Ivan, Hello Problem solved. I have mentioned my solution below, but now comes another question, sorry :) How is it possible to authenticate CHAP clients using an external program and not the rlm_chap module? I made two instances of the rlm_exec module. One as the authorization external program and one as the authentication external program. The point is that the Cleartext-Password should be sent out as a configuration item in the authorization external program, in other words, what the authorization program outputs should be configuration items (in this case). Well, in my previous configuration, the authorization program has been output attribute-value pairs as reply messages and that was wrong. Using radiusd.conf, I changed the output type of the authorization external program to config items. Now I can access User-Name, CHAP-Password, CHAP-Challenge attribute-value pairs in my authentication external program. By the way, the authorization external program sets my customized Auth-Type so that in the authentication section, I can use it to authenticate clients using my authentication external program which is another instance of the rlm_exec module (the second one). The main problem is the way that authentication should take place for CHAP, MS-CHAP and MS-CHAPv2 clients in the authentication external program. Kind Regards Ali Majdzadeh Kohbanani