How to log failed login attempts?

Hi, i am using FreeRADIUS 2.0.5. Successfull logins into cisco routers are logged great (using Accounting), but i need to log also the failed attempts. In /var/log/radius.log radius does log the failed attempts, BUT if in clients.conf i have created client as 10.0.0.0/8 (a network, not a host), then in the log file i will see the NAS ip address 10.0.0.0/8, which is not enough. I need to see the exact NAS ip address. It would be insane to add every single router into the clients.conf file, so i assume there is a way how to solve this. I hope u guys can help me, i will appreciate it ;) Thanks.