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''Forwarding'' is the relaying of packets from one network link to another by [[node (networking)|nodes]]
in a [[packet switching|packet switched]] [[computer network]].
The simplest forwarding model - [[unicast|unicasting]] - involves a packet being
relaying from link to link along a chain lead from the packet's
source to its destination. However, other forwarding strategies
are commonly using. 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.
Less common than broadcasting, but perhaps of greater
utility and theorical signicicance is [[multicast|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.
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