The invisible pillars of the Internet: the services you use every day without even realizing it
The Internet is not just a vast ocean of information, it is also a highly organized and clearly structured set of services. It is these basic services that support our daily operations such as browsing the web, sending emails, downloading files, and remotely accessing servers. Shenchang will take you to learn about the most core basic services on the Internet and see how they work together.
1. Domain Name System
Remember the last time you typed www.baidu.com, did you ever wonder: How does the browser know the IP address behind it?
This is done by the Domain Name System (DNS). The role of DNS is to convert human-readable domain names (such as example.com) into computer-readable IP addresses (such as 93.184.216.34). Just like you look up a phone number by a contact name, DNS is the "phone book" of the Internet.
When you visit a website, the computer will first query the DNS server to obtain the IP address corresponding to the domain name, and then initiate the actual network request.
3. File Transfer Protocol
Need to upload or download large files? FTP (File Transfer Protocol) is born for this.
FTP provides the ability to upload, download, rename, and delete files between the client and the server. It adopts the client-server mode, uses the TCP protocol (usually port 21), and supports user authentication and directory browsing.
However, it should be noted that traditional FTP is also a plain text transmission. If sensitive data is involved, it is recommended to use an encrypted version such as FTPS or SFTP (a file transfer protocol based on SSH).
2. Remote Login (Telnet / SSH)
In the Internet world, distance is no longer a problem. With the help of remote login services, you can easily remotely access and operate another computer.
Telnet is the earliest remote login protocol, which is based on plain text transmission and has security risks.
SSH (Secure Shell) is the modern mainstream remote login protocol, which supports encrypted transmission and is more secure and reliable.
Remote login is often used in scenarios such as operation and maintenance, development, and debugging. For example, you can control a cloud server locally, install software, view logs, restart services, and other operations as if you were right next to it.
4. Email Service
Although instant messaging is already very developed, email is still an important form of Internet communication.
Common email-related protocols include:
SMTP (Simple Mail Transfer Protocol): responsible for sending emails.
POP3 (Post Office Protocol v3): download emails from the server to the local computer, and the emails will be deleted by default after downloading.
IMAP (Internet Message Access Protocol): emails are stored on the server side and support multi-terminal simultaneous viewing.
Through email clients or web mailboxes, users can easily send and receive emails and exchange information.
5. WWW and Hypertext Transfer Protocol HTTP
WWW (World Wide Web) is the most intuitive form of the Internet and the service we come into contact with most every day. It consists of web pages, pictures, videos and other resources on the World Wide Web, and these resources are accessed through browsers.
Communication between browsers and servers relies on a protocol: HTTP (HyperText Transfer Protocol).
HTTP defines how clients and servers request and respond to resources.
Every time you visit a web page in a browser, you will go through multiple steps such as DNS query, TCP connection, HTTP request, etc. before you can see the content you want.
With the increase in security requirements, it is now more recommended to use HTTPS (HTTP with an encryption layer).
The following is the TCP three-way handshake and four-wave process:
VI. Conclusion
These basic Internet services are like the steel skeleton of a building. Although most users never directly feel their existence, they silently support every web page access, file download, and remote login: