Implementing clipping in 3D Space

I would like to implement the Cohen-Sutherland Algorithm with dynamic clipping volume in 3D Space. (i.e. with 27 regions). Assume I have somthing like this:

Code :

glBegin(GL_LINES);
glVertex3f(x1, y1, z1);
glVertex3f(x2, y2, z2);
glEnd();

1. Is clipping automatically done as default? If yes, how can I deactivate it to use my own algorithm?

2. I couldn't find an implementation for Sutherland in 3D Space. Do you know where I can find it?

Principally any algorithm would be fine as long as it does 3D clipping.

Thanks for your help!