The answer is a host on the network is infected with malware that is generating many outbound connections. This is correct because the high tcp_src_session anomaly indicates an excessive number of TCP sessions originating from a single source IP, which is a classic sign of malware or a compromised host attempting to communicate with command-and-control servers, propagate, or exfiltrate data. On the Fortinet NSE 4 Network Security Professional exam, this scenario tests your ability to interpret the output of 'diagnose ips anomaly list' and correlate it with real-world symptoms like slow internet. A common trap is to blame the firewall or a bandwidth issue, but the key is that the anomaly is source-based, not destination-based. Remember the memory tip: "One source, many sessions—think infection, not congestion."
NSE4 Security Profiles Practice Question
This NSE4 practice question tests your understanding of security profiles. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
An administrator runs the command 'diagnose ips anomaly list' and sees many entries for 'tcp_src_session' with high counts. Users report slow internet. What is the most likely issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A host on the network is infected with malware that is generating many outbound connections
High tcp_src_session counts indicate many TCP sessions from a single source, often due to a host generating excessive connections (e.g., malware or P2P).
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 IPS signature database is corrupted
Why it's wrong here
Anomaly detection is separate from signature database.
✗
The FortiGate has a hardware failure
Why it's wrong here
Hardware failure would not cause specific anomaly entries.
✓
A host on the network is infected with malware that is generating many outbound connections
Why this is correct
A single source with excessive sessions is typical of malware or P2P activity.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The FortiGate is under a DDoS attack
Why it's wrong here
While possible, the specific anomaly indicates many sessions from one source, not distributed.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related NSE4 NAT questions on configuration and troubleshooting.
Security Profiles — This question tests Security Profiles — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: A host on the network is infected with malware that is generating many outbound connections — High tcp_src_session counts indicate many TCP sessions from a single source, often due to a host generating excessive connections (e.g., malware or P2P).
What should I do if I get this NSE4 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related NSE4 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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