Note: This guide is not totally complete, there are some things I need to switch around, and maybe add, like router firmware and a walkthrough for people without a router.

This guide is safe if you follow instructions, but if you mess up that is what the reset button is for.
Part 1

For people with a router and a modem, your 360 and computer must be using the same router.

2 things, when your plugged directly into your modem, your default gateway is your modems address. When your plugged into your router, your default gateway is your routers address.
You will understand what I mean as I go on.

You will need to access your modem and router settings. To do that if your using windows go to command prompt, if you can't find it click start and run. Then type in cmd, that will bring up command prompt. For linux users as well as Mac OS users, you want the terminal.

When you get there, type in ipconfig/all. That will give you a bunch of numbers, your modems address might be the DNS server (mine is), put that address into the address bar on your web browser (internet explorer, firefox, safari), and press enter. If that doesn't work plug your computer directly into your modem and go to command prompt and type in ipconfig/all.
It might take a minute for the changes, but your default gateway will then be your modems address. Type that into your address bar and press enter.

It will then ask you for a username and password, right now all I can say is press login and hope for the best. If someone else set up your network He/She might have changed it, if you can't get in I would suggest looking in the manual, or on the official website.
If all else fails you could call your ISP and ask them.

Now for your router, when your computer is plugged into your router access command prompt and type in ipconfig/all, your default gateway is your routers address. Enter that into your address bar. You will be asked for a username and password, I would suggest just trying to login, if that doesn't work, go here and find your routers username and password, if someone else set up your network He/She might have changed it.

Once you get into your router settings, you need to set up your router with a static IP address.
It will probably have automatic configuration, you want static IP. Then you need to enter some information from command prompt. Subnet Mask (255.255.255.0), static DNS - enter your DNS servers.

Now for your IP and gateway you need to find your modems address. Hook your computer directly into your modem and wait like 30 seconds for everything to register. Then go to command prompt and type in ipconfig/all. Your modem address will be the default gateway.

Hook your computer back into your router and put the modems address into the IP for your router, but change the last digit to something else.

Example: Your modems address is 192.168.2.1, you want your routers address to be something like 192.168.2.6.

For the default gateway just enter your modem address.
Done with the router for now, but we will come back to it.
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Now for your modem, enter your modems address into the address bar and press enter.
If you don't remember your modems address, hook your computer directly to your modem and access command prompt and type in ipconfig/all. Your modems address is the default gateway.


It will then ask you for a username and password, right now all I can say is press login and hope for the best. If someone else set up your network He/She might have changed it, if you can't get in I would suggest looking in the manual, or on the official website.
If all else fails you could call your ISP and ask them. (NOTE - Some/MOST modems will NOT ask for a username/password due to the fact that well, you're in the modem, why would you need a password, you obviously know the gateway address...)

Once you get in look for something DMZ or forward all ports.
Then enter your routers IP, the one where you changed the last digit.
Save and your done with the modem.
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Go to your 360 and on the tab all the way on the right there will be an option for network settings. Select that and then select edit settings.
Then select the settings with the IP address, the subnet mask and the gateway.
Select manual, then enter
for your IP address whatever your routers address is and then change the last few numbers.
Example: router address is 192.168.1.1 360's address is 192.168.137.

For the subnet mask, just enter the subnet mask, you can get it from your router or command prompt. (NOTE - Subnet Mask is going to 255.255.255.0... I am 99.9999999999999999% sure this is the same for ALL routers/modems)

For the gateway enter the IP address of your router, the address you go to access the settings.

Press done, and you will be asked to test your XBL connection. Do that and it will fail, that's OK.

Go back to the network settings and select the DNS servers and select manual.
Then enter your DNS servers, up to three, but I have only one.

If you want some pictures or some more detailed information to help you, go here.
Save and then go back to your router.

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Go to the section that deals with port forwarding and find DMZ.
Enter your 360's IP address into that and click enable.
Also make sure that UPnP is disabled on your router.
Save and your done.