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Unit 5: Operations of Network
Notes
Figure 5.16
5.4.3 Bridges
A network bridge connects multiple network segments at the data link layer (layer 2) of the
OSI model. Bridges broadcast to all ports except the port on which the broadcast was received.
However, bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which MAC
addresses are reachable through specific ports. Once the bridge associates a port and an address,
it will send traffic for that address to that port only.
Bridges learn the association of ports and addresses by examining the source address of frames
that it sees on various ports. Once a frame arrives through a port, its source address is stored and
the bridge assumes that MAC address is associated with that port. The first time that a previously
unknown destination address is seen, the bridge will forward the frame to all ports other than
the one on which the frame arrived.
Figure 5.17: A Bridge in OSI Model Layer
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