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Appendix D Wireless LANs
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291
WPA(2) with RADIUS Application Example
To set up WPA(2), you need the IP address of the RADIUS server, its port number (default is 1812),
and the RADIUS shared secret. A WPA(2) application example with an external RADIUS server
looks as follows. "A" is the RADIUS server. "DS" is the distribution system.
1
The AP passes the wireless client's authentication request to the RADIUS server.
2
The RADIUS server then checks the user's identification against its database and grants or denies
network access accordingly.
3
A 256-bit Pairwise Master Key (PMK) is derived from the authentication process by the RADIUS
server and the client.
4
The RADIUS server distributes the PMK to the AP. The AP then sets up a key hierarchy and
management system, using the PMK to dynamically generate unique data encryption keys. The
keys are used to encrypt every data packet that is wirelessly communicated between the AP and
the wireless clients.
Figure 176
WPA(2) with RADIUS Application Example
WPA(2)-PSK Application Example
A WPA(2)-PSK application looks as follows.
1
First enter identical passwords into the AP and all wireless clients. The Pre-Shared Key (PSK) must
consist of between 8 and 63 ASCII characters or 64 hexadecimal characters (including spaces and
symbols).
2
The AP checks each wireless client's password and allows it to join the network only if the password
matches.
3
The AP and wireless clients generate a common PMK (Pairwise Master Key). The key itself is not
sent over the network, but is derived from the PSK and the SSID.
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4
The AP and wireless clients use the TKIP or AES encryption process, the PMK and information
exchanged in a handshake to create temporal encryption keys. They use these keys to encrypt data
exchanged between them.
Figure 177
WPA(2)-PSK Authentication
Security Parameters Summary
Refer to this table to see what other security parameters you should configure for each
authentication method or key management protocol type. MAC address filters are not dependent on
how you configure these security features.
Antenna Overview
An antenna couples RF signals onto air. A transmitter within a wireless device sends an RF signal to
the antenna, which propagates the signal through the air. The antenna also operates in reverse by
capturing RF signals from the air.
Positioning the antennas properly increases the range and coverage area of a wireless LAN.
Table 108
Wireless Security Relational Matrix
AUTHENTICATION
METHOD/ KEY
MANAGEMENT PROTOCOL
ENCRYPTIO
N METHOD
ENTER
MANUAL KEY
IEEE 802.1X
Open
None
No
Disable
Enable without Dynamic WEP Key
Open
WEP
No
Enable with Dynamic WEP Key
Yes
Enable without Dynamic WEP Key
Yes
Disable
Shared
WEP
No
Enable with Dynamic WEP Key
Yes
Enable without Dynamic WEP Key
Yes
Disable
WPA
TKIP/AES
No
Enable
WPA-PSK
TKIP/AES
Yes
Disable
WPA2
TKIP/AES
No
Enable
WPA2-PSK
TKIP/AES
Yes
Disable
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Antenna Characteristics
Frequency
An antenna in the frequency of 2.4GHz (IEEE 802.11b and IEEE 802.11g) or 5GHz (IEEE 802.11a)
is needed to communicate efficiently in a wireless LAN
Radiation Pattern
A radiation pattern is a diagram that allows you to visualize the shape of the antenna’s coverage
area.
Antenna Gain
Antenna gain, measured in dB (decibel), is the increase in coverage within the RF beam width.
Higher antenna gain improves the range of the signal for better communications.
For an indoor site, each 1 dB increase in antenna gain results in a range increase of approximately
2.5%. For an unobstructed outdoor site, each 1dB increase in gain results in a range increase of
approximately 5%. Actual results may vary depending on the network environment.
Antenna gain is sometimes specified in dBi, which is how much the antenna increases the signal
power compared to using an isotropic antenna. An isotropic antenna is a theoretical perfect antenna
that sends out radio signals equally well in all directions. dBi represents the true gain that the
antenna provides.
Types of Antennas for WLAN
There are two types of antennas used for wireless LAN applications.
Omni-directional antennas send the RF signal out in all directions on a horizontal plane. The
coverage area is torus-shaped (like a donut) which makes these antennas ideal for a room
environment. With a wide coverage area, it is possible to make circular overlapping coverage
areas with multiple access points.
Directional antennas concentrate the RF signal in a beam, like a flashlight does with the light
from its bulb. The angle of the beam determines the width of the coverage pattern. Angles
typically range from 20 degrees (very directional) to 120 degrees (less directional). Directional
antennas are ideal for hallways and outdoor point-to-point applications.
Positioning Antennas
In general, antennas should be mounted as high as practically possible and free of obstructions. In
point-to–point application, position both antennas at the same height and in a direct line of sight to
each other to attain the best performance.
For omni-directional antennas mounted on a table, desk, and so on, point the antenna up. For
omni-directional antennas mounted on a wall or ceiling, point the antenna down. For a single AP
application, place omni-directional antennas as close to the center of the coverage area as possible.
For directional antennas, point the antenna in the direction of the desired coverage area.
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Appendix D Wireless LANs
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295
A
PPENDIX
E
IPv6
Overview
IPv6 (Internet Protocol version 6), is designed to enhance IP address size and features. The
increase in IPv6 address size to 128 bits (from the 32-bit IPv4 address) allows up to 3.4 x 10
38
IP
addresses.
IPv6 Addressing
The 128-bit IPv6 address is written as eight 16-bit hexadecimal blocks separated by colons (:). This
is an example IPv6 address
2001:0db8:1a2b:0015:0000:0000:1a2f:0000
.
IPv6 addresses can be abbreviated in two ways:
Leading zeros in a block can be omitted. So
2001:0db8:1a2b:0015:0000:0000:1a2f:0000
can
be written as
2001:db8:1a2b:15:0:0:1a2f:0
.
Any number of consecutive blocks of zeros can be replaced by a double colon. A double colon can
only appear once in an IPv6 address. So
2001:0db8:0000:0000:1a2f:0000:0000:0015
can be
written as
2001:0db8::1a2f:0000:0000:0015
,
2001:0db8:0000:0000:1a2f::0015
,
2001:db8::1a2f:0:0:15
or
2001:db8:0:0:1a2f::15
.
Prefix and Prefix Length
Similar to an IPv4 subnet mask, IPv6 uses an address prefix to represent the network address. An
IPv6 prefix length specifies how many most significant bits (start from the left) in the address
compose the network address. The prefix length is written as “/x” where x is a number. For
example,
2001:db8:1a2b:15::1a2f:0/32
means that the first 32 bits (
2001:db8
) is the subnet prefix.
Link-local Address
A link-local address uniquely identifies a device on the local network (the LAN). It is similar to a
“private IP address” in IPv4. You can have the same link-local address on multiple interfaces on a
device. A link-local unicast address has a predefined prefix of fe80::/10. The link-local unicast
address format is as follows.
Table 109
Link-local Unicast Address Format
1111 1110 10
0
Interface ID
10 bits
54 bits
64 bits

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