ZyXEL Communications G-2000 Plus V2, Руководство пользователя

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ZyXEL G-2000 Plus v2 User’s Guide
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By generating unique data encryption keys for every data packet and by creating an integrity
checking mechanism (MIC), with TKIP and AES it is more difficult to decrypt data on a Wi-Fi
network than WEP and difficult for an intruder to break into the network.
The encryption mechanisms used for WPA(2) and WPA(2)-PSK are the same. The only
difference between the two is that WPA(2)-PSK uses a simple common password, instead of
user-specific credentials. The common-password approach makes WPA(2)-PSK susceptible to
brute-force password-guessing attacks but it’s still an improvement over WEP as it employs a
consistent, single, alphanumeric password to derive a PMK which is used to generate unique
temporal encryption keys. This prevent all wireless devices sharing the same encryption keys.
(a weakness of WEP)
User Authentication
WPA and WPA2 apply IEEE 802.1x and Extensible Authentication Protocol (EAP) to
authenticate wireless stations using an external RADIUS database. WPA2 reduces the number
of key exchange messages from six to four (CCMP 4-way handshake) and shortens the time
required to connect to a network. Other WPA2 authentication features that are different from
WPA include key caching and pre-authentication. These two features are optional and may not
be supported in all wireless devices.
Key caching allows a wireless client to store the PMK it derived through a successful
authentication with an AP. The wireless client uses the PMK when it tries to connect to the
same AP and does not need to go with the authentication process again.
Pre-authentication enables fast roaming by allowing the wireless client (already connecting to
an AP) to perform IEEE 802.1x authentication with another AP before connecting to it.
Wireless Client WPA Supplicants
A wireless client supplicant is the software that runs on an operating system instructing the
wireless client how to use WPA. At the time of writing, the most widely available supplicant is
the WPA patch for Windows XP, Funk Software's Odyssey client, and Meetinghouse Data
Communications' AEGIS client.
The Windows XP patch is a free download that adds WPA capability to Windows XP's built-
in "Zero Configuration" wireless client. However, you must run Windows XP to use it.
The Funk Software's Odyssey client is bundled free (at the time of writing) with the client
wireless adaptor(s).
WPA with RADIUS Application Example
You need the IP address of the RADIUS server, its port number (default is 1812), and the
RADIUS shared secret. A WPA 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.