[network planning] (I) hub, bridge, switch, router and other concepts

This article will introduce some basic concepts in computer network , And some common equipment in our life （ Switch 、 Router, etc ） The role of .

The concept of the Internet

Internet , Wide area network 、 An international computer network composed of a local area network and a single computer according to a certain communication protocol . The Internet refers to two or more computer terminals 、 client 、 The result that the server connects with each other by means of computer information technology . The Internet can be divided into LAN （LAN, Local Area Network）、 Metropolitan area network (MAN, Metropolitan)、 Wide area network (WAN, Wide Area Network).

You think the network connection diagram is like this ？

The actual network connection diagram is like this ：

Connection of the whole network , There are many devices interspersed in the middle , For example, routers are common 、 Switches and so on .

What is network protocol

agreement (Protocol) The concept of , Very common in life , For example, the labor contract signed when looking for a job 、 Rental contracts and so on , Can be called an agreement . Corresponding to the computer network , The effect of the agreement is the same , It's all about restraint . In different scenarios , Use different protocols .

Baidu Encyclopedia definition ： Network protocol refers to the set of rules that must be obeyed when exchanging information between peers in computer network .

In the interview , Perhaps the most important thing to master is HTTP、HTTPS、TCP、UDP、IP、NET、DNS Such agreement .

The concept of client and server ！

client ： It refers to the end that needs services , Mobile phone, for example 、 Computer, etc. .

The server ： It refers to the end that can provide services , For example, cloud servers .

The client sends data to the server , be called request ; The server sends data to the client , be called Respond to .

Network interconnection model

In order to better promote the research and development of Internet , International Organization for Standardization (ISO, International Standardination Organization) stay 1985 The network interconnection model was formulated in ：OSI Reference model (Open System Interconnect Reference Model, Open Systems Interconnection Reference Model ), The details are as follows 7 The layer structure .

Pictured above , except OSI Referring to the model 7 Outside the layer structure , also TCP/IP Protocol cluster 4 Layer structure and common in textbooks 5 The layer structure .

OSI Reference model , It is based on theory , It is not so detailed in practical application , Later in the design , It's still used TCP/IP Four layer structure in the protocol .

Network transmission , Data encapsulation process ：

Each layer has network protocols and data transmission units ：

How computers communicate with each other

You want to communicate between two computers , Then you need to connect to the Internet , So how to identify one of the many computers ？ This involves IP The concept of address . If this wants to communicate with other computers , Just You have to know about other computers first IP Address . But I only know IP The address is not enough , Because the data sent out , It is sent to other computers network card On , So we need to network address , That is to say MAC Address .

But in life , We don't seem to need to know MAC Address , Can also communicate . The reason lies in , Yes ARP(Address Resolution Protocol) Address resolution protocol , When we first visited a strange IP Address time , First it will pass radio broadcast Send a ARP package , This package contains the purpose IP Address , Received from the server ARP Packet time , Find out ARP Bag Destination address Same as this machine , It will return to the local computer through broadcasting MAC Address .

Here is the Cisco simulator , Simulated communication process ：

Bear in mind ,ARP The agreement is through radio broadcast Forward , The broadcast address is all 1, The network address is all 0.

Network cable direct connection

Between two computers , You can use it directly Twisted pair （ Ethernet cable ） communicate , Of course, you need to use Cross line , instead of Through line .（ Cross lines are used between the same equipment , Through lines are used between different equipment ）.

Coaxial cable (Coaxial)

1. Half duplex communication ： Between two computers , At the same time , Only one computer can send data , Another computer receives data , Both cannot send data at the same time . The counterpart is Full duplex communication , The corresponding is at the same time , Data can be sent between two computers at the same time .
2. Easy to conflict ： The reason is that it is half duplex communication , At the same time , Only one computer can send data .
3. unsafe ： It's not safe here , It refers to the process of data transmission , Easy to be caught , Leading to data leakage . Because when two computers communicate , Data sent by one of them , Will send data to every computer in this line , Just after arriving at the computer network card When , The network card finds that this data is not for this computer , Will discard this data .

A hub (Hub)

In order to solve some problems of the coaxial cable , Later, there was a hub , The problem to be solved is that the line connecting a computer to the hub is broken , It will not affect the whole network .

But there is still a problem , such as ： Suppose a hub is connected to hundreds of computers at the same time , Now the computer 1 And computers 2 Need to communicate , As mentioned above , Communicating with a strange computer for the first time , Need to get another computer's MAC Address , Here's the picture ：

Pictured above , You can see... Very clearly , The original intention is to make Computer 4 and Computer 3 signal communication , As a result, both of them occupy the bandwidth of the whole network , That doesn't make sense . Take a closer look. , In addition to these two computers , Other computers will receive a packet Red x, The reason is that the network card finds that this package is not for this computer , And then they abandoned it , That is to say, this package is for this machine , No dice , It also takes up bandwidth .

