1、 Part three lesson two ：IP Address and domain name
2、 Part three lesson three Notice ： agreement
Part three lesson two ：IP Address and domain name
Last lesson we said in Web In , There are countless machines all over the world , Some act as clients , Some serve as servers .
So how do these machines find and identify each other ？ Isn't it “ Just because I saw you in the crowd , Never think of your face again ” Do you ？
If I surf the Internet with my browser , How do I know which server is sending me this website ？
To solve this problem ,IT The scientists used a method called IP Address stuff （ Things seem a little too ugly ,IP It's not a good thing at all ）.
IP yes Internet Protocol For short , English means “ Internet Protocol ”.
IP The address is used to represent every connection Web Of a machine . And it's the only sign （ Of course we are 【TCP/IP Journey of exploration 】 We'll talk about different categories of IP Address , Some are repeatable , It's about the local area network , Wide area network , Public address and private address, etc , Let's not delve into it ）.
For the time being, we just need to know ： On a large scale , Every computer in the world has a unique IP Address , It's like its only name plate . We can “ The computer ” Compared to the “ Telephone ”, that “IP Address ” Equivalent to “ Phone number ”.
IPv4 and IPv6
IPv4 and IPv6 yes IP Different versions of the address ,v4 It's the fourth edition （v It's English version The first letter of ,version Meaning for “ edition ”）, that v6 It's the sixth edition .
IPv4 The address length of is 32 position ( share 2^32（2 Of 32 Power ） individual IP Address ), It is divided into 4 paragraph , Each paragraph 8 position , Expressed in decimal digits , The range of numbers in each paragraph is 0～255, Separate paragraphs with periods . for example 18.104.22.168.
IPv6 The address length of is 128 position ( share 2^128（2 Of 128 Power ） individual IP Address ), It is divided into 8 paragraph , Each paragraph 16 position , Expressed in decimal digits , The range of numbers in each paragraph is 0～65535, Separate paragraphs with periods . If each 16 Bit use 16 Hexadecimal said , So for example 1080:0000:0000:0000:0008:0800:200C:417A.
The current use of the Internet is mainly based on IPv4 Agreed 32 Bit address , The total capacity of the address is close to 43 One hundred million . and IPv6 The address is 128 Bit mark , The number of 2 Of 128 Power , amount to IPv4 Address space 4 The next power .
Some people used to compare it figuratively ：“IPv6 Every grain of sand on the earth can have one IP Address .”
actually , Not in a hurry to promote IPv6, Just in the existing IPv4 On the basis of general 32 Bit expansion 8 A to 40 position , Can solve IPv4 The problem of insufficient address . In this way, the number of available addresses is expanded 256 times .
Our course is still based on IPv4 For example .
For example, we have the following IP Address ：
Every time we surf the Internet , Do I have to enter this number in the address bar to find the page I want ？ It's too tired , I can't do it .
Then what shall I do? ？ So the domain name came into being .
Because remember each one directly IP The address is too difficult , So people came up with the idea of replacing numbers with easy to remember names . such as , In the above example 22.214.171.124, Actually, once Google On the front page IP Address . So we use a domain name （domain name） Instead of , That is to say ：google.com
But our servers only recognize digital forms IP Address . So we need one “ A middleman ”, take google.com This domain name first resolves to 126.96.36.199, And then find the corresponding page .
The middleman is DNS,Domain Name System（ The domain name system ）, yes Internet A service of . It is used to IP A distributed database with address mapping , Can make people more convenient access to the Internet .
With DNS, We can easily enter... In the address bar google.com, And then pass by DNS analysis , Change to the corresponding IP Address , And then read by the server .
DNS It is composed of domain name parser and domain name server . A domain name server is a server that stores the domain names of all hosts in the network IP Address , And has the ability to convert the domain name to IP Address function server . The domain name must correspond to one IP Address , and IP The address doesn't have to have a domain name .
IP The address allows us to find every computer on the planet connected to the Internet .
Remember domain names are better than IP The address is convenient , And from domain names to IP The address is resolved through DNS.
Part three lesson three preview
That's all for today's class , Come on ！
Next lesson we'll learn ： agreement
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