This setting controls whether the device forwards IP directed broadcast datagrams, i.e., packets addressed to the broadcast address of a remote subnet rather than the local one, a behavior governed by RFC2644 largely for security reasons since directed broadcasts have historically been abused in smurf-style denial-of-service amplification attacks. An administrator typically leaves this set to notForwarding on internet-facing or untrusted interfaces to close off that amplification vector, while some internal networks might still rely on directed broadcast forwarding for legacy applications. For example, a router with this set to notForwarding(2) on its WAN interface will silently drop, rather than forward, any inbound packet addressed to a remote subnet's broadcast address.