Allied Telesis AT-8088/xx (MT and SC) - Manual (Page 39)

AT-8000 Series Fast Ethernet Switches Installation Guide
39
A Few Basics about Ethernet Switching
An Ethernet switch interconnects network devices, such as workstations,
printers, routers, and other Ethernet switches, so that they can
communicate with each other by sending and receiving Ethernet
frames.
MAC Address
Table
Most of the hardware devices on your network have a unique MAC
address. This address is assigned to a device by the device’s
manufacturer. For example, when you install a Network Interface Card
(NIC) in a computer so that you can connect it to the network, the NIC
already has a MAC address assigned to it by its manufacturer.
An AT-8000 Series Fast Ethernet Switch has a MAC address table of
4 kilobytes. The switch uses the table to store the MAC addresses of the
network end-nodes connected to the ports, along with the port number
on which each address was learned.
A switch learns the MAC addresses of the end-nodes by examining the
source address of each packet received on a port. It adds the address
and port on which the packet was received to the MAC table if the
address had not already been entered in the table. The result is a table
that contains all the MAC addresses of the devices that are connected to
the switch’s ports, and the port number where each address was
learned.
When the switch receives a packet, it also examines the destination
address and, by referring to its MAC address table, determines the port
on which the destination end-node is connected. It then forwards the
packet to the appropriate port and on to the end-node. This increases
network bandwidth by limiting each frame to the appropriate port when
the intended end-node is located, freeing the other switch ports for
receiving and transmitting data.
If the switch receives a packet with a destination address that is not in
the MAC address table, it floods the packet to all the ports on the switch.
If the ports have been grouped into virtual LANs, the switch floods the
packet only to those ports which belong to the same VLAN as the port
on which the packet was received. This prevents packets from being
forwarded into inappropriate LAN segments, increasing network
security. When the destination an end-node responds, the switch adds
its MAC address and port number to the table.