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. On both ends, check you have a raw RSA key using: ipsec showhostkey --left
    • If not, run "ipsec newhostkey --output /etc/ipsec.secrets" on each host missing a key.

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

    • conn vpn
    authby=rsasigkey
    left=10.15.109.36
    leftsubnet=192.168.50.0/24
    leftsourceip=192.168.50.X
    leftnexthop=10.15.109.5
    leftid=@vpngw1
    leftrsasigkey=0sAQNXXXXXX
    right=10.15.109.5
    rightsubnet=192.168.1.0/24
    rightsourceip=192.168.1.X
    rightnexthop=10.15.109.36
    rightid=@vpngw2
    rightrsasigkey=0sAQNXXXXX
      • To get the proper rsasigkey values, use ipsec showhostkey. On left (vpgw1) run: ipsec showhostkey --left On right (vpngw2) run: ipsec showhostkey --right The left/rightsourceip are the local internal IP's of the vpngw's that are part of the subnet tunnel
  4. Restart ipsec: 
    • /etc/init.d/ipsec restart
  5. Now you can ping from host 1 to host 2!