Quick algorithm description:
round-robin forwarders are assigned to hosts in strict rotation in the order that ARP requests are received by the active virtual gateway.
This is the default setting when this command is not configured.
host-dependant the forwarder chosen for a particular host will remain the same while the number of virtual forwarders does not change.
The choice is made based on the host's MAC address, so equal load balancing depends on a random distribution of host MAC addresses.
weighted the proportion of hosts that are assigned to each forwarder depends on the weighting of each forwarder.
A higher forwarder weighting means the forwarder's MAC address will be used in a higher proportion of the ARP replies.
The default load balancing method is round-robin.
When a host sends an ARP request for the virtual router's IP address, the active virtual gateway responds with the virtual MAC address of one of the virtual forwarders. The MAC address used will be chosen by the active virtual gateway to keep the load over the virtual forwarders balanced as determined by the selected method. Although the packets from a single host on the LAN will be processed by a single virtual forwarder, the load from all the hosts on the LAN will be balanced among all the virtual forwarders. When a host refreshes its ARP cache, the active virtual gateway may reassign it to a different virtual forwarder to keep the load over the forwarders balanced.
The method of load balancing can be disabled, in which case only the active gateway forwards packets and all other routers simply wait to take over if the active gateway fails. With the default method of load balancing, ARP replies will cycle through all the virtual MAC addresses in turn. The second method of load balancing is host-dependent, in which the virtual MAC address used in the ARP reply is chosen based on the MAC address of the requesting host. As a result, the host on the LAN will always direct packets through the same forwarder while the number of available
forwarders remains the same. Finally, the third method of load balancing is weighted load balancing, where the percentage of ARP replies using the MAC address of a particular forwarder will be proportional to that router's weighting.
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