sending Challenge + EAP-Notification before Reject?

Alan DeKok aland at
Tue Feb 18 18:19:43 CET 2014

Stefan Winter wrote:
> recently, RFC4284 was brought to my attention, which speaks of ways to
> notify EAP peers that there is no service for them - with a displayable
> message as EAP-Notification in a Access-Challenge before the final
> EAP-Failure in a Reject.

  IIRC, some switches will close the port when they receive an
EAP-Notification in an Access-Challenge.

> Is this in any way doable with FreeRADIUS?

  Yes.  Arran was doing this a while ago, which is how he ran into the
above problem.

> I'm thinking of two scenarios primarily:
> * FreeRADIUS proxy can't reach home server, so writes "Sorry, your home
> server is unreachable" in a Challenge+EAP-Notification and after the
> next Request then crafts Reject.
> * FreeRADIUS sees the realm, figures that it's not wanted, so writes "We
> don't serve that realm here." and then after the subsequent Request
> sends Access-Reject.

  I thought that the Reply-Message in an Access-Reject could also be
turned into an EAP-Notification by the NAS.  I can't recall where I saw
that, though.  But it would make sense.

> I could also imagine that it could signal its own module failures as
> reason; e.g. if an rlm_sql doesn't work, instead of an immediate reject
> or do_not_reply it could send an extra round with "Unable to
> authenticate you: rlm_sql failed. Try again later"; and only then the
> Reject.
> I have no clue how to configure such a behaviour. Is it possible at all?

  Probably with some magic.  But will the supplicants display the
notification to the end user?  I doubt it.

  Alan DeKok.

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