Stuck at authenticating

I can almost never login because I am stuck at "Authenticating" part. I've flushed my DNS and used hextech repair tool but I still most of the times can't login or if I wait long enough and I manage to log in then I can't start a game because the client is constantly losing connection. And if I somehow manage to play a game it's very laggy. The very same problem has everyone in my house who uses same ethernet. It happened all of a sudden and don't have a clue how to make a stable connetion with RIOT again... I am not the first one with this problem but it seems that there's still no solution for it.