clive gould wrote:

Our ITNS team have just rebuilt the IAS server after it suffered a hardware failure failed and since the rebuild it is now rejecting FreeRADIUS proxy requests.

Likely because the IAS configuration changed.

IAS will still respond to my Moodle PHP RADIUS authentication module, but since the rebuild is rejecting authentication requests from the FreeRADIUS proxy (yes the new shared secret is correct and I'm logging on with the same id to both systems :)

Then use the debugging features on IAS (such as they are) to see why it's rejecting the user.

I'm using MSCHAP for authentication with FreeRADIUS.

I am wondering if the problem could be to do with http://technet.microsoft.com/en-us/library/cc786978.aspx#BKMK_5 ?

Well, there's a whole lot of Q&A at that web site, and I don't care enough about IAS internals to read it. In short, you broke IAS, and now it doesn't work. There is very little you can do to FreeRADIUS to fix IAS. Alan DeKok.