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Page 121 / 324 Scroll up to view Page 116 - 120
Chapter 8 Wireless LAN
P-660HN-TxA User’s Guide
121
The wireless network is the part in the blue circle. In this wireless network,
devices
A
and
B
use the access point (
AP
) to interact with the other devices (such
as the printer) or with the Internet. Your ZyXEL Device is the AP.
Every wireless network must follow these basic guidelines.
•
Every device in the same wireless network must use the same SSID.
The SSID is the name of the wireless network. It stands for Service Set
IDentifier.
•
If two wireless networks overlap, they should use a different channel.
Like radio stations or television channels, each wireless network uses a specific
channel, or frequency, to send and receive information.
•
Every device in the same wireless network must use security compatible with
the AP.
Security stops unauthorized devices from using the wireless network. It can also
protect the information that is sent in the wireless network.
Radio Channels
In the radio spectrum, there are certain frequency bands allocated for unlicensed,
civilian use. For the purposes of wireless networking, these bands are divided into
numerous channels. This allows a variety of networks to exist in the same place
without interfering with one another. When you create a network, you must select
a channel to use.
Since the available unlicensed spectrum varies from one country to another, the
number of available channels also varies.
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8.8.2
Additional Wireless Terms
The following table describes some wireless network terms and acronyms used in
the ZyXEL Device’s Web Configurator.
8.8.3
Wireless Security Overview
By their nature, radio communications are simple to intercept. For wireless data
networks, this means that anyone within range of a wireless network without
security can not only read the data passing over the airwaves, but also join the
network. Once an unauthorized person has access to the network, he or she can
steal information or introduce malware (malicious software) intended to
compromise the network. For these reasons, a variety of security systems have
been developed to ensure that only authorized people can use a wireless data
network, or understand the data carried on it.
These security standards do two things. First, they authenticate. This means that
only people presenting the right credentials (often a username and password, or a
“key” phrase) can access the network. Second, they encrypt. This means that the
information sent over the air is encoded. Only people with the code key can
understand the information, and only people who have been authenticated are
given the code key.
Table 39
Additional Wireless Terms
TERM
DESCRIPTION
RTS/CTS Threshold
In a wireless network which covers a large area, wireless devices
are sometimes not aware of each other’s presence.
This may cause
them to send information to the AP at the same time and result in
information colliding and not getting through.
By setting this value lower than the default value, the wireless
devices must sometimes get permission to send information to the
ZyXEL Device. The lower the value, the more often the devices must
get permission.
If this value is greater than the fragmentation threshold value (see
below), then wireless devices never have to get permission to send
information to the ZyXEL Device.
Preamble
A preamble affects the timing in your wireless network. There are
two preamble modes: long and short. If a device uses a different
preamble mode than the ZyXEL Device does, it cannot communicate
with the ZyXEL Device.
Authentication
The process of verifying whether a wireless device is allowed to use
the wireless network.
Fragmentation
Threshold
A small fragmentation threshold is recommended for busy networks,
while a larger threshold provides faster performance if the network
is not very busy.
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Chapter 8 Wireless LAN
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123
These security standards vary in effectiveness. Some can be broken, such as the
old Wired Equivalent Protocol (WEP). Using WEP is better than using no security at
all, but it will not keep a determined attacker out. Other security standards are
secure in themselves but can be broken if a user does not use them properly. For
example, the WPA-PSK security standard is very secure if you use a long key
which is difficult for an attacker’s software to guess - for example, a twenty-letter
long string of apparently random numbers and letters - but it is not very secure if
you use a short key which is very easy to guess - for example, a three-letter word
from the dictionary.
Because of the damage that can be done by a malicious attacker, it’s not just
people who have sensitive information on their network who should use security.
Everybody who uses any wireless network should ensure that effective security is
in place.
A good way to come up with effective security keys, passwords and so on is to use
obscure information that you personally will easily remember, and to enter it in a
way that appears random and does not include real words. For example, if your
mother owns a 1970 Dodge Challenger and her favorite movie is Vanishing Point
(which you know was made in 1971) you could use “70dodchal71vanpoi” as your
security key.
The following sections introduce different types of wireless security you can set up
in the wireless network.
8.8.3.1
SSID
Normally, the ZyXEL Device acts like a beacon and regularly broadcasts the SSID
in the area. You can hide the SSID instead, in which case the ZyXEL Device does
not broadcast the SSID. In addition, you should change the default SSID to
something that is difficult to guess.
