Dear All,
I faced the same problem, I have written answers to your questions below,

1. Can the user get authenticated at *all*?
Yes..User is getting authenticated via DB
2. Have you set 'Simultaneous-Use = 1' for the user?
Yes.an entry for user is added in radcheck table like mention below
"username@hotmail.com";"Simultaneous-Use";":=";"1"
3. Is the server receiving ANY accounting packets?
Yes. My NAS is sending the accounting requests
4. After the user gets authenticated, does FreeRADIUS receive accounting
packets for that user?
yes. Interim packets are recieved, but I havent enabled query to add interim accounting request data to DB, only Start/Stop packets are saved
5. Is the radutmp / sql module logging those accounting packets?
I can see the packets coming in logs
6. Do the accounting packets have enough information to uniquely
identify a session?  i.e. no "NAS-Port = 0" for all users
Accounting packets have username, session id  field in them, which are unique but there are no NAS-Port field. 
7. Is the nas_type in the "client" configuration set to a known NAS,
where the server can double-check logins?
NAS type is set to other

7. When the user logs in a second time, does FreeRADIUS even try
Simultaneous-Use checking?
Nope, I am unable to see any such simultaneous check query in logs, queries are enabled in dialup.conf and sql option is uncommented in session section.

Thanks



On Sat, May 10, 2014 at 5:31 PM, Alan DeKok <aland@deployingradius.com> wrote:
Russell Mike wrote:
> Thank you very much for your response in answer to my request. Sure, i
> shall send the debug version soon. i want to understand also, how
> simultaneous check works. Is there any documentation which i can read to
> understand the process stage?

   The server comes with a file "doc/Simultaneous-Use".

> Could you kindly, tell me at which stage
> of the process simultaneous login check is performed ? such as "post
> auth" or ?

  It's in it's own section, called "session" for historical reasons.

> Yesterday i forgot to mention that all related include directives in
> "radiusd.conf" are opened, such as include "dialup.conf". i also did not
> mentioned that i do use MySQL DBMS with radius accounting. Yes,
> accounting is logged in database. FreeRADIUS has been installed on
> UBUNTU 12.4LTS & Version is Following

  None of that matters.

1. Can the user get authenticated at *all*?

2. Have you set 'Simultaneous-Use = 1' for the user?

3. Is the server receiving ANY accounting packets?

4. After the user gets authenticated, does FreeRADIUS receive accounting
packets for that user?

5. Is the radutmp / sql module logging those accounting packets?

6. Do the accounting packets have enough information to uniquely
identify a session?  i.e. no "NAS-Port = 0" for all users

7. Is the nas_type in the "client" configuration set to a known NAS,
where the server can double-check logins?

7. When the user logs in a second time, does FreeRADIUS even try
Simultaneous-Use checking?

  The configuration is composed of a set of interlocking pieces.  They
ALL have to be configured correctly for Simultaneous-Use to work.  Some
of the problems can be due to the NAS, which misbehaves.

  Alan DeKok.
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