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200-201 Practice Question: An analyst uses Wireshark to investigate a…

An analyst uses Wireshark to investigate a suspicious download. The TCP stream shows a GET request for a .exe file from an external IP, followed by a 200 OK response. The response contains the file but the last packet in the stream has a FIN flag set from the server. The client sends an ACK but then immediately sends a RST. What does this behavior suggest?

⚠ Common exam trap

Cisco often tests the difference between a graceful TCP teardown (FIN/ACK exchange) and an abrupt reset (RST), and the trap here is assuming that any ACK followed by a RST indicates a crash or normal behavior, rather than recognizing the RST as an intentional evasion tactic.

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

The client intentionally terminated the connection to evade detection

The client sending a RST immediately after acknowledging the FIN indicates an abnormal termination. In a normal TCP teardown, the client would send its own FIN to close the connection gracefully. The RST suggests the client application intentionally aborted the connection, which is a common evasion technique to avoid detection by network monitoring tools that may not fully process the RST.

Answer analysis

Option-by-option breakdown

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

  • The client application crashed after receiving the file

    Why it's wrong here

    Crash would likely not send a clean ACK then RST.

  • Normal completion of download

    Why it's wrong here

    Normal completion does not include a RST after ACK.

  • The server is performing a delayed response

    Why it's wrong here

    Server is not initiating the RST.

  • The client intentionally terminated the connection to evade detection

    Why this is correct

    RST after receiving data can be used to avoid logging.

Visual reference

Client Server SYN (seq=100) SYN-ACK (seq=200, ack=101) ACK (ack=201) Connection established — data transfer begins

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Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

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