This type of security is fairly weak, however, because there are ways for
unauthorized wireless devices to get the SSID. In addition, unauthorized wireless
devices can still see the information that is sent in the wireless network.
8.8.3.2
MAC Address Filter
Every device that can use a wireless network has a unique identification number,
called a MAC address.
1
A MAC address is usually written using twelve hexadecimal
characters
2
; for example, 00A0C5000002 or 00:A0:C5:00:00:02. To get the MAC
address for each device in the wireless network, see the device’s User’s Guide or
other documentation.
1.
Some wireless devices, such as scanners, can detect wireless networks but cannot use wireless networks.
These kinds of wireless devices might not have MAC addresses.
2.
Hexadecimal characters are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, and F.
Page 124 / 324
Chapter 8 Wireless LAN
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124
You can use the MAC address filter to tell the ZyXEL Device which devices are
allowed or not allowed to use the wireless network. If a device is allowed to use
the wireless network, it still has to have the correct information (SSID, channel,
and security). If a device is not allowed to use the wireless network, it does not
matter if it has the correct information.
This type of security does not protect the information that is sent in the wireless
network. Furthermore, there are ways for unauthorized wireless devices to get the
MAC address of an authorized device. Then, they can use that MAC address to use
the wireless network.
8.8.3.3
User Authentication
Authentication is the process of verifying whether a wireless device is allowed to
use the wireless network. You can make every user log in to the wireless network
before using it. However, every device in the wireless network has to support IEEE
802.1x to do this.
For wireless networks, you can store the user names and passwords for each user
in a RADIUS server. This is a server used in businesses more than in homes. If you
do not have a RADIUS server, you cannot set up user names and passwords for
your users.
Unauthorized wireless devices can still see the information that is sent in the
wireless network, even if they cannot use the wireless network. Furthermore,
there are ways for unauthorized wireless users to get a valid user name and
password. Then, they can use that user name and password to use the wireless
network.
8.8.3.4
Encryption
Wireless networks can use encryption to protect the information that is sent in the
wireless network. Encryption is like a secret code. If you do not know the secret
code, you cannot understand the message.
The types of encryption you can choose depend on the type of authentication.
(See
Section 8.8.3.3 on page 124
for information about this.)
Table 40
Types of Encryption for Each Type of Authentication
NO AUTHENTICATION
RADIUS SERVER
Weakest
No Security
WPA
Static WEP
WPA-PSK
Strongest
WPA2-PSK
WPA2
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Chapter 8 Wireless LAN
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125
For example, if the wireless network has a RADIUS server, you can choose
WPA
or
WPA2
. If users do not log in to the wireless network, you can choose no
encryption,
Static WEP
,
WPA-PSK
, or
WPA2-PSK
.
Usually, you should set up the strongest encryption that every device in the
wireless network supports. For example, suppose you have a wireless network
with the ZyXEL Device and you do not have a RADIUS server. Therefore, there is
no authentication. Suppose the wireless network has two devices. Device A only
supports WEP, and device B supports WEP and WPA. Therefore, you should set up
Static WEP
in the wireless network.
Note: It is recommended that wireless networks use
WPA-PSK
,
WPA
, or stronger
encryption. The other types of encryption are better than none at all, but it is still
possible for unauthorized wireless devices to figure out the original information
pretty quickly.
When you select
WPA2
or
WPA2-PSK
in your ZyXEL Device, you can also select
an option (
WPA compatible
) to support WPA as well. In this case, if some of the
devices support WPA and some support WPA2, you should set up
WPA2-PSK
or
WPA2
(depending on the type of wireless network login) and select the
WPA
compatible
option in the ZyXEL Device.
Many types of encryption use a key to protect the information in the wireless
network. The longer the key, the stronger the encryption. Every device in the
wireless network must have the same key.
8.8.4
Signal Problems
Because wireless networks are radio networks, their signals are subject to
limitations of distance, interference and absorption.
Problems with distance occur when the two radios are too far apart. Problems with
interference occur when other radio waves interrupt the data signal. Interference
may come from other radio transmissions, such as military or air traffic control
communications, or from machines that are coincidental emitters such as electric
motors or microwaves. Problems with absorption occur when physical objects
(such as thick walls) are between the two radios, muffling the signal.
8.8.5
BSS
A Basic Service Set (BSS) exists when all communications between wireless
stations or between a wireless station and a wired network client go through one
access point (AP).
Intra-BSS traffic is traffic between wireless stations in the BSS. When Intra-BSS
traffic blocking is disabled, wireless station A and B can access the wired network

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