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Networking Concepts

Networking concepts form the theoretical foundation every technician builds on. This chapter covers the OSI and TCP/IP models, common ports and protocols, IP addressing and subnetting, topologies, and cloud and virtualization fundamentals. Mastering these ideas makes every later hands-on task easier to reason about.

The OSI Model and Encapsulation

The OSI model divides communication into seven layers, from the physical transmission of bits up to the application interface. Each layer serves the one above it and relies on the one below, and data is encapsulated with headers as it moves down the stack. Understanding which functions live at each layer lets you map symptoms to a likely cause.

Memorize the seven layers in order

Physical, Data Link, Network, Transport, Session, Presentation, and Application from Layer 1 to Layer 7.

Know the PDU at each layer

Bits at Layer 1, frames at Layer 2, packets at Layer 3, and segments or datagrams at Layer 4.

Match devices to layers

Hubs at Layer 1, switches at Layer 2, routers at Layer 3, and firewalls that can operate up through Layer 7.

Ports and Protocols

Applications identify themselves using well-known port numbers over TCP or UDP. Knowing which protocol uses which port and transport speeds firewall configuration and troubleshooting. TCP provides reliable, ordered delivery while UDP trades reliability for low overhead.

Learn the common well-known ports

HTTP 80, HTTPS 443, SSH 22, DNS 53, SMTP 25, and RDP 3389 are frequently referenced.

Distinguish TCP from UDP

TCP uses a three-way handshake for reliability; UDP is connectionless and favored for real-time traffic.

Associate protocols with functions

DHCP assigns addressing, DNS resolves names, and NTP synchronizes time.

IP Addressing and Subnetting

IP addressing assigns logical identifiers to hosts, and subnetting divides address space into manageable broadcast domains. Classless addressing with CIDR notation and VLSM lets administrators size subnets to need. Both IPv4 and IPv6 addressing must be understood.

Reserve two addresses per subnet

Every subnet loses one address for the network ID and one for the broadcast address.

Use private RFC 1918 ranges internally

10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are non-routable on the public internet.

Recognize special IPv6 prefixes

FE80::/10 is link-local, and global unicast addresses are internet-routable.

Apply CIDR math

Borrowing n host bits yields 2^n subnets, and remaining host bits determine usable hosts.

Topologies, Cabling, and Media

Physical and logical topologies describe how devices connect and how data flows. Media choices, from twisted-pair copper to fiber, determine distance, speed, and interference resistance. Selecting the right topology and medium balances cost, performance, and resilience.

Prefer star topologies in modern LANs

Central switches provide fault isolation so one cable failure affects only one node.

Respect copper distance limits

Twisted-pair Ethernet runs are limited to 100 meters including patch cables.

Choose fiber for distance and EMI immunity

Single-mode fiber spans long backbone links and resists electromagnetic interference.

Cloud and Virtualization

Cloud computing delivers scalable resources over the network under service models like IaaS, PaaS, and SaaS. Virtualization abstracts physical hardware into flexible virtual machines and networks. These models change how networks are designed and consumed.

Differentiate cloud service models

IaaS offers infrastructure, PaaS a development platform, and SaaS finished applications.

Know deployment models

Public, private, hybrid, and community clouds trade control against convenience and cost.

Understand elasticity

Cloud resources scale up or down on demand, aligning capacity with actual load.

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Network Implementation

Last updated: July 2026