DDOS Attack on Minecraft Tekkit Classic Server

So a few days ago I was on a tekkit server and suddenly this guy joins and threatens a DDOS attack, now the server is down because of this, what the owner has asked everyone to attempt to find a fix, any suggestions? He wants a program that's free to use. Any help is appreciated.

Just get him to clear the cache and restart the server(s).
DDoS's are temporary, they will just go away after a while. The same applies to any website and server.

Try ipstresser and just google it and make a account, use all of the data at once so the crash is garunteed to work.