Protocols

In networking, protocols are the rules that allow devices to communicate. Adding port numbers and OSI/TCP layer information helps understand exactly how data flows in a network.

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1. Application Layer Protocols

Protocol	Function	Port Number	OSI/TCP Layer
HTTP	Transfers web pages	TCP 80	Application
HTTPS	Secure web browsing	TCP 443	Application
FTP	File transfer	TCP 20/21	Application
SFTP	Secure file transfer	TCP 22	Application
SMTP	Sending emails	TCP 25	Application
IMAP	Email retrieval (server-side)	TCP 143	Application
POP3	Email download	TCP 110	Application
DNS	Domain name resolution	TCP/UDP 53	Application
Telnet	Remote login (insecure)	TCP 23	Application
SSH	Secure remote login	TCP 22	Application
DHCP	Dynamic IP assignment	UDP 67/68	Application
NTP	Time synchronization	UDP 123	Application
LDAP	Directory services	TCP/UDP 389	Application

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2. Transport Layer Protocols

Protocol	Function	Port Number	OSI/TCP Layer
TCP	Connection-oriented, reliable delivery	N/A	Transport
UDP	Connectionless, fast, unreliable	N/A	Transport
SCTP	Multi-stream, reliable delivery	N/A	Transport

Note: TCP and UDP define how data is packaged and delivered; ports are assigned at the application level.

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3. Internet / Network Layer Protocols

Protocol	Function	Port Number	OSI/TCP Layer
IP	Addressing and routing packets	N/A	Network
ICMP	Error reporting, diagnostics (ping)	N/A	Network
IGMP	Manages multicast groups	N/A	Network
ARP	Maps IP to MAC addresses	N/A	Network
RARP	Maps MAC to IP addresses	N/A	Network

Note: These protocols usually do not use ports; they operate at Layer 3 (Network) in OSI.

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4. Network Access / Data Link Layer Protocols

Protocol	Function	Port Number	OSI/TCP Layer
Ethernet	Wired LAN communication	N/A	Data Link
Wi-Fi (IEEE 802.11)	Wireless LAN communication	N/A	Data Link
PPP	Point-to-Point connection	N/A	Data Link
HDLC	Synchronous serial communication	N/A	Data Link
Frame Relay	WAN connections	N/A	Data Link
ATM	High-speed WAN communication	N/A	Data Link

Note: These protocols manage physical transmission and do not use port numbers.

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5. Security Protocols

Protocol Function Port Number OSI/TCP Layer SSL/TLS Encrypts communication TCP 443 (HTTPS), TCP 993 (IMAPS), TCP 465 (SMTPS) Application IPSec Secure IP communication N/A Network Kerberos Network authentication TCP/UDP 88 Application HTTPS HTTP over TLS TCP 443 Application