2. Link Bonding Poll Mode Driver Library

In addition to Poll Mode Drivers (PMDs) for physical and virtual hardware, DPDK also includes a pure-software library that allows physical PMDs to be bonded together to create a single logical PMD.

Fig. 2.5 Bonding PMDs

The Link Bonding PMD library(librte_net_bond) supports bonding of groups of rte_eth_dev ports of the same speed and duplex to provide similar capabilities to that found in Linux bonding driver to allow the aggregation of multiple (member) NICs into a single logical interface between a server and a switch. The new bonding PMD will then process these interfaces based on the mode of operation specified to provide support for features such as redundant links, fault tolerance and/or load balancing.

The librte_net_bond library exports a C API which provides an API for the creation of bonding devices as well as the configuration and management of the bonding device and its member devices.

Note

The Link Bonding PMD Library is enabled by default in the build configuration, the library can be disabled using the meson option “-Ddisable_drivers=net/bonding”.

2.1. Link Bonding Modes Overview

Currently the Link Bonding PMD library supports following modes of operation:

Round-Robin (Mode 0):

../_images/bond-mode-0.svg — Fig. 2.6 Round-Robin (Mode 0)

This mode provides load balancing and fault tolerance by transmission of packets in sequential order from the first available member 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.

Active Backup (Mode 1):

../_images/bond-mode-1.svg — Fig. 2.7 Active Backup (Mode 1)

In this mode only one member in the bond is active at any time, a different member becomes active if, and only if, the primary active member fails, thereby providing fault tolerance to member failure. The single logical bonding interface’s MAC address is externally visible on only one NIC (port) to avoid confusing the network switch.

Balance XOR (Mode 2):

../_images/bond-mode-2.svg — Fig. 2.8 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 members available to the bonding device to classify the packet to a specific member 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 member 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.

Note

The coloring differences of the packets are used to identify different flow classification calculated by the selected transmit policy

Broadcast (Mode 3):

../_images/bond-mode-3.svg — Fig. 2.9 Broadcast (Mode 3)

This mode provides fault tolerance by transmission of packets on all member ports.

Link Aggregation 802.3AD (Mode 4):

../_images/bond-mode-4.svg — Fig. 2.10 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 the application.

It needs to call `rte_eth_tx_burst` and `rte_eth_rx_burst` with 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 members. 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):

../_images/bond-mode-5.svg — Fig. 2.11 Transmit Load Balancing (Mode 5)

This mode provides an adaptive transmit load balancing. It dynamically changes the transmitting member, according to the computed load. Statistics are collected in 100ms intervals and scheduled every 10ms.

2.2. Implementation Details

The librte_net_bond bonding device is 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 bonding devices at application startup time during EAL initialization using the --vdev option as well as programmatically via the C API rte_eth_bond_create function.

Bonding devices support the dynamical addition and removal of member devices using the rte_eth_bond_member_add / rte_eth_bond_member_remove APIs.

After a member device is added to a bonding device member is stopped using rte_eth_dev_stop and then reconfigured using rte_eth_dev_configure the RX and TX queues are also reconfigured using rte_eth_tx_queue_setup / 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 member and configured as well. Any flow which was configured to the bond device also is configured to the added member.

Setting up multi-queue mode for bonding device to RSS, makes it fully RSS-capable, so all members are synchronized with its configuration. This mode is intended to provide RSS configuration on members transparent for client application implementation.

Bonding device stores its own version of RSS settings i.e. RETA, RSS hash function and RSS key, used to set up its members. 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 member 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 bonding members. 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 member RETAs’ sizes are different. If RSS Key is not set for bonding device, it’s not changed on the members and default key for device is used.

As RSS configurations, there is flow consistency in the bonding members for the next rte flow operations:

Validate:

Validate flow for each member, failure at least for one member causes to bond validation failure.

Create:

Create the flow in all members.
Save all the members created flows objects in bonding internal flow structure.
Failure in flow creation for existed member rejects the flow.
Failure in flow creation for new members in member adding time rejects the member.

Destroy:

Destroy the flow in all members and release the bond internal flow memory.

Flush:

Destroy all the bonding PMD flows in all the members.

Note

Don’t call members flush directly, It destroys all the member flows which may include external flows or the bond internal LACP flow.

Query:

Summarize flow counters from all the members, relevant only for RTE_FLOW_ACTION_TYPE_COUNT.

Isolate:

Call to flow isolate for all members.
Failure in flow isolation for existed member rejects the isolate mode.
Failure in flow isolation for new members in member adding time rejects the member.

All settings are managed through the bonding port API and always are propagated in one direction (from bonding to members).

