I didnt need to when i was at home but im at college now and you have to ask providers to open specific ports for games like WoW or LoL, i found these  
  
https://eu.battle.net/support/en/article/300479 
  
after unlocking them i was able to play on Elysium, but after realmlist change i cant so i have to open another port(s) to log in to server...but i dont know what ports... 
  
For example Kronos (vanilla private server), needs 8086 port to be open.