Allied Telesis AT-S25 - Manual (Page 147)

AT-S25 Management Software User’s Guide
147
MAC Address Overview
The AT-8300 Series switch has a MAC address table up to 12K in size. The
switch uses the table to store the MAC addresses of the network nodes
connected to its ports, along with the port number on which each
address was learned.
The devices that you connect to your network have a 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 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 a switch receives a packet, it also examines the destination
address and, by referring to its MAC Address Table, determines the port
where the destination 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 onto inappropriate LAN segments and increases
network security. When the destination 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 node and the
destination 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 too
increases network performance by preventing frames from being
forwarded unnecessarily to other network devices.