Cisco Systems DL-2159-05 manual Combining MAC-Based, EAP, and Open Authentication

Chapter 8 Security Setup

Security Overview

Figure 8-4 Sequence for Open Authentication
Client device			Access point
			or bridge
with WEP key = 321		with WEP key = 123
	1. Authentication request
	2. Authentication response

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•Shared key—Cisco provides shared key authentication to comply with the IEEE 802.11b standard. However, because of shared key’s security flaws, we recommend that you avoid using it.

During shared key authentication, the access point sends an unencrypted challenge text string to any device attempting to communicate with the access point. The device requesting authentication encrypts the challenge text and sends it back to the access point. If the challenge text is encrypted correctly, the access point allows the requesting device to authenticate. Both the unencrypted challenge and the encrypted challenge can be monitored, however, which leaves the access point open to attack from an intruder who calculates the WEP key by comparing the unencrypted and encrypted text strings. Because of this weakness, shared key authentication can be less secure than open authentication. Like open authentication, shared key authentication does not rely on a RADIUS server on your network.

Figure 8-5shows the authentication sequence between a device trying to authenticate and an access point using shared key authentication. In this example the device’s WEP key matches the access point’s key, so it can authenticate and communicate.

Figure 8-5 Sequence for Shared Key Authentication

Access point

Client device		or bridge
with WEP key = 123
	with WEP key = 123
	1. Authentication request
	2. Unencrypted challenge
	3. Encrypted challenge response
	4. Authentication response

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Combining MAC-Based, EAP, and Open Authentication

You can set up the access point to authenticate client devices using a combination of MAC-based and EAP authentication. When you enable this feature, client devices that associate to the access point using

802.11open authentication first attempt MAC authentication; if MAC authentication succeeds, the client device joins the network. If MAC authentication fails, the access point waits for the client device to attempt EAP authentication. See the “Authenticating Client Devices Using MAC Addresses or EAP” section on page 8-25for more information on this feature.

Cisco Aironet 1200 Series Access Point Software Configuration Guide

8-6 OL-2159-05