Linux Ethernet Bonding Driver HOWTO
Linux Ethernet Bonding Driver HOWTO
Latest update: 21 June 2005
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
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
- Bonding Driver Installation
- Bonding Driver Options
- 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 3.3.1 Configuring Multiple Bonds Manually
- Querying Bonding Configuration 5.1 Bonding Configuration 5.2 Network Configuration
- Switch Configuration
- 802.1q VLAN Support
- Link Monitoring 8.1 ARP Monitor Operation 8.2 Configuring Multiple ARP Targets 8.3 MII Monitor Operation
- Potential Trouble Sources 9.1 Adventures in Routing 9.2 Ethernet Device Renaming 9.3 Painfully Slow Or No Failed Link Detection By Miimon
- SNMP agents
- Promiscuous mode
- Configuring Bonding for High Availability 12.1 High Availability in a Single Switch Topology 12.2 High Availability in a Multiple Switch Topology 12.2.1 HA Bonding Mode Selection for Multiple Switch Topology 12.2.2 HA Link Monitoring for Multiple Switch Topology
- Configuring Bonding for Maximum Throughput 13.1 Maximum Throughput in a Single Switch Topology 13.1.1 MT Bonding Mode Selection for Single Switch Topology 13.1.2 MT Link Monitoring for Single Switch Topology 13.2 Maximum Throughput in a Multiple Switch Topology 13.2.1 MT Bonding Mode Selection for Multiple Switch Topology 13.2.2 MT Link Monitoring for Multiple Switch Topology
- Switch Behavior Issues 14.1 Link Establishment and Failover Delays 14.2 Duplicated Incoming Packets
- Hardware Specific Considerations 15.1 IBM BladeCenter
- Frequently Asked Questions
- 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 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, then continue below to install ifenslave.
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 work.
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).
IMPORTANT NOTE:
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/modules.conf or /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:
arp_interval
Specifies the ARP link monitoring frequency in milliseconds.
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.
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.
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.
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.
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 gratutious 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) 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. 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 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.
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 mode.
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 and 802.3ad modes. Possible values are:
layer2
Uses XOR of hardware MAC addresses to generate the
hash. The formula is
(source MAC XOR destination MAC) modulo slave count
This algorithm will place all traffic to a particular
network peer on the same slave.
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
((source port XOR dest port) XOR
((source IP XOR dest IP) AND 0xffff)
modulo slave count
For fragmented TCP or UDP packets and all other IP
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 policy is intended to mimic the behavior of
certain switches, notably Cisco switches with PFC2 as
well as some Foundry and IBM products.
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.
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.
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 (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
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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.conf or /etc/modprobe.conf configuration file.
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 or 4. 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:
/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.
Finally, it is necessary to edit /etc/modules.conf (or /etc/modprobe.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/modules.conf (or modprobe.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 version supplied with Fedora Core 3 and Red Hat Enterprise Linux 4 is reported to work) do 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
At this writing, the initscripts package does not directly support loading the bonding driver multiple times, so the process for doing so is the same as described in the "Configuring Multiple Bonds Manually" section, below.
NOTE: It has been observed that some Red Hat supplied kernels are apparently 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.
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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 /etc/modules.conf or /etc/modprobe.conf (as appropriate for the installed distro), 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 mode=balance-alb miimon=100 modprobe e100
ifconfig bond0 192.168.1.1 netmask 255.255.255.0 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.
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 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 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.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.
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: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
inet addr:XXX.XXX.XXX.YYY Bcast:XXX.XXX.XXX.255 Mask:255.255.252.0
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
inet addr:XXX.XXX.XXX.YYY Bcast:XXX.XXX.XXX.255 Mask:255.255.252.0
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
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 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.
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 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:
- Remove all VLAN interfaces then recreate them
- 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.
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 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.
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 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
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 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.
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 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 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 --ignore-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 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.
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 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.
12. 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.
12.1 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 13, "Configuring Bonding for Maximum Throughput" for information on configuring bonding with one peer device.
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 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.
12.2.1 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