Bonding (link aggregation)
==========================
Features
--------
* Full support of features offered by the bonding kernel module.
* Selectable bonding mode using a single parameter in rc.inet1.conf.
* Easy addition of interfaces to the bond using a parameter in rc.inet1.conf.
* Custom bonding module options can be provided using the generic parameter
IFOPTS[x] in the configuration file.
Configuration
-------------
Bonding interfaces can be configured via two new bond specific parameters in
rc.inet1.conf, plus use of the generic IFOPTS[x] parameter. New parameters
are:
BONDNICS[x]="" The space delimited list of interfaces to add to this
bond. The interfaces will be brought up and configured
while bringing up the interface, so do not need to be
previously defined in rc.inet1.conf. A bond can be
created with only 1 interface, but does not become
useful until at least 2 interfaces are configured.
BONDMODE[x]="" This parameter sets the bonding mode for this
interface. If not specified when BONDNICS[x] has been
used, the default is 'balance-rr'. See below for a
list of all bonding modes available.
The following bond modes are available:
balance-rr This mode is also known as round-robin mode. Packets
are sequentially transmitted and received through each
interface one by one. This mode provides load
balancing functionality along with fault tolerance.
active-backup When in this mode only one interface set to active,
while all other interfaces are in the backup state. If
the active interface fails, a backup interface replaces
it as the only active interface in the bond. This mode
only provides fault tolerance, no load balancing.
This mode requires that the 'primary <interface>'
option be configured with the IFOPTS[x] parameter.
balance-xor The source MAC address uses exclusive or (XOR) logic
with the destination MAC address. This calculation
ensures that the same slave interface is selected for
each destination MAC address. This mode provides fault
tolerance and load balancing.
broadcast All packets are sent to all the slaved interfaces. This
mode provides fault tolerance, but may result in
duplicate packets arriving at the destination.
802.3ad Also known as LACP. This mode creates aggregation
groups that share the same speed and duplex settings,
and it requires a switch that supports an IEEE 802.3ad.
This mode uses all interfaces to form the aggregation
group and provides fault tolerance and load balancing.
balance-tlb This mode ensures that the outgoing traffic
distribution is set according to the load on each
interface and that the current interface receives all
the incoming traffic. If the assigned interface fails
to receive traffic, another interface is assigned to
the receiving role. This provides fault tolerance and
load balancing.
balance-alb The receiving packets are load balanced through Address
Resolution Protocol (ARP) negotiation. This mode
provides fault tolerance and load balancing.
Module specific interface options can be set using the the IFOPTS[x] paramter,
which takes a pipe (|) delimited list of options for the interface. The
following are the most useful options which can be set with IFOPTS[x]:
miimon Specifies the MII link monitoring frequency in milliseconds.
This determines how often the link state of each slaved
interface is checked for link failures. A value of zero
disables MII link monitoring, but this is NOT advised. A value
of 100 is a good starting point. The default value is 0, so be
sure to set this option with ALL modes.
lacp_rate This option specifies the rate at which the host will ask the
link partner to transmit LACPDU packets in 802.3ad mode.
Possible values are:
slow Transmit LACPDUs every 30 seconds.
fast Transmit LACPDUs every 1 second.
The default is slow, but fast is recommended.
primary The interface (eth0, eth2, ...) selecting which slave is the
primary device. The specified interface will always be the
active slave while it is available. Only when the primary is
off-line will alternate interfaces be used. This is useful
when one interface is preferred over another (e.g. when one
interface has higher throughput than another). This option
is only valid for active-backup, balance-tlb, and balance-alb
modes.
xmit_hash_policy
Selects the transmit hash policy to use for interface selection
in balance-xor, 802.3ad, and balance-tlb modes. Possible
values are:
layer2 Use XOR of source/dest hardware MAC addresses
and packet type ID fields to generate the hash.
This algorithm will place all traffic to a
particular network peer on the same slave.
layer2+3 Use a combination of layer2 and layer3 protocol
information (hardware MAC addresses and IP
addresses) to generate the hash.
This algorithm will place all traffic to a
particular network peer on the same slave.
This policy is intended to provide a more
balanced distribution of traffic than layer2
alone, especially in environments where a
layer3 gateway device is required to reach most
destinations.
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 slave interfaces,
although a single connection will not span
multiple slaves.
The default value is layer2. Additional (lesser used) policies
are available, and documented in kernel source documentation:
/usr/src/linux/Documentation/networking/bonding.txt
The IFOPTS[x] option should always include the 'miimon' option - not using this
option will result in network degradation.
In 'active-backup' mode, the 'primary' option should also be supplied.
When using '802.3ad mode', set "lacp_rate fast" for faster recovery from an
interface failure.
In other modes, the 'xmit_hash_policy' should be set.
Full documentation of the bonding layer is available in the kernel source
documentation: /usr/src/linux/Documentation/networking/bonding.txt.
--
Darren 'Tadgy' Austin.
<darren (at) afterdark.org.uk>
