N10-009 Networking Concepts Practice Question
A network technician is explaining the concept of encapsulation to a junior technician. At which OSI layer does a packet get encapsulated with a source and destination IP address?
⚠ Common exam trap
Test-takers frequently confuse Layer 2 MAC addressing with Layer 3 IP addressing, mistakenly thinking the packet is encapsulated with IP addresses at the Data Link layer, but encapsulation with IP addresses occurs strictly at the Network layer.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Layer 3
At Layer 3 (the Network layer), the packet is encapsulated with a source and destination IP address. This is defined by the Internet Protocol (IP), which handles logical addressing and routing across networks. The IP header is added to the payload from the upper layers, creating a packet that can be forwarded by routers.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Layer 2
Why it's wrong here
Layer 2, the Data Link layer, is responsible for encapsulating the Layer 3 IP packet into a frame for transmission over a local network segment. While it adds its own header and trailer, which include MAC addresses for physical addressing within that segment and a Frame Check Sequence for error detection, it does not add IP addresses. IP addressing is a higher-level function handled exclusively by Layer 3.
When this WOULD be correct
This option would be correct if the question asked: 'At which OSI layer does a frame get encapsulated with source and destination MAC addresses?'
- ✓
Layer 3
Why this is correct
The Network layer (Layer 3) is precisely where the IP header is added to the Transport layer segment or datagram, creating an IP packet. This header contains the crucial source and destination IP addresses, enabling logical addressing across disparate networks. This encapsulation is fundamental for routing decisions, allowing data to traverse multiple routers and reach its ultimate destination beyond the local network segment.
- ✗
Layer 4
Why it's wrong here
The Transport layer (Layer 4) performs encapsulation by adding a header to application data, forming segments (TCP) or datagrams (UDP). This header includes source and destination port numbers, which are essential for directing data to the correct application process on the host, as well as managing flow control and reliability. However, Layer 4 operates above the network layer and is not involved in adding IP addresses, which are logical network identifiers.
When this WOULD be correct
A question asking 'At which OSI layer is a segment encapsulated with source and destination port numbers?' would make Layer 4 correct.
- ✗
Layer 1
Why it's wrong here
Layer 1, the Physical layer, is concerned solely with the physical transmission of raw bit streams across the network medium, such as cables or wireless signals. It defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating physical links. This layer does not perform any form of logical encapsulation or add any headers or trailers; it simply converts the frame's bits into a physical signal.
When this WOULD be correct
A question asking at which layer data is converted into electrical signals, light pulses, or radio waves for transmission over a physical medium would have Layer 1 as the correct answer.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓Layer 3Correct answer▾
Why this is correct
The Network layer (Layer 3) is precisely where the IP header is added to the Transport layer segment or datagram, creating an IP packet. This header contains the crucial source and destination IP addresses, enabling logical addressing across disparate networks. This encapsulation is fundamental for routing decisions, allowing data to traverse multiple routers and reach its ultimate destination beyond the local network segment.
✗Layer 2Wrong answer — click to see why▾
Why this is wrong here
Layer 2 (Data Link layer) uses MAC addresses for local network delivery, not IP addresses. Encapsulation with source and destination IP addresses occurs at Layer 3 (Network layer).
★ When this WOULD be the correct answer
This option would be correct if the question asked: 'At which OSI layer does a frame get encapsulated with source and destination MAC addresses?'
Why candidates choose this
Candidates often confuse the roles of Layer 2 and Layer 3, mistakenly thinking IP addresses are added at Layer 2 because both involve addressing.
✗Layer 4Wrong answer — click to see why▾
Why this is wrong here
Layer 4 (Transport) uses port numbers and manages end-to-end communication, not IP addressing. IP addresses are added at Layer 3 (Network).
★ When this WOULD be the correct answer
A question asking 'At which OSI layer is a segment encapsulated with source and destination port numbers?' would make Layer 4 correct.
Why candidates choose this
Candidates may confuse encapsulation of IP addresses with the Transport layer because TCP/UDP headers also contain addressing information (ports), leading to a mix-up between network and transport addressing.
✗Layer 1Wrong answer — click to see why▾
Why this is wrong here
Layer 1 (Physical) deals with raw bit transmission over physical media, not with IP addresses. Encapsulation with IP addresses occurs at Layer 3 (Network).
★ When this WOULD be the correct answer
A question asking at which layer data is converted into electrical signals, light pulses, or radio waves for transmission over a physical medium would have Layer 1 as the correct answer.
Why candidates choose this
Candidates may confuse the physical transmission of data with the encapsulation process, thinking that IP addresses are added at the lowest layer because they associate addressing with hardware interfaces.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
Go deeper
Related to this question
Learn chapter
Interior vs Exterior Routing Protocols
Key term
Encapsulation
Encapsulation is the process of wrapping data with protocol headers and trailers before sending it across a network.
Key term
Packet
A packet is a small unit of data that is sent over a network, containing both the actual data and control information for delivery.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the N10-009 exam.