To fix not being able to join yourself.
Insert both the IPV4 Address (CMD > Ipconfig) & WAN (which you can find here: https://www.whatsmyip.org/ ) in the blank spaces located:
Local Disk ( ?: ) - ?:\Users\[User]\AppData\Local\Microsoft\Halo 2\halo2config1.ini & halo2config2.ini
If you wish to...