TCP three-way handshake and four-way handshake with TCP status code

I. TCP three-way handshake and four-way handshake

Flag space:

Syn (synchronous online)

Ack (acknowledgement confirmation)

Psh (push transfer)

FIN (finish)

RST (reset)

URG (Urgent urgent)

 

Sequence Number:

Sequence Number (sequential number) -- seq

Acknowledge number (confirmation number) -- ack

 

 

 

 

Format of the first handshake packet:

 

The second handshake packet format:

 

Format of the third handshake packet:

Three-way handshake:

 

After the connection is established, the data transmission mainly depends on the P Flag bit:

 

Four Waves of data packets, mainly refer to the f flag bit:

Ii. TCP status code

Status	Description
Closed	Closed, no connection activity or in progress
Listen	Listening status, the server is waiting for connection to enter
SYN rcvd	Received a connection request, not confirmed
SYN sent	Connection Request sent, waiting for confirmation
Established	Connection established, normal data transmission status
Fin wait 1	(Active close) a close request has been sent, waiting for confirmation
Fin wait 2	(Active close) receives confirmation from the other party, waiting for the other party to close the request
Timed wait	Two-way close is completed, waiting for all groups to die
Closing	Both parties attempt to close the service at the same time and wait for confirmation from the other party.
Close wait	(Passive close) received the other party's close request, confirmed
Last ACK	(Passive close) Wait for the last close confirmation and wait for all groups to die