- A
The packets are sent to sequential IP addresses in the same subnet
Scanning often targets sequential or random IPs to find live hosts.
- B
No TCP three-way handshake completes for these connections
In scanning, the scanner often sends SYN and does not complete the handshake (SYN-ACK may be met with RST). Here, lack of completion is indicated by RST after timeout.
- C
The source IP is from an internal address
Why wrong: Internal source IP does not necessarily indicate scanning; it could be legitimate traffic.
- D
The same port is targeted across multiple IP addresses
Scanning a specific port across multiple hosts is a common reconnaissance technique.
- E
The payload contains exploit code for SMB vulnerability
Why wrong: Exploit code would be in later packets after a connection is established; SYN packets have no payload.
Quick Answer
The answer is that the same port is targeted across multiple IP addresses, as this is the primary indicator of a network scan via TCP SYN patterns. This is correct because a legitimate client typically initiates a TCP handshake to establish a single connection, whereas a scanner sends SYN packets to numerous hosts on a specific port—like port 445 for SMB—to probe for live systems, and the subsequent RST packets after a 15-second timeout confirm that the targets did not respond, revealing a sweep rather than normal traffic. On the CHFI exam, this concept tests your ability to differentiate between benign traffic and reconnaissance activity, often appearing in forensic analysis of packet captures; a common trap is mistaking the RST packets for a failed connection attempt rather than recognizing the systematic targeting of sequential IPs. Remember the mnemonic “SYN to many, RST to none” to recall that a scan sends SYN probes across a range and receives no SYN-ACK, only timeouts.
CHFI OS and Network Forensics Practice Question
This CHFI practice question tests your understanding of os and network forensics. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A security analyst captures network traffic and observes multiple TCP SYN packets sent to a range of IP addresses on port 445, followed by TCP RST packets after 15 seconds. Which THREE indicators suggest this is a network scan?
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 packets are sent to sequential IP addresses in the same subnet
TCP SYN packets to multiple IPs on a single port indicate a port scan. The RST packets after a timeout suggest the targets did not respond, which is common in a sweep. Sequential IPs and the use of port 445 (SMB) are typical of scanning. The lack of established connections and the specific pattern confirm scanning.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 packets are sent to sequential IP addresses in the same subnet
- ✓
No TCP three-way handshake completes for these connections
Why this is correct
In scanning, the scanner often sends SYN and does not complete the handshake (SYN-ACK may be met with RST). Here, lack of completion is indicated by RST after timeout.
Related concept
CIDR notation defines the prefix length.
- ✗
The source IP is from an internal address
Why it's wrong here
Internal source IP does not necessarily indicate scanning; it could be legitimate traffic.
- ✓
The same port is targeted across multiple IP addresses
Why this is correct
Scanning a specific port across multiple hosts is a common reconnaissance technique.
Related concept
CIDR notation defines the prefix length.
- ✗
The payload contains exploit code for SMB vulnerability
Why it's wrong here
Exploit code would be in later packets after a connection is established; SYN packets have no payload.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related CHFI subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this CHFI question test?
OS and Network Forensics — This question tests OS and Network Forensics — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The packets are sent to sequential IP addresses in the same subnet — TCP SYN packets to multiple IPs on a single port indicate a port scan. The RST packets after a timeout suggest the targets did not respond, which is common in a sweep. Sequential IPs and the use of port 445 (SMB) are typical of scanning. The lack of established connections and the specific pattern confirm scanning.
What should I do if I get this CHFI question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related CHFI subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
3 more ways this is tested on CHFI
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. A network analyst captures suspicious traffic and uses Wireshark to examine packets. The analyst notices many TCP SYN packets sent to various ports on a single host with no SYN-ACK replies. What type of activity is MOST likely observed?
medium- A.Denial of Service (DoS) attack
- ✓ B.Port scan
- C.DNS amplification
- D.ARP poisoning
Why B: A port scan sends SYN packets to multiple ports to identify open ones; lack of SYN-ACK replies indicates closed ports.
Variation 2. A network forensics analyst captures traffic and sees a series of TCP SYN packets sent to multiple ports on a target, with no corresponding SYN-ACK replies. What type of activity is MOST likely indicated?
medium- A.A denial-of-service (DoS) flood
- ✓ B.A port scan reconnaissance
- C.A man-in-the-middle attack
- D.Normal web browsing traffic
Why B: A port scan sends SYN packets to various ports; if no SYN-ACK is received, the ports are likely filtered or closed, characteristic of a scan.
Variation 3. A network analyst captures a packet with Wireshark showing a TCP SYN packet from IP 10.0.0.5 to 192.168.1.10 port 443, followed immediately by a SYN‑ACK from 192.168.1.10 to 10.0.0.5, then an RST from 10.0.0.5. What does this sequence MOST likely indicate?
hard- A.A man‑in‑the‑middle attack
- B.A denial‑of‑service (SYN flood) attack
- C.A normal HTTPS session initiation
- ✓ D.A TCP SYN scan (stealth scan)
Why D: A SYN followed by SYN‑ACK and then RST is typical of a port scan where the scanner sends a SYN, receives a SYN‑ACK (port open), and then immediately resets the connection to avoid completing the handshake.
Last reviewed: Jun 21, 2026
This CHFI practice question is part of Courseiva's free EC-Council 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 CHFI exam.
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