Rafixd is a project mainly written in C, it's free.
KAME's rafixd with portability enhancements
This program was initially developed by the KAME project.
http://www.kame.net/
The project can be found on Github (among other places):
http://github.com/kame/kame
The original BSD-only source on which this project is based is located here:
http://github.com/kame/kame/tree/master/kame/kame/rafixd
The program was initially ported to GNU/Linux by Eric Vyncke ([email protected]) in January 2008. It has since been updated by Gordon Stratton ([email protected]) to continue to build on modern GNU/Linux systems.
There are now two makefiles:
On a GNU/Linux system, you will use:
make -f Makefile.linux
and on BSD (maybe other?) systems, the usual 'make' should suffice.