Allied-telesis AT-8326GB Manuel d'utilisateur télécharger pdf (Page 36)

AT-8326GB Installation Guide

A Few Basics to Ethernet Switching

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 AT-8326GB Fast Ethernet switch contains an 8,000 entry MAC

address table. 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 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 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 packet to the appropriate port where 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, increasing 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.

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Allied-telesis AT-8326GB Manuel d'utilisateur Page 36

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