CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
Exhibit
Jan 15 10:30:15 router1 sshd[1234]: Failed password for admin from 192.0.2.100 port 22 ssh2
Jan 15 10:30:20 router1 sshd[1234]: Failed password for admin from 192.0.2.100 port 22 ssh2
Jan 15 10:30:25 router1 sshd[1234]: Failed password for admin from 192.0.2.100 port 22 ssh2
Jan 15 10:30:30 router1 sshd[1234]: Connection closed by 192.0.2.100 [preauth]
Jan 15 10:30:35 router1 sshd[1235]: Failed password for admin from 198.51.100.50 port 22 ssh2
Jan 15 10:30:40 router1 sshd[1235]: Failed password for admin from 198.51.100.50 port 22 ssh2
Jan 15 10:30:45 router1 sshd[1235]: Failed password for admin from 198.51.100.50 port 22 ssh2
Jan 15 10:30:50 router1 sshd[1235]: Connection closed by 198.51.100.50 [preauth]
Refer to the exhibit. An administrator reviews the logs on router1. Which statement describes the events?
Jan 15 10:30:15 router1 sshd[1234]: Failed password for admin from 192.0.2.100 port 22 ssh2
Jan 15 10:30:20 router1 sshd[1234]: Failed password for admin from 192.0.2.100 port 22 ssh2
Jan 15 10:30:25 router1 sshd[1234]: Failed password for admin from 192.0.2.100 port 22 ssh2
Jan 15 10:30:30 router1 sshd[1234]: Connection closed by 192.0.2.100 [preauth]
Jan 15 10:30:35 router1 sshd[1235]: Failed password for admin from 198.51.100.50 port 22 ssh2
Jan 15 10:30:40 router1 sshd[1235]: Failed password for admin from 198.51.100.50 port 22 ssh2
Jan 15 10:30:45 router1 sshd[1235]: Failed password for admin from 198.51.100.50 port 22 ssh2
Jan 15 10:30:50 router1 sshd[1235]: Connection closed by 198.51.100.50 [preauth]
A
The SSH service is disabled on router1.
Why wrong: Incorrect. The logs show SSH activity, so it is enabled.
B
A successful SSH login from 192.0.2.100 occurred.
Why wrong: Incorrect. The logs show only failed attempts and then connection closed.
C
The router is configured to allow unlimited SSH authentication attempts.
Why wrong: Incorrect. The connections were closed after three attempts, suggesting a limit.
D
Two different IP addresses attempted brute-force SSH authentication.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Two different IP addresses attempted brute-force SSH authentication.
The logs show repeated failed SSH login attempts for the user 'admin' from two different IP addresses (192.0.2.100 and 198.51.100.50). Each IP made three attempts before the connection was closed (likely due to authentication failure threshold). This pattern indicates a brute-force attack on the SSH service.
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 SSH service is disabled on router1.
Why it's wrong here
Incorrect. The logs show SSH activity, so it is enabled.
✗
A successful SSH login from 192.0.2.100 occurred.
Why it's wrong here
Incorrect. The logs show only failed attempts and then connection closed.
✗
The router is configured to allow unlimited SSH authentication attempts.
Why it's wrong here
Incorrect. The connections were closed after three attempts, suggesting a limit.
✓
Two different IP addresses attempted brute-force SSH authentication.
Static NAT maps one inside address to one outside address.
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.
Trap categories for this question
Command / output trap
Incorrect. The logs show SSH activity, so it is enabled.
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 security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
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 CISSP NAT questions on configuration and troubleshooting.
Communication and Network Security — This question tests Communication and Network Security — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Two different IP addresses attempted brute-force SSH authentication. — The logs show repeated failed SSH login attempts for the user 'admin' from two different IP addresses (192.0.2.100 and 198.51.100.50). Each IP made three attempts before the connection was closed (likely due to authentication failure threshold). This pattern indicates a brute-force attack on the SSH service.
What should I do if I get this CISSP 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 CISSP NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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