Application Level Gateway (ALG) objects providing protocol specific support for port forwarding. The first object returning non-null in a call to its connection method will be the one that handles that particular connection.
((protocol, in_port, forward_ip, forward_port)*). Sets up port forwarding listening to port in_host on the host machine and forwarding to port forward_port on ip forward_ip within the simulated environment. Protocol must be either tcp or udp.
TCP layer. Must implement the tcp interface.
((protocol, in_port, forward_ip, forward_port)*). The format of this attribute is identical to the connections attribute. This attribute contains temporary port mappings that are set up by the NAPT protocol handler.
UDP layer. Must implement the udp interface.