In addition to Poll Mode Drivers (PMDs) for physical and virtual hardware,
DPDK also includes a pure-software library that
allows physical PMD’s to be bonded together to create a single logical PMD.
The librte_pmd_bond library exports a C API which provides an API for the
creation of bonded devices as well as the configuration and management of the
bonded device and its slave devices.
10.1. Link Bonding Modes Overview
Currently the Link Bonding PMD library supports following modes of operation:
Fig. 10.2 Round-Robin (Mode 0)
This mode provides load balancing and fault tolerance by transmission of
packets in sequential order from the first available slave device through
the last. Packets are bulk dequeued from devices then serviced in a
round-robin manner. This mode does not guarantee in order reception of
packets and down stream should be able to handle out of order packets.
Fig. 10.3 Active Backup (Mode 1)
In this mode only one slave in the bond is active at any time, a different
slave becomes active if, and only if, the primary active slave fails,
thereby providing fault tolerance to slave failure. The single logical
bonded interface’s MAC address is externally visible on only one NIC (port)
to avoid confusing the network switch.
Fig. 10.4 Balance XOR (Mode 2)
This mode provides transmit load balancing (based on the selected
transmission policy) and fault tolerance. The default policy (layer2) uses
a simple calculation based on the packet flow source and destination MAC
addresses as well as the number of active slaves available to the bonded
device to classify the packet to a specific slave to transmit on. Alternate
transmission policies supported are layer 2+3, this takes the IP source and
destination addresses into the calculation of the transmit slave port and
the final supported policy is layer 3+4, this uses IP source and
destination addresses as well as the TCP/UDP source and destination port.
The coloring differences of the packets are used to identify different flow
classification calculated by the selected transmit policy
Fig. 10.5 Broadcast (Mode 3)
This mode provides fault tolerance by transmission of packets on all slave
- Link Aggregation 802.3AD (Mode 4):
Fig. 10.6 Link Aggregation 802.3AD (Mode 4)
This mode provides dynamic link aggregation according to the 802.3ad
specification. It negotiates and monitors aggregation groups that share the
same speed and duplex settings using the selected balance transmit policy
for balancing outgoing traffic.
DPDK implementation of this mode provide some additional requirements of
- It needs to call
intervals period of less than 100ms.
- Calls to
rte_eth_tx_burst must have a buffer size of at least 2xN,
where N is the number of slaves. This is a space required for LACP
frames. Additionally LACP packets are included in the statistics, but
they are not returned to the application.
- Transmit Load Balancing (Mode 5):
Fig. 10.7 Transmit Load Balancing (Mode 5)
This mode provides an adaptive transmit load balancing. It dynamically
changes the transmitting slave, according to the computed load. Statistics
are collected in 100ms intervals and scheduled every 10ms.
10.2. Implementation Details
The librte_pmd_bond bonded device are compatible with the Ethernet device API
exported by the Ethernet PMDs described in the DPDK API Reference.
The Link Bonding Library supports the creation of bonded devices at application
startup time during EAL initialization using the
--vdev option as well as
programmatically via the C API
Bonded devices support the dynamical addition and removal of slave devices using
After a slave device is added to a bonded device slave is stopped using
rte_eth_dev_stop and then reconfigured using
the RX and TX queues are also reconfigured using
rte_eth_rx_queue_setup with the parameters use to configure the bonding
device. If RSS is enabled for bonding device, this mode is also enabled on new
slave and configured as well.
Setting up multi-queue mode for bonding device to RSS, makes it fully
RSS-capable, so all slaves are synchronized with its configuration. This mode is
intended to provide RSS configuration on slaves transparent for client
Bonding device stores its own version of RSS settings i.e. RETA, RSS hash
function and RSS key, used to set up its slaves. That let to define the meaning
of RSS configuration of bonding device as desired configuration of whole bonding
(as one unit), without pointing any of slave inside. It is required to ensure
consistency and made it more error-proof.
RSS hash function set for bonding device, is a maximal set of RSS hash functions
supported by all bonded slaves. RETA size is a GCD of all its RETA’s sizes, so
it can be easily used as a pattern providing expected behavior, even if slave
RETAs’ sizes are different. If RSS Key is not set for bonded device, it’s not
changed on the slaves and default key for device is used.
All settings are managed through the bonding port API and always are propagated
in one direction (from bonding to slaves).