2.2.1. Link Status Change Interrupts / Polling

Link bonding devices support the registration of a link status change callback, using the 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 members, the link status will change to up when one member becomes active or change to down when all members become inactive. There is no callback notification when a single member changes state and the previous conditions are not met. If a user wishes to monitor individual members then they must register callbacks with that member 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 rte_eth_bond_link_monitoring_set API, the default polling interval is 10ms. When a device is added as a member to a bonding device it is determined using the RTE_PCI_DRV_INTR_LSC flag whether the device supports interrupts or whether the link status should be monitored by polling it.

2.2.2. Requirements / Limitations

The current implementation only supports devices that support the same speed and duplex to be added as a members to the same bonding device. The bonding device inherits these attributes from the first active member added to the bonding device and then all further members added to the bonding device must support these parameters.

A bonding device must have a minimum of one member before the bonding device itself can be started.

To use a bonding device dynamic RSS configuration feature effectively, it is also required, that all members 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 member devices support the same key size.

To prevent inconsistency on how members process packets, once a device is added to a bonding device, RSS and rte flow configurations should be managed through the bonding device API, and not directly on the member.

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 member devices after they have been to a bonding device since packets read directly from the member device will no longer be available to the bonding device to read.

2.2.3. Configuration

Link bonding devices are created using the rte_eth_bond_create API 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 bonding device are its member devices, its primary member, a user defined MAC address and transmission policy to use if the device is in balance XOR mode.

2.2.3.1. Member Devices

Bonding devices support up to a maximum of RTE_MAX_ETHPORTS member devices of the same speed and duplex. Ethernet devices can be added as a member to a maximum of one bonding device. Member devices are reconfigured with the configuration of the bonding device on being added to a bonding device.

The bonding also guarantees to return the MAC address of the member device to its original value of removal of a member from it.

2.2.3.2. Primary Member

The primary member is used to define the default port to use when a bonding 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 bonding device.

2.2.3.3. MAC Address

The bonding device can be configured with a user specified MAC address, this address will be inherited by the some/all member 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 members will retain their original MAC address. In mode 0, 2, 3, 4 all members devices are configure with the bonding devices MAC address.

If a user defined MAC address is not defined then the bonding device will default to using the primary members MAC address.

2.2.3.4. Balance XOR Transmit Policies

There are 3 supported transmission policies for bonding 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 member 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 member 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 member port the packet will be transmitted on.

All these policies support 802.1Q VLAN Ethernet packets, as well as IPv4, IPv6 and UDP protocols for load balancing.

2.3. Using Link Bonding Devices

The librte_net_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.

2.3.1. Using the Poll Mode Driver from an Application

Using the librte_net_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 rte_eth_tx_queue_setup / rte_eth_rx_queue_setup.

Member devices can be dynamically added and removed from a link bonding device using the rte_eth_bond_member_add / rte_eth_bond_member_remove APIs but at least one member device must be added to the link bonding device before it can be started using rte_eth_dev_start.

The link status of a bonding device is dictated by that of its members, if all member device link status are down or if all members 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 bonding device using the provided APIs rte_eth_bond_mode_set/ get, rte_eth_bond_primary_set/get, rte_eth_bond_mac_set/reset and rte_eth_bond_xmit_policy_set/get.

2.3.2. 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 net_bonding 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:

./<build_dir>/app/dpdk-testpmd -l 0-3 -n 4 --vdev 'net_bonding0,bond_opt0=..,bond opt1=..'--vdev 'net_bonding1,bond _opt0=..,bond_opt1=..'

2.3.2.1. 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 net_bondingX 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 member device is provided with for each bonding device definition.
The operation mode of the bonding 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).

mode=2

member: Defines the PMD device which will be added as member to the bonding device. This option can be selected multiple times, for each device to be added as a member. Physical devices should be specified using their PCI address, in the format domain:bus:devid.function

member=0000:0a:00.0,member=0000:0a:00.1

primary: Optional parameter which defines the primary member port, is used in active backup mode to select the primary member 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 member added to the device if it is specified. The primary device must be a member of the bonding device.

primary=0000:0a:00.0

socket_id: Optional parameter used to select which socket on a NUMA device the bonding devices resources will be allocated on.

socket_id=0

mac: Optional parameter to select a MAC address for link bonding device, this overrides the value of the primary member device.

mac=00:1e:67:1d:fd:1d

xmit_policy: Optional parameter which defines the transmission policy when the bonding 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)

xmit_policy=l23

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

lsc_poll_period_ms=100

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.

up_delay=10

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.

down_delay=50

2.3.2.2. Examples of Usage

Create a bonding device in round robin mode with two members specified by their PCI address:

./<build_dir>/app/dpdk-testpmd -l 0-3 -n 4 --vdev 'net_bonding0,mode=0,member=0000:0a:00.01,member=0000:04:00.00' -- --port-topology=chained

