernel, the bonding driver was maintained
+largely outside the kernel tree; patches for some earlier kernels are
+available on the bonding sourceforge site, although those patches are
+still several years out of date. Most users will want to use either
+the most recent kernel from kernel.org or whatever kernel came with
+their distro.
+ 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, then proceed to
+step 2.
+1.2 Install ifenslave Control Utility
+ The ifenslave user level control program is included in the
+kernel source tree, in the file Documentation/networking/ifenslave.c.
+It is generally recommended that you use the ifenslave that
+corresponds to the kernel that you are using (either from the same
+source tree or supplied with the distro), however, ifenslave
+executables from older kernels should function (but features newer
+than the ifenslave release are not supported). Running an ifenslave
+that is newer than the kernel is not supported, and may or may not
+ To install ifenslave, do the following:
+# gcc -Wall -O -I/usr/src/linux/include ifenslave.c -o ifenslave
+# cp ifenslave /sbin/ifenslave
+ If your kernel source is not in "/usr/src/linux," then replace
+"/usr/src/linux/include" in the above with the location of your kernel
+source include directory.
+ You may wish to back up any existing /sbin/ifenslave, or, for
+testing or informal use, tag the ifenslave to the kernel version
+(e.g., name the ifenslave executable /sbin/ifenslave-2.6.10).
+ If you omit the "-I" or specify an incorrect directory, you
+may end up with an ifenslave that is incompatible with the kernel
+you're trying to build it for. Some distros (e.g., Red Hat from 7.1
+onwards) do not have /usr/include/linux symbolically linked to the
+default kernel source include directory.
+2. Bonding Driver Options
+ Options for the bonding driver are supplied as parameters to
+the bonding module at load time. They may be given as command line
+arguments to the insmod or modprobe command, but are usually specified
+in either the /etc/modprobe.conf configuration file, or in a
+distro-specific configuration file (some of which are detailed in the
+next section).
+ 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:
+ Specifies the ARP monitoring frequency in milli-seconds. If
+ ARP monitoring is used in a load-balancing mode (mode 0 or 2),
+ the switch should be configured in a mode that evenly
+ distributes packets across all links - such as round-robin. 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.
+ Specifies the ip addresses to use 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 adresses must be
+ seperated 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.
+ 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.
+ 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 (default)
+ fast or 1
+ Request partner to transmit LACPDUs every 1 second
+ 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.
+ Specifies the frequency in milli-seconds that MII link
+ monitoring will occur. 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.
+ 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. This mode provides
+ fault tolerance. The primary option affects the
+ behavior of this mode.
+ balance-xor or 2
+ XOR policy: Transmit based on [(source MAC address
+ XOR'd with destination MAC address) modulo slave
+ count]. This selects the same slave for each
+ destination MAC address. 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.
+ Pre-requisites:
+ 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. The
+ outgoing traffic is distributed according to the
+ current load (computed relative to the speed) on each
+ slave. 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 intiating 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.
+ 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 mode.
+ 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.
+ 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.
+3. Configuring Bonding Devices
+ There are, essentially, two methods for configuring bonding:
+with support from the distro's network initialization scripts, and
+without. Distros generally use one of two packages for the network
+initialization scripts: initscripts or sysconfig. 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 and sysconfig 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 or
+initscripts, or don't know if it's new enough, have no fear.
+Determining this is fairly straightforward.
+ First, 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
+frontend 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. The name of the
+configuration file for each device will be of the form:
+ 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 muliple lines, and will look
+something like this:
+ Change the BOOTPROTO and STARTMODE lines to the following:
+ 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:
+BONDING_MODULE_OPTS="mode=active-backup miimon=100"
+values with the appropriate values for your network.
+ Note that configuring the bonding device with BOOTPROTO='dhcp'
+does not work; 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.
+ 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="ethX" for each slave,
+where "n" is an increasing value, one for each slave, and "ethX" is
+the name of the slave device (eth0, eth1, etc).
+ 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 paramters 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:
+ Note that the template does not document the various BONDING_
+settings described above, but does describe many of the other options.
+3.2 Configuration with initscripts support
+ This section applies to distros using a version of initscripts
+with bonding support, for example, Red Hat Linux 9 or Red Hat
+Enterprise Linux version 3. On these systems, the network
+initialization scripts have some knowledge of bonding, and can be
+configured to control bonding devices.
