hostapd + freeradius + windows users problem

Alan DeKok aland at
Fri Nov 14 09:20:16 CET 2008

Jouni Malinen wrote:
> The following RFC 3580 Chapter 2.1 text is one reason for hostapd behavipr:

  Hmm... OK.

> As far as I can tell, that is describing multiple re-authentications
> for a single RADIUS session. Should the Supplicant decide to change
> its identity (e.g., switch between user and machine credentials)
> without stopping the session (disassociate/EAPOL-Logoff), I don't see
> how the Authenticator (NAS) should handle this case.

  That's really a problem with RADIUS.  There is no definition of what
defines a "session".

> It sounds like
> you are asking to arbitrarily pick the first identity (or create a new
> session, which would not comply with this RFC 3850 text) while hostapd
> is arbitrarily picking the last used identity within the same session.

  Look at it from the point of view of the RADIUS server, or the
administrator running it.  A session starts, with a particular
User-Name, an Acct-Session-Id, and a bunch of other attributes
"identifying" the session.  Then at some later point, the same
Acct-Session-Id is used with a *different* set of attributes
"identifying" the session.

  This is confusing.

  The administrator *cannot* rely on Acct-Session-Id to uniquely
identify sessions, and then ignore other attributes such as User-Name.
There are just too many broken NASes that send the same Acct-Session-Id
for completely independent sessions.

  So... the administrator has to rely on a *collection* of attributes as
"identifying" the session.  That collection traditionally includes
User-Name.  This means that changing User-Name in the middle of a
"session" will wreak havoc with people's accounting setups.

  The NAS, of course, is stuck in the middle here.  If the supplicant
suddenly changes it's EAP identity on re-authentication, it's not
unreasonable for the NAS to simply copy that into the User-Name attribute.

  But this means that the supplicant is broken (IMHO).  If the
supplicant can't keep the same identity during a session, that seems
very strange to me.

  Alan DeKok.

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