Shulou(Shulou.com)06/02 Report--

The structure of this chapter:

Introduction of 1.TCP Protocol

2.TCP message format

3.TCP three-way handshake

4.TCP waved four times.

Introduction of 5.UDP Protocol

6. Common protocols and their ports

1.

TCP (Transmission Control Protocol) is a connection-oriented, reliable process-to-process communication protocol.

TCP provides full-duplex service, that is, data can be transmitted in both directions at the same time.

TCP message paragraph:

A.TCP groups several bytes into a packet, called Segment.

B.TCP message segments are encapsulated in IP datagrams.

two。

Source port number: source port address

Destination port number: destination port address

Serial number: the sender numbers each byte to facilitate the correct reorganization of the receiver

Confirmation number: used to confirm the information of the sender

Window size: used to indicate the number of locally acceptable data segments. The window size is variable.

Header length: header length of data segment

URG: emergency pointer bit. 1: on; 0: off (submitted to the other party without cache)

PSH: fast receive and transfer to the application layer. 1: enable; 0: disable (need to be cached, wait for a batch of message segments to arrive, and send directly to the application layer)

SYN: request flag for establishing a connection (marked as 1)

FIN: request flag for disconnection (marked as 1)

ACK: confirm bit (confirm marked as 1)

RST: reconnect, send, equivalent to reset

Checksum: check format, check for errors

Option: optional

3.

If PC1 wants to establish a connection with pc2, first the pc1 side will send a data requesting to establish a connection to pc2, then pc2 will also send the data to accept the request to pc1 after receiving it, and confirm the connection with pc1 at the same time. Finally, pc1 will receive the data and send the confirmation data to pc2. In this way, a two-way communication connection is established between pc1 and pc2.

4.

If PC1 wants to disconnect from pc2, first the pc1 side will send a disconnected request data to pc2 and confirm that it is disconnected from pc2. After receiving it, pc2 first confirms that TCP is in a semi-closed state (pc1 cannot send data to pc2, but pc2 can still send data to pc1). Pc2 then sends disconnected data to pc1, confirming that it is disconnected from pc1. Finally, the pc1 receives the data and sends the confirmation data to the pc2. In this way, the two-way communication between pc1 and pc2 is broken.

5.

A.UDP: user Datagram Protocol

UDP length: used to indicate the total length of the UDP and add data to the header

Checksum: used to complete error checking of UDP data. It is the only reliable mechanism provided by UDP protocol.

6.

a. Commonly used TCP ports, protocols and their functions:

Port-protocol-function

20Murray-FTP--- data connection

21Murray-FTP--- control connection

23Murray-TELNET--- is used for remote login and can remotely control and manage the target computer (plaintext)

22Murray-ssh--- is used for remote login and can remotely control and manage the target computer (ciphertext)

25Murray-SMTP--- is used to send mail.

80Murray-HTTP--- Hypertext transfer Protocol

443Murray-https--- hypertext transfer protocol server

110Murray-POP3--- for email reception

b. Commonly used UDP port numbers and their functions:

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.