CompTIA Network +
Chapter 8
Connecting Wirelessly
Objectives
How do various wireless LAN (WLAN) technologies
function, and what wireless standards are in common
use?
What are some of the most important WLAN design
considerations?
What WLAN security risks exist, and how can those risks
be mitigated?
Introducing Wireless LANs
The popularity of wireless LANs (WLAN) has exploded
over the past decade, allowing users to roam within a
WLAN coverage area, allowing users to take their
laptops with them and maintain network connectivity as
they move throughout a building or campus environment.
Wireless device, such as laptops and smart phone, often
have a built-in wireless card that allows those devices to
communicate on a WLAN.
WLAN Concepts and Components
Wireless Routers
The wireless router obtains an IP address via DHCP
from the Internet service provider(ISP).
The router uses PAT, to provide IP addressing
services to devices attaching to it wireless or through
a wired connection.
The process through which a wireless client attaches
with a wireless router (or wireless AP) is called
association.
All wireless devices associating with a single wireless
router or AP share a collision domain.
WLAN Concepts and Components
WLAN Concepts and Components
Wireless Access Point
A wireless access Point (AP) interconnects a wired
LAN with a WLAN, it does not interconnect two
networks
The AP connects to the wired LAN, and the wireless
devices that connect to the wired LAN via the AP are
on the same subnet as the AP.
WLAN Concepts and Components
WLAN Concepts and Components
Antennas
The coverage area of a WLAN is largely determined by the type
of antenna used on the wireless AP or wireless router.
Design goals to keep in mind when selecting an antenna include
the following
Required distance between an AP and a wireless client.
Pattern of coverage area (for example, the coverage area might
radiate out in all directions, forming a spherical coverage area
around an antenna, or and antenna might provide increased
coverage in only one or two directions.
Indoor or outdoor environment
Avoiding interference with other APs
WLAN Concepts and Components
Omnidirectional: An
omnidirectional antenna radiates
power at relatively equal power
levels in all directions.
Unidirectional: Unidirectional
antennas can focus their power in
a specific direction, thus avoiding
interference with other wireless
devices and perhaps reaching
greater distances.
WLAN Concepts and Components
WLAN Concepts and Components
WLAN Concepts and Components
Frequencies and Channels
A characteristic to watch out for is the frequencies at which these
standards operate.
There are some country-specific variations, certain frequency
ranges (or frequency bands) have been reserved internationally
for industrial, scientific, and medical purposes.
These frequency bands are called the ISM bands.
Two of these bands are commonly used for WLANs.
2.4 GHz – 2.5 GHz range. Referred to as the 2.4 GHz band.
5.75 GHz – 5.875 GHz range. Referred to as the 5 GHz Band
Within each band are specific frequencies (or channels) at
which device operate.
WLAN Concepts and Components
• 3 nonoverlapping channels in US: 1, 6, 11
WLAN Concepts and Components
CSMA/CA
We already learned that Ethernet’s carrier sense
multiple access / collision detection (CSMA/CD)
technology is used to control traffic on a wired
network.
WLAN use a similar technology called carrier sense
multiple access/collision avoidance (CSMA/CA).
A WLAN device listens for a transmission on a
wireless channel to determine if it is safe to transmit.
WLAN Concepts and Components
Transmission Methods
Earlier you saw the frequencies used for various
wireless channels.
Those frequencies are considered to be the center
frequencies of a channel.
In actual operation, a channel uses more than one
frequency, which is a transmission method called
spread spectrum.
These frequency are, however, very close to one
another, which is called narrowband transmission.
WLAN Concepts and Components
Transmission Methods
WLAN use one of the following types of spread-spectrum
technology:
Direct-sequence spread spectrum (DSSS)
Modulates data over an entire range of frequencies.
Frequency-hopping spread spectrum (FHSS)
Allows the participants in a communication to hop
between predetermined frequencies or channels.
Orthogonal frequency division multiplexing (OFDM)
Uses a relatively slow modulation rate, combined with
the simultaneous transmission of data over 52 data
streams.
