Option fail_over_mac

The fail_over_mac option is only valid when a bonding is set with active-backup mode. There are three possible values:

none (0)

The default value is none (0). However, this setting disables fail_over_mac and sets all of the slaves to the same MAC address. In a typical network environment on Linux on Z, active-backup bonds are set up with shared OSA adapters on layer 2 mode. In this case, without fail_over_mac the bonds may not work as expected, and packets will be directed to the inactive slaves. Therefore the value none (0) should not be used.

active (1)

With the value active (1), the bond master’s MAC address is always the MAC address of the active slave. If the slave is changed during a failover, the bond’s MAC address is then changed to match the new active slave. Always set fail_over_mac to the value active (1); this is especially important for the scenario of using shared OSA adapters (see Figure 2).

Note: During a failover, every device on the network must be updated via gratuitous ARP broadcasting the update of the bond’s MAC address. If the gratuitous APR is lost, the communication might be disrupted. However, considering that failover rarely happens and in most cases the gratuitous ARP is reliable, this should not prevent you from using the value active.

follow (2)

The value follow (2) specifies the fail_over_mac policy that during a failover, the active slave will get the MAC address of the bond and the formerly active slave receives the newly active slave’s MAC address. This is not recommended for Linux on Z.

Figure 1. Bonding option fail_over_mac