checksimul callback

[Alan DeKok]

Dmitry V. Krivenok wrote:
> I just want to know what is the simplest way to
> disallow 2 simultaneous sessions.
> Are there any standard solutions?

  Of course.  See doc/Simultaneous-Use.

> I found (in source of rlm_sql), that checking is based on
> analysis of accounting information.
> 
> What if 2 Access-Requests arrive "simultaneously"?
> There is no accounting information available yet (it will
> become available just after receiving Accounting-Start).
> Hence it's not reliable to rely on accounting information only.
> Am I right?

  Yes.

> It seems to me that AAA and NAS may be not synchronized.
> So, we need to contact NAS somehow to determine active
> sessions and match them with accounting info.
> Looks like very complex task :(

  That's what the "checkrad" program is for.

  None of these issues are new.  People thought of them, and came up
with solutions, 10 years ago.  These solutions are even documented in
the server.

  Alan DeKok.