IPSec is tricky, but worse than that, existing documentation is very messy.

• IPSec Exchange modes
• IPSec policy

	 setkey                racoon  <-------(IKE)-------> somebody
	   |                    ^  |      (5)
	   |                    |  |(6)
	   |(1)           +-----+  +---+
	   |           (4)|            |
	   v              |            v
	+-----+  (2)      |    (3)  +-----+
	| SPD |<----- kernel ------>| SAD |
	+-----+         |           +-----+
                        |(7)
                        v

This sums up some of the technical details about IPSec. Starters should read a more detailed documentation.