Firewalls are usually placed at the connection to the internet. They shield local networks from outside attacks by screening incoming traffic and rejecting connection attempts to host inside the firewalls by outside machines. Most firewall systems allow hosts inside the firewall to connect to hosts outside it (outgoing traffic), however, incoming traffic is most often disabled entirely.
Tunnels are host protocols which encapsulate other protocols by multiplexing them at one end and demultiplexing them at the other end. Any protocol can be tunneled by a tunnel protocol.
The most restrictive setups of firewalls usually disable all incoming traffic, and only enable a few selected ports for outgoing traffic. In the solution below, it is assumed that 2 TCP ports are enabled for outgoing ports; one for the gossip daemon and one for the JRouter.