WLAN Standard
Standard Band Max. Bandwidth Transmission Max. Range
method
802.11 2.4GHz 1 Mbps or 2 Mbps DSSS or FHSS 20m indoors/100
m outdoors
802.11a 5 GHz 54 Mbps OFDM 35m
indoors/120m
outdoors
802.11b 2.4GHz 11 Mbps DSSS 32m
indoors/140m
outdoors
802.11g 2.4GHz 54 Mbps OFDM or DSSS 32m indoors /
140m outdoors
802.11n 2.4GHz 130-150Mbps OFDM 70m
or 5GHz > 300 Mbps (with indoors/250m
(or both) channel bonding) outdoors
WLAN Standard
Independent Basic Service Set (IBSS) WLAN (ad-hoc)
WLAN Standard
Basic Service Set (BSS) WLAN
WLAN Standard
Extended Service Set (ESS) WLAN
Sources of Interference
A major issue for WLANs is radio frequency interference
(RFI) caused by other devices using similar frequencies
to the WLAN device.
Other WLAN devices
Cordless Phone/ Baby Monitors
Microwave ovens
Wireless security systems devices
Physical obstacles
Signal strength
Wireless AP Placement
WLAN using more than one AP (an ESS WLAN) require
careful planning to prevent the Aps from interfering with
one another, which still servicing a desired coverage
area.
An overlapping of coverage between APs should exist to
allow uninterrupted roaming from one WLAN cell (which
is the coverage area provided by the AP) to another.
However, those overlapping coverage areas should not
use overlapping frequencies.
Wireless AP Placement
10-15 % Coverage Overlap in Coverage Area for
Non-overlapping Channels
Wireless AP Placement
Non-overlapping Coverage Cells for the 2.4-GHz Band
Securing Wireless LANs
Security Issues
WLANs introduce some unique concerns to your
network.
Improperly installed wireless APs, and routers are
roughly equivalent to putting an Ethernet Port in a
building’s parking lot, where anyone can drive up and
have access to your network.
Today hackers and those who want to use free internet
access perform reconnaissance, known as war driving,
looking for unsecured WLANs
*CCSF Wardriving
*Thu., Nov. 7, 2013, 6 PM
*Meet in MUB 180
*Bring laptop or car if you have
one
*Install Vistumbler
*Or just come with nothing
*CCSF Wardriving
Securing Wireless LANs
Other WLAN security threat include the following
WEP cracking – WEP is worthless, easily cracked
My students crack WEP as a CNIT 123 project
WPA and WPA-2 are both very secure
WPS ruins it (Wi-Fi Protected Setup)
Rouge access points – A malicious user could set up his own AP
to which legitimate users would connect.
Securing Wireless LANs
Approaches to WLAN Security
A WLAN that does not require any authentication or provide and
encryption for wireless devices is said to be using open
authentication.
To protect WLAN traffic from eavesdroppers, a variety of security
standards and practices have been developed, including the
following.
MAC address Filtering
Disabling SSID broadcast
Preshared Key
IEEE 802.1X
Securing Wireless LANs
IEEE 802.1x Security for a WLAN
Securing Wireless LANs
Security Standards
When configuring a wireless client for security, the
most common security standards form which you can
select are as follows:
Wired Equivalent Privacy (WEP)
Wi-Fi Protected Access (WPA)
Wi-Fi Protected Access version 2 (WPA2)
Securing Wireless LANs
WEP
40-bit WEP Key
APs and client must use the same key.
24-bit initialization vector (IV)
Sent in clear text.
It could be compromised with a brute-force
attack.
Securing Wireless LANs
WAP
Can require a user to authenticated before keys are exchanged.
The keys used between a wireless client and an access point
are temporary session keys.
Temporal Key Integrity Protocol (TKIP)
Message Integrity Check (MIC)
WAP2
Counter Mode with Cipher Block Chaining Message
Authentication Code Protocol (CCMP)
Advanced Encryption Standard (AES)
