Common Protocols: HTTP, FTP, SMTP, DNS, etc.

1. HTTP (Hypertext Transfer Protocol)

• Purpose: Used for transferring web pages and resources (HTML, CSS, JavaScript).
• Port: 80 (HTTP), 443 (HTTPS).
• Key Features:
  • Stateless protocol (does not remember previous requests).
  • Supports methods like GET, POST, PUT, DELETE, etc.
• Example: Accessing a website (http://gyanarth.com).

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2. FTP (File Transfer Protocol)

• Purpose: Transfers files between a client and a server.
• Port: 20 (data), 21 (control).
• Key Features:
  • Supports authentication (username/password).
  • Modes: Active and Passive FTP.
• Example: Uploading a website to a server.

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3. SMTP (Simple Mail Transfer Protocol)

• Purpose: Sends emails from a client to a server or between servers.
• Port: 25 (default), 587 (secure).
• Key Features:
  • Works with protocols like IMAP and POP3 for retrieving emails.
  • Push protocol (sends data to a recipient).
• Example: Sending an email using Gmail.

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4. DNS (Domain Name System)

• Purpose: Resolves domain names (e.g., gyanarth.com) into IP addresses.
• Port: 53.
• Key Features:
  • Hierarchical structure: Root, TLDs (e.g., .com), and SubDomains.
  • Records:
    • A Record: Maps domain to IPv4.
    • AAAA Record: Maps domain to IPv6.
    • MX Record: Mail exchange servers.
• Example: Typing www.gyanarth.com in a browser, which resolves to its IP address.

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5. HTTPS (Secure HTTP)

• Purpose: Secure version of HTTP, encrypting data using SSL/TLS.
• Port: 443.
• Key Features:
  • Ensures confidentiality, integrity, and authentication.
• Example: Online banking or e-commerce websites (https://flipkart.com).

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6. POP3 (Post Office Protocol v3)

• Purpose: Retrieves emails from a server to a local device.
• Port: 110 (default), 995 (secure).
• Key Features:
  • Downloads emails and deletes them from the server.
• Example: Accessing emails via an old desktop mail client.

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7. IMAP (Internet Message Access Protocol)

• Purpose: Accesses emails stored on a mail server.
• Port: 143 (default), 993 (secure).
• Key Features:
  • Allows syncing across multiple devices.
  • Does not delete emails from the server unless specified.
• Example: Using Gmail on both phone and laptop simultaneously.

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8. SNMP (Simple Network Management Protocol)

• Purpose: Manages and monitors network devices (routers, switches).
• Port: 161 (default).
• Key Features:
  • Uses MIB (Management Information Base) to store data.
  • Versions: SNMPv1, SNMPv2, SNMPv3 (secure).

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9. Telnet

• Purpose: Provides remote access to devices via text commands.
• Port: 23.
• Key Features:
  • Unencrypted; not secure (replaced by SSH).
• Example: Accessing a router’s configuration remotely.

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10. SSH (Secure Shell)

• Purpose: Provides encrypted remote login and file transfer.
• Port: 22.
• Key Features:
  • Secure alternative to Telnet.
• Example: Administering a Linux server remotely.

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Port Number	Protocol	Mnemonic Tip
20/21	FTP	File Transfer Protocol: 20 for data, 21 for control
22	SSH	Secure Shell: 22
23	Telnet	Telecommunication Network: 23
25/587	SMTP	Simple Mail Transfer Protocol: 25 is “mail on its way,” like sending a letter.
53	DNS	Domain Name System: 53 is “5-3 letters,” mapping domains to IPs.
67/68	DHCP	Dynamic Host Configuration Protocol: 67 is the server, 68 is the client
80	HTTP	HyperText Transfer Protocol: Think “80 lanes of highway for web traffic.”
110	POP3	Post Office Protocol 3: 110 is a 1-to-1 mailbox for retrieving emails.
143	IMAP	Internet Message Access Protocol: 143 is like a tree—access emails from multiple branches.
161/162	SNMP	Simple Network Management Protocol: 161 is the manager, 162 is the agent sending alerts.
389	LDAP	Lightweight Directory Access Protocol: 389 is like “three-directory system.”
443	HTTPS	Secure HTTP: Add 4 (secure) to HTTP’s 80, making 443. Think of “lock and key” security.
3389	RDP	Remote Desktop Protocol: A complex number like 3389 matches the complexity of remote access.

MCQ

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