CCNA Cisco Certified Network Associate Study Guide - FTP Server

FIGURE 6.1 Flat network structure
Broadcast Control
1 2 3 4
• Each segment has its own collision domain.
• All segments are in the same broadcast domain.
Virtual LANs 301
Because layer-2 switching creates individual collision domain segments
for each device plugged into the switch, the Ethernet distance constraints are
lifted, which means larger networks can be built. The larger the number of
users and devices, the more broadcasts and packets each device must handle.
Another problem with a flat layer-2 network is security, as all users can
see all devices. You cannot stop devices from broadcasting and users trying
to respond to broadcasts. Your security is passwords on the servers and
other devices.
By creating VLANs, you can solve many of the problems associated with
layer-2 switching, as shown in the upcoming sections.
Broadcasts occur in every protocol, but how often they occur depends upon
the protocol, the application(s) running on the internetwork, and how these
services are used.
Some older applications have been rewritten to reduce their bandwidth
needs. However, there is a new generation of applications that are bandwidthgreedy,
consuming all they can find. These are multimedia applications that
use broadcasts and multicasts extensively. Faulty equipment, inadequate
segmentation, and poorly designed firewalls can also add to the problems
of broadcast-intensive applications. This has added a new chapter to network
design, since broadcasts can propagate through the switched network.
Routers, by default, send broadcasts only within the originating network,