Allied-telesis AT-GS900/8E User Manual download pdf (Page 17)

AT-GS900/xE Gigabit Ethernet Switch Installation Guide

A Few 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-GS900/xE switches can store up to 8K

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 had

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 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 into

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 on the

switch, there is no reason for the switch to forward the packet.

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Allied-telesis AT-GS900/8E User Manual Page 17