One of the primary functions of a switch is to forward packets to the correct next hop. This necessitates knowing the unique MAC addresses of all connected hosts and switches to a network interface. In dynamic environments like campus networks, the hosts often come and go, which means the number of connected hosts that the switch knows about expands continuously. Therefore, it becomes necessary to have a mechanism for the switch to eventually discard information about MAC addresses that are no longer active in the network. 

When multiple IPv6 addresses are assigned to an interface, the source address selection is based on the rules in RFC6724. However, when the matching criteria is the same for all addresses, the selection address depends on the Kernel, which is likely to be the address that is added last. This feature allows addresses to be configured as least preferred so that source addresses can be selected in a more deterministic manner.