Computing level network notes

1.URL

The first level domain name is stipulated by international organizations , Just those .

The secondary domain name is applied to the national institution , The largest agent in China is China wanwang （ Artificial application , The only global , Judge the snapper website by this ）

The third level domain name is defined by itself

2. Internet access method

ADSL: Find Telecom mobile broadband , Use the telephone line to surf the Internet , Dial-up Internet access

 

 

  Community broadband ： Broadband sharing , Big lan , All information on the Internet is in the LAN , Others can monitor and share through LAN through technical means , Although some have made network segment separation , However, all equipment online information must pass through the general router of the community , In fact, it's still not safe .

3.OSI Of 7 Layer model

  The real data transmission is the lower four layers , A unit with data transmission , The upper three layers are for users to interact ,

The physical layer ： For example, the physical connection between the computer host and the TV screen

Data link layer ： The data to be transmitted , Join in MAC Address （ The addresses of the two hosts , For example, each network card comes with one as soon as it leaves the factory MAC Address , LAN internal devices , by MAC Address for transmission ）

The network layer ： The data to be transmitted , Join in IP Address , Equivalent to the address of a letter .

Transport layer ： Determine the transmitted data , Is it transmitted in a reliable or unreliable way （ The distribution corresponds to TCP UDP agreement ）, And error checking and flow control . Will add the data to the header , For example, mail delivery , Will be added to the sender's source port , The mail port is 25, Then write the target port of the recipient ,110. The port number is equivalent to the sender and receiver of a letter , Determine which service this letter is sent to , That is, let the receiver know which software is sent to which local machine to process the received data .

The session layer ： Determine whether the user has a remote session , Don't pass it down if you don't need it

The presentation layer ： Data representation of transmitted data , For example, documents transferred , Conduct ASCII Code said , And compression encryption . The data layer of the receiver , Judge what the received data is , It's documentation , it ASCII Code code

application layer ： Interface between user and computing level

4.TCP Four layer model of

 

1. Network interface layer

  There's a ARP Address resolution protocol , That is, through IP The address can be found MAC Address , This is what the switch does , Learn from everyone MAC Address , And record it in your cache .

2. The network layer

 3. Transport layer ：

and UDP It's a direct message , Handshake without prior communication , It's like texting , But faster , Occasions with high real-time performance , and TCP It is an occasion requiring high reliability .

  The port number can be changed , But some conventional port numbers remain unchanged . You can check the common ports ( Known as port ) Determine which services the computer has turned on .

4. application layer

 5. Data encapsulation process

5. Network layer protocols and IP Address partition

1.

 2.IP

 

 IP Address range

IP The previous number of the address represents the network segment , Only this number is the same , That is, in the same network segment , Only in the LAN can they communicate with each other , Otherwise, the communication between different network segments can only be carried out through the router .  But in the same network segment IP Address , As long as you can communicate with each other through a switch .

Ordinary IP You have to buy , You can't just use it , But private IP You can use , And as long as it is in a LAN , Can overlap . But Intranet IP You cannot directly access the public network , Public network IP You can't directly access the intranet .

2. Subnet mask

  The subnet mask is 1 The bits of represent different network segments , by 0 Represents different hosts

3. Network address and broadcast address

The network address represents the starting address of a network segment , The broadcast address represents the last address of a network segment

 4.ICMP agreement

  Mainly come Pin