General knowledge of network (detailed)

One 、 The Internet osi Model  

  The benefits of layering ： Make the whole process clearer , Simplify complex problems It's easier to find problems and solve them

2.OSI Characteristics of the reference model

1、 The same layer of different nodes has the same function
2、 Adjacent layers in the same node communicate through interfaces
3、 The lower level serves the upper level
4、 Data transmission at the bottom  

3.OSI The model,

application layer 、 The presentation layer 、 The conversation layer is the third layer , yes User oriented Of

The network layer 、 Data link layer 、 The physical layer is the lower three layers , yes For hardware Of

The communication at and below the network layer is point-to-point communication （ Host and host ）

The communication of the transport layer is end-to-end （ Port to port ）

Information transmission protocol （ Transport layer ）：

The transport layer relies on these two protocols to transmit data

Tcp： Slow speed , More reliable , Retransmission not found

Udp： Fast , unreliable , If it is not found, it will not be retransmitted

Network layer protocol ：

Ip agreement ：icmp agreement ：ping（ Troubleshoot network problems ）

IGMP agreement ： multicast protocol

ARP： take mac Address converted to ip Address

RARP： take ip Address converted to mac Address

Application layer protocol ：

http： Hypertext protocol    Default port number ：80  

https： Encrypted hypertext protocol Default port 443

ftp： Text transfer protocol Default port 20 21

Tftp： Simple text transfer protocol Default port 69

Dhcp： Automatic access to ip Address   Default port 53

Dns： take ip Address to domain  192.168.200.76 transformation www.****.com Port number 67 68

4. Data encapsulation process （ Unpacking is from bottom to top ）

1. When the data of the software process is sent to the application layer , The application layer adds the control header of this layer to the data , Number of application layers organized     According to the service unit , And then down to the transport layer ;

2. After the transport layer receives the data , Add this layer of TCP The header forms a data segment , The transport layer sends data segments to the network layer ;

3. The network layer adds IP Head , Constitute a packet , Then send the data packet to the data link layer ;

4. The data link layer receives data packets , add MAC Header information , Data frames constituting the data link layer , Send to physical layer ;

5. The physical layer will be transmitted through the transmission medium in the form of bit stream . 

5. summary

 OSI The encapsulation process of the seven layer protocol needs to be remembered , The protocols that need to be used at all levels also need to be remembered