10.2.1. Link Status Change Interrupts / Polling
Link bonding devices support the registration of a link status change callback,
rte_eth_dev_callback_register API, this will be called when the
status of the bonding device changes. For example in the case of a bonding
device which has 3 slaves, the link status will change to up when one slave
becomes active or change to down when all slaves become inactive. There is no
callback notification when a single slave changes state and the previous
conditions are not met. If a user wishes to monitor individual slaves then they
must register callbacks with that slave directly.
The link bonding library also supports devices which do not implement link
status change interrupts, this is achieved by polling the devices link status at
a defined period which is set using the
API, the default polling interval is 10ms. When a device is added as a slave to
a bonding device it is determined using the
whether the device supports interrupts or whether the link status should be
monitored by polling it.
10.2.2. Requirements / Limitations
The current implementation only supports devices that support the same speed
and duplex to be added as a slaves to the same bonded device. The bonded device
inherits these attributes from the first active slave added to the bonded
device and then all further slaves added to the bonded device must support
A bonding device must have a minimum of one slave before the bonding device
itself can be started.
To use a bonding device dynamic RSS configuration feature effectively, it is
also required, that all slaves should be RSS-capable and support, at least one
common hash function available for each of them. Changing RSS key is only
possible, when all slave devices support the same key size.
To prevent inconsistency on how slaves process packets, once a device is added
to a bonding device, RSS configuration should be managed through the bonding
device API, and not directly on the slave.
Like all other PMD, all functions exported by a PMD are lock-free functions
that are assumed not to be invoked in parallel on different logical cores to
work on the same target object.
It should also be noted that the PMD receive function should not be invoked
directly on a slave devices after they have been to a bonded device since
packets read directly from the slave device will no longer be available to the
bonded device to read.
Link bonding devices are created using the
which requires a unique device name, the bonding mode,
and the socket Id to allocate the bonding device’s resources on.
The other configurable parameters for a bonded device are its slave devices,
its primary slave, a user defined MAC address and transmission policy to use if
the device is in balance XOR mode.
10.2.3.1. Slave Devices
Bonding devices support up to a maximum of
RTE_MAX_ETHPORTS slave devices
of the same speed and duplex. Ethernet devices can be added as a slave to a
maximum of one bonded device. Slave devices are reconfigured with the
configuration of the bonded device on being added to a bonded device.
The bonded also guarantees to return the MAC address of the slave device to its
original value of removal of a slave from it.
10.2.3.2. Primary Slave
The primary slave is used to define the default port to use when a bonded
device is in active backup mode. A different port will only be used if, and
only if, the current primary port goes down. If the user does not specify a
primary port it will default to being the first port added to the bonded device.
10.2.3.3. MAC Address
The bonded device can be configured with a user specified MAC address, this
address will be inherited by the some/all slave devices depending on the
operating mode. If the device is in active backup mode then only the primary
device will have the user specified MAC, all other slaves will retain their
original MAC address. In mode 0, 2, 3, 4 all slaves devices are configure with
the bonded devices MAC address.
If a user defined MAC address is not defined then the bonded device will
default to using the primary slaves MAC address.
10.2.3.4. Balance XOR Transmit Policies
There are 3 supported transmission policies for bonded device running in
Balance XOR mode. Layer 2, Layer 2+3, Layer 3+4.
- Layer 2: Ethernet MAC address based balancing is the default
transmission policy for Balance XOR bonding mode. It uses a simple XOR
calculation on the source MAC address and destination MAC address of the
packet and then calculate the modulus of this value to calculate the slave
device to transmit the packet on.
- Layer 2 + 3: Ethernet MAC address & IP Address based balancing uses a
combination of source/destination MAC addresses and the source/destination
IP addresses of the data packet to decide which slave port the packet will
be transmitted on.
- Layer 3 + 4: IP Address & UDP Port based balancing uses a combination
of source/destination IP Address and the source/destination UDP ports of
the packet of the data packet to decide which slave port the packet will be
All these policies support 802.1Q VLAN Ethernet packets, as well as IPv4, IPv6
and UDP protocols for load balancing.
10.3. Using Link Bonding Devices
The librte_pmd_bond library supports two modes of device creation, the libraries
export full C API or using the EAL command line to statically configure link
bonding devices at application startup. Using the EAL option it is possible to
use link bonding functionality transparently without specific knowledge of the
libraries API, this can be used, for example, to add bonding functionality,
such as active backup, to an existing application which has no knowledge of
the link bonding C API.
