OSI Model Layers, Network Protocols, Ports & Functions

Layer 7 - Application Layer

Provides network services directly to user applications (HTTP, HTTPS, DNS, DHCP, FTP, SSH, Telnet, SMTP)

Layer 6 - Presentation Layer

Translates data formats between application and network (SSL/TLS, JPEG, GIF, ASCII)

Layer 5 - Session Layer

Manages communication sessions and dialogs between hosts (NetBIOS, PPTP, RPC)

Layer 4 - Transport Layer

Provides reliable or unreliable delivery and flow control (TCP, UDP)

Layer 3 - Network Layer

Handles logical addressing, routing, and packet forwarding (IP, ICMP, IPSec, OSPF, routers)

Layer 2 - Data Link Layer

Handles physical addressing, framing, and error detection (Ethernet, MAC addresses, switches, ARP)

Layer 1 - Physical Layer

Transmits raw bit streams over a physical medium (Cables, hubs, repeaters, RJ45, fiber optics)

HTTP (Hypertext Transfer Protocol)

OSI Layer 7 (Application) - Used for transmitting unencrypted web pages (Port 80)

HTTPS (HTTP Secure)

OSI Layer 7 (Application) - Secure web traffic using SSL/TLS encryption (Port 443)

DNS (Domain Name System)

OSI Layer 7 (Application) - Resolves human-readable domain names to IP addresses (Port 53)

DHCP (Dynamic Host Configuration Protocol)

OSI Layer 7 (Application) - Dynamically assigns IP addresses to devices on a network (Ports 67/68)

FTP (File Transfer Protocol)

OSI Layer 7 (Application) - Transfers files between a client and a server (Ports 20/21)

SSH (Secure Shell)

OSI Layer 7 (Application) - Secure remote command-line access and tunneling (Port 22)

Telnet

OSI Layer 7 (Application) - Insecure remote command-line access (Port 23)

SMTP (Simple Mail Transfer Protocol)

OSI Layer 7 (Application) - Sends email between mail servers (Port 25)

SNMP (Simple Network Management Protocol)

OSI Layer 7 (Application) - Monitors and manages network devices (Ports 161/162)

TCP (Transmission Control Protocol)

OSI Layer 4 (Transport) - Connection-oriented, reliable protocol with error recovery and flow control

UDP (User Datagram Protocol)

OSI Layer 4 (Transport) - Connectionless, unreliable protocol for fast, low-overhead transmission

IP (Internet Protocol)

OSI Layer 3 (Network) - Provides logical addressing and packet routing across networks (IPv4/IPv6)

ICMP (Internet Control Message Protocol)

OSI Layer 3 (Network) - Used for diagnostic and error messaging (e.g., Ping and Traceroute)

ARP (Address Resolution Protocol)

OSI Layer 2 (Data Link) - Resolves an IPv4 address to a physical MAC address on a local network