Bridge
A bridge is a data communication device that connects two or
more segments of data communication networks by forwarding packets between them.
The bridge operates as a physical connector and buffer between similar types of
networks.
Bridges extend the reach of the LAN from one segment to another.
Bridges have memory that allows them to store and forward packets. Bridges are
protocol independent as the do not perform protocol adaptations.
Bridges contain a packet address-forwarding table (routing table)
that they use to determine if the packets should be forwarded between networks.
A network administrator may initially program the packet-forwarding table or it
can be programmed through the discovery of packet addresses ( self-learned) that
are received by the bridge. A self-learning bridge monitors the packet traffic
in the network to continually update its packet-forwarding table.
Bridges primarily operate at the physical layer and link layers of
the OSI reference model. A bridge receives packets from one network, review the
address of the packet to determine if it should be routed to the other
network(s) it is connected to, and retransmits the packet following the standard
protocol rules for the systems it is connected to.
Figure 10 shows the
basic operation of a bridge that is connecting 3 segments of a LAN network.
Segment 1 of the LAN has addresses 101 through 103, segment 2 of the LAN has
addresses 201 through 203, and segment 3 of the LAN has addresses 301 through
303. The table contained in the bridge indicates the address ranges that should
be forwarded to specific ports. This diagram shows a packet that is received
from LAN segment 3 that contains the address 102 will be forwarded to LAN
segment 1. When a data packet from computer 303 contains the address 301, the
bridge will receive the packet but the bridge will ignore (not forward) the
packet.
Sections
