1.1. Networking Basics:
- Each point(=computer, router, …) on a network has an IP address to uniquely identify that point. Compare this with sending someone a letter through the post: the postman needs to know the destination address to deliver the letter to the right person.
- There are two networks at play:
(1)– the internet. The internet uses ‘public’ IPs (=unique in the whole world).
(2)– your Local Area Network (LAN) in your home (can be just one computer). The LAN uses ‘private’ IPs (=unique on your LAN only). Why the two? Well, each IP address on a network needs to be unique on that network to make sure that the data arrives at the right point. Checking whether an IP is unique on a small network is a lot faster than checking it against every IP in the world. Note that the point which connects the LAN to the internet (=the “accesspoint”) holds two IPs: the public IP that uniquely identifies the accesspoint on the internet, and a private IP that uniquely identifies the accesspoint on your LAN. For example: a router will be identified by the public IP on its public side, and by the private IP on its private side. If you’re having trouble with more than one device, like a modem+router, then just draw a schematic of your LAN, and write down the IP(s) next to each device – remember that some devices will have two IPs: one on each side. This will make it easier to spot which IPs can be seen directly by a device – a router will always shield the devices connected to its private side from being seen by devices connected to its public side (=the router’s NAT function). - Ports are just channels for sending data through. If you had just one port, then only one program at a time would be able to use the connection, so that’s why you have 0-65535 ports. Ports below ~3000 are mostly associated with a particular program, so it’s better not to use those because some ISPs block certain ports to block the associated programs (sometimes virusses/worms). For BitTorrent, it’s best to choose a random high-numbered port (like in the 20000-65535 range) that is marked as “unassigned” by the list on this page:
IANA Port Numbers
I used port 54321 in all the examples below because it’s an easy to remember number. Remember also that the port that you’re forwarding on the router, or opening on a firewall, needs to be the port that your BTclient is using (or that your game is using, if you’re using this guide to open a port for an online multiplayer game). BTclient programs allow you to change the port(s) that’s being used. - Note that each port can only be forwarded to one computer at a time, and should only be used by one program on that computer. So if you are using a BitTorrent client on multiple computers, then each BTclient on every computer needs to have a different, unique portnumber that is not being used by any other computer or program.
- A connection can be initiated by either a computer on your Local Area Network (=Local connection), or by some outsider connecting to you via the internet (=Remote connection).
- A firewall is something that looks at each packet of data, and evaluates whether it is properly formatted, and whether the packet is allowed to reach its destination IP. By default, every firewall will keep all 0-65535 ports closed (the Operating System will open certain ports, like normal webbrowsing).
1.2 How to find IP address on your network?
- All connection info can be found by typing ipconfig into a CommandPrompt (type cmd into the START>RUN box to get a CommandPrompt). ipconfig will give you the following output:
If you want even more connection information, then type ipconfig /all
Quote:
– IP Address: the internal, private IP Address of your computer.
- Subnet Mask: not important
- Default Gateway: the private IP Address of your router (if you have one). Or in general: the IP of the device connected to your computer that offers you a ‘gateway’ to the internet.
1.3 How to set up a static IP for your computer?
The function that makes sure that the private IPs on your local network are all unique, is called the DHCP function. There should be only ONE device(=router, or Operating System on computer) that is configured as the DHCP Server, which tells the other devices(=DHCP clients) what their private IP is, so that all IPs are unique. To avoid problems with the DHCP Server assigning a different private IP to your computer while you’re using a BTclient, and thereby making the portforwarding invalid, it’s better to manually assign your computer a private IP which will not change (=static private IP). Here’s a guide for setting up a static private IP for your computer:
First, assuming that your normal internet connection is working correctly, use the ipconfig method described in section HowTo find IP addresses on your network (1.2) to write down the working set of IP Address, Subnet Mask and Default Gateway numbers.
Second:
START>All Programs>Accessories>Communications>Network Connections will show you the list of installed Network Connections on your computer. Choose the connection that you are using to connect to the internet. Rightclick it for its properties, and the dialog box that shows up, is the one shown in the picture above. Then follow these steps:
(1)– On the General page, select Internet Protocol (TCP/IP) in the item list.
(2)– Press the Properties button.
(3)– On the TCP/IP properties panel, on the General page, select the “Use the following IP Address” option.
