Accounting-Response Log ??

Hi, I have two radius servers. (Freeradius and Juniper SBR). Freeradius server be a radius proxy to proxy all auth/acct requests to Juniper SBR. Then I sometimes found there are some accounting-stop request don't arrival to Juniper SBR. Because Freeradius server and Juniper SBR is in the different subnet and through firewall. I think this problem may cause by firewall. In the radius accounting communication model there should have request and response. Is freeradius log the accounting-response result ? How to enable it ? I want to this log to identify the problem. Thanks. Rio Yang