Quote from wind2011
Bukkit should try to figure out a way to stop DDOSing from their servers, if it is possible. I know it's virtually impossible to see, but it would be nice to find a way.
It isn't possible, it is not a "client side" problem that can be corrected by software, it all happens on your ISP's side of your router. Take the good old "ping" function built into all routers, I send it four tiny packets of bits and it automatically sends them back to me to let me judge how fast and clear the connection is.
But if I and several other computers I control all ping it hundreds of times per second then it does not have time to do anything else except answer my useless requests to send my tiny packets back to me. By default it is programmed to answer my ping request first before dealing with your traffic so you end up either extremely laggy or shut out altogether.
That is how a DDOS attack works, multiple computers working together to flood the target server with so many useless requests, ping, http status acknowledgements, etc. that the server cannot process the other legitimate requests.