ZyXEL Communications VMG5313-B30A Guide de l'utilisateur télécharger pdf (Page 346)

Appendix D Wireless LANs

VMG1312-B Series User’s Guide

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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 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

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.

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ZyXEL Communications VMG5313-B30A Guide de l'utilisateur Page 346