Routers and Port Forwarding

One of the most common devices in any given network — after computers, of course — is the router. Sitting between the modem and the other devices in the network, the router's job is to route (direct) traffic to and from the Internet and devices in the local area network (LAN), sharing a single Internet connection between multiple devices.

A router is more than just a glorified cable splitter, however; in addition to intelligently juggling packets and priority between devices to ensure smooth data transfer, most routers include a variety of features including Quality of Service settings, virtual private network options, web content filtering, time-delimited access restrictions, and more.

At factory default, most routers are preconfigured with a variety of security settings, including a firewall set to reject new incoming connections to the network. This security measure is simple, effective, and rarely obtrusive; surfing the Internet, watching streaming video and chatting with friends and family is uninterrupted, since these connections are established first by an outgoing connection from the LAN.

Since the router's firewall prevents Internet visitors from reaching any devices in the LAN, the user must open a tunnel in the router's firewall to allow specific external connections to reach a specific destination device while keeping the rest of the network safe.

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:

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

The best source for more detailed information about routers and port forwarding, as well as step-by-step pictorial walkthroughs for most common routers, is PortForward.com. If you are setting up a new service and configuring your router for the first time, it is highly recommended to read their guides and walkthroughs to determine the necessary changes you will need to make to correctly forward ports in your router.