The DoS attack that was used to crash the server was most likely something called a TCP SYN flood attack (You can read up on it
here). As soon as someone tries to connect to a server through TCP (rcon as an example) the server sends a response to the client which the client has to respond to for the connection to open successfully (that way people can't fake their IP). The problem here is that the server pretty much stores the request for some time to wait for the client's response. A TCP SYN flood just spams tons of...