A multicast address is formed by modifying the manufacturer ID portion of the destination address. A broadcast address is an address that is meant to be heard by all stations on the network. A router is a Network Layer and Transport Layer device. It is an intelligent device that makes decisions about traffic flow based on packet content. Routers can be used to connect local area networks to other local area networks and also to wide are networks.
Routers determine the best way to route traffic, automatically, in heavily used networks.
When it is necessary to connect totally dissimilar networks a getaway is used. Gateways can be thought of as protocol converters and is protocol specific.