duplicate ip address ippool problem

[as3ad jamous]

 freeradius assign duplicate ip address , i using ippool module and file, for example user1 get the IP1 and some times (not always ) user2 get the same IP1 so LNS see duplicate ip address and drop the new user (no high load at radius but some times on database may be some load ),i dont know why freeradius retrun the used ip ,may it not sotre it  at the ippool files :
session-db and ip-index
? but whyfrom the side of the LNS i can see the authentication and accounting is okand acknowledged about authentication and accountingif there problem from side of database , the ippool store  the datat at local files at radius server and there is no problem of high cpu load or system load on it , I would be grateful if you can assist me in identifying why this happens, and how I can rectify this problemthank you in advance. i look forward to your reply.              
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