"Accounting-Start" and "Accounting-Stop" with same "user name" and "session Id" recorded in different RADIUS servers.

Question

Hi,
I have questions about "Accounting-Start" and "Accounting-Stop".
1.If a NAS configured to have a primary and a backup RADIUS server. To start with all the “Accounting-Start” records will be in the primary RADIUS server. Later on the primary server goes down (Primary server won’t tell the NAS?). When sessions stop, the NAS sends the “Accounting-Stop” to the secondary. I understand the “Start-Stop” record with the same “user name” and “session-id” ideally should be recorded in the same server. If this situation happens what should both the NAS and RADIUS server do?
2.A NAS configured to have a primary and backup RADIUS server. To start with all the “Accounting-Start” records will be in the primary RADIUS server. Later on the administrator decided to change the primary server (as there are problems with the previous primary). sessions stop, the NAS sends the “Accounting-Stop” to the new primary. This ends up the “Accounting-Start” and “Accounting-Stop” with the same “user name” and “session Id” in two RADIUS servers.
To summarize, how to avoid the ”start-stop” pair ends up in different servers ? If it does, is it  an issue for RADIUS application ?
Cheers,
1.If a NAS configured to have a primary and a backup RADIUS server. To start with all the “Accounting-Start” records will be in the primary RADIUS server. Later on the primary server goes down (Primary server won’t tell the NAS?). When sessions stop, the NAS sends the “Accounting-Stop” to the secondary. I understand the “Start-Stop” record with the same “user name” and “session-id” ideally should be recorded in the same server. If this situation happens what should both the NAS and RADIUS server do?
2.A NAS configured to have a primary and backup RADIUS server. To start with all the “Accounting-Start” records will be in the primary RADIUS server. Later on the administrator decided to change the primary server (as there are problems with the previous primary). sessions stop, the NAS sends the “Accounting-Stop” to the new primary. This ends up the “Accounting-Start” and “Accounting-Stop” with the same “user name” and “session Id” in two RADIUS servers.
To summarize, how to avoid the ”start-stop” pair ends up in different servers ? If it does, is it  an issue for RADIUS application ?
Cheers,

Answer 1

vignesh and BalusC,
following is the code in front controller's doFilter method. is this not thread safe?
        HttpServletRequest req = (HttpServletRequest) request;
        HttpServletResponse res = (HttpServletResponse) response;
        HttpSession session = req.getSession();
        somepackage.User user;
        if(session.getAttribute("user") == null){
            user = new somepackage.User();
            session.setAttribute("user", user);
        }else{           
            user = (somepackage.User) session.getAttribute("user");
        }user object maintains all information about a user. if it is in session scope, everything should work fine.
another observation is after some time of usage, both people in different systems are getting same session.getId()
in my logout page i am using
session.invalidate();
thanks,
moses