This object controls whether ARP forwards requests for addresses it doesn't recognize on to the bridge for further handling, equivalent to an IP Host Only mode when set otherwise. Setting it to forwarding, the default, lets unresolved ARP requests fall through to bridging, which matters on a router that's also acting as a bridge for non-routed traffic; setting notforwarding restricts the device to pure IP-host ARP behavior. An admin configuring the router to strictly act as an IP host without bridging unknown traffic would set this object to notforwarding(2).