ppp over ssh

VPN (Magosanyi 1997)
VPN (Bronson 2002)
VPN (Wilson 1999)

sshpppd - automate it

VPN Part 1, Linux Journal 12/99
VPN Part 2, Linux Journal 1/00
Titz: ssh+ppp=bad

Further Information

A vpn can be constructed by running ppp over ssh.

A ppp connection is established between two computers when they run the "ppp program" reciprocally.

ssh (1) allows triggering an arbitrary program to run on a remote computer, (2) encrypts the data stream between the participating pair of computers.

If for (1) you choose the ppp program as your "arbitrary program," plus run it locally and reciprocally, the ppp connection gets established. But it flows unlike normal within an encrypted data stream.

If each of the computers serves a LAN it belongs to as a gateway, the two LANs collectively become a vpn:

virtual - because they are not a single network
private - because data passing through public hands between them is in inaccessible form
network - because all arbitrary pairs of the computers can communicate by address