XORP design philosophy is:

• modularity
• extensibility
• performance
• robustness

This is achieved by carefully separating functionalities into independent modules, and by providing an API for each module.

XORP divides into two subsystems. The higher-level (“user-level”) subsystem consists of the routing protocols. The lower-level (“kernel”) manages the forwarding path, and provides APIs for the higher-level to access.

User-level XORP uses multi-process architecture with one process per routing protocol, and a novel inter-process communication mechanism called XRL (XORP Resource Locator).

The lower-level subsystem can use traditional UNIX kernel forwarding, or Click modular router. The modularity and independency of the lower-level from the user-level subsystem allows for its easily replacement with other solutions including high-end hardware-based forwarding engines.

Here are a few suggested readings, in order:

1. Slides of a brief presentation about XORP during the Ecode plenary meeting at INRIA Sophia Antipolis.
   The first pages should give an overview of what is XORP, and how it globally works. ^{1) 2)}
2. Read the XORP Design Documentation, it is suggested to read it in the following order:
   1. XORP Design Overview
   2. XORP Inter-Process Communication Library Overview
   3. XRL Interfaces: Specifications and Tools
   4. XORP Forwarding Engine Abstraction
   5. XORP Routing Information Base (RIB) Process
   6. XORP Router Manager Process (rtrmgr)
   7. XORP Libxorp Library Overview
   8. An Introduction to Writing a XORP Process

This will take you some time, for sure, but will be of great help when you will plunge into the code…

1. XORP Design Overview
2. XORP XIPC Inter-Process Communication Library Overview
3. XRL Interfaces: Specifications and Tools
4. XORP Forwarding Engine Abstraction
5. XORP Routing Information Base (RIB) Process
6. XORP Router Manager Process (rtrmgr)
7. XORP Libxorp Library Overview
8. An Introduction to Writing a XORP Process.
9. XORP Error Handling
10. XORP BGP Routing Daemon
11. XORP BGP Test Harness
12. XORP Multicast Routing Design Architecture
13. XORP Multicast Forwarding Engine Abstraction
14. XORP MLD/IGMP Daemon
15. XORP PIM-SM Routing Daemon
16. XORP PIM-SM Test Suite
17. Porting XORP

XORP Source code documentation

Run XORP Under Valgrind

How to do a XORP Release

The code is split into several directories, each containing libraries, components or implementation of the various XORP modules. Typically, documentation for each of them is available in one or more of the following places:

• The README file in each directory
• A high level architecture overview, available in docs/<modulename>/
• doxygen-generated documentation

The content of each of the directories is the following: