What process do you go through when entering a URL in your browser?

1: Related concept description:

1.1: DNS (Domain name System) cache: (Domain name system) (check the local ipconfig/displaydns)

After the computer resolves a domain name, it associates this domain name with the host IP address. The computer saves this relationship in the DNS cache table. The next time the computer enters www.baidu.com, the computer will By searching the DNS cache, you can know the IP address corresponding to this domain name. Domain name resolution is no longer required, which improves efficiency

1.2: ip address:

The IP address corresponds to the house number. We can find the location of the host through this address

1.3:domain name:

The IP address is four numbers, separated by commas. This thing is hard to remember. We usually use letters with numbers, such as .www.baidu.com. The IP address and the domain name are not one-to-one correspondence. A domain name Multiple IPs can be bound, but one domain name can only be resolved into one IP address at the same time (this task is completed by our DNS for us)

2: General process of related requests

1: The browser resolves the IP address based on the domain name

2: The browser performs Socket communication based on the IP address

3: The browser and the client communicate, the browser requests, and the server receives the request

4: The browser and server are disconnected

Three: Specific process

3.1: Search process

1: The browser first searches its own DNS table to see if there is .www.baidu.com (corresponding IP address)

2: Search from the DNS table in the operating system (a table that maintains the correspondence between domain names and IP addresses)

3: Search from the operating system host folder

4: The operating system sends the domain name to LDNS (Local Area Domain Name System). For example, if I am at the University of Technology, then the LDNS server is in our school, searches the DNS cache, and if it continues to fail, sends an iterative DNS resolution request.
4.1: LDNS sends the root name server (root domain name server, the domain where each domain name is stored), and the Root name Server returns the top-level domain name server address of the com domain
4.2: LDNS sends a request to the com top-level domain name server and returns the address of the www.bai.com domain name server
4.3: LDNS sends a request to the www.baidu.com domain name server and obtains the IP address of www.baidu.com

5: LDNS returns the IP address to the operating system and caches the IP address into the DNS table

6: The operating system returns the address to the browser. It also caches the IP address

7: Now the browser has got the IP address

3.2: Establish connection (three-way handshake) (using TCP protocol)

After knowing Baidu’s IP address, the next step is to implement the three-way handshake to connect

1: The client sends a connection establishment request to the server (Hello, nice to meet you)

2: After receiving the request, the server sends an agree connection request (ok, nice to meet you)

3: After receiving the server’s consent request, the client sends a confirmation signal to the server again (I’m also happy to meet you). Since then, the host and server have established a connection

3.3: Web page request and display

   建立連線之後,那麼伺服器與客戶機之間就會進行通訊

 3.1:客戶機瀏覽器依據IP位址產生Http請求,請求包含檔案的位置,請求的方式

 3.2:伺服器接收到http請求內容決定如何取得對應的HTML檔案

 3.3:伺服器將對應的HTML檔案傳送給瀏覽器

 3.4: 瀏覽器還沒完全接收HTML檔案的時候,開始渲染,顯示網頁

 3.5:依據html代碼,繼續要求圖片,

3.4:斷開過程(四次揮手過程)

1:客戶機向伺服器發送一個斷開的請求(不早了,我該走了)

2:伺服器接受到請求發送確認請求的訊號(知道了)

3:伺服器向客戶端發送斷開通知(我也該走了)

4:客戶機接受到斷開通知,回饋一個訊號(好的),伺服器接收到回授訊號斷開連結

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