NETGEAR ProSafe WG302 Reference Manual page 97

Reference Manual for the NETGEAR ProSafe 802.11g Wireless Access Point WG302
The AP sends Beacon Frames with WPA/WPA2 information element to the stations in the service
set. Information elements include the required authentication method (802.1x or Pre-shared key)
and the preferred cipher suite (WEP, TKIP, or AES). Probe Responses (AP to station) and
Association Requests (station to AP) also contain WPA information elements.
1. Initial 802.1x communications begin with an unauthenticated supplicant (client device)
attempting to connect with an authenticator (802.11 access point). The client sends an
EAP-start message. This begins a series of message exchanges to authenticate the client.
2. The access point replies with an EAP-request identity message.
3. The client sends an EAP-response packet containing the identity to the authentication server.
The access point responds by enabling a port for passing only EAP packets from the client to
an authentication server located on the wired side of the access point. The access point blocks
all other traffic, such as HTTP, DHCP, and POP3 packets, until the access point can verify the
client's identity using an authentication server (for example, RADIUS).
4. The authentication server uses a specific authentication algorithm to verify the client's identity.
This could be through the use of digital certificates or some other EAP authentication type.
5. The authentication server will either send an accept or reject message to the access point.
6. The access point sends an EAP-success packet (or reject packet) to the client.
7. If the authentication server accepts the client, then the access point will transition the client's
port to an authorized state and forward additional traffic.
The important part to know at this point is that the software supporting the specific EAP type
resides on the authentication server and within the operating system or application "supplicant"
software on the client devices. The access point acts as a "pass through" for 802.1x messages,
which means that you can specify any EAP type without needing to upgrade an 802.1x-compliant
access point. As a result, you can update the EAP authentication type to such devices as token
cards (Smart Cards), Kerberos, one-time passwords, certificates, and public key authentication, or
as newer types become available and your requirements for security change.
WPA/WPA2 Data Encryption Key Management
With 802.1x, the rekeying of unicast encryption keys is optional. Additionally, 802.11 and 802.1x
provide no mechanism to change the global encryption key used for multicast and broadcast
traffic. With WPA/WPA2, rekeying of both unicast and global encryption keys is required.
For the unicast encryption key, the Temporal Key Integrity Protocol (TKIP) changes the key for
every frame, and the change is synchronized between the wireless client and the wireless access
point (AP). For the global encryption key, WPA includes a facility (the Information Element) for
the wireless AP to advertise the changed key to the connected wireless clients.
Wireless Networking Basics
v0.1, December 2005
B-13