Dear Alan, Thanks for the response. If you could please answer the following 3 questions, it would be of great help:I am not able to understand these concepts. 1. What is the role of configuration item linked list? 2. How is the linked list and Red-Black trees associated with each other.3. How the structures conf_item and conf_part are related to each other struct conf_item {         struct conf_item *next;         struct conf_part *parent;         int lineno;         const char *filename;         CONF_ITEM_TYPE type;     }; struct conf_part {         CONF_ITEM item;         const char *name1;         const char *name2;         struct conf_item *children;         struct conf_item *tail; /* for speed */         CONF_SECTION    *template;         rbtree_t        *pair_tree; /* and a partridge.. */         rbtree_t        *section_tree; /* no jokes here */         rbtree_t        *name2_tree; /* for sections of the same name2 */         rbtree_t        *data_tree;         void            *base;         int depth;         const CONF_PARSER *variables; }; Thanks in advance.Regards,Sonu From: Alan DeKok <aland@deployingradius.com> Sent: Thu, 18 Sep 2014 19:07:48 To: FreeRadius users mailing list <freeradius-users@lists.freeradius.org> Subject: Re: Freeradius Queries Himanshu Pandey wrote: > I am very new to freeradius and right now I am going through the code of >  freeradius. I am facing problem to understand a couple of concepts. > They are: > > 1. What is the overall architecture of Freeradius?  Complicated.  We don't really have an architecture diagram.  For detailed API docs, see http://doc.freeradius.org/  As for the rest of your questions, they are both too vague and too specific.  The main reason to ask questions is to solve a particular problem.  You're asking a series of vague questions "how does it work", along with detailed questions "why is it done this way".  They're all nice questions, but they can usually be answered by reading the source.  The code is VERY well commented.  I see no reason to cut & paste those comments here.  Alan DeKok. - List info/subscribe/unsubscribe? See http://www.freeradius.org/list/users.html