PROTOCOL



✅ Application Layer Protocols (Line by Line)

1. DNS (Domain Name System)
🔹 Translates domain names (like google.com) into IP addresses.
🔸 Port: UDP 53 (and sometimes TCP 53)


2. DHCP (Dynamic Host Configuration Protocol)
🔹 Automatically assigns IP addresses to devices in a network.
🔸 Port: UDP 67 (server), UDP 68 (client)


3. FTP (File Transfer Protocol)
🔹 Transfers files between computers (requires login).
🔸 Port: TCP 20 (data), TCP 21 (control)


4. TFTP (Trivial File Transfer Protocol)
🔹 Simplified version of FTP, no authentication, used for booting devices.
🔸 Port: UDP 69


5. SMTP (Simple Mail Transfer Protocol)
🔹 Sends emails from client to server or server to server.
🔸 Port: TCP 25 (unsecured), TCP 587 (secured), TCP 465 (SSL)


6. POP3 (Post Office Protocol version 3)
🔹 Downloads emails from server to client and deletes them from server.
🔸 Port: TCP 110 (unsecured), TCP 995 (SSL)


7. IMAP4 (Internet Message Access Protocol version 4)
🔹 Accesses and manages emails on the server without deleting them.
🔸 Port: TCP 143 (unsecured), TCP 993 (SSL)


8. Telnet
🔹 Remote access to a device's command line (insecure).
🔸 Port: TCP 23


9. SNMP (Simple Network Management Protocol)
🔹 Monitors and manages network devices like routers and switches.
🔸 Port: UDP 161 (agent), UDP 162 (trap)


10. NNTP (Network News Transfer Protocol)
🔹 Used for reading and posting messages to Usenet newsgroups.
🔸 Port: TCP 119


11. HTTP (HyperText Transfer Protocol)
🔹 Used to load web pages over the internet.
🔸 Port: TCP 80


12. HTTPS (HTTP Secure)
🔹 Secure version of HTTP using SSL/TLS encryption.
🔸 Port: TCP 443


13. LDAP (Lightweight Directory Access Protocol)
🔹 Accesses and maintains distributed directory services (like user lists).
🔸 Port: TCP/UDP 389 (unencrypted), TCP 636 (LDAPS – secure)


14. PPTP (Point-to-Point Tunneling Protocol)
🔹 VPN protocol that encapsulates PPP frames in IP datagrams.
🔸 Port: TCP 1723


15. L2TP (Layer 2 Tunneling Protocol)
🔹 VPN protocol, often used with IPsec for encryption.
🔸 Port: UDP 1701


16. RDP (Remote Desktop Protocol)
🔹 Allows users to remotely connect to another computer's GUI.
🔸 Port: TCP 3389




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✅ Summary Table

Protocol Port No. Description

DNS 53 UDP/TCP Domain name to IP resolution
DHCP 67/68 UDP Auto IP allocation
FTP 20, 21 TCP File transfer
TFTP 69 UDP Simple file transfer
SMTP 25/465/587 TCP Email sending
POP3 110/995 TCP Email receiving (download & delete)
IMAP4 143/993 TCP Email access (leave on server)
Telnet 23 TCP Remote command-line login
SNMP 161/162 UDP Network monitoring
NNTP 119 TCP Newsgroup access
HTTP 80 TCP Web browsing
HTTPS 443 TCP Secure web browsing
LDAP 389/636 TCP/UDP Directory services
PPTP 1723 TCP VPN tunneling
L2TP 1701 UDP VPN tunneling (with IPsec)
RDP 3389 TCP Remote desktop


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