CCNA Network Infrastructure and Connectivity Practice Question
A network engineer is troubleshooting a connectivity issue between two hosts on different subnets. The sending host has constructed a packet with a destination IP address of 192.168.2.10. As the packet travels down the OSI model layers on the sending host, which Protocol Data Unit (PDU) name is assigned to the data at the Transport layer after TCP segments are created, and at which layer does the IP address get encapsulated?
⚠ Common exam trap
Cisco often tests the precise PDU naming per layer (segment for TCP at Transport, packet for IP at Network) and the layer where IP addresses are added, tricking candidates who confuse 'packet' with 'segment' or think IP addresses are added at the Transport 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
✓
PDU is a segment; IP address is added at the Network layer.
At the Transport layer, TCP divides data into segments, so the PDU is called a segment, making B correct. The destination IP address (192.168.2.10) is added at the Network layer, where the IP header encapsulates the segment into a packet. Option A is wrong because a frame is a Data Link layer PDU, and IP addresses are not added at that layer. Option C is wrong because the PDU at the Transport layer is a segment, not a packet, and IP addresses are added at the Network layer, not the Transport layer. Option D is wrong because 'datagram' typically refers to UDP’s Transport layer PDU (not TCP), and IP addresses are not added at the Transport layer.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
PDU is a frame; IP address is added at the Data Link layer.
Why it's wrong here
A frame is a Layer 2 PDU that contains packet data and is used for media access, but the PDU created by TCP at the Transport layer is still a segment. The IP address is never added at the Data Link layer; instead, Layer 3 appends IP addresses to form a packet, and then Layer 2 creates a frame with MAC addresses. This option confuses data-link addressing with network-layer addressing.
- ✓
PDU is a segment; IP address is added at the Network layer.
Why this is correct
At the Transport layer, TCP encapsulates the application data into a segment, adding source and destination port numbers. This segment is then passed down to the Network layer, where the IP header—containing source and destination IP addresses—is added to create a packet. This is the correct sequence of encapsulation for TCP/IP communication.
- ✗
PDU is a packet; IP address is added at the Transport layer.
Why it's wrong here
A packet is the PDU at the Network layer, so labeling the Transport-layer PDU as a packet is a layer violation. IP addresses are added exactly at that Network layer during IP encapsulation, not at the Transport layer, where port numbers and sequence numbers are appended. Thus both the PDU type and the listed encapsulation layer are incorrect.
- ✗
PDU is a datagram; IP address is added at the Transport layer.
Why it's wrong here
A datagram is the PDU defined for UDP at the Transport layer, but the encapsulation described here uses TCP, which creates a segment. Furthermore, the source and destination IP addresses are appended when the segment is wrapped in a packet at the Network layer (Layer 3), not at Layer 4. Therefore this answer fails on both the PDU name and the layer where IP addressing occurs.
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 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓PDU is a segment; IP address is added at the Network layer.Correct answer▾
Why this is correct
At the Transport layer, TCP encapsulates the application data into a segment, adding source and destination port numbers. This segment is then passed down to the Network layer, where the IP header—containing source and destination IP addresses—is added to create a packet. This is the correct sequence of encapsulation for TCP/IP communication.
✗PDU is a frame; IP address is added at the Data Link layer.Wrong answer — click to see why▾
Why this is wrong here
The PDU at the Transport layer is a segment, not a frame. Frames are the PDU at the Data Link layer (Layer 2). Additionally, IP addresses are added at the Network layer (Layer 3), not the Data Link layer.
Why candidates choose this
Students often confuse the Data Link layer with the Network layer because both involve addressing (MAC vs. IP). The term 'frame' is commonly associated with encapsulation, leading to the mistaken belief that IP addresses are added at Layer 2.
✗PDU is a packet; IP address is added at the Transport layer.Wrong answer — click to see why▾
Why this is wrong here
A packet is the PDU at the Network layer (Layer 3), not the Transport layer. The IP address is added at the Network layer, not the Transport layer. The Transport layer PDU is a segment (for TCP) or a datagram (for UDP).
Why candidates choose this
The term 'packet' is widely used in networking and often misapplied to any encapsulated data unit. Students may incorrectly associate the IP address with the Transport layer because both are involved in end-to-end communication.
✗PDU is a datagram; IP address is added at the Transport layer.Wrong answer — click to see why▾
Why this is wrong here
A datagram is the PDU for UDP at the Transport layer, but the question specifies TCP segments. Even if it were UDP, the IP address is still added at the Network layer, not the Transport layer.
Why candidates choose this
Students may recall that UDP uses datagrams and think that the IP address is part of the Transport layer encapsulation. However, IP addressing is always a Network layer function, regardless of the Transport protocol.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
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
The OSI Model
Key term
Internet Protocol
Internet Protocol (IP) is the set of rules that governs how data is addressed, routed, and sent from one device to another across networks, including the internet.
Key term
Frame
A frame is a unit of data at the Data Link layer of networking, containing header, payload, and trailer information for local network delivery.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco 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 200-301 exam.