The answer is the Transport layer, specifically Layer 4 of the OSI model, where the web browser’s HTTP request data gets encapsulated with a TCP segment header. This is correct because the Transport layer takes the payload from the upper Application layer and adds the TCP header—containing source and destination ports, sequence numbers, and checksum—to form a segment, which is then passed to the Network layer for IP encapsulation. On the CompTIA Network+ N10-009 exam, this concept tests your understanding of the encapsulation process and the specific role each OSI layer plays; a common trap is confusing the Transport layer’s segment header addition with the Network layer’s packet header or the Data Link layer’s frame header. To remember, think of the mnemonic “Please Do Not Throw Sausage Pizza Away” and note that the “Transport” layer is where the TCP header is “transported” onto the data, making it the correct encapsulation point for segment headers.
N10-009 Networking Concepts Practice Question
This N10-009 practice question tests your understanding of networking concepts. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network technician is reviewing the OSI model to understand how data is encapsulated when a web request is sent from a client to a server. At which layer does the web browser's HTTP request data get encapsulated with a TCP segment header?
Why wrong: The Application layer (Layer 7) provides network services to applications (e.g., HTTP). It does not add transport headers; it passes data to the Transport layer.
B
Presentation layer
Why wrong: The Presentation layer (Layer 6) handles data formatting, encryption, and compression. It does not add TCP segment headers.
C
Session layer
Why wrong: The Session layer (Layer 5) manages sessions between applications. It does not add transport headers; that is the role of the Transport layer.
D
Transport layer
The Transport layer (Layer 4) takes data from upper layers, segments it, and adds a TCP or UDP header. For HTTP, the TCP segment header is added at this layer.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Transport layer
The Transport layer (Layer 4) is responsible for encapsulating application data with a TCP or UDP segment header. When a web browser sends an HTTP request, the HTTP data is passed down from the Application layer to the Transport layer, where the TCP segment header (including source/destination ports, sequence numbers, and checksum) is added. This encapsulation occurs at Layer 4, not at any higher layer.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Application layer
Why it's wrong here
The Application layer (Layer 7) provides network services to applications (e.g., HTTP). It does not add transport headers; it passes data to the Transport layer.
✗
Presentation layer
Why it's wrong here
The Presentation layer (Layer 6) handles data formatting, encryption, and compression. It does not add TCP segment headers.
✗
Session layer
Why it's wrong here
The Session layer (Layer 5) manages sessions between applications. It does not add transport headers; that is the role of the Transport layer.
✓
Transport layer
Why this is correct
The Transport layer (Layer 4) takes data from upper layers, segments it, and adds a TCP or UDP header. For HTTP, the TCP segment header is added at this layer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the Application layer (where HTTP data is generated) with the layer where the TCP header is added, mistakenly thinking encapsulation happens at Layer 7 instead of Layer 4.
Detailed technical explanation
How to think about this question
Under the hood, the TCP segment header includes fields such as source port (e.g., ephemeral port 49152-65535), destination port (e.g., 80 or 443), sequence number, acknowledgment number, and a 16-bit checksum for error detection. In a real-world scenario, if a firewall is inspecting traffic at Layer 4, it examines the TCP header to allow or deny the segment based on port numbers, while the HTTP payload remains untouched until it reaches the Application layer on the server.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Networking Concepts — This question tests Networking Concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Transport layer — The Transport layer (Layer 4) is responsible for encapsulating application data with a TCP or UDP segment header. When a web browser sends an HTTP request, the HTTP data is passed down from the Application layer to the Transport layer, where the TCP segment header (including source/destination ports, sequence numbers, and checksum) is added. This encapsulation occurs at Layer 4, not at any higher layer.
What should I do if I get this N10-009 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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