If you need an open port on your router then you need to create a port forward. Open ports are used to allow a connection in to your home network from the Internet. They are common in gaming, torrenting, and VOIP configurations.
From Inside of Your Network
Here’s a map of a simple home network.
As you can see, you’ve got three computers with unique IP addresses all connected to a router. You can easily access the other computers, but when they all access the internet, they go through the router. The router has an IP address that’s relative for you network, but it also has an external IP, one that it uses when interacting with things outside of your network. Whenever these computers make a request towards the internet, they all use the same IP – 127.34.73.214 in our example. Simple requests, such as loading web sites, are automatically handled by the router and are sent to their appropriate places. It’s not too difficult because each computer starts with a unique request, so it’s not hard for the router to figure out where things should go.
Ports and Protocols
Ports help make this process easier. If an IP is like a building’s address, then ports are like the apartment numbers for the residences in the building. Lower numbered ports have specific applications which are standards throughout the computing industry. When you fetch a web page, for example, it uses port 80. The receiving computer’s software knows that port 80 is used for serving http documents, so it listens there and responds accordingly. If you send an http request over a different port – say, 143 – the web server won’t recognize it because it’s not listening there, although something else might be.
Each port can be used via either TCP or UDP. TCP, or Transmission Control Protocol, is what’s used most commonly. UDP, or User Datagram Protocol, is less widely used in home applications with one major exception: BitTorrent. Depending on what is listening, it’ll be expecting requests to be made in either one or the other of these protocols.
From Outside Your Network
Now let’s take a look at what happens when a device outside of the network starts a request.
Let’s say you’re out and about and what to access a file on your network. Your computer makes a request to your home network’s IP, 127.34.73.214, which then goes to your router. Your router doesn’t know which computer to send it to.
Thankfully for us, we can configure our router to forward ports. This means that depending on the port number that the request is sent over, the router can pass it along to different IP addresses.
If you want to know how to configure your router to forward a port, please see the link below: