A VirtualPrivateNetwork is a private network connecting (some of its) nodes by tunneling traffic over a public network. Alternatively, if you have far too much money, instead of tunneling, you can use a dedicated data circut provided by your TelCo. Most VPNs only tunnel a single connection between two end points that serve to merge two LANs.

VPNs often run on SSL (a Free implementation is OpenVPN) or IPSec.

The MetaNet is an uncommon VPN, in that it is multipoint, and doesn't do encryption, authentication, or compression.

Why not? Those things sound kinda useful -- CraigBox

Simple answer: too difficult to code :) more important getting the easy bit going first. Also encryption/compression could very easily overwhelm some people's gateway boxen -- PerryLorier

The new wand/wansd implementation that I sort of have coded, will do authentication, I personally don't think encryption / compression should be done at this layer, use IPsec, HTTPS etc. -- MattBrown