It is a denial of service (DoS) attack in which an attacker deliberately violate the three-way handshake and makes a large number of half-open TCP/IP connections.Any server provided TCP-based services (FTP, Web, etc) is potentially subject to this attack because all possible connections could be run out. Therefore, an legitimate user can't get a connection.One-to-one or one-to-many, connectionless and unreliable protocolUsed for the transmission of small amount of data Accuracy is not of prime concernThe overhead of establishing a TCP connection is not warrantedUsed in video and audio castingMulticastingBroadcasting Also used for multimedia transmissionFaster compared to TCP IP addr. : let packet can be correctly routed to the LAN in which the destination host exists, through the Internet. MAC addr. : decide which network card (which host) should receive the frame in the local area network (LAN) Port number: let the proper application handle the coming packet.(maybe several applications are running in the destination host; which program should handle the packet?)