94 Chapter 3: Switched/Campus LAN Solutions
and switched networks, in which packets are often forwarded to LANs that have no need for
them.
Implementation of VLANs also improves scalability, particularly in LAN environments that
support broadcast--or multicast-intensive protocols and applications that flood packets
throughout the network. Figure 3-9 shows a traditional network with LAN segmentation and a
segmented network using switches.
Figure 3-9
LAN and VLAN Segmentation
Communication Between VLANs
Communication between VLANs is accomplished through routing. The traditional security and
filtering functions of the router can be used. Cisco IOS software provides network services such
as security filtering, QoS, and accounting on a per-VLAN basis. As switched networks evolve
to distributed VLANs, Cisco IOS provides key inter-VLAN communication and allows the
network to scale.
CDDI/FDDI
concentrator
Shared hub
Traditional wiring closet
Traditional backbone
Cisco router
Hub
The new wiring closet
Shared hub
LAN switch (Layer 2)
Multilayer switch
(Layers 2 and 3)
ATM campus
switch
Cisco Router
The new backbone
87200333.book Page 94 Wednesday, August 22, 2001 2:18 PM