Topology: 

host 1 ------------------- vpn-gw 1 <----------------------------> vpn-gw 2 ------------------ host 2
                                               |                                       |
                                |                                     |
<--192.168.50.0/24-->    10.15.109.36                  10.15.109.5      <--192.168.1.0/24-->

Setup:

  1. Install the openswan package. Now we got 2 main files: /etc/ipsec.secrets and /etc/ipsec.conf
  2. Edit ipsec.secrets for vpn-gw 1: 

      10.15.109.36 10.15.109.5 : PSK "password
  1. Edit ipsec.secrets for vpn-gw 1: 

      10.15.109.5 10.15.109.36 : PSK "password"

  1. Edit ipsec.conf for vpn-gw 1 & vpn-gw 2 (same exact stuff): 

      conn vpn
      authby=secret
      left=10.15.109.36
      leftsubnet=192.168.50.0/24
      leftnexthop=10.15.109.5
      right=10.15.109.5
      rightsubnet=192.168.1.0/24
      rightnexthop=10.15.109.36
  1. Restart ipsec: 

      /etc/init.d/ipsec restart
  1. Now you can ping from host 1 to host 2!