31.8. Specific Kernel Module Capabilities

Bonding Interface Parameters

arp_interval=<time_in_milliseconds>

Specifies (in milliseconds) how often ARP monitoring occurs. When configuring this setting, a good starting point for this parameter is 1000.

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 the bonding.txt file in the kernel-doc package (see Section 31.9, “Additional Resources”).

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.

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 eth0, 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 slave 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 via the first available bonded slave interface. Another bonded slave interface is only used if the active bonded slave interface fails.
• balance-xor or 2 — Sets an XOR (exclusive-or) policy for fault tolerance and load balancing. Using this method, the interface matches up the incoming request's MAC address with the MAC address for one of the slave NICs. Once this link is established, transmissions are sent out sequentially beginning with the first available interface.
• broadcast or 3 — Sets a broadcast policy for fault tolerance. All transmissions are sent on all slave 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 slaves 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 slave interface. Incoming traffic is received by the current slave. If the receiving slave fails, another slave takes over the MAC address of the failed slave. 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.

num_unsol_na=<number>

Specifies the number of unsolicited IPv6 Neighbor Advertisements to be issued after a failover event. One unsolicited NA is issued immediately after the failover.

The valid range is 0 - 255; the default value is 1. This parameter affects only the active-backup mode.

primary=<interface_name>

Specifies the interface name, such as eth0, 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 the bonding.txt file in the kernel-doc package (see Section 31.9, “Additional Resources”).

primary_reselect=<value>

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

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

The primary_reselect setting is ignored in two cases:

• If no slaves are active, the first slave to recover is made the active slave.
• When initially enslaved, the primary slave is always made the active slave.

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

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/ETHROOL 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 slave 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 slave, 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 slaves, although a single connection will not span multiple slaves.
  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 slave. 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.