10.3.1. Using the Poll Mode Driver from an Application
Using the librte_pmd_bond libraries API it is possible to dynamically create
and manage link bonding device from within any application. Link bonding
devices are created using the
rte_eth_bond_create API which requires a
unique device name, the link bonding mode to initial the device in and finally
the socket Id which to allocate the devices resources onto. After successful
creation of a bonding device it must be configured using the generic Ethernet
device configure API
rte_eth_dev_configure and then the RX and TX queues
which will be used must be setup using
Slave devices can be dynamically added and removed from a link bonding device
APIs but at least one slave device must be added to the link bonding device
before it can be started using
The link status of a bonded device is dictated by that of its slaves, if all
slave device link status are down or if all slaves are removed from the link
bonding device then the link status of the bonding device will go down.
It is also possible to configure / query the configuration of the control
parameters of a bonded device using the provided APIs
10.3.2. Using Link Bonding Devices from the EAL Command Line
Link bonding devices can be created at application startup time using the
--vdev EAL command line option. The device name must start with the
eth_bond prefix followed by numbers or letters. The name must be unique for
each device. Each device can have multiple options arranged in a comma
separated list. Multiple devices definitions can be arranged by calling the
--vdev option multiple times.
Device names and bonding options must be separated by commas as shown below:
$RTE_TARGET/app/testpmd -c f -n 4 --vdev 'eth_bond0,bond_opt0=..,bond opt1=..'--vdev 'eth_bond1,bond _opt0=..,bond_opt1=..'
10.3.2.1. Link Bonding EAL Options
There are multiple ways of definitions that can be assessed and combined as
long as the following two rules are respected:
- A unique device name, in the format of eth_bondX is provided,
where X can be any combination of numbers and/or letters,
and the name is no greater than 32 characters long.
- A least one slave device is provided with for each bonded device definition.
- The operation mode of the bonded device being created is provided.
The different options are:
- mode: Integer value defining the bonding mode of the device.
Currently supports modes 0,1,2,3,4,5 (round-robin, active backup, balance,
broadcast, link aggregation, transmit load balancing).
- slave: Defines the PMD device which will be added as slave to the bonded
device. This option can be selected multiple times, for each device to be
added as a slave. Physical devices should be specified using their PCI
address, in the format domain:bus:devid.function
- primary: Optional parameter which defines the primary slave port,
is used in active backup mode to select the primary slave for data TX/RX if
it is available. The primary port also is used to select the MAC address to
use when it is not defined by the user. This defaults to the first slave
added to the device if it is specified. The primary device must be a slave
of the bonded device.
- socket_id: Optional parameter used to select which socket on a NUMA device
the bonded devices resources will be allocated on.
- mac: Optional parameter to select a MAC address for link bonding device,
this overrides the value of the primary slave device.
- xmit_policy: Optional parameter which defines the transmission policy when
the bonded device is in balance mode. If not user specified this defaults
to l2 (layer 2) forwarding, the other transmission policies available are
l23 (layer 2+3) and l34 (layer 3+4)
- lsc_poll_period_ms: Optional parameter which defines the polling interval
in milli-seconds at which devices which don’t support lsc interrupts are
checked for a change in the devices link status
- up_delay: Optional parameter which adds a delay in milli-seconds to the
propagation of a devices link status changing to up, by default this
parameter is zero.
- down_delay: Optional parameter which adds a delay in milli-seconds to the
propagation of a devices link status changing to down, by default this
parameter is zero.
10.3.2.2. Examples of Usage
Create a bonded device in round robin mode with two slaves specified by their PCI address:
$RTE_TARGET/app/testpmd -c '0xf' -n 4 --vdev 'eth_bond0,mode=0, slave=0000:00a:00.01,slave=0000:004:00.00' -- --port-topology=chained
Create a bonded device in round robin mode with two slaves specified by their PCI address and an overriding MAC address:
$RTE_TARGET/app/testpmd -c '0xf' -n 4 --vdev 'eth_bond0,mode=0, slave=0000:00a:00.01,slave=0000:004:00.00,mac=00:1e:67:1d:fd:1d' -- --port-topology=chained
Create a bonded device in active backup mode with two slaves specified, and a primary slave specified by their PCI addresses:
$RTE_TARGET/app/testpmd -c '0xf' -n 4 --vdev 'eth_bond0,mode=1, slave=0000:00a:00.01,slave=0000:004:00.00,primary=0000:00a:00.01' -- --port-topology=chained
Create a bonded device in balance mode with two slaves specified by their PCI addresses, and a transmission policy of layer 3 + 4 forwarding:
$RTE_TARGET/app/testpmd -c '0xf' -n 4 --vdev 'eth_bond0,mode=2, slave=0000:00a:00.01,slave=0000:004:00.00,xmit_policy=l34' -- --port-topology=chained