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OSI Model
OSI Model — 7 Layers Explained
Break down each layer with real packet flow examples you can visualize.
Computer networking connects devices so they can share information. Every email, video call, and webpage load depends on networks working correctly. Whether you are preparing for CompTIA Network+, a CCNA certification, or simply want to troubleshoot your home Wi-Fi, this guide gives you a solid foundation.
💡 Tip: Think of networking like a postal system — IP addresses are street addresses, routers are sorting facilities, and protocols are the rules for how mail (data packets) is handled and delivered.
OSI Model — 7 Layers Roadmap
Layer 7–6
Application & Presentation
HTTP, FTP, SMTP at Layer 7. Encryption and data formatting at Layer 6. This is what users interact with directly.
Layer 5
Session Layer
Manages connections between applications — establishing, maintaining, and terminating sessions.
Layer 4
Transport Layer (TCP/UDP)
TCP provides reliable, ordered delivery. UDP is faster but connectionless. Ports identify specific services.
Layer 3
Network Layer (IP)
IP addressing, routing, and packet forwarding. Routers operate at this layer to connect different networks.
Layer 2–1
Data Link & Physical
MAC addresses, switches, Ethernet frames at Layer 2. Cables, Wi-Fi signals, and hardware at Layer 1.
TCP/IP Protocol Suite Roadmap
Phase 1
TCP/IP Overview
The four layers: Link, Internet, Transport, Application. How TCP/IP maps to the OSI model in practice.
Phase 2
Key Protocols
HTTP/HTTPS, FTP, SSH, ICMP (ping), ARP, and DHCP — what each does and when it is used.
Phase 3
Packet Analysis
Use Wireshark to capture and inspect real packets. Trace a web request from DNS lookup to HTTP response.
DNS, Routers & Switches
DNS
Domain Name System
How DNS resolves domain names to IP addresses. A, AAAA, CNAME, MX records, and the DNS lookup process.
Routers
Routing & Gateways
Default gateways, static vs. dynamic routing, NAT, and how home routers connect your LAN to the internet.
Switches
Switching & VLANs
MAC address tables, switch vs. hub vs. router, VLAN segmentation, and basic switch configuration concepts.
IP Addressing Roadmap
Phase 1
IPv4 Fundamentals
32-bit addresses, dotted decimal notation, public vs. private IPs, and common ranges (10.x, 172.16.x, 192.168.x).
Phase 2
Subnetting
Subnet masks, CIDR notation (/24, /16), calculating network and broadcast addresses, and dividing networks.
Phase 3
IPv6 Introduction
128-bit addresses, hexadecimal notation, why IPv6 matters, and dual-stack deployment basics.
📝 Note: Hands-on practice beats memorization. Set up a home lab with a router, run
ping and traceroute, and configure a simple network in Cisco Packet Tracer or GNS3.
Featured Networking Tutorials
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TCP/IP
TCP vs UDP — When to Use Each
Compare reliability, speed, and use cases for TCP and UDP protocols.
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DNS
How DNS Resolution Works
Follow a domain lookup from browser to nameserver and back in milliseconds.
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IP Addressing
Subnetting Made Easy
Learn subnet masks and CIDR with step-by-step practice problems.