Implementation Considerations

So much for the theory, but where does IEEE 802.1X reside in real systems? For most Wi-Fi LANs, the logical place to put IEEE 802.1X is in the access point. In fact the close coupling between IEEE 802.1X and key management makes it hard to place it anywhere else. There were proposals in the standards work that would allow the key management and wireless access point functions to be separated so IEEE 802.1X could be placed on a separate access box to which the access point was connected. This approach was not adopted for WPA/RSN.

It is possible to build wireless LANs without an access point using IBSS or ad-hoc mode. In this case, it is necessary for every mobile device to have both a supplicant and an authenticator operating in parallel (see Chapter 13).

Some operating systems such as Microsoft Windows XP have support for IEEE 802.1X supplicants built in. When configuring the clients, you only need to enable IEEE 802.1X-based authentication and choose the authentication method. Of course the choice of authentication methods may be limited and you may have to install additional software to get the method you need. In older operating systems, IEEE 802.1X is probably not built in and you will need to install special drivers from the manufacturer of the Wi-Fi equipment you are installing. In all cases, supporting generic IEEE 802.1X is not enough for Wi-Fi LAN. There are other special requirements of WPA/RSN related to key management that must be built into the IEEE 802.1X implementation. In general the manufacturer of the adapter card provides all the necessary hooks and drivers to implement this extra stuff when the operating system does not. You should confirm that when a vendor advertises RSN or IEEE 802.11i compatibility that it does properly integrate with the operating system you intend to use. Systems labeled "Wi-Fi WPA" are likely to have the necessary software and will have been tested for interoperability with other vendors.

IEEE 802.1X can also be used in embedded mobile devices such as mobile phones or PDAs. In this case, the operating system may not be visible to the user. If the device supports IEEE 802.11i RSN or WPA, all the integration issues should be taken into account in the device. However, you will probably have little or no flexibility on the authentication method available. Be sure to find out what authentication method is used on such a device and confirm that your authentication server can support it.

As a final note, remember that IEEE 802.1X itself does not define the way that EAP messages are passed between the authenticator and the authentication server. However, it strongly hints that RADIUS is a good way to go in IP networks. It even includes an annex section outlining how RADIUS might be used. RADIUS has already been mentioned and is covered in the next section. Remember that RADIUS is needed only if the authentication server is remote to the authenticator. IEEE 802 deals with LAN protocols generally and is applicable to LANs regardless of whether they use TCP/IP. IEEE 802.1X does not specify RADIUS because it is based on IP packets, which are part of the TCP/IP protocol family. In reality, IP networks are by far the most common, but this was not always the case and IP still isn't used everywhere. Here we assume that you are using an IP network and we focus on RADIUS where there is a network connection between the authenticator and the authentication server. WPA goes further and defines RADIUS as a mandatory implementation choice to help ensure interoperability.

    Part II: The Design of Wi-Fi Security