Port Forwarding
Lets say College University has a LOT of Biology teachers. Some have classrooms in Building 1, while others are in Buildings 2 or 3. If someone writes a letter addressed to the Biology Department, where does it go? For something like this, you’d want the mail room staff to know that all letters for the Biology Department should go to the head of the department in Building 1.
Similarly, if someone on the internet tries to pull up a webpage from your IP address (9.9.9.1), which computer does the router send that traffic to? You’ve got to tell the router that all webpage requests should go to your web server at 192.168.1.101.
Different types of internet traffic run on different “ports”. WWW traffic usually runs on port 80. Whether you know it or not, when you open up “MakeTechEasier.com” you’re really opening up “MakeTechEasier.com port 80″. Go ahead and try it, you can put “maketecheasier.com:80″ into your address bar. What you’re doing is asking for our web site’s WWW department. That same address, with a different port number, wouldn’t give you anything. Try “maketecheasier.com:99″. Nothing, right? That’s because you’re asking your web browser the equivalent of “Show me MakeTechEasier.com’s Pancake Department”. Well, sad to say, we don’t have a pancake department.
Port numbers can go up above 65,000. Some port numbers are reserved for certain kinds of common internet traffic, like port 80 for WWW traffic or port 23 for telnet. Most of those 65,000 or so are available to be used at your own discretion. If I want to run, say, a music streaming server from my home computer, that streaming software will be set to use a certain port number like 8080. If someone wants to access my music share, they would look for it at my IP address with a port number of 8080, such as “http://9.9.9.1:8080″. I would need to tell my router to send all traffic for port 8080 to my computer (192.168.1.100).
Most routers can be accessed by entering their IP address into your web browser, most commonly “192.168.1.1″. You log in with the router’s username and password, and look for port forwarding (sometimes called Virtual Servers) settings. You’ll need the source port (8080) as well as the computer that will be getting that traffic (192.168.1.x) and all requests for port 8080 will be forwarded to the computer you specified.
Conclusion
Obviously, there’s a lot more that could be said about home networking. Things like DNS, firewalls, PPPoE, all these can change the way your computer connects to the internet. The subjects listed here are the ones people deal with every day when it comes to things like web browsing, gaming, and file sharing. Some routers will give out addresses completely different from our examples (such as 10.0.0.x) but the same principles apply. Everything has an IP address, and for traffic to go both ways you sometimes need to know about how NAT and ports affect your connection. Next time your torrents run too slow, or you want to host files over FTP for your friends, you’ll be prepared.
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Thanks Josh for making a layman understand Home Networking in such an easy and interesting way. I have found a website http://www.aafter.com, where finding one’s computer IP address is much easier. You simply have to type IP in the search box and the search box provides the IP address. The site also happens to be the first in the entire web world to provide a large search box where as many characters could be entered.
Josh, I look forward to more such interesting posts from you.
Tony Smith.
Nice article, I wouldn’t advice people who just learned what a ip address is to start forwarding ports in their router though. This could easily create a big security hole.
Anyone forwarding a port to their internal network should be pretty sure there are no known security leaks in the software they have listening on that port (and then still).
But it’s a nice article though!
I included port forwarding because it’s the kind of thing that just about everyone needs these days with torrents and all. You’re right though, a security warning might be a good idea.
This is a little bit of an oversimplification of IP masquerading. I know that you were trying to make it simple, but as long as you were going to bring up ports anyway, the statement, “The rest of the world doesn’t need to know anything but your main outside IP address,” is not quite accurate. You could either say, “The rest of the world doesn’t need to know any IP address but your main outside one,” or else explain how ports figure in to translation. I know it’s a nitpick, but when simplifying I always try to stick with technical accuracy as far as possible, or clearly identify each statement that is not technically accurate, but close enough for the depth of the explanation. Incidentally, the other private address range should be listed as 10.x.x.x, since only the 10 is static.
Hmmm… “IP addresses come in the form of “x.x.x.x”, each x being a number from 0 to 254″
I think you mean “from 0 to 255″
@ Frank
255 is typically reserved as a broadcast address and therefore not assigned anywhere.
Sorry, (to clarify), it is not used in an IP address range
You beat me to it. Yes I deliberately left it at 254 as the highest usable address for a device in most circumstances.
http://www.tonyphamilyman.com