1st Dowload a File Edit for your server client like Interlude, Kamael, Hellbound etc
2st Open with File Edit in system forder the file l2.ini
3rd Found The Server Address and change it with your ip or no-ip or localhost(127.0.0.1)
4th Safe it with protocol 413 and it's ok run l2.exe and play
*I hope i help ;)