Linux bonding provides a method for aggregating multiple network interfaces (slaves) into a single logical bonded interface (bond). Cumulus Linux supports two bonding modes:
- The IEEE 802.3ad link aggregation mode, which allows one or more links to be aggregated together to form a link aggregation group (LAG), such that a media access control (MAC) client can treat the link aggregation group as if it were a single link.
- The balance-xor mode, where the bonding of slave interfaces are static and all slave interfaces are active for load balancing and fault tolerance purposes. This is useful for MLAG deployments.
The benefits of link aggregation include:
- Linear scaling of bandwidth as links are added to LAG
- Load balancing
- Failover protection
Cumulus Linux uses version 1 of the LAG control protocol (LACP).
To temporarily bring up a bond even when there is no LACP partner, use LACP Bypass.
Egress traffic through a bond is distributed to a slave based on a packet hash calculation, providing load balancing over the slaves; many conversation flows are distributed over all available slaves to load balance the total traffic. Traffic for a single conversation flow always hashes to the same slave.
The hash calculation uses packet header data to pick which slave to transmit the packet to:
- For IP traffic, IP header source and destination fields are used in the calculation.
- For IP + TCP/UDP traffic, source and destination ports are included in the hash calculation.
In a failover event, the hash calculation is adjusted to steer traffic over available slaves.
Creating a Bond
Bonds can be created and configured using the Network Command Line Utility (NCLU). Follow the steps below to create a new bond:
SSH into the switch.
Add a bond using the
net add bondcommand, replacing
[bond-name]with the name of the bond, and
[slaves]with the list of slaves:
The name of the bond must be:
Compliant with Linux interface naming conventions.
Unique within the switch.
The configuration options, and their default values, are listed in the table below.
bond slaves,is set to the recommended value by default in Cumulus Linux. They should only be configured if a different setting is needed. For more information on configuration values, refer to the Related Information section below.
|NCLU Configuration Option|
The defined bonding mode.
Cumulus Linux supports IEEE 802.3ad link aggregation mode and balance-xor mode. You should use balance-xor mode only if you cannot use LACP for some reason. See below for more information.
|The list of slaves in the bond.||N/A|
|Defines how often the link state of each slave is inspected for failures.|
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.
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.
|Determines the link state.|
Hash method used to select the slave for a given packet.
This setting must not be changed.
|Enables LACP bypass.||N/A|
Sets the rate to ask the link partner to transmit LACP control packets.
You can set the LACP rate to slow using NCLU:
Defines the minimum number of links that must be active before the bond is put into service.
A value greater than
Enabling balance-xor Mode
When you enable balance-xor mode, the bonding of slave interfaces are static and all slave interfaces are active for load balancing and fault tolerance purposes. Packet transmission on the bond is based on the hash policy specified by
When using balance-xor mode to dual-connect host-facing bonds in an MLAG environment, the
clag_id parameter must be configured on the MLAG bonds and must be the same on both MLAG switches. Otherwise, the bonds are treated by the MLAG switch pair as if they were single-connected.
You should use balance-xor mode only if you cannot use LACP for some reason, as LACP can detect mismatched link attributes among bond members and can even detect misconnections.
In order to change the mode of an existing bond, you must first delete the bond, then recreate it with the balance-xor mode. Assuming the bond doesn't exist on the host, you can configure it as follows:
These commands create the following configuration in the
To view the bond, use NCLU:
Example Configuration: Bonding 4 Slaves
In the following example, the front panel port interfaces swp1-swp4 are slaves in bond0, while swp5 and swp6 are not part of bond0.
Example Bond Configuration
The following commands create a bond with four slaves:
These commands create this code snippet in the
If you are intending that the bond become part of a bridge, you don't need to specify an IP address.
When networking is started on switch, bond0 is created as MASTER and interfaces swp1-swp4 come up in SLAVE mode, as seen in the
ip link show command:
All slave interfaces within a bond have the same MAC address as the bond. Typically, the first slave added to the bond donates its MAC address as the bond MAC address, while the other slaves’ MAC addresses are set to the bond MAC address.
The bond MAC address is used as source MAC address for all traffic leaving the bond, and provides a single destination MAC address to address traffic to the bond.
Caveats and Errata
- An interface cannot belong to multiple bonds.
A bond can have subinterfaces, but not the other way around.
- A bond cannot enslave VLAN subinterfaces.
- Slave ports within a bond should all be set to the same speed/duplex, and should match the link partner’s slave ports.