VPN Planning
To properly configure FreeS/WAN, you must understand a little about how it works. FreeS/ WAN creates a virtual network by binding a virtual device ipsec0-ipsec999 to a real device such as eth0, tr0, ppp0, or any other real communications device attached to your system. Entries are made in the system routing table. Routes going from one encrypted system to another will be more specific than the general default route, so the ipsec device will be chosen to send the message. Messages sent through the ipsec device are encrypted when they are transmitted.
This explanation glosses over a few things. The most important point it glosses over is which packets (from which sources) will be encrypted. Later in the configuration you will choose ...
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