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There are times when it is necessary to break up a large
LAN into smaller, more easily managed segments. This
decreases the amount of traffic on a single LAN and can
extend the geographical area past what a single LAN can
support. The devices that are used to connect network
segments together include bridges, switches, routers,
and gateways. Switches and bridges operate at the Data
Link layer of the OSI model. The function of the bridge
is to make intelligent decisions about whether or not to
pass signals on to the next segment of a network. |
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When a bridge receives a frame on the network, the
destination MAC address is looked up in the bridge table
to determine whether to filter, flood, or copy the frame
onto another segment. This decision process occurs as
follows:
• Flooding: If the destination address is unknown to the
bridge, the bridge forwards the frame to all segments
except the one on which it was received. This process is
known as flooding.
• Forwarding: If the destination device is on a
different segment, the bridge connects the two segments
to send the frame to the appropriate segment. This
process is called forwarding.
• Filtering: If the destination device is on the same
segment as the frame, the bridge blocks the frame from
going on to other segments. This process is known as
filtering.
If placed strategically, a bridge can greatly improve
network performance. |
