Forwarding is the relaying of packets from one network segment to another by nodes in a packet switched computer network.
The simplest forwarding model - unicasting - involves a packet being relayed from link to link along a chain leading from the packet's source to its destination. However, other forwarding strategies are commonly used. Broadcasting requires a packet to be duplicated and copies sent on multiple links with the goal of delivering a copy to every device on the network. In practice, broadcast packets are not forwarded everywhere on a network, but only to devices within a broadcast ___domain. Less common than broadcasting, but perhaps of greater utility and theoretical signicicance is multicasting, where a packet is selectively duplicated and copies delivered to each of a set of recipients.
At nodes where multiple outgoing links are available, the choice of which, all, or any to use requires a decision making process that, while simple in concept, is of sometimes bewildering complexity. Since a forwarding decision must be made for every packet handled by a node, the total time required for this can become a major limiting factor in the overall performance of a packet-switched network. Much of the design effort of high-speed routers has been focused on making rapid forwarding decisions for large numbers of packets.
The forwarding decision is generally made using one of two processes: routing, which uses information encoded in a device's address to infer its ___location on the network, or bridging, which makes no assumptions about where addresses are located and depends heavily on broadcasting to located unknown addresses. The heavy overhead of broadcasting has led to the dominance of routing in large networks, particuarly the Internet; bridging is largely relegated to small networks where the overhead of broadcasting is tolerable. However, since large networks are usually composed of many smaller networks linked together, it would be inaccurate to state that bridging has no use on the Internet; rather, its use is localized.