Allied Telesis AT-S62 - Manual (Page 109)

AT-S62 Menus Interface User’s Guide
Section I: Basic Operations 109
MAC Address Overview
The AT-8500 Series switch contains a MAC address table with a storage
capacity of 8,000 entries. 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 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 is not already in the table. The result is a table that contains all
the MAC addresses of the devices 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
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 packets.
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 where 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.
The type of MAC address described above is referred to as a dynamic
MAC address. Dynamic MAC addresses are addresses that the switch
learns by examining the source MAC addresses of the frames received
on the ports.
Dynamic MAC addresses are not stored indefinitely in the MAC address
table. The switch deletes a dynamic MAC address from the table if it does
not receive any frames from the node after a specified period of time.
The switch assumes that the node with that MAC address is no longer
active and that its MAC address can be purged from the table. This