Q & A on DOS (Denial of Service) Attacks Q: How does deny service work? Send packets too fast? A: There are several possibilities for denial of service: 1) Merely send arbitrary packets so fast to a particular server that the CPU or network leading to that server become saturated. 2) Send a series of TCP SYN packets packets (the first of the three-way handshake to open a connection), but never complete any of the handshakes. 3) Repeatedly open a connection to the server and then send packets that are ignored (e.g., if the application ignores leading blanks, send an infinite stream of blank characters). 4) Repeatedly open a connection to the server, send a partial request, and never complete it. The first relies on having so many computers send simultaneously that they overwhelm the server (difficult for large, multiprocessor servers). The others rely on finite limits in the server system (number of TCP connections, number of processes), etc. By the way, according to the newspaper, all of these are now considered illegal.