7.7. Using Channel Bonding

Bonding Interface Parameters

ad_select=value

Specifies the 802.3ad aggregation selection logic to use. Possible values are:

• stable or 0 — Default setting. The active aggregator is chosen by largest aggregate bandwidth. Reselection of the active aggregator occurs only when all ports of the active aggregator are down or if the active aggregator has no ports.
• bandwidth or 1 — The active aggregator is chosen by largest aggregate bandwidth. Reselection occurs if:

  • A port is added to or removed from the bond;
  • Any port's link state changes;
  • Any port's 802.3ad association state changes;
  • The bond's administrative state changes to up.
• count or 2 — The active aggregator is chosen by the largest number of ports. Reselection occurs as described for the bandwidth setting above.

The bandwidth and count selection policies permit failover of 802.3ad aggregations when partial failure of the active aggregator occurs. This keeps the aggregator with the highest availability, either in bandwidth or in number of ports, active at all times.

arp_interval=time_in_milliseconds

Specifies, in milliseconds, how often ARP monitoring occurs.

Important

It is essential that both arp_interval and arp_ip_target parameters are specified, or, alternatively, the miimon parameter is specified. Failure to do so can cause degradation of network performance in the event that a link fails.

If using this setting while in mode=0 or mode=2 (the two load-balancing modes), the network switch must be configured to distribute packets evenly across the NICs. For more information on how to accomplish this, see https://www.kernel.org/doc/Documentation/networking/bonding.txt.

The value is set to 0 by default, which disables it.

arp_ip_target=ip_address[,ip_address_2,…ip_address_16]

Specifies the target IP address of ARP requests when the arp_interval parameter is enabled. Up to 16 IP addresses can be specified in a comma separated list.

arp_validate=value

Validate source/distribution of ARP probes; default is none. Other valid values are active, backup, and all.

downdelay=time_in_milliseconds

Specifies (in milliseconds) how long to wait after link failure before disabling the link. The value must be a multiple of the value specified in the miimon parameter. The value is set to 0 by default, which disables it.

fail_over_mac=value

Specifies whether active-backup mode should set all ports to the same MAC address at the point of assignment (the traditional behavior), or, when enabled, perform special handling of the bond's MAC address in accordance with the selected policy. Possible values are:

• none or 0 — Default setting. This setting disables fail_over_mac, and causes bonding to set all ports of an active-backup bond to the same MAC address at the point of assignment.
• active or 1 — The “active” fail_over_mac policy indicates that the MAC address of the bond should always be the MAC address of the currently active port. The MAC address of the ports is not changed; instead, the MAC address of the bond changes during a failover.
  This policy is useful for devices that cannot ever alter their MAC address, or for devices that refuse incoming broadcasts with their own source MAC (which interferes with the ARP monitor). The disadvantage of this policy is that every device on the network must be updated by gratuitous ARP, as opposed to the normal method of switches snooping incoming traffic to update their ARP tables. If the gratuitous ARP is lost, communication may be disrupted.
  When this policy is used in conjunction with the MII monitor, devices which assert link up prior to being able to actually transmit and receive are particularly susceptible to loss of the gratuitous ARP, and an appropriate updelay setting may be required.
• follow or 2 — The “follow” fail_over_mac policy causes the MAC address of the bond to be selected normally (normally the MAC address of the first port added to the bond). However, the second and subsequent ports are not set to this MAC address while they are in a backup role; a port is programmed with the bond's MAC address at failover time (and the formerly active port receives the newly active port's MAC address).
  This policy is useful for multiport devices that either become confused or incur a performance penalty when multiple ports are programmed with the same MAC address.

lacp_rate=value

Specifies the rate at which link partners should transmit LACPDU packets in 802.3ad mode. Possible values are:

• slow or 0 — Default setting. This specifies that partners should transmit LACPDUs every 30 seconds.
• fast or 1 — Specifies that partners should transmit LACPDUs every 1 second.

miimon=time_in_milliseconds

Specifies (in milliseconds) how often MII link monitoring occurs. This is useful if high availability is required because MII is used to verify that the NIC is active. To verify that the driver for a particular NIC supports the MII tool, type the following command as root:

~]# ethtool interface_name | grep "Link detected:"

In this command, replace interface_name with the name of the device interface, such as enp1s0, not the bond interface. If MII is supported, the command returns:

Link detected: yes

If using a bonded interface for high availability, the module for each NIC must support MII. Setting the value to 0 (the default), turns this feature off. When configuring this setting, a good starting point for this parameter is 100.

Important

It is essential that both arp_interval and arp_ip_target parameters are specified, or, alternatively, the miimon parameter is specified. Failure to do so can cause degradation of network performance in the event that a link fails.

mode=value

Allows you to specify the bonding policy. The value can be one of:

