Port Forwarding

All TCP and UDP traffic on the Internet uses ports to identify the procotol being used, such as port 80 for HTTP (web) and port 25 for SMTP (email). To solve the firewall problem and let visitors into the network, the user instructs the router to allow traffic to pass through on a given port. This is known as port forwarding, as the router forwards (directs) all Internet requests on a specific port to the local machine. With port forwarding, external visitors are able to connect to the server while other internal devices remain protected.
There are three different kinds of port forwarding:

• Port Forwarding: Standard port forwarding is an "always on" tunnel through your router's firewall. Any visitor may connect to your network on the given port at any time. This is the correct choice for "always on" services such as webservers and mailservers.
• Port Triggering: This is a special kind of "temporary" port forwarding that requires an initial outgoing connection. Once the connection is established, the router begins forwarding all new incoming connections to the local machine; when the local machine closes the connection, the forwarding rule is turned off. This rule is most commonly used in gaming, video conferencing and other applications that receive incoming connections on a need-only basis.
• DMZ (DeMilitarized Zone): This feature effectively places the destination device outside of the router's protective firewall by forwarding all incoming connections on all ports to the single local machine. The DMZ is mostly used for troubleshooting purposes and advanced network configurations; as such, it is not recommended to use the DMZ for general hosting purposes.

In most routers, a port forwarding rule take the following information:

• Application Name: The label for the forwarding rule.
• Start and End Port: The application's port(s), e.g. 80 for HTTP. Many routers will allow you to forward an array of ports with a single rule.
• Protocol: The protocol (TCP, UDP or Both) for the forwarding rule. The protocol depends on the type of service you are providing (e.g. webservers use TCP).
• IP Address: The internal IP address of the destination device in the LAN, usually beginning with 192.168.x. If your router dynamically assigns internal IPs with DHCP, you will need to configure the server device to use an internal static IP address.