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Red Hat Enterprise Linux - What is the fail_over_mac Bonding Option?


In active backup bonding mode, the mac address of the bond interface is typically set to that of the first active slave interface. The bonding option fail_over_mac can change this behavior. It is set in the BONDING_OPTS parameter in the file /etc/sysconfig/network-scripts/ifcfg-bondx file.


The original default behavior is to set all slaves to the same mac address as that of the first active slave interface. But if the fail_over_mac is specified, it can be one of three settings: none which is the default setting "none", the other two are "active" or "follow".

none or 0:

This setting disables fail_over_mac, and causes bonding to set all slaves of an active-backup bond to the same MAC address at enslavement time. This is the default, and original behavior.

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 slave. The MAC address of the slaves 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 down side of this policy is that every device on the network must be updated via gratuitous ARP, vs. just updating a switch or set of switches (which often takes place for any traffic, not just ARP traffic, if the switch snoops incoming traffic to update its tables) for the traditional method. 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.

An appropriate updelay setting may also be required if the switch has a forward delay period that might prevent the gratitous arp from being forwarded.

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 slave added to the bond). However, the second and subsequent slaves are not set to this MAC address while they are in a backup role; a slave is programmed with the bond's MAC address at failover time (and the formerly active slave receives the newly active slave'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. Some switch security features such as the Cisco switch port security may have to configured so that the mac address moving to another port does not trigger a security lockout.

Legal Disclaimer: Products sold prior to the November 1, 2015 separation of Hewlett-Packard Company into Hewlett Packard Enterprise Company and HP Inc. may have older product names and model numbers that differ from current models.

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Document title: Red Hat Enterprise Linux - What is the fail_over_mac Bonding Option?
Document ID: emr_na-c02695249-3
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