Scenario
This article describes how to create a secure network-level transport between two hosts. All traffic sent between both hosts will be encrypted automatically as in enters the TCP/IP stack at the network (IP) level by using IPSec Encapsulating Security Payload (ESP) protocol.
For more details about IPSec, read IPSec pilot between glass and teapot.
Security Policy Database [...]

I have established a secured ESP-only IPSec link between glass and teapot using Fedora Linux Core 2 native network interface configuration. I have opted for manually keyed Security Associations since there are a few glitches when using racoon’s ISAKMP implementation and KAME 2.6 kernels IPSec implementation that I’m describing right now:

Userspace and on-demand SA establishment [...]