Unicast private address can not be forwarded to the external network, private multicast address that is local multicast address may be forwarded to the external network.
A local area network sending host before checking whether the destination IP unicast message and the machine in the same network segment,
If the same network, it broadcasts an ARP query packet present in the destination IP LAN MAC address, and then transmits the MAC address information obtained in the communication so that the same does not pass through a router in the network, will not be forwarded to the external network.
A host sends a multicast message LAN, no matter what the address is sent, the LAN gateway router will receive, in PIM sparse mode, the router will send a multicast packet to a neighbor PIM router; if there are local network segment multicast member of the destination multicast address, the router will also send a copy of each multicast packet to multicast group members.
