CompTIA Network+ (N10-009)
Network infrastructure and operations
7
Modules
180
Practice Questions
5
Field Missions
N10-009
CompTIA
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Exam Details
Free Preview — Module 1
Module 1 — The OSI Model and Network Communication Fundamentals
Build the mental model that every network engineer uses: the OSI layers, encapsulation, PDUs, and the critical differences between TCP and UDP.
Why the OSI Model Matters
The shared language of networking — why every troubleshooting conversation references layers, and what 'Layer 2 problem' or 'Layer 7 issue' actually means.
The Seven Layers Explained
From Physical bits to Application protocols — the job of each layer, the devices that live there, and the protocols that operate at each level.
Encapsulation and PDUs
How data gets wrapped in headers as it moves down the stack: Data → Segment → Packet → Frame → Bits, and the reverse on receipt.
TCP vs. UDP and the TCP/IP Model
Connection-oriented vs. connectionless delivery, the three-way handshake, and how the four-layer TCP/IP model maps to the OSI model.
Sample Practice Questions
Question 1
A network engineer says 'this problem is at Layer 3.' Which device is most likely involved?
Routers operate at Layer 3 (Network), handling logical addressing and routing between networks. Hubs and repeaters operate at Layer 1; switches operate at Layer 2.
Question 2
Which Layer 4 protocol guarantees delivery through acknowledgments and retransmission of lost segments?
TCP is connection-oriented, using acknowledgments, sequence numbers, and retransmission to guarantee delivery. UDP is connectionless and does not guarantee delivery. ICMP is Layer 3; IP is Layer 3.
Question 3
What is the correct name for the Protocol Data Unit (PDU) at the Data Link layer?
The Data Link layer PDU is a Frame, which includes MAC address headers and a CRC trailer. Packet is Layer 3; Segment is the TCP Layer 4 PDU; Datagram is the UDP Layer 4 PDU.
Full course includes 7 modules, 180 practice questions, and 5 field missions.
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