The answer is that a host at 10.0.0.100 is repeatedly attempting to access the web server at 192.168.1.1 and being blocked by ACL ACL_INBOUND. This is correct because the log output shows a clear pattern of denied TCP packets from a single source IP, each with an incrementing source port, targeting the same destination IP and port 80—classic evidence of ACL denied traffic analysis where a host is trying to establish HTTP connections but is stopped by the inbound access list. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your ability to interpret syslog messages for ACL hits and distinguish between a legitimate misconfiguration and a potential reconnaissance attempt, such as a port scan. A common trap is misreading the incrementing source ports as a random attack when it could simply be a client retrying a blocked web request. Memory tip: “Same destination, climbing source ports—think blocked client, not random source.”
300-410 Network Logging and Syslog Practice Question
This 300-410 practice question tests your understanding of network logging and syslog. 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.
A network engineer runs the following command on Router R6:
R6# show logging | include %SEC-6-IPACCESSLOGP
*Mar 1 00:01:15.123: %SEC-6-IPACCESSLOGP: list ACL_INBOUND denied tcp 10.0.0.100(12345) -> 192.168.1.1(80), 1 packet
*Mar 1 00:01:20.456: %SEC-6-IPACCESSLOGP: list ACL_INBOUND denied tcp 10.0.0.100(12346) -> 192.168.1.1(80), 1 packet
*Mar 1 00:01:25.789: %SEC-6-IPACCESSLOGP: list ACL_INBOUND denied tcp 10.0.0.100(12347) -> 192.168.1.1(80), 1 packet
*Mar 1 00:01:30.012: %SEC-6-IPACCESSLOGP: list ACL_INBOUND denied tcp 10.0.0.100(12348) -> 192.168.1.1(80), 1 packet
Based on this output, what is the most likely problem?
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 at 10.0.0.100 is attempting to access a web server at 192.168.1.1 and is being blocked by the ACL.
The output shows repeated denied packets from source 10.0.0.100 to destination 192.168.1.1 on port 80 (HTTP). This indicates that a host at 10.0.0.100 is trying to access a web server at 192.168.1.1 but is being blocked by ACL ACL_INBOUND. The pattern suggests a possible scan or attack, or a legitimate access that is being denied due to misconfiguration.
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 ACL ACL_INBOUND is permitting traffic from 10.0.0.100 to 192.168.1.1 on port 80.
Why it's wrong here
The log shows denied packets, so the ACL is blocking, not permitting.
✓
A host at 10.0.0.100 is attempting to access a web server at 192.168.1.1 and is being blocked by the ACL.
Why this is correct
The log messages clearly indicate that packets from 10.0.0.100 to 192.168.1.1 port 80 are being denied by ACL ACL_INBOUND.
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 router is experiencing a DoS attack from 192.168.1.1.
Why it's wrong here
The source is 10.0.0.100, not 192.168.1.1.
✗
The ACL ACL_INBOUND is not configured on any interface.
Why it's wrong here
If it were not configured, no log messages would be generated.
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
The log shows denied packets, so the ACL is blocking, not permitting.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 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 300-410 NAT questions on configuration and troubleshooting.
Network Logging and Syslog — This question tests Network Logging and Syslog — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: A host at 10.0.0.100 is attempting to access a web server at 192.168.1.1 and is being blocked by the ACL. — The output shows repeated denied packets from source 10.0.0.100 to destination 192.168.1.1 on port 80 (HTTP). This indicates that a host at 10.0.0.100 is trying to access a web server at 192.168.1.1 but is being blocked by ACL ACL_INBOUND. The pattern suggests a possible scan or attack, or a legitimate access that is being denied due to misconfiguration.
What should I do if I get this 300-410 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 300-410 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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