User's Manual

SME VoIP System Guide, Version 1.5
Proprietary and Confidential
Chapter: VLAN Setup Management
78
The physical location of an end station does not define its LAN boundary.
1. An end station can be physically moved from one switch port to another without losing
its “view of the network”. That is, the set of stations it can communicate with at the
Data Link Layer remains the same, provided that its VLAN membership is also migrated
from port to port.
2. By reconfiguring the VLAN membership of the switch port an end station is attached to,
you can change the network view of the end station easily, without requiring a physical
move from port to port.
12.2 Backbone/ VLAN Aware Switches
To implement a VLAN in your network, you must use VLAN-aware switches.
Before we continue, let consider two rules to remember regarding the functioning of a regular
LAN switch:
1. When the switch receives a broadcast or multicast frame from a port, it floods (or
broadcasts) the frame to all other ports on the switch.
2. When the switch receives a unicast frame, it forwards it only to the port to which it is
addressed.
A VLAN-aware switch changes the above two rules as follows:
1. When the switch receives a broadcast or multicast frame from a port, it floods the frame to
only those ports that belong to the same VLAN as the frame.
2. When a switch receives a unicast frame, it forwards it to the port to which it is addressed,
only if the port belongs to the same VLAN as the frame.
3. A unique number called the VLAN ID identifies each VLAN.
Which VLAN Does a Frame Belong To?
The previous section notes that a frame can belong to a VLAN. The next question is—how is this
association made?
A VLAN-aware switch can make the association based on various attributes of the type of
frame, destination of MAC address, IP address, TCP port, Network Layer protocol, and so
on.