Conclusion ： The hub has no other functions , The only function is to make the whole network Star topology , It does not have a cache MAC Address function . And it will forward each received packet to all computers （ Except source host ）.

bridge (Bridge)

bridge Appearance , To make up for the shortcomings of the hub above , The hub mentioned above does not have a cache MAC Address function , So here comes the bridge .

Upper figure , You will find that there are only two bridges RJ-45 The interface of , in other words , It is used as follows ：

It can be seen that , The bridge is placed between two hubs , The specific functions are shown in the following two dynamic diagrams ：

Mission ：1、 First, let Computer 1 And Computer 4 signal communication ;2、 let Computer 2 And Computer 4 signal communication ;

After the above communication , bridge Will record the computer 1 And computers 4 Of MAC Address . And you will find this correspondence , Computer 1 Emitted ARP package , Will be forwarded to Hub on the right side of the bridge .

Suppose the data table recorded inside the bridge is as follows ：

Left side area ： Computer 1 Of MAC Address ：xxxxxx; Computer 4 Of MAC Address ：xxxxxxx;

Right side area ： nothing .

Look again. Computer 2 And Computer 4 Communication process ：

Can be seen clearly , Last time Computer 1 and Computer 4 After communication , Of these two computers MAC Address Stored in the bridge . here Computer 2 And again Computer 4 signal communication , When the data comes to the bridge , The bridge will find this data Destination address , Not in the right area of the bridge , Therefore, the data will not be forwarded to the right area .

Conclusion ：

• The bridge can automatically save the MAC Address .
• So as to isolate the conflict area .

Pictured above , It can isolate the left and right areas , In the left and right areas , Can make it communicate at the same time . give an example ： Left side area Computer 1 And computers 2 When communication , On the right side Regional PC8 and PC7 Can also communicate at the same time .

Switch (Switch)

There are two types of switches ： Two-layer switch 、 Three layer switch . Only layer-2 switches are introduced here . Layer 3 switches are a little more advanced , It has routing function .

The layer-2 switch is equivalent to a hub + A comprehensive version of the bridge .

The working process after the computer is connected to the switch ：

It can be clearly seen from the above figure , When computers 1 And computers 2 First communication , I don't know the computer at this time 2 Of MAC Address , So it will be broadcast first ARP package , Ask the computer 2 Of MAC Address , This result will be recorded by the switch . That's why Send later ICMP package （ The purple bag above ） When , The switch will not send to all computers , But only to Destination address The computer .

The characteristics of the switch ：

• It's equivalent to a bridge with more interfaces .
• Full duplex communication ： As mentioned above , It means at the same time , Between two computers , Can send data at the same time .
• Safer than hubs ： Because the subsequent data will only be sent to Destination address The computer , It will not be forwarded to other computers , Reduce the probability of data leakage .

The network cable mentioned above is directly connected 、 A hub 、 bridge 、 Switch , Are used in Same segment Network for communication . If you want to be in Different segments Communicate with each other , Then you need a router , Next, let's look at the router .

Router (Router)

Router （Router） It's a hardware device that connects two or more networks , Start from the Internet gateway The role of , It's a dedicated intelligent network device that reads the address in each packet and decides how to transmit it .

As we mentioned above, the network cable is directly connected 、 A hub 、 bridge 、 Switches are all applied in the same network segment , They can broadcast between them , The router has two functions ：1、 Forward data between different network segments ;2、 to be isolated Broadcast area .

As shown in the figure above , On both sides of the router are LANs of different network segments . If the computer on the left LAN wants to communicate with the computer on the right LAN , It must be forwarded through the router .

The figure above mentions gateway , In a nutshell , gateway Is similar to the Uncle security .

Here's the picture , The causes of the epidemic in recent years , Some places are sealed , A block by block blockade is formed , That different area wants to communicate , But people can't leave the blockade , It is stipulated at this time , Only by Uncle security （ gateway ） To transfer data , Let security uncle communicate with the outside world , People in the blockade area want to communicate with the outside world , Only let the security uncle （ gateway ） Transit .

Know what role the router plays in the network , Now you can take a look at , How computers communicate between two different network segments .

As shown in the figure above ,PC0 and PC3 When communicating ,PC0 You will find that I want to communicate with computers in another network segment , Then I just need to give the data to ** Router （ gateway ）** that will do , Let the router forward the data . So first ,PC0 You still need to know the gateway first MAC Address , So it will be broadcast first ARP package , Get gateway address , The next step is to send the data to the gateway . Here's the picture

stay PC0 After sending the data to the router , The router goes to find the next transit point . Before the gateway on the right sends data to the outside , I will find out that there is no PC3 Of MAC Address , So first of all, it will be sent ARP package , obtain PC3 Of MAC After the address , Before forwarding other data .

Here's the picture , That is, each device records the corresponding MAC After the address , Transmission process ：

All right. , All of the above is the content of this article , Let's see you next time ！！！！