Create a bonding device in round robin mode with two members specified by their PCI address and an overriding MAC address:

./<build_dir>/app/dpdk-testpmd -l 0-3 -n 4 --vdev 'net_bonding0,mode=0,member=0000:0a:00.01,member=0000:04:00.00,mac=00:1e:67:1d:fd:1d' -- --port-topology=chained

Create a bonding device in active backup mode with two members specified, and a primary member specified by their PCI addresses:

./<build_dir>/app/dpdk-testpmd -l 0-3 -n 4 --vdev 'net_bonding0,mode=1,member=0000:0a:00.01,member=0000:04:00.00,primary=0000:0a:00.01' -- --port-topology=chained

Create a bonding device in balance mode with two members specified by their PCI addresses, and a transmission policy of layer 3 + 4 forwarding:

./<build_dir>/app/dpdk-testpmd -l 0-3 -n 4 --vdev 'net_bonding0,mode=2,member=0000:0a:00.01,member=0000:04:00.00,xmit_policy=l34' -- --port-topology=chained

2.4. Testpmd driver specific commands

Some bonding driver specific features are integrated in testpmd.

2.4.1. create bonding device

Create a new bonding device:

testpmd> create bonding device (mode) (socket)

For example, to create a bonding device in mode 1 on socket 0:

testpmd> create bonding device 1 0
created new bonding device (port X)

2.4.2. add bonding member

Adds Ethernet device to a Link Bonding device:

testpmd> add bonding member (member id) (port id)

For example, to add Ethernet device (port 6) to a Link Bonding device (port 10):

testpmd> add bonding member 6 10

2.4.3. remove bonding member

Removes an Ethernet member device from a Link Bonding device:

testpmd> remove bonding member (member id) (port id)

For example, to remove Ethernet member device (port 6) to a Link Bonding device (port 10):

testpmd> remove bonding member 6 10

2.4.4. set bonding mode

Set the Link Bonding mode of a Link Bonding device:

testpmd> set bonding mode (value) (port id)

For example, to set the bonding mode of a Link Bonding device (port 10) to broadcast (mode 3):

testpmd> set bonding mode 3 10

2.4.5. set bonding primary

Set an Ethernet member device as the primary device on a Link Bonding device:

testpmd> set bonding primary (member id) (port id)

For example, to set the Ethernet member device (port 6) as the primary port of a Link Bonding device (port 10):

testpmd> set bonding primary 6 10

2.4.6. set bonding mac

Set the MAC address of a Link Bonding device:

testpmd> set bonding mac (port id) (mac)

For example, to set the MAC address of a Link Bonding device (port 10) to 00:00:00:00:00:01:

testpmd> set bonding mac 10 00:00:00:00:00:01

2.4.7. set bonding balance_xmit_policy

Set the transmission policy for a Link Bonding device when it is in Balance XOR mode:

testpmd> set bonding balance_xmit_policy (port_id) (l2|l23|l34)

For example, set a Link Bonding device (port 10) to use a balance policy of layer 3+4 (IP addresses & UDP ports):

testpmd> set bonding balance_xmit_policy 10 l34

2.4.8. set bonding mon_period

Set the link status monitoring polling period in milliseconds for a bonding device.

This adds support for PMD member devices which do not support link status interrupts. When the mon_period is set to a value greater than 0 then all PMD’s which do not support link status ISR will be queried every polling interval to check if their link status has changed:

testpmd> set bonding mon_period (port_id) (value)

For example, to set the link status monitoring polling period of bonding device (port 5) to 150ms:

testpmd> set bonding mon_period 5 150

2.4.9. set bonding lacp dedicated_queue

Enable dedicated tx/rx queues on bonding devices members to handle LACP control plane traffic when in mode 4 (link-aggregation-802.3ad):

testpmd> set bonding lacp dedicated_queues (port_id) (enable|disable)

2.4.10. set bonding agg_mode

Enable one of the specific aggregators mode when in mode 4 (link-aggregation-802.3ad):

testpmd> set bonding agg_mode (port_id) (bandwidth|count|stable)

2.4.11. show bonding config

Show the current configuration of a Link Bonding device, it also shows link-aggregation-802.3ad information if the link mode is mode 4:

testpmd> show bonding config (port id)

For example, to show the configuration a Link Bonding device (port 9) with 3 member devices (1, 3, 4) in balance mode with a transmission policy of layer 2+3:

testpmd> show bonding config 9
  - Dev basic:
     Bonding mode: BALANCE(2)
     Balance Xmit Policy: BALANCE_XMIT_POLICY_LAYER23
     Members (3): [1 3 4]
     Active Members (3): [1 3 4]
     Primary: [3]