In
telecommunication networks, a bridge is a product that connects
a local area network (LAN) to another local area network
that uses the same protocol (for example, Ethernet or Token
Ring). You can envision a bridge as being a device that
decides whether a message from you to someone else is going
to the local area network in your building or to someone
on the local area network in the building across the street.
A bridge examines each message on a LAN, "passing"
those known to be within the same LAN, and forwarding those
known to be on the other interconnected LAN (or LANs).
In bridging networks, computer or node addresses have no
specific relationship to location. For this reason, messages
are sent out to every address on the network and accepted
only by the intended destination node. Bridges learn which
addresses are on which network and develop a learning table
so that subsequent messages can be forwarded to the right
network.
Bridging
networks are generally always interconnected local area
networks since broadcasting every message to all possible
destinations would flood a larger network with unnecessary
traffic. For this reason, router networks such as the Internet
use a scheme that assigns addresses to nodes so that a message
or packet can be forwarded only in one general direction
rather than forwarded in all directions.
A
bridge works at the data-link (physical network) level of
a network, copying a data frame from one network to the
next network along the communications path.
A
bridge is sometimes combined with a router in a product
called a brouter.
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