This is about the L2NET use, i will give you some pictures to be easier to understand:
(This progres of changing ports is "auto" on latest L2NET)
Open L2net
Logon Window
Chose IG and Chose Server IP (loginlist)
Lunch LineageII (Directly from l2.exe or edit the Interface.txt)
Press "Listen" and Login as normal
Open "Game Window"
To do that and run the game IG must have the System that i provide (blue) and the HOSTS that i provide also.
(check first post of this topic)
Good luck.