14 Chapter 2: Medium-Sized Switched Network Construction
Understanding VLANs
Understanding how VLANs operate and what the associated protocols are is important for
con?¬?guring, verifying, and troubleshooting VLANs on Cisco access switches. This section
describes VLAN operations and their associated protocols.
A poorly designed network has increased support costs, reduced service availability,
security risks, and limited support for new applications and solutions. Less-than-optimal
performance affects end users and access to central resources directly. Some of the issues
that stem from a poorly designed network include the following:
?– Failure domains: One of the most important reasons to implement an effective
network design is to minimize the extent of problems when they occur. When Layer 2
and Layer 3 boundaries are not clearly de?¬?ned, failure in one network area can have a
far-reaching effect.
?– Broadcast domains: Broadcasts exist in every network. Many applications and
network operations require broadcasts to function properly; therefore, it is not possible
to eliminate them completely. In the same way that avoiding failure domains involves
clearly de?¬?ning boundaries, broadcast domains should have clear boundaries and
include an optimal number of devices to minimize the negative impact of broadcasts.
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