Port theory, Port Map software and Minecraft

Paul P

Hello all,

both my son and I use Macs, he being on Leopard 10.5.8 with all updates, and me on Snow Leopard 10.6.8 with all updates. My son has recently expressed a desire to set up a server for Minecraft, so that he can invite his school friends to play. His reading on the internet suggested that a software called Port Map would help.

Unfortunately my knowledge of "Port Theory" is nil, so I cannot help him at all.

I am just wondering if anyone out there could help me with this issue ? Some things to consider :

1. I have a wired Ethernet router, directly connected to my computer, which connects to the internet, and my son piggy backs off this router by connecting an ethernet cable form his computer to one of the router's ports.

2. As my internet needs have always been simple, I have always had the "allow only essential services" checked in the firewall section of the OS X Security preference pane. I need to uncheck this to get Mac Port to recognise the router, which makes me a little uncomfortable.

3. I have no idea where to even start with Port map software, as I don't understand port theory at all. Any suggested settings, or attempts to explain this, would be most appreciated.

4. Do my son's friends need Port Map as well ? They are mixed Windows and Mac users.

Thanks to all in advance.


U.S.D.A. Prime
You don't need port map software, you simply need to "forward" the ports on your router to the proper computer connected to the router.

Software communicates via IP addresses combined with "ports" -- for example, if you were to run a web server on a computer behind your router, you would want to forward port 80 to that computer's local IP address, because web traffic happens (most often) on port 80. If a different computer was running an FTP server and you wanted people on the internet to access that FTP server, you would forward port 21 to that computer's local IP address (like 192.168.0.XXX or 10.0.0.XXX), because FTP typically operates on port 21.

First step is to figure out which "port" or "ports" Minecraft uses to communicate. It appears that Minecraft servers use port 25565 (information taken from here, which is a tutorial on how to set up a Minecraft server: http://www.minecraftwiki.net/wiki/Tutorials/Setting_up_a_server).

Next step is to figure out the local, static IP address of the computer running the Minecraft server. If your router is simply a "plug-and-play" configuration, meaning you simply plug an ethernet cord in to the router and the computer and the computer is "automatically" on the internet, you're likely using DHCP on the router, which simply assigns an IP address to that computer when you plug it in -- this may not work, because DHCP may not ALWAYS give that computer the SAME IP address every time it connects or reboots or gets turned off/on. This is a problem because if that computer has IP address, and you forward port 25565 to, and then the computer reboots, it may get an IP address of next time -- meaning your port forwarding "rule" is no longer valid, as it's pointing to an IP address that is no longer assigned to a computer. It's best to set up the computer running the Minecraft server with a STATIC IP address.

Imagine giving someone your home address ("123 Main St."), but then you move. People have your old home address, which is no longer valid, and no one will answer the door when they come there. Physical street addresses are like IP addresses -- they tell computers where, specifically, a certain computer is located. If the computer "moves" (gets assigned a different IP address), then the old one is no longer valid and no one will "answer the door" when trying to make a connection. Computers can "move" more often than people switch houses, making this a bigger issue in the computer world than in real-life with actual houses.

The third step is to actually do the forwarding on the router -- this process will be similar, but different, depending on the router you're using (make/model). It's simple, but we need to know what type of router you're using to give you precise instructions.

So, checklist time:

1) Find out whether the Minecraft server computer has a STATIC (yay!) or DYNAMIC/DHCP-assigned (boo!) IP address. Change it to be static. We can help with this, just let us know.

2) Specify the exact make and model of your router, so we can provide instructions on how to do a) port forwarding, and b) static IP address assignment for that particular router.

Nobody but you needs to do anything to their computers in terms of ports or forwarding or anything to get connected to your server, much like you don't need to do anything to your computer to access Google (Google does all the port forwarding and static IP assignments to their servers, then you just "connect" to them anytime you want without doing anything to your computer). Anyone trying to connect to the server doesn't need to do anything but specify your EXTERNAL IP address when connecting. This may also be problematic -- most residential internet connections also use dynamic IP assignment, so when the power goes out or your modem reboots, you may be assigned a different IP address -- meaning the IP address you gave all your friends may not actually be your IP address anymore. This can be solved with the use of a dynamic IP address service, like dyndns.org, which simply gives you a static "name" to use (like "myminecraftserver.kicks-ass.net") and then keeps track of your changing IP address so that people can always reach your server, even if your IP changes.

I know that's a lot to digest for someone just starting out, but it's really simple in theory -- we just need to walk through it step-by-step, tackling each issue in order.
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Paul P


Wow. That was quite a long post, and would have taken you a good to deal of time to write. My humble thanks to you for your efforts on my behalf.

In terms of the information you require :

1. The router is a Netgear DG834 (version 4). It is a wired ethernet router.

2. The router is set to Dynamic IP address, but does have the functionality to set a static IP address.

A few more points which may assist you in assisting me :

a. In Mac OS X, I use the "manually" option to configure the ethernet IPv4 settings on both my son's and my computer. I do not use the DHCP or DHCP with Manual Address setting. I don't know if this makes any difference.

b. As I previously stated, the router is physically connected to my computer (i.e the ethernet port on the back of my computer connects to the router), and then my son connects his computer to one of the router's ports.

c. What are the practical implications of changing from Dynamic to static IP address ? Does it make the internet connection slower, less stable, more prone to outside attacks etc ? Will it annoy my ISP ?

d. I wish to maintain as much internet security as I possibly can in doing all this. The firewall in the router is on, and I have also always used the Mac OS X firewall as well (always checking the "allow only essential services" option in the Firewall pane). Will any of this be compromised in setting up my son's computer for Minecraft ?

e. If at all possible, I would prefer to only make changes to my son's computers settings, rather than my computer and the router. If this is not possible, I understand. My son is only permitted 1 hour of internet time per day, and then only if I am present. It would be ok for me to make the changes required when he needs to play Minecraft, then change everything back to my current settings if need be.

Many thanks once again.

I wish you a good day.
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