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Switch Operation Overview
Address Table Operation
Address Learning. As devices are connected to the switch ports, either
directly or through hubs or other switches, the MAC addresses of those
devices are learned automatically and stored in the 4096-entry address table
featured by the SMC6624M. The switch also identifies the number of the port
on which each address is learned so they know the network location of each
connected device.
Forwarding, Filtering, Flooding. When the switch receives a packet, it
determines the destination address and looks for the address in the address
table. Based on the port location of that address, the switch then determines
whether to forward, filter-out, or flood the packet.
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forward - if the destination address is on a different port than the one on
which the packet was received, the packet is forwarded to the destination
port and on to the destination device.
filter out - if the destination address is on the same port as the one on
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which the packet was received, the packet is filtered out. The switch
thereby isolates local traffic so the rest of the network connected to the
switch does not lose bandwidth dealing with unnecessary traffic.
flood - whenever a new destination address is found in a packet received
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on a switch port, the destination address will not yet be in the switch's
address table and the switch cannot know whether to forward or filter out
the packet. In this case, it sends the packet to all the other switch ports.
This is referred to as "flooding". When the destination device receives the
packet, and it replies, the switch learns the new address from the reply
packet. Then, all future packets destined for that address are forwarded
or filtered out appropriately.
Note: Usually, multicast and broadcast packets are flooded, although
configuration of sofware features influence that behavior.
Introducing the TigerSwitch 10/100 SMC6624M
Switch Operation Overview
1-7
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