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P-334U/P-335U User’s Guide
Appendix E Wireless LANs 289
User Authentication
WPA and WPA2 apply IEEE 802.1x and Extensible Authentication Protocol (EAP) to
authenticate wireless clients 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.
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.
WPA(2) 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(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 The RADIUS server distributes a Pairwise Master Key (PMK) key to the AP that then
sets up a key hierarchy and management system, using the pair-wise key to dynamically
generate unique data encryption keys to encrypt every data packet that is wirelessly
communicated between the AP and the wireless clients.