Allied Telesis AT-GS900/8 - Manual (Page 23)

AT-GS900/8 Gigabit eco-friendly Ethernet Switches Installation Guide
23
Ethernet Switching Basics
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
Every hardware device on your network has a unique MAC address. This
address is assigned to the 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.
The AT-GS900/8 can store up to 8000 MAC addresses in its MAC address
table. Each 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
has 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 to the end-node. This increases network
bandwidth by limiting each frame to the appropriate port where 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.
When the destination end-node responds, the switch adds its MAC
address and port number to the table.
If the switch receives a packet with a destination address that is on the
same port on which the packet was received, it discards the packet without
forwarding it on to any port. Since both the source end-node and the
destination end-node for the packet are located on the same port on the
switch, there is no reason for the switch to forward the packet.
Duplex Mode
Duplex mode refers to how an end-node receives and transmits data. If an
end-node can either receive or transmit data, but not both simultaneously,
the end-node is operating in what is referred to as half-duplex mode. If an