MCSA/MCSE Self-Paced Training Kit (Exam 70-270): Installing ...

15-34 Chapter 15 Configuring Network and Internet Connections
One of the biggest threats to wireless networks is that operating systems such as Windows
XP Professional make it very easy to locate and connect to wireless networks—
so easy, in fact, that people often connect to unsecured wireless networks without
even realizing that it has happened. There are also more deliberate threats to wireless
networks. Attackers can gain access to unsecured (or improperly secured) networks by
connecting with their wireless stations, or even by installing unauthorized APs on an
existing wired network. Once connected, attackers can inspect, modify, or damage
vital resources.
Fortunately, there are a number of ways to secure a wireless network against such
threats. These methods are the focus of the next few sections.
MAC Address Filtering
A very basic way to protect an infrastructure wireless network is to implement media
access control (MAC) filtering. Every network adapter (wireless network adapters
included) contains an address known as a MAC address. An administrator can configure
an AP so that it accepts communications only from specified MAC addresses.
Although MAC filtering does offer some level of protection from casual intrusion, it is
far from useful as a single security solution. Following are some concerns about using
MAC filtering:
■ It is relatively easy to spoof a MAC address. Many software products exist that let
an intruder modify the MAC address on a wireless network adapter.
■ Most APs require that you manually enter MAC addresses. For networks with large
numbers of wireless clients, this means a lot of work for administrators. In addition,
most APs have a limit to the number of MAC addresses you can authorize.
■ MAC filtering can stop an unauthorized computer, but not an unauthorized user. If
an intruder gains access to a computer that has an approved MAC address, the
intruder can gain access to the wireless network.
Service Set Identifier (SSID) Broadcasting
Every infrastructure network is named with a service set identifier (SSID). This name
distinguishes the network from other wireless networks. By default, most APs broadcast
their SSID so that wireless clients can easily locate and connect to the network.
SSID broadcasting provides a great deal of convenience because wireless clients (especially
those that roam among different wireless networks) can easily detect networks
without requiring much configuration from the user.
You can disable SSID broadcasting on most APs, which can prevent casual intruders
from discovering a network. However, intruders who are looking for your network will
likely be able to find it anyway. Several software programs exist that can scan for wireless
networks and identify the SSID of a network, even if SSID broadcasting is disabled.