+ 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:
+ 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:
+ 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:
+ Be sure to change the networking specific lines (IPADDR,
+NETMASK, NETWORK and BROADCAST) to match your network configuration.
+ Finally, it is necessary to edit /etc/modules.conf to load the
+bonding module when the bond0 interface is brought up. The following
+sample lines in /etc/modules.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.
+3.3 Configuring Bonding Manually
+ 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 methodology for these systems is to place the
+bonding module parameters into /etc/modprobe.conf, then add modprobe
+and/or ifenslave 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 -obond0 mode=balance-alb miimon=100
+modprobe e100
+ifconfig bond0 netmask up
+ifenslave bond0 eth0
+ifenslave bond0 eth1
+ Replace the example bonding module parameters and bond0
+network configuration (IP address, netmask, etc) with the appropriate
+values for your configuration. The above example loads the bonding
+module with the name "bond0," this simplifies the naming if multiple
+bonding modules are loaded (each successive instance of the module is
+given a different name, and the module instance names match the
+bonding interface names).
+ 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 bond0
+# rmmod e100
+ Again, for convenience, it may be desirable to create a script
+with these commands.
+3.4 Configuring Multiple Bonds
+ This section contains information on configuring multiple
+bonding devices with differing options. If you require multiple
+bonding devices, but all with the same options, see the "max_bonds"
+module paramter, documented above.
+ To create multiple bonding devices with differing options, it
+is necessary 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
+ 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.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.
+ This may be repeated any number of times, specifying a new and
+unique name in place of bond0 or bond1 for each instance.
+ When the appropriate module paramters are in place, then
+configure bonding according to the instructions for your distro.
+5. Querying Bonding Configuration
+5.1 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.
+5.2 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:
+ 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
+ inet addr:XXX.XXX.XXX.YYY Bcast:XXX.XXX.XXX.255 Mask:
+ 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
+ inet addr:XXX.XXX.XXX.YYY Bcast:XXX.XXX.XXX.255 Mask:
+ 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
+6. 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
+ 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.
+7. 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 offloding, the bonding
+interface declares itself as fully hardware offloaing 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 promiscouos
+mode, which might not be what you want.
+8. Link Monitoring
+ The bonding driver at present supports two schemes for
+monitoring a slave device's link state: the ARP monitor and the MII
+ 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.
+8.1 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, and transmit start time,
+dev->trans_start. If these are not updated by the driver, 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.
+8.2 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
+ Multiple ARP targets must be seperated by commas as follows:
+# example options for ARP monitoring with three targets
+alias bond0 bonding
+options bond0 arp_interval=60 arp_ip_target=,,
+ 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=
+8.3 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
+ 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
+9. Potential Sources of Trouble
+9.1 Adventures in Routing
+ When bonding is configured, it is important that the slave
+devices not have routes that supercede 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
+ U 40 0 0 eth0
+ U 40 0 0 eth1
+ U 40 0 0 bond0
+ 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 supercede routes of their master. This should generally be the
+case, but unusual configurations or errant manual or automatic static
+route additions may cause trouble.
+9.2 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 either /etc/modules.conf or
+/etc/modprobe.conf (depending upon which is installed on the system).
+ 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.conf (or modprobe.conf.local),
+an equivalent problem can occur. In this case, the following can be
+added to modprobe.conf (or modprobe.conf.local, as appropriate), as
+follows (all on one line; it has been split here for clarity):
+install bonding /sbin/modprobe tg3; /sbin/modprobe e1000;
+ /sbin/modprobe --ignore-install bonding
+ This will, when loading the bonding module, rather than
+performing the normal action, instead execute the provided command.
+This command loads the device drivers in the order needed, then calls
+modprobe with --ingore-install to cause the normal action to then take
+place. Full documentation on this can be found in the modprobe.conf
+and modprobe manual pages.
+9.3. 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.
+10. 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 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 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. = 5
+ ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 2
+ ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 4
+ ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 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 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. = 6
+ ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 2
+ ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 5
+ ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex. = 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
+11. 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 propogates the setting to the slave
+ For the balance-rr, balance-xor, broadcast, and 802.3ad modes,
+the promiscuous mode setting is propogated to all slaves.
+ For the active-backup, balance-tlb and balance-alb modes, the
+promiscuous mode setting is propogated 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 propogated to the new active slave.
