What is the URL

Uniform Resource Locator URL Full name Uniform Resource Locator, which has two common forms:

  • Uniform resource locator —URL
  • Unified Resource Name —URN

There are two main differences between the two:

  • URLCommonly referred to as a web address, for examplebaidu.com. throughURLOpen the url, the content is uncertain
  • URNCan determine the unique content, similar to our ID card. The most common one is used in books, one must be available before each book is publishedURNThrough theURNYou can find the book.

The composition of the URL

The URL is mainly composed of the following six parts:

  • Agreements, for exampleHTTP
    • It is used to transfer information between the Web browser and the Web server. Generally, the protocol can be HTTP or HTTPS
  • Domain name or IP, for examplebaicu.com
    • IP is used to locate a device and encapsulate data packets to communicate with other devices (such as the computer at home, router, network, etc.). They all have their own independent IP addresses. IP is also divided into internal IP and external IP
  • Ports, for example8080
    • Ports in an IP address refer to logical ports, which are logically used to distinguish services
  • Paths, for example/s
    • Used to access the same website of different pages, you can request static resources, query background data
  • Query parameters, such as? name=zhangsan&age=18
    • Used to access different data on the same page
  • Anchor points, for example# 1
    • Used to locate the location in the page, and does not support Chinese, the browser will convert it to a string, the anchor is only browser related, not uploaded to the server

DNS function and nslookup command

The role of DNS

DNS can match a domain name to an IP address, so that users can access a website by entering a domain name instead of entering a long and difficult IP address, because the DNS service will automatically convert the domain name to the correct IP address.

Noslookup command

The nslookup command is used to query DNS records to check whether domain name resolution is normal and diagnose network faults.

The process of entering a URL in the browser address bar

  1. The browser requests the DNS server (domain name system/service) to resolve the IP address corresponding to the domain name in the URL
  2. The TCP connection is established with the server based on the obtained IP address and port number
  3. The browser sends an HTTP request to read the file. The request packet is sent to the server as the third packet of the TCP three-way handshake
  4. The server responds to the browser request and sends the corresponding HTML text to the browser, releasing TCP
  5. Display the captured page to the user

The function of IP and the ping command

The role of IP

IP is used to locate a device and encapsulate data packets to communicate with other devices (such as home computers, routers, networks, etc.). They all have their own IP.

IP addresses are classified into Intranet IP addresses and extranet IP addresses. The Intranet and extranet do not interfere with each other and can only communicate with each other through a router (gateway).

The ping command

You can use ping on the command line to test whether the network is connected. As shown in the picture below, under the condition of normal network, the website baidu.com will be requested.

The domain name

A domain name is just another name for IP. (for example: QQ.com baidu.com) It is divided into top-level domain name, level-1 domain name, level-2 domain name and level-3 domain name.

Usually we call the.com end a top-level domain; Xxx.com is a level 2 domain name (commonly known as level 1 domain name; www.xxx.com is a level 3 domain name (commonly known as level 2 domain name)

Compared to IP, domain names are easier to remember

  • comA commercial organization or company
  • cnChinese domain name
  • orgA non-profit organization or group
  • govThe government department
  • milThe military
  • netAn organization or company that works on the Internet
  • ccunlimited
  • tvunlimited
  • acScientific research institutions