[lug] Listening services and NAT on both ends

[Chris Riddoch]

Here's a scenario: two users across the internet from each other would
like to provide each other access to their systems - perhaps SSH, or
HTTP, but the specific service doesn't really matter.  Both are behind
NAT.

If one user has access to the system doing the NAT, they can set up a
port forwarding rule to direct appropriate ports to the system
providing the service.  This isn't even that hard anymore.

But suppose both users are on laptops at coffee shops, where neither
has access to set up port forwarding rules, and neither has a hosted
server someplace else they could both connect through - they're
nontechnical users, with no need for such a server in general.

For most cases of chat services or VoIP, they'll both be connecting
through some outside server.  But suppose it were a service that's not
designed for use with intermediaries, like SSH or VNC?  Something
where you'd ordinarily set up a port forward, if you had permission to
do so?

Someone asked me about a specific case of this problem the other day,
and honestly, I'm stumped.  What would you suggest?

-- 
Chris Riddoch