dos攻击（Dos攻击）.docVIP

dos攻击（Dos攻击） DoS attack Is one of the most common network attacks. Its defects deliberately attack network protocol by some means or directly attack the object being depleted resources, the purpose is to make the target computer or network can not provide normal services or access to resources, make the target service system to stop responding or even collapse, and in this attack does not invade the target server or target network device. These resources include network, broadband service system, the process of opening up the stack. Or allow connection. This attack will lead to the depletion of resources, fast processing speed of the computer, no matter how much memory capacity, network bandwidth is much faster to avoid the consequences of the attack. Any resources have a limit, so you always find a way to make the requested value greater than the threshold value, the service provided by the depletion of resources. There are many types of DoS attacks, including Land attack, death, tears, Ping Smurf and SYN flood attack. According to statistics, in the event of all attacks, SYN Flood attack is one of the most common and most DoS attack technique is easy to use. 1. attack principle To understand the SYN flood attack, we must first understand the three handshake connection TCP (Three-wayhandshake). In the TCP/IP protocol, TCP protocol to provide reliable connectivity, the three shook hands with the establishment of a connection. The first handshake: establish a connection, the client sends a SYN packet to the server ((SYN=i) SYN, and enter the SEND state, waiting for the server to confirm; Second handshake: SYN packets received from the server, the client must confirm that SYN (ACK=i+1), with}Jj own also sends a SYN packet (SYN (J)} SYN+ACK packets, the server in the SYN_RECV state; Third Handshake: client server received SYN ten ACK package, ACK confirmation packet sent to the server (ACK=j+1), the packet is sent, the client and server into the ESTABLISHED state, comp