Allied Telesis AT-S68 - Manual (Page 72)

System Configuration
72
MAC Address Overview
Every hardware device that you connect to your network has an unique
MAC address. A MAC address is assigned to a device by the device’s
manufacturer. For example, every network interface card that you use to
connect your computers to your network has a MAC address assigned to
it by the adapter’s manufacturer.
The AT-FS7000 Series Switch’s MAC address table can contain up to 4
kilobytes. The switch uses the table to store the MAC addresses of the
network end-nodes connected to its ports, along with the port number
on which each address was learned.
The 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 address 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 numbers 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
where the destination end-node is connected. It then forwards the
packet to the appropriate port and onto 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 onto inappropriate LAN segments and increases network
security. When the destination end-node responds, the switch add 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. This also increases network performance by preventing frames
from being forwarded unnecessarily to other network devices.