+12. High Availability Information
+ High Availability refers to configurations that provide
+maximum network availability by having redundant or backup devices,
+links and switches between the host and the rest of the world.
+ There are currently two basic methods for configuring to
+maximize availability. They are dependent on the network topology and
+the primary goal of the configuration, but in general, a configuration
+can be optimized for maximum available bandwidth, or for maximum
+network availability.
+12.1 High Availability in a Single Switch Topology
+ If two hosts (or a host and a switch) are directly connected
+via multiple physical links, then there is no network availability
+penalty for optimizing for maximum bandwidth: there is only one switch
+(or peer), so if it fails, you have no alternative access to fail over
+Example 1 : host to switch (or other host)
+ +----------+ +----------+
+ | |eth0 eth0| switch |
+ | Host A +--------------------------+ or |
+ | +--------------------------+ other |
+ | |eth1 eth1| host |
+ +----------+ +----------+
+12.1.1 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 tradeoffs 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 often 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, and the maximum useful value is 127.
+ For a four interface balance-rr bond, expect that a single
+ TCP/IP stream will utilize no more than approximately 2.3
+ interface's worth of throughput, even after adjusting
+ tcp_reordering.
+ 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, it does not require
+ any configuration of the switch.
+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 may be desirable if you have a large
+ network with many hosts. It is likely to be suboptimal if all
+ your traffic is passed through a single router, however. 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
+ usable 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), so in general all traffic to a particular
+ destination will use the same interface. Finally, the 802.3ad
+ mode mandates the use of the MII monitor, therefore, the ARP
+ monitor is not available in this mode.
+balance-tlb: This mode is also a good choice for this type of
+ topology. It has no special switch configuration
+ requirements, and balances outgoing traffic by peer, in a
+ vaguely intelligent manner (not a simple XOR as in balance-xor
+ or 802.3ad mode), so that unlucky MAC addresses will not all
+ "bunch up" on a single interface. Interfaces may be of
+ differing speeds. 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 peers (as described in
+ the Bonding Module Options section, above). The only extra
+ 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 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 assurance
+as the ARP monitor).
+12.2 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 tradeoff 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.
+12.2.1 Bonding Mode Selection for Multiple Switch Topology
+ In a topology such as this, the active-backup and broadcast
+modes are the only useful bonding modes; 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 independant. 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.
+12.2.2 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 link
+failures. Additionally, it 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.
+12.3 Switch Behavior Issues for High Availability
+ You may encounter issues with 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, but note that if all links are down, then updelay is ignored
+when any link becomes active (the slave closest to completing its
+updelay is chosen).
+ Note that when a bonding interface has no active links, the
+driver will immediately reuse the first link that goes up, even if
+updelay parameter was specified. 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.
+ 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. 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.
+13.1 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
+JS20 network adapter information
+ All JS20s come with two Broadcom Gigabit Ethernet ports
+integrated on the planar. 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,
+ 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
+ Normally, Ethernet Switch Modules (ESM) 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).
+ An optical passthru module (OPM) connects the I/O module
+directly to an external switch. By using OPMs 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 ESM and OPM modules, the network
+will appear to bonding as either a single switch topology (all OPM
+modules) or as a multiple switch topology (one or more ESM modules,
+zero or more OPM modules). It is also possible to connect ESM modules
+together, resulting in a configuration much like the example in "High
+Availability in a multiple switch topology."
+Requirements for specifc modes
+ The balance-rr mode requires the use of OPM 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 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.
+ 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 delays issues when using bonding.
+14. 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). They need not
+be of the same speed.
+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
+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 section on High
+Availability for additional information.
+ Link monitoring can be enabled via either the miimon or
+arp_interval paramters (described in the module paramters 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 degredation 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 unmananged 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 paramters, above).
+ In 802.3ad mode, it works with 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?
+ If not explicitly configured with ifconfig, 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 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 bond0 hw ether 00:11:22:33:44:55
+ 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
+15. 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
+Discussions regarding the bonding driver take place primarily on the
+bonding-devel mailing list, hosted at sourceforge.net. If you have
+questions or problems, post them to the list.
+There is also a project site on sourceforge.
+Donald Becker's Ethernet Drivers and diag programs may be found at :
+ - http://www.scyld.com/network/
+You will also find a lot of information regarding Ethernet, NWay, MII,
+etc. at www.scyld.com.
+-- END --