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200-201 TCP Sequence Number Practice Question

During an incident, an analyst captures network traffic. Which field in a TCP header is used to reassemble fragmented packets?

⚠ Common exam trap

Cisco often tests the distinction between IP fragmentation (handled by the Identification field and fragment offset in the IP header) and TCP reassembly (handled by the Sequence Number), causing candidates to confuse the two layers.

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

✓

Sequence number

The Sequence Number field in the TCP header is used to reassemble the original data stream from received TCP segments. It indicates the byte offset of the segment's data within the overall stream, allowing the receiver to order segments correctly. Note that IP fragmentation (splitting packets at the network layer) relies on the Identification field and Fragment Offset in the IP header, not the TCP Sequence Number.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • ✗

    Flags

    Why it's wrong here

    Incorrect. Flags control connection state, not reassembly.

  • ✗

    Window size

    Why it's wrong here

    Incorrect. Window size is used for flow control.

  • ✗

    Acknowledgment number

    Why it's wrong here

    Incorrect. ACK number is used for reliable delivery, not reassembly.

  • ✓

    Sequence number

    Why this is correct

    Correct. The sequence number indicates the order of bytes for reassembly.

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JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

This 200-201 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 200-201 exam.