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200-201 Practice Question: A security analyst is reviewing IDS alerts and…
A security analyst is reviewing IDS alerts and notices multiple TCP resets sent from an internal host with IP 10.10.10.25 to various external IPs on port 443. The alerts indicate that these resets occur immediately after the corresponding SYN-ACK from the external server, before any data exchange. The analyst suspects a TCP reset attack. Which action is most likely occurring?
⚠ Common exam trap
Cisco often tests the distinction between a legitimate RST (sent by a host to abort a connection due to an error or policy) and a spoofed RST (sent by an attacker to disrupt a connection), and the trap here is that candidates may assume the RST is from a firewall or a normal closure without considering the timing and source IP spoofing.
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
✓
An attacker is spoofing the client IP to send forged RST packets.
The described behavior—TCP RST packets sent immediately after the SYN-ACK, before any data exchange, from an internal host to multiple external IPs on port 443—is characteristic of a TCP reset attack. In this attack, an adversary spoofs the source IP of the legitimate client (10.10.10.25) and sends forged RST segments to the external servers, causing them to abort the TCP handshake prematurely. This prevents the completion of the three-way handshake and disrupts the connection before any application data can be exchanged.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A firewall is sending RST packets to block outbound traffic.
Why it's wrong here
A firewall would typically send RST with its own IP, not the client's IP.
- ✗
A client is properly closing a session after receiving data.
Why it's wrong here
Normal closure would occur after data exchange, not immediately after SYN-ACK.
- ✗
The client is retransmitting lost TCP segments.
Why it's wrong here
Retransmissions are data packets, not reset packets.
- ✓
An attacker is spoofing the client IP to send forged RST packets.
Why this is correct
This is a classic TCP reset attack where the attacker spoofs the client's IP to terminate a connection.
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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.