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8.4 Modifying the RADIUS Protocol

It may be frustrating to have to employ workarounds to inherent deficiencies in the RADIUS protocol. As informed, knowledgeable RADIUS users (and you are knowledgeable now that you are reading this book), we need to push for a protocol revision. Joshua Hill, of InfoGard Laboratories, eloquently makes a case for a revision in the following mini-essay.

So, why attempt to modify RADIUS at all? Why not just go to another (presumably more modern and more secure) protocol? Well, for the most part, the answer is, "because such a protocol doesn't currently exist." In the near future, however, Diameter is likely to be released by the IETF.

Diameter is the planned RADIUS replacement. The great majority of all the protocol work that has gone into Diameter has been directed at removing some of the functional limitations imposed by the RADIUS protocol. Effectively, no work has been done that relates to the client/server security of the protocol. (CMS is defined, but this is a security layer for the proxy to proxy interaction, not the client to proxy/server interaction.)

So, does this mean that they continue to use even RADIUS' ad hoc system? No: they removed all security functionality from the protocol. In essence, the developers did the protocol designer's equivalent of punting. Section 2.2 of the current Diameter protocol spec says:

"Diameter clients, such as Network Access Servers (NASes) and Foreign Agents MUST support IP Security, and MAY support TLS. Diameter servers MUST support TLS, but the administrator MAY opt to configure IPSec instead of using TLS. Operating the Diameter protocol without any security mechanism is not recommended."

So, IPSec and/or TLS handle all security aspects of the protocol. From a security aspect, this strikes me as a very good idea. Both IPSec and TLS are fully featured (sometimes too fully featured) protocols that many people have reviewed. That's already much better than RADIUS ever did.

Examining this from a slightly different angle gives me some cause for concern, however. It strikes me that the overhead imposed by a full TLS/IPSec implementation is very significant for many current-day embedded devices. This would seem to indicate that (at least in the near future) manufactures are going to either continue to use RADIUS or ignore the Diameter standard and perform Diameter without TLS or IPSec.

Because of this, I suspect that it would be advantageous to push for at least minimal RADIUS protocol revision.

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