hardMultiple ChoiceObjective-mapped
Port Scan Detection: Recognizing Connect() Scans in Packet Captures
Exhibit
09:32:45.123456 IP 10.0.0.5.12345 > 192.168.1.1.80: Flags [S], seq 12345 09:32:45.123789 IP 192.168.1.1.80 > 10.0.0.5.12345: Flags [S.], seq 54321, ack 12346 09:32:45.124000 IP 10.0.0.5.12345 > 192.168.1.1.80: Flags [R], seq 12346
Refer to the exhibit. What does this packet capture indicate?
Quick Answer
The correct answer is a port scan, specifically a SYN scan. This is identified by observing multiple TCP SYN packets sent to a single host, such as 10.10.10.10, targeting different ports like 80, 443, 22, and 21, with no subsequent ACK or RST responses completing the three-way handshake. In a normal connection, the client would respond to a SYN-ACK with an ACK, but here the sender never finishes the handshake, instead moving on to probe the next port. On the Cisco CyberOps Associate 200-201 exam, this pattern tests your ability to recognize reconnaissance activity in packet captures, often appearing as a scenario where you must distinguish a scan from a legitimate connection attempt. A common trap is confusing this with a half-open scan, but remember: a connect() scan completes the handshake and then sends an RST, whereas this SYN scan never completes it. Memory tip: “SYN alone, no ACK in sight—that’s a scan, not a handshake right.”
⚠ Common exam trap
Cisco often tests the distinction between a SYN flood (volume-based attack on a single port) and a SYN scan (probing multiple ports), where candidates mistakenly associate any SYN traffic with a flood rather than recognizing the multi-port pattern as reconnaissance.
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
✓
Port scan
The packet capture shows multiple TCP SYN packets sent to a single host (10.10.10.10) targeting different ports (80, 443, 22, 21) with no subsequent ACK or RST responses. This pattern is characteristic of a port scan, specifically a SYN scan, where the attacker sends SYN packets to probe for open ports without completing the three-way handshake.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
SYN flood
Why it's wrong here
Incorrect. A SYN flood would not complete the handshake.
- ✓
Port scan
Why this is correct
The pattern matches a SYN scan (also known as half-open scan), where the attacker sends SYN packets to multiple ports and does not complete the three-way handshake, allowing them to probe for open ports without establishing a full connection.
- ✗
Session hijack
Why it's wrong here
Incorrect. Session hijacking involves spoofing and does not end with RST.
- ✗
Normal HTTP traffic
Why it's wrong here
Incorrect. Normal traffic would continue with HTTP requests, not an immediate RST.
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Same concept, more angles
1 more way this is tested on 200-201
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Given a packet capture showing TCP packets with flags: first packet SYN, second packet SYN-ACK, third packet ACK, then a fourth packet with RST flag. What should the analyst suspect?
hard- ✓ A.Port scan
- B.Normal traffic
- C.SYN flood
- D.Denial of service
Why A: The three-way handshake (SYN, SYN-ACK, ACK) completes a TCP connection, but the immediate RST after the ACK indicates the client terminated the connection without sending any application data. This pattern is characteristic of a port scan (e.g., using nmap's connect scan), where the scanner verifies the port is open by completing the handshake and then immediately resets to avoid leaving the connection half-open.
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.