Allied Telesis AT-GS950/8 - Manual (Page 22)

Chapter 1: Overview
22
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 MAC address table in the AT-GS950/8 switch can store up to 4K of
MAC addresses. 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 is
not already 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 to
inappropriate LAN segments, decreasing network security. 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,
there is no reason for the switch to forward the packet.