Network Interview Questions

TCP Three handshakes , And the reason for the three handshakes ？

hypothesis A For the client ,B For the server side .

First B be in LISTEN（ monitor ） state , Waiting for customer's connection request .

A towards B Send connection request message ,SYN=1,ACK=0, Choose an initial sequence number x.

B Receive connection request message , If you agree to establish a connection , to A Send connection confirmation message ,SYN=1,ACK=1, The confirmation number is x+1, Also choose an initial sequence number y.

A received B After the connection confirmation message of , And to B Send a confirmation , The confirmation number is y+1, Serial number is x+1.B received A After the confirmation of , Connection is established .

The purpose of triple handshake is to establish a reliable communication channel , The main purpose of the three handshakes is for both parties to confirm their relationship with each other Sending and receiving are normal .

The third handshake is to prevent invalid connection requests from reaching the server , Let the server open the connection by mistake .