[Protocol] Common application layer protocols and their uses

Foreword:

        In computer networks, an application layer protocol is a set of rules and conventions used for communication between different computers. These protocols define the format, semantics, and sequence of data exchange to implement specific application requirements.

        This article will introduce some common application layer protocols and their uses to help readers better understand and apply these protocols.

• HTTP (Hypertext Transfer Protocol)Hypertext Transfer Protocol 

  • Port: 80 (HTTP), 443 (HTTPS) Port: 80 (HTTP), 443 (HTTPS)
  • Common uses: web browsing, fetching web pages, interacting with web servers.

• HTTPS (HTTP Secure)HTTP secure version

  • Port: 443Port: 443
  • Common uses: Secure variant of HTTP, encrypted web browsing, ensuring confidentiality and integrity of web communications.

• FTP (File Transfer Protocol) file transfer protocol 

  • Port: 20 (FTP data), 21 (FTP control)
  • Common uses: File transfer and management between clients and servers.

• SFTP (SSH File Transfer Protocol)SSH File Transfer Protocol

  • Port: 22Port: 22
  • Common uses: Securely transfer files through SSH to achieve secure remote file operations.

• SMTP (Simple Mail Transfer Protocol) Simple Mail Transfer Protocol

  • Port: 25Port: 25
  • Common uses: Sending and relaying email between mail servers.

• POP3 (Post Office Protocol version 3) Post Office Protocol version 3

  • Port: 110Port: 110
  • Common use: Retrieve email from mail server to local client.

• IMAP (Internet Message Access Protocol) Internet Message Access Protocol

  • Port: 143Port: 143
  • Common uses: Access and manage email on a mail server.

• DNS (Domain Name System) domain name system

  • Port: 53Port: 53
  • Common uses: Resolve domain names into IP addresses, convert human-readable domain names into machine-readable IP addresses.

• SSH (Secure Shell) secure shell

  • Port: 22Port: 22
  • Common uses: Securing remote logins and command execution on remote servers.

• Telnet remote login

  • Port: 23Port: 23
  • Common uses: remote login and command execution on remote hosts (unencrypted).

• SNMP (Simple Network Management Protocol) simple network management protocol

  • Port: 161 (SNMP), 162 (SNMP Trap)Port: 161 (SNMP), 162 (SNMP Trap)
  • Common uses: manage and monitor network devices, collect and modify device information.

• RDP (Remote Desktop Protocol)Remote Desktop Protocol

  • Port: 3389Port: 3389
  • Common uses: Remote access and control of Windows-based systems, graphical desktop sharing.

• NTP (Network Time Protocol) Network Time Protocol

  • Port: 123Port: 123
  • Common uses: Time synchronization to ensure accurate timing across networked devices.

• MQTT (Message Queuing Telemetry Transport) message queue telemetry transport

  • Port: 1883 (MQTT)、8883 (MQTT over TLS)端口： 1883 （MQTT）、8883 （MQTT over TLS）
  • Common uses: A lightweight messaging protocol for IoT devices that enables efficient and reliable communication between devices.

        The above are some common application layer protocols and their uses. Understanding and becoming familiar with these protocols can help developers and network administrators better build and manage network applications and services.

(Note: The port numbers and uses mentioned in this article only represent common situations. Specific applications and configurations may vary depending on the system and environment. When using these protocols, please refer to relevant documents and standards for configuration and implementation.)