Shulou(Shulou.com)06/01 Report--

TCP three-way handshake:

The first handshake: Client sets SYN to 1, randomly generates a value seq=J, and sends the packet to Server. Client enters SYN_SENT state and waits for Server confirmation.

Second handshake: After receiving the data packet, the Server knows that the Client requests to establish a connection from the flag bit SYN=1. The Server sets the flag bits SYN and ACK to 1, ack=J+1, randomly generates a value seq=K, and sends the data packet to the Client to confirm the connection request. The Server enters the SYN_RCVD state.

Third handshake: After receiving the acknowledgement, the Client checks whether the ack is J+1 and whether the ACK is 1. If it is correct, the flag bit ACK is set to 1, ack=K+1, and sends the data packet to the Server. The Server checks whether the ack is K+1 and whether the ACK is 1. If it is correct, the connection is successfully established. The Client and the Server enter the ESTABLISHED state to complete the three-way handshake. Then the Client and the Server can start transmitting data.

In short, it's

When a connection is established, the client sends a SYN packet (SYN=i) to the server and enters the SYN-SEND state, waiting for an acknowledgement from the server.

When the server receives the SYN packet, it must acknowledge the SYN (ack=i+1) of the client, and at the same time send a SYN packet (SYN=k), i.e., SYN+ACK packet. At this time, the server enters the SYN-RECV state.

The client receives the SYN+ACK packet from the server and sends an acknowledgement ACK (ack=k+1) to the server. After the packet is sent, the client and the server enter the ESTABLISHED state and complete the three-way handshake. The client and the server begin to transmit data.

TCP waved four times:

First wave: Client sends a FIN to close data transfer from Client to Server, Client enters FIN_WAIT_1 state.

The second wave: After receiving the FIN, the Server sends an ACK to the Client, confirming that the serial number is received +1 (the same as SYN, a FIN occupies a serial number), and the Server enters the CLOSE_WAIT state.

The third wave: Server sends a FIN to close the server-to-Client data transfer, and Server enters the LAST_ACK state.

The fourth wave: After the Client receives the FIN, the Client enters the TIME_WAIT state, and then sends an ACK to the Server, confirming that the serial number is received. The Server enters the CLOSED state and completes the four waves.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.