TCP establishes a two way connection (SYN, SYN-ACK, ACK), so you can send the original SYN but the SYN-ACK will go to someone else and be discarded. UDP is fire

TCP establishes a two way connection (SYN, SYN-ACK, ACK), so you can send the original SYN but the SYN-ACK will go to someone else and be discarded. UDP is fire and forget, in contrast. There is a proposal from 2000 that is mentioned in the article (http://tools.ietf.org/html/rfc2827 http://tools.ietf.org/html/rfc2827) that recommends that source networks filter out originating traffic that isn't legitimate. It is being implemented slowly.