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Illustrated network: the principle behind TCP three-time handshake, why can't two-time handshake?
2022-07-06 00:37:00 【InfoQ】
What is? TCP?
- English full name :
Transmission Control Protocol
- Chinese name :Transmission control protocol
TCP Three handshakes
Three handshakes in life
- Xiao Ming : Hello , Is it Xiaomei ?【The first handshake】
- Xiaomei : Yes , I'm Xiaomei .【The second handshake】
- Xiao Ming : well , I know you are Xiaomei .【The third handshake】
Three professional handshakes
- Server side: The server is a physical computer dedicated to running services to meet the needs of other computers
- client: The client is the computer hardware device or software that accesses the services provided by the server
- SYN: Sync serial number (Synchronize Sequence Number), This is the first packet from the client to the server , It can be described as a request to establish a connection , If SYN by 1, It means that the device needs to establish a secure connection , Otherwise not .
- ACK: confirm (Acknowledgement), Can be said to be SYN Response , If ACK by 1, The device has received SYN Message and confirm , Otherwise no .
- First step :TCP The client sends... To the server TCP SYN Packets to start the connection , The packet contains a random serial number n, It represents the serial number of the data that the client should transmitStart.
- The second step : The server receives the packet , And use its serial number (m) To respond , Its response also includes the confirmation number , That is, the serial number of the client plus 1, Here is n+1.
- The third step : The client responds to the server by sending a confirmation number , The confirmation number is the serial number of the server plus 1, Here is m+1.
TCP Analysis of three handshakes
172.16.16.128:2826
212.58.226.142:80
- First step : host
172.16.16.128:2826
Host computer212.58.226.142:80
send out [SYN] Seq=0
- The second step : host
212.58.226.142:80
Host computer172.16.16.128:2826
send out [SYN,ACK] Seq=0,Ack=1
- The third step : host
172.16.16.128:2826
Host computer212.58.226.142:80
send out [ACK] Seq=1,Ack=1
TCP window
Win=8192
The other parameters
- MSS(Maximum Segment Size), Maximum segment size .
- WS(Windows Scaling), Used to control the maximum TCP Receive window size .
TCP Why can't a second handshake establish a connection
- The server needs to confirm that the server can receive packets from the client
- The client needs to confirm that the client can receive packets from the server
- The client needs to confirm that the server can receive packets from the client
- The server needs to confirm that the client can receive packets from the server
- Xiaoming asked :“ Hello , Excuse me, Shi Xiaomei ?”: After sending successfully , Xiaoming is sure that he can receive information from Xiaomei , The first condition is verified 【The server needs to confirm that the server can receive packets from the client】
- Xiaomeihui :“ Yes , I'm Xiaomei ”: After sending successfully , Xiaomei is sure that she can receive information from Xiaoming , It can also confirm that Xiao Ming can receive information from her , Verified the second 、 The third condition 【The client needs to confirm that the client can receive packets from the server】【The client needs to confirm that the server can receive packets from the client】
- Xiaoming returns :“ well , I know you are Xiaomei ”: After sending successfully , Xiaoming is sure that Xiaomei can receive information from him , Four conditions are verified 【The server needs to confirm that the client can receive packets from the server】
summary
- What is? TCP?
- TCP Three handshakes
- Three handshakes in life
- Three professional handshakes
- TCP Analysis of three handshakes
- TCP window
- The other parameters
- TCP Why can't a second handshake establish a connection
- summary
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