Panasonic NN46240-502 - Manual (Page 63)

4 VLAN configuration
Nortel Secure Router 8000 Series
Configuration - LAN Access and MAN Access
Isolating broadcast areas
To reduce broadcast, isolate hosts that do not need to access each other. To achieve this, you
can group the ports on a switch. Each group forms a broadcast area. Information between
groups is isolated. Thus, broadcast packets can be transmitted only within a group.
You can use various technologies to isolate a broadcast area. For example, routers choose a
route on the basis of the Layer 3 IP addresses. Therefore, using a router to connect two
network segments can effectively suppress the broadcast. However, routers are costly, so the
VLAN is introduced to help resolve this problem.
4.1.2 Application of a VLAN
VLAN technology
A VLAN divides a LAN into several logical LANs (VLANs), with each VLAN being a
broadcast area. In each VLAN, the hosts can communicate with each other just as they do in a
LAN; however, the VLANs cannot interact with each other directly. Therefore, broadcast
packets are restricted to one VLAN.
Besides partitioning broadcast areas, the VLAN has more complex network applications. For
example, a building is rented by different enterprise clients and they want to build their own
LANs, but the total cost of the LANs is high. In addition, if all the clients share the same LAN,
information security cannot be guaranteed. By using a VLAN, different clients can share a
LAN, and information security is guaranteed.
Figure 4-3 shows a typical VLAN network application. Three switches are placed at different
sites, such as on different floors in a building. Each switch is connected with three PCs. The
PCs belong to three different VLANs, which are enclosed by dashed blocks representing the
different enterprise clients.
Figure 4-3 Schematic diagram of VLAN networking
Router
Switchl Switch2
1—1
L
■—I
L L
VLAN-A
1-------------
VLAN-B 1
1
_1
\
__1
1
VLAN-C
t t
91
4-4 Nortel Networks Inc. Issue 5.3 (30 March 2009)