• balance-rr or 0 — Sets a round-robin policy for fault tolerance and load balancing. Transmissions are received and sent out sequentially on each bonded port interface beginning with the first one available.
• active-backup or 1 — Sets an active-backup policy for fault tolerance. Transmissions are received and sent out through the first available bonded port interface. Another bonded port interface is only used if the active bonded port interface fails.
• balance-xor or 2 — Transmissions are based on the selected hash policy. The default is to derive a hash by XOR of the source and destination MAC addresses multiplied by the modulo of the number of port interfaces. In this mode traffic destined for specific peers will always be sent over the same interface. As the destination is determined by the MAC addresses this method works best for traffic to peers on the same link or local network. If traffic has to pass through a single router then this mode of traffic balancing will be suboptimal.
• broadcast or 3 — Sets a broadcast policy for fault tolerance. All transmissions are sent on all port interfaces.
• 802.3ad or 4 — Sets an IEEE 802.3ad dynamic link aggregation policy. Creates aggregation groups that share the same speed and duplex settings. Transmits and receives on all ports in the active aggregator. Requires a switch that is 802.3ad compliant.
• balance-tlb or 5 — Sets a Transmit Load Balancing (TLB) policy for fault tolerance and load balancing. The outgoing traffic is distributed according to the current load on each port interface. Incoming traffic is received by the current port. If the receiving port fails, another port takes over the MAC address of the failed port. This mode is only suitable for local addresses known to the kernel bonding module and therefore cannot be used behind a bridge with virtual machines.
• balance-alb or 6 — Sets an Adaptive Load Balancing (ALB) policy for fault tolerance and load balancing. Includes transmit and receive load balancing for IPv4 traffic. Receive load balancing is achieved through ARP negotiation. This mode is only suitable for local addresses known to the kernel bonding module and therefore cannot be used behind a bridge with virtual machines.

For details about required settings on the upstream switch, see Section 7.6, “Overview of Bonding Modes and the Required Settings on the Switch”.

primary=interface_name

Specifies the interface name, such as enp1s0, of the primary device. The primary device is the first of the bonding interfaces to be used and is not abandoned unless it fails. This setting is particularly useful when one NIC in the bonding interface is faster and, therefore, able to handle a bigger load.

This setting is only valid when the bonding interface is in active-backup mode. See https://www.kernel.org/doc/Documentation/networking/bonding.txt for more information.

primary_reselect=value

Specifies the reselection policy for the primary port. This affects how the primary port is chosen to become the active port when failure of the active port or recovery of the primary port occurs. This parameter is designed to prevent flip-flopping between the primary port and other ports. Possible values are:

• always or 0 (default) — The primary port becomes the active port whenever it comes back up.
• better or 1 — The primary port becomes the active port when it comes back up, if the speed and duplex of the primary port is better than the speed and duplex of the current active port.
• failure or 2 — The primary port becomes the active port only if the current active port fails and the primary port is up.

The primary_reselect setting is ignored in two cases:

• If no ports are active, the first port to recover is made the active port.
• When initially assigned to a bond, the primary port is always made the active port.

Changing the primary_reselect policy through sysfs will cause an immediate selection of the best active port according to the new policy. This may or may not result in a change of the active port, depending upon the circumstances

resend_igmp=range

Specifies the number of IGMP membership reports to be issued after a failover event. One membership report is issued immediately after the failover, subsequent packets are sent in each 200ms interval.

The valid range is 0 to 255; the default value is 1. A value of 0 prevents the IGMP membership report from being issued in response to the failover event.

This option is useful for bonding modes balance-rr (mode 0), active-backup (mode 1), balance-tlb (mode 5) and balance-alb (mode 6), in which a failover can switch the IGMP traffic from one port to another. Therefore a fresh IGMP report must be issued to cause the switch to forward the incoming IGMP traffic over the newly selected port.

updelay=time_in_milliseconds

Specifies (in milliseconds) how long to wait before enabling a link. The value must be a multiple of the value specified in the miimon parameter. The value is set to 0 by default, which disables it.

use_carrier=number

Specifies whether or not miimon should use MII/ETHTOOL ioctls or netif_carrier_ok() to determine the link state. The netif_carrier_ok() function relies on the device driver to maintains its state with netif_carrier_on/off; most device drivers support this function.

The MII/ETHTOOL ioctls tools utilize a deprecated calling sequence within the kernel. However, this is still configurable in case your device driver does not support netif_carrier_on/off.

Valid values are:

• 1 — Default setting. Enables the use of netif_carrier_ok().
• 0 — Enables the use of MII/ETHTOOL ioctls.

Note

If the bonding interface insists that the link is up when it should not be, it is possible that your network device driver does not support netif_carrier_on/off.

xmit_hash_policy=value

Selects the transmit hash policy used for port selection in balance-xor and 802.3ad modes. Possible values are:

• 0 or layer2 — Default setting. This parameter uses the XOR of hardware MAC addresses to generate the hash. The formula used is:

  (source_MAC_address XOR destination_MAC) MODULO slave_count

  This algorithm will place all traffic to a particular network peer on the same port, and is 802.3ad compliant.
• 1 or layer3+4 — Uses upper layer protocol information (when available) to generate the hash. This allows for traffic to a particular network peer to span multiple ports, although a single connection will not span multiple ports.
  The formula for unfragmented TCP and UDP packets used 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 the layer2 transmit hash policy.
  This policy intends to mimic the behavior of certain switches; particularly, Cisco switches with PFC2 as well as some Foundry and IBM products.
  The algorithm used by this policy is not 802.3ad compliant.
• 2 or layer2+3 — Uses a combination of layer2 and layer3 protocol information to generate the hash.
  Uses XOR of hardware MAC addresses and IP addresses to generate the hash. The formula is:

  (((source_IP XOR dest_IP) AND 0xffff) XOR
    ( source_MAC XOR destination_MAC ))
      MODULO slave_count

  This algorithm will place all traffic to a particular network peer on the same port. For non-IP traffic, the formula is the same as for the layer2 transmit hash policy.
  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.
  This algorithm is 802.3ad compliant.