Totally not the wrong forum, and a good question that I'm sure many people have had. I've dealt with this problem as well, so I'll give you the steps that I took to getting it working. You may have done many of these already, but I'll just list them all in case other people need the help as well.
DISCLAIMER - These are the steps that worked for me, and are not guaranteed to work for you. Everyone has different networking setups, and I can't speak for them all. I make no claims of being able to fix everyone's problem, but if you follow along, you can probably adapt this to your own specific setup fairly easily.
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First you need to get the laptop ready to serve the 360 correctly so that the 360 will be able to communicate with the outside world
through the laptop...
- Plug the ethernet cable from the 360 into the laptop, and turn on the 360.
- Open Terminal and type in "ifconfig en0"
- Find the line labeled "inet" and note the IP address (it is probably 192.168.2.1)
- Open up System Prefs on the laptop, go to the Sharing section, and turn on "Internet Sharing"
- Go to the Network section, select the Ethernet connection, and from the Configure drop-down, select "Manually"
- For the IP address, put in the address you got earlier (192.168.2.1), and for Subnet put in "255.255.255.0"
The next steps will be done on the 360. You will be manually entering in IP address information so that it will now communicate correctly back to the laptop...
- Now go back to the 360, and go to the "System Settings" section.
- Go down to Network Settings and click "Configure Network"
- Click to setup the IP address on the Basic Settings section, and select "Manual" when asked.
- You will now manually enter the addresses of the IP Address, the Subnet Mask, and the Gateway.
- For IP Address use the IP Address you found earlier in Terminal, but add 1 more to the last section (for example, mine is 192.168.2.2)
- For Subnet Mask enter the same one from before (255.255.255.0)
- And for Gateway enter the original IP you found exactly as it was in Terminal (192.168.2.1)
- After you have done that, select "Done" to save the settings.
- Select the DNS section, and again select "Manual" to edit these.
- For both the Primary and Secondary servers, enter the original IP address you found in Terminal (192.168.2.1)
- Again, select "Done" when finished to save the settings.
- Now, turn off the 360 to be sure the settings save, and go back to the laptop for a couple more steps.
Now, there is just a couple final steps to do on the laptop in order for the 360 to have full access to the
Xbox LIVE system...
- You will next need to enable "UPnP" on your router. This can vary from brand to brand, so I can't really help you here.
- Enabling UPnP will allow the laptop and 360 to tell the router what ports it needs open on its own, without the need for you to manually open them.
- Once you have enabled that, there is just one last step on the laptop. You need to open the ports on the laptop.
- Open up terminal, and enter "sudo killall natd"
- It will ask you for your password, enter it.
- Next type "sudo natd -interface en1 \"
- Next you will be typing in 6 different ports for the laptop to open.
- For the IP address to type, you will use the one you manually gave the 360 (for my example 192.168.2.2)
- Type the following red commands into Terminal exactly, adjusting if needed for your own specific IP Address
- -redirect_port tcp 192.168.2.2:3074 3074 \
- -redirect_port udp 192.168.2.2:3074 3074 \
- -redirect_port tcp 192.168.2.2:53 53 \
- -redirect_port udp 192.168.2.2:53 53 \
- -redirect_port tcp 192.168.2.2:80 80 \
- -redirect_port udp 192.168.2.2:88 88
- You can now exit out of Terminal as you are done.
All of the steps on both the laptop and the 360 are now complete. With everything plugged in and ready, turn on the 360.
- Go back to the Network Settings" section.
- Click on "Test Xbox LIVE Connection" in that first menu.
- It will now run a diagnostic check of your settings.
- If you entered everything correctly, it will complete all steps with no errors, and you will be good to go.
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Normally, if you have your 360 plugged directly into the router, all that you need to do is enable
UPnP and you would be good to go. The Xbox has a certain set of ports it needs open, and UPnP would handle that all just fine. But, when you put a laptop in the middle of the 360 and the router, it would get a little trickier. You would be able to connect to Live, and play games just fine, but every now and then you would get an error saying
"Your NAT settings are Moderate" etc, and it wouldn't let you connect to people. This is because even though the router might be opening the ports correctly for the 360, the laptop wouldn't. The last steps in my rundown, where you entered a bunch of stuff in Terminal, fixes that and allows the laptop to open those ports and pass the info through to the 360 correctly.
I hope all that helps. I'm no networking genius or anything, I've just dealt with this problem in the past. This setup that I described is a mixture of a bunch of different guides that I found online when trying to correct this exact problem myself. Hope it all works for you, or anyone else reading this. If you have any questions, ask away, and I might be able to help.
Here are my links I used previously...
http://macapper.com/2009/01/29/tutorial-mac-internet-sharing-with-xbox-360/
http://www.soundc.de/blog/2009/01/24/mac-os-x-port-forwarding-with-internet-connection-sharing/