DNS domain name system

Anyone who knows Ethernet knows , The message is based on the purpose IP The address to send , And when we're browsing the web , You don't have to know the other server's IP Address , Instead, a web address , Domain name

DNS

Why use domain names instead of IP Address , Obvious , Take Baidu server for example ：

• One of Baidu ip The address is ：202.108.22.5
• Baidu's domain name is ：www.baidu.com

Which of the two ways is easier to remember ？

Domain names, of course

But it also creates a problem , People remember domain names , But the network sends messages , Messages don't use domain names directly , The message needs the other party's IP Address , So you have to get it through the domain name IP Address

From whom ？

So many web sites around the world , So many domain names , Every domain name has its own IP Address , There are more than one IP Address , These domain names and IP Addresses map to each other , It's a distributed database , This distributed database is stored on some servers , We call it DNS Domain name server

DNS

Domain Name System, perhaps Domain Name Service, Domain name system or domain name service , Its main function is to transfer our familiar Web address （ domain name ）“ translate ” It can be understood by computers IP Address , This process is called DNS Domain name resolution

What is the process of domain name resolution ？

DNS This is the process of domain name resolution , Here's the problem , Why does the system go to DNS The domain name resolution request sent by the server is UDP Message instead of TCP？

It's also very simple , because UDP There is no process of connecting and disconnecting , Faster

DNS How to resolve a domain name ？

take www.baidu.com Come on , The real domain name is www.baidu.com., Last . Called the root domain , Because each domain has a root domain , So you can omit

and .com or .net It's a primary domain name , We call it “ Top-level domain name ”

Again, the first level domain name is “ Subdomains ”, Like here .baidu, This level of domain name can be registered by users

The next level is the hostname , Also known as “ Three level domain name ”, such as www, This is the name assigned by the user to the server in his own domain , It's something that users can assign at will

The process of domain name resolution becomes hierarchical search

• The system is in the local computer first DNS Richter , If you find it, go back to
• If you can't find it, go to the root server , Take a look at the root server .com, Just manage .com Domain DNS Server's IP The address is returned to the system , The system takes this IP Just go to .com In the domain of
• .com Not at all www.baidu.com This domain name , But it knows the next level domain .baidu Of the server IP Address , Put the IP Send it to the system , Let the system go .baidu Ask in the library
• The system takes this IP ask again .baidu, It happens that www.baidu.com This domain name , So I put this domain name IP The address was sent to the system

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