gvpe

creates a virtual ethernet between multiple endpoints
GVPE creates a virtual ethernet (broadcasts supported, any protocol that
works with a normal ethernet should work with GVPE) by creating encrypted
host-to-host tunnels between multiple endpoints.
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Unlike other virtual private "network" solutions which merely create a
single tunnel, GVPE creates a real network with multiple endpoints.
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It is designed to be very simple and robust (cipher selection done at
compiletime etc.), and easy to setup (only a single config file shared
unmodified between all hosts).
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VPN hosts can neither sniff nor fake packets, that is, you can use
MAC-based filtering to ensure authenticity of packets even from member
nodes.
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GVPE can also be used to tunnel into some vpn network using a variety
of protocols (raw IP, UDP, TCP, HTTPS-proxy-connect, ICMP and DNS). It
is, however, primarily designed to sit on the gateway machines of
company branches to connect them together.