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Get Programs to Point to Your Computer within Your Home/Office Network or Through the Internet. Ports are one of the many complex methods used to transmit data between computers. Learning how to manipulate and work with these ports will greatly increase your knowledgeable of networking.
Computers generally send data to each other by a network built by cables (physical connection) or wireless (radio frequencies). For normal cases, computers cannot simply connect to each other directly, they have to be placed in networks and identify themselves with an IP address. Routers are usually the gateways for networks; every network has a router that holds together the entire network. The router connects all the network devices in your home together, such as computers, printers, security cameras and more. The router assigns an IP (a unique number with with 4 sequences x.x.x.x "example: 192.168.1.105") to each network device and makes sure they are all connected to each other through the router . These IP addresses are used by the devices to decide which IP they want to send information to. For example, a computer might want to print to Network Printer B, instead of printing to Network Printer A. To do so, the computer will send the print command to Network Printer B's IP address (192.168.1.108) instead of Network Printer A's IP address of (192.168.1.109). Some things to remember: - IP's assigned by your home/office router are considered INTERNAL IP's or Local Area Network (LAN IP's) IP's. The reason is because your computer is not identified to the rest of the world using that IP. That IP address is only to identify your computer from WITHIN that network. - Every internet service account is assigned it's own IP. This IP is called an EXTERNAL IP. When you connect to another computer outside of your network, it identifies you by this IP. This basically means that all computers in one network will have different INTERNAL IP addresses, but will all share the same EXTERNAL IP address. For example if all 5 or your computers from within the same network send information over the internet to another computer, the receiving computer will see the same External IP address 5 times. - External computers (PC's outside your network) will NEVER associate with your Internal IP, only your external one. And internal computers (PC's inside your network) will only associate with your internet IP. So you as you can see... IP addresses are used as directional markers to transmit data, but how are ports used? Ok, think of the data path as a highway. The highway goes forwards (NORTH/outgoing) and backwards (SOUTH/incoming). The cars traveling on this highway would be the bits of data traveling back and forth. Each lane resembles a different port. For example, Lane 1 going SOUTH would be considered PORT 1 INCOMING, Lane 1 going NORTH would be considered PORT 1 OUTGOING, Lane 2 going SOUTH would be considered PORT 2 INCOMING, and so on and so forth. So more or less, the ports are different lanes on the highway sending data out from one device to another. Here comes more important concepts to remember:
- Every program sends data through a DIFFERENT PORT! No two programs can share the same port!
- There are thousands of ports available for use! I think from you can use Port 1 - Port 64,000.
- You can block use to certain programs by blocking the ports that the programs use. Internet browsers use port 80, AOL Instant Messenger uses port 5190, RealVNC uses port 5900, Outlook uses port 110 incoming for receiving emails and port 587 for sending outgoing emails, and so forth. Some programs use the same port to send and receive information, others use different port numbers to send/receive information. The bottom line is, if you block any of these ports with a firewall program, the program won't connect and won't work. Security - Yes, ports are open holes into your network and your computers. If you've ever wondered what Firewall programs really did, here is the perfect time to ask! Ok, so what DOES a firewall program do? Firewall programs more or less, block all the ports that your computer doesn't use. And then when you or someone else tries to use or send data with a new program, the new program will try to access a blocked port, which causes your firewall program to prompt you with a window asking you to Grant Access or Block Access to the program (which means opening/closing the port). Port forwarding is a method used by routers to deliver data to a specific computer on the network. Usually, port forwarding is required when the diagram below is in effect: PC A - > Router -> Internet -> Modem -> Router - > PC B As you can see, remote access is needed when two computers are trying to connect to each other from different networks. PC A could be China on its own network and PC B could be in Mexico on its own network. They are connecting to each other outside of their own networks THROUGH the internet. This situation is tricky because the two computers aren't on the same network anymore. Suppose they WERE on the same network, PC A could send information to PC B simply by sending the data through PC B's network IP (192.168.1.137). - Now we all know the situation isn't that simple. So how does it work? Easy! All you have to do. Is to tell the router to FORWARD THE PORT to a specific computer. For example, let's say we're setting up RealVNC (remote desktop access software), so that you can connect to your home computer while you're out traveling the world). We are going to pretend that your network diagram looks as follows: PC A -> -> Internet -> Modem (assigned external IP by ISP 72.190.2.41) -> Router (assigned external IP By modem 72.190.2.41) -> PC B (assigned internal IP 192.168.137 by router)
PC C (assigned internet IP 192.168.1.136 by router)
PC D (assigned internal IP 192.168.135 by router). RealVNC uses port 5900 by default. So lets say that PC A sends info to PC B, by sending it to IP address 72.190.2.41 through port 5900. Notice how the information will get to the router and then the router won't know where to send the data. There's nothing else in the data that tells the router where to send it. In this case, we use port forwarding. Port forwarding can be used by going to the Port Forwarding options in your router setup page. Your router setup page is usually located at the router's IP for most people that's 192.168.1.1. If you don't know your router's IP, go to the command prompt and type "ipconfig" or go look in the routers manual. Many routers will list the names of the Port Forwarding option differently. Some will name it "Port Forwarding". Others will call it "Virtual Server", "Applications & Gaming", "Port Options", "Advanced Options", "Ports", etc. The reason for all the different naming schemes is because the router companies want to make it easier for average user to find and edit these options. The only problem is that by assuming that all computer-users are "beginners", they end up confusing the users with different names amongst the brands. What we would have to do is type in the information so that Data coming from port range (5900-5900) will get forwarded to the PC B's internal IP address (192.168.1.137). From here, your program should instantly work and connect. You can repeat the same steps for different programs, ports, and computers and enjoy the great flexibility of port forwarding! Some more tips:
- If your programs still don't connect, check the PC on the receiving end and make sure you have the ports open in the firewall. Don't forget that Windows XP comes with a built-in firewall. The easiest way to see if it's the firewall, is to just disable all your firewall programs. You can also try using another port. You can also check the port forwarding settings on the router setup page and make sure that the port forwarding is "ENABLED" (many people miss out on this one). - If you have want to use 1 program to connect to two different computers remotely, EXAMPLE: simply configure one computer to use another port. And then in the router port forwarding settings, forward one port number to PC B, and the other port number to PC C.
- Also check the external IP address of the computer you are trying to connect to. Don't forget that most DSL users have a dynamic IP address, which means the IP will change constantly (even several times within the hour!). Also check the internal IP address of the computer your are trying to connect to (you can do this by typing "ipconfig" at the command prompt). - A good tip is to assign an IP manually to your computers instead of using the obtain IP automatically option. You can edit these settings at Control Panel > Network Connections > goto Properties for LAN connection> select Internet Protocol TCP/IP > Properties. Assign IP's is usually a good idea because the computer's IP will always be the same even if you restart it. A changing IP means you have to keep editing the port forwarding settings (you don't want this). So remember to assign a static IP on the computers that take remote connections. I hope you like this guide and that it made things fun and easy for you to learn about ports and port forwarding. I wish you the best of luck and do visit our forums if you still have questions! There are tons of programs that require port forwarding. Most programs that require port forwarding are the ones that host data remotely. For example, a remote access program like RealVNC. You can check out our guide HERE. And learn how to work with Port Forwarding.
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