IPsec and racoon, custom function

Question

Im working on setting up IP sec and im a bit confused.

 setkey                racoon  <-------(IKE)-------> somebody
   |                    ^  |      (5)
   |                    |  |(6)
   |(1)           +-----+  +---+
   |           (4)|            |
   v              |            v
+-----+  (2)      |    (3)  +-----+
| SPD |<----- kernel ------>| SAD |
+-----+         |           +-----+
                |(7)
                v
(1)The administrator sets a policy to SPD by using setkey.
(2)Kernel refers to SPD in order to make a decision of applying IPsec to a packet.
(3)If IPsec is required, then kernel get the Key for IPsec-SA from SAD.
(4)If it is failed, then kernel send a request to get the Key to racoon.
(5)racoon exchange the Key by using IKE with the other to be established IPsec-SA.
(6)racoon put the Key into SAD.
(7)Kernel can send a packet applied IPsec.

That was on the KAME website. How does Racoon set itself up to recive requests fromm the kernel? Im using Ubuntu, and I don't understand the interface. I need to write a program to go between the kernel and racoon.