How does one do firewall-busting? Is that a valid term? Say I wish to communicate with another host directly, without the use of central servers, even though both I and the other host are behind firewalls? Can the two cooperate to help open firewall holes for each other? I presume that I would either need to use a central server first or some established working service, like email (!) - the latter would be desperate - in order to bootstrap the conversation.
