hostapd + freeradius + windows users problem

Alan DeKok aland at
Thu Nov 13 23:01:56 CET 2008

Jouni Malinen wrote:
> On Thu, Nov 13, 2008 at 9:22 PM,  <tnt at> wrote:
>> "It MAY be sent in an Access-Accept packet, in which case the
>>      client SHOULD use the name returned in the Access-Accept packet in
>>      all Accounting-Request packets for this session."
> And which Access-Accept would this be referring to? 

  The specs are a little silent on this issue.  However...

  One Access-Accept is pretty much one accounting session.  Re-using the
same Acct-Session-Id across multiple sessions is very bad.  Very, very,
bad.  Very, very, very, bad.

  I really can't emphasize that enough.

> The problem here
> is that there can be multiple authentication runs (re-authentication
> based on supplicant request or authenticator policy) and should the
> supplicant change its identity, the second Access-Accept is likely to
> have a different identity in that case.

  There is no such thing as "multiple authentication runs" in RADIUS.
Each authentication is completely independent of all other
authentications.  (Barring some CoA issues where State is used to tie
sessions together.)

> While it may be reasonable to arbitrarily decide to use User-Name (if
> present) from the first Access-Accept, it does  not sound like that
> good of an idea for a RADIUS server to depend on this behavior based
> on current RADIUS RFCs.

  The issue is less User-Name than Acct-Session-Id.  From RFC 2866:

             A user may have multiple sessions in parallel or
             series if the NAS supports that, with each session
             generating a separate start and stop accounting record with
             its own Acct-Session-Id.

  Individual sessions have their own Acct-Session-Id.  Creating unique
Acct-Session-Id's is MUCH less of an issue than re-using them.

  i.e. If Acct-Session-Id is something like MD5(session start time +
User-Name + NAS-IP-Address), you will VERY likely not run into problems.
 If you re-use Acct-Session-Id... EVER, then you will have people
hunting you with pitchforks.

  Please don't re-use Acct-Session-Id.  Ever.

  Alan DeKok.

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