====== UPDATED 2021 -Limiting Simultaneous Sessions  ======
  * If you want to limit the simultaneous sessions a user can have this this page is for you.

===== Why implement it =====
  * If you are driven by sales of vouchers, limiting the amount of people who can use the voucher at one time can result in more sales.
  * If you are very strict on limiting the amount of data a user can use, it is wise to restrict the sessions even to only one in order to ensure accurate data cap calculations.

===== There is a catch =====
  * You might get more support calls since it may just happen that a person was connected through the captive portal and got disconnected. 
  * The back-end still thinks he is connected.
  * If the person then tries to connect again and there is a limit on the sessions to e.g. 1, he will not be able to connect again.
  * Usually there is a reply attribute called **Idle-Timeout** which you can set to a low value to auto-disconnect the user from the Captive Portal's side when there is no data flow.
  * Another option is to let the Back-end auto close stale sessions by editing the Dynamic Client under **RADIUS** menu and go to **Dynamic Client** -> **Enhancements** and select **Auto Close Stale Sessions** with a time.
  * These items are just a heads-up before you implement this limit.

===== Check if enabled =====
  * Check if it is enabled in FreeRADIUS
<code bash>
vi /etc/freeradius/3.0/mods-config/sql/main/mysql/queries.conf
</code>

  * Look for this section
<code bash>
#######################################################################
# Simultaneous Use Checking Queries
#######################################################################
# simul_count_query     - query for the number of current connections
#                       - If this is not defined, no simultaneous use checking
#                       - will be performed by this module instance
# simul_verify_query    - query to return details of current connections
#                               for verification
#                       - Leave blank or commented out to disable verification step
#                       - Note that the returned field order should not be changed.
#######################################################################
</code>
  * Lets do a bit of explanation of these two items.
        * In the FreeRADIUS config is a dedicated **session** section.
        * If this section has **sql** specified, FreeRADIUS will initiate these queries (one or both) to try and determine the amount of active sessions a user has.
        * We are **NOT** using  **simul_verify_query** and thus it needs to be commented out.
        * If **simul_verify_query** is specified the FreeRADIUS program will try and contact the nas if possible to inquire directly from it the current session count for a user. For this it uses the **checkrad** program.
        * We will thus comment **simul_verify_query** out to NOT use it.

<code bash>
simul_count_query = "\
        SELECT COUNT(*) \
        FROM ${acct_table1} \
        WHERE username = '%{SQL-User-Name}' \
        AND acctstoptime IS NULL"

#simul_verify_query = "\
#       SELECT \
#               radacctid, acctsessionid, username, nasipaddress, nasportid, framedipaddress, \
#               callingstationid, framedprotocol \
#       FROM ${acct_table1} \
#       WHERE username = '%{SQL-User-Name}' \
#       AND acctstoptime IS NULL"
</code>
  * Restart if you made changes
<code bash>
#20.04
service freeradius stop
service freeradius start
</code>

===== Applying the limit =====
  * Consider the following screenshot

{{ :technical_discussions:simultaneous_2.png?nolink |}}

<WRAP center round tip 100%>
You can also add this to a **Profile Component**
</WRAP>


===== See the limit in action =====
  * Here it is preventing a second connection
{{ :technical_discussions:simultaneous_1.png?nolink }}