I have written a simple tunnel client/server daemon, the UDP Tunnel
Daemon (UTD), that demonstrates both the UDP encapsulation and the socket
delegation features of gre(4).  UTD is useful for tunneling through NAT
gateways.  I announce it here just in case it is useful to somebody else,
and just in case somebody would like to collaborate on the development.

UTD has neither authentication nor privacy features, but those need not
be difficult to add.  I believe UTD can set a tunnel's IPsec policy using
setsockopt(s, IPPROTO_IP, IP_IPSEC_POLICY, ...) on the UDP socket before
delegating the socket to gre(4).

UTD will work best with NetBSD-current of 21 Mar 2007 or later.

The sources for UTD are at
<http://svn.cuwireless.net/svn/cuw/trunk/src/utd/>.  It depends on some
libraries one directory above it.

Dave

-- 
David Young             OJC Technologies
dyoung@ojctech.com      Urbana, IL * (217) 278-3933