(4)– You can then fill in the working set of IP Address, Subnet Mask, and Default Gateway that you wrote down earlier by checking with ipconfig (see section HowTo find IP addresses on your network) . If you make a mistake, you can always reset the option to “obtain an IP address automatically” or press the Cancel button. Press the OK buttons until you’re out of all dialogboxes, and you will have set up a static IP for your computer. DONE! Note: on some routers (like Linksys), the static IP of the computer should be outside the default range (try 192.168.0.XXX <<XXX below 100). Some routers, particularly those given out by ISPs, might require you to use a specific private IP for your computer. The method above will work in all cases, but I just mention it to show that you’re not free to choose just any IP address.
1.4 How to open ports on most routers?
Most routers have built-in webpages that allow you to configure the router. You can access those webpages by typing the router’s private IP into the URL-AddressBar of your normal webbrowser. You can find the router’s private IP by typing ipconfig into a CommandPrompt (type cmd into the START>RUN box to get a CommandPrompt). The router’s private IP will be listed as the IP for “Default Gateway” (see section HowTo find IP addresses on your network). Because outsiders (normally) only know your public IP, the router needs to make sure that datapackets sent to that public IP, end up on the computer that is running the program which needs the data in the datapackets (a router isn’t a computer so it can’t use the data itself, just deliver the packets of data to the right IP address). But a router will always shield the devices connected to its private side from the outsiders on the public side, so the router needs to be told explicitly that datapackets sent to the public IP are allowed to be sent on to the private IP Address of your computer. This is called the NAT function (Network Address Translation) and as there are 0-65535 ports that data can be channeled through, the router can be configured to do this on specific ports only, via the NAPT function (Network Address Port Translation — “Network Address” is another name for an “IP Adress”). The NAPT function is also known as PortForwarding, because you basically tell the router to forward control over [the data coming in on] a specific port, to another point on your network – usually to the computer with the program that will handle the data. PortForward.comThe site above has specific portforwarding guides for different router-models. The procedure of portforwarding will differ from router to router, and manufacturers often use their own names for certain functions and settings. So my guide below is meant to give you a general idea of how to forward a port on your router if your router does not have a specific guide on that website:
- External IP: your normal, public IP. You can find out what that is by browsing to WhatsMyIP.com and the router’s webpages will certainly mention it somewhere too. Note that if you have a dynamic public IP which changes occasionally, you will either have to redo the portforwarding each time the IP changes, or you can use 0.0.0.0 as external IP which will make the router automatically replace it with your current public IP.
- Internal IP: this is the private IP of your computer. Check section HowTo find IP addresses on your network to find out what it is. If your router only needs one IP Address to be given, then this is the IP that you should fill in, as your router just needs to know where to send the datapackets to.
- external & internal port: the port that you are opening by forwarding control over it from your router to your computer. This is the port that your BT client should be configured to. Use the same port number for both internal & external. Avoid using the standard BitTorrent portrange (6881-6889), best is to pick a random port number between 20000 to 65000, but keep in mind that your BT client must be configured to use that same port, and make sure that no other program is using it – either on the same computer or on any other computer on your network. Each BTclient on every computer needs to have its own port(s)!
- protocol: TCP is used for normal downloading and uploading. This may change to UDP in the future, though.
1.5 How to open port in Windows?
There are several methods for opening a port in Windows (I’ll list three). Method 1 & 3 are only available in Windows XP with ServicePack2. Method 2 will also work in Windows XP SP2, and a part of method 2 (from step 4)can be used in other Windows versions.
First, for all three methods: make sure that the Windows Firewall Service is active. Type services.msc into the START>Run box to view the list of XP Services. Find the Windows Firewall/Internet Connection Sharing (ICS) service and right click it for ‘Properties’. On the General page of its properties, set the “Startup Type” to Automatic, press Apply, and then press the Start button so the service is activated. —————————[Method 1]
ControlPanel>Windows Firewall will then give you the dialogbox shown in the picture. Follow these steps in there:
(1)– On the General page, turn the Firewall ON
(2)– disable the option “Don’t allow exceptions”
(3)– On the Exceptions page, press the “Add Port” button
(4)– On the ‘Add a port’ panel, fill in:
Name: Whatever you want to call it (example: BitTorrent).
