Each interface object is allocated a MAC, keyed by the port group and VLAN tag of the interface. This is used for dynamic IPv6 allocation on the interface using router announcements (RA) as well as OSPF and any other interface specific uses that are not related to a subnet.

Each subnet object is allocated a MAC, which is used for all of the IPs listed in that subnet object. This allows many IPs to have the same MAC by listing them in the same subnet object. The MAC allocation is keyed on the port group and VLAN tag and the first listed IP address in the subnet. If a later subnet has the same first IP listed then this is allocated a separate MAC (i.e. the key for the MAC is also based on which instance of this specific first IP it is, 1st, 2nd, 3rd, within the interface).

DCHP client subnets work in much the same way - they are based on the port group and VLAN tag and which instance of DHCP client they are (1st, 2nd, 3rd, etc) within the interface. The special case for DHCP clients is that the first of these within an interface is given the same MAC as the interface itself.

Each PPPoE object is given a MAC. This is keyed on the port group and VLAN and works in the same way as if it was a DHCP client subnet in a corresponding interface. i.e. where there is an interface with same port group and VLAN the PPPoE object gets the interface MAC.

The allocations are recorded in persistent data, so if an object is removed from the config and later put back it should get the same MAC address. If however there are not enough MAC addresses when loading a config, then previous assignments are re-used. If there are too many interface, subnet and ppp objects within the config to allocate MAC addresses (even reusing old allocations) then an error is given and the config cannot be loaded.