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Appendix D. Bonding Options

You can bundle multiple physical NICs together to form a single logical channel known as a bond. Bonds can be configured to provide redundancy for high availability systems or increased throughput.

D.2. Open vSwitch Bonding Options

The Overcloud provides networking through Open vSwitch (OVS). The following table describes support for OVS kernel and OVS-DPDK for bonded interfaces. The OVS/OVS-DPDK balance-tcp mode is available as a technology preview only.


The bonding options described in the following table require OVS 2.9 or later.

OVS Bond mode



Compatible LACP options


High availability (active-passive)


active, passive, or off


Increased throughput (active-active)

  • Performance is affected by extra parsing per packet.
  • There is a potential for vhost-user lock contention.

active, passive, or off

balance-tcp (tech preview only )

Not recommended (active-active)

  • Recirculation needed for L4 hashing has a performance impact.
  • As with balance-slb, performance is affected by extra parsing per packet and there is a potential for vhost-user lock contention.
  • LACP must be enabled.

active or passive

You can configure a bonded interface in the network environment file using the BondInterfaceOvsOptions parameter as shown in this example:

  BondInterfaceOvsOptions: "bond_mode=balance-slb"

D.3. Considerations for balance-tcp Mode

If you decide to use balance-tcp mode despite its tech preview status and the known performance issues, you must manually delete the following lines from each network interface configuration (NIC) file before deployment:

      - allowed_pattern: "^((?!balance.tcp).)*$"
        description: |
          The balance-tcp bond mode is known to cause packet loss and
          should not be used in BondInterfaceOvsOptions.

After you delete the constraint from each NIC file, you can set the bond mode option in the bond interface parameter:


D.4. Linux Bonding Options

You can use LACP with Linux bonding in your network interface templates. For example:

      - type: linux_bond
        name: bond1
        - type: interface
          name: nic2
        - type: interface
          name: nic3
        bonding_options: "mode=802.3ad lacp_rate=[fast|slow] updelay=1000 miimon=100"
  • mode - enables LACP.
  • lacp_rate - defines whether LACP packets are sent every 1 second, or every 30 seconds.
  • updelay - defines the minimum amount of time that an interface must be active before it is used for traffic (this helps mitigate port flapping outages).
  • miimon - the interval in milliseconds that is used for monitoring the port state using the driver’s MIIMON functionality.

For more information on Linux bonding options, see 4.5.1. Bonding Module Directives in the Red Hat Enterprise Linux 7 Networking Guide.

D.5. Bonding Options

The following table provides some explanation of these options and some alternatives depending on your hardware.

Table D.1. Bonding Options


Balances flows based on source MAC address and output VLAN, with periodic rebalancing as traffic patterns change. Bonding with balance-slb allows a limited form of load balancing without the remote switch’s knowledge or cooperation. SLB assigns each source MAC and VLAN pair to a link and transmits all packets from that MAC and VLAN through that link. This mode uses a simple hashing algorithm based on source MAC address and VLAN number, with periodic rebalancing as traffic patterns change. This mode is similar to mode 2 bonds used by the Linux bonding driver.


This mode offers active/standby failover where the standby NIC resumes network operations when the active connection fails. Only one MAC address is presented to the physical switch. This mode does not require any special switch support or configuration, and works when the links are connected to separate switches. This mode does not provide load balancing.


Controls the Link Aggregation Control Protocol (LACP) behavior. Only certain switches support LACP. If your switch does not support LACP, use bond_mode=balance-slb or bond_mode=active-backup.


Sets the LACP behavior to switch to bond_mode=active-backup as a fallback.


Set the LACP heartbeat to 1 second (fast) or 30 seconds (slow). The default is slow.


Set the link detection to use miimon heartbeats (miimon) or monitor carrier (carrier). The default is carrier.


If using miimon, set the heartbeat interval in milliseconds.


Number of milliseconds a link must be up to be activated to prevent flapping.


Milliseconds between rebalancing flows between bond members. Set to zero to disable.