Port Number: the port that your client is using. (port 54321 is just an example)
TCP: the TCP protocol is the one BitTorrent uses (may change to UDP in the future).
Press the OK buttons until you’re out of the Windows Firewall dialogbox and you will have opened that port in Windows! DONE!
—————————[Method 2]
ControlPanel>Windows Firewall will then give you the dialogbox shown in the picture. Follow these steps in there:
(1)– On the General page, turn the Firewall ON
(2)– disable the option “Don’t allow exceptions”
(3)– On the Advanced page, Select your Local Area Connection, or if there’s more than one, select the connection which you are using to connect to the internet.
(4)– Press the “Settings…” button to see the ‘Advanced Settings’ Panel. This is the panel that will be shown in other Windows versions (and XP without ServicePack 2) when you use Microsoft’s explanation of “Adding a Service to a connection” (5)– Press the “Add…” button to show the ‘Service Settings’ panel, and on this page you can fill in the following:
-
- Description of service: Whatever you want to call it (example: BitTorrent).
- Name or IP address : the private IP of your computer. To find out what that is, check section HowTo find IP addresses on your network
- External Port number: the port that your client is using. (port 54321 is just an example).
- Internal Port number: the port that your client is using. Same as External Port number.
- TCP: the TCP protocol is the one BitTorrent uses (may change to UDP in the future).
Press the OK buttons until you’re out of the Windows Firewall dialogbox and you will have opened that port in Windows! DONE!—————————[Method 3]
Instead of opening a port, you can also tell the Windows Firewall to allow a program to open and use the ports it needs. This is the guide for that:
ControlPanel>Windows Firewall will give you the dialogbox shown in the picture of [Method 1]. Follow these steps in there:
(1)– On the General page, turn the Firewall ON
(2)– You can partly use the picture for [Method 1] to guide you, but instead of pressing the “Add Port” button, press the “Add Program” button to add your BTclient program to the list of XP Firewall Exceptions.
(3)– On the following “Add a Program” panel, press the “Browse” button to select the program you want to give full access to the internet. Note that for most BitTorrent-clientprograms, you can simply select their main .exe program (for example: btdownloadgui.exe for BitTornado — in its install folder), but for older versions of Azureus, you need to specify the javaw.exe program, which can usually be found in this folder (or a similar one, depending on the Java version):
C:\Program Files\Java\jre1.5.0_04\bin
For the latest version of Azureus, it’s simply the azureus.exe in its installfolder.
(4)– After selecting the program, set the scope for it by pressing the “Change Scope” button. Set it to “Any computer on the internet” so your BitTorrentClient can connect to others.
(5)– Press the OK buttons until you’re out of the Windows Firewall dialogbox and you will have opened that port in Windows! DONE!
1.6 Automatic Portfowarding via UPnP
Some BTclients have the ability to forward the port(s) they use automatically via UPnP (Universal Plug And Play). What’s needed to make this work, is:
– have a router that supports UPnP, and its UPnP function enabled. Check the router’s built-in webpages or the manual.
– the router needs to be connected directly to the computer (no other devices inbetween).
– the Operating System (Windows) must support UPnP and have it enabled. In XP, check the XP Services by typing services.msc into the START>Run box. Look through the list of services and find these two:
- (1)– SSDP Discovery Service
(2)– Universal Plug and Play Device Host
For both services (in that order), rightclick them for Properties, and on the General page of their properties, set the “Startup Type” to Automatic, press ‘Apply’, and then Start the service. The next time you start your BTclient, the portforwarding will then be done automatically. Note that this may lead to error-messages if the ports were not closed automatically when exiting your BTclient.If the services are not in the list, then you need to install UPnP first. Here’s a Microsoft guide on how to do that: Microsoft KB821371
1.7 How to test whether a port is really open or not
The port is open if you FAIL the ShieldsUp test at http://www.GRC.com/ (shown partly in the picture)
(1)– Type the portnumber into the textbox in the middle of the screen.
(2)– Press the “User Specified Custom Port Probe” button to start the test
(3)– Result of the port-test. You need to FAIL the test for ‘Solicited TCP packets’. If you fail the test, then the port is open, even though it may say “closed” for status, because your BT client isn’t using the port at that moment.
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