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A bond is an aggregation of multiple network interface cards into a single software-defined device. Because bonded network interfaces combine the transmission capability of the network interface cards included in the bond to act as a single network interface, they can provide greater transmission speed than that of a single network interface card. Also, because all network interface cards in the bond must fail for the bond itself to fail, bonding provides increased fault tolerance. However, one limitation is that the network interface cards that form a bonded network interface must be of the same make and model to ensure that all network interface cards in the bond support the same options and modes.
The packet dispersal algorithm for a bond is determined by the bonding mode used.
Modes 1, 2, 3 and 4 support both virtual machine (bridged) and non-virtual machine (bridgeless) network types. Modes 0, 5 and 6 support non-virtual machine (bridgeless) networks only.
Red Hat Virtualization uses Mode 4 by default, but supports the following common bonding modes:
Mode 0 (round-robin policy)
- Transmits packets through network interface cards in sequential order. Packets are transmitted in a loop that begins with the first available network interface card in the bond and end with the last available network interface card in the bond. All subsequent loops then start with the first available network interface card. Mode 0 offers fault tolerance and balances the load across all network interface cards in the bond. However, Mode 0 cannot be used in conjunction with bridges, and is therefore not compatible with virtual machine logical networks.
Mode 1 (active-backup policy)
- Sets all network interface cards to a backup state while one network interface card remains active. In the event of failure in the active network interface card, one of the backup network interface cards replaces that network interface card as the only active network interface card in the bond. The MAC address of the bond in Mode 1 is visible on only one port to prevent any confusion that might otherwise be caused if the MAC address of the bond changed to reflect that of the active network interface card. Mode 1 provides fault tolerance and is supported in Red Hat Virtualization.
Mode 2 (XOR policy)
- Selects the network interface card through which to transmit packets based on the result of an XOR operation on the source and destination MAC addresses modulo network interface card slave count. This calculation ensures that the same network interface card is selected for each destination MAC address used. Mode 2 provides fault tolerance and load balancing and is supported in Red Hat Virtualization.
Mode 3 (broadcast policy)
- Transmits all packets to all network interface cards. Mode 3 provides fault tolerance and is supported in Red Hat Virtualization.
Mode 4 (IEEE 802.3ad policy)
- Creates aggregation groups in which the interfaces share the same speed and duplex settings. Mode 4 uses all network interface cards in the active aggregation group in accordance with the IEEE 802.3ad specification and is supported in Red Hat Virtualization.
Mode 5 (adaptive transmit load balancing policy)
- Ensures the distribution of outgoing traffic accounts for the load on each network interface card in the bond and that the current network interface card receives all incoming traffic. If the network interface card assigned to receive traffic fails, another network interface card is assigned to the role of receiving incoming traffic. Mode 5 cannot be used in conjunction with bridges, therefore it is not compatible with virtual machine logical networks.
Mode 6 (adaptive load balancing policy)
- Combines Mode 5 (adaptive transmit load balancing policy) with receive load balancing for IPv4 traffic without any special switch requirements. ARP negotiation is used for balancing the receive load. Mode 6 cannot be used in conjunction with bridges, therefore it is not compatible with virtual machine logical networks.